JP7631474B2 - Agents for preventing or improving neuropathy - Google Patents

Description

The present invention relates to an agent for preventing or improving nerve disorders.

When nerve tissue is damaged, the effector organs controlled by the damaged nerves are impaired. The number of stroke patients, a typical example of nerve damage, is extremely high in Japan, at approximately 1.2 million, resulting in enormous social losses.

When nerve damage occurs due to a stroke or traffic accident, rehabilitation is recommended to restore nerve function. However, the current rehabilitation method is insufficient in terms of restoring the function, and there are many reported cases where the patient is left with a residual disability or unable to return to society even after rehabilitation. As such, there is a limit to the effectiveness of conventional rehabilitation in restoring nerve function, and there is a demand for useful methods that can promote the effects of rehabilitation.

Neuropathy is also a common complication of diabetes (diabetic neuropathy), and in this case symptoms include repeated constipation and diarrhea, erectile dysfunction, dizziness, abnormal sweating, and other autonomic neuropathy symptoms, as well as sensory neuropathy, which causes numbness and abnormal sensations. These symptoms are thought to be the result of abnormalities in various parts of the body caused by the loss of peripheral nerve fibers and reduced nerve function. In many cases, symptoms begin with subjective symptoms such as numbness and pain in the feet, and gradually spread to the central nerves. If appropriate treatment is not given, the loss of sensory nerve fibers will cause the patient to be unable to feel pain or heat. As a result, foot ulcers will form, and if left untreated, this can lead to gangrene, and in the worst case scenario, the patient may have to have their lower limbs amputated, significantly reducing the patient's quality of life (QOL).

The cause of diabetic neuropathy is believed to be metabolic abnormalities in peripheral nerve tissue caused by persistent hyperglycemia, and reduced blood flow due to thickening and narrowing of small blood vessels. Risk factors involved in the onset and progression of diabetic neuropathy include poor glycemic control, duration of diabetes, hypertension, dyslipidemia, smoking, and alcohol consumption. Of these, the most important factor is poor glycemic control, and it is said that neuropathy occurs frequently in cases of poor glycemic control. However, even if poor glycemic control is a risk factor for onset and progression, it has not been necessarily established whether strict glycemic control can suppress onset and progression.

To date, no cure for diabetic neuropathy has been established, and the main treatments are symptomatic treatments to alleviate pain symptoms and treatments to slow the progression of neuropathy, such as with aldose reductase inhibitors (e.g., Epalrestat).

It has also been reported that decreased nerve function contributes to the decline in muscle function associated with aging (Non-Patent Document 1), and in Japan, which is an ultra-aging society, it is important to develop technologies that improve decreased nerve function and prevent the decline in nerve function.

When nerves are damaged, they are often perceived as pain (neuropathic pain). Pain can cause inconvenience and discomfort in daily life, a decrease in motivation to work, and a decrease in quality of life. Neuropathic pain occurs when the damaged nerves remain excited and release excessive amounts of pain-transmitting substances from the damaged nerves. As a result, even if the cause of the pain or the source of the disease is removed and the disease is cured, the pain may continue for a long time, be severe with even a slight stimulus, be affected by changes in weather or climate, or be felt even without moving. Neuropathic pain often manifests as symptoms such as an electric shock-like pain or severe numbness.

One of the mechanisms of neuropathic pain is thought to be that calcium enters nerve cells through calcium channels, causing the nerve cells to become excited and release excessive neurotransmitters, so calcium channel blockers are often used to treat and prevent it. Antidepressants and antiepileptic drugs may also be used. Furthermore, if these drugs do not relieve the pain and it interferes with daily activities, narcotic analgesics such as opioids are also used.

On the other hand, it is known that hydroxybenzoic acid compounds such as vanillic acid and protocatechuic acid have a neuroprotective effect and an improving effect against neuropathic pain when administered in high doses (e.g., 100 mg/kg body weight/day) to animals such as mice and rats. For example, it has been reported that vanillic acid has a neuroprotective effect (Non-Patent Document 2), and protocatechuic acid also has a neuroprotective effect (Non-Patent Document 3) and an improving effect against neuropathic pain (Non-Patent Document 4).

However, it is not known that hydroxybenzoic acid compounds, when used in combination with certain lactone compounds, have an excellent effect on improving nerve disorders.

Nutrition 28: 495-503, 2012 Pharm Biol. May;53(5):630-6, 2015 Neuroscience. May 21;491:23-31, 2022 Bosn J Basic Med Sci. Apr 1;22(2):217-228, 2022

The present invention relates to providing an agent for preventing or improving neuropathy caused by nerve damage or decreased nerve function due to diabetic neuropathy.

The inventors have searched for materials that improve nerve function and have found that a combination of a specific lactone compound and a hydroxybenzoic acid compound is effective in improving decreased nerve function caused by nerve damage and diabetic neuropathy.

That is, the present invention relates to the following 1) to 12).
1) An agent for preventing or improving nerve disorders comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.
2) An agent for preventing or improving diabetic neuropathy comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.
3) A nerve regeneration promoter comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
4) An agent for promoting recovery of motor function after nerve damage, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.
5) An agent for inhibiting muscle atrophy after nerve injury, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.
6) An agent for preventing or improving neuropathic pain, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
7) A food for preventing or improving nerve disorders, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.
8) A food for preventing or improving diabetic neuropathy comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2):
9) A food for promoting nerve regeneration comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
10) A food for promoting recovery of motor function after nerve damage, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2):
11) A food for inhibiting muscle atrophy after nerve damage, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
12) A food for preventing or improving neuropathic pain, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2):
13) A composition for preventing or improving a nerve disorder, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
14) A composition for preventing or improving diabetic neuropathy, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
15) A composition for promoting nerve regeneration comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2):
16) A composition for promoting recovery of motor function after nerve injury, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
17) A composition for inhibiting muscle atrophy after nerve injury, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
18) A composition for preventing or ameliorating neuropathic pain, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

（式中、Ｒ^１は水素原子又はヒドロキシ基を示し、Ｒ^２は水素原子又はメチル基を示す。）

(In the formula, ^R1 represents a hydrogen atom or a hydroxyl group, and ^R2 represents a hydrogen atom or a methyl group.)

According to the present invention, it is possible to provide a medicine, quasi-drug, food, or supplement for preventing or improving nerve damage. According to the present invention, it is possible to promote recovery of nerve function and relieve pain associated with nerve damage using food or supplements, and therefore it is possible to provide a new means of contributing to improving the QOL of elderly people, patients receiving care at home due to nerve damage, and patients with disabilities due to diabetes.

Effect on motor function after spinal cord crush injury (1). * p<0.05 vs. Crush by Dunn test Effect on motor function after spinal cord crush injury (2). * p<0.05 vs. Crush by Dunn test Effect on nerve regeneration after sciatic nerve crush injury (1). * p< 0.05, ** p< 0.01, *** p< 0.001 vs. Crush by Dunnett test Effect on blood glucose level. ** p < 0.01 vs. B by Dunnett test Effect on diabetic neuropathy. ** p < 0.01 vs. B by Dunnett test Effect on nerve regeneration after sciatic nerve crush injury (2). * p< 0.05, *** p< 0.001 vs. Crush by Dunn test Effect of SNI treatment on neuropathic pain. * p< 0.05, ** p< 0.01 vs. control group by Mann-Whitney U test

In the present invention, the following formulas (1a) and (1b);

（式中、Ｒ^１は水素原子又はヒドロキシ基を示す。）

(In the formula, R ¹ represents a hydrogen atom or a hydroxy group.)

Among the lactone compounds represented by the formula (1a), the lactone compound represented by the formula (1a) is D-ribonolactone (R ¹ : hydroxy group) or 2-deoxy-D-ribono-1,4-lactone (R ¹ : hydrogen atom), and the lactone compound represented by the formula (1b) is glucono delta-lactone.

The lactone compound used in combination with the hydroxybenzoic acid compound represented by formula (2) or its salt may be one or more of the compounds represented by formulas (1a) and (1b), and two or more of them may be used, but is preferably any one of D-ribonolactone, 2-deoxy-D-ribono-1,4-lactone, and glucono delta-lactone.

Also, the following formula (2):

（式中、Ｒ^２は水素原子又はメチル基を示す。）

(In the formula, ^R2 represents a hydrogen atom or a methyl group.)

The hydroxybenzoic acid compound represented by the formula (I) refers to vanillic acid (R ² : methyl group) or protocatechuic acid (R ² : hydrogen atom).

Examples of salts of the compound represented by formula (2) include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium and magnesium, and ammonium salts such as ammonium chloride, tetraethylammonium, and tetramethylammonium.

One or more of the hydroxybenzoic acid compounds represented by the formula (2) or salts thereof may be used. Either vanillic acid or a salt thereof, or protocatechuic acid or a salt thereof may be used, or both may be used in combination.
Suitable combinations of the lactone compound and the hydroxybenzoic acid compound or a salt thereof include, for example, a) a combination of 2-deoxy-D-ribono-1,4-lactone and protocatechuic acid and/or vanillic acid, b) a combination of D-ribonolactone and protocatechuic acid and/or vanillic acid, and c) a combination of glucono delta lactone and protocatechuic acid and/or vanillic acid.

The lactone compound represented by the formula (1a) or (1b) and the hydroxybenzoic acid compound represented by the formula (2) or a salt thereof can be obtained by isolating them from natural products such as plants or by chemically synthesizing them according to known methods. In addition, it is also possible to use commercially available products as shown in the examples described later.

In the present invention, one or more lactone compounds represented by the formulae (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the formula (2) are used in combination (concomitant use), but the form is not limited thereto. That is, they may be a composition in which effective amounts of each compound are formulated in a single dosage form at an appropriate mixing ratio as a combination drug, or a kit in which drugs containing effective amounts of each compound are formulated separately and can be used simultaneously or separately at intervals, but simultaneous use is preferred.

When one or more lactone compounds represented by the formulae (1a) and (1b) are combined with one or more hydroxybenzoic acid compounds or salts thereof represented by the formula (2) to prepare a compounding agent, the compounding ratio can be appropriately selected depending on the material, application, or type of preparation, but is generally 1:0.0001-10, preferably 1:0.001-5, and more preferably 1:0.01-2, in terms of the mass ratio of lactone compound to hydroxybenzoic acid compound (in terms of free form).

As shown in the Examples below, the combined use of the lactone compound and the hydroxybenzoic acid compound exhibits a nerve regeneration promoting effect (inhibitory effect on the reduction of myelin area) in a nerve regeneration model (mouse) by sciatic nerve crush treatment at a dosage that does not show an effect when the lactone compound and the hydroxybenzoic acid compound are used alone. In addition, the combined use of the lactone compound and the hydroxybenzoic acid compound or a salt thereof improves motor disorders and promotes nerve regeneration in a central nerve regeneration model (zebrafish) by spinal cord crush treatment at a dosage that does not show an effect when the lactone compound and the hydroxybenzoic acid compound are used alone. Furthermore, the combined use of the lactone compound and the hydroxybenzoic acid compound improves the decrease in nerve conduction velocity in a diabetic neuropathy model without showing a blood sugar lowering effect.

Mice treated with sciatic nerve crush are known as a nerve regeneration model (Gaudet et al., Journal of Neuroinflammation 2011, 8:110, Nico L. et al., Arch Phys Med Rehabil, 78, 70-7 (1997), Takemura et al., PLOS ONE 2012, 7: e44592), and the suppression of the decrease in myelin area in this model means that the regeneration of peripheral nerves is promoted. In addition, zebrafish treated with spinal nerve crush are known as a central nerve regeneration model (Mayssa H. et al., Science, 354, 630-634 (2016)), and the promotion of recovery of motor function in this model means that the regeneration of central nerves is promoted.

Therefore, a combination of one or more lactone compounds represented by the formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the formula (2) or salts thereof can be a preventive or ameliorating agent for neuropathy, a preventive or ameliorating agent for diabetic neuropathy, a nerve regeneration promoter, a motor function recovery promoter after nerve damage, a muscle atrophy inhibitor after nerve damage, or a preventive or ameliorating agent for pain associated with neuropathy (neuropathic pain) (referred to as a "preventive or ameliorating agent for neuropathy, etc."), and can be used to manufacture the preventive or ameliorating agent for neuropathy, etc. That is, a combination of one or more lactone compounds represented by the formulas (1a) and (1b) of the present invention and one or more hydroxybenzoic acid compounds represented by the formula (2) or salts thereof can be used for preventing or ameliorating neuropathy, preventing or ameliorating diabetic neuropathy, promoting nerve regeneration, promoting motor function recovery after nerve damage, promoting muscle atrophy inhibition after nerve damage, or preventing or ameliorating neuropathic pain.
Here, the use may be therapeutic or non-therapeutic. "Non-therapeutic" refers to a concept that does not include medical procedures, i.e., a concept that does not include a method of surgery, therapy, or diagnosis of a human being, and more specifically, a concept that does not include a method of surgery, therapy, or diagnosis performed on a human being by a physician or a person under the instruction of a physician.

In the present invention, "neuropathy" refers to a pathological condition in which nerve functions are impaired due to damage to nerves, aging, or the like, resulting in impairment of Schwann cells and oligodendrocytes that form nerve cells and myelin sheaths. Specific symptoms include pain, loss of sensation (including anesthesia), a tingling or burning sensation in the limbs or extremities, paresthesia, muscle weakness, muscle mass loss, impaired motor function, impaired neuromuscular reflexes, convulsions, neuromuscular paralysis, and sexual dysfunction.
Here, "nerve damage" mainly includes physical damage, hemorrhagic or ischemic damage to central nerves such as the trigeminal nerve, spinal cord, and nerve roots, or peripheral nerves such as the sciatic nerve and median nerve, caused by trauma, contusion, compression, etc., and is preferably physical damage.
Age-related neurological dysfunction includes changes in the central nervous system, such as a decrease in motor cortex excitability and changes in cortical plasticity, and changes in the peripheral nervous system, such as a decrease in the number of axons, thinning of the myelin sheath, and fragmentation of acetylcholine receptors.

"Diabetic neuropathy" refers to neuropathy that appears after the onset of diabetes. "Diabetic neuropathy" is divided into distal symmetric polyneuropathy and focal mononeuropathy, and the diabetic neuropathy of the present invention includes both of them.
Distal symmetric polyneuropathy is divided into sensory/motor neuropathy and autonomic neuropathy. In sensory/motor neuropathy, a decrease in nerve conduction velocity is observed in nerve conduction tests early on in the disease, and sensory abnormalities such as spontaneous pain, numbness, paresthesias, and hypoesthesia appear in the distal lower limbs, as well as motor abnormalities such as muscle weakness, muscle atrophy, and impaired balance. As the symptoms ascend, symptoms also appear in the distal upper limbs. Eye and facial movements are also impaired.
Autonomic neuropathy presents a variety of symptoms, including pupillary dysfunction, orthostatic hypotension, cardiac nerve disorders (sudden death, painless myocardial infarction), sweating disorders, gastrointestinal motility disorders (constipation, diarrhea), bladder dysfunction, erectile dysfunction, etc. Localized mononeuropathy includes cranial nerve disorders (especially external ophthalmoplegia), trunk and limb neuropathy, and diabetic amyotrophy (lumbosacral root plexus neuropathy).

"Improvement" of neuropathy (including diabetic neuropathy) includes "prevention or treatment." "Prevention" of neuropathy means preventing or delaying the onset of neuropathy, and "treatment" means alleviating the symptoms of neuropathy or preventing or delaying the progression (worsening) of the symptoms.

"Nerve regeneration" means at least a partial reproduction of the normal developmental process in nerves, i.e., reproduction of at least one of the phenomena occurring during nerve repair or developmental processes such as cell proliferation, differentiation, and maturation (tissue regeneration), and preferably the result of this is a complete or partial recovery of the original nerve function (functional regeneration).

"Promoting recovery of motor function after nerve damage" means recovering from motor dysfunction (for example, motor paralysis, muscle weakness) that occurs in the region innervated by the damaged nerve due to nerve damage.
The nerve damage may be either peripheral nerve damage or central nerve damage, but is preferably peripheral nerve damage. The cause of the nerve damage is not particularly limited, and nerve damage caused by various causes such as trauma, compression by a cast, electric shock injury, herniated disc, and stroke is applicable.

"Suppression of muscle atrophy after nerve damage" means suppression of the loss of muscle mass that occurs in the area controlled by the damaged nerve due to nerve damage.

"Neuropathic pain" refers to pain caused by a lesion or disease of the somatosensory nervous system. Symptoms include a burning or tingling sensation, and hypersensitivity to touch and cold. The sense of touch may also become so sensitive that even a light touch can cause pain (allodynia, hyperesthesia). Symptoms are often present even when the patient is at rest (spontaneous pain).

For example, neuropathic pain can be diagnosed by answering the following seven questions on a five-point scale (0 points, a little (1 point), some (2 points), very much (3 points), very much (4 points)), and then determining the total score (a score of 6 or more indicates neuropathic pain) (Rinsei Gait 47: 565-574, 2012).
1) You feel a needle-like pain. 2) You feel an electric shock-like pain. 3) You feel a burning, stinging pain. 4) You feel a strong numbness. 5) You feel pain even when clothing rubs against your skin or when exposed to cold air. 6) You feel a decrease in sensation or hypersensitivity in the painful area. 7) The skin in the painful area swells or turns red or reddish purple.

The main diseases that cause neuropathic pain include the above-mentioned nerve disorders or diseases that can cause nerve disorders, such as, but not limited to, herniated disc, low back pain, entrapment neuropathy, sciatica, trigeminal neuralgia, carpal tunnel syndrome, lumbar spondylolisthesis, spinal canal stenosis, multiple sclerosis, Guillain-Barré syndrome, sequelae of stroke, pain after herniorrhaphy, and postherpetic neuralgia.

"Improvement" of neuropathic pain includes "prevention or treatment." "Prevention" of neuropathic pain means preventing or delaying the onset of neuropathic pain, and "treatment" means reducing neuropathic pain or preventing or delaying the progression (worsening) of neuropathic pain.

The agent for preventing or improving neuropathy of the present invention can itself be various compositions, such as a medicine, quasi-drug or food, that exhibits the effect of preventing or improving neuropathy, the effect of preventing or improving diabetic neuropathy, the effect of promoting nerve regeneration, the effect of promoting recovery of motor function after nerve damage, the effect of inhibiting muscle atrophy after nerve damage, or the effect of preventing or improving neuropathic pain, or can be a material or preparation for incorporation into these.
In addition, the above-mentioned foods (also referred to as "foods for preventing or ameliorating neuropathy caused by nerve damage or aging,""foods for preventing or ameliorating diabetic neuropathy,""foods for promoting nerve regeneration,""foods for promoting motor function recovery after nerve damage,""foods for inhibiting muscle atrophy after nerve damage," and "foods for preventing or ameliorating neuropathic pain") include not only general foods and beverages, but also foods, functional foods, foods for the sick, foods for specified health uses, foods with functional claims, and supplements that are labeled as such as necessary.

The above-mentioned pharmaceuticals (including quasi-drugs) containing the active ingredient of the present invention may be administered in any dosage form, but oral administration is preferred. When administering, the active ingredient can be mixed with a solid or liquid pharmaceutical non-toxic carrier suitable for administration methods such as oral administration, rectal administration, and injection, and administered in the form of a conventional pharmaceutical formulation.

Examples of such preparations include solid preparations such as tablets, granules, powders, and capsules; liquid preparations such as solutions, suspensions, and emulsions; and lyophilized preparations. These preparations can be prepared by conventional methods for preparations by appropriately adding conventional additives such as stabilizers, wetting agents, emulsifiers, binders, isotonicity agents, and excipients.

The food containing the active ingredient of the present invention may be in the form of soft drinks, tea drinks, coffee drinks, fruit juice drinks, carbonated drinks, jellies, wafers, biscuits, bread, noodles, sausages, and other foods and beverages, nutritional foods, and other foods, as well as nutritional supplement compositions in the same form as the oral preparations described above (solid preparations such as tablets, capsules, and lozenges). Among these, tablets are preferred.
Foods of various forms can be prepared using the active ingredient of the present invention alone or in appropriate combination with other food ingredients, solvents, softeners, oils, emulsifiers, preservatives, flavorings, stabilizers, colorants, antioxidants, moisturizers, thickeners, etc.

The content of the lactone compound represented by formula (1a) or (1b) in the above composition (e.g., pharmaceuticals, quasi-drugs, foods) varies depending on the form of use, but is preferably 0.0000001% by mass or more, more preferably 0.000001% by mass or more, and preferably 0.01% by mass or less, more preferably 0.005% by mass or less, and also preferably 0.0000001 to 0.01% by mass, more preferably 0.000001 to 0.005% by mass.

The content of the hydroxybenzoic acid compound represented by formula (2) or its salt in the above composition (e.g., pharmaceutical product, quasi-drug, food) varies depending on the form of use, but is preferably 0.00000002% by mass or more, more preferably 0.0000002% by mass or more, and preferably 0.001% by mass or less, more preferably 0.0005% by mass or less, and also preferably 0.00000002 to 0.001% by mass, more preferably 0.0000002 to 0.0005% by mass, calculated as the free hydroxybenzoic acid compound.

The dosage or intake of the above-mentioned medicines (including quasi-drugs) and foods may vary depending on the condition, body weight, sex, age, or other factors of the subject. In the case of oral administration or intake, the amount of the lactone compound represented by formula (1a) or (1b) per adult (body weight 60 kg) per day is preferably 0.6 mg or more, more preferably 1 mg or more, and preferably 50 mg or less, more preferably 20 mg or less, and is preferably 0.6 to 50 mg, more preferably 2 to 20 mg.
The amount of the hydroxybenzoic acid compound represented by formula (2) or a salt thereof, calculated as the free form of the hydroxybenzoic acid compound, per day is preferably 0.0002 mg or more, more preferably 0.002 mg or more, and preferably 5 mg or less, more preferably 4 mg or less, and is preferably 0.0002 to 5 mg, more preferably 0.002 to 4 mg.

Subjects to whom the present invention is administered for the prevention or improvement of neuropathy include, for example, humans with reduced nerve function and various symptoms of neuropathy (sensory loss, paresthesia, muscle weakness, reduced neuromuscular reflexes, convulsions, neuromuscular paralysis, etc.), diabetic patients with sensory/motor neuropathy, autonomic neuropathy, or localized mononeuropathy, diabetic patients or humans with high blood sugar levels who wish to prevent, suppress, or delay the onset of such neuropathy, people who wish to maintain or improve nerve function, and people who have developed or are at risk of developing various symptoms of neuropathic pain (burning pain or tingling sensation in the buttocks, thighs, shins, calves, knees, ankles, toes, elbows, fingers, shoulders, back, lower back, etc., allodynia, hypersensitivity, etc.).

With respect to the above-mentioned embodiment, the present invention further discloses the following aspects.

<1> An agent for preventing or improving nerve disorders comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<2> An agent for preventing or improving diabetic neuropathy comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<3> A nerve regeneration promoter comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<4> An agent for promoting recovery of motor function after nerve damage, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<5> An agent for inhibiting muscle atrophy after nerve injury, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<6> An agent for preventing or improving neuropathic pain, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.
<7> A food for preventing or improving nerve disorders, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<8> A food for preventing or improving diabetic neuropathy, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<9> A food for promoting nerve regeneration comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<10> A food for promoting recovery of motor function after nerve damage, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<11> A food for inhibiting muscle atrophy after nerve damage, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<12> A food for preventing or improving neuropathic pain, comprising a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).

<13> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof, for the production of an agent for preventing or improving a nerve disorder.
<14> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for the production of an agent for preventing or improving diabetic neuropathy.
<15> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2) for producing a nerve regeneration promoter.
<16> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2) for producing an agent for promoting motor function recovery after nerve damage.
<17> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for producing an agent for inhibiting muscle atrophy after nerve damage.
<18> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for the production of an agent for preventing or ameliorating neuropathic pain.
<19> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2) for producing a food for preventing or improving a nerve disorder.
<20> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for producing a food for preventing or improving diabetic neuropathy.
<21> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2) for producing a food for promoting nerve regeneration.
<22> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2) for producing a food for promoting recovery of motor function after nerve damage.
<23> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2) for producing a food for inhibiting muscle atrophy after nerve damage.
<24> Use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds or salts thereof represented by the following formula (2) for producing a food for preventing or improving neuropathic pain.

<25> A combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for preventing or ameliorating nerve disorders.
<26> A combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for preventing or ameliorating diabetic neuropathy.
<27> A combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for promoting nerve regeneration.
<28> A combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for promoting recovery of motor function after nerve damage.
<29> A combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for suppressing muscle atrophy after nerve damage.
<30> A combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for preventing or ameliorating neuropathic pain:

<31> Non-therapeutic use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for preventing or ameliorating a nerve disorder.
<32> Non-therapeutic use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for preventing or ameliorating diabetic neuropathy.
<33> Non-therapeutic use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for promoting nerve regeneration.
<34> Non-therapeutic use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof, for promoting recovery of motor function after nerve damage.
<35> Non-therapeutic use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for suppressing muscle atrophy after nerve damage.
<36> Non-therapeutic use of a combination of one or more lactone compounds represented by the following formulas (1a) and (1b) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof for preventing or ameliorating neuropathic pain.

<37> A method for preventing or improving a nerve disorder, comprising ingesting or administering to a subject in need thereof one or more of lactone compounds represented by the following formulas (1a) and (1b) in combination with one or more of hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<38> A method for preventing or improving diabetic neuropathy, comprising ingesting or administering to a subject in need thereof one or more of lactone compounds represented by the following formulas (1a) and (1b) in combination with one or more of hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<39> A method for promoting nerve regeneration, comprising ingesting or administering to a subject in need thereof one or more of lactone compounds represented by the following formulas (1a) and (1b) in combination with one or more of hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<40> A method for promoting recovery of motor function after nerve damage, comprising ingesting or administering to a subject in need thereof one or more of lactone compounds represented by the following formulas (1a) and (1b) in combination with one or more of hydroxybenzoic acid compounds or salts thereof represented by the following formula (2):
<41> A method for inhibiting muscle atrophy after nerve damage, comprising ingesting or administering to a subject in need thereof one or more of lactone compounds represented by the following formulas (1a) and (1b) in combination with one or more of hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).
<42> A method for preventing or ameliorating neuropathic pain, comprising ingesting or administering to a subject in need thereof one or more of lactone compounds represented by the following formulas (1a) and (1b) in combination with one or more of hydroxybenzoic acid compounds or salts thereof represented by the following formula (2).

<43> A composition for preventing or improving a nerve disorder, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
<44> A composition for preventing or improving diabetic neuropathy, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
<45> A composition for promoting nerve regeneration, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
<46> A composition for promoting recovery of motor function after nerve damage, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
<47> A composition for inhibiting muscle atrophy after nerve injury, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:
<48> A composition for preventing or ameliorating neuropathic pain, comprising one or more lactone compounds represented by the following formulas (1a) and (1b), and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

In <49>, <1>, <7>, <13>, <25>, <31>, <37> and <43>, the neuropathy is preferably a decrease in neuropathy due to a decrease in neuropathy caused by physical damage to the central or peripheral nerves.
<50> In the agent, food or composition in <1> to <24> and <43> to <48>, the content of the lactone compound represented by the following formula (1a) or (1b) is preferably 0.0000001% by mass or more, more preferably 0.000001% by mass or more, and preferably 0.01% by mass or less, more preferably 0.005% by mass or less, and also preferably 0.0000001 to 0.01% by mass, more preferably 0.000001 to 0.005% by mass.
<51> In the agent, food or composition in <1> to <24> and <43> to <48>, the content of the hydroxybenzoic acid compound represented by the following formula (2) or a salt thereof, calculated as the free hydroxybenzoic acid compound, is preferably 0.00000002% by mass or more, more preferably 0.0000002% by mass or more, and preferably 0.001% by mass or less, more preferably 0.0005% by mass or less, and also preferably 0.00000002 to 0.001% by mass, more preferably 0.0000002 to 0.0005% by mass.
<52> In <1> to <42>, the administration or intake amount of the lactone compound represented by the following formula (1a) or (1b) and the hydroxybenzoic acid compound represented by the following formula (2) or a salt thereof, or of a medicine (including quasi-drugs) or food containing the same, in the case of oral administration or intake, is preferably 0.5 mg or more, more preferably 1 mg or more, and preferably 60 mg or less, more preferably 20 mg or less, and also preferably 0.5 to 60 mg, more preferably 1 to 20 mg, per adult (body weight 60 kg) per day, as the lactone compound represented by the following formula (1).
<53> In <1> to <42>, the administration or intake amount of the lactone compound represented by the following formula (1a) or (1b) and the hydroxybenzoic acid compound represented by the following formula (2) or a salt thereof, or of the medicine (including quasi-drug) or food containing the same, in the case of oral administration or intake, is preferably 0.00005 mg or more, more preferably 0.0005 mg or more, and preferably 5 mg or less, more preferably 4 mg or less, and also preferably 0.00005 to 5 mg, more preferably 0.0005 to 4 mg, per adult (body weight 60 kg) per day, calculated in terms of the free hydroxybenzoic acid compound, of the hydroxybenzoic acid compound represented by the following formula (2) or a salt thereof.

（式中、Ｒ^１は水素原子又はヒドロキシ基を示し、Ｒ^２は水素原子又はメチル基を示す。）

(In the formula, ^R1 represents a hydrogen atom or a hydroxyl group, and ^R2 represents a hydrogen atom or a methyl group.)

Example 1: Improvement of nerve damage in a central nervous system regeneration model induced by spinal cord crush injury (1)
Zebrafish (Danio rerio) aged 3 to 12 months were grouped into equal groups based on body weight and maximum swimming speed (n=5-24).
1. Sham group, control diet: (Sham)
2. Crush group, control diet: (Crush)
3. Crush group, 2-deoxy-D-ribono-1,4-lactone diet: (Crush+L)
4. Crush group, protocatechuic acid diet: (Crush + P)
5. Crush group, vanillic acid diet: (Crush + V)
6. Crush group, 2-deoxy-D-ribono-1,4-lactone + protocatechuic acid diet: (Crush + PL)
7. Crush group, 2-deoxy-D-ribono-1,4-lactone + vanillic acid diet: (Crush + VL)

The sham and spinal nerve crush groups were fed regular food, Otohime (Nisshin Marubeni Feed), while the groups administered each ingredient were fed the same food with the active ingredient dissolved in 50% EtOH mixed in. The content ratio of each ingredient in the food is shown in Table 1 below.

The food was then freeze-dried using a freeze dryer and coated with lard at a ratio of 20% of the weight of the food. Each animal was given 10 mg of food per day (5 mg twice a day, at 9:00 in the morning and 16:00 in the evening).

As 2-deoxy-D-ribono-1,4-lactone, protocatechuic acid, and vanillic acid, the following commercially available products (model numbers, manufacturers) were used.
・2-Deoxy-ribono-1,4-lactone (QB-2141, Fujifilm Wako Pure Chemical Industries, Ltd.)
Protocatechuic acid (P6857, LKT Labs, Inc.)
Vanillic acid (084-04462, Fujifilm Wako Pure Chemical Industries, Ltd.)

Spinal Cord Crush (SCC) treatment was performed by incising the base of the dorsal fin of the fish by about 3 mm with a razor and applying pressure with tweezers for 1 second to crush the dorsal fin. In the sham group, only incision was performed. After surgery, the fish were kept in a methylene blue (Nichido, diluted about 6000 times) solution for 3 days to prevent infection from the wound. Feeding was started one week before SCC treatment, and the fish were kept until 21 days after treatment, and maximum swimming speed and body weight were measured as appropriate.
Maximum swimming speed was measured using a running water exercise load device (Personal Tank PT-70S (Nishi Nippon Fluid Engineering Research Institute Co., Ltd.) modified for zebrafish testing). After acclimatizing the fish at a speed of 1 Hz for 10 minutes, the speed was accelerated at 1 Hz every minute, and the maximum swimming speed was defined as the flow speed just before the stage at which the fish could no longer swim (1 Hz = 4.5 cm/sec). "No longer able to swim" refers to a state in which the fish could no longer resist the water flow and was stuck to the net downstream of the tank. Statistics were performed using the Dunn test, with a significance level of P<0.05.

The results are shown in Figure 1.
Compared to the Crush group, no effect was observed in the groups administered with the lactone compound or the hydroxybenzoic acid compound alone (Crush+L group, Crush+P group, Crush+V group), while the groups administered with the lactone compound and the hydroxybenzoic acid compound in combination (Crush+PL group, Crush+VL group) showed an accelerated recovery of maximum swimming speed (n=4-7 at the endpoint).

Example 2: Improvement of nerve damage in a central nervous system regeneration model induced by spinal cord crush injury (2)
Six-month-old zebrafish (Danio rerio) were divided into groups (n=6-16) based on the weight and maximum swimming speed.
1. Sham group, control diet: (Sham)
2. Crush group, control diet: (Crush)
3. Crush group, protocatechuic acid + vanillic acid + glucono delta-lactone diet: (Crush + PVGDL)
4. Crush group, protocatechuic acid + vanillic acid + D-ribonolactone diet: (Crush + PVDr)

The sham and spinal nerve crush groups were fed regular food, Otohime (Nisshin Marubeni Feed), while the groups administered each ingredient were fed the same food, but with the active ingredient dissolved in 50% EtOH mixed in. The content ratio of each ingredient in the food is as shown in Table 2 below.

The food was then freeze-dried using a freeze dryer and coated with lard at a ratio of 20% of the weight of the food. Each animal was given 10 mg of food per day (5 mg twice a day, at 9:00 in the morning and 16:00 in the evening).

Glucono-delta-lactone, D-ribonolactone, protocatechuic acid, and vanillic acid were used as the following commercially available products (model numbers, manufacturers).
Gluconodeltalactone (42009, Fuso Chemical Industries)
D-ribonolactone (355-20541, Fujifilm Wako Pure Chemical Industries, Ltd.)
Protocatechuic acid (P6857, LKT Labs, Inc.)
Vanillic acid (084-04462, Fujifilm Wako Pure Chemical Industries, Ltd.)

Spinal Cord Crush (SCC) treatment was performed by incising the base of the dorsal fin of the fish by about 3 mm with a razor and applying pressure with tweezers for 1 second to crush the dorsal fin. In the sham group, only incision was performed. After surgery, the fish were kept in a methylene blue (Nichido, diluted about 6000 times) solution for 3 days to prevent infection from the wound. Feeding was started one week before SCC treatment, and the fish were kept until 21 days after treatment, and maximum swimming speed and body weight were measured as appropriate.
The maximum swimming speed was measured using a running water exercise load device (Personal Tank PT-70S (Nishi Nippon Fluid Engineering Research Institute Co., Ltd.) modified for zebrafish testing). After acclimating the fish at a speed of 1 Hz for 10 minutes, the speed was accelerated at 1 Hz every minute, and the maximum swimming speed was defined as the flow speed just before the stage at which the fish could no longer swim (1 Hz = 4.5 cm/sec). "No longer able to swim" refers to a state in which the fish could no longer resist the water flow and was stuck to the net downstream of the tank. Statistics were performed using the Dunn test, with a significance level of P<0.05.

The results are shown in Figure 2.
Acceleration of recovery of maximum swimming speed was confirmed in the groups administered with a hydroxybenzoic acid compound and a lactone compound in combination (Crush+PVGDL group, Crush+PVDr group) as compared with the Crush group (n=6-15 at the endpoint).

Example 3: Improvement of nerve damage in a nerve regeneration model induced by sciatic nerve crush treatment (1)
Seven-week-old C57BL/6J mice were pre-bred for one week and then divided into the following eight groups so that their body weights were equal (n=10 per group).
1. Sham group, control diet: (Sham)
2. Crush group, control diet: (Crush)
3. Crush group, lactone diet: (Crush + L)
4. Crush group, protocatechuic acid diet: (Crush + P)
5. Crush group, vanillic acid diet: (Crush + V)
6. Crush group, lactone + protocatechuic acid diet: (Crush + PL)
7. Crush group, lactone + vanillic acid diet: (Crush + VL)
8. Crush group, lactone + protocatechuic acid + vanillic acid diet: (Crush + PVL)

After being raised with each diet for 7 days with free feeding, the right leg was subjected to sciatic nerve crush treatment. The hair of the mouse thigh was shaved, and the sciatic nerve was exposed after incision of about 1 cm. The sciatic nerve was crushed by compressing it with tweezers for 10 seconds, and the incision was sutured and disinfected with isodine. For the sham operation group, the hair of the mouse thigh was shaved, and the incision of about 1 cm was made, and the sciatic nerve was exposed after suture and disinfected with isodine. After the sciatic nerve crush, each diet was allowed to be fed ad libitum. The diet composition is shown in Table 3.
The protocatechuic acid, vanillic acid, and lactone used were the commercially available products (model numbers, manufacturers) shown below.

Protocatechuic acid (P6857, LKT Labs, Inc.)
Vanillic acid (084-04462, Fujifilm Wako Pure Chemical Industries, Ltd.)
・2-Deoxy-ribono-1,4-lactone (QB-2141, Fujifilm Wako Pure Chemical Industries, Ltd.)

Five weeks after the sciatic nerve crush, mice were dissected. The peroneal nerve was isolated and pre-fixed in 2.5% glutaraldehyde (4°C, overnight) and post-fixed in 1% osmic acid (4°C, 2 hours). After embedding in Epon resin, semi-thin (1.5 um) sections were prepared and stained with 0.5% toluidine blue. After imaging with an all-in-one fluorescent microscope (Keyence), the area of the myelin sheath was quantified using a Hybrid Cell Count (Keyence). Quantification was performed on all myelinated axons in the peroneal nerve (n=5-8 per group). Statistics were performed using the Dunnett test, with a significance level of P<0.05 (* p<0.05, ** p<0.01, *** p<0.001).

The results are shown in Figure 3.
The Crush+PL group, Crush+VL group, and Crush+PVL group significantly suppressed the decrease in myelin area caused by sciatic nerve crush. That is, the hydroxybenzoic acid compound and the lactone compound did not show activity by themselves, but the combination of the hydroxybenzoic acid compound (protocatechuic acid or vanillic acid, or both) with the lactone compound (2-deoxy-ribono-1,4-lactone) showed a nerve regeneration promoting effect (Figure 3).

Example 4 Neuropathy Improvement Effect of Streptozotocin Administration on Diabetic Neuropathy Model 1) Streptozotocin (150 mg/kg, diluted with citrate buffer pH 4.0) or citrate buffer (pH 4.0) was intraperitoneally administered to 3-week-old C57BL/6J mice, and 5 days after administration, blood was sampled from the tail vein and blood glucose levels were measured. Individuals with blood glucose levels of 280 mg/dL or higher were selected. For individuals with blood glucose levels below 280 mg/dL, streptozotocin was administered again, and individuals with blood glucose levels of 280 mg/dL or higher 5 days after administration were selected. The mice were divided into groups so that there would be no large difference in blood glucose levels (solvent-administered control diet group, streptozotocin-administered 2-deoxy-ribono-1,4-lactone group, streptozotocin-administered vanillic acid group, streptozotocin-administered 2-deoxy-ribono-1,4-lactone + vanillic acid group; n=6-10 per group) and kept on each diet. The diet composition is shown in Table 4.

The following commercially available compounds (model numbers, manufacturers) were used.
Vanillic acid (084-04462, Fujifilm Wako Pure Chemical Industries, Ltd.)
・2-Deoxy-ribono-1,4-lactone (QB-2141, Fujifilm Wako Pure Chemical Industries, Ltd.)

2) Eight weeks after feeding, blood was collected from the tail and blood glucose levels were measured at regular intervals.

3) After 9 weeks of dietary loading, the sensory nerve conduction velocity (SNCV) of the sural nerve was measured under anesthesia using an electromyographic evoked potential tester (MEB-9402MB).
Statistics were performed using the Dunnett test, with the significance level set at P<0.05.

4) Results a) Blood glucose levels after 8 weeks of dietary loading are shown in FIG.
The administration of streptozotocin caused a marked increase in blood glucose levels, but no change in blood glucose levels was observed after the intake of each component diet.
b) The results of nerve conduction test after 9 weeks of food loading are shown in FIG.
Streptozotocin administration significantly decreased SNCV, while lactone + vanillic acid diet significantly improved the decrease in nerve conduction velocity caused by streptozotocin administration (Figure 5).

Example 5: Improvement of nerve damage in a nerve regeneration model induced by sciatic nerve crush treatment (2)
Seven-week-old C57BL/6J mice were pre-bred for one week and then divided into the following eight groups so that their body weights were equal (n=10 per group).
1. Sham group, control diet: (Sham)
2. Crush group, control diet: (Crush)
3. Crush group, lactone + vanillic acid (VL) diet: (Crush + VL)
4. Crush group, glucono-delta-lactone + vanillic acid (VG) diet: (Crush + VG)
5. Crush group, vanillic acid (V) diet: (Crush + V)
6. Crush group, GDL (G) diet: (Crush+G)

After being raised with each diet for 7 days with free feeding, the right leg was subjected to sciatic nerve crush treatment. The hair of the mouse thigh was shaved, and the sciatic nerve was exposed after incision of about 1 cm. The sciatic nerve was crushed by compressing it with tweezers for 10 seconds, and the incision was sutured and disinfected with isodine. For the sham operation group, the hair of the mouse thigh was shaved, and the incision of about 1 cm was made, and the sciatic nerve was exposed after suture and disinfected with isodine. After the sciatic nerve crush, each diet was allowed to be fed ad libitum. The diet composition is shown in Table 3.
The vanillic acid, lactone, and glucono-delta-lactone used were the following commercially available products (model numbers, manufacturers).

Vanillic acid (084-04462, Fujifilm Wako Pure Chemical Industries, Ltd.)
・2-Deoxy-ribono-1,4-lactone (QB-2141, Fujifilm Wako Pure Chemical Industries, Ltd.)
Gluconodeltalactone (073-01572, Fujifilm Wako Pure Chemical Industries, Ltd.)

Five weeks after the sciatic nerve crush, mice were dissected. The peroneal nerve was isolated and pre-fixed in 2.5% glutaraldehyde (4°C, 2 hours) and post-fixed in 1% osmic acid (4°C, 1.5 hours). After embedding in Epon resin, semi-thin (1.5 um) sections were prepared and stained with 0.5% toluidine blue. After imaging with an all-in-one fluorescent microscope (Keyence), the area of the myelin sheath was quantified using a Hybrid Cell Count (Keyence). Quantification was performed on all myelinated axons in the peroneal nerve (n=7-9 per group). Statistics were performed using the Dunn test, with a significance level of P<0.05 (* p<0.05, *** p<0.001).

The results are shown in Figure 6.
The Crush+VL group and Crush+VG group significantly suppressed the decrease in myelin area caused by sciatic nerve crush. That is, the hydroxybenzoic acid compound (vanillic acid) and glucono delta lactone did not show activity by themselves, but the combination of the hydroxybenzoic acid compound (vanillic acid) and the lactone compound (glucono delta lactone) showed a nerve regeneration promoting effect (Figure 6).

Example 6 Effect of 2-deoxy-ribono-1,4-lactone and vanillic acid combined on a neuropathic pain model caused by nerve branch ligation injury (spare nerve injury) 1) Spared nerve injury (SNI) treatment was performed on male C57BL/6J mice aged 51-54 weeks. Specifically, the hair of the left thigh of the mouse was shaved and disinfected with alcohol and isodine. The thigh was incised about 1 cm, and the tibial nerve and peroneal nerve of the left leg were ligated with 8-0 silk thread. The tibial nerve and peroneal nerve distal to the ligation site were excised with 2-4 mm scissors, and the incision was sutured with 6-0 silk thread. The mice were fed each diet (control diet, 2-DL+VA diet) (n=12-16 per group) starting one week before SNI treatment. The diet was solid and was made with Oriental Yeast. The diet composition is shown in Table 6.
"2-DL" refers to 2-deoxy-ribono-1,4-lactone and "VA" refers to vanillic acid.
The following commercially available compounds (model numbers, manufacturers) were used.
・2-DL: QB-2141, Fujifilm Wako Pure Chemicals ・VA: 084-04462, Fujifilm Wako Pure Chemicals

2) Pain evaluation was performed by Von Frey test 1 and 2 weeks after SNI treatment. From 2 days before Von Frey test, the mice were placed on a lattice wire mesh and habituated in the animal chamber for 60 minutes every day. On the day of the test, the mice were habituated in the chamber for 40 minutes or more, and it was confirmed that spontaneous movement had disappeared. Semmes-Weinstein monofilament 0.16g was pressed vertically against the little toe, which is the area controlled by the sural nerve, for 3 seconds, and the escape reaction was observed. A 3-minute interval was given for each stimulation, and the response rate was shown for 5 stimulations.
Pain assessment was treated as count data and the Mann-Whitney U test was used, with the significance level set at p<0.05.

3) Results a) The results of the Von Frey test 1 and 2 weeks after SNI treatment are shown in FIG.
In order to investigate the combined effect of 2-DL and VA on neuropathic pain caused by SNI treatment, pain was evaluated using the Von Frey test. Compared to the control group, the combined 2-DL and VA (2-DL + VA) group showed a significant decrease in the response rate of the Von Frey test 1 and 2 weeks after SNI treatment. In other words, it was shown that the combined intake of 2-DL and VA significantly suppressed neuropathic pain.

Claims (9)

An agent for preventing or improving nerve disorders comprising a combination of a lactone compound represented by the following formula (1a) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.) A nerve regeneration promoter comprising a combination of a lactone compound represented by the following formula (1a) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof.

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.) An agent for promoting recovery of motor function after nerve injury, comprising a combination of a lactone compound represented by the following formula (1a) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.) A food for preventing or improving nerve disorders, comprising a combination of a lactone compound represented by the following formula (1a) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.) A food for promoting nerve regeneration comprising a combination of a lactone compound represented by the following formula (1a) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.) A food for promoting recovery of motor function after nerve damage, comprising a combination of a lactone compound represented by the following formula (1a) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.) The agent according to claim 1 or the food according to claim 4 , wherein the nerve disorder is a decrease in nerve function caused by physical damage to the central or peripheral nerves. A composition for preventing or improving a nerve disorder, comprising a lactone compound represented by the following formula (1a) : and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.) A composition for promoting nerve regeneration, comprising a lactone compound represented by the following formula (1a) and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.)
[Claim 10] (Original claim 17)
A composition for promoting recovery of motor function after nerve injury, comprising a lactone compound represented by the following formula (1a) : and one or more hydroxybenzoic acid compounds represented by the following formula (2) or salts thereof:

(In the formula, ^R1 represents a hydroxy group, and ^R2 represents a hydrogen atom or a methyl group.)