WO2002015901A1

WO2002015901A1 - Myricetin as an inhibitor of serotonin n-acetyltransferase

Info

Publication number: WO2002015901A1
Application number: PCT/KR2001/001416
Authority: WO
Inventors: Kyong-Tai Kim; Bo-Hwa Choi
Original assignee: Neuronex Co., Ltd.
Priority date: 2000-08-22
Filing date: 2001-08-22
Publication date: 2002-02-28
Also published as: KR100407399B1; AU2001280234A1; KR20020015609A

Abstract

The present invention relates to a reading that myricetin acts as an effective inhibitor of serotonin N-acetyltransferase, and a pharmaceutical composition for treating a serotonin N-acetyltransferase-associated disease which comprises myricetin as an active ingredient. The pharmaceutical composition of the present invention is particularly useful for treating sleep-disorder, depression, stress-related diseases or obesity.

Description

Myricetin As An Inhibitor of Serotonin N-acetyltransferase

FIELD OF THE INVENTION

The present invention relates to a finding that myricetin (5,7,3 ',4',5'- pentahydroxyflavonol) acts as an effective inhibitor of serotonin N- acetyltransferase, and a pharmaceutical composition for treating a serotonin N- acetyltransferase-associated disease, which comprises myricetin as an active ingredient.

BACKGROUND OF THE INVENTION

Serotonin and melatonin are important neurotransmitter and neurohormone involved in the pathological pathway of depression, and they are produced in the pineal gland located between the two cerebral hemispheres. Serotonin synthesized from tryptophan is converted by the action of serotonin N- acetyltransferase into N-acetylserotonin which is in turn converted to melatonin by hydroxyindole-O-methyltransferase (see Fig. 1).

Thus, the amount of serotonin and melatonin synthesized in the pineal gland is regulated by the activity of serotonin N-acetyltransferase, and these neuromodulators participate in regulating various functions of CNS (central nervous system) and PNS (peripheral nervous system): Serotonin takes part in regulating depression, anxiety, appetite, imperative idea mentism, delusions, temper, arousal, offensive traits, pain, sleep, learning, memory, and fear; and melatonin, sleep, temper, reproduction, cancer's growth and aging.

It has been reported that the concentrations of serotonin and its metabolites in the brain of a suicide are abnormally low, and that the abnormally high concentration of melatonin leads to depression. In fact, there have appeared a large number of reports which propose that serotonin and melatonin are closely related to such disorders as depression, seasonal affective disorder, premenstrual syndrome (PMS), insomnia, jet-leg, delayed-sleep syndrome and obesity. For instance, it has been reported that administration of medicine such as tricyclic anti-depressants or selective serotonin reuptake inhibitors is effective for women suffered from serious mental and emotional problems that periodically appear every month before menstruation (Sundbald C. et al., Neuropsychopharmacology 9:133-145, 1993).

It has been also discovered that the activity of serotonin N-acetyltransferease is reduced when the cultured pineal gland is treated with the hormone whose secretion is stimulated by stress. When rats got thirst stress by stopping the water supply for some days, it was observed that the concentration of cortisol in blood was increased while that of serotonin in midbrain and hypothalamus was decreased (Yuwiler A., Journal of Neurochemistry 52:46-53, 1989; Papova N. K. et al., Neurosci. Behav. Physiol. 31(3):327-332, 2001).

Furthermore, it has been accepted through many research results accumulated in the last ten years that selective serotonin reuptake inhibitor (SSRI) has an effect on reducing the body weight. For example, it is reported that fluoxetine, one of SSRI, increased the concentration of serotonin in the synapse, thereby reducing the appetite (Li D. L. et ah, Obesity Research 3:481S-490S, 1995; Levine L. R. et al., International Journal of Obesity 13:635-645, 1989). This result shows that not only fluoxetine but also the other SSRI may be used for obesity treatment, and it is an important task of obesity clinic to search such a useful candidate.

Therefore, many attempts have been made to develop drugs for treating various neurotransmitter-related diseases, which yielded, for example, selective serotonin or noradrenalin reuptake inhibitors such as fluoxetine, paroxetine, imipramine, desipramine. However, these drugs exhibit only limited effectiveness in the treatment of the above-mentioned disorder.

The present inventors have endeavored to develop an effective inhibitor of serotonin N-acetyltransferase, and have found that myricetin specifically acts on serotonin N-acetyltransferase and can be used for treating serotonin N- acetyltransferase activity-related diseases, especially sleep-disorder, depression, stress, and obesity.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a compound that inhibits serotonin N-acetyltransferase activity in a specific manner.

It is a further object of this invention to provide a composition which can be used for the treatment of serotonin N-acetyltransferase activity-related diseases, e.g., depression, stress-related disease, and obesity.

In accordance with one aspect of the present invention, there is provided a serotonin N-acetyltransferase inhibitor comprising myricetin as an active ingredient.

The present invention also provides a pharmaceutical composition for treating a serotonin N-acetyltransferase-associated disease which comprises myricetin as an active ingredient.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, which respectively show:

FIG. 1 : The biosynthesis pathway to melatonin via the steps of tryptophan hydroxylation, serotonin acetylation, and conversion of 5-hydroxy group into methoxy group; FIG. 2: Inhibition of serotonin N-acetyltransferase activity exerted by Myrica rubra Siebold et Zuccarini cortex extract;

FIG. 3a and 3b: Inhibition of serotonin N-acetyltransferase activity exerted by myricetin; FIG. 4a: A Lineweaver-Burk plot showing that myricetin acts as a non- competitive inhibitor with tryptamine;

FIG. 4b: A Lineweaver-Burk plot showing that myricetin acts as a non- competitive inhibitor with acetyl CoA; FIGs. 5 a and 5b: Forced swimming test results obtained for rats administered with myricetin and for control rats.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout the specification, the term "serotonin N-acetyltransferase- associated disease" means a disease caused by higher-than-normal serotonin N- acetyltransferase activity which reduces serotonin while rising melatonin beyond normal levels in the central and peripheral nervous system. Examples of such a disease include depression-related disease, stress-related disease, and obesity.

The term "depression-related disease" means a disease caused by an abnormally low serotonin level in the synapse. Examples of such a disease include seasonal affective disorder, premenstrual syndrome, unipolar depression, bipolar depression, manic-depressive psychosis and atypical depression and depression-related sleep-disorder.

The "stress-related disease" is also caused by an abnormally low serotonin level, and examples thereof include depression, posttraumatic stress disorder, stress-related bodily disorders like idiopathic pain syndromes and chronic fatigue syndrome.

The term "depression-related sleep disorder" means a sleep disorder which is caused by dysfunction of the serotonin and melatonin system. Examples of such a disease include insomnia, hypersomnia, parasomnia, dysomnia, fibromyalgia, jet- leg, shift-work sleep disorder, delayed-sleep phase syndrome, and advanced-sleep phase syndrome.

To achieve the above-stated objects, the present invention provides myricetin of formula 1 as an effective inhibitor of serotonin N-acetyltransferase.

Myricetin (5,7,3',4',5'-pentahydroxyflavonol) of formula 1 is a flavonol isolated from an extract of Myrica rubra Siebold et Zuccarini cortex. Myricetin has previously been used as an anti-tumor, anti-inflammatory or diuretic agent.

The present invention discloses for the first time that it can be used as an inhibitor of serotonin N-acetyltransferase.

Myricetin acts specifically on serotonin N-acetyltransferase to inhibit its activity, and therefore, can be effectively used as a therapeutic agent for treating

CNS related-diseases which are associated with serotonin N-acetyltransferase activity. The present invention also provides a pharmaceutical composition for treating a serotonin N-acetyltransferase associated disease which comprises myricetin of formula 1 as an active ingredient.

Since the pharmaceutical composition containing myricetin of the present invention regulates the serotonin and melatonin concentrations through suppressing abnormal serotonin N-acetyltransferase activity, it can be used for the treatment of depression, stress-related diseases or obesity.

The inhibition activity of myricetin isolated from a hot-water or alcohol extract of Myrica rubra Siebold et Zuccarini cortex is measurable by examining its influence on the serotonin N-acetyltransferase activity in the reaction of [³H]- acetyl CoA and tryptamine, i.e., by quantifying the amount of [³H]- acetyltryptamine produced. Such a measurement shows that the serotonin N- acetyltransferase activity is inhibited to the extent of 50% at a myricetin concentration of 2.2 μM; and 98%, at 30 μM. Thus, myricetin is an effective serotonin N-acetyltransferase inhibitor.

The inventive pharmaceutical composition containing myricetin or an extract of Myrica rubra Siebold et Zuccarini cortex, which can be advantageously used for the treatment of serotonin N-acetyltransferase-associated diseases, e. g., depression, stress-related diseases or obesity, may further comprise pharmaceutical acceptable fillers, extenders, binders, wetting agents, disintegrating agents, diluents such as surfactant, or excipients, and may be administered orally or parenterally.

The inventive composition may be formulated in dosage units, in the form of e.g., tablet, coated tablet, capsules, pill, suppository and ampule.

Nontoxic, inactive, pharmaceutical acceptable excipients are solid, semi- solid or liquid diluents, fillers and all kinds of formulation supporting agents.

Preferred pharmaceutical formulations which may be mentioned are tablets, coated tablets, capsules, pills, granules, suppositories, solutions, suspensions and emulsions, pastes, ointments, gels, creams, lotions, dusting powders and sprays.

As the 50% inhibition concentration (IC₅₀) of myricetin is about 2.2 μM, a dose may contain myricetin in an amount to bring its concentration in the range of

0.01 μM ~ l M.

In accordance with another aspect of this invention, it is also provided a method for inhibiting the activity of serotonin N-acetyltransferase in a mammal, comprising administering thereto an effective dose of myricetin or the extract of Myrica rubra Siebold et Zuccarini cortex.

A typical daily dose of myricetin or the extract may range from about 1 βg to 10 g myricetin/kg body weight, preferably, from 0.001 to 10 mg of myricetin/ kg body weight . However, it should be understood that the amount of the active ingredient actually administered ought to be determined in light of various relevant factors including the chosen route of administration, the age, sex and body weight of the individual patient, and the severity of the patient's symptom; and, therefore, the above dose should not be intended to limit the scope of the invention in any way.

Myricetin or the extract of Myrica rubra Siebold et Zuccarini cortex may also be incorporated in foods, as an additive or a dietary supplement, for the purpose of preventing or treating emotional instability and obesity. Accordingly, the present invention also provides a functional food composition effective for preventing or treating emotional instability and obesity, comprising an effective amount of myricetin or the extract. The inventive food composition may be prepared by mixing any of various foodstuffs; beverages; gums; teas; vitamin complexes; and health foods with an effective amount of myricetin or an extract of Myrica rubra Siebold et Zuccarini cortex.

The following Examples are intended to further illustrate the present invention without limiting its scope.

Example 1: Inhibition of serotonin N-acetyltransferase activity by a hot- water extract of Myrica rubra Siebold et Zuccarini cortex

Myrica rubra Siebold et Zuccarini cortex was treated with hot water for more than 3 hours to obtain a hot- water extract, and then, a part of the extract was freeze-dried and weighed.

Male white rats (Sprague Dawley, 200-250 g) were acclimated to a 12-hour day and a 12-hour night cycle for more than 1 week at a standard environment (indoor temperature 23 ± 1 ^°C, comparative humidity 60 ± 10%) before using in the following experiments. The pineal gland of the brain of white rat was excised under a red light at midnight, subjected to ultrasonic treatment to break up the tissue, centrifuged, and serotonin N-acetyltransferase was recovered from the supernatant.

The activity of serotonin N-acetyltransferase was determined by adding tryptamine, acetyl CoA, [³H]-acetyl CoA and myricetin thereto, incubating at 37 ^°C for 30 min, and then measuring radioactivity with a liquid scintillation counter.

To be specific, 13 μi of a pineal gland extract containing 5 βi of 10 mM tryptamine, 1 μi of 0.5 mM acetyl CoA, 1 μi of [³H] -acetyl CoA (3.6 Ci/mmol, 250 μCi/ml) and serotonin N-acetyltransferase was incubated at 37 ^°C for 30 min, and then, 180 μJL of 50 mM phosphate buffer (pH 6.8) was added thereto to stop the reaction. Water-immiscible Econofluor solution (Dupont NEN) containing 99.25%o (v/v) of 1,2,4-trimethylbenzene, 0.7%> (w/v) of 2,5-diphenyloxazole and 0.05% (w/v) of p-bis(o-methylstyril)benzene was used for fractionation of the reaction product. The above method was based on the difference of solubility between acetyltryptamine and acetyl CoA in the scintillation solution. The [³H]- acetyltryptamine produced in the above reaction is taken up by the scintillation solution, while unreacted [ H] -acetyl CoA remained in the aqueous layer. [ H]- Acetyltryptamine thus separated was quantified by measuring the radioactivity of the scintillation solution layer with a liquid scintillation counter.

The extents of serotonin N-acetyltransferase inhibition by the hot-water extract of Myrica rubra Siebold et Zuccarini obtained above were measured at various concentrations, and the result shows that the extent of serotonin N- acetyltransferase activity inhibition increases with increasing concentration of Myrica rubra Siebold et Zuccarini cortex extract (see Fig. 2). At a concentration of 36.2 g/m. of the above extract, about 50% inhibition effect was observed, and at 1.5 mg/m-β, the extract inhibited more than 98% of serotonin N-acetyltransferase activity. Example 2: Inhibition of serotonin N-acetyltransferase activity by myricetin

The procedure of Example 1 was repeated using myricetin in phase of the extract.

The result shows that the serotonin N-acetyltransferase activity is inhibited by myricetin in a concentration-dependent manner (see FIG. 3a). At 2.2 μM of myricetin, about 50% of the serotonin N-acetyltransferase activity was inhibited, and at 30 μM, more than 98% inhibition was observed.

Further, to examine the inhibition effect of myricetin to serotonin N- acetyltransferase according to the treatment time, the enzyme reaction and the measurement of its activity were conducted by the same procedure described in the

Example 1 except that the serotonin N-acetyltransferase activity was measured at 3,

6, 9, 12, 15 and 18 min., respectively, after treatment of 0.1 mM myricetin.

The result represents that the serotonin N-acetyltransferase activity is decreased according as the treatment time of myricetin is increased (see FIG. 3b). Myricetin represents about 30% inhibition effect at 3 min after treatment and about 50% inhibition effect at 15 min after treatment.

Example 3: Inhibitory mechanism of myricetin

In order to investigate the mechanism on how myricetin inhibits the activity of serotonin N-acetyltransferase, Lineweaver-Burk plots used on the Michaelis- Menten equation were obtained by way of measuring the activity variation while varying the initial concentration of tryptamine from 0.05 to 1 mM at a constant initial concentration of acetyl CoA 2 mM, and also while varying the initial concentration of acetyl CoA from 1.8 to 29 μM at a constant initial concentration of tryptamine 2.5 mM.

The result shows that myricetin acts as a noncompetitive inhibitor either with tryptamine or with acetyl CoA in the serotonin N-acetyltransferase-mediated reaction (see Fig. 4a and Fig. 4b).

Example 4: Examination of anti-depressant effect of myricetin via forced swimming test The anti-depressant effect of myricetin was measured by conducting a forced swimming test which is a standardized behavioral despair test employed in the measurement of the anti-depressant effect of a candidate therapeutic agent.

In a transparent acryl cylindrical water bath (40 cm in height, 18 cm in diameter) filled with water and maintained at 25 ^°C , white rats were forced to swim for 15 min. under a condition that their feet could not touch the bottom (1^st forced swimming). After 24 hours from the 1^st forced swimming, the rats again were subjected to forced swimming for a period of 5 min (2^nd forced swimming), and their behavior were observed. The rat's behavioral pattern at the 2^nd forced swimming was divided into "immobile", "swimming', and "climbing" conditions. The immobile condition was represented by the cumulative immobile period time, and the swimming and climbing conditions were each measured by counting the number of time units during which at least one such behavior was observed, after dividing the 5 min. test period into 5-second units. Myricetin was administered to each rat at a dose of 20 mg/kg by intraperitoneal injection after 15 min of the 1^st forced swimming, and at 5 hours and 1 hour before the 2^nd forced swimming.

As can be seen in FIG. 5a and FIG. 5b, the white rats administered with myricetin exhibited a much shorter immobile condition period as well as more active swimming and climbing behaviors, as compared to the control. This result thus suggests that myricetin is an effective anti-depressant agent.

INDUSTRIAL APPLICABILITY

The present invention reveals that myricetin inhibits serotonin N- acetyltransferase activity by specifically acting on serotonin N-acetyltransferase. Therefore, a pharmaceutical composition containing myricetin as an active ingredient may be advantageously used for the treatment of melatonin and serotonin-related diseases. The pharmaceutical composition of the present invention is particularly useful for treating sleep-disorder, depression, stress- related diseases or obesity.

While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art which also fall within the scope of the invention as defined by the appended claims.

Claims

What is Claimed is:

1. A use of myricetin (5,7,3 ',4',5'-pentahydroxyflavonol) for inhibiting serotonin N-acetyltransferase activity.

2. The use of claim 1, wherein 50% inhibition concentration (IC₅₀) of myricetin ranges from 2.0 to 2.5 μM.

3. A method for inhibiting the activity of serotonin N-acetyltransferase in a mammal, comprising administering thereto an effective dose of myricetin.

4. The method of claim 3, wherein the mammal is human.

5. The method of claim 3, wherein the effective dose ranges from 1 μg to 10 g myricetin/kg body weight/day.

6. A pharmaceutical composition for treating a serotonin N-acetyltransferase- related disease, which comprises myricetin as an active ingredient.

7. The composition of claim 6, wherein the serotonin N-acetyltransferase-related disease is a depression-related disease, a stress-related disease or obesity.

8. The composition of claim 7, wherein the depression-related disease is selected from the group consisting of seasonal affective disorder, premenstrual syndrome, unipolar depression, bipolar depression, manic-depressive psychosis and atypical depression and depression-related sleep-disorder.

9. The composition of claim 7, wherein the depression-related sleep-disorder is selected from the group consisting of insomnia, hypersomnia, parasomnia, dysomnia, fibromyalgia, delayed-sleep phase syndrome and advanced-sleep phase syndrome.

10. The composition of claim 6, wherein myricetin is present in the form of an extract of Myrica rubra Siebold et Zuccarini cortex.

11. The composition of claim 10, wherein the extract is a hot- water or ethanol extract of Myrica rubra Siebold et Zuccarini cortex.

12. A health food composition for emotional stability or anti-obesity which comprises myricetin as an active ingredient.

13. The composition of claim 12, wherein the myricetin is present in the form of an extract of Myrica rubra Siebold et Zuccarini cortex.