JP2005082489A6 - Novel feeding promoting peptide, novel growth hormone secretion promoting peptide - Google Patents

Abstract

An object of the present invention is to design a small peptide ligand that acts as an agonist or antagonist to the receptor for ghrelin.
According to the present invention, peptides such as GSWF-NH ₂ , GSWFR, and FWSG-NH ₂ have been provided as agonists of the ghrelin receptor. These peptides as agonists capable of binding to the ghrelin receptor are considered to be effective as feeding enhancers or growth promoters.
[Selection] Figure 4

Description

  The present invention relates to a novel peptide that is a ghrelin receptor ligand that acts as a feeding promoting peptide or a growth hormone secretion promoting peptide.

  Growth hormone secretagogue (GHS) is a generic name for non-naturally occurring synthetic compounds that stimulate growth hormone secretion from the pituitary gland, and the GHS receptor is a protein that has been identified as a GHS receptor. . Since GHS is an artificial compound that does not exist in nature, its endogenous ligand has been explored.

  As a result of the search, ghrelin was isolated as an endogenous ligand for the GHS receptor. This ghrelin is a peptide hormone consisting of 28 amino acids and was isolated from the rat stomach in 1999. Through the GHS receptor expressed in the pituitary gland, ghrelin exhibits potent growth hormone secretion-promoting activity in both peripheral and central administration. Ghrelin has been reported to be most abundant in the stomach and also in the hypothalamus. Many GHS receptors are present in the pituitary gland and hypothalamus, but their expression is also observed in the stomach.

  Ghrelin has a characteristic structure in which the third residue serine is modified with octanoic acid, and this modifying group is essential for its activity expression. The chemical structure of ghrelin and its physiological action are shown in FIG. Ghrelin is known to have growth hormone secretion-promoting activity and strong feeding-promoting activity, but it also has various physiological functions such as increased gastrointestinal motility, promotion of gastric acid secretion, and blood pressure-lowering effect. It has become clear. In addition, recent knowledge about ghrelin is described in various reviews (Non-Patent Documents 1-4).

Yoshitake Minamitake Bio Clinica 18 (6), 2003 p57-61 Masayasu Kojima Bio Clinica 18 (6), 2003 p18-22 Masayasu Kojima Hormone and Clinical 49 (4), 2001 p303-310 Hosoda Yoji Pharmacia 38 (10), 2002 p925-929

  By the way, it is said that a decrease in growth hormone is one of the causes of aging. Therefore, an agonist (agonist) of ghrelin is expected not only to improve various dysfunctions associated with a decrease in growth hormone secretion, but also to be effective in preventing and improving anorexia and anorexia due to aging. Further, ghrelin antagonists (antagonists) can be used to suppress obesity caused by overeating, and thus to prevent or improve lifestyle-related diseases caused by obesity. Therefore, an object of the present invention is to design a small peptide ligand that acts as an agonist or antagonist for the receptor of ghrelin in order to obtain a peptide exhibiting such useful physiological action.

In order to obtain a peptidic ligand, the present inventors designed a peptide having 3 to 5 residues based on an N-terminal tetrapeptide in which the octanoylserine residue of ghrelin was substituted with a tryptophan residue. Specifically, GSWF based on a (Gly-Ser-Trp-Phe ) sequences and derivatives of these series of peptides, FWSG-NH ₂ peptide that is a retro peptide interchanged N-terminus and C-terminus of GSWF A series of derivatives were designed. When the affinity for the GHS receptor was evaluated by a receptor assay, it was revealed that GSWF-NH ₂ , GSWFR, the retro peptide FWSG-NH _2, etc. showed high receptor affinity.

In order to investigate whether these peptides are agonists or antagonists, physiological effects were examined in in vivo experiments. The above peptides showed feeding promotion and growth hormone secretion promoting effects. . Therefore, the above peptides are considered to be agonists. Therefore, the present invention provides peptides such as GSWF-NH ₂ , GSWFR, and FWSG-NH ₂ as agonists of the ghrelin receptor.

  Considering the physiological function of the ghrelin receptor, the peptide ligand of the present invention having the binding ability to the ghrelin receptor is considered to be effective as a feeding promoter or a growth promoter. Further, based on the knowledge of the present invention, it is possible to search for further peptide ligands. The ghrelin ligand thus obtained also has the physiological action as the agonist or antagonist described above. You can expect.

The present invention is a novel peptide characterized by being represented by GSWF-NH ₂ (Gly-Ser-Trp-Phe-NH ₂ ). Here, Phe-NH ₂ refers to an amino acid obtained by amidating the carboxyl group of Phe to CONH ₂ . Furthermore, the present invention is a novel peptide characterized by being represented by GSWFR (Gly-Ser-Trp-Phe-Arg). Furthermore, the present invention is a novel peptide characterized by being represented by GSWFK (Gly-Ser-Trp-Phe-Lys). Furthermore, the present invention is a novel peptide characterized by being represented by FWSG-NH ₂ (Phe-Trp-Ser-Gly-NH ₂ ). Here, Gly-NH ₂ is an amino acid obtained by amidating the carboxyl group of Gly to CONH ₂ . Furthermore, the present invention is a novel peptide characterized by being represented by FWSGR (Phe-Trp-Ser-Gly-Arg). All such amino acids are in the L-form.

  The peptide of the present invention can be obtained by various methods, preferably by a peptide synthesis method. That is, in a liquid phase method or a solid phase method, which is a method usually used for peptide synthesis, a raw material having a reactive carboxyl group corresponding to one of two kinds of fragments bisected at an arbitrary position of the peptide bond, and the other An active ester such as 2- (1H-benzotriazol-1-yl) -1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) and a raw material having a reactive amino group corresponding to the fragment The condensation can be carried out by using a method using carbodiimide or a method using carbodiimide. When the resulting condensate has a protecting group, it can also be produced by removing the protecting group.

  In this reaction step, functional groups that should not participate in the reaction are protected by protecting groups. Examples of amino-protecting groups include benzyloxycarbonyl (Bz), t-butyloxycarbonyl (Boc), p-biphenylisopropyloxycarbonyl, 9-fluorenylmethyloxycarbonyl (Fmoc) and the like. Examples of the carboxyl group-protecting agent include groups capable of forming alkyl esters, benzyl esters, etc., but in the solid phase method, the C-terminal carboxyl group is a chlorotrityl resin, chloromethyl resin, oxymethyl resin, P- It is bound to a carrier such as an alkoxybenzyl alcohol resin. The condensation reaction is carried out in the presence of a condensing agent such as carbodiimide or using an N-protected amino acid active ester or peptide active ester.

  After completion of the condensation reaction, the protecting group is removed, but in the solid phase method, the bond between the C-terminus of the peptide and the resin is further cleaved. Furthermore, the peptides of the present invention are purified according to conventional methods. Examples thereof include ion exchange chromatography, reverse phase liquid chromatography, affinity chromatography and the like. The synthesized peptides are analyzed by a protein sequencer that reads the amino acid sequence from the C-terminal by the Edman degradation method, GC-MS, or the like.

In the following examples, GSWF-NH ₂ , GSWFR, and FWSG-NH ₂ are administered into the rat ventricle in order to examine the feeding promoting action. In addition, GSWFR is administered intravenously to rats in order to investigate the growth hormone secretion promoting action. However, there is a possibility that administration routes such as oral administration, transdermal administration, and rectal administration may be adopted, and the administration route of the peptide of the present invention is not limited to the administration routes described in the Examples.

  The dose of this peptide varies depending on the type of compound, administration method, patient's symptoms, age, etc., but is usually 0.01 mg / kg to 10 g / kg, preferably 10.1 mg / kg to 1 g / kg per day. Preferably, it is 1 mg / kg to 100 mg / kg. The peptide of the present invention is usually administered in the form of a preparation prepared by mixing with a pharmaceutical carrier. As a pharmaceutical carrier, a substance that is commonly used in the pharmaceutical field and does not react with the peptide of the present invention is used.

  Specifically, examples of such substances are lactose, glucose, mannitol, dextrin, cyclodextrin, starch, sucrose, magnesium aluminate metasilicate, synthetic aluminum silicate, sodium carboxymethylcellulose, hydroxypropyl starch, carboxymethylcellulose calcium. , Ion exchange resin, methylcellulose, gelatin, gum arabic, hydroxypropylcellulose, hydroxypropylmethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol, light anhydrous silicic acid, magnesium stearate, talc, tragacanth, bentonite, bee gum, titanium oxide, sorbitan fatty acid ester, Sodium lauryl sulfate, glycerin, fatty acid glycerin ester, purified lanolin, glycerogelatin, polyso Bate, macrogol, vegetable oils, waxes, liquid paraffin, white petrolatum, fluorocarbons, nonionic surfactants, propylene glycol, water and the like.

  The dosage form is most preferably an injection, but there are also dosage forms such as tablets, capsules, granules, powders, syrups, suspensions, suppositories, ointments, creams, gels, patches, inhalants, etc. It is possible to employ as necessary. These preparations are prepared according to a conventional method. The liquid preparation may be dissolved or suspended in water or other appropriate solvent at the time of use. Tablets and granules may be coated by a known method. In the case of injection, it is prepared by dissolving the peptide of the present invention in water, but it may be dissolved in physiological saline or glucose solution as necessary, and a buffer or preservative may be added. Good.

  These preparations may contain the peptide of the present invention in a proportion of 0.01% to 100% by weight, preferably 1 to 90% by weight. These formulations may also contain other therapeutically valuable ingredients.

  In order to produce injections, the active ingredients are adjusted to pH, such as hydrochloric acid, sodium hydroxide, lactose, lactic acid, sodium, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium chloride, glucose, etc. It can be dissolved in distilled water for injection together with an isotonic agent, filtered aseptically and filled into ampoules, or further lyophilized by adding mannitol, dextrin, cyclodextrin, gelatin, etc. . In addition, reticin, polysorbate 80, polyoxyethylene hydrogenated castor oil, etc. may be added to the active ingredient and emulsified in water to give an emulsion for injection.

  In order to produce a solid preparation for oral administration, an active ingredient and excipient components such as lactose, starch, crystalline cellulose, calcium lactate, anhydrous silicic acid and the like are mixed to form a powder, or if necessary, sucrose, Add a binder such as hydroxypropylcellulose and polyvinylpyrrolidone, a disintegrant such as carboxymethylcellulose and carboxymethylcellulose calcium, and wet or dry granulate to form granules. In order to produce tablets, these powders and granules may be tableted as they are or after adding a lubricant such as magnesium stearate or talc. These granules or tablets should be coated with an enteric solvent base such as hydroxypropylmethylcellulose phthalate or methacrylic acid-methyl methacrylate polymer and coated with an enteric solvent preparation, or with ethylcellulose, carnauba wax, hydrogenated oil, etc. You can also. In order to produce capsules, powders or granules are filled into hard capsules, or active ingredients are dissolved as they are or dissolved in glycerin, polyethylene glycol, sesame oil, olive oil, etc., and then coated with a gelatin film to form soft capsules. Can do.

  In order to produce a liquid preparation for oral administration, an active ingredient and a sweetener such as sucrose, sorbitol, and glycerin are dissolved in water to add a transparent syrup, further essential oil, ethanol, etc. to make an elixir, Gum arabic, tragacanth, polysorbate 80, sodium carboxymethyl cellulose and the like may be added to form an emulsion or suspension. These liquid preparations may contain a flavoring agent, a coloring agent, a preservative and the like as desired.

  To produce a rectal dosage form, the active ingredient is moistened with a suppository base material such as cacao butter, fatty acid tri, di- and monoglycerides, polyethylene glycol, etc., dissolved, poured into a mold and cooled, or the active ingredient is polyethylene. What is necessary is just to coat | cover with a gelatin film | membrane after melt | dissolving in glycol, soybean oil, etc.

  In order to produce an external preparation for skin, the active ingredient is added to white petrolatum, beeswax, liquid paraffin, polyethylene glycol, etc., and if necessary, moistened and kneaded to make an ointment, or rosin, alkyl acrylate polymer After being kneaded with an adhesive such as polyalkyl, it is spread on a non-woven fabric such as polyalkyl to obtain a tape.

The present invention will be described in more detail in the following examples, but the following description does not limit the scope of the present invention.
A sample peptide, ¹²⁵ I-ghrelin 100 pM, a membrane fraction collected from the pituitary gland of a pig was incubated at 20 ° C. for 60 minutes, filtered through a GF / C glass filter, and then radioactivity was measured with a gamma counter.

  In ghrelin, the third residue, octanoyl serine, is essential for activity, and it is known that the activity is lost when the octanoyl group is removed. Studies on the structure-activity relationship of ghrelin have reported that even if the octanoyl serine residue of full-length ghrelin is substituted with tryptophan, it has affinity for the ghrelin receptor. Therefore, the octanoylserine residue of ghrelin was substituted with a tryptophan residue, and a peptide having 3 to 5 residues based on the ghrelin N-terminal tetrapeptide was designed. Derivatives of these series of peptides based on the sequence of GSWF (Gly-Ser-Trp-Phe) are referred to as the GSWF series. Fig. 2 shows the design concept of the GSWF series. In the future, it was synthesized using L-form amino acids in consideration of production in proteins by genetic manipulation.

Table 1 shows the results of evaluating the affinity of the GSWF series in the GHS receptor assay system. From Table 1, IC ₅₀ of ghrelin was 11 nM. The C-terminal free GSWF had an IC ₅₀ of 180 uM, about 1/500 that of ghrelin. Since there are cases where peptide activity is enhanced by introducing an amide group at the C-terminus, the affinity of GSWF-NH ₂ with an amide group introduced at the C-terminus for the GHS receptor was examined. Showed sex.

In consideration of producing a peptide in a protein, a peptide in which a basic amino acid lysine or arginine was introduced instead of an amide group was designed. GSWFK substituted with lysine had a lower affinity than GSWF-NH ₂ , whereas GSWFR substituted with arginine showed about three times higher affinity. In addition, two types of tripeptide amides with C-terminal and N-terminal of GSWF-NH ₂ were prepared and GHS receptor assay was performed. Their affinity was low. Therefore, the four residues on the N-terminal side are considered to be the smallest unit for having affinity for the GHS receptor.

An example is known in which the affinity for a receptor is increased by exchanging the N-terminal side and the C-terminal side of a peptide showing affinity for the receptor to form a retropeptide having the reverse sequence. Therefore, a peptide called FWSG-NH _2, which is a retropeptide in which the N-terminus and C-terminus of GSWF are exchanged, was created. A series of derivatives of this peptide is referred to as the FWSG series. Table 2 shows the results of GHS receptor assay for the FWSG series. Although no increase in affinity was observed, there was a tendency for the affinity to increase slightly by substituting the amide group for arginine as in GSWF-NH ₂ .

  Motilin is a 22-amino acid gastrointestinal peptide belonging to the same family as ghrelin and has a similar sequence to ghrelin. Motilin exhibits stronger gastrointestinal motility activity and weaker feeding promotion effect than ghrelin through the motilin receptor. To examine the selectivity of the various peptides designed above, a motilin receptor assay was performed.

A HEK-293 cell membrane fraction expressing a sample peptide, ¹²⁵ I-Motilin 0.26 nM and human motilin receptor was incubated at 25 ° C. for 60 minutes, filtered through a GF / C glass filter, and then measured with a gamma counter.

The results of evaluating the binding ability to the motilin receptor are shown in Table 3. In the motilin receptor assay, the IC ₅₀ of the endogenous ligand motilin was 1.6 nM. The affinity of the peptide having a ghrelin-derived sequence for the motilin receptor was low. However, as in the case of evaluating the binding ability to the GHS receptor, GSWFR in which the C terminus was substituted with arginine showed higher affinity than GSWF-NH ₂ . The same tendency was observed in the FWSG series, which is a retropeptide.

In Table 3, the index of receptor selectivity of each peptide is shown at the right end of the table (Motilin / GHS). The larger this value, the higher the selectivity for GHS-R. It has been reported that the low molecular weight peptide FVWI-NH ₂ having a sequence referring to the N-terminus of motilin exhibits affinity for the motilin receptor. GSWFR and GSWF-NH ₂ derived from the ghrelin sequence were more selective for the GHS receptor than FVWI-NH ₂ derived from the motilin sequence. From the above, GSWFR into which arginine was introduced had a high affinity for the GHS receptor and showed the highest selectivity among low molecular peptides.

  Furthermore, considering the possibility that the above-mentioned peptides act as agonists or antagonists of the GHS receptor, the effects of these peptides on feeding and growth hormone secretion were investigated.

  A 7-week-old male ddY mouse was used as an experimental animal, a guide cannula was inserted and fixed in the third ventricle under Nembutal anesthesia, and a feeding experiment was conducted after a recovery period of 1 week. After the peptide was dissolved in artificial spinal fluid ACSF, 4 μl was intraventricularly administered to unanesthetized mice, and the weight of solid feed was measured at four time points before administration, 20 minutes, 60 minutes, and 120 minutes after administration. The amount of meal was calculated.

FIG. 4 shows the results of studying the amount of food saving in mice administered with GSWFR, GSWF-NH ₂ , and GSWFR. In FIG. 4, the horizontal axis represents the dose, and the vertical axis represents the amount of food consumed for 20 to 60 minutes after administration, which is the ratio when the amount of food consumed in the control group is 100%. In FIG. 4, white circles indicate FWSG-NH ₂ , black squares indicate GSWFR, and white triangles indicate GSWF-NH ₂ . GSWFR, which showed the highest affinity in the receptor assay, showed a stronger feeding promotion effect than GSWF-NH ₂ . Therefore, these peptides are considered to be GHS receptor agonists. The retro form of FWSG-NH ₂ also showed a feeding-enhancing effect. These peptides have an effect of promoting feeding depending on the strength of affinity of the GHS receptor.

Using [D-Lys ₃ ] -GHRP-6, which is a GHS receptor antagonist, whether or not the feeding promoting action of GSWFR is mediated by the GHS receptor was examined. As a result, the increase in food intake by GSWFR administration was significantly inhibited by coadministration with 1 nmol antagonist, indicating that GSWFR promotes food intake via the GHS receptor.

  Furthermore, growth hormone secretion ability was examined. Wistar male rats (280-400 g) were used as experimental animals, and a catheter for blood collection was inserted into the femoral artery and a catheter for peptide administration into the femoral vein under anesthesia. The blood growth hormone concentration is known to show a spontaneous spike-like peak separately from the circadian rhythm. In order to suppress this, the experiment was conducted under Nembutal anesthesia. GSWFR was dissolved in physiological saline, intravenously administered, blood was collected over time, plasma was separated, and growth hormone concentration was measured by ELISA.

  FIG. 5 shows changes in blood growth hormone concentration when GSWFR was intravenously administered at 7 mg / kg (white triangles) or 50 mg / kg (black squares). There was no change in the growth hormone concentration after intravenous administration of 7 mg / kg. On the other hand, in the case of intravenous administration of 50 mg / kg, the growth hormone concentration increased from 5 minutes after administration, and showed a peak about 4 times that before administration after 15 minutes. Thus, GSWFR was found to stimulate growth hormone secretion. From the above results, it was revealed that GSWFR showing affinity to the GHS receptor not only shows feeding promotion action as a GHS receptor agonist but also has growth hormone secretion promoting action.

According to the present invention, peptides such as GSWF-NH ₂ , GSWFR, and FWSG-NH ₂ were provided as agonists of the ghrelin receptor. Since these peptides are agonists capable of binding to the ghrelin receptor, they are considered to be effective as feeding stimulants or growth promoters. Therefore, the peptide of the present invention is expected not only to improve various dysfunctions associated with a decrease in growth hormone secretion, but also to be effective in preventing and improving anorexia and anorexia due to aging. It is also possible to search for other peptide ligands based on the knowledge of the present invention. The peptide ligand thus obtained can also be expected to have a physiological effect as an agonist or antagonist of the ghrelin receptor.

FIG. 1 is a diagram showing the chemical structure of human ghrelin and its physiological action. FIG. 2 is a diagram showing a design strategy of GSWF series peptides. FIG. 3 is a diagram comparing the amino acid sequences of ghrelin and motilin. FIG. 4 is a graph showing the results of studying the amount of food saving in mice administered with GSWFR, GSWF-NH ₂ , and GSWFR. FIG. 5 is a graph showing the results of examining growth hormone secretion ability of mice administered with GSWFR.

Claims (12)

GSWF-NH ₂ (Gly-Ser-Trp-Phe-NH _2, where Phe-NH ₂ is an amino acid in which the carboxyl group of Phe is amidated to CONH ₂ ) peptide.   A novel peptide characterized by being represented by GSWFR (Gly-Ser-Trp-Phe-Arg).   A novel peptide characterized by being represented by GSWFK (Gly-Ser-Trp-Phe-Lys). FWSG-NH ₂ (Phe-Trp-Ser-Gly-NH _2, where Gly-NH ₂ is an amino acid in which Gly's carboxyl group is amidated to CONH ₂ ) peptide.   A novel peptide characterized by being represented by FWSGR (Phe-Trp-Ser-Gly-Arg).   The peptide according to any one of claims 1 to 5, wherein the peptide acts as an agonist of a ghrelin receptor.   The peptide according to any one of claims 1 to 5, which has a feeding promoting action.   The peptide according to any one of claims 1 to 5, which has a growth hormone secretion promoting action.   A feeding promoter comprising the peptide according to any one of claims 1 to 5 as an active ingredient.   A growth hormone secretagogue comprising the peptide according to any one of claims 1 to 5 as an active ingredient.   A method for promoting feeding using the peptide according to any one of claims 1 to 5.   A method for promoting the secretion of growth hormone using the peptide according to any one of claims 1 to 5.

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