An orally active plant Rubisco-derived peptide increases neuronal leptin responsiveness.

Nutrient excess, such as the intake of a high-fat diet, reduces hypothalamic responses to exogenously administered leptin and induces dietary obesity; however, orally active components that attenuate neural leptin dysregulation have yet to be identified. We herein demonstrated that YHIEPV, derived from the pepsin-pancreatin digestion of the green leaf protein Rubisco, increased the leptin-induced phosphorylation of STAT3 in ex vivo hypothalamic slice cultures. We also showed that YHIEPV mitigated palmitic acid-induced decreases in leptin responsiveness. Furthermore, orally administered YHIEPV promoted leptin-induced reductions in body weight and food intake in obese mice. In addition, dietary-induced body weight gain was significantly less in mice orally or centrally administered YHIEPV daily than in saline-control mice. Cellular leptin sensitivity and the levels of proinflammatory-related factors, such as IL1ß and Socs-3, in the hypothalamus of obese mice were also restored by YHIEPV. YHIEPV blocked cellular leptin resistance induced by forskolin, which activates Epac-Rap1 signaling, and reduced the level of the GTP-bound active form of Rap1 in the brains of obese mice. Collectively, the present results demonstrated that the orally active peptide YHIEPV derived from a major green leaf protein increased neural leptin responsiveness and reduced body weight gain in mice with dietary obesity.

Rap1 in the VMH regulates glucose homeostasis.

The hypothalamus is a critical regulator of glucose metabolism and is capable of correcting diabetes conditions independently of an effect on energy balance. The small GTPase Rap1 in the forebrain is implicated in high-fat diet-induced (HFD-induced) obesity and glucose imbalance. Here, we report that increasing Rap1 activity selectively in the medial hypothalamus elevated blood glucose without increasing the body weight of HFD-fed mice. In contrast, decreasing hypothalamic Rap1 activity protected mice from diet-induced hyperglycemia but did not prevent weight gain. The remarkable glycemic effect of Rap1 was reproduced when Rap1 was specifically deleted in steroidogenic factor-1-positive (SF-1-positive) neurons in the ventromedial hypothalamic nucleus (VMH) known to regulate glucose metabolism. While having no effect on body weight regardless of sex, diet, and age, Rap1 deficiency in the VMH SF1 neurons markedly lowered blood glucose and insulin levels, improved glucose and insulin tolerance, and protected mice against HFD-induced neural leptin resistance and peripheral insulin resistance at the cellular and whole-body levels. Last, acute pharmacological inhibition of brain exchange protein directly activated by cAMP 2, a direct activator of Rap1, corrected glucose imbalance in obese mouse models. Our findings uncover the primary role of VMH Rap1 in glycemic control and implicate Rap1 signaling as a potential target for therapeutic intervention in diabetes.

Anti-Hypertensive Effects of Peptides Derived from Rice Bran Protein.

Hypertension is one of the major risk factors for arteriosclerosis. Anti-hypertensive peptides derived from animal proteins, such as milk, eggs and fish, are well studied. Anti-hypertensive peptides have also been identified from plant proteins such as soybeans. Rice bran, a byproduct of white rice polishing, is rich in protein and its high protein efficiency ratio is well known. This review discusses the anti-hypertensive peptides identified from rice bran protein and their mechanisms. In addition, we describe protease-digested rice bran from which functional peptides have not been isolated.

Ser-Tyr and Asn-Ala, vasorelaxing dipeptides found by comprehensive screening, reduce blood pressure via different age-dependent mechanisms.

To understand the changes in physiological responses due to aging, a number of bioactive probes based on different signal transduction pathways are necessary. In this study, we comprehensively and systematically investigated changes in blood vessel function with age using a 336-dipeptide library. In the early stage of hypertension, the most potent vasorelaxant dipeptide was Ser-Tyr (SY) in the mesenteric artery isolated from spontaneously hypertensive rats (SHR). SY-induced vasorelaxation and anti-hypertensive effects were blocked by L-NAME, an inhibitor of nitric oxide synthase (NOS), suggesting that SY activates the NO system. On the other hand, the patterns of dipeptides with vasorelaxation activity in early and advanced stages of hypertension were different. In the advanced stage, the most potent vasorelaxing dipeptide was Asn-Ala (NA). Orally administered NA (1.5 mg/kg) reduced the blood pressure in the advanced stage, at which drugs were sometimes less effective, and the anti-hypertensive effects lasted for 6 hr. The NA-induced vasorelaxation and anti-hypertensive activity was blocked by lorglumide, an antagonist of the cholecystokinin CCK1 receptor, suggesting that NA activated the CCK system. Taken together, in the early and advanced stages of hypertension, SY and NA exhibited vasorelaxing and anti-hypertensive effects via the NO and CCK systems, respectively.

Vasorelaxant and Antihypertensive Effects That Are Dependent on the Endothelial NO System Exhibited by Rice Bran-Derived Tripeptide.

We recently identified a novel, potent antihypertensive peptide, Leu-Arg-Ala (LRA; minimum effective dose = 0.25 mg/kg), from rice bran protein. In this study, we found that LRA potently relaxed mesenteric arteries isolated from spontaneously hypertensive rats (SHRs) (EC50 = 0.1 µM). In contrast, the vasorelaxant activity of each amino acid that constitutes the LRA tripeptide was remarkably attenuated. The LRA-induced vasorelaxant activity was inhibited by N(G)-nitro-l-arginine methyl ester (L-NAME; NO synthase [NOS] inhibitor) but not by an antagonist of bradykinin B2 and Mas receptors or by a phosphoinositide 3-kinase inhibitor. The antihypertensive effect induced after the oral administration of LRA was inhibited by L-NAME. LRA also induced the phosphorylation of endothelial NOS in human umbilical vein endothelial cells. Taken together, LRA may exhibit antihypertensive effects via NO-mediated vasorelaxation. LRA is the first example of a NO-dependent vasorelaxant peptide identified from rice bran protein.

l-Ornithine stimulates growth hormone release in a manner dependent on the ghrelin system.

We found that intraduodenal administration of l-ornithine (l-Orn) stimulates growth hormone (GH) secretion in Wistar rats, and then investigated its mechanism. GH-releasing activity after intraduodenal administration of l-Orn was blocked by [d-Lys3]-GHRP-6, an antagonist of the ghrelin receptor; however, l-Orn (100 µM) has no affinity for the ghrelin receptor, suggesting that the GH-releasing activity of l-Orn is mediated via ghrelin release and activation of the ghrelin receptor. Intraduodenally administered l-Orn increased ghrelin mRNA expression in the duodenum but not in the stomach or hypothalamus. In addition, l-Orn-induced GH-releasing activity was inhibited by propranolol, an antagonist of ß-adrenergic receptor, which is known to be coupled to ghrelin release. In conclusion, intraduodenally administered l-Orn stimulates GH secretion through the sympathetic nervous and ghrelin systems.

Brain-specific natriuretic peptide receptor-B deletion attenuates high-fat diet-induced visceral and hepatic lipid deposition in mice.

C-type natriuretic peptide (CNP) and its receptor, natriuretic peptide receptor-B (NPR-B), are abundantly distributed in the hypothalamus. To explore the role of central CNP/NPR-B signaling in energy regulation, we generated mice with brain-specific NPR-B deletion (BND mice) by crossing Nestin-Cre transgenic mice and mice with a loxP-flanked NPR-B locus. Brain-specific NPR-B deletion prevented body weight gain induced by a high-fat diet (HFD), and the mesenteric fat and liver weights were significantly decreased in BND mice fed an HFD. The decreased liver weight in BND mice was attributed to decreased lipid accumulation in the liver, which was confirmed by histologic findings and lipid content. Gene expression analysis revealed a significant decrease in the mRNA expression levels of CD36, Fsp27, and Mogat1 in the liver of BND mice, and uncoupling protein 2 mRNA expression was significantly lower in the mesenteric fat of BND mice fed an HFD than in that of control mice. This difference was not observed in the epididymal or subcutaneous fat. Although previous studies reported that CNP/NPR-B signaling inhibits SNS activity in rodents, SNS is unlikely to be the underlying mechanism of the metabolic phenotype observed in BND mice. Taken together, CNP/NPR-B signaling in the brain could be a central factor that regulates visceral lipid accumulation and hepatic steatosis under HFD conditions. Further analyses of the precise mechanisms will enhance our understanding of the contribution of the CNP/NPR-B system to energy regulation.

Orally administered δ opioid agonist peptide rubiscolin-6 stimulates food intake in aged mice with ghrelin resistance.

SCOPE: It is known that a decline in food intake occurs with aging. In this study, we investigated changes in parameters associated with food intake in response to aging, and whether orexigenic peptides stimulated food intake after peripheral administration even in aged mice. METHODS AND RESULTS: Food intake and body weight of 27-month-old male C57BL/6N mice were lower than those of 15-month-old mice. Epididymal and mesenteric fat mass, blood glucose, triglyceride, and leptin levels were also decreased. Meanwhile, the hypothalamic mRNA expression of endogenous orexigenic peptides such as neuropeptide Y (NPY) and agouti-related protein, also called agouti-related peptide, was increased. Next, we tested responsiveness to exogenously administered orexigenic peptides coupled to NPY in aged as well as young mice. Orally administered rubiscolin-6, a δ opioid agonist hexapeptide derived from a major green leaf protein Rubisco, stimulated food intake in 27-month-old mice. In contrast, ghrelin was ineffective after intraperitoneal administration to aged mice, suggesting that the NPY system downstream of ghrelin but not δ opioid receptors might be impaired in aged mice. CONCLUSION: Orally administered rubiscolin-6 stimulates food intake in aged mice with ghrelin resistance.

Lupeol supplementation improves blood pressure and lipid metabolism parameters in stroke-prone spontaneously hypertensive rats.

Supplementation with lupeol (0.67 g·kg(-1)) of the AIN-93M-based diet fed for 7 weeks to stroke-prone spontaneously hypertensive rats caused significantly decreased blood pressure as compared with a control group. Urinary 8-hydroxy-2'-deoxyguanosine was significantly lower in the lupeol group. Finally, lupeol suppressed the hepatic mRNA expression levels of the genes involved in triglyceride and cholesterol synthesis.

Zinc as an appetite stimulator - the possible role of zinc in the progression of diseases such as cachexia and sarcopenia.

Zinc is required by humans and animals for many physiological functions, such as growth, immune function, and reproduction. Zinc deficiency induces a number of physiological problems, including anorexia, growth retardation, dermatitis, taste disorder, and hypogonadism. Although it is clear that zinc deficiency produces specific and profound anorexia in experimental animals, the connection between zinc deficiency and anorexia is less certain. We were the first to show that orally, but not intraperitoneally, administered zinc rapidly stimulates food intake through orexigenic peptides coupled to the afferent vagus nerve using rats during early-stage zinc deficiency without decreased zinc concentrations in plasma and tissues. We confirmed that a zinc-sufficient diet containing zinc chloride acutely stimulated food intake after short-term zinc deprivation. We also found that orally administered zinc sulfate increased the expression of NPY and orexin mRNA after administration. Using vagotomized rats, we tested whether the increase in food intake after oral administration of zinc was mediated by the vagus nerve. In sham-operated rats, the oral administration of zinc stimulated food intake, whereas zinc and saline administrations did not exhibit differing effects in vagotomized rats. We conclude that zinc stimulates food intake in short-term zinc-deficient rats through the afferent vagus nerve with subsequent effects on hypothalamic peptides associated with food intake regulation. In this review, we describe recent research investigating the roles of zinc as an appetite stimulator in food intake regulation, along with research about hypothalamus, ghrelin, leptin and zinc receptor, and clinical application about anorexia nervosa, cachexia and sarcopenia. The article also presents some promising patents on zinc.

Complement C5a stimulates food intake via a prostaglandin D(2)- and neuropeptide Y-dependent mechanism in mice.

We have recently found that prostaglandin (PG) D(2) stimulates food intake via DP(1) receptor. Here we show that complement C5a stimulates food intake by activating the orexigenic PGD(2) system. C5a (30-100 pmol/mouse), after intracerebroventricular administration, stimulated food intake in non-food-deprived mice. The orexigenic activity of C5a was blocked by co-administration of a DP(1) receptor antagonist, BWA868C. Central administration of C5a elevated the hypothalamic mRNA expression of COX-2 but not COX-1, and the food intake stimulation of C5a was inhibited by pretreatment with a COX-2 inhibitor, celecoxib, suggesting that C5a activates COX-2 upstream of the PGD(2)-DP(1) system. The orexigenic activity of C5a was also inhibited by an antagonist for neuropeptide Y (NPY) Y(1) receptor, which was activated downstream of the PGD(2)-DP(1) system. These results suggest that C5a stimulates food intake via a PGD(2)- and NPY-dependent mechanism. C5a is the first example of orexigenic peptides acting through the PGD(2)-NPY system in the central nervous system.

Orally administered zinc increases food intake via vagal stimulation in rats.

We investigated the role of zinc in food intake regulation using rats during early-stage zinc deficiency without decreased zinc concentrations in plasma and tissues. Plasma, liver, and hypothalamic zinc concentrations were not affected in male Sprague-Dawley rats fed a zinc-deficient (Zn-Def) diet for 3 d compared with the pair-fed control group, which was fed a zinc-sufficient diet to the intake of the Zn-Def diet. Zinc sulfate at a dose of 19 micromol/kg body weight was orally or intraperitoneally (i.p.) administered to rats fed a Zn-Def diet for 3d and food intake was measured. We found that zinc stimulated food intake after oral but not i.p. administration. The mRNA expression of neuropeptide Y (NPY) and orexin in the hypothalamus significantly increased 3 h after oral but not i.p. administration of zinc. Pretreatment with an antagonist for the NPY Y(1) receptor or the orexin OX(1) receptor blocked orexigenic activity after oral administration of zinc. The stimulation of food intake by oral administration of zinc was abolished by vagotomy. Taken together, orally administered zinc may stimulate food intake via orexigenic peptides coupled to the afferent vagal stimulation in rats after short-term treatment with a Zn-Def diet.

Central prostaglandins in food intake regulation.

Prostaglandin (PG) E(2) and PGD(2), produced in the mammalian central nervous system, are known to have a variety of central actions on sleep, body temperature, and pain response via G-protein-coupled seven-transmembrane receptors. We found that centrally administered PGE(2) suppressed food intake via the EP(4) receptor, whereas PGD(2) increased food intake via the DP(1) receptor coupled to the neuropeptide Y Y(1) receptor. In this review, we summarize roles of central PGs in food intake regulation and discuss the relation between PGs and neuropeptides controlling food intake.

Central prostaglandin D(2) stimulates food intake via the neuropeptide Y system in mice.

We found that prostaglandin (PG) D(2), the most abundant PG in the central nervous system, stimulates food intake after intracerebroventricular administration in mice. The orexigenic effect of PGD(2) was mimicked by a selective agonist for the DP(1) receptor among two receptor subtypes for PGD(2), and abolished by its antagonist. Central administration of an antagonist or antisense oligodeoxynucleotide for the DP(1) receptor remarkably decreased food intake, body weight and fat mass. Hypothalamic mRNA levels of lipocalin-type PGD synthase were up-regulated after fasting. The orexigenic activity of PGD(2) was also abolished by an antagonist for neuropeptide Y (NPY) Y(1) receptor. Taken together, PGD(2) may stimulate food intake through central DP(1) receptor coupled to the NPY system.

Vitamin K deficiency reduces testosterone production in the testis through down-regulation of the Cyp11a a cholesterol side chain cleavage enzyme in rats.

Vitamin K (K) is an essential factor for the posttranslational modification of blood coagulation factors as well as proteins in the bone matrix (Gla proteins). It is known that K is not only distributed in the liver and bones but also abundantly distributed in the brain, kidney, and gonadal tissues. However, the role of K in these tissues is not well clarified. In this study, we used DNA microarray and identified the genes whose expression was affected in the testis under the K-deficient (K-def) state. The expression of genes involved in the biosynthesis of cholesterol and steroid hormones was decreased in the K-def group. The mRNA levels of Cyp11a - a rate-limiting enzyme in testosterone synthesis - positively correlated with the menaquinone-4 (MK-4) concentration in the testis. Moreover, as compared to the control (Cont) and K-supplemented (K-sup) groups, the K-def group had decreased testosterone concentrations in the plasma and testis. These results suggested that K is involved in steroid production in the testis through the regulation of Cyp11a.