Kazuhisa Honda

Investigation of the Anti-Obesity Action of Licorice Flavonoid Oil in Diet-Induced Obese Rats

Licorice flavonoid oil (LFO), which contains hydrophobic flavonoids from Glycyrrhiza glabra LINNE, is a new ingredient for functional foods. In this study, we investigated the anti-obesity action of LFO in diet-induced obese rats. The addition of 2% LFO in a high-fat diet significantly decreased the weight of abdominal adipose tissue and the levels of hepatic and plasma triglycerides. We found that the enzymatic activities of acetyl-CoA carboxylase and fatty acid synthase, the rate-limiting enzymes in the fatty acid synthetic pathway, were significantly decreased by LFO, whereas the enzymatic activity of acyl-CoA dehydrogenase, the rate-limiting enzyme in the fatty acid oxidative pathway, was significantly increased. All our findings suggest that the anti-obesity action of LFO is controlled by regulation of the rate-limiting enzymes in the fatty acid synthetic and oxidative pathways in the liver.

Central administration of insulin suppresses food intake in chicks

Although the orexigenic action of peptide hormones such as ghrelin and growth hormone releasing peptide is different between chickens and mammals, the anorexigenic action of peptide hormones is similar in both species. For example, central administration of peptide hormones such as leptin, cholecystokinin or glucagon has been shown to suppress food intake behavior in chickens and mammals. Central administration of insulin suppresses food intake in mammals. However, the anorexigenic action of insulin in chickens has not yet been identified. In the present study, we investigated the effects of central administration of insulin on food intake in chicks. Intracerebroventricular administration of insulin in chicks significantly suppressed food intake. Central administration of insulin significantly upregulated mRNA levels of proopiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART) and corticotropin-releasing factor (CRF), but did not influence mRNA levels of neuropeptide Y and agouti-related protein in the hypothalamus. These results suggest that alpha-melanocyte stimulating hormone (alpha-MSH, an anorexigenic peptide from the post-translational cleavage of POMC), CART and CRF are involved in the anorexigenic action of insulin in chicks. Furthermore, central administration of alpha-MSH or CART significantly suppressed food intake. In addition, alpha-MSH significantly upregulated CRF mRNA expression, suggesting that the anorexigenic action of alpha-MSH is mediated by CRF. Our findings demonstrate that insulin functions in chicks as an appetite-suppressive peptide in the central nervous system and suggest that this anorexigenic action is mediated by CART, alpha-MSH and CRF.

Central administration of glucagon suppresses food intake in chicks

Food intake in chickens is regulated in a manner similar to that in mammals. Corticotropin-releasing factor (CRF), which increases the plasma corticosterone concentration, plays an important role as a mediator of many appetite-suppressive peptides in the central nervous system in both species. Central administration of glucagon suppresses food intake in rats. However, the anorexigenic action of glucagon in chicks has not yet been identified. In the present study, we investigated the effects of central administration of glucagon on food intake in chicks. Intracerebroventricular administration of glucagon in chicks significantly suppressed food intake and significantly induced hyperglycemia. In contrast, peripheral administration of the same dose of glucagon did not influence food intake and plasma glucose concentration. These results suggest that glucagon functions in chicks as an appetite-suppressive peptide in the central nervous system. Intracerebroventricular administration of glucagon in chicks also significantly increased CRF mRNA expression and plasma corticosterone concentration, suggesting that CRF acts as a downstream molecule for a glucagon-induced appetite-suppressive pathway in chicks. It is likely that the induction of hyperglycemia by central administration of glucagon is involved in its anorexigenic action, because peripheral administration of glucose in chicks suppressed food intake. These results suggest that CRF- and/or hyperglycemia-mediated pathways are involved in the anorexigenic action of glucagon in chicks.

Neuropeptide Y effect on food intake in broiler and layer chicks.

Broiler chicks eat more food than layer chicks. In this study, we examined the involvement of orexigenic peptide neuropeptide Y (NPY) in the difference in food intake between broiler and layer chicks (Gallus gallus). First, we compared the hypothalamic mRNA levels of NPY and its receptors (Y1 and Y5 receptors) between these strains at 1, 2, 4, and 8 days of age. Daily food intake was significantly higher in broiler chicks than layer chicks after 2 days of age. However, the hypothalamic NPY mRNA level was significantly lower in broiler chicks than layer chicks except at 8 days of age. In addition, the mRNA levels of NPY receptors were also significantly lower in broiler chicks than layer chicks at 2 and 4 days of age (Y1 receptor) or 2 days of age (Y5 receptor). These results suggest that the differences in the expressions of hypothalamic NPY and its receptors do not cause the increase in food intake in broiler chicks. To compare the orexigenic effect of NPY between broiler and layer chicks, we next examined the effects of central administration of NPY on food intake in these strains. In both strains, central administration of NPY significantly increased food intake at 2, 4 and 8 days of age. All our findings demonstrated that the increase in food intake in broiler chicks is not accompanied with the over-expression of NPY or its receptor.

Central administration of neuromedin U suppresses food intake in chicks

The appetite-suppressive action of brain-gut peptides is similar in both chickens and mammals. In mammals, the brain-gut peptide neuromedin U (NMU) suppresses food intake via hypothalamic neuropeptides, corticotropin-releasing factor (CRF), oxytocin, and arginine-vasopressin. In chickens, central administration of CRF, oxytocin, or arginine-vasotocin (AVT, a nonmammalian equivalent of arginine-vasopressin) suppresses food intake. However, the anorexigenic action of NMU in chickens has not yet been identified. In the present study, we analyzed the effects of the central administration of NMU on food intake and hypothalamic mRNA levels of CRF, AVT and mesotocin (a nonmammalian equivalent of oxytocin) in chicks. Intracerebroventricular administration of NMU in chicks significantly suppressed food intake and induced wing-flapping behavior. NMU also significantly upregulated mRNA expression of CRF and AVT, but did not influence mRNA expression of mesotocin in the hypothalamus. These results suggest that NMU functions as an appetite-suppressive peptide via CRF and AVT in the central nervous system in chicks.

Effects of central administration of glucagon on feed intake and endocrine responses in sheep.

This study was conducted to investigate effects of glucagon intracerebroventricularly administered on feed intake and endocrine changes in sheep. Four male sheep (48-55 kg BW) were used. The animals were acclimatized to be fed alfalfa hay cubes at 12.00 hour. Human glucagon (40 and 80 microg/0.5 mL) was injected into the lateral ventricle at 12.00 hour. Blood samples were taken every 10 min from 30 min before to 180 min after the glucagon injection. Soon after the injection, the animals were given alfalfa hay cubes, and the amounts of the feed eaten within 2 h were measured. Feed intakes were significantly (P < 0.05) suppressed by 80 microg of glucagon. Plasma glucose levels in control animals were gradually decreased after the feeding, whilst those in glucagon-treated animals were temporarily elevated just after the feeding and then kept higher than control levels. Plasma insulin was abruptly elevated after the feeding and was maintained at higher levels than before the feeding in all treatments. Plasma NEFA concentrations were decreased after the feeding in all treatments. A tendency of increase in plasma cortisol levels occurred in glucagon-injected animals. The present study provides the first evidence that glucagon directly acts on the brain, then inhibiting feeding behavior and inducing endocrine responses in ruminants.

The mechanism underlying the central glucagon-induced hyperglycemia and anorexia in chicks

We investigated the mechanism underlying central glucagon-induced hyperglycemia and anorexia in chicks. Male 8-day-old chicks (Gallus gallus) were used in all experiments. Intracerebroventricular administration of glucagon in chicks induced hyperglycemia and anorexia from 30 min after administration. However, the plasma insulin level did not increase until 90 min after glucagon administration, suggesting that glucose-stimulated insulin secretion from pancreatic beta cells may be suppressed by central glucagon. The plasma corticosterone concentration significantly increased from 30 min to 120 min after administration, suggesting that central glucagon activates the hypothalamic pituitary adrenal (HPA) axis in chicks. However, central administration of corticotropin-releasing factor (CRF), which activates the HPA axis in chicken hypothalamus, significantly reduced not only food intake but also plasma glucose concentration, suggesting that CRF and the activation of the HPA axis are related to the glucagon-induced anorexia but not hyperglycemia in chicks. Phentolamine, an α-adrenergic receptor antagonist, significantly attenuated the glucagon-induced hyperglycemia, suggesting that glucagon induced hyperglycemia at least partly via α-adrenergic neural pathway. Co-administration of phentolamine and α-helical CRF, a CRF receptor antagonist, significantly attenuated glucagon-induced hyperglycemia and anorexia. It is therefore likely that central administration of glucagon suppresses food intake at least partly via CRF-induced anorexigenic pathway in chicks.

Alpha-melanocyte stimulating hormone plays an important role in the regulation of food intake by the central melanocortin system in chicks

Proopiomelanocortin (POMC, a precursor of melanocortin peptides) neurons in the hypothalamus play an important role in the central regulation of food intake in mammals. There is evidence that human melanocortin peptides alpha-, beta- and gamma2-melanocyte-stimulating hormone (α-, β- and γ2-MSH) significantly decreased food intake in chickens. However, the amino acid sequences of β- and γ2-MSH of chickens are different from those of humans whereas the amino acid sequence of α-MSH is conserved between these species. In the present study, we examined the effects of the central administration of α-, chicken β-, and chicken γ2-MSH on food intake in chicks. Central administration of α-MSH significantly suppressed food intake in chicks. In contrast, β- and γ2-MSH did not influence food intake in chicks. Central administration of HS014, a melanocortin 4 receptor antagonist, significantly reversed the anorexigenic action of α-MSH, suggesting that this action is mediated by the melanocortin 4 receptor in chicks as well as in mammals. These results suggest that α-MSH may play an important role in the regulation of food intake by the central melanocortin system in chicks.

The molecular mechanism underlying the reduction in abdominal fat accumulation by licorice flavonoid oil in high fat diet-induced obese rats

Licorice (Glycyrrhiza glabra) has been widely used in traditional medicines, and its flavonoid oil (LFO) decreases abdominal adipose tissue weight in mammals. In the present study, we investigated the molecular mechanisms underlying the decrease in abdominal adipose tissue weight by LFO. LFO significantly decreased the mRNA levels of rate-limiting enzymes in the hepatic fatty acid synthetic pathway, whereas LFO significantly increased the mRNA levels of a rate-limiting enzyme in the hepatic fatty acid oxidative pathway. LFO significantly decreased the mRNA levels of sterol regulatory element-binding protein-1c (SREBP-1c) (a transcription factor that promotes hepatic fatty acid synthesis), whereas the mRNA levels of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) (a transcription factor that promotes hepatic fatty acid oxidation) was significantly increased. All our findings suggest that the decrease in abdominal adipose tissue weight by LFO is mediated by the transcriptional regulation of SREBP-1c and PPAR-alpha in the liver. Thus, we infer that the natural ingredient LFO is a promising candidate for use as a feed additive to reduce abdominal fat accumulation in domestic animals.

Corticotropin-releasing factor is a downstream mediator of the beta-melanocyte-stimulating hormone-induced anorexigenic pathway in chicks.

Proopiomelanocortin (POMC, a precursor of anorexigenic neuropeptides) neurons in hypothalamus suppresses food intake in both mammals and chickens. In mammals, several lines of evidence suggest that POMC-derived anorexigenic peptides upregulate mRNA levels of anorexigenic peptides such as corticotropin-releasing factor (CRF) and thyrotropin-releasing factor and downregulate mRNA levels of orexigenic peptides such as orexin and melanin-concentrating hormone. However, the POMC-induced anorexigenic pathway in chickens has not been well characterized. In the present study, we investigated how POMC neurons regulate mechanisms of food intake using an anorexigenic peptide, beta-melanocyte-stimulating hormone (beta-MSH), derived from the post-transcriptional cleavage of POMC. Central administration of beta-MSH in chicks significantly suppressed food intake, and importantly, this suppression was accompanied by a significant upregulation of CRF mRNA levels. Furthermore, the CRF type 2 receptor antagonist alpha-helical CRF significantly reversed the anorexigenic action of beta-MSH. These findings indicate that CRF and its receptor, CRF type 2 receptor, act as the major mediators in beta-MSH-induced anorexigenic action in chicks. beta-MSH significantly increased orexin mRNA levels and did not alter mRNA levels of thyrotropin-releasing factor and melanin-concentrating hormone in chicks, suggesting that the beta-MSH-induced anorexigenic pathway in chicks is different from that in mammals. Increases in orexin mRNA levels were accompanied by significant decreases in plasma glucose concentration, suggesting that orexin mRNA might be stimulated by beta-MSH-induced hypoglycemia. Thus, this study demonstrates the direct evidence that CRF is a critical downstream target in the beta-MSH-induced anorexigenic pathway in chicks.