L-citrulline inhibits body weight gain and hepatic fat accumulation by improving lipid metabolism in a rat nonalcoholic fatty liver disease model.

BACKGROUND: Body weight gain is a social issue all over the world. When body weight increased, hepatic fat accumulation also increased and it causes fatty liver disease. Therefore, developing a new treatment method and elucidating its mechanism is necessary. L-citrulline (L-Cit) is a free amino acid found mainly in watermelon. No reports regarding its effects on the improvement of hepatic steatosis and fibrogenesis are currently available. The aim of this study was to clarify the effect and the mechanism of L-Cit on inhibition of body weight gain and hepatic fat accumulation in high-fat and high-cholesterol fed SHRSP5/Dmcr rats. METHODS: L-Cit or water (controls) was administered to six-week-old male SHRSP5/Dmcr rats by gavage for nine weeks. We recorded the level of body weight and food intake while performing the administration and sacrificed rats. After that, the blood and lipid metabolism-related organs and tissues were collected and analyzed. RESULTS: L-Cit treatment reduced body weight gain and hepatic TC and TG levels, and serum levels of AST and ALT. L-Cit enhanced AMPK, LKB1, PKA, and hormone-sensitive lipase (HSL) protein phosphorylation levels in the epididymal fat. L-Cit treatment improved steatosis as revealed by HE staining of liver tissues and enhanced AMPK and LKB1 phosphorylation levels. Moreover, activation of Sirt1 was higher, while the liver fatty acid synthase (FAS) level was lower. Azan staining of liver sections revealed a reduction in fibrogenesis following L-Cit treatment. Further, the liver levels of TGF-ß, Smad2/3, and α-SMA, fibrogenesis-related proteins and genes, were lower in the L-Cit-treated group. CONCLUSIONS: From the results of analysis of the epididymal fat and the liver, L-Cit inhibits body weight gain and hepatic fat accumulation by activating lipid metabolism and promoting fatty acid ß-oxidation in SHRSP5/Dmcr rats.

Evaluation of the Effects and Mechanism of L-Citrulline on Anti-obesity by Appetite Suppression in Obese/Diabetic KK-Ay Mice and High-Fat Diet Fed SD Rats.

L-Citrulline (L-Cit), a free amino acid from watermelon, has effects on hypertension and anti-oxidization; however, there are few reports of effects related to obesity. This study investigated the effects and mechanism of L-Cit on anti-obesity in obese/diabetic KK-Ay mice and high-fat diet fed Sprague-Dawley (SD) rats. L-Cit induced significant reduction of food intake, body weight and fat tissue mass in obese/diabetic KK-Ay mice. Moreover, blood glucose level did not change but free fatty acid level and serum insulin level were significantly decreased by treatment with L-Cit, suggesting that L-Cit improved glucose and fatty metabolism in obesity model mice. As well as obese/diabetic KK-Ay mice, there was a significant decrease in food intake and a tendency of body weight to decrease in high-fat diet fed SD rats treated with L-Cit. Also, levels of proopiomelanocortin (POMC), a food intake suppression peptide, increased in the hypothalamus. Our study suggests that L-Cit improves metabolic syndrome through decreased body weight by appetite suppression.

L-Citrulline increases hepatic sensitivity to insulin by reducing the phosphorylation of serine 1101 in insulin receptor substrate-1.

BACKGROUND: Insulin resistance is characterized by deficient responses to insulin in its target tissues. In the present study, we examined the effects of L-Citrulline (L-Cit) on insulin sensitivity and signaling cascades in rat hepatoma H4IIE cells and SHRSP.Z-Leprfa/IzmDmcr rats. METHODS: H4IIE cells were pretreated in the presence or absence of 250 µM L-Cit in serum-free medium and then incubated in the presence or absence of 0.1 nM insulin. Rats were allocated into 2 groups; a control group (not treated) and L-Cit group (2 g/kg/day, L-Cit) and treated for 8 weeks. RESULTS: L-Cit enhanced the insulin-induced phosphorylation of Akt in H4IIE cells. Moreover, the inhibited expression of Dex/cAMP-induced PEPCK mRNA by insulin was enhanced by the L-Cit treatment. The phosphorylation of tyrosine, which is upstream of Akt, in insulin receptor substrate-1 (IRS-1) was increased by the L-Cit treatment. The L-Cit-induced enhancement in insulin signaling was not related to the binding affinity of insulin to the insulin receptor or to the expression of the insulin receptor, but to a decrease in the phosphorylation of serine 1101 in IRS-1. These results were also confirmed in animal experiments. In the livers of L-Cit-treated rats, PI3K/Akt signaling was improved by decreases in the phosphorylation of serine 1101. CONCLUSIONS: We herein demonstrated for the first time the beneficial effects of L-Cit on improved insulin resistance associated with enhanced insulin sensitivity. These results may have clinical applications for insulin resistance and the treatment of type-2 diabetes.

Evaluation of the effect of methionine and glucosamine on adjuvant arthritis in rats.

In the present study, we evaluated the effects of individual administration of methionine or glucosamine (GlcN) and compared with the combined administration of methionine and GlcN on the adjuvant arthritis model of rheumatoid arthritis in rats. Adjuvant arthritis was induced in female Lewis rats by injecting Freund's complete adjuvant (FCA) into the right hind paws, and methionine (200 mg/kg body weight/day) and/or GlcN (400 mg/kg/day) were orally administered for 21 days. The progression of the adjuvant arthritis was clinically evaluated for characteristic signs and symptoms by employing an arthritis score. The administration of methionine combined with GlcN suppressed the swelling of FCA-uninjected left hind paws and the arthritis score. Additionally, histopathological examination revealed that the combined administration of methionine and GlcN markedly suppressed synovial hyperplasia and the destruction of the cartilage surface and articular meniscus of the knee joints of FCA-injected right hind paws. Furthermore, combined methionine and GlcN administration suppressed the increase in the levels of nitric oxide, prostaglandin E(2) and hyaluronic acid in the plasma of rats with adjuvant arthritis. By contrast, individual administration of methionine or GlcN suppressed arthritis only slightly. These observations suggest that the combined administration of methionine and GlcN is more effective compared with individual administrations of methionine or GlcN in suppressing the progression of adjuvant arthritis (identified as swelling of joints and arthritis score), possibly by synergistically inhibiting synovial inflammation (identified as synovial hyperplasia and the destruction of the cartilage surface and articular meniscus) and the production of inflammatory mediators.