Effects of dietary vitamins on obesity-related metabolic parameters.

Type 2 diabetes mellitus (T2DM) is one of the leading causes of death worldwide. Genetic factors, some underlying medical conditions, and obesity are risk factors of T2DM. Unlike other risk factors which are non-modifiable, obesity is preventable and usually treatable, and is largely contributed by lifestyle factors. Management of these lifestyle factors may curb the development of T2DM and reduces T2DM prevalence. Dietary vitamins have been recommended as a lifestyle modification intervention to support obesity treatment. Vitamins correlate negatively with body weight, body mass index and body composition. Some of the vitamins may also have anti-adipogenic, anti-inflammatory and antioxidant effects. However, results from pre-clinical and clinical studies of the effects of vitamins on obesity are inconsistent. A clear understanding of the effects of vitamins on obesity will help determine dietary intervention that is truly effective in preventing and treating obesity as well as obesity-related complications including T2DM. This article reviews existing evidences of the effects of vitamin supplementation on obesity and obesity-related metabolic status.

Lipopolysaccharide reduces gonadotrophin-releasing hormone (GnRH) gene expression: role of RFamide-related peptide-3 and kisspeptin.

RFamide-related peptide (RFRP)-3 reduces luteinising hormone (LH) secretion in rodents. Stress has been shown to upregulate the expression of the RFRP gene (Rfrp) with a concomitant reduction in LH secretion, but an effect on expression of the gonadotrophin-releasing hormone (GnRH) gene (Gnrh1) has not been shown. We hypothesised that lipopolysaccharide (LPS)-induced stress affects expression of Rfrp, the gene for kisspeptin (Kiss1) and/or Gnrh1, leading to suppression of LH levels in rats. Intracerebroventricular injections of RFRP-3 (0.1, 1, 5 nmol) or i.v. LPS (15µgkg-1) reduced LH levels. Doses of 1 and 5 nmol RFRP-3 were then administered to analyse gene expression by in situ hybridisation. RFRP-3 (5 nmol) had no effect on Gnrh1 or Kiss1 expression. LPS stress reduced GnRH and Kiss1 expression, without affecting Rfrp1 expression. These data indicate that LPS stress directly or indirectly reduces Gnrh1 expression, but this is unlikely to be due to a change in Rfrp1 expression.

Phenylacetic acids were detected in the plasma and urine of rats administered with low-dose mulberry leaf extract.

The use of a high quercetin dose to demonstrate its absorption and bioavailability does not reflect the real dietary situation because quercetin glycosides are usually present in small amounts in the human diet. This study aimed to demonstrate the absorption and bioavailability of quercetin in mulberry leaves that represents a more physiologic dietary situation. Mulberry leaf ethanol extract was prepared similar to tea infusion, which is the way the tea leaves are generally prepared for consumption. Accordingly, rats were fed by oral intubation the mulberry leaf ethanol extract (15 g%/rat per day) or pure rutin (135 microg/rat per day) for 2 weeks. The control group received a similar volume of the vehicle, 10% ethanol. There was a significant increase in total antioxidant activity (TAA) in the urine and feces of the antioxidants-fed rats. Phenylacetic acid, a microbial metabolite of quercetin, was detected in the urine of the test animals, and quercetin was present in the fecal samples. By using an in situ intestinal preparation, 3-hydroxyphenylacetic acid, another microbial metabolite of quercetin, was detected in the plasma when the duodenal segment was instilled with 2 mg of rutin. This microbial metabolite retained 50% of the TAA of quercetin. The results of this study indicate that in a more realistic dietary situation, an increase in TAA in the body after consumption of quercetin-containing foods is contributed mainly by the microbial metabolites.