Brown adipose tissue (BAT), a major site for mammalian nonshivering thermogenesis, could be a target for prevention and treatment of human obesity. Transient receptor potential vanilloid 2 (TRPV2), a Ca 2+-permeable non-selective cation channel, plays vital roles in the regulation of various cellular functions. Here, we show that TRPV2 is expressed in brown adipocytes and that mRNA levels of thermogenic genes are reduced in both cultured brown adipocytes and BAT from TRPV2 knockout (TRPV2KO) mice. The induction of thermogenic genes in response to b-adrenergic receptor stimulation is also decreased in TRPV2KO brown adipocytes and suppressed by reduced intracellular Ca 2+ concentrations in wild-type brown adipocytes. In addition, TRPV2KO mice have more white adipose tissue and larger brown adipocytes and show cold intolerance, and lower BAT temperature increases in response to b-adrenergic receptor stimulation. Furthermore, TRPV2KO mice have increased body weight and fat upon high-fat-diet treatment.Based on these findings, we conclude that TRPV2 has a role in BAT thermogenesis and could be a target for human obesity therapy.

AIM:To investigate whether nicotinamide overload plays a role in type 2 diabetes. METHODS:Nicotinamide metabolic patterns of 14 diabetic and 14 non-diabetic subjects were compared using HPLC. Cumulative effects of nicotinamide and N 1 -methylnicotinamide on glucose metabolism, plasma H2O2 levels and tissue nicotinamide adenine dinucleotide (NAD) contents of adult Sprague-Dawley rats were observed. The role of human sweat glands and rat skin in nicotinamide metabolism was investigated using sauna and burn injury, respectively. RESULTS:Diabetic subjects had significantly higher plasma N 1 -methylnicotinamide levels 5 h after a 100-mg nicotinamide load than the non-diabetic subjects (0.89 ± 0.13 μmol/L vs 0.6 ± 0.13 μmol/L, P < 0.001). Cumulative doses of nicotinamide (2 g/kg) significantly increased rat plasma N 1 -methylnicotinamide concentrations associated with severe insulin resistance, which was mimicked by N 1 -methylnicotinamide. Moreover, cumulative exposure to N 1 -methylnicotinamide (2 g/kg) markedly reduced rat muscle and liver NAD contents and erythrocyte NAD/ NADH ratio, and increased plasma H2O2 levels. Decrease in NAD/NADH ratio and increase in H2O2 generation were also observed in human erythrocytes after exposure to N 1 -methylnicotinamide in vitro . Sweating eliminated excessive nicotinamide (5.3-fold increase in sweat nicotinamide concentration 1 h after a 100-mg nicotinamide load). Skin damage or aldehyde oxidase inhibition with tamoxifen or olanzapine, both being notorious for impairing glucose tolerance, delayed N 1 -methylnicotinamide clearance. CONCLUSION:These findings suggest that nicotinamide overload, which induced an increase in plasma N 1 -methylnicotinamide, associated with oxidative stress and insulin resistance, plays a role in type 2 diabetes.

China has an extremely low overall IDDM incidence rate. China also has the greatest geographic and ethnic variation seen for any country.