Differential effects of cobalt and mercury on lipid metabolism in the white adipose tissue of high-fat diet-induced obesity mice

Metals and metalloid species are involved in homeostasis in energy systems such as glucose metabolism. Enlarged adipocytes are one of the most important causes of obesity-associated diseases. In this study, we studied the possibility that various metals, namely, CoCl₂, HgCl₂, NaAsO₂ and MnCl₂ pose risk to or have beneficial effects on white adipose tissue (WAT). Exposure to the four metals resulted in decreases in WAT weight and the size of enlarged adipocytes in mice fed a high-fat diet (HFD) without changes in liver weight, suggesting that the size and function of adipocytes are sensitive to metals. Repeated administration of CoCl₂ significantly increased serum leptin, adiponectin and high-density lipoprotein (HDL) cholesterol levels and normalized glucose level and adipose cell size in mice fed HFD. In contrast, HgCl₂ treatment significantly decreased serum leptin level with the down-regulation of leptin mRNA expression in WAT and a reduction in adipocyte size. Next, we tried to investigate possible factors that affect adipocyte size. Repeated exposure to HgCl₂ significantly decreased the expression levels of factors upon the regulation of energy such as the PPARα and PPARγ mRNA expression levels in adipocytes, whereas CoCl₂ had little effect on those genes expressions compared with that in the case of the mice fed HFD with a vehicle. In addition, repeated administration of CoCl₂ enhanced AMPK activation in a dose-dependent manner in the liver, skeletal muscle and WAT; HgCl₂ treatment also enhanced AMPK activation in the liver. Thus, both Co and Hg reduced WAT weight and the size of enlarged adipocytes, possibly mediated by AMKP activation in the mice fed HFD. However, inorganic cobalt may have a preventive role in obesity-related diseases through increased leptin, adiponectin and HDL-cholesterol levels, whereas inorganic mercury may accelerate the development of such diseases. These results may lead to the development of new approaches to establishing the role of metals in adipose tissue of obesity-related diseases.