Adiponectin Expression and Oxidative Stress in Hearts of Mice Fed a High-fat Diet

Abstract

Evidence suggests that excess superoxide generation leading to oxidative stress and/or the reduced capacity of organisms to regulate oxidative/redox environments play a major role in the initiation and progression of obesity related diseases. Oxidative stress contributes to the progression of numerous diseases throughout the body, including the cardiovascular system. Adiponectin is a protein hormone previously thought to be secreted only from adipose tissue. Adiponectin is generally lower in obese individuals and has been shown to play a cardio protective role. The purpose of our study was to examine the effects of niacin on antioxidant gene expression and activity in hearts of a mouse model of obesity and to also look at expression of adiponectin in the mouse heart, which could lead to a better understanding of adiponectin regulation and its role in cardiovascular and metabolic diseases. Mice were fed high fat (60% kcal as fat) or normal diets for 11 weeks (10% kcal fat) as part of a separate study. Niacin was added to the drinking water to half of the mice for the last 5 weeks. At the end of the study, hearts were rapidly frozen in liquid nitrogen for the determination of sirtuins (SIRT), glutathione peroxidase (Gpx-1), superoxide dismutase-1 (SOD1), and superoxide dismutase-2 SOD2 gene expression, superoxide dismutase activity, and protein carbonylation. Mice fed the high fat diet had significantly increased body weights (p<0.001). There was no change in antioxidant gene expression between the four groups and no sign of protein carbonylation, an oxidative stress marker, in the high-fat diet group compared to the control group. Increase in gene expression of SIRT1 and SIRT5 was seen in the high fat diet compared to normal diet. Niacin fed groups had an increase in SIRT1 protein expression compared to the groups without niacin. Real-time PCR showed expression of adiponectin in the mouse heart, with a slight increase of expression in the high-fat diet compared to control. Western blot analysis of adiponectin showed that adiponectin protein expression was significantly lowered in the high-fat diet compared to the control diet (p<0.05). Mice on a high fat diet for 11 weeks did not show alterations in antioxidant gene expression, SOD activity, or protein carbonylation compared to control group. These results suggest that an 11 week high-fat diet was not a long enough period to induce significant oxidative stress on the mouse heart. Increases in mRNA expression of SIRT1 and SIRT5 in the high-fat and niacin diets, and increased SIRT1 protein expression in niacin fed hearts could be due to a protective role against oxidative stress. Western blot and RT-PCR analysis show protein and mRNA expression of adiponectin in the mouse heart, and could potentially be eliciting a local response, along with circulating adiponectin. The type of tissue or cells in the heart expressing adiponectin is unknown and future studies examining adiponectin in isolated mouse myocytes could provide insight on which area of the heart is producing adiponectin.