Effects of mild calorie restriction on the markers related to lipid metabolism and inflammation in liver and adipose tissue

Abstract

The incidence of obesity and disorders induced by obesity is increasing worldwide. With obesity, the excess energy storage leads to the expansion of adipocyte and the number of macrophages in white adipose tissue increases, which results in release of pro-inflammatory cytokines from the adipose tissue. Calorie restriction (CR) has been reported to decrease adiposity and inflammation. However, most CR models use 30~60% of calorie reduction, which is hard to achieve in human. We investigated the effects of mild CR on hepatic lipid metabolism and inflammation. Seven-week-old C57BL/6 mice were fed control diet containing 10% kcal fat (Control) or high fat diet containing 60% kcal fat (HFD) or reduced amount of control diet to achieve 14.1% calorie restriction (CR). We measured body weight, food intake, liver weight, hepatic lipid contents, serum levels of triglyceride (TG), cholesterol, non-esterified fatty acid (NEFA), alanine transaminase (ALT), aspartate transaminase (AST), glucose, leptin, adiponectin, and fetuin-A. The mRNA levels of hepatic and epididymal IL-1b, IL-6, Mcp-1, Tnf-a, and Socs3, hepatic Pparg, Ppara, Fasn, Srebf-1c, Adipor2, and Cpt1a and protein level of hepatic SIRT1 and pSTAT3/STAT3 were determined. CR group had significantly lower body weight gain, adipose tissue amount, liver weight, and liver TG, and cholesterol levels than the Control and HFD groups. Serum level of TG was significantly lower in CR group than HFD group (P = 0.024) and serum levels of cholesterol and glucose were significantly lower in CR group than Control and HFD groups. Hepatic expression of genes related to lipogenesis, Pparg and Srebf-1c, were significantly lower in CR and Control groups compared with HFD group. In epididymal adipose tissue, CR group showed significantly lower mRNA expression of pro-inflammatory chemokine, Mcp-1, compared with other two groups. The mRNA expression of epididymal IL-6 was significantly lower in CR group than HFD group (P < 0.001) and tended to be lower in CR group, compared with Control group (P = 0.057). Also, the mRNA levels of epididymal IL-1b, Tnf-a, and Socs3 in CR group were significantly lower than HFD group, but not significantly lower than Control group. In liver tissue, Mcp-1 mRNA level was lower in CR group than Control and HFD groups (63% and 74% lower, respectively). Hepatic Tnf-a mRNA level was lower in CR group than HFD group (47% lower). However, mRNA levels of IL-6 and Socs3 were significantly higher in CR group than HFD group (IL-6, P = 0.013

Socs3, P = 0.009). Also, the hepatic Lepr mRNA level was significantly higher in CR group than Control and HFD groups (P = 0.001 and, P < 0.001, respectively). Hepatic IL-6 mRNA level was correlated positively with hepatic Socs3 (r = 0.446, P = 0.049), and pSTAT3/STAT3 ratio (r = 0.476, P = 0.034), and tended to correlate negatively with serum glucose (r = -0.419, P = 0.066). Also, hepatic expression of Lepr showed correlations with hepatic Socs3 (r = 0.699, P< 0.001), and serum glucose level (r = -0.717, P < 0.001), and tended to have positive correlation with pSTAT3/STAT3 ratio (r = 0.432, P = 0.051). It suggested that low level of serum glucose in CR group increased hepatic IL-6 expression and leptin sensitivity, resulted in up-regulated Socs3 expression through JAK-STAT3 signaling to spare glucose. In conclusion, mild CR group reduced body weight gain, and hepatic lipid levels and alleviated inflammatory responses in adipose and liver tissues. Also CR might have caused beneficial hepatic insulin resistance to prevent consumption of glucose in the liver.