An in Vitro Model of Nicotine-Induced Adipose Tissue Lipolysis and Hepatic Steatosis
Presentation Number: MON 514
Date of Presentation: April 3rd, 2017
Mohammad Kamrul Hasan*1, Amiya P Sinha-Hikim2 and Theodore C Friedman3
1Charles R Drew University of Medicine and Science, Los Angeles, CA, 2Charles R. Drew University of Medicine and Science, Los Angeles, CA, 3Charles R. Drew Univeristy of Medicine and Science, Los Angeles, CA
Background: Cigarette smoking is a major risk factor for diabetes, cardiovascular disease and, nonalcoholic fatty liver disease. However, smokers are lean due to the weight loss properties of nicotine, which make smokers reluctant to quit smoking. In our previous study, we reported that nicotine exacerbates hepatic steatosis in a mouse model of diet induced obesity (DIO). Using acipimox, a lipolysis inhibitor, we further confirmed that nicotine induces lipolysis in white adipose tissue and that is responsible for triggering the fat accumulation in liver and in muscle (1). In this study, we established a novel in vitro cellular model to explore the mechanisms of nicotine-induced adipose tissue lipolysis contributing to hepatic steatosis.
Materials and Methods: We used pre-adipocyte 3T3L-1 cells and hepatic HepG2 cells, to establish an in vitro model for lipolysis and steatosis, respectively. We treated differentiated 3T3L1 cells with 10-100 nM of nicotine for 8 days changing medium every alternate day. The collected conditioned medium from adipocyte culture was then added to HepG2 cell culture and 72 hr after incubation, Oil-o-Red staining was done to monitor accumulation of lipid in HepG2 cells. Levels of triglyceride (TG) in adipocytes and free fatty acid (FFA) in the conditioned medium were determined. Expression of silent information regulator 1 (SIRT1) and lipolytic genes in adipocytes and lipogenesis genes in hepatic cells was monitored by western blotting and RT-PCR.
Results: We observed that nicotine-treated conditioned medium contain significant amount of FFAs that can induce steatosis in HepG2 cells as revealed by presence of increased amount of lipid droplets in HepG2 cells. Using this model, we further showed that nicotine enhanced the expression of Sirt1 and adipose triglyceride lipase in adipocytes that can be associated with lipid mobilization leading to ectopic lipid accumulation in HepG2 cells.
Conclusions: We conclude that similar to our in vivo model of nicotine and HFD-induced hepatic steatosis, nicotine can also induce hepatic steatosis through release of FFA from adipocytes in an in vitro setting. This in vitro cellular model of lipolysis and steatosis will be helpful for mechanistic understanding of nicotine-induced lipolysis leading to hepatic steatosis. This model can also be used to search for inhibitor of nicotine induced lipolysis and, in turn, mitigation of hepatic steatosis.
Nothing to Disclose: MKH, APS, TCF