Additive Effects of Nicotine and High-Fat Diet on Hepatic Steatosis in Male Mice

Abstract

Smoking is a major risk factor for diabetes and cardiovascular disease and may contribute to nonalcoholic fatty liver disease. We hypothesize that in the presence of nicotine, high-fat diet (HFD) causes more severe hepatic steatosis in obese mice. Adult C57BL6 male mice were fed a normal chow diet or HFD and received twice daily injections of nicotine (0.75 mg/kg body weight, ip) or saline for 10 wk. Light microscopic image analysis revealed significantly higher lipid accumulation in livers from mice on HFD plus nicotine (190 ± 19 μm(2)), compared with mice on HFD alone (28 ± 1.2 μm(2)). A significant reduction in the percent volume of endoplasmic reticulum (67.8%) and glycogen (49.2%) was also noted in hepatocytes from mice on HFD plus nicotine, compared with mice on HFD alone. The additive effects of nicotine on the severity of HFD-induced hepatic steatosis was associated with significantly greater oxidative stress, increased hepatic triglyceride levels, higher incidence of hepatocellular apoptosis, inactivation (dephosphorylation) of AMP-activated protein kinase, and activation of its downstream target acetyl-coenzyme A-carboxylase. Treatment with acipimox, an inhibitor of lipolysis, significantly reduced nicotine plus HFD-induced hepatic lipid accumulation. We conclude that: 1) greater oxidative stress coupled with inactivation of AMP-activated protein kinase mediate the additive effects of nicotine and HFD on hepatic steatosis in obese mice and 2) increased lipolysis is an important contributor to hepatic steatosis. We surmise that nicotine exposure is likely to exacerbate the metabolic abnormalities induced by high-fat intake in obese patients.

Nicotine plus a high-fat diet triggers cardiomyocyte apoptosis

“…The apoptotic nature of the cell death and the identity of the dying cardiomyocyte were further confirmed by electron microscopy (Friedman et al 2012; Sinha-Hikim et al 2011a, 2014). Enumeration of TUNEL-positive (apoptotic) and TUNEL-negative (non-apoptotic) nuclei was carried out in left ventricular sections stained with the ApopTag peroxidase kit by using an American Optical Microscope with a ×40 objective and a pair of ×10 eyepieces.…”

“…Mice on either diet ( n = 5) received twice-daily intraperitoneal (IP) injections of nicotine (0.75 mg/kg body weight [BW]) or saline for 16 weeks. The rationale for using twice daily IP administration of nicotine (0.75 mg/kg BW) was based on the results of our previous studies, which demonstrated that this dose level of nicotine, when combined with HFD, triggered greater oxidative stress, activated hepatocellular apoptosis, amplified HFD-induced hepatic steatosis (Friedman et al 2012) and caused intramyocellular lipid accumulation and intramyofibrillar mitochondrial abnormalities in the skeletal muscle (Sinha-Hikim et al 2014). Notably, the daily dosage of 1.5 mg/kg BW in mice appeared to be similar to the clinically relevant concentrations found in habitual cigarette smokers and users of nicotine-containing chewing gum (Wu et al 2015).…”

“…Altogether, five batches were processed. Portions of glutaraldehyde-fixed left ventricles were further diced into small pieces, post-fixed in 1 % osmium tetroxide and embedded in Epon 812 as described previously (Friedman et al 2012; Sinha-Hikim et al 2011a, 2014). Thin sections from selected tissue blocks were cut with an LKB ultramicrotome, stained with uranyl acetate and lead citrate and examined with a Hitachi electron microscope (Hitachi, Indianapolis, Ind., USA).…”

“…We have previously shown that nicotine when combined with a high-fat diet (HFD) triggers greater oxidative stress, activates hepatocellular apoptosis and amplifies HFD-induced hepatic steatosis (Friedman et al 2012) and that the caspase-2-mediated intrinsic pathway constitutes a critical component of apoptotic signaling for nicotine and HFD-induced hepatocellular apoptosis (Ivey et al 2014). Recently, we further demonstrated the detrimental effects of the combined treatment of nicotine and HFD on skeletal muscle (Sinha-Hikim et al 2014).…”

Perinatal exposure to bisphenol A exacerbates nonalcoholic steatohepatitis-like phenotype in male rat offspring fed on a high-fat diet

“…For instance, chronic inhalation of low levels of ambient air particulate matter (PM 2.5) has been was reported to induce hepatic steatosis and lipid peroxidation and, moreover, increase hepatic inflammatory and fibrosis stage in mice (Tomaru et al 2007, Tan et al 2009). Exposure to nitrosamines and nicotine has also been found to play critical roles in the pathogenesis of NAFLD (Tong et al 2009, Azzalini et al 2010, Friedman et al 2012.…”