High omega arachidonic acid/docosahexaenoic acid ratio induces mitochondrial dysfunction and altered lipid metabolism in human hepatoma cells

Abstract

BACKGROUND Non-alcoholic fatty liver disease (NAFLD) is a common cause of liver disease worldwide and is a growing epidemic. A high ratio of omega-6 fatty acids to omega-3 fatty acids in the diet has been implicated in the development of NAFLD. However, the inflicted cellular pathology remains unknown. A high ratio may promote lipogenic pathways and contribute to reactive oxygen species (ROS)-mediated damage, perhaps leading to mitochondrial dysfunction. Therefore, these parameters were investigated to understand their contribution to NAFLD development.

AIM To examine the effect of increasing ratios of omega-6:3 fatty acids on mitochondrial function and lipid metabolism mediators.

METHODS HepG2-derived VL-17A cells were treated with normal (1:1, 4:1) and high (15:1, 25:1) ratios of omega-6: omega-3 fatty acids [arachidonic acid (AA): docosahexaenoic acid (DHA)] at various time points. Mitochondrial activity and function were examined via MTT assay and Seahorse XF24 analyzer, respectively. Triglyceride accumulation was determined by using EnzyChrom™ and levels of ROS were measured by fluorescence intensity. Protein expression of the mediators of lipogenic, lipolytic and endocannabinoid pathways was assessed by Western blotting.

RESULTS High AA:DHA ratio decreased mitochondrial activity (<i>P</i> < 0.01; up to 80%) and promoted intracellular triglyceride accumulation (<i>P</i> < 0.05; 40%-70%). Mechanistically, it altered the mediators of lipid metabolism; increased the expression of stearoyl-CoA desaturase (<i>P</i> < 0.05; 22%-35%), decreased the expression of peroxisome proliferator-activated receptor-alpha (<i>P</i> < 0.05; 30%-40%) and increased the expression of cannabinoid receptor 1 (<i>P</i> < 0.05; 31%). Furthermore, the high ratio increased ROS production (<i>P</i> < 0.01; 74%-115%) and reduced mitochondrial respiratory functions such as basal and maximal respiration, ATP production, spare respiratory capacity and proton leak (<i>P</i> < 0.01; 35%-68%).

CONCLUSION High AA:DHA ratio induced triglyceride accumulation, increased oxidative stress and disrupted mitochondrial functions. Stimulation of lipogenic and steroidal transcription factors may partly mediate these effects and contribute to NAFLD development.

Core tip: A high ratio of omega 6:3 fatty acids in the diet has been implicated in the development of non-alcoholic fatty liver disease, a growing epidemic of major concern. The cellular pathology induced by such high ratios remains unknown. Here, we observed that in human hepatoma HepG2 (VL-17A) cells, high omega-6:omega-3 ratio reduced mitochondrial activity, increased triglyceride accumulation, elevated reactive oxygen species levels and interrupted several mitochondrial functions. Moreover, the increased expression of stearoyl-CoA desaturase, decreased expression of peroxisome proliferator-activated receptor alpha and elevation in cannabinoid receptor-1 expression collectively lead to lipogenesis and lipotoxicity, which are key features of non-alcoholic fatty liver disease development.