Mechanisms into the development of fatty liver disease: role of free fatty acids and alcohol

Background: Alcohol and Free fatty acids such as palmitate are known to promote liver injury. However less mechanistic information is available regarding omega fatty acids ratios with/out alcohol. In healthy populations omega 6/3 ratios are between 1:1 to 4:1, whereas high ratios (>15:1) are thought to correlate with the pathogenesis of fatty liver disease. This study aimed to investigate liver lipotoxicity and mitochondrial dysfunction due to imbalanced omega 6/3 ratios alone or in the presence of alcohol.

Method: Human hepatoma cell line, VL-17A cells were treated with individual fatty acids (Palmitic (PA), Stearic (SA), Linoleic (LA), alpha-Linolenic (ALA), Arachidonic (AA) and Docosahexaenoic (DHA) acids) with various concentrations ranging between 0.5 μM to 300 μM and omega 6/3 ratios (1:1, 4:1, 15:1 and 25:1) with/out alcohol (100 mM) for 24, 48 and 72 h after which lipid accumulation and cell toxicity was assessed. Subsequent studies at 24 hr examined oxidative stress, mitochondrial function and lipogenic proteins.

Results: PA treatment showed a detrimental effect on cell viability and lipid accumulation than SA after 48 h and 72 h (P<0.05); omega 3 (ALA and DHA) did not show any significant effect; LA exhibited a significant reduction in cell viability at 24 h only without causing any change in lipid accumulation; AA treatment significantly reduced cell viability at 48 h and 72 h (P<0.05) but only showed a significant lipid accumulation after 48 h. AA/DHA (omega 6/3) ratios (15:1 & 25:1) caused a significant reduction in cell viability after 24 h, 48 h and 72 h (P<0.001) and only (15:1) ratio inversely corresponded to an elevation in lipid level after 24 h and 48 h (P<0.01). At 24 hr treatment, high AA/DHA ratio of 25:1 led to increased expression of stearoyl-CoA desaturase (SCD1) and decreased peroxisome proliferator activated receptor alpha (PPARα) expression at 15:1 and 25:1 (P<0.05), while all ratios showed a significant decrease in the cannabinoid receptor (CB2) expression compared to control but actually increased when compared to the 1:1 ratio. Although the expression of CB1 was slightly increased (P>0.05), sterol regulatory element-binding protein 1 (SREBP1) did not show any change. AA/DHA ratios also showed a significant decrease in ATP production (P<0.01), basal respiration, maximal respiration and spare mitochondrial capacity and this effect was greater with high ratios (P<0.001). Reactive oxygen species (ROS) production increased significantly, particularly with high AA/DHA ratios (15:1 and 25:1) (P<0.001) alone and in the presence of alcohol (P<0.01).

Conclusion: The data suggests that lipid accumulation and toxicity occur with saturated and unsaturated fatty acids and high omega 6/3 ratios. The latter possibly due to the pro-inflammatory products of AA. This study confirms that high AA/DHA ratios with/out alcohol increase ROS production and high AA/DHA alone induce mitochondrial dysfunction and increase lipogenesis pathways by activating lipogenic factors causing steatosis and consequently promoting the development of fatty liver disease. Further work aims to elucidate the effect of fatty acid/alcohol on lipid synthetic and endocannabinoid pathways, which will further our understanding of fatty liver disease development.