Effect of branched-chain fatty acid on lipid dynamics in mice lacking liver fatty acid binding protein gene

Although a role for liver fatty acid protein (L-FABP) in the metabolism of branched-chain fatty acids has been suggested based on data obtained with cultured cells, the physiological significance of this observation remains to be demonstrated. To address this issue, the lipid phenotype and metabolism of phytanic acid, a branched-chain fatty acid, were determined in L-FABP gene-ablated mice fed a diet with and without 1% phytol (a metabolic precursor to phytanic acid). In response to dietary phytol, L-FABP gene ablation exhibited a gender-dependent lipid phenotype. Livers of phytol-fed female L-FABP−/− mice had significantly more fatty lipid droplets than male L-FABP−/− mice, whereas in phytol-fed wild-type L-FABP+/+ mice differences between males and females were not significant. Thus L-FABP gene ablation exacerbated the accumulation of lipid droplets in phytol-fed female, but not male, mice. These results were reflected in the lipid profile, where hepatic levels of triacylglycerides in phytol-fed female L-FABP−/− mice were significantly higher than in male L-FABP−/− mice. Furthermore, livers of phytol-fed female L-FABP−/− mice exhibited more necrosis than their male counterparts, consistent with the accumulation of higher levels of phytol metabolites (phytanic acid, pristanic acid) in liver and serum, in addition to increased hepatic levels of sterol carrier protein (SCP)-x, the only known peroxisomal enzyme specifically required for branched-chain fatty acid oxidation. In summary, L-FABP gene ablation exerted a significant role, especially in female mice, in branched-chain fatty acid metabolism. These effects were only partially compensated by concomitant upregulation of SCP-x in response to L-FABP gene ablation and dietary phytol.