In recent decades, addition to the diet of synthetically hydrogenated vegetable oils has markedly increased human consumption of trans fatty acids. Epidemiological studies have linked this change in diet to current high rates of atherosclerotic cardiovascular disease. Despite recognition of this important connection, the basic mechanisms by which trans fatty acids contribute to the pathogenesis of atherosclerosis are still not well understood. In the present studies we examined the effects of trans fatty acids on macrophage functions and their possible role in the pathogenesis of atherosclerosis. Human macrophages, derived from peripheral blood mononuclear cells, were treated with the trans fat elaidic acid (C18:Δ9–10 trans), the corresponding cis fatty acid oleic acid (C18:Δ9–10 cis), or the saturated fatty acid stearic acid (C18:0). We examined changes in macrophage fat metabolism using GC/MS to measure cell fatty acid content and intermediates, and MS/MS to identify acylcarnitine derivatives, and assayed fatty acid oxidation using fatty acids radiolabeled at the [1–14C] position and the double bond at the [C9-C103H] position. After 44 hours treatment with 100 micromolar elaidic acid, macrophages showed an accumulation of multiple unsaturated fatty acid intermediates, both long-chain and short-chain, by GC/MS analysis, that were not observed in cultures containing either oleic or stearic acid. Using acylcarnitine analysis, we observed an increase in C12 and C18 intermediates in the macrophages exposed to trans fat (either as fatty acids or partially hydrogenated soy oil) compared to controls. These results suggest a block in acyl-CoA removal one group proximate to the trans bond. Beta-oxidation assays using carbon-1 radiolabeled oleic and elaidic acids revealed enhanced entry of the trans-fat into the catabolic cycle compared to the entry of the natural cis-fatty acid. Using carbon 9–10 radiolabeled oleic acid to study oleic acid catabolism, we discovered that in the presence of the trans fat, oxidation of the cis fat was diminished. Thus, in addition to the block in the catabolism of the trans fat itself, the degradation of the cis monounsaturated fatty acids are also impaired in the presence of the trans fat. We then examined the effects of inhibited fatty acid catabolism on macrophage function by examining changes in gene expression. Initial results from Affymetrix gene expression profiling, were confirmed using quantitative real time PCR. These studies revealed that exposure to trans fatty acid, compared to cis fatty acids, markedly upregulated macrophage expression of interleukin 1 beta, an inflammatory cytokine previously implicated in the pathogenesis of atherosclerosis. Also increased was expression of heparin-binding epidermal growth factor, previously implicated as a stimulus for vascular smooth muscle proliferation in atherosclerosis. The results overall suggest that the deleterious effects of trans fats may be linked to impaired macrophage fatty acid catabolism, contributing to lipid accumulation in the atheroma, and also to increased macrophage production of inflammatory mediators.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.