Highlights  Cellular metabolism and toxicity of TFAs are still to be elucidated.  TFAs were incorporated in RINm5F insulinoma cells like palmitate or oleate.  Similarly to oleate and unlike palmitate, TFAs were of mild toxicity.  FA-induced cell damage correlated with ceramide and diglyceride accumulation.  Incorporation of TFAs in ceramides and diglycerides exceeded that of oleate.

Dietary trans fatty acids (TFAs) have been implicated in serious health risks, yet little is known about their cellular effects and metabolism. We aim to undertake an in vitro comparison of two representative TFAs (elaidate and vaccenate) to the best-characterized endogenous cis-unsaturated FA (oleate). The present study addresses the possible protective action of TFAs on palmitate-treated RINm5F insulinoma cells with special regards to apoptosis, endoplasmic reticulum stress and the underlying ceramide and diglyceride (DG) accumulation. Both TFAs significantly improved cell viability and reduced apoptosis in palmitate-treated cells. They mildly attenuated palmitate-induced XBP-1 mRNA cleavage and phosphorylation of eukaryotic initiation factor 2α (eIF2α) and stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK), but they were markedly less potent than oleate. Accordingly, all the three unsaturated FAs markedly reduced cellular palmitate incorporation and prevented harmful ceramide and DG accumulation. However, more elaidate or vaccenate than oleate was inserted into ceramides and DGs. Our results revealed a protective effect of TFAs in short-term palmitate toxicity, yet they also provide important in vitro evidence and even a potential mechanism for unfavorable long-term health effects of TFAs compared to oleate.

Putative health effects of dietary trans fatty acids (TFAs) receive a growing attention; while very little is known about the metabolism of these special food components. In vitro studies carried out in cultured cells provide an efficient and standardizable approach to follow the metabolic fate of TFAs, but it requires suitable techniques for the quantitative measurement of FAs in cell samples. Here, the development and validation of a simple and reliable method for the quantification of a group of relevant FAs by gas chromatography and flame ionization detection is presented. Sample preparation used a fast one-step and chloroform-free process for simultaneous extraction and esterification, and chromatographic separation was achieved in 25 min using a Zebron ZB-88 capillary column. A linear calibration (of R2 >0.99) was obtained in the concentration range of 1-200 µg/mL for each FA. Recovery rate was 82 % for samples of non-esterified FAs and >95 % for complex lipids, such as ceramides, diglycerides and triglycerides. The LOD and LOQ were below 0.5 µg/mL, and a robust method precision was achieved (RSD % was below 6 % for each lipid classes). The present method was also tested on a cultured cell line with or without FA treatment at close to physiological concentration, and the observed changes in the metabolite concentration levels revealed characteristic differences between the metabolism of cis and trans unsaturated FAs.

Elevated fatty acid (FA) levels contribute to severe metabolic diseases. Unbalanced oversupply of saturated FAs is particularly damaging, which renders stearoyl‐CoA desaturase (SCD1) activity an important factor of resistance. A SCD1‐related oxidoreductase protects cells against palmitate toxicity, so we aimed to test whether desaturase activity is limited by SCD1 itself or by the associated electron supply. Unsaturated/saturated FA ratio was markedly elevated by SCD1 overexpression while it remained unaffected by the overexpression of SCD1‐related electron transfer proteins in HEK293T cells. Electron supply was not rate‐limiting either in palmitate‐treated cells or in cells with enhanced SCD1 expression. Our findings indicate the rate‐limiting role of SCD1 itself, and that FA desaturation cannot be facilitated by reinforcing the electron supply of the enzyme.