The effects on markers of cellular stress and RAGE splicing in cellular models and in subjects receiving dietary CLA supplementation

Abstract

The dietary lipid Conjugated Linoleic Acid (CLA) has been the subject of a large body of research in relation to its anti-inflammatory and immunoregulatory role in many cell types and animal models. This study aimed to investigate the effect of a mixture of the 9:11 and 10:12 isomers of CLA as well as the effect of the 9:11 isomer alone on the human monocytic cell-line THP-1 cells and human endothelial cells (HUVEC). The effect of supplementation with 2g/day CLA (a 50:50 mixture of 9:11 and 10:12 CLA) and 9:11 CLA in a cross-over trial in subjects with metabolic syndrome was also investigated. Neither CLA nor 9:11 CLA demonstrated any significant endoplasmic reticulum stress or induced apoptosis when cells were treated with the lipids over a concentration range of 20-200μM. Both lipids were able to upregulate gene expression of the nuclear transcription factor PPARγ in both cell types, with CLA having the most marked effect. A significant increase in the PPARγ dependant gene CD36 was also observed and a significant increase in PPARα mRNA was seen with CLA. However, no significant increase in the PPARα dependant CXCL2 gene was observed. PPAR activity in these cells did not appear to be mediated by the induction of endogenous ligands by Cycloxygenase-2. Both lipids were capable of upregulating another transcription factor LXRα, suggesting an important role for both lipids in cholesterol homeostasis. Both CLA and 9:11 CLA increased mRNA expression for the receptor for advanced glycated end-products (RAGE) and induced solubilisation of the receptor that was not mediated by increasing activation of the metalloproteinase enzyme ADAM10. There was significant induction of RAGE splice variants secretion in particular esRAGE after CLA supplementation. The clinical trial demonstrated that dietary supplementation with both isomers induced increased sRAGE secretion, and improved markers of endothelial function and diastolic blood pressure. Improved platelet function was also observed and a non-significant but beneficial trend was observed for HDL-cholesterol and LDL-cholesterol. Multiregression analysis would suggest that the most significant predictor of the reduction in DBP was the increase in sRAGE secretion induced by both CLA and 9:11 CLA. In conclusion, this study would support a beneficial role for CLA and its 9:11 isomer in mediating the pro-atherogenic effects observed in inflammatory disorders such as type 2 Diabetes Mellitus.