Increased Endogenous Production of Pro‐inflammatory Adipokines by 3T3‐L1 Adipocytes Differentiated with Arachidonic Acid

Abstract

Inflammatory factors derived from adipose tissue (AT) can set the stage for chronic, low‐grade inflammation. This meta‐inflammation can predispose the individual to further inflammatory‐based disorders and diseases. Polyunsaturated fatty acids (PUFAs) are known to have immune modulating effects, with omega‐6 (n‐6) PUFAs typically being associated with increased production of inflammatory molecules, and n‐3 PUFAs having been shown to be anti‐inflammatory, in both in vivo and in vitro studies. The 3T3‐L1 cell line is an embryonic mouse fibroblast line that can be differentiated into an adipocyte phenotype making it a suitable line for studies on the effects of PUFAs on inflammatory molecule production by AT. The aim of this research was to determine the effects of n‐6 and n‐3 PUFAs on the release of inflammatory adipokines in lipopolysaccharide (LPS)‐challenged and LPS‐unchallenged adipocytes. Fibroblasts were differentiated into adipocytes with the addition of 100 μM of linoleic acid (LA; n‐6), arachidonic acid (ARA; n‐6) or eicosapentaenoic acid (EPA; n‐3) throughout the differentiation period, followed by a 6 h, 1 μg/ml LPS challenge. Cell‐conditioned media was collected before and after the LPS challenge for interleukin (IL)‐6 and prostaglandin E2 (PGE2) quantification via enzyme‐linked immunosorbent assays. Differentiation of adipocytes with n‐6 ARA caused a significant increase in PGE2 levels compared to control cells, or cells differentiated with LA or EPA, both after LPS challenge (two‐way ANOVA; p<0.0001) and before LPS challenge (two‐way ANOVA; p<0.0001). We did not observe differences in PGE2 levels between LPS‐challenged and non‐challenged cells differentiated with ARA (matched pairs t‐test; p=0.42) and EPA (p=0.57), while control (p=0.0005) and LA‐treated cells (p=0.0003) produced higher amounts of PGE2 after LPS stimulation. Interestingly, quantified levels of IL‐6 across treatments did not differ before and after LPS stimulation (matched pairs t‐test; p=0.75), although, as observed with PGE2, there was a significant increase in IL‐6 production by ARA‐differentiated cells compared to control, LPS, LA, and EPA‐treated cells (two‐way ANOVA; p=0.004). In conclusion, use of ARA in the differentiation process of 3T3‐L1 fibroblasts into a final adipocyte phenotype increases their endogenous (non‐LPS stimulated) production of IL‐6 and PGE2.