Anthocyanins inhibit high-glucose-induced cholesterol accumulation and inflammation by activating LXRα pathway in HK-2 cells

The dysregulation of cholesterol metabolism and inflammation plays a significant role in the progression of diabetic nephropathy (DN). Anthocyanins are polyphenols widely distributed in food and exert various biological effects including antioxidative, anti-inflammatory, and antihyperlipidemic effects. However, it remains unclear whether anthocyanins are associated with DN, and the mechanisms involved in the reciprocal regulation of inflammation and cholesterol efflux are yet to be elucidated. In this study, we evaluated the regulation of cholesterol metabolism and the anti-inflammatory effects exerted by anthocyanins (cyanidin-3-O-beta-glucoside chloride [C3G] or cyanidin chloride [Cy]) and investigated the underlying molecular mechanism of action using high-glucose (HG)-stimulated HK-2 cells. We found that anthocyanins enhanced cholesterol efflux and ABCA1 expression markedly in HK-2 cells. In addition, they increased peroxisome proliferator-activated receptor alpha (PPAR alpha) and liver X receptor alpha (LXR alpha) expression and decreased the HG-induced expression of the proinflammatory cytokines intercellular adhesion molecule-1 (ICAM1), monocyte chemoattractant protein-1 (MCP1), and transforming growth factor-beta 1 (TGF beta 1), as well as NF kappa B activation. Incubation with the PPAR alpha-specific inhibitor GW6471 and LXR alpha shRNA attenuated the anthocyanin-mediated promotion of ABCA1 expression and cholesterol efflux, suggesting that anthocyanins activated PPAR alpha-LXR alpha-ABCA1-dependent cholesterol efflux in HK-2 cells. Moreover, the knockout of LXR alpha abrogated the anti-inflammatory effect of anthocyanins, whereas the PPAR alpha antagonist GW6471 does not have this effect. Further investigations revealed that LXR alpha might interfere with anthocyanin-induced decreased ICAM1, MCP1, and TGF beta 1 expression by reducing the nuclear translocation of NF kappa B. Collectively, these findings suggest that blocking cholesterol deposition and inhibiting the LXR alpha pathway-induced inflammatory response might be one of the main mechanisms by which anthocyanins exert their protective effects in DN.