Background: Advanced glycation end products (AGEs) are pathogenic factors of renal tubular lipid accumulation and play a negative role in diabetic kidney disease (DKD). Glucose cotransporter (SGLT) 2 inhibition offers strong renoprotection in the progression of DKD. The aim of the current study was to investigate the effects of empagliflozin (EMPA, a potent and selective SGLT2 inhibitor) on AGEs-induced renal tubular lipid accumulation in both diabetic mice fed with a high-AGEs diet and AGEs-treated cultured human renal proximal tubular epithelial (HK-2) cells.
Methods: In vivo, EMPA was used to treat db/db mice fed a high-AGEs diet or an AIN-76 basal diet. In an in vitro study, HK-2 cells were treated with AGEs-bovine serum albumin (BSA) and/or EMPA. Sterol regulatory element binding protein (SREBP) cleavage-activating protein (SCAP) translocation was detected by confocal microscopy.
Results: EMPA reduced tubular lipid droplets and intracellular cholesterol content, as well as the expression of proteins involved in the synthesis and absorption of cholesterol in the kidneys of basal diet-fed db/db mice, high-AGEs diet-fed db/db mice and AGEs-BSA-treated HK-2 cells. AGEs-BSA loading promoted the formation of SCAP-SREBP-2 complexes and enhanced the transport of the complexes to the Golgi, but these effects were markedly inhibited by EMPA in HK-2 cells. EMPA reduced renal inflammation both in basal diet-fed db/db mice and high-AGEs diet-fed db/db mice, and suppressed NLRP3 inflammasome activation in AGEs-BSA-treated HK-2 cells. In addition, EMPA reduced the serum AGEs level in vivo and inhibited renal tubular endoplasmic reticulum (ER) stress and receptor of AGEs (RAGE) expression both in vivo and in vitro.
Conclusions: EMPA attenuated AGEs synthesis and inhibited the AGEs-RAGE signaling pathway, thereby suppressing ER stress and inhibiting abnormal cholesterol metabolism and release of inflammatory cytokines, thus alleviating renal tubular lipid accumulation and inflammation.