Berberine alleviates palmitic acid­induced podocyte apoptosis by reducing reactive oxygen species­mediated endoplasmic reticulum stress.

Lipid accumulation in podocytes can lead to the destruction of cellular morphology, in addition to cell dysfunction and apoptosis, which is a key factor in the progression of chronic kidney disease (CKD). Berberine (BBR) is an isoquinoline alkaloid extracted from medicinal plants such as Coptis chinensis, which has been reported to have a lipid­lowering effect and prevent CKD progression. Therefore, the present study aimed to investigate the effect of BBR on palmitic acid (PA)­induced podocyte apoptosis and its specific mechanism using an in vitro model. Cell death was measured using the Cell Counting Kit­8 colorimetric assay. Cell apoptotic rate was assessed by flow cytometry. The expression of endoplasmic reticulum (ER) stress­ and apoptosis­related proteins was detected by western blotting or immunofluorescence. Reactive oxygen species (ROS) were evaluated by 2',7'­dichlorofluorescein diacetate fluorescence staining. The results of the present study revealed that BBR treatment decreased PA­induced podocyte apoptosis. In addition, 4­phenylbutyric acid significantly reduced PA­induced cell apoptosis and the expression of ER stress­related proteins, which indicated that ER stress was involved in PA­induced podocyte apoptosis. In addition, N­acetylcysteine inhibited PA­induced excessive ROS production, ER stress and cell apoptosis of podocytes. BBR also significantly reduced PA­induced ROS production and ER stress in podocytes. These results suggested that PA mediated podocyte apoptosis through enhancing ER stress and the production of ROS. In conclusion, BBR may protect against PA­induced podocyte apoptosis, and suppression of ROS­dependent ER stress may be the key mechanism underlying the protective effects of BBR.

Inhibition of soluble epoxide hydrolase attenuates renal tubular mitochondrial dysfunction and ER stress by restoring autophagic flux in diabetic nephropathy.

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD), and renal tubular cell dysfunction contributes to the pathogenesis of DN. Soluble epoxide hydrolase (sEH) is an enzyme that can hydrolyze epoxyeicosatrienoic acids (EETs) and other epoxy fatty acids (EpFAs) into the less biologically active metabolites. Inhibition of sEH has multiple beneficial effects on renal function, however, the exact role of sEH in hyperglycemia-induced dysfunction of tubular cells is still not fully elucidated. In the present study, we showed that human proximal tubular epithelial (HK-2) cells revealed an upregulation of sEH expression accompanied by the impairment of autophagic flux, mitochondrial dysfunction, ubiquitinated protein accumulation and enhanced endoplasmic reticulum (ER) stress after high glucose (HG) treatment. Furthermore, dysfunctional mitochondria accumulated in the cytoplasm, which resulted in excessive reactive oxygen species (ROS) generation, Bax translocation, cytochrome c release, and apoptosis. However, t-AUCB, an inhibitor of sEH, partially reversed these negative outcomes. Moreover, we also observed increased sEH expression, impaired autophagy flux, mitochondrial dysfunction and enhanced ER stress in the renal proximal tubular cells of db/db diabetic mice. Notably, inhibition of sEH by treatment with t-AUCB attenuated renal injury and partially restored autophagic flux, improved mitochondrial function, and reduced ROS generation and ER stress in the kidneys of db/db mice. Taken together, these results suggest that inhibition of sEH by t-AUCB plays a protective role in hyperglycemia-induced proximal tubular injury and that the potential mechanism of t-AUCB-mediated protective autophagy is involved in modulating mitochondrial function and ER stress. Thus, we provide new evidence linking sEH to the autophagic response during proximal tubular injury in the pathogenesis of DN and suggest that inhibition of sEH can be considered a potential therapeutic strategy for the amelioration of DN.