Foods and animal feeds frequently become contaminated with the nephrotoxic ochratoxin A (OTA). Our prior research has indicated that ursolic acid (UA), which is widely present in fruits and medicinal plants, has the potential to alleviate nephrotoxicity triggered by OTA. Additionally, excessive induction of endoplasmic reticulum (ER)-phagy exacerbates OTA-induced apoptosis. Therefore, further investigation is essential to comprehend whether UA can mitigate OTA-induced apoptosis by influencing ER-phagy. This objective is accomplished through a series of experiments involving assessments of cell viability, apoptosis, fluorescence microscopy, and western blot analysis. The outcomes of these experiments reveal that pre-treatment with 4 μmol/L UA for 2 h can markedly reverse the elevated apoptotic rate, the co-localization of ER and lysosomes, and the protein expressions of GRP78, p-eIF2α, Chop, Bax, and Bak, as well as the reduced cell viability and the protein expressions of Lonp1, Trap1, p62, Tex264, FAM134B, Bcl-2, and Bcl-xl, all caused by exposure to 1 μmol/L OTA for 24 h in human proximal tubule epithelial-originated kidney-2 (HK-2) cells (P < 0.05). Interestingly, the increased expression of LC3B-II induced by OTA is further amplified by UA pre-treatment (P < 0.05). In conclusion, OTA triggers a harmful feedback loop between ER stress (ERS) and excessive ER-phagy, thereby further promoting ERS- and mitochondrial-mediated apoptosis in vitro. However, this effect is significantly mitigated by UA through the inhibition of autophagosome-lysosome fusion, consequently blocking the excessive ER-phagic flux.

Ochratoxin A (OTA), a secondary fungal metabolite known for its nephrotoxic effects, is widespread in various foods and animal feeds. Our recent investigation suggests a correlation between OTA-induced nephrotoxicity and Sigma-1 receptor (Sig-1R)-mediated mitochondrial apoptosis in human proximal tubule epithelial-originated kidney-2 (HK-2) cells. However, the involvement of Sig-1R in OTA-induced nephrotoxicity, encompassing other forms of regulated cell death like ferroptosis, remains unexplored. In this research, cell viability, apoptotic rate, cholesterol levels, mitochondrial glutathione (mGSH) levels, reactive oxygen species (ROS) levels, and protein expressions in HK-2 cells treated with OTA and/or blarcamesine hydrochloride (Anavex 2-73) were evaluated. The results suggest that OTA induces mitochondrial apoptosis and ferroptosis by inhibiting Sig-1R, subsequently promoting sterol regulatory element-binding protein 2 (SREBP2), 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), GRAM domain-containing protein 1B (GRAMD1B), steroidogenic acute regulatory protein, mitochondrial (StARD1), 78 kDa glucose-regulated protein (GRP78), CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), cyclophilin D (CypD), Cleaved-Caspase-3, B-cell lymphoma-2-associated X protein (BAX), and long-chain fatty acid-CoA ligase 4 (ACSL4), inhibiting tumor necrosis factor receptor-associated protein 1 (TRAP1), mitochondrial 2-oxoglutarate/malate carrier protein (SLC25A11), B-cell lymphoma-2-like protein 1 (BCL-XL), and glutathione peroxidase 4 (GPX4), reducing mGSH levels, and increasing total cholesterol, mitochondrial cholesterol, and ROS levels. In conclusion, OTA induces mitochondrial apoptosis and ferroptosis by inhibiting Sig-1R, thereby disrupting redox and cholesterol homeostasis in vitro. The regulation of cholesterol homeostasis by Sig-1R and its involvement in OTA-induced mitochondrial apoptosis and ferroptosis are reported here for the first time.

Foods and animal feeds frequently become contaminated with the nephrotoxic ochratoxin A (OTA). Our prior research has indicated that ursolic acid (UA), which is widely present in fruits and medicinal plants, has the potential to alleviate nephrotoxicity triggered by OTA. Additionally, excessive induction of endoplasmic reticulum (ER)-phagy exacerbates OTA-induced apoptosis. Therefore, further investigation is essential to comprehend whether UA can mitigate OTA-induced apoptosis by influencing ER-phagy. This objective is accomplished through a series of experiments involving assessments of cell viability, apoptosis, fluorescence microscopy, and western blot analysis. The outcomes of these experiments reveal that pre-treatment with 4 μmol/L UA for 2 h can markedly reverse the elevated apoptotic rate, the co-localization of ER and lysosomes, and the protein expressions of GRP78, p-eIF2α, Chop, Bax, and Bak, as well as the reduced cell viability and the protein expressions of Lonp1, Trap1, p62, Tex264, FAM134B, Bcl-2, and Bcl-xl, all caused by exposure to 1 μmol/L OTA for 24 h in human proximal tubule epithelial-originated kidney-2 (HK-2) cells (P < 0.05). Interestingly, the increased expression of LC3B-II induced by OTA is further amplified by UA pre-treatment (P < 0.05). In conclusion, OTA triggers a harmful feedback loop between ER stress (ERS) and excessive ER-phagy, thereby further promoting ERS- and mitochondrial-mediated apoptosis in vitro. However, this effect is significantly mitigated by UA through the inhibition of autophagosome-lysosome fusion, consequently blocking the excessive ER-phagic flux.