Anti-renal interstitial fibrosis effect of norcantharidin is exerted through inhibition of PP2Ac-mediated C-terminal phosphorylation of Smad3.

Norcantharidin (NCTD), the demethylated analog of cantharidin isolated from Mylabris, is known to inhibit renal fibrosis. However, the underlying mechanism is largely unknown. The present study investigates whether NCTD exerts this effect through regulation of the protein phosphatase 2A catalytic subunit (PP2Ac)-Smad3 pathway. HK-2 human renal proximal tubule cells exposed to transforming growth factor (TGF)-ß1 were used as an in vitro model of renal fibrosis. The levels of total Smad3, C-terminal-phosphorylated Smad3 (p-Smad3), PP2Ac, and fibronectin (Fn) were evaluated by Western blotting. A PP2Ac overexpression plasmid and the PP2Ac inhibitor okadaic acid (OA) were used for functional analyses. The subcellular localization of Smad3 was visualized by immunofluorescence labeling. The results showed that PP2Ac overexpression increased Smad3 phosphorylation and nuclear translocation in HK-2 cells, while pharmacologic inhibition of PP2Ac with OA had the opposite effect. NCTD suppressed Fn and p-Smad3 expression and TGF-ß1-induced nuclear entry of Smad3, but these effects were abrogated by inhibition of PP2Ac. Thus, the anti-renal interstitial fibrosis effect of NCTD is exerted through inhibition of PP2Ac-mediated C-terminal phosphorylation of Smad3. These findings highlight the therapeutic potential of NCTD for the treatment of renal interstitial fibrosis.

Stanniocalcin-1 Alleviates Contrast-Induced Acute Kidney Injury by Regulating Mitochondrial Quality Control via the Nrf2 Pathway.

Contrast-induced acute kidney injury (CI-AKI) is the third common cause of acute kidney injury (AKI), which is associated with poor short- and long-term outcomes. Currently, effective therapy strategy for CI-AKI remains lacking. Stanniocalcin-1 (STC1) is a conserved glycoprotein with antiapoptosis and anti-inflammatory functions, but the role of STC1 in controlling CI-AKI is unknown. Here, we demonstrated a protective role of STC1 in contrast-induced injury in cultured renal tubular epithelial cells and CI-AKI rat models. Recombinant human STC1 (rhSTC1) regulated mitochondrial quality control, thus suppressing contrast-induced mitochondrial damage, oxidative stress, inflammatory response, and apoptotic injury. Mechanistically, activation of the Nrf2 signaling pathway contributes critically to the renoprotective effect of STC1. Together, this study demonstrates a novel role of STC1 in preventing CI-AKI and reveals Nrf2 as a molecular target of STC1. Therefore, this study provides a promising preventive target for the treatment of CI-AKI.

Comparison of iohexol and iodixanol induced nephrotoxicity, mitochondrial damage and mitophagy in a new contrast-induced acute kidney injury rat model.

Recent progress in angiography and interventional therapy has revived interest in comparison of nephrotoxicity of low-or iso-osmolar contrast media, but detailed mechanisms and effective treatments of contrast-induced acute kidney injury (CI-AKI) remain elusive. We established a new model of CI-AKI and compared the nephrotoxicity of iohexol and iodixanol with a focus on renal oxidative stress, mitochondrial damage and mitophagy. Our results showed that 48-h dehydration plus furosemide injection before iohexol administration successfully induced CI-AKI in rats. Compared with iodixanol, iohexol induced a greater decrease in renal function, more severe morphological damage and mitochondrial ultrastructural changes, an increased number of apoptotic cells, decreased antioxidative enzymes with activation of NLRP3 inflammasome in renal tissue. Renal contrast media kinetics showed the immediate excretion of iohexol and the transient renal accumulation of iodixanol. Plasma mtDNA Tc numbers were positively correlated with markers of renal mitochondrial disruption but negatively correlated with the level of serum creatinine and the score of tubular injury. Of note, iodixanol appeared to induce a stronger activation of mitophagy than iohexol, evidenced by greater protein levels of LC3II and PINK1/Parkin in the renal tissue of iodixanol-treated rats. Taken together, our results indicate that iohexol induced more severe nephrotoxicity than iodixanol in vivo due to apoptosis, destruction of antioxidative defense machinery, activation of NLRP3 inflammasome, mitochondrial damage and mitophagy. Plasma mtDNA may serve as a biological marker for renal mitochondrial disruption and damage in CI-AKI. Antioxidative defense and mitophagy are involved in the process of CI-AKI and may be promising targets of therapies.

Mitophagy Plays a Protective Role in Iodinated Contrast-Induced Acute Renal Tubular Epithelial Cells Injury.

BACKGROUND/AIMS: Contrast induced-acute kidney injury (CI-AKI) is one of the most common causes of acute kidney injury (AKI) in hospitalized patients. Mitophagy, the selective elimination of mitochondria via autophagy, is an important mechanism of mitochondrial quality control in physiological and pathological conditions. In this study, we aimed to determine effects of iohexol and iodixanol on mitochondrial reactive oxygen species (ROS), mitophagy and the potential role of mitophagy in CI-AKI cell models. METHODS: Cell viability was measured by cell counting kit-8. Cell apoptosis, mitochondrial ROS and mitochondrial membrane potential were detected by western blot, MitoSOX fluorescence and TMRE staining respectively. Mitophagy was detected by the colocalization of LC3-FITC with MitoTracker Red, western blot and electronic microscope. RESULTS: The results showed that mitophagy was induced in human renal tubular cells (HK-2 cells) under different concentrations of iodinated contrast media. Mitochondrial ROS displayed increased expression after the treatment. Rapamycin (Rap) enhanced mitophagy and alleviated contrast media induced HK-2 cells injury. In contrast, autophagy inhibitor 3-methyladenine (3-MA) down-regulated mitophagy and aggravated cells injury. CONCLUSIONS: Together, our finding indicates that iohexol and iodixanol contribute to the generation of mitochondrial ROS and mitophagy. The enhancement of mitophagy can effectively protect the kidney from iodinated contrast (iohexol)-induced renal tubular epithelial cells injury.