Renal ischemia/reperfusion injury in rats is probably due to the activation of the 5-HT degradation system in proximal renal tubular epithelial cells.

AIMS: To explore the relationship between renal ischemia/reperfusion injury (RIRI) and the activation of the renal 5-HT degradation system, including 5-HT2A receptor (5-HT2AR), 5-HT synthases and monoamine oxidase-A (MAO-A). MAIN METHODS: Rat RIRI was induced by removing the right kidney, causing ischemia of the left kidney for 45 min and reperfusion for different times. RIRI model (ischemia for 45 min and reperfusion for 24 h) was pretreated with 5-HT2AR antagonist sarpogrelate hydrochloride (SH) and the 5-HT synthase inhibitor carbidopa. In HK-2 cells, cellular damage was induced by hypoxia (24 h)/reoxygenation (12 h) (H/R) and treated with SH, carbidopa or the MAO-A inhibitor clorgyline. Hematoxylin-eosin, immunohistochemistry, TUNEL and fluorescent probe staining, RT-qPCR, western blotting, ELISA, etc. were used in the tests. KEY FINDINGS: The development of RIRI and the emergence of the RIRI peak were consistent with renal 5-HT degradation system activation. The highest expression regions of the 5-HT degradation system overlapped with those of the most severe lesions in the kidney, which were in proximal renal tubules. Rat RIRI and HK-2 cell damage, including oxidative stress, inflammation and apoptosis, could be almost abolished by synergistic inhibition of SH and carbidopa. Clorgyline also abolished the cellular damage induced by H/R. H/R-induced production of mitochondrial ROS in HK-2 cells was due to MAO-A-catalyzed 5-HT degradation, and 5-HT2AR was involved by mediating the expression of 5-HT synthases and MAO-A. SIGNIFICANCE: These findings revealed a close association between RIRI and activation of the renal 5-HT degradation system.

2-Methoxyestradiol synergizes with Erlotinib to suppress hepatocellular carcinoma by disrupting the PLAGL2-EGFR-HIF-1/2α signaling loop.

Erlotinib, an EGFR tyrosine kinase inhibitor has been introduced into cancer chemotherapy. However, the therapeutic effects of erlotinib in hepatocellular carcinoma (HCC) remain vaguely understood. Our previous study found that a hypoxia-mediated PLAGL2-EGFR-HIF-1/2α signaling loop in HCC decreased response to erlotinib. The current study has demonstrated that the combination of erlotinib and 2ME2 exerted synergistic antitumor effects against HCC. Further investigation showed that erlotinib increased the expression level of EGFR, HIF-2α, and PLAGL2, which contributes to the insensitivity of hypoxic HCC cells to erlotinib. The simultaneous exposure to 2ME2 effectively inhibited the expression level of EGFR, HIF-2α, and PLAGL2 that was induced by erlotinib. This contributes to the synergistic effect of the two therapeutic agents. Furthermore, the combination of erlotinib and 2ME2 induced apoptosis and inhibited the stemness of hypoxic HCC cells. Our findings potentially explain the mechanism of HCC insensitivity to erlotinib and provide a new strategy of combining EGFR and HIF1/2α inhibitors for HCC treatment.