Metixene hydrochloride hydrate mitigates kidney tubulointerstitial fibrosis by inhibiting Smad3 phosphorylation

Chronic Kidney disease (CKD), in which renal fibrosis is the defining pathological feature, poses significant global health and economic challenges. Despite its high clinical prevalence, effective therapies to prevent or reverse renal fibrosis remain scarce. Metixene hydrochloride hydrate (MHH), an anticholinergic drug once used for Parkinson's disease, has not been evaluated for renal fibrosis. Here, we investigated whether MHH mitigates renal fibrosis in a unilateral ureteral obstruction (UUO) mouse model and evaluated its effects on transforming growth factor-β1 (TGF-β1) signaling in renal cells. MHH did not affect the cell viability of NRK-49F cells at concentrations ranging from 0.5 to 5 μM. In vitro, MHH effectively suppressed TGF-β1-induced PAI-1 expression (both mRNA and protein) and secretion in renal fibroblasts, as well as PAI-1 secretion and protein expression in renal glomerular endothelial cells. Furthermore, TGF-β1 stimulated the mRNA and protein expressions of key renal fibrotic factors, including collagen type I, fibronectin, and alpha-smooth muscle actin, in NRK-49F cells. MMH significantly inhibited the expression of these renal fibrotic factors in these cells. UUO kidneys exhibited markedly increased tubular atrophy and interstitial fibrosis, as well as increased expression of renal fibrotic markers. MHH treatment significantly mitigated these pathological parameters and expression of renal fibrotic markers. Mechanistically, MHH suppressed TGF-β1-induced Smad3 phosphorylation both in vitro and in vivo. Our findings indicate that MHH exerts potent antifibrotic effects by downregulating the TGF-β1/Smad3 signaling pathway and suppressing the expression of fibrotic factors in renal cells and obstructed kidneys. Therefore, MHH could be repositioned as a therapeutic agent for renal fibrosis in various kidney diseases.