Elocalcitol

It has previously been reported that 1,25-(OH)₂D₃ inhibits high glucose-induced epithelial-to-mesenchymal transition (EMT) in HK-2 cells. However, the mechanism of this renoprotective action remains unclear. Elocalcitol (BXL-628), a vitamin D analog, has been suggested to be effective on the RhoA/Rho associated protein kinase (ROCK) pathway, which serves a crucial role in high glucose-induced EMT. The aim of the present study was to investigate the effect of 1,25-(OH)₂D₃ and its analogue BXL-628 on high glucose-induced activation of the RhoA/ROCK pathway in human renal proximal tubular cells. HK-2 cells were co-treated with high glucose and either 1,25-(OH)2D3 or BXL-628. The RhoA expression levels and ROCK activity of the membrane were assessed via western blot analysis or immunofluorescence. α-smooth muscle actin (α-SMA) and epithelial (E)-cadherin were detected using western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), whereas collagen I and fibronectin levels were measured by ELISA and RT-qPCR. The results demonstrated that 1,25-(OH)₂D₃ and BXL-628 both significantly downregulated the expression of active RhoA and ROCK activity induced by high glucose (P<0.05). Furthermore, the expressions of α-SMA, collagen I, and fibronectin were significantly downregulated at both protein and mRNA (P<0.05) levels, whereas the expression of E-cadherin was significantly increased (P<0.05) by 1,25-(OH)₂D₃ or BXL-628 treatment. In conclusion, the vitamin D receptor agonist 1,25-(OH)₂D₃ and its analogue BXL-628 were both able to attenuate high glucose-induced EMT and extracellular matrix accumulation of HK-2 cells by suppressing the RhoA/ROCK signaling pathway in vitro.

Vitamin D plays a pivotal role to maintain skeletal muscle integrity and health. Vitamin D deficiency characterizes inflammatory myopathy (IM) and diabetes, often overlapping diseases involving skeletal muscle damage. Vitamin D receptor (VDR) agonists likely exert beneficial effects in both IM and metabolic disturbances. We aim to evaluate in vitro the effect of elocalcitol, a non-hypercalcemic VDR agonist, on the biomolecular metabolic machinery of human skeletal muscle cells (Hfsmc), vs. insulin (I). We analyzed GLUT4, Flotillin-1, Caveolin-3 and Caveolin-1 cell expression/localization; mTOR, AKT, ERK and 4E-BP1 phosphorylation; IL-6 myokine release; VDR expression. We investigated in vivo vitamin D status in IM subjects, evaluating VDR muscular expression and serum vitamin D with metabolism-related parameters, as glycemia, triglycerides, cholesterol, resistin and adiponectin. In Hfsmc, elocalcitol exerted an I-like effect, promoting GLUT4 re-localization in Flotillin-1, Caveolin-3 and Caveolin-1 positive sites and mTOR, AKT, ERK, 4E-BP1 activation; it enhanced IL-6 myokine release. IM subjects, all normoglycemic, showed VDR/vitamin D deficiency that, together with high lipidemic and resistin profile, possibly increases the risk to develop metabolic diseases. VDR agonists as elocalcitol may be therapeutic tools for skeletal muscle integrity/function maintenance, an indispensable condition for health homeostasis.