Adaptive homeostasis of the vitamin D–vitamin D nuclear receptor axis in 8-methoxypsoralen-induced hepatotoxicity

8-methoxypsoralen (8-MOP) with ultraviolet A radiation therapy (PUVA) is the standard therapy for patients with psoriasis, despite the reported potential risks of 8-MOP-induced cholestatic liver injury in both humans and animals. Usually, patients with chronic cholestasis exhibit lower serum 25-hydroxy vitamin D (25(OH)D) levels. But those patients receiving PUVA for psoriasis showed an increase in serum 25(OH)D levels, probably highlighting that the vitamin D-vitamin D nuclear receptor (VD-VDR) axis play a protective role in 8-MOP-induced hepatotoxicity. The present study confirmed 8-MOP could increase serum 25(OH)D levels in conventional lighting and diet (CLD) and vitamin D deficient (VDD) Sprague-Dawley rats. Potential liver risks were also found in CLD and VDD rats after 8-MOP treatment. We proved that 8-MOP could be a potent ligand for VDR using molecular docking and luciferase report assay. Effect of 8-MOP on VDR subcellular distribution was determined using human liver cell line L02. We found 8-MOP could increase VDR protein expression in the nuclear and cytosol extracts and also total cell extracts in L02. siRNAs for VDR were used to determine the role of VDR in protecting 8-MOP-induced cholestasis and potential cellular mechanisms. The results showed 8-MOP could affect the CYP7A1, SHP and MRP3 expression via VDR, and such effects could be reversed by knockdown of VDR expression, suggesting a vital role of VDR involved in 8-MOP-regulated bile acid synthesis and transportation. In conclusion, these results revealed activation of VD-VDR axis may play a beneficial role in 8-MOP-mediated regulation of bile acid synthesis and transportation.