Presence of 25(OH)D deficiency and its effect on vitamin D receptor mRNA expression.

Background and Objectives: Vitamin D and its metabolites act through vitamin D receptor (VDR). We hypothesized that subjects with low serum 25(OH)D levels but normal PTH might have increased VDR expression.
Design and Methods: VDRmRNA expression was assessed by real time PCR in duodenal mucosa and PBMC (peripheral blood mononuclear cells) in 45 subjects with normal duodenoscopy and in PBMC alone in 48 healthy volunteers with hypovitaminosis D. 25(OH)D, PTH and VDRmRNA expression in PBMC was reassessed after 8 weeks of oral cholecalciferol (60 000 IU per week) in a subset (n=23) of healthy volunteers.
Results and Conclusions: The VDRmRNA expressions in the duodenum and PBMC were significantly correlated (r=0.42), but the expression was 13 times higher in the former than the latter. The mean VDRmRNA expression was similar in 25(OH)D-deficient subjects with or without PTH elevation, both in the duodenum and PBMC. The PBMC VDRmRNA expression showed no significant change after cholecalciferol supplementation. A weak correlation coefficient between duodenal mucosa and PBMC VDRmRNA suggests that caution needs to be exercised while using the latter as a surrogate for other sites.