Inhalation with Vitamin D3 Metabolites-A Novel Strategy to Restore Vitamin D3 Deficiencies in Lung Tissue

Vitamin D3 deficiency has been recognized as a pandemic with serious health consequences including chronic respiratory diseases. Unfortunately, improvement in this situation by using vitamin D supplementation has failed. The direct delivery of 1,25(OH)2-vitamin D3 and its precursor into the respiratory tract, by nebulization, seemed to be a better option, as verified in the presented study. To induce vitamin D deficiency, mice received a diet with 0.05 IU/g cholecalciferol, while control animals were given feed with 0.5 IU/g cholecalciferol. Vitamin-D-deficient mice were exposed to different doses of calcidiol or calcitriol via nebulization for at least 7 days. At the end of the experiment, whole-body plethysmography was conducted. Pulmonary and serum levels of calcitriol were examined using ELISA. The calcitriol concentrations in mice on standard vs. deficient diet were 30.31/18.20 pg/mg (lungs) and 132.24/98.61 pg/mL (serum), respectively. Restoration of the physiological level of calcitriol in vitamin-D-deficient mice required 1-week exposure to 100 pg/g of calcidiol or 5 pg/g of calcitriol. The inhalations did not cause any side changes in murine respiratory function. The presented study revealed the usefulness and safety of chronic inhalation with a bioactive form of vitamin D3 or its precursor for the restoration of physiological calcitriol levels in animals with vitamin D deficiencies.