Effects of vitamin D and its metabolites on cell viability and Staphylococcus aureus invasion into bovine mammary epithelial cells

Vitamin D has been found have various biological effects that may be potent in preventing bovine mastitis. Two forms of vitamin D, vitamin D2 (D2) and vitamin D3 (D3), can be hydroxylated to functional metabolites in cattle. The objectives of the present study were to investigate the potential of vitamin D compounds for controlling bovine mastitis using in vitro cell models, and to compare the differences between D2 and D3 compounds. Results showed that D2 compounds have comparable effects to their D3 analogues on inhibiting MAC-T cell viability in vitro. S. aureus growth was inhibited by high concentrations of D2, D3, 25(OH)D2 and 25(OH)D3. 25(OH)D2 and 25(OH)D3 induced CYP24A1 expression but reduced VDR mRNA expression, whereas the expression of CYP27B1, occludin, and E-cadherin did not change. Additionally, the induction of CYP24A1 expression by 25(OH)D3 was higher than that of 25(OH)D2, which may contribute to their differences in inhibiting cell viability. S. aureus invaded into MAC-T cells and universally inhibited gene expressions. Pre-treat MAC-T cells with 25(OH)D2 reduced S. aureus adhesion while pre-treatment with 25(OH)D3 inhibited S. aureus invasion, but neither of the compounds attenuated the S. aureus-induced gene expression reduction. In conclusion, the present study shows that D2 compounds have comparable effects on inhibiting cell viability and S. aureus invasion to their D3 analogues in vitro, suggesting that D2 and its metabolites have potential in controlling bovine mastitis.