Maternal Vitamin D Status in Preeclampsia: Seasonal Changes Are Not Influenced by Placental Gene Expression of Vitamin D Metabolizing Enzymes

Preeclampsia, a hypertensive disorder in pregnancy develops in 2-8% of pregnancies worldwide. Winter season and vitamin D deficiency have been associated with its onset. Objective: To investigate the influence of season on maternal vitamin D status and placental vitamin D metabolism. Methods: 25-OH vitamin D and 1,25-(OH)(2) vitamin D were measured in maternal serum obtained during the winter or summer months from 63 pregnant women at delivery (43 healthy, 20 preeclampsia). In a subgroup, mRNA expression of CYP24A1 (24-hydroxylase), CYP27B1 (1 alpha-hydroxylase) and VDR (vitamin D receptor) were quantified by real time PCR in placental samples of 14 women with normal pregnancies and 13 with preeclampsia. Results: In patients with preeclampsia,25-OH vitamin D levels were lower, but differed significantly from controls only in summer (18.21 +/- 17.1 vs 49.2 +/- 29.2 ng/mL, P<0.001), whereas 1,25-(OH)(2) vitamin D levels were significantly lower only in winter (291 +/- 217 vs 612.3 +/- 455 pmol/mL, P<0.05). A two-factorial analysis of variance produced a statistically significant model (P<0.0001) with an effect of season (P<0.01) and preeclampsia (P = 0.01) on maternal 25-OH vitamin D levels, as well as a significant interaction between the two variables (P = 0.02). Placental gene expression of CYP24A1, CYP27B1, and VDR did not differ between groups or seasons. A negative correlation between placental gene expression of CYP24A1 and CYP27B1 was observed only in healthy controls (r = -0.81, P<0.0001). Summary: Patients with preeclampsia displayed lower vitamin D serum levels in response to seasonal changes. The regulation of placental CYP24A1, but not of the VDR or CYP27B1 might be altered in preeclampsia.