Placental transporter-mediated drug interactions and offspring congenital anomalies.

AIMS: P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are efflux transporters expressed in the placenta, limiting their substrates from reaching the foetus. Our aim was to investigate if concomitant prenatal exposure to several substrates or inhibitors of these transporters increases the risk of congenital anomalies. METHODS: The national Drugs and Pregnancy database, years 1996-2014, was utilized in this population-based birth cohort study. In the database, the Medical Birth Register, the Register on Induced Abortions, the Malformation register and the Register on Reimbursed Drug Purchases have been linked. The University of Washington Metabolism and Transport Drug Interaction Database was used to identify substrates and inhibitors of P-gp and BCRP. We included singleton pregnancies ending in birth or elective termination of pregnancy due to foetal anomaly. Known teratogens were excluded. We identified women exposed 1 month before pregnancy or during the first trimester to P-gp/BCRP polytherapy (n = 21 186); P-gp/breast cancer resistance protein monotherapy (n = 97 906); non-P-gp/BCRP polytherapy (n = 78 636); and unexposed (n = 728 870). We investigated the association between the exposure groups and major congenital anomalies using logistic regression adjusting for several confounders. RESULTS: The prevalence of congenital anomalies was higher in the P-gp/BCRP polytherapy group (5.5%) compared to the P-gp/BCRP monotherapy (4.7%, OR 1.13; 95% CI 1.05-1.21), the non-P-gp/BCRP polytherapy (4.9%, OR 1.14; 95% CI 1.06-1.22), and to the unexposed groups (4.2%, OR 1.23; 95% CI 1.15-1.31). CONCLUSION: The results suggest a role of placental transporter-mediated drug interactions in teratogenesis.

Drug-Mediated Gene Regulation of Vitamin D3 Metabolism in Primary Human Dermal Fibroblasts.

Vitamin D metabolism was studied in primary human dermal fibroblasts with focus on drug-mediated gene regulation related to adverse side effects of antiretroviral drugs used in HIV therapy. The fibroblasts expressed mRNA for cytochrome P450 (CYP) enzymes catalysing bioactivating (CYP2R1, CYP27A1 and CYP27B1) and catabolic reactions (CYP24A1). The cells produced both 25-hydroxyvitamin D3 and 1α,25-dihydroxyvitamin D3 . The results demonstrate that primary dermal fibroblasts have an active vitamin D3 -metabolizing system. High incidence of low bone mineral density is a concern for HIV-infected patients treated with antiretroviral drugs. Osteomalacia and severe vitamin D deficiency have been reported. We investigated whether drug-mediated gene regulation could be a possible mechanism behind these adverse drug effects. Fibroblasts were treated with different drugs used in HIV therapy, and the 1α,25-dihydroxyvitamin D3 levels and relative mRNA levels for crucial enzymes were determined. Efavirenz, stavudine and ritonavir significantly down-regulated the bioactivating CYP2R1 and up-regulated the catabolic CYP24A1. The drugs reduced bioactivating enzyme activities and cellular levels of 1α,25-dihydroxyvitamin D3 . The current results indicate that effects on gene expression may lead to disturbed vitamin D metabolism and decreased cellular levels of active vitamin D3 . The data are consistent with the impaired bone health in patients treated with certain antiretroviral drugs.

Which drugs can be used during pregnancy?

In many cases the decisions on drug therapy during pregnancy have to be made without evidence-based information about the effectiveness and safety of the treatment. While few drugs are known with certainty to be harmful for fetal development, the evidence for evaluating harm to the fetus is insufficient for the majority of drugs. The differentiation of fetal organs takes place during the early weeks of pregnancy, whereby it is imperative that the mother's medication be revised already when planning a pregnancy. A drug should primarily be chosen, for which experience has accumulated about its use during pregnancy and is not suspected or known to be associated with adverse effects.

Regulation of human vitamin D(3) 25-hydroxylases in dermal fibroblasts and prostate cancer LNCaP cells.

In this study, we examined whether 1alpha,25-dihydroxyvitamin D(3) (calcitriol), phenobarbital, and the antiretroviral drug efavirenz, drugs used by patient groups with high incidence of low bone mineral density, could affect the 25-hydroxylase activity or expression of human 25-hydroxylases in dermal fibroblasts and prostate cancer LNCaP cells. Fibroblasts express the 25-hydroxylating enzymes CYP2R1 and CYP27A1. LNCaP cells were found to express two potential vitamin D 25-hydroxylases-CYP2R1 and CYP2J2. The presence in different cells of nuclear receptors vitamin D receptor (VDR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR) was also determined. Phenobarbital suppressed the expression of CYP2R1 in fibroblasts and CYP2J2 in LNCaP cells. Efavirenz suppressed the expression of CYP2R1 in fibroblasts but not in LNCaP cells. CYP2J2 was slightly suppressed by efavirenz, whereas CYP27A1 was not affected by any of the two drugs. Calcitriol suppressed the expression of CYP2R1 in both fibroblasts and LNCaP cells but had no clear effect on the expression of either CYP2J2 or CYP27A1. The vitamin D(3) 25-hydroxylase activity in fibroblasts was suppressed by both calcitriol and efavirenz. In LNCaP cells, consumption of substrate (1alpha-hydroxyvitamin D(3)) was used as indicator of metabolism because no 1alpha,25-dihydroxyvitamin D(3) product could be determined. The amount of 1alpha-hydroxyvitamin D(3) remaining in cells treated with calcitriol was significantly increased. Taken together, 25-hydroxylation of vitamin D(3) was suppressed by calcitriol and drugs. The present study provides new information indicating that 25-hydroxylation of vitamin D(3) may be regulated. In addition, the current results may offer a possible explanation for the impaired bone health after treatment with certain drugs.

Phenobarbital suppresses vitamin D3 25-hydroxylase expression: a potential new mechanism for drug-induced osteomalacia.

Prolonged therapy with phenobarbital may cause vitamin D deficiency or osteomalacia. In the current study, we propose a novel mechanism for drug-induced osteomalacia involving impaired bioactivation of vitamin D(3) due to decreased 25-hydroxylation of vitamin D(3) in liver. The present data, using the pig as model, demonstrate direct effects by phenobarbital on the expression of CYP27A1 and CYP2D25, two important 25-hydroxylases. Treatment by phenobarbital markedly reduced the rate of 25-hydroxylation by primary hepatocytes and suppressed the cellular CYP27A1 mRNA levels. The rate of 25-hydroxylation by two different purified 25-hydroxylases, microsomal CYP2D25, and mitochondrial CYP27A1, respectively, was dose-dependently inhibited by phenobarbital. Reporter assay experiments in liver-derived HepG2 cells revealed a marked PXR-mediated transcriptional downregulation of the CYP2D25 promoter. In addition, the data indicate that phenobarbital might affect the mRNA stability of CYP2D25. Taken together, the data suggest that vitamin D(3) 25-hydroxylation may be suppressed by phenobarbital. A downregulation of 25-hydroxylation by phenobarbital may explain, at least in part, the increased risk of osteomalacia, bone loss, and fractures in long-term phenobarbital therapy.