ESPE Abstracts (2019) 92 FC3.3

Variability in Drug Metabolizing Cytochrome P450 Activities Caused by Human Genetic Variations in NADPH Cytochrome P450 Oxidoreductase (POR)

Maria Natalia Rojas Velazquez1,2, Shaheena Parween1,2, Amit V Pandey1,2


1University Children's Hospital Bern, Bern, Switzerland. 2Department of Biomedical Research, University of Bern, Bern, Switzerland


Background: A broad spectrum of human diseases, including abnormalities in steroidogenesis, are caused by mutations in the NADPH cytochrome P450 oxidoreductase (POR) (1-2). Cytochrome P450 proteins perform several reactions, including metabolism of steroids, drugs and other xenobiotics. Therefore, genetic variations in POR can impact many different metabolic pathways by changing the activities of cytochromes P450 (1). In 2004 the first human patients with defects in POR were reported, and over 200 variations in POR are known (2).

Methods: By analyzing the POR sequences from sequencing projects, we identified potentially disease-causing variations and characterized these by functional studies using recombinant proteins. Proteins were expressed in bacteria and purified for activity assays. Activities of cytochrome P450 enzymes were tested in liposomes prepared with lipids into which P450 and P450 reductase proteins were embedded and assayed using fluorogenic substrates on a microplate spectrofluorometer.

Results: Here we are reporting the effect of POR variants on drug metabolizing enzymes CYP2C9, CYP2C19, and CYP3A5 which are responsible for the metabolism of many drugs. POR Variants A115V, T142A, A281T, P284T, P284L and A287P and Y607C inhibited activities of all P450 proteins tested. Interestingly, the POR variant Q153R showed a reduction of 20-50 activities with CYP2C9 and CYP2C19 but had a 400% increased activity with CYP3A5. Similarly, the common polymorphism in POR, A503V showed several fold higher activities with all drug metabolizing P450s studied.

Conclusions: The A287P is most common POR mutation found in patients of European origin, and significantly inhibited drug metabolism activities have important consequences for monitoring and treatment of patients. Similarly, higher drug metabolism activities from A503V variant of POR suggests monitoring the patients with this variant carefully. The A503V is the common polymorphism in POR present in about 25% of all alleles and is often ignored in diagnostic reports. These results indicate that detailed knowledge of POR effects is necessary for correct diagnosis and treatment options for persons with POR deficiency and the role of changes in drug metabolism needs to be addressed. Changes in drug and steroid metabolism due to genetic variations can be addressed using personalized metabolic profiling and supplementation.

References: 1. Parween S et al. P450 Oxidoreductase Deficiency: Loss of Activity Caused by Protein Instability From a Novel L374H Mutation. J Clin Endocrinol Metab. 101:4789-4798 (2017).

2. Burkhard FZ et al. P450 Oxidoreductase deficiency: Analysis of mutations and polymorphisms. J Steroid Biochem Mol Biol. 165:38-50 (2017).

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