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Abstract
Little is known about what roles the pregnane X receptor (PXR) and constitutive androstane receptor (CAR) play in drug metabolism in high-altitude hypoxia. Likewise, the potential interaction of nuclear receptors and drug metabolism enzymes during drug metabolism of high-altitude hypoxia is not fully understood. In this work, we investigated the effects of high-altitude hypoxia on transcriptional regulation of cytochrome P450 (CYP450) and UDP-glucuronosyltransferase 1A1 (UGT1A1) genes mediated by PXR and CAR proteins. The protein and mRNA expressions of CYP450, UGT1A1, PXR, and CAR were determined by enzyme-linked immunosorbent assay and qPCR in rats and HepG2 cell lines under hypoxia. Hypoxia potently inhibited the CYP450 isoforms, UGT1A1, PXR, and CAR protein and mRNA expression. To clarify whether PXR and CAR regulate various genes involved in drug metabolism of high-altitude hypoxia, we investigated the expression of CYP1A2, CYP2C9, CYP2E1, CYP3A4, and UGT1A1 using a dual-luciferase reporter assay after treatment with Ketoconazole (KCZ) and Retinoic acid (RA), or silenced PXR and CAR gene expression. In HepG2 cells, hypoxia, KCZ, and RA inhibited CYP450 isoforms and UGT1A1 expression. Activation of PXR and CAR in cells treated with 6-(4-chlorophenyl)-imidazo (2,1-b) thiazole-5-carbaldehyde (CITCO) and rifampicin (Rif) resulted in the enhancement of CYP450 isoforms, UGT1A1, PXR, and CAR. In contrast, this effect was not observed under hypoxia. Taken together, our results suggest that hypoxia inhibits CYP1A2, CYP2C9, CYP2E1, CYP3A4, and UGT1A1 expression via the PXR and CAR regulatory pathway.
Highlights
The high-altitude environment is characterized by increased solar radiation, decreased ambient oxygen tension, extreme diurnal ranges in temperature, arid climate, and poor soil quality; of these, hypoxia is the main factor with the potential to affect human life and activity (Eide and Asplund, 2012)
We examined the physiological and gene transcriptional changes in rats after acute or chronic high-altitude exposure, the contents of red blood cells (RBC), HGB, and BIL were significantly increased in high-altitude hypoxia
We found that hypoxia affected expression of drug metabolism enzymes and nuclear receptors, and determined that pregnane X receptor (PXR) and constitutive androstane receptor (CAR) were the mechanisms for regulation of cytochrome P450 (CYP450) and UDP-glucuronosyltransferase 1A1 (UGT1A1) in hypoxia
Summary
The high-altitude environment is characterized by increased solar radiation, decreased ambient oxygen tension, extreme diurnal ranges in temperature, arid climate, and poor soil quality; of these, hypoxia is the main factor with the potential to affect human life and activity (Eide and Asplund, 2012). There are many places on the planet above 3,000 m that humans live in conditions of hypobaric hypoxia, which is known to induce physiological changes in most people (Eide and Asplund, 2012). Hypoxia-induced fluctuations in organism function, metabolism, and structure underly the pathological basis of disease at high altitude (Zhou et al, 2018). High-altitude hypoxia has negative effects on the cardiovascular system, nervous system, and metabolism, which contribute to potential changes in drug metabolism (Mairbaurl, 1994). The altitude and duration of exposure to hypoxia play a key role in drug metabolism
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