Progress in Epigenetic Modification Regulating Drug Transporters in the Hypoxic Environment.

Drug transporters are critical factors influencing the pharmacokinetics of drugs under hypoxic conditions. Studies have shown significant changes in drug transporter levels in the hypoxic environment. In addition to being regulated by HIF-1, nuclear receptors, and inflammatory factors, hypoxia can also regulate transporters through epigenetic modifications, thereby affecting drug absorption, distribution, metabolism, and excretion. In recent years, increasing attention has been paid to the role of epigenetic modifications in regulating drug transporters under hypoxic conditions at high altitude. In this paper, we comprehensively review the effects of hypoxia on drug transporters and epigenetic modifications and explore the regulatory mechanism of epigenetic modifications on drug transporter expression under hypoxic conditions. The aim is to provide a reference for exploring the epigenetic regulation mechanism of drug transporter expression in the hypoxic environment at high altitude, and then guide the study of pharmacokinetics and promote effective and safe medication at high altitude.

Effect of High Altitude Environment on Pharmacokinetic and Pharmacodynamic of Warfarin in Rats.

BACKGROUND: High altitude environment affects the pharmacokinetic (PK) parameters of drugs and the PK parameters are an important theoretical basis for guiding the rational clinical use of drugs. Warfarin is an oral anticoagulant of the coumarin class commonly used in clinical practice, but it has a narrow therapeutic window and wide individual variation. However, the effect of high altitude environment on PK and pharmacodynamic (PD) of warfarin is unclear. OBJECTIVE: The objective of this study is to investigate the effect of a high altitude environment on PK and PD of warfarin in rats. METHOD: Rats were randomly divided into plain group and high altitude group and blood samples were collected through the orbital venous plexus after administration of 2 mg/kg warfarin. Warfarin concentrations in plasma samples were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and PK parameters were calculated by the non-compartment model using WinNonlin 8.1 software. Meanwhile, the expression of PXR, P-gp and CYP2C9 in liver tissues was also determined by western blotting. The effect of high altitude environment on PD of warfarin was explored by measuring activated partial thromboplastin time (APTT) and prothrombin time (PT) values and then calculated international normalized ratio (INR) values based on PT. RESULTS: Significant changes in PK behaviors and PD of warfarin in high altitude-rats were observed. Compared with the plain-rats, the peak concentration (Cmax) and the area under the plasma concentration-time curve (AUC) increased significantly by 50.9% and 107.46%, respectively. At the same time, high altitude environment significantly inhibited the expression of PXR, P-gp and CYP2C9 in liver tissues. The results of the PD study showed that high altitude environments significantly prolonged PT, APTT and INR values. CONCLUSION: High altitude environment inhibited the metabolism and increased the absorption of warfarin in rats and increased the effect of anticoagulant effect, suggesting that the optimal dose of warfarin for patients at high altitude should be reassessed.

Effects of hypoxia on the expression and function of P-gp in Caco-2 cells. / 低氧对Caco-2细胞P-gp表达及功能的影响.

OBJECTIVES: Hypoxia can alter the oral bioavailability of drugs, including various substrates (drugs) of P-glycoprotein (P-gp), suggesting that hypoxia may affect the function of P-gp in intestinal epithelial cells. Currently, Caco-2 monolayer model is the classic model for studying the function of intestinal epithelial P-gp. This study combines the Caco-2 monolayer model with hypoxia to investigate the effects of hypoxia on the expression and function of P-gp in Caco-2 cells, which helps to elucidate the mechanism of changes in drug transport on intestinal epithelial cells in high-altitude hypoxia environment. METHODS: Normally cultured Caco-2 cells were cultured in 1% oxygen concentration for 24, 48, and 72 h, respectively. After the extraction of the membrane proteins, the levels of P-gp were measured by Western blotting. The hypoxia time, with the most significant change of P-gp expression, was selected as the subsequent study condition. After culturing Caco-2 cells in transwell cells for 21 days and establishing a Caco-2 monolayer model, they were divided into a normoxic control group and a hypoxic group. The normoxic control group was continuously cultured in normal condition for 72 h, while the hypoxic group was incubated for 72 h in 1% oxygen concentration. The integrity and polarability of Caco-2 cells monolayer were evaluated by transepithelial electrical resistance (TEER), apparent permeability (Papp) of lucifer yellow, the activity of alkaline phosphatase (AKP), and microvilli morphology and tight junction structure under transmission electron microscope. Then, the Papp of rhodamine 123 (Rh123), a kind of P-gp specific substrate, was detected and the efflux rate was calculated. The Caco-2 cell monolayer, culturing at plastic flasks, was incubated for 72 h in 1% oxygen concentration, the expression level of P-gp was detected. RESULTS: P-gp was decreased in Caco-2 cells with 1% oxygen concentration, especially the duration of 72 h (P<0.01). In hypoxic group, the TEER of monolayer was more than 400 Ω·cm2, the Papp of lucifer yellow was less than 5×10-7 cm/s, and the ratio of AKP activity between apical side and basal side was greater than 3. The establishment of Caco-2 monolayer model was successful, and hypoxia treatment did not affect the integrity and polarization state of the model. Compared with the normoxic control group, the efflux rate of Rh123 was significantly reduced in Caco-2 cell monolayer of the hypoxic group (P<0.01). Hypoxia reduced the expression of P-gp in Caco-2 cell monolayer (P<0.01). CONCLUSIONS: Hypoxia inhibits P-gp function in Caco-2 cells, which may be related to the decreased P-gp level.

Research Progress of Epigenetic Modification on the Regulation of Transporters Under Hypoxia.

Epigenetic modification refers to the heritable changes caused by chromosomal changes without changing the DNA sequence. Epigenetics runs through the entire growth and differentiation process of the body, which causes varied diseases. Hypoxia is a physiological astate of lowered partial oxygen partial pressure that affects cell and tissue function. Transporters are proteins that maintain a normal and stable state of cells. Transporter's expression levels when hypoxia occurs influence the absorption, distribution, metabolism, and excretion of drugs, thereby affecting the utilization and efficacy of drugs. Epigenetic modification is assumed to play an important role in the metabolism of drugs. Changes in epigenetic modification and transporter expression levels under hypoxia are explored in our work, and the effect of epigenetic modification on transporter expression and how this regulatory mechanism works and affects drugs under hypoxia are questioned. It is important for drug development, treatment of diseases and rational use of drugs.

Effects of high-altitude environment on pharmacokinetic parameters of gliquidone in rats.

OBJECTIVE: To investigate the effect of high-altitude hypoxia on the pharmacokinetics parameters of gliquidone. METHODS: Twelve healthy male Wistar rats were randomly divided into plain group and high-altitude group with 6 rats in each group. Blood samples were collected after intragastric administration of gliquidone (6.3 mg/kg). Ultra-fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS) was used to determine the concentration of gliquidone in rat plasma samples. And the expression of CYP2C9 in rat liver tissues was determined by Western blotting. RESULTS: Compared with the plain group, the peak concentration of gliquidone in the high-altitude rats was significantly increased, the absorption rate constant was decreased, the elimination rate constant and the absorption half-life were increased, the elimination half-life was shortened, the mean residence time and apparent volume of distribution were decreased (all P<0.05). Western blotting showed that the expression of CYP2C9 was significantly up-regulated in the liver tissues of high altitude group rats, compared with the plain group (4.18 ±0.06 vs. 2.13±0.06, t=11.57, P<0.01). CONCLUSION: Under the high-altitude hypoxia environment, the absorption of gliquidone in rats was reduced and the metabolism was accelerated in rats, which may be related to the up-regulation of CYP2C9 expression in liver tissues.

Development of tartaric acid derived chiral guanidines and their application to catalytic enantioselective α-hydroxylation of ß-dicarbonyl compounds.

A novel library of chiral guanidines featuring a tartaric acid skeleton was developed from diethyl l-tartrate. These guanidines are easily accessed with tunable steric and electronic properties. The utilities of the guanidines were highlighted by their ability to catalyze the α-hydroxylation of ß-ketoesters and ß-diketones with remarkable efficiency and excellent enantioselectivity.