Objective:Plateau hypoxia exposure causes changes in pharmacokinetic parameters and cerebral-blood distribution of drugs,including many substrates of P-glycoprotein(P-gp).Levetiracetam,a kind of antiepileptic drugs,is a substrate of P-gp.Whether plateau hypoxia exposure changes its pharmacokinetic characteristics and cerebral-blood distribution remains unclear.This study aims to investigate the effects of plateau hypoxia on the pharmacokinetics and cerebra-blood distribution of levetiracetam. Methods:Wistar rats were divided into a low-altitude control group,a high-altitude group,a solvent group,and a P-gp induction group.After 24 h of exposure at altitude of 4 010 m,rats in the high-altitude group were given levetiracetam orally or intravenously.The plasma was respectively collected at 0.083,0.25,0.5,0.83,1.25,2,4,6,8,10,12,and 24 h after oral administration of the drug,while both plasma and brain were respectively collected at 5,45,60,120 and 240 min after intravenous injection.After 3 days administration of dexamethasone,plasma and brain of rats in the P-gp induction group were collected at 120 min after intravenously giving levetiracetam.Plasma and brain concentrations of the drug were determined by high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS).The expression of P-gp in blood-brain barrier was detected by Western blotting. Results:Compared with the low-altitude control group,the area under the curve(AUC)and mean residence time(MRT)of levetiracetam were respectively decreased by 14.69%(P<0.01)and 15.42%(P<0.01),while the clearance(CL)was increased by 16.67%(P<0.01)in the high-altitude group.The ratio of brain/blood plasma drug concentration was decreased by 22.82%(P<0.05),12.42%(P<0.05),17.40%(P<0.01),and 13.22%(P<0.01)at 5,45,120,and 240 min after injection,respectively.The expression of P-gp on the blood-brain barrier was increased by 86.3%(P<0.05).Compared with the solvent control group,the expression of P-gp on the blood-brain barrier in the P-gp induction group was increased by 56.3%(P<0.05),the ratio of brain/blood plasma drug concentration was decreased by 19.3%(P<0.05). Conclusion:After acute plateau hypoxia exposure,the pharmacokinetic of levetiracetam in rats are altered,and the cerebral-blood distribution of the drug in rats is decreased,which may be related to the up-regulation of P-gp expression on the blood-brain barrier.

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.
Humans ; ATP Binding Cassette Transporter, Subfamily B, Member 1 ; Caco-2 Cells ; ATP Binding Cassette Transporter, Subfamily B ; Hypoxia ; Oxygen