Decreased expression of hepatic cytochrome P450 1A2 (CYP1A2) in a chronic intermittent hypoxia mouse model

Abstract

Background: Hepatic cytochrome P450 (CYP) isoforms, CYP1A2, is one of important enzymes for many drugs metabolism. Studies have confirmed that sustained hypoxia can influence the expression of hepatic CYP, including CYP1A2. The impact of chronic intermittent hypoxia (CIH), a marked characteristic of sleep apnea, on CYP1A2 remains unclear. The aim of the present study was to evaluate the effect of CIH on the expression of hepatic CYP1A2 in a mouse model with sleep apnea.

Methods: Twenty four old male (6-8 weeks) C57BL/6J mice (n=12 in each group) were randomly assigned to either normoxia group or CIH group. Mice in CIH group underwent 12 weeks intermittent hypoxia exposure. The different gene expression of hepatic CYP1A2 between two groups was analyzed by quantity real-time polymerase chain reaction. The protein levels of hepatic CYP1A2 in each group were observed by using western blotting and immunohistochemistry.

Results: After 12 weeks of exposure to intermittent hypoxia, the expression of hepatic CYP1A2, at the mRNA and protein levels was decreased more significantly in the CIH group than the normoxia group (P<0.01).

Conclusions: CIH contributes to inhibiting the expression of hepatic CYP1A2. This implies that the dosage of drugs metabolized by CYP1A2, should be adjusted in patients with sleep apnea.

Keywords: Intermittent hypoxia; cytochrome P450 1A2 (CYP1A2); drug metabolism; hepatic cytochrome P450 (hepatic CYP); sleep apnea.

Figure 1

Comparison of (A) body weight and liver weight, (B) alanine transaminase (ALT) and aspartate transaminase (AST) in mice between normoxia and chronic intermittent hypoxia (CIH) groups. (A) In comparison with normoxia group, both body weight and liver weight were decreased in mice among CIH group. The difference of ALT and AST between two groups did not reach statistically significant. Data are presented as means ± standard deviation (SD). *, P<0.05 vs. normoxia group; **, P<0.01 vs. normoxia group.

Figure 2

Histopathological examination of liver in mice subjected to normoxia and chronic intermittent hypoxia (CIH). No abnormal liver architecture change, namely inflammation, steatosis, hepatocyte swelling or necrosis, was detected under light microscope in both groups. The morphology of hepatic cells in two groups was detected by hematoxylin-eosin (HE).

Figure 3

RT-PCR results of CYP isoforms mRNA. After 12 weeks of exposure to CIH, the mRNA levels of CYP1A2 were decreased, while the other CYP isoforms were not altered. *, P<0.05 when compared with control group; CYP, cytochrome P450; CIH, chronic intermittent hypoxia; RT-PCR, real-time polymerase chain reaction.

Figure 4

Western blotting results of CYP1A2 and CYP2E1. When compared with mice exposed to normoxia, the protein levels of hepatic CYP1A2 in the CIH group were decreased, however, the CYP2E1 protein levels remained no change in CIH group. **, P<0.01 when compared with control group; CYP, cytochrome P450; CIH, chronic intermittent hypoxia.

Figure 5

Total CYP450 levels of hepatic microsomes were lower in CIH group than that in normoxia group. **, P<0.01 vs. normoxia group; CYP, cytochrome P450; CIH, chronic intermittent hypoxia.

Figure 6

Chronic intermittent hypoxia (CIH) contributed to down-regulation of hepatic CYP1A2 expression. (A) RT-PCR results showed that in comparison with normoxia group, CYP1A2 mRNA levels were markedly inhibited in mice exposed to CIH. CYP1A2 in cytoplasm manifested as a brown color after immunohistochemical staining; (B) compared with normoxia group, immunochemistry assay illustrated a decreasing number of CYP1A2 immune-positive hepatocytes in CIH-induced mice. Western blotting results also confirmed that the protein levels of CYP1A2 were decreased in both whole (C) hepatic tissue fraction and (D) hepatic microsomal fraction among mice treated with CIH. GAPDH was served as loading control. Data are expression as means ± standard deviation (SD). *, P<0.05 vs. normoxia group; **, P<0.01 vs. normoxia group; RT-PCR, real-time polymerase chain reaction.

Figure 7

Western blotting results delineated that when compared with normoxia group, the protein expression levels of HIF-1α, NF-κB and p-P44/42 MAPK were enhanced in mice exposed to chronic intermittent hypoxia (CIH). GAPDH (in HIF-1α, NF-κB groups) and P44/42 MAPK (in p-P44/42 MAPK group) were served as loading control. *, P<0.05 vs. normoxia group; **, P<0.01 vs. normoxia group.