Drug Metabolism In Hepatocytes Research Articles

Inflammatory signaling on cytochrome P450-mediated drug metabolism in hepatocytes.

Cytochrome P450 (CYP450) enzymes are membrane-bound blood proteins that are vital to drug detoxification, cell metabolism, and homeostasis. CYP450s belonging to CYP families 1-3 are responsible for nearly 80% of oxidative metabolism and complete elimination of approximately 50% of all common clinical drugs in humans liver hepatocytes. CYP450s can affect the body's response to drugs by altering the reaction, safety, bioavailability, and toxicity. They can also regulate metabolic organs and the body's local action sites to produce drug resistance through altered drug metabolism. Genetic polymorphisms in the CYP gene alone do not explain ethnic and individual differences in drug efficacy in the context of complex diseases. The purpose of this review is to summarize the impact of new inflammatory-response signaling pathways on the activity and expression of CYP drug-metabolizing enzymes. Included is a summary of recent studies that have identified drugs with the potential to regulate drug-metabolizing enzyme activity. Our goal is to inspire the development of clinical drug treatment processes that consider the impact of the inflammatory environment on drug treatment, as well as provide research targets for those studying drug metabolism.

Cyclin-dependent Kinase 2 Negatively Regulates Human Pregnane X Receptor-mediated CYP3A4 Gene Expression in HepG2 Liver Carcinoma Cells

The human pregnane X receptor (hPXR) regulates the expression of critical drug metabolism enzymes. One of such enzymes, cytochrome P450 3A4 (CYP3A4), plays critical roles in drug metabolism in hepatocytes that are either quiescent or passing through the cell cycle. It has been well established that the expression of P450, such as CYP3A4, is markedly reduced during liver development or regeneration. Numerous studies have implicated cellular signaling pathways in modulating the functions of nuclear receptors, including hPXR. Here we report that inhibition of cyclin-dependent kinases (Cdks) by kenpaullone and roscovitine (two small molecule inhibitors of Cdks that we identified in a screen for compounds that activate hPXR) leads to activation of hPXR-mediated CYP3A4 gene expression in HepG2 human liver carcinoma cells. Consistent with this finding, activation of Cdk2 attenuates the activation of CYP3A4 gene expression. In vitro kinase assays revealed that Cdk2 directly phosphorylates hPXR. A phosphomimetic mutation of a putative Cdk phosphorylation site, Ser(350), significantly impairs the function of hPXR, whereas a phosphorylation-deficient mutation confers resistance to Cdk2. Using HepG2 that has been stably transfected with hPXR and the CYP3A4-luciferase reporter, enriched in different phases of the cell cycle, we found that hPXR-mediated CYP3A4 expression is greatly reduced in the S phase. Our results indicate for the first time that Cdk2 negatively regulates the activity of hPXR, and suggest an important role for Cdk2 in regulating hPXR activity and CYP3A4 expression in hepatocytes passing through the cell cycle, such as those in fetal or regenerating adult liver.

Hepatitis C virus therapy, hepatocyte drug metabolism, and risk for acute cellular rejection

We recently reported on a series of patients who experienced acute cellular rejection (ACR) during the treatment of hepatitis C virus (HCV) infection in our posttransplantation cohort. Our hypothesis is that HCV clearance improves hepatic microsomal function, which in turn results in lower trough cyclosporine (CyA) and tacrolimus (TAC) levels, predisposing the patient to ACR. Records of all patients receiving transplants for HCV infection at our center from 1993 to June 2002 were reviewed. Two hundred three patients were identified. Thirty-seven patients (18%) were treated with interferon-based therapies in combination with ribavirin. Twelve patients were selected for analysis because they became HCV RNA negative during therapy, and 18 patients with no antiviral response were selected as controls (7 other patients had incomplete data or had switched from one immunosuppression [IS] therapy to the other). Baseline IS levels were compared with the first available level after documented negative HCV RNA results in the study group and the last on-treatment IS level in the control group. We also compared frequency and percentage of change in IS levels during therapy. Mean decline in CyA trough levels in the study group was from 187.28 ng/mL at baseline to 118.14 ng/mL immediately after becoming HCV RNA negative (-36.92%; P =.018). Mean decline in TAC levels was from 7.34 ng/mL at baseline to 5.02 ng/mL immediately after becoming HCV RNA negative (-29.17%; P =.044). Overall, 6 of 12 patients who cleared HCV RNA during therapy experienced ACR; 1 patient died as a result of ACR. Using percentage of decrease from baseline IS level, we combined results for patients administered CyA and TAC and found a significant decrease from baseline IS levels in responders (-31.8% after HCV RNA clearance on treatment; P =.0001). Nonresponders experienced a 0.98% decline in IS levels while on treatment, and the difference was significant compared with the change in the responder group (P =.006). A greater proportion of antiviral therapy responders also experienced trough IS levels 20% less than baseline than nonresponder controls during therapy (P =.0006). In conclusion, IS levels decreased significantly in patients responding favorably to anti-HCV therapy. This decrease in IS levels may have a key role in predisposing these patients to ACR.

Expression and inducibility of cytochrome P450 IIIA family within intrasplenically transplanted fetal hepatocytes

With the development of transplantation of hepatocytes into the spleen, interest has focused on the metabolic changes associated with hepatocyte proliferation. As these changes are important for drug metabolism in hepatocytes, we examined the expression and inducibility of the cytochrome P450 IIIA family within transplanted hepatocytes. Fetal hepatocytes were harvested at 20 days of gestation from spontaneously hypertensive rats (SHRs) and transplanted into recipient adult SHR spleens. Microscopic examination of the recipient spleens 4 and 10 wk after transplantation revealed masses of hepatocytes with cord-like structures in the red pulp. Proliferating hepatocytes were detected with a bromodeoxyuridine (BrdU) immunohistochemical stain. Immunochemical studies detected cytochromes (cytos) P450 p and P450 HLp in fetal hepatocytes before transplantation without prior induction. And although these cytos were not detected by 10 wk after transplantation, they were induced with dexamethasone. These results demonstrated that fetal hepatocytes can be transplanted successfully into recipient spleens and suggested that fetal hepatocytes grow in the spleen, similar to the adult hepatocyte response.