Efflux transporters- and cytochrome P-450-mediated interactions between drugs of abuse and antiretrovirals

Abstract

Multidrug regimens and corresponding drug interactions cause many adverse reactions and treatment failures. Drug efflux transporters: P-gp, MRP, BCRP in conjunction with metabolizing enzymes (CYPs) are major factors in such interactions. Most effective combination antiretrovirals (ARV) therapy includes a PI or a NNRTI or two NRTI. Coadministration of such ARV may induce efflux transporters and/or CYP3A4 resulting in sub-therapeutic blood levels and therapeutic failure due to reduced absorption and/or increased metabolism. A similar prognosis is true for ARV-compounds and drugs of abuse combinations. Morphine and nicotine enhance CYP3A4 and MDR1 expression in vitro. A 2.5 fold rise of cortisol metabolite was evident in smokers relative to nonsmokers. Altered functions of efflux transporters and CYPs in response to ARV and drugs of abuse may result in altered drug absorption and metabolism. Appropriate in vitro models can be employed to predict such interactions. Influence of genetic polymorphism, SNP and inter-individual variation in drug response has been discussed. Complexity underlying the relationship between efflux transporters and CYP makes it difficult to predict the outcome of HAART as such, particularly when HIV patients taking drugs of abuse do not adhere to HAART regimens. HIV(+) pregnant women on HAART medications, indulging in drugs of abuse, may develop higher viral load due to such interactions and lead to increase in mother to child transmission of HIV. A multidisciplinary approach with clear understanding of mechanism of interactions may allow proper selection of regimens so that desired therapeutic outcome of HAART can be reached without any side effects.

Fig. 1

Localization of efflux transporters on intestinal epithelium. ‘A’ represents ATP binding sites.

Fig. 2

Drug (D) diffusing into the cells will be pumped out by P-gp/MRP/BCRP and have another chance to diffuse in: more metabolite (M) formed and less parent drug will cross the membrane to the blood. ‘A’ represents ATP binding sites.

Fig. 3

Effect of PI, their binary and ternary combinations on the expression of MDR1 mRNA expression in MDCK-MDR1 cells after 72 h treatment. 0.5% DMSO was used as the control. R: Ritonavir, S: Saquinavir, I: Indinavir, N: Nelfinavir. (*indicates significant difference compared to control; p<0.05, n=8±S.D.).

Fig. 4

MDCK cell culture models for drug interaction studies. E: efflux transporter (P-gp or MRP2 or BCRP) and M: metabolizing enzyme (CYP3A4). This figure is a schematic representation of an integrated cell culture system. The upper reservoir containing MDCK-EM monolayer resembles the mucosal surface of intestine can be exposed to the given drug or combination of drugs. The lower reservoir resembling the serosal compartment contains the HepG2-transfected with CYP3A4 and/CYP2D6 mimicking liver enzymes or hepatocytes. The transported drug molecules will be metabolized in the basal chamber.

Fig. 5

Immunoblot showing 56.5 kD band for CYP3A4 protein: lane 1) molecular marker, lane 2) MDCK-WT, lane 3) MDCK-WT-CYP3A4, lane 4) MDCK-MDR1, lane 5) MDCK-MDR1-CYP3A4, lane 6) blank, lanes 7 through 9) human intestinal microsomes. Lanes 2–5 were loaded with 20 μg microsomal protein where as lanes 7 to 9 were loaded with 10, 5 and 2.5 μg microsomal proteins respectively.

Fig. 6

Transport of 500 μM cortisol in MDCK-WT and MDCK-MDR1 cells transfected with CYP3A4. Time dependent formation of CYP3A4-mediated metabolite of cortisol (6β-hydroxy cortisol) is shown in this figure. p<0.05, n=6±S.D.

Fig. 7

Transport of 50 μM methadone in MDCK-MDR1 cells transfected with CYP3A4. p<0.05, n=6±S.D.

Fig. 8

Oral pharmacokinetics of lopinavir in Sprague-Dawley rats. p<0.05, n=3±S.D.

Fig. 9

Expression of MDR1 mRNA in Caco-2 in presence of 3 μM morphine and 2.5 μM nicotine (* indicates significant difference compared to control; p<0.05, n=3±S.D).

Fig. 10

Quantitative changes in CYP3A4 mRNA levels following induction with 3 μM morphine and 2.5 μM nicotine in HepG2. Results are expressed as relative fold difference (* indicates significant difference compared to control; p<0.05, n=4±S.D.).

Fig. 11

Enhanced activity of CYP3A4 in HepG2 in the presence of morphine and nicotine. HepG2 cells were treated with DMSO (0.1% v/v), morphine (3 μM), nicotine (2.5 μM), omeprazole (100 μm) and rifampicin (50 μm). (* indicates significant difference relative to control; p<0.05, n=8±S.D).

Fig. 12

Dose dependent induction of BCRP in Calu-3 cells by nicotine suggests heavy smokers will have more expression of efflux transporter (BCRP) than nonsmoker or moderate smoker. (* indicates significant difference compared to control; p value <0.05%, n=3±S.D).

Fig. 13

Cortisol metabolism in human lung microsomes (commercially available). (* indicates significant difference compared to control; p value <0.05%).

Fig. 14

Cortisol metabolism in lung microsomes from control and nicotine (3.0 mg /kg body weight, twice daily for five days) treated rats. (* indicates significant difference compared to control; p value <0.05%).