Pharmacokinetic influences of selected phytochemical compounds from herbal medicine used by HIV- positive patients on drugs-metabolising proteins of HIV-1 protease inhibitor drugs.

Abstract

Doctoral Degree. University of KwaZulu-Natal, Durban.Introduction: Sub-Saharan Africa has the highest incidence of HIV/AIDS and AIDS-related deaths in the world. Although there is currently no cure for the disease, significant progress has been made in developing antiretroviral drugs (ARVs) that can inhibit disease progression. However, despite the availability of these ARVs, HIV-positive patients use traditional herbal medicines (THMs) either alone or simultaneously with conventional ARVs. This simultaneous usage may cause serious adverse effects due to herb-drug interactions, although there are also possible positive effects such as the enhanced bioavailability of the ARVs or possible antiviral activity. Aim: These potential interactions prompted this study which examined the pharmacokinetic properties and influences of selected phytochemical compounds (PCs) commonly found in THMs on drug-metabolising proteins involved in the metabolism of protease inhibitor drugs (PIs) as well as their potential as inhibitors of HIV-1 protease. Method: The potential inhibitory activities of fifteen PCs (Epigallocatechin gallate (EGCG), Fisetin (FST), Ellagic acid (EGA), Cholesta-4,6-dien-3-ol (CHD), Lanosteol (LNT), Benzyl Isothiocyanate (BIT), Gallic acid, (GA), Isosteviol (IST), Stigmasterol (STG), Phthalic acid (PTA), Naringenin (NGN), Kaempferol-7-glucoside (K7G), Luteolin (LUT), Geranin (GER), Apigenin (APG)) against the South African sub-type C HIV-1 protease enzyme and PIs’ drug-metabolizing proteins were investigated, using molecular dynamic (in-silico) techniques. Furthermore, an in vitro evaluation of the cytotoxicity assays, cell viability profiles and modulatory influences of the most promising antiviral PCs on the mRNA and protein expressions of the drug-metabolising proteins in two human cell lines (liver (HepG2) and kidney (HEK293)) was carried out. Result: Four of the fifteen PCs (EGCG, K7G, LUT and EGA) were predicted to be potential inhibitors of HIV-1 protease, as well as inhibitors of cytochrome P450 3A4 (CYP3A4) and Pglycoprotein P-gp/ABCB1. Results from the in vitro study showed that these four PCs were not toxic to HepG2 cells at their IC50 (50% cell viability) and IC20 (80% cell viability). ATP (adenosine triphosphate) levels increased at IC20, with no significant change at IC50. In addition, no significant change in LDH (lactate dehydrogenase) was seen (with the exception of LUT).In the HepG2 cells, ABCB1 protein expression (western blot) decreased overall. While all PCs decreased CYP3A4 protein expression at IC20, (with the exception of LUT) xxv protein expression increased at IC50. mRNA levels were decreased for EGCG and K7G at IC20. InHEK293 cells, all PCs were non-toxic. ATP concentrations were similar to the control except for EGCG which decreased at IC20, and K7G which increased at IC50. LDH concentration decreased when exposed to the PCs at IC20, but a significant (p < 0.05) increase was recorded in LUT IC50. ABCB1 protein expression increased at both IC20 and IC50 concentrations, although LUT and EGA mRNA expression decreased at IC50. The decreased protein activities of CYP3A4 in K7G IC50 and LUT IC20 correlates with increased intracellular ATP. Conclusion: The study therefore suggests that EGCG, K7G, LUT and EGA could decrease the biotransformation of drugs, and eventually increase drug plasma concentrations in the systemic circulation. These natural compounds that can serve as inhibitors of drugmetabolizing proteins and the HIV-1 protease enzymecould be useful in the treatment of HIV-1