Pharmacokinetic Interactions between Bioenhancers of Herbal Origin and Antiretroviral Drugs Using Cytochrome P450 3A Inhibition Approach

Abstract

The co-administration of oral therapeutic agents with natural compounds is currently on the increase with resultant increase in herb-drug interaction cases involving mainly cytochrome P450 enzymes and drug transporters. HIV infection because of its chronic and comorbid nature often necessitate the use of multiple drugs including herbs to relief symptoms. Meanwhile, most natural products have been shown to modulate drug metabolising enzymes, resulting in alteration in co-administered drug concentrations. The aims of this study therefore, were to evaluate the in vitro and in vivo effects of some identified herb extracts used by HIV-infected patients on liver and intestinal cytochrome P450 3A enzymes and also to determine the extracts pretreatment effect on the bioavailability of some antiretroviral agents. The study adopted both survey and exprimental designs.A cross sectional study was conducted in HIV clinic using a 25-item adapted questionnaire to identify the prevalence and pattern of herbal drug use among HIV infected patients on antiretroviral therapy. Some of the identified herbs were collected and extracted using aqueous and non-aqueous solvents and concentrated using lyophilizer and rotary evaporator respectively. In vitro inhibition of the cytochrome P450 3A enzymes by the extracts were assessed in liver and intestinal microsomes using erythromycin-N-demethylation assay (EMND) method while their in vivo effects were determined by estimating simvastatin (CYP3A probe substrate) plasma concentrations in female rate model. The effect of the extracts on two antiretroviral agents’ pharmacokinetics were determined by the administrations of the drug and the extracts to different rats divided into different groups of 5 rats per group and their plasma drug concentrations determined at different time intervals using HPLC. Pharmacokinetic parameters were determined using non-compartmental anaysis as implemented in WinNonlin pharmacokineticsoftware application. The effects of the extracts and the antiretroviral agents, administered concurrently, on hematological and biochemical parameters were determined. HPLC fingerprinting assay was done to determine the extracts chemical constituents. All results were presented as mean±SEM. The data were subjected to one-way analysis of variance (ANOVA) test and group differences determined using post hoc test (LSD) using SPSS. Results were considered statistically significant at P<0.05. The prevalence of herbs among the surveyed population was 54.10 % while the prevalence of its concurrent use with antiretroviral agents among HIV infected patients on antiretroviral therapy who admitted using herbal agents as medication was 45.5 %. Ginger, Garlic, Mangiferaindica, Millettia aboensis, Denniettia tripetala, Moringa olifera and Aframomum melegueta were among the herbs commonly used by the patients. Aqueous extracts of D. Tripetala (ADT) and A. melengueta (AAM), petroleum ether extract of D. Tripetala (PEDT) and ethanol extracts of A. melengueta (EAM), M. aboensis (EMA), and M. oleifera (EMO) indicated the presence of different phyto-constituents at varying concentrations. EMND assay with intestinal microsomes indicated that ADT and AAM significantly (P<0.05) inhibited intestinal CYP 3A activity at both 50 µg and 100 µg concentrations. 100 µg concentrations of PEDT, EAM and EMA inhibited CYP3A activity in contrast to their 50 µg concentrations. All the extracts showed a dose dependent CYP 3A inhibition with the liver microsomes in vitro. In vivo analysis showed that pre-treatment with the extracts enhanced systemic absorption of simvastatin with reductions in metabolizing enzymes activity as indicated in significant (P<0.05) increases in maximal concentration (Cmax), area under curve (AUC), area under moment curve (AUMC) and mean resident time (MRT) of simvastatin. Cmax increased from 2.22±0.021 to 4.39±0.145, 3.43±0.009, 3.38±0.017, 5.54±0.041 and3.37±0.010(µg/ml) in ADT, AAM, EMA, PEDT and EAM pre-treated groups respectively while their time to reach Cmax correspondingly changed from 1.00±0.000 in the absence of the herbs to 3.00±1.000, 4.50±4.950, 8.00±0.000, 4.00±0.000 and3.00±1.000 (h) in the respective pre-treated groups. The AUC increased from 29.5±0.345 without the herbs to 73.1±0.719, 69.6±0.793, 69.6±0.636, 69.6±0.604 and 49.9±0.224µg/ml/hrin the presence of ADT, AAM, EMA, PEDT and EAMrespectively. There were observed reduction in simvastatin volume of distributions and clearance compared to the dexamethasone and vehicle treated control group. The result of the effect of the extracts on efavirenz pharmacokinetics revealed that the bioenhancers did not have immediate interactions with efavirenz but prolonged administrations enhanced the bioavailability of the drug with marked suppression of metabolising enzyme activity. AAM and ADT significantly (P<0.05) enhanced the rate (from 0.67±0.167 to2.17±1.014 and 1.00±0.500h respectively)and extent of nevirapine absorption (for AUC, from 61.3±0.342 to 70.0±0.100 and 64.9±0.080 µg/ml/h and then, for Cmax, from 2.82±0.007 to 3.65±0.003 and 3.19±0.014 µg/ml) respectively for AAM and ADT. They also reduced nevirapine clearance while its bioavailability was paradoxically reduced by EMA (AUC reduced from61.3±0.342 to 47.7±0.045 µg/ml/h). Hematological studies revealed no significant (P > 0.05) change between the treated groups and the controls. However, biochemical studies indicated increase in ALP, ALT and AST with the drugs alone which was reversed with co-administration of AAM and EMA but not with ADT. The serum creatinine was increased with co-administration of the drugs and AAM, there was no significant (P > 0.05) change in serum creatinine with ADT and EMA co-administrations. HPLC fingerprinting suggested the presence of quercetin and kampferol in EMA, phenylactic acid in ADT, mauritamide and palitantin in PEDT, paxilline, bastadin and kampferol in AAM and pyrrole carboxaldehyde derivative, bastadin and naamine G in EAM with the presence of the constituents confirming the observed extracts’ bioenhancing properties. This study indicated that some herbs used by the surveyed patients inhibited cytochrome P450 3A enzymes with significant effects on the bioavailability of orally administered efavirenz and nevirapine. Our results therefore underscored the clinical importance of concurrent use of herb and conventional medications and the need for further research in this area to furnish the healthcare professionals with adequate data to educate their patients and the general public.