Abstract:
Highly active antiretroviral therapy (HAART) has greatly improved health parameters
of HIV infected individuals. However, there are several challenges associated with the chronic
nature of HAART administration. For populations in health transition, dual use of medicinal
plant extracts and conventional medicine poses a significant challenge. There is need to evaluate
interactions between commonly used medicinal plant extracts and antiretroviral drugs used against
HIV/AIDS. Efavirenz (EFV) and nevirapine (NVP) are the major components of HAART both
metabolized by CYP2B6, an enzyme that can potentially be inhibited or induced by compounds
found in medicinal plant extracts. The purpose of this study was to evaluate the effects of extracts
of selected commonly used medicinal plants on CYP2B6 enzyme activity. Recombinant human
CYP2B6 was used to evaluate inhibition, allowing the assessment of herb-drug interactions (HDI) of
medicinal plants Hyptis suaveolens, Myrothamnus flabellifolius, Launaea taraxacifolia, Boerhavia diffusa
and Newbouldia laevis. The potential of these medicinal extracts to cause HDI was ranked accordingly
for reversible inhibition and also classified as potential time-dependent inhibitor (TDI) candidates.
The most potent inhibitor for CYP2B6 was Hyptis suaveolens extract (IC50 = 19.09 ˘ 1.16 µg/mL),
followed by Myrothamnus flabellifolius extract (IC50 = 23.66 ˘ 4.86 µg/mL), Launaea taraxacifolia extract
(IC50 = 33.87 ˘ 1.54 µg/mL), and Boerhavia diffusa extract (IC50 = 34.93 ˘ 1.06 µg/mL).
Newbouldia laevis extract, however, exhibited weak inhibitory effects (IC50 = 100 ˘ 8.71 µg/mL) on
CYP2B6. Launaea taraxacifolia exhibited a TDI (3.17) effect on CYP2B6 and showed a high concentration
of known CYP450 inhibitory phenolic compounds, chlorogenic acid and caffeic acid. The implication for these observations is that drugs that are metabolized by CYP2B6 when co-administered with
these herbal medicines and when adequate amounts of the extracts reach the liver, there is a high
likelihood of standard doses affecting drug plasma concentrations which could lead to toxicity.
