Studies have suggested an increasing practice of concurrent herb-drug consumption. One of the major clinical risks of such
concomitant herb-drug use is pharmacokinetic herb-drug interaction (HDI). This is brought about by the ability of phytochemicals to inhibit or
induce the activity of metabolic enzymes. The aim of this study was to investigate the potential of the crude aqueous extracts of three popular
medicinal herbs used in South Africa to inhibit major cytochrome P450 (CYP) enzymes.
Materials and Methods:
The extracts of Bowiea volubilis
, Spirostachys africana
and Tulbaghia violacea
were incubated with human liver
microsomes (HLM) to monitor the phenacetin O-deethylation, diclofenac 4’-hydroxylation, S-mephenytoin 4’-hydroxylation and testosterone 6β-
hydroxylation as respective probe reactions for CYP1A2, CYP2C9, CYP2C19 and CYP3A4. The inhibitory activity, where observed, was
profiled against the extract concentration.
Extracts of Bowiea volubilis
inhibited the metabolic activity of CYP1A2 and CYP3A4 with IC50
values of 92.3 ± 5.5 μg/mL and 8.1 ±
0.6 μg/mL respectively. Similar observation with Spirostachys africana
showed inhibitory activity against CYP1A2 and CYP3A4 with respective
values of 14.3 ± 0.6 μg/mL and 47.4 ± 2.4 μg/mL. Tulbaghia violacea
demonstrated relatively weak inhibitory activity against CYP1A2
(767.4 ± 10.8 μg/mL) and CYP2C9 (921 ± 15.3 μg/mL).
The results suggest the potential for HDI between the herbs and the substrates of the affected enzymes, if sufficient in vivo
concentration is attained.