Background: Strobilanthes crispus (L.) Bremek (Acanthaceae) leaves are used traditionally in Malaysia, Thailand, and Indonesia for anti-diabetic, anti-lytic, diuretic, and laxative purposes. Herb-drug interactions may potentiate or antagonize the absorption and metabolism of drugs which may result in potential toxicity. The aim of the present study was to investigate the effect of juice, hot aqueous, cold aqueous and methanol extracts of S. crispus leaves on phase I cytochrome 3A4 (CYP3A4) and Cytochrome 2E1 (CYP2E1) and phase II human liver enzyme UDP-glucuronosyl transferase (UGT).
Methods: The herb-drug interactions of the leaf extracts and juice were determined by specific enzyme activity of CYP isoforms with specific probe substrate using spectrophotometry. CYP3A4 activity was measured for aminopyrine specific metabolite (formaldehyde) at 415 nm. CYP2E1 activity was determined using p-nitrophenol specific metabolite (p-nitrocatechol) at 535 nm. UGT activity was quantified through the consumption of p-nitrophenol by UGT at 405 nm.
Results: All the S. crispus preparations showed significant inhibition of CYP3A4 activity. Only the methanolic extract of showed a significant inhibition in CYP2E1. All the S. crispus extracts showed a significant effect on UGT activation at the higher concentration (1000 ng/ml). Only the cold aqueous extract and the juice showed UGT inhibition at lower concentration (1 ng/ml).
Conclusion: S. crispus preparations showed in-vitro drug-herb interaction effects on human liver microsomes. Therefore, there is a possibility of drug-herb interaction could occur with S. crispus leaves through its effect on CYP3A4. Inhibition of the herb extracts on CYP2E1 could show anti-carcinogenesis effects. The potency of drugs that metabolized via UGT pathway may be affected when co-administered with S. crispus leaf preparations.