Assessing the potential for drug interactions

Picking, D., Chambers, B., Barker, J., Shah, I., Porter, R. and Delgoda, R. (2017) Assessing the potential for drug interactions. In: PhytoPharm 2017; 02 - 04 Jul 2017, Graz, Austria. (Unpublished)


Understanding the potential for adverse drug reactions (ADRs), resulting from plant-drug interactions,is a key aspect of medicinal plant safety. The aim of this study was to provide an in-depth assessment of standardised extracts of Hyptis verticillata Jacq. through its impact on the activities of key human cytochrome P450 (CYP) enzymes in vitro and antioxidant properties. Crude extracts were prepared from fresh and dried aerial plant material (leaf and stem). The aqueous dried plant extract, was evaluated for its ability to inhibit the activities of human CYPs 1A1, 1A2, 1B1, 3A4 and 2D6, and characterised using high performance liquid chromatography (HPLC) and liquid chromatography – mass spectrometry (LC-MS/MS). Individual key phytochemicals identifi ed were further assessed for their ability to inhibit the activity of the enzyme most impacted. All crude extracts were assessed for antioxidant properties, using a standard DPPH radical scavenging assay. The dried plant aqueous extract demonstrated potent inhibition (IC50 values < 10 ug/ml) against the activities of CYPs 1A1 (7.6 ug/ml), 1A2 (1.9 ug/ml), 1B1 (9.4 ug/ml) and 3A4 (6.8 ug/ml) and its analysis confirmed the identity of seven phytochemicals, five lignans and two triterpenes. Screening these phytochemicals against the activity of CYP1A2 failed to identify a single agent responsible for the plant extract’s potent bioactivity. Further analysis of other crude extracts demonstrated potent inhibition of CYP1A2 activity for a dried plant ethanol extract (1.5 ug/ml), fresh plant ethanol extract (3.9 ug/ml), and moderate activity for a fresh plant aqueous extract (27.8 ug/ml). All four extracts demonstrated strong antioxidant activity (IC50 values<10 ug/ml), compared to the positive control, ascorbic acid (1.3 ug/ml), with the dried plant ethanol extract being the most potent (1.6 ug/ml). Aqueous extracts, prepared following ethnomedical recipes for H. verticillata, demonstrated inhibition of key drug metabolising enzymes in vitro. Further analysis on the potential impact of this plant on key drug metabolizing enzymes in vivo appears warranted, given the extensive use of this plant in the Americas. Key phytochemical(s) responsible for the extracts’ bioactivity could not be pinpointed, and led to one of two possible explanations: Firstly, the phytochemical(s) responsible has/have not yet been identified, or, secondly, the potent bioactivity is due to synergistic interactions amongst the many constituents of the whole plant extract being greater than the sum of individual phytochemical bioactivities tested. Four traditional preparations demonstrated strong antioxidant activity, which, together with the plant extracts potent inhibition of known carcinogen activators, CYPs 1A1 and 1B1, and previously reported anti-inflammatory and anticancer properties, warrants further research into the potential chemopreventive properties of this interesting plant.

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