ABSTRACT
Phyllanthus amarus has long been used as a herbal medicine in several countries. Phytochemicals in herbal medicine may interact with cytochromes P450 (CYP) and thus raise the potential of herb-drug interactions; therefore, the inhibitory effects of P. amarus and its major phytochemicals phyllanthin and hypophyllanthin on CYP isoforms were determined using human liver microsomes and selective substrates. Both ethanolic and aqueous extracts of P. amarus inhibited CYP1A2, CYP2D6, CYP2E1 and CYP3A4 in a dose-dependent manner. Compared to known CYP3A inhibitors, the IC(50) values of the ethanolic and aqueous extracts on testosterone 6ß-hydroxylation were higher than that of ketoconazole but were lower than those of erythromycin and clarithromycin. Both extracts were weak inhibitors of CYP1A2, CYP2D6 and CYP2E1. In addition, phyllanthin and hypophyllanthin were potent mechanism-based inhibitors of CYP3A4 with K(I) values of 1.75 ± 1.20 µM and 2.24 ± 1.84 µM and k(inact) values of 0.18 ± 0.05 min(-1) and 0.15 ± 0.06 min(-1), respectively. The k(inact)/K(I) ratios of these lignans were higher than those reported for some therapeutic drugs that act as mechanism-based inhibitors of CYP3A4. These results suggest that co-administration of P. amarus with drugs that are metabolized by CYP3A4 may potentially result in herb-drug interactions.
Subject(s)
Aryl Hydrocarbon Hydroxylases/antagonists & inhibitors , Cytochrome P-450 CYP3A , Herb-Drug Interactions/physiology , Microsomes, Liver/enzymology , Plant Extracts/pharmacology , Aryl Hydrocarbon Hydroxylases/metabolism , Cytochrome P-450 CYP3A/metabolism , Cytochrome P-450 CYP3A Inhibitors , Dose-Response Relationship, Drug , Humans , Inhibitory Concentration 50 , Ketoconazole/pharmacology , Lignans/pharmacology , Microsomes, Liver/drug effects , Phyllanthus/metabolism , Plant Extracts/chemistryABSTRACT
NMR signal reassignments for a cytotoxic glycosphingolipid compound, 2, ß-O-D-glucopyranosyl-2-(2'-hydroxy-Z-6'-enecosamide)sphingosine, isolated from an ethanolic extract of the herb Murdannia loriformis, have been achieved by use of FAB-MS, and 1D and 2D 1H and 13C NMR. The amount of 2 in the herb juice was quantitatively determined by use of a validated HPLC method (RP-18, MeOH-H2O, UV detection at 210 nm). The immunomodulatory effect of the herb juice and of 2 was proved by means of in vitro cellular immunological assays. Compound 2 at a concentration of 13 nmol L-1 stimulated PBMC proliferation and increased the CD 3,4:CD 3,8 ratio in T lymphocytes.