Isosilybin A is a partial PPARγ agonist, it significantly induced ABCA1 protein expression, it inhibited both monophenolase (IC50=1.7-7.6μM) and diphenolase (IC50=12.1-44.9μM) of tyrosinase. Isosilybin A shows anti-angiogenic efficacy, it has anti-prostate cancer (PCA) activity that is mediated via cell cycle arrest and apoptosis induction.

To investigate the effects of milk thistle extract and its main flavonolignans (silybin A, silybin B, Isosilybin A and isosilybin B) on CYP2C8 activity at relevant concentrations, the effect of milk thistle extract and the flavonolignans on CYP2C8 enzyme activity was studied in vitro using human liver microsomes (HLM) incorporating an enzyme-selective substrate for CYP2C8, amodiaquine. Metabolite formation was analyzed using liquid chromatography-tandem mass spectrometry (LC/MS-MS). The concentration causing 50% inhibition of enzyme activity (IC50) was used to express the degree of inhibition. Isosilibinin, a mixture of the diastereoisomers Isosilybin A and isosilybin B, was found to be the most potent inhibitor, followed by isosilybin B with IC50 values (mean ± SE) of 1.64 ± 0.66 μg/mL and 2.67 ± 1.18 μg/mL, respectively. The rank order of observed inhibitory potency after isosilibinin was silibinin > Isosilybin A > silybin A > milk thistle extract > and silybin B[1]