Free radical scavenging activity and lipoxygenase inhibition of Mahonia aquifolium extract and isoquinoline alkaloids

Roots and stem-bark of Mahonia aquifolium (Oregon grape) (Berberidaceae) are effectively used in the treatment of skin inflammatory conditions. In the present study, the effect of Mahonia aquifolium crude extract and its two representative alkaloid fractions containing protoberberine and bisbenzylisoquinoline (BBIQ) alkaloids on activity of 12-lipoxygenase (12-LOX), was studied. The reactivity with 1,1-diphenyl-2-picryl-hydrazyl (DPPH), a free stable radical, was evaluated to elucidate the rate of possible lipid-derived radical scavenging in the mechanism of the enzyme inhibition. The results indicate that although the direct radical scavenging mechanism cannot be ruled out in the lipoxygenase inhibition by Mahonia aquifolium and its constituents, other mechanisms based on specific interaction between enzyme and alkaloids could play the critical role in the lipoxygenase inhibition rather than non-specific reactivity with free radicals.

Mahonia root and stem bark have long been considered to have anti-inflammatory, anti-bacterial, anti-fungal activity and they are used particularly for treatment of skin diseases. They are indicated for treatment of the eczema, psoriasis, and other skin conditions. Alkaloids representing the main compounds in Mahonia aquifolium, belong to two major classes: the protoberberines and the bisbenzylisoquinolines (BBIQ). Through bioassay-guided fractionation, protoberberine alkaloids, such as berberine and jatrorrhizine, were isolated as the main active alkaloids responsible for the relevant effects in numerous studies conducted so far. In particular, the berberine was reported to exhibit a range of pharmacological and biological activities, and interest has been focused on its antioxidative potential. Berberine was found to inhibit the single-strand cleveage of DNA. It did exhibit a strong superoxide anion radical quenching ability rather than a strong hydroxyl radical scavenging activity. It was reported to exert a protective effect against ONOO- , NO. , and O2 .-, induced oxidative damage in vitro and to increase cell viability.