Mahonia aquifolium, also known as Oregon grape root, belongs to the Berberidaceae or barberry family. This evergreen shrub, native to the American northwest and adjacent areas of Canada, has been used in folk medicine to treat chronic eruptions and various rashes, especially those containing pustules or resulting from consumption of fatty foods (Dermatol. Ther. 2003;16:106–13).
In numerous investigations, Oregon grape root has displayed a wide range of biologic activities, including antioxidant, antimicrobial, and antimutagenic properties. Although this column will focus on the Mahonia aquifolium species, it is worth noting that Mahonia bealei (also of the Berberidaceae family), native to China, exhibits anti-influenza effects in vitro (Zhong Yao Cai. 2003;26:29–30).
Research on the extract of the bark of Mahonia aquifolium has indicated that its primary bioactive characteristic is the inhibition of lipid peroxidation, and that its main constituents are the alkaloids berberine, berbamine, and oxyacanthine (Planta Med. 1994;60:421–4).
Mahonia aquifolium bark extract has been shown to inhibit keratinocyte growth. In one study, berberine was as effective as the mahonia extract at inhibiting cell growth, while berbamine and oxyacanthine, the benzylisoquinoline alkaloid constituents of mahonia, were three times as effective at cell growth suppression (Planta Med. 1995;61:74–5).
Berberine-containing herbs have been used in folk medicine to relieve neonatal jaundice (Comp. Med. East West 1977;5:161–8), as anti-inflammatory agents (for lumbago and rheumatism), and as antinociceptive and antipyretic medications (Life Sci. 2002;72:645–57; J. Ethnopharmacol. 1998;59:211–5). Further, researchers studying the use of berberine as an antiacne medication in Japanese Kampoh (Japanese herbal medicine based on Chinese methods) found that the alkaloid inhibited lipogenesis in hamster sebaceous glands by 63% (Skin Pharmacol. 1993;6:56–60).
Antimicrobial Actions
In a study more than a decade ago, researchers screened 100 methanolic plant extracts for antifungal activity against nine species of fungi. In all, 81 of the extracts had some antifungal activity, and 30 extracts demonstrated activity against at least four of the fungal species assayed. Mahonia was one of six extracts showing the greatest antifungal activity (J. Ethnopharmacol. 1994;44:157–69).
In a more recent study, investigators evaluated the activity of Mahonia aquifolium stem bark extract and three of its constituents—berberine, palmatine, and jatrorrhizine—against various dermatophytes and two Candida species of human origin. Jatrorrhizine was the most effective against all the fungi tested. Investigators concluded that this component of mahonia would be more suitable than berberine, palmatine, and the crude extract for further investigation as a potential antifungal agent (Phytother Res. 2003;17:834–7).
In vitro antimicrobial activity was also exhibited by the crude extract of Mahonia aquifolium stem bark and its two main protoberberine alkaloids, berberine and jatrorrhizine, in a wide-ranging evaluation of antibacterial and antifungal activity.
The crude extract and key constituents displayed various levels of activity against 20 strains of coagulase-negative staphylococci, 20 strains of Propionibacterium acnes isolated from skin lesions of patients with severe acne, and 20 strains of Candida isolated from chronic vulvovaginal candidoses. Investigators concluded that the results buttressed the traditional use of Mahonia aquifolium for the treatment of localized skin and mucosal infections, and that the herb warrants consideration for inclusion in formulations to treat acne and chronic yeast infections (Phytother. Res. 2004;18:674–6).
Evidence of berberine's antimicrobial activity against several bacterial and fungal species has been gathering for several years (Folia Microbiol. 1999;44:164–6; Planta Med. 1997;63:196–8; J. Pharm. Sci. 1994;83:404–6; Canad. J. Microbiol. 1969;15:1067–76).
Antitumor Activity
Berberine has been shown to induce apoptosis in promyelocytic leukemia HL-60 and 3T3 fibroblast cells (Arch. Pharmacol. 1996;354:102–6; Cancer Lett. 1995;93:193–200), and protoberberines have exhibited significant toxicity against topoisomerases (Biochem. Pharmacol. 1998;56:1157–66).
Berberine, which is also the main alkaloid constituent of goldenseal, an herb used medically in eyewash and skin lotion formulations, was evaluated recently for its photochemical interactions with different solvents and potential phototoxicity to HaCaT keratinocytes. The alkaloid was a weak photosensitizer in water, but capable of generating superoxide anions and other radicals in a nonpolar setting. Significant reductions in cell viability and simultaneous elevation in DNA damage were observed in HaCaT keratinocytes exposed to UVA in the presence of berberine. The investigators concluded that exposure to the sun or to artificial UVA is contraindicated in people using topical products containing berberine (Chem. Res. Toxicol. 2001;14:1529–34).
In a study of the antimutagenic activity of crude extract fractions of the bark of Mahonia aquifolium against the common direct-acting mutagen acridine orange, investigators found that while antimutagenic properties were associated with both bis-benzylisoquinoline and protoberberine alkaloid fractions, only the protoberberine derivatives, jatrorrhizine and berberine, exhibited significant concentration-dependent inhibitory activity against the mutagen.
This was particularly true of berberine, which was threefold stronger than jatrorrhizine. In fact, even at very low doses, berberine suppressed the acridine orange-induced mutagenicity and consistently demonstrated the highest cytotoxicity among the mahonia components tested (BMC Complement Altern. Med. 2002;2:2).