A role for non-alkaloidal constitutes in the antibacterial activity of Hydrastis canadensis

Abstract

The medicinal plant goldenseal (Hydrastis canadensis) has been used historically to treat infection [1], and it is currently among the top ten best selling botanicals in the US. This plant has demonstrated activity in vitro against a number of bacteria, including multidrug-resistant Staphylococcus aureus (MRSA) [2]. Previous studies have implicated several alkaloids, including berberine, in the antibacterial activity of H. canadensis [2, 3]. Recent results from our laboratories, however, have led to the hypothesis that non-alkaloidal constituents also play an important role. An extract from the aerial portions of H. canadensis was separated into 12 fractions using flash chromatography. One of these fractions contained only very low (1000 x < MIC) concentrations of alkaloids, but it enhanced significantly the antibacterial activity of berberine. LC-MS analysis of all 12 of the fractions indicated three potential active compounds (thus far unidentified) that were present at the highest concentration in the active fraction. On the basis of experiments comparing antibacterial activity against wild type and efflux pump knockout mutants of S. aureus, the active constituents of the fraction appear to act as efflux pump inhibitors. Our studies indicate that goldenseal's mechanism of antibacterial activity may be more complex than previously reported, and suggest that H. canadensis could be useful for the treatment of drug resistant bacterial infections, particularly as a topical agent. In addition, we demonstrate the effectiveness of combining bioassay guided fractionation with comprehensive LC-MS analysis to identify potential potentiators/synergists in medicinal plants. Acknowledgements: Bill Burch, Bear Wallow Ginseng, Hendersonville, NC; Research Corporation Cottrell College Science Award CC6642; NSF-MRI Award 0420292.