Isolation and characterization of an antibacterial biflavonoid from an African chewing stick Garcinia kola Heckel (Clusiaceae).

ETHNOPHARMACOLOGICAL RELEVANCE: The use of African chewing sticks in maintaining oral health is widely practiced in African countries. It has been reported that chewing stick users have a lower rate of dental caries and a better general oral health than non-users. It is generally thought that the beneficial effect of chewing stick is attributed to the mechanical cleansing effect and antimicrobial substances present in the stick. However, the active antimicrobial substances remain uncharacterized. AIM OF THE STUDY: To provide a scientific basis for the anti-caries effect of African chewing sticks, the authors purify an active antibacterial compound from Garcinia kola Heckel, a Nigerian chewing stick and examined the antibacterial activity of this compound against the cariogenic bacterium Streptococcus mutans. MATERIALS AND METHODS: Methanol extract was prepared from Garcinia kola and was further fractionated by solvent extractions. Silica gel chromatography was used to purify the antibacterial compound from the active fraction. The identity of the purified compound was determined by NMR analysis. The antibacterial activity of the purified compound was examined by standard microbiological assays. RESULTS: The antibacterial activity was found in the ether fraction and the active compound was isolated and determined to be a biflavonoid named GB1. GB1 was active against Streptococcus mutans and other oral bacteria with minimum inhibitory concentration (MIC) values of 32-64µg/ml. The basis for the antibacterial effect of GB1 was investigated using Streptococcus mutans as the target. At 256µg/ml, GB1 exhibited some bacteriocidal activity against Streptococcus mutans and induced the aggregation of Streptococcus mutans. GB1 has no apparent effects on protein synthesis and DNA synthesis but inhibited glucose uptake and utilization by Streptococcus mutans suggesting that GB1 exerts its antibacterial effect by inhibiting metabolism. GB1 also inhibited the formation of water-insoluble glucan by the extracellular glucosyltransferases from Streptococcus mutans in a dose-dependent manner. Streptococcus mutans did not develop resistance to GB1 upon subculturing in the presence of sub-MIC level of the biflavonoid. CONCLUSION: The antibacterial effect and glucan synthesis-inhibition property of this biflavonoid may account for some of the beneficial effects reported in the chewing stick users.

Chemical properties, mode of action, and in vivo anti-herpes activities of a lignin-carbohydrate complex from Prunella vulgaris.

The chemical nature, the mode of action, and the in vitro and in vivo anti-HSV activities of the polysaccharide from Prunella vulgaris were characterized. The polysaccharide was isolated by ethanol precipitation, dialysis, CTAB precipitation, and gel exclusion chromatography. The isolated compound (PPS-2b) was a lignin-carbohydrate complex with a molecular weight of 8500. The carbohydrate moiety was composed of glucose, galactose, mannose, galacturonic acid, rhamnose, xylose, and arabinose with glucose as the major sugar. In plaque reduction assay, PPS-2b showed activities against HSV-1 and HSV-2. The anti-HSV activity could be abolished by periodate oxidation. Mechanism studies showed that PPS-2b inactivated HSV-1 directly, blocked HSV-1 binding to Vero cells, and inhibited HSV-1 penetration into Vero cells. A similar inhibition was observed with a gC-deficient strain of HSV-1. The in vivo activities of a Prunella cream formulated with a semi-purified fraction was assessed in a HSV-1 skin lesion model in guinea pigs and a HSV-2 genital infection model in BALB/c mice. Guinea pigs that received the Prunella cream treatment showed a significant reduction (P<0.01) in skin lesions. Mice that received the Prunella cream treatment showed a significant reduction (P<0.01) in mortality. In conclusion, the anti-HSV compound from P. vulgaris is a lignin-polysaccharide complex with potent activity against HSV-1 and HSV-2. Its mode of action appears to be inhibiting viral binding and penetration into host cells.

The antibacterial principle of Caesalpina sappan.

Using a bioassay-directed purification scheme, the active antibacterial principle from Caesalpina sappan was isolated and identified to be brasilin. This compound showed potent activity against antibiotic-resistant bacteria, notably methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE), multi-drug resistant Burkholderia cepacia as well as a number of other bacteria. The minimal inhibitory concentrations ranged from 4 to 32 microg/mL. The results from time-kill studies showed that brasilin is bactericidal against MRSA. The addition of brasilin to growing MRSA cells resulted in a rapid inhibition of incorporation of [(3)H] thymidine or [(3)H] serine into DNA and proteins, respectively. Exposure of MRSA to a sub-MIC level of brasilin for ten consecutive subcultures did not induce resistance to the compound. The Trypan blue dye exclusion test showed that brasilin lacked cytotoxicity against Vero cells. In conclusion, brasilin is an antibacterial principle from C. sappan and it has the potential to be developed into an antibiotic.