CAY-1, a fungicidal saponin from Capsicum sp. fruit

Saponins are steroidal or terpenoid-based glycosides with surface active properties. A steroidal saponin, CAY-1, with a molecular weight of 1243.35 Da, was isolated and purified to homogeneity from commercially available dry, ground fruit of Capsicum frutescens. CAY-1 was shown to be a potent fungicide for the germinating conidia of Aspergillus flavus, A. fumigatus, A. parasiticus and A. niger with species-dependent LD₉₀values between 3 and 20 μM. Activity against some Aspergillus species was affected by the test medium used. In vitro assays, CAY-1 was effective against Pneumocystis carinii (IC₅₀: 9.5 μM) and Candida albicans (IC₉₀: 6.2 μM). CAY-1 had no effect on the viability of the nongerminating conidia of the two filamentous fungi, P. carinii and C. albicans, nor on the conidial type of Fusarium oxysporum. It was ineffective against the bacteria Enterobacter agglomerans, Bacillus subtilis, Escherichia coli and Staphylococcus aureus. CAY-1 was not cytotoxic to A 549 lung carcinoma cells or HeLa cells at effective fungicidal concentrations. The results indicate that CAY-1 is an effective fungicide for Aspergillus species, C. albicans and P. carinii at concentrations below the threshold for mammalian cell toxicity.