Acute and subchronic toxicity and genotoxicity of SE5-OH, an equol-rich product produced by Lactococcus garvieae

The consumption of soy-based products is associated with a number of health benefits and much of these benefits are proposed to be due to the soy isoflavones daidzein, genistein, glycitein, their glycosides, and equol, an isoflavone naturally produced from daidzein. Equol is a naturally bacterially-derived metabolite of daidzein and is produced by bacteria in the gut of those humans capable of hosting the particular organism. To allow all humans to enjoy the health benefits of equol, a new functional food ingredient has been developed that relies on bacterial conversion of daidzein to equol under strictly controlled conditions. This new food substance, termed SE5-OH, has been studied extensively for its acute and subchronic toxicity in Sprague–Dawley rats, as well as for its potential genotoxicity. The oral LD50 is >4000 mg/kg. In a 91-day, subchronic study, the no-observed-adverse-effect-level (NOAEL) was 2000 mg/kg/day, the highest dose tested. SE5-OH was negative in Salmonella typhimurium tester strains TA98, TA100, TA1535 and TA1537 and in Escherichia coli tester strain WP2uvrA with and without metabolic activation. SE5-OH was negative for chromosome aberrations in Chinese hamster lung cells up to 3000 μg/ml with and without metabolic activation and did not induce increases in micronucleated polychromatic erythrocytes taken from Sprague–Dawley rats administered (via gavage) up to 4000 mg/kg SE5-OH twice daily for two consecutive days.