Safety evaluation of Chlorella sorokiniana strain CK-22 based on an in vitro cytotoxicity assay and a 13-week subchronic toxicity trial in rats

•Chlorella sorokiniana strain CK-22 powder (CK-22P) was used as a food supplement.•CK-22P was evaluated for cytotoxicity and subchronic toxicity.•The 50% viability inhibitory effect (IC50) value for Hw-Ex and Et-Ex were estimated as greater than 73 and 17 μg/ml, respectively.

The genus Chlorella contains unicellular green algae that have been used as food supplements. The purpose of this work was to evaluate the safety of the Chlorella sorokiniana strain CK-22 using powdered preparation (CK-22P) both by in vitro and in vivo assays. These included an experiment for cytotoxicity using Chinese hamster lung fibroblasts (V79 cells) and a 13-week repeated-dose oral toxicity trial using Wistar rats. The cytotoxicity was evaluated by MTT assay of a hot water extract (Hw-Ex) and 80% ethanol extract (Et-Ex) of CK-22P, and no effect on cell viability was observed. The 50% viability inhibitory effect (IC50) value for Hw-Ex and Et-Ex were estimated as greater than 73 and 17 μg/ml, respectively. In the subchronic toxicity test, pelleted rodent diet containing 0%, 2.5%, 5% or 10% CK-22P was given to Wistar rats (ten animals/sex/groups) for 13 weeks. During the experimental period, no CK-22P treatment-induced differences in general condition, body weight gain, food and water consumption, ophthalmology, urinalysis, hematology, clinical chemistry, gross pathology, organ weights, histopathology, or animal death were observed. The no-observed-adverse-effect levels (NOAEL) were estimated to be 5.94 g/kg body-weight/day for males and 6.41 g/kg body-weight/day for females.