The aim of this study was to evaluate the safety of Chlorella vulgaris CK-22 as a food supplement. We examined mutagenicity, acute toxicity and subacute toxicity using Wistar rats administered Chlorella powder (CP). In the mutagenesis test, CP exhibited no mutagenecity in the in vitro assay. In the acute toxicity test, CP was administered orally at 0 mg/kg, 1,000 mg/kg, 2,000 mg/kg and 5,000 mg/kg body weight to Wistar rats (five animals/sex/group). No significance changes were observed test article-related during the 14-day observation period. The LD 50 of CP was estimated to be more than 5,000 mg/kg body weight in rats. In the subacute toxicity test, CP was administered at 0%, 2.5%, 5% and 10% in pelleted rodent diet to Wistar rats (ten animals/sex/groups). No mortality or treatment-related clinical signs were observed in any of the groups during the 28-day observation period. In both sexes, renal histopathology was conducted in the control and 10% groups, because absolute and relative renal weights increased in the 10% groups compared to the control groups. Based on the histopathology of the kidneys, the no-observed-adverse-effect level (NOAEL) is greater 8.57 g/kg body weight/day for males and 8.62 g/kg body weight/day for females.

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.