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

Abstract

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.

A Toxicological Evaluation of Chlamydomonas reinhardtii, a Green Algae

“…Toxicological investigations of several members of the green algae genus Chlorella, which has a history of traditional food use and is widely consumed as food, as well as other green algal species have demonstrated a lack of toxicological concern in various in vitro and in vivo assays. [33][34][35][36][37][38] Yet while the studied organisms and C reinhardtii are all green algae, the designation is an informal grouping of distantly related organisms encompassing 2 taxonomic divisions of algae. On the other hand, a certain level of safety can be understood to exist based on the research history of C reinhardtii without mention of expression of toxic proteins, toxic metabolites, or other harmful substances.…”

Treatment with Modified Extracts of the Microalga Planktochlorella nurekis Attenuates the Development of Stress-Induced Senescence in Human Skin Cells

“…Interestingly, the extract-mediated effect depended on replicative age of HDFs, namely, stimulatory effects in pre-senescent and senescent HDFs were noticed when 200 and 100 µg/mL water extract was used, respectively, and the concentrations ranging from 500 to 800 µg/mL decreased cell viability of senescent HDFs [24]. Water and 80% ethanolic extracts of Chlorella sorokiniana did not affect the cell viability of Chinese hamster lung fibroblasts (V79 cells) when used at the concentrations up to 80 and 20 µg/mL, respectively [23]. However, treatment with 12.5, 25, and 50 µg/mL hot water extract of Chlorella vulgaris increased cell viability by 124%, 135.4%, and 155.0% in IEC-6 rat small intestine epithelial cells compared to untreated cells [21].…”

“…Two types of skin cells were selected for the analysis, namely, normal human fibroblasts (BJ cells) and normal human keratinocytes (HEK cells). As extracts of different Chlorella species may act on human and rodent cells at a wide range of concentrations and the effects may also rely on solvents used [20][21][22][23][24], we decided to study both water and ethanolic extracts and the concentrations ranging from 1 to 1000 µg/mL ( Figure 1).…”

Safety assessment of Synechococcus sp. PCC 7002 biomass: genotoxicity, acute and subchronic toxicity studies

“…Himuro et al (2017) evaluated the subchronic toxicity of Chlorella sorokiniana strain CK-22 in diet, and no adverse effects were found in the 13-week feeding experiment using rats with NOAELs estimated to be 5.94 and 6.41 g per kg BW per day for males and females, respectively. 25 Similarly, the oral toxicology study for the lyophilized biomass of Tetraselmis chuii as an ingredient in foods was carried out following the OECD Guideline 408, and the NOAEL was greater than the highest tested dose of 2.5 g per kg BW per day. 26 According to Brickel et al (2018), the NOAEL of dried algal biomass derived from Klebsormidium flaccidum var.…”