Investigation of the cytotoxicity of food-grade nanoemulsions in Caco-2 cell monolayers and HepG2 cells

Nanoemulsions represent one of the emerging formulations for nutraceutical delivery. However, the possible toxicity associated with the small droplet size (diameter <200 nm) is still unknown. In this study, three nanoemulsions emulsified by modified starch, Tween 20 and whey protein isolate, respectively, were prepared and their cytotoxicity was examined by comparing with the corresponding micron-sized emulsions. Caco-2 cell monolayers were used to mimic the small intestine epithelium. Integrity of the cell membrane and tight junctions was tested by measuring the lactate dehydrogenase leakage and transepithelial electrical resistance, respectively. All three nanoemulsions did not reveal significant difference from their micron-sized counterparts, suggesting no apparent toxicity of the nanoemulsions on the small intestine. Meanwhile, the possible hepatic toxicity was investigated using MTT assay on HepG2 cells. It was found that nanoemulsions made with modified starch and whey protein isolate, but not Tween 20, affected the cell viability/proliferation more than did the micron-sized emulsions. Further in vivo investigation is required to examine the possible hepatic toxicity of nanoemulsions.