Antioxidant and antiproliferative activities of spirulina and chlorella water extracts

Liver fibrosis is a chronic liver disease that will further develop to cirrhosis if severe damage continues to form. A potential treatment for liver fibrosis is to inhibit activated hepatic stellate cell (HSC) proliferation and, subsequently, to induce HSC apoptosis. It has been reported that antioxidants are able to inhibit the proliferation of HSCs. In this study, the aqueous extract of spirulina was chosen as the source of antioxiclant to investigate the inhibitory effect on the proliferation of HSC. The growth inhibitory effects of aqueous spirulina and chlorella extract on human liver cancer cells, HepG2, were also studied and compared in pairs. Results indicated that the total phenol content of spirulina was almost five times greater than that of chlorella (6.86 +/- 10.58 vs 1.44 +/- 0.04 mg tannic acid equivalent/g of algae powder, respectively). The antioxiclant activity of spirulina determined by the ABTS(center dot+) method was higher than chlorella (EC50: 72.44 +/- 0.24 umol of trolox equivalent/g of spirulina extract vs 56.09 +/- 1.99 mu mol of trolox equivalent/g of chlorella extract). Results of DPPH center dot assay also showed a similar trend as the ABTS(center dot+) assay (EC50: 19.39 +/- 0.65 mu mol of ascorbic acid equivalent/g of spirulina extract vs 14.04 +/- 1.06 mu mol of ascorbic acid equivalent/g of chlorella extract). The aqueous extracts of these two algae both showed antiproliferative effects on HSC and HepG2, but spirulina was a stronger inhibitor than chlorella. Annexin-V staining showed that aqueous extract of spirulina induced apoptosis of HSC after 12 h of treatment. In addition, the aqueous extract of spirulina triggered a cell cycle arrest of HSC at the G2/M phase.