Neuroprotective effects of porphyran derivatives against 6-hydroxydopamine-induced cytotoxicity is independent on mitochondria restoration

We previously reported that acetylated and phosphorylated derivatives of porphyran extracted from Porphyra haitanensis exhibit antioxidant activity in cell-free system. The aim of the present study was to investigate the neuroprotective effects of porphyran and its derivatives on 6-hydroxydopamine (6-OHDA)-induced cytotoxicity. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to measure cell viability. Changes in the mitochondrial transmembrane potential (ΔΨm) were measured by rhodamine123 using flow cytometry. The results showed that porphyran and its two derivatives, acetylated porphyran (AP) and phosphorylated porphyran (PP) (<1 mg/mL) alone did not have any toxic effects on MES23.5 cells. The cell viability decreased when cells were treated with 25 µmol/L 6-OHDA. Both AP and PP, rather than porphyran, significantly antagonized 25 µmol/L 6-OHDA-induced cytotoxicity. However, neither AP nor PP could antagonize 6-OHDA-induced mitochondrial transmembrane potential (ΔΨm) collapse. None of the three materials were effective on cell survival when cells were cotreated with 75 µmol/L 6-OHDA. These results suggest that two derivatives of porphyran, AP and PP, could antagonize the weak toxicity of 6-OHDA on MES23.5 dopaminergic cells, possessing minor neuroprotective effects independent of mitochondria restoration.