[In vitro effect of daphnetin on cytochrome C oxidase and ribonucleotide reductase of plasmodium falciparum].

To test the in vitro effect of daphnetin on cytochrome C oxidase (COX) and ribonucleotide reductase (RNR) activity of Plasmodium falciparum. P. falciparum (FCC1/HN) was cultured in vitro using the method of Trager and Jensen. The effect of daphnetin and daphnetin-Fe complex on COX and RNR activity of P. falciparum was tested by ultraviolet spectrophotometer and electron spin resonance (ESR) respectively. The parasites synchronized with sorbitol in vitro was treated by daphnetin and daphnetin-Fe complex. The inhibition level of the COX activity by daphnetin after being treated for 2, 4, 8 and 12 h were 0.6%, 73% and 80% respectively and the inhibition level by daphnetin at different concentrations (0.1, 1, 100 and 1 mmol/L) for 6h was 3%, 31%, 53% and 84%, respectively. No considerable effect was observed on the COX activity of P. falciparum treated with daphnetin-Fe complex. The tyrosyl free radical was tested to reflect the RNR activity of P. falciparum at various times by ESR. The inhibition level by daphnetin for 1, 2, 3 and 4 h were 7%, 51%, 69% and 75% respectively, while the values treated by daphnetin-Fe complex were 8%, 6%, 11% and 9% respectively. The inhibition level by daphnetin at different concentrations (0.1, 1, 100 and 1 mmol/L) for 6 h was 3%, 31%, 58% and 93% respectively and while the values treated by daphnetin-Fe complex were 8%, 6%, 11% and 9%. Daphnetin significantly reduces the COX and RNR activities of Plasmodium falciparum in vitro.