Lysis of Plasmodium falciparum by ferriprotoporphyrin IX and a chloroquine-ferriprotoporphyrin IX complex.

Ferriprotoporphyrin IX (FP) and a chloroquine-FP complex lysed isolated Plasmodium falciparum parasites as judged by decreases in the turbidity of parasite suspensions and by ultrastructural changes. Exposure of parasite suspensions to 50 microM FP or to a complex formed from 50 microM FP and 20 MicroM chloroquine reduced the number of identifiable parasites and caused swelling and loss of internal detail in those that were identifiable. The amount of lysis was dose-dependent over the range of 10 to 50 microM FP. Formation of a chloroquine-FP complex reduced, but did not eliminate, the toxicity of FP. Since there is evidence indicating that a chloroquine-FP complex forms when chloroquine-susceptible parasites are exposed to chloroquine, we suggest that accumulation of this complex may account for the chemotherapeutic effect of chloroquine against P. falciparum.