Plasmodium berghei: sensitivity of chloroquine-resistant and chloroquine-sensitive strains to irradiation and the effect of irradiated malaria parasites on cytochrome P450-dependent monooxygenases.

Differences in sensitivities of chloroquine-sensitive and chloroquine-resistant strains of Plasmodium berghei were observed following irradiation of the parasites. A dose of 15 kilorads from a cobalt-60 source killed the erythrocytic stages of the chloroquine-sensitive strain and no parasitemias were observed when mice were injected with these irradiated parasites. In contrast, when the chloroquine-resistant strain was irradiated with the same dose of cobalt-60 and injected into mice, an infection rate of 12.5% was observed, indicating that the latter strain was more resistant to inactivation by irradiation. Following injection of these irradiated strains of P. berghei into mice, significant decreases in mouse hepatic cytochrome P450 and benzo(a)pyrene hydroxylase activity, with no significant effect on N-demethylase activity, were observed. Serum glutamic-oxaloacetic transaminase (SGOT) and glutamic-pyruvic transaminase (SGPT) levels of mice injected with the irradiated parasites fell within the range of the serum enzyme levels in normal laboratory mice.