[Detection of a system of microsomal monooxygenases in the rodent malaria parasite Plasmodium berghei]. / Vyiavlenie sistemy mikrosomal'nykh monooksigenaz u maliariinogo parazita gryzunov Plasmodium berghei.

A microsomal fraction from the cells of the malaria parasite of rodent Plasmodium berghei was obtained. The spectral properties of microsomal preparations suggest that P. berghei microsomes contain cytochromes b5 and P-420. Electrophoretic separation of microsomal proteins revealed the presence of proteins whose molecular mass corresponds to NADPH-cytochrome c reductase, cytochrome P-450 and epoxide hydratase. The activities of NADPH-cytochrome c reductase and benzpyrene hydroxylase were determined. The spectral parameters, electrophoretic data and enzymatic activities of microsomal proteins indicate that P. berghei cells contain a cytochrome P-450 monooxygenase system. The interrelationship between the activity of the microsomal monooxygenase system and the resistance of P. berghei cells to the antimalaria preparation chloroquine is discussed.

Suppression of the chloroquine resistance of Plasmodium berghei by treatment of infected mice with a microsomal monooxygenase inhibitor.

Administration of a combination of chloroquine and the copper-lysine complex, copper(lysine)(2), an inhibitor of microsomal monooxygenases, considerably decreased the parasitaemia level of mice infected with a chloroquine-resistant strain of Plasmodium berghei. When given separately, chloroquine and the complex had no antimalarial effect. Use of a combination of monooxygenase inhibitors and chloroquine therefore appears to be a promising addendum to the chemotherapy of malaria caused by chloroquine-resistant parasites.

Chloroquine resistance of Plasmodium berghei: biochemical basis and countermeasures.

Microsomal monooxygenases, enzymes that metabolize xenobiotics, may be responsible for the chloroquine resistance of malarial parasites. Plasmodium cells contain cytochrome P-450 and exhibit aryl hydrocarbon hydroxylase and aminopyrine N-dimethylase activity, two monooxygenases that inactivate chloroquine. The activities of these monooxygenases are considerably higher in chloroquine-resistant strains of Plasmodium berghei than in the chloroquine-sensitive strain of the parasite. Inhibitors of microsomal monooxygenases have the potential to overcome the chloroquine resistance of Plasmodium spp., and, of those inhibitors tested, the copper-lysine complex, copper(lysine)(2), was the most effective.

[Chloroquine metabolism in the mono-oxygenase system of mouse liver microsomes]. / Issledovanie metabolizma khlorokhina v monooksigenaznoi sisteme mikrosom pecheni myshei.

Metabolism of chloroquine in microsomes of mice liver tissue was studied in vitro by means of thin-layer and microcolumn liquid chromatographies. Chloroquine was metabolized in the system with liver microsomal monooxygenases. The products of its oxidation, involving side chain and aminoquinoline nucleus, were studied. As the enzymatic system is principally similar in various species, analogous metabolites of chloroquine appear to be produced after oxidation of the substance in the plasmodium microsomal monooxygenase system. Thus, this metabolic pathway is responsible for chloroquine resistance of the malarial parasite.

[Microsomal monooxygenase inhibitors as promising agents for overcoming the drug resistance of the malaria parasite]. / Ingibitory mikrosomal'nykh monooksigenaz kak perspektivnye sredstva preodoleniia lekarstvennoi ustoichivosti u maliariinogo parazita.

A relationship was found between resistance of malarial plasmodium to chloroquine and the increased activity of microsomal monooxygenases, metabolizing drugs in the parasite. A search for effective inhibitors of the enzymatic system was initiated. For this purpose inhibitory effects of 17 alpha-hydrodeoxycorticosterone (substance S), 21-acetate-17 alpha-hydroxydeoxycorticosterone (acetate of substance S), 4-bromomethyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl (RBr), Cu(lysine)2 on activity of arylhydroxycarbone hydroxylase were studied using mice liver microsomes and homogenate of mice malaria cells Plasmodium berghei. Cu(lysine)2 and phenylhydrazine were found to be the most effective inhibitors of the enzyme in samples containing mice liver microsomes or malarial parasite. The data obtained suggest that the inhibitors of microsomal monooxygenases may serve as means for a decrease in malarial parasite resistance to chloroquine.

[Higher microsomal monooxygenase activity in chloroquine-resistant strains of malarial plasmodium as a possible cause of drug stability]. / Povyshennaia aktivnost' mikrosomal'nykh monooksigenaz khlorokhinorezistentnykh shtammov maliariinogo plazmodiia kak veroiatnaia prichina lekarstvennoi ustoichivosti.

Ability to hydroxylate benz(alpha)pyrene--a substrate of arylhydrocarbone hydroxylase (AHH) was distinctly increased in lysates of erythrocytes containing malarial plasmodium. Hydroxylation of benz(alpha)pyrene was inhibited by methyrapone--an inhibitor of microsomal monooxygenases. Activity of AHH was increased from 2- to 3-fold in chloroquine-resistant plasmodium strains as compared with the drug-sensitive strains. Resistance of Plasmodium berghei to chloroquine appears to involve an activation of the monooxygenases system in the parasite.