V.C. Pandey

Heme oxygenase and related indices in chloroquine-resistant and -sensitive strains of Plasmodium berghei

Chloroquine-resistant (CQR) and -sensitive (CQS) Plasmodium berghei K173 strains possessed significant activities of heme oxygenase, biliverdin reductase and heme polymerase. Heme oxygenase and biliverdin reducatase activities of CQR were significantly higher (7-10 fold) as compared to that of CQS P. berghei, whereas heme polymerase showed a reverse trend (two-fold decrease). However, a 10-fold increase in heme, three-fold increase in ferriprotoporphyrin IX and a two-fold increase in hemozoin levels were noted in CQS as compared to CQR strains of P. berghei. This study suggests the importance of heme oxygenase and related components in the biochemical regulation of malaria parasites and in understanding the mechanism of the acquisition of chloroquine resistance.

Effect of Plasmodium yoelli nigeriensis infection and chloroquine on the hepatic mixed function oxidase system of mice

Plasmodium yoelii nigeriensis infection in albino mice significantly altered the hepatic microsomal mixed function oxidase system. Cytochrome P-450 (the terminal monooxygenase) and other monooxygenases, viz. aniline hydroxylase, aminopyrine-N-demethylase and benzo(a)pyrene hydroxylase were significantly lowered while microsomal heme showed 4-fold increase at 80% parasitaemia. Noticeable impairment in the other components like NADH:cytochrome b5 reductase, NADPH:cytochrome c reductase, cytochrome b5 and glucose-6-phosphatase was also observed. Oral treatment of normal and P. y. nigeriensis infected mice with chloroquine (64 mg per kg body weight for 4 days) caused lowering of mixed function oxidase activities which however showed a recovering trend, a week after cessation of treatment.

Status of oxidative stress and antioxidant defences during Plasmodivm knowlesi infection and chloroquine treatment in Macaca mulatta

Plasmodium knowlesi (a simian malarial parasite) infection resulted in elevation of hepatic oxidative stress in monkeys. Further, the antioxidant defence system of the host was also noticeably affected. The infected monkeys showed a marked increase in the levels of superoxide (O2-), lipid peroxidation (LPO), glutathione (GSH) and xanthine oxidase (XO), and decreased levels of superoxide dismutase (SOD) and catalase. Oral administration of chloroquine (20 mg kg body wt-1 for 3 days) to infected monkeys caused recovery trends in oxidative stress and antioxidant defences to almost normal a week after cessation of drug treatment.

Potential inhibitors of plasmodial heme oxygenase; an innovative approach for combating chloroquine resistant malaria.

Syntheses of imidazo-pyridines and substituted prolines and their effect on heme oxygenase activity of Plasmodium yoelii and corresponding infected host have been studied. Six compounds in vitro and one in vivo showed selective inhibition of parasite enzyme which may be further exploited in the development of resistant reversal agents.

Permeability function related to cerebral microvessel enzymes during ageing in rats.

Cerebral microvessels from rats were prepared and characterized by their enrichment of specific markers, namely alkaline phosphatase (AP) and τ‐glutamyl transpeptidase (τ‐GT). Further, it was observed that AP and τ‐GT registered marked increase in aged rats. On the contrary, lactate dehydrogenase (LDH) activity decreased with the increasing age. Monoamine oxidase A activity in the microvessels decreased with age whereas MAO‐B moved in the reverse direction. No noticeable change was seen in acetylcholinesterase activity with increasing age of rats.

Effect of Plasmodium berghei infection and chloroquine on the hepatic drug metabolizing system of mice

The hepatic microsomal mixed-function oxidase (MFO) system was markedly impaired during Plasmodium berghei infection in mice. Cytochrome P-450 and other mono-oxygenases, viz. aniline hydroxylase, aminopyrine-N-demethylase and benzo(a)pyrene hydroxylase, were significantly decreased while microsomal heme showed a four-fold increase at peak parasitemia (greater than 50%). Oral treatment with chloroquine (16 mg kg-1 body wt for 4 days) of P. berghei-infected mice cleared the parasitemia within 72 h and almost normalized the altered levels of MFO indices, a week after cessation of treatment. The findings were further supported by the isoenzymic profile and drug-binding properties of terminal mono-oxygenase, cytochrome P-450.

Mitochondrial heme oxygenase of Mastomys coucha

While studying the fate of heme generated during malaria infection, it was observed that mitochondrial preparations were highly enriched with heme compared to other subcellular particles. With this background, the present study aimed to determine the status of mitochondrial heme oxygenase and compare it with the microsomal enzyme. Mitochondrial and microsomal preparations were obtained from liver, spleen, kidney and brain of normal, inducer (cobalt chloride and hemin)-treated and Plasmodium berghei-infected Mastomys coucha. Heme oxygenase activity was determined by monitoring the formation of bilirubin. Biliverdin reductase activity was assayed by following the decrease in biliverdin content. Heme levels were measured by pyridine haemochromogen formation. Mitochondria from different tissues showed significant activity of heme oxygenase only after inducer (CoCl2 and hemin) treatment. In contrast, cerebral mitochondria did not show any enzyme activity. Hepatic, splenic and renal mitochondria of P. berghei-infected M. coucha showed noticeable heme oxygenase and biliverdin reductase activity. The response of hepatic mitochondrial heme oxygenase towards Triton X-100, trypsin, hydrogen peroxide, temperature, freezing and thawing and hemin was distinguishable from microsomal heme oxygenase. It is concluded that the mitochondria of different tissues from Mastomys display stress (biological and chemical)-induced activity of heme oxygenase. In addition, distinct differences between microsomal and mitochondrial heme oxygenase were observed.

Effect of chloroquine on hepatic heme-oxygenase during Plasmodium berghei infection in mice

Hepatic heme-oxygenase and heme levels were monitored during Plasmodium berghei infection and chloroquine treatment in Swiss albino mice. A progressive increase in heme-oxygenase and heme levels was noticed with the rise in parasitemia. Further, chloroquine treatment did not result in any change towards normal heme-oxygenase and heme content, when they were assayed a week after cessation of drug treatment. Chloroquine treatment of non-parasitized and parasitized mice resulted in significant loss of the enzyme activity after about 6 weeks.

Characterization of lactate dehydrogenase of Plasmodium knowlesi

Some properties of purified lactate dehydrogenase, (EC. 1.1.1.27) from schizonts of Plasmodium knowlesi are described. The plasmodial enzyme migrated as single entity on polyacrylamide gel, and resembled rabbit muscle (M4) lactate dehydrogenase in its electrophoretic mobility. The P. knowlesi enzyme consisted of four identical subunits of 31 kDa. Purified lactate dehydrogenase was inhibited almost completely when incubated with 100 microM p-chloromercuribenzoate, Ag+ or Hg+ and such inhibition could be reversed by the addition of beta-mercaptoethanol or L-cysteine. Metal chelators did not show any remarkable effect. Oxalic acid is a competitive inhibitor of pyruvate reduction by this enzyme with apparent Ki of approximately equal to 0.41 mM.

Status of hepatic glutathione-S-transferase(s) during Plasmodium berghei infection and chloroquine treatment in Mastomys natalensis.

Plasmodium berghei infection in Mastomys natalensis impaired the hepatic mitochondrial, microsomal and cytosolic glutathione-S-transferase(s) activity with 1-chloro-2,4-dinitrobenzene as substrate. The enzyme activity was concomitantly decreased with rise in parasitaemia. The decreased enzyme activity due to infection was almost normalized with oral treatment of 16 mg (kg body wt)-1 of chloroquine for 4 days.