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A B Vaidya

Publications and source records attributed to A B Vaidya.

At least 19 recordsLinked to original sources
PubMed2001

Two classes of plant-like vacuolar-type H(+)-pyrophosphatases in malaria parasites.

In plants, cytosolic inorganic pyrophosphate (PP(i)) is hydrolyzed by energy-conserving vacuolar-type H(+)-pyrophosphatases (V-PPases) that harness the free energy of PP(i) hydrolysis to establish transmembrane H(+) gradients. Here we describe the identification and cloning of two genes, PfVP1 and PfVP2, from the malaria parasite Plasmodium falciparum. Inferred to encode type I (K(+)-dependent) and type II (K(+)-independent) V-PPases, respectively, PfVP1 and PfVP2 appeared more sequence divergent from each other than from their type I and type II counterparts in plants. The steady state levels of PfVP1 mRNA were high in comparison to PfVP2 mRNA throughout the erythrocytic phases of infection. Western analyses of trophozoite membranes using generic V-PPase antibodies (PAB(HK) and PAB(TK)) demonstrated appreciable amounts of a Mr 67000 polypeptide whose associated aminomethylenediphosphonate- (AMDP) inhibitable PPase activity was markedly stimulated by K(+). Immunofluorescence microscopy of infected erythrocytes revealed PfVP antigen associated with both the parasite plasma membrane and punctate intracellular inclusions. Transient transfection of a PfVP1-GFP fusion further supported the localization of PfVP1 to the parasite plasma membrane. Based on these findings and the growth-retarding effects of AMDP, P. falciparum is concluded to possess both type I and type II V-PPases of which the former has the greatest potential for contributing to the establishment of H(+) gradients across the parasite plasma membrane under conditions of energy limitation.

Amino Acid Sequence↗
PubMed1999

Resistance mutations reveal the atovaquone-binding domain of cytochrome b in malaria parasites.

Atovaquone represents a class of antimicrobial agents with a broad-spectrum activity against various parasitic infections, including malaria, toxoplasmosis and Pneumocystis pneumonia. In malaria parasites, atovaquone inhibits mitochondrial electron transport at the level of the cytochrome bc1 complex and collapses mitochondrial membrane potential. In addition, this drug is unique in being selectively toxic to parasite mitochondria without affecting the host mitochondrial functions. A better understanding of the structural basis for the selective toxicity of atovaquone could help in designing drugs against infections caused by mitochondria-containing parasites. To that end, we derived nine independent atovaquone-resistant malaria parasite lines by suboptimal treatment of mice infected with Plasmodium yoelii; these mutants exhibited resistance to atovaquone-mediated collapse of mitochondrial membrane potential as well as inhibition of electron transport. The mutants were also resistant to the synergistic effects of atovaquone/ proguanil combination. Sequencing of the mitochondrially encoded cytochrome b gene placed these mutants into four categories, three with single amino acid changes and one with two adjacent amino acid changes. Of the 12 nucleotide changes seen in the nine independently derived mutants 11 replaced A:T basepairs with G:C basepairs, possibly because of reactive oxygen species resulting from atovaquone treatment. Visualization of the resistance-conferring amino acid positions on the recently solved crystal structure of the vertebrate cytochrome bc1 complex revealed a discrete cavity in which subtle variations in hydrophobicity and volume of the amino acid side-chains may determine atovaquone-binding affinity, and thereby selective toxicity. These structural insights may prove useful in designing agents that selectively affect cytochrome bc1 functions in a wide range of eukaryotic pathogens.

Amino Acid Sequence↗
PubMed1999

A mechanism for the synergistic antimalarial action of atovaquone and proguanil.

A combination of atovaquone and proguanil has been found to be quite effective in treating malaria, with little evidence of the emergence of resistance when atovaquone was used as a single agent. We have examined possible mechanisms for the synergy between these two drugs. While proguanil by itself had no effect on electron transport or mitochondrial membrane potential (DeltaPsim), it significantly enhanced the ability of atovaquone to collapse DeltaPsim when used in combination. This enhancement was observed at pharmacologically achievable doses. Proguanil acted as a biguanide rather than as its metabolite cycloguanil (a parasite dihydrofolate reductase [DHFR] inhibitor) to enhance the atovaquone effect; another DHFR inhibitor, pyrimethamine, also had no enhancing effect. Proguanil-mediated enhancement was specific for atovaquone, since the effects of other mitochondrial electron transport inhibitors, such as myxothiazole and antimycin, were not altered by inclusion of proguanil. Surprisingly, proguanil did not enhance the ability of atovaquone to inhibit mitochondrial electron transport in malaria parasites. These results suggest that proguanil in its prodrug form acts in synergy with atovaquone by lowering the effective concentration at which atovaquone collapses DeltaPsim in malaria parasites. This could explain the paradoxical success of the atovaquone-proguanil combination even in regions where proguanil alone is ineffective due to resistance. The results also suggest that the atovaquone-proguanil combination may act as a site-specific uncoupler of parasite mitochondria in a selective manner.

Animals↗
PubMed1998

Divergent evolutionary constraints on mitochondrial and nuclear genomes of malaria parasites.

Genetic variation among malaria parasites has important consequences with regard to drug resistance, pathogenicity, immunity, transmission, and speciation. In this regard, malaria parasites have been shown to display a high degree of inter- and intra-species genetic divergence. The nuclear genomes of Plasmodium falciparum, Plasmodium yoelii, and Plasmodium gallinaceum are vastly divergent yet share a similar codon usage and total A/T content of approximately 82%. This is in contrast to other primate-specific species including P. vivax which have an A/T content of approximately 67%. To assess the effects of this evolutionary divergence on the conservation of gene content, organization, and codon usage in the mitochondrial DNA (mtDNA) of malaria parasites, we have cloned and sequenced the mitochondrial genome of Plasmodium vivax, and compared it with the mtDNAs of P. falciparum, P. yoelii, and P. gallinaceum. The P. vivax mitochondrial genome was found to be 5990 base pairs in length, and displayed a gene organization identical to that of P. falciparum, P. yoelii, and P. gallinaceum. Furthermore, there was a remarkable 90% conservation of sequence identity between the mitochondrial genomes of all four species. As an example of intra-species conservation, comparison of mtDNAs from two independently cloned P. falciparum isolates, Malay Camp and C10, revealed only a single nucleotide substitution. A/T content of the P. vivax mitochondrial genome was found to be identical to other species of Plasmodium, hence, we have postulated that the mitochondrial genomes of malaria parasites were refractory to the evolutionary shifts in nucleotide content seen among the nuclear genomes of malaria parasites. Among different Plasmodium species, the second position of mitochondrial codons were found to be the least prone to substitutions and displayed a significant bias in pyrimidines. These aspects of mitochondrial codon usage were distinct from the nuclear genome and may reflect functional aspects of decoding by the mitochondrial translational system.

Amino Acid Sequence↗
PubMed1998

An open clinical trial of benazepril--a new ACE inhibitor in mild-moderate hypertension.

Benazepril hydrochloride, a new non-sulfhydryl ACE inhibitor (ACEI) was studied in a titrated dose of 10 mg-20 mg once a day for 6 weeks in 42 mild to moderate adult hypertensive patients with sitting diastolic blood pressure (SDBP) 95-114 mm Hg. The pre-drug SDBP(mean +/- SE) of 102.5 +/- 0.8 mm Hg showed a significant reduction to 87.5 +/- 0.93 mm Hg at the end of treatment. BP was controlled (SDBP < or = 90 mm Hg) in 34 (81%) patients and a drop of at least 10 mm Hg from the pre-treatment SDBP value was noted in 34 (81%) patients. Common adverse reaction was cough in 8(19%) patients. Clinically significant changes in laboratory evaluations were not seen in any patient. Study showed that benazepril in a dose range of 10 to 20 mg per day is an effective agent for treatment of mild to moderate hypertension.

Adult↗
PubMed1997

Atovaquone, a broad spectrum antiparasitic drug, collapses mitochondrial membrane potential in a malarial parasite.

At present, approaches to studying mitochondrial functions in malarial parasites are quite limited because of the technical difficulties in isolating functional mitochondria in sufficient quantity and purity. We have developed a flow cytometric assay as an alternate means to study mitochondrial functions in intact erythrocytes infected with Plasmodium yoelii, a rodent malaria parasite. By using a very low concentration (2 nM) of a lipophilic cationic fluorescent probe, 3,3'dihexyloxacarbocyanine iodide, we were able to measure mitochondrial membrane potential(DeltaPsim) in live intact parasitized erythrocytes through flow cytometry. The accumulation of the probe into parasite mitochondria was dependent on the presence of a membrane potential since inclusion of carbonyl cyanide m-chlorophenylhydrazone, a protonophore, dissipated the membrane potential and abolished the probe accumulation. We tested the effect of standard mitochondrial inhibitors such as myxothiazole, antimycin, cyanide and rotenone. All of them except rotenone collapsed the DeltaPsim and inhibited respiration. The assay was validated by comparing the EC50 of these compounds for inhibiting DeltaPsim and respiration. This assay was used to investigate the effect of various antimalarial drugs such as chloroquine, tetracycline and a broad spectrum antiparasitic drug atovaquone. We observed that only atovaquone collapsed DeltaPsim and inhibited parasite respiration within minutes after drug treatment. Furthermore, atovaquone had no effect on mammalian DeltaPsim. This suggests that atovaquone, shown to inhibit mitochondrial electron transport, also depolarizes malarial mitochondria with consequent cellular damage and death.

Animals↗
PubMed1996

A developmental defect in Plasmodium falciparum male gametogenesis.

Asexually replicating populations of Plasmodium parasites, including those from cloned lines, generate both male and female gametes to complete the malaria life cycle through the mosquito. The generation of these sexual forms begins with the induction of gametocytes from haploid asexual stage parasites in the blood of the vertebrate host. The molecular processes that govern the differentiation and development of the sexual forms are largely unknown. Here we describe a defect that affects the development of competent male gametocytes from a mutant clone of P. falciparum (Dd2). Comparison of the Dd2 clone to the predecessor clone from which it was derived (W2'82) shows that the defect is a mutation that arose during the long-term cultivation of asexual stages in vitro. Light and electron microscopic images, and indirect immunofluorescence assays with male-specific anti-alpha-tubulin II antibodies, indicate a global disruption of male development at the gametocyte level with at least a 70-90% reduction in the proportion of mature male gametocytes by the Dd2 clone relative to W2'82. A high prevalence of abnormal gametocyte forms, frequently containing multiple and unusually large vacuoles, is associated with the defect. The reduced production of mature male gametocytes may reflect a problem in processes that commit a gametocyte to male development or a progressive attrition of viable male gametocytes during maturation. The defect is genetically linked to an almost complete absence of male gamete production and of infectivity to mosquitoes. This is the first sex-specific developmental mutation identified and characterized in Plasmodium.

Animals↗
PubMed1996

Nifedipine, captopril, metoprolol and nifedipine with metoprolol in hypertensive crisis in non-intensive care setting.

In 102 cases of severe hypertension (DBP > or = 115 mm Hg), with or without acute complications, efficacy and safety of SL Nifedipine 10 mg (NIF), SL Captopril 25 mg (CAP), IV Metoprolol 15 mg (MET) and SL NIF + IV MET were studied in an inpatient trial. Maximum mean percent reduction in SBP was 13.3, 9.7, 15.7 and 19.9 and in DBP was 21.2, 13.9, 12.5 and 20.4 with NIF, CAP, MET and NIF + MET respectively. A safe DBP of < or = 110 mm Hg (Kaplan) was achieved in 90, 61, 72.2 and 95.2 percent of patients. A statistically significant fall in DBP was observed at 5 minutes with all regimens except CAP which was at 15 minutes. Mild side effects observed were palpitations and flushing (NIF n = 4), taste disturbances (CAP n = 3), heaviness of head (CAP n = 1) and giddiness (MET n = 2, NIF + MET n = 2). The trial data suggest that hypertensive crisis can be managed, without intensive care facility, with all four regimens; this implies significant cost containment.

Acute Disease↗
PubMed1995

A genetic locus on Plasmodium falciparum chromosome 12 linked to a defect in mosquito-infectivity and male gametogenesis.

Infection of mosquitoes by Plasmodium spp. requires sexual differentiation of the malarial parasite in the vertebrate host and mating of the heterogametes in the vector midgut. A Plasmodium falciparum clone, Dd2, differentiates into normal-appearing gametocytes, yet poorly infects mosquitoes. The Dd2 clone, however, effectively cross-fertilized HB3, a Central American P. falciparum clone, and yielded several independent recombinant progeny. We have examined 11 HB3 x Dd2 progeny for their ability to infect mosquitoes and to differentiate into male gametes. Our analyses indicate that the poor mosquito-infectivity of the Dd2 clone results from a defect in male gametogenesis. This defect was inherited as a single locus in the independent recombinant progeny of HB3 x Dd2. Comparison with a restriction fragment length polymorphism map of the HB3 x Dd2 cross indicates that the defective phenotype of Dd2 maps to a locus on P. falciparum chromosome 12. This genetic locus may contain determinants that play a crucial role in male gametogenesis by P. falciparum.

Animals↗