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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of antimalarial treatment on the blood oxygen-transporting properties and on the tissue hypoxia were investigated in severe murine malaria, using mice infected with Plasmodium berghei (NK65). Five week old male ddY mice were inoculated intraperitoneally with 1 X 10(7) of P. berghei-infected red blood cells and treated with Fansidar (20 mg/kg body weight sulfadoxine and 1 mg/kg body weight pyrimethamine orally) on day 5 after inoculation. Parasitemia in these mice decreased rapidly on day 1 after treatment. Blood hemoglobin concentration, however, decreased on days 1 and 2 of treatment, then began to increase. The actual oxygen equilibrium curve (OEC) in vivo (actual pH; actual Pco2; 36.5 degrees C) was calculated from the measured OEC and the results of blood gas analysis. Looking from arterial and venous Po2 of each group, blood oxygen-transporting properties decreased markedly on day 2 of treatment. This decrease resulted mainly from the decrease of hemoglobin concentration and also partly from the raised hemoglobin affinity for oxygen. Adenosine triphosphate concentration in liver tissues, however, began to increase on day 1 of treatment. Adenylate energy charge of liver tissues also recovered on day 1. Blood glucose concentration began to increase and blood lactate concentration began to decrease simultaneously on day 1 of treatment. Glucose concentration in liver tissues, in contrast, decreased on days 1 and 2 of inoculation. Lactate concentration in liver tissue decreased earlier on day 1. These data indicate that tissue hypoxia was removed on day 1 following antimalarial treatment although blood oxygen-transporting properties decreased on days 1 and 2 after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Trends of tissue hypoxia following chemotherapy of acute malaria in mice]. 178

It has been postulated that differentiation of the human malaria parasite, Plasmodium falciparum, is controlled by cAMP levels. We have determined that P. falciparum synthesizes an adenylate cyclase with several properties distinct from those of the mammalian host cell enzyme. Adenylate cyclase activity was compared in P. falciparum-infected erythrocytes, isolated parasites free of host cell material, and uninfected erythrocyte membranes. The parasite enzyme was unaffected by GTP gamma S, AlF4-, and forskolin, while the erythrocyte enzyme was markedly stimulated by each of these compounds. The parasite adenylate cyclase also exhibited a striking preference for Mn2+ over Mg2+, which was not evident in the erythrocyte enzyme. Moreover, differing cation and pH sensitivities were observed for adenylate cyclase activity in the two cell types. When infected and uninfected erythrocytes were compared, the basal adenylate cyclase activity of infected cells was 7 and 49 times that measured in uninfected erythrocytes in the presence of Mg2+ and Mn2+, respectively. Furthermore, adenylate cyclase activity in infected cells exhibited properties typical of the parasite enzyme. This indicates that synthesis of the parasite enzyme rather than stimulation of the host enzyme accounts for the increased activity in infected cells.
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PMID:Plasmodium falciparum-infected erythrocytes contain an adenylate cyclase with properties which differ from those of the host enzyme. 190 86

It has been shown that the entry of the malaria parasite into the red blood cell requires the presence of ATP in the host cell cytoplasm. In red blood cell ghosts that contain no ATP the receptor on the extracellular surface remains in place and parasites will bind to the membrane, but will not enter. ATP is thus necessary for one of the steps in the invasion sequence that follows recognition and attachment. The process of entry appears to involve the active participation of the host cell membrane cytoskeleton. We have suggested that the function of the intracellular ATP may be to regulate phosphorylation of the cytoskeleton. We now present evidence that the activity of the membrane-associated cyclic AMP-independent kinase of the red blood cell is inseparable from invasion; the active substrate may be spectrin.
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PMID:Control of malarial invasion by phosphorylation of the host cell membrane cytoskeleton. 353 6

Asexual proliferation of malaria parasites proceeds by multiplication of the parasites within red cells. Following rupture of the host cells the released merozoites re-invade other red cells. On re-invasion, a proportion of merozoites become, not asexual parasites but gametocytes, the sexual stages infective to the mosquito vectors. Conversion of asexual parasites to gametocytes occurs not only during natural infections but also in continuous in vitro culture as reported first by Trager and Jensen and by others. We showed previously that the proportion of early intra-erythrocytic stages (ring stages) of Plasmodium falciparum which developed into gametocytes in culture was influenced by culture conditions. Gametocyte formation was rare in conditions supporting rapid proliferation but frequent when parasite densisites were static. We now show that nearly 100% of ring stages develop into gametocytes in response to 1mM cyclic AMP in static cultures whereas in rapidly growing cultures few rings become gametocytes in response to cyclic AMP.
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PMID:Gametocytogenesis by malaria parasites in continuous culture. 625 67

Through use of techniques for continuous erythrocyte culture and novel chromatographic procedures we have identified the major salvage pathways for metabolism of purine bases in P. falciparum infected human erythrocytes. The malaria parasitized erythrocyte (PRBC) differs from the unparasitized mature erythrocyte (RBC) in the following ways: PRBC primarily utilize hypoxanthine for synthesis of both adenylates and guanylates; PRBC incorporate the base guanine into guanylates at a higher rate than control RBC, PRBC do not appear to use adenine effectively due to an overwhelming competition for this base by the whole erythrocyte population; although PRBC cultures show an initial increase in [ATP] this change is interpreted to reflect a generalized RBC response to malaria infection and not a response restricted to PRBC. Our observations have identified a purine pathway involving adenylosuccinate (AMPs) present only in PRBC (HYP leads to IMP leads to AMPS leads to AMP). They also demonstrate the importance of guanylate synthesis to the malaria parasite. We have shown that the purine metabolism of unparasitized erythrocytes is perturbed during malaria infection, an effect reflected primarily by an increase in erythrocyte ATP. This increase in host erythrocyte ATP not only improves metabolic conditions for parasite growth but also places a demand on available purine resources that has implications for the severe disruption of normal erythrocyte function.
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PMID:Purine metabolism during continuous erythrocyte culture of human malaria parasites (P. falciparum). 702 71

Malaria causes a number of clinical complications, including diarrhoea. There are relatively few reports on the frequency of diarrhoea in malaria, but diarrhoea attributable to malaria is thought to be more common among children and nonimmune adults with hyperparasitaemia. The reported incidence of diarrhoea during malaria varies from 5 to 38%. The pathological changes in patients infected with malaria are very complex and involve many organs, including the small bowel. However, the causes of gastrointestinal manifestations during malaria are still not clear, and the mechanism of diarrhoea during malaria is likely to be multifactorial. Massive gastrointestinal bleedings with multiple foci of mucosal haemorrhage have also been observed. Tumor necrosis factor has been implicated in malaria and free oxygen radicals which can cause tissue injury in the liver, pancreas and intestine are enhanced during malaria infection; this can result in various disorders of the digestive system including diarrhoea and intestinal bleeding. Prostaglandins and cyclic AMP may also be involved in the development of diarrhoea in malaria.
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PMID:Malaria as a cause of diarrhoea--a review. 794 65

We have previously shown that infection with Plasmodium yoelii malaria or injection of extracts from malaria-parasitized red cells induces hypoglycemia in normal mice and normalizes the hyperglycemia in mice made moderately diabetic with streptozotocin. Inositol phosphoglycans (IPGs) are released outside cells by hydrolysis of membrane-bound glycosylphosphatidylinositols (GPIs), and act as second messengers mediating insulin action. The C57BL/Ks-db/db and C57BL/6J-ob/ob mice offer good models for studies on human obesity and Type 2 diabetes. In the present study, we show that a single iv injection of IPG-A or IPG-P extracted from P. yoelii significantly (P < 0.02) lowers the blood glucose in STZ-diabetic, db/db, and in ob/ob mice for at least 4--6 h. Using rat white adipocytes, IPG-P increased lipogenesis by 20--30% in the presence and absence of maximal concentrations of insulin (10(-8) M) (P < 0.01) and stimulated pyruvate dehydrogenase (PDH) phosphatase in a dose-related manner. Both IPG-A and IPG-P inhibited c-AMP-dependent protein kinase (PKA) in a dose-related manner. Compositional analysis of IPGs after 24 h hydrolysis revealed the presence of myo-inositol, phosphorus, galactosamine, glucosamine, and glucose in both IPG-A and IPG-P. However, hydrolysis of IPGs for 4 h highlighted differences between IPG-A and IPG-P. There are some functional similarities between P. yoelii IPGs and those previously described for mammalian liver. However, this is the first report of the hypoglycemic effect of IPGs in murine models of Type 2 diabetes. We suggest that IPGs isolated from P. yoelii, when fully characterized, may provide structural information for the synthesis of new drugs for the management of diabetes mellitus.
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PMID:Reversal of type 2 diabetes in mice by products of malaria parasites. II. Role of inositol phosphoglycans (IPGs). 1146 Nov 92

In the absence of the de novo purine nucleotide biosynthetic pathway in parasitic protozoa, purine salvage is of primary importance for parasite survival. Enzymes of the salvage pathway are, therefore, good targets for anti-parasitic drugs. Adenylosuccinate synthetase (AdSS), catalysing the first committed step in the synthesis of AMP from IMP, is a potential target for anti-protozoal chemotherapy. We report here the crystal structure of adenylosuccinate synthetase from the malaria parasite, Plasmodium falciparum, complexed to 6-phosphoryl IMP, GDP, Mg2+ and the aspartate analogue, hadacidin at 2 A resolution. The overall architecture of P. falciparum AdSS (PfAdSS) is similar to the known structures from Escherichia coli, mouse and plants. Differences in substrate interactions seen in this structure provide a plausible explanation for the kinetic differences between PfAdSS and the enzyme from other species. Additional hydrogen bonding interactions of the protein with GDP may account for the ordered binding of substrates to the enzyme. The dimer interface of PfAdSS is also different, with a pronounced excess of positively charged residues. Differences highlighted here provide a basis for the design of species-specific inhibitors of the enzyme.
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PMID:Crystal structure of fully ligated adenylosuccinate synthetase from Plasmodium falciparum. 1472 41

Mosquito natriuretic peptide (MNP), an uncharacterised peptide from the yellow fever mosquito, Aedes aegypti, acts via cyclic AMP to stimulate secretion of Na+-rich urine by opening a Na+ conductance in the basolateral membrane of Malpighian tubule principal cells. Corticotropin releasing factor (CRF)-related peptides and calcitonin (CT)-like diuretic peptides use cyclic AMP as a second messenger and were therefore considered likely candidates for MNP. BLAST searches of the genome of the malaria mosquito Anopheles gambiae, gave sequences for the CRF-related peptide Anoga-DH44 and the CT-like peptide Anoga-DH31, which were synthesised and tested for effects on Malpighian tubules from An. gambiae and Ae. aegypti, together with 8-bromo-cyclic AMP. The cyclic AMP analogue stimulated secretion of Na+-rich urine by An. gambiae Malpighian tubules, reproducing the response to MNP in Ae. aegypti. It also depolarised the principal cell basolateral membrane voltage (Vb) while hyperpolarising the transepithelial voltage (Vt) to a similar extent. Anoga-DH4) and Anoga-DH31 stimulated production of cyclic AMP, but not cyclic GMP, by Malpighian tubules of An. gambiae. Both peptides had diuretic activity, but only Anoga-DH31 had natriuretic activity and stimulated fluid secretion to the same extent as 8-bromo-cyclic AMP. Likewise, Anoga-DH31 reproduced the effects of cyclic AMP on tubule electrophysiology, whereas Anoga-DH44 initially hyperpolarised Vb and depolarised Vt, which is the opposite of the effect of Anoga-DH31. Anoga-DH44 and Anoga-DH31 were also tested for effects on fluid secretion and ion transport by Ae. aegypti tubules. As in An. gambiae, the CRF-related peptide Anoga-DH44 had a non-specific effect on the transport of Na+ and K+, whereas the CT-like peptide Anoga-DH31 specifically stimulated transepithelial Na+ transport. We conclude that the CT-like peptide Anoga-DH31 is the previously uncharacterised mosquito natriuretic peptide.
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PMID:Mosquito natriuretic peptide identified as a calcitonin-like diuretic hormone in Anopheles gambiae (Giles). 1610 90

Plasmodium falciparum, the causative agent of the fatal form of malaria, synthesizes GMP primarily from IMP and, hence, needs active GMPS (GMP synthetase) for its survival. GMPS, a G-type amidotransferase, catalyses the amination of XMP to GMP with the reaction occurring in two domains, the GAT (glutamine amidotransferase) and ATPPase (ATP pyrophosphatase). The GAT domain hydrolyses glutamine to glutamate and ammonia, while the ATPPase domain catalyses the formation of the intermediate AMP-XMP from ATP and XMP. Co-ordination of activity across the two domains, achieved through channelling of ammonia from GAT to the effector domain, is the hallmark of amidotransferases. Our studies aimed at understanding the kinetic mechanism of PfGMPS (Plasmodium falciparum GMPS) indicated steady-state ordered binding of ATP followed by XMP to the ATPPase domain with glutamine binding in a random manner to the GAT domain. We attribute the irreversible, Ping Pong step seen in initial velocity kinetics to the release of glutamate before the attack of the adenyl-XMP intermediate by ammonia. Specific aspects of the overall kinetic mechanism of PfGMPS are different from that reported for the human and Escherichia coli enzymes. Unlike human GMPS, absence of tight co-ordination of activity across the two domains was evident in the parasite enzyme. Variations seen in the inhibition by nucleosides and nucleotide analogues between human GMPS and PfGMPS highlighted differences in ligand specificity that could serve as a basis for the design of specific inhibitors. The present study represents the first report on recombinant His-tagged GMPS from parasitic protozoa.
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PMID:Kinetic and biochemical characterization of Plasmodium falciparum GMP synthetase. 1786 38


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