Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0024530 (malaria)
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Worldwide, tuberculosis (TB) remains the most frequent and important infectious disease causing morbidity and death. One-third of the world's population is infected with Mycobacterium tuberculosis (MTB), the etiologic agent of TB. The World Health Organization estimates that about eight to ten million new TB cases occur annually worldwide and the incidence of TB is currently increasing. In this context, TB is in the top three, with malaria and HIV being the leading causes of death from a single infectious agent, and approximately two million deaths are attributable to TB annually. In particular, pulmonary TB, the most common form of TB, is a highly contagious and life-threatening infection. Moreover, enhanced susceptibility to TB in HIV-infected populations is another serious health problem throughout the world. In addition, multidrug-resistant TB (MDR-TB) has been increasing in incidence in many areas, not only in developing countries but industrialized countries as well, during the past decade. These situations, particularly the global resurgence of TB and the rapid emergence of MDR-TB, underscore the importance of the development of new antituberculous drugs and new protocols for efficacious clinical control of TB patients using ordinary antimycobacterial drugs. Concerning the development of new antituberculous drugs, the following points are of particular importance. (1) Development of drugs which display lasting antimycobacterial activity in vivo is desirable, since they can be administered with long intervals and consequently facilitate directly observed therapy and enhance patient compliance. (2) Development of novel antituberculosis compounds to combat MDR-TB is urgently needed. (3) The eradication of slowly metabolizing and, if possible, dormant populations of MTB organisms that cause relapse, using new classes of anti-TB drugs is very promising for prevention of TB incidence, because it will markedly reduce the incidence of active TB from persons who are latently infected with MTB. Unfortunately, no new drugs except rifabutin and rifapentine has been marketed for TB in the US and other countries during the 40 years after release of rifampicin. There are a number of constraints that have deterred companies from investing in new anti-TB drugs. The research is expensive, slow and difficult, and requires specialized facilities for handling MTB. There are few animal models that closely mimic the human TB disease. Development time of any anti-TB drug will be long. In fact, clinical trials will require the minimum six-month therapy, with a follow-up period of one year or more. In addition, it is hard to demonstrate obvious benefit of a new anti-TB agents over pre-existing drugs, since clinical trials involve multidrug combination therapy using highly effective ordinary anti-TB drugs. Finaly, there is the perceived lack of commercial return to companies engaged in the development of new anti-TB drugs, because over 95% of TB cases worldwide are in developing countries. In this symposium, we reviewed the following areas. 1. Critical new information on the entire genome of MTB recently obtained and increasing knowledge of various mycobacterial virulence genes are greatly promoting the identification of genes that code for new drug targets. In this context, Dr. Namba reviewed the status of new types of compounds which are being developed as anti-TB drug. He also discussed the development of new antimycobacterial drugs according to new and potential pharmacological targets and the best clinical development plans for new-TB drugs in relation to corporate strategy. 2. Using such findings for mycobacterial genomes, bioinformatics/genomics/proteomics-based drug design and drug development using quantitative structure-activity relationships may be possible in the near future. In this context, Dr. Suwa and Dr. Suzuki reviewed the usefulness of chemical genomics in searching novel drug targets for development of new antituberculous drugs. The authors reviewed (1) the history and present status of chemical genomics that is defined as the systemic search for a selective small molecular modulator for each function of all gene products, (2) recent studies of the authors on profiles of the interactions between various kinds of human proteins and small molecule modulators using the new technology devised by Reverse Proteomics Research Institute, and (3) future prospects of the development of new antituberculous drugs based on chemical genomics. 3. It appears also promising to develop new types of drug administration systems using drug vehicles, which enable efficacious drug delivery to their target in vivo. Dr. Izumikawa, Dr. Ohno and Dr. Kohno reviewed the usefulness of liposome- and polymer-based technologies, which enable efficacious delivery of encapsulated drugs at required doses for prolonged periods of time with only a single shot without toxicity, and also enable highly targeted delivery of drugs to their target in vivo. They indicated that the applications of drug delivery system using conventional anti-mycobacterial agents are challenging to improve the compliance of treatment and better clinical outcome. 4. Immunoadjunctive therapy appears to be promising in improving outcome of clinical control of refractory mycobacterial infections, including MDR-TB and M. avium complex infection. Dr. Shimizu, Dr. Sato and Dr. Tomioka reviewed the present status of immunotherapy of mycobacterial infections in combination with antimycobacterial drugs. They indicated that the development of new classes of immunomodulators other than cytokines (IL-2, IFN-gamma, GM-CSF, IL-12, etc.) particularly those with no severe side-effects, are urgently needed. Their review dealed with some promising immunoadjunctive agents, especially ATP and its analogues, which potentiate macrophage antimycobacterial activity via purinergic P2 receptors. The aim of this symposium is to address the future prospects of the development of new drugs and drug regimens for anti-TB chemotherapy. There are a number of difficulties in drug-design for the development of new drug formulations with increased potential for antimycobacterial effects, excellent pharmacokinetics, and tolerability. It should be emphasized that the most urgent goal of chemotherapy of TB and MAC infections, especially that associated with HIV infection, is to develop highly active, low-cost drugs which can be used not only in industrialized countries but also in developing countries, since the incidences of AIDS-associated intractable TB and MAC infections are rapidly increasing in the latter. We strongly wish a great advance of fundametal and practical studies in developing such kinds of new anti-TB drugs in the near future. 1. Prospects for non-clinical or clinical development of new antituberculous drugs in relation to corporate strategy: Kenji NAMBA (New Product Research Laboratories I, Daiichi Pharmaceutical Co., Ltd.) Tuberculosis (TB) remains one of the deadliest threats to public health. No new anti-TB drugs have been brought into the clinic in the past 40 years. Current non-clinical works with progressed technology and Global Alliance for TB Drug Development, a non-profit organization established in 2000, accelerate research and development of faster-acting anti-TB compounds. We reviewed the status of new types of compounds which are being developed as anti-TB drug, such as diarylquinoline (TMC 207), nitroimidazole (PA-824 and OPC-67683), and moxifloxacin (MFLX). We also discussed the best clinical development plans for new-TB drugs in relation to corporate strategy. 2. Exploring novel drug targets through the chemical genomics approach and its possible application to the development of anti-tuberculosis drugs: Yorimasa SUWA (Reverse Proteomics Research Institute Co., Ltd.), Yohji SUZUKI (Teijin Ltd.) Recently, chemical genomics approach has been focused as an emerging technology for the drug discovery. In advance to a very large scale national project in US started last year, Reverse Proteomics Research Institute Co., Ltd. (REPRORI) has developed the core technologies for chemical genomics. Here we describe the outline of chemical genomics study, especially that of REPRORI, and discuss about its possible application to the development of anti-tuberculosis drugs. 3. Anti-mycobacterial agents and drug delivery: Koichi IZUMIKAWA, Hideaki OHNO, Shigeru KOHNO (Second Department of Internal Medicine, Nagasaki University School of Medicine) Mycobacterium infection is a major clinical concern in whole world. Since the newly developed anti-mycobacterial agents are few and still unavailable in clinical settings, the applications of drug delivery system using conventional anti-mycobacterial agents are challenging to improve the compliance of treatment and better efficacy. The efficacy of anti-mycobacterial agents modified by liposome or polymer based technology have been investigated and reported using various animal models. Drug delivery system increased and prolonged the drug concentrations at the blood and targeted organs and the duration of sustained drug release, respectively. These effects lead to decrease in the frequency of drug administrations dramatically and better efficacy rates. The studies, however, were performed only in animal models, the further investigations and evaluations in human are required for practical use. 4. Adjunctive immunotherapy of mycobacterial infections: Toshiaki SHIMIZU, Katsumasa SATO, Haruaki TOMIOKA (Department of Microbiology and Immunology, Shimane University School of Medicine) There is an urgent need to develop new antimicrobials and protocols for the administration of drugs that are potently efficacious against intractable mycobacterial infections. Unfortunately, development of the new drugs for solving this problem is not progressing. (ABSTRACT TRUNCATED)
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PMID:[Development of antituberculous drugs: current status and future prospects]. 1724 Sep 21

Upon exposure to low Po(2), the red blood cells of most species, including humans, release increased amounts of ATP that ultimately serves as a regulator of vascular tone matching oxygen supply with demand. In pathological conditions such as malaria and sepsis, a maldistribution of perfusion exists with its severity often correlated with the extent of elevation of serum lactate frequently in the absence of an alteration in pH. We hypothesized that the increased levels of lactate might impair the ability of red blood cells to appropriately respond to conditions of low Po(2), thus preventing its important blood flow regulatory role. Using an in vitro system and rabbit red blood cells, we evaluated the capacity of cells incubated with lactate to release increased amounts of ATP in response to acute exposure to low Po(2). We found that in the presence of lactate, the red blood cells did not release ATP. However, when sodium dichloroacetate, a drug used clinically to lower blood lactate levels, was added, ATP release was restored to levels that were not different from that of control cells (no lactate), even though intracellular levels of ATP were not. These results support the presence of a distinct flow regulatory pool of ATP within the red blood cell that can be independently regulated, and that lactate interferes with the ATP production within this pool, thereby diminishing the amount of ATP available for release on exposure to low Po(2). Therefore, if lactate levels can be reduced, the vascular regulatory capacity of the red blood cell should be restored, thus enabling the appropriate matching of oxygen supply with oxygen demand.
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PMID:Lactate interferes with ATP release from red blood cells. 1730 94

The operation of a type II NADH:quinone oxidoreductase (PfNDH2), also known as alternative Complex I, in the mitochondrion of the human malaria parasite, Plasmodium falciparum, has recently been described. Unlike the Complex I of typical mitochondria, type II NADH:quinone oxidoreductases do not have transmembrane domains and are not involved directly in proton (H(+)) pumping. Here, we present a predictive model of PfNDH2, describing putative NADH-, flavin- and quinone-binding sites, as well as a possible membrane 'anchoring' region. In addition, we hypothesize that the alternative Complex I is an evolutionary adaptation to a microaerophilic lifestyle enabling (proton) uncoupled oxidation of NADH. This adaptive feature has several advantages, including: (i) a reduction of proton 'back-pressure' in the absence of extensive ATP synthesis; (ii) a reduction of mitochondrial superoxide generation; and (iii) a mechanism for the deregulated oxidation of cytosolic NADH.
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PMID:The malaria parasite type II NADH:quinone oxidoreductase: an alternative enzyme for an alternative lifestyle. 1802 19

Hypoxanthine, a nucleobase, serves as the major source of the essential purine group for the intraerythrocytic malaria parasite. In this study we have measured the uptake of hypoxanthine, and that of the related purine nucleobase adenine, by mature blood-stage Plasmodium falciparum parasites isolated from their host cells by saponin-permeabilisation of the erythrocyte and parasitophorous vacuole membranes. The uptake of both [3H]hypoxanthine and [3H]adenine was comprised of at least two components; in each case there was a rapid equilibration of the radiolabel between the intra- and extracellular solutions via a low-affinity transport mechanism, and an accumulation of radiolabel (such that the estimated intracellular concentration exceeded the extracellular concentration) via a higher-affinity process. The uptake of [3H]adenine was studied in more detail. The rapid, low-affinity equilibration of [3H]adenine between the intra-and extracellular solution was independent of the energy status of the parasite whereas the higher-affinity accumulation of the radiolabel was ATP-dependent. A kinetic analysis of adenine uptake revealed that the low-affinity (equilibrative) process had a Km of approximately 1.2mM, similar to the value of 0.82 mM estimated here (using the Xenopus laevis oocyte expression system) for the Km for the transport of adenine by PfENT1, a parasite-encoded member of the 'equilibrative nucleoside/nucleobase transporter' family. The results indicate that nucleobases enter the intraerythrocytic parasite via a rapid, equilibrative process that has kinetic characteristics similar to those of PfENT1.
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PMID:Purine nucleobase transport in the intraerythrocytic malaria parasite. 1776 2

Helicases are ubiquitous molecular motor proteins that have an important role in the metabolism of nucleic acids. The gene encoding a helicase was cloned from the human malaria parasite Plasmodium falciparum. The polypeptide of 398 amino acid residues has a molecular mass of 45 kDa, contains striking homology to eukaryotic translation initiation factor 4A (eIF4A) and all the conserved domains of the DEAD-box family. The recombinantly expressed and homogeneous P. falciparum protein PfH45 is an ATP-dependent DNA and RNA helicase, with ATPase and ATP-binding activities. PfH45 is a unique bipolar helicase that contains both the 3' to 5' and 5' to 3' directional helicase activities and anti-PfH45 antibodies curtail all its activities. PfH45 is expressed in all the intraerythrocytic developmental stages of the parasite and has a role in translation. Parasite cultures treated with PfH45 double-stranded RNA or purified immunoglobulins against PfH45 exhibited approximately 60% and approximately 55% growth inhibition, respectively. This inhibitory effect was due to interference with expression of the cognate messenger and down-regulation of synthesis of PfH45 protein in the parasite culture and was associated with morphologic deformation of the parasite. These studies indicate that PfH45 is an indispensable enzyme that is essential for growth, and probably survival, of P. falciparum.
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PMID:Bipolar, Dual Plasmodium falciparum helicase 45 expressed in the intraerythrocytic developmental cycle is required for parasite growth. 1782 10

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

The enzymes of the non-mevalonate pathway for isoprenoid biosynthesis are attractive targets for the development of novel drugs against malaria and tuberculosis. This pathway is used exclusively by the corresponding pathogens, but not by humans. A series of water-soluble, cytidine-based inhibitors that were originally designed for the fourth enzyme in the pathway, IspD, were shown to inhibit the subsequent enzyme, the kinase IspE (from Escherichia coli). The binding mode of the inhibitors was verified by co-crystal structure analysis, using Aquifex aeolicus IspE. The crystal structures represent the first reported example of a co-crystal structure of IspE with a synthetic ligand and confirmed that ligand binding affinity originates mainly from the interactions of the nucleobase moiety in the cytidine binding pocket of the enzyme. In contrast, the appended benzimidazole moieties of the ligands adopt various orientations in the active site and establish only poor intermolecular contacts with the protein. Defined binding sites for sulfate ions and glycerol molecules, components in the crystallization buffer, near the well-conserved ATP-binding Gly-rich loop of IspE were observed. The crystal structures of A. aeolicus IspE nicely complement the one from E. coli IspE for use in structure-based design, namely by providing invaluable structural information for the design of inhibitors targeting IspE from Mycobacterium tuberculosis and Plasmodium falciparum. Similar to the enzymes from these pathogens, A. aeolicus IspE directs the OH group of a tyrosine residue into a pocket in the active site. In the E. coli enzyme, on the other hand, this pocket is lined by phenylalanine and has a more pronounced hydrophobic character.
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PMID:Synthesis and characterization of cytidine derivatives that inhibit the kinase IspE of the non-mevalonate pathway for isoprenoid biosynthesis. 1803 14

Transport ATPases can be lumped into four distinct types, P, F, V, and ABC, with the first three designated 20 years ago (Pedersen, P.L. and Carafoli, E., Trends Biochem. Sci. 12, 146-150, 1987) and the ABC type included more recently. The mini-reviews (>20) that comprise this volume of the Journal of Bioenergetics and Biomembranes describe work presented at the 2007 FASEB Conference (6th) on Transport ATPases (Kathleen Sweadner, Chair; Rajini Rao, Co-Chair). Since these conferences began in 1997, the "transport ATPase field" has seen tremendous progress. Advances include a much better understanding of the structure, mechanism, and regulation of each of the four major ATPase types as well as their physiological and medical relevance. In fact, the transport ATPase field has entered a new era in which work on these enzymes is likely to contribute to new therapies for multiple diseases that affect both people and animals. Among these are cancer and heart disease, mitochondrial diseases, osteoporosis, macromolecular degeneration, immune deficiency, cystic fibrosis, diabetes, ulcers, nephro-toxicity, hearing loss, skin disorders, lupus, and malaria. In addition, as several members of the transport ATPase family include those involved in drug resistance their study may help alleviate this recurring problem in drug development. Finally, the transport ATPase field is also paving the way for nanotechnology focused on nano-motors with work on the F-type ATPases (F(0)F(1)) leading the way. These ATPases driven in reverse by a proton gradient have the capacity to interconvert electrochemical energy into mechanical energy and finally into chemical energy conserved in the terminal bond of ATP. In mammalian mitochondria these events occur on a larger complex or "nano-machine" called the "ATP synthasome" that consists of the ATP synthase in complex formation with carriers for P(i) and ADP/ATP.
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PMID:Transport ATPases into the year 2008: a brief overview related to types, structures, functions and roles in health and disease. 1817 9

We report that administration of the low-molecular-weight thiol pantethine prevented the cerebral syndrome in Plasmodium berghei ANKA-infected mice. The protection was associated with an impairment of the host response to the infection, with in particular a decrease of circulating microparticles and preservation of the blood-brain barrier integrity. Parasite development was unaffected. Pantethine modulated one of the early steps of the inflammation-coagulation cascade, i.e., the transbilayer translocation of phosphatidylserine at the cell surface that we demonstrated on red blood cells and platelets. In this, pantethine mimicked the inactivation of the ATP-binding-cassette transporter A1 (ABCA1), which also prevents the cerebral syndrome in this malaria model. However, pantethine acts through a different pathway, because ABCA1 activity was unaffected by the treatment. The mechanisms of pantethine action were investigated, using the intact molecule and its constituents. The disulfide group (oxidized form) is necessary to lower the platelet response to activation by thrombin and collagen. Thio-sensitive mechanisms are also involved in the impairment of microparticle release by TNF-activated endothelial cells. In isolated cells, the effects were obtained by cystamine that lacks the pantothenic moiety of the molecule; however, the complete molecule is necessary to protect against cerebral malaria. Pantethine is well tolerated, and it has already been administered in other contexts to man with limited side effects. Therefore, trials of pantethine treatment in adjunctive therapy for severe malaria are warranted.
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PMID:Protection against cerebral malaria by the low-molecular-weight thiol pantethine. 1819 63

Malaria is a major threat to world health. The identification of parasite targets for drug development is a priority and parasitic protein kinases suggest themselves as suitable targets as many display profound structural and functional divergences from their host counterparts. In this paper, we describe the structure of the orphan protein kinase, Plasmodium falciparum protein kinase 7 (PFPK7). Several Plasmodium protein kinases contain extensive insertions, and the structure of PFPK7 reveals how these may be accommodated as excursions from the canonical eukaryotic protein kinase fold. The constitutively active conformation of PFPK7 is stabilized by a structural motif in which the role of the conserved phosphorylated residue that assists in structuring the activation loop of many protein kinases is played by an arginine residue. We identify two series of PFPK7 ATP-competitive inhibitors and suggest further developments for the design of selective and potent PFPK7 lead compounds as potential antimalarials.
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PMID:Structures of P. falciparum protein kinase 7 identify an activation motif and leads for inhibitor design. 1827 14


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