Search PubMed⌕ Search

Biomedical subjects

S Krishna

Publications and source records attributed to S Krishna.

At least 19 recordsLinked to original sources
PubMed1998

A splice junction mutation in the alpha(M) gene of phosphorylase kinase in a patient with myopathy.

In a 28-year-old man with myopathy and phosphorylase kinase (PhK) deficiency, we found a G-to-C substitution at the 5' end of an intron in the muscle-specific alpha-subunit gene. The mutation destroys the high-consensus GT sequences at the 5' splice junction of the intron, which causes skipping of the preceding exon. This is the second molecular genetic defect identified in the myopathic variant of PhK deficiency.

Adult↗
PubMed1998

Pioneer axon guidance by UNC-129, a C. elegans TGF-beta.

The unc-129 gene, like the unc-6 netrin gene, is required to guide pioneer motoraxons along the dorsoventral axis of Caenorhabditis elegans. unc-129 encodes a member of the transforming growth factor-beta (TGF-beta) superfamily of secreted signaling molecules and is expressed in dorsal, but not ventral, rows of body wall muscles. Ectopic expression of UNC-129 from ventral body wall muscle disrupts growth cone and cell migrations that normally occur along the dorsoventral axis. Thus, UNC-129 mediates expression of dorsoventral polarity information required for axon guidance and guided cell migrations in C. elegans.

Amino Acid Sequence↗
PubMed1998

Expression of substrate-specific transporters encoded by Plasmodium falciparum in Xenopus laevis oocytes.

When the malarial parasite Plasmodium falciparum multiplies in erythrocytes it dramatically increases uptake of essential metabolic precursors (nucleosides, nucleobases and glucose) and export of lactic acid by undefined mechanisms. The first evidence is provided here, by a detailed study in Xenopus laevis oocytes, that several specific nutrient transporters are the product of P. falciparum genes. We report the expression of nucleoside, nucleobase, hexose and monocarboxylate transport systems in Xenopus oocytes when injected with mRNA isolated from asexual stages of developing P. falciparum parasites. Their properties are distinct from transport events occurring at the infected erythrocyte membrane or the electrophysiologically identified channel localised to the parasitophorous vacuolar membrane. These novel transporters are substrate-specific and stereoselective, and represent a key regulatory step in the acquisition and export of metabolites by intraerythrocytic P. falciparum.

Adenosine↗
PubMed1998

TGF-beta signaling, Smads, and tumor suppressors.

The transforming growth factor-beta (TGF-beta) superfamily is used throughout animal development for regulating the growth and patterning of many tissue types. During the past few years, rapid progress has been made in deciphering how TGF-beta signals are transduced from outside the cell to the nucleus. This progress is based on biochemical studies in vertebrate systems and a combination of genetic studies in Drosophila and Caenorhabditis elegans. These studies have identified a novel family of signaling proteins, the Smad family. Smads can act positively and be phosphorylated by TGF-beta-like receptors or can act negatively and prevent activation of the positively acting group. The positively acting Smads translocate to the nucleus, bind DNA, and act as transcriptional activators. Thus, genetic and biochemical studies suggest a very simple signaling pathway, in which Smads are the primary downstream participant.

Animals↗
PubMed1998

Crithidia luciliae: functional expression of nucleoside and nucleobase transporters in Xenopus laevis oocytes.

The expression of purine-specific nucleoside and base transporters of Crithidia luciliae has been demonstrated in Xenopus laevis oocytes. Poly(A)+-mRNA from C. luciliae, cultured in either purine-replete or purine-starved conditions, was microinjected into X. laevis oocytes. For "purine-replete" mRNA, expression of adenosine and hypoxanthine uptake in microinjected X. laevis oocytes was increased on average 9- and 3-fold above water-injected controls, respectively. Expression of adenosine and hypoxanthine uptake in oocytes microinjected with "purine-starved" mRNA was 8 and 3-fold above water-injected controls, respectively. Substrate competition indicated an adenosine/deoxyadenosine transporter and a separate base transporter specific for hypoxanthine. In contrast to C. luciliae in vivo, where the level of activity of adenosine and hypoxanthine transport was regulated by the level of purines in the medium, the heterologous expression of these transporters (from both purine replete and deplete cultures) in X. laevis oocytes was independent of the extracellular purine concentration. These results may suggest that the presence of specific transporter message is independent of the extracellular purine content, indicating that the regulation of activation and expression of these transporters in C. luciliae may not be under transcriptional control.

Adenosine↗
PubMed1998

Severe falciparum malaria in children: current understanding of pathophysiology and supportive treatment.

Severe falciparum malaria is one of the most lethal parasitic infections in the world and is responsible for more than one million deaths in African children per year. Changes to management over the last 40 years have not improved survival. A reduction in the mortality and morbidity may only come about by a better understanding of the pathophysiological processes that are responsible for severe disease and that determine the outcome before antimalarials have had time to work. This review discusses potential adjunctive therapies for severe malaria that are under development following such detailed clinical and pathophysiological studies.

Animals↗
PubMed1998

Metal ion homeostasis and intracellular parasitism.

Bacteria possess multiple mechanisms for the transport of metal ions. While many of these systems may have evolved in the first instance to resist the detrimental effects of toxic environmental heavy metals, they have since become adapted to a variety of important homeostatic functions. The 'P'-type ATPases play a key role in metal ion transport in bacteria. A Cu+-ATPase from the intracellular bacterium Listeria monocytogenes is implicated in pathogenesis, and similar pumps in Mycobacterium tuberculosis and M. leprae may play a comparable role. Intracellular bacteria require transition metal cations for the synthesis of superoxide dismutases and catalases, which constitute an important line of defence against macrophage-killing mechanisms. The macrophage protein Nramp1, which confers resistance to a variety of intracellular pathogens, has also been shown recently to be a divalent amphoteric cation transporter. Mycobacterial homologues have recently been identified by genomic analysis. These findings suggest a model in which competition for divalent cations plays a pivotal role in the interaction between host and parasite.

Adenosine Triphosphatases↗
PubMed1997

The human transcription enhancer factor-1, TEF-1, can substitute for Drosophila scalloped during wingblade development.

The human transcription enhancer factor-1 (TEF-1) belongs to a family of evolutionarily conserved proteins that have a DNA binding TEA domain. TEF-1 shares a 98% homology with Drosophila scalloped (sd) in the DNA binding domain and a 50% similarity in the activation domain. We have expressed human TEF-1 in Drosophila under the hsp-70 promoter and find that it can substitute for Sd function. The transformants rescue the wingblade defects as well as the lethality of loss-of-function alleles. Observation of reporter activity in the imaginal wing discs of the enhancer-trap alleles suggests that TEF-1 is capable of promoting sd gene regulation. The functional capability of the TEF-1 product was assessed by comparing the extent of rescue by heat shock (hs)-TEF-1 with that of hs-sd. The finding that TEF-1 can function in vivo during wingblade development offers a potent genetic system for the analysis of its function and in the identification of the molecular partners of TEF-1.

Amino Acid Sequence↗
PubMed1997

Assessment of pfmdr 1 gene copy number by tandem competitive polymerase chain reaction.

The pfmdr 1 gene encodes a Plasmodium falciparum homologue of the human P-glycoprotein expressed on the surface of the parasite food vacuole. Variation in copy number and specific codon mutations of pfmdr 1 have been implicated in the development of parasite resistance to antimalarial drugs. We describe here the technique of Tandem-Competitive Polymerase Chain Reaction (TC-PCR), which allows accurate measurement of pfmdr 1 copy number in parasite DNA obtained directly from small quantities (100 microliters) of red blood cells. We reliably quantified pfmdr1 in previously well characterised strains of Plasmodium falciparum with differing pfmdr1 gene copy numbers using starting amounts of between 3,000 and 40,000 gene copies. We then used TC-PCR to determine pfmdr1 gene copy number in field specimens of venous blood taken from 10 patients with malaria contracted along the Thai-Burmese border. In this region of high grade parasite resistance to mefloquine greater than 70% of samples had a copy number greater than 1 of pfmdr1 determined with a repeatability coefficient of 0.58.

ATP-Binding Cassette Transporters↗
PubMed1997

Polymerase chain reaction for the detection of Burkholderia pseudomallei.

Melioidosis is a potentially lethal infection of humans and animals in Southeast Asia and northern Australia. Current methods for detection of the causative organism, Burkholderia pseudomallei, lack both speed and sensitivity. We report the development of a highly sensitive polymerase chain reaction-based method that can detect as few as 35 colony-forming units of B. pseudomallei/mL in saline suspensions. This polymerase chain reaction test also detected the presence of B. pseudomallei DNA in culture-negative splenic tissue obtained from mice infected with the organism, but without clinical evidence of disease. Specificity has been confirmed using a variety of pathogenic and nonpathogenic organisms, including B. mallei, B. cepacia, and Pseudomonas species. The clinical usefulness of this test should be assessed prospectively and compared with conventional diagnostic techniques.

Animals↗
PubMed1997

Cytokeratin patterns of expression in human epithelial cell lines correlate with transcriptional activity of the human papillomavirus type 16 upstream regulatory region.

A comparison of the CAT reporter activity of a plasmid which contains the 232 bp epithelial specific enhancer alone with that of plasmids which contain additional sequences from the human papillomavirus type 16 (HPV-16) upstream regulatory region (URR) revealed two markedly different patterns, in an analysis of six human epithelial cell lines. In HeLa, C33A and SiHa, the CAT reporter activities of all the constructs were comparable. In contrast, in CaSki, HK2bE6-E7 and HaCaT we detected very low levels of CAT reporter activity using the constructs with the additional HPV-16 URR sequences. The ability of HPV-16 E2 to transactivate a construct with 2 E2 binding sites also differed markedly and showed the same pattern. Cytokeratin staining revealed a correlation between cytokeratin 10 and 14 expression and the transcriptional differences observed. We also found alterations in the activity of one of the constructs on altering the growth conditions of the HaCaT cell line.

Cell Differentiation↗
PubMed1997

The link between integration and expression of human papillomavirus type 16 genomes and cellular changes in the evolution of cervical intraepithelial neoplastic lesions.

We have matched a PCR assay which detects disruptions in the E2 reading frame of human papillomavirus type 16, with RNA in situ hybridization patterns and shown that in 15 out of 16 cervical intraepithelial neoplastic (CIN) III lesions and in 19 out of 19 tumours, the E2 gene is disrupted with no detectable E2 transcripts. Varying levels of E6-E7 transcripts are detected in CIN III lesions, with stronger signals in tumours. The cytokeratin profile of most tumours: cytokeratin 10-, 14- and 19-positive and 4-, 13- and 18-negative, is also detected in CIN III lesions. The changes in levels of alpha 2, beta 1 and beta 4 integrins, CD44 and E-cadherin occur during the evolution of high-grade CIN lesions. Increases in the levels of expression of CD44 and E6-E7 transcripts, coupled with changes in the cellular localization of the Notch protein, define the transition from CIN III lesions to tumours.

Cadherins↗
PubMed1997

Clinical trials of interactive computerized patient education: implications for family practice.

A systematic review of randomized clinical trials was conducted to evaluate the acceptability and usefulness of computerized patient education interventions. The Columbia Registry, MEDLINE, Health, BIOSIS, and CINAHL bibliographic databases were searched. Selection was based on the following criteria: (1) randomized controlled clinical trials, (2) educational patient-computer interaction, and (3) effect measured on the process or outcome of care. Twenty-two studies met the selection criteria. Of these, 13 (59%) used instructional programs for educational intervention. Five studies (22.7%) tested information support networks, and four (18%) evaluated systems for health assessment and history-taking. The most frequently targeted clinical application area was diabetes mellitus (n = 7). All studies, except one on the treatment of alcoholism, reported positive results for interactive educational intervention. All diabetes education studies, in particular, reported decreased blood glucose levels among patients exposed to this intervention. Computerized educational interventions can lead to improved health status in several major areas of care, and appear not to be a substitute for, but a valuable supplement to, face-to-face time with physicians.

Adolescent↗
PubMed1996

Antimalarial drugs reduce cytoadherence and rosetting Plasmodium falciparum.

The in vivo and in vitro effects of antimalarials on cytoadherence and rosette formation were studied in 17 patients with severe and 46 with uncomplicated falciparum malaria. Cytoadherence was increased in severe malaria (P<.001). Artesunate and artemether were more potent than quinine in inhibiting both adherence properties. Artesunate was the most rapidly acting drug tested, producing >50% inhibition of both cytoadherence and rosetting in vivo and in vitro within 2 hr of drug exposure. Exposure to quinine for > or = to 4 h in vivo reduced rosetting by >50%, but not cytoadherence. Quinine did not reduce cytoadherence or rosetting significantly in vitro with exposure times of < or = to 8 h. These results suggest that artemisinin derivatives are more effective than quinine in preventing pathologic processes in parasitized erythrocytes that contribute to microvascular obstruction in severe malaria.

Adolescent↗
PubMed1996

The disposition and effects of two doses of dichloroacetate in adults with severe falciparum malaria.

1 Dichloroacetate (DCA) is a promising treatment for lactic acidosis complicating severe malaria. The pharmacokinetics, pharmacodynamics and toxicity of dichloroacetate were evaluated in 11 patients with severe malaria, and their lactate responses compared with nine control patients in an open-label prospective study. 2 Intravenous DCA (46 mg kg-1 infused in 30 min) or saline placebo was given on admission to the study, and 12 h later, as an adjunct to standard quinine treatment. 3 An open one-compartment model with the following parameters described the pharmacokinetics of DCA after one dose (mean [s.d.]): V = 0.44(0.2) 1 kg-1; CL = 0.13 [0.027] 1 h-1 kg-1; Cmax = 106[28] mg1-1; t1/2 = 3.4(2.2) h. After two doses of DCA (n = 9) the pharmacokinetic parameters were similar to those after the first dose. 4 DCA decreased venous plasma lactate concentrations by 42% of baseline values 8 h after admission, normalized arterial pH from a mean(s.d.) of 7.367(0.063) to 7.39(0.1), and decreased the calculated base deficit from 9.2(7.3) mEq 1-1 to 6.4(10.4) mEq 1-1. In control patients lactate concentrations fell by approximately 14% of baseline concentrations (P < 0.02 compared with DCA recipients). Venous lactate concentrations fell a further 16% from baseline values after the second dose of DCA but this change was not significantly different from controls. There was no electrocardiographic or other evidence of toxicity associated with DCA. 5 These data suggest that a single intravenous infusion of DCA rapidly reduces hyperlactataemia in patients severely ill with malaria, and that DCA should be evaluated further as an adjunct to conventional antimalarial and supportive measures for such patients with lactic acidosis.

Acidosis, Lactic↗
PubMed1996

Pharmacokinetics of quinine, chloroquine and amodiaquine. Clinical implications.

Malaria is associated with a reduction in the systemic clearance and apparent volume of distribution of the cinchona alkaloids; this reduction is proportional to the disease severity. There is increased plasma protein binding, predominantly to alpha 1-acid glycoprotein, and elimination half-lives (in healthy adults quinine t1/2z = 11 hours, quinidine t1/2z = 8 hours) are prolonged by 50%. Systemic clearance is predominantly by hepatic biotransformation to more polar metabolites (quinine 80%, quinidine 65%) and the remaining drug is eliminated unchanged by the kidney. Quinine is well absorbed by mouth or following intramuscular injection even in severe cases of malaria (estimated bioavailability more than 85%). Quinine and chloroquine may cause potentially lethal hypotension if given by intravenous injection. Chloroquine is extensively distributed with an enormous total apparent volume of distribution (Vd) more than 100 L/kg, and a terminal elimination half-life of 1 to 2 months. As a consequence, distribution rather than elimination processes determine the blood concentration profile of chloroquine in patients with acute malaria. Parenteral chloroquine should be given either by continuous intravenous infusion, or by frequent intramuscular or subcutaneous injections of relatively small doses. Oral bioavailability exceeds 75%. Amodiaquine is a pro-drug for the active antimalarial metabolite desethylamodiaquine. Its pharmacokinetic properties are similar to these of chloroquine although the Vd is smaller (17 to 34 L/kg) and the terminal elimination half-life is 1 to 3 weeks.

Amodiaquine↗