Biomedical subjects

Peter J Smith

Publications and source records attributed to Peter J Smith.

31 records · Page 2Linked to original sources

PubMed2005

ATPase activity of purified plasma membranes and digestive vacuoles from Plasmodium falciparum.

The ATPase activity of the human malaria parasite, Plasmodium falciparum was investigated using two experimental systems, (i) digestive vacuoles, and (ii) purified plasma membranes isolated from a chloroquine-sensitive and a chloroquine-resistant strain. No correlation between the level of ATPase activity and chloroquine sensitivity could be detected. In both systems, the ATPase activity of the chloroquine-resistant and -sensitive strain was decreased in the presence of the P-glycoprotein inhibitor vanadate. Susceptibility to inhibition by vanadate together with the lack of effect of ouabain implies a P-type ATPase activity in the plasma membrane. Furthermore, the inhibition of Fac8 ATPase activity by oligomycin both in the digestive vacuoles and the plasma membranes would be consistent with higher levels of Pgh1 in Fac8. Our data are consistent with the presence of a V-type H+-ATPase in the parasite food vacuole. Bafilomycin A1 and N-ethylmaleimide decreased the vacuolar ATPase activity in both chloroquine-resistant and -sensitive strains. Interestingly, a 30% decrease was observed between the ATPase activity of plasma membranes isolated from Fac8 and D10 in the presence of bafilomycin A1, suggesting the presence of a V-type ATPase in D10 plasma membrane that is underexpressed or altered in the plasma membrane of the chloroquine-resistant Fac8. The chemosensitisers tested had no effect on the ATPase activity of chloroquine-resistant P. falciparum in both systems suggesting that their activity is not mediated through an ATP-dependent mechanism. No effect was observed on the vacuolar ATPase activity in the presence of the antimalarials tested indicating that an ATP-dependent transport has not been activated.

Adenosine Triphosphatases↗

PubMed2005

Accuracy of computed tomography guided core needle biopsy of musculoskeletal tumours.

BACKGROUND: The accurate diagnosis of musculoskeletal tumours is important for successful treatment. Image guided biopsy is gaining increasing acceptance for obtaining tissue for diagnosis. The aim of the present study is to assess the accuracy of computed tomography (CT)-guided core needle biopsy of musculoskeletal tumours. METHODS: This is a retrospective study on a series of 127 patients with a musculoskeletal tumour. The biopsies were performed over a 4-year period from 1998 to 2001. The accuracy of the CT-guided core needle biopsy was determined by comparing the histology of the biopsy with the final histology of the specimen obtained at open biopsy or surgical resection of the tumour. The effective accuracy was determined by the accuracy of the biopsy to distinguish between a benign and malignant tumour. RESULTS: Computed tomography guided core needle biopsy in the present series has an overall accuracy of 80.3%. The effective accuracy as determined by a malignant versus benign lesion was 89%. There were 86 malignant tumours with a biopsy accuracy of 81.4% and there were 41 benign tumours with a biopsy accuracy of 78%. The positive predictive value (PPV) of a malignant tumour is 98.9% and the PPV of benign tumour 90.2%. The most common site of biopsy was from the femur and thigh, together accounting for 39.4% of the tumours. The most common tumours in this series were liposarcoma (n = 12), osteosarcoma (n = 11) and giant cell tumour (n = 11). There were no reported complications arising from the biopsy. CONCLUSION: Computed tomography guided core needle biopsy is a safe and effective procedure that is important in the diagnosis and management of musculoskeletal tumours. It should be performed in a specialized institution with a multidisciplinary musculoskeletal tumour team.

Adolescent↗

PubMed2005

Association between the pharmacokinetics and in vivo therapeutic efficacy of sulfadoxine-pyrimethamine in Malawian children.

Sulfadoxine-pyrimethamine (SP) has been widely used in recent years to treat acute uncomplicated Plasmodium falciparum malaria. Risk factors for SP therapeutic failure include young age, subtherapeutic SP concentrations, and resistance-conferring genetic mutations in parasite target enzymes. A substantial proportion of patients are able to clear genetically highly resistant P. falciparum genotypes. To determine whether blood SP concentrations independently affect the patient's ability to clear resistant genotypes, we compared SP pharmacokinetics of cases of adequate clinical and parasitological response (ACPR) with cases of treatment failure (TF). When patients with ACPR and TF were compared, mean values were similar for the day 3 blood pyrimethamine (205 ng/ml versus 172 ng/ml; P = 0.25) and estimated maximum sulfadoxine (79 +/- 6.52 versus 69 +/- 6.27 mug/ml; P = 0.60) concentrations, for sulfadoxine terminal-phase elimination half-lives (7.15 versus 6.41 days; P = 0.42), and for the extents of sulfadoxine absorption (areas under the concentration-time curve of 932 +/- 100 versus 888 +/- 78.9 mug day ml(-1); P = 0.72). Among patients infected with the quintuple resistant parasites, day 3 blood pyrimethamine concentrations were higher in those who cleared the infection than in those who did not (305 +/- 35.4 versus 228 +/- 21.7 ng/ml; P = 0.037). Within this subgroup, this finding remained significant after adjusting for endogenous folate levels, age, site, and resistance-conferring mutations (odds ratio: 1.011 [1.003 to 1.024]; P = 0.018). However, as a subgroup analysis, our biologically plausible observation that higher blood pyrimethamine concentrations enhance the ability of patients to clear resistant P. falciparum should be interpreted with caution and needs further validation.

Animals↗

PubMed2005

Blood folate concentrations and in vivo sulfadoxine-pyrimethamine failure in Malawian children with uncomplicated Plasmodium falciparum malaria.

Folate antagonizes the antimalarial action of sulfadoxine-pyrimethamine (SP) in vitro, but its role in vivo is not well understood. We measured blood folate concentrations and SP therapeutic outcomes in Malawian children. Children with late treatment failure and those with adequate clinical and parasitologic responses had similar demographic characteristics, prevalence of parasite mutations conferring resistance to SP, and blood concentrations of anti-malarial drugs following treatment. However, a higher folate concentration was associated with late treatment failure. Patients from a low malaria transmission site had higher blood folate concentrations than those in a higher transmission site (mean +/- SEM = 39 +/- 9.3 ng/mL versus 29 +/- 10 ng/mL; P < 0.0001), and there was a higher rate of late treatment failure in the low transmission area (54.4% versus 40.2%; P = 0.010). This study also provides the first evidence of the independent role of physiologic folate concentrations in in vivo SP therapeutic efficacy, and the critical role of pyrimethamine concentrations in the therapeutic efficacy of SP when one controls physiologic folate levels and the frequency of critical dihydrofolate reductase/dihydropteroate synthase mutations.

Analysis of Variance↗

PubMed2004

In vitro antimalarial activity of a series of cationic 2,2'-bipyridyl- and 1,10-phenanthrolineplatinum(II) benzoylthiourea complexes.

We have synthesized a series of novel 2,2'-bipyridyl and 1,10-phenanthroline benzoylthiourea complexes of platinum(II) with various substituents on the bipyridyl and phenanthroline ligands. All of these square-planar mixed-ligand cationic complexes were found to form moderately strong complexes with ferriprotoporphyrin IX in 40% aqueous DMSO (log K ranging from 4.81 to 6.24). The complexes also all inhibit beta-hematin (synthetic hemozoin or malaria pigment) formation in acetate solution. Four of the compounds were found to exhibit in vitro antimalarial activity, with (N-benzoyl-N',N'-di(2-hydroxyethyl)thioureato)(4,4'-di-tert-butyl-2,2'-bipyridyl)platinum(II) chloride being particularly active. These active complexes exhibited equally strong activity against both the D10 chloroquine sensitive and K1 chloroquine resistant strains of malaria parasite. Cytotoxicity testing of the four most active compounds shows that they exhibit selective activity against malaria parasites with selectivity indices greater than 85. These compounds represent a new family of potential antimalarials.

2,2'-Dipyridyl↗

PubMed2004

In vitro antiplasmodial activity of medicinal plants native to or naturalised in South Africa.

The increasing prevalence and distribution of malaria has been attributed to a number of factors, one of them being the emergence and spread of drug resistant parasites. Efforts are now being directed towards the discovery and development of new chemically diverse antimalarial agents. The present study reports on the in vitro antiplasmodial activity of 134 plant taxa native to or naturalised in South Africa, representing 54 families, which were selected semi-quantitatively using weighted criteria. The plant extracts were tested for in vitro activity against a Plasmodium falciparum strain D10 using the parasite lactate dehydrogenase (pLDH) assay. Of the 134 species assayed, 49% showed promising antiplasmodial activity (IC(50)< or = 10 microg/ml), while 17% were found to be highly active (IC(50)< or = 5 microg/ml). Several plant species and genera were shown for the first time to possess in vitro antiplasmodial activity. These results support a rational rather than random approach to the selection of antiplasmodial screening candidates, and identify a number of promising taxa for further investigation as plant-based antimalarial agents.

Animals↗

PubMed2003

Mitochondrial respiration and Ca2+ waves are linked during fertilization and meiosis completion.

Fertilization increases both cytosolic Ca(2+) concentration and oxygen consumption in the egg but the relationship between these two phenomena remains largely obscure. We have measured mitochondrial oxygen consumption and the mitochondrial NADH concentration on single ascidian eggs and found that they increase in phase with each series of meiotic Ca(2+) waves emitted by two pacemakers (PM1 and PM2). Oxygen consumption also increases in response to Ins(1,4,5)P(3)-induced Ca(2+) transients. Using mitochondrial inhibitors we show that active mitochondria sequester cytosolic Ca(2+) during sperm-triggered Ca(2+) waves and that they are strictly necessary for triggering and sustaining the activity of the meiotic Ca(2+) wave pacemaker PM2. Strikingly, the activity of the Ca(2+) wave pacemaker PM2 can be restored or stimulated by flash photolysis of caged ATP. Taken together our observations provide the first evidence that, in addition to buffering cytosolic Ca(2+), the egg's mitochondria are stimulated by Ins(1,4,5)P(3)-mediated Ca(2+) signals. In turn, mitochondrial ATP production is required to sustain the activity of the meiotic Ca(2+) wave pacemaker PM2.

Adenosine Triphosphate↗

PubMed2002

Loss of microsatellite diversity and low effective population size in an overexploited population of New Zealand snapper (Pagrus auratus).

Although the effects of overfishing on species diversity and abundance are well documented, threats to the genetic diversity of marine fish populations have so far been largely neglected. Indeed, there seems to be little cause for concern, as even "collapsed" stocks usually consist of several million individuals, whereas population genetics theory suggests that only very small populations suffer significant loss of genetic diversity. On the other hand, in many marine species the genetically effective population size (N(e)), which determines the genetic properties of a population, may be orders of magnitude smaller than the census population size (N). Here, microsatellite analyses of a time series of archived scales demonstrated a significant decline in genetic diversity in a New Zealand snapper population during its exploitation history. Effective population sizes estimated both from the decline in heterozygosity and from temporal fluctuations in allele frequency were five orders of magnitude smaller than census population sizes from fishery data. If such low N(e)/N ratios are commonplace in marine species, many exploited marine fish stocks may be in danger of losing genetic variability, potentially resulting in reduced adaptability, population persistence, and productivity.

Animals↗

PubMed2002

Fate of haem iron in the malaria parasite Plasmodium falciparum.

Chemical analysis has shown that Plasmodium falciparum trophozoites contain 61+/-2% of the iron within parasitized erythrocytes, of which 92+/-6% is located within the food vacuole. Of this, 88+/-9% is in the form of haemozoin. (57)Fe-Mössbauer spectroscopy shows that haemozoin is the only detectable iron species in trophozoites. Electron spectroscopic imaging confirms this conclusion.

Animals↗

PubMed2002

Stromal interaction molecule 1 (STIM1), a transmembrane protein with growth suppressor activity, contains an extracellular SAM domain modified by N-linked glycosylation.

Stromal interaction molecule 1 (STIM1) is a cell surface transmembrane glycoprotein implicated in tumour growth control and stromal-haematopoietic cell interactions. A single sterile alpha motif (SAM) protein-protein interaction domain is modelled within its extracellular region, a subcellular localisation not previously described for other SAM domain-containing proteins. We have defined the transmembrane topology of STIM1 by determining the sites of N-linked glycosylation. We have confirmed that STIM1 is modified by N-linked glycosylation at two sites within the SAM domain itself, deduced as asparagine residues N131 and N171, demonstrating that STIM1 is translocated across the membrane of the endoplasmic reticulum such that the SAM domain resides within the endoplasmic reticulum (ER) lumen. Both N-linked oligosaccharides remain endoglycosidase H-sensitive, indicating absence of full processing within the ER and Golgi. This immature modification is nevertheless sufficient and critical for cell surface expression of STIM1. We show that STIM1-STIM1 homotypic interactions are mediated via the cytoplasmic rather than the extracellular region of STIM1, excluding an essential role for the SAM domain in these protein interactions. These studies provide the first evidence for an extracellular localisation of a SAM domain within any protein, and the first example of a SAM domain modified by N-linked glycosylation.

Cloning, Molecular↗

PubMed2002

Expression and mutation analysis of the Wilms' tumor 1 gene in human neural tumors.

The Wilms' tumor 1 gene, WT1, encodes a zinc-finger protein that is implicated in the development of Wilms' tumor. Mutant or aberrantly expressed WT1 isoforms have also been described in desmoplastic small round cell tumor, acute leukemias, mesothelioma, breast tumors and melanoma. During early development, WT1 is expressed in the brain and spinal cord, however its role in the malignancies that affect these tissues has not been previously investigated. In our study we have examined neural tumors including brain tumors and neuroblastomas for WT1 expression and for mutations affecting the zinc-fingers. Although WT1 expression was detected in gliomas, medulloblastomas and neuroblastomas, neither zinc-finger region mutations nor splicing anomalies affecting the KTS site were detected. We therefore conclude that WT1 does not play a significant role in the etiology of human neural tumors.

Alternative Splicing↗

PubMed2002

A dinitrogenous alkaloid from Cyrtanthus obliquus.

The ethanolic extract of bulbs of Cyrtanthus obliquus (L.f.) Ait yielded the new dinitrogenous alkaloid obliquine (1), 3S, 4aS, 11S, 10bS-3,4,4a,13,11,5,6-heptahydro-5[2-(4-hydroxyphenyl)ethyl]-3-methoxy-13-methyl-[1,3-dioxolo[4,5-g]indolo[3,3a-c]-isoquinolin-12-one, together with the five known structures 11alpha-hydroxygalanthamine, 3-epimacronine, narcissidine, tazettine and trisphaeridine. All structures were established using 1D and 2D NMR techniques and HREIMS. The alkaloids were tested for cytotoxicity against two mammalian cell lines and did not show activity at concentrations up to 100 microg/ml.

Alkaloids↗

PubMed2002

Prospective assessment of magnetic resonance cholangiopancreatography for noninvasive imaging of the biliary tree.

BACKGROUND: Traditionally, ERCP has been the only reliable method for imaging the biliary tree, but it is invasive and carries a risk of complications. Magnetic resonance cholangiopancreatography (MRCP) is a noninvasive method for imaging the biliary tree. The aim of this study was to prospectively assess the accuracy of MRCP in a large number of patients. METHODS: Consecutive patients referred to a teaching hospital for ERCP were eligible for study entry. MRCP was performed within 24 hours before ERCP. MRCP findings were compared with ERCP findings or, when the initial ERCP was unsuccessful, with results of repeat ERCP, percutaneous transhepatic cholangiography, or surgery. RESULTS: One hundred forty-six patients underwent 149 ERCP/MRCP procedures, of which 129 were evaluable with successful MRCP and ERCP or an ERCP-equivalent study. Diagnoses included choledocholithiasis in 46 and biliary stricture in 12 patients. The sensitivity, specificity, positive, and negative predictive values for MRCP in the diagnosis of choledocholithiasis were 97.9%, 89.0%, 83.6%, and 98.6%, respectively. All 12 strictures were diagnosed by MRCP (sensitivity 100%, specificity 99.1%). CONCLUSIONS: MRCP is an accurate, noninvasive alternative to ERCP for imaging the biliary tree. Choledocholithiasis and biliary strictures can be reliably diagnosed or excluded by MRCP. MRCP should be used increasingly in patients with suspected biliary obstruction to select those who require a therapeutic procedure.

Adolescent↗