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Biomedical subjects

S A Ward

Publications and source records attributed to S A Ward.

At least 55 records · Page 3Linked to original sources
PubMed2000

Relative contribution of cytochromes P-450 and flavin-containing monoxygenases to the metabolism of albendazole by human liver microsomes.

AIMS: Albendazole (ABZ; methyl 5-propylthio-1H-benzimidazol-2-yl carbamate) is a broad spectrum anthelmintic whose activity resides both in the parent compound and its sulphoxide metabolite (ABS). There are numerous reports of ABZ metabolism in animals but relatively few in humans. We have investigated the sulphoxidation of ABZ in human liver microsomes and recombinant systems. METHODS: The specific enzymes involved in the sulphoxidation of ABZ were determined by a combination of approaches; inhibition with an antiserum directed against cytochrome P450 reductase, the effect of selective chemical inhibitors on ABZ sulphoxidation in human liver microsomes, the capability of expressed CYP and FMO to mediate the formation of ABS, regression analysis of the rate of metabolism of ABZ to ABS in human liver microsomes against selective P450 substrates and regression analysis of the rate of ABS sulphoxidation against CYP expression measured by Western blotting. RESULTS: Comparison of Vmax values obtained following heat inactivation (3min at 45 degrees C) of flavin monoxygenases (FMO), chemical inhibition of FMO with methimazole and addition of an antiserum directed against cytochrome P450 reductase indicate that FMO and CYP contribute approximately 30% and 70%, respectively, to ABS production in vitro. Comparison of CLint values suggests CYP is a major contributor in vivo. A significant reduction in ABZ sulphoxidation (n = 3) was seen with ketoconazole (CYP3 A4; 32-37%), ritonavir (CYP3 A4: 34-42%), methimazole (FMO: 28-49%) and thioacetamide (FMO; 32-35%). Additive inhibition with ketoconazole and methimazole was 69 +/- 8% (n = 3). ABS production in heat - treated microsomes (3 min at 45 degrees C) correlated significantly with testosterone 6beta-hydroxylation (CYP3A4; P < 0.05) and band intensities on Western blots probed with an antibody selective for 3A4 (P < 0.05). Recombinant human CYP3 A4, CYP1A2 and FMO3 produced ABS in greater quantities than control microsomes, with those expressing CYP3A4 producing threefold more ABS than those expressing CYP1A2. Kinetic studies showed the Km values obtained with both CYP3A4 and FMO3 were similar. CONCLUSIONS: We conclude that the production of ABS in human liver is mediated via both FMO and CYP, principally CYP3A4, with the CYP component being the major contributor.

Albendazole↗
PubMed2000

Potent enhancement of the sensitivity of Plasmodium falciparum to chloroquine by the bisbenzylisoquinoline alkaloid cepharanthin.

Cepharanthin is a proprietary extract of Stephania cepharantha, widely used in Japan for the treatment of inflammatory diseases. Cephranthin, its component alkaloids, and the standard resistance modulator verapamil were tested against Plasmodium falciparum for capacity to modulate sensitivity to chloroquine. Cepharanthin enhanced the activity of chloroquine against resistant clones by a factor of 15 at a concentration of only 200 nM (1.2 ng/ml). It is 50 times more potent than verapamil and 3 times more potent than the sum of its individual alkaloids. Combinations of component alkaloids acted synergistically to sensitize the parasite to chloroquine, possibly explaining the enhanced potency of Cepharanthin. Cepharanthin differed from verapamil in that it further sensitized clones that are considered to be fully susceptible, improving the baseline activity of chloroquine. Potent sensitization of parasites to chloroquine in vitro coupled with low toxicity suggests that coadministration of Cepharanthin might extend the clinical utility of chloroquine.

Alkaloids↗
PubMed2000

Biliary metabolites of beta-artemether in rats: biotransformations of an antimalarial endoperoxide.

beta-Artemether (AM), the O-methyl ether prodrug of dihydroartemisinin (DHA), is an endoperoxide antimalarial. The biliary metabolites of AM in adult male Wistar rats were characterized with particular reference to potential antimalarial compounds and stable derivatives of free radical intermediates. [13-(14)C]-AM (35 micromol kg(-1), i.v.) was administered to anesthetized rats. Within 0 to 3 h, 38.6 +/- 4.8% (mean +/- S.D., n = 6) of the radiolabel was recovered in bile; the 0- to 5-h recovery was 42.3 +/- 4.3%. The major metabolites (0-3 h) were the glucuronides of 9alpha-hydroxyAM (33.4 +/- 6.8% biliary radioactivity) and alpha-DHA (22.5 +/- 4.4%); four stereochemically unassigned monohydroxyAM glucuronides (II, 3.1 +/- 0.9; IV, 4.4 +/- 1.7%; V, 21.4 +/- 3.0%; VI, 3.0 +/- 1.1%) and a dihydroxyAM glucuronide (6.0 +/- 2.1%) were also identified. A sixth monohydroxyAM glucuronide (VIIa) and desoxyDHA glucuronide were detected in trace amounts. The furano acetate isomer of DHA glucuronide, indicative of the formation of a radical intermediate, was also found in trace amounts. O-methyl substitution of DHA favors ring hydroxylation in vivo. However, the principal hydroxylated metabolite, 9alpha-hydroxyAM, is unlikely to possess significant antimalarial activity.

Animals↗
PubMed1999

Novel, potent, semisynthetic antimalarial carba analogues of the first-generation 1,2,4-trioxane artemether.

Ten novel, second-generation, fluorinated ether and ester analogues of the potent first-generation analogues artemether (4a) and arteether (4b) have been designed and synthesized. All of the compounds demonstrate high antimalarial potency in vitro against the chloroquine-sensitive HB3 and -resistant K1 strains of Plasmodium falciparum. The most potent derivative 8 was 15 times more potent than artemisinin (2) against the HB3 strain of P. falciparum. In vivo, versus Plasmodium berghei in the mouse, selected derivatives were generally less potent than dihydroartemisinin with ED(50) values of between 5 and 8 mg/kg. On the basis of the products obtained from the in vitro biomimetic Fe(II)-mediated decomposition of 8, the radical mediator of biological activity of this series may be different from that of the parent drug, artemisinin (2).

Animals↗
PubMed1999

Simultaneous determination of artemether and its major metabolite dihydroartemisinin in plasma by gas chromatography-mass spectrometry-selected ion monitoring.

A sensitive, selective, and reproducible GC-MS-SIM method was developed for determination of artemether (ARM) and dihydroartemisinin (DHA) in plasma using artemisinin (ART) as internal standard. Solid phase extraction was performed using C18 Bond Elut cartridges. The analysis was carried out using a HP-5MS 5% phenylmethylsiloxane capillary column. The recoveries of ARM, DHA and ART were 94.9 +/- 1.6%, 92.2 +/- 4.1% and 81.3 +/- 1.2%, respectively. The limit of quantification in plasma was 5 ng/ml (C.V. < or = 17.4% for ARM and 15.2% for DHA). Calibration curves were linear with R2 > or = 0.988. Within day coefficients of variation were 3-10.4% for ARM and 7.7-14.5% for DHA. Between day coefficients of variations were 6.5-15.4% and 7.6-14.1% for ARM and DHA. The method is currently being used for pharmacokinetic studies. Preliminary data on pharmacokinetics showed Cmax of 245.2 and 35.6 ng/ml reached at 2 and 3 h and AUC0-8 h of 2463.6 and 111.8 ngh/ml for ARM and DHA, respectively.

Adult↗
PubMed1999

Inferences from pulmonary O2 uptake with respect to intramuscular [phosphocreatine] kinetics during moderate exercise in humans.

1. In the non-steady state of moderate intensity exercise, pulmonary O2 uptake (Vp,O2) is temporally dissociated from muscle O2 consumption (Vm,O2) due to the influence of the intervening venous blood volume and the contribution of body O2 stores to ATP synthesis. A monoexponential model of Vp,O2 without a delay term, therefore, implies an obligatory slowing of Vp,O2 kinetics in comparison to Vm, O2. 2. During moderate exercise, an association of Vm,O2 and [phosphocreatine] ([PCr]) kinetics is a necessary consequence of the control of muscular oxidative phosphorylation mediated by some function of [PCr]. It has also been suggested that the kinetics of Vp,O2 will be expressed with a time constant within 10 % of that of Vm,O2. 3. Vp,O2 and intramuscular [PCr] kinetics were investigated simultaneously during moderate exercise of a large muscle mass in a whole-body NMR spectrometer. Six healthy males performed prone constant-load quadriceps exercise. A transmit-receive coil under the right quadriceps allowed determination of intramuscular [PCr]; Vp,O2 was measured breath-by-breath, in concert with [PCr], using a turbine and a mass spectrometer system. 4. Intramuscular [PCr] decreased monoexponentially with no delay in response to exercise. The mean of the time constants (tauPCr) was 35 s (range, 20-64 s) for the six subjects. 5. Two temporal phases were evident in the Vp, O2 response. When the entire Vp,O2 response was modelled to be exponential with no delay, its time constant (tau'Vp,O2) was longer in all subjects (group mean = 62 s; range, 52-92 s) than that of [PCr], reflecting the energy contribution of the O2 stores. 6. Restricting the Vp,O2 model fit to phase II resulted in matching kinetics for Vp,O2 (group mean tauVp,O2 = 36 s; range, 20-68 s) and [PCr], for all subjects. 7. We conclude that during moderate intensity exercise the phase II tauVp,O2 provides a good estimate of tauPCr and by implication that of Vm,O2 (tauVm,O2).

Adenosine Triphosphate↗
PubMed1999

New 4-aminoquinoline Mannich base antimalarials. 1. Effect of an alkyl substituent in the 5'-position of the 4'-hydroxyanilino side chain.

A new series of 4-aminoquinoline Mannich base derivatives have been synthesized, in which the 3'-diethylamino function of amodiaquine (AQ) is replaced by a 3'-tert-butylamino group and an aliphatic hydrocarbon entity is incorporated into the 5'-position of the 4'-hydroxyanilino side chain. Seven alkyl Mannich base derivatives were screened and found to be active against both chloroquine-sensitive and -resistant strains of Plasmodium falciparum in vitro. The propyl and isopropyl alkyl derivatives were found to be the most active; consequently these derivatives were tested against a nonsensitive strain of Plasmodium berghi in vivo and found to be 3-fold more active than AQ, irrespective of the route of administration (oral or intraperitoneal).

Aniline Compounds↗
PubMed1999

Cellular uptake of chloroquine is dependent on binding to ferriprotoporphyrin IX and is independent of NHE activity in Plasmodium falciparum.

Here we provide definitive evidence that chloroquine (CQ) uptake in Plasmodium falciparum is determined by binding to ferriprotoporphyrin IX (FPIX). Specific proteinase inhibitors that block the degradation of hemoglobin and stop the generation of FPIX also inhibit CQ uptake. Food vacuole enzymes can generate cell-free binding, using human hemoglobin as a substrate. This binding accounts for CQ uptake into intact cells and is subject to identical inhibitor specificity. Inhibition of CQ uptake by amiloride derivatives occurs because of inhibition of CQ-FPIX binding rather than inhibition of the Na+/H+ exchanger (NHE). Inhibition of parasite NHE using a sodium-free medium does not inhibit CQ uptake nor does it alter the ability of amilorides to inhibit uptake. CQ resistance is characterized by a reduced affinity of CQ-FPIX binding that is reversible by verapamil. Diverse compounds that are known to disrupt lysosomal pH can mimic the verapamil effect. These effects are seen in sodium-free medium and are not due to stimulation of the NHE. We propose that these compounds increase CQ accumulation and overcome CQ resistance by increasing the pH of lysosomes and endosomes, thereby causing an increased affinity of binding of CQ to FPIX.

Amiloride↗
PubMed1999

Chloroquine uptake and activity is determined by binding to ferriprotoporphyrin IX in Plasmodium falciparum.

The selective antimalarial activity of chloroquine and related compounds stems from the extensive saturable uptake of these drugs into malaria parasites. Chloroquine resistant strains of Plasmodium falciparum have evolved a mechanism to reduce the saturable uptake. The molecular mechanism of saturable chloroquine uptake is controversial and attention is currently focused on mutually exclusive models of active chloroquine uptake and intracellular chloroquine binding. We sum up recent evidence which conclusively proves that the saturable accumulation of chloroquine is due to intracellular binding to ferriprotoporphyrin IX rather than active transport into the parasite via the sodium/hydrogen exchanger. We discuss recent findings that the affinity of chloroquine binding to ferriprotoporphyrin IX is reduced in resistant parasites. The mechanism responsible for reduced binding affinity can be overcome by verapamil and various lysosomotropic agents, and is thought to be the basis of chloroquine resistance.

Animals↗
PubMed1999

Post partum creatine phosphokinase and its muscle-brain isoenzyme elevation and transient Q-wave in a patient with idiopathic hypertrophic subaortic stenosis.

A primigravida with idiopathic hypertrophic subaortic stenosis, New York Heart Association Classification III, developed acute chest pain with significant ST segment depression together with a new Q-wave in chest lead V6 on the electrocardiograph following delivery under lumbar epidural analgesia. An intrapartum myocardial infarct was suspected because serial creatine phosphokinase and its muscle-brain isoenzyme levels were elevated in the postpartum period. However, the ST segment and the Q-wave changes returned to baseline within 4 h, thus eliminating the possibility of acute myocardial infarction. The uterus and placenta release creatine phosphokinase and its muscle-brain isoenzyme substantially during normal vaginal delivery, thus mimicking acute myocardial infarction. Consequently, the elevations of creatine phosphokinase and its muscle-brain fraction alone are not diagnostic of myocardial infarction in the postpartum period. The diagnosis of myocardial infarction must be based on the clinical picture, serial electrocardiogram recording and determination of lactate dehydrogenase and aspartate amino transferase.

Journal Article↗
PubMed1999

Energy expenditure and substrate utilization in adults with cystic fibrosis and diabetes mellitus.

BACKGROUND: The onset of cystic fibrosis-related diabetes mellitus (CFDM) is often associated with a decline in clinical and nutritional status. OBJECTIVE: The purpose of this study was to characterize energy expenditure (EE) and substrate utilization during rest, exercise, and recovery from exercise in patients with CF diagnosed with diabetes mellitus. DESIGN: EE, substrate utilization, minute ventilation, tidal volume, and respiratory rate were calculated by indirect calorimetry durng rest; a 30-min, low-to-medium-intensity exercise bout on a treadmill; and a 45-min postexercise recovery period (in reclining position) in 10 CF, 7 CFDM, and 10 control subjects between 18 and 45 y of age. RESULTS: In all 3 periods, minute ventilation was higher in the CF and CFDM groups than in the control subjects (P < 0.01). During rest and exercise, the CF and CFDM groups maintained EE values at the high end of the normal range of the control subjects. However, during recovery, EE was higher in the CF and CFDM groups than in the control group (P < 0.01). CONCLUSIONS: EE may be higher than usual for the patients with CF and CFDM during periods of recovery from mild exercise or activity because of increased work of breathing consistent with higher ventilatory requirements. This information may be useful for patients receiving nutritional counseling who may choose to exercise regularly, but are concerned about possible weight loss.

Adult↗
PubMed1999

Effect of altered body CO2 stores on pulmonary gas exchange dynamics during incremental exercise in humans.

The lactate threshold is a widely used and, at times, controversial construct in exercise physiology and pathophysiology. Its non-invasive estimation during incremental exercise depends upon CO2 output increasing as a function of O2 uptake, i.e. 'V-slope', as a result of bicarbonate buffering during the lactic acidosis. However, we hypothesised that the V-slope deflection could also occur as a consequence of metabolic CO2 being diverted proportionally more into the CO2 stores in the early phase of exercise. Eight healthy males performed two incremental exercise tests on a cycle ergometer, with and without controlled prior hyperventilation; the hyperventilation caused end-tidal PCO2 to decline by 10 mmHg, with the clearance of a CO2 volume averaging 2547 ml. This corresponded to an 'effective' CO2 capacitance of some 3.12 ml mmHg-1 kg-1. Gas exchange was determined breath-by-breath, and blood was sampled from the dorsum of the heated hand. Our results demonstrate that the early dynamics of CO2 wash-in to the previously depleted body stores can result in a 'pseudo-threshold', i.e. significantly before the onset of the actual lactic acidosis. Precautions should therefore be taken to avoid hyperventilation prior to non-invasive estimation of the lactate threshold.

Adolescent↗
PubMed1999

Diagnostic utility of metabolic exercise testing in a patient with cardiovascular disease.

Disproportionate exercise limitation in patients with cardiovascular disease is a common problem faced by clinical cardiologists and other physicians. Symptoms may be attributed to psychological factors or hypothetical pathophysiological mechanisms that are difficult to confirm clinically. This case report describes how the use of metabolic exercise testing in a 28 year old woman with morphologically and haemodynamically mild hypertrophic cardiomyopathy and severe exercise limitation led to the diagnosis of an alternative cause for the patient's symptoms, namely a primary disturbance of the mitochondrial respiratory chain probably caused by a nuclear encoded gene defect.

Adult↗
PubMed1999

Simultaneous determination of muscle 31P and O2 uptake kinetics during whole body NMR spectroscopy.

Our understanding of O2 uptake (VO2) control mechanisms during exercise may be improved by the simultaneous determination of the kinetics of intramuscular high-energy phosphate turnover and pulmonary VO2. We therefore developed a technique for remote gas-exchange analysis while subjects exercised in a whole body 1.5-T NMR system. Knee-extension exercise was performed against restraining rubber bands in the prone position. Free induction decays were acquired every 1,875 ms by using a transmit-receive coil, which was placed under the quadriceps. This allowed 31P spectra of intramuscular ATP, Pi, and creatine phosphate dynamics to be determined every 15 s. Airflow was measured with a custom-designed turbine and a 45-ft.-long cable to reach the volume-measuring module. This was located in an adjacent radio-frequency-shielded room, as was the respiratory mass spectrometer, which also used a 45-ft.-long sampling line. The respired gas profiles were not discernibly different from those that used the standard inlet; the increase in the delay was readily incorporated into the breathby-breath algorithm, allowing the VO2 kinetics to be determined in concert with those of intramuscular phosphate metabolism.

Adenosine Triphosphate↗
PubMed1999

Phenotypic and genotypic characteristics of recently adapted isolates of Plasmodium falciparum from Thailand.

The drug sensitivity characteristics and Plasmodium falciparum pfmdr1 status of five isolates of P. falciparum recently isolated from patients presenting for treatment from the Thailand/Myanmar border have been investigated. The aim of the study was to avoid the criticisms of some earlier studies by focusing on newly collected isolates from a specific geographic location. Three of the isolates studied exhibited clear resistance to chloroquine similar to that observed in the K1 Thai standard isolate obtained in the 1970s, and the other two isolates were of intermediate sensitivity to chloroquine with concentrations of drug that inhibit parasite growth by 50% of 50 and 43 nmol. The sensitivity of all isolates was enhanced by verapamil but we found no clear association between chloroquine sensitivity and gene copy number or intra-allelic variation of pfmdr1. In contrast, clear cross-resistance was seen between mefloquine and halofantrine, with the most sensitive isolates carrying the K1 mutation in pfmdr1.

Animals↗
PubMed1998

A comparison of the phenomenology and genetics of multidrug resistance in cancer cells and quinoline resistance in Plasmodium falciparum.

Plasmodium falciparum is the causative agent of the most deadly form of human malaria. Chemotherapy traditionally has been the main line of defense against this parasite, and chloroquine, the drug of choice, has been one of the most successful drugs ever developed. Unfortunately, the evolution and spread of resistance to chloroquine and other quinoline-containing drugs means that these compounds are now virtually useless in many endemic areas. Future prospects for the use of quinoline compounds improved considerably when it was demonstrated that chloroquine resistance could be circumvented in vitro by a number of structurally and functionally unrelated compounds such as verapamil and desipramine. The phenomenon of resistance reversal by compounds such as verapamil is also a key feature of drug resistance in mammalian cells, and this has raised the possibility that the underlying mechanisms of drug resistance of the two cell types could be similar. This hypothesis has prompted a large number of studies into the genetics and biochemistry of resistance to quinoline-containing drugs in P. falciparum. Both the genetic and the biochemical studies have raised issues of controversy and stimulated much debate. These issues are discussed in this review, in the context of a comparison with the genetics and biochemistry of multidrug resistance in mammalian cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗