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Biomedical subjects

D Lloyd

Publications and source records attributed to D Lloyd.

At least 199 records · Page 11Linked to original sources
PubMed1988

The effect of dialysate on peritoneal phagocyte oxidative metabolism.

The respiratory and oxidative responses of human peritoneal polymorphonuclear leukocytes (PMN) and peritoneal macrophages (PM phi) following exposure to unused continuous ambulatory peritoneal dialysis fluid (CAPD) and early dwell effluent were studied using an open oxygen (O2) electrode system and by measurement of oxygen radical-derived luminol-dependent chemiluminescence. Both cell types responded to stimulation by increasing O2 consumption and by generating chemiluminescence even at external O2 concentrations below 50 microM O2. Oxygen concentrations in the dialysate, as measured by blood gas analysis, were never lower than 118 +/- 8.3 microM O2 even during active peritonitis. Thus oxygen availability does not appear to be rate limiting for phagocyte oxidative metabolism in the peritoneal cavity. Preexposure of both inflammatory cell types to unused fluid or early dwell CAPD effluent significantly reduced both stimulated oxygen uptake and the subsequent ability of these cells to generate chemiluminescence without significantly affecting their viability. Further investigation of this down regulatory phenomenon using unused fluid and laboratory prepared dialysis fluid revealed that low pH (5.3) and high sodium lactate concentration in combination are directly responsible for the suppressive effect of unused fluid and early dwell effluent on cell function. These observations demonstrate that cellular host defense may be impaired early in the dialysis cycle as a result of lactate mediated "stunning" of resident phagocytes. The precise nature of the molecular species responsible for this suppressive effect remains to be identified.

Dialysis Solutions↗
PubMed1987

Hydrogen peroxide production in uncoupled mitochondria of the parasitic nematode worm Nippostrongylus brasiliensis.

1. Mitochondria from the parasitic nematode worm Nippostrongylus brasiliensis produce H2O2 in the energized state; higher rates of H2O2 production were observed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone. 2. Antimycin A inhibits respiration and H2O2 production by 70 and 65% respectively; the residual activities can be attributed to alternative electron-transport pathway(s). 3. o-Hydroxydiphenyl and 1,3,5-trihydroxybenzene, inhibitors of alternative electron transport, inhibit respiration by 37% and H2O2 production by 26%. 4. Another inhibitor of alternative electron transport, salicylhydroxamic acid, shows a complex mode of action; low concentrations (less than 0.5 mM) stimulate respiration and H2O2 production, whereas 2 mM-salicylhydroxamic acid inhibited respiration by 35% and stopped H2O2 production completely. 5. O2 thresholds were observed for the inhibition of respiration at O2 concentrations greater than 57.7 microM and inhibition of H2O2 production (greater than 20.5 microM-O2); apparent Km values for oxygen were 5.5 microM and 3.0 microM respectively. 6. In the presence of antimycin A the O2-inhibition thresholds and apparent Km values for O2 of respiration and H2O2 production matched closely, suggesting that the alternative oxidase is a likely site of H2O2 production. 7. These results are discussed in relation to O2 toxicity to N. brasiliensis.

Animals↗
PubMed1987

Effects of inhibitors on the oxygen kinetics of Nippostrongylus brasiliensis.

Endogenous respiration of the parasitic nematode Nippostrongylus brasiliensis and the succinate oxidase activity of isolated mitochondria were partially inhibited by antimycin A; the remaining respiratory activity was sensitive to salicylhydroxamic acid (SHAM). Sub-millimolar concentrations of SHAM markedly stimulated respiration by 60% in whole N. brasiliensis and isolated mitochondria; stimulation by SHAM was not observed in the presence of antimycin A. Little change in the relative fluxes of electrons through the classical, antimycin A-sensitive pathway and the alternative SHAM sensitive pathway was observed between low and high O2 concentrations; this may suggest that the O2 affinities of both pathways are similar. O2 dependence of respiration showed O2 thresholds above which respiration decreases; in the absence of inhibitors whole N. brasiliensis and isolated mitochondria had threshold values around 60 microM O2. Increased O2 threshold values were observed in the presence of SHAM and antimycin A. The apparent Km values for O2 of whole N. brasiliensis and isolated mitochondria were 31 +/- 2 microM O2 and 3.5 +/- 0.2 microM O2 respectively; this difference in apparent Km values may reflect the presence of O2 gradients in the whole worm. The Km and O2 inhibition threshold values observed for whole N. brasiliensis are in good agreement with the proposed range of O2 concentrations thought to exist within the worm's natural environment. H2O2 production was detected in respiring uncoupled mitochondria, but H2O2 could not be detected in the medium surrounding whole N. brasiliensis. SHAM-stimulated respiration was accompanied by increased H2O2 production which was prevented by the addition of antimycin A.

Animals↗
PubMed1987

Study of common bile duct exploration and endoscopic sphincterotomy in a consecutive series of 438 patients.

The outcome of 438 consecutive patients who had exploration of the common bile duct and/or endoscopic sphincterotomy (ES) in a 5-year period was reviewed. Patients were analysed according to four groups: 59 patients had planned ES followed by surgery resulting in 14 major complications (23.7 per cent) including 3 deaths (5.1 per cent) (group 1); 248 patients had surgery alone with 21 major complications (8.5 per cent) including 10 deaths (4.0 per cent) (group 2); 114 patients with gallbladder in situ underwent ES alone with 22 major complications (19.3 per cent) including 9 deaths (7.9 per cent) (group 3); 17 patients with remote cholecystectomy also had ES alone with 3 major complications (17.6 per cent) including 3 deaths (17.6 per cent) (group 4). There was no difference in mortality between the groups. Compared with group 2, major complications were significantly higher in group 1 (chi 2 = 11.0, d.f. = 1, P less than 0.001) and in group 3 (chi 2 = 8.6, d.f. = 1, P less than 0.003). Patients in group 3, however, were significantly older than those in groups 1 and 2, and the former also had higher medical and total risk factor scores than the latter (all P less than 0.001). The results indicate that routine pre-operative ES is of questionable value. ES alone is justified in elderly high risk patients; mortality in this group might be reduced by improved management of post-ES complications.

Adolescent↗
PubMed1987

CO-reacting haemoproteins of neutrophils: evidence for cytochrome b-245 and myeloperoxidase as potential oxidases during the respiratory burst.

Room temperature, CO-difference spectra of intact rat polymorphonuclear leucocytes (neutrophils) revealed the presence of a number of CO-binding haemoproteins. Absorption maxima at 413, 540 and 570 nm were attributed to the CO-complex of cytochrome b-245 whereas an absorption maximum at 595 nm was assigned to the contribution from a myeloperoxidase complex, since an identical absorption maximum was observed in CO-difference spectra of purified myeloperoxidase in the presence of H2O2. Photochemical action spectra for the relief of CO-inhibited O2 uptake revealed contributions from both cytochrome b-245 and myeloperoxidase. The potential of these two O2- and CO-binding haemoproteins to function as oxidases during the respiratory burst is discussed.

Animals↗
PubMed1987

Nitroimidazole and oxygen derived radicals detected by electron spin resonance in hydrogenosomal and cytosolic fractions from Trichomonas vaginalis.

Hydrogenosome-enriched fractions from Trichomonas vaginalis reduce a number of nitroimidazole derivatives to their respective electron spin resonance-detectable nitro-anion radicals. In the presence of of oxygen and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) a superoxide spin trapped adduct of DMPO was formed; the rate-determining step was the prior formation of the nitro-anion radical. Oxygen-derived radicals were detected with cytosolic fractions from a metronidazole-resistant isolate (CDC-85) when incubated with NADH or NADPH as respiratory substrate. The requirement for superoxide dismutase and catalase to completely abolish formation of these signals suggests contributions from both superoxide and peroxide. No oxygen-derived radicals were observed with cytosolic fractions from a metronidazole-susceptible strain (C1-NIH).

Animals↗
PubMed1987

Reduction of niridazole by metronidazole resistant and susceptible strains of Trichomonas vaginalis.

The inhibitory effect of niridazole on hydrogen production by metronidazole-resistant (CDC-85) and susceptible (C1-NIH) Trichomonas vaginalis strains was investigated. The results show that niridazole is more effective than metronidazole in inhibiting hydrogen production by the resistant isolate. In CDC-85 aerobic inhibition requires a 4-fold increase in metronidazole concentration compared with that required anaerobically, but the corresponding factor for niridazole is only 1.5-fold. Reduction of the drug by a hydrogenosome-enriched preparation gave rise to a multiline electron spin resonance detectable signal, which is due to a nitrogen-centred radical.

Animals↗
PubMed1987

A temperature-compensated ultradian clock explains temperature-dependent quantal cell cycle times.

The effects of sublethal heat pulses on cell division have provided insights into possible molecular mechanisms. Thus Zeuthen's findings of 'set-backs' up to a transition point provides the basis for the idea that the continuous accumulation of a compound needed for cell division spans a major portion of the cell cycle. The accumulating substance is a 'division protein' which forms part of a structure which is unstable until completely assembled at the transition point. Experiments showing phase resetting of mammalian cells by temperature perturbation indicate limit-cycle oscillator control of the cell cycle with a phase-response curve with a repeat interval equal to the period of the clock. As well as providing a method for establishing synchronized cultures these observations have found application in the selective effects of hyperthermia as an antitumour agent. Circadian rhythms display several unique features distinguishing them from other periodic processes. Only recently has it been recognized that some of these characteristics may be properties of ultradian rhythms as well. The probably most striking feature of circadian timekeeping, i.e. independence of ambient temperature, was found for ultradian rhythmicity even at the level of the unicellular organization. Synchronous cultures of some lower eukaryotes were prepared by centrifugal size selection methods. Experiments with asynchronous control cultures substantiated the view that the conditions employed were such as to minimize any perturbative effects: most importantly the organisms were never removed from their culture medium. Whereas the control cultures showed smoothly increasing respiration rates, total RNA, total protein, enzyme activities and enzyme protein (e.g. for cytochrome aa3, ATPase, catalase), in synchronous cultures all these parameters showed oscillatory behaviour. Different periods were observed in different organisms: thus in Acanthamoeba castellanii the period was about 70 min, in Tetrahymena pyriformis strain ST it was about 50 min, in T. pyriformis AII it was 30 min, and in Candida utilis it was about 30 min (all measurements at 30 degrees C). In A. castellanii the periods of both the oscillations in rate of respiration and the total cell protein were hardly affected by the temperature of growth over the range 20 to 30 degrees C. The oscillations show no damping during experiments lasting 12 h: these properties suggest that we are observing temperature-compensated endogenous rhythms which presumably serve a timekeeping function in cells undergoing growth and division.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity Cycles↗
PubMed1987

Temperature-compensated ultradian variation in cellular protein content of Acanthamoeba castellanii revisited.

Synchronous cultures of the soil amoeba Acanthamoeba castellanii, established in the laboratory by selection procedures, show oscillations of total cell protein, as well as respiration. Previously, time series analysis by Aspect, a University of Warwick Computer Unit Program, showed an average period of 76 min. A reanalysis by least-squares rhythmometry revealed that, in general, the analyses accompanying the original paper and those in this replication agree very well. The periods extracted by the two approaches differ by only 1 to 5 min. In one case, when the original analysis did not detect a statistically significant period, however, the analysis used here does so. While the incubation temperatures used varied from 20 to 30 degrees C and cell division time increased from 7.8 hr at 30 degrees C to 16 hr at 20 degrees C, the metabolic bioperiodicity appeared to be temperature compensated. Decimation studies indicate that the sampling interval of 5 to 15 min must not be further reduced. It is promising to incorporate the study of ultradian metabolic rhythms into a broad spectral approach, i.e., for a concomitant assessment of ultradian, circadian, and infradian rhythms.

Activity Cycles↗
PubMed1987

Temperature-compensated ultradian rhythms in lower eukaryotes: timers for cell cycles and circadian events?

During the cell cycles of synchronous cultures of several different yeasts and protozoa, oscillations in the rate of respiration and of total cellular protein content have been demonstrated. Energy supply (from mitochondrial oxidative phosphorylation) and energy demand (biosynthetic reactions, especially protein accumulation) are closely coupled oscillating systems. Phase correspondence between O2 consumption rates, intracellular ADP pool size, and total cellular protein indicates that it is energetic demand that determines mitochondrial activity (respiratory control in vivo). The dynamics of the coupled oscillators indicate that the rate-determining control circuit operates on a time scale expected of epigenetic reactions (transcription and translation). Thus the energy-yielding reactions are enslaved to the slower time constants of biosynthesis. Temperature compensation indicates a timing function, and a common phase reference point makes subcycles commensurate with the cell cycle. It is suggested that cell-cycle timing, by counting subcycles in growing cells, may become dominated by circadian control in slowly growing natural populations and that the same subcycles may be used for circadian timekeeping. The discontinuous nature of growth suggests extensive and rapid turnover of macromolecular cell components organized in alternating temporal compartments of biosynthetic and degradative processes, reminding us that "Structures are slow processes of long duration, functions are quick processes of short duration" (von Bertalanffy).

Activity Cycles↗
PubMed1986

Changes in proteinase activities and subcellular distribution during inactivation of alcohol oxidase in Candida boidinii.

Adaptation of methanol-grown Candida boidinii to ethanol utilization was accompanied by an increase in proteolytic activities, which behaved like known vacuolar enzymes. Degradation of alcohol oxidase protein was partially prevented by the serine proteinase inhibitor phenylmethanesulphonyl fluoride, but not by the carboxyl proteinase inhibitor pepstatin. Fractionation of cell-free extracts, by high-speed zonal centrifugation, of methanol-grown C. boidinii showed non-sedimentable and sedimentable proteolytic activities. Naturally occurring inhibitors of vacuolar proteinases were non-sedimentable. Fractionation of extracts prepared from methanol-grown cells which had been adapted to ethanol utilization for 5 h revealed significant changes in the sedimentability and distribution of proteolytic and acid phosphatase activities. These results suggest the possible involvement of a vacuolar process during alcohol oxidase degradation.

Alcohol Oxidoreductases↗
PubMed1986

Ferredoxin-dependent reduction of nitroimidazole derivatives in drug-resistant and susceptible strains of Trichomonas vaginalis.

The inhibitory effect of a range of nitroimidazole-derivatives on H2 production by metronidazole resistant (CDC-85) and susceptible (C1-NIH) Trichomonas vaginalis strains was investigated. The 2-, 4-, and 5-nitro-derivatives used had one-electron reduction potentials within the range -250 to -525 mV. Nitroimidazole concentrations giving 50% inhibition of H2 production (kiH2) for compounds with one-electron reduction potentials in the range -250 to -425 mV were found to be similar for both strains tested. Compounds with one-electron reduction potentials below -425 mV give 10-fold higher KiH2 values for the metronidazole resistant isolate. Both strains showed increased KiH2 for compounds with potentials lower than -500 mV. The addition of 2.1 kPa (0.02 atm) O2 to the gas phase resulted in increasing the kiH2 values for all the compounds tested, but had the greater effect on results obtained with the resistant isolate using nitroimidazoles in the range -425 to -490 mV. The results enable the proposal that the resistant isolate CDC-85 has a ferredoxin with altered redox properties or reduced intracellular levels.

Animals↗
PubMed1986

Formation of myeloperoxidase compound II during aerobic stimulation of rat neutrophils.

We have made simultaneous spectrophotometric and O2 measurements on suspensions of rat neutrophils during activation of the respiratory burst. Under aerobic conditions an absorption increase attributable to myeloperoxidase compound II was observed in parallel with the rapid phase of O2 uptake. Identification of this compound was confirmed by analysis of a spectrum obtained with purified myeloperoxidase and H2O2. Whereas a second addition of stimulus did not increase O2 uptake any further, a second phase of myeloperoxidase release and compound II formation was observed. These results suggest that in vivo myeloperoxidase reacts with H2O2 generated via the respiratory burst to form compound II under conditions in which the chlorination reaction would be the expected major pathway.

Aerobiosis↗
PubMed1986

Metronidazole-resistant clinical isolates of Trichomonas vaginalis have lowered oxygen affinities.

Oxygen affinities of metronidazole susceptible and resistant isolates of the parasitic flagellate protozoon Trichomonas vaginalis were determined by mass spectrometric methods. Apparent O2Km values for the respiration of non-proliferating cell suspensions were about 10-fold higher for metronidazole resistant strains than for the susceptible strains C1-NIH or NYH-286. Simultaneous monitoring of hydrogen evolution in the presence of increasing O2 tensions enabled apparent Ki values for H2 to be determined; and this function was independent of metronidazole susceptibility. Apparent O2 affinities of the hydrogenosomal and non-sedimentable fractions were determined for the strains CDC 85 (metronidazole resistant) and C1-NIH, which showed the deficiency in the O2 scavenging capacity by the resistant strain to be associated with the hydrogenosome-containing fraction.

Animals↗