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J M Weber

Publications and source records attributed to J M Weber.

At least 37 records · Page 2Linked to original sources
PubMed2000

The human circadian pacemaker can see by the dawn's early light.

The authors' previous experiments have shown that dawn simulation at low light intensities can phase advance the circadian rhythm of melatonin in humans. The aim of this study was to compare the effect of repeated dawn signals on the phase position of circadian rhythms in healthy participants kept under controlled light conditions. Nine men participated in two 9-day laboratory sessions under an LD cycle 17.5:6.5 h, < 30:0 lux, receiving 6 consecutive daily dawn (average illuminance 155 lux) or control light (0.1 lux) signals from 0600 to 0730 h (crossover, random-order design). Two modified constant routine protocols before and after the light stimuli measured salivary melatonin (dim light melatonin onset DLMOn and offset DLMOff) and rectal temperature rhythms (midrange crossing time [MRCT]). Compared with initial values, participants significantly phase delayed after 6 days under control light conditions (at least -42 min DLMOn, -54 min DLMOff, -41 min MRCT) in spite of constant bedtimes. This delay was not observed with dawn signals (+10 min DLMOn, +2 min DLMOff, 0 min MRCT). Given that the endogenous circadian period of the human circadian pacemaker is slightly longer than 24 h, the findings suggest that a naturalistic dawn signal is sufficient to forestall this natural delay drift. Zeitgeber transduction and circadian system response are hypothesized to be tuned to the time-rate-of-change of naturalistic twilight signals.

Adult↗
PubMed2000

Energy metabolism of the Virginia opossum during fasting and exercise.

Rates of oxygen consumption and CO(2) production were measured in Virginia opossums (Didelphis virginiana) during fasting and prolonged exercise to quantify changes in total energy expenditure and oxidative fuel selection. We hypothesized that fasting would cause metabolic depression and a progressive shift towards lipid utilization to spare alternative substrates. It was also predicted that prolonged exercise would cause the same relative changes in fuel preference as fasting, but on a compressed time scale. The results show that hypometabolism is not used by the Virginia opossum to cope with food deprivation. However, a rapid exhaustion of limited carbohydrate reserves is prevented through a sixfold reduction in the percentage contribution of carbohydrates to total energy expenditure made possible by an increase in lipid utilization. No protein sparing is observed in this species. Prolonged low-intensity exercise elicits a potent mobilization of lipids that allows maximal running time to be extended by delaying the depletion of limited carbohydrate reserves. We conclude that fasting and prolonged low-intensity exercise cause similar changes in the relative use of lipids and carbohydrates, but on a different time scale, supporting the idea that endurance exercise is the metabolic equivalent of 'accelerated fasting'. The absence of metabolic depression and protein sparing during fasting shows that such physiological strategies have not been necessary for the rapid range expansion towards the North recently shown by this species.

Animals↗
PubMed1999

A 15-year experience with varicella infections in a pediatric burn unit.

Because of their well described global immunosuppression, varicella infection may be hazardous in burned children. It is therefore important to prevent cross-infections within pediatric burn units. We describe a 15-year experience with varicella in a pediatric burn unit, focusing on the morbidity associated with the infection and measures that have been effective in the prevention of cross-infection. We found that varicella infection in acutely burned children is associated with pneumonitis, but little wound related morbidity. Despite the deceptively long incubation period, prompt identification and isolation of index cases was associated with an extremely low incidence of cross-infection. Until widespread administration of varicella vaccine confers herd immunity, varicella remains a threat to hospitalized young children, highlighting the importance of a well planned and executed index case isolation strategy.

Boston↗
PubMed1999

Effect of high-altitude acclimation on NEFA turnover and lipid utilization during exercise in rats.

Relative exercise intensity (or %maximum O(2) consumption, VO(2 max)) controls fuel selection at sea level (SL) and after high-altitude acclimation (HA) in rats. In this context we used indirect calorimetry, [1-(14)C]palmitate infusions, and muscle triacylglycerol (TAG) measurements to determine 1) total lipid oxidation, 2) the relationship between circulatory nonesterified fatty acid (NEFA) flux and concentration, and 3) muscle TAG depletion after exercise in HA-acclimated rats. Aerobic capacity is decreased in trained rats after 10 wk of acclimation. Both SL and HA showed the same relative use of lipids at 60% [62 +/- 5% (HA) and 61 +/- 3% (SL) of O(2) consumption (VO(2))] and 80% [46 +/- 6% (HA) and 47 +/- 5% (SL) of VO(2)] of their respective VO(2 max). At 60% VO(2 max), plasma [NEFA] were higher in HA, but rate of appearance was essentially the same in both groups (at 30 min, 38 +/- 9 vs. 49 +/- 6 micromol. kg(-1). min(-1) in HA and SL, respectively). At this intensity SL showed no significant decrease in muscle TAG, but in HA it decreased by 64% in soleus and by 90% in red gastrocnemius. We conclude that 1) the relative contributions of total lipid are the same in SL and HA, contrary to differences in [NEFA], because the relationship between flux rate and [NEFA] is modified after acclimation, and 2) muscle TAG may play a more important role at HA.

Acclimatization↗
PubMed1999

Photodynamic therapy: tumor targeting with adenoviral proteins.

A brief summary of the mechanisms involved in photodynamic therapy (PDT) and the role of delivery vehicles for photosensitizer targeting is addressed. Phthalocyanines (Pc) have been coupled to adenovirus type 2 capsid proteins including the hexon, the penton base and the fiber to enhance their target selectivity. Adenovirus penton base proteins contain the arginine-glycine-aspartic acid peptidic sequence (RGD) motif known to bind with great affinity and high specificity to integrin receptors, expressed by several types of cancer. Tetrasulfonated aluminum phthalocyanine (AlPcS4) was covalently coupled to the various capsid proteins via one or two caproic acid spacer chains (A1 or A2) in 7:1 up to 66:1 molar ratios. The capacity of the bioconjugates for singlet oxygen production, as measured by an L-tryptophan oxidation assay, was strongly reduced, likely reflecting scavenging by the carrier. Cell adsorption and in vitro photocytotoxicity assays were carried out using the A549 and HEp2 human cell lines expressing integrin receptors, and one murine, the EMT-6 cell line, which lacks receptors for the RGD sequence. The AlPcS4A2-protein complexes induced greater cytotoxicity as compared to the analogous AlPcS4A1 preparations. The penton base-AlPcS4A2 derivative was the more phototoxic for all cell lines tested. Tumor response studies using Balb/c mice with EMT-6 tumor implants demonstrated that the free AlPcS4A2 induced complete tumor regression at a dose of 1 mumol/kg and 400 J/cm2, which is comparable to the activity of the known AlPcS2adj. A mixture of adenovirus type 2 soluble proteins covalently labeled with AlPcS4A2 required 0.5 mumol/kg to induce the same response with the same light dose, suggesting that the high affinity RGD/receptor complex is able to target Pc for PDT.

Animals↗
PubMed1998

Carbohydrate utilization during exercise after high-altitude acclimation: a new perspective.

At high altitude (HA), carbohydrate (CHO) is thought to be the preferred fuel because of its higher yield of ATP per mole of O2. We used indirect calorimetry and D-[6-3H]glucose infusions to determine total CHO and circulatory glucose utilization during exercise in HA-acclimated and sea level (SL) rats. We hypothesized that the percent contribution of CHO to total metabolism (VO2) is determined by exercise intensity relative to an aerobic maximum (% VO2max). HA rats run under hypoxia (FIO2 = 0.12) showed a decrease in VO2max compared with SL (67.55 +/- 1.26 vs. 89.30 +/- 1.23 ml kg-1 min-1). When exercised at 60% of their respective VO2max, both groups showed the same relative use of CHO (38 +/- 3% and 38 +/- 5% of VO2, at the beginning of exercise, in HA and SL, respectively). In both HA and SL, circulatory glucose accounted for approximately 20% of VO2, the balance was provided by muscle glycogen (approximately 18% of VO2). After 20 min at a higher intensity of 80% VO2max, 54 +/- 5% (HA) and 59 +/- 4% (SL) of VO2 was accounted for by CHO. We conclude the following: (i) the relative contributions of total CHO, circulatory glucose, and muscle glycogen do not increase after HA acclimation because the O2-saving advantage of CHO is outweighed by limited CHO stores; and (ii) relative exercise intensity is the major determinant of metabolic fuel selection at HA, as well as at SL.

Acclimatization↗
PubMed1998

Adenovirus endopeptidase and papain are inhibited by the same agents.

Adenoviruses encode a cysteine protease (AVP) which carries out highly specific cleavages on at least seven viral proteins and two cellular proteins. Virus infectivity is dependent on this function. The three-dimensional positions of the amino acids involved in catalysis display a striking similarity to those of papain, suggesting a similar catalytic mechanism. This similarity has prompted us to compare the effect of papain inhibitors on the two enzymes. AVP and papain activity was tested on a fluorescent peptide substrate as well as on metabolically labeled adenovirus (Ad2) precursor proteins. Hep2 cells infected with Ad2 were exposed to inhibitors and assayed for, (a) infectious virus, (b) in situ Ad2 protease activity, (c) physical particle production and their polypeptide composition. We found that in both substrate systems AVP was sensitive to the papain inhibitors benzamidoacetonitrile, acetamidoacetonitrile and N-methoxyphenylalanine glycylnitrile, and that the degree of sensitivity was influenced by the substrate. Unlike papain, AVP was relatively insensitive to E64. In ex vivo tests, Hep2 cells infected with Ad2 were exposed to inhibitors and assayed for, (a) infectious virus, (b) in situ Ad2 protease activity, (c) physical particle production and their polypeptide composition. A 4-fold reduction in virus titer was obtained when the inhibitors were added between 17 and 25 h after infection. Processing of precursor proteins was also inhibited yet the production of physical particles was only reduced 2-fold. These experiments show that papain inhibitors are also capable of inhibiting the adenovirus protease both in vitro and ex vivo, thus forging a possible link between structural similarity and functionality.

Acetonitriles↗
PubMed1997

Isolation of isoflavones from soy-based fermentations of the erythromycin-producing bacterium Saccharopolyspora erythraea.

A search for an abundant and economical source of isoflavones, particularly genistein, led to the discovery that the erythromycin-producing organism Saccharopolyspora erythraea also produces this promising new cancer-prevention agent. Erythromycin fermentation is a large-scale, soybean-based process used world-wide for the commercial production of this medically important antibiotic. Results from this study indicate that genistin (the glucoside form of genistein), which is added to the fermentation in the soybean media, was converted to genistein through the action of a beta-glucosidase produced by the organism. Genistein was co-extracted with erythromycin from the fermentation broth, then separated from erythromycin during the second step of the purification process for the production of erythromycin.

Chromatography, High Pressure Liquid↗
PubMed1997

Femoral venous access is safe in burned children: an analysis of 224 catheters.

OBJECTIVE: To document the incidence of septic and mechanical complications associated with femoral venous catheters in a subgroup of patients thought to be at particularly high risk of both: young children with large burns. DESIGN: An analysis of data collected prospectively on all femoral venous catheters placed during a 4-year period at a regional pediatric burn facility. RESULTS: There were 224 femoral catheters placed in 86 children with an average age of 5.3 +/- 5.1 years and an average burn size of 38% +/- 23%. Catheters were left in place for a mean duration of 5.7 days. Catheter-related sepsis occurred with 4.9% of the catheters, and mechanical complications occurred in 3.5% of the patients. There was no statistically significant association between the risk of catheter sepsis and the placement of catheters through burned versus unburned skin. Similarly, the risk of sepsis was equivalent between lines placed over a guide wire and those placed of a new site. CONCLUSION: Femoral venous catheters are safe in burned children and are associated with a low incidence of infectious and mechanical complications.

Burns↗
PubMed1997

Nosocomial infections in pediatric patients with burns.

BACKGROUND: Nosocomial infections (NI) are believed to occur more commonly in patients with burns than in patients undergoing surgery, but benchmark rates have not been well described, and widely accepted definitions of NI in patients with burns are not available. We present a clinically useful set of definitions for NI for the pediatric burn population and provide benchmark infection rates for NI at selected sites. METHODS: Centers for Disease Control and Prevention definitions were modified to more accurately describe nosocomial burn infection and secondary bloodstream infections (BSI) in the burn population. A surveillance system was developed and included calculation of NI rates by 1000 patient or device days, stratified into one of three risk groups (< 30% burn injury, 30% to 60% burn injury, and > 60% burn injury). All patients with acute burns admitted from January 1990 to December 1991 were included, and NI rates were calculated for burn infection, primary and secondary BSI, ventilator-related pneumonia and urinary catheter-related urinary tract infection (UTI). RESULTS: Overall 12.5% of patients with central venous catheters had development of primary BSI for a rate of 4.9/1000 central venous catheter-days. Incidence of secondary BSI was 5.8% of patients for a rate of 5.3/1000 patient-days. Incidence of burn infection was 10.1% of patients for a rate of 5.6/1000 patient-days. Incidence of ventilator-related pneumonia was 17.5% of patients for a rate of 11.4/1000 ventilator-days. Incidence of urinary catheter-related UTI was 17.9% of patients, for a rate of 13.2/1000 urinary catheter-days. When rates were stratified by risk groups, incidence increased with increasing burn size for secondary BSI (p < or = 0.0001) and urinary catheter-related UTI (p = 0.08), although rates based on number of patient-days or device-days more accurately reflected risk of infection over time. CONCLUSIONS: Infection remains a cause of significant morbidity and death for patients with burns. The definitions and benchmark rates reported here may be useful in evaluation of NI surveillance strategies and calculation of infection rates, which could then be used to evaluate current treatment modalities and improve outcomes for the burn population.

Burns↗
PubMed1997

Glucose kinetics of the Virginia opossum: possible implications for predicting glucose turnover in mammals.

Primed continuous infusions of 6-3H-glucose, respirometry and measurements of nitrogen excretion were carried out in adult Virginia opossums (Didelphis virginiana). Our goals were to determine resting glucose turnover rate, to establish the relative importance of this oxidative fuel in the energy budget of this species, to assess whether metabolic rate is a better predictor of glucose turnover rate than body mass and to demonstrate that glucose kinetics can be measured in the opossum for future use of this animal model in studies of mammalian glucoregulation. Results show that the resting glucose turnover rate of opossums averages 17.5 +/- 0.9 mumol/kg.min (n = 9), that 31% of total glucose flux is oxidized and that glucose oxidation represents 9% of their metabolic rate. An allometric equation predicting glucose turnover rate from body mass for placental mammals overestimates the measured turnover rate of this marsupial by 30%, suggesting that turnover rate is better predicted from metabolic rate than from body mass. Finally, this study demonstrates that the Virginia opossum is a convenient model to study glucose metabolism in vivo, and we propose that the very rapid aging characteristics of this species should be exploited to investigate the effects of aging on glucose homeostasis.

Aging↗
PubMed1997

Amantadine susceptibility in influenza A virus isolates: determination methods and lack of resistance in a Canadian sample, 1991-94.

BACKGROUND: Influenza A infections are an important cause of morbidity and mortality in the elderly and patients affected by chronic diseases or immunodeficiencies. Treatment and prevention of infection in hospitals and nursing homes often involve the use of amantadine, but resistant viruses may arise. OBJECTIVES: To assess the effectiveness of specific and sensitive methods for rapid screening and sequence confirmation of amantadine resistance, and the occurrence of amantadine resistance in recent influenza A virus isolates in Canada. STUDY DESIGN: A chicken antiserum-based enzyme linked immunoassay (ELISA) was developed and used to screen fifty influenza A isolates for amantadine resistance. Drug sensitivity was expressed as a percentage of virus growth inhibition. The efficiency of the assay was compared to that of a monoclonal antibody (mab)-based ELISA using influenza A strains from 1968 to 1994. Specific PCR primers, generated to amplify the M2 gene region where amantadine resistance mutations occur, were tested over a wide range of strains. Direct sequencing of the PCR fragments was performed to confirm the presence of resistance mutations. RESULTS: The polyclonal antiserum-based ELISA detected antigens from all recent H1N1 strains and H3N2 strains tested at an inoculum dilution ten-fold lower than the mab-based ELISA. Primers for the detection of amantadine resistance mutations consistently amplified a wide range of strains. The direct sequencing of the RT-PCR amplicons generated, detected resistance mutations in reassortant and control viruses, the only strains found resistant by ELISA. All influenza A isolates (H3N2, H1N1) tested, except resistant controls and two reassortant viruses, were amantadine-sensitive as indicated by greater than 50% virus growth inhibition. CONCLUSIONS: Influenza A virus susceptibility to amantadine could be detected by using an antiserum-based ELISA, offering a simple and more sensitive alternative to the mab-based assay. Coupled with direct sequencing of the M2 gene, it provides a reliable way to detect and confirm resistance in influenza isolates. However, no resistant clinical isolates were detected in the sample.

Amantadine↗
PubMed1997

Evolution of the hemagglutinin gene of influenza B virus was driven by both positive and negative selection pressures.

Nucleotide sequences of the hemagglutinin (HA) gene of twelve influenza B strains and their deduced amino acid sequences were extracted from the GenBank and compared to those of early isolates. Separate analyses of nonsynonymous and synonymous substitutions for the HA1 and HA2 regions individually indicate that the percentage of nonsynonymous substitutions in the HA1 ranges from 44.4-56.0% but in the HA2 from 0.0-6.5%. The results suggest that positive selection as well as negative selection played a role in the evolution of the influenza B HA gene with the former acting on the HA1 and the latter on the HA2.

Amino Acid Sequence↗
PubMed1997

Effects of hypoxia and low temperature on substrate fluxes in fish: plasma metabolite concentrations are misleading.

Oxygen levels and temperature can fluctuate rapidly in aquatic environments. Ever though the effects of environmental stresses on fish metabolism have been studied extensively, information on fue kinetics is extremely limited because it relies almost exclusively on changes in substrate concentrations. The turnover rate of nonesterified fatty acids (NEFA) has never been measured in fish. Therefore, our goal was to quantify glucose and NEFA fluxes in rainbow trout acutely exposed to severe hypoxia (25% O2 saturation) or low temperature (6 degrees C for fish acclimated to 15 degrees C) by performing continuous infusions of 6-[3H]glucose and 1-[14C]palmitate in vivo. Results show that hypoxia causes a 53% decrease in NEFA turnover rate, together with a transient increase in hepatic glucose production, whereas a rapid drop in temperature induces equivalent declines in glucose, NEFA, and oxygen fluxes [temperature coefficient approximately equal to 2]. More importantly, kinetic changes in glucose and NEFA fluxes are not accompanied by interpretable changes in the plasma concentrations of these metabolites. Thus using concentration changes to draw conclusions about fluxes must be avoided.

Acclimatization↗
PubMed1996

Cleavage efficiency by adenovirus protease is site-dependent.

The adenovirus protease cleaves consensus sequences (M/I/L)XGX-G and (M/I/L)XGG-X. Using purified recombinant protease, we showed that a peptide bearing the GX-G site was hydrolyzed more rapidly than a peptide bearing the GG-X site. The GX-G site was also preferentially cleaved on viral protein pVI which bears both sites of cleavage. Evidence is presented that suggests a biological role for this differential cleavage efficiency.

Adenoviruses, Human↗
PubMed1996

New stimulation ligand of the adenovirus 2 protease.

The catalytic activity of the adenovirus cysteine peptidase is increased by a specific 11-amino-acid peptide adduct (GVQSLKRRRCF, referred to as pVIc). To identify additional peptides which might bind and alter the activity of the protease, a cysteine-constrained random peptide phage library was screened. Of 29 different phages which were isolated, 7 contained the consensus sequence VEGGS. Despite a superficial similarity to the substrate cleavage site of the protease, the peptide was not digested by the enzyme. VEGGS and pVIc altered protease activity similarly without sharing sequence similarity. To similar degrees, pVIc and VEGGS (a) stimulated the activity of the recombinant protease, (b) had no effect on viral protease, (c) increased the fluorescence emission of tryptophan residues in the protease, suggesting a conformational change, and (d) inhibited wt virus infection, but rescued ts1 infection at the nonpermissive temperature. The experiments also suggest that once the protease has been stimulated by one peptide, the other peptide has no further activity on the recombinant adenovirus cysteine protease, suggesting that the two peptides bring about the same change on the protease via different binding sites.

Adenoviruses, Human↗
PubMed1996

Mutagenesis of conserved residues of the adenovirus protease.

Based on the alignment of 12 adenovirus protease sequences, we have identified eleven conserved residues for mutagenesis. Eight of these, E5, D26, N44, E71, D77, D102, N144, and N170, are potential candidates for the third residue of the active site triad. N44, E71, N144, and N170 proved to be essential for enzyme activity. Glutamic acid 71 was proposed for the active site. Mutation of the three conserved cysteines suggested that C122 is the active nucleophile, C104 is the target for activation by peptide pVIc, and C126 is dispensable. Rescue of enzyme activity of the C104 G mutant by pVIc suggested that disulfide bond formation between the peptide and the protease may not be absolutely essential for stimulation of enzyme activity.

Adenoviruses, Human↗