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Biomedical subjects

J McMaster

Publications and source records attributed to J McMaster.

At least 19 recordsLinked to original sources
PubMed2002

Principles and problems underlying testing the effectiveness of blast protective footwear.

Anti-personnel landmines are a continuing threat to soldiers and civilians working overseas in post conflict situations. Several groups of governmental and commercial scientists are currently designing and/or testing footwear to protect the lower leg from the effects of close proximity blast. The general principles surrounding testing of protective footwear are examined together with an assessment of the known progress to date and the strengths and weaknesses of the designs produced.

Blast Injuries↗
PubMed2001

A phenoxyl radical complex of copper(II).

A new N,O-bidentate pro-ligand (HL), [ML2] (M = Cu, Zn) and [CuL2][BF4] have been synthesised; [CuL2].4DMF and [CuL2][BF4].2CH2Cl2 have been crystallographically and spectroscopically characterised; these data indicate that [CuL2]+ cations are constituted as [Cu2+(L.)(L-)]+ and involve the phenoxyl radical L..

Journal Article↗
PubMed2001

Electronic spectral studies of molybdenyl complexes. 2. MCD spectroscopy of [MoOS4]- centers.

Magnetic circular dichroism (MCD) and absorption spectroscopies have been used to probe the electronic structure of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] complexes (edt = ethane-1,2-dithiolate). The results of density functional calculations (DFT) on [MoO(SMe)4]- and [MoO(edt)2]- model complexes were used to provide a framework for the interpretation of the spectra. Our analysis shows that the lowest energy transitions in [MoVOS4] chromophores (S4 = sulfur donor ligand) result from S-->Mo charge transfer transitions from S valence orbitals that lie close to the ligand field manifold. The energies of these transitions are strongly dependent on the orientation of the S lone-pair orbitals with respect to the Mo atom that is determined by the geometry of the ligand backbone. Thus, the lowest energy transition in the MCD spectrum of [PPh4][MoO(p-SC6H4X)4] (X = H) occurs at 14,800 cm-1, while that in [PPh4][MoO(edt)2] occurs at 11,900 cm-1. The identification of three bands in the absorption spectrum of [PPh4][MoO(edt)2] arising from LMCT from S pseudo-sigma combinations to the singly occupied Mo 4d orbital in the xy plane suggests that there is considerable covalency in the ground-state electronic structures of [MoOS4] complexes. DFT calculations on [MoO(SMe)4]- reveal that the singly occupied HOMO is 53% Mo 4dxy and 35% S p for the equilibrium C4 geometry. For [MoO(edt)2]- the steric constraints imposed by the edt ligands result in the S pi orbitals being of similar energy to the Mo 4d manifold. Significant S pseudo-sigma and pi donation may also weaken the Mo identical to O bond in [MoOS4] centers, a requirement for facile active site regeneration in the catalytic cycle of the DMSO reductases. The strong dependence of the energies of the bands in the absorption and MCD spectra of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] on the ligand geometry suggests that the structural features of the active sites of the DMSO reductases may result in an electronic structure that is optimized for facile oxygen atom transfer.

Circular Dichroism↗
PubMed2001

Underappreciation of sleep disorders as a cause of motor vehicle crashes.

Despite an increased risk of motor vehicle crashes (MVC) in patients with obstructive sleep apnea (OSA), we hypothesized that OSA was not considered in drivers admitted to trauma centers after an injury-producing MVC. A retrospective study on drivers involved in MVCs admitted to a level 1 trauma center was performed, with crash cause determined and the frequency of sleep studies recorded. A questionnaire was also mailed to 240 trauma centers seeking information on evaluation of patients with unexplained causes for MVCs, including screening for OSA. There were 122 drivers of MVCs admitted to our hospital, 60/122 (49%) had unexplained crashes and no sleep studies were performed. There were 70 survey respondents (30% return rate), 35/70 (50%) centers routinely screened for syncope after unexplained MVC, however, no center screened for OSA. US trauma centers do not screen for sleep disorders despite the associated increased crash risk and the high prevalence of crashes that can not be explained by other causes. We believe this reflects a lack of awareness of sleep disorders by health care professionals caring for trauma victims and education is of utmost importance.

Accidents, Traffic↗
PubMed2000

An MCD spectroscopic study of the molybdenum active site in sulfite oxidase: insight into the role of coordinated cysteine.

Temperature-dependent magnetic circular dichroism (MCD) spectroscopy has been used for the first time to probe the electronic structure of the Mo active site in sulfite oxidase (SO). The enzyme was poised in the catalytically relevant [Mo(V):Fe(II)] state by anaerobic reduction of the enzyme with the natural substrate, sulfite, in the absence of the physiological oxidant cytochrome c. The [Mo(V):Fe(II)] state is of particular importance, as it is proposed to be a catalytic intermediate in the oxidative half reaction, where SO is reoxidized to the resting [Mo(VI):Fe(III)] state by two sequential one-electron transfers to cytochrome c. The MCD spectrum of the enzyme shows no charge transfer transitions below approximately 17000 cm(-1). This has been interpreted to result from (1) a severe reduction in ene-1,2-dithiolate sulfur in-plane and out-of-plane p orbital mixing, (2) a decrease in the dithiolate sulfur out-of-plane p-Mo d(xy) orbital overlap, and (3) an orthogonal orientation between the vertical cysteine sulfur p (perpendicular to the Mo-Scys sigma-bond) and Mo d(xy) orbitals. The spectroscopically determined cysteine sulfur p-Mo d(xy) bonding scheme in the [Mo(V):Fe(II)] state is consistent with the crystallographically determined O-Mo-Scys-C dihedral angle of approximately 90 degrees and precludes a covalent interaction between the vertical cysteine sulfur p orbital and Mo d(xy), effectively decoupling the cysteine from an effective through-bond electron transfer pathway. We have tentatively assigned a 22250 cm(-1) positive C-term feature in the MCD as the cysteine S(sigma)-->Mo d(xy) charge transfer that becomes allowed by a combination of configuration interaction and low-symmetry; however, the orbital overlap is anticipated to be quite small due to the near orthogonality of these orbitals. Therefore, we propose that the primary role of the coordinated cysteine is to decrease the effective nuclear charge on Mo by charge donation to the metal, statically poising the active site at more negative reduction potentials during electron transfer (ET) regeneration. Finally, the results of this study are consistent with the pyranopterin ene-1,2-dithiolate acting to couple the Mo site into efficient superexchange pathways for ET regeneration following oxygen atom transfer to the substrate.

Animals↗
PubMed2000

Effects of atorvastatin treatment on the oxidatively modified low density lipoprotein in hyperlipidemic patients.

Atorvastatin is an established HMG-CoA reductase inhibitor which effectively reduces the plasma low density lipoprotein (LDL)-cholesterol level in hyperlipidemic patients. The present study was designed to investigate whether atorvastatin treatment can modify the biochemical content of oxidized LDL in hyperlipidemic patients and the ability of oxidized LDL to impair the endothelium-dependent relaxation of blood vessels. With atorvastatin (10 mg/day) treatment for 4 weeks in 19 type IIa hyperlipidemic patients, total cholesterol level was lowered by 23%, LDL-cholesterol was lowered by 32% and triacylglycerol was lowered by 19% as compared with dietary therapy alone. High density lipoprotein levels increased by approximately 9%. The ability of oxidized LDL from hyperlipidemic patients after atorvastatin treatment to impair the endothelium-dependent relaxation was significantly reduced as compared with dietary intervention alone. Analysis of the biochemical contents of oxidized LDL from this group revealed that there was an 11% reduction in lysophosphatidylcholine (LPC) as compared with the group that received only dietary counseling. A decrease in the C16:0 moiety with a corresponding increase in the C18:0 moiety of LPC in the oxidized LDL was also observed in the atorvastatin treated group. We propose that the observed reduction and the change in composition of acyl groups in LPC in the oxidized LDL of the atorvastatin-treated group results from a combination of the continued dietary treatment as well as drug therapy. In view of an observation that both C16:0 and C18:0 LPC species are equally potent in the impairment of endothelium-dependent relaxation of the aortic rings, we feel that the reduced level of LPC in the oxidized LDL produced by atorvastatin treatment is partially responsible for the improvement in endothelium control of vascular tone.

Adult↗
PubMed2000

Two-dimensional gel analysis of haemolymph proteins from Plasmodium-melanizing and -non-melanizing strains of Anopheles gambiae.

Haemolymph polypeptides from Plasmodium-refractory and -susceptible mosquitoes were compared by one- and two-dimensional gel electrophoresis. The refractory strain of Anopheles gambiae kills malaria parasites by a humoral melanization mechanism whereas the parasites develop normally in susceptible mosquitoes. The two strains respond in a similar manner to carboxy-methyl-Sephadex beads that have been injected into the thoracic haemocoel, i.e. beads are strongly melanized in refractory but not susceptible mosquitoes. Protein profiles were compared between strains following cold shock (naïve control), saline injection and Sephadex bead injection. Using the susceptible naïve control as the standard, eight constitutively expressed polypeptides were specific to naïve susceptible mosquitoes while twelve other spots were reduced, enhanced or specific to refractory mosquitoes. Several of the strain-specific spots probably comprise related pairs (one in each strain) which vary only in isoelectric focusing point. Nine spots were induced by sham injection or by an injection of beads or saline, but none was reproducibly different between the strains. Amino acid sequence analysis of one of the refractory strain-specific spots identified it as AgSp14D1, an A. gambiae infection-responsive serine protease that is most similar to the Drosophila gene easter and Manduca prophenoloxidase activating enzyme. This gene maps to polytene chromosome division 14, which has been implicated in the melanization phenotype by quantitative trait loci mapping.

Animals↗
PubMed1999

Inhibition of endothelium-dependent vascular relaxation by lysophosphatidylcholine: impact of lysophosphatidylcholine on mechanisms involving endothelium-derived nitric oxide and endothelium derived hyperpolarizing factor.

Hyperlipidemia has been associated with an increase in the incidence of atherosclerosis. The oxidation of low density lipoprotein (LDL) plays an important role in the initiation and progression of atherosclerosis, one of its effects being the inhibition of endothelium dependent relaxation (EDR). The elevated level of lysophosphatidylcholine (LPC) in oxidatively modified LDL has been shown to be a biochemical factor responsible for the impairment of EDR in vascular ring preparations. Several endothelium-derived modulators are thought to control vascular responsiveness. The present work examined whether acetylcholine (ACh)-induced EDR in rat aorta (pre-contracted with phenylephrine, PE) involved both endothelium-derived nitric oxide (EDNO) and endothelium-dependent hyperpolarizing factor (EDHF) and whether LPC inhibited either of these selectively. Indomethacin (10(-5) M), had no significant effect on EDR, indicating that products of cyclooxygenase, including prostacyclin, are not involved. Treatment with either N(W)-nitro-L-arginine methyl ester (L-NAME, 6.8 microM) to inhibit the production of EDNO or with elevated K+ (15 mM), to block the hyperpolarizing effect of EDHF impaired EDR considerably (each of these shifting the inhibitory dose-response relationship to ACh by almost one log unit); in muscles treated with both of these agents EDR was completely inhibited. In each of L-NAME- and K-treated muscles, the addition of LPC (20 microM) further impaired EDR. LPC did not independently raise the tone of resting- or PE-contracted aorta. We conclude that the inhibition of EDR of rat aorta by LPC involves the actions of both EDNO and EDHF.

Acetylcholine↗
PubMed1998

The active sites of molybdenum- and tungsten-containing enzymes.

Protein X-ray crystallography has revealed the structures of the active sites of several molybdenum- and tungsten-containing enzymes that catalyze formal hydroxylation and oxygen atom transfer reactions. Each molybdenum (or tungsten) atom is coordinated by one (or two) ene-dithiolate groups of a novel pterin (molybdopterin), and the active sites are further differentiated from one another by the number of terminal oxo and/or sulfido groups and by coordinated amino acid residues. These active-site structures have no precedent in the coordination chemistry of molybdenum and tungsten.

Aldehyde Oxidoreductases↗
PubMed1997

The menopausal experiences of women in a developing country: "there is a time for everything: to be a teenager, a mother and a granny".

The menopausal experiences of 26 Zimbabwean women were explored, using a structured open-ended interview schedule. Interviews were carried out in Harare in 1995. An analysis of the consensual data indicated that these women do experience the menopause symptoms that have been claimed elsewhere to be universal. Their experiences of menopause were not, however, regarded generally as distressing and were interpreted as a normal stage in the life cycle. Particular cultural beliefs are described which impact on women's understandings and reactions to the menopause.

Adaptation, Psychological↗
PubMed1996

Lay beliefs about diarrhoeal diseases: their role in health education in a developing country.

This study examines the beliefs and understandings concerning diarrhoea among 2 groups of Zimbabwean women. Mothers with formal education are compared to those with less formal education. Differences and commonalities of beliefs are examined. The findings show that traditional explanations of an illness such as diarrhoea can inhibit health education campaigns against this disease which kills many children every year.

Adult↗
PubMed1995

Reactions to repeated STD infections: psychosocial aspects and gender issues in Zimbabwe.

This study explores psychosocial and gender issues related to multiple STD infections within the context of marriage. Thirty men and thirty women, currently married and attending a municipal clinic for treatment for repeated STD infections were interviewed. A semi-structured interview schedule was administered to explore themes of knowledge and beliefs about STDs, psychological reactions to repeated infections and power aspects of sexuality. It was found that men and women differed in how they interpreted and reacted to multiple STD infections. There was clear evidence of women's lack of power to negotiate safe sex within marriage and of the lack of social support networks for infected women.

Adolescent↗
PubMed1994

Perceptions of normal alcohol use held by Zimbabwean high school students.

Perceptions of the normal or no-problem use of alcohol held by male and female high school students were investigated. A sample of 127 male and 113 female high school students were asked to indicate their perceptions of the normal use of alcohol for their own sex and the opposite sex using a structured questionnaire. The students were also asked to select from a list of reasons those reasons they considered were non-problem reasons for using alcohol. Male and female students set levels of normal alcohol use for males that were significantly higher than those set for females. Over half the male sample and a large proportion of the female students selected inappropriate reasons for using alcohol. Appropriate health education programmes based on these findings are discussed; in particular the need to educate adolescents to recognize and deal with their inappropriate reasons for using alcohol.

Adolescent↗
PubMed1994

The practice of testicular self examination: a comparative study of British and Zimbabwean undergraduates.

The practice of testicular self examination was investigated amongst a sample of 170 British and 153 Zimbabwean male undergraduates using a questionnaire based on the health belief model. Knowledge of testicular cancer and of self examination was found to be low in both groups. Both groups, though, showed high general health awareness and a perception that the benefits of self examination would be great. It is recommended that knowledge of testicular cancer and the value of self examination should become part of general community based health programmes in both countries.

Adult↗