Biomedical subjects

P A Guy

Publications and source records attributed to P A Guy.

9 recordsLinked to original sources

PubMed2001

Comparison of analytical techniques to quantify malondialdehyde in milk powders.

Several analytical methods were compared to quantify malondialdehyde (MDA) in milk powders. Modified thiobarbituric acid (TBA) methods, using either visible spectrophotometry (direct absorbance reading or after third derivative transformation of the spectrum) or HPLC, required derivatisation at elevated temperature, which appeared to catalyse artefactual MDA formation and thus overestimate the MDA content. In contrast to the TBA derivatisation method, the measurement of MDA as the dinitrophenylhydrazone derivative by HPLC or as the phenylhydrazone product by GC-MS with a deuterated internal standard resulted in lower estimates in the ranges of 2-17- and 3-30-fold, respectively; apparently due to the milder derivatisation conditions. The estimates of MDA determined by both HPLC-UV and GC-MS techniques result in lower values which are similar in magnitude even though the GC-MS technique is more sensitive.

Animals↗

PubMed2001

Using baseline respiratory function data to optimize cycle exercise test duration.

BACKGROUND: It is often difficult to select an appropriate workload increment for progressive cycle exercise tests in order to achieve optimal test duration (8-12 min). We hypothesize that baseline respiratory function can be systematically used to select appropriate workload increment to optimize test duration in patients referred to the clinical laboratory. METHODOLOGY: One hundred and eighty consecutive exercise tests (with increments of 15 W/min) were retrospectively assessed. Using regression analysis, an equation was generated that predicts the work rate increment that would provide exercise duration of 8-12 min. The validity of this equation was tested prospectively in 231 consecutive tests performed with the calculated workload increment rounded to the nearest 5 watts (W). RESULTS: The best regression equation was: workload increment (W/min)=1.94 x FEV1 (L) + 0.63 x TLCO (mmol/min per kPa) - 0.07 x age + 1.94 x gender (male=1, female=0) + 4.12 (r=0.85, P < 0.0001). Using this equation allowed selection of the most appropriate workload increment in 79% of tests and reduced the number of tests of non-optimal duration from 72% (for a fixed increment of 15 W/min) to 38%. CONCLUSIONS: Utilization of this regression equation allows standardization in the selection of workload increment, and reduces the number of cycle exercise tests of inadequate duration.

Algorithms↗

PubMed2000

Quantitative analysis of mutagenic heterocyclic aromatic amines in cooked meat using liquid chromatography-atmospheric pressure chemical ionisation tandem mass spectrometry.

Five mutagenic heterocyclic aromatic amines (HAAs) were quantified from meat extracts, and grilled and pan fried bacon samples using stable isotopically labeled internal standards. These compounds were isolated from the matrices by a tandem solid-phase extraction procedure, followed by separation on reversed-phase liquid chromatography (HPLC) and quantified by atmospheric pressure chemical ionization tandem mass spectrometry (APCIMS-MS). Tandem mass spectrometry (MS-MS) acquisition was done in selected reaction monitoring (SRM) mode to provide a high degree of sensitivity and selectivity for accurate quantification of HAAs. The detection and quantification limits of these HAAs approached 0.015 and 0.045 microg/kg (part-per-billion), respectively, with only 4 g of meat. The HAA levels ranged widely from 0.045 to 45.500 microg/kg, and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was the predominant HAA found in these samples. The amount of HAAs formed was highly dependent upon the type of meat and method of preparation. An intralaboratory comparison of the extraction procedure showed that estimates of these HAAs obtained by three different individuals at HAA levels below 2 microg/kg were within 5% with coefficients of variation below 19%, indicating the robustness of the analytical method. Moreover, because all of these HAAs from this class of molecules undergo facile cleavage at the N-methylimidazole moiety under collision-induced dissociation (CID) conditions, MS-MS analysis in the constant neutral loss mode of [M+H]+-15 enabled the identification of two other HAAs, 2-amino-3-methylimidazo[4,5-f]quinoxaline (IQx) and 2-amino-1,7,9-trimethylimidazo[4,5-g]quinoxaline (7,9-DiMeIgQx), which have rarely been reported in cooked meats.

Amines↗

PubMed2000

Flow-volume curve changes in patients with obstructive sleep apnoea and brief upper airway dysfunction.

OBJECTIVE: Patients with obstructive sleep apnoea (OSA) and those with brief upper airway dysfunction (BUAD) have been reported to have abnormalities of maximal flow-volume curves. This study was designed to assess the ability of flow-volume curves to predict the presence of OSA or BUAD. METHODOLOGY: Four maximal flow-volume manoeuvres performed by 33 OSA patients and 16 BUAD patients were compared with those of 36 normal subjects. Flow-volume indices, their variability, saw-toothing in the curve and an algorithm based on the flow ratios and shape of the curves were assessed. RESULTS: When the confounding factors, body mass index (BMI), age, gender and smoking status were taken into account, there was no significant difference in a variety of indices derived from the flow-volume curves between OSA and normal subjects. No BUAD patient had normal flow-volume curves as determined with the algorithm. After BMI, age, gender and smoking status were accounted for, decreased forced expiratory volume in 1 s (FEV1), and increased variability of peak expiratory flow (PEF)/peak inspiratory flow (PIF) and FEV1/PEF remained significantly associated with BUAD. CONCLUSIONS: These findings suggest that flow-volume curve indices have no value in predicting OSA. Some abnormalities are found in patients with BUAD; a normal flow-volume curve makes the diagnosis of BUAD unlikely.

Adult↗

PubMed1999

Quantitative analysis of clenbuterol in meat products using liquid chromatography-electrospray ionisation tandem mass spectrometry.

A method is presented that allows quantitation of clenbuterol in meat and liver products at the ng/kg level by liquid chromatography-electrospray ionisation tandem mass spectrometry (LC-ESIMS-MS) using a stable isotopically labeled internal standard. The practical procedure involves acid extraction followed by two solid-phase clean-up steps with C18 and strong cation-exchange (SCX) resins. The typical recovery of the analyte spiked at 0.4 microg/kg in meat and liver samples was at 63+/-7%. Mass spectral acquisition was done in multiple reaction monitoring (MRM) to provide a high degree of sensitivity, achieving a limit of detection and quantitation at 10 and 15 ng/kg, respectively. Two precursor ions at m/z 277 and 279, corresponding to the characteristic isotopic cluster of the two chlorine atoms of clenbuterol, were monitored by LC-ESIMS-MS to provide unambiguous identity of the analyte. Samples of meat and liver of various origins with either incurred residues or spiked with known amounts of clenbuterol were used to validate the method.

Adrenergic beta-Agonists↗

PubMed1999

Metal-ion binding and limited proteolysis of betabellin 15D, a designed beta-sandwich protein.

Betabellin 15D is a 64-residue, disulfide-bridged homodimer. When folded into a beta structure, the protein is predicted to have two clusters of three histidine residues, each cluster able to bind a divalent metal ion. When the protein was incubated with Cu2+, Zn2+, Co2+, or Mn2+, metal complexes of betabellin 15D were observed by electrospray-ionization mass spectrometry. The relative abundances of the ionic complexes suggested an order of affinities of Cu2+ > Zn2+ > Co2+ > Mn2+, consistent with solution-phase affinities for nitrogen- or sulfur-containing ligands. Limited proteolysis of betabellin 15D by immobilized pepsin, as measured by nanoelectrospray-ionization mass spectrometry, showed that the Phe12-Ser13 peptide bond of betabellin 15D was cleaved more slowly in the presence of Cu2+ than in its absence. Because Cu2+ has little or no effect on the catalytic rate of pepsin, the slower cleavage of the Phe12-Ser13 peptide bond may be due to its decreased accessibility caused by Cu(2+)-induced folding of betabellin 15D.

Amino Acid Sequence↗

PubMed1999

Nonsymbiotic haemoglobins in plants.

General aspects regarding the presence of nonsymbiotic haemoglobin in plants are presented with the emphasis on those related to its function. As it becomes apparent that the nonsymbiotic haemoglobins are widespread across the plant kingdom and that they represent a more primitive and evolutionary older form of the plant globin genes, the question of their function becomes more attractive. While the physiological functions of the symbiotic haemoglobins in plants are well understood, almost nothing is known about their nonsymbiotic predecessors. Therefore, the known and hypothetical functions of haemoglobins in various systems are described along with information concerning properties and the regulation of expression of the nonsymbiotic haemoglobins. Interestingly, a number of nonsymbiotic haemoglobins have been shown to be hypoxia-inducible. The spatial and temporal pattern of this induction in barley may suggest that it is an integral part of the plants response to limiting oxygen stress.

Biological Evolution↗

PubMed1998

Altering hemoglobin levels changes energy status in maize cells under hypoxia.

Nonsymbiotic hemoglobins are broadly present across the plant kingdom; however, the function of these proteins is unknown. Cultured maize cells have been transformed to constitutively express a barley hemoglobin gene in either the sense (HB+) or antisense (HB-) orientation. Hemoglobin protein in the transformed cell lines correspondingly was higher or lower than in wild-type cells under normal atmospheric conditions. Limiting oxygen availability, by placing the cells in a nitrogen atmosphere for 12 hr, had little effect on the energy status of cells constitutively expressing hemoglobin, but had a pronounced effect on both wild-type and HB- cells, where ATP levels declined by 27% and 61%, respectively. Total adenylates in these cells were approximately 35% lower than in HB+ cells. Energy charge was relatively unaffected by the treatment in HB+ and wild-type cells, but was reduced from 0.91 to 0.73 in HB- cells, suggesting that the latter were incapable of maintaining their energy status under the low oxygen regime. Treatment of the cells grown in an air atmosphere with antimycin A gave essentially the same results. It is suggested that nonsymbiotic hemoglobins act in plants to maintain the energy status of cells in low oxygen environments and that they accomplish this effect by promoting glycolytic flux through NADH oxidation, resulting in increased substrate-level phosphorylation. Hypoxic acclimation of plants is an example of this effect in nature. Nonsymbiotic hemoglobins are likely ancestors of an early form of hemoglobin that sequestered oxygen in low oxygen environments, providing a source of oxygen to oxidize NADH to provide ATP for cell growth and development.

Journal Article↗

PubMed1997

Analysis of macromolecules using nanoelectrospray ionization mass spectrometry and low-energy collision activation.

The mass spectrometric analysis of several proteins using nanoelectrospray (nanoES) with elastic collisions showed an improvement in the sensitivity over nanoES without collisional activation. We believe this effect is due to a better declusterization/ionization process. Optimization of the collision parameters can be easily performed during the long experiment time allowed using the nanoES source. Moreover, an apparent shift in the charge-state distribution is observed, with lower charged ions becoming relatively more abundant with increasing either target gas pressure or kinetic energy of the precursor ions. Higher charge-state ions might be expected to have higher collision frequencies and correspondingly lose more kinetic energy than lower charge-state ions.

Animals↗