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Tom Preston

Publications and source records attributed to Tom Preston.

17 recordsLinked to original sources
PubMed2006

Identifying source correlation parameters for hydrocarbon wastes using compound-specific isotope analysis.

A preliminary evaluation of compound-specific isotope analysis (CSIA) as a novel, alternative method for identifying source correlation compounds in soils contaminated with residual heavy or weathered petroleum wastes is presented. Oil-contaminated soil microcosms were established using soil (sandy-loam, non-carbonaceous cley) amended with ballast-, crude- or No.6 fuel oil. Microcosms were periodically sampled over 256 days and delta(13)C values (which express the ratio of (13)C to (12)C) determined at each time point for five n-alkanes and the isoprenoid norpristane using gas chromatography-isotope ratio mass spectrometry (GC-IRMS). Although some temporal variation was observed, no significant temporal shifts in the delta(13)C values for the five n-alkanes were measured in all three oils. Isoprenoid isotope ratios (delta(13)C) appeared to be least affected by biotransformation, especially in the No.6 fuel oil. The research suggests that the delta(13)C of isoprenoids such as norpristane, may be of use as source correlation parameters.

Biodegradation, Environmental↗
PubMed2006

Advantages of deuterium-labelled mixed triacylglycerol in studies of intraluminal fat digestion.

The (13)C-mixed triacylglcerol (MTG, 1,3-distearyl, 2-[1-(13)C]octanoyl glycerol) breath test is a non-invasive measure of intraluminal fat digestion. Recovery of (13)C in breath CO(2) is incomplete (<50%) owing to sequestration of (13)C into organic molecules via the tricarboxylic acid (TCA) cycle. In addition lack of knowledge of CO(2) production rate (VCO(2)) during the test leads to errors in the calculated percentage dose recovered (PDR). (2)H sequestration into organic molecules is low ( approximately 4%) and is not influenced by factors that affect VCO(2) such as food intake or physical activity. After oxidation of (2)H-labelled macromolecules, the label appears in body water, which can be sampled non-invasively in urine or saliva. After an overnight fast, two healthy adults consumed [(2)H]MTG (1,3-distearyl, 2-[(2)H(15)]octanoyl glycerol) and [(13)C]MTG (1,3 distearyl, 2-[1-(13)C]octanoyl glycerol) simultaneously. Total body water (TBW) was measured by (18)O dilution and also estimated from height and weight. Urine and saliva were sampled at baseline and for 10 h after consumption of the test meal. The abundance of (2)HOH and H(2) (18)O in urine and saliva was measured by continuous-flow isotope-ratio mass spectrometry. Cumulative PDR of (2)H and (18)O was calculated from the plateau enrichment, which was reached by 6 h in both saliva and urine. Recovery of (2)H calculated using measured TBW was compared with that using an estimated value of TBW. Mean recovery of (2)H in saliva was 99.3% and in urine was 96.4%. Errors introduced by estimating TBW were <5%. [(2)H]MTG could provide a simpler, more robust, indirect test of intraluminal fat digestion compared with the (13)C-breath test. Further studies are required in pancreatic insufficient patients.

Administration, Oral↗
PubMed2006

A medical ethics assessment of the case of Terri Schiavo.

The social, legal, and political discussion about the decision to stop feeding and hydration for Terri Schiavo lacked a medical ethics assessment. The authors used the principles of medical indications, quality of life, patient preference, and contextual features as a guide to medical decision-making in this case. Their conclusions include the following: (a) the use of a feeding tube inserted directly in to the stomach constituted artificial treatment; (b) the treatment prolonged biological life but did not lead to a cure and did not restore health; (c) quality of life was absent for the patient, with no sensation and no motor or cognitive functioning; and (d) by preponderance of medical opinion, she would have chosen not to live in a persistent vegetative state. The authors find the withdrawal of treatment was permissible and correct. It was not a choice between living and dying, but a decision of when to allow dying consistent with the patient's choice.

Adult↗
PubMed2006

Acetate correction for postabsorption metabolism does not improve the [13C]mixed triacylglycerol breath test.

OBJECTIVE: The [C]mixed triacylglycerol (MTG) breath test is a noninvasive measure of fat digestion. After absorption and oxidation, C appears in breath CO2. Recovery is no more than 50% in healthy subjects because of sequestration of acetate in intermediary metabolism. The aims of this study were to investigate interindividual variation and postabsorptive metabolism of MTG using oral [1-C]acetate and to examine the use of correction factors to account for the "missing" label. PATIENTS AND METHODS: [C]mixed triacylglycerol and [1-C]acetate breath tests were performed on 8 healthy adults, 9 healthy children and 3 children with cystic fibrosis. Breath was sampled for 6 hours on each occasion. The enrichment of CO2 in breath was measured by isotope ratio mass spectrometry. Cumulative percentage dose recovered CO2 during the MTG test was corrected for label absorbed, but not completely oxidized using the cumulative percentage dose recovered during the acetate test. RESULTS: Mean recovery of C during the [C]MTG test with an acetate correction was close to 100% in healthy subjects: 103.1% (SD, 11.6%) in adults and 98.9% (SD, 30.3%) in children, but the wide variance indicated that some of the assumptions governing the use of acetate corrections with oral tracers may not be valid. CONCLUSION: The need to perform 2 tests, variation in physical activity between tests and differences in intermediary metabolism preclude the use of acetate correction factors when using [C]MTG to assess intraluminal fat digestion, especially in children.

Acetates↗
PubMed2006

Butyrate production from oligofructose fermentation by the human faecal flora: what is the contribution of extracellular acetate and lactate?

Butyrate is an important substrate for maintenance of colonic health and oligofructose fermentation by human faecal bacteria can increase butyrate production in vitro. However, oligofructose appears to be fermented by mainly acetate and lactate-producing bacteria rather than butyrate-producing bacteria. Isotope labelling studies using [U-(13)C(6)]glucose were used to show that (13)C(2) and (13)C(4) were the major labelled butyrate species produced from glucose fermentation, via [(13)C(2)]acetate-acetyl CoA as intermediate. Bacterial interconversion reactions were quantified and acetate conversion to butyrate and lactate conversion to acetate, propionate and butyrate were observed. Addition of oligofructose to faecal batch cultures significantly increased butyrate production. Of the newly synthesised butyrate from oligofructose fermentation, 80 % was derived from interconversion of extracellular acetate and lactate, with acetate being quantitatively more significant. Carbohydrates, such as oligofructose, have prebiotic properties. In addition, oligofructose selectively stimulates the bacterial conversion of acetate and lactate to butyrate. Carbohydrates with similar properties represent a refinement of the prebiotic definition, termed butyrogenic prebiotics, because of their additional functionality.

Acetates↗
PubMed2005

A simple prediction of total body water to aid quality control in isotope dilution studies in subjects 3-87 years of age.

The principal method of measuring total body water (TBW) is by isotope dilution. Also, the doubly labelled water method, which is the method of choice for measuring total energy expenditure (TEE) in free-living individuals, includes calculation of TBW as the dilution space of the tracer. TBW was measured in 261 subjects (135 males and 126 females), aged 3-87, including healthy children, children with HIV and adults with non-insulin dependent diabetes mellitus (type 2 diabetes), mild hypertension, pancreatic cancer and lung cancer, either in studies of body composition or TEE. A linear relationship was found between TBW and height in all subjects. When TBW is plotted against height cubed (Ht3, m3) the regression line can be forced through the origin. Considering only adults with 18.5>body mass index <29.9 and all children (n=220), this yielded TBW (l)=7.40 x Ht3, R2=0.95. This simple linear relationship between measured TBW and Ht3 compared favourably with other prediction methods, assuming TBW is a constant proportion (55%) of body weight and TBW predicted from height and weight (mean difference between measured and predicted TBW 0.55 l compared with -1.95 and -1.20 l, respectively). Absolute errors were greater at higher TBW, but use of a log10 transformation reduced this effect. This simple relationship of TBW with Ht3 is too crude to be used as a body composition predictor in individual subjects as it ignores, for instance, body shape. However, it can be used as a quality control tool. Here, use of a log10 transformation and residual plot can serve to identify outliers, which can be checked for gross errors in data input and if necessary samples are re-analysed.

Adolescent↗
PubMed2005

Helicobacter pylori colonization in infants in a peri-urban community in Karachi, Pakistan.

BACKGROUND: The prevalence and incidence of Helicobacter pylori in children in Pakistan is not known. OBJECTIVES: To measure the prevalence and age of acquisition of Helicobacter pylori infection/colonization in infants in a peri-urban community in Karachi, Pakistan. SETTING: Field based epidemiologic study in a peri-urban community in Karachi, Pakistan. METHODS: Infants aged 1 to 3 months were recruited from a birth cohort from the community. C-urea breath test (C-UBT) was performed on recruitment, and the test was repeated at 2, 3, 6, and 9 months of age. RESULTS: One hundred forty-eight infants were recruited and had C-UBT on 319 occasions over a period of 2 years. Two hundred thirty-one=(72%) tests were positive: 80% (49/61) infants at 1 month of age, 79% (33/42) at 2 month of age, 76% (92/121) at 3 month of age, 58% (37/64) at 6 months of age, and 67% (20/30) at 9 months of age. CONCLUSIONS: The study reveals an early colonization/infection of infants and a high prevalence of Helicobacter pylori in a peri-urban community in Karachi, Pakistan.

Age Distribution↗
PubMed2005

Meal-induced gastric relaxation and emptying in horses after ingestion of high-fat versus high-carbohydrate diets.

OBJECTIVE: To evaluate the effect of ingestion of a high-carbohydrate versus a high-fat meal on relaxation of the proximal portion of the stomach and subsequent gastric emptying in horses. ANIMALS: 6 healthy adult horses. PROCEDURE: The study consisted of 2 phases. In phase I, horses were offered a high-fat (8% fat) or a high-carbohydrate (3% fat) pelleted meal (0.5 g/kg) of identical volume, caloric density, and protein content. In phase II, meals consisted of a commercial sweet feed meal (0.5 g/kg) or this meal supplemented with corn oil (12.3% fat) or an isocaloric amount of glucose (2.9% fat). Proximal gastric tone was measured by variations in volume of an intragastric bag introduced through a gastric cannula and maintained with a constant internal pressure by an electronic barostat. Rate of gastric emptying was measured simultaneously with the 13C-octanoic acid breath test. Interaction between both techniques was studied in additional experiments. RESULTS: Meals with higher carbohydrate content induced a significantly more prolonged receptive relaxation of the proximal portion of the stomach than those with higher fat content, but the accommodation response was similar. Labeling the meals with the breath test marker influenced the accommodation response measured by the barostat. Gastric emptying rates were not significantly different between meals, although those high in carbohydrate initially emptied more slowly. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, in contrast to most species, dietary fat supplementation may not have a profound effect on gastric motility.

Animal Feed↗
PubMed2004

A streamlined approach to the analysis of volatile fatty acids and its application to the measurement of whole-body flux.

Volatile fatty acids (VFAs) are produced in the human colon by the bacterial breakdown of carbohydrates that escape digestion and absorption in the small intestine. They have important local and systemic effects on gastrointestinal and nutritional functions. Measuring their production is difficult because of inaccessibility of sampling sites and low circulating concentrations. Stable isotope tracer techniques are a way to measure VFA production but require measurement of isotope dilution in blood and other biological fluids. We have developed a streamlined and robust method to measure the concentration and enrichment of [(2)H]-labelled VFAs by gas chromatography/mass spectrometry (GC/MS) and [(13)C]-labelled VFAs by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Both types of analysis were carried out on the same samples allowing multiple tracer studies to be conducted. Good accuracy and repeatability were found for GC/MS analysis of [(2)H]-labelled VFAs. Careful handling of the background contribution, especially acetate, allowed quantitation of concentration and enrichment within the analysis. GC/C/IRMS analysis of [(13)C] VFAs was also achieved with good accuracy and repeatability. This methodology was used to determine whole-body acetate production in two subjects using multiple tracers ([(2)H(3)]- and [1-(13)C]acetate) and blood and urine sampling. Whole-body acetate flux was similar when measured either with [(2)H(3)]- or [1-(13)C]acetate, and when flux was determined from plasma or urine tracer enrichment. This new method will permit rapid and accurate measurement of VFA flux using [(2)H]- and/or [(13)C]-labelled VFAs as tracers. Measurements of the contribution of colonic VFA production to whole-body VFA flux are now possible.

Acetates↗
PubMed2004

Modulation of the liver export protein synthetic response to feeding by an n-3 fatty-acid-enriched nutritional supplement is associated with anabolism in cachectic cancer patients.

The acute-phase protein response is associated with accelerated weight loss and shortened survival in cancer. This may be due to hepatic protein synthesis increasing demand for amino acids. An n -3 fatty-acid-enriched nutritional supplement will moderate aspects of cachexia in cancer patients. The present study examined the effect of such a supplement on hepatic synthesis of albumin and fibrinogen. Albumin and fibrinogen synthesis were measured in the fed and fasting state in eight weight-losing patients with pancreatic cancer by an intravenous flooding dose technique. Tracer incorporation into proteins was measured by GC/MS. Patients were restudied after 3 weeks of oral supplement enriched with fish oil (providing 2510 kJ/day and 2 g of eicosapentaenoic acid/day). At baseline, all patients were losing weight (median, 2.4 kg/month). After 3 weeks of consumption of the fish-oil-enriched nutritional supplement, patients' weight stabilized (median change, +1 kg; P = 0.01). At baseline, albumin and fibrinogen synthesis rates were stimulated in the fed compared with the fasting state [14.2 compared with 11.3 g/day (29% rise; P = 0.01) and 4.5 compared with 3.3 g/day (38% rise; P = 0.01) respectively]. After 3 weeks of the supplement, this stimulation in the fed state was no longer observed for albumin and was reduced for fibrinogen [11.2 compared with 10.5 g/day (3% rise; P = 0.21) and 3.7 compared with 2.9 g/day (17% rise; P = 0.01) respectively]. After 3 weeks, the combined albumin plus fibrinogen synthetic rate tended to fall in the fasting state (14.7 compared with 12.3 g/day; P = 0.09) and was significantly reduced in the fed state (18.7 compared with 14.6 g/day; P = 0.01). Modulation of hepatic export protein synthesis with feeding may have contributed to the net whole-body anabolism observed with administration of the n -3 fatty-acid-enriched oral supplement.

Aged↗
PubMed2004

Is there an advantage in normalising the results of the Helicobacter pylori [13C]urea breath test for CO2 production rate in children?

The urea breath test (UBT) is a non-invasive diagnostic test to detect the presence of Helicobacter pylori in the stomach, and is the simplest way to confirm eradication after treatment. The test is based on the capacity of H. pylori to secrete the enzyme urease, which hydrolyses urea to ammonia and carbon dioxide. The aim of this study was to determine whether there is an advantage in expressing the results of UBTs in terms of urea hydrolysis rate (UHR), rather than breath 13C enrichment alone. Retrospective analysis of data collected between 1995 and 2002 from 260 patients undergoing UBTs was performed. The cut-offs for positive tests using breath 30-minute enrichment (E30), UHR calculated using VCO2 estimated from height and weight (H/WT) and VCO2 estimated from weight only were determined using two-graph receiver operator characteristic (TG-ROC) analysis. The cut-off points were 3.5/1000 or 38.7 ppm 13C excess, 7.04 micromol/h and 7.08 micromol/h, respectively. There was no advantage in expressing the results as UHR (theta0, Theta-zero, where sensitivity = specificity = 0.97 (UHR H/WT), 0.98 (UHR WT) and 1.00 (E30)) rather than breath 13CO2 enrichment alone. Differences in the extent of H. pylori colonisation and urease activity are more important than variation in VCO2 in determining breath 13CO2 enrichment in the UBT.

Adolescent↗
PubMed2004

Comparison of the carbon 13-labeled octanoic acid breath test and ultrasonography for assessment of gastric emptying of a semisolid meal in dogs.

OBJECTIVE: To compare the rate of gastric emptying of a semisolid meal by use of the carbon 13-labeled octanoic acid breath test (13C-OBT) and gastric emptying ultrasonography (GEU) in dogs. ANIMALS: 10 healthy dogs. PROCEDURE: Food was withheld from dogs for 12 hours before ingestion of a test meal (bread, egg, and skimmed milk) containing 13C-octanoic acid. The gastric antrum was visualized by use of a 6.5-MHz microconvex transducer, and the area of the ellipse defined by the craniocaudal and ventrodorsal diameters of the stomach was measured. Samples of expired air and antral images were obtained 30 minutes before ingestion of the test meal and then every 15 minutes for 4 hours and every 30 minutes for a further 2 hours. The half-dose recovery time with the 13C-OBT (t1/2[BT]) and the gastric half emtying time with GEU (t50%[GEU]) was calculated. RESULTS: Mean +/- SD values for the t1/2(BT) and t50%(GEU) were 3.44 +/- 0.48 hours and 1.89 +/- 0.78 hours, respectively. A significant correlation was detected between the t1/2(BT) and t50%(GEU), although there was a large (1.55 hours) mean difference between these indices. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that there was a correlation between the rate of solid-phase gastric emptying assessed by use of GEU and the 13C-OBT in dogs. Gastric emptying ultrasonography may be a useful, noninvasive method for assessment of the rate of solid-phase gastric emptying in dogs.

Animals↗
PubMed2003

Novel mechanism of nitrosative stress from dietary nitrate with relevance to gastro-oesophageal junction cancers.

High luminal concentrations of nitric oxide are generated at the human gastro-oesophaegal junction and within Barrett's oesophagus due to the reduction of salivary nitrite to nitric oxide by acidic gastric juice. Salivary nitrite is derived from the entero-salivary recirculation of dietary nitrate. Our aim was to determine whether nitric oxide generated within the lumen will exert nitrosative stress on the adjacent epithelium. A benchtop model was constructed reproducing the nitrite chemistry occurring within the lumen of the upper gastrointestinal tract where saliva encounters acidic gastric juice. It incorporated an epithelial compartment maintained at pH 7.4 and separated from the lumen by a hydrophobic barrier with the properties of the epithelial lipid cell membrane. The secondary amine morpholine was used to measure N-nitroso compound formation in both the lumen and epithelial compartment. Adding 100 micro M nitrite to the acidic (pH 1.5) luminal compartment depleted of ascorbic acid generated 6.2 +/- 2.0 micro M (mean +/- SE) N-nitrosomorpholine in that compartment and 2.2 +/- 0.1 micro M nitrosomorpholine in the epithelial compartment at 30 min. When 100 micro M nitrite was added to the acidic luminal compartment containing physiological concentrations of ascorbic acid, all the nitrite was immediately converted to nitric oxide and no N-nitrosomorpholine was formed within that compartment. However, the nitric oxide rapidly diffused from the luminal compartment into the epithelial compartment and there generated very high concentrations of N-nitrosomorpholine (137 +/- 5.6 micro M at 30 min). The addition of ascorbic acid or glutathione to the epithelial compartment could only reduce nitric oxide-induced nitrosation within that compartment by 40%. The nitrate-derived nitric oxide generated within the lumen where saliva encounters gastric acid is likely to exert substantial nitrosative stress on the adjacent epithelium. This may contribute to the high prevalence of mutagenesis at this anatomical site.

Ascorbic Acid↗
PubMed2002

Modeling 13C breath curves to determine site and extent of starch digestion and fermentation in infants.

BACKGROUND: The colon salvages energy from starch, especially when the capacity of the small intestine to digest it is limited. The aim of this study was to determine the site and relative extent of starch digestion and fermentation in infants. METHODS: Thirteen infants (10 male and 3 female infants), median age 11.8 months (range, 7.6-22.7 months), were fed a starchy breakfast containing 13C-labeled wheat flour after an overnight fast. Duplicate breath samples were obtained before breakfast and every 30 minutes for 12 hours. Breath 13CO2 enrichment was measured using isotope ratio mass spectrometry, and results were expressed as percentage dose recovered (PDR) for each 30 minutes. The PDR data were analyzed and mathematically modeled assuming either a constant estimate of CO2 production rate or adjusted for physical activity. RESULTS: Mean +/- SD cumulative 13C PDR (cPDR) at 12 hours was 21.3% +/- 8.4% for unadjusted data and 26.5% +/- 11.6% for adjusted data. A composite model of two curves fit significantly better than a single curve. Modeling allowed estimation of cPDRs of small intestine (17.5% +/- 6.5% and 22.7% +/- 9.3% for unadjusted and adjusted data, respectively) and colon (4.6% +/- 2.9% and 6.3% +/- 5.4%). CONCLUSIONS: Modeling of 13CO2 enrichment curves after ingestion of 13C-enriched wheat flour is an attractive means to estimate the contribution of the upper and lower gut to starch digestion and fermentation.

Breath Tests↗
PubMed2002

Stable isotope techniques in human nutrition research: concerted action is needed.

Use of stable isotopes in applied nutrition has been a developing field for over 60 years. The past 20 years has seen improvements in computer and mass-spectrometer technology that has opened up even greater possibilities in the understanding of human metabolism. While improvements in technology can bring great opportunities, it can also cause problems if there is no consensus among the stable isotope user-community on standardization of new techniques and methods. Users of stable isotopes have traditionally been split into two groups; those who work with heavy isotopes (e.g., 58Fe, 70Zn) and those who work with light isotopes (e.g., 2H218O). Standardization issues have been addressed by the light isotope users and awareness of this type of problem is starting to emerge within the heavy isotope community.

Bias↗