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G A Mills

Publications and source records attributed to G A Mills.

At least 19 recordsLinked to original sources
PubMed2001

Headspace solid-phase microextraction profiling of volatile compounds in urine: application to metabolic investigations.

Volatile compounds contribute substantially to the metabolic pool in man. Their analysis in body fluids is problematic. We investigated headspace solid-phase microextraction (HS-SPME) with Carboxen-polydimethylsiloxane fibres and gas chromatography-mass spectrometry for profiling urinary volatile components. These fibres were more sensitive for very volatile and sulfur compounds than three other phases tested. We detected a wide range of compounds in normal urine at acid and alkaline pH. Profiles presented for five individuals with metabolic disturbances demonstrate abnormal accumulation of sulfur compounds, fatty acids and plasticisers. HS-SPME can complement profiling of non-volatile compounds in metabolic investigations and could be a useful extension of the diagnostic repertoire.

Adult↗
PubMed2001

Urine 4-heptanone: a beta-oxidation product of 2-ethylhexanoic acid from plasticisers.

4-Heptanone is a common volatile constituent of human urine and is of unknown origin. We hypothesised that it arises from in vivo beta-oxidation of 2-ethylhexanoic acid (EHA) from plasticisers, similar to formation of 3-heptanone from valproic acid. We investigated urine from individuals with normal and increased plasticiser exposure. Using GC/MS, solvent-extracted organic acids were analysed as trimethylsilyl (TMS) derivatives and heptanone with headspace solid-phase microextraction. We identified 3-oxo-2-ethylhexanoic acid, the beta-oxidation product of EHA, as an enol in all samples. This is the first report of its TMS mass spectrum. We also found 2-ethyl-1,6-hexanedioic acid and 5-hydroxyEHA, omega- and omega-1-oxidation products of EHA, respectively, and 2-ethylhexanoylglucuronide, but only in trace amounts in some plasticiser samples. These compounds have not been reported in human urine, nor has the TMS mass spectrum of 5-hydroxyEHA. The median concentrations of 3-oxoethylhexanoic acid and total 4-heptanone of seven plasticiser samples were around 30--175-fold higher than normal samples. 4-Heptanone was barely detectable and 3-oxoethylhexanoic acid was not increased in an eighth plasticiser sample, from a baby with deficiency of 2-methylbranched-chain acyl-CoA dehydrogenase. beta-Oxidation is a major catabolic pathway of EHA in man, and might be involved in the metabolism of other branched-chain drugs and environmental pollutants.

Caproates↗
PubMed2000

Pyridoxal phosphate de-activation by pyrroline-5-carboxylic acid. Increased risk of vitamin B6 deficiency and seizures in hyperprolinemia type II.

We previously identified vitamin B6 deficiency in a child presenting with seizures whose primary diagnosis was the inherited disorder hyperprolinemia type II. This is an unrecognized association, which was not explained by diet or medication. We hypothesized that pyridoxal phosphate (vitamin B6 coenzyme) was de-activated by L-Delta(1)-pyrroline-5-carboxylic acid, the major intermediate that accumulates endogenously in hyperprolinemia type II. The proposed interaction has now been investigated in vitro with high resolution 1H nuclear magnetic resonance spectroscopy and mass spectrometry at a pH of 7.4 and temperature of 310 K. Three novel adducts were identified. These were the result of a Claisen condensation (or Knoevenagel type of reaction) of the activated C-4 carbon of the pyrroline ring with the aldehyde carbon of pyridoxal phosphate. The structures of the adducts were confirmed by a combination of high performance liquid chromatography, nuclear magnetic resonance, and mass spectrometry. This interaction has not been reported before. From preliminary observations, pyrroline-5-carboxylic acid also condenses with other aromatic and aliphatic aldehydes and ketones, and this may be a previously unsuspected generic addition reaction. Pyrroline-5-carboxylic acid is thus found to be a unique endogenous vitamin antagonist. Vitamin B6 de-activation may contribute to seizures in hyperprolinemia type II, which are so far unexplained, but they may be preventable with long term vitamin B6 supplementation.

Aldehydes↗
PubMed2000

Headspace solid-phase microextraction procedures for gas chromatographic analysis of biological fluids and materials.

Solid-phase microextraction (SPME) is a new solventless sample preparation technique that is finding wide usage. This review provides updated information on headspace SPME with gas chromatographic separation for the extraction and measurement of volatile and semivolatile analytes in biological fluids and materials. Firstly the background to the technique is given in terms of apparatus, fibres used, extraction conditions and derivatisation procedures. Then the different matrices, urine, blood, faeces, breast milk, hair, breath and saliva are considered separately. For each, methods appropriate for the analysis of drugs and metabolites, solvents and chemicals, anaesthetics, pesticides, organometallics and endogenous compounds are reviewed and the main experimental conditions outlined with specific examples. Then finally, the future potential of SPME for the analysis of biological samples in terms of the development of new devices and fibre chemistries and its coupling with high-performance liquid chromatography is discussed.

Body Fluids↗
PubMed2000

Development of a novel passive sampling system for the time-averaged measurement of a range of organic pollutants in aquatic environments.

A new sampling system has been developed for the measurement of time-averaged concentrations of organic micropollutants in aquatic environments. The system is based on the diffusion of targeted organic compounds through a rate-limiting membrane and the subsequent accumulation of these species in a bound, hydrophobic, solid-phase material. It provides a novel and robust solution to the problem of monitoring in situations where large temporal fluctuations in pollutant levels may occur. Accumulation rates are regulated by choice of diffusion-limiting membrane and bound solid-phase material and have been found to be dependent on the physico-chemical properties of individual target analytes. Two separate prototype systems are described: one suitable for the sampling of non-polar organic species with log octanol/water partition coefficient (log P) values greater than 4, the other for more polar species with log P values between 2 and 4. Both systems use the same solid-phase material (47 mm C18 Empore disk) as a receiving phase but are fitted with different rate-limiting membrane materials (polysulfone for the polar and polyethylene for the non-polar analytes). The two systems complement each other and together can be used for sampling a wider range of organic analytes than generally possible using current passive sampling techniques. Calibration data are presented for both devices. In each case, linear uptake kinetics were sustained, under constant conditions, for deployment periods of between 1 and 9 days. The effects of water temperature and turbulence on sampling rates have been quantitatively assessed. The performance of the system was further investigated by means of field exposures for one and two weeks in marine environments where calibrated samplers were used to determine the time-averaged concentrations of the polar biocides diuron and irgarol 1051. The quantitative results obtained using the passive sampler were compared with those obtained using spot sampling.

Environmental Monitoring↗
PubMed2000

Fits, pyridoxine, and hyperprolinaemia type II.

The rare inherited disorder hyperprolinaemia type II presents with fits in childhood, usually precipitated by infection. A diagnosis of hyperprolinaemia type II and vitamin B(6) deficiency was made in a well nourished child with fits. It is thought that pyridoxine deficiency was implicated in her fits and was the result of inactivation of the vitamin by the proline metabolite, pyrroline-5-carboxylate.

Female↗
PubMed1999

Headspace solid-phase microextraction with 1-pyrenyldiazomethane in-fibre derivatisation for analysis of faecal short-chain fatty acids.

Short chain fatty acids (SFCAs) are nutritionally important products of colonic bacteria. Their analysis in faeces is problematic. We report a headspace solid-phase microextraction procedure in which faecal SCFAs are derivatised on the fibre in-situ with 1-pyrenyldiazomethane. With this method sharp, well-resolved chromatographic peaks were obtained with no interferences. Inclusion of deuterated analogues enabled accurate quantification. Good linearity, recoveries and precision were achieved. Differences observed between the SCFA profiles of normal subjects and patients with cystic fibrosis indicate the potential of this new technique for clinical studies. 2-Methylbutyric acid was found in all faecal samples. Few have reported this before.

Case-Control Studies↗
PubMed1999

Quantitative determination of trimethylamine in urine by solid-phase microextraction and gas chromatography-mass spectrometry.

Trimethylaminuria (fish odour syndrome) is diagnosed from an increase in urinary excretion of trimethylamine with decreased trimethylamine oxide. We report a new quantitative stable isotope dilution gas chromatography-mass spectrometry procedure for the analysis of these metabolites using solid-phase microextraction (SPME). Both polydimethylsiloxane and mixed Carboxen-polydimethylsiloxane SPME fibres were found to be suitable for the headspace extraction of TMA. This new sampling technique could have wide application for the analysis of volatile and semi-volatile compounds by metabolic screening laboratories.

Gas Chromatography-Mass Spectrometry↗
PubMed1997

Neonatal encephalopathy with a pungent body odour.

A neonate had transient unexplained bleeding into the gut, severe encephalopathy, and an abnormal pungent body odour. An inherited metabolic defect was excluded. The malodour was due to methanethiol and hydrogen sulphide, identified in urine. These sulphur compounds may have contributed to encephalopathy. Colonic bacteria were the probable source.

Brain Diseases↗
PubMed1996

Effects of hypoxia on urinary organic acid and hypoxanthine excretion in fetal sheep.

Severe birth asphyxia leads to a transient organic aciduria and increased hypoxanthine excretion. To investigate its origin and timing, we analyzed urine from 12 late gestation fetal sheep in utero subjected to moderately severe isocapnic hypoxia for 1 h. In six fetuses the carotid sinus nerves were cut to determine whether reflex peripheral vasoconstriction contributed to the changes in excretion. After a control period of 1 h, maternal inspired oxygen was reduced for 1 h so that fetal arterial oxygen tension fell significantly from 2.86 +/- 0.12 kPa (mean +/- SEM) to 1.55 +/- 0.04 kPa. The ewes were returned to normoxia, and monitoring was continued for 1 h. Fetal heart rate, arterial blood pressure, and femoral arterial blood flow (intact fetuses only) were recorded, and arterial pH, blood gases, and lactate were measured. Urine collected via a bladder catheter was analyzed for organic acids and hypoxanthine with gas chromatography-mass spectrometry. In intact fetuses, hypoxia increased excretion of hypoxanthine and several organic acids, notably lactic acid and intermediates of valine catabolism. Changes were apparent by 15 min, significant by 45 min, and maximal after reoxygenation. In denervated fetuses, there were small, significant, increases in organic acids and hypoxanthine by 45 min of hypoxia, but there was no surge in excretion posthypoxia. Hypoxia caused a large, significant, fall in femoral arterial blood flow in intact fetuses. We conclude that the extent of the reflex peripheral vasoconstriction, particularly in skeletal muscle, determines the amount of organic acid and hypoxanthine excretion and may explain similar biochemical disturbances after birth asphyxia. Urinary lactic acid measurement has a potential value for grading birth asphyxia.

Animals↗
PubMed1993

Automated headspace gas chromatographic analysis of faecal short-chain fatty acids.

A method was developed and validated for analysis of faecal short-chain fatty acids using automated headspace gas chromatography. Quantification was by standard addition. Ghosting was minimized by lining the transfer tube from the headspace sampler to the gas chromatograph with deactivated fused silica and addition of formic acid to sample vials. Saturation of samples with lithium sulphate increased recoveries. The method was used to analyse small amounts of faecal matter collected from premature babies. Advantages of the technique are rapid, accurate, analysis of faecal specimens in batches, with minimum sample preparation.

Artifacts↗
PubMed1992

Identification of urinary acylcarnitines using gas chromatography-mass spectrometry: preliminary clinical applications.

Many disorders of organic acid metabolism are associated with abnormalities in the levels of acylcarnitines excreted in urine. Profiling of urinary acylcarnitines allows diagnosis and characterisation of many acidurias and acidemias, monitoring dietary treatment of such patients, and elucidation of the metabolism of some exogenous acidic compounds. Urine (ca. 0.5 ml) was subjected to a simple work-up by ion-exchange chromatography, and the isolated acylcarnitines were derivatized by cyclization in 35 min to give volatile lactones that are compatible with gas chromatography-mass spectrometry using electron or chemical ionization. The feasibility of this new and affordable procedure has been confirmed by identifying urinary acylcarnitines in cases of medium-chain acyl-coenzyme A dehydrogenase deficiency, propionic acidemia and isovaleric acidemia.

Acylation↗
PubMed1992

Effects of birth asphyxia on urinary organic acid excretion.

Using capillary gas chromatography-mass spectrometry, the effects of birth asphyxia on the urinary organic acid profile of term babies was investigated. Random urine samples were collected on days 1 and 8 from 19 babies with fetal distress, 19 with moderate birth asphyxia and 12 with severe asphyxia causing encephalopathy. Controls were 27 well neonates. Statistically significant abnormalities were found only for the severely asphyxiated group: increased concentrations of lactic, pyruvic, 3-hydroxybutyric, 4-hydroxyphenyllactic and 4-hydroxy-3-methoxymandelic acids, and excretion of four abnormal metabolites, 2-hydroxybutyric, 2-oxoisocaproic, 2-hydroxyisovaleric and 2-oxo-3-methylvaleric acids. Six other babies had increased lactic acid excretion, associated in four with transient 'jitterness' or hypotonia. Organic acid studies may help to grade the severity of perinatal asphyxia in the outcome or intervention studies.

3-Hydroxybutyric Acid↗
PubMed1990

Evaluation of a bladder advancement extension graft technique.

A bladder advancement extension technique was developed to provide a reliable method for creating an extra length of bladder in continuity, so that Boari flap and psoas hitch procedures, with or without the extension grafts, would reach sufficiently high routinely to permit these procedures to become the preferred practical options for accommodating significant proximal ureteric deficiencies or for replacing the whole of the ureter. In addition, an omentally supported bladder graft was established separately for use in a "retrieval" procedure should extension graft stenosis develop subsequently. Of 10 dogs studied for 6 months, 2 required "retrieval" pedicled island patch grafts for stenoses at extension graft/upper ureteric junctions. Healthy urothelium with muscle in the walls was seen in grafts resting on their supporting omental beds. At the time of sacrificing, none of the operated upper tracts was obstructed.

Animals↗