Plasma homocyst(e)ine levels and folic acid supplementation.
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Erythrocytes↗
Biomedical subjects
J C Deutsch
Publications and source records attributed to J C Deutsch.
Spontaneous hydrolysis and dehydration of dehydroascorbic acid in aqueous solution.
The interaction of water with dehydroascorbic acid was examined by incubating dehydroascorbic acid and ascorbic acid in 18O-labeled water for various amounts of time and then oxidizing the products with hydrogen peroxide or reducing the products with mercaptoethanol, with analysis by gas chromatography mass spectrometry. Based on mass changes, dehydroascorbic acid readily exchanged three oxygen atoms with H218O. When mercaptoethanol was used to reduce dehydroascorbic acid (which had been incubated in H218O) to ascorbic acid, the newly formed ascorbic acid also contained three labeled oxygen atoms. However, ascorbic acid incubated in H218O for the same amount of time under identical conditions exchanged only two labeled oxygen atoms. Electron impact mass spectrometry of derivatized ascorbic acid created a decarboxylation product which had only two labeled oxygen atoms, regardless if 3-oxygen-labeled or 2-oxygen-labeled ascorbic acid was the parent compound, isolating the extra oxygen addition to carbon 1. These data suggest that dehydroascorbic acid spontaneously hydrolyzes and dehydrates in aqueous solution and that the hydrolytic-hydroxyl oxygen is accepted by carbon 1. Ascorbic acid, on the other hand, does not show this same tendency to hydrolyze.
Ascorbic Acid↗
Ascorbic acid oxidation by hydrogen peroxide.
The oxidative degradation of ascorbic acid by hydrogen peroxide was examined to determine routes of degradation and identify the initial products which form when ascorbic acid is oxidized. When reacted with hydrogen peroxide, solutions of ascorbic acid and dehydroascorbic acid are both ultimately oxidized to the same species, having a mass spectrum consistent with threonic acid. When the intermediate steps in the oxidation of ascorbic acid are examined in detail, ascorbic acid, dehydroascorbic acid, and solutions containing hydrolyzed dehydroascorbic acid are all oxidized through a six-carbon compound previously proposed to be tetrahydroxydiketohexanoic acid. Both dehydroascorbic acid and hydrolyzed dehydroascorbic acid (diketogulonic acid) are more susceptible to hydrogen peroxide oxidation than ascorbic acid. Based on mass spectral analysis, diketogulonic acid serves as an oxygen sink, implying that it may be a better reducing agent for toxic oxygen species than ascorbic acid. These data indicate that oxidation of ascorbic acid by hydrogen peroxide primarily proceeds through three major six-carbon intermediates, each with distinctive redox properties. The stable metabolite diketogulonic may be a critical antioxidant in ascorbic-acid-containing systems.
2,3-Diketogulonic Acid↗
Prostate cancer masquerading as a large rectal cancer: diagnosis by endoscopic ultrasound.
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Adenocarcinoma↗
Normal digestive physiology and the evaluation of digestive function.
Normal digestion is a complex and coordinated process that breaks food into constitutive molecules, some of which are absorbed and others passed through the body as waste. Many of the conditions associated with wasting syndromes alter normal digestive function and can lead to or exacerbate malnutrition. Digestive function can be defined by applying the principles of normal physiology. Our laboratory has developed a relatively comprehensive stable isotope method to assess function, which shows promise as a screening tool in evaluating patients with wasting syndromes. This and other tests of digestive function can be used to define the abnormalities associated with wasting and to direct or optimize antiwasting therapy.
Diagnostic Techniques, Digestive System↗
Ascorbic acid and dehydroascorbic acid interconversion without net oxidation or reduction.
The interconversion of ascorbic acid and dehydroascorbic acid was examined in aqueous solution using unlabeled dehydroascorbic acid and nonlabile, stable isotope-labeled ascorbic acid by gas chromatographic/mass spectrometric analysis. Although the formation of unlabeled ascorbic acid from unlabeled dehydroascorbic acid or labeled dehydroascorbic acid from labeled ascorbic acid did not occur to any significant extent when either solutions of unlabeled dehydroascorbic acid or labeled ascorbic acid were incubated alone, significant amounts of both labeled dehydroascorbic acid and unlabeled ascorbic acid formed when unlabeled dehydroascorbic acid was incubated with labeled ascorbic acid at acid pH. At alkaline pH, interconversion did not occur to any appreciable extent. Likewise, interconversion did not appear to occur in plasma at physiologic concentrations of ascorbic acid, but did occur with pharmacologic concentrations. These data show that ascorbic acid and dehydroascorbic acid interconvert in acidic solution, suggesting the reducing hydrogen atoms are delocalized when ascorbic acid is paired with dehydroascorbic acid under these circumstances. Alkaline pH and plasma inhibit the interconversion.
Ascorbic Acid↗
Determination of p-hydroxyphenylpyruvate, p-hydroxyphenyllactate and tyrosine in normal human plasma by gas chromatography-mass spectrometry isotope-dilution assay.
The synthesis and purification of [13C2]p-hydroxyphenyllactic acid from [13C2]p-hydroxyphenylpyruvic acid, the characterization of tert.-butyldimethylsilyl-derivatized tyrosine, p-hydroxyphenylpyruvic acid and p-hydroxyphenyllactic acid, and an isotope-dilution assay for these substances in normal human plasma using gas chromatography-mass spectrometry (GC-MS) are described. Using this method plasma p-hydroxyphenylpyruvate, p-hydroxyphenyllactate and tyrosine levels of 68 +/- 42 ng/ml, 118 +/- 45 ng/ml and 16.6 +/- 6.3 micrograms/ml, respectively, were found in 9 normal adults. Isotope-dilution assays are sensitive enough to determine tyrosine, p-hydroxyphenylpyruvate and p-hydroxyphenyllactate content in normal subjects, and may be useful for studying disorders of tyrosine metabolism, including inborn errors of metabolism, liver disease and ascorbic acid deficiencies.
Carbon Isotopes↗
Gas chromatographic/mass spectrometric measurement of ascorbic acid and analysis of ascorbic acid degradation in solution.
L-Ascorbic acid, DHA, and the oxidized products derived from AA can be accurately measured using GC/MS. Owing to the complex nature of the reactions through which AA proceeds, we believe that GC/MS is currently the procedure of choice in making AA-related measurements. The methods described are useful in defining reactions involving AA. The methods may indicate in vivo oxidative injury and may allow the use of AA-derived products to determine if antioxidant modulations are effective.
Animals↗
Unpredictable intra-individual variations in serum homocysteine levels on folic acid supplementation.
OBJECTIVE: To determine if changes in serum homocysteine values during folic acid supplementation can identify objectively healthy subjects with subclinical folate deficiency. DESIGN: Blood drawn and processed in a regimented fashion from fasting subjects. Serum homocysteine values determined by gas chromatography-mass spectrometry twice before and on days 5 and 8 of daily folic acid supplementation. SETTING: Outpatient University Hospital Clinical Research Center, Denver, Colorado. SUBJECTS: Subjectively healthy adults with normal hematologic and biochemical screening tests. INTERVENTION: Folic acid 1 mg daily for eight consecutive days. RESULTS: Homocysteine values of the group fell significantly during folic acid supplementation. Values pre supplementation were 7.8 +/- 1.8 and 7.4 +/- 2.4 mumol/L while values on days 5 and 8 of supplementation were 6.5 +/- 2.2 and 6.3 +/- 2.2 mumol/L. However, the homocysteine values of any given individual varied up to 60% (rises up to 7 mumol/L and falls of 5 mumol/L) during folic acid supplementation despite the controlled circumstances of blood handling, and an assay coefficient of variation of 8%. CONCLUSIONS: Although group values of serum homocysteine fall during folic acid supplementation, intraindividual variation is so great that subjects with subclinical folate deficiency can not be identified using this study design. Furthermore, these data suggest than an individuals homocysteine values vary enough that single values must be interpreted with caution.
Adolescent↗
Isolation and characterization of microsatellite loci in the cichlid fish Pseudotropheus zebra.
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Alleles↗
Quantitation of homogentisic acid in normal human plasma.
A new stable isotope dilution gas chromatograph-mass spectrometric method of analysis of homogentisic acid is described. Using this method, homogentisic acid is measured for the first time in normal human plasma. The assay of sera from nine normal individuals yielded a range of values from 2.4 to 12 ng/ml. The method appears to be very sensitive and may be useful in the characterization of heterozygotes for alkaptonuria and other disorders of tyrosine degradation.
Alkaptonuria↗
Efficacy of metformin in non-insulin-dependent diabetes mellitus.
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Diabetes Mellitus, Type 2↗
Quantitation of red blood cell folates by stable isotope dilution gas chromatography-mass spectrometry utilizing a folate internal standard.
We report a new gas chromatography-mass spectrometry (GC-MS) method of measurement of red blood cell folates utilizing a stable isotope-labeled bacterial synthesized folate internal standard. The GC-MS method exploits the fact that the common feature of all folate molecules is a p-aminobenzoic acid moiety sandwiched between a pteridine ring and a polyglutamate chain of varying length. In this method, red blood cell folates together with a folate internal standard are specifically purified using bovine folate binding protein and the folates are subsequently chemically cleaved to p-aminobenzoic acid, pteridines, and glutamic acids. Since all six carbon atoms of the benzene ring in the p-aminobenzoic acid moiety of the folate internal standard are labeled with [13C], it is possible to use selected ion monitoring and stable isotope dilution GC-MS to quantitate folates. The method appears to be sensitive, specific, and accurate. The method has been applied to generate a reference range of red blood cell folates based on assay of 25 normal individuals.
4-Aminobenzoic Acid↗
A noninvasive stable-isotope method to simultaneously assess pancreatic exocrine function and small bowel absorption.
OBJECTIVE: To determine if a single-step noninvasive stable isotope method of assessing digestive function could separate normal subjects from subjects with pancreatic insufficiency (maldigestion) or small bowel dysfunction (malabsorption) and to see if subjects with maldigestion could be simultaneously separated from subjects with malabsorption. METHODS: Forty (40) normal volunteers, 18 adults with cystic fibrosis and four adults with celiac sprue, ingested a liquid test meal along with bentiromide, [13C6]PABA, and xylose (PABAX test). Serum was collected at 1 h and analyzed for PABA, [13C6]PABA, and xylose by stable isotope dilution methods using gas chromatography mass spectrometry. RESULTS: All subjects with cystic fibrosis had abnormal pancreatic function test results, whereas three of four adults with sprue had normal values of pancreatic function. All subjects with sprue had abnormal small bowel absorption tests, whereas all adults with cystic fibrosis had apparently normal intestinal function. CONCLUSION: The one-step, 1-h PABAX test can reliably separate normal subjects from those with either maldigestion or malabsorption and can also separate subjects with maldigestion from those with malabsorption.
4-Aminobenzoic Acid↗
Measurement of excitatory sulfur amino acids, cysteine sulfinic acid, cysteic acid, homocysteine sulfinic acid, and homocysteic acid in serum by stable isotope dilution gas chromatography-mass spectrometry and selected ion monitoring.
Oxidized sulfur-containing amino acids are recognized as agonists of excitatory amino acid receptors in the mammalian nervous system. Homologues of glutamic acid (homocysteine sulfinic acid and homocysteic acid) and aspartic acid (cysteine sulfinic acid and cysteic acid) have been shown to be agonistic to N-methyl-D-aspartate receptors in animal brain and have been demonstrated in brain tissue. Considerable evidence exists for the role of homocysteic acid and cysteine sulfinic acid as endogenous ligands for excitatory amino acid receptors. We report, for the first time, the quantitation of these compounds in normal human serum, by a newly developed gas chromatography-mass spectrometry method that employs stable isotope-dilution selected ion monitoring using internal standards prepared in our laboratory. We also report new methods of synthesis of stable isotope-labeled internal standards used in measuring cysteine sulfinic acid, cysteic acid, homocysteine sulfinic acid, and homocysteic acid.
Aspartic Acid↗
Are neuropsychiatric manifestations of folate, cobalamin and pyridoxine deficiency mediated through imbalances in excitatory sulfur amino acids?
Folate, cobalamin and pyridoxine deficiency are associated with psychiatric or neurological symptomatology. Disturbances in sulfur amino acid metabolism leading to accumulation of homocysteine occurs in all three conditions as the metabolism of homocysteine depends on enzymes requiring these vitamins as cofactors. Oxidation products of homocysteine (homocysteine sulfinic acid and homocysteic acid) and cysteine (cysteine sulfinic acid and cysteic acid) are excitatory sulfur amino acids and may act as excitatory neurotransmitters, whereas taurine and hypotaurine (decarboxylation products of cysteic acid and cysteine sulfinic acid) may act as inhibitory transmitters. Homocysteic acid and cysteine sulfinic acid have been considered as endogenous ligands for the N-methyl-D-aspartate (NMDA) type of glutamate receptors. The profile of these sulfur amino acid neurotransmitters could be altered in a similar fashion in states of decreased availability of folate, cobalamin or pyridoxine. It is proposed that the mechanism of neuropsychiatric manifestations in all three conditions result from a combination of two insults to homocysteine catabolism in the brain.
Amino Acids, Sulfur↗
Serum xylose analysis by gas chromatography/mass spectrometry.
A gas chromatography/mass spectrometric (GC/MS) isotope dilution assay for xylose was developed using tertbutyldimethylsilyl-derivatized xylose and [13C]1xylose, and applied to human serum samples. A calibration curve in serum using this assay showed < 3% variation (< 10 mg/L) for any given point. The correlation coefficient for xylose measurements made on 27 sera between a colorimetric method performed by a national commercial reference laboratory and the GC/MS method developed here was .952. However, xylose determinations of 10 of 27 samples differed by > 10% (up to 150 mg/L) when colorimetric values were compared to GC/MS. Two of these samples had borderline-low xylose values by GC/MS, but were well within the normal range by colorimetric analysis. gas chromatography/mass spectrometric isotope dilution assay appears to be an accurate method to measure xylose in serum. These data also suggest that further prospective studies comparing GC/MS to colorimetric methods are indicated for subjects undergoing oral xylose testing.
Colorimetry↗
Ascorbate and dehydroascorbate measurements in aqueous solutions and plasma determined by gas chromatography-mass spectrometry.
The tert-butyldlmethylsllyl derivatives of ascorbic acid and dehydroascorbic acid were characterized by gas chromatography-mass spectrometry, and an isotope dilution assay for ascorbate and dehydroascorbate was developed using [13C6]ascorbic acid and [13C6]- and [6,6-2H2]dehydroascorbate. This assay was used to monitor ascorbic acid loss and the resulting rise of dehydroascorbic acid in aqueous solutions and plasma. Ascorbic acid was shown to rapidly decompose in aqueous solutions containing transition metal ions or when exposed to oxygen. Ethylenedlaminetetraacetic acid chelation did not prevent ascorbic acid degradation in aqueous solution, and ascorbate in ethylenedlaminetetraacetic acid chelated plasma was converted to dehydroascorbate on freezing. Gas chromatography-mass spectrometry appears to be a satisfactory method for determining the ascorbate and dehydroascorbate content of solutions including human blood plasma, whether or not there is ongoing oxidation of ascorbate in those solutions.
Ascorbic Acid↗