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Biomedical subjects

Donald H Chace

Publications and source records attributed to Donald H Chace.

12 recordsLinked to original sources
PubMed2005

Carnitine treatment inhibits increases in cerebral carnitine esters and glutamate detected by mass spectrometry after hypoxia-ischemia in newborn rats.

BACKGROUND AND PURPOSE: Cerebral ischemic insults disrupt normal respiratory activity in mitochondria. Carnitine plays an essential role in mitochondrial metabolism and in modulating excess acyl-coenzyme A (acyl-CoA) levels. The effects of cerebral ischemia on carnitine metabolism are not well understood, although the newborn may be particularly vulnerable to carnitine deficiency. We used a newborn rat model of hypoxia-ischemia (HI) to test the hypothesis that HI alters acyl-CoA:CoA homeostasis and that this effect can be prevented by treatment with carnitine. METHODS: A total of 120 postnatal day 7 rats were subjected to 70 minutes of HI after treatment with 16 mmol/kg intraperitoneal l-carnitine or diluent. Carnitine, acylcarnitines, and excitatory amino acids were measured by mass spectrometry, and carnitine acetyl transferase activity, superoxide, and levels of the mitochondrial phospholipid cardiolipin (CL) were measured at 2- and 24-hour recovery. RESULTS: HI and hypoxia were associated with a significant increase in the ratio of acyl-CoA:CoA, which was prevented by treatment with carnitine. Carnitine treatment also prevented increases in glutamate, glycine, superoxide, and decrease of CL. CONCLUSIONS: Carnitine metabolic pathways are compromised in HI and hypoxia. The protective effect of carnitine treatment on HI injury may be attributable to maintaining mitochondrial function.

Animals↗
PubMed2005

Tetrahydrobiopterin and nitric oxide synthase dimer levels are not changed following hypoxia-ischemia in the newborn rat.

The effect of hypoxia-ischemia on the nitric oxide synthase (NOS) cofactor tetrahydrobiopterin (BH4) and changes in the enzyme dimer state have not previously been studied. Cell-based studies have demonstrated the regulation of nitric oxide (NO) synthesis by intracellular BH4 levels. Activation of NOS requires two NOS polypeptides to form a homodimer. Dimerization results in the creation of high-affinity binding sites for BH4 and L-arginine. Our previous studies have indicated that nNOS activity falls 2 h post-hypoxia-ischemia in the immature rodent model. Thus, the objective of this study was to determine whether changes in nNOS dimeric state could be responsible for the decrease in nNOS activity. Using the immature rat model of HI in conjunction with LT-PAGE and Western blot analysis, we determined the effect of HI on NOS dimer state in hippocampus and cortex and the effects of pharmacologic modulation of NO levels during HI on dimer formation. Using high-performance liquid chromatography (HPLC) and electrospray tandem mass spectrometry (MS-MS), we measured BH4 and L-arginine levels respectively after HI under the same conditions. We found minimal or no changes in either BH4 levels or NOS dimer state at 2 h, 24 h and 7 day recovery from HI on postnatal day 7. In contrast, L-arginine levels were transiently increased in the hypoxic ischemic hemisphere. Thus, our data suggest that the previously described decrease in NOS activity after HI is not associated with depletion of the cofactor BH4, L-arginine substrate or changes in the NOS enzyme dimer state.

Analysis of Variance↗
PubMed2005

A biochemical perspective on the use of tandem mass spectrometry for newborn screening and clinical testing.

The first newborn screen was a clinical test to detect a disorder of the biochemistry of the amino acid, phenylalanine. This disorder, known as phenylketonuria, produces profound mental retardation if not detected and treated early in life. Early screening programs relied on inexpensive population screening techniques that have all but been replaced by more accurate analytical methods such as tandem mass spectrometry (MS/MS). MS/MS enables a multianalyte approach for detecting biochemical disorders such that a metabolic profile is obtained rather than a single analyte measurement. The metabolic profile has clearly shown improvements in the detection of diseases such as phenylketonuria and several new disorders arising from errors in fatty acid oxidation and organic acid metabolism. MS/MS is a powerful tool for accessing the metabolic status of a newborn and can detect both inborn metabolic errors as well as examine the effect of acquired diseases or pharmacologic intervention on intermediary metabolism.

Amino Acids↗
PubMed2005

Impact of haemodialysis on individual endogenous plasma acylcarnitine concentrations in end-stage renal disease.

BACKGROUND: Patients with end-stage renal disease (ESRD) undergoing long-term haemodialysis exhibit low L-carnitine and elevated acylcarnitine concentrations. This study evaluated endogenous concentrations of an array of acylcarnitines (carbon chain length up to 18) in healthy individuals and ESRD patients receiving haemodialysis, and examined the impact of a single haemodialysis session on acylcarnitine concentrations. METHODS: Blood samples were collected from 60 healthy subjects and 50 ESRD patients undergoing haemodialysis (pre- and post-dialysis samples). Plasma samples were analysed for individual acylcarnitine concentrations by electrospray MS/MS. RESULTS: Of the 31 acylcarnitines, 29 were significantly (P<0.05) elevated in ESRD patients compared with healthy controls; in particular, C5 and C8:1 concentrations were substantially elevated. For acylcarnitines with a carbon chain length less than eight, plasma acylcarnitine concentrations decreased significantly over the course of a single dialysis session; however, post-dialysis concentrations invariably remained significantly higher than those in healthy subjects. Dialytic removal of acylcarnitines diminished once the acyl chain length exceeded eight carbons. CONCLUSIONS: The accumulation of acylcarnitines during long-term haemodialysis suggests that removal by haemodialysis is less efficient than removal from the body by the healthy kidney. Removal is significantly correlated to acyl chain length, most likely due to the increased molecular weight and lipophilicity that accompanies increased chain length.

Adolescent↗
PubMed2004

Steroid profiling by tandem mass spectrometry improves the positive predictive value of newborn screening for congenital adrenal hyperplasia.

Congenital adrenal hyperplasia (CAH) is primarily caused by 21-hydroxylase deficiency and leads to an accumulation of 17-hydroxyprogesterone and reduced cortisol levels. Newborn screening for CAH is traditionally based on measuring 17-hydroxyprogesterone by different immunoassays. Despite attempts to adjust cutoff levels for birth weight, gestational age, and stress factors, the positive predictive value for CAH screening remains less than 1%. To improve this situation, we developed a method using liquid chromatography-tandem mass spectrometry to measure 17-hydroxyprogesterone, androstenedione, and cortisol simultaneously in blood spots. A total of 1222 leftover blood spots from six different screening programs using different immunoassays (fluorescent immunoassay and ELISA) were reanalyzed in a blinded fashion by liquid chromatography-tandem mass spectrometry. Thirty-one samples were from babies with CAH, 190 had yielded false-positive results by immunoassay, and the remaining 1001 samples were from babies with normal screening results. Steroid profiling allowed for an elimination of 169 (89%) of the false-positive results and for an improvement of the positive predictive value from the reported 0.5 to 4.7%. Although this method is not suitable for mass screening due to the length of the analysis (12 min), it can be used as a second-tier test of blood spots with positive results for CAH by the conventional methods. This would prevent unnecessary blood draws, medical evaluations, and stress to families.

17-alpha-Hydroxyprogesterone↗
PubMed2003

Neonatal blood carnitine concentrations: normative data by electrospray tandem mass spectometry.

Despite a number of published reports, there is limited information about carnitine metabolism in the newborn. To establish normative data, we analyzed whole-blood carnitine concentrations in 24,644 newborns at age 1.85 +/- 0.95 d and umbilical cord whole blood and plasma carnitine concentrations in 50 full-term newborns. Total carnitine (TC), free carnitine (FC), and acylcarnitine (AC) were measured by electrospray tandem mass spectrometry. AC/FC ratios were derived from these measurements. The entire cohort was stratified according to TC values into a middle TC group representing 90% of the population and lower and upper TC groups representing 5% of the population, respectively. Normative data were derived from the middle TC group of full-term infants (N = 19,595). TC was 72.42 +/- 20.75 microM, FC was 44.94 +/- 14.99 microM, AC was 27.48 +/- 8.05 microM, and AC/FC ratio was 0.64 +/- 0.19 (+/-SD). These values differed significantly from umbilical cord whole blood TC values of 31.27 +/- 10.54 microM determined in 50 samples. No meaningful correlation was found between TC and gestational age or birth weight in any group. In controlled analyses, prematurity was not associated with TC levels, whereas low birth weight (<2500 g) and male sex were significantly associated with higher TC levels. The association of low birth weight with higher TC values may be related to decreased tissue carnitine uptake. The sex effect may be related to hormonal influences on carnitine metabolism. Our study provides normative data of carnitine values measured by the highly precise method of electrospray tandem mass spectrometry in a large cohort of newborns and provides the basis for future studies of carnitine metabolism in health and disease states during the neonatal period.

Carnitine↗
PubMed2003

Use of tandem mass spectrometry for multianalyte screening of dried blood specimens from newborns.

BACKGROUND: Over the past decade laboratories that test for metabolic disorders have introduced tandem mass spectrometry (MS/MS), which is more sensitive, specific, reliable, and comprehensive than traditional assays, into their newborn-screening programs. MS/MS is rapidly replacing these one-analysis, one-metabolite, one-disease classic screening techniques with a one-analysis, many-metabolites, many-diseases approach that also facilitates the ability to add new disorders to existing newborn-screening panels. METHODS: During the past few years experts have authored many valuable articles describing various approaches to newborn metabolic screening by MS/MS. We attempted to document key developments in the introduction and validation of MS/MS screening for metabolic disorders. Our approach used the perspective of the metabolite and which diseases may be present from its detection rather than a more traditional approach of describing a disease and noting which metabolites are increased when it is present. CONTENT: This review cites important historical developments in the introduction and validation of MS/MS screening for metabolic disorders. It also offers a basic technical understanding of MS/MS as it is applied to multianalyte metabolic screening and explains why MS/MS is well suited for analysis of amino acids and acylcarnitines in dried filter-paper blood specimens. It also describes amino acids and acylcarnitines as they are detected and measured by MS/MS and their significance to the identification of specific amino acid, fatty acid, and organic acid disorders. CONCLUSIONS: Multianalyte technologies such as MS/MS are suitable for newborn screening and other mass screening programs because they improve the detection of many diseases in the current screening panel while enabling expansion to disorders that are now recognized as important and need to be identified in pediatric medicine.

Amino Acid Metabolism, Inborn Errors↗
PubMed2002

The application of tandem mass spectrometry to neonatal screening for inherited disorders of intermediary metabolism.

This review is intended to serve as a practical guide for geneticists to current applications of tandem mass spectrometry to newborn screening. By making dried-blood spot analysis more sensitive, specific, reliable, and inclusive, tandem mass spectrometry has improved the newborn detection of inborn errors of metabolism. Its innate ability to detect and quantify multiple analytes from one prepared blood specimen in a single analysis permits broad recognition of amino acid, fatty acid, and organic acid disorders. An increasing number of newborn screening programs are either utilizing or conducting pilot studies with tandem mass spectrometry. It is therefore imperative that the genetics community be familiar with tandem mass spectrometric newborn screening.

Amino Acid Metabolism, Inborn Errors↗