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Biomedical subjects

D Halliday

Publications and source records attributed to D Halliday.

At least 109 records · Page 6Linked to original sources
PubMed1990

Protein metabolism in phenylketonuria and Lesch-Nyhan syndrome.

Animal and in vitro studies have implicated decreased protein synthesis in the pathogenesis of tissue damage in phenylketonuria (PKU) and of growth failure in Lesch-Nyhan syndrome. Protein turnover was measured in vivo in ten young adult subjects with classical PKU, two subjects with hyperphenylalaninemia, and three children with Lesch-Nyhan syndrome using techniques based on continuous infusions of [13C]leucine and, in Lesch-Nyhan subjects, [2H5]phenylalanine. The PKU subjects had various degrees of dietary phenylalanine restriction and plasma phenylalanine levels at the time of study ranged from 450-1540 mumol/L (mean 1106). Plasma phenylalanine in the two hyperphenylalaninemic subjects was 533 and 402 mumol/L. Rates of protein synthesis in all PKU subjects (mean 3.71 g/kg/24 h, range 2.68-5.10, [13C]leucine as tracer) were in a range similar to or above control values (mean 2.97, range 2.78-3.22, n = 6), as were rates of protein catabolism (PKU mean 4.23 g/kg/24 h, range 3.15-5.45; controls 3.64, 3.50-3.91). Protein turnover values in hyperphenylalaninemia were also similar to those in controls. With [13C]leucine as tracer, both mean protein synthesis and catabolism values in Lesch-Nyhan subjects (mean 4.80 and 5.64 g/kg/24 h, respectively) were higher than values in control children matched for protein intake (synthesis 4.32 +/- 0.74 (SD) and catabolism 4.85 +/- 0.57 (g/kg/24 h, n = 5). Similar results were obtained in Lesch-Nyhan subjects using [2H5]phenylalanine as tracer. These results suggest that protein turnover is not decreased in either PKU or Lesch-Nyhan syndrome. This conclusion is inconsistent with the hypothesis that tissue damage in PKU results from impaired protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Influence of insulin on albumin and non-albumin protein fractional synthetic rates in post-absorptive type I diabetic patients.

Two 8-h primed continuous infusions of L-[1-13C] leucine were used to determine fractional synthesis rates of albumin and non-albumin plasma protein in post-absorptive Type I diabetic patients during insulin infusion and its withdrawal. Fractional protein synthetic rates were calculated from the rate of incorporation of 13C-label into protein and employing plasma 13C-alpha-ketoisocaproic acid enrichment to represent the precursor pools label. Incorporation of 13C into albumin and non-albumin plasma protein was linear over the latter 6 h of the 8-h L-[1-13C] leucine infusion. Fractional synthetic rates of plasma albumin and non-albumin proteins were similar during insulin withdrawal and its infusion. The increased whole-body protein synthesis observed during insulin withdrawal in Type I diabetic patients appears unrelated to events in albumin and non-albumin plasma protein fractions. These data are further evidence that insulin per se does not stimulate protein synthesis in man.

Adult↗
PubMed1990

Albumin synthetic rate: a comparison of arginine and alpha-ketoisocaproate precursor methods using stable isotope techniques.

The validity of [15N]glycine and [13C]leucine as tracers for investigating albumin fractional synthetic rate (FSR) has been explored by simultaneous infusion of both amino acids into 5 normal female subjects. Albumin FSR, calculated from the urinary [15N]urea plateau value and the incorporation of arginine into albumin was 0.2250 +/- 0.038 per cent/h (mean +/- s.d.). The infusion of leucine, using alpha-ketoisocaproate enrichment to represent the precursor pool, and with measurement of the direct incorporation of leucine into plasma albumin gave a FSR of 0.2516 +/- 0.044 per cent/h. Calculated absolute albumin synthetic rates (ASR) were 11.29 +/- 1.73 mg/kg/h and 11.13 +/- 2.24 mg/kg/h for the glycine and leucine methods respectively. It is concluded that the latter approach is valid as the two amino acids yielded such similar values. The glycine-arginine protocol used represents an improvement compared with previous methods in that the study is completed within 12 h.

Adult↗
PubMed1989

Contribution of aminoacid catabolism to propionate production in methylmalonic acidaemia.

The rates of propionate production and aminoacid catabolism in 5 children with methylmalonic acidaemia were measured by use of stable isotope techniques. Total propionate production was 55-186 mumol/kg per h, to which the maximum contribution of protein catabolism was 10-35 mumol/kg per h (5-40%). These findings indicate important sources of propionate other than protein catabolism, which may account for the limited efficacy of dietary protein restriction in treatment of methylmalonic acidaemia.

Acyl Coenzyme A↗
PubMed1989

Leucine kinetics in surgical patients. I: A study of the effect of surgical 'stress'.

At present there is no consensus about the effect of surgical and accidental trauma on protein metabolism. Leucine kinetics, an index of protein turnover, have been studied in ten patients before intra-abdominal surgery and on either the third (n = 5) or seventh (n = 5) postoperative day. Only small changes in leucine kinetics were noted in the early postoperative study but, by the seventh day, there was evidence of increased synthesis as part of an overall elevation of turnover rates. It is suggested that the previously expressed opinion that protein synthesis is reduced after surgery must be re-examined.

Aged↗
PubMed1989

Leucine kinetics in surgical patients. II: A study of the effect of malignant disease and tumour burden.

Isotope studies of protein turnover have given conflicting evidence about the effects of a malignant tumour on the protein metabolism of the host. Leucine kinetics have been studied, as an index of protein turnover, using a well established methodology. Twenty patients were studied, five with benign disease of the colon, ten with localized malignant tumours of the large bowel, and five in whom there was evidence of metastatic disease from a colonic primary. No effect was observed on the leucine turnover of the patients that might be attributable to the presence or size of the tumour burden. It is suggested that some of the previously conflicting results may be attributable to variability in the experimental design, the heterogeneous patient groups studied and the methods used to express the results obtained.

Aged↗
PubMed1989

Practical considerations in the use of stable isotope labelled compounds as tracers in clinical studies.

Increasingly widespread usage of stable isotope tracers to aid clinical diagnosis and support basic research has stemmed from both advances in mass spectrometry and the availability of competitively priced labelled compounds. Stable isotopes have been used generally to investigate normal and abnormal metabolic pathways, to estimate energy expenditure and body composition and to quantitate substrate flux and oxidation rates. Despite the fact that the underlying principles relating to the use of stable isotopes for in vivo studies are straightforward, careful consideration must be given to all aspects of human studies. This review highlights some of these, including choice of label and tracer molecule, mode of tracer administration and sampling site, analytical instrumentation, interpretation of data and ethical constraints.

Carbon Isotopes↗
PubMed1989

Muscle protein synthesis in steroid-induced proximal myopathy: a case report.

A 51-year-old man with proven adenosquamous carcinoma of the lung presented with clinically acute steroid myopathy. Postabsorptive whole body leucine kinetics and fractional mixed muscle protein synthesis rate (MPSR) were determined by a steady-state approach during continuous L-(1-13C) leucine infusion. Plasma 13C alpha-ketoisocaproic acid enrichment was taken to represent labeling of the precursor pool. Postabsorptive whole body leucine flux and protein synthesis were less than the 1 in 500 confidence intervals of control values. Fractional MPSR was significantly reduced (P less than 0.01). Simultaneous calculation of MPSR from two adjacent sites was in excellent agreement (0.0372 and 0.0395% h-1). This is the first report that steroid myopathy is associated with reduced whole body protein synthesis and fractional MPSR in man.

Dexamethasone↗
PubMed1989

The response to Epstein-Barr virus infection in Sjögren's syndrome.

To assess the response to Epstein-Barr virus (EBV) infection in patients with primary Sjögren's syndrome (SS), the frequency of detection of EBV DNA was studied in salivary gland biopsies and the antibody and idiotypic response to the virus was compared with healthy controls and infectious mononucleosis (IM). Viral DNA, detected by in-situ hybridization, was found in biopsies from two out of 12 patients with SS and six out of 10 controls. IgG, IgA and IgM antibodies to the virus, measured by ELISA using synthetic peptides (early antigen and EBNA-1) and a cloned fusion protein (EBNA-1), were normal in sera from 20 patients with SS, whereas infectious mononucleosis patients showed an increase in IgM antibodies to EBNA-1 and IgG antibodies to early antigen. One similarity between infectious mononucleosis and Sjögren's syndrome was a significant increase in the germline heavy chain idiotype G6 in both diseases, suggesting activation of similar B-cell subsets. It is possible that this is due to EBV, though the low frequency of EBV DNA in biopsies and the normal levels of EBV antibodies in SS does not lend any evidence that the virus itself is the causative agent.

Antibodies, Viral↗
PubMed1989

Substrate disposal in metabolic disease: a comparison between rates of in vivo propionate oxidation and urinary metabolite excretion in children with methylmalonic acidemia.

The relative importance of endogenous metabolism and urinary metabolite excretion was assessed in vivo in six children with methylmalonic acidemia by examining the kinetics of the immediate precursor to methylmalonate, propionate. Total production and oxidation of propionate were measured by means of a continuous infusion of (1-13C)propionate and were compared with the urinary excretion of propionate metabolites. Propionate oxidation was substantial (mean 48.9 mumol/kg/hr +/- SD 18.0) and, in four children, exceeded urinary metabolite excretion (mean urinary excretion in all subjects 40 mumol/kg/hr +/- 25). The sum of urinary excretion and oxidation rates (88 mumol/kg/hr +/- 29) approximated the total propionate production (93.4 +/- 37.0), suggesting that these routes together constitute the major mechanisms of propionate disposal. These results suggest that propionate oxidation is an important route of disposal in methylmalonic acidemia. Variations in the relative proportions of propionate disposal through oxidation and urinary excretion may be one reason for the often poor correlation between clinical status and urinary metabolite excretion. Measurement of urinary metabolite concentration alone may not always reflect clinical status and responses to treatment accurately.

Humans↗
PubMed1989

Rapid measurement of whole body and forearm protein turnover using a [2H5]phenylalanine model.

Whole body protein turnover was measured in six normal adults using a model based on a primed constant infusion of [2H5]phenylalanine and, independently, by an established method of a primed constant infusion of [1-13C]leucine. Isotopic plateau in plasma was achieved within 2 h for [2H5]phenylalanine and, in four of the subjects who received a priming dose of [2H4]tyrosine, for [2H4]tyrosine. In all subjects whole body protein turnover measured with the phenylalanine model (mean protein synthesis, 2.65 +/- (SD) 0.16 g.kg-1.24 h-1; catabolism, 3.58 +/- 0.26 g.kg-1.24 h-1) was similar to that measured using the leucine model (synthesis, 3.09 +/- 0.27 g.kg-1.24 h-1; catabolism, 3.70 +/- 0.35 g.kg-1.24 h-1). Mean forearm fractional muscle protein synthesis calculated by the phenylalanine model was 0.06 +/- 0.03%/h, which compares closely with literature values derived by other methods. The phenylalanine model allows the rapid assessment of whole body and muscle protein turnover from plasma samples alone, obviating the need for measurement of expired air CO2 production or enrichment.

Adult↗
PubMed1989

Effect of testosterone on muscle mass and muscle protein synthesis.

We have studied the effect of a pharmacological dose of testosterone enanthate (3 mg.kg-1.wk-1 for 12 wk) on muscle mass and total-body potassium and on whole-body and muscle protein synthesis in normal male subjects. Muscle mass estimated by creatinine excretion increased in all nine subjects (20% mean increase, P less than 0.02); total body potassium mass estimated by 40K counting increased in all subjects (12% mean increase, P less than 0.0001). In four subjects, a primed continuous infusion protocol with L-[1-13C]leucine was used to determine whole-body leucine flux and oxidation. Whole-body protein synthesis was estimated from nonoxidative flux. Muscle protein synthesis rate was determined by measuring [13C]leucine incorporation into muscle samples obtained by needle biopsy. Testosterone increased muscle protein synthesis in all subjects (27% mean increase, P less than 0.05). Leucine oxidation decreased slightly (17% mean decrease, P less than 0.01), but whole-body protein synthesis did not change significantly. Muscle morphometry showed no significant increase in muscle fiber diameter. These studies suggest that testosterone increases muscle mass by increasing muscle protein synthesis.

Adult↗
PubMed1989

Stable isotopes as tracers in clinical research.

The increased availability of an extensive range of stable isotope-labelled substrates and their ever decreasing cost, as well as the availability of sensitive analytical instruments, suggests that stable isotopes will increasingly be employed in all branches of medical research. It seems likely that within the near future they will totally replace radioactive isotopes in quantitative metabolic studies involving human subjects.

Clinical Trials as Topic↗
PubMed1989

Failure of insulin infusion to stimulate fractional muscle protein synthesis in type I diabetic patients. Anabolic effect of insulin and decreased proteolysis.

We evaluated the influence of insulin on fractional mixed skeletal muscle protein synthesis (FMPS) in eight type I (insulin-dependent) diabetic patients in the postabsorptive state. FMPS was calculated from the increment in [13C]leucine in mixed skeletal muscle protein obtained by serial percutaneous needle biopsy during a continuous 8-h intravenous infusion of L-[13C]leucine. We used the plasma [13C]-alpha-ketoisocaproate (representing intracellular leucine labeling) as the precursor pool of protein synthesis for our calculations. FMPS during the insulin treatment (0.0472 +/- 0.0046%/h; plasma glucose 4.6 +/- 1.0 mM) was not different from FMPS during insulin deprivation (0.0499 +/- 0.0046%/h; plasma glucose 16.4 +/- 0.5 mM). Using plasma [13C]-alpha-ketoisocaproate at isotopic plateau for calculation of leucine flux and as the precursor for leucine oxidation, we further confirmed the findings of our group and others that insulin treatment decreases leucine flux, leucine oxidation, and the nonoxidative portion of leucine flux. Our data on direct measurement of FMPS provide further evidence that the anabolic effect of insulin in the postabsorptive type I diabetic patient is mediated via reduction of proteolysis rather than by increasing protein synthesis.

Adult↗
PubMed1989

Antibodies in rheumatoid arthritis react specifically with the glycine alanine repeat sequence of Epstein-Barr nuclear antigen-1.

Antibodies to rheumatoid arthritis nuclear antigen (RANA) are four- to sixfold increased in sera from patients with rheumatoid arthritis (RA), whereas levels of antibodies to other EBV encoded antigens are slightly elevated or normal. We have demonstrated that the major epitopes recognised by anti-RANA antibodies are represented by a synthetic peptide, P62, corresponding to part of the internal repeat sequence which contains only the amino acids glycine and alanine. In an enzyme-linked immunosorbent assay, anti-P62 antibodies in rheumatoid arthritis sera were four fold higher than healthy and disease controls. By contrast, levels of antibodies to a cloned fusion protein, representing the C-terminus of EBNA-1 and excluding the IR3 region, were normal in RA, but elevated fivefold in nasopharyngeal carcinoma (NPC). Affinity purified anti-P62 antibodies reacted with EBNA-1 and RANA but also with a 60 kD protein present in tissue extracts which has been tentatively identified as cytokeratin. This suggests that the specific increase of anti-P62 antibodies in RA may be due to cross-reactions with autoantibodies to structural proteins with repeat sequences containing glycine. Such sequences are found in cytokeratin and proteoglycans, suggesting that anti-P62 (and hence anti-RANA) antibodies may be cross-reactive antibodies of pathogenic significance in RA, though not necessarily indicating an aetiological role for EBV.

Alanine↗
PubMed1989

Effect of triiodothyronine on leucine kinetics, metabolic rate, glucose concentration and insulin secretion rate during two weeks of fasting in obese women.

We investigated the effect of the fasting-induced reduction in triiodothyronine (T3) on metabolic changes that occur during fasting. In five obese women (T3 group) the serum T3 level during a 2200 kcal/day diet was 3.34 +/- 0.23 nmol/l while taking 20 micrograms T3 8-hourly, 0.65 +/- 0.04 after one week of fasting while not taking T3, and 2.9 +/- 0.3 after a second week of fasting while taking T3 20 micrograms 8-hourly. In three other obese women (control group) who did not take T3, T3 concentrations decreased during fasting and remained low at the end of both the first and second week of fasting. In the T3 group, resting metabolic rate (RMR) (O2 ml/min) decreased 11.7 percent at the end of one week of fasting, but then increased by 5.3 percent at the end of the second week of fasting, whereas in the control group RMR decreased by 13.1 percent after one week of fasting and a further fall of 13.3 percent occurred by the end of the second week of fasting. The RMR at the end of 2 weeks of fasting of the control group was significantly lower (P less than 0.05) than predicted using the equation of Dore, whereas that of the T3 group was as predicted using the same equation. The changes in leucine flux, leucine oxidation and non-oxidative portion of leucine flux were not different during fasting between the T3 group and the control group. Plasma concentrations of glucose, insulin and C-peptide increased from the end of one week of fasting to the end of 2 weeks of fasting in the T3 group, whereas they decreased in the control group. It is concluded that the changes in T3 concentration during fasting affected RMR, glucose metabolism and insulin secretion but failed to influence leucine metabolism.

Adult↗