Synthesis of erythrocyte glutathione in healthy adults consuming the safe amount of dietary protein

BACKGROUND

The finding that plasma glutathione turnover decreases as dietary protein intake decreases suggests that the safe amount of dietary protein, although sufficient for maintenance of nitrogen balance, may be insufficient for maintenance of cellular glutathione.

OBJECTIVE

Our objective was to determine the effect of the safe protein intake on the erythrocyte glutathione synthesis rate and its relation with urinary 5-L-oxoproline excretion.

DESIGN

Erythrocyte glutathione synthesis and urinary 5-L-oxoproline excretion were measured in young adults (6 men and 6 women) by using an infusion of [(13)C(2)]glycine on 3 occasions: initially during the subjects' habitual protein intake (1.13 g.kg(-1).d(-1)) and on days 3 and 10 of consumption of a diet providing the safe protein intake (0.75 g.kg(-1).d(-1)).

RESULTS

Compared with baseline values, the fractional synthesis rate of erythrocyte glutathione was significantly lower (P < 0.05) on days 3 and 10 of the diet with the safe protein intake. Urinary 5-L-oxoproline excretion increased significantly (P < 0.05) above baseline by the third day of the diet with the safe protein intake and remained elevated. Erythrocyte glutathione concentrations and absolute synthesis rates decreased by day 3 but recovered to baseline values by day 10. Erythrocyte concentrations of cysteine, methionine, and serine remained unchanged, whereas erythrocyte concentrations of glycine, glutamic acid, and glutamine increased significantly by day 10.

CONCLUSION

During adaptation to the safe amount of dietary protein, there are changes in the concentration and kinetics of erythrocyte glutathione that suggest a reduced antioxidant capacity and possible increased susceptibility to oxidant stress.

Pathophysiology of dyslipidemia and increased cardiovascular risk in HIV lipodystrophy: a model of 'systemic steatosis'

PURPOSE OF REVIEW

This review addresses a syndrome of dyslipidemia and lipodystrophy that has emerged in HIV-infected patients receiving highly active antiretroviral therapy (HAART). The term 'HIV/HAART associated dyslipidemic lipodystrophy (HADL)' describes this syndrome. Although HAART increases patient survival rates, their increased longevity and dyslipidemias place them at risk for cardiovascular disease. Identification of rationally based therapies requires an understanding of the mechanistic basis of HADL.

RECENT FINDINGS

A case definition for HIV lipodystrophy, based on age, gender, duration of HIV disease, serum HDL cholesterol and anthropometry, provides high diagnostic sensitivity and specificity. The dyslipidemias, mainly hypercholesterolemia, hypertriglyceridemia and low-plasma HDL cholesterol, among HIV-infected patients in the pre- and post-HAART eras are summarized. Clinical studies of HADL patients show increased lipolysis, which increases free fatty acid transfer to liver for incorporation into lipoprotein triglycerides that are secreted, and to skeletal muscle where they impair normal insulin signaling. A model of HADL that includes preferential lipolysis in femoral-gluteal fat depots is presented. Relevant therapies include those that inhibit lipolysis (niacin) or increase hepatic fatty acid oxidation (fibrates).

SUMMARY

HADL is one of several disorders characterized by dyslipidemia, insulin resistance, and lipodystrophy. The relative acuteness of HADL should facilitate identification of the sequence of metabolic changes that gives rise to the syndrome. Current evidence suggests that deranged energy storage in femoral-gluteal and other peripheral sites is important; the molecular details for the derangement are unknown but are under scrutiny by many investigators.

Short- and long-term effects of growth hormone (GH) replacement on protein metabolism in GH-deficient adults

Reduced fat-free mass (FFM) in GH-deficient (GHD) adults is improved by GH replacement, but the protein metabolic changes are unclear. Using iv [(2)H(3)]leucine and oral l-[(13)C(1)]leucine infusions and dual emission x-ray absorptiometry, we compared leucine kinetics and body composition in eight GHD adults and eight healthy controls in the fasted and fed states, before and after 2 wk and 6 months of GH replacement. Leucine kinetics were not different between pretreatment GHD subjects and controls. After 2 wk of GH treatment, leucine oxidation decreased in the GHD subjects compared with baseline values [fasted, 41 +/- 6 vs. 30 +/- 5 micromol/kg FFM.h (P < 0.01); fed, 49 +/- 3 vs. 41 +/- 3.6 micromol/kg FFM.h (P < 0.05)], leucine balance improved [fasted, -14 +/- 4 vs. -3.5 +/- 3 micromol/kg FFM.h (P < 0.01); fed, 65 +/- 10 vs. 72 +/- 7 micromol/kg FFM.h (P = 0.07)], and protein synthesis increased [fasted, 116 +/- 5 vs. 131 +/- 6 micromol/kg FFM.h (P < 0.05); fed, 103 +/- 6 vs. 116 +/- 6 micromol/kg FFM.h (P < 0.05)]. After 6 months of GH treatment, these changes were not maintained in the fed state. The five GHD subjects with decreased FFM at baseline showed a significant increase after 6 months of GH treatment (P < 0.05). GH replacement in GHD acutely improves protein balance by stimulating synthesis and inhibiting catabolism. After 6 months, protein kinetics reached a new homeostasis to maintain the net gain in FFM.

Arginine flux and nitric oxide production during human pregnancy and postpartum

OBJECTIVE

To compare second-trimester, third-trimester, and postpartum arginine flux and nitric oxide production using infusions of the stable isotope L-[(15)N(2)]-arginine in normal human gestation.

METHODS

Kinetic measurements were made in pregnant volunteers with uncomplicated singleton gestations in mid gestation, late gestation, and more than 8 weeks postpartum. A bolus of 4.95 micromol/kg of labeled arginine was administered, followed by an infusion at 4.95 micromol/kg per hour for 6 hours. The isotopic enrichment of plasma arginine and nitrite or nitrate (NO(x)) was determined by gas chromatography, mass spectrometry, or both. We used the Kolmogorov-Smirnov test for normality, repeated-measures analysis of variance, and Newman-Keuls test. P <.05 denoted statistical significance.

RESULTS

The rate of turnover of the intravascular NO(x) pool was significantly higher in mid gestation compared with late gestation and almost reached statistical significance when compared with postpartum values (6.2 +/- 0.9 versus 4.3 +/- 0.8 [P <.02] versus 3.7 +/- 2.1% pool/hour; P =.08). Arginine flux was significantly higher in early compared with late gestation and postpartum (107.8 +/- 13.9 versus 72.5 +/- 16.1 versus 82 +/- 8.8 micromol/kg per hour, respectively; P <.01).

CONCLUSION

Arginine and nitric oxide production is higher in mid gestation. This suggests a role for nitric oxide in early cardiovascular adaptation in human gestations.

The protein metabolic response to HIV infection in young children

BACKGROUND

Growth failure often precedes secondary infections in HIV-infected infants and children, suggesting that inadequate protein deposition may be an early manifestation of infection by the virus. However, the protein metabolic response elicited by the virus in young children is unknown.

OBJECTIVE

We compared children with HIV infection and age-matched children without HIV infection with regard to whole-body and splanchnic protein kinetics and synthesis of acute phase proteins (APPs).

DESIGN

Whole-body and splanchnic leucine kinetics and fractional and absolute synthesis rates of 2 positive and 4 negative APPs were measured in 6 asymptomatic, HIV-infected children (4 males and 2 females) aged 6-17 mo and 4 uninfected children (3 females and 1 male) aged 7-9 mo who were in the fed state.

RESULTS

Compared with the control children, the HIV-infected children had significantly lower dietary energy and protein intakes and leucine balance and significantly faster leucine flux and fractional splanchnic leucine extraction; there was no significant difference between the groups in leucine oxidation rates. The HIV-infected children also had significantly higher plasma concentrations and absolute synthesis rates of the positive APPs and a significantly higher fractional synthesis rate of fibrinogen. The concentrations of 2 of the 4 negative APPs, albumin and HDL apolipoprotein A-I, were significantly lower in the HIV-infected children but were not associated with slower synthesis rates.

CONCLUSIONS

Children with HIV infection but without secondary infection have reduced protein balance because of an inability to down-regulate protein catabolism. Furthermore, the acute phase protein response elicited by HIV infection is characterized by higher concentrations and synthesis rates of positive APPs without lower concentrations of some negative APPs.

The acute-phase protein response to infection in edematous and nonedematous protein-energy malnutrition

BACKGROUND

Immune structure and function are more compromised in edematous protein-energy malnutrition (PEM) than in nonedematous PEM. Whether the positive acute-phase protein (APP) response to infection is affected remains unknown.

OBJECTIVE

We assessed whether children with edematous PEM can mount a general APP response and compared the kinetic mechanisms of the response in children with edematous PEM with those in children with nonedematous PEM.

DESIGN

Plasma C-reactive protein, alpha(1)-acid glycoprotein, alpha(1)-antitrypsin, haptoglobin, and fibrinogen concentrations and the fractional and absolute synthesis rates of alpha(1)-antitrypsin, haptoglobin, and fibrinogen were measured in 14 children with edematous PEM, aged 11.4 +/- 2 mo, and 9 children with nonedematous PEM, aged 10.1 +/- 1.4 mo, at 3 times: approximately 2 d after hospital admission (period 1), when they were malnourished and infected; approximately 8 d after admission (period 2), when they were malnourished but free of infection; and approximately 54 d after admission (period 3), when they had recovered.

RESULTS

Children with edematous and nonedematous PEM had higher plasma concentrations of 4 of 5 APPs in period 1 than in period 3. The magnitude of the difference in concentration and in the rate of synthesis of the individual APPs was less in the children with edematous PEM than in those with nonedematous PEM. The kinetic data show that the characteristics of the APP response were different in the 2 groups.

CONCLUSIONS

These results suggest that severely malnourished children can mount only a partial APP response to the stress of infection and that the magnitude of this response is less in those with edema.

Congenital maltase-glucoamylase deficiency associated with lactase and sucrase deficiencies

BACKGROUND

Multiple enzyme deficiencies have been reported in some cases of congenital glucoamylase, sucrase, or lactase deficiency. Here we describe such a case and the investigations that we have made to determine the cause of this deficiency.

METHODS AND RESULTS

A 2.5 month-old infant, admitted with congenital lactase deficiency, failed to gain weight on a glucose oligomer formula (Nutramigen). Jejunal mucosal biopsy at 4 and 12 months revealed normal histology with decreased maltase-glucoamylase, sucrase-isomaltase, and lactase-phlorizin hydrolase activities. Testing with a C-starch/breath CO loading test confirmed proximal starch malabsorption. Sequencing of maltase-glucoamylase cDNA revealed homozygosity for a nucleotide change (C1673T) in the infant, which causes an amino acid substitution (S542L) 12 amino acids after the N-terminal catalytic aspartic acid. The introduction of this mutation into "wildtype" N-terminus maltase-glucoamylase cDNA was not associated with obvious loss of maltase-glucoamylase enzyme activities when expressed in COS 1 cells and this amino-acid change was subsequently found in other people. Sequencing of the promoter region revealed no nucleotide changes. Maltase-glucoamylase, lactase, and sucrase-isomaltase were each normally synthesized and processed in organ culture.

CONCLUSIONS

The lack of evidence for a causal nucleotide change in the maltase-glucoamylase gene in this patient, and the concomitant low levels of lactase and sucrase activity, suggest that the depletion of mucosal maltase-glucoamylase activity and starch digestion was caused by shared, pleiotropic regulatory factors.

Application of stable isotopic techniques in the prevention of degenerative diseases like obesity and NIDDM in developing societies

Economic development in developing societies characterized by industrialization, urbanization, and globalization has seen the emergence of an epidemic of diet- and life-style-related chronic degenerative diseases. A research project was initiated under the aegis of the International Atomic Energy Agency (IAEA), Vienna, Austria under its Coordinated Research Programme (CRP) to promote the use of stable isotopic techniques to document the extent of the problem and to understand the determinants of this epidemic. The principal objectives of this CRP involving countries both in the North and the South are to define the magnitude of the problem of obesity and non-insulin dependent diabetes mellitus (NIDDM) in developing countries, to identify the vulnerable groups at increased risk, and to attempt to describe the metabolic and physiological mechanisms underlying this phenomenon. These comparative international studies of obesity and NIDDM are looking at the effects of childhood malnutrition (Brazil) and socioeconomic differentials (Mexico) on adult risk factors; the composition of the daily diet on obesity (Chile); levels of patterns of physical activity of older adults (China) as well as their influence on weight gain and obesity (Cuba, Nigeria); the impact of body composition and energy expenditure on the evolution frank diabetes from impaired glucose tolerance (Jamaica), and of body compositional changes and the role of inflammatory cytokines on impaired glucose tolerance (India). The last study conducted in New Zealand was aimed at comparing the energy expenditures of Maori (Pacific Island) with New Zealanders of European descent.

Response of splanchnic and whole-body leucine kinetics to treatment of children with edematous protein-energy malnutrition accompanied by infection

BACKGROUND

Although the reduction in whole-body protein turnover and net protein loss induced by protein-energy malnutrition (PEM) has been well documented, it is unclear whether the protein-sparing mechanisms elicited by chronically inadequate intakes of dietary protein and energy are affected by the protein catabolic response to infection.

OBJECTIVE

The objective of this study was to determine whether the presence of infection alters the PEM-induced reduction in whole-body protein metabolism.

DESIGN

We determined whole-body leucine kinetics in 4 boys and 3 girls aged 6-15 mo with edematous PEM and infection approximately 3 d after admission (study 1), when they were both infected and malnourished; approximately 11 d after admission (study 2), when infection had resolved but they were still anthropometrically malnourished; and at recovery (study 3), when weight-for-length was at least 90% of that expected.

RESULTS

The children had significantly less leucine flux in both study 1 and study 2 than they had in study 3. There were no significant differences in the amount of leucine released from protein breakdown or used for protein synthesis between study 1 and study 2. There were no significant differences in leucine balance or in either the amount or percentage of enteral leucine extracted by the splanchnic tissues among the 3 studies.

CONCLUSIONS

When subjects are in the fed state, severe PEM induces a marked reduction in whole-body protein synthesis and breakdown rates, and the presence of infection does not alter this adaptation and hence the overall protein balance. A corollary is that children with severe PEM do not mount a protein catabolic response to infection.

Cysteine supplementation improves the erythrocyte glutathione synthesis rate in children with severe edematous malnutrition

BACKGROUND

Children with severe edematous malnutrition have higher than normal oxidant damage and lower concentrations of the antioxidant reduced glutathione (GSH), which are associated with slower synthesis of GSH and with low extra- and intracellular concentrations of the precursor amino acid cysteine.

OBJECTIVE

We tested whether early dietary supplementation with cysteine could restore a normal GSH concentration and synthesis rate in these children.

DESIGN

Erythrocyte cysteine and GSH concentrations and the fractional and absolute synthesis rates of GSH were measured in 2 groups of 16 edematous malnourished children, 10 boys and 6 girls aged 6-18 mo, at 3 times after hospital admission: at approximately 2 d (period 1), when they were malnourished and infected; at approximately 11 d (period 2), when they were malnourished but cleared of infection; and at approximately 50 d (period 3), when they had recovered. Supplementation with either 0.5 mmol. kg(-1). d(-1) N-acetylcysteine (NAC group) or alanine (control group) started immediately after period 1 and continued until recovery.

RESULTS

From period 1 to period 2 the concentration and the absolute synthesis rate of GSH increased significantly (P < 0.05) in the NAC group but not in the control group. The increases in the GSH concentration and synthesis rate were approximately 150% and 510% greater, respectively, in the NAC group than in the control group. The increases in the NAC group were associated with a significant effect of supplement (P < 0.03) on erythrocyte cysteine concentration.

CONCLUSION

These results suggest that the GSH synthesis rate and concentration can be restored during the early phase of treatment if patients are supplemented with cysteine.

Metabolic basis of HIV-lipodystrophy syndrome

Human immunodeficiency virus (HIV)-lipodystrophy syndrome (HLS) is characterized by hypertriglyceridemia, low high-density lipoprotein-cholesterol, lipoatrophy, and central adiposity. We investigated fasting lipid metabolism in six men with HLS and six non-HIV-infected controls. Compared with controls, HLS patients had lower fat mass (15.9 +/- 1.3 vs. 22.3 +/- 1.7 kg, P < 0.05) but higher plasma glycerol rate of appearance (R(a)), an index of total lipolysis (964.71 +/- 103.33 vs. 611.08 +/- 63.38 micromol x kg fat(-1) x h(-1), P < 0.05), R(a) palmitate, an index of net lipolysis (731.49 +/- 72.36 vs. 419.72 +/- 33.78 micromol x kg fat(-1) x h(-1), P < 0.01), R(a) free fatty acids (2,094.74 +/- 182.18 vs. 1,470.87 +/- 202.80 micromol x kg fat(-1) x h(-1), P < 0.05), and rates of intra-adipocyte (799.40 +/- 157.69 vs. 362.36 +/- 74.87 micromol x kg fat(-1) x h(-1), P < 0.01) and intrahepatic fatty acid reesterification (1,352.08 +/- 123.90 vs. 955.56 +/- 124.09 micromol x kg fat(-1) x h(-1), P < 0.05). Resting energy expenditure was increased in HLS patients (30.51 +/- 2.53 vs. 25.34 +/- 1.04 kcal x kg lean body mass(-1) x day(-1), P < 0.05), associated with increased non-plasma-derived fatty acid oxidation (139.04 +/- 24.17 vs. 47.87 +/- 18.81 micromol x kg lean body mass(-1) x min(-1), P < 0.02). The lipoatrophy observed in HIV lipodystrophy is associated with accelerated lipolysis. Increased hepatic reesterification promotes the hypertriglyceridemia observed in this syndrome.

Endogenous glycine and tyrosine production is maintained in adults consuming a marginal-protein diet

BACKGROUND

The adequacy of indispensable amino acid supplies has received much attention in studies of protein requirements, but the availability of nitrogen for synthesis and maintenance of the supply of dispensable amino acids has been overlooked.

OBJECTIVE

We aimed to determine whether nitrogen balance and the endogenous supply of the dispensable amino acids glycine and tyrosine can be maintained with a marginal protein intake.

DESIGN

Phenylalanine, glycine, and tyrosine kinetics were measured in young adults (6 men, 6 women) on 4 occasions during a reduction in habitual protein intake (1.13 g x kg(-1) x d(-1)) to a marginal intake (0.75 g x kg(-1) x d(-1)) by using a multiple stable-isotope-infusion protocol.

RESULTS

During the 10-d period of marginal protein intake, nitrogen excretion fell initially, then remained constant such that nitrogen balance was negative for the first 2 d and then positive or zero thereafter. Whole-body protein degradation and synthesis predicted from phenylalanine kinetics declined significantly (P < 0.05) over the period of marginal protein intake. Despite the reduction in the amount of glycine and tyrosine derived from whole-body proteolysis, the fluxes of glycine and tyrosine were maintained.

CONCLUSIONS

The results show that adaptation to a marginal intake of dietary protein consisted of an overall reduction in whole-body protein turnover, net protein catabolism, and the rate of nitrogen excretion. The conserved nitrogen was sufficient to maintain the endogenous synthesis and hence the supply of glycine and tyrosine.

Energy expenditure in ill premature neonates

BACKGROUND/PURPOSE

The energy needs of critically ill premature neonates undergoing surgery remain to be defined. Results of studies in adults would suggest that these neonates should have markedly increased energy expenditures. To test this hypothesis, a recently validated stable isotopic technique was used to measure accurately the resting energy expenditure (REE) of critically ill premature neonates before and after patent ductus arteriosus (PDA) ligation.

METHODS

Six ventilated, fully total parenteral nutrition (TPN)-fed, premature neonates (24.5 plus minus 0.5 weeks' gestational age) were studied at day of life 7.5 plus minus 0.7, immediately before and 16 plus minus 3.7 hours after standard PDA ligation. REE was measured with a primed continuous infusion of NaH(13)CO(3), and breath samples were analyzed by isotope ratio mass spectroscopy. Serum CRP and cortisol concentrations also were obtained. Statistical analyses were made by paired sample t tests and linear regression.

RESULTS

The resting energy expenditures pre- and post-PDA ligation were 37.2 plus minus 9.6 and 34.8 plus minus 10.1 kcal/kg/d (not significant, P =.61). Only preoperative energy expenditure significantly (P <.01) predicted postoperative energy expenditure (R(2) = 88.0%). Pre- and postoperative determinations of CRP were 2.1 plus minus 1.5 and 7.1 plus minus 4.2 mg/dL (not significant, P =.34), and cortisol levels were 14.1 plus minus 2.3 and 14.9 plus minus 2.1 microgram/dL (not significant, P =.52).

CONCLUSIONS

Thus, critically ill premature neonates do not have elevated REE, and, further, there is no increase in REE evident the first day after surgery. This suggests that routine allotments of excess calories are not necessary either pre-or postoperatively in critically ill premature neonates. Given the high interindividual variability in REE, actual measurement is prudent if protracted nutritional support is required.

Synthesis of hepatic secretory proteins in normal adults consuming a diet marginally adequate in protein

The plasma concentration and hepatic synthesis rates of albumin, transthyretin, very low-density lipoprotein apolipoprotein B-100 (VLDL-apoB-100), high-density lipoprotein apolipoprotein A-1, fibrinogen, alpha1-antitrypsin, and haptoglobin were measured in six normal adults before and after consuming a protein intake of 0.6 g. kg body wt(-1). day(-1) for 7 days. The synthesis of hepatic proteins was measured from the incorporation of [(2)H(5)]- phenylalanine, following prime/continuous infusion, using plasma VLDL-apoB-100 isotopic enrichment to represent the precursor pool. Synthesis of albumin declined by 50% (P < 0.001) following the lower-protein diet, VLDL-apoB-100 declined by 20% (P < 0.001), and apoA-1 declined by 16% (P < 0.05). By contrast, synthesis increased for fibrinogen (50%, P < 0.05) and haptoglobin (90%, P < 0.001). This pattern of change, with decreased synthesis of nutrient transport proteins and increased formation of acute-phase proteins, suggestive of a low-grade inflammatory response, was accompanied by increased plasma concentration of the inflammatory cytokine interleukin 6 (30%, P < 0.05). The pattern of change in the synthesis of hepatic secretory proteins following 7 days on the low-protein diet may be of functional relevance for lipid transport and the capacity to cope with stress.

Amino acid, glucose, and lipid kinetics after palliative resection in a patient with glucagonoma syndrome

Glucagon excess causes catabolic changes, including enhanced glucose production, lipolysis, and amino acid oxidation. In this study, we evaluate the metabolic effects of debulking surgery on a patient with glucagon-producing tumor. Stable isotope tracer methods were used to measure glucose, glycerol, and alpha-ketoisocaproic acid (alpha KICA) rates of appearance (Ra) into plasma. Measurements were obtained 25 days after surgery in the basal state and during hormonal suppression of glucagon production by infusing somatostatin with insulin replacement. Basal plasma glucagon concentration (14,100 pg/mL) remained high after debulking surgery. Somatostatin infusion decreased plasma glucagon concentration to 6,735 pg/mL and basal substrate kinetics (alpha-KICA Ra from 1.97 to 1.48 micromol/kg/min; glucose Ra from 16.89 to 11.56 micromol/kg/min; and glycerol Ra from 3.33 to 2.74 micromol/kg/min). We conclude that debulking surgery fails to adequately suppress glucagon production and the alterations in substrate metabolism associated with excess glucagon. In these patients, somatostatin therapy can be an effective method to suppress secretion of glucagon and help attenuate its catabolic effects.

Do critically ill surgical neonates have increased energy expenditure?

BACKGROUND/PURPOSE

Adult metabolic studies suggest that critically ill patients have increased energy expenditures and thus require higher caloric allotments. To assess whether this is true in surgical neonates the authors utilized a validated, gas leak-independent, nonradioactive, isotopic technique to measure the energy expenditures of a stable postoperative group and a severely stressed cohort.

METHODS

Eight (3.46+/-1.0 kg), hemodynamically stable, total parenteral nutrition (TPN)-fed, nonventilated, surgical neonates (5 with gastroschisis, 2 with intestinal atresia, and 1 with intestinal volvulus) were studied on postoperative day 15.5+/-11.9. These were compared with 10 (BW = 3.20+/-0.2 kg), TPN-fed, extracorporeal life support (ECLS)-dependent neonates, studied on day of life 7.0+/- 2.8. Energy expenditure was obtained using a primed, 3-hour infusion of NaH(13)CO(3'), breath (13)CO(2) enrichment determination by isotope ratio mass spectroscopy, and the application of a standard regression equation. Interleukin (IL)-6 levels and C-reactive protein (CRP) concentrations were measured to assess metabolic stress. Comparisons between groups were made using 2 sample Student's t tests.

RESULTS

The mean energy expenditure was 53+/-5.1 kcal/kg/d (range, 45.6 to 59.8 kcal/kg/d) for the stable cohort and 55+/-20 kcal/kg/d (range, 32 to 79 kcal/kg/d) for the ECLS group (not significant, P =.83). The IL-6 and CRP levels were significantly higher in the ECLS group (29 +/-11.5 v 0.7+/-0.6 pg/mL [P<.001], and 31+/-22 v 0.6+/-1.3 mg/L [P<.001], respectively). Mortality rate was 0% for the stable postoperative patients and 30% for the ECLS group.

CONCLUSIONS

Severely stressed surgical neonates, compared with controls, generally do not show increased energy expenditures as assessed by isotopic dilution methods. These data suggest that the routine administration of excess calories may not be warranted in critically ill surgical neonates and support the hypothesis that neonates obligately redirect energy, normally used for growth, to fuel the stress response. This is a US government work. There are no restrictions on its use.

Glutathione in disease

Altered glutathione metabolism in association with increased oxidative stress has been implicated in the pathogenesis of many diseases. However, whether strategies aimed at restoring glutathione concentration and homeostasis are effective in ameliorating or modifying the natural history of these states is unknown. In this review we discuss the pathogenic role for altered glutathione metabolism in such diseases as protein energy malnutrition, seizures, Alzheimer's disease, Parkinson's disease, sickle cell anaemia, chronic diseases associated with ageing and the infected state. In addition, we discuss the efficacy of glutathione precursors in restoring glutathione homeostasis both in vitro and in vivo.

Methods for measuring glutathione concentration and rate of synthesis

Altered gamma-glutamylcysteinylglycine homeostasis has been implicated in a wide variety of human diseases. The measurement of the rates of synthesis or loss of gamma-glutamylcysteinylglycine is necessary in order to make meaningful inferences about changes in gamma-glutamylcysteinylglycine concentration in these diseased states. In this review, we discuss methods for measuring gamma-glutamylcysteinylglycine concentration in biological samples as well as how improvements in the sensitivity of gas chromatography-mass spectrometric analyses have permitted the development of new and convenient stable isotope tracer methods for the in-vivo measurement of gamma-glutamylcysteinylglycine kinetics.

Ligation of a patent ductus arteriosus under fentanyl anesthesia improves protein metabolism in premature neonates

BACKGROUND/PURPOSE

Although surgical ligation effectively reverses the cardiopulmonary failure associated with patent ductus arteriosus (PDA), previous findings have suggested that such surgery itself elicits a catabolic response in premature neonates. Therefore, the authors sought to quantitatively assess whether PDA ligation under fentanyl anesthesia aggravated or improved the protein metabolism of premature neonates.

METHODS

Seven ventilated, premature neonates (birth weight 815 +/- 69 g) underwent PDA ligation with standardized fentanyl anesthesia (15 microg/kg) on day-of-life 8.4 +/- 1.2 and were studied immediately pre- and 16 to 24 hours postoperatively while receiving continuous total parenteral nutrition (TPN). Whole-body protein kinetics were calculated using intravenous 1-[13C]leucine, and skeletal muscle protein breakdown was measured from the urinary 3-methylhistidine to creatinine ratio (MH:Cr).

RESULTS

Whole-body protein breakdown (10.9 +/- 1.2 v8.9 +/- 0.8 g/kg/d, P < .05), turnover (17.4 +/- 1.2 v 15.4 +/- 0.8 g/kg/d, P< .05), and MH:Cr (1.95 +/- 0.20 v 1.71 +/- 0.16 micromol:mg, P< .05) decreased significantly after operation. This resulted in a 60% improvement in protein balance (1.6 +/- 0.8 v 2.6 +/- 0.6 g/kg/d, P = 0.08) postoperatively.

CONCLUSIONS

Because of decreased whole-body protein breakdown, whole-body protein turnover, skeletal muscle protein breakdown, and increased protein accrual, surgical PDA ligation under fentanyl anesthesia promptly improves the protein metabolism of premature neonates enduring the stress of a PDA.

In vivo urea cycle flux distinguishes and correlates with phenotypic severity in disorders of the urea cycle

Urea cycle disorders are a group of inborn errors of hepatic metabolism that result in often life-threatening hyperammonemia and hyperglutaminemia. Clinical and laboratory diagnosis of partial deficiencies during asymptomatic periods is difficult, and correlation of phenotypic severity with either genotype and/or in vitro enzyme activity is often imprecise. We hypothesized that stable isotopically determined in vivo rates of total body urea synthesis and urea cycle-specific nitrogen flux would correlate with both phenotypic severity and carrier status in patients with a variety of different enzymatic deficiencies of the urea cycle. We studied control subjects, patients, and their relatives with different enzymatic deficiencies affecting the urea cycle while consuming a low protein diet. On a separate occasion the subjects either received a higher protein intake or were treated with an alternative route medication sodium phenylacetate/benzoate (Ucephan), or oral arginine supplementation. Total urea synthesis from all nitrogen sources was determined from [(18)O]urea labeling, and the utilization of peripheral nitrogen was estimated from the relative isotopic enrichments of [(15)N]urea and [(15)N]glutamine during i.v. co-infusions of [5-(amide)(15)N]glutamine and [(18)O]urea. The ratio of the isotopic enrichments of (15)N-urea/(15)N-glutamine distinguished normal control subjects (ratio = 0.42 +/- 0.06) from urea cycle patients with late (0.17 +/- 0.03) and neonatal (0.003 +/- 0.007) presentations irrespective of enzymatic deficiency. This index of urea cycle activity also distinguished asymptomatic heterozygous carriers of argininosuccinate synthetase deficiency (0. 22 +/- 0.03), argininosuccinate lyase deficiency (0.35 +/- 0.11), and partial ornithine transcarbamylase deficiency (0.26 +/- 0.06) from normal controls. Administration of Ucephan lowered, and arginine increased, urea synthesis to the degree predicted from their respective rates of metabolism. The (15)N-urea/(15)N-glutamine ratio is a sensitive index of in vivo urea cycle activity and correlates with clinical severity. Urea synthesis is altered by alternative route medications and arginine supplementation to the degree that is to be expected from theory. This stable isotope protocol provides a sensitive tool for evaluating the efficacy of therapeutic modalities and acts as an aid to the diagnosis and management of urea cycle patients.

Validation of a [13C]bicarbonate tracer technique to measure neonatal energy expenditure

The use of a stable isotope-labeled [13C]bicarbonate infusion to measure energy expenditure is advantageous, as a complete collection of expired air is not required. This technique allows for facile measurements of energy expenditure in intubated neonates. The aim of the present study was to determine the accuracy of energy expenditure estimates in postsurgical neonates by using the [13C]bicarbonate method compared with the current standard, indirect calorimetry. Eight neonates who were receiving total parenteral nutrition [98 +/- 21 (SD) kcal x kg(-1) x d(-1); 3.1 +/- 0.7 (SD) protein g x kg(-1) x d(-1)] were studied on postoperative d 15.5 +/- 11.9. A primed continuous 3-h intravenous infusion of NaH13CO3 and indirect calorimetry were performed simultaneously. Energy expenditure was calculated separately from the Weir equation and from the dilution of 13CO2 in the breath in combination with the individual energy equivalents of CO2 from the diet. The rate of CO2 appearance and energy expenditure calculated from the bicarbonate method (0.725 +/- 0.021 mol x kg(-1) x d(-1); 89.5 +/- 2.5 kcal x kg(-1) x d(-1)) highly correlated (r = 0.94 and 0.98, respectively) with the CO2 excretion and energy expenditure determined by indirect calorimetry (0.489 +/- 0.016 mol x kg(-1) x d(-1); 60.2 +/- 2.0 kcal x kg(-1) x d(-1)) when analyzed nonproportionately to weight. Bland-Altman analysis demonstrated the 95% confidence interval to be +/- 8.2 kcal x kg(-1) x d(-1). Linear regression analysis revealed a highly statistically significant equation relating the two energy expenditures: Indircal (kcal/d) = -9.341 + [0.705 x Bicarb (dcal/d)]; p < 0.001, r2 = 96.4%. We conclude that energy expenditure in neonates can be accurately determined using the [13C]bicarbonate method and a regression equation. Therefore, the bicarbonate method may be useful for determining energy expenditure in neonates not readily accessible to indirect calorimetry, such as those being mechanically ventilated or on extracorporeal life support.

Lipolysis and lipid oxidation in cirrhosis and after liver transplantation

On the basis of the finding that plasma glycerol concentration is not controlled by clearance in healthy humans, it has been proposed that elevated plasma free fatty acid (FFA) and glycerol concentrations in cirrhotic subjects are caused by accelerated lipolysis. This proposal has not been validated. We infused 10 volunteers, 10 cirrhotic subjects, and 10 patients after orthotopic liver transplantation (OLT) with [1-(13)C]palmitate and [(2)H(5)]glycerol to compare fluxes (R(a)) and FFA oxidation. Cirrhotic subjects had higher plasma palmitate (52%) and glycerol (33%) concentrations than controls. Palmitate R(a) was faster (1.45+/-0.18 vs. 0.85+/-0.17 micromol x kg(-1) x min(-1)) but glycerol R(a) and clearance slower (1.20+/-0.09 vs. 1.90+/-0.24 micromol x kg(-1) x min(-1) and 21.2+/-1.2 vs. 44.7+/- 4.9 ml x kg(-) x h(-1), respectively) than in controls. After OLT, plasma palmitate and glycerol concentrations and palmitate R(a) did not differ, but glycerol R(a) (1.16+/-0.11 micromol x kg(-1) x min(-1)) and clearance (26.7+/-2.4 ml x kg(-1) x h(-1)) were slower than in controls. We conclude that 1) impaired reesterification, not accelerated lipolysis, elevates FFA in cirrhotic subjects; 2) normalized FFA after OLT masks impaired reesterification; and 3) plasma glycerol concentration poorly reflects lipolytic rate in cirrhosis and after OLT.

Intestinal glutamate metabolism

Although it is well known that the intestinal tract has a high metabolic rate, the substrates that are used to generate the necessary energy remain poorly established, especially in fed animals. Under fed conditions, the quantification of substrate used by the gut is complicated by the fact that potential oxidative precursors are supplied from both the diet and the arterial circulation. To circumvent this problem, and to approach the question of the compounds used to generate ATP in the gut, we combined measurements of portal nutrient balance with enteral and intravenous infusions of [U-(13)C]substrates. We studied rapidly growing piglets that were consuming diets based on whole-milk proteins. The results revealed that 95% of the dietary glutamate presented to the mucosa was metabolized in first pass and that of this, 50% was metabolized to CO(2). Dietary glucose was oxidized to a very limited extent, and arterial glutamine supplied no >15% of the CO(2) production by the portal-drained viscera. Glutamate was the single largest contributor to intestinal energy generation. The results also suggested that dietary glutamate appeared to be a specific precursor for the biosynthesis of glutathione, arginine and proline by the small intestinal mucosa. These studies imply that dietary glutamate has an important functional role in the gut. Furthermore, these functions are apparently different from those of arterial glutamine, the substrate that has received the most attention.

Deficiency in peripheral glutamine production in pediatric patients with burns

Plasma glutamine levels decrease in association with severe injury, which suggests that the consumption of glutamine exceeds the production of glutamine or possibly represents a deficit in the release of glutamine from skeletal muscle. The goal of this study was to assess the peripheral glutamine kinetic response to prolonged stress in children with critical injuries. To accomplish this purpose, we quantitated peripheral glutamine kinetics in vivo with the use of 5N15 glutamine in 5 children with severe burns (total body surface area, 74%+/-14%; mean +/- SEM) and 3 children who underwent elective scar reconstruction. In the children with severe burns, leg blood flow was significantly elevated (16.2+/-2.1 vs 7.5 +/-0.3 mL/min/100 mL leg volume, P < .02) and the arterial concentration of glutamine was significantly reduced (0.31+/-0.04 vs 0.84+/-0.05 mmol/L, P < .001). The rate of glutamine turnover within the leg was significantly reduced in the patients with acute burns, whereas the net efflux of glutamine was similar between the 2 groups. These findings suggest that plasma glutamine concentrations decrease during severe stress as a result of a deficit in peripheral glutamine release in conjunction with an increased central consumption. This preliminary study supports the notion that exogenous glutamine supplementation in pediatric patients with severe injuries may be needed because of this inadequate skeletal muscle response.

In vivo rates of erythrocyte glutathione synthesis in children with severe protein-energy malnutrition

Although the compromised GSH status of children with edematous protein-energy malnutrition (PEM) has been documented, the in vivo kinetic mechanism(s) responsible for this is not known. To determine if decreased synthesis contributes to the alteration of GSH homeostasis, the fractional and absolute rates of synthesis of erythrocyte GSH were determined shortly after admission (study 1), approximately 9 days postadmission (study 2), and at recovery (study 3) in seven children with edematous PEM and seven children with nonedematous PEM. Children with edematous PEM had significantly lower erythrocyte GSH and slower absolute rates of GSH synthesis than children with nonedematous PEM both shortly after admission, when they were both malnourished and infected, and approximately 9 days later, when the infection had resolved but they were still malnourished. At these times, the edematous group also had significantly lower erythrocyte GSH concentrations and absolute rates of synthesis than at recovery. Plasma and erythrocyte-free cysteine concentrations of the edematous group were significantly lower at studies 1 and 2 than at recovery. In contrast, erythrocyte GSH concentrations, rates of GSH synthesis, and plasma and erythrocyte free cysteine concentrations of the nonedematous group were similar at all three time points and greater at studies 1 and 2 than in the edematous group. These results confirm that GSH deficiency is characteristic of edematous PEM and suggest that this is due to a reduced rate of synthesis secondary to a shortage in cysteine.