Yong-Ming Yu

The 24-h whole body leucine and urea kinetics at normal and high protein intakes with exercise in healthy adults

In healthy adult men adapted to a diet/exercise regimen for 6 days, the effects of small, frequent meals supplying daily protein intakes of 1 (n = 8) or 2.5 g . kg-1 . day-1 (n = 6) on leucine oxidation, urea production, and whole body protein synthesis (PS) and degradation (PD) have been compared with the use of a 24-h continuous intravenous [13C]leucine and [15N,15N]urea infusion protocol. Two 90-min periods of exercise (approximately 50% maximal O2 consumption) were included during the fasting and the fed periods of the 24-h day. Subjects were determined to be at approximate energy, nitrogen, and leucine balances on both diets. Increased protein intake raised the urea production rate; the absolute rate of urea hydrolysis was the same on both diets. When the first-pass splanchnic uptake of leucine was taken to be 25% of intake, PS was stimulated by feeding (after an overnight fast) at both protein intake levels (P < 0.05 and P < 0.01), whereas PD declined significantly (P < 0.01) at both protein levels. Protein gain at a high protein intake appears to be the result of both a stimulation of PS and a marked decline in PD, whereas at a less generous intake, the gain appears to be a result of a fall in PD with a less evident change in PS. Exercise moderately decreased PS during and/or immediately after exercise at each protein level, and there was a postexercise-induced increase (P < 0.01) in PD, which was more dramatic when feeding was at the higher protein intake level.In healthy adult men adapted to a diet/exercise regimen for 6 days, the effects of small, frequent meals supplying daily protein intakes of 1 ( n = 8) or 2.5 g ⋅ kg-1 ⋅ day-1( n = 6) on leucine oxidation, urea production, and whole body protein synthesis (PS) and degradation (PD) have been compared with the use of a 24-h continuous intravenous [13C]leucine and [15N,15N]urea infusion protocol. Two 90-min periods of exercise (∼50% maximal O2 consumption) were included during the fasting and the fed periods of the 24-h day. Subjects were determined to be at approximate energy, nitrogen, and leucine balances on both diets. Increased protein intake raised the urea production rate; the absolute rate of urea hydrolysis was the same on both diets. When the first-pass splanchnic uptake of leucine was taken to be 25% of intake, PS was stimulated by feeding (after an overnight fast) at both protein intake levels ( P < 0.05 and P < 0.01), whereas PD declined significantly ( P < 0.01) at both protein levels. Protein gain at a high protein intake appears to be the result of both a stimulation of PS and a marked decline in PD, whereas at a less generous intake, the gain appears to be a result of a fall in PD with a less evident change in PS. Exercise moderately decreased PS during and/or immediately after exercise at each protein level, and there was a postexercise-induced increase ( P < 0.01) in PD, which was more dramatic when feeding was at the higher protein intake level.

Plasma arginine and leucine kinetics and urea production rates in burn patients

We measured plasma arginine and leucine kinetics and rates of urea production (appearance) in 12 severely burned patients (mean body surface burn area, 48%) during a basal state (low-dose intravenous glucose) and while receiving routine, total parenteral nutrition ([TPN] fed state) including an L-amino acid mixture, supplying a generous level of nitrogen (mean, 0.36 g N.kg-1.d-1). The two nutritional states were studied in random order using a primed 4-hour constant intravenous tracer infusion protocol. Stable-nuclide-labeled tracers were L-[guanidino-13C]arginine, L-[1-13C]leucine, [18O]urea, and NaH13CO3 (prime only), with blood and expired air samples drawn at intervals to determine isotopic abundance of arginine, citrulline, ornithine, alpha-ketoisocaproate ([KIC] for leucine), and urea in plasma and 13CO2 in breath. Results are compared with data obtained in these laboratories in healthy adults. Leucine kinetics (flux and disappearance into protein synthesis) indicated the expected higher turnover in burn patients than in healthy controls. Mean leucine oxidation rates are also higher and compared well with values predicted from urea production rates, provided that urea nitrogen recycling via intestinal hydrolysis is taken into account. The plasma urea flux was also higher than for normal subjects. Arginine fluxes as measured in the systemic whole body, via the plasma pool, were correspondingly higher in burned patients than in healthy controls and were in good agreement with values predicted from leucine-KIC kinetics. However, systemic whole-body arginine flux measured via the plasma pool was only 20% of the arginine flux estimated from the urea flux plus the rate of protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma arginine kinetics in adult man: Response to an arginine-free diet

To explore the response of whole-body arginine metabolism to a change in arginine intake, plasma arginine kinetics were investigated in eight healthy adult men who received an L-amino acid diet supplying an Arg-rich or Arg-free intake for 6 days before undergoing a tracer study on day 7. The tracer protocol lasted for 8 hours. For the first 3 hours subjects remained in the postabsorptive (fasted) state, and during the following 5 hours they consumed small meals at 30-minute intervals. Primed continuous intravenous infusions of L-[guanidino-13C]arginine, L-[5,5,5-2H3]leucine, and [15N2]urea were administered to estimate plasma amino acid fluxes and the rate of urea production. For the fasted and fed states, plasma arginine fluxes (mumol.kg-1.h-1, mean +/- SD) were 69 +/- 8 and 87 +/- 12 (P < .01), respectively, for the Arg-rich diet and 63 +/- 14 and 51 +/- 7 (P < .01, from Arg-rich) for the Arg-free diet. Compared with the Arg-rich results, fed-state plasma arginine and ornithine concentrations were decreased (P < .01) and citrulline concentration was increased (P < .01) during the Arg-free diet period. Leucine fluxes and rates of urea production did not differ between the diet groups. The lower fed-state arginine flux in subjects receiving the Arg-free compared with the Arg-rich diet appears to be entirely due to the decreased rate of entry of arginine from the intestine in the former group.(ABSTRACT TRUNCATED AT 250 WORDS)

Maximal Parenteral Glucose Oxidation in Hypermetabolic Young Children: A Stable Isotope Study

BACKGROUND During periods in which nutrition support of critically ill young children must be parenteral, glucose infusions are administered at up to 10 or more mg.kg-1.min-1 to meet predicted energy needs. However, data in adults suggest that such high glucose loads exceed the ability to oxidize glucose in the hormonal milieu that characterizes critical illness. The purpose of this study was to determine if these high glucose loads are oxidized by critically ill young children. METHODS Ten young children with serious burns were enrolled in a stable isotope study of glucose metabolism. These five boys and five girls were an average age of 5.2 years (range, 1 to 11 years), weight of 18.4 kg (range, 10 to 31 kg) and burn size of 51.6% of the body surface (range, 35% to 86%). During clinically required episodes of parenteral nutrition support, we used the [13C6]glucose tracer to assess the efficacy of glucose oxidation at both 5 and 8 mg.kg-1.min-1. Serum glucose was recorded and indirect calorimetry was performed. RESULTS The fraction of exogenous glucose oxidation fell from 59% +/- 5% to 47% +/- 5% (p < .05). Although there was a significantly increased level of total glucose oxidation (3.2 to 3.8 mg.kg-1.min-1), this increment (29% +/- 9%) was accompanied by a significant decrease in the efficiency of energy production, because the bulk of the additional glucose above 5 mg.kg-1.min-1 was not being oxidized. Plasma glucose concentration did not change (145 +/- 4 vs 137 +/- 4 mg/dL, p < .01) and whole-body expired gas respiratory quotients remained consistent with a mixed fuel oxidation, implying that there exists an increased rate of exogenous glucose uptake by tissues in nonoxidative pathways. CONCLUSIONS Maximum glucose oxidation in severely burned children occurs at intakes approximating 5 mg.kg-1.min-1. Exogenous glucose in excess of this amount enters nonoxidative pathways and is unlikely to improve energy balance. Clinical markers such as serum glucose levels or expired respiratory quotient may not detect inefficient glucose utilization.

Stem cells and burns: review and therapeutic implications.

Despite significant advances in burn resuscitation and wound care over the past 30 years, morbidity and mortality from thermal injury remain high. Limited donor skin in severely burned patients hinders effective wound excision and closure, leading to infectious complications and prolonged hospitalizations. Even with large-volume fluid resuscitation, the systemic inflammatory response syndrome compromises end-organ perfusion in burn patients, with resultant multiorgan failure. Stem cells, which enhance wound healing and counteract systemic inflammation, now offer potential therapies for these challenges. Through a review of the literature, this article seeks to illustrate applications of stem cell therapy to burn care and to highlight promising areas of research.

A kinetic study of leucine metabolism in severely burned patients. Comparison between a conventional and branched-chain amino acid-enriched nutritional therapy.

A cross-over design study was used to examine the metabolic consequences of enterai feeding for 48 to 96 hours with cither a branched-chain amino acid (BCAA)-enrichcd (44% BCAA) or a conventional egg protein formulation in 12 severely burned adult patients. A stable isotope labeled leucine (L-I-13C-Ieu-cine) tracer approach was used to measure leucine flux and oxidation and to estimate rates of whole body protein synthesis and breakdown. Additionally, 15N2-urca and 6,6-2H-glucose were administered to assess the status of urea and glucose kinetics with these two nutritional treatments. Average patient age was 54 years, and average burn surface area was 36%. Studies were conducted at an average of 25 days postburn. Leucine flux and oxidation were significantly (p < 0.01, by paired t-test) elevated with BCAA feeding as compared to the egg protein formulation. However, there were no significant differences in the rates of leucine incorporation into, or release from, proteins (p > 0.05) between the two dietary periods. Mean rates of body protein synthesis and breakdown for each diet were about twice the rates reported for healthy young adults. Apparent nitrogen balance measurements were not statistically different (p > 0.1) between the two diet periods. Furthermore, urea and glucose kinetics failed to show significant differences between the two diet periods. It appears from these results that the major consequences of increased intake of leucine from the BCAA formula is an enhanced rate of leucine oxidation. In conclusion, (1) the availability of BCAAs is not rate-limiting for enhanced protein synthesis in burn patients, and (2) the use of enriched BCAA formulas in burn therapy does not appear to offer advantages over a routinely used cn-tcral egg protein formula, at least based on the present determinations.

Proton NMR spectroscopy shows lipids accumulate in skeletal muscle in response to burn trauma-induced apoptosis

Burn trauma triggers hypermetabolism and muscle wasting via increased cellular protein degradation and apoptosis. Proton nuclear magnetic resonance (1H NMR) spectroscopy can detect mobile lipids in vivo. To examine the local effects of burn in skeletal muscle, we performed in vivo 1H NMR on mice 3 days after burn trauma; and ex vivo, high‐resolution, magic angle spinning 1H NMR on intact excised mouse muscle samples before and 1 and 3 days after burn. These samples were then analyzed for apoptotic nuclei using a terminal deoxynucleotidyl transferase‐mediated dUTP nick end‐labeling (TUNEL) assay. To confirm our NMR and cell biology results, we used transcriptome analysis to demonstrate that burn trauma alters the expression of genes involved in lipid metabolism and apoptosis. Our results demonstrate that burn injury results in a localized intramyocellular lipid accumulation, which in turn is accompanied by burn‐induced apoptosis and mitochondrial dysfunction, as seen by the up‐regulation of apoptotic genes and down‐regulation of genes that encode lipid oxidation and the peroxisomal proliferator activator receptor γ coactivator PGC‐1β. Moreover, the increased levels of bisallylic methylene fatty acyl protons (2.8 ppm) and vinyl protons (5.4 ppm), in conjunction with the TUNEL assay results, further suggest that burn trauma results in apoptosis. Together, our results provide new insight into the local physiological changes that occur in skeletal muscle after severe burn trauma. Astrakas, L. G., Goljer, I., Yasuhara, S., Padfield, K. E., Zhang, Q., Gopalan, S., Mindrinos, M. N., Dai, G., Yu, Y.‐M., Jeevendra Martyn, J. A., Tompkins, R. G., Rahme, L. G., Tzika, A. A. Proton NMR spectroscopy shows lipids accumulate in skeletal muscle in response to burn trauma induced apoptosis. FASEB J. 19, 1431–1440 (2005)

Simvastatin treatment improves survival in a murine model of burn sepsis: Role of interleukin 6.

Infection is the most common and most serious complication of a major burn related to burn size. Recent studies have demonstrated that statin treatment can decrease mortality in murine or human sepsis. In the current study mice were anesthetized and subjected to a dorsal 30% TBSA scald burn. Simvastatin or placebo were administered by intraperitoneal injection once daily or every 12h. On post burn day 7 cecal ligation and puncture with a 21-gauge needle (CLP) was performed under ketamine/xylazine anesthesia, the two different dosing schedules were continued and survival was monitored. In other groups of mice, interleukin-6 (IL-6) levels in blood were measured in mice at 7 days after injury. A simvastatin dependent improvement in survival was observed in the burn sepsis model. This protection was found to be dose and time dependent. In addition, statin treatment reduced the elevation in IL-6 levels of mice burned 7 days previously. However, IL-6 levels in burned mice with or without statin treatment were elevated by CLP to the same degree. The results of these studies suggest that statin treatment reduces mortality in mice with burns and CLP and that this effect may not be mediated via IL-6 levels.

Regulation of signaling pathways downstream of IGF-I/insulin by androgen in skeletal muscle of glucocorticoid-treated rats.

BACKGROUND The mechanisms by which androgens ameliorate glucocorticoid-induced muscle wasting are still under investigation. In the present study, we tested the hypothesis that androgens effects in reversing muscle wasting are related to activating the signaling pathways downstream of insulin-like growth factor-1 (IGF-I)/insulin. METHODS Forty female Sprague-Dawley rats were randomly divided into four groups: control group, dexamethasone (DEX) group, testosterone (TES) group, and TES + DEX group. Each group was injected with saline or DEX (0.1 mg/100 g/d) for 10 days and sesame oil or TES (0.5 mg/100 g/d) for 13 days. Several downstream targets of IGF-I/insulin in skeletal muscle including protein kinase B (Akt), p70 ribosomal protein S6 kinase (p70S6K), and glycogen synthase kinase-3beta (GSK-3beta) that are associated with protein synthesis were examined. Two proteolysis-related ubiquitin E3-ligases, muscle atrophy F-box, and muscle RING finger-1 that are also regulated by IGF-I/insulin were also assessed. RESULTS TES attenuated gastrocnemius muscle atrophy induced by DEX. TES prevented the DEX-induced decrease of IGF-I expression in gastrocnemius muscle, but not in serum. TES ameliorated DEX-induced dephosphorylation of Akt and p70S6K and promoted the phosphorylation of GSK-3beta in gastrocnemius muscle. The total amount of Akt, p70S6K, or GSK-3beta proteins was not changed among these groups. TES did not show any effects on the DEX-induced upregulation of muscle atrophy F-box, and muscle RING finger-1 mRNA in gastrocnemius muscle. CONCLUSION This findings suggest that the effects of TES in reversing DEX-induced muscle atrophy are related to signaling pathways downstream of IGF-I/insulin that are associated with protein synthesis.

Comparative Evaluation of the Quantitative Utilization of Parenterally and Enterally Administered Leucine and L-[1-13C,15N]Leucine Within the Whole Body and the Splanchnic Region

BACKGROUND The purpose of this study was to quantify the kinetic aspects of leucine metabolism in the whole body and within the splanchnic region when an amino acid mixture is administered by the enteral route as compared with administration by the parenteral route. METHODS Seven chronically catheterized dogs were studied during an intragastric infusion of L-[1-13C,15N]leucine with 0.24 g of complete amino acid mixture (kg-1.h-1) for 6 hours. The results are compared with those previously reported for nine dogs studied under essentially identical experimental conditions except that the tracer and amino acid mixtures were given by vein. RESULTS At the whole body level, the various parameters of leucine metabolism (flux, oxidation, and disappearance into and release from proteins) were not significantly different among animals that were infused enterally and those that were infused parenterally. Leucine metabolism within the splanchnic region and gut was more extensive for enteral administration than for parenteral administration. For the splanchnic region, 31.4%, 27.9%, and 6.0% of enterally administered leucine was used for protein synthesis, deamination, and oxidization, respectively, compared with respective mean values of 19.5% (p < .001), 13.4% (p < .001), and 4.1% (p < .05) for parenterally administered leucine. For liver, 4.8% of enterally administered leucine was oxidized compared with 2.3% (p < .001) of parenterally administered leucine. These findings are qualitatively similar to those reported previously by us when comparing enteral and parenteral amino acid intakes but with an IV tracer infusion. CONCLUSION Enteral administration seems to be more effective than an acute parenteral feeding regimen, at least in maintaining leucine (protein) balance in gut tissues.