Glutamine and Protein Metabolism in the Newborn Satish C. Kalhan, M.D. Cleveland Clinic

Transcription

1 and Protein Metabolism in the Newborn Satish C. Kalhan, M.D. Cleveland Clinic Protein Metabolism in Vivo Quantification of Protein Metabolism in Vivo Diet (in) Diet Proteins Amino Acids Proteins AA Tracee Amino Acids Equilibrium : Input = Output - Loss (out) - Energy 13 C, 2 H Tracer AA -Leucine -Phenylalanine -Valine t / T - Loss [tracer CO 2 - Energy ] Biological Actions of Most abundant dispensable amino acid in blood and tissues. Virtually synthesized by every tissue Rapid decrease in tissue and plasma levels in acute stress Signaling molecule Glutathione biosynthesis Amino acid pools Metabolic fuel synthesis Nucleotide biosynthesis Protein synthesis Hexosamine synthesis Ammonia scavenger Glucose/glycogen biosynthesis 1

2 Synthesis from TCA Cycle Anaplerosis and Cataplerosis Asn Pyruvate Ala, Ser, Cys, Gly, Thr Glu Asp Oxaloacetate Acetyl CoA Phe, Tyr Fumarate Citrate FA Val, Ile, Met Succinyl CoA α-ketoglutarate Leu, Ile, Val α-ketoacids Nov 3, 25 Mother BCAA Fetal-Placental Exchange NADH NAD Malate Placenta Steroid Synthesis Pyruvate TCA αkg CO 2 BCAA G.S. KIC Fetus Glycogen and Phenylalanine Kinetics in Term Infants Ra Ra (D) Phenylalanine Ra Leucine and Kinetics in Term Infants Relationship Between Leucine (C) and Phenylalanine Flux in Neonates Leucine (C) flux ( ) r 2 =.66 p =.1 Leucine N Leucine C Phenylalanine flux ( ) 2

3 Correlation Between Rate of Appearance of Leucine (N) and 1 Correlation Between Ra and Synthesis in Newborn Infants 3 flux ( ) r 2 =.59 p = Leucine ( N) flux ( ) Synthesis ( ) flux ( ) r 2 =.39 p =.3 OBJECTIVES Effect of 5 days enteral glutamine (.6 g.kg -1.d -1 ) on Enteral in LBW Infants Whole body protein turnover (phenylalanine kinetics) turnover and de novo synthesis Transamination of BCAA synthesis Methods Preterm infants: Gestational age <32 weeks Birth Weight <15 g Control (n=8) Preterm infant formula (PF 24, Ross Labs),5d (n=9) PF 24 + glutamine.6g.kg -1.d -1, 5d Tracers: [ 2 H 5 ]phenylalanine, [1-15 N, 13 C]leucine, [5-15 N]glutamine, [ 15 N 2 ]urea STUDY DESIGN Tracer Infusion Prime Blood Sample Feeds / / h 1h 2h 3h 4h 5h Feed 3

4 Clinical Characteristics of Study Infants Kinetics Birth Weight g Gestation wk Age at Study d Postconceptional Age at Study wk Weight at Study g Ra De Novo Synthesis Control (n=8) 1161 ± ± 3 39 ± 2 34 ± ± 33 (n=9) 1216 ± ± 2 41 ± 2 34 ± ± 37 Control (n=8) 765 ± ± ± ± 123 (n=9) 69 ± ± ± ± 97 and Kinetics Phenylalanine and Leucine Kinetics from Proteolysis Ra Phenylalanine Ra Leucine (N) Ra Control (n=8) 11 ± ± ± ± 47 (n=9 12 ± ± ± ± 97 P.1.1 Control (n=8) 96 ± ± ± ± 94 (n=9) 96 ± ± ± ± 92 P ns ns.7 ns Phenylalanine and Leucine Kinetics (cont) SUMMARY Leucine (C) Ra Leucine Reamination Control (n=8) 273 ± ± ± ± 83 (n=9) 298 ± ± ± ± 71 P ns ns.5 ns Enteral administration of glutamine in growing LBW infants results in: No measurable change in glutamine systemic Ra Increase in transamination of leucine An equimolar increase in urea Ra A positive linear correlation between reamination of BCAA and urea synthesis No detectable change in whole body phenylalanine or leucine C kinetics 4

5 CONCLUSION Splanchnic Metabolism of Enterally administered glutamine does not have a measurable impact on whole body protein kinetics. The equimolar increase in urea synthesis and unchanged systemic glutamine Ra suggests a first pass oxidation of glutamine in the gut. Gut Liver NH 3 OAA Aspartate TCA αkg PEP KIC Leucine Alanine CO 2 Ornithine Citrulline Proline αkg Supplementation in LBW Infants Parenteral glutamine Clinical advantages - Length of hospital stay - Ventilatory support Lower rate of sepsis Lower stimulation of immune system (Neu J. et al; J Pediatr 1997) (Lacey et al; JPEN 1996) Parenteral Supplement - Rationale In isolated skeletal muscle: Positive correlation between (cellular) glutamine levels and protein synthesis inhibited protein breakdown Parenteral Supplement - Rationale Experimental Depletion of : No effect on Ra Leucine Phenylalanine Decreased hepatic (a) release of protein (b) KIC oxidation (MacLennan et al, 1987) 5

6 Effect of parenteral on Amino Acid Kinetics In Preterm Infants Endogenous Ra of, Phenylalanine and Control µmoles.kg. -1.h P=.1 P=.3 Control Ra Leucine N Ra Phenylalanine Ra 1 Phenylalanine SUMMARY Our data show that in LBW infants, parenteral glutamine supplementation results in: a decrease in the rate of appearance (Ra) of glutamine and phenylalanine, no change in the rate of urea synthesis, and CONCLUSIONS Since decrease in whole body proteolysis is associated with protein accretion, parenteral glutamine supplement may benefit LBW infants by enhancing protein synthesis and growth. a lower rate of turnover of leucine N. Parental Amino Acids and Protein Kinetics Increased Parenteral Amino Acids and Protein Metabolism in LBW Infants In healthy adults, infusion of amino acids for 3-4 hours - decreased leucine Ra (proteolysis) - increased NOD of leucine (synthesis) - increased incorporation of leucine in skeletal muscle Phenylalanine tracer similar data (Pacey et al 1988; Bennet et al 1989, 199) 6

7 Parental Amino Acids and Protein Kinetics SPECIFIC AIM Healthy full term and preterm infants respond to exogenous infusion of amino acids by suppressing protein breakdown (leucine, phenylalanine). (Denne et al 1996; Clark et al 1997) Examine the effect of parenteral amino acids on whole body nitrogen kinetics. HYPOTHESIS Study Population Administration of intravenous amino acids to LBW infants during the immediate neonatal period, when they are acutely stressed, will result in greater amino acid oxidation. Low birth weight infants, <32 weeks gestation (a) Age 3-5 days (b) Age <48 h Isotopic Tracers Short Study ring [ 2 H 5 ]Phenylalanine [5-15 N] [ 15 N 2 ] [1-13 C, 15 N]leucine TPN: 1.5 g.kg -1.d -1 Tracers glutamine, phenylalanine, leucine, urea TPN: 3 g.kg -1.d Blood Sample Prime-constant rate infusion h 7

8 Extended Study Clinical Characteristics TPN: 1.5 g.kg -1.d -1 Tracer Infusion Tracer Infusion TPN: 3 g.kg -1.d Blood Sample Birth Gestational Weight Weight Age Age at Study g wks d g Group 1 (12) 1139 ± ± 2 5 ± 1 19 ± 27 Group 2 (5) 1189 ± ± 2 5 ± ± h Group 1: 1.5g for 2h, 3 g for 5h. Group 2: 1.5g for 2h, 3g for 2h. Data shown are mean ± SD Plasma Concentration of Amino Acid Phenylalanine Ra During High and Low TPN Group 1 Group g 3. g 1.5 g 3. g Leucine 97 ± ±34 12 ± ±3 Phenylalanine 64 ± ± ± ± ± ± ± ± 74 Alanine 9 ± ± 5 84 ± ± 93 Serine 114 ± ± ±4 239 ±7 mean ± SD g 3.g 1.5g 3.g Short (n=12) Extended (n=5) Total Endogenous and Kinetics Infants Less Than 48h Age g 3.g 1.5g 3.g Short (n=12) Extended (n=5) Gln D Gln Birth Gestational Weight Age SNAP (g) (wks) (median) Short Study (7) 1234 ± ± (1-18) Ext. Study (5) 147 ± ± (1-18) Data shown are mean ± SD 8

9 Leucine, and Kinetics (<48 h age) Endogenous Phenylalanine Ra during TPN g 3.g 1.5g 3.g Short (n=12) Extended (n=5) Leu N D Gln Short Study Extended Study 1.5g 3.g SUMMARY SUMMARY (cont d) Higher amino acid infusion causes a transient effect on whole body rate of proteolysis and protein oxidation (urea synthesis). Acutely stressed LBW infants also respond to acute amino acid load by suppressing whole body proteolysis and protein oxidation. SUMMARY (cont d) Short Study Sustained amino acid load, following the initial response, results in higher rate of glutamine and urea synthesis (cataplerosis and oxidation). Proteins N Amino Acids BCAA (Leucine) Ketoacid N TCA Cycle α-kg 9

10 Extended Study SPECULATION Proteins N Amino Acids BCAA (Leucine) Ketoacid N TCA Cycle α-kg Adaptation to higher amino acid concentration may have resulted in down-regulation of amino acid transporter or other intracellular signaling systems. Effect of Increasing Dose of Amino Acids on Skeletal Muscle Protein Dynamics Time Course of Synthesis of Mixed Muscle Protein During Amino Acid Infusion Svanberg et al, AJP 1996 Bohe at al, J Physiol 21 Amino Acids and Protein Dynamics Skeletal Muscle: - Increase synthesis Splanchnic Compartment: - Increase synthesis - Inhibit breakdown Proteolytic Pathways Autophagic - lysosomal Ubiquitin - proteosome 1

11 Autophagic Lysosomal Pathway Autophagic Lysosomal Pathway - Controlled by plasma amino acids - Activated by: Starvation Amino acid deficiency Hypoxia High temperature Partial autodigestion to provide nutrients to maintain cell viability. - Responsible genes: atg Regulated by P13 kinase - IgF 1 and others activate P13 and inhibit autophagy Synthesis and Breakdown of Proteins by Amino Acids AA Infusion Intracellular Amino Acid 4EBP-1 eif4e mtor p7 S6K Plasma Amino Acid? Autophagy? Oxidation Insulin IRS-1 PI3K Akt - FOXO-1 Receptor MAFbx (atrogin), MuRF1 Clinical Trials PROTEIN SYNTHESIS PROTEIN BREAKDOWN Parental Supplement in LBW Infants Parental Supplement in LBW Infants Lang et al (1996) Thompson (23) Poindexter (24) (NICHD) Shorter duration of ventilation and TPN; Early full feeds Early full feeds No effect Why variable response? - Heterogeneity of population - Difficulties in delivery targeted amino acids and glutamine - Complex outcome parameters Mortality, sepsis, etc. 11

12 Enteral Supplement in LBW Infants - Lower rate of sepsis - Less feeding intolerance - Neu, J Pediatr van den Berg, AJCN 25 - Vaughn P, J Pediatr 23 My colleagues Prabhu Parimi Chantal Cripe-Mamie Mark Kadrofske Colleen Nye Joyce Nolan Ed Burkett Carole Bennett Clarita Duenas Jose Mariappuram Lourdes Gruca Acknowledgment Thank You My colleagues: Prabhu Parimi, M.D. Mark Kadrofske, M.D. Lourdes Gruca, M.S. 12