Reduced Protein Breakdown Research Articles

Effects of glucagon-like peptide 1 on glycemia control and its metabolic consequence after severe thermal injury—studies in an animal model

Hyperglycemia with insulin resistance is commonly seen in severely burned patients and tight glycemia control with insulin may be beneficial in this condition. The most potent insulinotropic hormone, glucagon-like peptide 1 (GLP-1), stimulates insulin secretion in a glucose-dependent manner. Because infusion of GLP-1 never reduces glucose levels to below ∼70 mg/dL, the risk of hypoglycemia by using insulin is reduced. In this study we investigated the metabolic effects of GLP-1 infusion after burn injury in an animal model. Male CD rats were divided in 3 groups: burn injury with saline, burn injury with GLP-1 treatment, and sham burn (SB). Burn injury was full thickness 40% total body surface area. The burn injury with GLP-1 treatment group received GLP-1 infusion via osmotic pump. Fasting blood glucose, plasma insulin, and plasma GLP-1 levels were measured during intraperitoneal glucose tolerance tests. Expressions of caspase 3 and bcl-2 were evaluated in pancreatic islets. In a subset of animals, protein metabolism and total energy expenditure were measured. Fasting GLP-1 was reduced in burn injury with saline compared to SB or burn injury with GLP-1 treatment. Burn injury with GLP-1 treatment showed reduced fasting blood glucose, improved intraperitoneal glucose tolerance test results, with increased plasma insulin and GLP-1 responses to glucose. GLP-1 reduced protein breakdown and total energy expenditure in burn injury with GLP-1 treatment versus burn injury with saline, with improved protein balance. Increased expression of caspase 3 and decreased expression of bcl-2 in islet cells by burn injury were ameliorated by GLP-1. Burn injury reduced plasma GLP-1 in association with insulin resistance. GLP-1 infusion improved glucose tolerance and showed anabolic effects on protein metabolism and reduced total energy expenditure after burn injury, possibly via insulinotropic and non insulinotropic mechanisms.

Interaction between Testosterone and Growth Hormone on Whole-Body Protein Anabolism Occurs in the Liver

GH and testosterone both exert protein-anabolic effects and may act synergistically. Liver and muscle are major sites of protein metabolism. Our objective was to determine whether the site of GH and testosterone interaction on protein metabolism is primarily hepatic or extrahepatic. In this open-label randomized crossover study, the impact on whole-body protein metabolism of oral (solely hepatic testosterone exposure) and transdermal (systemic testosterone exposure) testosterone replacement in the presence or absence of GH was compared. Eleven hypopituitary men with GH and testosterone deficiency were randomized to 2-wk treatments with transdermal testosterone (10 mg) or oral testosterone (40 mg), with or without GH replacement (0.6 mg/d). The dose of testosterone administered orally achieves physiological portal testosterone concentrations without spillover into the systemic circulation. Whole-body leucine turnover was measured, from which leucine rate of appearance (LRa), an index of protein breakdown, and leucine oxidation (Lox), a measure of irreversible protein loss, were estimated at the end of each treatment. In the absence of GH, neither transdermal nor oral testosterone affected LRa or Lox. GH therapy significantly increased LRa, an effect equally reduced by transdermal and oral testosterone administration. GH replacement alone did not significantly change Lox, whereas addition of testosterone treatment reduced Lox, with the effect not significantly different between transdermal and oral testosterone. In the doses used, testosterone stimulates protein anabolism by reducing protein breakdown and oxidation only in the presence of GH. Because the net effect on protein metabolism during GH therapy is not different between systemic and solely hepatic testosterone administration, we conclude that the liver is the primary site of this hormonal interaction.

JunB transcription factor maintains skeletal muscle mass and promotes hypertrophy

The size of skeletal muscle cells is precisely regulated by intracellular signaling networks that determine the balance between overall rates of protein synthesis and degradation. Myofiber growth and protein synthesis are stimulated by the IGF-1/Akt/mammalian target of rapamycin (mTOR) pathway. In this study, we show that the transcription factor JunB is also a major determinant of whether adult muscles grow or atrophy. We found that in atrophying myotubes, JunB is excluded from the nucleus and that decreasing JunB expression by RNA interference in adult muscles causes atrophy. Furthermore, JunB overexpression induces hypertrophy without affecting satellite cell proliferation and stimulated protein synthesis independently of the Akt/mTOR pathway. When JunB is transfected into denervated muscles, fiber atrophy is prevented. JunB blocks FoxO3 binding to atrogin-1 and MuRF-1 promoters and thus reduces protein breakdown. Therefore, JunB is important not only in dividing populations but also in adult muscle, where it is required for the maintenance of muscle size and can induce rapid hypertrophy and block atrophy.

Protein Balance in Nondiabetic Versus Diabetic Patients Undergoing Colon Surgery

Surgical injury provokes a stress response that is thought to be pronounced in patients with diabetes mellitus type 2 (DM2) leading to intensified catabolism. The aim of this study was to compare the effects of perioperative epidural analgesia (EDA) versus patient controlled analgesia (PCA) and amino acid infusion on postoperative metabolism in patients with and without DM2. For this study, 12 nondiabetic patients and 12 diabetic patients undergoing colorectal surgery were randomly assigned to 4 groups (n = 6 per group) receiving either EDA (nondiabetic EDA and diabetic EDA [DEDA group]) or PCA with morphine (nondiabetic PCA and diabetic PCA) for perioperative pain control. Protein and glucose kinetics were measured on the second postoperative day using L-[1-13C]leucine and [6,6-2H2]glucose infusion during a fasted state and a 3-hr fed state with amino acid infusion. The transition from the fasted to fed state suppressed endogenous rate of appearance (Ra) of glucose (P G 0.001) with a distinct effect for the DEDA group (P G 0.001). The Ra of leucine and the endogenous rate of appearance of leucine tended to be lower in the DEDA group(P = 0.056 and P = 0.07). Leucine oxidation was more suppressed in the DEDA group (P = 0.02) and when receiving amino acids(P = 0.001). Diabetic patients achieved a higher protein balance than nondiabetic patients (P = 0.032) and when receiving EDA instead of PCA (P = 0.012) or infusion of amino acids (P = 0.014). A short-term infusion of amino acids reduced protein breakdown, increased protein synthesis, and rendered protein balance positive. This anabolic effect was pronounced in diabetic patients with EDA compared with nondiabetic patients or PCA, respectively, and prevented an undesirable hyperglycemia.

Latent and Active Polyphenol Oxidase (PPO) in Red Clover (Trifolium pratense) and Use of a Low PPO Mutant To Study the Role of PPO in Proteolysis Reduction

Polyphenol oxidase (PPO) activity in leaf extracts of wild type (WT) red clover and a mutant line expressing greatly reduced levels of PPO (LP red clover) has been characterized. Both latent and active forms of PPO were present, with the latent being the predominant form. PPO enzyme and substrate (phaselic acid) levels fluctuated over a growing season and were not correlated. Protease activation of latent PPO was demonstrated; however, the rate was too low to have an immediate effect following extraction. A novel, more rapid PPO activation mechanism by the enzyme's own substrate was identified. Rates of protein breakdown and amino acid release were significantly higher in LP red clover extracts compared with WT extracts, with 20 versus 6% breakdown of total protein and 1.9 versus 0.4 mg/g FW of free amino acids released over 24 h, respectively. Inclusion of ascorbic acid increased the extent of protein breakdown. Free phenol content decreased during a 24 h incubation of WT red clover extracts, whereas protein-bound phenol increased and high molecular weight protein species were formed. Inhibition of proteolysis occurred during wilting and ensilage of WT compared with LP forage (1.9 vs 5 and 17 vs 21 g/kg of DM free amino acids for 24 h wilted forage and 90 day silage, respectively). This study shows that whereas constitutive red clover PPO occurs predominantly in the latent form, this fraction can contribute to reducing protein breakdown in crude extracts and during ensilage.

The NF-kB inhibitor curcumin reduces protein breakdown in septic muscle

The NF-kB inhibitor curcumin reduces protein breakdown in septic muscle

Ovarian suppression with gonadotropin-releasing hormone agonist reduces whole body protein turnover in women

The age-related decline in fat-free mass is accelerated in women after menopause. The role of ovarian hormone deficiency in the regulation of fat-free mass, however, has not been clearly defined. To address this question, we examined the effect of ovarian hormone suppression on whole body protein metabolism. Whole body protein breakdown, oxidation, and synthesis were measured using [(13)C]leucine in young, healthy women with regular menstrual patterns before and after 2 mo of treatment with gonadotropin-releasing hormone agonist (GnRHa; n = 6) or placebo (n = 7). Protein metabolism was measured under postabsorptive and euglycemic-hyperinsulinemic-hyperaminoacidemic conditions. Ovarian suppression did not alter whole body or regional fat-free mass or adiposity. In the postabsorptive state, GnRHa administration was associated with reductions in protein breakdown and synthesis (P < 0.05), whereas no change in protein oxidation was noted. Under euglycemic-hyperinsulinemic-hyperaminoacidemic conditions, a similar reduction (P < 0.05) in protein synthesis and breakdown was noted, whereas, protein oxidation increased (P < 0.05) in the placebo group. Testosterone, steroid hormone precursors, insulin-like growth factor I, and their respective binding proteins were not altered by GnRHa administration, and changes in these hormones over time were not associated with GnRHa-induced alterations in protein metabolism, suggesting that changes in protein turnover are not due to an effect of ovarian suppression on other endocrine systems. Our findings provide evidence that endogenous ovarian hormones participate in the regulation of protein turnover in women.

Observations of Branched-Chain Amino Acid Administration in Humans

Since the in vitro study of Buse and Reid in 1975 showing a stimulatory effect of leucine upon rat muscle protein synthesis and reduction in proteolysis, a similar effect has been sought in humans. In 1978, Sherwin demonstrated in humans an improvement in N balance with infusion of leucine in obese subjects fasting to lose weight. A variety of subsequent studies have been performed in humans where leucine alone or the BCAAs have been administered in varying amounts and durations, and the effect upon protein metabolism has been measured. Measurements of changes in muscle amino acid metabolism were made by arteriovenous difference measurements and by biopsies. An anabolic effect of leucine and the branched-chain amino acids (BCAAs) on reduction of muscle protein breakdown was found in these studies, with no measured effect upon muscle protein synthesis. Later studies using stable isotope tracers to define both whole-body protein turnover and leg or arm protein metabolism have similarly concluded that leucine administration specifically induces a reduction in protein breakdown without increasing protein synthesis. This anabolic effect, produced through a reduction of protein breakdown in vivo in humans by leucine is contrary to in vitro studies of rat muscle where stimulation of protein synthesis, has been demonstrated by leucine. Likewise an increase in protein synthesis has also been demonstrated by insulin in rat muscle that is not seen in humans. Of the various studies administering BCAAs or leucine to humans for varying periods of time and amount, the results have been consistent. In addition, no untoward effects have been reported in any of these studies from infusion of the BCAAs at upward 3 times basal flux or 6 times normal dietary intake during the fed portion of the day.

Protein Breakdown in Muscle from Burned Rats Is Blocked by Insulin-Like Growth Factor I and Glycogen Synthase Kinase-3β Inhibitors

We reported previously that IGF-I inhibits burn-induced muscle proteolysis. Recent studies suggest that activation of the phosphotidylinositol 3-kinase (PI3K)/Akt signaling pathway with downstream phosphorylation of Forkhead box O transcription factors is an important mechanism of IGF-I-induced anabolic effects in skeletal muscle. The potential roles of other mechanisms in the anabolic effects of IGF-I are less well understood. In this study we tested the roles of mammalian target of rapamycin and glycogen synthase kinase-3beta (GSK-3beta) phosphorylation as well as MAPK- and calcineurin-dependent signaling pathways in the anticatabolic effects of IGF-I by incubating extensor digitorum longus muscles from burned rats in the presence of IGF-I and specific signaling pathway inhibitors. Surprisingly, the PI3K inhibitors LY294002 and wortmannin reduced basal protein breakdown. No additional inhibition by IGF-I was noticed in the presence of LY294002 or wortmannin. Inhibition of proteolysis by IGF-I was associated with phosphorylation (inactivation) of GSK-3beta. In addition, the GSK-3beta inhibitors, lithium chloride and thiadiazolidinone-8, reduced protein breakdown in a similar fashion as IGF-I. Lithium chloride, but not thiadiazolidinone-8, increased the levels of phosphorylated Foxo 1 in incubated muscles from burned rats. Inhibitors of mammalian target of rapamycin, MAPK, and calcineurin did not prevent the IGF-I-induced inhibition of muscle proteolysis. Our results suggest that IGF-I inhibits protein breakdown at least in part through a PI3K/Akt/GSK3beta-dependent mechanism. Additional experiments showed that similar mechanisms were responsible for the effect of IGF-I in muscle from nonburned rats. Taken together with recent reports in the literature, the present results suggest that IGF-I inhibits protein breakdown in skeletal muscle by multiple mechanisms, including PI3K/Akt-mediated inactivation of GSK-3beta and Foxo transcription factors.

Insulin-like growth factor I slows the rate of denervation induced skeletal muscle atrophy

Loss of the nerve supply to skeletal muscle results in a relentless loss of muscle mass (atrophy) over time. The ability of insulin-like growth factor-1 to reduce atrophy resulting from denervation was examined after transection of the sciatic nerve in transgenic MLC/mIGF-1 mice that over-express mIGF-1 specifically in differentiated myofibres. The cross sectional area (CSA) of all types of myofibres and specifically type IIB myofibres was measured in tibialis anterior muscles from transgenic and wild-type mice at 28 days after denervation. There was a marked myofibre atrophy (∼60%) in the muscles of wild-type mice over this time with increased numbers of myofibres with small CSA. In the muscles of MLC/mIGF-1 mice, over-expression of mIGF-1 reduced the rate of denervation induced myofibre atrophy by ∼30% and preserved myofibres with larger CSA, compared to wild-type muscles. It is proposed that the protective effect of mIGF-1 on denervated myofibres might be due to reduced protein breakdown.

Sepsis-induced muscle proteolysis is blocked by glycogen synthase kinase (GSK)-3 beta inhibitors

Abstract Introduction: Muscle wasting in sepsis is mainly caused by increased degradation of proteins, in particular the myofibrillar proteins actin and myosin. Recent studies suggest that inactivation of GSK-3beta, a downstream enzyme in the PI3K signaling pathway, may prevent muscle atrophy. The role of GSK-3beta in sepsis-induced muscle proteolysis is not known. We tested the hypothesis that inhibition of GSK-3beta reduces protein breakdown in septic muscle. Methods: Male Sprague-Dawley rats underwent induction of sepsis by cecal ligation and puncture (CLP) or were sham-operated. After 16 hours, paired extensor digitorum longus (EDL) muscles were incubated for 2 hours under physiological conditions in the absence or presence of one of the GSK-3beta inhibitors, lithium chloride (LiCl, 50 millimolar) or thiadiazolidinone-8 (TDZD-8, 25 micromolar). Protein breakdown rates were determined by measuring the net release of free tyrosine. Results: Sepsis resulted in a substantial increase in muscle protein breakdown, confirming previous observations. Treatment of incubated muscles with either of the GSK-3beta inhibitors significantly reduced protein breakdown in muscle from septic rats. LiCl also reduced basal protein degradation. ∗−LiCl+LiCl−TDZD-8+TDZD-8SHAM266.7 ± 21.7186.6 ± 15.1∗272.9 ± 8.6210.2 ± 15.7CLP475.0 ± 43.1301.7 ± 16.6∗418.6 ± 42.8301.4 ± 31.4∗∗Results are mean ± SEM with n=8 in each group;∗p Conclusions: Inhibition of GSK-3beta may reduce muscle protein breakdown during sepsis and perhaps other muscle-wasting conditions as well.

Intravenous insulin decreases protein breakdown in infants on extracorporeal membrane oxygenation

Background/Purpose Infants requiring extracorporeal membrane oxygenation (ECMO) have the highest rates of protein catabolism ever reported. Recent investigations have found that such extreme protein breakdown is refractory to conventional nutritional management. In this pilot study, the authors sought to use the anabolic hormone insulin to reduce the profound protein degradation in this cohort. Methods Four parenterally fed infants on ECMO were enrolled in a prospective, randomized, crossover trial. Subjects were administered an insulin infusion using a 4-hour hyperinsulinemic euglycemic clamp followed by a control saline infusion on consecutive days in random order. Whole-body protein flux and breakdown were quantified using a primed continuous infusion of the stable isotope l-[1- 13C]leucine. Statistical analyses were performed using paired t tests. Results Serum insulin levels were increased 15-fold during the insulin clamp compared with the saline control (407 ± 103 v 26 ± 12 μU/mL; P < .05). During the insulin infusion, infants had decreased rates of total leucine flux (214 ± 25 v 298 ± 38 μmol/kg/h; P < .05) and leucine flux derived from protein breakdown (156 ± 40 v 227 ± 54 μmol/kg/h; P < .05) when compared with saline control. Overall, insulin administration produced a 32% reduction in protein breakdown ( P < .05). Conclusions In this pilot study, the anabolic hormone insulin markedly reduced protein breakdown in critically ill infants on ECMO. Because elevated protein breakdown correlates with mortality and morbidity, the administration of intravenous insulin may ultimately have broad applicability to the metabolic management of critically ill infants.

A study of parenteral versus enteral nutrition following caecal ligation and puncture in the rat: Influence on survival and tissue protein turnover

Background & aims: Methods of nutritional management in abdominal sepsis remain controversial. Methods: Sprague Dawley rats were either fed via a central line in the right internal jugular vein or duodenally via a gastrostomy tube, and were randomised to undergo either caecal ligation and puncture (CLP) or laparotomy only. Post-operatively, animals received either parenteral nutrition, enteral nutrition or saline only (parenteral and enteral nutrition protocols were isocaloric and isonitrogenous). After 72 h, fractional rate of protein synthesis ( K s, %/day) was measured in gastrocnemius muscle and liver, and protein breakdown was measured in incubated epitrochlearis muscles. Serum insulin-like growth factor-I (IGF-I), acid-labile subunit (ALS) and IGF binding protein-1 (IGFBP-1) levels were determined by specific radioimmunoassay methods. Results: After CLP, when compared with starved animals, only enteral nutrition resulted in a significant decrease in survival to 72 h ( P<0.001). Parenteral nutrition, but not enteral nutrition, increased muscle ( P=0.02) and liver ( P<0.001) K s, IGF-I ( P<0.001) and ALS levels ( P<0.001), whereas both parenteral and enteral nutrition reduced IGFBP-1 levels ( P<0.001). Neither enteral nor parenteral nutrition reduced protein breakdown in septic animals. Conclusions: In this model of severe abdominal sepsis where gut function cannot be assessed, enteral nutrition was associated with increased mortality and was less effective than parenteral nutrition in augmenting muscle and liver protein synthesis.

Differential regulation of protein dynamics in splanchnic and skeletal muscle beds by insulin and amino acids in healthy human subjects.

To determine the in vivo effect of amino acids (AAs) alone or in combination with insulin on splanchnic and muscle protein dynamics, we infused stable isotope tracers of AAs in 36 healthy subjects and sampled from femoral artery and vein and hepatic vein. The subjects were randomized into six groups and were studied at baseline and during infusions of saline (group 1), insulin (0.5 mU. kg(-1). min(-1)) (group 2), insulin plus replacement of AAs (group 3) insulin plus high-dose AAs (group 4), or somatostatin and baseline replacement doses of insulin, glucagon and GH plus high dose of AAs (group 5) or saline (group 6). Insulin reduced muscle release of AAs mainly by inhibition of protein breakdown. Insulin also enhanced AA-induced muscle protein synthesis (PS) and reduced leucine transamination. The main effect of AAs on muscle was the enhancement of PS. Insulin had no effect on protein dynamics or leucine transamination in splanchnic bed. However, AAs reduced protein breakdown and increased synthesis in splanchnic bed in a dose-dependent manner. AAs also enhanced leucine transamination in both splanchnic and muscle beds. Thus insulin's anabolic effect was mostly on muscle, whereas AAs acted on muscle as well as on splanchnic bed. Insulin achieved anabolic effect in muscle by inhibition of protein breakdown, enhancing AA-induced PS, and reducing leucine transamination. AAs largely determined protein anabolism in splanchnic bed by stimulating PS and decreasing protein breakdown.

Glutamine starvation of monocytes inhibits the ubiquitin–proteasome proteolytic pathway

Peripheral blood monocytes utilize free glutamine (Gln) in addition to glucose as an important energy substrate. Although this demand increases upon activation, monocytes are commonly confronted with decreased plasma Gln during critical illness and thus suffer from Gln-starvation. Here we investigate the influence of Gln-starvation on protein stability and its effects on the monocyte proteome. Gln-starvation caused a reduction of protein degradation which was accompanied by an accumulation of ubiquitin–protein conjugates and a reduction of intracellular ATP. Similar effects were observed under ATP-reducing conditions and in the presence of a proteasome inhibitor. Using two-dimensional gel electrophoresis we identified the IL-1β precursor protein (pIL-1β) as the, by far, most induced protein in endotoxin-treated monocytes. The degradation of the short-lived pIL-1β was strongly reduced during Gln-starvation, while the degradation of the long-lived, constitutively expressed β-actin was less affected. This indicates that although Gln-starvation reduces protein breakdown on the overall proteasome level, it leads to differential changes in the stability of specific proteins. This selective effect is likely to contribute to the immunocompromised state of monocytes commonly observed during critical illness.

Dietary macronutrients, endocrine functioning and intermediary metabolism in broiler chickens: Pair wise substitutions between protein, fat and carbohydrate

Three pens of male broiler chicks were raised under standard conditions and fed from 7 to 42 days of age three isocaloric diets each with 15.8; 19.6 and 19.5% of CP; and 51, 51, and 44% of CHO; and 6.5; 3.0 and 7.7% of fat, and designated as the low protein (LowCP), low lipid (LowL) and low carbohydrate (LowCHO) diets, respectively. Body weights and feed intake were monitored weekly and blood samples were collected at the same time for posterior analysis of hormone and metabolite content. Chickens fed the LowCP diet were characterized by a reduced body weight gain and feed intake and poorer feed conversion efficiency compared to those fed the LowL and LowCHO diets, which were very similar in this respect. Plasma corticosterone and glucose levels and creatine kinase activity were not significantly changed by diet composition. LowCP chickens were characterised by the lowest plasma T 4 and uric acid levels (indicative for reduced protein breakdown and lower protein ingestion) but highest plasma triglyceride levels (congruent with their higher fat deposition) compared to the LowL and LowCHO chickens. LowL chickens had on average higher plasma T 3 and free fatty acid levels compared to the LowCP and LowCHO chickens. In conclusion, a limited substitution of carbohydrate for fat in iso-nitrogenous, iso-energetic diets has no pronounced effects on plasma hormone and metabolite levels, except for the elevation in T 3 (may enhance glucose uptake) and free fatty acid levels in the plasma of the chickens fed the LowL diet. The protein content of the diet has a greater impact on zootechnical performance, and underlying endocrine regulation of the intermediary metabolism compared to the dietary lipid and CHO fraction.

Phosphatidylinositol 3-Kinase Activity Is Required for Epidermal Growth Factor to Suppress Proteolysis

Suppression of protein breakdown occurs commonly in cell growth, but the pathways responsible for controlling proteolysis are poorly understood. Protein breakdown in NRK-52E renal epithelial cells treated with epidermal growth factor (EGF) and intracellular signaling inhibitors or dominant negative signaling molecules contained in an adenoviral vector were measured. The tyrosine kinase inhibitor, herbimycin A, eliminated the suppression of proteolysis induced by EGF. In contrast, the Src inhibitor, PP1, had no effect. Expression of dominant negative H-RasY57 blocked the ability of EGF to stimulate downstream targets of Ras and also reduced the ability of EGF to suppress proteolysis. Inhibiting MEK did not influence the ability of EGF to suppress proteolysis, but the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY249002, stimulated basal proteolysis and completely eliminated the proteolytic response to EGF. Use of an adenovirus that expresses a dominant negative p85 subunit of class 1 PI 3-kinase completely blocked the ability of EGF to suppress proteolysis, whereas use of an adenovirus expressing a K227E constitutively active p110 subunit reproduced the reduction in protein breakdown. It was concluded that EGF suppresses proteolysis by a mechanism that involves Ras and class 1 PI 3-kinase.

Reversal of cancer-related wasting using oral supplementation with a combination of β-hydroxy-β-methylbutyrate, arginine, and glutamine

Background: Cancer-related cachexia is caused by a diverse combination of accelerated protein breakdown and slowed protein synthesis. The hypothesis proposed in this study is that supplementation of specific nutrients known to positively support protein synthesis and reduce protein breakdown will reverse the cachexia process in advanced cancer patients. Methods: Patients with solid tumors who had demonstrated a weight loss of at least 5% were considered for the study. Patients were randomly assigned in a double-blind fashion to either an isonitrogenous control mixture of nonessential amino acids or an experimental treatment containing β-hydroxy-β-methylbutyrate (3 g/d), L-arginine (14 g/d), and L-glutamine (14 g/d [HMB/Arg/Gln]). The primary outcomes measured were the change in body mass and fat-free mass (FFM), which were assessed at 0, 4, 8, 12, 16, 20, and 24 weeks. Results: Thirty-two patients (14 control, 18 HMB/Arg/Gln) were evaluated at the 4-week visit. The patients supplemented with HMB/Arg/Gln gained 0.95 ± 0.66 kg of body mass in 4 weeks, whereas control subjects lost 0.26 ± 0.78 kg during the same time period. This gain was the result of a significant increase in FFM in the HMB/Arg/Gln-supplemented group (1.12 ± 0.68 kg), whereas the subjects supplemented with the control lost 1.34 ± 0.78 kg of FFM ( P = 0.02). The response to 24-weeks of supplementation was evaluated by an intent-to-treat statistical analysis. The effect of HMB/Arg/Gln on FFM increase was maintained over the 24 weeks (1.60 ± 0.98 kg; quadratic contrast over time, P <0.05). There was no negative effect of treatment on the incidence of adverse effects or quality of life measures. Conclusions: The mixture of HMB/Arg/Gln was effective in increasing FFM of advanced (stage IV) cancer. The exact reasons for this improvement will require further investigation, but could be attributed to the observed effects of HMB on slowing rates of protein breakdown, with improvements in protein synthesis observed with arginine and glutamine.

Flux of amino acids and energy substrates across the leg in weight-stable HIV-infected patients with acute opportunistic infections: indication of a slow protein wasting process.

Increased whole-body proteolysis with muscle protein net degradation has been suggested as one of the causes of weight loss in patients infected with human immunodeficiency virus (HIV). We studied the exchange rates of amino acids and energy substrates across the lower extremity in 16 HIV patients and 16 age-matched controls with similar body cell mass. The patients had either opportunistic infections or chronic diarrhea but no signs of clinical malnutrition. The following findings were obtained in the HIV patients: an augmented peripheral net release of arginine and lysine; an increase in both the negative arterial-venous difference and the efflux of the nitrogen contained in nonmetabolized amino acids; diminished export of 3-methylhistidine; lowered plasma and erythrocyte amino acid concentrations; reduced output of glycerol and furthermore; and neither a net release nor a net uptake of free fatty acids. The findings concerning nitrogen metabolism support the hypothesis that, in the presence of a reduction in protein breakdown, peripheral protein synthesis is severely depressed, making a slow protein wasting process likely to occur. The balances of glycerol and free fatty acids are due not only to the leg tissues but perhaps also in part to increased net retention of these substrates by skeletal muscle.

Regulation of protein and energy metabolism by the somatotropic axis

The somatotropic axis plays a key role in the co-ordination of protein and energy metabolism during postnatal growth. This review discusses the complexity of the regulation of protein and energy metabolism by the somatotropic axis using three main examples: reduced nutrition, growth hormone (GH) treatment and insulin-like growth factor-1 (IGF-1) treatment. Decreased nutrition leads to elevated GH secretion, but it reduces hepatic GH receptor (GHR) number and plasma levels of IGF-1; it also changes the relative concentrations of IGF binding proteins (IGFBPs) in plasma. GH treatment improves the partitioning of nutrients by increasing protein synthesis and decreasing protein degradation and by modifying carbohydrate and lipid metabolism. However, these well-established metabolic responses to GH can change markedly in conditions of reduced nutritional supply or metabolic stress. Short-term infusion of IGF-1 in lambs reduces protein breakdown and increases protein synthesis. However, long-term IGF-1 administration in yearling sheep does not alter body weight gain or carcass composition. The lack of effect of IGF-1 treatment can be explained by activation of feedback mechanisms within the somatotropic axis, which lead to a reduction in GH secretion and hepatic GHR levels. The somatotropic axis has multiple levels of hormone action, with complex feedback and control mechanisms, from gene expression to regulation of mature peptide action. Given that GH has a much wider range of biologic functions than previously recognized, advances in research of the somatotropic axis will improve our understanding of the normal growth process and metabolic disorders.