Leucine Infusion Research Articles

A high protein diet upregulates whole‐body protein turnover during energy deficit

The effects of dietary protein level on whole‐body protein turnover (WBPTO) during energy deficit (ED) are not well described. Using a randomized‐block design, 24 males and five females (21 ± 3 yr) participated in a controlled trial. Volunteers consumed either standard (SP; 0.8 g·kg−1·d−1), moderate (MP; 1.6 g·kg−1·d−1), or high (HP; 2.4 g·kg−1·d−1) protein diets for 31 days. A weight maintenance (WM, days 1–10) period was followed by 21 days of ED (days 11–31), during which energy intake was restricted to 60% of total daily energy expenditure. Whole‐body protein breakdown, synthesis, and oxidation were determined at rest during WM (day 10) and ED (day 31) using primed, continuous [13C]‐leucine infusions. Volunteers lost (P < 0.05) 3.3 ± 0.9 kg body mass in response to ED regardless of dietary protein level. Protein breakdown decreased (P < 0.05) in response to ED for SP and MP diets, but did not change for HP. Synthesis decreased (P < 0.05) following ED regardless of dietary protein level. Protein oxidation (μmol·kg−1·h−1) increased linearly between SP (9.7 ± 0.5), MP (11.8 ± 0.5), and HP (13.9 ± 0.5) diets during WM, with increased oxidation observed only for HP (16 ± 0.7) during ED (diet‐by‐energy interaction, P < 0.05). These data demonstrate that the level of dietary protein intake modulates WBPTO during sustained ED, as consumption of a high protein diet upregulates WBPTO during ED.

Effect of resistance training on changes in body composition and macronutrient utilization after weight loss in older women

We assessed the effect of resistance training (RT) on energy restriction (ER)‐induced changes in body composition and macronutrient utilization (MU) in older, overweight women. Sixteen women (age 68 ± 1 y, BMI 29 ± 1 kg/m2) consumed controlled diets with 1.0 g protein/kg•d for 16 wk. During wk 1–3 and 15–16, energy intake matched the subject's energy need, while during wk 4–14 it was 500 kcal/d below need. Each woman either performed RT 3 d/wk (n=8) or remain sedentary (SED, n=8). Fasting and postprandial (PP) energy utilization and PP energy storage from macronutrients were determined using indirect calorimetry and 1‐[13C] leucine infusion data at wk 2 and 15. PP energy and macronutrient intakes were the same pre and post intervention. Over time, body mass (SED −5.8 ± 0.6; RT −5.0 ± 0.2 kg) and fat mass decreased (SED −4.1 ± 0.9; RT −4.7 ± 0.5 kg) with no difference between groups. Fat‐free mass (FFM) decreased in SED (−1.6 ± 0.4 kg, P ≤ 0.05) but was unchanged in RT (−0.3 ± 0.4 kg, P = 0.07). At baseline, carbohydrate (CHO), fat and protein accounted for ~10, 76, and 14% of total MU (kcal/kg FFM•h) while fasting and ~35, 43, and 22% PP. PP energy storage was ~65, 25, and 10% CHO, fat, and protein. Weight loss and RT did not influence these proportions. Resistance training is an effective way for older women to preserve fat‐free mass after weight loss without affecting macronutrient utilization and storage.Grant Funding Source : NIH R29 AG13409 and UL1 RR025761

Differential regulation of protein synthesis in skeletal muscle and liver of neonatal pigs by leucine through an mTORC1-dependent pathway

Neonatal growth is characterized by a high protein synthesis rate that is largely due to an enhanced sensitivity to the postprandial rise in insulin and amino acids, especially leucine. The mechanism of leucine's action in vivo is not well understood. In this study, we investigated the effect of leucine infusion on protein synthesis in skeletal muscle and liver of neonatal pigs. To evaluate the mode of action of leucine, we used rapamycin, an inhibitor of mammalian target of rapamycin (mTOR) complex-1 (mTORC1). Overnight-fasted 7-day-old piglets were treated with rapamycin for 1 hour and then infused with leucine (400 μmol·kg-1·h-1) for 1 hour. Leucine infusion increased the rate of protein synthesis, and ribosomal protein S6 kinase 1 (S6K1) and eukaryotic initiation factor (eIF) 4E-binding protein-1 (4E-BP1) phosphorylation in gastrocnemius and masseter muscles (P < 0.05), but not in the liver. The leucine-induced stimulation of protein synthesis and S6K1 and 4E-BP1 phosphorylation were completely blocked by rapamycin, suggesting that leucine action is by an mTORC1-dependent mechanism. Neither leucine nor rapamycin had any effect on the activation of the upstream mTORC1 regulators, AMP-activated protein kinase and protein kinase B, in skeletal muscle or liver. The activation of eIF2α and elongation factor 2 was not affected by leucine or rapamycin, indicating that these two pathways are not limiting steps of leucine-induced protein synthesis. These results suggest that leucine stimulates muscle protein synthesis in neonatal pigs by inducing the activation of mTORC1 and its downstream pathway leading to mRNA translation.

Hypothalamic Leucine Metabolism Regulates Liver Glucose Production

Amino acids profoundly affect insulin action and glucose metabolism in mammals. Here, we investigated the role of the mediobasal hypothalamus (MBH), a key center involved in nutrient-dependent metabolic regulation. Specifically, we tested the novel hypothesis that the metabolism of leucine within the MBH couples the central sensing of leucine with the control of glucose production by the liver. We performed either central (MBH) or systemic infusions of leucine in Sprague-Dawley male rats during basal pancreatic insulin clamps in combination with various pharmacological and molecular interventions designed to modulate leucine metabolism in the MBH. We also examined the role of hypothalamic ATP-sensitive K+ channels (KATP channels) in the effects of leucine. Enhancing the metabolism of leucine acutely in the MBH lowered blood glucose through a biochemical network that was insensitive to rapamycin but strictly dependent on the hypothalamic metabolism of leucine to α-ketoisocaproic acid and, further, insensitive to acetyl- and malonyl-CoA. Functional KATP channels were also required. Importantly, molecular attenuation of this central sensing mechanism in rats conferred susceptibility to developing hyperglycemia. We postulate that the metabolic sensing of leucine in the MBH is a previously unrecognized mechanism for the regulation of hepatic glucose production required to maintain glucose homeostasis.

Protein consumption following aerobic exercise increases whole-body protein turnover in older adults

Research measuring whole-body protein turnover (WBPT) after both exercise and nutrition has generally focused on resistance exercise; however, there is a paucity of data regarding the effect of postaerobic exercise nutrition, especially in older adults. It is not known if postexercise protein feeding has a beneficial effect on protein turnover after low- to moderate-intensity exercise. We investigated whether consuming protein plus carbohydrate (PRO) immediately after an acute bout of aerobic exercise has an additive effect over carbohydrate alone (CHO) on WBPT in older individuals. Twelve healthy older adults (age, 59 ± 4 years) were studied on 2 separate occasions after 1 h of exercise at approximately 50% of maximal rate of oxygen uptake, followed by 4 h of recovery. Immediately following exercise, subjects ingested a CHO (60 g) or an isocaloric PRO beverage (40 g carbohydrate, 20 g whey protein). Whole-body protein metabolism was determined using [1-13C]leucine infusion (60 mg prime; 75 mgh(-1) continuous), and sampling blood and expired breath. Rates of whole-body leucine appearance and oxidation, and nonoxidative leucine disposal during the third and fourth hours of postexercise recovery were higher in the PRO group (2.51 ± 0.55, 0.78 ± 0.37, and 1.71 ± 0.44 micromol kg(-1)·min(-1), respectively) than in the CHO group (1.81 ± 0.27, 0.33 ± 0.14, and 1.47 ± 0.25 micromol kg(-1)·min-1, respectively; p = 0.001). Our results indicate that consumption of a PRO beverage after aerobic exercise increased WBPT to a greater extent than a CHO beverage.

Effect of duodenal infusions of leucine on milk yield and plasma amino acids in dairy cows

Four high-yielding lactating Holstein cows fitted with duodenal cannulas were used in the experiment. Cows were divided into 2 groups &amp;ndash; control (Control) with leucine deficiency and experimental (Leucine) with a leucine supplement. The experiment was divided into 4 periods of 7 days, each consisting of a 3-day preliminary period followed by a 4-day experimental period. In the first period, 2 cows were assigned to Control and the remaining 2 to Leucine. In the subsequent period the cows were switched to the other treatment. Cows were fed individually twice daily the basal diet based on maize silage, lucerne hay and supplemental mixture. Infusions of amino acids in Leucine consisted of methionine (12.6 g/day), lysine (20.7 g/day), histidine (10.7 g/day) and leucine (19.3 g/day). The composition of amino acid infusate in Control was the same except for leucine that was replaced with monosodium L-glutamate. The intake of dry matter was not affected by the treatment (P &amp;gt; 0.05). No effect of leucine infusion on milk yield and composition was observed (P &amp;gt; 0.05), nevertheless the concentration of protein and casein in milk tended to be higher in Leucine (38.3 and 31.3 g/kg) than in Control (37.4 and 30.4 g/kg, respectively, P &amp;lt; 0.1). The yield of milk components was not affected by the treatment (P &amp;gt; 0.05). Duodenal infusion of leucine resulted in a decreased plasma level of isoleucine in Leucine compared to Control (P &amp;lt; 0.01). Concentrations of leucine, cysteine and citrulline tended to be higher and the concentration of tyrosine tended to be lower in Leucine in comparison with Control (P &amp;lt; 0.10).

Leucine and α-Ketoisocaproic Acid, but Not Norleucine, Stimulate Skeletal Muscle Protein Synthesis in Neonatal Pigs , ,

The branched-chain amino acid, leucine, acts as a nutrient signal to stimulate protein synthesis in skeletal muscle of young pigs. However, the chemical structure responsible for this effect has not been identified. We have shown that the other branched-chain amino acids, isoleucine and valine, are not able to stimulate protein synthesis when raised in plasma to levels within the postprandial range. In this study, we evaluated the effect of leucine, α-ketoisocaproic acid (KIC), and norleucine infusion (0 or 400 μmol·kg−1·h−1 for 60 min) on protein synthesis and activation of translation initiation factors in piglets. Infusion of leucine, KIC, and norleucine raised plasma levels of each compound compared with controls. KIC also increased (P < 0.01) and norleucine reduced (P < 0.02) plasma levels of leucine compared with controls. Administration of leucine and KIC resulted in greater (P < 0.006) phosphorylation of eukaryotic initiation factor (eIF) 4E binding protein-1 (4E-BP1) and eIF4G, lower (P < 0.04) abundance of the inactive 4E-BP1·eIF4E complex, and greater (P < 0.05) active eIF4G·eIF4E complex formation in skeletal muscle compared with controls. Protein synthesis in skeletal muscle was greater (P < 0.02) in leucine- and KIC-infused pigs than in those in the control group. Norleucine infusion did not affect muscle protein synthesis or translation initiation factor activation. In liver, neither protein synthesis nor activation of translation initiation factors was affected by treatment. These results suggest that the ability of leucine to act as a nutrient signal to stimulate skeletal muscle protein synthesis is specific for leucine and/or its metabolite, KIC.

Differential effects of long-term leucine infusion on tissue protein synthesis in neonatal pigs

Leucine is unique among the amino acids in its ability to promote protein synthesis by activating translation initiation via the mammalian target of rapamycin (mTOR) pathway. Previously, we showed that leucine infusion acutely stimulates protein synthesis in fast-twitch glycolytic muscle of neonatal pigs but this response cannot be maintained unless the leucine-induced fall in amino acids is prevented. To determine whether leucine can stimulate protein synthesis in muscles of different fiber types and in visceral tissues of the neonate in the long-term if baseline amino acid concentrations are maintained, overnight fasted neonatal pigs were infused for 24 h with saline, leucine (400 micromol kg(-1) h(-1)), or leucine with replacement amino acids to prevent the leucine-induced hypoaminoacidemia. Changes in the fractional rate of protein synthesis and activation of mTOR, as determined by eukaryotic initiation factor 4E binding protein (4E-BP1) and S6 kinase 1 (S6K1) phosphorylation, in the gastrocnemius and masseter muscles, heart, liver, jejunum, kidney, and pancreas were measured. Leucine increased mTOR activation in the gastrocnemius and masseter muscles, liver, and pancreas, in both the absence and presence of amino acid replacement. However, protein synthesis in these tissues was increased only when amino acids were infused to maintain baseline levels. There were no changes in mTOR signaling or protein synthesis in the other tissues we examined. Thus, long-term infusion of leucine stimulates mTOR signaling in skeletal muscle and some visceral tissues but the leucine-induced stimulation of protein synthesis in these tissues requires sustained amino acid availability.

A Method To Study In Vivo Protein Synthesis In Slow- And Fast-twitch Human Muscle Fibers

PURPOSE: To develop an approach to directly assess protein fractional synthesis rate (FSR) in isolated human muscle fibers and to examine potential differences in FSR between slow (MHC I) and fast twitch (MHC IIa) fibers. METHODS: Individual muscle fibers were isolated from biopsies of the vastus lateralis (VL) and soleus (SOL) obtained from eight young men during a primed, continuous infusion of 2H3 leucine performed under basal conditions. To determine mixed protein FSR, a portion of each fiber was used to identify fiber type, fibers of the same fiber type were pooled, and the 2H3 leucine enrichment determined via GC-MS. RESULTS: In the VL, MHC I fibers exhibited a 33% faster (p<0.05) mixed protein FSR compared to MHC IIa fibers (0.0900.005 vs. 0.0680.002 %/hr). Similar (p>0.05) mixed protein FSR values were observed between MHC I fibers from the SOL (0.0820.006 %/hr) and MHC I fibers from the VL. Feasibility of processing isolated fibers for myofibrillar (MF) protein FSR was also determined in non-fiber typed pooled fibers from the VL, resulting in a MF protein FSR of 0.0730.004 %/hr. CONCLUSION: These methods can be applied to the study of fiber type specific responses in human skeletal muscle, and the need for this level of investigation is underscored by the different basal protein synthesis rates in MHC I and MHC IIa fibers originating from the same muscle. Supported by NIH R01 AG025032; NASA NNJ06HF59G

Effect of Laparoscopy and Laparotomy on Energy and Protein Metabolism in Children: A Randomized Controlled Trial

To compare the effects of surgery on energy and protein metabolism in children randomized to undergo laparoscopic and open surgery. We randomized 41 patients to open or laparoscopic Nissen fundoplication. Anesthesia and postoperative management were standardized. We recorded core temperature, respiratory gas exchange preoperatively, intraoperatively, and 4 and 24 hours postoperatively and calculated resting energy expenditure (REE). Protein breakdown was measured by using stable isotopic leucine infusion preoperatively and 4 hours postoperatively. Intraoperative core temperature and oxygen consumption increased in the laparoscopic group compared with the open group. REE decreased in the early postoperative period in the open group, but did not decrease after laparoscopy. REE at 4 hours was higher after laparoscopy. Protein breakdown also decreased in the early postoperative period; the pattern of change between open and laparoscopic groups was of borderline significance. Laparoscopy in children may alter the changes in energy metabolism observed after open surgery. These differences may be partially caused by alterations in intraoperative thermoregulation and protein breakdown during laparoscopy in children.

Prolonged leucine infusion differentially affects tissue protein synthesis in neonatal pigs

Leucine (Leu) acutely stimulates protein synthesis by activating the mammalian target of rapamycin complex 1 (mTORC1) pathway. To determine whether Leu can stimulate protein synthesis in muscles of different fiber types and visceral tissues of the neonate for a prolonged period and to determine the role of other amino acids in the response, overnight fasted neonatal pigs were infused for 24 h with saline, Leu (400 μmol • kg‐1 • h‐1), or Leu with replacement amino acids to prevent the Leu induced fall in other amino acids. Protein synthesis rates and phosphorylation of 4E binding protein (4E‐BP1) and S6 kinase 1 (S6K1), indicators of mTORC1 activation, were measured. Leu increased 4E‐BP1 and S6K1 phosphorylation in the longissimus dorsi, gastrocnemius, and masseter muscles, liver, and pancreas, in both the absence and presence of amino acid replacement. However, protein synthesis was increased only when amino acids were infused to prevent hypoaminoacidemia. Leu had no affect on mTORC1 signalling or protein synthesis in the heart, jejunum, and kidney. Thus, prolonged infusion of leucine stimulates mTORC1 signaling in skeletal muscle and some visceral tissues but the Leu‐induced stimulation of protein synthesis in these tissues requires sustained amino acid availability. (Supported by Ajinomoto Amino Acid Research Program and USDA 58‐6250‐6‐001).

Changes in Apolipoprotein B100-Containing Lipoprotein Metabolism Due to an Estrogen Plus Progestin Oral Contraceptive: A Stable Isotope Kinetic Study

Oral contraceptives with estrogen plus progestin are likely to influence apolipoprotein B (apoB)-containing lipoprotein metabolism by changing the expression of different enzymes or receptors that play a major role in this metabolism. However, the precise changes in apoB kinetic parameters induced by oral contraceptives that are now currently used are unknown. We studied the impact of Moneva, containing 30 microg ethinylestradiol and 75 microg gestodene, on the apoB production rate and fractional catabolic rate of very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL). Using a 16-h [(13)C]leucine infusion, we performed an apoB kinetic study in nine normolipidemic women before and 3 months after beginning Moneva. On Moneva, serum triglycerides increased moderately (+12%, P = 0.04) in the fed state, whereas serum LDL remained unchanged. LDL particles were richer in triglycerides in women on Moneva (7.5 +/- 1.5 vs. 4.3 +/- 1.0% of total LDL mass, P < 0.01). The apoB production rate of VLDL, IDL, and LDL increased by 49 (P = 0.04), 55 (P = 0.05), and 51% (P = 0.01), respectively. The fractional catabolic rate of apoB in LDL increased by 36% (P = 0.04). Consequently, the serum LDL apoB pool size remained unchanged (26.49 +/- 6.98 vs. 23.96 +/- 5.37 mg/kg). Oral contraception with ethinylestradiol plus gestodene induces an increase in the production rate of apoB-containing lipoproteins all along the VLDL-->IDL-->LDL cascade. The increased production rate of apoB in LDL is counterbalanced by a higher fractional catabolic rate of apoB in LDL, thus precluding an increase in the concentration of atherogenic LDL particles.

Stimulation of Muscle Protein Synthesis by Prolonged Parenteral Infusion of Leucine Is Dependent on Amino Acid Availability in Neonatal Pigs

The postprandial rise in amino acids, particularly leucine, stimulates muscle protein synthesis in neonates. Previously, we showed that a 1-h infusion of leucine increased protein synthesis, but this response was not sustained for 2 h unless the leucine-induced decrease in amino acids was prevented. To determine whether a parenteral leucine infusion can stimulate protein synthesis for a more prolonged, clinically relevant period if baseline amino acid concentrations are maintained, overnight food-deprived neonatal pigs were infused for 24 h with saline, leucine (400 μmol·kg−1· h−1), or leucine with replacement amino acids. Amino acid replacement prevented the leucine-induced decrease in amino acids. Muscle protein synthesis was increased by leucine but only when other amino acids were supplied to maintain euaminoacidemia. Leucine did not affect activators of mammalian target of rapamycin (mTOR), i.e. protein kinase B, AMP-activated protein kinase, tuberous sclerosis complex 2, or eukaryotic elongation factor 2. There was no effect of treatment on the association of mTOR with regulatory associated protein of mammalian target of rapamycin (raptor), G-protein β subunit-like protein, or rictor or the phosphorylation of raptor or proline-rich Akt substrate of 40 kDa. Phosphorylation of mTOR and its downstream targets, eukaryotic initiation factor (eIF) 4E binding protein and ribosomal protein S6 kinase, and the eIF4E · eIF4G association were increased and eIF2α phosphorylation was reduced by leucine and was not further altered by correcting for the leucine-induced hypoaminoacidemia. Thus, prolonged parenteral infusion of leucine activates mTOR and its downstream targets in neonatal skeletal muscle, but the stimulation of protein synthesis also is dependent upon amino acid availability.

Effects of rosiglitazone and pioglitazone on lipoprotein metabolism in patients with Type 2 diabetes and normal lipids

Previous studies have suggested that plasma lipids are affected differently by the peroxisome proliferators-activated receptor (PPAR)-gamma agonists pioglitazone and rosiglitazone. The aim of this study was to perform a quantitative lipoprotein turnover study to determine the effects of PPAR-gamma agonists on lipoprotein metabolism. Twenty-four subjects with Type 2 diabetes treated with diet and/or metformin were randomized in a double-blind study to receive 30 mg pioglitazone, 8 mg rosiglitazone or placebo once daily for 3 months. Before and after treatment, absolute secretion rate (ASR) and fractional catabolic rate (FCR) of very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL) and low-density lipoprotein (LDL) apolipoprotein B100 were measured with a 10-h infusion of 1-13C leucine. There was a significant decrease in glycated haemoglobin (HbA(1c)) and non-esterified fatty acids with pioglitazone (P = 0.01; P = 0.02) and rosiglitazone (P = 0.04; P = 0.003), respectively, but no change in plasma triglyceride or high-density lipoprotein (HDL) cholesterol. Following rosiglitazone, there was a significant reduction in VLDL apolipoprotein B100 (apoB) ASR (P = 0.01) compared with baseline, a decrease in VLDL triglyceride/apoB (P = 0.01), an increase in LDL2 cholesterol (P = 0.02) and a decrease in LDL3 cholesterol (P = 0.02). There was a decrease in VLDL triglyceride/apoB (P = 0.04) in the pioglitazone group. There was no significant difference in change in VLDL ASR or FCR among the three groups. In patients with Type 2 diabetes and normal lipids, treatment with rosiglitazone or pioglitazone had no significant effect on lipoprotein metabolism compared with placebo.

Long‐term leucine induced stimulation of muscle protein synthesis is amino acid dependent

Infusing leucine for 1 h increases skeletal muscle protein synthesis in the neonate, but this is not sustained for 2 h unless the corresponding fall in amino acids is prevented. This study aimed to determine whether a continuous leucine infusion can stimulate protein synthesis for a prolonged period when baseline amino acid concentrations are maintained. Overnight fasted neonatal pigs (n = 18) were infused for 24 h with saline, leucine (400 µmol · kg−1 · h −1),or leucine with replacement amino acids. Leucine stimulated muscle protein synthesis only when other amino acids were maintained at fasting. Leucine had no effect on the phosphorylation of protein kinase B, AMP‐activated protein kinase, tuberous sclerosis complex 2, or eukaryotic elongation factor 2, the association of mTOR with raptor, G‐protein ßsubunit‐like protein, or rictor, or the phosphorylation of raptor or proline‐rich Akt Substrate of 40 kDa. Phosphorylation of mTOR, eukaryotic initiation factor (eIF) 4E binding protein (4EBP1) and ribosomal protein S6 kinase, and eIF4E▸eIF4G association were increased and eIF2 phosphorylation was reduced by leucine, in the absence and presence of replacement amino acids. Thus, prolonged infusion of leucine activates mTOR and its downstream targets in skeletal muscle; however, protein synthesis stimulation is dependent upon amino acid availability. (Supported by Ajinomoto Amino Acid Research Program).

Adaptation to a long term (4 weeks) arginine- and precursor (glutamate, proline and aspartate)-free diet

It is not known whether arginine homeostasis is negatively affected by a "long term" dietary restriction of arginine and its major precursors in healthy adults. To assess the effects of a 4-week arginine- and precursor-free dietary intake on the regulatory mechanisms of arginine homeostasis in healthy subjects. Ten healthy adults received a complete amino acid diet for 1 week (control diet) and following a break period, six subjects received a 4-week arginine, proline, glutamate and aspartate-free diet (APF diet). The other four subjects continued for 4 weeks with the complete diet. On days 4 and 7 of the first week and days 25 and 28 of the 4-week period, the subjects received 24-h infusions of arginine, citrulline, leucine and urea tracers. During the 4-week APF, plasma arginine fluxes for the fed state, were significantly reduced. There were no significant differences for citrulline, leucine or urea fluxes. Arginine de novo synthesis was not affected by the APF intake. However, arginine oxidation was significantly decreased. In healthy adults, homeostasis of arginine under a long term arginine- and precursor-free intake is achieved by decreasing catabolic rates, while de novo arginine synthesis is maintained.

Effects of dietary protein restriction on albumin and fibrinogen synthesis in macroalbuminuric type 2 diabetic patients

Diabetic nephropathy is associated with hypoalbuminaemia and hyperfibrinogenaemia. A low-protein diet has been recommended in patients with diabetic nephropathy, but its effects on albumin and fibrinogen synthesis are unknown. We compared the effects of a normal (NPD; 1.38 +/- 0.08 g kg(-1) day(-1)) or low (LPD; 0.81 +/- 0.04 g kg(-1) day(-1)) -protein diet on endogenous leucine flux (ELF), albumin and fibrinogen synthesis (L-[5,5,5,-2H3]leucine infusion), and markers of inflammation in nine type 2 diabetic patients with macroalbuminuria. Six healthy participants on NPD served as control participants. In comparison with healthy participants, type 2 diabetic patients on an NPD had similar ELF, reduced serum albumin (38 +/- 1.1 vs 42 +/- 0.8 g/l; p < 0.05), similar fractional synthesis rates (FSR) and absolute synthesis rates (ASR) of albumin, and both increased plasma fibrinogen concentration [10.7 +/- 0.6 vs 7.2 +/- 0.5 micromol/l (3.64 +/- 0.22 vs 2.45 +/- 0.18 g/l); p < 0.05] and fibrinogen ASR [11.03 +/- 1.17 vs 6.0 +/- 1.8 micromol 1.73 m(-2) day(-1) (3.7 +/- 0.4 vs 1.9 +/- 0.3 g 1.73 m(-2) day(-1)); p < 0.01]. After LPD, type 2 diabetic patients had the following changes in comparison with NPD: reduced proteinuria (2.74 +/- 0.4 vs 4.51 +/- 0.8 g/day; p < 0.05), ELF (1.93 +/- 0.08 vs 2.11 +/- 0.08 micromol kg(-1) min(-1); p < 0.05) and total fibrinogen pool; increased serum albumin (42 +/- 1 vs 38 +/- 1 g/l; p < 0.01) and albumin ASR (14.1 +/- 1 vs 9.9 +/- 1 g 1.73 m(-2) day(-1); p < 0.05); and reduced plasma IL-6 levels, which were correlated with albumin ASR (r = -0.749; p < 0.05). LPD in type 2 diabetic patients with diabetic nephropathy reduces low-grade inflammatory state, proteinuria, albuminuria, whole-body proteolysis and ASR of fibrinogen, while increasing albumin FSR, ASR and serum concentration.

Effect of metabolizable protein intake on rates of plasma leucine turnover and protein synthesis in heifers

SUMMARYAn isotope dilution method using [1-13C]leucine (Leu) infusion together with open-circuit calorimetry was applied to determine the effect of metabolizable protein (MP) intake on rates of plasma Leu turnover and whole body protein synthesis (WBPS) in six heifers. WBPS rate was estimated from rate of plasma Leu turnover and Leu oxidation to carbon dioxide. The experiment consisted of three levels of MP intake and was conducted in a two 3×3 Latin square designs of three 21-day periods. The experimental diet consisted of mixed hay, maize and soybean meal. Dietary MP intake of each dietary treatment was 4·3, 4·5 and 4·9 g/kg BW0·75/day by changing maize and soybean meal weights. Metabolizable energy (ME) intake was similar for all dietary treatments. When plasma α-[1-13C]keto-isocaproic acid enrichments were used as markers indicating intracellular Leu enrichments, plasma Leu turnover rate (LeuTR) increased (P=0·012) and WBPS tended to increase (P=0·091) as MP intake increased. In contrast, plasma LeuTR and WBPS were not influenced if plasma [1-13C]Leu was taken to indicate intracellular Leu enrichments. Total and plasma Leu oxidation rates did not change but intracellular Leu oxidation increased (P=0·044) with increasing MP intake. In heifers, it is suggested that rates of plasma Leu turnover and WBPS are influenced by dietary MP intake, independent of ME intake, although the change in MP intake was relatively small.

The Effects of Nutritional Supplementation Throughout an Endurance Run on Leucine Kinetics during Recovery

This study determined the effect of nutritional supplementation throughout endurance exercise on whole-body leucine kinetics (leucine rate of appearance [Ra], oxidation [Ox], and nonoxidative leucine disposal [NOLD]) during recovery. Five trained men underwent a 2-h run at 65% VO(2max), during which a carbohydrate (CHO), mixed protein-carbohydrate (milk), or placebo (PLA) drink was consumed. Leucine kinetics were assessed during recovery using a primed, continuous infusion of 1-13C leucine. Leucine Ra and NOLD were lower for milk than for PLA. Ox was higher after milk-supplemented exercise than after CHO or PLA. Although consuming milk during the run affected whole-body leucine kinetics, the benefits of such a practice for athletes remain unclear. Additional studies are needed to determine whether protein supplementation during exercise can optimize protein utilization during recovery.

Amino acid availability and age affect the leucine stimulation of protein synthesis and eIF4F formation in muscle

We have previously shown that a physiological increase in plasma leucine for 60 and 120 min increases translation initiation factor activation in muscle of neonatal pigs. Although muscle protein synthesis is increased by leucine at 60 min, it is not maintained at 120 min, perhaps because of the decrease in plasma amino acids (AA). In the present study, 7- and 26-day-old pigs were fasted overnight and infused with leucine (0 or 400 micromol.kg(-1).h(-1)) for 120 min to raise leucine within the postprandial range. The leucine was infused in the presence or absence of a replacement AA mixture (without leucine) to maintain baseline plasma AA levels. AA administration prevented the leucine-induced reduction in plasma AA in both age groups. At 7 days, leucine infusion alone increased eukaryotic initiation factor (eIF) 4E binding protein-1 (4E-BP1) phosphorylation, decreased inactive 4E-BP1.eIF4E complex abundance, and increased active eIF4G.eIF4E complex formation in skeletal muscle; leucine infusion with replacement AA also stimulated these, as well as 70-kDa ribosomal protein S6 kinase, ribosomal protein S6, and eIF4G phosphorylation. At 26 days, leucine infusion alone increased 4E-BP1 phosphorylation and decreased the inactive 4E-BP1.eIF4E complex only; leucine with AA also stimulated these, as well as 70-kDa ribosomal protein S6 kinase and ribosomal protein S6 phosphorylation. Muscle protein synthesis was increased in 7-day-old (+60%) and 26-day-old (+40%) pigs infused with leucine and replacement AA but not with leucine alone. Thus the ability of leucine to stimulate eIF4F formation and protein synthesis in skeletal muscle is dependent on AA availability and age.