Stéphane Walrand

Ingestion of a protein hydrolysate is accompanied by an accelerated in vivo digestion and absorption rate when compared with its intact protein

BACKGROUND It has been suggested that a protein hydrolysate, as opposed to its intact protein, is more easily digested and absorbed from the gut, which results in greater plasma amino acid availability and a greater muscle protein synthetic response. OBJECTIVE We aimed to compare dietary protein digestion and absorption kinetics and the subsequent muscle protein synthetic response to the ingestion of a single bolus of protein hydrolysate compared with its intact protein in vivo in humans. DESIGN Ten elderly men (mean +/- SEM age: 64 +/- 1 y) were randomly assigned to a crossover experiment that involved 2 treatments in which the subjects consumed a 35-g bolus of specifically produced L-[1-(13)C]phenylalanine-labeled intact casein (CAS) or hydrolyzed casein (CASH). Blood and muscle-tissue samples were collected to assess the appearance rate of dietary protein-derived phenylalanine in the circulation and subsequent muscle protein fractional synthetic rate over a 6-h postprandial period. RESULTS The mean (+/-SEM) exogenous phenylalanine appearance rate was 27 +/- 6% higher after ingestion of CASH than after ingestion of CAS (P < 0.001). Splanchnic extraction was significantly lower in CASH compared with CAS treatment (P < 0.01). Plasma amino acid concentrations increased to a greater extent (25-50%) after the ingestion of CASH than after the ingestion of CAS (P < 0.01). Muscle protein synthesis rates averaged 0.054 +/- 0.004% and 0.068 +/- 0.006%/h in the CAS and CASH treatments, respectively (P = 0.10). CONCLUSIONS Ingestion of a protein hydrolysate, as opposed to its intact protein, accelerates protein digestion and absorption from the gut, augments postprandial amino acid availability, and tends to increase the incorporation rate of dietary amino acids into skeletal muscle protein.

Dietary Protein Digestion and Absorption Rates and the Subsequent Postprandial Muscle Protein Synthetic Response Do Not Differ between Young and Elderly Men

Impaired digestion and/or absorption of dietary protein lowers postprandial plasma amino acid availability and, as such, could reduce the postprandial muscle protein synthetic response in the elderly. We aimed to compare in vivo dietary protein digestion and absorption and the subsequent postprandial muscle protein synthetic response between young and elderly men. Ten elderly (64 +/- 1 y) and 10 young (23 +/- 1 y) healthy males consumed a single bolus of 35 g specifically produced, intrinsically l-[1-(13)C]phenylalanine-labeled micellar casein (CAS) protein. Furthermore, primed continuous infusions with l-[ring-(2)H(5)]phenylalanine, l-[1-(13)C]leucine, and l-[ring-(2)H(2)]tyrosine were applied and blood and muscle tissue samples were collected to assess the appearance rate of dietary protein-derived phenylalanine in the circulation and the subsequent muscle protein fractional synthetic rate over a 6-h postprandial period. Protein ingestion resulted in a rapid increase in exogenous phenylalanine appearance in both the young and elderly men. Total exogenous phenylalanine appearance rates (expressed as area under the curve) were 39 +/- 3 mumol.6 h.kg(-1) in the young men and 38 +/- 2 mumol.6 h.kg(-1) in the elderly men (P = 0.73). In accordance, splanchnic amino acid extraction did not differ between young (72 +/- 2%) and elderly (73 +/- 1%) volunteers (P = 0.74). Muscle protein synthesis rates, calculated from the oral tracer, were 0.063 +/- 0.006 and 0.054 +/- 0.004%/h in the young and elderly men, respectively, and did not differ between groups (P = 0.27). We conclude that protein digestion and absorption kinetics and the subsequent muscle protein synthetic response following the ingestion of a large bolus of intact CAS are not substantially impaired in healthy, elderly men.

Changes in Basal and Insulin and Amino Acid Response of Whole Body and Skeletal Muscle Proteins in Obese Men

CONTEXT Obesity-related insulin resistance of glucose and lipid metabolism may also affect protein kinetics, notably at the muscle level. OBJECTIVE We hypothesized that muscle protein response to insulin and amino acid is blunted during obesity. RESEARCH DESIGN AND METHODS Total (Tot) and mitochondrial (Mit) muscle proteins fractional synthesis rates (FSR) together with whole-body protein kinetics (WB) have been determined in postabsorptive state (PA) and during a hyperinsulinemic, hyperaminoacidemic, euglycemic clamp by using a continuous infusion of (13)C-leucine in six obese and eight nonobese subjects. RESULTS Responses of WB glucose disposal rate and protein breakdown to insulin and amino acid infusion were significantly lower in obese than in nonobese subjects (P < 0.05). In PA, Tot and Mit FSR were significantly lower (P < 0.05) in obese (Tot, 0.044 +/- 0.005% . h(-1); Mit, 0.064 +/- 0.008% . h(-1)) in comparison with nonobese subjects (Tot, 0.082 +/- 0.010% . h(-1); Mit, 0.140 +/- 0.006% . h(-1)). Tot FSR was similarly stimulated by insulin and amino acid in both groups (0.094 +/- 0.013 vs. 0.117 +/- 0.006% . h(-1), obese vs. nonobese; P < 0.05). Mit FSR was increased in nonobese subjects (0.179 +/- 0.007% . h(-1); P < 0.05) but not in obese subjects (0.078 +/- 0.012% . h(-1); P = not significant). CONCLUSIONS The obesity-related impairment of protein metabolism is characterized by 1) a reduced turnover rate of skeletal muscle proteins in PA; 2) a lack of stimulation of mitochondrial protein synthesis by insulin and amino acid; and 3) a lower inhibition of WB proteolysis by insulin and amino acid. Alterations of selective muscle protein kinetics may predispose obese subjects to muscle metabolic dysfunction leading to type 2 diabetes.

The role of dietary protein and vitamin D in maintaining musculoskeletal health in postmenopausal women : A consensus statement from the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO)

From 50 years of age, postmenopausal women are at an increased risk of developing sarcopenia and osteoporosis as a result of deterioration of musculoskeletal health. Both disorders increase the risk of falls and fractures. The risk of developing sarcopenia and osteoporosis may be attenuated through healthy lifestyle changes, which include adequate dietary protein, calcium and vitamin D intakes, and regular physical activity/exercise, besides hormone replacement therapy when appropriate. Protein intake and physical activity are the main anabolic stimuli for muscle protein synthesis. Exercise training leads to increased muscle mass and strength, and the combination of optimal protein intake and exercise produces a greater degree of muscle protein accretion than either intervention alone. Similarly, adequate dietary protein intake and resistance exercise are important contributors to the maintenance of bone strength. Vitamin D helps to maintain muscle mass and strength as well as bone health. These findings suggest that healthy lifestyle measures in women aged >50 years are essential to allow healthy ageing. The European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO) recommends optimal dietary protein intake of 1.0-1.2g/kgbodyweight/d with at least 20-25g of high-quality protein at each main meal, with adequate vitamin D intake at 800IU/d to maintain serum 25-hydroxyvitamin D levels >50nmol/L as well as calcium intake of 1000mg/d, alongside regular physical activity/exercise 3-5 times/week combined with protein intake in close proximity to exercise, in postmenopausal women for prevention of age-related deterioration of musculoskeletal health.

Physiopathological Mechanism of Sarcopenia

The etiology of sarcopenia is multifactorial but still poorly understood, and the sequelae of this phenomenon represent a major public health issue. Age-related loss of muscle mass can be counteracted by adequate metabolic interventions including nutritional intake and exercise training. Other strategies including changes in daily protein pattern, the speed of protein digestion, or specific amino acid supplementation may be beneficial to improve short-term muscle anabolic response in elderly people. A multimodal approach combining nutrition, exercise, hormones, and specific anabolic drugs may be an innovative treatment for limiting the development of sarcopenia with aging.

In vivo evidences that insulin regulates human polymorphonuclear neutrophil functions.

Polymorphonuclear neutrophils (PMN) are able to destroy invasive mircoorganisms by a wide variety of functions. Whereas insulin does not stimulate hexose transport in PMN, previous reports have clearly shown that this hormone regulates glucose metabolism inside this cell, raising the question of insulin action on PMN functions in humans. It is interesting that in vitro studies established a strong relationship between specific binding of insulin to its PMN membrane receptor and the activation of the main PMN functions. Therefore, investigation in healthy subjects under strict euglycemia and physiological insulinemia was performed to understand the in vivo‐specific action of insulin on PMN functions without hyperglycemia interferences. We determined numerous PMN functions before and after hyperinsulinemia (0.5 mU/kg/min) and euglycemia (0.9 g/l) clamp for 4 h in eight adult healthy volunteers (24±6 years). The total number of PMN and the number of PMN expressing CD11b, CD15, CD62L, and CD89 were significantly increased over baseline (P<0.001), whereas the density of these receptors was down‐regulated (P<0.01) by insulin. PMN chemotaxis (+117%, P<0.05), phagocytosis (+29%, P<0.001), and bactericidal (+17–25%, P<0.001) capacities were increased during the insulin clamp (P<0.05). Therefore, insulin treatment may modulate PMN functions not only by attainment of a better metabolic control, as suggested by in vivo studies in diabetic patients, but also through a direct effect of insulin.

1,25(OH)2-vitamin D3 enhances the stimulating effect of leucine and insulin on protein synthesis rate through Akt/PKB and mTOR mediated pathways in murine C2C12 skeletal myotubes

SCOPE In recent years, there has been a growing body of evidence pointing to an effect of vitamin D on muscle mass and function. Our aim was to investigate the combined effect of 1,25(OH)2-vitamin D3 (1,25(OH)2D3) with anabolic factors insulin and leucine on protein fractional synthesis rate (FSR) and regulation in the mouse C2C12 myotube. METHODS AND RESULTS After differentiation, myotubes were cultured in 1,25(OH)2D3 solutions at 0, 1, or 10 nM for 72 h. Cells were treated by L-[1-(13) C]valine and puromycin in presence or not of leucine and insulin, and protein FSR was determined by measuring tracer enrichments and puromycin incorporation in proteins, respectively. Protein expression and phosphorylation state of insulin receptor (IR), Akt, GSK3, mTOR, p70 S6 kinase, rpS6, and 4EBP1 were measured by Western blot. Transcript levels of IR and 1,25(OH)2D3 receptor (VDR) were determined by qPCR. 1,25(OH)2D3 (10 nM) with leucine and insulin increased protein FSR in C2C12 myotubes (14-16%). IR and VDR mRNA expression was increased with 1,25(OH)2D3 treatment. The Akt/mTOR-dependent pathway was activated by insulin and leucine and further enhanced by 1,25(OH)2D3. CONCLUSION 1,25(OH)2D3 sensitizes the Akt/mTOR-dependant pathway to the stimulating effect of leucine and insulin, resulting in a further activation of protein synthesis in murine C2C12 skeletal myotubes.

Muscle and bone, two interconnected tissues

As bones are levers for skeletal muscle to exert forces, both are complementary and essential for locomotion and individual autonomy. In the past decades, the idea of a bone-muscle unit has emerged. Numerous studies have confirmed this hypothesis from in utero to aging works. Space flight, bed rest as well as osteoporosis and sarcopenia experimentations have allowed to accumulate considerable evidence. Mechanical loading is a key mechanism linking both tissues with a central promoting role of physical activity. Moreover, the skeletal muscle secretome accounts various molecules that affect bone including insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor (FGF-2), interleukin-6 (IL-6), IL-15, myostatin, osteoglycin (OGN), FAM5C, Tmem119 and osteoactivin. Even though studies on the potential effects of bone on muscle metabolism are sparse, few osteokines have been identified. Prostaglandin E2 (PGE2) and Wnt3a, which are secreted by osteocytes, osteocalcin (OCN) and IGF-1, which are produced by osteoblasts and sclerostin which is secreted by both cell types, might impact skeletal muscle cells. Cartilage and adipose tissue are also likely to participate to this control loop and should not be set aside. Indeed, chondrocytes are known to secrete Dickkopf-1 (DKK-1) and Indian hedgehog (Ihh) and adipocytes produce leptin, adiponectin and IL-6, which potentially modulate bone and muscle metabolisms. The understanding of this system will enable to define new levers to prevent/treat sarcopenia and osteoporosis at the same time. These strategies might include nutritional interventions and physical exercise.

Synergistic effects of caloric restriction with maintained protein intake on skeletal muscle performance in 21-month-old rats: a mitochondria-mediated pathway

Caloric restriction (CR) delays the onset of age‐related mitochondrial abnormalities but does not prevent the decline in ATP production needed to sustain muscle protein fractional synthesis rate (FSR) and contractile activity. We hypothesized that improving mitochondrial activity and FSR using a CR diet with maintained protein intakes could enhance myofibrillar protein FSR and consequently improve muscle strength in aging rats. Wistar rats (21 months old) were fed either an ad libitum (AL), 40% protein‐energy restricted (PER) or 40% AL‐isonitrogenous energy restricted (ER) diet for 5 months. ATP production, electron transport chain activity, reactive oxygen species (ROS) generation, protein carbonyl content and FSR were determined in both tibialis anterior (TA) and soleus muscle mitochondria. Myosin and actin FSR and grip force were also investigated. The ER diet led to improved mitochondrial activity and ATP production in the TA and soleus muscles in comparison with PER. Furthermore, mitochondrial FSR in the TA was enhanced under the ER diet but diminished under the PER. Mitochondrial protein carbonyl content was decreased by both the ER and PER diets. The ER diet was able to improve myosin and actin FSR and grip force. Therefore, the synergistic effects of CR with maintained protein intake may help to limit the progression of sarcopenia by optimizing the turnover rates and functions of major proteins in skeletal muscle.—Zangarelli, A., Chanseaume, E., Morio, B., Brugère, C., Mosoni, L., Rousset, P., Giraudet, C., Patrac, V., Gachon, P., Boirie, Y., Walrand, S. Synergistic effects of caloric restriction with maintained protein intake on skeletal muscle performance in 21‐month‐old rats: a mitochondria‐mediated pathway. FASEB J. 20, 2439–2450 (2006)

Cellular mechanisms underlying temporal changes in skeletal muscle protein synthesis and breakdown during chronic β‐adrenoceptor stimulation in mice

Chronic stimulation of β‐adrenoceptors with β‐adrenoceptor agonists (β‐agonists) can induce substantial skeletal muscle hypertrophy, but the mechanisms mediating this muscle growth have yet to be elucidated. We investigated whether chronic β‐adrenoceptor stimulation in mice with the β‐agonist formoterol alters the muscle anabolic response following β‐adrenoceptor stimulation. Twelve‐week‐old C57BL/6 mice were treated for up to 28 days with a once‐daily injection of either saline (control, n= 9) or formoterol (100 μg kg−1; n= 9). Rates of muscle protein synthesis were assessed at either 1, 7 or 28 days of treatment, 6 h after injection. Protein synthesis rates were higher in formoterol‐treated mice at day 7 (∼1.5‐fold, P < 0.05), but not at day 1 or 28. The increased muscle protein synthesis was associated with increased phosphorylation of S6K1 (r= 0.49, P < 0.01). Formoterol treatment acutely reduced maximal calpain activity by ∼25% (P < 0.05) but did not affect atrogin‐1 protein levels and proteasome‐mediated proteolytic activity, despite significantly enhanced phosphorylation of Akt (P < 0.05). Formoterol increased CREB phosphorylation by ∼30% (P < 0.05) and PPARγ coactivator‐1α (PGC‐1α) by 11‐fold (P < 0.05) on day 1 only. These observations identify that formoterol treatment induces muscle anabolism, by reducing calpain activity and by enhancing protein synthesis via increased PI‐3 kinase/Akt signalling.