Amino acid metabolism and regulatory effects in aging

Carbohydrate co-ingestion with protein does not further augment post-prandial muscle protein accretion in older men

Background

A blunted muscle protein synthetic response to protein ingestion may contribute to the age related loss of muscle tissue. We hypothesized that the greater endogenous insulin release following co-ingestion of carbohydrate facilitates post-prandial muscle protein accretion after ingesting a meal-like bolus of protein in older males.

Methods

Twenty-four healthy older men (75±1 y) were randomly assigned to ingest 20 g intrinsically L-[1-¹³C] phenylalanine-labeled casein protein with (PRO-CHO) or without (PRO) 40 g carbohydrate. Ingestion of specifically produced intrinsically L-[1-¹³C] phenylalanine labeled protein allowed us to assess post-prandial incorporation of dietary protein derived amino acids into muscle protein. Blood samples were collected at regular intervals, with muscle biopsies being obtained prior to and 2 and 6 h after protein ingestion.

Results

Plasma glucose and insulin concentrations showed a greater increase in PRO-CHO compared with PRO (P<0.001). Muscle protein-bound L-[1-¹³C] phenylalanine enrichments tended to increase to a greater extent in PRO-CHO compared with PRO during the first 2 h after protein ingestion (0.0072±0.0013 vs 0.0046±0.010 MPE, respectively; P=0.13). However, 6 h after protein ingestion, differences in muscle protein-bound L-[1-¹³C] phenylalanine enrichments were no longer observed between experiments (0.0213±0.0024 vs 0.0185±0.0010 MPE, respectively; P=0.30).

Conclusions

This study shows that carbohydrate ingestion may accelerate, but does not further augment post-prandial incorporation of dietary protein derived amino acids into muscle protein in healthy elderly men.

Effect of food form on postprandial plasma amino acid concentrations in older adults

To assess the effect of food form (FF) on postprandial (PP) plasma amino acid (AA) concentrations, ten older adults (five men and five women, age 72 (sem 2) years, BMI 26.0 (sem 0.9) kg/m2) consumed, on separate days, energy and macronutrient-matched test meal replacement products (MRP) (approximately 25 % of the subject's daily energy need; approximately 54 % carbohydrate, 21 % protein, 25 % fat) in beverage and solid form. Blood samples were taken during fasting and throughout the 4 h PP period; plasma AA concentrations were assessed using HPLC. Consumption of each MRP led to an increase in total AA, branched-chain AA (BCAA), essential AA (EAA), non-essential AA (NEAA) and leucine concentrations (4 h area under the curve, AUC) (time effect; P < 0.05). The beverage MRP resulted in a greater initial (i.e. 30 min) and sustained (4 h AUC) increase in total AA, BCAA, EAA, NEAA and leucine concentrations compared with the solid MRP (each effect of FF; P < 0.05). Although there was no effect of FF on PP insulin response, glucose concentration was greater 1 and 2 h after the solid MRP was consumed (FF × time interaction; P < 0.05). For all PP time points combined, total AA concentration was positively associated with plasma insulin (r 0.25) and glucose (r 0.24) concentrations for the solid MRP but not for the beverage MRP. In conclusion, older adults can achieve higher plasma AA concentrations when a protein-containing MRP is ingested in beverage form. The implications of the higher AA availability on anabolic processes warrant investigation.

Exercise training attenuates MuRF-1 expression in the skeletal muscle of patients with chronic heart failure independent of age: the randomized Leipzig Exercise Intervention in Chronic Heart Failure and Aging catabolism study

BACKGROUND

Muscle wasting occurs in both chronic heart failure (CHF) and normal aging and contributes to exercise intolerance and increased morbidity/mortality. However, the molecular mechanisms of muscle atrophy in CHF and their interaction with aging are still largely unknown. We therefore measured the activation of the ubiquitin-proteasome system and the lysosomal pathway of intracellular proteolysis in muscle biopsies of CHF patients and healthy controls in two age strata and assessed the age-dependent effects of a 4-week endurance training program on the catabolic-anabolic balance.

METHODS AND RESULTS

Sixty CHF patients (30 patients aged ≤55 years, mean age 46±5 years; 30 patients aged ≥65 years, mean age 72±5 years) and 60 healthy controls (30 subjects aged ≤55 years, mean age 50±5 years; 30 subjects aged ≥65 years, mean age 72±4 years) were randomized to 4 weeks of supervised endurance training or to a control group. Before and after the intervention, vastus lateralis muscle biopsies were obtained. The expressions of cathepsin-L and the muscle-specific E3 ligases MuRF-1 and MAFbx were measured by real-time polymerase chain reaction and confirmed by Western blot. At baseline, MuRF-1 expression was significantly higher in CHF patients versus healthy controls (mRNA: 624±59 versus 401±25 relative units; P=0.007). After 4 weeks of exercise training, MuRF-1 mRNA expression was reduced by -32.8% (P=0.02) in CHF patients aged ≤55 years and by -37.0% (P<0.05) in CHF patients aged ≥65 years.

CONCLUSIONS

MuRF-1, a component of the ubiquitin-proteasome system involved in muscle proteolysis, is increased in the skeletal muscle of patients with heart failure. Exercise training results in reduced MuRF-1 levels, suggesting that it blocks ubiquitin-proteasome system activation and does so in both younger and older CHF patients.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00176319.

Metabolic diversity of progressive kidney disease in 325 patients with type 1 diabetes (the FinnDiane Study)

Type 1 diabetic patients with varying severity of kidney disease were investigated to create multimetabolite models of the disease process. Urinary albumin excretion rate was measured for 3358 patients with type 1 diabetes. Prospective records were available for 1051 patients, of whom 163 showed progression of albuminuria (8.3-year follow-up), and 162 were selected as stable controls. At baseline, serum lipids, lipoprotein subclasses, and low-molecular weight metabolites were quantified by NMR spectroscopy (325 samples). The data were analyzed by the self-organizing map. In cross-sectional analyses, patients with no complications had low serum lipids, less inflammation, and better glycemic control, whereas patients with advanced kidney disease had high serum cystatin-C and sphingomyelin. These phenotype extremes shared low unsaturated fatty acids (UFAs) and phospholipids. Prospectively, progressive albuminuria was associated with high UFAs, phospholipids, and IDL and LDL lipids. Progression at longer duration was associated with high HDL lipids, whereas earlier progression was associated with poor glycemic control, increased saturated fatty acids (SFAs), and inflammation. Diabetic kidney disease consists of diverse metabolic phenotypes: UFAs, phospholipids, IDL, and LDL may be important in the subclinical phase, high SFAs and low HDL suggest accelerated progression, and the sphingolipid pathway in advanced kidney injury deserves further research.

Features, causes and consequences of splanchnic sequestration of amino acid in old rats

Rationale

In elderly subjects, splanchnic extraction of amino acids (AA) increases during meals in a process known as splanchnic sequestration of amino acids (SSAA). This process potentially contributes to the age-related progressive decline in muscle mass via reduced peripheral availability of dietary AA. SSAA mechanisms are unknown but may involve an increased net utilization of ingested AA in the splanchnic area.

Objectives

Using stable isotope methodology in fed adult and old rats to provide insight into age-related SSAA using three hypotheses: 1) an increase in protein synthesis in the gut and/or the liver, 2) an increase in AA oxidation related to an increased ureagenesis, and 3) Kupffer cell (KC) activation consequently to age-related low-grade inflammation.

Findings

Splanchnic extraction of Leu (SPELeu) was doubled in old rats compared to adult rats and was not changed after KC inactivation. No age-related effects on gut and liver protein synthesis were observed, but urea synthesis was lower in old rats and negatively correlated to liver Arg utilization. Net whole-body protein synthesis and arterial AA levels were lower in old rats and correlated negatively with SPELeu.

Conclusion

SSAA is not the consequence of age-related alterations in ureagenesis, gut or liver protein synthesis or of KC activity. However, SSAA may be related to reduced net whole-body protein synthesis and consequently to the reduced lean body mass that occurs during aging.

Clinical use of amino acids as dietary supplement: pros and cons

Nitrogen supply is pivotal for the maintenance of life. Amino acids can be utilized to synthesize both glucose and lipids. The opposite, i.e., production of amino acids from either one of them, is not possible in the absence of other amino acids as donors of nitrogen. The quality of amino acid content in protein has been re-evaluated recently, and the relevance of essential amino acids has been repeatedly underlined. Essential amino acid requirements in different mammals are not identical, and ratios among them should be taken into account when projecting an efficient formulation. Recent research has demonstrated that genes respond to different qualities and quantities of nutritional supply, and increased provision of essential amino acids increases lifespan in animal experiments through mitochondriogenesis and maintenance of elevated rates of synthesis of anti-oxidant molecules. Moreover, genetic expression of key controllers of synthesis, like mTOR, may be particularly important for understanding skeletal muscle maintenance. Losses of muscle mass and impaired immune function are related to reduced protein supply, and there is increasing evidence that regular essential amino acid intake as part of an oral diet is effective in reversing muscle catabolism, promoting muscle anabolism, and restoring immunological function. Therefore, the use of amino acids as supplements to diet would be expanding in the near future. Is this safe? Few data are available on amino acid toxicity, and only one essential amino acid may be considered to have clinically relevant toxicity: methionine, because it is transformed into a toxic intermediate, homocysteine, when cysteine synthesis is required by metabolic needs. Matching of stoichiometric ratios between methionine and cysteine may solve the problem of supplying sufficient amounts of sulfur to the body. Arginine and glutamine are two non-essential amino acids than can become "conditionally essential" because of elevated needs during pathological conditions, and metabolism may not be able to maintain their concentrations at sufficient levels to match metabolic requirements. Chronic exogenous arginine supplementation has not proven to exert positive clinical effects in different trials, and sequential articulation of the knowledge of introduction of arginine-driven transcriptional, translational, and epigenetic adaptations may give us a key for interpreting those puzzling results.

PKB signaling and atrogene expression in skeletal muscle of aged mice

The purpose of this study was to determine if PKB signaling is decreased and contractile protein degradation is increased in extensor digitorum longus (EDL) and soleus (SOL) muscles from middle-aged (MA) and aged (AG) mice. We also examined the effect of age on atrogene expression in quadriceps muscle. PKB activity, as assessed by Thr(308) and Ser(473) phosphorylation, was significantly higher in EDL and SOL muscles from AG than MA mice. The age-related increase in PKB activity appears to be due to an increase in expression of the kinase, as PKB-α and PKB-β levels were significantly higher in EDL and SOL muscles from AG than MA mice. The phosphorylation of forkhead box 3a (FOXO3a) on Thr(32), a PKB target, was significantly higher in EDL muscles from AG than MA mice. The rate of contractile protein degradation was similar in EDL and SOL muscles from AG and MA mice. Atrogin-1 and muscle-specific RING finger protein 1 (MuRF-1) mRNA levels did not change in muscles from AG compared with MA mice, indicating that ubiquitin-proteasome proteolysis does not contribute to sarcopenia. A significant decrease in Bcl-2 and 19-kDa interacting protein 3 (Bnip3) and GABA receptor-associated protein 1 (Gabarap1) mRNA was observed in muscles from AG compared with MA mice, which may contribute to age-related contractile dysfunction. In conclusion, the mechanisms responsible for sarcopenia are distinct from experimental models of atrophy and do not involve atrogin-1 and MuRF-1 or enhanced proteolysis. Finally, a decline in autophagy-related gene expression may provide a novel mechanism for impaired contractile function and muscle metabolism with advancing age.

Dietary protein and exercise training in ageing

Ageing is accompanied by a progressive loss of skeletal muscle mass and strength, leading to the loss of functional capacity and an increased risk for developing chronic metabolic diseases such as diabetes. The age-related loss of skeletal muscle mass results from a chronic disruption in the balance between muscle protein synthesis and degradation. As basal muscle protein synthesis rates are likely not different between healthy young and elderly human subjects, it was proposed that muscles from older adults lack the ability to regulate the protein synthetic response to anabolic stimuli, such as food intake and physical activity. Indeed, the dose-response relationship between myofibrillar protein synthesis and the availability of essential amino acids and/or resistance exercise intensity is shifted down and to the right in elderly human subjects. This so-called 'anabolic resistance' represents a key factor responsible for the age-related decline in skeletal muscle mass. Interestingly, long-term resistance exercise training is effective as a therapeutic intervention to augment skeletal muscle mass, and improves functional performance in the elderly. The consumption of different types of proteins, i.e. protein hydrolysates, can have different stimulatory effects on muscle protein synthesis in the elderly, which may be due to their higher rate of digestion and absorption. Current research aims to elucidate the interactions between nutrition, exercise and the skeletal muscle adaptive response that will define more effective strategies to maximise the therapeutic benefits of lifestyle interventions in the elderly.

Effect of protein intake on bone and muscle mass in the elderly

The aging process is frequently characterized by an involuntary loss of muscle (sarcopenia) and bone (osteoporosis) mass. Both chronic diseases are associated with decreased metabolic rate, increased risk of falls/fracture, and, as a result, increased morbidity and loss of independence in the elderly. The quality and quantity of protein intake affects bone and muscle mass in several ways and there is evidence that increased essential amino acid or protein availability can enhance muscle protein synthesis and anabolism, as well as improve bone homeostasis in older subjects. A thorough evaluation of renal function is important, since renal function decreases with age. Finally, protein and calcium intake should be considered in the prevention or treatment of the chronic diseases osteoporosis and sarcopenia.

A specific protein-enriched enteral formula decreases cortisolemia and improves plasma albumin and amino acid concentrations in elderly patients

BACKGROUND

Old age is associated with an involuntary and progressive but physiological loss of muscle mass. The aim of this study was to evaluate the effects of exclusive consumption for 6 months of a protein-enriched enteral diet with a relatively high content of branched-chain amino acids on albuminemia, cortisolemia, plasma amino acids, insulin resistance, and inflammation biomarkers in elderly patients.

METHODS

Thirty-two patients from the Clinical Nutrition Outpatient Unit at our hospital exclusively consumed a protein-enriched enteral diet for 6 months. Data were collected at baseline and at 3 and 6 months on anthropometric and biochemical parameters and on plasma concentrations of amino acids, cortisol, adrenocorticotropic hormone, urea, creatinine, insulin resistance, and inflammation biomarkers.

RESULTS

The percentage of patients with albumin concentration below normal cut-off values decreased from 18% to 0% by the end of the study. At 6 months, concentrations of total plasma (p = 0.008) and essential amino acids (p = 0.011), especially branched-chain amino acids (p = 0.031), were higher versus baseline values, whereas 3-methylhistidine (p = 0.001), cortisol (p = 0.001) and adrenocorticotropic hormone (p = 0.004) levels were lower.

CONCLUSIONS

Regular intake of specific protein-enriched enteral formula increases plasma essential amino acids, especially branched-chain amino acids, and decreases cortisol and 3-methylhistidine, while plasma urea and creatinine remain unchanged.

The RNA editor gene ADAR1 is induced in myoblasts by inflammatory ligands and buffers stress response

Muscle atrophy remains a significant concern in multiple inflammatory conditions, including injury, sepsis, cachexia, and HIV-associated wasting. Herein, we show that inflammatory stressors, including TNF-alpha, IFN-gamma, or lipopolysaccharide, potently induced the novel expression of the RNA editor ADAR1, an observation not previously described in muscle cells. We also observed that cytokine stimulation suppressed muscle-associated microRNAs, an observation also not previously demonstrated. To map potential effects of ADAR1 induction in the muscle program, we conducted knockdown and overexpression studies in the mouse C2C12 muscle precursor cell (MPC) line and in primary human MPCs. We show that knockdown of stress-induced ADAR1 increased inflammation-mediated declines in the muscle differentiation markers Myogenin and myosin heavy chain, and knockdown reduced levels of active phosphorylated Akt (phospho-Akt), but had no effect on microRNA transcript levels, suggesting a role for ADAR1 in buffering inflammatory stress effects on myogenic transcription and protein synthesis pathways. In addition, overexpression of recombinant ADAR1 suppressed active phosphorylated double-stranded RNA (dsRNA)-dependent protein kinase (phospho-PKR), consistent with a role for ADAR1 in limiting inflammation-driven catabolic atrophy pathways. Collectively, these data identify a novel regulatory role for ADAR1 activation under inflammatory stress to both promote muscle protein synthesis pathways and limit atrophy pathways.

Energy expenditure and aging

The study of energy expenditure (EE) has deep roots in understanding aging and lifespan in all species. In humans, total EE decreases substantially in advanced age resulting from parallel changes in resting metabolic rate (RMR) and activity EE. For RMR, this reduction appears to be due to a reduction in organ mass and specific metabolic rates of individual tissues. However, these anatomical changes explain very little regarding the decline in activity EE, which is governed by both genetic and environmental sources. The biological control centers for activity EE are closely coupled with body mass fluctuations and seem to originate in the brain. Several candidate neuromodulators may be involved in the age-related reduction of activity EE that include: orexin, agouti-related proteins and dopaminergic pathways. Unfortunately, the existing body of research has primarily focused on how neuromodulators influence weight gain and only a few studies have been performed in aging models. Recent evidence suggests that activity EE has an important role in dictating lifespan and thus places emphasis on future research to uncover the underlying biological mechanisms. The study of EE continues to unlock clues to aging.

Understanding sarcopenia as a geriatric syndrome

PURPOSE OF REVIEW

Highly prevalent in the population older than 65 years and leading to poor outcomes (functional decline and its related consequences), sarcopenia does not benefit yet either of a clear understanding of its pathophysiology or of precise clinical or biological markers allowing its identification.

RECENT FINDINGS

The new scientific definition of 'geriatric syndromes' challenges the authors to review the current sarcopenia literature, allowing them to affirm that sarcopenia cannot be considered as an age-related disease but as a true 'geriatric syndrome'. More than 50% of the population older than 80 years suffer from this medical condition, which is linked to multiple causations: the ageing process itself, genetic susceptibility, certain life habits, changes in living conditions and a number of chronic diseases. Moreover, sarcopenia favours poor outcomes such as mobility disorders, disability, poor quality of life and death.

SUMMARY

Considering sarcopenia as a geriatric syndrome allows us to request its recognition and assess its multiple risk factors, to implement a clinical and public health approach to the management of sarcopenic patients and population at risk and to disentangle the links among sarcopenia, frailty, disability and mortality.

Carla Task Force on Sarcopenia: propositions for clinical trials

In the presence of an aging population, public health priorities need to evolve. As the populations gets older, the already existing pathologies have become commonplace with specific geriatric clinical syndromes like frailty, mobility disability, or cognitive impairment, among others. Sarcopenia is a good example for which geriatricians, neurologists, physiologists, nutritionists and epidemiologists need to find a consensual definition and diagnostic tool as well as guidelines for the management of clinical trials and possible treatments. The Carla Sarcopenia Task Force, which met in the south of France (Toulouse) for an expert consensus meeting called "Les Entretiens du Carla", have addressed a series of existing issues to place Sarcopenia into a nosological context: a definition which should be a composite of a change in muscle mass and a change in strength/function depending on either a progressive and chronic wasting process or an acute onset of loss of muscle mass; a recommendation for DXA and the Short Physical Performance Battery as a clinical pragmatic approach of Sarcopenia; a differentiated approach for clinical studies according to prevention or treatment objectives and depending on the sub-groups and target populations; and finally, a summary of therapeutic strategies currently recommended. The aim of "Les Entretiens du Carla", based on an expert meeting panel, was to address a series of unsolved issues in the field of Sarcopenia by combining the expert opinion with a revision of the existing literature on the topic. Through this report, the reader will appreciate the determination to find conclusions on the various issues and further studies to be developed to determine the best multidisciplinary approach needed.

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.

Acid-base balance and weight gain: are there crucial links via protein and organic acids in understanding obesity?

Obesity is associated with ever increasing social costs posing a general public health challenge. The most obvious reason for obesity, given healthy body functioning, is a positive calorie balance. This article delves into the lesser studied realm of the relationship of weight gain, in particular adipose tissue gain, with increased hydrogen ion concentration, taking protein and organic acids as important caveats in this discussion. The review opens the topic with the contradictory result of various studies reporting a positive relationship between chronic metabolic acidosis and weight loss. It goes to explain a process of weight gain, primarily adipose tissue gain, on acidogenic diets. Insufficient dietary protein could lead to muscle loss, and individual organic acids might indicate if there is any fatty acid oxidation or accumulation of hydrogen ion. The solution to the acid accumulation is discussed not in protein limitation but an increase in the consumption of vegetables and fruits. Finally, this review article based on studies published puts forward a physiological basis including a hypothesis to explain the possible link between hydrogen ion concentration and weight gain. This link could possibly explain the development of diseases and aging partially, and warrants research.

Alcohol-induced decrease in muscle protein synthesis associated with increased binding of mTOR and raptor: Comparable effects in young and mature rats

BACKGROUND

Acute alcohol (EtOH) intoxication decreases muscle protein synthesis via inhibition of mTOR-dependent translation initiation. However, these studies have been performed in relatively young rapidly growing rats in which muscle protein accretion is more sensitive to growth factor and nutrient stimulation. Furthermore, some in vivo-produced effects of EtOH vary in an age-dependent manner. The hypothesis tested in the present study was that young rats will show a more pronounced decrement in muscle protein synthesis than older mature rats in response to acute EtOH intoxication.

METHODS

Male F344 rats were studied at approximately 3 (young) or 12 (mature) months of age. Young rats were injected intraperitoneally with 75 mmol/kg of EtOH, and mature rats injected with either 75 or 90 mmol/kg EtOH. Time-matched saline-injected control rats were included for both age groups. Gastrocnemius protein synthesis and the activity of the mTOR pathway were assessed 2.5 h after EtOH using [³H]-labeled phenylalanine and the phosphorylation of various protein factors known to regulate peptide-chain initiation.

RESULTS

Blood alcohol levels (BALs) were lower in mature rats compared to young rats after administration of 75 mmol/kg EtOH (154 ± 23 vs 265 ± 24 mg/dL). However, injection of 90 mmol/kg EtOH in mature rats produced BALs comparable to that of young rats (281 ± 33 mg/dL). EtOH decreased muscle protein synthesis similarly in both young and high-dose EtOH-treated mature rats. The EtOH-induced changes in both groups were associated with a concomitant reduction in 4E-BP1 phosphorylation, and redistribution of eIF4E between the active eIF4E.eIF4G and inactive eIF4E.4EBP1 complex. Moreover, EtOH increased the binding of mTOR with raptor in a manner which appeared to be AMPK- and TSC-independent. In contrast, although muscle protein synthesis was unchanged in mature rats given low-dose EtOH, compared to control values, the phosphorylation of rpS6 and eIF4G was decreased.

CONCLUSION

These data indicate that muscle protein synthesis is equally sensitive to the inhibitory effects of EtOH in young rapidly growing rats and older mature rats which are growing more slowly, but that mature rats must be given a relatively larger dose of EtOH to achieve the same BAL. Based on the differential response in mature rats to low- and high-dose EtOH, the decreased protein synthesis was associated with a reduction in mTOR activity which was selectively mediated via a reduction in 4E-BP1 phosphorylation and an increase in mTOR.raptor formation.

Sarcopenia: its assessment, etiology, pathogenesis, consequences and future perspectives

Sarcopenia is a loss of muscle protein mass and loss of muscle function. It occurs with increasing age, being a major component in the development of frailty. Current knowledge on its assessment, etiology, pathogenesis, consequences and future perspectives are reported in the present review. On-going and future clinical trials on sarcopenia may radically change our preventive and therapeutic approaches of mobility disability in older people.

Gene polymorphisms of oxidative stress enzymes: prediction of elderly renutrition

BACKGROUND

The free radical theory of aging suggests that damage caused by oxidative stress leads to impaired physiologic functions. This damage is stemmed by an adequate antioxidant status, which minimizes the occurrence of infection, thus potentially playing a role in improving nutritional status. The role played by genetic factors remains unknown.

OBJECTIVE

The aim of this study was to investigate whether a single nucleotide polymorphism (SNP) of a gene coding for endogenous antioxidant enzymes could influence either nutritional status or renutrition process in an elderly population.

DESIGN

Nutritional and inflammatory status were studied in 77 elderly outpatients and in 99 malnourished elderly inpatients over 6 wk of health care treatment. Renutrition efficiency was evaluated with use of the ratio between initial transthyretinemia and 6-wk variation. A genetic study was performed on superoxide dismutase (Ala-9Val), glutathione peroxidase (Pro197Leu), and catalase (from promoter to the first intron).

RESULTS

Among the SNPs studied, the G-844A, A-89T, and C-20T catalase SNPs could each be markers predicting renutrition efficiency. These catalase mutant alleles were associated with a lower efficiency of renutrition in malnourished elderly subjects, regardless of initial nutritional and inflammatory status. Genotyping one of these catalase SNPs could make it possible to identify a high-risk subpopulation of mutant allele carriers within the elderly polypathological population.

CONCLUSION

In a malnutrition setting, this subpopulation should be given personalized health care, including a strengthened refeeding program. Thus, catalase genotyping could enable earlier recovery of satisfactory nutritional status and thus avoid the consequences of malnutrition, which are especially deleterious in the elderly.