The metabolic homoeostatic role of muscle and its function as a store of protein

Protein and Exercise to Reverse Frailty in Older Men and Women Undergoing Transcatheter Aortic Valve Replacement: Design of the PERFORM-TAVR Trial

Despite the high procedural success of transcatheter aortic valve replacement (TAVR), 2 out of 5 older adults report poor physical performance and health-related quality of life (HRQOL) in the ensuing months, particularly those with frailty. There has yet to be a trial examining the synergistic effects of exercise and protein supplementation to counteract frailty and improve patient-centred outcomes following TAVR. The PERFORM-TAVR trial is a multicentre parallel-group randomised clinical trial that is enrolling 200 frail older adults ≥ 70 years of age undergoing TAVR. Patients will be randomly allocated to 1 of 2 treatment groups: standard-of-care lifestyle education (control group) or protein-rich oral nutritional supplement for 4 weeks before TAVR with the addition of home-based supervised exercise sessions for 12 weeks after TAVR (intervention group). The primary outcome will be physical performance as measured by a blinded observer using the Short Physical Performance Battery at 3 months. Secondary outcomes at 3, 6, and 12 months will include HRQOL, as measured by the Short-Form 36 Physical and Mental Component summary scores, and a composite safety end point. The PERFORM-TAVR trial is testing a novel frailty intervention in older adults undergoing TAVR to optimise recovery and downstream HRQOL. This represents a potential paradigm shift that highlights the value of assessing and treating patients' frailty in parallel with their underlying heart valve disease. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifier: NCT03522454.

Functional and tissue enrichment analyses suggest that SARS-CoV-2 infection affects host metabolism and catabolism mediated by interference on host proteins

Infection by SARS-CoV-2, the causative agent of COVID-19, is critically connected with host metabolism. Through functional enrichment analysis, the present study aims to evaluate the biological processes involving host proteins interfered by SARS-CoV-2 to verify the potential metabolic impact of the infection. Furthermore, tissue enrichment analyses and differential gene expression of host proteins were applied to understand the interference by SARS-CoV-2 on tissue levels. Results based on functional and tissue-specific enrichment analyses, presented in this study, suggest that SARS-CoV-2, mediated interference on host proteins, can affect the metabolism and catabolism of molecular building blocks and control intracellular mechanisms, including gene expression in metabolism-related organs, to support viral demands. Thus, SARS-CoV-2 can broadly affect the host metabolism and catabolism at tissue and physiological levels contributing to a more severe disease.

The Sit Up Squat Stand test and Hand Grip Strength: What is the role of tests of muscle power in risk assessment in Anorexia Nervosa?

OBJECTIVES

To investigate the validity and reliability of two variants of the Sit Up Squat Stand Test (SUSS) and Hand Grip Strength (HGS) in predicting BMI and BMI risk level in hospitalised patients with Anorexia Nervosa (AN).

METHODS

25 inpatients with AN were tested roughly weekly for up to 16 weeks. Muscle power was assessed by two independent researchers.

RESULTS

Intra-class coefficients (ICCs) indicated high Inter-Rater Reliability (IRR) for the HGS (10 participants). Cohen's Kappa showed moderate IRR for the SUSS test (25 participants). Stepwise multiple regression showed that the SUSS tests plus HGS predicted BMI and BMI risk level explaining about two-third of the variance. Each test individually had lower predictive value. There was a little difference between the two versions of the SUSS tested.

CONCLUSIONS

HGS and SUSS are valid and reliable measurements of muscle power in AN. Together, the SUSS tests and the HGS represent a useful and effective measure of muscle power and hence one aspect of physical risk in Anorexia Nervosa. In the light of Covid restrictions, the SUSS test is one way that physical state can be monitored on video link in a way that is hard to falsify.

Hemoglobin Levels are Low in Sarcopenic and Osteosarcopenic Older Persons

Anemia is commonly associated with osteoporosis and sarcopenia in older persons. However, there is a common subset of patients identified as osteosarcopenic at a higher risk of adverse outcomes. Whether these patients are also at a higher risk of anemia remains unknown. In this study, we aimed to compare hemoglobin (Hb) levels in osteosarcopenic older subjects versus those with sarcopenia, osteopenia/osteoporosis alone and controls. Cross-sectional study in 558 community-dwelling participants older than 65 (mean age 79 ± 7.5 years) from Western Sydney, Australia. Associations of anemia with sarcopenia, osteopenia/osteoporosis and osteosarcopenia were assessed. Participants were able to mobilize independently, reported a risk/history of falls and were not cognitively impaired. We used the original (EWGOP) and revised (EWGSOP2) European consensus on definition of sarcopenia, and WHO definitions of osteoporosis and osteopenia. Based on both European definitions of sarcopenia prevalence of anemia was the highest among sarcopenic patients (39%), followed by osteosarcopenic (34%), osteoporotic/penic (26%), and controls (24%). Anemia prevalence in total was 176/553 (31.5%). Osteosarcopenic patients on average had 6.3 g/L lower Hb levels compared to controls (p = 0.001), and 3.7 g/L lower Hb than patients with osteoporosis/penia (p < 0.026). Interestingly, levels of Hb did not differ between sarcopenic vs osteosarcopenic patients (p = 0.817) and between osteoporotic/osteopenic patients vs controls (p > 0.259). The higher prevalence of anemia and lower hemoglobin in sarcopenic and osteosarcopenic subjects compared to osteoporotic/penic participants and controls was established. However, the previously reported associations between osteoporosis and anemia were not confirmed. A likely explanation can be inclusion of osteosarcopenic subjects as osteoporotic in previous studies.

Hyperammonemia and lactic acidosis in adults: Differential diagnoses with a focus on inborn errors of metabolism

The adult endocrinologist may be asked to consult on a patient for unexplained biochemical disturbances that could be caused by an underlying inborn error of metabolism. A genetic disorder is generally less likely to be the cause as these disorders are individually rare, however inborn errors of metabolism are collectively not infrequent and important to consider as they may be treatable and tragic outcomes avoided. Hyperammonemia or lactic acidosis are most often secondary markers of an acquired primary disease process, but they may be a clue to the presence of a genetic disorder. Herein is presented an approach to the differential diagnosis of elevated ammonia and lactate, and a brief discussion of management for when an inborn error is diagnosed.

Sarcopenia from mechanism to diagnosis and treatment in liver disease

Sarcopenia or loss of skeletal muscle mass is the major component of malnutrition and is a frequent complication in cirrhosis that adversely affects clinical outcomes. These include survival, quality of life, development of other complications and post liver transplantation survival. Radiological image analysis is currently utilized to diagnose sarcopenia in cirrhosis. Nutrient supplementation and physical activity are used to counter sarcopenia but have not been consistently effective because the underlying molecular and metabolic abnormalities persist or are not influenced by these treatments. Even though alterations in food intake, hypermetabolism, alterations in amino acid profiles, endotoxemia, accelerated starvation and decreased mobility may all contribute to sarcopenia in cirrhosis, hyperammonemia has recently gained attention as a possible mediator of the liver-muscle axis. Increased muscle ammonia causes: cataplerosis of α-ketoglutarate, increased transport of leucine in exchange for glutamine, impaired signaling by leucine, increased expression of myostatin (a transforming growth factor beta superfamily member) and an increased phosphorylation of eukaryotic initiation factor 2α. In addition, mitochondrial dysfunction, increased reactive oxygen species that decrease protein synthesis and increased autophagy mediated proteolysis, also play a role. These molecular and metabolic alterations may contribute to the anabolic resistance and inadequate response to nutrient supplementation in cirrhosis. Central and skeletal muscle fatigue contributes to impaired exercise capacity and responses. Use of proteins with low ammoniagenic potential, leucine enriched amino acid supplementation, long-term ammonia lowering strategies and a combination of resistance and endurance exercise to increase muscle mass and function may target the molecular abnormalities in the muscle. Strategies targeting endotoxemia and the gut microbiome need further evaluation.

Older patients' use of technology for a post-discharge nutritional intervention - A mixed-methods feasibility study

BACKGROUND

Malnutrition is frequent in older people and a precursor for morbidity and hospitalisation; furthermore low intake and weight loss during and after hospitalisation is well-described. Such patients are often excluded from technology projects on account of lack of skills. This is a barrier for their access to many current and future health care offers.

OBJECTIVES

To test the acceptability, feasibility and preliminary efficacy of technology-supported energy- and protein-enforced homedelivered meals for older patients discharged from hospital.

DESIGN

Mixed method design including a quasi-experimental controlled feasibility trial and embedded qualitative interviews.

PARTICIPANTS

Older medical patients (mean age 79.4 years; women 66.7%) at nutritional risk and discharged to own home were included consecutively to first the control group (n=18) and later the intervention group (n=18). Nine intervention and 16 control group patients completed the project.

METHODS

Intervention: group received: 1) enriched meals delivered to participants' homes 12 weeks after discharge, and 2) a tablet computer combining goal setting for intake with self-monitoring and feedback. Control group were treated as usual. Data collection was done at baseline, and at six and 12 weeks follow-up. Feasibility evaluation focused on 1) inclusion and retention and 2) acceptability and functionality of the intervention. Efficacy primary endpoint: Muscle strength and BMI. Secondary: Health related quality of life (HRQoL), depression; readmissions, mortality.

RESULTS

Technology challenges were related to immaturity of the out-of hospital app version; however, participants were motivated and capable of using the device. Inclusion and retention was challenged by the acceptability of the nutritional intervention and exhaustion among patients. Mortality was high. Although weaker at baseline the intervention group increased their muscle strength more consistently than did the control group: Handgrip strength with 2.5kg vs 0.9kg and chairto-stand-test with 3.3 vs. 1.8 times. They also improved their depression score and HRQoL more, and patients reported increased intake, appetite, and energy in the interviews. Relatives confirmed this and also reported positive impact on their level of worry and on the relationship with the older person.

CONCLUSION

The study provided valuable insight into appropriate methods and procedures as well as older people's preferences and views on barriers to successful intervention and use of technology in health care. This will guide the design of a future sufficiently powered study. Effect evaluation provided guidance for future sample size calculation.

Hand-grip strength does not correlate with treatment-related weight loss in patients with head and neck cancer

BACKGROUND

Hand-grip strength has been shown to be a reliable predictor of health outcomes. However, evidence supporting its use as an indicator of nutritional status is inconsistent. This study investigated its use in monitoring nutritional status in patients with head and neck cancer.

METHODS

A prospective audit of patients treated for head and neck cancer was undertaken at four centres over a three-month period in 2009. Nutritional outcomes were collected at 3, 6 and 12 months, and the data were statistically analysed.

RESULTS

Data from 114 patients showed that mean weight, but not hand-grip strength, fell significantly at 3, 6 and 12 months post-treatment (p < 0.003 vs p < 0.126).

CONCLUSION

A fall in weight does not coincide with a drop in hand-grip strength in patients receiving treatment for head and neck cancer. Hand-grip strength may therefore not be of benefit in the nutritional assessment of these patients and should not be part of routine assessment.

Responsiveness of muscle size and strength to physical training in very elderly people: a systematic review

The purpose of this review was to determine whether very elderly muscle (>75 years) hypertrophies in response to physical training. The databases MEDLINE; EMBASE; CINAHL Plus and SPORTDiscus were systematically literature searched with reference lists of all included studies and relevant reviews. Controlled trials (inactive elderly control group) involving healthy elderly participants over 75 years participating in an intervention complying with an established definition of physical training were included. Data extraction and quality assessment were performed using the PEDro scale. Data analysis was performed on muscle size and strength using RevMan (software version 5.1). Four studies were included of which four of four measured changes in gross muscle size. Training induced increases in muscle size from 1.5%-15.6% were reported in three of four studies, and one of four studies reported a decrease in muscle size (3%). The greatest gain in muscle mass was observed in a study of whole body vibration training. Meta-analysis of three studies found an increase of thigh muscle cross-sectional area (mean difference 2.31 cm(2) or 0.2%, 95% confidence interval (CI): 0.62 to 4.00; P = 0.008) and muscle strength (standardized mean difference 1.04, 95% CI: 0.65 to 1.43; P < 0.001). Physical training when delivered as resistance training has the ability to elicit hypertrophy and increase muscle strength in very elderly muscle.

Why critically ill patients are protein deprived

Critical illness dramatically increases muscle proteolysis and more than doubles the dietary protein requirement. Yet surprisingly, most critically ill patients receive less than half the recommended amount of protein during their stay in a modern intensive care unit. What could explain the wide gap between the recommendations in clinical care guidelines and actual clinical practice? We suggest that an important aspect of the problem is the failure of guidelines to explain the pathophysiology of protein-energy malnutrition and the ways critical illness modifies protein metabolism. The difficulty created by the lack of a framework for reasoning about appropriate protein provision in critical illness is compounded by the many ambiguous and often contradictory ways the word malnutrition is used in the critical care literature. Failing to elucidate these matters, the recommendations for protein provision in the guidelines are incoherent, unconvincing, and easy to ignore.

Maternal and paternal genomes differentially affect myofibre characteristics and muscle weights of bovine fetuses at midgestation

Postnatal myofibre characteristics and muscle mass are largely determined during fetal development and may be significantly affected by epigenetic parent-of-origin effects. However, data on such effects in prenatal muscle development that could help understand unexplained variation in postnatal muscle traits are lacking. In a bovine model we studied effects of distinct maternal and paternal genomes, fetal sex, and non-genetic maternal effects on fetal myofibre characteristics and muscle mass. Data from 73 fetuses (Day153, 54% term) of four genetic groups with purebred and reciprocal cross Angus and Brahman genetics were analyzed using general linear models. Parental genomes explained the greatest proportion of variation in myofibre size of Musculus semitendinosus (80–96%) and in absolute and relative weights of M. supraspinatus, M. longissimus dorsi, M. quadriceps femoris and M. semimembranosus (82–89% and 56–93%, respectively). Paternal genome in interaction with maternal genome (P<0.05) explained most genetic variation in cross sectional area (CSA) of fast myotubes (68%), while maternal genome alone explained most genetic variation in CSA of fast myofibres (93%, P<0.01). Furthermore, maternal genome independently (M. semimembranosus, 88%, P<0.0001) or in combination (M. supraspinatus, 82%; M. longissimus dorsi, 93%; M. quadriceps femoris, 86%) with nested maternal weight effect (5–6%, P<0.05), was the predominant source of variation for absolute muscle weights. Effects of paternal genome on muscle mass decreased from thoracic to pelvic limb and accounted for all (M. supraspinatus, 97%, P<0.0001) or most (M. longissimus dorsi, 69%, P<0.0001; M. quadriceps femoris, 54%, P<0.001) genetic variation in relative weights. An interaction between maternal and paternal genomes (P<0.01) and effects of maternal weight (P<0.05) on expression of H19, a master regulator of an imprinted gene network, and negative correlations between H19 expression and fetal muscle mass (P<0.001), suggested imprinted genes and miRNA interference as mechanisms for differential effects of maternal and paternal genomes on fetal muscle.

Appropriate protein provision in critical illness: a systematic and narrative review

BACKGROUND

Widely varying recommendations have been published with regard to the appropriate amount of protein or amino acids to provide in critical illness.

OBJECTIVE

We carried out a systematic review of clinical trials that compared the metabolic or clinical effects of different protein intakes in adult critical illness and comprehensively reviewed all of the available evidence pertinent to the safe upper limit of protein provision in this setting.

DESIGN

MEDLINE was searched for clinical trials published in English between 1948 and 2012 that provided original data comparing the effects of different levels of protein intake on clinically relevant outcomes and evidence pertinent to the safe upper limit of protein provision to critically ill adults.

RESULTS

The limited amount and poor quality of the evidence preclude conclusions or clinical recommendations but strongly suggest that 2.0-2.5 g protein substrate · kg normal body weight⁻¹ · d⁻¹ is safe and could be optimum for most critically ill patients. At the present time, most critically ill adults receive less than half of the most common current recommendation, 1.5 g protein · kg⁻¹ · d⁻¹, for the first week or longer of their stay in an intensive care unit.

CONCLUSION

There is an urgent need for well-designed clinical trials to identify the appropriate level of protein provision in critical illness.

Effect of sexual dimorphism on muscle strength in cachexia

BACKGROUND

Reduced muscle strength is a cardinal feature in cachexia. We investigated whether weight loss is associated differently with muscle strength in men and women in a large cohort of hospitalized patients.

METHODS

One thousand five hundred hospitalized patients (whereof 718 men, mean age 57.6 ± 16.0 years, mean body mass index (BMI) 24.6 ± 4.8 kg/m²) were included in the study. Non-edematous involuntary weight loss was determined with Subjective Global Assessment; isometric maximal muscle strength was evaluated by hand grip strength. Mid-upper arm circumference and triceps skinfold were used to calculate arm muscle area. Interrelationship between sex and weight loss was evaluated by regression analysis performed with the general linear model (GLM) allowing adjustment for continuous and categorical variables and corrected for age, arm muscle area (AMA), BMI, and diagnosis category (benign/malignant disease) as potentially confounding covariates.

RESULTS

Both men and women exhibited a significant stepwise decrease of hand grip strength with increasing weight loss. Age, sex, moderate and severe weight loss, BMI, and AMA were significant predictors of hand grip strength. The GLM moreover revealed a significant sex × weight loss effect, since grip strength was similarly decreased in moderate weight loss in men and women when compared to control patients without weight loss (8.5% in men and 10.5% in women, not significant (n.s.)), but the further reduction of grip strength in severe weight loss was significantly different between men and women (10.6% vs. 4.1%, P = 0.033).

CONCLUSIONS

Our findings indicate sex-specific differences in muscle strength response to weight loss.

Effects of two commercially available feline diets on glucose and insulin concentrations, insulin sensitivity and energetic efficiency of weight gain

A low-carbohydrate, high-protein (LCHP) diet is often recommended for the prevention and management of diabetes in cats; however, the effect of macronutrient composition on insulin sensitivity and energetic efficiency for weight gain is not known. The present study compared the effect in adult cats (n 32) of feeding a LCHP (23 and 47 % metabolisable energy (ME)) and a high-carbohydrate, low-protein (HCLP) diet (51 and 21 % ME) on fasting and postprandial glucose and insulin concentrations, and on insulin sensitivity. Tests were done in the 4th week of maintenance feeding and after 8 weeks of ad libitum feeding, when weight gain and energetic efficiency of each diet were also measured. When fed at maintenance energy, the HCLP diet resulted in higher postprandial glucose and insulin concentrations. When fed ad libitum, the LCHP diet resulted in greater weight gain (P < 0.01), and was associated with higher energetic efficiency. Overweight cats eating the LCHP diet had similar postprandial glucose concentrations to lean cats eating the HCLP diet. Insulin sensitivity was not different between the diets when cats were lean or overweight, but glucose effectiveness was higher after weight gain in cats fed the HCLP diet. According to the present results, LCHP diets fed at maintenance requirements might benefit cats with multiple risk factors for developing diabetes. However, ad libitum feeding of LCHP diets is not recommended as they have higher energetic efficiency and result in greater weight gain.

[Isoniazid-induced myopathy]

Drug-induced muscle disorders are now well known and vary from a simple isolated increase in muscle enzymes to severe drug-induced myopathy. The list of drugs inducing myopathy is very long and continues to grow. The onset of muscle disorders under isoniazid often falls within a drug-induced neuropathy or a drug-induced lupus. However, the occurrence of isolated isoniazid-induced drug myopathy without neuropathy is an extremely rare condition especially with non-toxic doses. The authors report the case of a 28-year-old man, without a previous medical history, hospitalized for pulmonary tuberculosis. After initiating tuberculosis treatment for five days, he presented muscle pain, fasciculation and weakness initially involving the lower left limb that quickly propagated to all four limbs. The physical examination noted a left ankle flush, a swollen left calf and fasciculation of both calves while the neurological examination was normal. The CPK was normal. Electromyography confirmed the myopathy without neuropathic findings. Isoniazid withdrawal was marked by the rapid disappearance of the symptoms. The reintroduction of a half-dose of isoniazid only induced a few transitional muscular fasciculations. The onset of the symptoms under tuberculosis treatment, the absence of later muscle disorders, the absence of any other cause of myopathy and the total disappearance of the symptoms after isoniazid withdrawal confirmed the diagnosis of isoniazid-induced myopathy.

Hand grip strength: outcome predictor and marker of nutritional status

BACKGROUND & AIMS

Among all muscle function tests, measurement of hand grip strength has gained attention as a simple, non-invasive marker of muscle strength of upper extremities, well suitable for clinical use. This review outlines the prognostic relevance of grip strength in various clinical and epidemiologic settings and investigates its suitability as marker of nutritional status in cross-sectional as well as intervention studies.

METHODS

Studies investigating grip strength as prognostic marker or nutritional parameter in cross-sectional or intervention studies were summarized.

RESULTS AND CONCLUSIONS

Numerous clinical and epidemiological studies have shown the predictive potential of hand grip strength regarding short and long-term mortality and morbidity. In patients, impaired grip strength is an indicator of increased postoperative complications, increased length of hospitalization, higher rehospitalisation rate and decreased physical status. In elderly in particular, loss of grip strength implies loss of independence. Epidemiological studies have moreover demonstrated that low grip strength in healthy adults predicts increased risk of functional limitations and disability in higher age as well as all-cause mortality. As muscle function reacts early to nutritional deprivation, hand grip strength has also become a popular marker of nutritional status and is increasingly being employed as outcome variable in nutritional intervention studies.

Myostatin expression is increased by food deprivation in a muscle-specific manner and contributes to muscle atrophy during prolonged food deprivation in mice

During food deprivation (FD), skeletal muscle protein is broken down to produce amino acids for hepatic gluconeogenesis to maintain blood glucose levels. However, it is unclear what role, if any, the secreted antigrowth factor myostatin (MSTN) plays in the muscle atrophy induced by FD. We therefore examined expression and function of MSTN in FD in mice. Two days of FD significantly decreased muscle mass and protein content and increased mRNA levels of ubiquitin ligases MuRF-1 and atrogin-1 in fast-twitch tibialis anterior (TA) muscle but not slow-twitch soleus (Sol) muscle, while 2 days of refeeding returned these to fed values in TA. MSTN mRNA levels were significantly increased approximately threefold by 2 days, but not 1 day, of FD and returned to fed levels with 2 days of refeeding in TA but were not significantly affected by FD or refeeding in Sol. TA mass decreased to a similar amount after 1 day of FD in wild-type mice and mice null for the MSTN gene but was decreased to a greater amount in wild-type than MSTN-null mice by 2 days of FD. In addition, blood glucose levels decreased and corticosterone levels increased to a greater extent in MSTN-null mice after 2 days of FD, but surprisingly muscle MuRF-1 and atrogin-1 mRNA levels were not affected by the lack of MSTN during FD. Similarly, changes in hepatic enzyme expression in response to FD were identical between wild-type and MSTN-null mice. Our data are consistent with the hypothesis that MSTN is dispensable for the initial atrophy occurring in response to FD but attenuates the decrease in fast-twitch muscle mass during prolonged FD.

Starvation physiology: reviewing the different strategies animals use to survive a common challenge

All animals face the possibility of limitations in food resources that could ultimately lead to starvation-induced mortality. The primary goal of this review is to characterize the various physiological strategies that allow different animals to survive starvation. The ancillary goals of this work are to identify areas in which investigations of starvation can be improved and to discuss recent advances and emerging directions in starvation research. The ubiquity of food limitation among animals, inconsistent terminology associated with starvation and fasting, and rationale for scientific investigations into starvation are discussed. Similarities and differences with regard to carbohydrate, lipid, and protein metabolism during starvation are also examined in a comparative context. Examples from the literature are used to underscore areas in which reporting and statistical practices, particularly those involved with starvation-induced changes in body composition and starvation-induced hypometabolism can be improved. The review concludes by highlighting several recent advances and promising research directions in starvation physiology. Because the hundreds of studies reviewed here vary so widely in their experimental designs and treatments, formal comparisons of starvation responses among studies and taxa are generally precluded; nevertheless, it is my aim to provide a starting point from which we may develop novel approaches, tools, and hypotheses to facilitate meaningful investigations into the physiology of starvation in animals.

Stable isotopes may provide evidence for starvation in reptiles

Previous studies have attempted to correlate stable isotope signatures of tissues with the nutritional condition of birds, mammals, fishes, and invertebrates. Unfortunately, very little is known about the relationship between food limitation and the isotopic composition of reptiles. We examined the effects that starvation has on delta13C and delta15N signatures in the tissues (excreta, carcass, scales, and claws) of six, distantly related squamate reptiles (gaboon vipers, Bitis gabonica; ball pythons, Python regius; ratsnakes, Elaphe obsoleta; boa constrictors, Boa constrictor; western diamondback rattlesnakes, Crotalus atrox, and savannah monitor lizards, Varanus exanthematicus). Analyses revealed that the isotopic composition of reptile carcasses did not change significantly in response to bouts of starvation lasting up to 168 days. In contrast, the isotopic signatures of reptile excreta became significantly enriched in 15N and depleted in 13C during starvation. The isotopic signatures of reptile scales and lizard claws were less indicative of starvation time than those of excreta. We discuss the physiological mechanisms that might be responsible for the starvation-induced changes in 13C and 15N signatures in the excreta, and present a mixing model to describe the shift in excreted nitrogen source pools (i.e. from a labile source pool to a nonlabile source pool) that apparently occurs during starvation in these animals. The results of this study suggest that naturally occurring stable isotopes might ultimately have some utility for characterizing nitrogen and carbon stress among free-living reptiles.

Morphometric changes induced by amino acid supplementation in skeletal and cardiac muscles of old mice

Aging is associated with progressive structural disorganization of muscular and cardiac fibers, decreasing functional capacity, and increased rates of disease and death. Aging is also characterized by disturbances in protein synthesis with impaired cellular organelle functions, particularly in the mitochondria. The availability of amino acids is a key factor for the overall metabolism of mammals and exogenous supplements of amino acid mixtures (AAm) could be a valid therapeutic strategy to improve quality of life, avoiding malnutrition and muscle wasting in the elderly. We investigated the morphoquantitative effects of long-term AAm supplementation on the mitochondria and sarcomeres (by electron microscope) and on collagen matrix deposition (by histologic techniques) in both skeletal and cardiac muscles of young and aged mice. Our data showed that old animals have fewer mitochondria and massive fibrosis in both muscles. Long-term AAm supplementation increased the number and volume of mitochondria and sarcomeres and decreased fibrosis in both skeletal muscle and hearts in old rats. These findings indicate that AAm restored muscular morphologic parameters and probably improved the mechanical performance of these organs.

Mechanism of age-dependent susceptibility and novel treatment strategy in glutaric acidemia type I

Glutaric acidemia type I (GA-I) is an inherited disorder of lysine and tryptophan metabolism presenting with striatal lesions anatomically and symptomatically similar to Huntington disease. Affected children commonly suffer acute brain injury in the context of a catabolic state associated with nonspecific illness. The mechanisms underlying injury and age-dependent susceptibility have been unknown, and lack of a diagnostic marker heralding brain injury has impeded intervention efforts. Using a mouse model of GA-I, we show that pathologic events began in the neuronal compartment while enhanced lysine accumulation in the immature brain allowed increased glutaric acid production resulting in age-dependent injury. Glutamate and GABA depletion correlated with brain glutaric acid accumulation and could be monitored in vivo by proton nuclear magnetic resonance (1H NMR) spectroscopy as a diagnostic marker. Blocking brain lysine uptake reduced glutaric acid levels and brain injury. These findings provide what we believe are new monitoring and treatment strategies that may translate for use in human GA-I.

Body condition assessment and prediction of fasting endurance in wild rabbits (Oryctolagus cuniculus)

In many species, reproductive success, resistance to food shortage and immune response to parasitism depend on body nutrient reserves. Thus, determining body fuels is important for studying the impact of the environment on animal fitness. As an alternative to the usual biochemical methods, we have defined models for estimating body composition in rabbits (Oryctolagus cuniculus). The accuracy of the indices obtained on a source group was tested on an independent group. The models were applicable regardless of age, sex or season. The intact body mass already accounted for 90% of the protein variability. The most accurate equation combining dry body mass and interscapular fat mass explained 99% of the protein variations. Intact body mass and the kidney fat index were poor estimators of lipid stores (r2 = 0.45) but 90% of the variation was explained by an equation combining the interscapular fat mass and the hind leg length. None of the predictive equations significantly over- or underestimated body reserves. The usefulness of the models was assessed by estimating fasting endurance during winter. Individual estimates, ranging from two to eight days, did not differ by more than 0.5 day from the fasting endurance obtained from actual mobilisable body nutrients. In such lean species (adiposity 2–4%), proteins may account for up to 40% of the available energy reserves and survival is likely to be linked to the continuous availability of food resources. These results stress the need to determine proteins and not only lipids to have a pertinent tool for the management of wild animal populations, particularly in lean species.

Wasting and the substrate-to-energy controlled pathway: a role for insulin resistance and amino acids

Amino acids contained in proteins can be transformed either in glucose precursors or in acetate, the end product of free fatty acid (FFA) oxidation. The dynamics of glucose, FFA, and amino acid competition for entry into the citric acid cycle (tricarboxylic acid [TCA] cycle) are very complex and not fully understood. Conditions where glucose is insufficiently driven to full oxidation are characterized by lowest efficiency in energy production per mole of oxygen consumed. Moreover, acetate provided by oxidation of FFA increases consumption of amino acids as precursors of the oxaloacetate required for condensation with acetate and for maintenance of citrate synthesis. Increased consumption of amino acids in the TCA cycle, if not matched by adequate intake, leads to muscular wasting and cachexia. Therefore, amino acid needs are very complex, and their intake must provide a balanced ratio of glucogenic and ketogenic precursors suitable to trigger entry of glucose to full oxidation and blunt the level of FFA utilization. Optimization of substrate entry into energy production must also be coupled with sufficient availability of amino acids in ratios suitable for maintaining protein synthesis, inhibiting the catabolic drive, and promoting integrity of cellular proteic structures. Alimentary proteins have a content of amino acids that is far from the stoichiometric ratios of essential amino acids required by humans. An amino acid formulation suitable to match energy needs, control carbohydrate and lipid flow into the TCA cycle, and promote protein synthesis in contracting cells is detailed in this article.

Muscle strength as a predictor of loss of functional status in hospitalized patients

OBJECTIVE

The incidence of protein-calorie malnutrition in hospitalized adult patients can reach 30% to 50% and adversely affect clinical outcome. We evaluated the efficacy of muscle strength to predict functional derangement and detect early changes in nutrition status in hospitalized patients.

METHODS

Patients hospitalized at medical and surgical wards from two different hospitals in Santiago, Chile, were studied during their hospital stay. Subjective Global Assessment of nutrition status and laboratory parameters were measured on admission. Anthropometric measures, handgrip dynamometry, and maximal inspiratory and expiratory pressures were measured on admission and discharge. The Karnofsky index was used to assess functional status. Twice weekly, caloric balance was calculated with indirect calorimetry and assessment of dietary intake.

RESULTS

From the initial selection of patients (n = 70), 50 patients (26 men and 24 women) completed the study. Median hospital stay was 10 d. Subjective Global Assessment was associated with anthropometric data, handgrip dynamometry, and serum levels of total proteins. Patients in whom functional status declined during hospital stay, on admission had lower left handgrip strength, a worse Subjective Global Assessment classification, were older, and had lower fat mass. No association between caloric balance during hospital stay and changes in muscle strength was observed.

CONCLUSIONS

Subjective Global Assessment, handgrip strength, and fat mass were good predictors for the decline in functional status during hospital stay. No association between caloric balance and changes in muscle strength was observed.

Muscle protein synthesis rate decreases 24 hours after abdominal surgery irrespective of total parenteral nutrition

BACKGROUND

Muscle protein synthesis rate is known to decrease postoperatively as a part of the catabolic response to trauma. Conventional total parenteral nutrition (TPN) in the postoperative period does not seem to counteract the decrease in protein synthesis. However, it is still unclear if ongoing TPN given continuously after surgery would inhibit this fall in muscle protein synthesis.

METHODS

The rate of protein synthesis in skeletal muscle was determined before and 24 hours after open cholecystectomy, used as a standardized human model of trauma. Patients (n = 14) were randomized to receive either TPN continuously throughout the postoperative period or saline as postoperative fluid therapy. The protein synthesis rate was calculated from the increase in enrichment of labeled phenylalanine in protein after an IV flooding dose of [2H5] phenylalanine, 45 mg/kg body weight.

RESULTS

The fractional synthesis rate decreased by 31% from 1.74 +/- 0.13% to 1.15 +/- 0.10% per 24 hours in the saline group (p < .02) and by 23% from 1.59 +/- 0.10% to 1.22 +/- 0.07% per 24 hours in the group receiving TPN (p < .01), showing no significant difference between the two groups.

CONCLUSION

A continuous and ongoing infusion of conventional TPN started immediately after surgery did not counteract the obligatory decline of muscle protein synthesis, observed 24 hours postoperatively.

Laparoscopic cholecystectomy does not prevent the postoperative protein catabolic response in muscle

OBJECTIVE

The authors determined the effect of laparoscopic cholecystectomy on protein synthesis in skeletal muscle. In addition to a decrease in muscle protein synthesis, after open cholecystectomy, the authors previously demonstrated a decrease in insulin sensitivity. This study on patients undergoing laparoscopic and open surgery, therefore, included simultaneous measurements of protein synthesis and insulin sensitivity.

SUMMARY BACKGROUND DATA

Laparoscopy has become a routine technique for several operations because of postoperative benefits that allow rapid recovery. However, its effect on postoperative protein catabolism has not been characterized. Conventional laparotomy induces a drop in muscle protein synthesis, whereas degradation is unaffected.

METHODS

Patients were randomized to laparoscopic or open cholecystectomy, and the rate of protein synthesis in skeletal muscle was determined 24 hours postoperatively by the flooding technique using L-(2H5)phenylalanine, during a hyperinsulinemic normoglycemic clamp to assess insulin sensitivity.

RESULTS

The protein synthesis rate decreased by 28% (1.77 +/- 0.11%/day vs. 1.26 +/- 0.08%/day, p < 0.01) in the laparoscopic group and by 20% (1.97 +/- 0.15%/day vs. 1.57 +/- 0.15%/day, p < 0.01) in the open cholecystectomy group. In contrast, the fall in insulin sensitivity after surgery was lower with laparoscopic (22 +/- 2%) compared with open surgery (49 +/- 5%).

CONCLUSIONS

Laparoscopic cholecystectomy did not avoid a substantial decline in muscle protein synthesis, despite improved insulin sensitivity. The change in the two parameters occurred independently, indicating different mechanisms controlling insulin sensitivity and muscle protein synthesis.

The effect of carbidopa on the pharmacokinetics and metabolism of intravenously administered levodopa in blood plasma and skeletal muscle

The effect of carbidopa on the pharmacokinetics and metabolism of levodopa (L-dopa) in blood plasma and skeletal muscle extracellular fluid (ECF) has been studied by repeated measurements in one beagle dog. The administration of a single dose of L-dopa (25 mg/kg i.v.) without carbidopa pretreatment (controls) resulted in an increase in the concentrations of L-dopa and 3-O-methyldopa (3-OMD) in blood plasma and skeletal muscle ECF dialysates. This effect was clearly potentiated for L-dopa in blood plasma (186% increase in AUC) and 3-OMD in skeletal muscle dialysates (108% increase in AUC) after pretreatment with carbidopa (100 mg/day). In addition, carbidopa prolonged the half-life of the elimination of L-dopa in blood plasma by 48% and in skeletal muscle ECF by 66% but did not influence its blood plasma distribution half-life (t 1/2 alpha = 0.17 h). The elimination half-life of L-dopa in the controls was higher in muscle (t 1/2 beta = 1.76 h) than in blood plasma (t 1/2 beta = 0.50 h). Carbidopa pretreatment resulted in a relatively small increase (29%) in the L-dopa content of skeletal muscle ECF as indicated by the AUC. The accumulation of 3-OMD in muscle dialysates, in contrast to that in plasma, was significantly enhanced after the administration of L-dopa following treatment with carbidopa. In the control experiments, dopamine (DA) was detectable only in the dialysates from muscle ECF.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo pharmacokinetics of levodopa and 3-O-methyldopa in muscle. A microdialysis study

In the present study in vivo microdialysis sampling coupled to high-performance liquid chromatography with electrochemical detection, was used to study the pharmacokinetics of levodopa and 3-O-methyldopa in skeletal muscle in dog, after intravenous administration of levodopa. For comparison, the pharmacokinetic parameters of both compounds were simultaneously determined in plasma using blood collection. Muscle microdialysis samples and blood were continuously collected for 4 h after the administration of levodopa (25 mg/kg). Pharmacokinetic profiles of levodopa in plasma and muscle were different. The mean Tmax value of levodopa in plasma and muscle was 0.16 h and 1.0 h, respectively. The AUC0----inf for levodopa in plasma was nearly 18-fold higher in plasma than in muscle. The 3-O-methyldopa concentration increased very rapidly after the administration of levodopa, to reach a plateau after 2.5 h and 3 h in plasma and muscle, respectively. The AUC0----4 for 3-O-methyldopa was 3.6-fold higher in plasma than in muscle. The ratio levodopa/3-O-methyldopa, reflecting the metabolic rate of levodopa, was 3.5 times higher in plasma than in muscle, at the peak value of levodopa, and then rapidly declined to values lower than 1, one hour after administration of the drug. We compared our results with literature data from postmortem studies done in rat experiments. We concluded that levodopa is not accumulating in muscle as such, but is converted to 3-O-methyldopa probably before leaving the plasma compartment.

Amino acids in surgical nutrition. Principles and practice

Amino acids will always be an integral part of nutritional support in all patients. The use of specific amino acids in pharmacologic doses may be beneficial to certain critically ill patients, indicating that such compounds are conditionally essential. As our knowledge of the altered regulation of amino acid metabolism in surgical patients improves, the design of more effective feeding regimens will follow. The goal should be to provide the best nutrition to all patients at all times.

Neutral amino acid transport into rat skeletal muscle: competition, adaptive regulation, and effects of insulin

Amino acid (AA) transport systems A and L, which transfer preferentially small neutral AA (SNAA) and large neutral AA (LNAA), respectively, were studied in the isolated soleus muscle with the specific models, 2-(methylamino)isobutyrate (MeAIB) and 2-aminobicyclo[2,2,1]heptane-2-carboxylate (BCH). Affinity for MeAIB was greater than for BCH (Km = 3.2 +/- 0.2 and 8.7 +/- 0.2 mm, respectively). Rate of transport of MeAIB (Vmax = 104 +/- 3 pmol/microL/min) was slower than for BCH (970 +/- 12 pmol/microL/min), but accumulation was far more concentrative; transport of BCH, but not MeAIB, rapidly reached a steady-state level. MeAIB transport was reduced in the presence of SNAA; BCH transport was reduced to a lesser extent only by LNAA. Mixtures of AA at concentrations resembling those in plasmas of rats fed either a 6% or 50% casein diet reduced transport of MeAIB, whereas BCH transport was low only with the latter mixture. Only MeAIB transport was stimulated by insulin. Preincubation of muscles for 5 hours in a AA-free medium stimulated subsequent MeAIB uptake by about twofold to fourfold; this effect was suppressed by inhibitors of protein synthesis. Selective differences were thus observed in transport by skeletal muscle of model AA for the A and L systems: increased transport resulting from various stimuli was limited to the model for the A system, and transport of either model was depressed with mixtures containing physiological levels of AA. Changes in dietary protein or AA intake may thus alter transport of certain neutral AA into skeletal muscle via changes in plasma AA pools.

Effects of branched-chain amino acids on protein turnover

Amino acid availability rapidly regulates protein synthesis and degradation. Increasing amino acid concentrations above the levels found in post-absorptive plasma stimulates protein synthesis in a dose-dependent manner at the level of mRNA translation-initiation and inhibits protein degradation by inhibiting lysosomal autophagy. The anabolic effects of insulin on protein synthesis and protein degradation are exerted at the same sites (i.e., peptide chain initiation and lysosomal stabilization) allowing for a rapid synergistic response when both amino acids and insulin increase after a protein-containing meal. In perfused liver preparations, protein anabolic effects are exerted by a group of amino acids acting in concert. The BCAA are among the amino acids required for stimulation of hepatic protein synthesis, but there is no evidence that BCAA or leucine alone are effective. Leucine alone is an important inhibitor of hepatic protein degradation, but maximal inhibition requires in addition several other regulatory amino acids. In heart and skeletal muscle in vitro, increasing the concentration of the three BCAA or of leucine alone reproduces the effects of increasing the supply of all amino acids in stimulating protein synthesis and inhibiting protein degradation. Skeletal muscle is the largest repository of metabolically active protein and a major contributor to total body nitrogen balance. Supplying energy alone (i.e., carbohydrate and lipids) cannot prevent negative nitrogen balance (net protein catabolism) in animals or humans; only provision of amino acids allows the attainment of nitrogen balance. In rats and in humans nourished parenterally, provision of balanced amino acid solutions or of only the three BCAA cause similar improvements in nitrogen balance for several days. There is some evidence that infusions of leucine alone can stimulate muscle protein synthesis in vivo; the effect may be transitory and was not observed by all investigators; provisions of excess leucine alone does not seem to affect total body or muscle protein degradation in vivo. In postabsorptive rats, in vivo, infusion of the three BCAA together stimulates muscle protein synthesis as much as the infusion of a complete amino acid mixture or of a mixture of essential amino acids; the in vivo effect requires coinfusion of glucose or of small (physiological) doses of insulin, suggesting synergism between insulin and amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)

Grip strength: a measure of the proportion of protein loss in surgical patients

Measurements of voluntary hand grip strength (GS) are a sensitive predictor of postoperative complications. The loss of body protein is thought to be important in the development of these postoperative complications, but the relationship between GS and body protein status has not been studied. We have measured GS (by hand dynamometry), total body protein (indirectly by mid-arm muscle circumference, and directly by in vivo neutron activation analysis) and the proportion of protein loss (protein index) in 80 patients with gastrointestinal disease and 87 normal volunteers. Using regression analysis, a matched study and clinical decision analysis, it has been demonstrated that GS is a sensitive measurement of the degree of protein loss. The results support more widespread use of GS measurements in the identification of patients at high risk of postoperative complications and in the monitoring of patient response to nutritional intervention.

The effect of carbidopa on plasma and muscle levels of L-dopa, dopamine, and their metabolites following L-dopa administration to rats

Administration of L-dopa (L-3,4-dihydroxyphenylalanine) (200 mg/kg p.o.) to rats produced elevated plasma and muscle concentrations of both L-dopa and 3-O-methyldopa (3-OMD). This effect was potentiated by simultaneous administration of carbidopa (25 mg/kg p.o.). Both L-dopa and 3-OMD accumulated in muscle after administration of L-dopa with or without carbidopa. Elevated dopamine levels were detected in both muscle and plasma after treatment with L-dopa alone. Concurrent administration of carbidopa only diminished dopamine levels in plasma, and the duration of raised dopamine levels in muscle was increased. Carbidopa administration had no effect on the elevated plasma concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) caused by L-dopa administration. In muscle, carbidopa treatment tended to prolong the duration of raised metabolite levels. Muscle appears to accumulate L-dopa at a site where decarboxylation is not totally prevented by concurrent carbidopa administration, and where dopamine is not degraded as actively as in other tissues. The muscle sink for L-dopa may influence the plasma profile of the amino acid, which has implications for the therapeutic response to L-dopa in Parkinson's disease.

Fractional rates of muscle protein synthesis and degradation in chickens with genetic muscular dystrophy

Rates of synthesis (ks) and degradation (Kd) of muscle protein of normal (+/+) and muscular dystrophic (am/am) chicks of the GNS/2 strain obtained from a Fayoumi population were estimated based on the urinary excretion of N tau-methylhistidine. Both fractional rates of muscle protein synthesis and degradation of the line with muscular dystrophy at 4 and 20 weeks of age were greater than that of normal chicks. The muscular dystrophy gene affected the increase in rate of degradation more than the increase in fractional rate of synthesis.

Polyribosome concentration in human skeletal muscle after starvation and parenteral or enteral refeeding

Posttraumatic and septic states cause a loss of body proteins resulting in a negative nitrogen balance. The major part of the excreted nitrogen is derived from the proteins of skeletal muscle. The loss in proteins is due to a decrease in protein synthesis rather than an increase in protein degradation. Nutritional support may increase protein synthesis, and determination of its activity in skeletal muscle will give information on the utilization of nutrients in catabolic patients. The effect of nutritional support on healthy subjects was studied to achieve a background for future clinical studies. Male volunteers between 20 and 40 years old were refed parenterally or enterally after three days of starvation. Muscle biopsies (50 mg) were analyzed for the size distribution of ribosomes in a sucrose density gradient, and the ribosome concentration was determined per mg of DNA. Changes in the percentage content of polyribosomes preceded those of the total ribosome concentration. The total polyribosome concentration per gram wet weight of skeletal muscle decreased significantly during starvation. After one and two days of refeeding, a significant increase was observed, but the original level of the nonstarved subjects was not reached. The total ribosome concentration increased upon refeeding, but was not significantly different from that of the starved condition. The nitrogen balance was negative during starvation but attained equilibrium after two days of refeeding. Nutrition administered by the parenteral or enteral route were equally effective in restoring protein synthesis.

Analysis of (1-13C)leucine and (13C)KIC in plasma by capillary gas chromatography/mass spectrometry in protein turnover studies

The methods used for the determination of the concentration and isotope enrichment of (1-13C)leucine and its metabolite (13C) alpha-ketoisocaproic acid (KIC) in plasma for the study of whole-body protein turnover are described. Leucine was analysed as its N-heptafluorobutyryl isobutyl ester and KIC as its quinoxalinol-TMS derivative, both by chemical ionization selected ion monitoring gas chromatography/mass spectrometry (GC/MS). The sensitivity of the leucine assay was improved 30 times by monitoring the negative ions under the conditions described. The coefficient of variation for enrichment and concentration measurements were 0.5% and 2%, respectively, with a minimum detectable enrichment of 0.1 at% excess for both assays.

Hand grip--a simple test for morbidity after fracture of the neck of femur

Seventy-six female patients, having sustained a fracture of the neck of femur, were assessed preoperatively by measuring their muscle strength in the form of grip using a hand-held dynamometer and by measuring serum albumin. A grip strength of less than 15 kg was found to be a reliable predictor of subsequent postoperative complications in female patients over the age of 80. Serum albumin had no predictive value. There was no significant difference in complication rates between different surgeons.