Dietary Acid Load but Not Mediterranean Diet Adherence Score Is Associated With Metabolic and Cardiovascular Health State: A Population Observational Study From Northern Italy

Diet plays a pivotal role in shaping the trajectory of chronic diseases. In this regard, the Mediterranean diet has been widely shown to exert beneficial effects on cardiometabolic health. On the contrary, the Western diet, which has also been reported to be an acidogenic dietary pattern, elicits detrimental effects on both metabolic and cardiovascular (CV) health. However, the role of dietary acid load (DAL) as a predictor of cardiometabolic prognosis remains to be elucidated. Thus, this study aims to compare Mediterranean diet adherence (MDA) and DAL focusing on their relationship with metabolic and CV prognosis. A total of 448 individuals aged 55–80 years were grouped depending on their MDA, assessed using food frequency questionnaires, or DAL, evaluated using potential renal load acid (PRAL) and net-endogenous acid production (NEAP). Study participants underwent anthropometric and biochemical measurements. The metabolic syndrome (MetS) prevalence was evaluated according to the National Cholesterol Education Program-Adult Treatment Panel III. Finally, the CV risk was evaluated using three independent algorithms: atherosclerotic cardiovascular disease (ASCVD), European Systematic COronary Risk Evaluation (SCORE), and Cuore risk scores. Mediterranean diet adherence was negatively associated with PRAL and NEAP. Individuals in the higher MDA tertile group had higher HDL cholesterol as well as lower homeostasis model assessment index (HOMA-IR) and fat mass relative to the lowest MDA tertile. However, in the high-MDA tertile group, there was neither a significantly lower MetS prevalence nor CV risk. Instead, both the MetS prevalence and CV risk were higher in individuals in the higher acid PRAL quartile relative to the lower alkaline PRAL quartile. Dietary acid load, especially assessed using PRAL but not MDA, was associated with indices of metabolic and CV prognosis. Thus, DAL assessed by 24-h dietary recalls may represent a better predictor of cardiometabolic health if compared to MDA evaluated using food frequency questionnaires.

The Aging Muscle in Experimental Bed Rest: A Systematic Review and Meta-Analysis

Background: Maintaining skeletal muscle mass and function in aging is crucial for preserving the quality of life and health. An experimental bed rest (BR) protocol is a suitable model to explore muscle decline on aging during inactivity. Objective: The purpose of this systematic review and meta-analysis was, therefore, to carry out an up-to-date evaluation of bed rest, with a specific focus on the magnitude of effects on muscle mass, strength, power, and functional capacity changes as well as the mechanisms, molecules, and pathways involved in muscle decay. Design: This was a systematic review and meta-analysis study. Data sources: We used PubMed, Medline; Web of Science, Google Scholar, and the Cochrane library, all of which were searched prior to April 23, 2020. A manual search was performed to cover bed rest experimental protocols using the following key terms, either singly or in combination: "Elderly Bed rest," "Older Bed rest," "Old Bed rest," "Aging Bed rest," "Aging Bed rest," "Bed-rest," and "Bedrest". Eligibility criteria for selecting studies: The inclusion criteria were divided into four sections: type of study, participants, interventions, and outcome measures. The primary outcome measures were: body mass index, fat mass, fat-free mass, leg lean mass, cross-sectional area, knee extension power, cytokine pattern, IGF signaling biomarkers, FOXO signaling biomarkers, mitochondrial modulation biomarkers, and muscle protein kinetics biomarkers. Results: A total of 25 studies were included in the qualitative synthesis, while 17 of them were included in the meta-analysis. In total, 118 healthy elderly volunteers underwent 5-, 7-, 10-, or 14-days of BR and provided a brief sketch on the possible mechanisms involved. In the very early phase of BR, important changes occurred in the skeletal muscle, with significant loss of performance associated with a lesser grade reduction of the total body and muscle mass. Meta-analysis of the effect of bed rest on total body mass was determined to be small but statistically significant (ES = -0.45, 95% CI: -0.72 to -0.19, P < 0.001). Moderate, statistically significant effects were observed for total lean body mass (ES = -0.67, 95% CI: -0.95 to -0.40, P < 0.001) after bed rest intervention. Overall, total lean body mass was decreased by 1.5 kg, while there was no relationship between bed rest duration and outcomes (Z = 0.423, p = 672). The meta-analyzed effect showed that bed rest produced large, statistically significant, effects (ES = -1.06, 95% CI: -1.37 to -0.75, P < 0.001) in terms of the knee extension power. Knee extension power was decreased by 14.65 N/s. In contrast, to other measures, meta-regression showed a significant relationship between bed rest duration and knee extension power (Z = 4.219, p < 0.001). Moderate, statistically significant, effects were observed after bed rest intervention for leg muscle mass in both old (ES = -0.68, 95% CI: -0.96 to -0.40, P < 0.001) and young (ES = -0.51, 95% CI: -0.80 to -0.22, P < 0.001) adults. However, the magnitude of change was higher in older (MD = -0.86 kg) compared to younger (MD = -0.24 kg) adults. Conclusion: Experimental BR is a suitable model to explore the detrimental effects of inactivity in young adults, old adults, and hospitalized people. Changes in muscle mass and function are the two most investigated variables, and they allow for a consistent trend in the BR-induced changes. Mechanisms underlying the greater loss of muscle mass and function in aging, following inactivity, need to be thoroughly investigated.

Physical capacities and leisure activities are related with cognitive functions in older adults

OBJECTIVE

This study aimed to evaluate the relationship between physical activity habits, physical performance and cognitive capacity in older adults' population of Italy and Slovenia.

METHODS

Anthropometric characteristics and body composition bioelectrical impedance analysis (BIA) were evaluated in 892 older adults (60-80 y). Aerobic capacity was measured using the 2km walking test and handgrip and flexibility tests were performed. Physical activity habits and cognitive functions were evaluated by the Global-Physical-Activity-Questionnaires (GPAQ) and by Montreal-Cognitive-Assessment (MoCA) questionnaires, respectively.

RESULTS

GPAQ scores were associated with lower BMI (r=-0.096; p=0.005), lower percentage of fat-mass (r=-0.138; p=0.001), better results in the 2km-walk test (r=-0.175; p=0.001) and a higher percentage of fat-free mass (r=0.138; p=0.001). We also evaluated that, a higher MoCA score correlates with age (r=-0.208; p=0.001), 2km-walk test (r=-0.166; p=0.001), waist-hip ratio (r=-0.200; p=0.001), resting heart-rate (r=-0.087; p=0.025) and heart-rate at the end of 2km-walk test (r=0.189; p=0.001).

CONCLUSIONS

Older adults with a higher level of daily physical activity showed reduction in fat mass and BMI, and higher aerobic fitness; these characteristics have a protection effect on cognitive function.

Contraction and nutrition interaction promotes anabolism in cachectic muscle

PURPOSE OF REVIEW

Cachexia is a disease-related multifactorial syndrome characterized by inflammation, massive muscle protein catabolism and carbohydrate and lipid metabolism disorder.Several studies tried to define the impact of either nutrition or physical exercise (single approach strategy) or their combination (multimodal approach strategy) on prevention and/or treatment of muscle wasting in cachectic patients.

RECENT FINDINGS

Single approach strategies (i.e. nutrition or physical exercise) have the potential of preventing and improving features of the cachexia syndrome possibly with a differential impact according to the underlying disease. Limited information is available on the beneficial effect of multimodal approach strategies.

SUMMARY

Multimodal approaches appear to be more effective than those based on single interventions in physiological condition and in cachectic patients with COPD or chronic kidney disease. Further studies, however, are required in cachexia induced by heart failure, cancer and critical illness.

Effects of Hypoxia and Bed Rest on Markers of Cardiometabolic Risk: Compensatory Changes in Circulating TRAIL and Glutathione Redox Capacity

In chronic diseases, hypoxia and physical inactivity are associated with atherosclerosis progression. In contrast, a lower mortality from coronary artery disease and stroke is observed in healthy humans residing at high altitude in hypoxic environments. Eleven young, male volunteers completed the following 10-day campaigns in a randomized order: hypoxic ambulatory, hypoxic bed rest and normoxic bed rest. Before intervention, subjects were evaluated in normoxic ambulatory condition. Normobaric hypoxia was achieved in a hypoxic facility simulating 4000 m of altitude. Following hypoxia, either in bed rest or ambulatory condition, markers of cardiometabolic risk shifted toward a more atherogenic pattern consisting of: (a) lower levels of total HDL cholesterol and HDL2 sub-fraction and decreased hepatic lipase; (b) activation of systemic inflammation, as determined by C-reactive protein and serum amyloid A; (c) increased plasma homocysteine; (d) decreased delta-5 desaturase index in cell membrane fatty acids, a marker of insulin sensitivity. Bed rest and hypoxia additively decreased total HDL and delta-5 desaturase index. In parallel to the pro-atherogenic effects, hypoxia activated selected anti-atherogenic pathways, consisting of increased circulating TNF-related apoptosis-inducing ligand (TRAIL), a protective factor against atherosclerosis, membrane omega-3 index and erythrocyte glutathione availability. Hypoxia mediated changes in TRAIL concentrations and redox glutathione capacity (i.e., GSH/GSSG ratio) were greater in ambulatory conditions (+34 ± 6% and +87 ± 31%, respectively) than in bed rest (+17 ± 7% and +2 ± 27% respectively). Hypoxia-induced cardiometabolic risk is blunted by moderate level of physical activity as compared to bed rest. TRAIL and glutathione redox capacity may contribute to the positive interaction between physical activity and hypoxia.

Highlights:

– Hypoxia and bed rest activate metabolic and inflammatory markers of atherogenesis.

– Hypoxia and physical activity activate selected anti-atherogenic pathways.

– Hypoxia and physical activity positive interaction involves TRAIL and glutathione.

Alkalinization with potassium bicarbonate improves glutathione status and protein kinetics in young volunteers during 21-day bed rest

BACKGROUND & AIMS

Physical inactivity is associated with lean body mass wasting, oxidative stress and pro-inflammatory changes of cell membrane lipids. Alkalinization may potentially counteract these alterations. We evaluated the effects of potassium bicarbonate supplementation on protein kinetics, glutathione status and pro- and anti-inflammatory polyunsaturated fatty acids (PUFA) in erythrocyte membranes in humans, during experimental bed rest.

METHODS

Healthy, young, male volunteers were investigated at the end of two 21-day bed rest periods, one with, and the other without, daily potassium bicarbonate supplementation (90 mmol × d^-1), according to a cross-over design. Oxidative stress in erythrocytes was evaluated by determining the ratio between reduced (GSH) and oxidized glutathione (GSSG). Glutathione turnover and phenylalanine kinetics, a marker of whole body protein metabolism, were determined by stable isotope infusions. Erythrocyte membranes PUFA composition was analyzed by gas-chromatography.

RESULTS

At the end of the two study periods, urinary pH was 10 ± 3% greater in subjects receiving potassium bicarbonate supplementation (7.23 ± 0.15 vs. 6.68 ± 0.11, p < 0.001). Alkalinization increased total glutathione concentrations by 5 ± 2% (p < 0.05) and decreased its rate of clearance by 38 ± 13% (p < 0.05), without significantly changing GSH-to-GSSG ratio. After alkalinization, net protein balance in the postabsorptive state improved significantly by 17 ± 5% (p < 0.05) as well as the sum of n-3 PUFA and the n-3-to-n-6 PUFA ratio in erythrocyte membranes (p < 0.05).

CONCLUSIONS

Alkalinization during long-term inactivity is associated with improved glutathione status, anti-inflammatory lipid pattern in cell membranes and reduction in protein catabolism at whole body level. This study suggests that, in clinical conditions characterized by inactivity, oxidative stress and inflammation, alkalinization could be a useful adjuvant therapeutic strategy.

Body weight and its association with impulsivity in middle and old age individuals

Impulsivity, conceptualized as impulsive personality trait, poor inhibitory control and enhanced reward sensitivity, has been strongly linked to obesity. In particular, a disequilibrium between cognitive control and reward sensitivity has been observed in obese individuals in both behavioural and imaging studies. While this issue has been widely investigated in children and adults, it has received little attention in older adults. Here, obese and non-obese participants aged between 40 and 70 years completed the Barratt Impulsiveness scale (assessing motor, non-planning and attentional impulsiveness), a Go/no-go task with foods and non-foods (assessing inhibitory control) and a reward sensitivity battery with high and low caloric foods (assessing liking, wanting, tastiness and frequency of consumption). We observed that participants with higher BMI reported increased wanting for high calorie foods, but did not show poorer inhibitory control. Interestingly, participants who scored lower on the MMSE reported to consume high calorie more than low calorie foods. Finally, those who presented low scores on non-planning and motor impulsiveness subscales reported higher tastiness ratings for low calorie foods. These results show that increased reward sensitivity but not reduced inhibitory control may characterize higher BMI during aging. Importantly, they also highlight new findings concerning food preferences among older adults.

Intermittent vs. continuous enteral feeding to prevent catabolism in acutely ill adult and pediatric patients

PURPOSE OF REVIEW

In clinical management of acutely ill adults and children, continuous enteral feeding (CEF), being considered the most tolerable approach, in comparison to other temporal patterns of nutrient administration (i.e. intermittent, cyclic and bolus), is the most frequently applied method. However, uncertainties remain about the most efficient approach to counteract protein catabolism.

RECENT FINDINGS

In critically ill adults, protein loss is mainly driven by increased protein breakdown whereas, in pediatric patients, acute illness is mainly characterized by blunted regulation of protein synthesis and stunted growth. Kinetic studies in fed adult volunteers indicate that protein synthesis can be stimulated for a limited period only. However, continuous feeding persistently improves protein balance through a sustained suppression of protein breakdown. This leads to the hypothesis that CEF could be more anticatabolic than intermittent enteral feeding (IEF) in these patients. Differently from adults, experimental models of acute disease in growing animals have consistently indicated that IEF can improve protein anabolism more efficiently than CEF, mainly through protein synthesis stimulation. The scarce number of clinical studies in acutely ill adults or pediatric patients, mostly performed with inadequate methodology, could not define the best approach to maintain protein balance.

SUMMARY

There is a need for pragmatic studies to directly compare the protein anabolic action of CEF and IEF using accurate methodologies, such as stable isotopes of amino acids, in both adult and pediatric patients with acute illness.

Higher protein intake is associated with improved muscle strength in elite senior athletes

OBJECTIVE

The optimal protein intake for elderly individuals who exercise regularly has not yet been clearly defined. The aim of this study was to test the hypothesis that protein intake level is associated with muscle strength in elderly elite athletes.

METHODS

We evaluated 50 elite senior athletes (38 men and 12 women) participating in the European Master Games 2011 in an observational cross-sectional study. Participants were divided into two groups-lower (LPI) or higher (HPI) protein intake-according to the median value of their ratio of urinary urea nitrogen to urinary creatinine (i.e., 8.8 g/L), as a marker of protein intake. A dietary interview confirmed differences in protein consumption between the LPI and HPI groups. We also evaluated body composition (bioimpedance), muscle strength, and hematochemical indices.

RESULTS

LPI and HPI groups were homogeneous for age (72 [68-74] and 71 [68-74] y, respectively), fat-free mass index (18.4 [17-19.4] and 18.2 [17-19.1] kg/m²), body fat (18.3% [12.3-20.7%] and 16.6% [13.6-21.2%]), and glomerular filtration rate (57.7 [53.8-64.9] and 62.7 [56.1-69.3] mL/min/1.73 m²). The HPI group showed greater leg and trunk muscle strength (N) compared with the LPI group (left leg extension, 339 [238-369] versus 454 [273-561], respectively, P < 0.05; right leg extension, 319 [249-417] versus 432 [334-635], P ≤ 0.05; trunk extension, 435 [370-467] versus 464 [390-568], P ≤ 0.05).

CONCLUSIONS

Higher protein intake in elite senior athletes is associated with a greater muscle strength.

What factors influence protein synthesis and degradation in critical illness?

PURPOSE OF REVIEW

The optimal approach to improve protein metabolism in critical illness is not yet fully defined. Here, we have summarized recent literature dealing with the main catabolic and anabolic factors influencing protein kinetics in acute hypercatabolic patients.

RECENT FINDINGS

Protein/amino acid intake levels should be adapted to type and severity of illness, keeping in mind that energy overfeeding is associated with poor outcome. A number of anticatabolic nutraceuticals and drugs have been tested in acute patients. The encouraging results have been obtained with β-hydroxy-β-methylbutyrate, omega-3 fatty acids, oxandrolone, propranolol, and metformin. Their efficacy and lack of side-effects need to be confirmed. Physical therapy, including muscle electro-stimulation, appears a very promising intervention, both effective and safe.

SUMMARY

Protein catabolism can be minimized in acute patients by adequate nutritional support, early mobilization, and, possibly, pharmacological and nutraceutical interventions. A combination of these strategies should be tested in randomized controlled trials.

Omega-3 fatty acids and protein metabolism: enhancement of anabolic interventions for sarcopenia

PURPOSE OF REVIEW

The increased age observed in most countries, with the associated higher rates of chronic illnesses and cancer, and a diffuse sedentary lifestyle, will increase the number of patients with clinically relevant anabolic resistance, sarcopenia and its complications. The need for solutions to this major health issue is, therefore, pressing.

RECENT FINDINGS

The metabolic derangements and other consequences associated with sarcopenia can be slowed or even prevented by specific nutritional interventions. New evidence is available about the efficacy of omega-3 fatty acid dietary supplementation to improve protein metabolism and counteract anabolic resistance through indirect effects. Studies show that the anabolic stimuli from substrates (e.g. amino acids or proteins), hormones (e.g. insulin) and/or physical activity in skeletal muscle can be enhanced by long-term fish oil administration.

SUMMARY

The review of data from recent studies on this topic suggests that dietary omega-3 fatty acid supplementation, in association with an anabolic stimulus, could potentially provide a safe, simple and low-cost intervention to counteract anabolic resistance and sarcopenia. This intervention may contribute to prevent cachexia and disabilities. Supplementation should be given in the earlier stages of sarcopenia (e.g. precachexia). Further research should, however, be performed to better understand the mechanisms involved and the best dosage and timing of administration.

Pentoxifylline acutely reduces protein catabolism in chronically uremic patients

BACKGROUND

We investigated the ability of pentoxifylline, a drug with hemorheological actions known to block tumor necrosis factor-alpha (TNF-alpha) release, to modulate whole-body protein kinetics in undialyzed patients with chronic uremia.

METHODS

Leucine rate of appearance (Ra) from proteolysis and leucine oxidation, a marker of net protein loss, were determined by infusing l-[1-13C]leucine and using the reciprocal pool model for calculations.

RESULTS

Intravenous infusion of pentoxifylline in the postabsorptive state (1 mg/kg within 3 hours) decreased the intracellular leucine Ra from proteolysis by -16% +/- 4% versus -3% +/- 2% of saline (P = 0.02) and leucine oxidation by -16% +/- 4% versus +4% +/- 2% of saline (P = 0.003). Combined infusions of pentoxifylline and a balanced amino acid mixture (0.2 mg/kg/min) decreased whole-body proteolysis by -53% +/- 7% versus -26% +/- 6% of amino acid infusion alone (P = 0.02). Circulating levels of TNF-alpha and TNF-alpha soluble receptors (sTNF-Rs) were elevated (P < 0.001) in patients compared with healthy controls. Pentoxifylline infusion did not significantly affect TNF-alpha levels, but decreased sTNF-Rs both in the postabsorptive state and during hyperaminoacidemia.

CONCLUSION

Pentoxifylline acutely decreased whole-body proteolysis in chronically uremic patients. Potential explanations for these pharmacological effects may include downregulation of the TNF-alpha system or other mechanisms related to the rheological action of the drug (eg, increased amino acid or insulin delivery to target cells).

Regulation of muscle cathepsin B proteolytic activity in protein-depleted patients with chronic diseases

BACKGROUND & AIMS

The lysosomal cathepsin system contributes to degrading cellular skeletal muscle proteins in many catabolic diseases. We have assessed the relationships between cathepsin B mRNA levels and the enzyme activity for this protease in the skeletal muscle of acutely ill patients with severe trauma (n=7) and in patients with a variety of chronic disease states (hemodialysis, n=3; nervous anorexia, n=1; type 2 diabetes, n=2; prolonged immobilization, n=1).

METHODS

Muscle biopsies were taken from the vastus lateralis muscle in patients and controls to assess tissue levels of cathepsin B mRNA by competitive-quantitative polymerase chain reaction, cathepsin B proteolytic activity and myofibrillar protein content as alkali-soluble protein to DNA ratio (ASP/DNA). In the trauma patients, muscle protein loss was assessed by the arteriovenous balance technique as rate of phenylalanine release from leg muscle.

RESULTS

The acute trauma patients exhibited a significant net phenylalanine release from leg muscle (33+/-4 nmol phenylalanine/min/100 ml leg volume) despite a continuous nutritional support. The muscle ASP/DNA ratio was lower (P<0.05) in the patients with chronic diseases (383+/-33) than in groups of healthy controls (554+/-41) or of uncomplicated, moderately obese subjects (525+/-26). Cathepsin B mRNA levels were 6-10 times greater (P<0.05) in the patients with acute trauma or chronic catabolic diseases than in the healthy subjects. Cathepsin B enzymatic activity were 2-3 times greater (P<0.05) in the chronic and acute patients than in the group of uncomplicated, moderately obese subjects. Regression analysis between cathepsin B mRNA and cathepsin B enzymatic activity indicates a significant direct correlation (r=0.84; P<0.05) in the chronic catabolic conditions, but not in the acute trauma patients (r=-0.05).

CONCLUSIONS

In skeletal muscle of patients with stable chronic catabolic diseases, cathepsin B activity is directly related to cathepsin B mRNA levels, suggesting that in these patients this enzyme could be mainly regulated at the level of gene transcription.

Carnitine metabolism in uremia

Carnitine is a conditionally essential metabolite that plays a critical role in cell physiology by participating in transesterification reactions and preventing organic acid accumulation. A number of disease states are characterized by carnitine depletion that may lead to metabolic and clinical disturbances. In maintenance hemodialysis, carnitine is lost through dialytic membranes, leading in selected patients to carnitine depletion with a relative increase of the esterified forms. Carnitine supplementation after or during dialysis counteracts such alterations and may be associated with some clinical benefits. Recent meta-analyses of the literature indicate that carnitine supplementation in hemodialysis patients may improve the hematological status (allowing a reduction of the requirement for erythropoietin), the exercise tolerance, the plasma lipid profile, and the intradialytic symptoms. In addition, carnitine supplementation may improve cardiac functions, protein metabolism, and insulin resistance. Carnitine supplementation has been recently approved by the US Food and Drug Administration not only for the treatment, but also for the prevention of carnitine depletion in dialysis patients. Furthermore, clinical guidelines developed by both American and European nephrological societies suggest that a trial with carnitine supplementation could be recommended in selected dialysis patients who do not adequately respond to standard therapy for certain conditions, such as severe and persistent muscle cramps or hypotension during dialysis, lack of energy affecting quality of life, skeletal muscle weakness or myopathy, cardiomyopathy, and anemia of uremia unresponsive to or requiring large doses of erythropoietin.

Slower activation of insulin action in hypertension associated with obesity

OBJECTIVE

To determine whether kinetic abnormalities in the onset of insulin action contribute to the insulin resistance in obesity-associated hypertension.

DESIGN

We monitored the rate of increase in glucose infusion during 6 h of hyperinsulinemic (40 mU/m2 per min) euglycemic clamps in hypertensive and normotensive obese subjects. The two groups of hypertensive (n=9) and normotensive (n=9) subjects were matched for age (48+/-2 versus 45+/-5 years), sex (five males and four females versus four males and five females) and body mass index (42+/-3 versus 40+/-2 kg/m2).

RESULTS

In all subjects, the glucose infusion rate required to maintain euglycemia increased progressively during the clamp studies to achieve maximal, steady-state values within the fifth hour. During the first 2 h of the clamp, mean glucose infusion rate, the traditional approach to assessing insulin sensitivity, was lower in the hypertensive than in the normotensive obese patients (2.04+/-0.13 versus 3.29+/-0.41 mg/kg per min, respectively; P < 0.05). In contrast, the maximal steady-state glucose infusion rate, calculated as the mean value during the sixth hour of clamping, was similar in the hypertensive and in the normotensive obese patients (4.48+/-0.43 versus 4.81+/-0.45 mg/kg per min, respectively; NS). The time required to reach the half-maximal glucose infusion rate was greater in the hypertensive than normotensive obese patients (91+/-12 versus 38+/-5 min, respectively; P< 0.05).

CONCLUSION

In obesity, hypertension was associated with a slower rate of activation of the insulin effect on glucose metabolism, whereas the maximal steady-state insulin effects were not altered by elevated blood pressure. Thus, the link between obesity and hypertension may be associated with the kinetics of onset of insulin action.

Relationship between whole-body protein turnover and serum creatinine in chronically uremic patients

To investigate the relationship between decline in renal function and alterations of protein metabolism we determined the rate of whole-body protein turnover in a group of 15 postabsorptive chronically uremic patients (9 males and 6 females) with different levels of serum creatinine concentrations (average 5.7 +/- 0.4 (SE) mg x dl(-1); range 3.3-9.1). Patients' age and body mass index were 53 +/- 4 years (range 26-73) and 24.7 +/- 0.6 kg/m2 (range 20.3-28.7), respectively. Nutritional status (plasma albumin 3.6 +/- 0.4 g x dl[-1]) and acid-base equilibrium (arterial pH 7.38 +/- 0.01) were fairly controlled by therapy. Whole-body leucine rate of appearance (Ra), an index of whole-body protein turnover, was assessed using a stable isotope technique. L-[1-(13)C]leucine was continuously infused and plasma [1-(13)C]alpha-ketoisocaproic acid enrichment was determined in steady-state conditions as a marker of the intracellular leucine enrichment. The average leucine Rawas 2.03 +/- 0.13 micromol x kg(-1) x min(-1) (range 1.29-3.19). Using simple linear regression analysis, the coefficient of correlation between the individual values of serum creatinine concentration and leucine Ra was 0.59 (n = 15; p = 0.02). Leucine Ra did not significantly correlate with blood pH or plasma albumin. In conclusion, we found a positive linear relationship between the values of plasma creatinine concentration and the rate of whole-body protein degradation. This correlation suggests that the progression of renal insufficiency is associated with accelerated rates of turnover of body proteins.

Amino acid and protein therapy in chronic renal failure

Malnutrition and protein wasting are common features of chronically uremic patients, whether on conservative or dialysis treatment. Optimization of protein-energy intake is difficult because of anorexia, catabolic factors (acidosis, insulin resistance, cytokines, etc.) and intercurrent infections. The use of growth hormone may improve the efficiency of dietary protein utilization. Evidence suggests a small but appreciable effect of very low protein diets on progression of renal insufficiency.

Modulation of protein kinetics in chronic renal failure

Many factors are involved in inducing muscle wasting and derangements of protein metabolism in chronic renal failure. Anorexia, low protein intake, hormonal abnormalities (increased cortisol and parathyroid hormone secretion, and insulin resistance), acidosis, abnormalities of the cytokine system, and other unidentified uremic toxins create a negative nitrogen balance and stimulate protein catabolism. The protein turnover rate (i.e., synthesis and degradation) is generally decreased in non-acidotic uremic patients. However, in uncorrected acidosis, protein degradation is accelerated and a rapid loss of body proteins supervenes. Nutrition can be improved in chronically uremic patients through pharmacological therapy that can control protein catabolism. Administration of growth hormone and insulin-like growth factor-1 has been shown to be effective. These hormones influence both glucose and glutamine metabolism. Another approach is the administration of pentoxifylline, which may have an anticatabolic effect by interfering with the tumor necrosis factor-alpha system.

Mechanisms of malnutrition in uremia

The pathogenesis of protein wasting in chronic renal failure is multifactorial. Potential mediators of protein catabolism in chronic uremia include anorexia, low protein-energy intake, increased cortisol and parathyroid hormone secretion, insulin resistance, metabolic acidosis and unidentified uremic toxins. In non-acidotic uremic patients the rate of protein turnover (that is, synthesis and degradation) has often been found to be decreased. Malnutrition also decreases both protein synthesis and degradation. In contrast, during acidosis protein degradation is primarily accelerated and results in rapid loss of body proteins. Cytokine concentrations have often been found increased in both dialyzed and undialyzed chronically uremic patients. Our study determined the circulating levels of TNF-alpha and of type I (60 kDa) and type II (80 kDa) soluble TNF-alpha receptors in undialyzed uremic patients, and found that their plasma levels were greatly increased. Serum creatinine correlated with TNF-alpha soluble receptors but not with the TNF-alpha. Thus, TNF-alpha is potentially an important mediator of protein wasting in chronically uremic patients. Pharmacological therapy of protein catabolism in chronic uremia may include the administration of pentoxifylline, which has been shown to decrease protein degradation by interfering with the TNF-alpha system (that is, TNF-alpha and its soluble receptors) in experimental models. Growth hormone and insulin-like growth factor-1 administration may also be beneficial in these patients, but further evaluation of the hormone effects on glucose and glutamine metabolism is called for.

Metabolic response to injury and sepsis: changes in protein metabolism

The metabolic response to trauma and sepsis involves an increased loss of body proteins. Specific sites of changes of protein and amino acid metabolism have been identified. In skeletal muscle, the rate of proteolysis is accelerated greatly. The rate of protein synthesis also may be increased but not enough to match the increase in degradation. Intramuscular glutamine concentration is decreased because of increased efflux and possibly decreased de novo synthesis. In the liver, the rate of synthesis of selected proteins (i.e., albumin, transferrin, prealbumin, retinol-binding protein, and fibronectin) is decreased, whereas acute phase protein synthesis is accelerated. Tissues characterized by rapidly replicating cells, such as enterocytes, immune cells, granulation tissue, and keratinocytes, exhibit early alterations in the case of decreased protein synthesis capacity. In these tissues, glutamine use is accelerated. Increased stress hormone (cortisol and glucagon) and cytokine secretion, as well as intracellular glutamine depletion, are potential mediators of altered protein metabolism in trauma and sepsis. However, the relative importance of these factors has not been clarified. Therapy of acute protein catabolism may include the use of biosynthetic human growth hormone, possibly in combination with insulin-like growth factor-1, and the administration of metabolites at pharmacologic doses. We recently studied the effects of carnitine and alanyl-glutamine administration in severely traumatized patients. We found that both carnitine and the glutamine dipeptide restrained whole-body nitrogen loss without affecting selected indices of protein metabolism in the skeletal muscle.

Effects of growth hormone administration on skeletal muscle glutamine metabolism in severely traumatized patients: preliminary report

We have investigated the effects of 24 h human recombinant growth hormone (hGH) administration on leg muscle glutamine exchange and protein kinetics in severely traumatized patients. Muscle amino acid exchange and protein balance were evaluated using the leg arteriovenous balance technique, whereas changes in skeletal muscle free amino acid concentrations were evaluated in biopsy specimens. hGH infusion decreased phenylalanine release from protein degradation by 56 +/- 14%, and the rate of branched chain amino acid catabolism by 51 +/- 10%. Glutamine release from leg muscle was suppressed by 58 +/- 12%. This latter effect was completely accounted for by a hGH-mediated suppression of glutamine synthesis in skeletal muscle. In conclusion, growth hormone administration in trauma patients may restrain protein and amino acid catabolism in skeletal muscle. However, the growth hormone-mediated suppression of glutamine production we have observed in this study could decrease the systemic availability of this amino acid. During growth hormone treatment, this potential side-effect could be prevented by an exogenous glutamine administration.

Effect of intravenous supplementation of a new essential amino acid formulation in hemodialysis patients

Protein energy undernutrition (PEU) and abnormalities of amino acid (AA) metabolism are common in maintenance hemodialysis patients (MHP). A new EAA formulation (BS695), enriched with valine and threonine, containing some histidine, and low in phenylalanine and methionine was recently developed. We randomly supplemented 11 MHP with this solution (treated group, TG) and 10 MHP with a standard AA solution containing both essential and non-essential AA (control group, CG). Both groups received 3.65 g of nitrogen, i.v. three times per week during hemodialysis for six months. During treatment, dietary intake remained stable in both groups. Before treatment, after three and six months of treatment, and six months after the end of treatment, we determined routine blood chemistries, anthropometry, serum protein levels (albumin, transferrin), delayed cutaneous sensitivity (Multi-test), protein catabolic rate (PCR), plasma AA content and motor nerve conduction velocity (MNCV). Before treatment PEU, predominantly of marasmic type, was common. After treatment anthropometry and immune response were unchanged in both groups; PCR increased more in CG than in TG; serum albumin levels decreased significantly only in CG; MNCV improved in TG and worsened in CG. These preliminary results suggest that this new EAA formulation may have beneficial effects on some nutrition related abnormalities of MHP. Better results might occur with long-term AA supplementation, particularly if it is associated with a higher energy intake.

Muscle biopsy studies on protein-energy malnutrition in patients with chronic relapsing pancreatitis

Malnutrition is a common finding in chronic pancreatitis and its pathogenesis is multifactorial. In 14 patients with chronic pancreatitis we assessed the dietary intake, some anthropometric indices and the concentration of some serum proteins. In muscle specimens obtained by needle biopsy we examined the DNA, RNA and non-collagen alkali-soluble protein (ASP) content. In muscle we determined also the activity of cathepsin D, an enzyme involved in intracellular myofibrillar catabolism. Protein and energy intake were lower than in the normal healthy population. Plasma protein content (an index of liver protein synthesis) was generally in the normal range, whereas anthropometry and the biochemical muscle indices were generally subnormal, suggesting a depressed muscle protein content and synthesis (evaluated, respectively, by the ASP: DNA and RNA: DNA ratios). Cathepsin D activity was lower than in controls, and the percentage of 'free' activity tended to be higher but not significantly. This study suggests that muscle protein content and synthesis are reduced in patients with chronic pancreatitis, whereas liver protein synthesis is generally preserved. Possibly as a consequence of metabolic abnormalities and/or of an inadequate protein and energy intake, the nutritional status was often abnormal in our patients and a nutritional support therapy was needed.