Urinary 3-methylhistidine/creatinine ratio as a clinical tool: correlation between 3-methylhistidine excretion and metabolic and clinical states in healthy and stressed premature infants

The impact of sarcopenia and acute muscle mass loss on long-term outcomes in critically ill patients with intra-abdominal sepsis

BACKGROUND

Sarcopenia is a known risk factor for poor outcomes across many chronic diseases. The impact on outcomes of both pre-existing sarcopenia and acute muscle wasting (AMW) in acute critical illness caused by sepsis remain unclear.

METHODS

We conducted a prospective longitudinal cohort study of critically ill patients with intra-abdominal sepsis utilizing abdominal computed tomography at sepsis onset to determine baseline skeletal muscle index (SMI). Biomarkers of inflammation and catabolism were measured through 28 days while hospitalized. We performed follow-up evaluations of strength and physical function at 3, 6, and 12 months, with interval CT analyses at 3 and 12 months to evaluate changes in muscle mass. Measured clinical outcomes included development of chronic critical illness (≥14 days in intensive care with persistent organ dysfunction), long-term functional status, and 1 year mortality.

RESULTS

Among 47 sepsis patients enrolled (mean age 53 ± 14 years), half (n = 23; 49%) were sarcopenic at baseline. Overall, sepsis patients exhibited acute and persistent muscle wasting with an average 8% decrease in SMI from baseline at 3 months (P = 0.0008). Sarcopenic (SAR) and non-sarcopenic (NSAR) groups were similar in regards to age and comorbidity burden. SAR patients had greater acute physiologic derangement (APACHE II, 18 vs. 12.5), higher incidence of multiple organ failure (57% vs. 17%), longer hospital (21 vs. 12 days) and intensive care unit length of stays (13 vs. 4 days), and higher inpatient mortality (17% vs. 0%; all P < 0.05). Pre-existing SAR was a strong independent predictor of early death or developing chronic critical illness (odds ratio 11.87, 95% confidence interval CI 1.88-74.9; P = 0.009, area under the curve 0.880) and was associated with significantly higher risk of 1-year mortality (34.9% vs. 4.2%, p = 0.007). Lower baseline SMI was also predictive of poor functional status at 12 months (OR 0.89, 95% confidence interval 0.80-0.99; p = 0.039, area under the curve 0.867). Additionally, SAR patients had AMW with persistent muscle mass loss at 3 months that was associated with decreased health-related quality of life and SF-36 physical function domains (P < 0.05). Persistent AMW at 3 months was not predictive of mortality or poor functional status, with return to near-baseline muscle mass among sepsis survivors by 6 months.

CONCLUSIONS

Critically ill patients have an acute and persistent loss of muscle mass after intra-abdominal sepsis, which is associated with decreased health-related quality of life and physical function at 3 months. However, pre-existing sarcopenia, rather than persistent acute muscle mass loss at 3 months after sepsis, is independently associated with poor long-term functional status and increased 1 year mortality.

Serum creatinine is a poor marker of a predicted change in muscle mass in lactating sows

Serum creatinine (SCr) in humans has proven to be a reliable biomarker of body protein breakdown and/or muscle mass change. This study set out to investigate the potential of SCr to indicate a loss in sow muscle mass over lactation, validated against 3 methyl histidine (3MH) and blood urea nitrogen (BUN), markers of dietary and/or body protein breakdown. A total of 40 sows were allocated to four treatment groups aimed to induce body weight changes by restrictively feeding sows using a stepwise percentage reduction model. Data were pooled and reallocated into three groups representing the 25^th , 50^th and 75^th percentiles based on body weight change over lactation in the range -22.3 to -4.1% (treatment 25), -4.0 to 6.2% (Treatment 50), and 6.3-15.2% (Treatment 75). Indirect measures for the prediction of protein (3MH, BUN) or fat change (caliper, P2) were taken on entry into the farrowing house, day 5 of lactation, and at weaning. Serum was collected on these days, and SCr, 3MH and BUN were analysed. Piglet weaning weight and average daily feed intake did not differ between treatments (p > .05). There were no changes (p > .05) in indirect measures of body composition (sow caliper score, P2) and analytes (SCr, 3MH, BUN) over lactation. By day 20, those sows in treatment 25 had higher (p < .05) 3MH concentrations whilst changes from day 5 to 20 were not different (p > .05) and did not correlate with SCr change (p > .05) but were highly correlated to BUN change (R² = 0.691, p < .001). The data suggested that concentrations of SCr and BUN may have been the result of dietary and/or body protein breakdown and/or changes in muscle mass. In the current testing conditions, SCr was not a reliable marker of changes in muscle mass.

β-Hydroxy β-methylbutyrate free acid alters cortisol responses, but not myofibrillar proteolysis, during a 24-h fast

This study was a randomised, double-blind, placebo-controlled cross-over trial examining the effects of β-hydroxy β-methylbutyrate free acid (HMB-FA) supplementation on muscle protein breakdown, cortisol, testosterone and resting energy expenditure (REE) during acute fasting. Conditions consisted of supplementation with 3 g/d HMB-FA or placebo during a 3-d meat-free diet followed by a 24-h fast. Urine was collected before and during the 24-h fast for analysis of 3-methylhistidine:creatinine ratio (3MH:CR). Salivary cortisol, testosterone, their ratio (T:C), and the cortisol awakening response were assessed. ANOVA was used to analyse all dependent variables, and linear mixed models were used to confirm the absence of carryover effects. Eleven participants (six females, five males) completed the study. Urinary HMB concentrations confirmed compliance with supplementation. 3MH:CR was unaffected by fasting and supplementation, but the cortisol awakening response differed between conditions. In both conditions, cortisol increased from awakening to 30 min post-awakening (P=0·01). Cortisol was reduced from 30 to 45 min post-awakening with HMB-FA (-32 %, d=-1·0, P=0·04), but not placebo (PL) (-6 %, d=-0·2, P=0·14). In males, T:C increased from 0 to 24 h of fasting with HMB-FA (+162 %, d=3·0, P=0·001), but not placebo (+13 %, d=0·4, P=0·60), due to reductions in cortisol. REE was higher at 24 h of fasting than 16 h of fasting independent of supplementation (+4·0 %, d=0·3, P=0·04). In conclusion, HMB-FA may affect cortisol responses, but not myofibrillar proteolysis, during acute 24-h fasting.

Effects of age on plasma metabolites and hormones in finishing Belgian Blue double-muscled cull females

Two groups of 12 Belgian Blue double-muscled cull females were used successively in a 2-year repeated experiment and divided into three groups according to age, allowing four animals per group each year. The aim of the trial was to relate, during the finishing period, the metabolic and endocrine parameters with age. Females were fattened with a diet based on maize silage and were blood sampled on several occasions. The average daily gain (ADG) decreased with the age of the cows. Plasma glucose and triglycerides decreased also with age while the youngest females showed lower concentrations of urea than those older. The composition of plasma non-esterified fatty acids also differed considerably between groups. The hormones that best related with ADG were IGF-1 and insulin. Plasma concentrations of thyroid hormones were lower in the oldest animals. No difference between groups was found for GH. Heifers presented lower concentrations of GH and IGF-1 than those reported elsewhere in fattening bulls of the same breed. It may be concluded that in Belgian Blue double-muscled females, glucose, IGF-1 and insulin are good indicators of the growth potential. Young adult cows presented intermediate characteristics of metabolic and endocrine status that were close either to younger or to older cows.

Tight Glycemic Control With Insulin Does Not Affect Skeletal Muscle Degradation During the Early Postoperative Period Following Pediatric Cardiac Surgery

OBJECTIVE

Critical illness is associated with significant catabolism, and persistent protein loss correlates with increased morbidity and mortality. Insulin is a potent anticatabolic hormone; high-dose insulin decreases skeletal muscle protein breakdown in critically ill pediatric surgical patients. However, insulin's effect on protein catabolism when given at clinically utilized doses has not been studied. The objective was to evaluate the effect of postoperative tight glycemic control and clinically dosed insulin on skeletal muscle degradation in children after cardiac surgery with cardiopulmonary bypass.

DESIGN

Secondary analysis of a two-center, prospective randomized trial comparing tight glycemic control with standard care. Randomization was stratified by study center.

PATIENTS

Children 0-36 months who were admitted to the ICU after cardiac surgery requiring cardiopulmonary bypass.

INTERVENTIONS

In the tight glycemic control arm, insulin was titrated to maintain blood glucose between 80 and 110 mg/dL. Patients in the control arm received standard care. Skeletal muscle breakdown was quantified by a ratio of urinary 3-methylhistidine to urinary creatinine.

MEASUREMENTS AND MAIN RESULTS

A total of 561 patients were included: 281 in the tight glycemic control arm and 280 receiving standard care. There was no difference in 3-methylhistidine to creatinine between groups (tight glycemic control, 249 ± 127 vs standard care, 253 ± 112, mean ± SD in μmol/g; p = 0.72). In analyses restricted to the patients in tight glycemic control arm, higher 3-methylhistidine to creatinine correlated with younger age, as well as lower weight, weight-for-age z score, length, and body surface area (p < 0.005 for each) and lower postoperative day 3 serum creatinine (r = -0.17; p = 0.02). Sex, prealbumin, and albumin were not associated with 3-methylhistidine to creatinine. During urine collection, 245 patients (87%) received insulin. However, any insulin exposure did not impact 3-methylhistidine to creatinine (t test, p = 0.45), and there was no dose-dependent effect of insulin on 3-methylhistidine to creatinine (r = -0.03; p = 0.60).

CONCLUSION

Although high-dose insulin has an anabolic effect in experimental conditions, at doses necessary to achieve normoglycemia, insulin appears to have no discernible impact on skeletal muscle degradation in critically ill pediatric cardiac surgical patients.

Energy requirements

The determination of the appropriate energy and nutritional requirements of a newborn infant requires a clear goal of the energy and other compounds to be administered, valid methods to measure energy balance and body composition, and knowledge of the neonatal metabolic capacities. Providing an appropriate amount of energy to newborn infants remains a challenge considering the great number of newborn infants who suffer in-hospital growth retardation. The energy requirements of a newborn infant are influenced by several factors - basal metabolism, growth, energy expenditure, and energy losses - which change continuously during development. Calculating the energy requirements of preterm infants is subject to error if general recommendations are applied without recognition of the large variation in factors that influence, for example, energy expenditure. Therefore, energy recommendations should be individualized and preferably based on measurements of energy expenditure. In particular, extremely low birth-weight and very low birth-weight infants are prone to develop negative energy and nutrient balances, due to low energy intake, low energy reserves and high energy demands. Early energy accretion is not only essential for growth but also influences neurodevelopmental outcome and physical health in the long term, thereby underlining the importance of adequate neonatal nutrition.

Metabolic effects of infection and postnatal steroids

Optimal development of the newborn depends on rapid accretion of substrate in the neonatal period, particularly in the premature infant. Steroids and infection not only induce catabolism, but associated endogenous responses reprioritize crucial substrate to restore homeostasis. The result is a protein/energy deficit and concomitant delay in growth and development. Innovative feeding strategies and novel therapies are needed to reduce the impact of catabolism in this population.

Muscle proteolysis and weight loss in a neonatal rat model of sepsis syndrome

Our hypothesis is that nitrogen loss in septic neonates is caused by increased muscle proteolysis. Sprague-Dawley rat pups (P7) were injected intraperitoneally with NaCl or 4 mg/kg/BW lipopolysaccharide (LPS) and then sacrificed at 2, 4, 24, and 48 hr. Sepsis syndrome was confirmed by elevated serum tumor necrosis factor (24.6 ng/mL +/- 18.4 [LPS] and < 1.0 ng/mL [controls]; p < .05). Proteolysis in gastrocnemius/soleus muscle was analyzed by quantitation of tissue tyrosine loss. The neonatal rats injected with LPS had significant media tyrosine release at 24 hr compared to the controls (0.39 +/- 0.14 versus 0.25 +/- 0.11 micromol tyrosine/g muscle; p < .05). At 48 hr, LPS-induced muscle tyrosine release ceased (0.24 +/- 0.04 [control] versus 0.23 +/- 0.03 micromol tyrosine/g muscle [LPS]). After 48 hr, gastrocnemius/soleus weight was less in the LPS-injected rats (50.5 +/- 4.8 to 31.2 +/- 4.0 g; p < .0001). Similar changes were not seen in the extensor digitorum longus, suggesting that some muscles were relatively preserved. Also, LPS resulted in significant weight loss. We conclude that selective muscle proteolysis contributes to nitrogen loss in neonatal sepsis. Although proteolysis abates by 48 hr, short-term injury results in significant muscle-mass deficit.

Protein metabolism in the extremely low-birth weight infant

Although extensive data are available on the impact of nutrient and protein administration on growth, plasma amino acids, and nitrogen balance in the newborn and growing infants, relatively few studies have carefully examined the dynamic aspects of protein metabolism in vivo and particularly in the micropremie or ELBW infant. These studies show that the very preterm infants, either because of immaturity or because of the intercurrent illness, have high rates of protein turnover and protein breakdown. This high rate of proteolysis is not as responsive to nutrient administration. Intervention strategies aimed at promoting nitrogen accretion, such as insulin, human growth hormone, or glutamine, have not thus far resulted in enhanced protein accretion and growth. This may be, in part, due to limitations in delivery of adequate calorie and nitrogen.

Nitrogen balance in extremely low birth weight infants with nonoliguric hyperkalemia

We measured nitrogen balance and urinary 3-methylhistidine molar ratios in 33 extremely low birth weight infants (12 with hyperkalemia and 21 without) for the first 3 days of life. Although all infants were in negative nitrogen balance during the study, there was no difference in the degree of negative nitrogen balance between the two groups. There was also no difference in the 3-methylhistidine/creatinine molar ratios, indicating that muscle protein catabolism did not differ. We conclude that it is unlikely that catabolism contributes to the development of nonoliguric hyperkalemia in extremely low birth weight infants.

Catabolic effect of dexamethasone in the preterm baby

Most babies treated with dexamethasone for bronchopulmonary dysplasia exhibit an appreciable rise in the blood urea concentration, from a mean of 2.3 mmol/l before steroid to a mean of 7.1 mmol/l after. In order to discover whether this was primarily the result of increased protein catabolism, nitrogen balance studies before and after the start of dexamethasone were performed and a mean deficit in nitrogen retention of 158 mg/kg/24 hours was found. Similarly the urinary 3-methylhistidine (3MH):creatinine ratio before and after the commencement of dexamethasone treatment in a group of preterm babies was measured. It was found that there was a substantial increase in 3MH excretion after dexamethasone: from a mean 3MH:creatinine ratio of 46 in the week before steroids to a mean ratio of 77 in the week after. As 3MH emanates almost exclusively from the breakdown of actin in skeletal muscle cell, this finding implies the loss of muscle tissue. It was also found that the babies were in less positive nitrogen balance after dexamethasone, to a degree which is significant relative to their protein reserves. The long term consequences of a period of increased catabolism are not yet known but the authors suggest caution in the use of dexamethasone, at least in babies with milder degrees of bronchopulmonary dysplasia in whom the ratio of benefit to risk may be less favourable.

Hormonal and metabolic response to operative stress in the neonate

It is evident from this review that newborns, even those born prematurely, are capable of mounting an endocrine and metabolic response to operative stress. Unfortunately, many of the areas for which a relatively well-characterized response exists in adults are poorly documented in neonates. As is the case in adults, the response seems to be primarily catabolic in nature because the combined hormonal changes include an increased release of catabolic hormones such as catecholamines, glucagon, and corticosteroids coupled with a suppression of and peripheral resistance to the effects of the primary anabolic hormone, insulin.

Sequential urinary N tau-methylhistidine to creatinine ratios in premature infants

The present study was undertaken to establish normal values of the N tau-methylhistidine to creatinine excretion ratio in very premature infants, to observe changes with postnatal age, and to determine whether or not reliable data on this index of myofibrillar protein breakdown could be obtained from untimed urine samples without recourse to the 24-hour collections used previously. The normal range (95% confidence limits) of the molar excretion ratio for unstressed infants was established to be between 0.0248 and 0.0440. Narrower limits of variability occurred when nutrient intake was controlled at a satisfactory level or when comparisons were between sequential urine samples from single infants. No diurnal changes could be detected. We conclude that analyses of N tau-methylhistidine and creatinine on spot urine samples permit the calculation of an excretion ratio that is reproducible both within and between individual infants and that should be useful in assessing changes in myofibrillar protein breakdown caused by differences in clinical, pharmacologic, or nutritional status.

Free amino acids and calcium, magnesium and zinc levels in Friedreich's ataxia

Free amino acid levels and zinc, magnesium and calcium content have been determined in autopsy samples of 9 areas of the brain, two skeletal muscles, and the right ventricle, left ventricle and septum of the heart of a Friedreich's ataxia subject.

Studies on the role of taurine in Friedreich's ataxia

New studies were undertaken to verify the previous findings of increased urinary excretion of taurine, in the basal state and after challenge with a taurine load, in Friedreich's disease. Particular attention was paid to possible causes of error such as weight, muscle mass, creatine and creatinine excretion, variability with time and appropriate control groups. Although the overall findings were confirmed, their interpretation is open to question because of all these factors of error. Many possibilities must still be further explored to account for the apparent taurine retention defect observed in many cases of Friedreich's disease.

Urinary excretion of dimethylarginines in premature infants

Urinary excretion of NG,N'G-dimethylarginine (NG,N'G-Me2Arg) and NG,NG-dimethylarginine (NG,NG-Me2Arg) was measured in premature infants. The NG,N'G-Me2Arg/NG,NG-Me2Arg ratio was much higher in newborn infants than in older children or adults. Linear regression analysis showed a significant negative correlation between the degree of maturity and the excretion of NG,N'G-Me2Arg. A significant direct linear relationship also was found between the excretion of NG,N'G-Me2Arg and the rate of whole body nitrogen flux and of protein synthesis and catabolism. No correlation was found between the excretion of the dimethylarginines and 3-methylhistidine, but the dimethylarginine/3-methylhistidine ratio declined with advancing conceptual age. A direct linear relationship was found between excretion of NG,N'G-Me2Arg and NG,NG-Me2Arg and whole body nonskeletal muscle protein breakdown. No correlation was found between nonskeletal muscle protein catabolism and 3-methylhistidine excretion. We estimate that approximately 0.34 mumole of dimethylarginine are excreted per gram of nonskeletal muscle protein catabolized. Dietary intake did not affect the excretion of either NG,N'G-Me2Arg or NG,NG-Me2Arg. The data suggest that measurement of urinary dimethylarginines might be useful in the nutritional assessment of premature infants.

N tau-methyl histidine excretion by poultry: not all species excrete N tau-methyl histidine quantitatively

The rate of elimination of administered N tau-[14CH3]methyl histidine was used to assess the validity of N tau-methyl histidine excretion as an index of muscle protein breakdown in poultry. Broiler chicks (2-3 and 4-5 weeks old), laying hens, adult quail (Coturnix coturnix japonica), adult cockerels and turkey poults (2-4 weeks old) were tested. All except the turkey poults showed quantitative recoveries of N tau-[14CH3]methyl histidine within 1 week. Turkeys showed a different pattern of N tau-[14CH3]methyl histidine output; the mean total recovery after 14 d was less than 50% of the injected dose. The majority of the label remaining after this time was found in breast muscle. All birds tested excreted N tau-methyl histidine unchanged, although a small amount sometimes appeared as another metabolite. No significant oxidation of N tau-[14CH3]methyl histidine by broiler chicks turkey poults or adult quail was found. The results show that excretion of N tau-methyl histidine is a useful measure of muscle protein breakdown in the domestic fowl and quail but not in turkeys.

Urinary 3-methylhistidine excretion in man: the role of protein-bound and soluble 3-methylhistidine

The influence of dietary meat and meat stock intake on urinary excretion of 3-methylhistidine (3MH) was examined in human adults. In the absence of 3MH ingestion for 48 h, the study subjects adjusted to an intrinsic urinary 3MH: creatinine value. If the meat and meat stock-free diet was maintained on subsequent days, only minute diurnal variations occurred, and the values of random urine samples during the day were representative of the 24 h 3MH: creatinine value. The mean 3MH: creatinine value (SD) for a group of adults (n 7) was 0.105 +/- 0.023 (mumol of 3MH/mg creatinine), which is approximately 35% lower than the corresponding value in healthy growing infants (0.148 +/- 0.039) (Seashore et al. 1981). Ingestion of meat soup and meat causes different patterns of urinary excretion of 3MH which are consistent with the finding that meat extracts, such as soup and stock, contain considerable amounts of 3MH. The 3MH contents of beef, chicken and turkey were 3.8 +/- 0.15, 3.0 +/- 0.09 and 2.3 +/- 0.29 mumol/g dry wt meat respectively. All three meats contained a water-soluble 3MH-fraction (% total 3MH: beef 8, chicken 21, turkey 23). Amino acid analysis of the soluble fraction with or without hydrochloric acid hydrolysis demonstrated free 3MH in chicken and turkey (5.2 and 2.8% of the total respectively) but not in beef. Patients undergoing urinary 3MH measurements should maintain a diet that is free not only of solid meats, but also of meat stock. The ingestion of commercial food products (e.g. frozen or canned meals, sauces, pizza, etc.) may impair the validity of such measurements because of their meat-stock content. A dietary regimen is presented which is based on a shorter 12 h urine collection. The shorter collection time is satisfactory in the light of the steady rate of 3MH-excretion after 2 d of a diet free of meat and meat stock.

Urinary 3-methylhistidine excretion in juvenile-onset diabetics: evidence of increased protein catabolism in the absence of ketoacidosis

Urinary 3-methylhistidine excretion (an indicator of protein catabolism) was measured in ten diabetic patients and in age and weight matched control subjects. The diabetic group, while receiving their usual insulin dose, excreted 42% more 3-methylhistidine than the control group (2.7 versus 1.9 mumole/kg body weight/24 hr). When the insulin dose of the diabetic subject was reduced by 15% or 25%, the concentrations of blood and urinary glucose were significantly increased by the rate of urinary 3-methylhistidine excretion was not increased further. These findings demonstrate augmented protein catabolism in diabetics even in the absence of ketoacidosis. It appears that blood and urine glucose levels are more sensitive to changes in insulin availability than protein catabolism.