Greater plasma essential amino acids and lower 3-methylhistidine with higher protein intake during endurance training: a randomised control trial

Endurance exercise alters amino acid (AA) metabolism that necessitates greater AA intake in the post exercise recovery period to support recovery. Thus, daily AA ingestion during a period of endurance training may affect the metabolically active plasma free AA pool, which is otherwise maintained during periods of inadequate protein intake by the breakdown of skeletal muscle proteins. Nine endurance-trained males completed a 4-day running protocol (20 km, 5 km, 10 km and 20 km on days 1-4, respectively) on three occasions with a controlled diet providing different protein intakes [0.94(LOW), 1.20(MOD) or 1.83gprotein kgbody mass-1 day-1 (HIGH)]. Urine collected over 24 h on day-4 and plasma collected after an overnight fast on day-5 were analyzed for free AA (plasma) and 3-methylhistidine (3MH; plasma and urine), a marker of myofibrillar protein breakdown. There was an effect of protein intake (HIGH > MOD/LOW; P < 0.05) on fasted plasma essential AA, branched chain AA and 3MH but no effect on 24-h urinary 3-MH excretion. Consuming a previously determined optimal daily protein intake of 1.83 g kg-1 day-1 during endurance training maintains fasted plasma free AA and may attenuate myofibrillar protein catabolism, although this latter effect was not detected in 24-h urinary excretion. The maintenance of the metabolically active free plasma AA pool may support greater recovery from exercise and contribute to the previously determined greater whole-body net protein balance in this athletic population. TRN: NCT02801344 (June 15, 2016).

Meat intake and risk of mortality and graft failure in kidney transplant recipients

BACKGROUND

It is unknown whether meat intake is beneficial for long-term patient and graft survival in kidney transplant recipients (KTR).

OBJECTIVES

We first investigated the association of the previously described meat intake biomarkers 1-methylhistidine and 3-methylhistidine with intake of white and red meat as estimated from a validated food frequency questionnaire (FFQ). Second, we investigated the association of the meat intake biomarkers with long-term outcomes in KTR.

METHODS

We measured 24-h urinary excretion of 1-methylhistidine and 3-methylhistidine by validated assays in a cohort of 678 clinically stable KTR. Cross-sectional associations were assessed by linear regression. We used Cox regression analyses to prospectively study associations of log2-transformed biomarkers with mortality and graft failure.

RESULTS

Urinary 1-methylhistidine and 3-methylhistidine excretion values were median: 282; interquartile range (IQR): 132-598 µmol/24 h and median: 231; IQR: 175-306 µmol/24 h, respectively. Urinary 1-methylhistidine was associated with white meat intake [standardized β (st β): 0.20; 95% CI: 0.12, 0.28; P < 0.001], whereas urinary 3-methylhistidine was associated with red meat intake (st β: 0.30; 95% CI: 0.23, 0.38; P < 0.001). During median follow-up for 5.4 (IQR: 4.9-6.1) y, 145 (21%) died and 83 (12%) developed graft failure. Urinary 3-methylhistidine was inversely associated with mortality independently of potential confounders (HR per doubling: 0.55; 95% CI: 0.42, 0.72; P < 0.001). Both urinary 1-methylhistidine and urinary 3-methylhistidine were inversely associated with graft failure independent of potential confounders (HR per doubling: 0.84; 95% CI: 0.73, 0.96; P = 0.01; and 0.59; 95% CI: 0.41, 0.85; P = 0.004, respectively).

CONCLUSIONS

High urinary 3-methylhistidine, reflecting higher red meat intake, is independently associated with lower risk of mortality. High urinary concentrations of both 1- and 3-methylhistidine, of which the former reflects higher white meat intake, are independently associated with lower risk of graft failure in KTR. Future intervention studies are warranted to study the effect of high meat intake on mortality and graft failure in KTR, using these biomarkers.

Muscle deteriorations become prominent within 24 hours after admission in severely burned adults

BACKGROUND

Severe burn injury results in profound catabolic deterioration. Although burn-related catabolism has been well stated, it is unclear when the catabolic response begins. This study characterized acute changes of muscle protein breakdown at the admission and the day after in severely burned adults.

METHODS

Twelve patients (43 ± 19 years old) with 40% ± 21% total body surface area burns were prospectively enrolled into an observational study approved by institutional review board. Urinary samples were collected on admission day and the day after (day 1). Patient demographic and clinical data of vital signs, blood gas and chemistry, and coagulation status were collected. Catabolic changes of muscle breakdown were quantified by urinary excretion of 3-methylhisitidine, determined by gas chromatography and mass spectrometry analysis.

RESULTS

Compared with admission day, burned patients had elevated mean ± SD arterial pressure (from 90 ± 5 mm Hg to 108 ± 7 mm Hg) and heart rate (from 102 ± 7 beats per minute to 119 ± 4 beats per minute both p < 0.05) after 24 hours. Their 24-hour urinary output was 1,586 ± 813 mL at admission day to 1,911 ± 1,048 mL on day 1. The 24-hour urea excretion was elevated from 172 ± 101 mg/kg per day at admission day to 302 ± 183 mg/kg per day on day 1 (both p < 0.05), with no change in creatinine excretion. Urinary 3-methylhisitidine excretion increased from 0.75 ± 0.74 mg/kg per day at admission to 1.14 ± 0.86 mg/kg per day on day 1 (p < 0.05). The estimated skeletal muscle protein breakdown was increased from 1.1 ± 1.0 g/kg per day at admission day to 1.6 ± 1.2 g/kg per day on day 1 (p < 0.05). There were no changes in prothrombin time, activated partial thromboplastin time, or platelets.

CONCLUSION

In severely burned patients, catabolic muscle protein breakdown is elevated within 24 hours after admission and before changes in coagulation. These findings suggest that early interventions may be needed to effectively attenuate the catabolic responses in burn patients.

LEVEL OF EVIDENCE

Prospective and observational study, level II.

NAT8 Variants, N-Acetylated Amino Acids, and Progression of CKD

BACKGROUND AND OBJECTIVES

Genetic variants in NAT8, a liver- and kidney-specific acetyltransferase encoding gene, have been associated with eGFR and CKD in European populations. Higher circulating levels of two NAT8-associated metabolites, N-δ-acetylornithine and N-acetyl-1-methylhistidine, have been linked to lower eGFR and higher risk of incident CKD in the Black population. We aimed to expand upon prior studies to investigate associations between rs13538, a missense variant in NAT8, N-acetylated amino acids, and kidney failure in multiple, well-characterized cohorts.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted analyses among participants with genetic and/or serum metabolomic data in the African American Study of Kidney Disease and Hypertension (AASK; n=962), the Atherosclerosis Risk in Communities (ARIC) study (n=1050), and BioMe, an electronic health record-linked biorepository (n=680). Separately, we evaluated associations between rs13538, urinary N-acetylated amino acids, and kidney failure in participants in the German CKD (GCKD) study (n=1624).

RESULTS

Of 31 N-acetylated amino acids evaluated, the circulating and urinary levels of 14 were associated with rs13538 (P<0.05/31). Higher circulating levels of five of these N-acetylated amino acids, namely, N-δ-acetylornithine, N-acetyl-1-methylhistidine, N-acetyl-3-methylhistidine, N-acetylhistidine, and N2,N5-diacetylornithine, were associated with kidney failure, after adjustment for confounders and combining results in meta-analysis (combined hazard ratios per two-fold higher amino acid levels: 1.48, 1.44, 1.21, 1.65, and 1.41, respectively; 95% confidence intervals: 1.21 to 1.81, 1.22 to 1.70, 1.08 to 1.37, 1.29 to 2.10, and 1.17 to 1.71, respectively; all P values <0.05/14). None of the urinary levels of these N-acetylated amino acids were associated with kidney failure in the GCKD study.

CONCLUSIONS

We demonstrate significant associations between an NAT8 gene variant and 14 N-acetylated amino acids, five of which had circulation levels that were associated with kidney failure.

Suitability evaluation of new endogenous biomarkers for the identification of nitrite-based urine adulteration in mass spectrometry methods

Urine adulteration to circumvent positive drug testing is a fundamental challenge for toxicological laboratories all over the world. Untargeted mass spectrometry (MS) methods used in metabolomics had previously revealed uric acid (UA), histidine, methylhistidine, and their oxidation products, for example 5-hydroxyisourate (HIU) as potential biomarkers for urine adulteration using potassium nitrite (KNO₂ ). These markers should be further evaluated for their reliability, stability, and routine applicability. Influence of KNO₂ concentration, urinary pH, reaction time, and stability at room temperature, 4°C, and - 20°C was determined in urine under varying conditions. Analysis was performed after protein precipitation with acetonitrile by liquid chromatography-high resolution mass spectrometry (LC-HRMS). Receiver operating characteristics (ROC) analysis was applied for cut-off evaluation after biomarker quantification (n = 100 per group). Blinded measurements (n = 50) were performed to check the general applicability to identify adulterated samples under routine conditions. The higher the adulterant concentration, the lower the concentrations of histidine, methylhistidine, and UA. In return, amounts of their oxidation products increased. Highest changes were observed under weak acid conditions (pH 4-5). Storage at -20°C ensured sufficient stability for all oxidative markers over one month. ROC evaluated biomarker performance and application to unknown samples revealed satisfying results, with HIU as the most suitable biomarker (positive predictive value (PPV) 100%), followed by UA (PPV 93%). HIU and UA proved suitable markers to identify urine adulteration using KNO₂ and are ready for implementation into routine MS procedures.

Untargeted 1H NMR-Based Metabolomics Analysis of Urine and Serum Profiles after Consumption of Lentils, Chickpeas, and Beans: An Extended Meal Study To Discover Dietary Biomarkers of Pulses

High legume intake has been shown to have beneficial effects on the health of humans. The use of nutritional biomarkers, as a complement to self-reported questionnaires, could assist in evaluating dietary intake and downstream effects on human health. The aim of this study was to investigate potential biomarkers of the consumption of pulses (i.e., white beans, chickpeas, and lentils) by using untargeted NMR-based metabolomics. Meals rich in pulses were consumed by a total of 11 participants in a randomized crossover study and multilevel partial least-squares regression was employed for paired comparisons. Metabolomics analysis indicated that trigonelline, 3-methylhistidine, dimethylglycine, trimethylamine, and lysine were potential, though not highly specific, biomarkers of pulse intake. Furthermore, monitoring of these metabolites for a period of 48 h after intake revealed a range of different excretion patterns among pulses. Following the consumption of pulses, a metabolomic profiling revealed that the concentration ratios of trigonelline, choline, lysine, and histidine were similar to those found in urine. In conclusion, this study identified potential urinary biomarkers of exposure to dietary pulses and provided valuable information about the time-response effect of these putative biomarkers.

Whole Body Protein Turnover and Net Protein Balance After Pediatric Thoracic Surgery: A Noninvasive Single-Dose 15 N Glycine Stable Isotope Protocol With End-Product Enrichment

BACKGROUND

We used the 15 N glycine urinary end-product enrichment technique to quantify whole body protein turnover following thoracic surgery.

MATERIALS AND METHODS

A single dose of 15 N glycine (2 mg/kg) was administered orally on postoperative day 1 to children (1-18 years) following thoracic surgery. 15 N enrichment of ammonia and urea was measured in mixed urine after 12 and 24 hours, respectively, and protein synthesis, breakdown, and net balance determined. Nitrogen balance (dietary intake minus urinary excretion) was calculated. Urinary 3-methylhistidine:creatinine ratio was measured as a marker of skeletal muscle protein breakdown.

RESULTS

We enrolled 19 subjects-median (interquartile range): age, 13.8 years (12.2-15.1); weight, 49.2 kg (38.4-60.8)-who underwent thoracotomy (n = 12) or thoracoscopic (n = 7) surgery. Protein synthesis and breakdown by 15 N enrichment were 7.1 (5.5-9) and 7.1 (5.6-9) g·kg-1 ·d-1 with ammonia (12 hours) as the end product, and 5.8 (3.8-6.7) and 6.7 (4.5-7.6) with urea (24 hours), respectively. Net protein balance by the 15 N glycine and urinary urea nitrogen methods were -0.34 (-0.47, -0.3) and -0.48 (-0.65, -0.28) g·kg-1 ·d-1 , respectively (rs = 0.828, P < .001). Postoperative change in 3-methylhistidine:creatinine ratio did not correlate significantly with protein breakdown or balance.

CONCLUSION

The single-dose oral administration of 15 N glycine stable isotope with measurement of urinary end-product enrichment is a feasible and noninvasive method to investigate whole body protein turnover in children. After major surgery, children manifest increased protein turnover and net negative balance due to increased protein breakdown.

Protein feeding pattern, casein feeding, or milk-soluble protein feeding did not change the evolution of body composition during a short-term weight loss program

Studies have shown that timing of protein intake, leucine content, and speed of digestion significantly affect postprandial protein utilization. Our aim was to determine if one can spare lean body mass during energy restriction by varying the quality and the timing of protein intake. Obese volunteers followed a 6-wk restricted energy diet. Four groups were compared: casein pulse, casein spread, milk-soluble protein (MSP, = whey) pulse, and MSP spread (n = 10-11 per group). In casein groups, caseins were the only protein source; it was MSP in MSP groups. Proteins were distributed in four meals per day in the proportion 8:80:4:8% in the pulse groups; it was 25:25:25:25% in the spread groups. We measured weight, body composition, nitrogen balance, 3-methylhistidine excretion, perception of hunger, plasma parameters, adipose tissue metabolism, and whole body protein metabolism. Volunteers lost 7.5 ± 0.4 kg of weight, 5.1 ± 0.2 kg of fat, and 2.2 ± 0.2 kg of lean mass, with no difference between groups. In adipose tissue, cell size and mRNA expression of various genes were reduced with no difference between groups. Hunger perception was also never different between groups. In the last week, due to a higher inhibition of protein degradation and despite a lower stimulation of protein synthesis, postprandial balance between whole body protein synthesis and degradation was better with caseins than with MSP. It seems likely that the positive effect of caseins on protein balance occurred only at the end of the experiment.

Body composition and energy metabolism following Roux-en-Y gastric bypass surgery

Roux-en-Y gastric bypass (RYGB) surgery has become an accepted treatment for excessive obesity. We conducted a longitudinal study to assess regional body composition, muscle proteolysis, and energy expenditure before RYGB, and 6 and 12 months after RYGB. Whole-body and regional fat mass (FM) and lean mass (LM) were assessed via dual energy X-ray absorptiometry (DXA), and myofibrillar protein degradation was estimated by urinary 3-methylhistidine (3-MeH) in 29 subjects. Energy expenditure and substrate oxidation were also determined using a whole-room, indirect calorimeter in 12 of these subjects. LM loss constituted 27.8 +/- 10.2% of total weight loss achieved 12 months postoperatively, with the majority of LM loss (18 +/- 6% of initial LM) occurring in the first 6 months following RYGB. During this period, the trunk region contributed 66% of whole-body LM loss. LM loss occurred in the first 6 months after RYGB despite decreased muscle protein breakdown, as indicated by a decrease in 3-MeH concentrations and muscle fractional breakdown rates. Sleep energy expenditure (SEE) decreased from 2,092 +/- 342 kcal/d at baseline to 1,495 +/- 190 kcal/day at 6 months after RYGB (P < 0.0001). Changes in both LM and FM had an effect on the reduction in SEE (P < 0.001 and P = 0.005, respectively). These studies suggest that loss of LM after RYGB is significant and strategies to maintain LM after surgery should be explored.

Protein degradation and the regulation of protein balance in muscle

The rate of of protein degradation in muscle changes in many states but the nature of these changes is often paradoxical. Thus there can be increases during growth (anabolic increases) as well as during wasting (catabolic increases). Decreases can occur during growth (anabolic decreases) as well as during wasting (catabolic decreases). These changes are observed in man (as judged by changes in 3-methylhistidine excretion) and in experimental animals. The nature of the changes is not understood but it is possible that muscle growth induces increased degradation as part of the accompanying myofibre remodelling. The rate of protein degradation can also be influenced by thyroid status, since in thyroid deficiency degradation is reduced and can be stimulated by triiodothyronine. This response is independent of changes in muscle growth. Finally, acute exercise suppresses protein degradation in vivo in man as well as suppressing protein synthesis (in vivo in rats). When protein degradation rates change, acid proteinase activities also change in muscle. The anabolic increase in degradation appears to involve increases in mainly cathepsin D whereas catabolic increases in degradation are associated with an increase mainly in pepstatin-insensitive acid autolytic activity.

Determination of 1-methylhistidine and 3-methylhistidine by capillary and chip electrophoresis with contactless conductivity detection

CE with capacitively coupled contactless detection (C4D) was used to determine 3-methylhistidine (3-MH) and 1-methylhistidine (1-MH). The C4D response to 3-MH was studied in a BGE consisting of 500 mM acetic acid and ammonia at varying concentration and the results were compared with the theory. Complete separation of a model mixture of 3-MH, 1-MH, and histidine (His) was attained in two optimized BGEs, one containing 500 mM HAc, 20 mM NH4OH, and 0.1 % m/v hydroxyethylcellulose (HEC), pH 3.4 (I) and the other consisting of 100 mM morpholinoethanesulfonic acid (MES), 25 mM LiOH, and 0.1 % m/v HEC, pH 5.5 (II). These optimized BGEs were tested in CE/C4D analyses of urine. Promising results were obtained for separation and determination of 3-MH, 1-MH, and His on a silicon microchip, using aluminum strips as the C4D electrodes; the three analytes were baseline-separated within less than 30 s with a separation channel effective length of 38 mm. The LOD were satisfactory and amounted to 26.4 microM for 3-MH and 18.3 microM for 1-MH.

Effects of ornithine alpha-ketoglutarate on protein metabolism in Yoshida sarcoma-bearing rats

BACKGROUND & AIMS

Ornithine alpha-ketoglutarate (OKG) is recognized to improve nutritional status in various catabolic states, such as burn injury, trauma, and sepsis. However, in wasting diseases, such as induced by cancer, the data are scarce and the precise mechanisms by which OKG acts on protein metabolism are still unclear. The aim of this study was to evaluate the ability of OKG to affect protein metabolism in an aggressive model of cancer and to modulate the ubiquitin-proteasome-dependent pathway, which in skeletal muscle is the critical degradative pathway implicated in many catabolic states, including cancer-associated cachexia.

METHODS

Experiments were carried out in Yoshida sarcoma-bearing and healthy pair-fed rats. Three groups of 16 young male rats were studied during 9 days following tumor implantation: two groups of tumor-bearing rats fed a balanced regimen enriched with either OKG (5 g/kg body weight/day, OKG-K) or an isonitrogenous mixture of non-essential amino acids (C-K), and one group of healthy pair-fed rats (PF).

RESULTS

As expected, Yoshida sarcoma induced muscle atrophy, decreased nitrogen balance, enhanced 3-methylhistidine (3-MH) excretion and increased mRNA levels for ubiquitin and 14-kDa ubiquitin-conjugating enzyme E2. OKG supplementation did not improve muscle mass or protein balance and did not reduce enhanced 3-MH excretion in Yoshida sarcoma-bearing rats. Furthermore, OKG did not suppress in the cancer rats the enhanced expression of ubiquitin and 14-kDa E2, despite OKG decreased by 23% the ubiquitination rate in cancer rats (OKG-K vs. C-K, P<0.05).

CONCLUSIONS

These data suggest that OKG action is not universal; i.e. depending upon the model under study. In the circumstances, OKG did not counteract the increase in ubiquitin-proteasome-dependent proteolysis observed in Yoshida sarcoma-bearing rats.

Dose dependency of the effect of ornithine α-ketoglutarate on tissue glutamine concentrations and hypercatabolic response in endotoxaemic rats

The optimal dosage of ornithine α-ketoglutarate (OKG) for repleting tissue glutamine (Gln) concentrations and maintaining N homeostasis after injury is unknown. We set out to perform ‘dose-ranging’ of OKG supplementation after an endotoxaemic challenge. Sixty-one male Wistar rats were injected with 3 mg lipopolysaccharide (LPS) from Escherichia coli/kg (n 50) or saline vehicle (9 g NaCl/l; controls n 11). After a 24 h fast, survivors were fed by gavage for 48 h with a polymeric standard diet (879 kJ/kg per d and 1·18 g N/kg per d) supplemented with non-essential amino acids (control, n 11; LPS-OKG-0·0, n 9), or with 0·5 g OKG/kg per d (LPS-OKG-0·5, n 12), 1·5 OKG/kg per d (LPS-OKG-1.5, n 11) or 4·5 g OKG/kg per d (LPS-OKG-4·5, n 10). The diets for all groups were made isonitrogenous with the LPS-OKG-4·5 diet by adding an appropriate amount of non-essential amino acids. Rats were killed on day 3 for blood and tissue sampling (muscle, jejunum mucosa, liver). Urine was collected daily for 3-methylhistidine and total N assays. The OKG dose was correlated with Gln concentrations in every tissue and with cumulative N balance (Spearman test, P<0·01). 3-Methylhistidine excretion was increased in endotoxaemic groups compared with controls (ANOVA, P<0·05) except in the LPS-OKG-4·5 group. Only the LPS-OKG-4·5 group achieved a positive post-injury N balance (t test, P<0·05). In conclusion, OKG exerted a dose-dependent effect on tissue Gln concentration and N balance, but only the highest dosage counteracted myofibrillar hypercatabolism and caused a positive N balance.

Influence of branched-chain amino acid supplementation on urinary protein metabolite concentrations after swimming

OBJECTIVE

The influence of branched-chain amino acid (BCAA) supplementation on urinary urea nitrogen, hydroxyproline (HP), and 3-methylhistidine (3MH) concentrations after 25 min of breast stroke exercise (65-70% maximum heart rate reserved, 65-70% HRRmax) followed by a 600 m crawl stroke competition was investigated in a double-blind, counter-balanced study.

METHODS

Male university students (19-22 years old) majoring in physical education participated in the study. Based on the previous swimming time of a 600 m crawl stroke, the participants were divided into two groups: placebo (n = 9, BMI = 24.2 +/- 2.1 kg/m2; 12 g of glucose/day; in capsules) and BCAA (n = 10, BMI = 22.7 +/- 1.5 kg/m2; 12 g of BCAAs/day; in capsules: leucine 54%, isoleucine 19%, valine 27%) groups. The participants maintained a regular dietary intake (except the prescribed breakfast on day 15) and exercise activity at a moderate/low intensity (60-70% HRRmax, swimming and rowing, approximately 1.5 hour/day) during the 15-day study. A prescribed exercise program was performed on day 15. Urinary and blood samples were collected before, during, and after the prescribed exercise for the measurements of the urinary urea nitrogen, HP, and 3MH concentrations in urine, as well as the glucose, lactate, glutamine, alanine, and BCAA concentrations in plasma.

RESULTS

Two weeks of dietary supplementation did not induce any changes in the plasma glucose and total BCAA concentrations of either group, nor in the urinary urea nitrogen, HP, and 3MH concentrations in urine. On day 15, after 25 min of breast stroke exercise and a 600 m crawl stroke competition, plasma glucose concentration decreased significantly (p < 0.05) whereas plasma lactate concentration increased significantly (p < 0.05) in both groups. The exercise program prescribed in the study did not affect urinary urea nitrogen, HP, and 3MH concentrations. Twenty hours after the competition, however, a significant increase in the concentrations of urinary urea nitrogen, HP, and 3MH was found in the placebo group (p < 0.05), but not in the BCAA group.

CONCLUSIONS

The results obtained in this study suggest that swimming induced muscle proteolysis was prevented by BCAA supplementation. The mechanism could be attributed to the availability of ammonia provided by the oxidation of supplemented BCAAs during exercise.

Effect of whey and soy protein supplementation combined with resistance training in young adults

The purpose was to compare changes in lean tissue mass, strength, and myofibrillar protein catabolism resulting from combining whey protein or soy protein with resistance training. Twenty-seven untrained healthy subjects (18 female, 9 male) age 18 to 35 y were randomly assigned (double blind) to supplement with whey protein (W; 1.2 g/kg body mass whey protein + 0.3 g/kg body mass sucrose power, N = 9: 6 female, 3 male), soy protein (S; 1.2 g/kg body mass soy protein + 0.3 g/kg body mass sucrose powder, N= 9: 6 female, 3 male) or placebo (P; 1.2 g/kg body mass maltodextrine + 0.3 g/kg body mass sucrose powder, N = 9: 6 female, 3 male) for 6 wk. Before and after training, measurements were taken for lean tissue mass (dual energy X-ray absorptiometry), strength (1-RM for bench press and hack squat), and an indicator of myofibrillar protein catabolism (urinary 3-methylhistidine). Results showed that protein supplementation during resistance training, independent of source, increased lean tissue mass and strength over isocaloric placebo and resistance training (P < 0.05). We conclude that young adults who supplement with protein during a structured resistance training program experience minimal beneficial effects in lean tissue mass and strength.

Citrulline modulates muscle protein metabolism in old malnourished rats

Protein energy malnutrition is common in the elderly, especially in hospitalized patients. The development of strategies designed to correct such malnutrition is essential. Our working hypothesis was that poor response to nutrition with advancing age might be related to splanchnic sequestration of amino acids, which implies that fewer amino acids reach the systemic circulation. Administration of citrulline, which is not taken up by the liver, can offer a means of increasing whole body nitrogen availability and, hence, improve nutritional status. Thirty old (19 mo) rats were submitted to dietary restriction (50% of food intake) for 12 wk. They were randomized into three groups: 10 rats (R group) were killed and 20 others refed (90% of food intake) for 1 wk with a standard diet (NEAA group) or a citrulline-supplemented diet (Cit group). Before being killed, the rats were injected with [(13)C]valine, and the absolute protein synthesis rate (ASR) was measured in the tibialis using the flooding-dose method. When the rats were killed, the tibialis was removed for protein content analysis. Blood was sampled for amino acid and insulin analysis. The standard diet did not have any effect on protein synthesis or on the protein content in the muscle. Citrulline supplementation led to higher protein synthesis and protein content in muscle (117 +/- 9, 120 +/- 14, and 163 +/- 4 mg/organ for protein content in R, NEAA, and Cit groups, P < 0.05). The ASR were 0.30 +/- 0.04, 0.31 +/- 0.04, and 0.56 +/- 0.10 mg/h in the three groups, respectively (R and NEAA vs. Cit, P < 0.05). Insulinemia was significantly higher in the Cit group. For the first time, a realistic therapeutic approach is proposed to improve muscle protein content in muscle in frail state related to malnutrition in aging.

The equivocal metabolic response to endotoxaemia in type 2 diabetic and obese ZDF rats

AIMS/HYPOTHESIS

The metabolic and endocrine disturbances associated with obesity and type 2 diabetes may impair the normal metabolic response to injury. Our objective was to investigate amino acid metabolism in endotoxaemic type 2 diabetic obese rats.

MATERIALS AND METHODS

A metabolic study was performed over 4 days using male Zucker diabetic fatty (ZDF) rats (fa/fa) and lean littermates (fa/+) divided into three groups: ad libitum-fed groups which underwent no treatment, lipopolysaccharide (LPS)-treated groups receiving E. coli LPS by i.p. injection, and pair-fed groups to the respective LPS groups. We evaluated the effect of endotoxaemia on body weight, food intake and tissue weights. Nitrogen loss and muscular proteolysis were measured daily by determination of urinary 3-methylhistidine (3-MH) excretion. Plasma, intestine and muscle amino acid levels were measured.

RESULTS

The data showed that ad libitum-fed ZDF rats had lower plasma arginine and glutamine levels than ad libitum-fed control rats. Compared with control rats, the LPS-treated ZDF rats presented lower thymic involution, a lower 3-MH:creatinine ratio and higher cumulative nitrogen balance.

CONCLUSIONS/INTERPRETATION

Against our working hypothesis, ZDF rats did not show an impaired metabolic response, and even appeared to be less sensitive to the stress.

Skeletal Muscle Protein Synthesis after Active or Passive Ascent to High Altitude

INTRODUCTION

The effects of acute exposure to high altitude on muscle protein synthesis rates in human volunteers were examined after active and passive ascent.

METHODS

Measurements were made initially at low altitude (550 m) and again after ascent to high altitude (4,559 m). To be able to separate the contribution of physical exercise, one group was flown by helicopter (air group, N=8), whereas the other group climbed to high altitude (foot group, N=9). Fractional rates of muscle protein synthesis rates (FSR) were determined from the incorporation of isotope into protein after injection of [H5ring] phenylalanine.

RESULTS

In the air group, there was no change in FSR at high altitude, whereas in the foot group, there was a 35% increase in FSR (P<0.05 for interaction) measured 19-23 h after the end of climbing. At high altitude, the degree of hypoxia and alkalosis were not different between the groups. The plasma concentration of insulin-like growth factor-1, free thyroxin, free triiodothyronine, and thyroid-stimulating hormone were not different between the groups. Urinary 24-h cortisol excretion increased significantly in both groups after ascent, but the increase in the foot group was significantly higher compared with the air group.

CONCLUSION

Physical exercise appeared to be responsible for the observed increase in muscle FSR. The significantly higher increase of 24-h cortisol excretion in the foot group suggests that the increase in FSR occurred despite higher levels of glucocorticoids, which generally affect muscle protein turnover by inhibiting protein synthesis.

Negative chemical ionization gas chromatography/mass spectrometry to quantify urinary 3-methylhistidine: application to burn injury

A rapid method for measuring 3-methylhistidine (3MH) in rat and human urine with higher sensitivity and precision than any previously reported method is described using internal standard [1-(13)C]3MH (M+1) and negative chemical ionization (NCI) gas chromatography/mass spectrometry (GC/MS). Internal standard [1-(13)C]3MH (M+1) was added to rat and human urine samples, hydrolyzed, and absorbed onto cation exchange columns. The column eluent was dried and derivatized for GC/MS analysis. Quantification of 3MH levels was accomplished by monitoring the m/z 204 fragment. The m/z 204 fragment was chosen due to the fragment's abundance and stability as determined by analysis of [methyl-(2)H(3), (18)O(2)]3MH (M+7) and [methyl-(13)C]3MH (M+1) fragmentation patterns under NCI conditions. This method shows excellent linearity (0.9989) over the range studied (0-0.5 mol), high recovery (95.9%), and low coefficient of variation (4.7%). The described method is sensitive enough to detect 6.8 pmol amount of urinary 3MH with a precision of 9.1%. The in vivo utility of this method to quantify urinary 3MH was tested in a burn injury rat model and on urine specimens from pediatric burn patients. Data obtained from the urine of burn-injured rats and pediatric burn patients match previously reported trends and validate the in vivo utility of this method.

Liquid carbohydrate/essential amino acid ingestion during a short-term bout of resistance exercise suppresses myofibrillar protein degradation

A number of physiological events including the level of contractile activity, nutrient status, and hormonal action influence the magnitude of exercise-induced skeletal muscle growth. However, it is not the independent action of a single mechanism, but the complex interaction between events that enhance the long-term adaptations to resistance training. The purpose of the present investigation was to examine the influence of liquid carbohydrate (CHO) and essential amino acid (EAA) ingestion during resistance exercise and modification of the immediate hormonal response on myofibrillar protein degradation as assessed by 3-methylhistidine (3-MH) excretion. After a 4-hour fast, 32 untrained young men (18-29 years) performed a single bout of resistance exercise (complete body; 3 setsx10 repetitions at 75% of 1-repetition maximum; 1-minute rest between sets), during which they consumed a 6% CHO (n=8) solution, a 6-g EAA (n=8) mixture, a combined CHO+EAA (n=8) supplement, or placebo (PLA; n=8) beverage. Resistance exercise performed in conjunction with CHO and CHO+EAA ingestion resulted in significantly elevated (P<.001) glucose and insulin concentrations above baseline, whereas EAA ingestion only increased the postexercise insulin response (P<.05). Time matched at 60 minutes, the PLA group exhibited a peak cortisol increase of 105% (P<.001) with no significant change in glucose or insulin concentrations. Conversely, the CHO and CHO+EAA groups displayed a decrease in cortisol levels of 11% and 7%, respectively. Coinciding with these hormonal response patterns were significant differences in myofibrillar protein degradation. Ingestion of the EAA and CHO treatments attenuated 3-MH excretion 48 hours after the exercise bout. Moreover, this response was synergistically potentiated when the 2 treatments were combined, with CHO+EAA ingestion resulting in a 27% reduction (P<.01) in 3-MH excretion. In contrast, the PLA group displayed a 56% increase (P<.01) in 3-MH excretion. These data demonstrate that not only does CHO and EAA ingestion during the exercise bout suppress exercise-induced cortisol release; the stimulatory effect of resistance exercise on myofibrillar protein degradation can be attenuated, most dramatically when the treatments are combined (CHO+EAA). Through an "anticatabolic effect," this altered balance may better favor the conservation of myofibrillar protein.

Independent and combined effects of liquid carbohydrate/essential amino acid ingestion on hormonal and muscular adaptations following resistance training in untrained men

This investigation examined chronic alteration of the acute hormonal response associated with liquid carbohydrate (CHO) and/or essential amino acid (EAA) ingestion on hormonal and muscular adaptations following resistance training. Thirty-two untrained young men performed 12 weeks of resistance training twice a week, consuming ~675 ml of either, a 6% CHO solution, 6 g EAA mixture, combined CHO + EAA supplement or placebo (PLA). Blood samples were obtained pre- and post-exercise (week 0, 4, 8, and 12), for determination of glucose, insulin, and cortisol. 3-Methylhistidine excretion and muscle fibre cross-sectional area (fCSA) were determined pre- and post-training. Post-exercise cortisol increased (P<0.05) during each training phase for PLA. No change was displayed by EAA; CHO and CHO + EAA demonstrated post-exercise decreases (P<0.05). All groups displayed reduced pre-exercise cortisol at week 12 compared to week 0 (P<0.05). Post-exercise insulin concentrations showed no change for PLA; increases were observed for the treatment groups (P<0.05), which remained greater for CHO and CHO + EAA (P<0.001) than PLA. EAA and CHO ingestion attenuated 3-methylhistidine excretion 48 h following the exercise bout. CHO + EAA resulted in a 26% decrease (P<0.01), while PLA displayed a 52% increase (P<0.01). fCSA increased across groups for type I, IIa, and IIb fibres (P<0.05), with CHO + EAA displaying the greatest gains in fCSA relative to PLA (P<0.05). These data indicate that CHO + EAA ingestion enhances muscle anabolism following resistance training to a greater extent than either CHO or EAA consumed independently. The synergistic effect of CHO + EAA ingestion maximises the anabolic response presumably by attenuating the post-exercise rise in protein degradation.

[Effect of insulin intensive treatment on hyper-proteolysis of skeletal muscle in scalded rabbit with sepsis]

OBJECTIVE

To study the effect of insulin intensive treatment on hyper-proteolysis of skeletal muscle in scalded rabbit with sepsis.

METHODS

Male white rabbits were randomly divided into scald group (S group), scald sepsis group (SS group), scald with insulin treatment group (SI group), scald sepsis with insulin treatment group (SSI group), and control group (C group), with 6 animals in each group. The extent of scald injury was 30% total body surface area (TBSA) III degree in depth, and the model of scald sepsis was replicated by administration of endotoxin (2 mg/kg) into the peritoneal cavity immediately after scald injury. Insulin intensive treatment was given with injection of insulin to keep the plasma glucose level in physiologic range (4.4-6.1 mmol/L) for SI group and SSI group. The contents of 3-methylhistidine (3-MH) in extensor digitorum longus (EDL) muscles and urine were determined with high performance liquid chromatography. The expressions of ubiquitin mRNA in the EDL muscle were assessed with Northern blot analysis.

RESULTS

The contents of 3-MH in EDL muscles and urine of S group and SS group were increased significantly as compared with C group (all P<0.01), and that of SI group and SSI group were decreased markedly compared with S group and SS group (all P<0.01), respectively. The mRNA expression of ubiquitin of S group and SS group was enhanced significantly compared with C group (all P<0.01), and that of SI group and SSI group was down-regulated notably compared with S group and SS group (all P<0.01), respectively.

CONCLUSION

The activity of ubiquitin system, one of important protein degradation pathways, and the proteolysis in skeletal muscle are enhanced after scald injury, especially so sepsis sets in, and insulin intensive treatment can effectively alleviate hyper-proteolysis of skeletal muscle through inhibiting the activity of ubiquitin system at gene level.

The Effects of Conjugated Linoleic Acid Supplementation during Resistance Training

PURPOSE

We determined the effects of conjugated linoleic acid (CLA) supplementation during resistance training.

METHODS

Seventy-six subjects were randomized to receive CLA (5 g.d(-1)) or placebo (PLA) for 7 wk while resistance training 3 d.wk(-1). Seventeen subjects crossed over to the opposite group for an additional 7 wk. Measurements at baseline, 7 wk, and 14 wk (for subjects in the crossover study) included body composition, muscle thickness of the elbow flexors and knee extensors, resting metabolic rate (RMR), bench and leg press strength, knee extension torque, and urinary markers of myofibrillar degradation (3-methylhistidine (3MH) and bone resorption (cross-linked N-telopeptides (Ntx)).

RESULTS

After 7 wk the CLA group had greater increases in lean tissue mass (LTM) (+1.4 vs +0.2 kg; P < 0.05), greater losses of fat mass (-0.8 vs +0.4 kg; P < 0.05), and a smaller increase in 3MH (-0.1 vs + 1.3 micromol.kg LTM.d(-1); P < 0.05) compared with PLA. Changes between groups were similar for all other measurements, except for a greater increase in bench press strength for males on CLA (P < 0.05). In the crossover study subjects had minimal changes in body composition, but smaller increases in 3MH (-1.2 vs +2.2 micromol.kg LTM.d(-1); P < 0.01) and NTx (-4.8 vs +7.3 nmol.kg(-1) LTM.d(-1); P < 0.01) while on CLA versus PLA.

CONCLUSIONS

Supplementation with CLA during resistance training results in relatively small changes in body composition accompanied by a lessening of the catabolic effect of training on muscle protein.

Evaluation of a glycine-rich amino acid solution for parenteral nutrition in endotoxemic rats

OBJECTIVE

It has been shown recently that high amounts of glycine might have some pharmacologic effects (reduction of injury and mortality in endotoxemic rats), but its effects on the nutritional status and protein metabolism during injury are still unknown. The aim of this study was to compare the nutritional effects of a glycine-rich amino acid solution for parenteral nutrition (AFD) with a standard one (Vintene) (glycine, 15 vs. 9 g/L) in endotoxemic rats.

DESIGN

Laboratory investigation.

SETTING

University laboratory.

SUBJECTS

Male Wistar rats (198 +/- 11 g).

INTERVENTIONS

Rats were operated to receive total parenteral nutrition (250 kcal/kg/day, 2 g N/kg/day) with amino acids supplied by either AFD (n = 9) or Vintene (V, n = 6). One day after surgery, corresponding to day 0 of the experiment and to the first day of full-strength total parenteral nutrition, the AFD and V group rats received an endotoxemic shock by intraperitoneal injection of lipopolysaccharide (Escherichia coli, 8 mg/kg). The rats were then studied over 3 days and compared with a healthy ad libitum-fed group (AL, n = 10).

MEASUREMENTS AND MAIN RESULTS

The rats were weighed and urine was collected daily to determine nitrogen balance and 3-methylhistidine excretion. On day 3, the thymus, spleen, liver, intestinal mucosa, and muscles were weighed, and amino acids from plasma and tissues were analyzed. Lipopolysaccharide caused the classic endotoxemic shock, of similar intensity in the V and AFD groups (V and AFD not equal AL, p < .05): no weight gain, decreased nitrogen balance (day 3, AL 558 +/- 21, V 83 +/- 28, AFD 123 +/- 25 mg N/day), increased urinary 3-methylhistidine/creatinine excretion (day 3, AL 51 +/- 2, V 91 +/- 13, AFD 87 +/- 14 mumol/mmol), soleus (V -15% and AFD -26 % vs. AL) and thymus atrophy (V -36% and AFD -33%), and spleen hypertrophy (V 51% and AFD 83%). Compared with V solution, AFD has a reduced content of some essential amino acids and proline and an elevated content of glycine, aspartate, and glutamate. These differences were not reflected in tissue or plasma amino acids, except for plasma glycine, which in the AFD group was restored to the level of the AL group (AL 426 +/- 12 and AFD 379 +/- 50 vs. V 251 +/- 31 mumol/L, p < .05).

CONCLUSIONS

In endotoxemic rats, the nutritional effects of a glycine-rich AFD solution are similar to those of a standard amino acid solution for parenteral nutrition.

Determination of 3-methylhistidine and 1-methylhistidine in untreated urine samples by capillary electrophoresis

Capillary electrophoretic (CE) method was developed for the determination of urinary 3-methylhistidine (3MH) and 1-methylhistidine (1MH) indicating the extent of degradation of skeletal muscle proteins and thereby the state of human health. 3MH, 1MH and histidine can be separated in both acidic and alkaline media, where these amino acids form cation and anion, respectively. The effective mobility of all ionic forms was measured over a broad range of pH (1.67-11.80), which made it possible to evaluate the corresponding dissociation constants. 3MH and 1MH were determined together with creatinine in untreated urine samples with the limit of detection of 2.4 microM (0.4 mgL(-1)) and 3.0 microM (0.5 mgL(-1)), respectively. Determination was fast and took ca. 12 min including the column washing. Method was employed for an analysis of urine collected from healthy individuals, and from the patients hospitalized with obesity and diabetes mellitus II. This analysis has revealed differences between the healthy individuals and the patients pointing to a more extensive degradation of muscle proteins in the latter group.

Clinical and protein metabolic efficacy of glutamine granules-supplemented enteral nutrition in severely burned patients

As an abundant amino acid in the human body, glutamine has many important metabolic roles that may protect or promote tissue integrity and enhance the immune system. A relative deficiency of glutamine in such patients could compromise recovery and result in prolonged illness and an increase in late mortality. The purpose of this clinical study is to observe the effects of enteral supplement with glutamine granules on protein metabolism in severely burned patients. Forty-eight severe burn patients (total burn surface area 30-75%, full thickness burn area 20-58%) who met the requirements of the protocol joined this double-blind randomized controlled clinical trial. Patients were randomly divided into two groups: burn control group (B group, 23 patients) and glutamine treated group (Gln group, 25 patients). There was isonitrogenous and isocaloric intake in both groups, glutamine and B group patents were supplemented with glutamine granules or placebo (glycine) at 0.5 g/kg per day for 14 days with oral feeding or tube feeding, respectively. The level of plasma glutamine, plasma protein content, urine nitrogen and urine 3-methylhistidine (3-MTH) excretion were determined, wound healing rate of the burned area and hospital stay were recorded. The results showed that there were significant reductions in plasma glutamine level and abnormal protein metabolism. After supplement with glutamine granules for 14 days, the plasma glutamine concentration was significantly higher than that in B group (607.86+/-147.25 micromol/L versus 447.63+/-132.38 micromol/L, P<0.01) and the plasma prealbumin and transferrin in Gln group were remarkably higher than those in B group (P<0.01), but the concentration of total protein and albumin were not significantly changed compared with B group (P>0.05). On the other hand, the amount of urine nitrogen and 3-MTH excreted in Gln group were significantly lower than that in B group. In addition, wound healing was faster and hospital stay days were shorter in Gln group than B group (46.59+/-12.98 days versus 55.68+/-17.36 days, P<0.05). These indicated that supplement glutamine granules with oral feeding or tube feeding could abate the degree of glutamine depletion, promote protein synthesis, inhibit protein decompose, improve wound healing and reduce hospital stay.

Perioperative nutrition prevents the early protein losses in patients submitted to gastrointestinal surgery

BACKGROUND & AIMS

The metabolic response to surgery includes a net loss of proteins that influences negatively the clinical evolution of the patients. We investigated the effect of perioperative nutrition on protein metabolism alterations immediately after surgery.

METHODS

A control group of 21 surgery patients were submitted to conventional perioperative nutritional protocol (18 h of fasting plus low-dose glucose after surgery). An experimental group of eight similar patients was given complete parenteral nutrition during 24 h before and 24 h after surgery. Nitrogen balance, whole body protein synthesis, breakdown, and 3-methylhistidine were determined before surgery and 24 h after surgery.

RESULTS

The immediate response to surgery with conventional nutritional management was a net protein loss (-1.023 g prot. kg(-1) day(-1)), caused by an increase in the protein breakdown (137.9% of preoperative values), while the protein synthesis remained unchanged (98.4%). The 3-methylhistidine excretion was not increased in respect to perioperative values, suggesting that the degraded protein was not from muscular origin. The experimental group with perioperative nutrition showed neither protein loss (+0.075 g prot. kg(-1) day(-1)) nor changes in protein synthesis or breakdown vs. preoperative values (96.3% and 88.0%, respectively).

CONCLUSION

Perioperative nutrition prevents the early protein losses after gastrointestinal surgery.

Creatine monohydrate enhances strength and body composition in Duchenne muscular dystrophy

OBJECTIVE

To determine whether creatine monohydrate (CrM) supplementation increases strength and fat-free mass (FFM) in boys with Duchenne muscular dystrophy (DD).

METHODS

Thirty boys with DD (50% were taking corticosteroids) completed a double-blind, randomized, cross-over trial with 4 months of CrM (about 0.10 g/kg/day), 6-week wash-out, and 4 months of placebo. Measurements were completed of pulmonary function, compound manual muscle and handgrip strength, functional tasks, activity of daily living, body composition, serum creatine kinase and gamma-glutamyl transferase activity and creatinine, urinary markers of myofibrillar protein breakdown (3-methylhistidine), DNA oxidative stress (8-hydroxy-2-deoxyguanosine [8-OH-2-dG]), and bone degradation (N-telopeptides).

RESULTS

During the CrM treatment phase, there was an increase in handgrip strength in the dominant hand and FFM (p < 0.05), with a trend toward a loss of global muscle strength (p = 0.056) only for the placebo phase, with no improvements in functional tasks or activities of daily living. Corticosteroid use, but not CrM treatment, was associated with a lower 8-OH-2-dG/creatinine (p < 0.05), and CrM treatment was associated with a reduction in N-telopeptides (p < 0.05).

CONCLUSIONS

Four months of CrM supplementation led to increases in FFM and handgrip strength in the dominant hand and a reduction in a marker of bone breakdown and was well tolerated in children with DD.

Nutritional status and cytokine-related protein breakdown in elderly patients with gastrointestinal malignancies

BACKGROUND

Age-related factors affecting cytokine-related whole-body protein breakdown and their relation to clinical outcomes in cancer patients were investigated.

METHODS

For assessment of protein-calorie malnutrition and protein breakdown, the creatinine height index (CHI) and daily urinary excretion of 3-methylhistidine (3-MH) were measured in 70 patients with gastrointestinal malignancies. Perioperative cytokine profile was evaluated to assess its relation to perioperative protein catabolism.

RESULTS

In elderly patients, daily 3-MH excretion during the stable preoperative period decreased with the increase of tumor interleukin (IL)-6 production, suggestive of the activation of a metabolic compensation mechanism. However, these patients showed significant increases in postoperative 3-MH excretion in accord with perioperative systemic IL-6 response, and this deterioration of the compensating mechanism seemed to be associated with poor clinical outcome. An increase in 3-MH excretion under surgical stress was positively correlated with postoperative consumption of IL-6 soluble receptor (sR) in elderly patients with nutritional depletion.

CONCLUSIONS

In elderly cancer patients with protein-calorie malnutrition, metabolic compliance against intrinsic IL-6 may be compensated for in the preoperative stable period, but deteriorate from surgical insults. This mechanism might involve increased affinity of IL-6 with IL-6sR under surgical stress.

Proteasome production in human muscle during nutritional inhibition of myofibrillar protein degradation

Protein undernutrition inhibits adenosine triphosphate (ATP)-dependent muscle protein degradation-a hallmark of the proteasome system. Here we report decreased myofibrillar protein degradation during dietary protein restriction without a concomitant decrease in proteasome gene expression, proteasome protein abundance, or proteasome in vivo fractional synthesis rate. Healthy human subjects consuming the average minimum adult protein requirement (0.71 g x kg(-1) fat-free mass x d(-1)) exhibited substantially lower (68%) excretion of 3-methylhistidine, an indicator of myofibrillar protein breakdown, when compared with subjects consuming an ample, American-style protein intake (1.67 g x kg(-1) fat-free mass x d(-1)). However, they displayed no difference in the expression of mRNA for proteasome subunits C2 or C3, in the content of C2 protein, or in the rate of incorporation of stable isotopically labeled l-[1-(13)C]-leucine into proteasome proteins. The results demonstrate that nutritional inhibition of myofibrillar protein degradation does not involve suppression in vivo of proteasome production in man. This suggests that other elements of the ubiquitin-proteasome system, such as ubiquitination pathways, are more important than proteasome abundance in the nutritional regulation of skeletal muscle mass.

Bone resorption is induced on the second day of bed rest: results of a controlled crossover trial

The aim of the study was to analyze the kinetics of short-term changes in bone turnover. We studied in a randomized crossover design the effects of 6 days of bed rest on eight healthy male subjects (mean body wt: 70.1 +/- 5.7 kg; mean age: 25.5 +/- 2.9 yr). The metabolic ward period was divided into three parts: 4 ambulatory days, 6 days of either bed rest or non-bed rest periods, and 1 recovery day. The diet was identical in both bed rest and non-bed rest phases. Continuous urine collection started on the first day in the metabolic ward to analyze excretion of bone resorption markers, namely C-telopeptide (CTX) and N-telopeptide (NTX), creatinine, urea, and 3-methylhistidine. On the second ambulatory day and on the fifth day of bed rest or during the non-bed rest phase, blood was drawn to analyze bone formation markers and amino acid concentrations. Urinary calcium excretion was increased as early as the first day of bed rest (P < 0.01). CTX and NTX excretion stayed unchanged during the first 24 h of bed rest compared with the non-bed rest period. However, already on the second day, both resorption markers had increased significantly. NTX excretion increased by 28.7 +/- 14.0% (P < 0.01), whereas CTX excretion rose by 17.8 +/- 8.3% (P < 0.001). Creatinine, urea, and 3-methylhistidine excretion did not change. We conclude that 24 h of bed rest are sufficient to induce a significant rise in osteoclast activity in healthy subjects.

Effects of amino acid nutrition on the responses of dairy cows to milking more frequently with or without injection of growth hormone

The influence of amino acid nutrition on the response to milking more frequently, with or without injection of growth hormone, was examined in eight dairy cows in two 4 x 4 Latin squares with 28-d periods. The four treatments were a diet adequate in amino acids with or without injection of growth hormone and a diet inadequate in amino acids with or without injection of growth hormone. For all four treatments, during the last 14 d of each period, one half of the mammary gland was milked three times a day (3x), while the other half remained on twice-daily milking (2x). Both diets were based on grass silage given ad libitum and 4 kg/d of sugar beet pulp together with a supplement containing either fish meal (adequate diet) or feather meal (inadequate diet) as the only protein feeds. The diet containing feather meal is known to be deficient in His, Met, and Lys. On the fish meal diet, the cows responded positively to growth hormone and to milking more frequently and the responses to both treatments were additive. On the feather meal diet, however, even though injection of growth hormone increased the yield of milk protein by around 10%, milking more frequently did not affect milk production. It is concluded that milking more frequently has a weaker effect on the partitioning of amino acid use between body and udder than does growth hormone treatment.

Alpha-ketoglutarate-supplemented enteral nutrition: effects on postoperative nitrogen balance and muscle catabolism

Enteral feeding in the early postoperative phase may improve gut integrity and reduce infectious complications after trauma and surgery. The aim of the current study was to evaluate the feasibility of alpha-ketoglutarate enrichment of enteral feeding and the effect on protein metabolism after major surgery. Patients undergoing elective abdominal surgery were randomly allocated to receive a standard whole-protein-based enteral nutrition solution (n = 9) or an isonitrogenous, isocaloric solution enriched with alpha-ketoglutarate (n = 11) for 5 d postoperatively. The nutritional goals by day 4 were 25 kcal and 0.17 g of nitrogen, respectively, per kilogram of body weight every 24 h. Standard blood analysis, including prealbumin and C-peptide, was performed preoperatively and on days 1, 3, and 6. Urine was collected daily for nitrogen and 3-methylhistidine analyses. Due to restricted tolerance to enteral feeding, the nitrogen delivery reached only 0.10 g of nitrogen per kilogram of body weight. Transthyretin decreased by 25% in both groups, and albumin decreased significantly in the enriched group compared with the standard nutrition. There were no significant differences in nitrogen balance, excretion of 3-methylhistidine, or clinical outcome between groups. Enrichment of a whole-protein-based formula with alpha-ketoglutarate did not improve protein metabolism or decrease muscle catabolism after major abdominal surgery.

Decreased Blood Levels of Lactic Acid and Urinary Excretion of 3-Methylhistidine after Exercise by Chronic Taurine Treatment in Rats

Taurine is reported to increase contractility of skeletal muscle and cardiac myocyte, which can increase exercise performance. The present study aimed to clarify taurine's effect on chronic endurance exercise, especially accumulation of lactic acid (LA), a marker of fatigue and ability of aerobic exercise, and urinary secretion of 3-methylhistidine (3-MH), a marker of muscle breakdown in rats. After exercise blood levels of LA and urinary excretion of 3-MH were significantly increased and this increase was significantly less in those with chronic treatment of taurine. Taurine treatment also significantly decreased fat accumulation and blood levels of cholesterol and triglyceride, which might improve insulin resistance and utilization of fat and glucose. These results indicate taurine treatment is useful for reducing physical fatigue and muscle damage during exercise training in rats, presumably due to antioxidant property and improvement of muscle and cardiac functions by taurine.

Long-term effects of histidine depletion on whole-body protein metabolism in healthy adults

The essentiality of histidine in healthy adults is a controversial topic. To study the potential metabolic effects of a lack of exogenous histidine, four healthy adults consumed a histidine-free diet, with adequate energy and 1.0 g/(kg. d) of an L-amino acid mixture for 48 d. Protein metabolism was monitored every 4 d by using indicator amino acid (L-[1-(13)C]phenylalanine) oxidation (in four subjects) and [(15)N]glycine (in one subject). Urine samples (24-h) were collected for measurement of urea, total nitrogen, creatinine, 3-methylhistidine (3-MH), histidine and beta-alanine. Albumin, transferrin and hematologic concentrations were measured on d 0, 24 and 48. Urinary excretion of nitrogen, urea, creatinine and 3-MH were not affected by the histidine-free diet. However, there was a significant (P < 0.001) linear decline (24-28%) in whole-body protein turnover. Significant (P < 0.05) decreases in albumin (12%), transferrin (17%) and hemoglobin (Hb) (11%) concentrations occurred slowly over the histidine depletion period. The urinary excretion of beta-alanine (an index of carnosine catabolism) generally increased in the smallest subject during the consumption of histidine-free diet. This study demonstrates that a lack of histidine in the diet for a prolonged period resulted in an accommodation of protein turnover and phenylalanine oxidation, measured by the (13)C-phenylalanine indicator amino acid. The extensive metabolic accommodation, together with decreases in Hb, albumin and transferrin during histidine depletion, leaves unresolved the issue of whether histidine is a dietary essential amino acid in healthy adults.

Nitrogen balance of healthy Dutch women before and during pregnancy

BACKGROUND

Experimental studies including longitudinal nitrogen balance studies could provide insight into protein metabolism in pregnancy.

OBJECTIVE

Our aim was to determine the development of nitrogen balance during pregnancy compared with nitrogen balance before pregnancy in women consuming imposed constant diets. We also tracked changes in muscle mass and lean body mass by measuring urinary 3-methylhistidine (3-MeH) and urinary creatinine.

DESIGN

Nitrogen balance was determined over 8 d in 12 healthy Dutch women before pregnancy and at weeks 12, 23, and 34 of gestation. Complete daily diets were supplied during each balance period so that each subject's energy, protein, and macronutrient intakes were similar in amount and composition in all 4 balance periods.

RESULTS

Throughout pregnancy there was no significant change in loss of nitrogen in feces and therefore no change in protein digestibility. The amount of nitrogen excreted in urine in late pregnancy (11.0 +/- 1.4 g/d) was significantly (P < 0.01) less than in early pregnancy (12.6 +/- 1.3 g/d). Nitrogen retention increased toward term, even though energy balance became progressively negative. The difference between the first (-0.4 +/- 1.7 g N/d) and third (1.2 +/- 1.6 g N/d) trimester was significant (P < 0.05). No differences were found in either 3-MeH or creatinine excretion between trimesters.

CONCLUSIONS

These urinary nitrogen excretion and nitrogen retention data show that when the dietary supply remains constant, nitrogen balance increases toward the end of pregnancy, suggesting a more efficient use of dietary protein later in pregnancy. Urinary 3-MeH and creatinine excretion indicated no change in protein metabolism.

Growth hormone improves graft mucosal structure and recipient protein metabolism in rat small bowel transplantation

OBJECTIVE

To observe the effects of recombinant human growth hormone (rhGH) on graft structure and recipient protein metabolism in rat small bowel transplantation (SBT) and total parenteral nutrition (TPN) models.

METHODS

Twenty recipients of rat allogeneic heterotopic small bowel transplants (SD-->Wistar) were divided into two groups (GH group and control group). Both groups were supported by standard TPN. Acute rejection was suppressed with CsA 10 mg x kg(-1) x d(-1) intramuscularly. All rats in the experimental group received subcutaneous rhGH 1 U x kg(-1) x d(-1) after transplantation. Morphological mucosal indices of transplanted gut and metabolic parameters such as body weight, nitrogen balance, urinary 3-methyl histidine excretion and serum albumin of the recipients were compared between two groups.

RESULTS

The application of rhGH promoted graft recovery significantly compared with standard TPN support alone. On postoperative day 14, all morphological indexes of transplanted gut recovered to the preoperative state. Protein metabolism in the recipient was also significantly improved. rhGH decreased the catabolism of protein, accelerated regaining of positive nitrogen balance and corrected hypoalbuminemia.

CONCLUSION

GH is an effective metabolic intervention in SBT. It may promote the structural repair of the graft and correct the metabolic disturbance. It is useful in improving the outcome of clinical SBT.

Qualitative manipulation of amino acid supply during total parenteral nutrition in surgical patients

We investigated whether a qualitative manipulation of amino acid mixture could improve the nutritional status of patients undergoing surgery. Patients received total parenteral nutrition for 2 consecutive 5-day periods. Energy and nitrogen supplies were calculated using a modified Harris-Benedict equation, with an energy-to-nitrogen ratio of 125 kcal/g nitrogen (N). The mean kilocalorie lipids-to-glucose ratio was 35% to 65%. There were 6 patients in the control group and 7 patients in the experimental group. The control group received the same standard amino acid solution (Vintène, Baxter-Clintec, Maurepas, France) for the entire 10 days. The experimental group received the standard solution during the first 5 days but was switched to a more individualized solution during the last 5 days. The second solution was determined from a linear regression performed on day 3 comparing rate of infusion of each amino acid and its plasma variations after 3 hours of infusion with basal values. Amino acids were defined as oversupplied or undersupplied when not within the 95% confidence interval (above or below the curve, respectively). Daily nitrogen balance and urinary excretion of 3-methylhistidine were measured from day 1 to day 10 in all patients. For the patients in whom these measures were made, amino acid variations except those of lysine (11 of 12), ornithine (6 of 12), alanine (5 of 12), arginine (5 of 12), and glutamate (5 of 12) were within the 95% confidence interval. During the second 5-day period, imbalances persisted in the control group but were almost gone in the experimental group. Daily nitrogen balance was not significantly different between groups. However, when expressed as a mean over each period, nitrogen balance was significantly higher during the second period in the experimental group than in the control group: 4.5+/-0.8 g N/d versus 0.2+/-0.7 g N/d, p < .01. The ratio of urinary 3-methylhistidine to creatinine decreased from day 1 to day 10 in both groups. These findings suggest that the relationship between rate of infusion and plasma amino acid variation may offer a rational basis for choosing the most appropriate amino acid mixture for catabolic patients. An appropriate mixture would limit plasma amino acid imbalances and improve nitrogen retention. This therapy must now be tested in a larger population of patients.

Inverse relationship between urinary markers of animal protein intake and blood pressure in Chinese: results from the WHO Cardiovascular Diseases and Alimentary Comparison (CARDIAC) Study

BACKGROUND

This issue of the relationship between animal protein intake and blood pressure (BP) is unsolved. We examined the associations between urinary 3-methylhistidine (3MH) excretion (a biological marker of animal protein intake) and BP in 11 Chinese population samples (Urumqi, Altai, Lhasa, Tulufan, Hetian, Guiyang, Guangzhou, Shanghai, Beijing, Shijiazhuang and Taipei).

METHODS

This was a multi-centre cross-sectional study. In each centre, 100 men and 100 women aged 48-56 years were selected randomly from the general population. 3-methylhistidine in 24-hour (24-h) urine collections was measured by an Amino Acid Analyzer (Hitachi 835, Ibaragi, Japan). The total study sample included 966 men and 1025 women. Subjects who failed to collect complete 24-h urine samples were excluded in data analyses regarding associations between 3MH and BP.

RESULTS

The results showed that: (1) for within-centre analyses of individuals, the 3MH and 3MH to creatinine ratios (3MH:cre) were significantly and negatively associated with BP and hypertension. These associations remained significant after adjustment for age, sex, sodium to potassium ratio, body mass index, calcium and magnesium. The pooled regression coefficients (SE) of systolic blood pressure (SBP) and diastolic blood pressure (DBP) on 3MH were -0.020 (0.01) and -0.018 (0.01), and of SBP and DBP on 3MH:cre were -0.022 (0.01) and -0.016 (0.01), respectively. Subjects with lower 3MH excretion had higher relative risks of hypertension than those who had higher 3MH excretion. (2) In cross-centre analyses, mean SBP and DBP were significantly and negatively associated with the mean 3MH:cre across the 11 population samples (R(2) = 0.56, P < 0.01).

CONCLUSION

The results provide strong evidence that animal protein intake is associated inversely with BP in Chinese populations.

Comparison of carbohydrate and milk-based beverages on muscle damage and glycogen following exercise

This study examined effects of carbohydrate (CHO), milk-based carbohydrate-protein (CHO-PRO), or placebo (P) beverages on glycogen resynthesis, muscle damage, inflammation, and muscle function following eccentric resistance exercise. Untrained males performed a cycling exercise to reduce muscle glycogen 12 hours prior to performance of 100 eccentric quadriceps contractions at 120% of 1-RM (day 1) and drank CHO (n = 8), CHO-PRO (n = 9; 5 kcal/kg), or P (n = 9) immediately and 2 hours post-exercise. At 3 hours post-eccentric exercise, serum insulin was four times higher for CHO-PRO and CHO than P (p < .05). Serum creatine kinase (CK) increased for all groups in the 6 hours post-eccentric exercise (p < .01), with the increase tending to be lowest for CHO-PRO (p < .08) during this period. Glycogen was low post-exercise (33+/-3.7 mmol/kg ww), increased 225% at 24 hours, and tripled by 72 hours, with no group differences. The eccentric exercise increased muscle protein breakdown as indicated by urinary 3-methylhistidine and increased IL-6 with no effect of beverage. Quadriceps isokinetic peak torque was depressed similarly for all groups by 24% 24 hours post-exercise and remained 21% lower at 72 hours (p < .01). In summary, there were no influences of any post-exercise beverage on muscle glycogen replacement, inflammation, or muscle function.

Effect of glutamine supplementation combined with resistance training in young adults

The purpose of this study was to assess the effect of oral glutamine supplementation combined with resistance training in young adults. A group of 31 subjects, aged 18-24 years, were randomly allocated to groups (double blind) to receive either glutamine (0.9 g x kg lean tissue mass(-1) x day(-1); n = 17) or a placebo (0.9 g maltodextrin x kg lean tissue mass(-1) x day(-1); n = 14 during 6 weeks of total body resistance training. Exercises were performed for four to five sets of 6-12 repetitions at intensities ranging from 60% to 90% 1 repetition maximum (1 RM). Before and after training, measurements were taken of 1 RM squat and bench press strength, peak knee extension torque (using an isokinetic dynamometer), lean tissue mass (dual energy X-ray absorptiometry) and muscle protein degradation (urinary 3-methylhistidine by high performance liquid chromatography). Repeated measures ANOVA showed that strength, torque, lean tissue mass and 3-methylhistidine increased with training (P < 0.05), with no significant difference between groups. Both groups increased their 1 RM squat by approximately 30% and 1 RM bench press by approximately 14%. The glutamine group showed increases of 6% for knee extension torque, 2% for lean tissue mass and 41% for urinary levels of 3-methylhistidine. The placebo group increased knee extension torque by 5%, lean tissue mass by 1.7% and 3-methylhistidine by 56%. We conclude that glutamine supplementation during resistance training has no significant effect on muscle performance, body composition or muscle protein degradation in young healthy adults.

Ntau-methylhistidine excretion is a valid index of myofibrillar protein breakdown in the guineapig (Cavia porcellus)

The recovery of radioactivity in the urine of guineapigs following a bolus intravenous dose of chromatographically pure 14C-Ntau-methylhistidine was measured in order to test whether the excretion of Ntau-methylhistidine (Ntau-MH) is a valid index of myofibrillar protein breakdown in these animals. Four male and four female guineapigs were dosed and after 7 days, 91.65+/-2.82% and 3.58+/-0.91% of injected radioactivity was recovered in the excreta and tissues, respectively. The average total recovery of 95.2+/-3.0% was not significantly different from 100%. Male guineapigs excreted the radioactivity more slowly than females (70% of the dose excreted within 74 h vs 39 h, respectively) but cumulative excretion at 7 days was the same for each sex. Chromatographic analysis of the urine showed almost all of the radioactivity to be associated with a single peak corresponding to Ntau-MH, indicating a lack of significant metabolism. These data show that although the clearance of 14C-Ntau-MH is slower than in rats or humans the urinary excretion of Ntau-MH is a valid index for myofibrillar protein degradation in the guineapig.

A biochemical analysis of people with chronic fatigue who have Irlen Syndrome: speculation concerning immune system dysfunction

This study investigated the biological basis of visual processing disabilities in adults with Chronic Fatigue Syndrome. The study involved 61 adults with symptoms of Chronic Fatigue Syndrome who were screened for visual processing problems (Irlen Syndrome) and divided into two groups according to the severity of symptoms of Irlen Syndrome. Significant variations were identified in blood lipids and urine amino and organic acids of the two groups, which may be indicative of activation of the immune system due to some infective agent. It was suggested that metabolic profiling may help the development of more valid diagnostic categories and allow more investigation of immune system dysfunction as a possible causal factor in a range of learning and behaviour disorders.

Effect of pentoxifylline on nitrogen balance and 3-methylhistidine excretion in parenterally fed endotoxemic rats

Pentoxifylline interrupts early gene activation for tumor necrosis factor, interleukin-1, and interleukin-6 production and improves survival from experimental sepsis. These effects can alter nitrogen loss during critical illness. To determine the dose-dependent influence of pentoxifylline on nitrogen loss, 44 male Sprague-Dawley rats (220 to 265 g) were randomized to receive parenteral nutrition only (PN), PN plus continuous infusion of Escherichia coli 026:B6 lipopolysaccharide (LPS) at 9 mg x kg(-1) x d(-1), or PN plus LPS plus a continuous infusion of pentoxifylline at either 25 (PEN25) or 100 mg x kg(-1) x d(-1) (PEN100) for 48 h. Before randomization, all animals underwent intravenous cannulation and 40 h of PN adaptation. All animals received isocaloric, isonitrogenous PN (160 kcal x kg(-1) x d(-1) and 1.0 gN x kg(-1) x d(-1)) and were kept nil per os except for water ad libitum. Administration of LPS significantly worsened nitrogen balance for all three groups compared with PN control; however, pentoxifylline only modestly improved nitrogen balance compared with LPS (206 +/- 255, -497 +/- 331, -332 +/- 329, and -310 +/- 383 mg/48hr for the PN, LPS, PEN25, and PEN100 groups, respectively; P < 0.001). Pentoxifylline did not significantly change 3-methylhistidine urinary excretion compared with LPS (573 +/- 180, 705 +/- 156, 780 +/- 326, and 683 +/- 266 microg/48 h for the PN, LPS, PEN25, and PEN100 groups, respectively, P not significant). Pentoxifylline, given in therapeutic doses after an endotoxin challenge, modestly, but not significantly, improved nitrogen balance. Urinary 3-methylhistidine excretion was not influenced by pentoxifylline. A dose-dependent effect by pentoxifylline on these markers was not evident.

Apoptosis of muscle cells causes weight loss prior to impairment of DNA synthesis in tumor-bearing rabbits

The mechanism of weight loss induced by the growth of malignant tumors is still unknown. We investigated it by focusing on apoptosis of skeletal muscle. VX2-tumor was implanted into rabbits and the apoptotic index (AI) of skeletal muscle was measured by in situ end-labeling assay. Plasma of the tumor-bearing rabbits was perfused repeatedly through non-coated charcoal resin. The AI reached 54.6% early after tumor implantation, when weight loss amounted to an 18% decrease in lean body mass (LBM) without change in muscle DNA synthesis or urinary 3-methylhistidine / creatinine ratio (3-MH / Cr). When the decrease of LBM reached 30%, DNA synthesis was decreased by 48% and 3-MH / Cr was increased by 104%, whereas AI was only 4.7%. The plasma perfusion did not prevent apoptosis in muscle, but improved LBM, DNA synthesis, and 3-MH / Cr. There may be two mechanisms of muscle depletion during the tumor growth: apoptosis in the early stage and metabolic abnormalities in muscle in the late stage.

Effects of corticosterone on connectin content and protein breakdown in rat skeletal muscle

We examined the effects of a glucocorticoid, corticosterone, on calpain activity, connectin content and protein breakdown in rat muscle. The results indicated that calpain activity was increased by corticosterone and thus breakdown of connectin was stimulated followed by increased breakdown of skeletal muscle protein.

Short communication: effects of monensin on 3-methylhistidine excretion in transition dairy cows

Urinary 3 methyl-histidine excretion was measured in high yielding dairy cows between 10 and 3 d precalving and between 3 and 9 d postcalving. Cows received a sodium monensin controlled-release capsule or a placebo 3 wk before calving. Monensin did not affect urinary 3 methyl-histidine. Average urinary 3 methyl-histidine excretion was significantly higher postcalving (4.11 mmol d(-1)) than precalving (2.48 mmol d(-1)). This increase is assumed to be predominantly due to the negative nitrogen balance in the postcalving period caused by insufficient nutrient intake to meet nutrient requirements, which necessitates catabolism of mainly myofibrillar protein.