Markers Of Protein Breakdown Research Articles

Acute effects of oral mesna administration on the full amino acid profile and 3-methylhistidine: secondary results from the CYLOB dose-finding study

Plasma total cysteine (tCys) is strongly associated with fat mass in humans. Mesna lowers plasma tCys in a dose-dependent manner, but it is not known whether it interferes with metabolism of other amino acids or protein. In this Phase-1 study, we show that a single dose of mesna administered at 400, 800, 1200 or 1600 mg to 6–7 individuals per dose only slightly affects amino acid profiles, with increases in plasma valine across dose levels. There were no effects of mesna on 3-methylhistidine, a marker of protein breakdown.

Alcohol Worsens Cancer Cachexia and Anabolic Signaling in C26 Tumor Bearing Mice

Cancer cachexia results in a loss of skeletal muscle mass, leading to increased morbidity and mortality. Similarly, chronic alcohol consumption leads to skeletal muscle loss and dysfunction. It is unknown, whether prior alcohol intake or its continued use after cancer establishment, exacerbates cancer cachexia. Anabolic pathways are central to the maintenance of muscle mass and are notoriously decreased by alcohol intake. Among these pathways, the mTORC1 pathway and subsequent rates of protein synthesis are of central importance to the maintenance of muscle health. Purpose To determine if prior or concurrent alcohol consumption worsens skeletal muscle anabolic signaling (i.e. puromycin and mTOR pathway) during cancer cachexia. Methods Male CD2F1 mice (n=42), 12-weeks old, were randomized into 6 groups (n=6-8/gr): control (CON), control-cancer (CON-C), prior EtOH (PRIOR), prior EtOH-cancer (PRIOR-C), continuous EtOH (EtOH), and continuous EtOH w/cancer (EtOH-C). Mice were acclimated to a control liquid diet, after which the EtOH groups transitioned to the Lieber DeCarli EtOH diet at 20% kcal EtOH for 6 weeks. At week 7, PRIOR mice weaned off EtOH and remained on the control diet until sacrifice. Also at week 7, cancer mice were injected subcutaneously on the right flank with C26 colon carcinoma cells (1x106 cells) and consumed their assigned diet for 14 days while tumors developed. After a 4-hour fast, puromycin was injected and 30 minutes later the gastrocnemius (GAS) was excised. GAS protein was isolated and Western Blots performed. Data were analyzed via 1-way ANOVA with post hoc testing when appropriate. Data are presented relative to CON (set to 100%) as mean ± SE, with protein expression normalized either to ponceau staining or total levels of the given protein. Results Body weight at sacrifice was lower in the PRIOR-C and EtOH-C (p<0.05) indicating an alcohol effect. Tumor weight and tibia length were not different between groups. GAS weight was reduced by cancer in all groups, and most notably in PRIOR-C and EtOH-C mice (p<0.001). Protein synthesis, assessed by puromycin, decreased in all cancer groups, with a ~70% reduction in PRIOR-C and ~82% reduction in EtOH-C relative to CON. Similarly, phosphorylation of S6K1 Thr389, rpS6 Ser240/244 and Ser235/236 was significantly reduced in PRIOR-C and EtOH-C relative to CON (p<0.05), indicating a greater reduction in these markers of mTORC1 activity with alcohol intake. Surprisingly, no differences in 4E-BP1 Ser65, mTOR Ser2448, or mTOR Ser2481 were observed across groups. PRAS40 Thr246 was increased by cancer alone as well as in EtOH-C mice (35% vs. CON) (p<0.05). Increases in eEF2 Thr56 were also detected in PRIOR-C (50%) and EtOH-C (83%) (p<0.05), possibly indicating impaired peptide chain elongation. No changes were noted in markers of protein breakdown including ubiquitinated proteins, and autophagic proteins ULK1 Ser757 and LC3B-II/I. Conclusions The intake of alcohol both prior to, and during tumor development lead to greater decreases in GAS weight, protein synthesis and several markers of mTORC1 activity indicating that alcohol significantly worsened and accelerated the development of cancer cachexia.

Overexpression of the vitamin D receptor (VDR) induces skeletal muscle hypertrophy

ObjectiveThe Vitamin D receptor (VDR) has been positively associated with skeletal muscle mass, function and regeneration. Mechanistic studies have focused on the loss of the receptor, with in vivo whole-body knockout models demonstrating reduced myofibre size and function and impaired muscle development. To understand the mechanistic role upregulation of the VDR elicits in muscle mass/health, we studied the impact of VDR over-expression (OE) in vivo before exploring the importance of VDR expression upon muscle hypertrophy in humans. MethodsWistar rats underwent in vivo electrotransfer (IVE) to overexpress the VDR in the Tibialis anterior (TA) muscle for 10 days, before comprehensive physiological and metabolic profiling to characterise the influence of VDR-OE on muscle protein synthesis (MPS), anabolic signalling and satellite cell activity. Stable isotope tracer (D2O) techniques were used to assess sub-fraction protein synthesis, alongside RNA-Seq analysis. Finally, human participants underwent 20 wks of resistance exercise training, with body composition and transcriptomic analysis. ResultsMuscle VDR-OE yielded total protein and RNA accretion, manifesting in increased myofibre area, i.e., hypertrophy. The observed increases in MPS were associated with enhanced anabolic signalling, reflecting translational efficiency (e.g., mammalian target of rapamycin (mTOR-signalling), with no effects upon protein breakdown markers being observed. Additionally, RNA-Seq illustrated marked extracellular matrix (ECM) remodelling, while satellite cell content, markers of proliferation and associated cell-cycled related gene-sets were upregulated. Finally, induction of VDR mRNA correlated with muscle hypertrophy in humans following long-term resistance exercise type training. ConclusionVDR-OE stimulates muscle hypertrophy ostensibly via heightened protein synthesis, translational efficiency, ribosomal expansion and upregulation of ECM remodelling-related gene-sets. Furthermore, VDR expression is a robust marker of the hypertrophic response to resistance exercise in humans. The VDR is a viable target of muscle maintenance through testable Vitamin D molecules, as active molecules and analogues.

Muscle Glycogen Content during Endurance Training under Low Energy Availability

The present study investigated the effects of three consecutive days of endurance training under conditions of low energy availability (LEA) on the muscle glycogen content, muscle damage markers, endocrine regulation, and endurance capacity in male runners. Seven male long-distance runners (19.9 ± 1.1 yr, 175.6 ± 4.7 cm, 61.4 ± 5.3 kg, maximal oxygen uptake [V˙O2max]: 67.5 ± 4.3 mL·kg·min) completed two trials consisting of three consecutive days of endurance training under LEA (18.9 ± 1.9 kcal·kg FFM·d) or normal energy availability (NEA) (52.9 ± 5.0 kcal·kg FFM·d). The order of the two trials was randomized, with a 2-wk interval between trials. The endurance training consisted of 75 min of treadmill running at 70% of V˙O2max. Muscle glycogen content, respiratory gas variables, and blood and urine variables were measured in the morning for three consecutive days of training (days 1-3) and on the following morning after training (day 4). As an indication of endurance capacity, time to exhaustion at 19.0 ± 0.8 km·h to elicit 90% of V˙O2max was evaluated on day 4. During the training period, body weight, fat-free mass, and skeletal muscle volume were significantly reduced in LEA (P = 0.02 for body weight and skeletal muscle volume, P = 0.01 for fat-free mass). Additionally, muscle glycogen content was significantly reduced in LEA (~30%, P < 0.001), with significantly lower values than those in NEA (P < 0.001). Time to exhaustion was not significantly different between the two trials (~20 min, P = 0.39). Three consecutive days of endurance training under LEA decreased muscle glycogen content with lowered body weight. However, endurance capacity was not significantly impaired.

Acute estradiol treatment reduces skeletal muscle protein breakdown markers in early- but not late-postmenopausal women

ObjectivesMenopause and decline in estradiol (E2) may contribute to sarcopenia (i.e., age-related decline in muscle mass and strength) in women. E2 may directly impact skeletal muscle protein breakdown via estrogen receptor (ER) signaling, primarily ERα. It is not yet known whether: 1) E2 regulates pathways of skeletal muscle protein breakdown; 2) E2-mediated changes in protein breakdown markers are associated with ERα activation and insulin sensitivity; and 3) the effects of E2 on protein breakdown markers differ by increasing time since menopause. Study designWe studied 27 women who were ≤6 years past menopause (early postmenopausal, EPM; n = 13) or ≥10 years past menopause (late postmenopausal, LPM; n = 14). Fasted skeletal muscle samples were collected following 1 week of transdermal E2 or placebo treatment in a randomized cross-over design. Main outcome measuresWe analyzed for cytosolic protein content of the: 1) structural proteins myosin heavy chain (MHC) and tropomyosin; and 2) protein regulatory markers: protein kinase B (Akt), muscle-specific ring finger protein1 (MuRF1), atrogin1, and forkhead box O3 (FOXO3) using Western blot. ResultsIn response to acute E2, FOXO3 activation (dephosphorylation) and MuRF1 protein expression decreased in EPM but increased in LPM women (p < 0.05). ERα activation was not associated with these protein breakdown markers, but FOXO3 activation tended to be inversely correlated (r = −0.318, p = 0.065) to insulin sensitivity. ConclusionsThese preliminary studies suggest the effects of E2 on skeletal muscle protein breakdown markers were dependent on time since menopause, which is consistent with our previous study on insulin sensitivity.

Effects of 3-hydroxybutyrate and free fatty acids on muscle protein kinetics and signaling during LPS-induced inflammation in humans: anticatabolic impact of ketone bodies

Acute inflammation, and subsequent release of bacterial products (e.g. LPS), inflammatory cytokines, and stress hormones, is catabolic, and the loss of lean body mass predicts morbidity and mortality. Lipid intermediates may reduce protein loss, but the roles of free fatty acids (FFAs) and ketone bodies during acute inflammation are unclear. We aimed to test whether infusions of 3-hydroxybutyrate (3OHB), FFAs, and saline reduce protein catabolism during exposure to LPS and Acipimox (to restrict and control endogenous lipolysis). A total of 10 healthy male subjects were randomly tested 3 times, with: 1) LPS, Acipimox (Olbetam) and saline, 2) LPS, Acipimox, and nonesterified fatty acids (Intralipid), and 3) LPS, Acipimox, and 3OHB, during a 5-h basal period and a 2-h hyperinsulinemic, euglycemic clamp. Labeled phenylalanine, tyrosine, and urea tracers were used to estimate protein kinetics, and muscle biopsies were taken for Western blot analysis of protein metabolic signaling. 3OHB infusion increased 3OHB concentrations (P<0.0005) to 3.5 mM and decreased whole-body phenylalanine-to-tyrosine degradation. Basal and insulin-stimulated net forearm phenylalanine release decreased by >70% (P<0.005), with both appearance and phenylalanine disappearance being profoundly decreased. Phosphorylation of eukaryotic initiation factor 2α at Ser51 was increased in skeletal muscle, and S6 kinase phosphorylation at Ser235/236 tended (P=0.074) to be decreased with 3OHB infusion (suggesting inhibition of protein synthesis), whereas no detectable effects were seen on markers of protein breakdown. Lipid infusion did not affect phenylalanine kinetics, and insulin sensitivity was unaffected by interventions. During acute inflammation, 3OHB has potent anticatabolic actions in muscle and at the whole-body level; in muscle, reduction of protein breakdown overrides inhibition of synthesis. This trial was registered at clinicaltrials.gov as NCT01752348.

Protein imbalance in the development of skeletal muscle wasting in tumour-bearing mice.

BackgroundCancer cachexia occurs in approximately 80% of cancer patients and is a key contributor to cancer‐related death. The mechanisms controlling development of tumour‐induced muscle wasting are not fully elucidated. Specifically, the progression and development of cancer cachexia are underexplored. Therefore, we examined skeletal muscle protein turnover throughout the development of cancer cachexia in tumour‐bearing mice.MethodsLewis lung carcinoma (LLC) was injected into the hind flank of C57BL6/J mice at 8 weeks age with tumour allowed to develop for 1, 2, 3, or 4 weeks and compared with PBS injected control. Muscle size was measured by cross‐sectional area analysis of haematoxylin and eosin stained tibialis anterior muscle. 2H2O was used to assess protein synthesis throughout the development of cancer cachexia. Immunoblot and RT‐qPCR were used to measure regulators of protein turnover. TUNEL staining was utilized to measure apoptotic nuclei. LLC conditioned media (LCM) treatment of C2C12 myotubes was used to analyse cancer cachexia in vitro.ResultsMuscle cross‐sectional area decreased ~40% 4 weeks following tumour implantation. Myogenic signalling was suppressed in tumour‐bearing mice as soon as 1 week following tumour implantation, including lower mRNA contents of Pax7, MyoD, CyclinD1, and Myogenin, when compared with control animals. AchRδ and AchRε mRNA contents were down‐regulated by ~50% 3 weeks following tumour implantation. Mixed fractional synthesis rate protein synthesis was ~40% lower in 4 week tumour‐bearing mice when compared with PBS controls. Protein ubiquitination was elevated by ~50% 4 weeks after tumour implantation. Moreover, there was an increase in autophagy machinery after 4 weeks of tumour growth. Finally, ERK and p38 MAPK phosphorylations were fourfold and threefold greater than control muscle 4 weeks following tumour implantation, respectively. Inhibition of p38 MAPK, but not ERK MAPK, in vitro partially rescued LCM‐induced loss of myotube diameter.ConclusionsOur findings work towards understanding the pathophysiological signalling in skeletal muscle in the initial development of cancer cachexia. Shortly following the onset of the tumour‐bearing state alterations in myogenic regulatory factors are apparent, suggesting early onset alterations in the capacity for myogenic induction. Cancer cachexia presents with a combination of a loss of protein synthesis and increased markers of protein breakdown, specifically in the ubiquitin‐proteasome system. Also, p38 MAPK may be a potential therapeutic target to combat cancer cachexia via a p38‐FOX01‐atrogene‐ubiquitin‐proteasome mechanism.

The Effects of Fortetropin Supplementation on Body Composition, Strength, and Power in Humans and Mechanism of Action in a Rodent Model

Objective: The purpose of this study was to investigate the effects of Fortetropin on skeletal muscle growth and strength in resistance-trained individuals and to investigate the anabolic and catabolic signaling effects using human and rodent models.Methods: In the rodent model, male Wistar rats (250 g) were gavage fed with either 1.2 ml of tap water control (CTL) or 0.26 g Fortetropin for 8 days. Then rats participated in a unilateral plantarflexion exercise bout. Nonexercised and exercised limbs were harvested at 180 minutes following and analyzed for gene and protein expression relative to mammalian target of rapamycin (mTOR) and ubiquitin signaling. For the human model, 45 (of whom 37 completed the study), resistance-trained college-aged males were divided equally into 3 groups receiving a placebo macronutrient matched control, 6.6 or 19.8 g of Fortetropin supplementation during 12 weeks of resistance training. Lean mass, muscle thickness, and lower and upper body strength were measured before and after 12 weeks of training.Results: The human study results indicated a Group × Time effect (p ≤ 0.05) for lean mass in which the 6.6 g (+1.7 kg) and 19.8 g (+1.68 kg) but not placebo (+0.6 kg) groups increased lean mass. Similarly, there was a Group × Time effect for muscle thickness (p ≤ 0.05), which increased in the experimental groups only. All groups increased equally in bench press and leg press strength. In the rodent model, a main effect for exercise (p ≤ 0.05) in which the control plus exercise but not Fortetropin plus exercise increased both ubiquitin monomer protein expression and polyubiquitination. mTOR signaling was elevated to a greater extent in the Fortetropin exercising conditions as indicated by greater phosphorylation status of 4EBP1, rp6, and p70S6K for both exercising conditions.Conclusions: Fortetropin supplementation increases lean body mass (LBM) and decreases markers of protein breakdown while simultaneously increasing mTOR signaling.

Acute environmental hypoxia induces LC3 lipidation in a genotype‐dependent manner

Hypoxia-induced muscle wasting is a phenomenon often described with prolonged stays at high altitude, which has been attributed to altered protein metabolism. We hypothesized that acute normobaric hypoxia would induce a negative net protein balance by repressing anabolic and activating proteolytic signaling pathways at rest and postexercise and that those changes could be partially genetically determined. Eleven monozygotic twins participated in an experimental trial in normoxia and hypoxia (10.7% O2). Muscle biopsy samples were obtained before and after a 20-min moderate cycling exercise. In hypoxia at rest, autophagic flux was increased, as indicated by an increased microtubule-associated protein 1 light chain 3 type II/I (LC3-II/I) ratio (+25%) and LC3-II expression (+60%) and decreased p62/SQSTM1 expression (-25%; P<0.05), whereas exercise reversed those changes to a level similar to that with normoxia except for p62/SQSTM1, which was further decreased (P<0.05). Hypoxia also increased Bnip3 (+34%) and MAFbx (+18%) mRNA levels as well as REDD1 expression (+439%) and AMP-activated protein kinase phosphorylation (+22%; P<0.05). Among the molecular responses to hypoxia and/or exercise, high monozygotic similarity was found for REDD1, LC3-II, and LC3-II/I (P<0.05). Our results indicate that environmental hypoxia modulates protein metabolism at rest and after moderate exercise by primarily increasing markers of protein breakdown and, more specifically, markers of the autophagy-lysosomal system, with a modest genetic contribution.

Dose-dependent effects of leucine supplementation on preservation of muscle mass in cancer cachectic mice

Cancer cachexia, which is characterized by muscle wasting, is associated with increased morbidity and mortality. Because muscle protein synthesis may be increased and protein breakdown reduced by leucine supplementation, we used the C26 tumor-bearing cachectic mouse model to assess the effects of dietary supplementation with leucine on muscle weight and the markers of muscle protein breakdown (mRNA of atrogin and murf). Male CD2F1 mice were subcutaneously inoculated with tumor cells (tumor-bearing mice; TB) or were sham injected (control; C). They were fed standard diets or diets supplemented with leucine [1 gr (TB1Leu) or 8 gr (TB8Leu) supplemented leucine per kg feed]; TB and C received 8.7% Leu/g protein, TB1Leu received 9.6% Leu/g protein and TB8Leu received 14.6 Leu/g protein. After 21 days, the following were determined: body weights, plasma amino-acid concentrations, tumor size and muscle mass of the gastrocnemius (mG), tibialis anterior (mTA), extensor digitorum longus (mEDL) and soleus (mS) muscles. In tumor-bearing (TB) mice, carcass and skeletal muscle masses decreased, and levels of atrogin and murf mRNA in the mEDL increased. Muscle-mass loss was counteracted dose-dependently by leucine supplementation: relative to TB, the mass of the mG was +23% in TB8Leu, and +22% in mTA (p<0.05). However, leucine supplementation did not change atrogin and murf mRNA levels. Total plasma amino acid concentrations increased in TB, especially for taurine, lysine, arginine and alanine (p<0.05). Leucine supplementation attenuated the increase in total plasma amino-acid concentrations (p<0.05). Irrespective of changes in muscle protein breakdown markers, leucine supplementation reduced muscle wasting in tumor-bearing cachectic mice and attenuated changes in plasma amino acids.

Little change in markers of protein breakdown and oxidative stress in humans in immobilization-induced skeletal muscle atrophy

A number of studies in rodents suggest that disuse atrophy results from a large increase in proteolysis affected by, or accompanying, increased oxidative stress. Little information is available, however, about the effects of immobilization on markers of muscle protein breakdown and oxidative stress in humans. Therefore, the purpose of this investigation was to measure markers of breakdown or oxidative stress in subjects who underwent 14 days of knee-brace-mediated immobilization. Vastus lateralis samples taken from 21 young subjects before, and 2 days and 14 days after, single leg immobilization were measured for ubiquitin-protein conjugates, caspase 3/7 activity, the 14-kDa caspase-3 cleaved actin fragment, 4-hydroxy-2-nonenal (4-HNE) adducts, and protein carbonyls. Quadriceps cross-sectional area decreased by 5.7% +/- 1.1% (p < 0.0001) following immobilization. Ubiquitin-protein conjugates were elevated at 2 days of immobilization (12%, p < 0.05) but were not different from baseline at 14 days. Levels of the 14-kDa actin fragment and caspase 3/7 activity did not change over the immobilization period. The oxidative stress markers, 4-HNE adducts and protein carbonyls, did not change at any time point. These static measures of breakdown and oxidative modification suggest that a small increase in protein ubiquitination occurs early (2 days), but elevations in ubiquitinated or oxidatively modified proteins are not sustained during the later phase (14 days) of uncomplicated disuse atrophy in humans, suggesting that these pathways are not playing a major role in simple disuse-induced atrophic loss of protein mass.

Lack of Functional Benefit with Glutamine versus Placebo in Duchenne Muscular Dystrophy: A Randomized Crossover Trial

BackgroundOral glutamine decreases whole body protein breakdown in Duchenne muscular dystrophy (DMD). We evaluated the functional benefit of 4 months oral glutamine in DMD.Methodology/Principal Findings30 ambulant DMD boys were included in this double-blind, randomized crossover trial with 2 intervention periods: glutamine (0.5 g/kg/d) and placebo, 4 months each, separated by a 1-month wash-out, at 3 outpatient clinical investigation centers in France. Functional benefit was tested by comparing glutamine versus placebo on change in walking speed at 4 months. Secondary outcome measures were: 2-minute walk test, work, power, muscle mass (urinary creatinine), markers of myofibrillar protein breakdown (urinary 3-methyl-histidine/creatinine), serum creatine phospho-kinase, body composition (fat free mass, fat mass percentage), safety and oral nutrient intake. There was no improvement in the primary end point (walking speed) or in secondary measures of muscle function (2-minute walk test, work, power) in the glutamine group compared with placebo. However, subjects receiving glutamine or placebo showed no deterioration in functional measures over the course of the 9-month trial. No differences in muscle mass, markers of protein breakdown or serum creatine phosho-kinase were observed, except for a blunted increase in fat free mass in the glutamine group which led to a greater increase in fat mass percentage. Glutamine was safe and well-tolerated.ConclusionsThis trial did not identify additional benefit of 4 months oral glutamine over placebo on muscle mass or function in ambulatory DMD boys. Although apparently safe, current data cannot support routine supplementation in this population as a whole, until further research proves otherwise.Trial RegistrationClinicalTrials.gov NCT00296621

Prophylactic Supplementation Of A Nano-sized Silica Mineral Antioxidant Complex On Changes In Clinical Safety Parameters And Body Water.

A nano-sized silica mineral antioxidant complex (MIC) is purported to alter cellular chemistry kinetics by delivering reduced hydrogen ions to the cell and reducing blood lactate levels. Further, the chemical structure of MIC supports osmotic traits that may impact levels of body water. PURPOSE: This study examined the effects of 7 days of prophylactic MIC supplementation on changes in clinical safety parameters and body water. METHODS: On three occasions, fifteen males (23.6 3.7 yrs, 180 8 cm, 85 11 kg, 16 5%) were tested using identical procedures under a control (CON), rice flour placebo (PLA) and microhydrin (MIC) condition. PLA and MIC supplementation was done in a prophylactic fashion over a seven day period (4 × 250 mg capsules/day). After controlling for diet and exercise habits, participants arrived fasted and donated a blood sample before and after supplementation for determination of serum and whole blood clinical safety markers. Total body (TBW), extracellular (ECW) and intracellular (ICW) water measurements using bioelectrical impedance spectroscopy were taken before and after supplementation and before and after a peak VO2 test. Repeated measures (2 × 3) ANOVA were completed on all variables using a p-value of 0.05. RESULTS: No significant changes (p>0.05) were found for any component of the lipid and metabolic panels, kidney/liver enzymes, markers of protein breakdown and complete blood counts. Supplementation resulted in no change in TBW (p=0.43), ECW (p=0.65) and ICW (p=0.38) after each condition. Similarly, no significant group x time interactions were found for ECW (p=0.19), although TBW (p=0.09) and ICW (p=0.052) tended to change. Significant time effects for TBW (p<0.01) and ICW (p<0.001) were found. Within-group analysis of post-exercise body water revealed significant increases in ICW in PLA (+0.51 L; p<0.005) and MIC (+0.43 L; p<0.01) along with a significant increase in TBW for MIC (+0.59 L; p<0.01). CONCLUSION: Clinical safety markers did not change after seven days of prophylactic MIC supplementation and was well tolerated. MIC supplementation did not stimulate any changes in body water compartments, while immediate increases in TBW and ICW after maximal exercise were found. Post-exercise ICW levels increased in PLA and MIC while TBW only increased in MIC. Supported by RBC Life Sciences

Asymmetric and symmetric dimethylarginines: metabolism and role in severe sepsis

Asymmetric dimethylarginines (ADMA) and symmetric dimethylarginines (SDMA) are markers of protein breakdown; both compete with arginine for cellular transport and are excreted in urine. In addition, ADMA is a nonselective inhibitor of NO synthase, and is also metabolized by dimethylarginine-dimethylaminohydrolase (DDAH), a specific hydrolase whose activity in stress is controversial [1]. While the ADMA increase is associated with adverse events in many critical conditions, little attention has been focused on the role of SDMA [2].

Gene and protein expression associated with protein synthesis and breakdown in paraplegic skeletal muscle

Spinal cord injury reduces the rate of skeletal muscle protein synthesis and increases protein breakdown, resulting in rapid muscle loss. The purpose of this study was to determine whether long-term paraplegia would eventually result in a downregulation of muscle mRNA and protein expression associated with both protein synthesis and breakdown. After 10 weeks of spinal cord transection, soleus muscle from 12 rats (6 sham-control, 6 paraplegic) was studied for mRNAs and proteins associated with protein synthesis and breakdown using real-time polymerase chain reaction and immunoblotting techniques. Protein kinase B (PKB/Akt), ribosomal S6 kinase 1 (S6K1), and myogenin mRNA were downregulated, whereas muscle ring finger 1 (MuRF1) and phospho-forkhead transcription factor 4 (FoxO4) protein were increased in paraplegic rats. We conclude that gene and protein expression of pathways associated with protein synthesis are reduced, whereas some markers of protein breakdown remain elevated following chronic paraplegia. Clinical interventions designed to increase muscle protein synthesis may be helpful in preventing excessive muscle loss during long-term paraplegia.

Associated loss of fat-free mass and bone mineral density in chronic obstructive pulmonary disease.

We hypothesized that in patients with chronic obstructive pulmonary disease, loss of fat-free mass (FFM) and loss of bone mineral density (BMD) were related to (1) each other and may be clinically inapparent, (2) urinary markers of cellular and bone collagen protein breakdown, and (3) severity of lung disease. Eight-one patients and 38 healthy subjects underwent dual-energy X-ray absorptiometry to determine body composition and BMD. Urinary protein breakdown markers, inflammatory mediators, and their soluble receptors were determined. Thirty-three patients had a low fat-free mass index (kg/m(2)), 17 of whom had a normal body mass index. Thirty-two percent of patients (13% of healthy subjects) had osteoporosis at the hip or lumbar spine. The marker of cellular protein breakdown was elevated in patients and related to lung disease severity and body composition. The marker of bone collagen breakdown was greater in patients with osteoporosis. Inflammatory mediators were elevated in patients. Loss of FFM and loss of BMD were related, occurred commonly, and could be subclinical in patients with chronic obstructive pulmonary disease. Loss of both was greatest with severe lung disease. Increased excretion of cellular and bone collagen protein breakdown products in those with low FFM and BMD indicates a protein catabolic state in these patients.

Pulmonary Function, Body Composition, and Protein Catabolism in Adults with Cystic Fibrosis

Increased survival in cystic fibrosis (CF) is associated with bone thinning and fat-free mass (FFM) loss. We hypothesized that the severity of lung disease would be associated with increased protein catabolism and systemic inflammatory status in clinically stable patients. Forty adults with CF and 22 age-matched healthy subjects were studied. Body composition was determined by dual-energy X-ray absorptiometry. Urinary pseudouridine (PSU), a marker of protein breakdown, and cross-linked N-telopeptides of type I collagen (NTx), a marker of bone connective tissue breakdown, serum tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and their soluble receptors were measured. A 3-d food intake diary revealed 21 patients had a low energy intake. Excretion of PSU (p = 0.019) and NTx (p < 0.01) was increased in patients and was inversely related to FEV(1); PSU (r = - 0.53, p = 0.001) and NTx (r = - 0.43, p < 0.01). Increased excretion of PSU and NTx (p < 0.05 for both) was also related to a low FFM. All inflammatory mediators were greater in patients and were related to PSU and NTx. Clinically stable adults were catabolic with both cellular and connective tissue protein breakdown, which was related to lung disease severity, systemic inflammation, and body composition.