A rapid, sensitive method for the determination of 3-methylhistidine levels in urine and plasma using high-pressure liquid chromatography

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).

Quantification of Nτ -Methylhistidine and Nπ-Methylhistidine in Chicken Plasma by Liquid Chromatography-Tandem Mass Spectrometry

The concentration of N^τ-methylhistidine in plasma provides an index of skeletal muscle protein breakdown. This study aimed to establish a quantitative method for measuring the concentrations of N^τ-methylhistidine and its isomer N^π-methylhistidine in chicken plasma, using liquid chromatography-tandem mass spectrometry with stable isotope dilution analysis. The acceptable linear ranges of detection were 1.56-50.00 μmol/L for N^τ-methylhistidine and 0.78-25.00 μmol/L for N^π-methylhistidine. The proposed method detected changes in the plasma levels of N^τ-methylhistidine and N^π-methylhistidine in response to fasting and re-feeding. These results suggest that the method developed in this study can be used for the simultaneous measurement of N^τ-methylhistidine and N^π-methylhistidine in chicken plasma.

Cost-Effective Simultaneous Determination of τ- and π-Methylhistidine in Dairy Bovine Plasma from Large Cohort Studies Using Hydrophilic Interaction Ultra-High Performance Liquid Chromatography Coupled to Tandem Mass Spectrometry

The isomeric metabolites τ- and π-methylhistidine (formerly referred to as 3- and 1-methylhistidine) are known biomarkers for muscle protein breakdown and meat protein intake, frequently used in studies involving humans and animals. In the present study, we report the development and validation of a simple HILIC-MS/MS method for individual determination of τ-MH and π-MH in a large cohort of blood plasma samples from dairy cows. Their separate determination was achieved mainly through a mass spectrometry fragment ion study, which revealed that the two isomers exhibited distinct mass spectrometric behaviors at different collision energies. Chromatographic conditions were optimised to achieve better separation, minimizing inter-channel interference to less than 1% in both directions. A simple and effective sample clean-up method facilitated low laboratory manual workload. The analytical method was validated for the determination of τ-MH and π-MH in bovine plasma within a concentration range of 80 to 1600 μg/L and provided good linearity (>0.99 for both curves) and precision (<10%). Overall, the developed method enabled the determination of the two isomers in an efficient and economic-friendly manner suitable for large cohort bovine studies (involving hundreds to thousands of samples) mainly to provide data for statistical use.

Adenosine monophosphate-activated protein kinase attenuates cardiomyocyte hypertrophy through regulation of FOXO3a/MAFbx signaling pathway

Control of cardiac muscle mass is thought to be determined by a dynamic balance of protein synthesis and degradation. Recent studies have demonstrated that atrophy-related forkhead box O 3a (FOXO3a)/muscle atrophy F-box (MAFbx) signaling pathway plays a central role in the modulation of proteolysis and exert inhibitory effect on cardiomyocyte hypertrophy. In this study, we tested the hypothesis that adenosine monophosphate-activated protein kinase (AMPK) activation attenuates cardiomyocyte hypertrophy by regulating FOXO3a/MAFbx signaling pathway and its downstream protein degradation. The results showed that activation of AMPK with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) attenuated cardiomyocyte hypertrophy induced by angiotensin II (Ang II). The antihypertrophic effects of AICAR were blunted by AMPK inhibitor Compound C. In addition, AMPK dramatically increased the activity of transcription factor FOXO3a, up-regulated the expression of its downstream ubiquitin ligase MAFbx, and enhanced cardiomyocyte proteolysis. Meanwhile, the effects of AMPK on protein degradation and cardiomyocyte hypertrophy were blocked after MAFbx was silenced by transfection of cardiomyocytes with MAFbx-siRNA. These results indicate that AMPK plays an important role in the inhibition of cardiomyocyte hypertrophy by activating protein degradation via FOXO3a/MAFbx signaling pathway.

Dietary L-Lysine Suppresses Autophagic Proteolysis and Stimulates Akt/mTOR Signaling in the Skeletal Muscle of Rats Fed a Low-Protein Diet

Amino acids, especially L-leucine, regulate protein turnover in skeletal muscle and have attracted attention as a means of increasing muscle mass in people suffering from malnutrition, aging (sarcopenia), or a bedridden state. We previously showed that oral administration of L-lysine (Lys) by gavage suppressed proteolysis in skeletal muscles of fasted rats. However, the intake of Lys in the absence of other dietary components is unlikely in a non-experimental setting, and other dietary components may interfere with the suppressive effect of Lys on proteolysis. We supplemented Lys to a 10% casein diet and investigated the effect of Lys on proteolysis and autophagy, a major proteolytic system, in the skeletal muscle of rats. The rate of proteolysis was evaluated from 3-methylhisitidine (MeHis) released from isolated muscles, in plasma, and excreted in urine. Supplementing lysine with the 10% casein diet decreased the rate of proteolysis induced by intake of a low-protein diet. The upregulated autophagy activity [light chain 3 (LC3)-II/total LC3] caused by a low-protein diet was reduced, and the Akt/mTOR signaling pathway was activated by Lys. Importantly, continuous feeding of a Lys-rich 10% casein diet for 15 days increased the masses of the soleus and gastrocnemius muscles. Taken together, supplementation of Lys to a low-protein diet suppresses autophagic proteolysis through the Akt/mTOR signaling pathway, and continuous feeding of a Lys-rich diet may increase skeletal muscle mass.

Effects of Orally Administrated Amino Acids on Myofibrillar Proteolysis in Chicks

We examined the effects of orally administrated amino acids on myfibrillar proteolysis in food-deprived chicks. Plasma N(tau)-methylhistidine concentration, as an index of myofibrillar proteolysis, was decreased by the administration of Glu, Gly, Ala, Leu, Ile, Ser, Thr, Met, Trp, Asn, Gln, Pro, Lys and Arg but not by Asp, Val, Phe, Tyr or His to chicks. Orally administrated Cys was fatal to chicks. These results indicate that oral Glu, Gly, Ala, Leu, Ile, Ser, Thr, Met, Trp, Asn, Gln, Pro, Lys and Arg administration suppressed myofibrillar proteolysis in chicks.

Muscle protein metabolism during compensatory growth with changing dietary lysine levels from deficient to sufficient in growing rats

Livestock and laboratory animals show compensatory growth when they are fed ad libitum following a period of restriction feeding. Lysine is a major limiting essential amino acid in the diets both for humans and animals. We hypothesized that changing dietary lysine levels from deficient to sufficient induced compensatory growth in young rats. We elucidated the effect of lysine sufficiency on the dynamics of hormones, relevant to muscle protein synthesis and degradation, insulin-like growth factor-I (IGF-I) and corticosterone, and on the expression of proteolytic-related genes in skeletal muscle during compensatory growth. Lysine sufficiency where the dietary lysine level was increased from 0.46% to 1.30% after 2 wk of subjecting the rats to the lower lysine level induced 80% enhancement of growth rate of rats. During compensatory growth with the lysine sufficiency, fractional muscle protein synthesis rates were higher whereas fractional muscle protein degradation rates were lower than those of the control group (p<0.05). After lysine sufficiency, the expression of atrogin-1/MAFbx mRNA was decreased in gastrocnemius muscle (p<0.05). With the lysine sufficiency, serum IGF-I concentration increased (p<0.05) whereas serum corticosterone decreased (p<0.05). These findings suggest that compensatory growth with lysine sufficiency is due to a change of hormone levels before and after changing diets, resulting in incrementation of protein synthesis and suppression of protein degradation of skeletal muscle.

The dose-dependent effects of endotoxin on protein metabolism in two types of rat skeletal muscle

Endotoxin administration is frequently used as a model of systemic inflammatory response which is considered the important pathogenetic factor in muscle wasting development in severe illness, such as sepsis, cancer, injury, AIDS and others. The main purpose of this study was determining the effect of various doses of endotoxin on protein and amino acid metabolism in two types of rat skeletal muscle. Sepsis was induced by intraperitoneal administration of endotoxin in a dose of 1, 3 and 5 mg/kg body weight (bw); control animals received a corresponding volume of the saline solution. After 24 h, extensor digitorum longus (EDL) and soleus (SOL) muscles were isolated and used for determination of total and myofibrillar proteolysis, protein synthesis, activity of cathepsins B and L, chymotrypsin-like activity of proteasome and amino acid release. The endotoxemia induced the body weight loss, the rise of total cholesterol and triglyceride plasma concentration and the protein catabolic state in skeletal muscle, which was caused by a higher increase in protein breakdown (due to activation of the proteasome system) than protein synthesis. The more significant effect of endotoxin was seen in EDL than SOL. The dose of 5 mg of endotoxin/kg bw induced the most significant changes in parameters of the protein and amino acid metabolism measured and could be therefore considered appropriate for studies of protein catabolism in young rat skeletal muscle at 24 h after endotoxin treatment.

Measurement of 1- and 3-methylhistidine in human urine by ultra performance liquid chromatography-tandem mass spectrometry

BACKGROUND

Determination of 1-methylhistidine (1-MH) and 3-methylhistidine (3-MH) is important to monitor muscle protein catabolism. Here, an ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for quantification of 1-MH and 3-MH in human urine is described.

METHODS

Urine samples were prepared by dilution with water after addition of isotopic internal standard. The samples were chromatographed on a SB-aq (2.1×50 mm, 1.8 μm) column with acetonitrile -0.1% formic acid in water (2:98, v/v) as mobile phase. Mass spectrometric detection was performed on a triple quadrupole mass spectrometer using positive electrospray ionization (ESI). 1-MH and 3-MH were monitored by the following transitions: 1-MH, m/z 170.1→ m/z 126.1; 3-MH, m/z 170.1→ m/z 124.1.

RESULTS

For 1-MH and 3-MH, calibration curves were linear over the concentration range of 5-500 nmol/ml. The lower limit of quantification was 5 nmol/ml. The accuracy was within 85%-115% and precision was <15%. 1-MH and 3-MH were proved to be stable under different storage and processing conditions. In addition, the detection was independent of matrix effect.

CONCLUSION

This rapid and specific UPLC/MS-MS method is suitable for the determination of urinary 1-MH and 3-MH.

Short-term heavy resistance training eliminates age-related deficits in muscle mass and strength in healthy older males

The objective of this investigation was to determine whether short-term heavy resistance training (RT) in healthy older men could eliminate deficits in muscle mass and strength (ST) compared with healthy younger men. Seventeen older men (60-71 yr) performed supervised RT for 22 weeks. Before and after RT, measurements were made for lean tissue mass (LTM), muscle thickness (MT), and ST (leg and bench press 1 repetition maximum) and were compared with values of younger men (n = 22-60 for the different measures, 18-31 yr). Before training, older men had significantly lower (p < 0.05) LTM (58.4 ± 7.0 kg), MT (3.4 ± 0.7 cm), and ST (leg press = 168 ± 33 kg; bench press = 75 ± 18 kg) compared with younger men (LTM 64.3 ± 7.1 kg; MT 4.0 ± 0.8 cm; leg press = 231 ± 54 kg; bench press = 121 ± 31 kg). All deficits were eliminated after 22 weeks of RT (LTM = 60.5 ± 7.6 kg; MT = 4.0 ± 0.7 cm; leg press = 222 ± 48 kg; bench press = 107 ± 19 kg). Short-term, heavy RT in healthy older men is sufficient to overcome deficits in muscle mass and ST when compared with healthy younger men. The practical application from this research is that healthy older men can be prescribed a whole-body heavy RT program to substantially increase muscle mass and ST to levels similar to young, active individuals.

Acute hyperammonemia activates branched-chain amino acid catabolism and decreases their extracellular concentrations: different sensitivity of red and white muscle

Hyperammonemia is considered to be the main cause of decreased levels of the branched-chain amino acids (BCAA), valine, leucine, and isoleucine, in liver cirrhosis. In this study we investigated whether the decrease in BCAA is caused by the direct effect of ammonia on BCAA metabolism and the effect of ammonia on BCAA and protein metabolism in different types of skeletal muscle. M. soleus (SOL, slow-twitch, red muscle) and m. extensor digitorum longus (EDL, fast-twitch, white muscle) of white rat were isolated and incubated in a medium with or without 500 μM ammonia. We measured the exchange of amino acids between the muscle and the medium, amino acid concentrations in the muscle, release of branched-chain keto acids (BCKA), leucine oxidation, total and myofibrillar proteolysis, and protein synthesis. Hyperammonemia inhibited the BCAA release (81% in SOL and 60% in EDL vs. controls), increased the release of BCKA (133% in SOL and 161% in EDL vs. controls) and glutamine (138% in SOL and 145% in EDL vs. controls), and increased the leucine oxidation in EDL (174% of controls). Ammonia also induced a significant increase in glutamine concentration in skeletal muscle. The effect of ammonia on intracellular BCAA concentration, protein synthesis and on total and myofibrillar proteolysis was insignificant. The data indicates that hyperammonemia directly affects the BCAA metabolism in skeletal muscle which results in decreased levels of BCAA in the extracellular fluid. The effect is associated with activated synthesis of glutamine, increased BCAA oxidation, decreased release of BCAA, and enhanced release of BCKA. These metabolic changes are not directly associated with marked changes in protein turnover. The effect of ammonia is more pronounced in muscles with high content of white fibres.

Activation of AMPK inhibits cardiomyocyte hypertrophy by modulating of the FOXO1/MuRF1 signaling pathway in vitro

AIM

To examine the inhibitory effects of adenosine monophosphate-activated protein kinase (AMPK) activation on cardiac hypertrophy in vitro and to investigate the underlying molecular mechanisms.

METHODS

Cultured neonatal rat cardiomyocytes were treated with the specific AMPK activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and the specific AMPK antagonist Compound C, and then stimulated with phenylephrine (PE). The Muscle RING finger 1 (MuRF1)-small interfering RNA (siRNA) was transfected into cardiomyocytes using Lipofectamine 2000. The surface area of cultured cardiomyocytes was measured using planimetry. The protein degradation was determined using high performance liquid chromatography (HPLC). The expression of beta-myosin heavy chain (beta-MHC) and MuRF1, as well as the phosphorylation levels of AMPK and Forkhead box O 1 (FOXO1), were separately measured using Western blot or real-time polymerase chain reaction.

RESULTS

Activation of AMPK by AICAR 0.5 mmol/L inhibited PE-induced increase in cardiomyocyte area and beta-MHC protein expression and PE-induced decrease in protein degradation. Furthermore, AMPK activation increased the activity of transcription factor FOXO1 and up-regulated downstream atrogene MuRF1 mRNA and protein expression. Treatment of hypertrophied cardiomyocytes with Compound C 1 micromol/L blunted the effects of AMPK on cardiomyocyte hypertrophy and changes to the FOXO1/MuRF1 pathway. The effects of AICAR on cardiomyocyte hypertrophy were also blocked after MuRF1 was silenced by transfection of cardiomyocytes with MuRF1-siRNA.

CONCLUSION

The present study demonstrates that AMPK activation attenuates cardiomyocyte hypertrophy by modulating the atrophy-related FOXO1/MuRF1 signaling pathway in vitro.

The effect of new proteasome inhibitors, belactosin A and C, on protein metabolism in isolated rat skeletal muscle

The proteasome inhibitors are used as research tools to study of the ATP-dependent ubiquitin-proteasome system. Some of them are at present undergoing clinical trials to be used as therapeutic agents for cancer or inflammation. These diseases are often accompanied by muscle wasting. We herein demonstrate findings about new proteasome inhibitors, belactosin A and C, and their direct effect on protein metabolism in rat skeletal muscle. M. soleus (SOL) and m. extensor digitorum longus (EDL) were dissected from both legs of male rats (40-60 g) and incubated in a buffer containing belactosin A or C (30 microM) or no inhibitor. The release of amino acids into the medium was estimated using high performance liquid chromatography to calculate total and myofibrillar proteolysis. Chymotrypsin-like activity (CTLA) of proteasome and cathepsin B, L activity were determined by fluorometric assay. Protein synthesis and leucine oxidation were detected using specific activity of L-[1-14C] leucine added to medium. Inhibited and control muscles from the same rat were compared using paired t-test. The results indicate that after incubation with both belactosin A and C total proteolysis and CTLA of proteasome decreased while cathepsin B, L activity did not change in both SOL and EDL. Leucine oxidation was significantly enhanced in SOL, protein synthesis decreased in EDL. Myofibrillar proteolysis was reduced in both muscles in the presence of belactosin A only. In summary, belactosin A and C affected basic parameters of protein metabolism in rat skeletal muscle. The response was both muscle- and belactosin-type-dependent.

Low-dose creatine combined with protein during resistance training in older men

PURPOSE

To determine whether low-dose creatine and protein supplementation during resistance training (RT; 3 d x wk(-1); 10 wk) in older men (59-77 yr) is effective for improving strength and muscle mass without producing potentially cytotoxic metabolites (formaldehyde).

METHODS

Older men were randomized (double-blind) to receive 0.1 g x kg(-1) creatine + 0.3 g x kg(-1) protein (CP; n = 10), creatine (C; n = 13), or placebo (PLA; n = 12) on training days. Measurements before and after RT included lean tissue mass (air-displacement plethysmography), muscle thickness (ultrasound) of elbow, knee, and ankle flexors and extensors, leg and bench press strength, and urinary indicators of cytotoxicity (formaldehyde), myofibrillar protein degradation [3-methylhistidine (3-MH)],and bone resorption [cross-linked N-telopeptides of type I collagen (NTx)].

RESULTS

Subjects in C and CP groups combined experienced greater increases in body mass and total muscle thickness than PLA (P < 0.05). Subjects who received CP increased lean tissue mass (+5.6%) more than C (+2.2%) or PLA (+1.0%; P < 0.05) and increased bench press strength (+25%) to a greater extent than C and PLA combined (+12.5%; P < 0.05). CP and C did not differ from PLA for changes in formaldehyde production (+24% each). Subjects receiving creatine (C and CP) experienced a decrease in 3-MH by 40% compared with an increase of 29% for PLA (P < 0.05) and a reduction in NTx (-27%) versus PLA (+13%; P = 0.05).

CONCLUSIONS

Low-dose creatine combined with protein supplementation increases lean tissue mass and results in a greater relative increase in bench press but not leg press strength. Low-dose creatine reduces muscle protein degradation and bone resorption without increasing formaldehyde production.

Regulation of muscle protein degradation, not synthesis, by dietary leucine in rats fed a protein-deficient diet

The aim of this study was to elucidate the effects of long-term intake of leucine in dietary protein malnutrition on muscle protein synthesis and degradation. A reduction in muscle mass was suppressed by leucine-supplementation (1.5% leucine) in rats fed protein-free diet for 7 days. Furthermore, the rate of muscle protein degradation was decreased without an increase in muscle protein synthesis. In addition, to elucidate the mechanism involved in the suppressive effect of leucine, we measured the activities of degradation systems in muscle. Proteinase activity (calpain and proteasome) and ubiquitin ligase mRNA (Atrogin-1 and MuRF1) expression were not suppressed in animals fed a leucine-supplemented diet, whereas the autophagy marker, protein light chain 3 active form (LC3-II), expression was significantly decreased. These results suggest that the protein-free diet supplemented with leucine suppresses muscle protein degradation through inhibition of autophagy rather than protein synthesis.

Potential antiproteolytic effects of L-leucine: observations of in vitro and in vivo studies

The purpose of present review is to describe the effect of leucine supplementation on skeletal muscle proteolysis suppression in both in vivo and in vitro studies. Most studies, using in vitro methodology, incubated skeletal muscles with leucine with different doses and the results suggests that there is a dose-dependent effect. The same responses can be observed in in vivo studies. Importantly, the leucine effects on skeletal muscle protein synthesis are not always connected to the inhibition of skeletal muscle proteolysis. As a matter of fact, high doses of leucine incubation can promote suppression of muscle proteolysis without additional effects on protein synthesis, and low leucine doses improve skeletal muscle protein ynthesis but have no effect on skeletal muscle proteolysis. These research findings may have an important clinical relevancy, because muscle loss in atrophic states would be reversed by specific leucine supplementation doses. Additionally, it has been clearly demonstrated that leucine administration suppresses skeletal muscle proteolysis in various catabolic states. Thus, if protein metabolism changes during different atrophic conditions, it is not surprising that the leucine dose-effect relationship must also change, according to atrophy or pathological state and catabolism magnitude. In conclusion, leucine has a potential role on attenuate skeletal muscle proteolysis. Future studies will help to sharpen the leucine efficacy on skeletal muscle protein degradation during several atrophic states.

Skeletal muscle proteolysis in response to short-term unloading in humans

Skeletal muscle atrophy is evident after muscle disuse, unloading, or spaceflight and results from decreased protein content as a consequence of decreased protein synthesis, increased protein breakdown or both. At this time, there are essentially no human data describing proteolysis in skeletal muscle undergoing atrophy on Earth or in space, primarily due to lack of valid and accurate methodology. This particular study aimed at assessing the effects of short-term unloading on the muscle contractile proteolysis rate. Eight men were subjected to 72-h unilateral lower limb suspension (ULLS) and intramuscular interstitial levels of the naturally occurring proteolytic tracer 3-methylhistidine (3MH) were measured by means of microdialysis before and on completion of this intervention. The 3MH concentration following 72-h ULLS (2.01 +/- 0.22 nmol/ml) was 44% higher (P < 0.05) than before ULLS (1.56 +/- 0.20 nmol/ml). The present experimental model and the employed method determining 3MH in microdialysates present a promising tool for monitoring skeletal muscle proteolysis or metabolism of specific muscles during conditions resulting in atrophy caused by, e.g., disuse and real or simulated microgravity. This study provides evidence that the atrophic processes are evoked rapidly and within 72 h of unloading and suggests that countermeasures should be employed in the early stages of space missions to offset or prevent muscle loss during the period when the rate of muscle atrophy is the highest.

Protein metabolism in slow- and fast-twitch skeletal muscle during turpentine-induced inflammation

The aim of our study was to evaluate the differences in protein and amino acid metabolism after subcutaneous turpentine administration in the soleus muscle (SOL), predominantly composed of red fibres, and the extensor digitorum longus muscle (EDL) composed of white fibres. Young rats (40-60 g) were injected subcutaneously with 0.2 ml of turpentine oil/100 g body weight (inflammation) or with the same volume of saline solution (control). Twenty-four hours later SOL and EDL were dissected and incubated in modified Krebs-Heinseleit buffer to estimate total and myofibrillar proteolysis, chymotrypsin-like activity of proteasome (CHTLA), leucine oxidation, protein synthesis and amino acid release into the medium. The data obtained demonstrate that in intact rats, all parameters measured except protein synthesis are significantly higher in SOL than in EDL. In turpentine treated animals, CHTLA increased and protein synthesis decreased significantly more in EDL. Release of leucine was inhibited significantly more in SOL. We conclude that turpentine-induced inflammation affects more CHTLA, protein synthesis and leucine release in EDL compared to SOL.

Myofibrillar proteolysis in response to voluntary or electrically stimulated muscle contractions in humans

Knowledge about the effects of exercise on myofibrillar protein breakdown in human subjects is limited. Our purpose was to measure the changes in the degradation of myofibrillar proteins in response to different ways of eliciting muscle contractions using the local interstitial 3-methyl-histidine (3-MH) concentration as a marker for myofibrillar protein breakdown. Untrained males (n=8, 22-27 years, range) performed 210 maximal isokinetic eccentric contractions with each leg on an isokinetic dynamometer. One leg performed voluntary (VOL) and the other leg performed electrically induced contractions (ES). Microdialysis probes were placed in m. vastus lateralis in both the legs immediately after, and 1 and 3 days post-exercise. Interstitial 3-MH was higher in ES vs VOL immediately after exercise (P<0.05). One and 3 days post-exercise no difference between the two exercise types was observed. Only after ES did the histochemical stainings show significant disruption of cytoskeletal proteins. Furthermore, intracellular disruption and destroyed Z-lines were markedly more pronounced in ES vs VOL. In conclusion, the local level of interstitial 3-MH in the skeletal muscle was significantly enhanced after ES compared with VOL immediately after exercise, while the level of 3-MH did not change in the post-exercise period after VOL. These results indicate that the local myofibrillar breakdown is accelerated after ES associated with severe myofiber damage.

Changes of serum 3-methylhistidine concentration and energy-associated metabolites in dairy cows with ketosis

The present study examined the Serum 3-methylhistidine concentrations and energy-associated variables of 5 healthy Holstein cows and 5 Holstein cows with ketosis. The serum total cholesterol and apolipoprotein B-100 concentrations and lecithin-cholesterol acyltransferase (LCAT) activity of the ketotic cows were lower than those of the healthy cows 14 days before parturition. The serum non-esterified fatty acid (NEFA) concentration on the day of parturition and 3-methylhistidine concentration 14 days after parturition were higher in the ketotic cows. The serum 3-methylhistidine concentration 14 days after parturition was negatively correlated with the serum LCAT activity 14 days before parturition and was positively correlated with the serum NEFA concentration on the day of parturition. Insufficiency of cholesterol metabolism and acceleration of body fat degradation occur before parturition in cows with ketosis, and these characteristics are correlated with acceleration of protein degradation after parturition.

Effects of orally administered glycine on myofibrillar proteolysis and expression of proteolytic-related genes of skeletal muscle in chicks

We examined the effects of orally administered glycine on myofibrillar proteolysis in food-deprived chicks. Food-deprived (24 h) chicks were orally administered 57, 113, and 225 mg glycine/100 g body weight and killed after 2 h. The plasma N(tau)-methylhistidine concentration, used as myofibrillar proteolysis, was decreased by glycine. We also examined the expression of proteolytic-related genes by real-time PCR of cDNA from chick skeletal muscles. The mRNA expression of atrogin-1/MAFbx, proteasome C2 subunit, m-calpain large subunit, and cathepsin B was decreased by glycine in a dose-dependent manner. The plasma corticosterone concentration was also decreased by glycine, but the plasma insulin concentration was unaffected. These results indicate that orally administered glycine suppresses myofibrillar proteolysis and expression of proteolytic-related genes of skeletal muscle by decreasing the plasma corticosterone concentration in chicks.

AMPK activation stimulates myofibrillar protein degradation and expression of atrophy-related ubiquitin ligases by increasing FOXO transcription factors in C2C12 myotubes

In skeletal muscle, AMP-activated protein kinase (AMPK) is a metabolic master switch regulating glucose and lipid metabolism. Recently, AMPK has been implicated in the control of protein synthesis in skeletal muscle, but the effect of AMPK activation on myofibrillar protein degradation has yet to be elucidated. The present study was designed to examine the effect of 5-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR)-induced AMPK signaling on effector mechanisms of myofibrillar protein degradation and the expression of atrophy-related genes (atrogin-1/MAFbx, MuRF1, proteasome C2 subunit, calpains, cathepsin B, and caspase-3) in C2C12 myotubes. AICAR stimulated myofibrillar protein degradation (as measured by N(tau)-methylhistidine release), while also increasing the levels of atrogin-1/MAFbx and MuRF1 mRNA, but the expression of other atrophy-related genes was not enhanced by AICAR treatment in C2C12 myotubes. AICAR also stimulated the level of FOXO transcription factors mRNA and protein in C2C12 myotubes. These results indicate that activation of AMPK stimulates myofibrillar protein degradation through the expression of atrogin-1/MAFbx and MuRF1 by increasing FOXO transcription factors in skeletal muscles.

Suppression of myofibrillar proteolysis in chick skeletal muscles by α-ketoisocaproate

We previously reported that L-leucine suppresses myofibrillar proteolysis in chick skeletal muscles. In the current study, we compared the effects of L- and D-enantiomers of leucine on myofibrillar proteolysis in skeletal muscle of chicks. We also assessed whether leucine itself or its metabolite, alpha-ketoisocaproate (alpha-KIC), mediates the effects of leucine. Food-deprived (24 h) chicks were orally administered 225 mg/100 g body weight L-leucine, D-leucine or alpha-KIC and were sacrificed after 2 h. L-Leucine administration had an obvious inhibitory effect on myofibrillar proteolysis (plasma N(tau)-methylhistidine concentration) in chicks while D-leucine and alpha-KIC were much more effective. We also examined the expression of the proteolytic-related genes (ubiquitin, proteasome, m-calpain and cathepsin B) by real-time PCR of cDNA in chick skeletal muscles. Ubiquitin mRNA expression was decreased by D-leucine and alpha-KIC but not L-leucine. Proteasome and m-calpain mRNA expressions as well as cathepsin B mRNA expression were likewise decreased by L-leucine, D-leucine and alpha-KIC. These results indicate that D-leucine and alpha-KIC suppress proteolytic-related genes, resulting in an decrease in myofibrillar proteolysis while L-leucine is much less effective in skeletal muscle of chicks, may be explain by conversion of D-leucine to alpha-KIC.

The effect of strenuous aerobic exercise on skeletal muscle myofibrillar proteolysis in humans

Relatively little is known about the dynamics of the skeletal muscle protein pool following aerobic exercise. Myofibrillar protein synthesis has recently been shown to be substantially elevated for 3 days after a strenuous 60 min bout of one-legged aerobic exercise, and this increase was surprisingly equal to or greater than what has been shown numerous times following resistance exercise over the same time course. Because net protein accretion is the sum of protein synthesis and degradation, we sought to directly measure skeletal muscle myofibrillar proteolysis in five healthy young males in response to an identical strenuous 60 min aerobic exercise bout and at the same time points (rest, 6, and 24 h post-exercise and 48 and 72 h post-exercise in a subset of subjects). We measured skeletal muscle myofibrillar proteolysis by monitoring the release of the natural tracer 3-methylhistidine (3MH) from the vastus lateralis muscle into the interstitial space via microdialysis. Skeletal muscle interstitial 3MH concentration was no different (P>0.05) from rest (5.16+/-0.38 nmol/mL) after 6 (5.37+/-0.55 nmol/mL), 24 (5.40+/-0.26 nmol/mL), 48 (5.50+/-0.74 nmol/mL), or 72 h (4.73+/-0.28 nmol/mL). These results suggest that proteolysis of the myofibrillar fraction of skeletal muscle is relatively refractory to an intense aerobic exercise stimulus for up to 3 days, despite the large increase in synthesis of this muscle fraction following the same exercise stimulus. The apparent net myofibrillar protein accretion in the hours and days after exercise may occur in order to offset the large elevation in mixed muscle proteolysis that has been shown during similar bouts of intense one-legged aerobic exercise.

Protein supplementation before and after resistance training in older men

We determined the effects of protein supplementation immediately before (PRO-B) and after (PRO-A) resistance training (RT; 12 weeks) in older men (59-76 years), and whether this reduces deficits in muscle mass and strength compared to younger men (18-40 years). Older men were randomized to PRO-B (0.3 g/kg protein before RT + placebo after RT, n=9), PRO-A (placebo before + protein after RT, n=10), or PLA (placebo before and after RT, n=10). Lean tissue mass, muscle thickness of the elbow, knee, and ankle flexors and extensors, and leg and bench press strength were measured before and after RT and compared to databases of younger subjects (n=22-60). Myofibrillar protein degradation (3-methylhistidine) and bone resorption (cross-linked N-telopeptides) were also measured before and after RT. Lean tissue mass, muscle thickness (except ankle dorsi flexors), and strength increased with training (P<0.05), with little difference between groups. There were no changes in 3-methylhistidine or cross-linked N-telopeptides. Before RT, all measures were lower in the older compared to younger groups (P<0.05), except for elbow extensor muscle thickness. Following training, muscle thickness of the elbow flexors and ankle dorsi flexors and leg press strength were no longer different than the young, and elbow extensor muscle thickness was greater in the old men (P<0.05). Supplementation with protein before or after training has no effect on muscle mass and strength in older men. RT was sufficient to overcome deficits in muscle size of the elbow flexors and ankle dorsi flexors and leg press strength in older compared to younger men.

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.

Proteasome mediates removal of proteins oxidized during myocardial ischemia

Numerous proteins are known to be lost following myocardial ischemia/reperfusion yet little is known about the mediating proteinases. This study examines the hypothesis that proteasome plays a significant role in the removal of proteins oxidized during myocardial ischemia. Proteasome was inhibited by perfusing isolated rat hearts with buffer containing lactacystin, 2 micromol/L, for 10 min, which resulted in 51 and 42% decreases in 20S and 26S proteasome activities that persisted for a minimum of 90 min. Lactacystin pretreatment had minor effects on postischemic recovery of isolated hearts exposed to 30 min global ischemia and 60 min reperfusion. Protein carbonyl content of lactacystin-pretreated ischemic hearts was significantly (P < 0.05) increased. One band with approximate molecular mass of 50 kDa is known to contain oxidized actin. Actin degradation was quantitated by analysis of 3-methylhistidine which was significantly (P < 0.05) decreased by 15% following 30 min ischemia and 60 min reperfusion. Pretreatment of ischemic hearts with lactacystin prevented much of the loss (-6.5%) of 3-methylhistidine. Probing immunoprecipitated actin with an antibody specific for ubiquitin revealed no bands containing ubiquitinated homologues of this protein. These observations support the conclusion that proteasome mediates removal of some of the proteins oxidized during myocardial ischemia/reperfusion, and that at least oxidized actin is removed by the 20S proteasome.

Leucine suppresses myofibrillar proteolysis by down-regulating ubiquitin-proteasome pathway in chick skeletal muscles

In skeletal muscle, amino acids, together with hormones, are key regulators of protein metabolism. Leucine, in particular, has inhibitory effects of protein degradation in skeletal muscles, but the mechanisms are poorly understood. The present study addressed the role of leucine as a regulator of myofibrillar proteolysis in cultured chick myotubes and chick skeletal muscles, and aimed to determine which cellular responses regulate the process. In chick myotubes, leucine suppressed myofibrillar proteolysis (as measured by N(tau)-methylhistidine release), while also decreasing ubiquitin and proteasome C2 subunit mRNA. Oral administration of leucine also suppressed myofibrillar proteolysis (as measured by plasma N(tau)-methylhistidine concentration), while also decreasing proteasome C2 subunit mRNA in chick skeletal muscle. Leucine activated the phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC) (but not the mammalian target of rapamycin) inhibition of these pathways and increased myofibrillar proteolysis, ubiquitin and proteasome C2 subunit mRNA. Thus, an important component of muscle proteolysis inhibition by leucine, through the PI3K and PKC, is its ability to suppress transcription of the ubiquitin and proteasome C2 subunit, and degradation of myofibrillar protein.

Effects on skeletal muscle of intravenous glutamine supplementation to ICU patients

OBJECTIVE

To evaluate the effect of four doses of intravenous glutamine supplementation on skeletal muscle metabolism.

DESIGN

A prospective, blinded, randomized study.

SETTING

The general Intensive Care Unit (ICU) of a university hospital.

PATIENTS

ICU patients with multiple organ failure (n=40), who were expected to stay in the unit for more than five days.

INTERVENTION

Patients received 0, 0.28, 0.57 or 0.86 g of glutamine per kg bodyweight per day intravenously for five days as part of an isocaloric, isonitrogenous and isovolumetric diet.

RESULTS

Plasma glutamine concentration responded to glutamine supplementation with normalization of plasma levels in a dose-dependent way, while free muscle glutamine concentration, as well as muscle protein synthesis and muscle protein content, did not change significantly.

CONCLUSION

Intravenous glutamine supplementation to ICU patients for a period of five days resulted in normalization of plasma glutamine concentrations in a dose-dependent way whereas muscle glutamine concentrations were unaffected.

Influence of age and resistance exercise on human skeletal muscle proteolysis: a microdialysis approach

We combined the interstitial sampling method of microdialysis with the natural tracer qualities (i.e. non-recyclability) of the amino acid 3-methylhistidine (3MH) to uniquely study in vivo degradation of the two most abundant skeletal muscle proteins, myosin and actin. Interstitial 3MH concentration was measured before and for 24 h following a single bout of resistance exercise in eight young (27 +/- 2 years) and eight old (75 +/- 4 years) men. The exercise bout consisted of four exercises (3 sets of 8 repetitions at 80% one-repetition maximum (1RM) per exercise) emphasizing the quadriceps. Interstitial 3MH concentration was calculated using the internal reference method from microdialysate samples that were obtained from two microdialysis probes placed in the vastus lateralis. Resting interstitial 3MH concentration was 44% higher (P < 0.05) in the old (6.16 +/- 0.56 nmol ml(-1)) as compared with the young (4.28 +/- 0.27 nmol ml(-1)). Interstitial 3MH was not different (P > 0.05) from preexercise at any time point within the 24 h following exercise in both the young and the old. Leg arteriovenous exchange measurements in a separate group of young subjects also showed no increase in 3MH release during the 4 h following a resistance exercise bout compared with a non-exercised control leg (control leg: -28 +/- 6, exercise leg: -28 +/- 11 nmol min(-1)). These results suggest that myosin and actin proteolysis are not increased in the first 24 h following a standard bout of resistance exercise, and this response is not altered with ageing. The higher interstitial 3MH concentration in the old suggests an increased proteolysis of the two main contractile proteins in the rested and fasted state, which is consistent with a decrease in muscle mass with ageing. Microdialysis is an appropriate methodology for use in ageing individuals and is compatible with high-intensity resistance exercise.

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.

Muscle mass index in haemodialysis patients: a comparison of indices obtained by routine clinical examinations

BACKGROUND

Measurement of muscle mass is useful for evaluating protein nutritional status. Various methods for estimating muscle mass in haemodialysis patients have recently been developed.

METHODS

The validity of the estimate of creatinine production calculated with the creatinine kinetic model (CKM) was examined in 46 haemodialysis patients by comparing it with the actual creatinine production, this being determined from the sum of creatinine appearing in the dialysate and the estimated metabolic degradation. The correlation of various other muscle mass indices with creatinine production was also investigated in these patients.

RESULTS

The estimate of creatinine production using CKM was significantly correlated with creatinine production calculated from the spent dialysate plus an estimate for the extra-renal creatinine degradation (r=0.90, P<0.001). A Bland-Altman analysis revealed that the mean prediction error for the estimate of creatinine production by CKM was +0.10 g/day and the limits of agreement were +0.34 to -0.14 g/day. The cross-sectional area of the thigh muscle measured by computed tomography (CT) was also significantly correlated with creatinine production (r=-0.86, P<0.01). In contrast, the correlations of 3-methylhistidine production measured in the spent dialysate, the mid-upper arm muscle circumference and the skeletal muscle mass estimated by an anthropometric prediction model with creatinine production were lower (r<0.82).

CONCLUSION

Creatinine production calculated using CKM and CT measurement of thigh muscle area are valid methods for estimating muscle mass during routine clinical examinations of haemodialysis patients.

Rapid suppression of protein degradation in skeletal muscle after oral feeding of leucine in rats

A diet containing adequate amounts of protein rapidly suppresses myofibrillar protein degradation in rats and mice. This study determined whether dietary amino acids inhibit postprandial protein degradation in rat skeletal muscle. When rats fed on a 20% casein diet for 1 h after 18 h starvation, the rate of myofibrillar protein degradation measured by N(tau)-methylhistidine release from the isolated extensor digitorum longus muscle was significantly (p < 0.05) decreased at 4 h after refeeding. A diet containing an amino acid mixture which is the same composition as casein also reduced myofibrillar protein degradation at 4 h after refeeding (p < 0.05). An essential amino acid mixture (15.1%, corresponding to casein composition) and a leucine (2.9%) diets reduced the rate of myofibrillar protein degradation after refeeding (p < 0.05), whereas a protein free diet did not. Administration of leucine alone (0.135 g/100 g body weight) by a feeding tube induced a decrease in the rate of myofibrillar protein degradation at 2 h after administration (p < 0.05), whereas the serum insulin concentration was constant after leucine administration. These results suggested that leucine is one of regulating factors of myofibrillar protein degradation after refeeding of a protein diet.

Randomized trial of progressive resistance training to counteract the myopathy of chronic heart failure

Chronic heart failure (CHF) is characterized by a skeletal muscle myopathy not optimally addressed by current treatment paradigms or aerobic exercise. Sixteen older women with CHF were compared with 80 age-matched peers without CHF and randomized to progressive resistance training or control stretching exercises for 10 wk. Women with CHF had significantly lower muscle strength (P < 0.0001) but comparable aerobic capacity to women without CHF. Exercise training was well tolerated and resulted in no changes in resting cardiac indexes in CHF patients. Strength improved by an average of 43.4 +/- 8.8% in resistance trainers vs. -1.7 +/- 2.8% in controls (P = 0.001), muscle endurance by 299 +/- 66% vs. 1 +/- 3% (P = 0.001), and 6-min walk distance by 49 +/- 14 m (13%) vs. -3 +/- 19 m (-3%) (P = 0.03). Increases in type I fiber area (9.5 +/- 16%) and citrate synthase activity (35 +/- 21%) in skeletal muscle were independently predictive of improved 6-min walk distance (r2 = 0.78; P = 0.0024). High-intensity progressive resistance training improves impaired skeletal muscle characteristics and overall exercise performance in older women with CHF. These gains are largely explained by skeletal muscle and not resting cardiac adaptations.

Eimeria acervulina infection elevates plasma and muscle 3-methylhistidine levels in chickens

To assess muscle breakdown during avian coccidiosis, the level of the nonmetabolizable amino acid 3-methylhistidine (3MH) was determined in muscle, plasma and excreta from chickens infected with Eimeria acervulina. The changes in 3MH levels during infection were assessed at 1-29 days postinoculation (DPI) in animals given 5 x 10(5) oocysts per bird. The effect of levels of parasitism were evaluated at 8 DPI in birds receiving 5 x 10(3), 5 x 10(4), 5 x 10(5) or 1 x 10(6) oocysts each. The 3MH levels of plasma, muscle, and excreta samples were determined by high-pressure liquid chromatography after derivatization with fluorescamine. Weight gains, breast muscle weight, eviscerated weight, plasma carotenoid levels, dry weight of muscle, and gross lesion scores were also determined. Infected birds had significantly elevated plasma and muscle 3MH at 4 and 8 DPI following a single dose of E. acervulina. The increase in 3MH levels had an inverse relationship with the time course of weight gain and plasma carotenoid levels. Plasma and muscle 3MH levels returned to control values by 15 DPI and remained unchanged from control values through the remainder of the experiment (29 DPI). Breast weight was decreased in infected birds, but the ratio of breast weight to eviscerated body weight was unchanged. Excretion of 3MH decreased relative to controls at 4 and 8 DPI and returned to control levels on 15 DPI. The plasma and muscle levels of 3MH were related to severity of infection; however, levels of excreted 3MH were not. The results suggested that muscle breakdown, as assessed by plasma and muscle levels of 3MH, increased during the acute stage of E. acervulina infection. The underlying causes for this muscle breakdown was unclear but could involve a physiological response to anorexia and decreased food intake during the acute phase of infection. Levels of excreted 3MH did not increase during infection and this may be the result of decreased excreta output during infection. Plasma and muscle levels of 3MH were correlated with severity of E. acervulina infections but may not be as sensitive an indicator of infection as plasma carotenoid levels or other physiological parameters.

Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers

Insulin-like growth factor-1 (IGF-1) is perhaps the most important endogenous factor controlling growth. Most studies to date in livestock have shown that IGF-1 has greatest efficacy when animals are in a catabolic state. We have determined the effects of an i.v. infusion of the IGF-1 analog Long(R3)-IGF-1 on protein metabolism in beef heifers that were slowly losing liveweight because of restricted feeding. There was a tendency for both whole-body protein and skeletal muscle protein to be conserved in Long(R3)-IGF-1-treated heifers. Long(R3)-IGF-1 administration markedly reduced the plasma concentrations of all amino acids measured and glucose. There was a significant change in the profile differences of endogenous plasma IGF-1 concentrations during the 8-hr infusion period, with plasma IGF-1 decreasing sharply in the test group. There was a significant difference in mean profiles for plasma IGF-2 between the test and control groups. Overall, plasma IGF-2 for the control group decreased only slightly over time (about 40 ng/ml), whereas the test group decreased dramatically (by about 140 ng/ml). Increased plasma concentrations of a 31-32-kDa IGF-binding protein (possibly IGF-binding protein-1) in the treated group was detected by radioligand blot. We found that Long(R3)-IGF-1 infusion tended to preserve whole-body and muscle protein in beef heifers on a low-quality diet, and suggest that further investigation of this treatment may provide an alternative approach to reducing weight loss during the dry season.

Effect of a single bout of acute exercise on plasma human immunodeficiency virus RNA levels

Acute exercise is known to activate the immune system and thus could lead to increased human immunodeficiency virus (HIV) replication. We sought to determine whether a single acute bout of exercise, similar to what people experience when starting an intensive exercise program, has a detrimental effect on plasma HIV RNA levels. Twenty-five patients with HIV infection performed one 15-min bout of acute exercise. Absolute neutrophil counts, serum creatine phosphokinase, and 72-h urinary 3-methylhistidine (a marker of muscle protein breakdown) were measured before and after the exercise, along with plasma HIV RNA levels. There were increases in neutrophil counts (P < 0.06), serum creatine phosphokinase (P < 0. 01), and urinary 3-methylhistidine (P < 0.01) in response to exercise, indicating a mild acute-phase response with muscle proteolysis. However, mean HIV RNA, which was elevated at baseline in 22 of the 25 subjects (mean of 4 x 10(5) +/- 0.7 x 10(5) copies/ml), did not increase during the week after exercise (P = 0. 12). Small changes in RNA were seen in the three subjects with initially undetectable HIV RNA, but the significance of these changes is unclear. Acute exercise does not have a deleterious effect on HIV replication in adults with high viral loads. Because regular exercise training has not been shown to activate the acute-phase response, the lack of increased viral loads in response to an acute exercise intervention suggests that exercise training is safe in people with HIV infection.

Growth hormone and insulin-like growth factor-I therapy promote protein deposition and growth in dexamethasone-treated piglets

BACKGROUND

Dexamethasone treatment facilitates the weaning of premature infants from mechanical ventilation but impairs protein homeostasis, lean tissue deposition, and growth. The current study was conducted to investigate whether dexamethasone mediates these effects by reducing protein synthesis or elevating protein breakdown, and whether adjuvant growth hormone+/-insulin-like growth factor-I therapy can attenuate such effects.

METHODS

Piglets (n = 24) were randomized to placebo, a tapered course of dexamethasone (0.5, 0.3, 0.2 mg/kg per day for 5, 5 and 4 days each, respectively), dexamethasone + growth hormone 0.1 mg/kg per day, or dexamethasone + growth hormone + insulin-like growth factor-I 0.1 mg/kg per day for 14 days. On day 13, 15N-glycine was administered as a single oral dose, and urine was collected at timed intervals during the subsequent 48 hours.

RESULTS

Total urinary N and cumulative 15N excretion were higher in all dexamethasone groups than in control subjects. Protein synthesis was suppressed, whereas protein breakdown was unaltered by dexamethasone. Adjunctive growth hormone+/-insulin-like growth factor-I therapy enhanced protein synthesis, but only combined therapy improved net protein gain compared with dexamethasone alone. Higher circulating insulin-like growth factor-I may have mediated the greater net protein gain. Blood urea nitrogen was elevated in all dexamethasone-treated groups at days 6 and 11 but was normalized by day 15 with adjunctive growth hormone+/-insulin-like growth factor-I. From a functional perspective, both adjunctive growth hormone and growth hormone+/-insulin-like growth factor-I partially attenuated the dexamethasone-induced reduction in weight and length gain but not in whole body lean and fat mass.

CONCLUSION

Adjunctive growth hormone+/-insulin-like growth factor-I therapy partially reverses the dexamethasone-induced reduction in protein synthesis, resulting in improved growth when given concurrently with a low tapering dose of dexamethasone.

Myofibrillar protein catabolism is rapidly suppressed following protein feeding

The immediate response of protein degradation to food intake and the factors for its regulation in rat skeletal muscle were examined. The concentration of N tau-methylhistidine (MeHis) in serum and the rates of MeHis release from isolated soleus and extensor digitorum longus muscles were reduced in the period from 3 to 6 h after refeeding, indicating that the rate of myofibrillar protein degradation in the rat decreased immediately after refeeding. Changes in the serum concentration of insulin and corticosterone were not synchronized with those in the myofibrillar protein degradation. When rats were fed on a protein-free diet, no reduction of serum MeHis concentration or of the rate of MeHis release from isolated muscles after refeeding was apparent. Furthermore, there was a tendency toward suppressing myofibrillar protein degradation with a higher protein content of the diet. These results suggest that the suppression of myofibrillar protein degradation by food intake was regulated by dietary proteins.

Insulin-like growth factor (IGF)-I but not IGF-II promotes lean growth and feed efficiency in broiler chickens

The efficacy of exogenous IGFs to stimulate growth and modulate protein and fat deposition was examined in a number of broiler chicken lines. From around 600 g body weight the chickens received a continuous infusion of vehicle (0.1 M acetic acid), human recombinant IGF-I or [Gly1]IGF-II at 300 microg/kg body weight per day, or a combined infusion of 150 microg/kg/day of each IGF for 2 weeks. Experiment 1 used commercial broiler female chickens and included measurements of nitrogen balance, Ntau-methylhistidine excretion and muscle protein synthesis rates. In Experiment 2 the same treatments were applied to three experimental lines of chickens selected for high food consumption (relatively fat), high food utilisation efficiency (relatively lean), or at random (control). IGF-I, but not IGF-II, significantly increased growth rate and food utilisation efficiency by around 10-15% in each experiment, an effect which was consistent across all genotypes. Nitrogen balance was significantly increased by IGF-I in Experiment 1 as was carcass nitrogen content in Experiment 2, indicating that the increased growth was in lean tissue. Carcass fat was consistently reduced in chickens receiving IGF-I and was related to the levels of circulating IGF-I (r2 = 0.30, P < 0.01) but not triiodothyronine. Protein synthesis rates were unaffected by treatment and could not account for increased growth rate. However, there was a significant reduction in Ntau-methylhistidine excretion indicating a reduced rate of muscle protein breakdown in IGF-I-treated chickens (1. 56%/day vs 2.05%/day for IGF-I-treated vs controls, P < 0.05). The efficiency of feed utilisation was inversely related to the rate of protein breakdown (r2 = 0.25, P < 0.01). In conclusion, these experiments are the first to report an enhancement of growth and food utilisation efficiency by broiler chickens receiving exogenous IGF-I. Our results show that IGF-I may be important in controlling the growth and efficiency of food utilisation of young chickens at least in part by modulating the rates of protein breakdown.

The effect of insulin-like growth factor-I (IGF-I) on protein turnover in the meat-type chicken (Gallus domesticus)

Insulin-like growth factor-I (IGF-I) effects on chicken growth and development are poorly understood. This study examined the effect of IGF-I on protein synthesis rates in various tissues in the male broiler chicken. At three weeks of age, osmotic minipumps were subcutaneously implanted in the scapular area. Chickens were infused with either chicken IGF-I (450 micrograms/kg BW/day) or saline. After treatment for 5 days, the chickens received a flooding dose of [3H]-phenylalanine, and were sacrificed 20 min later. Wing vein blood samples were taken at 0, 5, 10 and 20 min post-injection. The following tissues were removed and frozen for analysis: pectoralis muscle, gastrocnemius muscle, heart, liver, and small intestine. In vivo total protein synthesis measurements were made using the double-label technique. Contractile protein degradation was evaluated using intracellular free 3-methylhistidine concentrations in skeletal muscle. There were no significant differences in absolute or relative body growth rates over the treatment period. Skeletal muscle (pectoralis and gastrocnemius) weights were significantly decreased with IGF-I treatment, while heart weight was significantly increased. Plasma insulin levels were significantly lower in IGF-treated chickens compared to that in control birds. There was no effect of IGF-I on protein synthesis rates in any of the tissues examined. Intracellular free 3-methylhistidine concentrations were higher in both the gastrocnemius (17%) and pectoralis muscles (25%) of chickens treated with IGF-I. This data demonstrates that IGF-I may have an indirect effect to regulate muscle protein turnover rates.