The regulation of body and skeletal muscle protein metabolism by hormones and amino acids

Whole-Body and Forearm Muscle Protein Metabolism in Patients With Acromegaly Before and After Treatment

BACKGROUND

Active acromegaly is characterized by increased lean body mass, but the mechanisms underlying the protein anabolic effect are unclear.

AIM

To study if active acromegaly induces reversible changes in whole-body and skeletal muscle protein kinetics.

PATIENTS AND METHODS

Eighteen patients with acromegaly were investigated before and 47 ± 10 weeks after disease control by surgery (n = 8) and/or medical treatment (n = 10). Labeled phenylalanine and tyrosine tracers were employed to assess whole-body and regional forearm muscle protein kinetics. Intramyocellular protein signaling was assessed in skeletal muscle biopsies, and whole-body dual-energy X-ray absorptiometry scan and indirect calorimetry assessed lean body mass (LBM) and resting energy expenditure, respectively.

RESULTS

Disease control induced a 7% decrease in lean body mass (P < .000) and a 14% decrease in LBM-adjusted energy expenditure. Whole-body phenylalanine breakdown decreased after disease control (P = .005) accompanied by a decrease in the degradation of phenylalanine to tyrosine (P = .005) and a decrease in whole-body phenylalanine synthesis (P = .030). Skeletal muscle protein synthesis tended to decrease after disease control (P = .122), whereas the muscle protein breakdown (P = .437) and muscle protein loss were unaltered (P = .371). Unc-51 like autophagy activating kinase 1 phosphorylation, an activator of protein breakdown, increased after disease control (P = .042).

CONCLUSIONS

Active acromegaly represents a reversible high flux state in which both whole-body protein breakdown and synthesis are increased, whereas forearm muscle protein kinetics are unaltered. Future studies are needed to decipher the link between protein kinetics and the structure and function of the associated growth hormone-induced increase in lean body mass.

Biological effects of iodine, selenium, sulfur citrates in broiler chickens

This study aimed at the assessment of the I, Se, S citrate effect on the organism of broiler chickens. Feeding of chickens of all groups was carried out by using standard balanced feeds – starter, grower, and finish with the use of group feeders placed at the appropriate height from the floor depending on the poultry height. For the chickens of experimental groups, I, Se, S citrate was added to drinking water daily during the 48th day. To the drinking water of chickens of experimental groups different amounts of the citrate solution were added I (200 mg/L), Se (50 mg/L), S (300 mg/L), prepared by the nanotechnology method. Chickens of the II group received the lowest dose of I, Se, S at the rate of 5 μg I/L, 1.25 μg Se/L, 7.5 μg S/L of drinking water, and for poultry of other experimental groups, it was increased by 2 (III), 4 (IV), 6 (V) and 8 (VI) times compared to II group. Coccidiostat "Kokcisan 12%" (KRKA, Slovenia) was added to the starter and grower feed at the stages of its manufacture in quantities of 0.5 kg/t of feed. Coccidiostat was not added to the final feed. During the 48-day technological period, the clinical condition of the poultry was monitored daily by forage and motor activity, safety, and every 7 days – for growth intensity with the individual determination of body weight on a laboratory scale. The investigation of the blood was carried out from the 35th or 48th day during the growing, period and also investigation of the internal organs – liver, heart, spleen, stomach, thymus, and bursa of Fabricius. The increase of cholesterol, triacylglycerols, and albumin in the blood of II, III, and VI chicken groups was established on the 35th day of the experiment, and the reduction of creatinine in III and VI groups. By that time, the effect of highest dose of I, Se, S caused a decrease in the T3 concentration in the blood of chickens in the VI group compared to the I and II groups. In particular, in the blood of chickens of IV, V and VI groups compared to the I, II, III group under these conditions there was a significant increase in the content of urea, Ca, P, cholesterol, as well as albumin – only in IV group on the 48th day. Triacylglycerols’ content increased in the blood serum of chickens in III and IV groups compared to the II and V groups, but in V group – decreased compared to the III, IV groups. The increase in liver, thymus, and heart mass in the II and V chicken groups was noticed and their decrease in the VI group was revealed compared with the control group. Reliable lower coefficients of the body mass of chickens of III and VI groups may indicate a less notable stimulating biological effect of I, Se, S citrate in these doses on liver development than on the whole organism. The addition of I, Se, S citrate to broiler chickens during the period of growing revealed the difference in their biological action in the presence and absence of the Kokcisan 12% in a mixed fodder. A more notable stimulating effect of low dose of I, Se, S citrate on the growth and development on the chickens' organism was established during the withdrawal of coccidiostatics from their diet. The effect may be due to its inhibitory influence on the biological activity of these elements in the first 35 days of growing. In the final period of chicken growing and withdrawal of ionophore Kokcisan from the diet more noticeable changes were revealed in the studied parameters.

Efficacy of Dietary and Supplementation Interventions for Individuals with Type 2 Diabetes

The prevalence of Type 2 diabetes (T2D) is increasing, which creates a large economic burden. Diet is a critical factor in the treatment and management of T2D; however, there are a large number of dietary approaches and a general lack of consensus regarding the efficacy of each. Therefore, the purpose of this narrative review is twofold: (1) to critically evaluate the effects of various dietary strategies on diabetes management and treatment, such as Mediterranean diet, plant-based diet, low-calorie and very low-calorie diets, intermittent fasting, low-carbohydrate and very low-carbohydrate diets, and low glycemic diets and (2) to examine several purported supplements, such as protein, branched-chain amino acids, creatine, and vitamin D to improve glucose control and body composition. This review can serve as a resource for those wanting to evaluate the evidence supporting the various dietary strategies and supplements that may help manage T2D.

Coupling Complete Blood Count and Steroidomics to Track Low Doses Administration of Recombinant Growth Hormone: An Anti-Doping Perspective

Growth Hormone (GH) under its human recombinant homologue (rhGH), may be abused by athletes to take advantage of its well-known anabolic and lipolytic properties; hence it is prohibited in sports by the World Anti-Doping Agency. Due to the rapid turnover of rhGH, anti-doping screening tests have turned to monitor two endocrine biomarkers (IGF-I and P-III-NP), but unfortunately, they show population-wise variability, limiting the identification rate of rhGH users. Previous studies have evidenced the numerous effects of GH on human physiology, especially in hematopoiesis and steroidogenesis. In this work, aiming to discover novel physiological rhGH biomarkers, we analyzed the complete blood count and the steroidomics profile of healthy, physically active, young males treated either with EPO + rhGH or EPO + placebo. The time-trends of these two physiological routes have been analyzed through geometric trajectory analysis (GTA) and OPLS-DA. Individuals supplemented with micro-doses of rhGH exhibited different leukopoietic and steroidal profiles compared to the control population, suggesting a role of the rhGH in both pathways. In the article, hypotheses on the observed differences are discussed according to the most recent literature and compared to results in animal models. The use of leukopoietic and steroidal biomarkers together with endocrine biomarkers (IGF-1 and P-III-NP) allows to correctly classify over 98% of samples with no false positives, miss-classifying only one single sample (false negative) over a total of 56; a promising result, if compared to the current rhGH detection strategies.

Altered Amino Acid Metabolism in Patients with Cardiorenal Syndrome Type 2: Is It a Problem for Protein and Exercise Prescriptions?

The goal of this retrospective study was to document any alterations in plasma amino acids (AAs) in subjects with cardiorenal syndrome type 2 (CRS 2). We analyzed data from sixteen patients with CRS 2 and eight healthy subjects (control group, C), whose plasma arterial (A) and venous (V) AA concentrations had been measured. Compared to C, the group of CRS 2 patients showed significant reductions by more than 90% in A (p < 0.01) and V (p < 0.01) individual AAs, whereas negative A-V differences that indicated a net muscle AA release (muscle hypercatabolism) were found in 59% of CRS 2 patients (p < 0.03). No significant differences in plasma A and V AA concentrations nor in A-V differences were found between patients with mild kidney damage (N = 5; estimated glomerular filtration rate, eGFR ≥ 60 mL/min/1.73 m²) and patients with moderate-severe kidney damage (N = 11; eGFR < 60 mL/min/1.73 m²). Several plasma arterial AAs correlated with hemodynamic variables, but not with GFR. The study showed that patients with CRS 2 had very low concentrations of circulating AAs, independent of the degree of GFR damage.

Effects of oral contraceptives on thyroid function and vice versa

BACKGROUND

Thyroid gland dysfunction represents an epidemiologically relevant disease in the female gender, where treatment with oral contraceptives (OCs) is frequently prescribed. Although OCs are able to impact the thyroid gland function, scanty data have been released on this matter so far.

AIM

The aim of this article was to review how hormonal OCs, including estrogen- or progesterone-only containing medications, interact with the hepatic production of thyroid-binding globulin (TBG) and, consequently, their effects on serum levels of thyroxine (T4) and triiodothyronine (T3). We also reviewed the effect of Levo-T4 (LT4) administration in women taking OCs and how they influence the thyroid function in both euthyroid women and in those receiving LT4.

REVIEW

The estrogenic component of the pills is capable of increasing various liver proteins, such as TBG, sex hormone-binding protein (SHBG) and coagulation factors. On the other hand, the role of progestogens is to modulate estrogen-dependent effects mainly through their anti-androgenic action. In fact, a reduction in the effects of androgens is useful to keep the thromboembolic and cardiovascular risks low, whereas OCs increase it especially in women with subclinical hypothyroidism or in those treated with LT4. Accordingly, subclinical hypothyroidism is known to be associated with a higher mean platelet volume than normal and this increases cardiovascular risk due to platelet hyperactivity caused by incomplete thrombocytopoietic maturation.

Insulin Stimulation of Protein Synthesis and mTOR Signaling in Chick Myotube Cultures

Insulin stimulates protein synthesis in skeletal muscles. Protein synthesis is controlled by the mechanistic target of rapamycin (mTOR) signaling in skeletal muscles. This study was conducted to investigate the effect of insulin on protein synthesis and mTOR signaling in chick myotube cultures. Chick myotubes were incubated with insulin (1 µg/ml) for 1 h. Protein synthesis, measured using the surface sensing of translation method, was significantly increased by insulin. The phosphorylation of AKT (Thr308 and Ser473), p70 ribosomal S6 kinase 1 (S6K1, Thr389), S6 ribosomal protein (Ser235/236), and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1, Thr37/46) was also significantly increased by insulin. These results suggest that insulin stimulates protein synthesis via mTOR signaling (phosphorylation of AKT, S6K1, S6 ribosomal protein, and 4E-BP1) in chick myotube cultures.

Muscle unloading: A comparison between spaceflight and ground-based models

Prolonged unloading of skeletal muscle, a common outcome of events such as spaceflight, bed rest and hindlimb unloading, can result in extensive metabolic, structural and functional changes in muscle fibres. With advancement in investigations of cellular and molecular mechanisms, understanding of disuse muscle atrophy has significantly increased. However, substantial gaps exist in our understanding of the processes dictating muscle plasticity during unloading, which prevent us from developing effective interventions to combat muscle loss. This review aims to update the status of knowledge and underlying mechanisms leading to cellular and molecular changes in skeletal muscle during unloading. We have also discussed advances in the understanding of contractile dysfunction during spaceflights and in ground-based models of muscle unloading. Additionally, we have elaborated on potential therapeutic interventions that show promising results in boosting muscle mass and strength during mechanical unloading. Finally, we have identified key gaps in our knowledge as well as possible research direction for the future.

Association of milk consumption frequency on muscle mass and strength: an analysis of three representative Korean population studies

PURPOSE

Sarcopenia is an involuntary loss of muscle mass, strength, and physical performance associated with aging. Sarcopenia contributes to adverse health outcomes. Milk contains essential amino acids important for maintaining muscle. We investigated the relationships among milk consumption frequency (MCF), muscle mass, and strength in Korean adults.

METHODS

We analyzed the data from 16,173 adults in the 2008-2011 Korean National Health and Nutrition Examination Survey (KNHANES), 13,537 adults in the 2014-2016 KNHANES, and 8254 adults in the Korean Genome and Epidemiology Study (KoGES). MCF was divided into two groups: (1) MCF less than once per day (MCF < 1 group) and (2) MCF greater than or equal to once per day (MCF ≥ 1 group). Low skeletal muscle mass index (LSMI) was defined using the Foundation for the National Institutes of Health sarcopenia project criteria for low muscle mass. Muscle strength was measured using the hand-grip strength test.

RESULTS

The odds ratio (95% confidence interval) for LSMI in the MCF < 1 group was 1.250 (1.013-1.543) after adjusting for confounding factors, compared with the MCF ≥ 1 group (2008-2011 KNHANES). The adjusted mean for hand-grip strength was higher in the MCF ≥ 1 group (2014-2016 KNHANES). After a mean follow-up of 9 years, fat-free mass/body mass index was higher in the MCF ≥ 1 group than the MCF < 1 group (KoGES).

CONCLUSION

We found that MCF ≥ 1 was significantly associated with higher skeletal muscle index and muscle strength than lower MCF. Milk consumption could help prevent sarcopenia in adults.

From marginal to essential: the golden thread between nutrient sensing, medium composition and Plasmodium vivax maturation in in vitro culture

Historically neglected, due to its biological peculiarities, the absence of a continuous long-term in vitro blood stage culture system and a propensity towards high morbidity rather than mortality, Plasmodium vivax was put back on the agenda during the last decade by the paradigm shift in the fight against malaria from malaria control to malaria eradication. While the incidence of the deadliest form of malaria, Plasmodium falciparum malaria, has declined since this paradigm shift took hold, the prospects of eradication are now threatened by the increase in the incidence of other human malaria parasite species. Plasmodium vivax is geographically the most widely distributed human malaria parasite, characterized by millions of clinical cases every year and responsible for a massive economic burden. The urgent need to tackle the unique biological challenges posed by this parasite led to renewed efforts aimed at establishing a continuous, long-term in vitro P. vivax blood stage culture. Based on recent discoveries on the role of nutrient sensing in Plasmodium’s pathophysiology, this review article critically assesses the extensive body of literature concerning Plasmodium culture conditions with a specific focus on culture media used in attempts to culture different Plasmodium spp. Hereby, the effect of specific media components on the parasite’s in vitro fitness and the maturation of the parasite’s host cell, the reticulocyte, is analysed. Challenging the wide-held belief that it is sufficient to find the right parasite isolate and give it the right type of cells to invade for P. vivax to grow in vitro, this review contends that a healthy side-by-side maturation of both the parasite and its host cell, the reticulocyte, is necessary in the adaptation of P. vivax to in vitro growth and argues that culture conditions and the media in particular play an essential role in this maturation process.

Effects of Aerobic Exercise Combined with Panaxatriol Derived from Ginseng on Insulin Resistance and Skeletal Muscle Mass in Type 2 Diabetic Mice

Insulin resistance reduces insulin-induced muscle protein synthesis and accelerates muscle protein degradation. Ginseng ingestion has been reported to improve insulin resistance through the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. We hypothesized that panaxatriol (PT) derived from ginseng in combination with aerobic exercise (EX) may further promote protein synthesis and suppress protein degradation, and subsequently maintain muscle mass through the amelioration of insulin resistance. KKAy insulin-resistant mice were divided into control, panaxatriol only (PT), exercise only (EX), and EX+PT groups. EX and EX+PT ran on the treadmill for 45 min at 15 m/min 5 d/wk for 6 wk. PT and EX+PT groups were fed a standard diet containing 0.2% PT for 6 wk. Homeostasis model assessment for insulin resistance (HOMA-R) values was significantly improved after exercise for 6 wk. Moreover, EX+PT mice showed improved HOMA-R as compared to EX mice. p70S6K phosphorylation after a 4 h fast was significantly higher in EX than in the non-exercise control, and it was higher in EX+PT mice than in EX mice. Atrogin1 mRNA expression was significantly lower in EX than in the non-exercise control, and was significantly lowered further by PT treatment. EX and EX+PT mice showed higher soleus muscle mass and cross-sectional area (CSA) of the soleus myofibers than control animals, with higher values noted for both parameters in EX+PT than in EX. These results suggest that aerobic exercise and PT ingestion may contribute to maintain skeletal muscle mass through the amelioration of insulin resistance.

Regulation of Autophagy in Chick Myotubes: Effects of Insulin, Insulin-Like Growth Factor-I, and Amino Acids

Autophagy, an intracellular bulk protein degradation system in skeletal muscle, is increased under catabolic conditions resulting in muscle atrophy. This study aimed to investigate the effects of insulin, insulin-like growth factor (IGF)-I, and amino acids on autophagy (LC3-II content and expression of autophagy-related genes) in chick myotubes. Chick myotubes were incubated with insulin (1 µg/ml), IGF-I (100 ng/ml), and amino acids for 3 h. The LC3-II content, an index of autophagosome formation, and mRNA expression of LC3B and GABARAPL1 were significantly decreased by insulin. The LC3-II content, but not mRNA expression of autophagy-related genes, was also significantly decreased by IGF-I. The LC3-II content and LC3B mRNA level were also significantly decreased by amino acids. The mRNA expression of atrogin-1/MAFbx, a muscle-specific ubiquitin ligase, was also significantly decreased by insulin, IGF-I, and amino acids in chick myotubes. These results indicated that insulin, IGF-I, and amino acids regulate autophagy as well as the ubiquitin-proteasome proteolytic pathway in chick myotubes.

Succinate promotes skeletal muscle protein synthesis via Erk1/2 signaling pathway

It is well known that endurance training is effective to attenuate skeletal muscle atrophy. Succinate is a typical TCA metabolite, of which exercise could dramatically increase the content. The present study aimed to investigate the effect of succinate on protein synthesis in skeletal muscle, and try to delineate the underlying mechanism. The in vitro study revealed that succinate dose‑dependently increased protein synthesis in C2C12 myotube along with the enhancement of phosphorylation levels of AKT Serine/Threonine Kinase 1(Akt), mammalian target of rapamycin, S6, eukaryotic translation initiation factor 4E, 4E binding protein 1 and forkhead box O (FoxO) 3a. Furthermore, it was demonstrated that 20 mM succinate markedly increased [Ca2+]i. Then, the phospho‑extracellular regulated kinase (Erk), ‑Akt level and the crosstalk between Erk and Akt were elevated in response to succinate. Notably, the Erk antagonist (U0126) or mTOR inhibitor (rapamycin) abolished the effect of succinate on protein synthesis. The in vivo study verified that succinate dose‑dependently increased the protein synthesis, in addition to phosphorylation levels of Erk, Akt and FoxO3a in gastrocnemius muscle. In summary, these findings demonstrated that succinate promoted skeletal muscle protein deposition via Erk/Akt signaling pathway.

Despite Inflammation, Supplemented Essential Amino Acids May Improve Circulating Levels of Albumin and Haemoglobin in Patients after Hip Fractures

Essential amino acids (EAAs) are nutritional substrates that promote body protein synthesis; thus we hypothesised that their supplementation may improve circulating albumin (Alb) and haemoglobin (Hb) in rehabilitative elderly patients following hip fractures (HF). Out of the 145 HF patients originally enrolled in our study, 112 completed the protocol. These subjects were divided into two randomised groups, each containing 56 patients. For a period of two months, one group (age 81.4 ± 8.1 years; male/female 27/29) received a placebo, and the other (age 83.1 ± 7.5 years; male/female 25/31) received 4 + 4 g/day oral EAAs. At admission, the prevalence of both hypoAlb (<3.5 g/dL) and hypoHb (<13 g/dL male, <12 g/dL female) was similar in the placebo group (64.3% hypoAlb, 66% hypoHb) and the treated group of patients (73.2% hypoAlb, 67.8% hypoHb). At discharge, however, the prevalence of hypoAlb had reduced more in EAAs than in placebo subjects (31.7% in EAAs vs. 77.8% in placebo; p < 0.001). There was a 34.2% reduction of anaemia in hypoHb in EAA subjects and 18.9% in placebo subjects, but the difference was not statistically significant. Oral supplementation of EAAs improves hypoAlb and, to a lesser extent, Hb in elderly rehabilitative subjects with hip fractures. Anaemia was reduced in more than one third of patients, which, despite not being statistically significant, may be clinically relevant.

Chronic Intake of Sucrose Accelerates Sarcopenia in Older Male Rats through Alterations in Insulin Sensitivity and Muscle Protein Synthesis

BACKGROUND

Today, high chronic intake of added sugars is frequent, which leads to inflammation, oxidative stress, and insulin resistance. These 3 factors could reduce meal-induced stimulation of muscle protein synthesis and thus aggravate the age-related loss of muscle mass (sarcopenia).

OBJECTIVES

Our aims were to determine if added sugars could accelerate sarcopenia and to assess the capacity of antioxidants and anti-inflammatory agents to prevent this.

METHODS

For 5 mo, 16-mo-old male rats were starch fed (13% sucrose and 49% wheat starch diet) or sucrose fed (62% sucrose and 0% wheat starch diet) with or without rutin (5 g/kg diet), vitamin E (4 times), vitamin A (2 times), vitamin D (5 times), selenium (10 times), and zinc (+44%) (R) supplementation. We measured the evolution of body composition and inflammation, plasma insulin-like growth factor 1 (IGF-I) concentration and total antioxidant status, insulin sensitivity (oral-glucose-tolerance test), muscle weight, superoxide dismutase activity, glutathione concentration, and in vivo protein synthesis rates.

RESULTS

Sucrose-fed rats lost significantly more lean body mass (-8.1% vs. -5.4%, respectively) and retained more fat mass (+0.2% vs. -33%, respectively) than starch-fed rats. Final muscle mass was 11% higher in starch-fed rats than in sucrose-fed rats. Sucrose had little effect on inflammation, oxidative stress, and plasma IGF-I concentration but reduced the insulin sensitivity index (divided by 2). Meal-induced stimulation of muscle protein synthesis was significantly lower in sucrose-fed rats (+7.3%) than in starch-fed rats (+22%). R supplementation slightly but significantly reduced oxidative stress and increased muscle protein concentration (+4%) but did not restore postprandial stimulation of muscle protein synthesis.

CONCLUSIONS

High chronic sucrose intake accelerates sarcopenia in older male rats through an alteration of postprandial stimulation of muscle protein synthesis. This effect could be explained by a decrease of insulin sensitivity rather than by changes in plasma IGF-I, inflammation, and/or oxidative stress.

Lysine nutrition in swine and the related monogastric animals: muscle protein biosynthesis and beyond

Improving feed efficiency of pigs with dietary application of amino acids (AAs) is becoming increasingly important because this practice can not only secure the plasma AA supply for muscle growth but also protect the environment from nitrogen discharge with feces and urine. Lysine, the first limiting AA in typical swine diets, is a substrate for generating body proteins, peptides, and non-peptide molecules, while excess lysine is catabolized as an energy source. From a regulatory standpoint, lysine is at the top level in controlling AA metabolism, and lysine can also affect the metabolism of other nutrients. The effect of lysine on hormone production and activities is reflected by the change of plasma concentrations of insulin and insulin-like growth factor 1. Lysine residues in peptides are important sites for protein post-translational modification involved in epigenetic regulation of gene expression. An inborn error of a cationic AA transporter in humans can lead to a lysinuric protein intolerance condition. Dietary deficiency of lysine will impair animal immunity and elevate animal susceptibility to infectious diseases. Because lysine deficiency has negative impact on animal health and growth performance and it appears that dietary lysine is non-toxic even at a high dose of supplementation, nutritional emphasis should be put on lysine supplementation to avoid its deficiency rather than toxicity. Improvement of muscle growth of monogastric animals such as pigs via dietary lysine supply may be due to a greater increase in protein synthesis rather than a decrease in protein degradation. Nevertheless, the underlying metabolic and molecular mechanisms regarding lysine effect on muscle protein accretion merits further clarification. Future research undertaken to fully elucidate the metabolic and regulatory mechanisms of lysine nutrition could provide a sound scientific foundation necessary for developing novel nutritional strategies to enhance the muscle growth and development of meat animals.

Morphometric analysis of somatotropic cells of the adenohypophysis and muscle fibers of the psoas muscle in the process of aging in humans

The aim of this research was to quantify changes of the adenohypophyseal somatotropes and types 1 and 2 muscle fibers with aging, as well as to establish mutual interactions and correlations with age. Material was samples of hypophysis and psoas major muscle of 27 cadavers of both genders, aged from 30 to 90 years. Adenohypophyseal and psoas major tissue sections were immunohistochemically processed and stained by anti-human growth hormone and anti-fast myosin antibodies, respectively. Morphometric analysis was performed by ImageJ. Results of morphometric analysis showed a significant increase in the somatotrope area, and significant decrease in somatotrope volume density and nucleocytoplasmic ratio with age. Cross-sectional areas of types 1 and 2, and volume density of type 2 muscle fibers decreased significantly with age. One Way ANOVA showed that the latter cited changes in the somatotropes and types 1 and 2 muscle fibers mostly become significant after the age of 70. Significant positive correlation was observed between the area of the somatotropes and volume density of type 2 muscle fibers. A significant negative correlation was detected between the nucleocytoplasmic ratio of the somatotropes and cross-sectional areas of types 1 and 2 muscle fibers. So, it can be concluded that after the age of 70, there is significant loss of the anterior pituitary's somatotropes associated with hypertrophy and possible functional decline of the remained cells. Age-related changes in the somatotropes are correlated with the simultaneous atrophy of type 1, as well as with the atrophy and loss of type 2 muscle fibers.

New approaches to thyroid hormones and purinergic signaling

It is known that thyroid hormones influence a wide variety of events at the molecular, cellular, and functional levels. Thyroid hormones (TH) play pivotal roles in growth, cell proliferation, differentiation, apoptosis, development, and metabolic homeostasis via thyroid hormone receptors (TRs) by controlling the expression of TR target genes. Most of these effects result in pathological and physiological events and are already well described in the literature. Even so, many recent studies have been devoted to bringing new information on problems in controlling the synthesis and release of these hormones and to elucidating mechanisms of the action of these hormones unconventionally. The purinergic system was recently linked to thyroid diseases, including enzymes, receptors, and enzyme products related to neurotransmitter release, nociception, behavior, and other vascular systems. Thus, throughout this text we intend to relate the relationship between the TH in physiological and pathological situations with the purinergic signaling.

Insulinotropic and muscle protein synthetic effects of branched-chain amino acids: potential therapy for type 2 diabetes and sarcopenia

The loss of muscle mass and strength with aging (i.e., sarcopenia) has a negative effect on functional independence and overall quality of life. One main contributing factor to sarcopenia is the reduced ability to increase skeletal muscle protein synthesis in response to habitual feeding, possibly due to a reduction in postprandial insulin release and an increase in insulin resistance. Branched-chain amino acids (BCAA), primarily leucine, increases the activation of pathways involved in muscle protein synthesis through insulin-dependent and independent mechanisms, which may help counteract the "anabolic resistance" to feeding in older adults. Leucine exhibits strong insulinotropic characteristics, which may increase amino acid availability for muscle protein synthesis, reduce muscle protein breakdown, and enhance glucose disposal to help maintain blood glucose homeostasis.

Supplementation of essential amino acids may reduce the occurrence of infections in rehabilitation patients with brain injury

BACKGROUND

To investigate whether supplementation with oral essential amino acids (EAAs) may reduce the occurrence of nosocomial infection among patients with brain injury (BI: stroke, trauma, anoxic coma).

METHODS

Patients (n = 125; 77 men, 48 women; mean age 63 ± 15 years) with stroke (68.8%), subarachnoid hemorrhage (17.6%), traumatic BI (7.2%), and anoxic BI (6.4%) 88 ± 15 days after the index event. Patients were randomly assigned to 2 months of oral EAAs (n = 63; 8 g/d) or placebo (n = 62).

RESULTS

Over the first month of rehabilitation, there were 60 infections in the whole population of 125 patients (48%); however, the rate was 23.2% lower in the EAA group (23 episodes/63 patients; 36.5%) than in the placebo group (37 episodes/62 patients; 59.7%) (P < .01). The types of infection were similarly distributed between the 2 groups. Serum levels of prealbumin <20 mg/dL and C-reactive protein (CRP) >0.3 mg/dL were the best predictors of future infection (prealbumin: odds ratio [OR] = 4.17, confidence interval [CI] 1.84-9.45, P < .001; CRP: OR = 3.8, CI 1.71-8.44, P < .001).

CONCLUSION

Supplementary EAAs may reduce the occurrence of nosocomial infections in rehabilitation patients with BI. Prealbumin and CRP are the best predictors of future infections.

Effects of dietary glutamine supplementation on the body composition and protein status of early-weaned mice inoculated with Mycobacterium bovis Bacillus Calmette-Guerin

Glutamine, one of the most abundant amino acids found in maternal milk, favors protein anabolism. Early-weaned babies are deprived of this source of glutamine, in a period during which endogenous biosynthesis may be insufficient for tissue needs in states of metabolic stress, mainly during infections. The objective of this study was to verify the effects of dietary glutamine supplementation on the body composition and visceral protein status of early-weaned mice inoculated with Mycobacterium bovis Bacillus Calmette-Guérin (BCG). Mice were weaned early on their 14th day of life and seperated into two groups, one of which was fed a glutamine-free diet (n = 16) and the other a glutamine-supplemented diet (40 g/kg diet) (n = 16). At 21 days of age, some mice were intraperitoneally injected with BCG. Euthanasia was performed at the 28th day of age. BCG inoculation significantly reduced body weight (P < 0.001), lean mass (P = 0.002), water (P = 0.006), protein (P = 0.007) and lipid content (P = 0.001) in the carcass. Dietary glutamine supplementation resulted in a significant increase in serum IGF-1 (P = 0.019) and albumin (P = 0.025) concentration, muscle protein concentration (P = 0.035) and lipid content (P = 0.002) in the carcass. In conclusion, dietary glutamine supplementation had a positive influence on visceral protein status but did not affect body composition in early-weaned mice inoculated with BCG.

Thyroid hormones and growth in health and disease

Thyroid hormones regulate growth by several mechanisms. In addition to their negative feedback effect on the stimulatory hormones thyrotropin-releasing hormone (TRH) and thyrotropin (TSH), thyroid hormones also regulate their receptors in various physiological and pathological conditions. Up-regulation and down-regulation of the thyroid receptors fine-tune the biological effects exerted by the thyroid hormones. Interestingly, the deiodinase enzyme system is another intrinsic regulator of thyroid physiology that adjusts the availability of thyroid hormones to the tissues, which is essential for normal growth and development. Almost all chronic diseases of childhood impair growth and development. Every disease may have a unique mechanism to halt linear growth, but reduced serum concentration or diminished local availability of thyroid hormones seems to be a common pathway. Therefore, the effects of systemic diseases on thyroid physiology must be taken into consideration in the evaluation of growth retardation in affected children.

Methionine deprivation regulates the S6K1 pathway and protein synthesis in avian QM7 myoblasts without activating the GCN2/eIF2 alpha cascade

Amino acids modulate mRNA translation through the 70 kDa ribosomal protein S6 kinase (S6K1) and the general control nondepressible 2 protein kinase (GCN2)/eukaryotic initiation factor 2 alpha eIF2 alpha pathways. The aim of the present study was therefore to explore the signaling cascades potentially modulated by methionine availability in quail muscle QM7 myoblasts using media providing all other amino acids. Methionine deprivation caused a lower S6K1 phosphorylation compared with control (Ctl) cells. Supplying the methionine-deprived media with L- and DL-methionine isomers restored S6K1 phosphorylation to the levels observed in Ctl cells. Methionine also regulated downstream S6K1 targets (i.e. ribosomal protein S6 and eukaryotic elongation factor 2), modulated translation preinitiation complex (PIC) assembly, and stimulated protein synthesis. Replacing the lacking methionine with D-methionine or its hydroxyanalog [2-hydroxy-(4-methylthio) butanoic acid] did not restore S6K1 activation or protein synthesis. Conversely, the S6K1 pathway was activated by a methionine precursor, the ketoanalog of methionine. Methionine availability regulated the GCN2/eIF2 alpha pathway. However, our results indicate that methionine deprivation led to lower protein synthesis without activating eIF2 alpha phosphorylation, a process known to limit the formation of the 43S PIC. Using the amino acid alcohol methioninol did not decrease S6K1 phosphorylation or activity and did not alter the regulation of protein synthesis by methionine. These findings suggest that methionine exerts an effect on S6K1 signaling and protein synthesis in avian QM7 myoblasts through a mechanism partly independent of the global regulation via tRNA charging.

Role of IGF-I in skeletal muscle mass maintenance

The recent identification of signaling elements that regulate skeletal muscle protein balance has provided the opportunity to determine how IGF-I alters these processes. Animal studies have revealed the important role of IGF-I in preventing muscle atrophy and enabled investigators to determine the hierarchy of signaling pathways and events within each pathway that are modulated by IGF-I. These discoveries provide opportunity for future studies to target these important signaling events and develop strategies to reverse loss of muscle mass that accompanies these catabolic states. Because there are no approved medical therapies that will reverse catabolism at present, this represents an opportunity to fulfill a major unmet medical need.

No major sex differences in muscle protein synthesis rates in the postabsorptive state and during hyperinsulinemia-hyperaminoacidemia in middle-aged adults

Men have more muscle than women, but most studies evaluating sex differences in muscle protein metabolism have been unable to discern sexual dimorphism in basal muscle protein turnover rates in young and middle-aged adults. We hypothesized that the anabolic response to nutritional stimuli (i.e., amino acids and insulin) would be greater in young/middle-aged men than women. We therefore measured the rates of muscle protein synthesis (MPS) in 16 healthy individuals [8 men and 8 women, matched for age (mean +/- SE: 37.7 +/- 1.5 yr) and body mass index (25.2 +/- 0.7 kg/m2)] after an overnight fast (plasma insulin approximately 5 microU/ml and plasma phenylalanine approximately 60 microM) and during a hyperinsulinemic-hyperaminoacidemic-euglycemic clamp (plasma insulin approximately 28 microU/ml; plasma phenylalanine approximately 110 microM; plasma glucose approximately 5.4 mM). The rates of MPS were not different between men and women (ANOVA main effect for sex; P = 0.49). During the clamp, the rate of MPS increased by approximately 50% (P = 0.003) with no difference in the increases from basal values between men and women (+0.019 +/- 0.004 vs. +0.018 +/- 0.010%/h, respectively; P = 0.93). There were also no differences between men and women in the basal concentrations of muscle phosphorylated Akt(Ser473), Akt(Thr308), mTOR(Ser2448), and p70s6k(Thr389) or in the hyperinsulinemia-hyperaminoacidemia-induced increases in phosphorylation of those signaling elements (P > or = 0.25). We conclude that there are no major differences in the rate of MPS and its intracellular control during basal conditions and during hyperinsulinemia-hyperaminoacidema between young and middle-aged adult men and women.

Retinoic acid reduces glucocorticoid sensitivity in C2C12 myotubes by decreasing 11beta-hydroxysteroid dehydrogenase type 1 and glucocorticoid receptor activities

Vitamin A is a nutrient with remarkable effects on adipose tissue and skeletal muscles, and plays a role in controlling energy balance. Retinoic acid (RA), the carboxylic form of vitamin A, has been associated with improved glucose tolerance and insulin sensitivity. In contrast, elevated glucocorticoids have been implicated in the development of insulin resistance and impaired glucose tolerance. Here, we investigated whether RA might counteract glucocorticoid effects in skeletal muscle cells by lowering 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1)-dependent local glucocorticoid activation and/or activation of glucocorticoid receptor (GR). We found a dose-dependent down-regulation of 11beta-HSD1 mRNA expression and activity upon incubation of fully differentiated mouse C2C12 myotubes with RA. In addition, RA inhibited GR transactivation by an 11beta-HSD1-independent mechanism. The presence of RA during myogenesis did not prevent myotube formation but resulted in relatively glucocorticoid-resistant myotubes, exhibiting very low 11beta-HSD1 expression and GR activity. The use of selective retinoic acid receptor (RAR) and retinoid X receptor ligands provided evidence that these effects were mediated through RARgamma. Importantly, short hairpin RNA against RARgamma abolished the effect of RA on 11beta-HSD1 and GR. In conclusion, we provide evidence for an important role of RA in the control of glucocorticoid activity during myogenesis and in myotubes. Disturbances of the nutrient and hormonal regulation of glucocorticoid action in skeletal muscles might be relevant for metabolic diseases.

Dietary intervention with vitamin D, calcium, and whey protein reduced fat mass and increased lean mass in rats

The aim of the current study was to determine the effects and the mechanisms of inclusion of dietary whey protein, high calcium, and high vitamin D intake with either a high-sucrose or high-fat base diets on body composition of rodents. Male Wistar rats were assigned to either no whey protein, suboptimal calcium (0.25%), and vitamin D (400 IU/kg) diet (LD), or a diet containing whey protein, high calcium (1.5%), and vitamin D (10 000 IU/kg) diet (HD), and either high-fat (40% of energy) or high-sucrose (60%) base diets for 13 weeks. Liver tissue homogenates were used to determine [(14)C]glucose and [(14)C]palmitate oxidation. mRNA expression of enzymes related to energy metabolism in liver, adipose, and muscle, as well as regulators of muscle mass and insulin receptor was assessed. The results demonstrated that there was reduced accumulation of body fat mass (P = .01) and greater lean mass (P = .03) for the HD- compared to LD-fed group regardless of the background diet. There were no consistent differences between the LD and HD groups across background diets in substrate oxidation and mRNA expression for enzymes measured that regulate energy metabolism, myostatin, or muscle vascular endothelial growth factor. However, there was an increase in insulin receptor mRNA expression in muscle in the HD compared to the LD groups. In conclusion, elevated whey protein, calcium, and vitamin D intake resulted in reduced accumulation of body fat mass and increased lean mass, with a commensurate increase in insulin receptor expression, regardless of the level of calories from fat or sucrose.

The UPS in diabetes and obesity

Type 2 diabetes is caused by defects in both insulin signaling and insulin secretion. Though the role of the ubiquitin proteasome system (UPS) in the pathogenesis of type 2 diabetes remains largely unexplored, the few examples present in the literature are interesting and suggest targets for drug development. Studies indicate that insulin resistance can be induced by stimulating the degradation of important molecules in the insulin signaling pathway, in particular the insulin receptor substrate proteins IRS1, IRS2 and the kinase AKT1 (Akt). In addition, a defect in insulin secretion could occur due to UPS-mediated degradation of IRS2 in the β-cells of the pancreas. The UPS also appears to be involved in regulating lipid synthesis in adipocytes and lipid production by the liver and could influence the development of obesity. Other possible mechanisms for inducing defects in insulin signaling and secretion remain to be explored, including the role of ubiquitylation in insulin receptor internalization and trafficking.

Republished from Current BioData's Targeted Proteins database (TPdb; ).

Growth hormone exerts acute vascular effects independent of systemic or muscle insulin-like growth factor I

CONTEXT

Endothelial dysfunction is common in patients with GH deficiency who are at increased risk for premature cardiovascular death. GH regulates vascular tone and reactivity in humans.

OBJECTIVE

Our objective was to explore the mechanisms underlying the GH's acute vascular effects. DESIGN AND STUDY SETTING: There were 10 healthy, lean and young, volunteers studied after an overnight fast. GH was infused systemically for 6 h at 0.06 microg/kg.min. Biopsy of the vastus lateralis muscle was done in seven subjects before and after GH infusion. Human aortic endothelial cells (HAECs) were incubated with GH in vitro.

RESULTS

GH infusion increased plasma GH to 32.9 +/- 1.5 ng/ml and forearm blood flow by 66% (P < 0.001). GH infusion did not significantly change plasma IGF-I concentrations, muscle IGF-I mRNA expression, and muscle Akt phosphorylation, suggesting a lack of IGF-I action in muscle. Because it was reported that GH exerts an acute vascular effect via a nitric oxide (NO)-dependent mechanism, we performed additional in vitro experiments using HAECs. HAECs express abundant GH receptors. Incubating HAECs with GH at 30 ng/ml for 3 or 6 h did not alter endothelial NO synthase (eNOS) protein content but time dependently increased the phosphorylation and activity of eNOS, thus demonstrating a direct effect of GH on endothelial cells.

CONCLUSIONS

GH exerts an acute vascular effect independent of both systemic and local IGF-I production, and this effect is likely via direct action on GH receptors and eNOS in the vascular endothelium.

Growth hormone effects on protein metabolism

Growth hormone (GH) has a pivotal role in regulating in vivo protein metabolism. GH enhances protein anabolism at the wholebody level, mainly by stimulating protein synthesis. It remains incompletely understood whether this important GH effect on protein synthesis occurs in all tissues. This effect of GH may be different with acute versus chronic administration. These differences in the GH exposure may have different effects based not only on direct GH stimulation of protein synthesis but also the variable effects at the level of gene transcription that ultimately affect protein metabolism. Other GH effects are likely to be mediated by changes in various metabolites and hormones that also likely differ based on the duration of GH administration.

Effect of intravenous amino acids on protein kinetics in preterm infants

PURPOSE OF REVIEW

To summarize recent findings of the effects of intravenous amino acids on protein kinetics in low-birth-weight infants and to describe the potential cellular mechanism for these observations.

RECENT FINDINGS

Amino acids administered intravenously for 3-5 h in infants have been shown to suppress whole-body proteolysis. Recent data in low-birth-weight infants show that an increase in the dose of amino acid caused a suppression of proteolysis, and a decrease in the rate of glutamine and urea synthesis. These responses returned to basal state, however, when the amino acid infusion continued for 20-24 h. Supplementation with glutamine sustained the suppression of proteolysis after 3-5 days. Plasma insulin concentration did not change during the amino acid infusion. Data from studies in adults and from in vitro studies suggest that the amino acids impact protein breakdown and synthesis via the mammalian target of rapamycin pathway, stimulating initiation of translation and suppressing autophagic proteolysis.

SUMMARY

Intravenous amino acids, by increasing extracellular amino acid concentration, transiently stimulate protein synthesis and suppress protein breakdown. These effects return to basal state when the amino acid infusions are prolonged. The mechanism of this adaptive response remains to be determined.