Skeletal Muscle Depletion Research Articles

Low body mass index and sarcopenia associated with dose-limiting toxicity of sorafenib in patients with renal cell carcinoma

BackgroundPatients with severe depletion of skeletal muscle (sarcopenia) are prone to dose-limiting toxicity (DLT) during fluoropyrimidine therapy. We hypothesized that sarcopenia may also predict toxicity of targeted therapy drugs. Materials and methodsMetastatic renal cell cancer (RCC) patients (n=55) received sorafenib 400 mg b.i.d. Weight, height and skeletal muscle cross-sectional area at the third lumbar vertebra were measured by computed tomography (CT). Toxicity was assessed. ResultsDLT occurred in 22% of patients overall, of which three-quarters were dose reductions to 400 mg and the remainder entailed termination of treatment. DLT was most common (41%) in sarcopenic patients whose body mass index (BMI) was <25 kg/m2 and least common (13%) in patients who were not sarcopenic and/or overweight or obese (P=0.03). Toxicity was especially prevalent in sarcopenic male patients with BMI < 25, with 71% of men with these characteristics being unable to continue treatment at 800 mg/day. By contrast, only 5% of male patients whose muscle index was above the cut-off for sarcopenia and only 11% of male patients whose BMI was >25 experienced a DLT. ConclusionBMI < 25 kg/m2 with diminished muscle mass is a significant predictor of toxicity in metastatic RCC patients treated with sorafenib.

Glutamine prevents myostatin hyperexpression and protein hypercatabolism induced in C2C12 myotubes by tumor necrosis factor-α

Depletion of skeletal muscle protein mainly results from enhanced protein breakdown, caused by activation of proteolytic systems such as the Ca2+-dependent and the ATP-ubiquitin-dependent ones. In the last few years, enhanced expression and bioactivity of myostatin have been reported in several pathologies characterized by marked skeletal muscle depletion. More recently, high myostatin levels have been associated with glucocorticoid-induced hypercatabolism. The search for therapeutical strategies aimed at preventing/correcting protein hypercatabolism has been directed to inhibit humoral mediators known for their pro-catabolic action, such as TNFα. The present study has been aimed to investigate the involvement of TNFα in the regulation of both myostatin expression and intracellular protein catabolism, and the possibility to interfere with such modulations by means of amino acid supplementation. For this purpose, C2C12 myotubes exposed to TNFα in the presence or in the absence of amino acid (glutamine or leucine) supplementation have been used. Myotube treatment with TNFα leads to both hyperexpression of the muscle-specific ubiquitin ligase atrogin-1, and enhanced activity of the Ca(2+)-dependent proteolytic system. These changes are associated with increased myostatin expression. Glutamine supplementation effectively prevents TNFα-induced muscle protein loss and restores normal myostatin levels. The results shown in the present study indicate a direct involvement of TNFα in the onset of myotube protein loss and in the perturbation of myostatin-dependent signaling. In addition, the protective effect exerted by glutamine suggests that amino acid supplementation could represent a possible strategy to improve muscle mass.

Regulation of human metabolism by hypoxia-inducible factor

The hypoxia-inducible factor (HIF) family of transcription factors directs a coordinated cellular response to hypoxia that includes the transcriptional regulation of a number of metabolic enzymes. Chuvash polycythemia (CP) is an autosomal recessive human disorder in which the regulatory degradation of HIF is impaired, resulting in elevated levels of HIF at normal oxygen tensions. Apart from the polycythemia, CP patients have marked abnormalities of cardiopulmonary function. No studies of integrated metabolic function have been reported. Here we describe the response of these patients to a series of metabolic stresses: exercise of a large muscle mass on a cycle ergometer, exercise of a small muscle mass (calf muscle) which allowed noninvasive in vivo assessments of muscle metabolism using (31)P magnetic resonance spectroscopy, and a standard meal tolerance test. During exercise, CP patients had early and marked phosphocreatine depletion and acidosis in skeletal muscle, greater accumulation of lactate in blood, and reduced maximum exercise capacities. Muscle biopsy specimens from CP patients showed elevated levels of transcript for pyruvate dehydrogenase kinase, phosphofructokinase, and muscle pyruvate kinase. In cell culture, a range of experimental manipulations have been used to study the effects of HIF on cellular metabolism. However, these approaches provide no potential to investigate integrated responses at the level of the whole organism. Although CP is relatively subtle disorder, our study now reveals a striking regulatory role for HIF on metabolism during exercise in humans. These findings have significant implications for the development of therapeutic approaches targeting the HIF pathway.

Hypothesis: Muscular glutamine deficiency in sepsis—A necessary step for a hibernation-like state?

Glutamine depletion in skeletal muscle of severely ill patients is an outstanding metabolic marker related to acute skeletal muscle wasting. To date it is unclear why intracellular glutamine concentrations are lowered in skeletal muscle to such an extent when simultaneously muscular glutamine synthesis and release are stimulated. This essay introduces a hypothesis that intracellular glutamine deficiency is part of a metabolic program maintaining cell integrity. This program seems to resemble short-term hibernation, which can be observed in various mammalian species during periods of starvation. Interestingly, even in septic patients who do not survive, there are no signs of apoptosis or necrosis in affected organs. Therefore, in severe illness evolutionarily conserved energy saving programs may be switched on for protecting the organs in a mode reminiscent of hibernation. This would explain the low energy expenditure as described for septic patients and the limited success of nutrition in avoiding skeletal muscle atrophy in sepsis.

Secondary mtDNA Defects Do Not Cause Optic Nerve Dysfunction in a Mouse Model of Dominant Optic Atrophy

The majority of patients with autosomal dominant optic atrophy (DOA) harbor pathogenic OPA1 mutations and certain missense mutations, mostly within the GTPase domain, have recently been shown to cause multiple mitochondrial DNA (mtDNA) deletions in skeletal muscle. This raises the possibility that the optic neuropathy could be the result of secondary mtDNA defects accumulating within retinal ganglion cells (RGCs). To explore this hypothesis, the authors looked for evidence of mitochondrial dysfunction in a mouse model of DOA and documented the visual and neurologic progression in aging mutant mice. Visual function was assessed with a rotating optokinetic (OKN) drum at ages 13 and 18 months and neurologic phenotyping was performed using the primary SHIRPA screen at age 13 months, comparing mutant Opa1(+/)(-) mice with wild-type C57Bl/6 mice. The presence of cytochrome c oxidase (COX) deficiency and multiple mtDNA deletions was investigated in gastrocnemius muscle and eye specimens harvested from 2- and 11-month-old Opa1(+/+) and Opa1(+/)(-) mice. At age 13 months, Opa1(+/)(-) mice had a statistically significant reduction in OKN responses compared to C57Bl/6 controls with both 2 degrees and 8 degrees gratings (P < 0.001). At age 18 months, the difference between the two groups was significant for the 8 degrees grating (P = 0.003) but not for the 2 degrees grating (P = 0.082). Opa1(+/)(-) mice did not exhibit any significant neuromuscular deficits and no COX deficient areas or secondary mtDNA deletions were identified in skeletal muscle or the RGC layer. There was also no evidence of significant mtDNA depletion or proliferation in skeletal muscle from Opa1(+/)(-) mice. COX deficiency and mtDNA abnormalities do not contribute to optic nerve dysfunction in pure DOA.

Sarcopenia as a Determinant of Chemotherapy Toxicity and Time to Tumor Progression in Metastatic Breast Cancer Patients Receiving Capecitabine Treatment

Body composition has emerged as an important prognostic factor in cancer patients. Severe depletion of skeletal muscle (sarcopenia) and, hence, of overall lean body mass may represent an occult condition in individuals with normal or even high body weight. Sarcopenia has been associated with poor performance status, 5-fluorouracil toxicity, and shortened survival in cancer patients. Here, we prospectively studied patients with metastatic breast cancer receiving capecitabine treatment in order to determine if sarcopenia was associated with a higher incidence of toxicity and a shorter time to tumor progression (TTP). Fifty-five women with metastatic breast cancer resistant to anthracycline and/or taxane treatment were included. Skeletal muscle cross-sectional area at the third lumbar vertebra was measured by computerized tomography, and sarcopenia was defined using a previously published cutoff point. Toxicity was assessed after cycle 1 of treatment, and TTP was determined prospectively. Approximately 25% of patients were classified as sarcopenic, and this feature was seen in normal weight, overweight, and obese individuals. Toxicity was present in 50% of sarcopenic patients, compared with only 20% of nonsarcopenic patients (P = 0.03), and TTP was shorter in sarcopenic patients (101.4 days; confidence interval, 59.8-142.9) versus nonsarcopenic patients (173.3 days; confidence interval, 126.1-220.5; P = 0.05). Sarcopenia is a significant predictor of toxicity and TTP in metastatic breast cancer patients treated with capecitabine. Our results raise the potential use of body composition assessment to predict toxicity and individualize chemotherapy dosing.

Treating hyperglycemia improves skeletal muscle protein metabolism in cancer patients after major surgery

Cancer and surgical stress interact to aggravate insulin resistance, protein catabolism, and glutamine depletion in skeletal muscle. We compared the effects of insulin-mediated euglycemia and moderate hyperglycemia on kinetics of protein and selected amino acids in skeletal muscle of female cancer patients after major surgery. In each patient, a 24-hr period of insulin-mediated tight euglycemia (mean blood glucose, 5.8 +/- 0.4 mmol/L) preceded or followed a 24-hr control period of moderate hyperglycemia (mean blood glucose, 9.6 +/- 0.6 mmol/L) on the first and second day after surgery, in randomized order, according to a crossover experimental design. Intensive care unit, cancer hospital. Cancer patients after abdominal radical surgery combined with intraoperative radiation therapy. Intensive (57 +/- 11 units/24 hrs) and conventional (25 +/- 5 units/24 hrs) insulin treatment during total parenteral nutrition. Muscle metabolism was assessed at the end of each 24-hr period of euglycemia and of hyperglycemia by leg arteriovenous catheterization with stable isotopic tracers. We found that euglycemia as compared with hyperglycemia was associated with higher (p < .05) fractional glucose uptake (16% +/- 4% vs. 9% +/- 3%); higher (p < .05) muscle protein synthesis and neutral net protein balance (-3 +/- 3 vs. -11 +/- 3 nmol phenylalanine x 100 mL(-1) x min(-1), respectively); lower (-52% +/- 12%, p < .01) muscle nonprotein leucine disposal (an index of leucine oxidation) and higher (p < .05) plasma leucine concentrations; and higher (3.6 +/- 1.7 times, p < .01) net de novo muscle glutamine synthesis and plasma glutamine concentrations (p < .05). Euglycemia was associated with higher (23% +/- 7%, p < .05) plasma concentrations of arginine but did not affect either arginine release from muscle or plasma concentration and muscle flux of asymmetrical dimethylarginine. Rate of muscle proteolysis correlated (p < .05) with muscle release of asymmetrical dimethylarginine. Treating hyperglycemia improves skeletal muscle protein and amino acid metabolism in cancer patients after major surgery.

Treatment of hyperglycemia for skeletal muscle metabolism in cancer patients after major surgery

20578 Background: Cancer and surgical stress interact to aggravate insulin resistance, protein catabolism and glutamine depletion in skeletal muscle. In the clinical setting, hyperglycemia and glutamine depletion were associated with poor outcome in critically ill patients. The present study was designed to explore the effects of insulin mediated euglycemia and moderate hyperglycemia on kinetics of protein and selected amino acids in skeletal muscle of cancer patients after major surgery. Methods: Adult cancer patients were studied after abdominal radical surgery. In each patient a 24-h period of insulin-mediated tight euglycemia (mean blood glucose: 5.8± 0.4 mmol/l) preceded or followed a 24-h period of moderate hyperglycemia (mean blood glucose: 9.6± 0.6 mmol/l) on the first and the second day after surgery (cross-over design with randomized sequence of treatments). Intensive (57±11 U/24-h) or conventional (25±5 U/24-h) insulin treatments were used to obtain euglycemia or moderate hyperglycemia during total parenteral nutrition. Muscle metabolism was assessed at the end of each 24-h period of tight glycemic control and of hyperglycemia by leg arteriovenous catheterization with stable isotopic tracers. Results in the two different experimental conditions were compared using the Wilcoxon Matched-Pairs Signed-Ranks Test. P values < 0.05 were taken as significantly different. Results: Plasma insulin levels were not significantly different at the end of intensive or conventional insulin treatment period. Strict glycemic control as compared to hyperglycemia was associated with higher (p<0.05) fractional glucose uptake (16±4 vs 9±3 percent); higher (p<0.05) muscle protein synthesis and neutral net protein balance (-3±3 vs - 11±3 mmol PHE · 100cc-1 · min-1, respectively); higher (3.6±1.7 times, p<0.01) net de novo muscle glutamine production. Conclusions: This study shows that, in cancer patients after major surgery, hyperglycemia with relative insulin deficiency promotes muscle wasting and blunted the ability of muscle to provide glutamine to extra-muscular tissues. This latter effect could contribute to increased morbidity and mortality in surgical cancer patients with poor metabolic control. No significant financial relationships to disclose.

A prospective study of decline in fat free mass and skeletal muscle strength in chronic obstructive pulmonary disease.

BackgroundSkeletal muscle depletion is an important complication of chronic obstructive pulmonary disease (COPD) but little prospective data exists about the rate at which it occurs and the factors that promote its development. We therefore prospectively investigated the impact of disease severity, exacerbation frequency and treatment with corticosteroids on change in body composition and maximum isometric quadriceps strength (QMVC) over one year.Methods64 patients with stable COPD (FEV1 mean (SD) 35.8(18.4) %predicted) were recruited from clinic and studied on two occasions one year apart. Fat free mass was determined using bioelectrical impedance analysis and a disease specific regression equation.ResultsQMVC fell from 34.8(1.5) kg to 33.3(1.5) kg (p = 0.04). The decline in quadriceps strength was greatest in those with the highest strength at baseline (R -0.28 p = 0.02) and was not correlated with lung function, exacerbation frequency or steroid treatment. Decline in fat free mass was similarly higher in those with largest FFM at baseline (R = -0.31 p = 0.01) but was more strongly correlated with greater gas trapping (R = -0.4 p = 0.001). Patients with frequent exacerbations (>1 per year) (n = 36) experienced a greater decline in fat free mass compared to infrequent exacerbators (n = 28) -1.3(3.7)kg vs. +1.2(3.1)kg (p = 0.005), as did patients on maintenance oral steroids (n = 8) -2.8(3.3) kg vs. +0.2(3.5) kg (p = 0.024) whereas in those who stopped smoking (n = 7) fat free mass increased; +2.7(3.1) kg vs. -0.51(3.5) kg (p = 0.026).ConclusionDecline in fat free mass in COPD is associated with worse lung function, continued cigarette consumption and frequent exacerbations. Factors predicting progression of quadriceps weakness could not be identified from the present cohort.

Cancer Cachexia Signaling Pathways Continue to Emerge Yet Much Still Points to the Proteasome

Cachexia is a life-threatening consequence of cancer that diminishes both quality of life and survival. It is a syndrome that is characterized by extreme weight loss resulting mainly from the depletion of skeletal muscle. Research from the past decades investigating the mechanisms of tumor-induced muscle wasting has identified several key cachectic factors that act through the ubiquitin-dependent proteasome system. Signaling pathways that mediate the effects of these cachectic factors have also subsequently emerged. Here, we review some of these pathways specific to myostatin, nuclear factor kappaB, and the newly elucidated dystrophin glycoprotein complex. Although these molecules are likely to employ distinct modes of action, results suggest that they nevertheless maintain a link to the proteasome pathway. Therefore, although the proteasome remains a preferred choice for therapy, the continually emerging upstream signaling molecules serve as additional promising therapeutic targets for the treatment of tumor-induced muscle wasting.

Integration of amino acid metabolism during intense lactation

This review focuses on research from the author's laboratory and that of N.L. Trottier concerning protein and amino acid metabolism during intense lactation, a physiological state characterized by high rates of the net transfer of amino acids from physiological reserves in skeletal muscle to the mammary gland. These studies have broader interest for our understanding of the supply and distribution of amino acids towards key processes. The synthesis of milk protein occurs at a distinct anatomical location, such that arterio-venous differences may be employed to identify all amino acid inputs into the mammary gland. These approaches can be used to determine the relative contributions to the mammary amino acid supply of systemic amino acid availability, transport system regulation and blood flow. Milk protein synthesis is partly reliant on the mobilization of endogenously stored protein in skeletal muscle, and our ability to modulate the size of physiological protein reserves and their rate of mobilization in an experimental context can be used to clarify the regulatory events that underlie the access to and eventual depletion of skeletal muscle protein. Massive rates of milk production are achieved by increased mammary blood flow and amino acid extraction. Muscle protein mobilization is a key resource in the overall amino acid supply, and the absolute size of the protein reserve at parturition is a key factor in supporting lactation. The progressive depletion of muscle may ultimately provide insufficient substrate to support this process.

Depleted skeletal muscle mitochondrial DNA, hyperlactatemia, and decreased oxidative capacity in HIV‐infected patients on highly active antiretroviral therapy

The nucleoside reverse transcriptase inhibitors (NRTIs), especially stavudine, may deplete mitochondrial (mt) DNA in human tissues by inhibiting the mitochondrial polymerase gamma, a setting, which is associated with hyperlactatemia. The aim of the present study was to examine whether hyperlactatemia is associated with depletion of skeletal muscle (sm)-mtDNA and decreased oxidative capacity in HIV-infected patients on NRTI based highly active antiretroviral therapy (HAART) and whether HIV infection itself is associated with sm-mtDNA depletion. Sm-mtDNA was determined in 42 HIV-infected patients (35 patients on HAART including at least one NRTI (HIV-NRTI) and 7 patients never treated with antiretroviral drugs (NAIVE)) and 14 healthy controls. Whole body oxidative capacity (DeltaGOX) was estimated in HIV-infected patients by indirect calorimetry. Hyperlactatemia (>or=2.0 mM) was detected in six HIV-NRTI, who all used Stavudine (P < 0.01), displayed depleted sm-mtDNA (P < 0.02) and decreased DeltaGOX (P < 0.01) compared with normolactatemic HIV-NRTI (n = 29). NAIVE displayed decreased sm-mtDNA (P < 0.05), increased HIV-RNA (P < 0.01) and increased plasma TNF-alpha (P < 0.05) compared to all HIV-NRTI (n = 35), in turn displaying decreased sm-mtDNA (P < 0.01) compared to healthy controls. Thus, hyperlactatemia in HIV-NRTI may be associated with pronounced depletion of sm-mtDNA, decreased oxidative capacity and current stavudine therapy. Further, HIV may deplete sm-mtDNA of NAIVE, which in part could be mediated through an enhanced pro-inflammatory response.

Regulation of Protein Catabolism by Muscle-Specific and Cytokine-Inducible Ubiquitin Ligase E3α-II during Cancer Cachexia

The progressive depletion of skeletal muscle is a hallmark of many types of advanced cancer and frequently is associated with debility, morbidity, and mortality. Muscle wasting is primarily mediated by the activation of the ubiquitin-proteasome system, which is responsible for degrading the bulk of intracellular proteins. E3 ubiquitin ligases control polyubiquitination, a rate-limiting step in the ubiquitin-proteasome system, but their direct involvement in muscle protein catabolism in cancer remains obscure. Here, we report the full-length cloning of E3alpha-II, a novel "N-end rule" ubiquitin ligase, and its functional involvement in cancer cachexia. E3alpha-II is highly enriched in skeletal muscle, and its expression is regulated by proinflammatory cytokines. In two different animal models of cancer cachexia, E3alpha-II was significantly induced at the onset and during the progression of muscle wasting. The E3alpha-II activation in skeletal muscle was accompanied by a sharp increase in protein ubiquitination, which could be blocked by arginine methylester, an E3alpha-selective inhibitor. Treatment of myotubes with tumor necrosis factor alpha or interleukin 6 elicited marked increases in E3alpha-II but not E3alpha-I expression and ubiquitin conjugation activity in parallel. E3alpha-II transfection markedly accelerated ubiquitin conjugation to endogenous cellular proteins in muscle cultures. These findings show that E3alpha-II plays an important role in muscle protein catabolism during cancer cachexia and suggest that E3alpha-II is a potential therapeutic target for muscle wasting.

Severely altered guanidino compound levels, disturbed body weight homeostasis and impaired fertility in a mouse model of guanidinoacetate N-methyltransferase (GAMT) deficiency.

We generated a knockout mouse model for guanidinoacetate N-methyltransferase (GAMT) deficiency (MIM 601240), the first discovered human creatine deficiency syndrome, by gene targeting in embryonic stem cells. Disruption of the open reading frame of the murine GAMT gene in the first exon resulted in the elimination of 210 of the 237 amino acids present in mGAMT. The creation of an mGAMT null allele was verified at the genetic, RNA and protein levels. GAMT knockout mice have markedly increased guanidinoacetate (GAA) and reduced creatine and creatinine levels in brain, serum and urine, which are key findings in human GAMT patients. In vivo (31)P magnetic resonance spectroscopy showed high levels of PGAA and reduced levels of creatine phosphate in heart, skeletal muscle and brain. These biochemical alterations were comparable to those found in human GAMT patients and can be attributed to the very similar GAMT expression patterns found by us in human and mouse tissues. We provide evidence that GAMT deficiency in mice causes biochemical adaptations in brain and skeletal muscle. It is associated with increased neonatal mortality, muscular hypotonia, decreased male fertility and a non-leptin-mediated life-long reduction in body weight due to reduced body fat mass. Therefore, GAMT knockout mice are a valuable creatine deficiency model for studying the effects of high-energy phosphate depletion in brain, heart, skeletal muscle and other organs.

Mitochondrial DNA abnormalities and autistic spectrum disorders

ObjectivesTo further characterize mtDNA defects associated with autistic features, especially the A3243G mtDNA mutation and mtDNA depletion. Study designFive patients with autistic spectrum disorders and family histories of mitochondrial DNA diseases were studied. We performed mtDNA analysis in all patients and magnetic resonance spectroscopy in three. ResultsThree patients manifested isolated autistic spectrum features and two had additional neurologic symptoms. Two patients harbored the A3243G mutation. In two others, the A3243G mutation was not found in accessible tissues but was present in tissues from their mothers. The fifth patient had 72% mtDNA depletion in skeletal muscle. ConclusionsAutistic spectrum disorders with or without additional neurologic features can be early presentations of the A3243G mtDNA mutation and can be a prominent clinical manifestation of mtDNA depletion. Mitochondrial dysfunction should be considered in patients who have autistic features and associated neurologic findings or who have evidence of maternal inheritance.

Mechanisms of skeletal muscle depletion in wasting syndromes: role of ATP-ubiquitin-dependent proteolysis.

Muscle protein wasting frequently complicates patient outcome in several chronic pathologies. The underlying mechanisms remain largely obscure, although studies on experimental models have clarified that a complex interplay of different factors such as nutrient supply, classical hormones, cytokines and other less well defined factors likely concur in causing muscle depletion. The aim of the present review is to highlight some crucial points in the interpretation of the data available about the contribution of the different proteolytic systems, with particular reference to the ubiquitin-proteasome system, in the onset of muscle protein wasting in disease states. Much effort has been directed to understanding the role of different signals, transduction pathways, and proteolytic mechanisms in the acceleration of muscle protein catabolism. Several reports propose that ATP-ubiquitin-dependent proteolysis plays a critical role in the enhancement of muscle protein catabolism observed in different pathological states. Other papers, however, suggest that the lysosomal or the calcium-dependent proteolytic pathways or both may be involved. Finally, the studies have been extended to evaluate the possibility of interfering pharmacologically with the onset of muscle protein hypercatabolism. As the present overview points out, several questions still remain unanswered in the issue of muscle wasting. While many different signals that have the potential to enforce the acceleration of muscle protein breakdown have been identified, it is largely unknown how they are transduced and converge into the hypercatabolic response and how the proteolytic pathways involved are activated. The concept seems to emerge that there may be a coordinated action of different proteolytic pathways in setting up muscle protein turnover towards excess catabolism.

WHOLE-BODY INSULIN SENSITIVITY IS NOT INCREASED IN HUMAN CREATINE DEPLETION (=GA)

The creatine (Cr)/phosphocreatine (PCr) system is essential for buffering and transport of high-energy phosphorus compounds especially in cells with high energy demands(1). Creatine depleted animals have enhanced glucose tolerance and improved insulin sensitivity(1). Glucose metabolism has never been studied in human Cr depletion. Gyrate atrophy (GA) is a rare inborn error of metabolism. Patients with GA have 50% PCr depletion in skeletal muscle, which provides a model of human Cr depletion in vivo. PURPOSE The purpose of this study was to investigate whether insulin sensitivity is increased in Cr depletion in man. METHODS We studied whole-body insulin sensitivity in 4 male patients (aged 33,41,47,49 years) with genetically verified GA and normal BMI (mean ±SD 21.3 ±2.2 kg/m2) using euglycemic insulin clamp technique(2). Plasma insulin was kept high by a primed continuos insulin infusion (1mU*kg-1*min-1) and normoglycemia (gluc 5mmol/l) was maintained by an infusion of 20% glucose. The rate of glucose infusion was regulated based on arterial plasma glucose every 5 minutes. Insulin sensitivity expressed as M-value (umol/kg*min) was calculated as described by DeFronzo(2). Values were compared to M-values from 31 healthy males (mean age 30.4 ±6 years; range 23 to 47 years) with normal BMI (23.2 ±1.9 kg/m2), previously studied at the same institute. RESULTS M-values of the patients with GA were 26, 25, 34 and 29. Mean M-value of the controls was 32 ±10 ranging between 14 and 45. Thus, the values from patients with GA were not increased. CONCLUSION In contrary to animal experiments, in this study whole-body insulin sensitivity is not increased in human Cr depletion. In fact, the M-values seem to be low. This may be explained by the lower grade of Cr depletion (50%) in this study compared to animal models (90%).

Profound skeletal muscle depletion of α-dystroglycan in Walker-Warburg syndrome

Walker-Warburg syndrome (WWS) is an autosomal recessive disorder characterized by the combined involvement of the central nervous and skeletal muscle systems. Although the molecular basis of WWS remains unknown, defects in the muscle fibre basal lamina are characteristic of other forms of congenital muscular dystrophy (CMD). In agreement with this, some forms of CMD, due to glycosyltransferase defects, display a reduction in the immunolabelling of α-dystroglycan, whilst β-dystroglycan labelling appears normal. Here we describe an almost complete absence of α-dystroglycan using both immunohistochemistry and immunoblotting in two patients with WWS. In addition, there was a mild reduction of laminin-α2. In contrast, immunohistochemical labelling of perlecan and collagen VI was normal. Linkage analysis excluded the recently identified POMT1 locus, responsible for a proportion of WWS cases. These results confirm that WWS is a genetically heterogeneous condition and suggest that disruption of the α-dystroglycan/laminin-α2 axis in the basal lamina may play a role in the degeneration of muscle fibres in WWS—also in cases not due to POMT1 defects.

Glutamine attenuates post-traumatic glutathione depletion in human muscle

Glutathione is quantitatively the most important endogenous scavenger system. Glutathione depletion in skeletal muscle is pronounced following major trauma and sepsis in intensive care unit patients. Also, following elective surgery, glutathione depletion occurs in parallel with a progressive decline in muscle glutamine concentration. The present study was designed to test the hypothesis that glutamine supplementation may counteract glutathione depletion in a human trauma model. A homogeneous group of patients (n = 17) undergoing a standardized surgical procedure were prospectively randomly allocated to receive glutamine (0.56g·day-1·kg-1) or placebo as part of isonitrogenous and isocaloric nutrition. Percutaneous muscle biopsies and blood samples were taken pre-operatively and at 24 and 72h after surgery. The concentrations of muscle glutathione and related amino acids were determined in muscle tissue and plasma. In the control (unsupplemented) subjects, total muscle glutathione had decreased by 47±8% and 37±11% and reduced glutathione had decreased by 53±10% and 45±16% respectively at 24 and 72h after surgery (P&lt;0.05). In contrast, in the glutamine-supplemented group, no significant post-operative decreases in total or reduced glutathione were seen following surgery. Muscle free glutamine had decreased at 72h after surgery in both groups, by 41.4±14.8% (P&lt;0.05) in the glutamine-supplemented group and by 46.0±14.3% (P&lt;0.05) in the control group. In conclusion, the present study demonstrates that intravenous glutamine supplementation attenuates glutathione depletion in skeletal muscle in humans following standardized surgical trauma.

Kinetics of taurine depletion and repletion in plasma, serum, whole blood and skeletal muscle in cats.

The relationship between taurine concentrations of plasma, whole blood, serum and skeletal muscle during taurine depletion and repletion was investigated in cats, to identify the most useful indicators of taurine status. Sixteen cats were fed a purified diet containing either 0 or 0.15 g/kg taurine for 5 months. Treatments were then reversed and the taurine concentration was measured during repletion and depletion phases. Plasma taurine exhibited the fastest rate (slow component) of depletion (t 1/2 = 4.8 wk), followed by serum (5.3 wk), whole blood (6.2 wk), and skeletal muscle (11.2 wk). Whole blood taurine was the first to replete at a rate of 0.74 wk to 1/2 maximal repletion, followed by serum (2.1 wk), skeletal muscle (3.5 wk), and plasma (3.5 wk). Whole blood more closely reflected skeletal muscle taurine concentrations than plasma during depletion, while plasma taurine concentrations appear to be the most valuable predictor of skeletal muscle taurine concentrations during repletion. This study suggests that the best clinical method to evaluate the taurine status of the cat is the determination and interpretation of both plasma and whole blood taurine concentrations.