Taurine and Skeletal Muscle Disorders

Exploring the metabolomics profile of frailty- a systematic review

Background

Frailty is a multifaceted geriatric syndrome characterized by an increased vulnerability to stressful events. metabolomics studies are valuable tool for better understanding the underlying mechanisms of pathologic conditions. This review aimed to elucidate the metabolomics profile of frailty.

Method

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) 2020 statement. A comprehensive search was conducted across multiple databases. Initially, 5027 results were retrieved, and after removing duplicates, 1838 unique studies were subjected to screening. Subsequently, 248 studies underwent full-text screening, with 21 studies ultimately included in the analysis. Data extraction was performed meticulously by two authors, and the quality of the selected studies was assessed using the Critical Appraisal Skills Program (CASP) checklist.

Results

The findings revealed that certain Branched-chain amino acids (BCAAs) levels were lower in frail subjects compared to robust subjects, while levels of glutamate and glutamine were higher in frail individuals. Moreover, sphingomyelins and phosphatidylcholines (PC) displayed a decreasing trend as frailty advanced. Additionally, other metabolic derivatives, such as carnitine, exhibited significant associations with frailty. These metabolites were primarily interconnected through biochemical pathways related to the tricarboxylic acid and urea cycles. Notably, frailty was associated with a decrease in metabolic derivatives, including carnitine.

Conclusion

This study underscores the intricate relationship between essential metabolites, including amino acids and lipids, and their varying levels in frail individuals compared to their robust counterparts. It provides a comprehensive panel of metabolites, shedding light on their potential associations with frailty and expanding our understanding of this complex syndrome.

Pre/postnatal taurine supplementation improves neurodevelopment and brain function in mice offspring: A persistent developmental study from puberty to maturity

Taurine (TAU) is a sulfur-containing amino acid abundantly found in the human body. Endogenously, TAU is synthesized from cysteine in the liver. However, newborns rely entirely on TAU's dietary supply (milk). There is no investigation on the effect of long-term TAU administration on next-generation neurological development. The current study evaluated the effect of long-term TAU supplementation during the maternal gestational and litter weaning time on several neurological parameters in mice offspring. Moreover, the effects of TAU on mitochondrial function and oxidative stress biomarkers as plausible mechanisms of its action in the whole brain and hippocampus have been evaluated. TAU (0.5 % and 1 % w/v) was dissolved in the drinking water of pregnant mice (Day one of pregnancy), and amino acid supplementation was continued during the weaning time (post-natal day; PND = 21) until litters maturity (PND = 65). It was found that TAU significantly improved cognitive function, memory performance, reflexive motor activity, and emotional behaviors in F1-mice generation. TAU measurement in the brain and hippocampus revealed higher levels of this amino acid. TAU and ATP levels were also significantly higher in the mitochondria isolated from the whole brain and hippocampus. Based on these data, TAU could be suggested as a supplement during pregnancy or in pediatric formula. The effects of TAU on cellular mitochondrial function and energy metabolism might play a fundamental role in the positive effects of this amino acid observed in this investigation.

Amino Acid Profiles in Older Adults with Frailty: Secondary Analysis from MetaboFrail and BIOSPHERE Studies

An altered amino acid metabolism has been described in frail older adults which may contribute to muscle loss and functional decline associated with frailty. In the present investigation, we compared circulating amino acid profiles of older adults with physical frailty and sarcopenia (PF&S, n = 94), frail/pre-frail older adults with type 2 diabetes mellitus (F-T2DM, n = 66), and robust non-diabetic controls (n = 40). Partial least squares discriminant analysis (PLS-DA) models were built to define the amino acid signatures associated with the different frailty phenotypes. PLS-DA allowed correct classification of participants with 78.2 ± 1.9% accuracy. Older adults with F-T2DM showed an amino acid profile characterized by higher levels of 3-methylhistidine, alanine, arginine, ethanolamine, and glutamic acid. PF&S and control participants were discriminated based on serum concentrations of aminoadipic acid, aspartate, citrulline, cystine, taurine, and tryptophan. These findings suggest that different types of frailty may be characterized by distinct metabolic perturbations. Amino acid profiling may therefore serve as a valuable tool for frailty biomarker discovery.

Muscle Pathology in Dystrophic Rats and Zebrafish Is Unresponsive to Taurine Treatment, Compared to the mdx Mouse Model for Duchenne Muscular Dystrophy

Inflammation and oxidative stress are strongly implicated in the pathology of Duchenne muscular dystrophy (DMD), and the sulphur-containing amino acid taurine ameliorates both and decreases dystropathology in the mdx mouse model for DMD. We therefore further tested taurine as a therapy using dystrophic DMD^mdx rats and dmd zebrafish models for DMD that have a more severe dystropathology. However, taurine treatment had little effect on the indices of dystropathology in both these models. While we and others have previously observed a deficiency in taurine in mdx mice, in the current study we show that the rat and zebrafish models had increased taurine content compared with wild-type, and taurine treatment did not increase muscle taurine levels. We therefore hypothesised that endogenous levels of taurine are a key determinate in potential taurine treatment efficacy. Because of this, we felt it important to measure taurine levels in DMD patient plasma samples and showed that in non-ambulant patients (but not in younger patients) there was a deficiency of taurine. These data suggest that taurine homeostasis varies greatly between species and may be influenced by age and disease progression. The potential for taurine to be an effective therapy may depend on such variables.

Metabolomic Analysis of Wooden Breast Myopathy Shows a Disturbed Lipid Metabolism

Myopathies have risen strongly in recent years, likely linked to selection for appetite. For white striping (WS), causes have been identified; but for wooden breast (WB), the cause remains speculative. We used metabolomics to study the breast muscle of 51 birds that were scored for both at 35 days of age to better understand potential causes. A partial least square discriminant analysis revealed that WS and WB had distinct metabolic profiles, implying different etiologies. Arginine and proline metabolism were affected in both, although differently: WB increased arginine in breast muscle implying that the birds did not use this pathway to increase tissue blood flow. Antioxidant defenses were impeded as shown by low anserine and beta-alanine. In contrast, GSH and selenium concentrations were increased. Serine, linked to anti-inflammatory properties, was increased. Taurine, which can stabilize the cell's sarcolemma as well as modulate potassium channels and cellular calcium homeostasis, was also increased. Mineral data and depressed phosphatidylethanolamine, cAMP, and creatine-phosphate suggested compromised energy metabolism. WB also had drastically lower diet-derived lipids, suggesting compromised lipid digestion. In conclusion, WB may be caused by impaired lipid digestion triggered by a very high appetite: the ensuing deficiencies may well impair blood flow into muscle resulting in irreparable damage.

Nutritional Compounds to Improve Post-Exercise Recovery

The metabolic and mechanical stresses associated with muscle-fatiguing exercise result in perturbations to bodily tissues that lead to exercise-induced muscle damage (EIMD), a state of fatigue involving oxidative stress and inflammation that is accompanied by muscle weakness, pain and a reduced ability to perform subsequent training sessions or competitions. This review collates evidence from previous research on a wide range of nutritional compounds that have the potential to speed up post-exercise recovery. We show that of the numerous compounds investigated thus far, only two-tart cherry and omega-3 fatty acids-are supported by substantial research evidence. Further studies are required to clarify the potential effects of other compounds presented here, many of which have been used since ancient times to treat conditions associated with inflammation and disease.

Therapeutic approaches to preserve the musculature in Duchenne Muscular Dystrophy: The importance of the secondary therapies

Muscular dystrophies (MDs) are heterogeneous diseases, characterized by primary wasting of skeletal muscle, which in severe cases, such as Duchenne Muscular Dystrophy (DMD), leads to wheelchair dependency, respiratory failure, and premature death. Research is ongoing to develop efficacious therapies, particularly for DMD. Most of the efforts, currently focusing on correcting or restoring the primary defect of MDs, are based on gene-addition, exon-skipping, stop codon read-through, and genome-editing. Although promising, most of them revealed several practical limitations. Shared knowledge in the field is that, in order to be really successful, any therapeutic approach has to rely on spared functional muscle tissue, restricting the number of patients eligible for clinical trials to the youngest and less compromised individuals. In line with this, many therapeutic strategies aim to preserve muscle tissue and function. This Review outlines the most interesting and recent studies addressing the secondary outcomes of DMD and how to better deliver the therapeutic agents. In the future, the effective treatment of DMD will likely require combinations of therapies addressing both the primary genetic defect and its consequences.

Investigation of the effect of taurine supplementation on muscle taurine content in the mdx mouse model of Duchenne muscular dystrophy using chemically specific synchrotron imaging

Duchenne muscular dystrophy (DMD) is a lethal genetic muscle wasting disorder, which currently has no cure. Supplementation with the drug taurine has been shown to offer therapeutic benefit in the mdx model for DMD, however the mechanism by which taurine protects dystrophic muscle is not fully understood. Mdx muscle is deficient in taurine, however it is not known if this deficiency occurs in the extracellular space, in other cells present in the tissue (such as immune cells) or in the myofibre itself. Likewise, the tissue location of taurine enrichment in taurine treated mdx muscle is not known. In this study we applied X-ray absorption near edge spectroscopy (XANES) at the sulfur K-edge in an imaging format to determine taurine distribution in muscle tissue. XANES is the only technique currently capable of imaging taurine directly in muscle tissue, at a spatial resolution approaching myocyte cell size (20-50 μm). Using a multi-modal approach of XANES imaging and histology on the same tissue sections, we show that in mdx muscle, it is the myofibres that are deficient in taurine, and taurine supplementation ameliorates this deficiency. Increasing the taurine content of mdx myofibres was associated with a decrease in myofibre damage (as shown by the percentage of intact myofibres) and inflammation. These data will help drive future studies to better elucidate the molecular mechanisms through which taurine protects dystrophic muscle; they also support the continued investigation of taurine as a therapeutic intervention for DMD.

Hyperreflexia and enhanced ripple oscillations in the taurine-deficient mice

In this study, we examined neuronal excitability and skeletal muscle physiology and histology in homozygous knockout mice lacking cysteine sulfonic acid decarboxylase (CSAD-KO). Neuronal excitability was measured by intracerebral recording from the prefrontal cortex. Skeletal muscle response was measured through stretch reflex in the ankle muscles. Specifically, we measured the muscle tension, amplitude of electromyogram and velocity of muscle response. Stretch reflex responses were evoked using a specialized stretching device designed for mice. The triceps surae muscle was stretched at various speeds ranging from 18 to 18,000° s^-1. A transducer recorded the muscle resistance at each velocity and the corresponding EMG. We also measured the same parameter in anesthetized mice. We found that at each velocity, the CSAD-KO mice generated more tension and exhibited higher EMG responses. To evaluate if the enhanced response was due to neuronal excitability or changes in the passive properties of muscles, we anesthetize mice to eliminate the central component of the reflex. Under these conditions, CSAD-KO mice still exhibited an enhanced stretch reflex response, indicating ultrastructural alterations in muscle histology. Consistent with this, we found that sarcomeres from CSAD-KO muscles were shorter and thinner when compared to control sarcomeres. Neuronal excitability was further investigated using intracerebral recordings of brain waves from the prefrontal cortex. We found that extracellular field potentials in CSAD-KO mice were characterized by reduced amplitude of low-frequency brain waves (delta, theta, alpha, beta and gamma) and increased in the high low-frequency brain waves (slow and fast ripples). Increased slow and fast ripple rates serve as a biomarker of epileptogenic brain. We have previously shown that taurine interacts with GABA_A receptors and induces biochemical changes in the GABAergic system. We suggest that taurine deficiency leads to alterations in the GABAergic system that contribute to the enhanced stretch reflex in CSAD-KO mice through biochemical mechanisms that involve alterations not only at the spinal level but also at the cortical level.

Case Studies in Management of Muscle Cramps

Muscle cramps, defined as a painful contraction of a muscle or muscle group, are a common symptom most people have experienced throughout their lifespan. In some cases cramps can be frequent, severe, and disabling, thus requiring medical assessment and intervention. Physiologic states such as pregnancy and exercise are associated with excessive muscle cramps, as are numerous medical and neurologic conditions, medications such as diuretics and statins, and peripheral nerve hyperexcitability syndromes. Treatment options for muscle cramps are limited, although recent studies have shown that mexiletine could be a safe and efficient alternative for patients with amyotrophic lateral sclerosis.

In Vivo and In Vitro Study of N-Methyltaurine on Pharmacokinetics and Antimuscle Atrophic Effects in Mice

Various types of seaweed are potential functional foods as they contain multiple bioactive compounds. N-Methyltaurine (NMT) is a taurine derivative metabolite found in a type of red algae. The functional actions of NMT in mammalian animals have not been investigated, but the parent compound, taurine, possesses a variety of cellular actions. To explore the beneficial role of NMT in animals, the present study analyzed the effect of NMT against glucocorticoid-induced skeletal muscle atrophy. Glucocorticoids are one of the major causes of pathological muscle atrophy. Initially, we assessed the bioavailability of ingested NMT by determining its concentration in mouse blood. The bioavailability of orally administered NMT was found to be 96.1% that of intravenously administered NMT. Mice maintained on water containing 0.5% NMT for several days lead to the distribution of the taurine derivative to various tissues, including skeletal muscles. Like taurine, the delivery of NMT to skeletal muscles or myoblast cells is cytoprotective. The treatment with NMT prevents dexamethasone-induced atrophy of myotubes derived from C2C12 cells. Similarly, the addition of 0.5% NMT to drinking water attenuates dexamethasone-mediated reduction in muscle mass of the treated mice. The present study supports the hypothesis that orally administered NMT partially reverses skeletal muscle atrophy.

Metabolite profile based on 1H NMR of broiler chicken breasts affected by wooden breast myodegeneration

The objective was to characterize the effect of wooden breast (WB) myodegeneration on the metabolite profile of chicken meat by ¹H NMR and multivariate data analysis. The results displayed that the metabonome of chicken breast consisted predominantly of 30 metabolites, including amino acids, organic acids, carbohydrates, alkaloids, nucleosides and their derivatives. WB-affected samples showed higher leucine, valine, alanine, glutamate, lysine, lactate, succinate, taurine, glucose, and 5'-IMP levels, but lower histidine, β-alanine, acetate, creatine, creatinine, anserine and nicotinamide adenine dinucleotide levels compared to normal fillets (p < 0.05). In conclusion, results indicated that WB-affected fillets possessed a unique biochemical signature. This unique profile could identify candidate biomarkers for diagnostic utilization and provide mechanistic insight into biochemical processes leading to WB myopathy in commercial broiler chickens.

The Beneficial Effects of Taurine to Counteract Sarcopenia

Aging is a multifactorial process characterized by several features including low-grade inflammation, increased oxidative stress and reduced regenerative capacity, which ultimately lead to alteration in morpho-functional properties of skeletal muscle, thus promoting sarcopenia. This condition is characterized by a gradual loss of muscle mass due to an unbalance between protein synthesis and degradation, finally conveying in functional decline and disability. The development of specific therapeutic approaches able to block or reverse this condition may represent an invaluable tool for the promotion of a healthy aging among elderly people. It is well established that changes in the quantity and the quality of dietary proteins, as well as the intake of specific amino acids, are able to counteract some of the physiopathological processes related to the progression of the loss of muscle mass and may have beneficial effects in improving the anabolic response of muscle in the elderly. Taurine is a non-essential amino acid expressed in high concentration in several mammalian tissues and particularly in skeletal muscle where it is involved in the modulation of intracellular calcium concentration and ion channel regulation and where it also acts as an antioxidant and anti-inflammatory factor. The aim of this review is to summarize the pleiotropic effects of taurine on specific muscle targets and to discuss its role in regulating signaling pathways involved in the maintenance of muscle homeostasis. We also highlight the potential use of taurine as a therapeutic molecule for the amelioration of skeletal muscle function and performance severely compromised during aging.

A Distinct Pattern of Circulating Amino Acids Characterizes Older Persons with Physical Frailty and Sarcopenia: Results from the BIOSPHERE Study

Physical frailty and sarcopenia (PF&S) are hallmarks of aging that share a common pathogenic background. Perturbations in protein/amino acid metabolism may play a role in the development of PF&S. In this initial report, 68 community-dwellers aged 70 years and older, 38 with PF&S and 30 non-sarcopenic, non-frail controls (nonPF&S), were enrolled as part as the "BIOmarkers associated with Sarcopenia and Physical frailty in EldeRly pErsons" (BIOSPHERE) study. A panel of 37 serum amino acids and derivatives was assayed by UPLC-MS. Partial Least Squares⁻Discriminant Analysis (PLS-DA) was used to characterize the amino acid profile of PF&S. The optimal complexity of the PLS-DA model was found to be three latent variables. The proportion of correct classification was 76.6 ± 3.9% (75.1 ± 4.6% for enrollees with PF&S; 78.5 ± 6.0% for nonPF&S). Older adults with PF&S were characterized by higher levels of asparagine, aspartic acid, citrulline, ethanolamine, glutamic acid, sarcosine, and taurine. The profile of nonPF&S participants was defined by higher concentrations of α-aminobutyric acid and methionine. Distinct profiles of circulating amino acids and derivatives characterize older people with PF&S. The dissection of these patterns may provide novel insights into the role played by protein/amino acid perturbations in the disabling cascade and possible new targets for interventions.

Unraveling the cause of white striping in broilers using metabolomics

White striping (WS) is a major problem affecting the broiler industry. Fillets affected by this myopathy present pathologies that compromise the quality of the meat, and most importantly, make the fillets more prone to rejection by the consumer. The exact etiology is still unknown, which is why a metabolomics analysis was performed on breast samples of broilers. The overall objective was to identify biological pathways involved in the pathogenesis of WS. The analysis was performed on a total of 51 muscle samples and distinction was made between normal (n = 19), moderately affected (n = 24) and severely affected (n = 8) breast fillets. Samples were analyzed using gas chromatographic mass spectral analysis and liquid chromatography quadrupole time-of-flight mass spectrometry. Data were subsequently standardized, normalized and analyzed using various multivariate statistical procedures. Metabolomics allowed for the identification of several pathways that were altered in white striped breast fillets. The tricarboxylic acid cycle exhibited opposing directionalities. This is described in literature as the backflux and enables the TCA cycle to produce high-energy phosphates through matrix-level phosphorylation and, therefore, produce energy under conditions of hypoxia. Mitochondrial fatty acid oxidation was limited due to disturbances in especially cis-5–14:1 carnitine (log2 FC of 2, P < 0.01). Because of this, accumulation of harmful fatty acids took place, especially long-chain ones, which damages cell structures. Conversion of arginine to citrulline increased presumably to produce nitric oxide, which enhances blood flow under conditions of hypoxia. Nitric oxide however also increases oxidative damage. Increases in taurine (log2 FC of 1.2, P < 0.05) suggests stabilization of the sarcolemma under hypoxic conditions. Lastly, organic osmolytes (sorbitol, taurine, and alanine) increased (P < 0.05) in severely affected birds; likely this disrupts cell volume maintenance. Based on the results of this study, hypoxia was the most likely cause/initiator of WS in broilers. We speculate that birds suffering from WS have a vascular support system in muscle that is borderline adequate to support growth, but triggers like activity results in local hypoxia that damages tissue.

Insights into the pharmaceuticals and mechanisms of neurological orphan diseases: Current Status and future expectations

Several rare or orphan diseases have been characterized that singly affect low numbers of people, but cumulatively reach ∼6%-10% of the population in Europe and in the United States. Human genetics has shown to be broadly effective when evaluating subjacent genetic defects such as orphan genetic diseases, but on the other hand, a modest progress has been achieved toward comprehending the molecular pathologies and designing new therapies. Chemical genetics, placed at the interface of chemistry and genetics, could be employed to understand the molecular mechanisms of subjacent illnesses and for the discovery of new remediation processes. This review debates current progress in chemical genetics, and how a variety of compounds and reaction mechanisms can be used to study and ultimately treat rare genetic diseases. We focus here on a study involving Amyotrophic lateral sclerosis (ALS), Duchenne Muscular Dystrophy (DMD), Spinal muscular atrophy (SMA) and Familial Amyloid Polyneuropathy (FAP), approaching different treatment methods and the reaction mechanisms of several compounds, trying to elucidate new routes capable of assisting in the treatment profile.

The Effect of Taurine on the Recovery from Eccentric Exercise-Induced Muscle Damage in Males

Eccentric exercise is known to bring about microstructural damage to muscle, initiating an inflammatory cascade involving various reactive oxygen species. This, in turn, can significantly impair physical performance over subsequent days. Taurine, a powerful endogenous antioxidant, has previously been shown to have a beneficial effect on muscle damage markers and recovery when taken for a few days to several weeks prior to eccentric exercise. However, to date no studies have looked at the effects of supplementing over the days following eccentric exercise on performance recovery. Thus, this study aimed to determine whether supplementing with taurine over three days following eccentric exercise attenuated the rise in serum creatine kinase and improved performance recovery in males. In a blinded, randomized, crossover design, ten recreationally-fit male participants completed 60 eccentric contractions of the biceps brachii muscle at maximal effort. Following this, participants were supplemented with 0.1 g∙kg⁻¹ body weight∙day⁻¹ of either taurine or rice flour in capsules. Over the next three mornings participants underwent blood tests for the analysis of the muscle damage marker creatine kinase and carried out performance measures on the isokinetic dynamometer. They also continued to consume the capsules in the morning and evening. The entire protocol was repeated two weeks later on the alternate arm and supplement. Significant decreases were seen in all performance measures from pre- to 24-h post-eccentric exercise (p < 0.001) for both taurine and placebo, indicating the attainment of muscle damage. Significant treatment effects were observed only for peak eccentric torque (p < 0.05). No significant time × treatment effects were observed (all p > 0.05). Serum creatine kinase levels did not significantly differ over time for either treatments, nor between treatments (p > 0.05). These findings suggest that taurine supplementation taken twice daily for 72 h following eccentric exercise-induced muscle damage may help improve eccentric performance recovery of the biceps brachii.

Benefits of Prenatal Taurine Supplementation in Preventing the Onset of Acute Damage in the Mdx Mouse

INTRODUCTION

Duchenne Muscular Dystrophy (DMD) is a debilitating muscle wasting disorder with no cure. Safer supplements and therapies are needed to improve the severity of symptoms, as severe side effects are associated with the only effective treatment, corticosteroids. The amino acid taurine has shown promise in ameliorating dystrophic symptoms in mdx mice, an animal model of DMD, however little work is in 21-28 (d)ay animals, the period of natural peak damage.

METHODS

This study compares the effect of prenatal taurine supplementation on tibialis anterior (TA) in situ contractile function, histopathological characteristics and the abundance of Ca2+-handling as well as pathologically relevant proteins in non-exercised mdx mice at 28 and 70 d.

RESULTS

Supplementation elevated TA taurine content by 25% (p<0.05), ameliorated in situ specific force by 60% (p<0.05) and improved histological characteristics in 28 d mdx mice; however no benefit was seen in 70 d mice, where background pathology was initially stable. Age specific effects in SERCA1, calsequestrin 1 (CSQ1), CSQ2, utrophin and myogenin protein abundances were seen between both 28 and 70 d mdx and mdx taurine-supplemented mice.

DISCUSSION

Considering these findings and that taurine is a relatively cost effective, readily accessible and side effect free dietary supplement, we propose further investigation into taurine supplementation during pregnancy in a protective capacity, reminiscent of folate in the prevention of spinal bifida.

Cartilaginous Metabolomic Study Reveals Potential Mechanisms of Osteophyte Formation in Osteoarthritis

Osteophyte is one of the inevitable consequences of progressive osteoarthritis with the main characteristics of cartilage degeneration and endochondral ossification. The pathogenesis of osteophyte formation is not fully understood to date. In this work, metabolomic approaches were employed to explore potential mechanisms of osteophyte formation by detecting metabolic variations between extracts of osteophyte cartilage tissues (n = 32) and uninvolved control cartilage tissues (n = 34), based on the platform of ultraperformance liquid chromatography tandem quadrupole time-of-flight mass spectrometry, as well as the use of multivariate statistic analysis and univariate statistic analysis. The osteophyte group was significantly separated from the control group by the orthogonal partial least-squares discriminant analysis models, indicating that metabolic state of osteophyte cartilage had been changed. In total, 28 metabolic variations further validated by mass spectrum (MS) match, tandom mass spectrum (MS/MS) match, and standards match mainly included amino acids, sulfonic acids, glycerophospholipids, and fatty acyls. These metabolites were related to some specific physiological or pathological processes (collagen dissolution, boundary layers destroyed, self-restoration triggered, etc.) which might be associated with the procedure of osteophyte formation. Pathway analysis showed phenylalanine metabolism (PI = 0.168, p = 0.004) was highly correlative to this degenerative process. Our findings provided a direction for targeted metabolomic study and an insight into further reveal the molecular mechanisms of ostophyte formation.

Levels of inflammation and oxidative stress, and a role for taurine in dystropathology of the Golden Retriever Muscular Dystrophy dog model for Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a fatal skeletal muscle wasting disease presenting with excessive myofibre necrosis and increased inflammation and oxidative stress. In the mdx mouse model of DMD, homeostasis of the amino acid taurine is altered, and taurine administration drastically decreases muscle necrosis, dystropathology, inflammation and protein thiol oxidation. Since the severe pathology of the Golden Retriever Muscular Dystrophy (GRMD) dog model more closely resembles the human DMD condition, we aimed to assess the generation of oxidants by inflammatory cells and taurine metabolism in this species. In muscles of 8 month GRMD dogs there was an increase in the content of neutrophils and macrophages, and an associated increase in elevated myeloperoxidase, a protein secreted by neutrophils that catalyses production of the highly reactive hypochlorous acid (HOCl). There was also increased chlorination of tyrosines, a marker of HOCl generation, increased thiol oxidation of many proteins and irreversible oxidative protein damage. Taurine, which functions as an antioxidant by trapping HOCl, was reduced in GRMD plasma; however taurine was increased in GRMD muscle tissue, potentially due to increased muscle taurine transport and synthesis. These data indicate a role for HOCl generated by neutrophils in the severe dystropathology of GRMD dogs, which may be exacerbated by decreased availability of taurine in the blood. These novel data support continued research into the precise roles of oxidative stress and taurine in DMD and emphasise the value of the GRMD dogs as a suitable pre-clinical model for testing taurine as a therapeutic intervention for DMD boys.

The effect of taurine and β-alanine supplementation on taurine transporter protein and fatigue resistance in skeletal muscle from mdx mice

This study investigated the effect of taurine and β-alanine supplementation on muscle function and muscle taurine transporter (TauT) protein expression in mdx mice. Wild-type (WT) and mdx mice (5 months) were supplemented with taurine or β-alanine for 4 weeks, after which in vitro contractile properties, fatigue resistance and force recovery, and the expression of the TauT protein and proteins involved in excitation-contraction (E-C) coupling were examined in fast-twitch muscle. There was no difference in basal TauT protein expression or basal taurine content between mdx than WT muscle. Supplementation with taurine and β-alanine increased and reduced taurine content, respectively, in muscle from WT and mdx mice but had no effect of TauT protein. Taurine supplementation reduced body and muscle mass, and enhanced fatigue resistance and force recovery in mdx muscle. β-Alanine supplementation enhanced fatigue resistance in WT and mdx muscle. There was no difference in the basal expression of key E-C coupling proteins [ryanodine receptor 1 (RyR1), dihydropyridine receptor (DHPR), sarco(endo)plasmic reticulum Ca²⁺-ATPase 1 (SERCA1) or calsequestrin 1 (CSQ1)] between WT and mdx mice, and the expression of these proteins was not altered by taurine or β-alanine supplementation. These findings suggest that TauT protein expression is relatively insensitive to changes in muscle taurine content in WT and mdx mice, and that taurine and β-alanine supplementation may be viable therapeutic strategies to improve fatigue resistance of dystrophic skeletal muscle.

Increased taurine in pre-weaned juvenile mdx mice greatly reduces the acute onset of myofibre necrosis and dystropathology and prevents inflammation

BACKGROUND

The mdx mouse model for the fatal muscle wasting disease Duchenne Muscular Dystrophy (DMD) shows a very mild pathology once growth has ceased, with low levels of myofibre necrosis in adults. However, from about 3 weeks of post-natal age, muscles of juvenile mdx mice undergo an acute bout of severe necrosis and inflammation: this subsequently decreases and stabilises to lower adult levels by about 6 weeks of age. Prior to the onset of this severe dystropathology, we have shown that mdx mice are deficient in the amino acid taurine (potentially due to weaning), and we propose that this exacerbates myofibre necrosis and inflammation in juvenile mdx mice.

OBJECTIVES

The purpose of this study was to increase taurine availability to pre-weaned juvenile mdx mice (from 14 days of age), to evaluate the impact on levels of myofibre necrosis and inflammation (at 22 days) during the acute period of severe dystropathology.

RESULTS

Untreated 22 day old mdx muscle was not deficient in taurine, with similar levels to normal C57 control muscle. However taurine treatment, which increased the taurine content of young dystrophic muscle (by 40%), greatly reduced myofibre necrosis (by 75%) and prevented significant increases in 3 markers of inflammation.

CONCLUSION

Taurine was very effective at preventing the acute phase of muscle damage that normally results in myofibre necrosis and inflammation in juvenile mdx mice, supporting continued research into the use of taurine as a therapeutic intervention for protecting growing muscles of young DMD boys.

Increasing taurine intake and taurine synthesis improves skeletal muscle function in the mdx mouse model for Duchenne muscular dystrophy

KEY POINTS

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease associated with increased inflammation, oxidative stress and myofibre necrosis. Cysteine precursor antioxidants such as N-acetyl cysteine (NAC) and l-2-oxothiazolidine-4-carboxylate (OTC) reduce dystropathology in the mdx mouse model for DMD, and we propose this is via increased synthesis of the amino acid taurine. We compared the capacity of OTC and taurine treatment to increase taurine content of mdx muscle, as well as effects on in vivo and ex vivo muscle function, inflammation and oxidative stress. Both treatments increased taurine in muscles, and improved many aspects of muscle function and reduced inflammation. Taurine treatment also reduced protein thiol oxidation and was overall more effective, as OTC treatment reduced body and muscle weight, suggesting some adverse effects of this drug. These data suggest that increasing dietary taurine is a better candidate for a therapeutic intervention for DMD.

ABSTRACT

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease for which there is no widely available cure. Whilst the mechanism of loss of muscle function in DMD and the mdx mouse model are not fully understood, disruptions in intracellular calcium homeostasis, inflammation and oxidative stress are implicated. We have shown that protein thiol oxidation is increased in mdx muscle, and that the indirect thiol antioxidant l-2-oxothiazolidine-4-carboxylate (OTC), which increases cysteine availability, decreases pathology and increases in vivo strength. We propose that the protective effects of OTC are a consequence of conversion of cysteine to taurine, which has itself been shown to be beneficial to mdx pathology. This study compares the efficacy of taurine with OTC in decreasing dystropathology in mdx mice by measuring in vivo and ex vivo contractile function and measurements of inflammation and protein thiol oxidation. Increasing the taurine content of mdx muscle improved both in vivo and ex vivo muscle strength and function, potentially via anti-inflammatory and antioxidant effects of taurine. OTC treatment increased taurine synthesis in the liver and taurine content of mdx muscle, improved muscle function and decreased inflammation. However, OTC was less effective than taurine treatment, with OTC also decreasing body and EDL muscle weights, suggesting that OTC had some detrimental effects. These data support continued research into the use of taurine as a therapeutic intervention for DMD, and suggest that increasing dietary taurine is the better strategy for increasing taurine content and decreasing severity of dystropathology.

Metabogenic and Nutriceutical Approaches to Address Energy Dysregulation and Skeletal Muscle Wasting in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a fatal genetic muscle wasting disease with no current cure. A prominent, yet poorly treated feature of dystrophic muscle is the dysregulation of energy homeostasis which may be associated with intrinsic defects in key energy systems and promote muscle wasting. As such, supplementative nutriceuticals that target and augment the bioenergetical expansion of the metabolic pathways involved in cellular energy production have been widely investigated for their therapeutic efficacy in the treatment of DMD. We describe the metabolic nuances of dystrophin-deficient skeletal muscle and review the potential of various metabogenic and nutriceutical compounds to ameliorate the pathological and clinical progression of the disease.

Taurine deficiency, synthesis and transport in the mdx mouse model for Duchenne Muscular Dystrophy

The amino acid taurine is essential for the function of skeletal muscle and administration is proposed as a treatment for Duchenne Muscular Dystrophy (DMD). Taurine homeostasis is dependent on multiple processes including absorption of taurine from food, endogenous synthesis from cysteine and reabsorption in the kidney. This study investigates the cause of reported taurine deficiency in the dystrophic mdx mouse model of DMD. Levels of metabolites (taurine, cysteine, cysteine sulfinate and hypotaurine) and proteins (taurine transporter [TauT], cysteine deoxygenase and cysteine sulfinate dehydrogenase) were quantified in juvenile control C57 and dystrophic mdx mice aged 18 days, 4 and 6 weeks. In C57 mice, taurine content was much higher in both liver and plasma at 18 days, and both cysteine and cysteine deoxygenase were increased. As taurine levels decreased in maturing C57 mice, there was increased transport (reabsorption) of taurine in the kidney and muscle. In mdx mice, taurine and cysteine levels were much lower in liver and plasma at 18 days, and in muscle cysteine was low at 18 days, whereas taurine was lower at 4: these changes were associated with perturbations in taurine transport in liver, kidney and muscle and altered metabolism in liver and kidney. These data suggest that the maintenance of adequate body taurine relies on sufficient dietary intake of taurine and cysteine availability and metabolism, as well as retention of taurine by the kidney. This research indicates dystrophin deficiency not only perturbs taurine metabolism in the muscle but also affects taurine metabolism in the liver and kidney, and supports targeting cysteine and taurine deficiency as a potential therapy for DMD.

Taurine: the appeal of a safe amino acid for skeletal muscle disorders

Taurine is a natural amino acid present as free form in many mammalian tissues and in particular in skeletal muscle. Taurine exerts many physiological functions, including membrane stabilization, osmoregulation and cytoprotective effects, antioxidant and anti-inflammatory actions as well as modulation of intracellular calcium concentration and ion channel function. In addition taurine may control muscle metabolism and gene expression, through yet unclear mechanisms. This review summarizes the effects of taurine on specific muscle targets and pathways as well as its therapeutic potential to restore skeletal muscle function and performance in various pathological conditions. Evidences support the link between alteration of intracellular taurine level in skeletal muscle and different pathophysiological conditions, such as disuse-induced muscle atrophy, muscular dystrophy and/or senescence, reinforcing the interest towards its exogenous supplementation. In addition, taurine treatment can be beneficial to reduce sarcolemmal hyper-excitability in myotonia-related syndromes. Although further studies are necessary to fill the gaps between animals and humans, the benefit of the amino acid appears to be due to its multiple actions on cellular functions while toxicity seems relatively low. Human clinical trials using taurine in various pathologies such as diabetes, cardiovascular and neurological disorders have been performed and may represent a guide-line for designing specific studies in patients of neuromuscular diseases.

Abnormalities in brain structure and biochemistry associated with mdx mice measured by in vivo MRI and high resolution localized (1)H MRS

Duchenne muscular dystrophy (DMD), an X-linked disorder caused by the lack of dystrophin, is characterized by the progressive wasting of skeletal muscles. To date, what is known about dystrophin function is derived from studies of dystrophin-deficient animals, with the most common model being the mdx mouse. Most studies on patients with DMD and in mdx mice have focused on skeletal muscle and the development of therapies to reverse, or at least slow, the severe muscle wasting and progressive degeneration. However, dystrophin is also expressed in the CNS. Both mdx mice and patients with DMD can have cognitive and behavioral changes, but studies in the dystrophic brain are limited. We examined the brain structure and metabolites of mature wild type (WT) and mdx mice using magnetic resonance imaging and spectroscopy (MRI/MRS). Both structural and metabolic alterations were observed in the mdx brain. Enlarged lateral ventricles were detected in mdx mice when compared to WT. Diffusion tensor imaging (DTI) revealed elevations in diffusion diffusivities in the prefrontal cortex and a reduction of fractional anisotropy in the hippocampus. Metabolic changes included elevations in phosphocholine and glutathione, and a reduction in γ-aminobutyric acid in the hippocampus. In addition, an elevation in taurine was observed in the prefrontal cortex. Such findings indicate a regional structural change, altered cellular antioxidant defenses, a dysfunction of GABAergic neurotransmission, and a perturbed osmoregulation in the brain lacking dystrophin.

Chondrocytic cells express the taurine transporter on their plasma membrane and regulate its expression under anisotonic conditions

Taurine is a small organic osmolyte which participates in cell volume regulation. Chondrocytes have been shown to accumulate and release taurine; in bone, taurine participates in bone metabolism. However, its role in skeletal cells is poorly understood, especially in chondrocytes. This study investigated the regulation of taurine transporter in chondrocytic cells. We examined the transcriptional regulation of the taurine transporter under anisotonia by reporter gene and real-time RT-PCR assays. The effect of providing supplementary taurine on cell viability was evaluated with the lactate dehydrogenase release assay. The localization of the taurine transporter in human chondrosarcoma cells was studied by overexpressing a taurine transporter-enhanced green fluorescent protein. We observed that the transcription of the taurine transporter gene was up-regulated in hypertonic conditions. Hyperosmolarity-related cell death could be partly abolished by taurine supplementation in the medium. As expected, the fluorescently labeled taurine transporter localized at the plasma membrane. In polarized epithelial MDCK cells, the strongest fluorescence signal was located in the lateral cell membrane area. We also observed that the taurine transporter gene was expressed in several human tissues and malignant cell lines. This is the first study to present information on the transcriptional regulation of taurine transporter gene and the localization of the taurine transporter protein in chondrocytic cells.

Tissue taurine depletion alters metabolic response to exercise and reduces running capacity in mice

Taurine is a sulfur-containing amino acid found in very high concentration in skeletal muscle. Taurine deficient mice engineered by knocking out the taurine transporter gene exhibit skeletal muscle wasting, structural defects, and exercise intolerance. In the present study, we investigated the mechanism underlying the development of metabolic abnormalities and exercise intolerance in muscle of the TauTKO phenotype. Running speed and endurance time of TauTKO mice were lower than those of control mice. Blood lactate level was elevated by >3-fold during treadmill running in TauTKO mice but remained largely unaltered by exercise in WT mice. Blood glucose was cleared faster during treadmill running in TauTKO mice than WT mice. AMP-activated kinase (AMPK) β-2 subunit was reduced in TauTKO muscle concomitant with a reduction in α1 and α2 subunits of AMPK. The level of PPARα and its targets, Gpx3, Cpt2, and Echs1, were also decreased in TauTKO muscle. Collectively, taurine depletion impairs metabolic adaptation to exercise in skeletal muscle, a phenomenon associated with a downregulation of AMPK and diminished NADH utilization by the mitochondrial respiratory chain. These findings suggest a crucial role of taurine in regulating energy metabolism in skeletal muscle of exercising TauTKO mice, changes that contribute to impaired exercise endurance.

Acute effects of taurine on sarcoplasmic reticulum Ca2+ accumulation and contractility in human type I and type II skeletal muscle fibers

Taurine occurs in high concentrations in muscle and is implicated in numerous physiological processes, yet its effects on many aspects of contractility remain unclear. Using mechanically skinned segments of human vastus lateralis muscle fibers, we characterized the effects of taurine on sarcoplasmic reticulum (SR) Ca2+ accumulation and contractile apparatus properties in type I and type II fibers. Prolonged myoplasmic exposure (>10 min) to taurine substantially increased the rate of accumulation of Ca2+ by the SR in both fiber types, with no change in the maximum amount accumulated; no such effect was found with carnosine. SR Ca2+ accumulation was similar with 10 or 20 mM taurine, but was significantly slower at 5 mM taurine. Cytoplasmic taurine (20 mM) had no detectable effects on the responsiveness of the Ca2+ release channels in either fiber type. Taurine caused a small increase in Ca2+ sensitivity of the contractile apparatus in type I fibers, but type II fibers were unaffected; maximum Ca2+-activated force was unchanged in both cases. The effects of taurine on SR Ca2+ accumulation 1) only became apparent after prolonged cytoplasmic exposure, and 2) persisted for some minutes after complete removal of taurine from the cytoplasm, consistent with the hypothesis that the effects were due to an action of taurine from inside the SR. In summary, taurine potentiates the rate of SR Ca2+ uptake in both type I and type II human fibers, possibly via an action from within the SR lumen, with the degree of potentiation being significantly reduced at low physiological taurine levels.

Mechanisms Underlying Taurine Protection Against Glutamate-Induced Neurotoxicity

Taurine appears to exert potent protections against glutamate (Glu)-induced injury to neurons, but the underlying molecular mechanisms are not fully understood. The possibly protected targets consist of the plasma membrane and the mitochondrial as well as endoplasmic reticulum (ER) membranes. Protection may be provided through a variety of effects, including the prevention of membrane depolarization, neuronal excitotoxicity and mitochondrial energy failure, increases in intracellular free calcium ([Ca2+]i), activation of calpain, and reduction of Bcl-2 levels. These activities are likely to be linked spatially and temporally in the neuroprotective functions of taurine. In addition, events that occur downstream of Glu stimulation, including altered enzymatic activities, apoptotic pathways, and necrosis triggered by the increased [Ca2+]i, can be inhibited by taurine. This review discusses the possible molecular mechanisms of taurine against Glu-induced neuronal injury, providing a better understanding of the protective processes, which might be helpful in the development of novel interventional strategies.

Taurine rescues cisplatin-induced muscle atrophy in vitro: a morphological study

Cisplatin (CisPt) is a widely used chemotherapeutic drug whose side effects include muscle weakness and cachexia. Here we analysed CisPt-induced atrophy in C2C12 myotubes by a multidisciplinary morphological approach, focusing on the onset and progression of autophagy, a protective cellular process that, when excessively activated, may trigger protein hypercatabolism and atrophy in skeletal muscle. To visualize autophagy we used confocal and transmission electron microscopy at different times of treatment and doses of CisPt. Moreover we evaluated the effects of taurine, a cytoprotective beta-amino acid able to counteract oxidative stress, apoptosis, and endoplasmic reticulum stress in different tissues and organs. Our microscopic results indicate that autophagy occurs very early in 50  μM CisPt challenged myotubes (4 h-8 h) before overt atrophy but it persists even at 24 h, when several autophagic vesicles, damaged mitochondria, and sarcoplasmic blebbings engulf the sarcoplasm. Differently, 25 mM taurine pretreatment rescues the majority of myotubes size upon 50  μM CisPt at 24 h. Taurine appears to counteract atrophy by restoring regular microtubular apparatus and mitochondria and reducing the overload and the localization of autophagolysosomes. Such a promising taurine action in preventing atrophy needs further molecular and biochemical studies to best define its impact on muscle homeostasis and the maintenance of an adequate skeletal mass in vivo.

Muscle cramps in liver disease

Muscle cramps are common in patients with liver disease and adversely influence quality of life. The exact mechanisms by which they occur remain unclear, although a number of pathophysiological events unique to liver disease may contribute. Clinical studies have identified alterations in 3 areas: nerve function, energy metabolism, and plasma volume/electrolytes. Treatments have focused on these particular areas with varied results. This review will focus on the clinical features of muscle cramps in patients with liver disease and review potential mechanisms and current therapies.

Does a physiological concentration of taurine increase acute muscle power output, time to fatigue, and recovery in isolated mouse soleus (slow) muscle with or without the presence of caffeine?

High concentrations of caffeine and taurine are key constituents of many ergogenic supplements ingested acutely to provide legal enhancements in athlete performance. Despite this, there is little evidence supporting the claims for the performance-enhancing effects of acute taurine supplementation. In-vitro models have demonstrated that a caffeine-induced muscle contracture can be further potentiated when combined with a high concentration of taurine. However, the high concentrations of caffeine used in previous research would be toxic for human consumption. Therefore, this study aimed to investigate whether a physiological dose of caffeine and taurine would directly potentiate skeletal muscle performance. Isolated mouse soleus muscle was used to examine the effects of physiological taurine (TAU), caffeine (CAF), and taurine-caffeine combined (TC) on (i) acute muscle power output; (ii) time to fatigue; and (iii) recovery from fatigue, compared with the untreated controls (CON). Treatment with TAU failed to elicit any significant difference in the measured parameters. Treatment with TC resulted in a significant increase in acute muscle power output and faster time to fatigue. The ergogenic benefit posed by TC was not different from the effects of caffeine alone, suggesting no acute ergogenic benefit of taurine.

Treatment with the cysteine precursor l-2-oxothiazolidine-4-carboxylate (OTC) implicates taurine deficiency in severity of dystropathology in mdx mice

Oxidative stress has been implicated in the pathology of the lethal skeletal muscle disease Duchenne muscular dystrophy (DMD), and various antioxidants have been investigated as a potential therapy. Recently, treatment of the mdx mouse model for DMD with the antioxidant and cysteine and glutathione (GSH) precursor n-acetylcysteine (NAC) was shown to decrease protein thiol oxidation and improve muscle pathology and ex vivo muscle strength. This study further investigates the mechanism for the benefits of NAC on dystrophic muscle by administering l-2-oxothiazolidine-4-carboxylate (OTC) which also upregulates intracellular cysteine and GSH, but does not directly function as an antioxidant. We observed that OTC, like NAC, decreases protein thiol oxidation, decreases pathology and increases strength, suggesting that the both NAC and OTC function via increasing cysteine and GSH content of dystrophic muscle. We demonstrate that mdx muscle is not deficient in either cysteine or GSH and that these are not increased by OTC treatment. However, we show that dystrophic muscle of 12 week old mdx mice is deficient in taurine, a by-product of disposal of excess cysteine, a deficiency that is ameliorated by OTC treatment. These data suggest that in dystrophic muscles, apart from the strong association of increased oxidative stress and protein thiol oxidation with dystropathology, another major issue is an insufficiency in taurine that can be corrected by increasing the availability of cysteine. This study provides new insight into the molecular mechanism underlying the benefits of NAC in muscular dystrophy and supports the use of OTC as an alternative drug for potential clinical applications to DMD.

Early metabolic changes measured by 1H MRS in healthy and dystrophic muscle after injury

Skeletal muscle injury is often assessed by clinical findings (history, pain, tenderness, strength loss), by imaging, or by invasive techniques. The purpose of this work was to determine if in vivo proton magnetic resonance spectroscopy ((1)H MRS) could reveal metabolic changes in murine skeletal muscle after contraction-induced injury. We compared findings in the tibialis anterior muscle from both healthy wild-type (WT) muscles (C57BL/10 mice) and dystrophic (mdx mice) muscles (an animal model for human Duchenne muscular dystrophy) before and after contraction-induced injury. A mild in vivo eccentric injury protocol was used due to the high susceptibility of mdx muscles to injury. As expected, mdx mice sustained a greater loss of force (81%) after injury compared with WT (42%). In the uninjured muscles, choline (Cho) levels were 47% lower in the mdx muscles compared with WT muscles. In mdx mice, taurine levels decreased 17%, and Cho levels increased 25% in injured muscles compared with uninjured mdx muscles. Intramyocellular lipids and total muscle lipid levels increased significantly after injury but only in WT. The increase in lipid was confirmed using a permeable lipophilic fluorescence dye. In summary, loss of torque after injury was associated with alterations in muscle metabolite levels that may contribute to the overall injury response in mdx mice. These results show that it is possible to obtain meaningful in vivo (1)H MRS regarding skeletal muscle injury.

The different impact of a high fat diet on dystrophic mdx and control C57Bl/10 mice

The absence of functional dystrophin protein in patients with Duchenne muscular dystrophy (DMD) and dystrophic mdx mice leads to fragile myofibre membranes and cycles of myofibre necrosis and regeneration. It is proposed that both DMD patients and mdx mice have an altered metabolism and impaired energy status and that nutritional supplementation may reduce the severity of dystropathology. This research compares the in vivo responses of dystrophic mdx and normal control C57Bl/10 mice to a high protein (50%) or a high fat (16%) diet. Consumption of a high protein diet had minimal effects on the body composition or muscle morphology in both strains of mice. In contrast, differences between the strains were seen in response to the high fat diet; this response also varied between mdx mice aged <24 weeks, and mdx mice aged 24 - 40 weeks. C57Bl/10 mice demonstrated many negative side effects after consuming the high fat diet, including weight gain, increased body fat, and elevated inflammatory cytokines. In contrast, after consuming the high fat diet for 16 weeks the mdx mice (< 24 weeks) remained lean with minimal fat deposition and were resistant to changes in body composition. These results support the proposal that energy metabolism in dystrophic mdx mice is altered compared to normal C57Bl/10 mice and this enables the mdx mice to better metabolise the high fat diet and avoid fat deposition. However, older mdx mice (24 - 40-week-old), with increased energy intake, exhibited some mild adverse effects of a high fat diet but to a far lesser extent than age-matched C57Bl/10 mice. Benefits of the high fat diet on dystrophic muscles of young mice were demonstrated by the significantly increased running ability (km) of voluntarily exercised mdx mice and significantly reduced myofibre necrosis in 24-week-old sedentary mdx mice. These novel data clearly identify an 'altered' response to a high fat diet in dystrophic mdx compared to normal C57Bl/10 mice. Our data indicate that the high fat diet may better meet the energy needs of mdx mice to reduce muscle damage and improve muscle function.

Evaluation of potential synergistic action of a combined treatment with alpha-methyl-prednisolone and taurine on the mdx mouse model of Duchenne muscular dystrophy

AIMS

Glucocorticoids are the sole drugs clinically used in Duchenne muscular dystrophy, in spite of the relevant side effects. Combination of glucocorticoids with synergistic drugs may be one strategy to lower doses and control side effects, meanwhile providing wider control of the complex pathology. This study is a preclinical evaluation of the effect of a combined treatment of α-methyl-prednisolone (PDN) with taurine, a safe aminoacid with positive effects on some pathology-related events.

METHODS

PDN (1 mg/kg/day i.p.) and taurine (1 g/kg/day orally) were administered either alone or in combination, for 4-8 weeks to male dystrophic mdx mice chronically exercised on a treadmill. Effects were assessed in vivo and ex vivo with a variety of methodological approaches.

RESULTS

In vivo, each treatment significantly increased fore limb strength, a marked synergistic effect being observed with the combination PDN + taurine. Ex vivo, PDN + taurine completely restored the mechanical threshold, an electrophysiological index of calcium homeostasis, of extensor digitorum longus myofibres and the benefit was greater than for PDN alone. In parallel, the overactivity of voltage-independent cation channels in dystrophic myofibres was reduced. No effects were observed on plasma levels of creatine kinase, while lactate dehydrogenase was decreased by taurine and, to a minor extent, by PDN + taurine. A similar histology profile was observed in PDN and PDN + taurine-treated muscles. PDN + taurine significantly increased taurine level in fast-twitch muscle and brain, by high-pressure liquid chromatography analysis.

CONCLUSIONS

The combination PDN + taurine has additive actions on in vivo and ex vivo functional end points, with less evident advantages on histopathology and biochemical markers of the disease.

Cardiac and skeletal muscle abnormality in taurine transporter-knockout mice

Taurine, a sulfur-containing β-amino acid, is highly contained in heart and skeletal muscle. Taurine has a variety of biological actions, such as ion movement, calcium handling and cytoprotection in the cardiac and skeletal muscles. Meanwhile, taurine deficiency leads various pathologies, including dilated cardiomyopathy, in cat and fox. However, the essential role of taurine depletion on pathogenesis has not been fully clarified. To address the physiological role of taurine in mammalian tissues, taurine transporter-(TauT-) knockout models were recently generated. TauTKO mice exhibited loss of body weight, abnormal cardiac function and the reduced exercise capacity with tissue taurine depletion. In this chapter, we summarize pathological profile and histological feature of heart and skeletal muscle in TauTKO mice.

Taurine supplementation increases skeletal muscle force production and protects muscle function during and after high-frequency in vitro stimulation

Recent studies report that depletion and repletion of muscle taurine (Tau) to endogenous levels affects skeletal muscle contractility in vitro. In this study, muscle Tau content was raised above endogenous levels by supplementing male Sprague-Dawley rats with 2.5% (wt/vol) Tau in drinking water for 2 wk, after which extensor digitorum longus (EDL) muscles were examined for in vitro contractile properties, fatigue resistance, and recovery from fatigue after two different high-frequency stimulation bouts. Tau supplementation increased muscle Tau content by approximately 40% and isometric twitch force by 19%, shifted the force-frequency relationship upward and to the left, increased specific force by 4.2%, and increased muscle calsequestrin protein content by 49%. Force at the end of a 10-s (100 Hz) continuous tetanic stimulation was 6% greater than controls, while force at the end of the 3-min intermittent high-frequency stimulation bout was significantly higher than controls, with a 12% greater area under the force curve. For 1 h after the 10-s continuous stimulation, tetanic force in Tau-supplemented muscles remained relatively stable while control muscle force gradually deteriorated. After the 3-min intermittent bout, tetanic force continued to slowly recover over the next 1 h, while control muscle force again began to decline. Tau supplementation attenuated F(2)-isoprostane production (a sensitive indicator of reactive oxygen species-induced lipid peroxidation) during the 3-min intermittent stimulation bout. Finally, Tau transporter protein expression was not altered by the Tau supplementation. Our results demonstrate that raising Tau content above endogenous levels increases twitch and subtetanic and specific force in rat fast-twitch skeletal muscle. Also, we demonstrate that raising Tau protects muscle function during high-frequency in vitro stimulation and the ensuing recovery period and helps reduce oxidative stress during prolonged stimulation.

Effects of taurine administration on exercise

Taurine concentration in rat skeletal muscles after endurance running, with and without taurine administration was studied. Taurine concentrations in skeletal muscles was significantly decreased in exercised groups without taurine administration. However, taurine administration reduced the decrease of taurine concentration in skeletal muscles in exercise. Oral administration of taurine has effect for maintaining taurine concentration in skeletal muscles in exercise. The duration of running time to exhaustion of rats, with and without taurine administration were studied. The duration of running time to exhaustion was significantly increased by taurine administration. Oral administration of taurine increases the ability of physical endurance. Rat urinary excretions of creatinine, creatine, 3-methylhistidine (3-MH) after treadmill running, with and without taurine administration were studied. Rat urinary excretions of creatinine, creatine, 3-MH after treadmill running was significantly decreased with taurine administration. Taurine administration was considered to reduce the exercise-induced muscle fatigue.