Dual effects of taurine on membrane ionic conductances of rat skeletal muscle fibers

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.

A long-term treatment with taurine prevents cardiac dysfunction in mdx mice

Taurine is an amino acid abundantly present in heart and skeletal muscle. Duchenne muscular dystrophy (DMD) is a genetic disorder in which the absence of dystrophin leads to skeletal muscle wasting and heart failure. An altered taurine metabolism has been described in dystrophic animals and short-term taurine administration exerts promising amelioration of early muscular alterations in the mdx mouse model of DMD. To reinforce the therapeutic and nutraceutical taurine potential in DMD, we evaluated the effects of a long-term treatment on cardiac and skeletal muscle function of mdx mice in a later disease stage. Taurine was administered in drinking water (1 g/kg/day) to wt and mdx mice for 6 months, starting at 6 months of age. Ultrasonography evaluation of heart and hind limb was performed, in parallel with in vivo and ex vivo functional tests and biochemical, histological and gene expression analyses. 12-month-old mdx mice showed a significant worsening of left ventricular function parameters (shortening fraction, ejection fraction, stroke volume), which were significantly counteracted by the taurine treatment. In parallel, histologic signs of damage were reduced by taurine along with the expression of proinflammatory myocardial IL-6. Interestingly, no effects were observed on hind limb volume and percentage of vascularization or on in vivo and ex vivo muscle functional parameters, suggesting a tissue-specific action of taurine in relation to the disease phase. A trend toward increase in taurine was found in heart and quadriceps from treated animals, paralleled by a slight decrease in mdx mice plasma. Our study provides evidences that taurine can prevent late heart dysfunction in mdx mice, further corroborating the interest on this amino acid toward clinical trials.

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.

Collaborative translational research leading to multicenter clinical trials in Duchenne muscular dystrophy: the Cooperative International Neuromuscular Research Group (CINRG)

Progress in the development of rationally based therapies for Duchenne muscular dystrophy has been accelerated by encouraging multidisciplinary, multi-institutional collaboration between basic science and clinical investigators in the Cooperative International Research Group. We combined existing research efforts in pathophysiology by a gene expression profiling laboratory with the efforts of animal facilities capable of conducting high-throughput drug screening and toxicity testing to identify safe and effective drug compounds that target different parts of the pathophysiologic cascade in a genome-wide drug discovery approach. Simultaneously, we developed a clinical trial coordinating center and an international network of collaborating physicians and clinics where those drugs could be tested in large-scale clinical trials. We hope that by bringing together investigators at these facilities and providing the infrastructure to support their research, we can rapidly move new bench discoveries through animal model screening and into therapeutic testing in humans in a safe, timely and cost-effective setting.

Immunocytochemical localization of taurine in different muscle cell types of the dog and rat

The presence and distribution of the amino acid taurine in different muscle cell types of the dog and rat was examined by immunocytochemical methods. The light microscope study revealed that smooth muscle cells were similarly immunoreactive for taurine, whereas skeletal muscle fibres showed wide differences in taurine immunoreactivity among individual cells. Some skeletal fibres were strongly immunoreactive whereas others did not display immunolabelling. Mononucleated satellite cells, found adjacent to skeletal fibres in a quiescent stage, were also immunostained. Other myoid cells, such as testicular peritubular cells showed a cytoplasmic and a nuclear pool of taurine. By means of electron microscope immunolabelling, the subcellular localization of taurine was studied in vascular and visceral smooth muscle cells. Taurine was present in most subcellular compartments and frequently appeared randomly distributed. Taurine was localized on myofilaments, dense bodies, mitochondria, the plasma membrane and the cell nucleus. Moreover, the labelling density within individual smooth muscle cells was variable and depended on the state of contraction of each single fibre. Contracted cells showed a higher density of gold particles than relaxed cells. Unmyelinated nerve fibres, found adjacent to smooth muscle cells from the muscularis mucosae and the lamina propria of the stomach, were unstained or poorly stained.