Effect of vitamin E and eccentric exercise on selected biomarkers of oxidative stress in young and elderly men

Muscle damage resulting from eccentric exercise provides a useful model of oxyradical-induced injury and can be used to examine age-related responses to oxidative stress. Sixteen young (26.4 ± 3.3 years) and 16 older (71.1 ± 4.0 years) healthy men were randomly assigned to 1000 IU/d vitamin E or placebo for 12 weeks and ran downhill for 45 min at 75% VO₂max, once before and following supplementation. Blood samples were obtained before (baseline) and immediately postexercise (0 h), and at 6, 24, and 72 h postexercise to determine antioxidant status, muscle damage, lipid peroxidation, and DNA damage. Following exercise, young and older men experienced similar increases in serum creatine kinase (CK), F₂-isoprostanes (iPF₂; p < .001) and malondialdehyde (MDA; p < .01), although iPF₂ peaked at 72 h postexercise and MDA peaked at 0 h. Oxygen Radical Absorbance Capacity (ORAC) decreased at 72 h (p < .01) and correlated with the rise in iPF₂, MDA, and CK in the young men (p < .05). Leukocyte 8-hydroxy-2′-deoxyguanosine (8-OHdG) was unaffected by exercise. Vitamin E decreased peak CK in young men, while in older men it decreased resting levels of iPF₂ and suppressed the 24 h postexercise increases in iPF₂ (p < .05). Thus, vitamin E supplementation induced modest changes eccentric exercise-induced oxidative stress, although differentially between the young and older subjects, while age had no direct influence on these responses among this group of physically fit subjects.     

Caldesmon inhibits the rotation of smooth actin subdomain-1 and alters its mobility during the ATP hydrolysis cycle

Smooth muscle thin filaments have been reconstituted in muscle ghost fibers by incorporation of smooth muscle actin, tropomyosin and caldesmon. For the first time, rotation of subdomain-1 and changes of its mobility in IAEDANS-labeled actin during the ATP hydrolysis cycle simulated using nucleotides and non-hydrolysable ATP analogs have been demonstrated directly. Binding of caldesmon altered the mobility and inhibited the rotation of actin subdomain-1 during the transition from AM∗∗·ADP·Pi to AM state, resulting in inhibition of both strong and weak-binding intermediate states. These new results imply that regulation of actomyosin interaction by caldesmon during the ATPase cycle is fulfilled via the inhibition of actin subdomain-1 rotation toward the periphery of the thin filament, which decreases the area of the specific binding between actin and myosin molecules and is likely to underlie at least in part the mechanism of caldesmon-induced contractility suppression.     

Knockdown of a galectin-1-like protein in zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) causes defects in skeletal muscle development

We previously identified and characterized four galectin-1-like proteins in zebrafish, Drgal1-L1, Drgal1-L2, Drgal1-L3, and one splice variant of Drgal1-L2, of distinct ontogenic expression. Drgal1-L1 is maternal; Drgal1-L2 is zygotic and strongly expressed in the notochord, while Drgal1-L3 is both maternal and zygotic. Knockdown experiments in zebrafish embryos using a morpholino-modified antisense oligo targeted to the 5’-UTR sequence of Drgal1-L2 resulted in a phenotype with a bent tail and disorganized muscle fibers. This effect was dose-dependent as follows: 62–66% at 17 ng, 29–35% at 5.7 ng, 21–28% at 1.9 ng, and 14–17% at 0.6 ng. However, no (or a negligible number of) Drgal1-L1 knockdown embryos showed similar morphological defects, indicating that the observed effects are sequence-specific, and not due to the toxicity of the morpholino-modified oligos. Further, ectopic expression of native Drgal1-L2 specifically rescued the phenotype, as co-injection of the full-length sense Drgal1-L2 mRNA with Drgal1-L2-MO yielded 60–62% normal embryos. As the notochord serves as the primary source of signaling molecules required for proper patterning of adjacent tissues, such as neural tube, somites, and heart, these results suggest that galectins produced by the notochord play a key role in somitic cell differentiation and development.     

Combining frequency and time domain approaches to systems with multiple spike train input and output

A frequency domain approach and a time domain approach have been combined in an investigation of the behaviour of the primary and secondary endings of an isolated muscle spindle in response to the activity of two static fusimotor axons when the parent muscle is held at a fixed length and when it is subjected to random length changes. The frequency domain analysis has an associated error process which provides a measure of how well the input processes can be used to predict the output processes and is also used to specify how the interactions between the recorded processes contribute to this error. Without assuming stationarity of the input, the time domain approach uses a sequence of probability models of increasing complexity in which the number of input processes to the model is progressively increased. This feature of the time domain approach was used to identify a preferred direction of interaction between the processes underlying the generation of the activity of the primary and secondary endings. In the presence of fusimotor activity and dynamic length changes imposed on the muscle, it was shown that the activity of the primary and secondary endings carried different information about the effects of the inputs imposed on the muscle spindle. The results presented in this work emphasise that the analysis of the behaviour of complex systems benefits from a combination of frequency and time domain methods. This article is part of a special issue on Neuronal Dynamics of Sensory Coding.     

A task-specific validation of homogeneous non-linear optimisation approaches

In biomechanics, musculoskeletal models are typically redundant. This situation is referred to as the distribution problem. Often, static, non-linear optimisation methods of the form “min: φ(f) subject to mechanical and muscular constraints” have been used to extract a unique set of muscle forces. Here, we present a method for validating this class of non-linear optimisation approaches where the homogeneous cost function, φ(f), is used to solve the distribution problem. We show that the predicted muscle forces for different loading conditions are scaled versions of each other if the joint loading conditions are just scaled versions. Therefore, we can calculate the theoretical muscle forces for different experimental conditions based on the measured muscle forces and joint loadings taken from one experimental condition and assuming that all input into the optimisation (e.g., moment arms, muscle attachment sites, size, fibre type distribution) and the optimisation approach are perfectly correct. Thus predictions of muscle force for other experimental conditions are accurate if the optimisation approach is appropriate, independent of the musculoskeletal geometry and other input required for the optimisation procedure. By comparing the muscle forces predicted in this way to the actual muscle forces obtained experimentally, we conclude that convex homogeneous non-linear optimisation approaches cannot predict individual muscle forces properly, as force-sharing among synergistic muscles obtained experimentally are not just scaled versions of joint loading, not even in a first approximation.     

High energy phosphate concentrations and AMPK phosphorylation in skeletal muscle from mice with inherited differences in hypoxic exercise tolerance

The effect of chronic hypobaric hypoxia (1/2 atmospheric pressure) on high energy phosphate (HEP) compounds was investigated in slow (soleus; SOL) and fast twitch (extensor digitorum longus; EDL) muscle from 3 strains of mice with large differences in hypoxic exercise tolerance (HET). Phosphocreatine concentration ([PCr]) decreased 16–29% following hypoxia in EDL and SOL in all strains, while [ADP] and [AMP] increased. In the EDL, HET was negatively correlated with the PCr/ATP ratio and positively correlated with the ATP/P_i ratio. The free energy of ATP hydrolysis (ΔG_obs) remained constant despite the substantial changes that occurred in HEP profiles. The alteration of HEP set points and preservation of ΔG_obs are consistent with the notion that (1) maximal rates of steady-state ATP turnover are reduced under hypoxia, and (2) HEP perturbations during rest to work transitions are reduced in skeletal muscle from hypoxia acclimated animals. We therefore expected a lower phosphorylation ratio of AMP-activated protein kinase (AMPK-P/AMPK) during stimulation in hypoxic acclimated animals. However, neither the resting nor stimulated AMPK-P/AMPK was influenced by hypoxia, although there were significant differences among strains.     

State of the art and the dark side of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a disorder that involves the degeneration of motor neurons, muscle atrophy, and paralysis. In a few familiar forms of ALS, mutations in the superoxide dismutase-1 (SOD1) gene have been held responsible for the degeneration of motor neurons. Nevertheless, after the discovery of the SOD1 mutations no consensus has emerged as to which cells, tissues and pathways are primarily implicated in the pathogenic events that lead to ALS. Ubiquitous overexpression of mutant SOD1 in transgenic animals recapitulates the pathological features of ALS. However, the toxicity of mutant SOD1 is not necessarily limited to the central nervous system. Views about ALS pathogenesis are now enriched by the recent discovery of mutations in a pair of DNA/RNA-binding proteins called TDP-43 and FUS/TLS as causes of familial and sporadic forms of ALS. Although the steps that lead to the pathological state are well defined, several fundamental issues are still controversial: are the motor neurons the first direct targets of ALS; and what is the contribution of non-neuronal cells, if any, to the pathogenesis of ALS? The state of the art of ALS pathogenesis and the open questions are discussed in this review.     

Mitochondrial dysfunction and lipotoxicity

Mitochondrial dysfunction in skeletal muscle has been suggested to underlie the development of insulin resistance and type 2 diabetes mellitus. Reduced mitochondrial capacity will contribute to the accumulation of lipid intermediates, desensitizing insulin signaling and leading to insulin resistance. Why mitochondrial function is reduced in the (pre-)diabetic state is, however, so far unknown. Although it is tempting to suggest that skeletal muscle insulin resistance may result from an inherited or acquired reduction in mitochondrial function in the pre-diabetic state, it cannot be excluded that mitochondrial dysfunction may in fact be the consequence of the insulin-resistant/diabetic state. Lipotoxicity, the deleterious effects of accumulating fatty acids in skeletal muscle cells, may lie at the basis of mitochondrial dysfunction: next to producing energy, mitochondria are also the major source of reactive oxygen species (ROS). Fatty acids accumulating in the vicinity of mitochondria are vulnerable to ROS-induced lipid peroxidation. Subsequently, these lipid peroxides could have lipotoxic effects on mtDNA, RNA and proteins of the mitochondrial machinery, leading to mitochondrial dysfunction. Indeed, increased lipid peroxidation has been reported in insulin resistant skeletal muscle and the mitochondrial uncoupling protein-3, which has been suggested to prevent lipid-induced mitochondrial damage, is reduced in subjects with an impaired glucose tolerance and in type 2 diabetic patients. These findings support the hypothesis that fat accumulation in skeletal muscle may precede the reduction in mitochondrial function that is observed in type 2 diabetes mellitus.