Effects of dietary omega-3 on dystrophic cardiac and diaphragm muscles as evaluated by 1 H magnetic resonance spectroscopy: Metabolic profile and calcium-related proteins

Biomarkers for Duchenne muscular dystrophy progression: impact of age in the mdx tongue spared muscle

BACKGROUND

Duchenne muscular dystrophy (DMD) is a severe form of muscular dystrophy without an effective treatment, caused by mutations in the DMD gene, leading to the absence of dystrophin. DMD results in muscle weakness, loss of ambulation, and death at an early age. Metabolomics studies in mdx mice, the most used model for DMD, reveal changes in metabolites associated with muscle degeneration and aging. In DMD, the tongue muscles exhibit unique behavior, initially showing partial protection against inflammation but later experiencing fibrosis and loss of muscle fibers. Certain metabolites and proteins, like TNF-α and TGF-β, are potential biomarkers for dystrophic muscle characterization.

METHODS

To investigate disease progression and aging, we utilized young (1 month old) and old (21-25 months old) mdx and wild-type tongue muscles. Metabolite changes were analyzed using 1H nuclear magnetic resonance, while TNF-α and TGF-β were assessed using Western blotting to examine inflammation and fibrosis. Morphometric analysis was conducted to assess the extent of myofiber damage between groups.

RESULTS

The histological analysis of the mid-belly tongue showed no differences between groups. No differences were found between the concentrations of metabolites from wild-type or mdx whole tongues of the same age. The metabolites alanine, methionine, and 3-methylhistidine were higher, and taurine and glycerol were lower in young tongues in both wild type and mdx (p < 0.001). The metabolites glycine (p < 0.001) and glutamic acid (p = 0.0018) were different only in the mdx groups, being higher in young mdx mice. Acetic acid, phosphocreatine, isoleucine, succinic acid, creatine, and the proteins TNF-α and TGF-β had no difference in the analysis between groups (p > 0.05).

CONCLUSIONS

Surprisingly, histological, metabolite, and protein analysis reveal that the tongue of old mdx remains partially spared from the severe myonecrosis observed in other muscles. The metabolites alanine, methionine, 3-methylhistidine, taurine, and glycerol may be effective for specific assessments, although their use for disease progression monitoring should be cautious due to age-related changes in the tongue muscle. Acetic acid, phosphocreatine, isoleucine, succinate, creatine, TNF-α, and TGF-β do not vary with aging and remain constant in spared muscles, suggesting their potential as specific biomarkers for DMD progression independent of aging.

Biomarkers for Duchenne muscular dystrophy progression: impact of age in the mdx tongue spared muscle

Background: Duchenne muscular dystrophy (DMD) is a severe form of muscular dystrophy without an effective treatment, caused by mutations in the DMD gene, leading to the absence of dystrophin. DMD results in muscle weakness, loss of ambulation and death at an early age. Metabolomics studies in mdx mice, the most used model for DMD, reveal changes in metabolites associated with muscle degeneration and aging. In DMD, the tongue muscles exhibit unique behavior, initially showing partial protection against inflammation but later experiencing fibrosis and loss of muscle fibers. Certain metabolites and proteins, like TNF-α and TGF-β, are potential biomarkers for dystrophic muscle characterization. Methods: To investigate disease progression and aging, we utilized young (1-month old) and old (21-25 months old) mdx and wild-type mice. Metabolite changes were analyzed using 1-H Nuclear Magnetic Resonance, while TNF-α and TGF-β were assessed using Western blotting to examine inflammation, and fibrosis. Morphometric analysis was conducted to assess the extent of myofiber damage between groups. Results: The histological analysis of the tongue showed no differences between groups. No differences were found between the concentrations of metabolites from wild type or mdx animals of the same age. The metabolites alanine, methionine, 3-methylhistidine were higher, and taurine and glycerol were lower in young animals in both wild type and mdx (p < 0.001). The metabolites glycine (p < 0.001) and glutamic acid (p = 0.0018) were different only in the mdx groups, being higher in young mdx mice. Acetic acid, phosphocreatine, isoleucine, succinic acid, creatine and the proteins TNF-α and TGF-β had no difference in the analysis between groups (p > 0.05). Conclusions: Surprisingly, histological and protein analysis reveals that the tongue of young and old mdx animals is protected from severe myonecrosis observed in other muscles. The metabolites alanine, methionine, 3-methylhistidine, taurine, and glycerol may be effective for specific assessments, although their use for disease progression monitoring should be cautious due to age-related changes. Acetic acid, phosphocreatine, isoleucine, succinate, creatine, TNF-α, and TGF-β do not vary with aging and remain constant in spared muscles, suggesting their potential as specific biomarkers for DMD progression independent of aging.

Intrafamilial phenotypic heterogeneity related to a new DMD splice site variant

Dystrophinopathies are a group of X-linked neuromuscular disorders that result from pathogenic variants in the DMD gene. Their pathophysiological substrate is the defective expression of dystrophin in many tissues. While patients from the same pedigree usually present similar dystrophin expression and clinical course, the extent of cardiac and skeletal muscle involvement may not correlate in the same individual. We identified a new splice site variant c.2803+5G>C (NM_004006) ClinVar VCV000803902, located in intron 22 of DMD in a Brazilian family that present a broad phenotypic and histological heterogeneity. One of the subjects had a typical Duchenne muscular dystrophy (DMD) phenotype, whereas the others had Becker muscular dystrophy (BMD). Cardiac involvement was remarkable in some of the BMD patients, but not in the DMD patient. Western blot analysis of skeletal muscle revealed much lower levels of calsequestrin in the most severely affected patient compared to his brother, whose phenotype is BMD, highlighting the potential role of proteins involved in skeletal muscle calcium homeostasis in differential degrees of dystrophinopathies.

Fish oil attenuated dystrophic muscle markers of inflammation via FFA1 and FFA4 in the mdx mouse model of DMD

In the present study we investigated the involvement of free fatty acid (FFA) receptors in the anti-inflammatory role of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in dystrophic muscles, by administering FFA blockers in the mdx mouse model of dystrophy. Mdx mice (3 months-old) were treated with fish oil capsules (FDC Vitamins; 0.4 g EPA and 0.2 g DHA; gavage) alone or concomitant to FFA1 and FFA4 blockers (GW1100 and AH7614; i.p.). C57BL/10 mice (3 months-old) and untreated-mdx mice received mineral oil and were used as controls. After 1 month of treatment, plasma markers of myonecrosis (total and cardiac creatine kinase; CK), the levels of FFA1 and FFA4 and of the markers of inflammation, nuclear transcription factor kappa B (NFkB), tumor necrosis factor alpha (TNF-α) and interleukin 1β (IL-1β) were analyzed in the diaphragm muscle and heart by western blot. Fish oil significantly reduced total CK, cardiac CK and the levels of NFkB (diaphragm), and of TNF-α and IL-1β (diaphragm and heart) in mdx. In the dystrophic diaphragm, FFA1 was increased compared to normal. Blockers of FFA1 and FFA4 significantly inhibited the effects of fish oil treatment in both dystrophic muscles. The anti-inflammatory effects of fish oil in dystrophic diaphragm muscle and heart were mediated through FFA1 and FFA4.

TRPC channels in exercise-mimetic therapy

Physical exercise yields beneficial effects on all types of muscle cells, which are essential for the maintenance of cardiovascular homeostasis and good blood circulation. Daily moderate exercise increases systemic antioxidative capacity, which can lead to the prevention of the onset and progression of oxidative stress-related diseases. Therefore, exercise is now widely accepted as one of the best therapeutic strategies for the treatment of ischemic (hypoxic) diseases. Canonical transient receptor potential (TRPC) proteins are non-selective cation channels activated by mechanical stress and/or stimulation of phospholipase C-coupled surface receptors. TRPC channels, especially diacylglycerol-activated TRPC channels (TRPC3 and TRPC6; TRPC3/6), play a key role in the development of cardiovascular remodeling. We have recently found that physical interaction between TRPC3 and NADPH oxidase (Nox) 2 under hypoxic stress promotes Nox2-dependent reactive oxygen species (ROS) production and mediates rodent cardiac plasticity, and inhibition of the TRPC3-Nox2 protein complex results in enhancement of myocardial compliance and flexibility similar to that observed in exercise-treated hearts. In this review, we describe current understanding of the roles of TRPC channels in striated muscle (patho)physiology and propose that targeting TRPC-based protein complexes could be a new strategy to imitate exercise therapy.

Skeletal Muscle Metabolism in Duchenne and Becker Muscular Dystrophy-Implications for Therapies

The interactions between nutrition and metabolism and skeletal muscle have long been known. Muscle is the major metabolic organ&mdash;it consumes more calories than other organs&mdash;and therefore, there is a clear need to discuss these interactions and provide some direction for future research areas regarding muscle pathologies. In addition, new experiments and manuscripts continually reveal additional highly intricate, reciprocal interactions between metabolism and muscle. These reciprocal interactions include exercise, age, sex, diet, and pathologies including atrophy, hypoxia, obesity, diabetes, and muscle myopathies. Central to this review are the metabolic changes that occur in the skeletal muscle cells of muscular dystrophy patients and mouse models. Many of these metabolic changes are pathogenic (inappropriate body mass changes, mitochondrial dysfunction, reduced adenosine triphosphate (ATP) levels, and increased Ca²⁺) and others are compensatory (increased phosphorylated AMP activated protein kinase (pAMPK), increased slow fiber numbers, and increased utrophin). Therefore, reversing or enhancing these changes with therapies will aid the patients. The multiple therapeutic targets to reverse or enhance the metabolic pathways will be discussed. Among the therapeutic targets are increasing pAMPK, utrophin, mitochondrial number and slow fiber characteristics, and inhibiting reactive oxygen species. Because new data reveals many additional intricate levels of interactions, new questions are rapidly arising. How does muscular dystrophy alter metabolism, and are the changes compensatory or pathogenic? How does metabolism affect muscular dystrophy? Of course, the most profound question is whether clinicians can therapeutically target nutrition and metabolism for muscular dystrophy patient benefit? Obtaining the answers to these questions will greatly aid patients with muscular dystrophy.