Doxycycline ameliorates the dystrophic phenotype of skeletal and cardiac muscles in mdx mice

Associations between antibiotic exposure and abnormal cardiac enzyme profiles in older Chinese adults

Biomonitoring methods can be used to measure exposure to antibiotics in the general population; however, epidemiological data on the associations between urinary antibiotic levels and the cardiac profiles of enzymes lactate dehydrogenase, creatine kinase, and creatine kinase isoenzyme in older adults remain sparse. We investigated these associations in 990 individuals from the Cohort of Elderly Health and Environment Controllable Factors. Antibiotic residues in urine samples were analyzed using high-performance liquid chromatography-tandem mass spectrometry. Urinary levels of 34 antibiotics were measured. The participants' cardiac enzyme profiles were influenced by sex, age, marital status, education level, cohabitation status, physical activity, dietary structure, body mass index, depression presence and salt, sugar, and oil consumption (P < 0.05). Oxytetracycline, tetracycline, doxycycline, sulfaclozine, and, florfenicol concentrations were negatively associated with the risk of having an abnormal cardiac enzyme profile. Older adults exposed to higher concentrations of norfloxacin had a higher risk of LDH anomalies. After antibiotics were classified, we identified associations between exposure to chloramphenicols, sulfonamides, or veterinary antibiotics and a lower risk of having an abnormal cardiac enzyme profile. Obtaining an accurate epidemiological profile of antibiotic exposure is indispensable for the prevention and detection of cardiac enzyme profile abnormalities in older adults.

Urinary antibiotic exposure and low grip strength risk in community-dwelling elderly Chinese by gender and age

Emerging studies have shown that environmental contaminants were related to decreased handgrip strength. Nevertheless, no prior research has investigated the relationship of exposure to environmental antibiotics with grip strength. Thus, we explored the relationship between urinary antibiotic burden and grip strength among the elderly in China. This study consisted of 451 men and 539 women from the baseline survey of a cohort study. Commonly used antibiotics for humans and animals were detected in 990 urine samples through a biomonitoring method. Grip strength was measured by an electronic dynamometer. We examined the associations of antibiotic exposure with low grip strength (LGS), grip strength, and grip strength index, respectively. Results suggested that 34.9% of participants developed LGS, and 93.0% of individuals were exposed to 1-10 antibiotics. Among women, oxytetracycline (Quartile 2: odds ratio: 2.97, 95% confidence interval: 1.36-6.50), florfenicol (Quartile 3: 2.60 [1.28-5.27]), fluoroquinolones (Quartile 4: 1.88 [1.07-3.30]), and chloramphenicols (Quartile 3: 2.73 [1.35-5.51]) could enhance LGS risk. Among men, ofloxacin (Quartile 2: 3.32 [1.45-7.59]) increased LGS risk, whereas tetracycline (Quartile 2: 0.31 [0.11-0.88]) was implicated in reduced LGS risk. In participants < 70 years, ofloxacin (Quartile 2: 3.00 [1.40-6.42]) could increase LGS risk. For participants who were 70 years of age or older, veterinary antibiotics (Quartile 3: 1.73 [1.02-2.94]) were linked to a 73% increased risk of LGS. Our findings suggested that antibiotics mainly pertained to LGS, and there were gender and age disparities in associations between antibiotic exposure and muscle strength indicators in the elderly Chinese population.

The Role of Matrix Metalloproteinases and Tissue Inhibitors of Metalloproteinases in Duchenne Muscular Dystrophy Cardiomyopathy

BACKGROUND

Cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD). Standard cardiac biomarkers are poor indicators of DMD cardiovascular disease. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) regulate collagen turnover. Given the cardiac fibrosis seen in DMD, we hypothesized that MMPs and TIMPs correlate with severity of DMD cardiomyopathy.

METHODS AND RESULTS

Prospectively enrolled DMD subjects (n = 42) underwent cardiac magnetic resonance imaging for function and late gadolinium enhancement (LGE), including LGE severity from 0 (no LGE) to 4 (severe). Serum from DMD and healthy male control subjects (n = 15) analyzed for MMPs 1, 2, 3, 7, 9, and 10 and TIMPs 1-4. MMP1, MMP7, and MMP10 were higher in DMD than in control (respectively, median 5080 pg/mL vs 2120 pg/mL [P = .007], 2170 pg/mL vs 1420 pg/mL [P < .001], and 216 pg/mL vs 140pg/mL [P = .040]); TIMP4 was lower in DMD (124 pg/mL vs 263 pg/mL; P = .046). Within DMD, MMP7 correlated inversely with left ventricular ejection fraction (r = -0.40; P = .012) and directly with strain (r = 0.54; P = .001) and LGE severity (r = 0.47; P = .003). MMP7 was higher in DMD patients with LGE compared with those without LGE and control subjects (P < .001).

CONCLUSIONS

Multiple MMPs are elevated in DMD compared with control subjects. MMP7 is related to DMD cardiac dysfunction and myocardial fibrosis, possibly through remodeling of the extracellular matrix.

Matrix Metalloproteinases and Tissue Inhibitor of Metalloproteinases in Inflammation and Fibrosis of Skeletal Muscles

In skeletal muscles, levels and activity of Matrix MetalloProteinases (MMPs) and Tissue Inhibitors of MetalloProteinases (TIMPs) have been involved in myoblast migration, fusion and various physiological and pathological remodeling situations including neuromuscular diseases. This has opened perspectives for the use of MMPs' overexpression to improve the efficiency of cell therapy in muscular dystrophies and resolve fibrosis. Alternatively, inhibition of individual MMPs in animal models of muscular dystrophies has provided evidence of beneficial, dual or adverse effects on muscle morphology or function. We review here the role played by MMPs/TIMPs in skeletal muscle inflammation and fibrosis, two major hurdles that limit the success of cell and gene therapy. We report and analyze the consequences of genetic or pharmacological modulation of MMP levels on the inflammation of skeletal muscles and their repair in light of experimental findings. We further discuss how the interplay between MMPs/TIMPs levels, cytokines/chemokines, growth factors and permanent low-grade inflammation favor cellular and molecular modifications resulting in fibrosis.

Dual Therapy Deflazacort/Doxycyclyne Is Better Than Deflazacort Monotherapy to Alleviate Cardiomyopathy in Dystrophin-Deficient mdx Mice

Cardiomyopathy related to the absence of dystrophin is an important feature in Duchenne muscular dystrophy (DMD) and in the mdx mouse. Doxycycline (DOX) could be a potential therapy for mdx skeletal muscles dystrophy. We investigated whether the corticoid deflazacort (DFZ) plus DOX could improve cardiac mdx dystrophy better than DFZ alone, later (17 months) in dystrophy. Mdx mice (8 months old) received DFZ/DOX or DFZ for 9 months. The combined therapy was greater than DFZ in reducing fibrosis (60% decrease with DFZ/DOX and 40% with DFZ alone) in the right ventricle and transforming growth factor β levels (6.8 ± 3.2 in untreated mdx mice, 2.8 ± 1.4 in combined therapy, and 4.6 ± 1.7 in DFZ; P < .05). Combined therapy more effectively ameliorated cardiac dysfunction (electrocardiogram [ECG]) than DFZ. Improvements were seen in the cardiomyopathy index (0.8 ± 0.1 in combined therapy and 1.0 ± 0.2 in DFZ), heart rate (418 ± 46 bpm in combined therapy and 457 ± 29 bpm in DFZ), QRS interval (11.3 ± 2 in combined therapy and 13.6 ± 1 in DFZ), and Q wave amplitude (-40.7 ± 21 in combined therapy and -90.9 ± 36 in DFZ). Both therapies decreased markers of inflammation (tumor necrosis factor α, nuclear factor κB, and metalloproteinase 9). DFZ/DOX improved mdx cardiomyopathy at this stage of the disease, supporting further clinical investigations.

Co-administration of deflazacort and doxycycline: a potential pharmacotherapy for Duchenne muscular dystrophy

The standard therapy used in the treatment of Duchenne muscle dystrophy (DMD) is corticoids, such as deflazacort and prednisone. However, they have limited therapeutic value, and their combination with drugs already in use to treat other human diseases could potentially increase corticoid outcomes in DMD. In the present study, we evaluated whether a combined therapy of the corticoid deflazacort with doxycycline could result in greater improvement in mdx dystrophy than deflazacort alone. Deflazacort alone or deflazacort/doxycycline were administered for 36 days (starting on postnatal day 0) in drinking water. Histopathological, biochemical (creatine kinase), functional (forelimb muscle grip strength and fatigue) parameters and inflammatory markers (MMP-9, TNF-α, NF-kB) were evaluated in biceps brachii and diaphragm muscles of the mdx mice. The combined therapy was superior in improving the dystrophic phenotype compared to monotherapy. The primary results were observed in attenuating muscle fatigue, decreasing muscle total calcium and inflammatory markers and increasing β-dystroglycan, a main component of the dystrophin-protein complex. Furthermore, the combined therapy was effective in preventing the loss of body mass observed with deflazacort alone at this very early stage of therapy. The present study offers preclinical data to support further studies with deflazacort/doxycycline combined therapy in DMD clinical trials.

Diaphragm degeneration and cardiac structure in mdx mouse: potential clinical implications for Duchenne muscular dystrophy

We examined the effects of exercise on diaphragm degeneration and cardiomyopathy in dystrophin-deficient mdx mice. Mdx mice (11 months of age) were exercised (swimming) for 2 months to worsen diaphragm degeneration. Control mdx mice were kept sedentary. Morphological evaluation demonstrated increased fibrosis in the diaphragm of exercised mdx mice (33.3 ± 6.0% area of fibrosis) compared with control mdx mice (20.9 ± 1.7% area of fibrosis). Increased (26%) activity of MMP-2, a marker of fibrosis, was detected in the diaphragms from exercised mdx mice. Morphological evaluation of the heart demonstrated a 45% increase in fibrosis in the right ventricle (8.3 ± 0.6% in sedentary vs. 12.0 ± 0.6% of fibrosis in exercised) and in the left ventricle (35% increase) in the exercised mdx mice. The density of inflammatory cells-degenerating cardiomyocytes increased 95% in the right ventricle (2.3 ± 0.6 in sedentary vs. 4.5 ± 0.8 in exercised) and 71% in the left ventricle (1.4 ± 0.6 sedentary vs. 2.4 ± 0.5 exercised). The levels of both active MMP-2 and the pro-fibrotic factor transforming growth factor beta were elevated in the hearts of exercised compared with sedentary mdx mice. The wall thickness to lumen diameter ratio of the pulmonary trunk was significantly increased in the exercised mdx mice (0.11 ± 0.04 in sedentary vs. 0.28 ± 0.12 in exercised), as was the thickness of the right ventricle wall, which suggests the occurrence of pulmonary hypertension in those animals. It is suggested that diaphragm degeneration is a main contributor to right ventricle dystrophic pathology. These findings may be relevant for future interventional studies for Duchenne muscular dystrophy-associated cardiomyopathy.

Therapeutic potential of matrix metalloproteinases in Duchenne muscular dystrophy

Matrix metalloproteinases (MMPs) are secreted proteinases that have physiologic roles in degradation and remodeling of extracellular matrix (ECM) in almost all tissues. However, their excessive production in disease conditions leads to many pathological features including tissue breakdown, inflammation, cell death, and fibrosis. Duchenne Muscular dystrophy (DMD) is a devastating genetic muscle disorder caused by partial or complete loss of cytoskeletal protein dystrophin. Progressive muscle wasting in DMD is accompanied by myofiber necrosis followed by cycles of regeneration and degeneration and inflammation that eventually result in replacement of myofiber by connective and adipose tissues. Emerging evidence suggests that gene expression and the activity of various MMPs are aberrantly regulated in muscle biopsies from DMD patients and in skeletal muscle of animal models of DMD. Moreover, a few studies employing genetic mouse models have revealed that different MMPs play distinct roles in disease progression in DMD. Modulation of the activity of MMPs improves myofiber regeneration and enhances the efficacy of transplantation and engraftment of muscle progenitor cells in dystrophic muscle in mouse models of DMD. Furthermore, recent reports also suggest that some MMPs especially MMP-9 can serve as a biomarker for diagnosis and prognosis of DMD. In this article, we provide a succinct overview of the regulation of various MMPs and their therapeutic importance in DMD.

Isobaric Tagging-Based Quantification for Proteomic Analysis: A Comparative Study of Spared and Affected Muscles from mdx Mice at the Early Phase of Dystrophy

Duchenne muscular dystrophy (DMD) is the most common childhood myopathy, characterized by muscle loss and cardiorespiratory failure. While the genetic basis of DMD is well established, secondary mechanisms associated with dystrophic pathophysiology are not fully clarified yet. In order to obtain new insights into the molecular mechanisms of muscle dystrophy during earlier stages of the disease, we performed a comparative proteomic profile of the spared extraocular muscles (EOM) vs. affected diaphragm from the mdx mice, using a label based shotgun proteomic approach. Out of the 857 identified proteins, 42 to 62 proteins had differential abundance of peptide ions. The calcium-handling proteins sarcalumenin and calsequestrin-1 were increased in control EOM compared with control DIA, reinforcing the view that constitutional properties of EOM are important for their protection against myonecrosis. The finding that galectin-1 (muscle regeneration), annexin A1 (anti-inflammatory) and HSP 47 (fibrosis) were increased in dystrophic diaphragm provides novel insights into the mechanisms through which mdx affected muscles are able to counteract dystrophy, during the early stage of the disease. Overall, the shotgun technique proved to be suitable to perform quantitative comparisons between distinct dystrophic muscles and allowed the suggestion of new potential biomarkers and drug targets for dystrophinopaties.

Wasting mechanisms in muscular dystrophy

Muscular dystrophy is a group of more than 30 different clinical genetic disorders that are characterized by progressive skeletal muscle wasting and degeneration. Primary deficiency of specific extracellular matrix, sarcoplasmic, cytoskeletal, or nuclear membrane protein results in several secondary changes such as sarcolemmal instability, calcium influx, fiber necrosis, oxidative stress, inflammatory response, breakdown of extracellular matrix, and eventually fibrosis which leads to loss of ambulance and cardiac and respiratory failure. A number of molecular processes have now been identified which hasten disease progression in human patients and animal models of muscular dystrophy. Accumulating evidence further suggests that aberrant activation of several signaling pathways aggravate pathological cascades in dystrophic muscle. Although replacement of defective gene with wild-type is paramount to cure, management of secondary pathological changes has enormous potential to improving the quality of life and extending lifespan of muscular dystrophy patients. In this article, we have reviewed major cellular and molecular mechanisms leading to muscle wasting in muscular dystrophy. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.