title: Primary role of functional ischemia, quantitative evidence for the two-hit mechanism, and phosphodiesterase-5 inhibitor therapy in mouse muscular dystrophy.
abstract: BACKGROUND
  Duchenne Muscular Dystrophy (DMD) is characterized by increased muscle damage and an abnormal blood flow after muscle contraction: the state of functional ischemia. Until now, however, the cause-effect relationship between the pathogenesis of DMD and functional ischemia was unclear. We examined (i) whether functional ischemia is necessary to cause contraction-induced myofiber damage and (ii) whether functional ischemia alone is sufficient to induce the damage.
  
  
  RESULTS
  In vivo microscopy was used to document assays developed to measure intramuscular red blood cell flux, to quantify the amount of vasodilatory molecules produced from myofibers, and to determine the extent of myofiber damage. Reversal of functional ischemia via pharmacological manipulation prevented contraction-induced myofiber damage in mdx mice, the murine equivalent of DMD. This result indicates that functional ischemia is required for, and thus an essential cause of, muscle damage in mdx mice. Next, to determine whether functional ischemia alone is enough to explain the disease, the extent of ischemia and the amount of myofiber damage were compared both in control and mdx mice. In control mice, functional ischemia alone was found insufficient to cause a similar degree of myofiber damage observed in mdx mice. Additional mechanisms are likely contributing to cause more severe myofiber damage in mdx mice, suggestive of the existence of a "two-hit" mechanism in the pathogenesis of this disease.
  
  
  CONCLUSIONS
  Evidence was provided supporting the essential role of functional ischemia in contraction-induced myofiber damage in mdx mice. Furthermore, the first quantitative evidence for the "two-hit" mechanism in this disease was documented. Significantly, the vasoactive drug tadalafil, a phosphodiesterase 5 inhibitor, administered to mdx mice ameliorated muscle damage.
authors.affiliation: Department of Anesthesiology and Critical Care, Shriners Hospital for Children, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America; Department of Geriatric Medicine, Graduate School of Medicine, University of Tokyo, Tokyo, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Asai
authors.forename: Nita
authors.initials: N
authors.lastname: Sahani
authors.forename: Masao
authors.initials: M
authors.lastname: Kaneki
authors.forename: Yasuyoshi
authors.initials: Y
authors.lastname: Ouchi
authors.forename: J A Jeevendra
authors.initials: JA
authors.lastname: Martyn
authors.forename: Shingo Egusa
authors.initials: SE
authors.lastname: Yasuhara
mesh_terms: D000818:Animals; D002243:Carbolines / Q000627:therapeutic use; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000378:metabolism; D004195:Disease Models, Animal; D006861:Hydrogen Peroxide / Q000378:metabolism; D007511:Ischemia / Q000150:complications*; D051379:Mice; D008822:Mice, Transgenic; D009119:Muscle Contraction; D009137:Muscular Dystrophy, Animal / Q000188:drug therapy* / Q000201:enzymology / Q000209:etiology*; D009569:Nitric Oxide / Q000096:biosynthesis; D058986:Phosphodiesterase 5 Inhibitors; D010726:Phosphodiesterase Inhibitors / Q000627:therapeutic use; D000068581:Tadalafil
chemical_list: D002243:Carbolines; D058986:Phosphodiesterase 5 Inhibitors; D010726:Phosphodiesterase Inhibitors; D009569:Nitric Oxide; D000068581:Tadalafil; D006861:Hydrogen Peroxide; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5