Abstract P2038: Synthetic Membrane Stabilizers Reduce Serum Ck And Immune Cell Infiltrate In Neonatal Mdx Skeletal Muscle Prior To Overt Muscle Necrosis Onset In Vivo

Abstract

Duchenne muscular dystrophy (DMD) is a fatal X-linked recessive disease caused by a mutation in the dystrophin gene resulting in a complete loss of dystrophin from the striated muscle. This leads to the disruption of the dystrophin-associated glycoprotein complex and altered mechanical and signaling functions subsequently causing membrane instability, necrosis, and progressive muscle wasting. Immune cell infiltration is a prominent feature of the DMD pathophysiology and is strongly associated with disease severity. To date, no curative treatment is available for DMD. A logical therapeutic approach for DMD is to directly target the primary defect of DMD, sarcolemma instability, and thus prevent contraction-induced membrane damage. First in class synthetic triblock copolymer, poloxamer 188 (P188), is a muscle membrane interfacing and stabilizing molecule that has been shown to protect dystrophic myocardium and skeletal muscle from acute stress induced injury in vivo . Creatine kinase (CK) is a well-established biomarker of DMD that reflects sarcolemma damage, and serum levels have been shown to dramatically increase in mdx mice, but this has not been fully characterized during the early postnatal growth period prior to overt disease onset at 3 weeks. Under standard laboratory housing conditions for adult mdx mice (6-9 month old), we found that daily administration of P188 for two weeks did not significantly change serum CK levels or Evan’s blue dye uptake by diaphragm, heart or tibialis anterior muscles. In order to evaluate P188’s ability to protect dystrophin-deficient striated muscle prior to the overt disease, serum CK levels need to be characterized during this time period to identify the earliest muscle membrane damage event in mdx striated muscle and thus the earliest time point for therapeutic intervention. Results show that mdx serum CK levels are significantly higher than control serum levels 15 days after birth and continue to increase dramatically to 20 days after birth, and then CK remains high for the lifespan. Systemic delivery of P188 to neonatal mdx mice (12 days old) prior to CK peak significantly reduced serum CK levels and blunted immune cell infiltrate as compared to saline control mdx mice. These findings support the hypothesis that early intervention with membrane stabilizers has the potential to mitigate muscle damage and blunt the inflammatory response characteristic of DMD disease pathology. More work must be done to fully understand the early pathophysiological changes associated with dystrophin deficiency in order to implement novel therapeutic strategies including membrane stabilizers to enhance the standard of care for these patients and their families.