Dynamics and mediators of acute graft attrition after myoblast transplantation to the heart

Survival and proliferation of skeletal myoblasts within the cardiac environment are crucial to the therapeutic efficacy of myoblast transplantation to the heart. We have analyzed the early dynamics of myoblasts implanted into the myocardium and investigated the mechanisms underlying graft attrition. At 10 min after implantation of [ 14 C]thymidine‐labeled male myoblasts into female mice hearts, 14 C measurement showed that 39.2 ± 3.0% of the grafted cells survived, and this steadily decreased to 16.0 ± 1.7% by 24 h and to 7.4 ± 0.9% by 72 h. PCR of male‐ specific Smcy gene calculated that the total (surviving plus proliferated) number of donor‐derived cells was 18.3 ± 1.6 and 23.3 ± 1.3% at 24 and 72 h, respectively, indicating that proliferation of the surviving cells began after 24 h. Acute inflammation became prominent by 24 h and was reduced by 72 h as indicated by myeloperoxidase activity and histological findings. Multiplex RT‐PCR revealed corresponding changes in IL‐1β, TGF‐β, IL‐6, and TNF‐α expression. Treatment with CuZn‐superoxide dismutase attenuated the initial rapid death and resulted in enhanced cell numbers afterward, giving a twofold increased total number at 72 h compared with the nontreatment. This effect was associated with reduced inflammatory response, suggesting a causative role for superoxide in the initial rapid graft death and subsequent inflammation. These data describe the early dynamics of myoblasts implanted into the myocardium and suggest that initial oxidative stress and following inflammatory response may be important mechanisms contributing to acute graft attrition, both of which could be potential therapeutic targets to improve the efficiency of cell transplantation to the heart.