Rationale: As of early 2014, 1,558 Veterans experienced major amputation of at least one limb, such as an arm, as a result of the wars in Iraq and Afghanistan. Within the field of reconstructive surgery, a specialized area known as vascularized composite allotransplant (VCA) research, is emerging to help these casualties, with the goal of transplanting donor limbs, also referred to as VCAs, onto wounded Warriors with limb amputations, and doing so in a successful and readily available fashion. Currently, donor limbs are preserved by a method called static storage at 4°C. Using this method of preservation, VCA preservation time is limited to 6 hours because of excessive damage to nerve and muscle tissue that interferes with successful transplantation of the limb. This limited preservation time leaves minimal time to transport and transplant the donated limb and effectively reduces the number of available donor limbs. In order to increase successful limb transplants and improve the lives of casualties suffering from amputations, improvements in VCA preservation is required.

Hydrogen sulfide (H2S) and hydrogen selenide (H2Se) are chemicals referred to as "suspended animation" agents. They induce a hibernation-like effect on tissues. In animal models of solid organ (e.g., kidney and liver) transplantation, both H2S and H2Se have been demonstrated to extend preservation time. This is presumed to be due to a reduction in tissue energy consumption, thereby prolonging the time the tissue can survive without oxygen (i.e., ischemia) before being transplanted, as well as protecting the tissue once transplanted from the sudden return of oxygen (i.e., reperfusion). Importantly, these suspended-animation techniques have not been evaluated in complex VCAs, such as an arm. Furthermore, no studies have evaluated H2S and H2Se in an animal model that very closely resembles humans or human tissue. We propose to evaluate the ability of H2S and H2Se to permit the successful extension of VCA preservation time out to 24 hours by using a non-human primate (NHP) arm as a large, complex VCA that translates directly to human clinical practice.

Objectives: The objective of the proposed study is to evaluate the ability of H2S and H2Se to extend the pre-transplant preservation time of NHP arm VCAs. We hypothesize that preservation of NHP arm VCAs prior to transplantation with the suspended animation agents H2S and H2Se will reduce the effects of ischemia and reperfusion and therefore extend the preservation time for VCAs. The long-term goal of this research is to expand the current clinical procedure for VCA preservation strategy by using suspended animation agents to (1) prolong preservation time to remove time barriers and increase the available donors and recipients of VCAs; (2) reduce cold ischemic injury and subsequent reperfusion injury; (3) optimize VCA outcomes including nerve and muscle function and graft survival; and (4) improve the function, wellness, and overall quality of life of wounded Warriors and their families.

Clinical Application: H2S is currently in Phase II and III Food and Drug Administration (FDA) clinical trials for acute myocardial infarction and coronary artery bypass graft surgeries. The preclinical evaluation of H2Se is limited and requires further validation before proceeding to clinical trials. Furthermore, neither agent has been evaluated in a NHP VCA model. The proposed NHP VCA model provides the advantage of preclinically evaluating the proposed preservation strategies in a species that most closely resembles humans and hence human VCAs; this greatly improves the ability of study results to be transferred into the human clinical setting. In addition to significant military relevance, patients sustaining amputations in medically underserved areas, such as Midwestern agriculture workers, or those with life-threatening comorbid injuries could directly benefit from prolonged VCA preservation and hence increased availability of VCA procedures.

Contribution: The research proposed will improve the current clinical VCA preservation standard of care. Ultimately the results of this study will (1) permit increased VCA preservation time to reduce current time barriers limiting VCA availability and success; (2) reduce tissue damage during ischemia and reperfusion; and (3) optimize VCA outcomes including overall nerve and muscle function, graft survival, and patient quality of life. If successful, the proposed treatment strategies would dramatically advance the entire field of reconstructive transplantation and could be universally applied to other complex tissues, including face, urinary, and genital VCAs, as well as solid organs.