Decreasing S-Nitroso-Hemoglobin (SNO-Hb) Levels in Brain Dead Donor Muscle Tissue Correlate with Hypoxia, Decreased Perfusion, and increased HIF-1 alpha Activity: Implications For Vascular Composite Allografts.
Mohamed Awad, MD, Cristin Coquillard, MD, Arvin Smith, Kelsey Isbester, Samuel Boas, Anil Manzanares, Anand Kumar, MD, James Reynolds, PhD.
Case Western Reserve University, Cleveland, OH, USA.
Introduction: Brain death (BD) is associated with sympathetic stimulation that in turn causes organ and extremity hypoperfusion and hypoxia. The effect of BD on muscle tissue in Vascular Composite Allograft (VCA) transplants has not been well studied. Our lab has demonstrated that decreased S-nitroso-hemoglobin (SNO-Hb) after BD correlates with tissue ischemia and hypoxia. We hypothesized that BD would significantly decrease (SNO-Hb) mediated microcirculation and upregulate HIF-1 alpha in VCA muscle tissue of hand and face transplants.Methods: Using a prospective cohort design, serial measurements of arterial S-nitroso-hemoglobin (SNO-Hb) were collected from 63 adult Death by Neurological Criteria (DNC) organ donors. Tissue oxygenation (StO2) was continuously measured by a tissue oxygen monitor (T-Stat) during donor support phase. Muscle samples(n=29) were harvested from the donor during organ recovery surgery and analyzed by western blot for hypoxia induced factor 1 alpha (HIF-1 alpha) expression. HIF-1 alpha was used as a sign of ischemia/ hypoxia, inducible NOS (iNOS/NOS2) as a sign of inflammation, and endothelial NOS (p-eNOS/eNOS) as a sign of vascular activity in tissue samples. Data was analyzed using R statistical software.
Results: Of the muscle samples analyzed, 90% of brain dead donors showed increased expression of HIF-1 alpha. High SNO-Hb was protective of hypoxia and negatively correlated with HIF-1 alpha (P=0.0012) (R=-0.6). High SNO-Hb was associated with increased endothelial vasodilatory p-eNOS/eNOS (P<0.05) (R=-0.39) and better tissue oxygenation (StO2) (P<0.05) (R=-0.8). All the tissue samples showed evidence of hypoxia as determined by expression of iNOS (NOS2) with a strong positive correlation of iNOS (NOS2) level and HIF-1 alpha expression (P=0.001) (R=0.75).Conclusion:Brain death negatively impacts the muscle tissue of VCAs through decreased level of SNO-Hb, subsequent decreased micro circulation, and increases in inflammatory markers such as HIF-1 alpha and iNOS/NOS2. S-nitrosylating modification agents are possible novel therapeutic targets to mitigate the effects of BD pathophysiology on potential transplant tissue.
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