Acute systemic changes in blood cells, proteins, coagulation, fibrinolysis, and platelet aggregation after frostbite injury in the rabbit

Proceedings of the 2021 American Burn Association State and Future of Burn Science Meeting

Periodically, the American Burn Association (ABA) has convened a State of the Science meeting on various topics representing multiple disciplines within burn care and research. In 2021 at the request of the ABA President, meeting development was guided by the ABA's Burn Science Advisory Panel (BSAP) and a subgroup of meeting chairs. The goal of the meeting was to produce both an evaluation of the current literature and ongoing studies, and to produce a research agenda and/or define subject matter-relevant next steps to advance the field(s). Members of the BSAP defined the topics to be addressed and subsequently solicited for nominations of expert speakers and topic leaders from the ABA's Research Committee. Current background literature for each topic was compiled by the meeting chairs and the library then enhanced by the invited topic and breakout discussion leaders. The meeting was held in New Orleans, LA on November 2nd and 3rd and was formatted to allow for 12 different topics, each with two subtopics, to be addressed. Topic leaders provided a brief overview of each topic to approximately 100 attendees, followed by expert-lead breakout sessions for each topic that allowed for focused discussion among subject matter experts and interested participants. The breakout and topic group leaders worked with the participants to determine research needs and associated next steps including white papers, reviews and in some cases collaborative grant proposals. Here, summaries from each topic area will be presented to highlight the main foci of discussion and associated conclusions.

Generation of Free Radicals During Cold Injury and Rewarming

Cold injury is often associated with irreversible cell damage. At present, however, the pathophysiology of cold injury is not known. This study examines the mechanism of such injury. New Zealand white rabbits were anesthetized and their femoral artery and vein were exposed. After baseline measurements one hind limb was cooled with a freezing mixture to 0°C, followed by rewarming. The other hind limb served as control. During the experiment blood samples were withdrawn from the femoral artery and vein for the subsequent analysis of creatine kinase (CK), lactate dehydrogenase (LDH), and malonaldehyde (MDA). At the end salicylate was injected through the femoral vein to trap any hydroxyl radical (OH°) formed. Rabbits were immediately sacrificed, and biop sies were withdrawn and frozen at liquid nitrogen temperature for analysis of OH° and high-energy phosphate compounds.

The results indicate that local blood flow in the cold-exposed hind limb was reduced significantly, suggesting that cold injury was associated with ischemic insult. CK and LDH increased after cold exposure and increased further during rewarming. MDA formation followed a similar pattern. OH° generated after cooling increased significantly upon rewarming. These results indicate that re warming is associated with an episode of ischemia/reperfusion with simultane ous generation of free radicals, which, at least in part, may be responsible for cellular injury associated with rewarming.

Reduction of cold injury by superoxide dismutase and catalase

The pathophysiology of cold injury was examined by cooling a hind leg of an anesthetized New Zealand white rabbit. A flow probe and a thermocouple were placed in the leg to be cooled to monitor the blood flow and tissue temperature. After baseline measurements, the leg was cooled with a freezing mixture up to 0 degrees C, which was followed by rewarming. The other leg served as control. In the experimental group, liposome-bound superoxide dismutase and catalase were infused through the femoral vein 15 minutes prior to putting the freezing mixture on the leg. Salicylic acid was injected through the femoral vein at the end of some experiments to assay hydroxy radical (OH). Our results demonstrated reduction of local blood flow in cold-exposed leg, indicating development of ischemia. Creatine kinase and lactage dehydrogenase were increased during rewarming in conjunction with hydroxyl radical formation, phospholipid breakdown, and lipid peroxidation. Treatment with superoxide dismutase and catalase reduced OH formation, prevented phospholipid degradation, and decreased creatine kinase, lactate dehydrogenase, and malonaldehyde formation. These results indicate that rewarming of cooled tissue is associated with "rewarming injury" similar to "reperfusion injury", and that oxygen-derived free radicals play a significant role in the pathophysiology of such injury.