Visualization of the consequences of Succinate Dehydrogenase Inhibition on Oxygen utilization During Hemorrhagic Shock using Hyperspectral Imaging
Authors: Breton Amanda , Munoz Carlos , Lucas Alfredo , Cabrales Pedro 
Published: April 2020

IntroductionHemorrhagic shock (HS) results in reduced pressure, limited blood flow, and inadequate oxygen delivery to maintain cellular function. Reduced microcirculatory blood flow results in ischemia, as the tissue is no longer properly perfused or oxygenated. During resuscitation from HS, reperfusion promotes the formation of reactive oxygen species (ROS) as a byproduct of the Krebs cycle. Itaconate limits formation of ROS generated during reperfusion by inhibiting succinate dehydrogenase (SDH) activity, thus limiting tissue and organ damage. Hyperspectral Imaging (HSI) can be used to interrogate hemoglobin oxygen (HbO2) saturation in microvessels. Thus, the objective of this study was to use HSI to monitor changes in oxygen utilization within the microcirculation during resuscitation from HS with itaconate pretreatment.Materials and MethodsGolden Syrian hamsters were instrumented with a dorsal window chamber. A Resonon Pika‐L (Resonon, Bozeman, MT, USA) bench top HSI system was used. Each image was fitted with a Spatial mean filter and Savitzky‐Golay filter to decrease scatter noise, and a vessel mask was applied based on an intensity threshold to remove tissue from blood vessels. Spectral rescaling and a linear least squares fit were used to provide abundance of Hb and HbO2. Hemorrhage was induced by withdrawing 50% of the animal’s blood volume (BV, estimated as 7% of body weight) over 10 minutes. During hemorrhage and shock, images were taken continuously using a custom Python algorithm controlling the camera and illumination with a custom build relay. Before fluid resuscitation, itaconate was administered. Fluid resuscitation was accomplished by infusion of 25% of the animal’s BV of HEXTEND® (6% Hetastarch in Lactated Electrolyte Injection. Hospira Inc, Lake Forest, IL). The animal was resuscitated over 10 minutes and images taken every minute. Recovery was monitored over a period of 1 hour with images taken every 5 minutes.Results and DiscussionIncreasing doses of itaconate restored HbO2 saturation in venules, which confirms the inhibition of SDH by itaconate. Itaconate limits oxygen consumption of the tissues, preventing the formation of ROS in tissue during reperfusion, as indicated by higher levels of venular O2 saturation. However, these effects are only temporary as the HbO2 saturation levels taper off over time.ConclusionsIn conclusion, the inhibition of SDH with itaconate lead to the accumulation of succinate, limited tissue oxygen utilization, and prevented the formation of ROS during reperfusion. With further research, itaconate could potentially help to reduce reperfusion sequalae post treatment of trauma injuries, surgery, and combat casualties. In future studies, we aim to administer itaconate as an additive to the resuscitation fluid with the goal of evaluating the long‐term implications of preventing reperfusion injury.Support or Funding InformationThis study was supported by NIH NHLBI R01HL126945 and R01HL138116.