Title of grant: Ischemia/Reperfusion Injury of Human Endothelium: Role of Glucose and Statins Ischemia-reperfusion (I/R) injury to vital organs and tissue can occur in a variety of clinical situations and contributes to adverse outcomes. A newer concept of "multi-organ" protection from I/R injury by volatile anesthetics might be explained by an effect of the volatile anesthetics on vascular endothelium. Anesthetic preconditioning (APC), i.e., a brief exposure to a volatile anesthetic before a harmful ischemic event, can substantially reduce the resulting endothelial injury. In animal models, hyperglycemia blocks the protection from I/R injury afforded by volatile anesthetics, and statins restore the protection and may independently protect endothelium from I/R injury. These interactions will be studied in humans. In addition, the involvement of reactive oxygen species (ROS) and the nitric oxide pathway in the harmful effects of hyperglycemia and the beneficial effects of statins will be explored. The following four hypotheses will be examined: 1) hyperglycemia blocks APC of human endothelium from I/R injury in a dose and time dependent manner;2) reactive oxygen species (ROS) are involved in the inhibition of APC by hyperglycemia;3) statins, or 3-hydroxy-3-methyl-glutaryl- coenzyme A reductase inhibitors, that are used routinely to lower blood cholesterol levels, modulate I/R injury in a dose related manner;and 4) statins reduce hyperglycemia inhibition of APC, and the nitric oxide pathway is integral to the effect in human endothelium. A standard model to evaluate forearm endothelial function will be used. Acetylcholine (ACH) will be infused into the brachial artery to provoke synthesis and release of endothelial nitric oxide (NO), and the ensuing increases in forearm blood flow (FBF) will be measured with venous occlusion plethysmography. ACH infusions will occur before and after temporary forearm endothelial I/R injury, or "stunning," with a 20-min arrest of the forearm circulation. Additional effects of I/R injury, APC, hyperglycemia and statins will be determined by evaluating vascular inflammatory responses (neutrophil activation) and cytokine generation before and after I/R injury. Several studies will involve varying the forearm blood glucose concentration for brief (30 min) to longer (2 hours) periods prior to APC and I/R injury. The ROS scavenger vitamin C will be used to evaluate the role of ROS in adverse effects of hyperglycemia. In additional studies, the modulatory role of simvastatin on I/R injury and on APC during hyperglycemia will be examined. The role of nitric oxide in the statin effect will be determined by employing L-NMMA (NG-monomethyl L-arginine), an inhibitor of the NO synthase pathway. APC has become an area of intense research interest because of its ability to protect tissue and organs from ischemia-reperfusion injury. The endothelium plays a key role in I/R injury. This research will examine, in vivo, several important modifiers of APC in human endothelium: hyperglycemia and statins. Thus, the proposed studies will advance our understanding of mechanisms of I/R injury in humans and explore important modifiers of APC protection from I/R injury.
Anesthetic gases are known to protect blood vessels and organs such as the heart, from injury during periods of low oxygen stress. Diabetes is a common disease in the VA and general population and has major problems related to its effect on blood vessel function. Diabetes worsens tissue and organ damage following periods of no or low blood flow and the return of the blood flow, such as might occur during strokes or heart surgeries. High blood sugar may be the means for undesirable tissue injury by way of an effect on the inner lining of blood vessels. Anesthetic gases can modify the risk for injury of blood vessels in diabetic patients. In addition, some medications (statins), now in widespread use to lower cholesterol levels have several other effects that oppose the harmful effects of high blood sugar. These studies will carefully describe the effects of glucose and statins on the function of the lining of blood vessels in humans. This new knowledge might lessen unwanted side effects related to diabetes.