Atherosclerotic vascular disease is a significant systemic problem and is extremely prevalent in veterans cared for in the VA Healthcare System. The conventional treatments for occlusive vascular lesions include angioplasty and stenting as well as surgical bypass but these therapies are limited by intimal hyperplasia (IH) which leads to restenosis and treatment failure. One very promising treatment for IH that has come to the forefront recently is carbon monoxide (CO). A short exposure to inhaled CO dramatically inhibits balloon angioplasty induced IH in animals without any evidence of toxicity. These preclinical studies strongly support the potential for inhaled CO to be an effective clinical treatment for IH. The overall goal of this proposal is to further develop inhaled CO for human application and to investigate the hypothesis that inhaled CO inhibits IH through both direct effects of CO on the arterial wall as well as through indirect effects that center around modulation of systemic inflammatory responsiveness. Therefore, we will focus on the following Aims.
Specific Aim I : Determine the lowest effective dose and duration of inhaled CO required for the inhibition and regression of IH following therapeutic vascular injury. There are known toxicities associated with high concentrations of inhaled CO through its ability to compete with oxygen for binding to hemoglobin (Hb) and reduces oxygen carrying capacity. Therefore, the lowest effective dose of CO and the shortest treatment duration need to be identified. In this Aim, the optimal dose and treatment duration of inhaled CO that will mediate a significant reduction in IH following therapeutic vascular injury will be identified. These studies will be performed in both rodent and pig models of vascular injury.
Specific Aim II : Evaluate the tolerability of CO on cardiac function and hemodynamic parameters in porcine models of preexisting cardiac dysfunction. Patients undergoing revascularization procedures possess many co-morbid conditions, the most significant being coronary artery disease. An important concern about the application of inhaled CO is that a reduction in O2 carrying capacity may induce significant cardiac ischemia and physiologic compromise in patients with little cardiac reserve. Therefore, in this Aim, the tolerability and safety of inhaled CO will be examined in pig models of acute myocardial ischemia as well as chronic myocardial dysfunction.
Specific Aim III : Define the contributions of the direct and indirect effects of CO on the inhibition of IH. CO has many cytoprotective properties that have been identified in a variety of tissues and cell types. These include anti-apoptotic actions in endothelial cells (EC), anti-inflammatory actions, and antioxidant functions. The benefit of inhaled CO appears to stem from its presence at the time of or immediately prior to vascular injury and would support that CO is modulating events involved in the initiation of the vascular injury response. Our preliminary studies reveal very distinct actions of CO when delivered systemically vs. its effects on cells and tissues that are directly exposed to CO. Our hypothesis is that CO mediates vasoprotection through both local effects of CO on the arterial wall and through systemic alterations of inflammatory responsiveness. Based on this, we will examine the contribution of direct and indirect actions of inhaled CO treatment to its role in vasoprotection. The studies performed under these Aims will better definite the efficacy and feasibility of inhaled CO for the inhibition of IH and will provide a mechanistic understanding of the vasoprotection offered by CO. The potential benefit of these studies to the health care of veterans is great by prolonging vascular patency after revascularization and increase functional status and limb preservation.
Project Narrative: Intimal hyperplasia or restenosis is a healing response that results in restenosis at sites of vascular bypass, angioplasty, and stent placement that are performed for coronary and peripheral arterial occlusive disease and greatly reduces the efficacy of these treatments. Inhaled carbon monoxide has been shown in animal models of vascular injury to inhibit intimal hyperplasia in a safe and tolerable fashion. The goal of this grant is to identify the lowest dose and shortest treatment duration for inhaled carbon monoxide that will effectively reduce intimal hyperplasia, examine the safety of this treatment in the setting of heart disease, and to understand how carbon monoxide is mediating these effects at a systemic and local level.