Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Medical Sciences

Major Professor

Narasaiah Kolliputi, Ph.D.

Committee Member

Robert Deschenes, Ph.D.

Committee Member

Peter Medveczky, M.D.

Committee Member

Ted Williams, Ph.D.

Committee Member

Yashwant Pathak, Ph.D., M.Pharm.

Committee Member

Viswanathan Natarajan, Ph.D.

Keywords

Injury Resolution, Lung, Lung Injury, Omega-3, Resolvin

Abstract

Acute Lung injury (ALI) and the more severe acute respiratory distress syndrome (ARDS) are respiratory maladies that present immense clinical challenges. ALI affects 200,000 individuals annually and features a 40% mortality rate. ALI can be initiated by both pathogenic and sterile insults originating locally in the lungs or systemically. While immense research has been poured into this disease in an effort to find a therapeutic strategy, the heterogeneously diffuse nature of the disease has not yielded a cure for the disease. Death from this disease is strongly attributed to reduced gas exchange from a severely compromised alveolar-capillary barrier. The only way currently to manage this disease is through enhanced ventilation and hyperoxic therapy.

Hyperoxic therapy is a common treatment given to over 800,000 patients each year to treat respiratory maladies such as ALI. Prolonged exposure to oxygen at high concentrations results in the development of a condition known as hyperoxic acute lung injury (HALI). In this disease, the formation of reactive oxygen species damages healthy tissue and impairs gas exchange. Hyperoxia is also a well-documented murine sterile lung injury model that replicates the symptoms of ALI in lung injury patients. The ability of non-lethal dosages of hyperoxia to resolve without lung fibrosis also enables the study of molecules associated with ALI resolution and repair, a process not clearly understood.

Inflammation in ALI is associated with disease progression, however pharmaceutical interventions aimed at targeting the inflammatory cascade have failed in clinical trials for ALI. Recent reports point to an aberrant injury resolution mechanisms that may be more strongly correlated with morbidity and mortality. There seems to be a homeostatic imbalance between endogenous inflammation progression and resolution initiation. This is especially the case with HALI, as significant ROS generation results in depletion of redox regulating antioxidants. Resolution mechanisms associated with ALI in the oxygen toxicity setting is poorly understood.

Polyunsaturated fatty acids such eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential fatty acids that show immense antioxidant and anti-inflammatory action in cases of acute injury. The lung mucosa is rich in DHA and following inflammatory insult DHA is readily converted to resolution phase interaction products (resolvins), which have shown immense proresolutionary potential in recent reports of acute injury. In the presence of aspirin, more potent and longer-acting aspirin-triggered resolvins are formed. The effects of resolvins and their aspirin triggered epimers have not been studied in an oxygen toxicity setting and are the focus of this dissertation. For the first time, we show that one of these resolvin molecules, aspirin triggered resolvin d1 (AT-RvD1), can enhance resolution of hyperoxic acute lung injury. In vitro results reveals that AT-RvD1 treatment resulted in reduced interaction of two key players in the HALI inflammatory cascade, the macrophage and alveolar epithelium. AT-RvD1 was able to blunt macrophage cytokine secretion as well as inhibit epithelial cell cytokine secretion and adhesion molecule expression. More importantly, AT-RvD1 blunted cytokine mediated leukocyte-epithelial cell interaction in vitro. In a sublethal hyperoxic injury model, mice given AT-RvD1 following hyperoxia exposure displayed reduced HALI pathological severity. ATRvD1 treatment resulted in reduced alveolar-capillary permeability, tissue inflammation, proinflammatory mediator secretion, epithelial cell death, and leukocyte influx. Taken together these novel results demonstrate the therapeutic potential of resolvins in the oxygen toxicity setting. These results also arouse the idea that resolvins could be used to lessen the comorbidities associated with oxygen therapy and improve recovery times of ALI patients.

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