LIVER-LUNG INTERACTIONS IN ACUTE LUNG INJURY

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We have shown that hyperexpression of the cyclooxygenase (COX) gene in the lungs prevents the direct effects of endotoxin on the lungs of experimental animals. However, direct effects of endotoxin are only part of the story. Both clinical experience and animal studies implicate effects on the liver as important for the full expression of endotoxin induced lung injury. A more thorough understanding of the biochemical, molecular and pathophysiological events related to liver-lung interactions in the endotoxin response is needed in order to identify potential interventions which would prevent the response in both organs. We propose the following hypotheses: 1) Endotoxin injures the lungs by both direct and indirect effects. The direct effects are mainly vasoconstriction resulting from local generation of thromboxane. Marked lung inflammation and increased pulmonary vascular permeability are indirect effects mediated by production of tumor necrosis alpha (TNFalpha) by the liver. 2) The endothelial derived prostanoid, prostaglandin E2 (PGE2), acts to modulate endotoxin responses in the organ where it is produced, independent of concentrations achieved in circulating blood (a "paracrine" effect). 3) Using a plasmid-cationic liposome delivery system, it is possible to target expression of a COX transgene to endothelial cells mainly in the lungs (intravenous delivery) or mainly in the liver (intra-arterial delivery). The resulting increased local concentrations of PGE2 will moderate principally the endotoxin effects on the transfected organ. We have developed a swine preparation which permits separate or common perfusion of the lungs and the liver. We will use this preparation to test the above hypotheses with the following specific aims: 1) We will determine effects of endotoxemia on pulmonary vascular resistance, lung vascular permeability, lung water content, tissue and perfusate concentrations of prostanoids and TNFalpha, bronchoalveolar lavage (BAL) total and differential cell counts, BAL concentrations of prostanoids and TNFalpha, expression of TNFalpha, COX-1 and COX-2 genes and activation of nuclear factor kappa B (NFkappaB) in the lungs (and liver) with and without inclusion of the liver in the perfusion circuit. 2) Since PGE2 is completely cleared from the blood in a single transit through the lungs or liver, we will increase concentrations of PGE2 selectivity in each organ by infusing PGE2 into the afferent blood supply and determine effects on the endotoxin response. 3) We will determine organ distribution of expression of a COX transgene following delivery of the gene in a plasmid complexed to cationic liposomes either intravenously, into the aortic root or by both routes. Having documented organ- specific transgene expression, we will determine effects of prior in vivo transfection by each route with the COX gene the endotoxin response. These studies will further clarify mechanisms of liver-lung interactions which are important to endotoxin induced lung injury, providing a basis for new therapeutic interventions.