No abstract

Right ventricular (RV) dysfunction is associated with poor clinical outcome following pulmonary embolism (PE). Previous studies in our laboratory show that influx of neutrophils contributes to acute RV damage seen in an 18 h rat model of PE. The present study describes the further progression of inflammation over 6 weeks and compares the neutrophil and monocyte responses. The RV outflow tract became white in colour by day 1 with influx of neutrophils (tissue myeloperoxidase activity increased 17-fold) and mononuclear cells with characteristics of M1 phenotype (high in Ccl20, Cxcl10, CcR2, MHCII, DNA microarray analysis). Matrix metalloproteinase activities were increased and tissue was thinned to produce a translucent appearance in weeks 1 through 6 in 40% of hearts. RV contractile function was significantly reduced at 6 weeks of PE. In this later phase, there was accumulation of myofibroblasts, the presence of mononuclear cells with M2 characteristics (high in scavenger mannose receptors, macrophage galactose lectin 1, PDGFR1, PDGFRbeta), enrichment of the subendocardial region of the RV outflow tract with neovesels (alpha-smooth muscle immunohistochemistry) and deposition of collagen fibres (picrosirius red staining) beginning scar formation. Thus, while neutrophil response is associated with the early, acute inflammatory events, macrophage cells continue to be present during the proliferative phase and initial deposition of collagen in this model, changing from the M1 to the M2 phenotype. This suggests that the macrophage cell response is biphasic.

Pulmonary thromboembolism (PEm) is a serious and life threatening disease and the most common cause of acute pulmonary vascular occlusion. Even following successful treatment of PEm, many patients experience long-term disability due to diminished heart and lung function. Considerable damage to the lungs presumably occurs due to reperfusion injury following anti-occlusive treatments for PEm and the resulting chronic inflammatory state in the lung vasculature. We have used a rat model of irreversible PEm to ask whether pulmonary vascular occlusion in the absence of reperfusion is itself sufficient to induce an inflammatory response in lungs. By adjusting the severity of the vascular occlusion, we were able to generate hypertensive and nonhypertensive PEm, and then examine lung tissue for expression of CXC and C-C chemokine genes and bronchoalveolar lavage (BAL) fluid for the presence of chemokine proteins. Hypertensive and nonhypertensive PEm resulted in increased expression of both CXC and C-C chemokines genes in lung tissues. Hypertensive PEm was also associated with a 50–100-fold increase in protein content in lung BAL fluid, which included the CXC chemokines cytokine-induced neutrophil chemoattractant and macrophage-inflammatory protein 2. The presence of chemokines in BALs was reflected by a potent neutrophil chemotactic activity in in vitro chemotaxis assays. Abs to cytokine-induced neutrophil chemoattractant blocked the in vitro neutrophil chemotactic activity of BAL by 44%. Our results indicate that the ischemia and hypertension associated with PEm are sufficient to induce expression of proinflammatory mediators such as chemokines, and establish a proinflammatory environment in the ischemic lung even before reperfusion.

Right ventricular (RV) dysfunction is a strong risk factor for poor clinical outcome following pulmonary embolism (PE), the third most prevalent cardiovascular disease. Previous studies in our laboratory demonstrated that RV failure during PE is mediated, in part, by neutrophil-dependant cardiac inflammation. In this study we use DNA microarray analysis of gene expression to demonstrate that PE results in increased expression of the CXC chemokines CINC-1 and CINC-2 between 6 and 18 h after the start of PE in a rat model of PE. Neutrophils accumulate in RV tissue by 18 h, and this inflammation is associated with decreased right heart function. Treatment of rats with Abs to CINC-1 significantly suppressed neutrophil accumulation in RVs during PE (52% reduction in tissue myeloperoxidase) and ameliorated RV failure. In addition, plasma concentration of cardiac troponin I, an established diagnostic marker for cardiac damage, was reduced by 90%. These results suggest that selective anti-inflammatory therapies targeted at neutrophil chemoattractants will reduce cardiac inflammation and reduce RV damage in the setting of PE.

Acute pulmonary embolism (PE) is the third leading cause of cardiovascular death in the United States. Moderate to severe PE can cause pulmonary arterial hypertension (PH) with resultant right ventricular (RV) heart damage. The mechanisms leading to RV failure after PE are not well defined, although it is becoming clear that PH-induced inflammatory responses are involved. We previously demonstrated profound neutrophil-mediated inflammation and RV dysfunction during PE that was associated with increased expression of several chemokine genes. However, a complete assessment of transcriptional changes in RVs during PE is still lacking. We have now used DNA microarrays to assess the alterations in gene expression in RV tissue during acute PE/PH in rats. Key results were confirmed with real-time RT-PCR. Nine CC-chemokine genes (CCL-2, -3, -4, -6, -7, -9, -17, -20, -27), five CXC-chemokine genes (CXCL-1, -2, -9, -10, -16), and the receptors CCR1 and CXCR4 were upregulated after 18 h of moderate PE, while one C-chemokine (XCL-1) and one CXC-chemokine (CXCL-12) were downregulated. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated increased expression of many inflammatory genes. There was also a major shift in the expression of components of metabolic pathways, including downregulation of fatty acid transporters and oxidative enzymes, a change in glucose transporters, and upregulation of stretch-sensing and hypoxia-inducible transcription factors. This pattern suggests an extensive shift in cardiac physiology favoring the expression of the "fetal gene program."