Pulmonary microcirculation during sepsis and obesity

Obesity represents a major health problem in the industrialized world in both children and adults. In the United States over 60% of the adults are overweight with more than half qualifying as obese or severely obese. Sepsis is the number one cause of death in non coronary intensive care units in the US. There are numerous studies showing that obesity significantly increases the severity and mortality of sepsis. The lung is the most frequently identified organ to fail in sepsis and represents also the most frequent primary site of infection leading to sepsis. Microcirculatory failure (impaired capillary perfusion, adhesion and migration of blood cells through the vascular endothelium) is considered to be a critical component during sepsis. However there is lack of data in the literature describing the pulmonary recruitment of blood cells, lung injury and the precise role of adhesion molecules in murine models of obesity and sepsis in an in vivo setting. We hypothesize that obesity creates a proinflammatory environment leading to increased leukocyte and platelet accumulation into the lung in different murine models of obesity following a septic stimulus due to an augmented expression of adhesion molecules. The first step to test this hypothesis will consist of describing the time- dependent changes of inflammatory parameters (levels of (adipo)cytokines, adhesion molecules, adipose tissue infiltration with macrophages) in two mouse models of genetic obesity (ob/ob and db/db) and one model of diet induced obesity (DIO) using standard laboratory procedures (ELISA, PCR, Immunohistochemistry). Using Intravital Fluorescence Microscopy (IVM) we plan to determine whether obese mice exhibit an increase of pulmonary adhesion of leukocytes and platelets and an augmented capillary leakage during sepsis induced by cecal ligation and puncture (CLP). In order to assess the mechanism of leukocyte and platelet recruitment and alveolar capillary leakage during polymicrobial sepsis in obese mice we will perform intravital microscopy in obese mice following CLP after immunoblockade of adhesion molecules (P-selectin, ICAM-1 and E-selectin) in three strains of obese mice (ob/ob, db/db. DIO), in ob/ob mice repleted with leptin and db/db mice treated with a leptin receptor antagonist. We plan to compare the obtained results to corresponding sham animals and a group of WT mice following either CLP or sham procedure. Results obtained from these studies will reveal what specific adhesion molecules contribute to the augmented leukocyte and platelet recruitment that is seen in mouse models of obesity during sepsis and whether the leptin pathway is involved in these changes. The knowledge derived from this work will help to develop therapeutic strategies related to acute inflammatory conditions appearing in obesity.

In the industrialized world obesity represents a serious health care problem in both children and adults. Some clinical studies show that obesity increases the morbidity and mortality of sepsis. Disturbances of the microcirculation with altered capillary perfusion, adhesion and migration of blood cells through the endothelium represents one of the hallmarks of sepsis. There is, however, a lack of knowledge about the mechanisms of the microvascular recruitment of blood cells and the exact role of adhesion molecules in the setting of sepsis and obesity. In the first part of the project we were able to demonstrate a state of low-grade inflammation in three different models of obesity at 4 and 10 weeks. Additionally, it could be shown that sepsis leads to a profound increase of the adhesion of blood cells (leukocytes and platelets) into the liver. The combination of sepsis and obesity, however, did not further increase the hepatic microcirculation when compared to septic normal weight mice. Nevertheless, septic obese mice had a significantly increased mortality rate when compared to their lean counterparts. In only one model of genetically caused obesity a significant role of the adhesion molecule ICAM-1 in mediating leukocyte adhesion was demonstrated. Nevertheless, treatment with an ICAM-1 blocking antibody caused a significant decrease of the expression of inflammatory parameters (Il-6 and TNF-a). The obtained results contributed to the ongoing debate about the still unclear question about the mechanism of the increased morbidity and mortality of sepsis in combination with obesity. The results were and will be published in peer-reviewed journals and presented at international conferences. During the project duration one dissertation, two diploma theses and 1 bachelor thesis were successfully completed.