Absence of Cardiac Immune Pathology in a Rat Model of Fat Embolism Syndrome

Abstract

Introduction Cardiopulmonary insufficiency is a common pathology associated with Fat Embolism Syndrome. We have previously demonstrated that fat embolism induced by intravenous injection of triolein (T) in rats induces severe histopathological pulmonary damage and significant mast cell and macrophage infiltration at 48 hours (hrs) that persists up to at least 10 weeks, but that hearts did not exhibit vasculitis of the coronary artery branches or myocardial inflammation. In light of the distinct pathological and clinical findings in heart and lung, we hypothesized that mast cell and macrophage infiltration would be associated with more severe injury in the lungs but not in the heart and examined this at 48 hrs and 10 weeks. Methodology 24 Sprague-Dawley rats were divided into four groups and treated with 0.2 ml saline or T for 48 hrs or 10 weeks. Hearts were collected and bisected coronally and the caudal portion was fixed in formaldehyde, embedded in paraffin and sectioned. Every fifth section was stained with Hematoxylin & Eosin, or trichrome to evaluate collagen. CD117 or CD68 immunostains were performed to identify mast cells or macrophages, respectively. Random photographed sections of the heart and lung at 100x and 400x were evaluated by two pathologists for mast cells and macrophage counts and histopathology. Statistical significance was calculated using a T-Test in GraphPad Software. Results Significant pulmonary damage was observed at 48 hrs and 10-weeks. In contrast, the heart did not show any histological damage. No statistically significant differences were found in mast cell (p=0.9651) or macrophage (p=0.7626) numbers in the myocardium of T-injected rats when compared to those in the saline controls. Mast cells and macrophages were found significantly elevated in the lungs of T-injected rats. Two distinct pulmonary macrophage morphologies were observed (very large cells with small fat droplets in the cytoplasm and the more numerous normal sized macrophages with few fat droplets). Such histopathological changes were not observed in the hearts of the T-injected animals. Conclusion The study confirms a significant difference between the presence and the severity of the histopathological damage in the lungs versus the heart in this model of fat embolization. These findings highlight the different cellular responses of different organs to a fat embolism insult. We are investigating the mechanisms that lead to pulmonary susceptibility and at the same time cardiac protection to better design a therapeutic intervention for Fat Embolism Syndrome.