The Presence of Fat Droplets in the Retina of Rats in a Model Fat Embolism

Introduction Fat embolism (FE) induced in rats by intravenous injection (IV) of the neutral fat triolein (T) results in the deposition of intrapulmonary lipid associated with septal and arterial inflammation. In humans, FE may also contribute to retinopathy. This study's goal is to determine the presence of fat droplets in the retina in our rat model at a time when pulmonary fat is known to accumulate. Material and Methods Sprague‐Dawley rats (250–300g) were injected with 0.2 ml of T (N=13) in the caudal vein; controls received injection of saline (N=13). 48 hours later, rats were euthanized using decapitation under isoflurane anesthesia. Lungs were dissected, frozen immediately and stored for histological analysis. Eyes were dissected and incubated in PBS at 4°C for two hours. The retinas were isolated, flattened into optimal cutting temperature (OCT) compound by making four peripheral incisions at 90° intervals, and frozen immediately in isopentane equilibrated to −80°C. Cryosections of five representative experimental and control samples were stained with Oil Red O to detect fat. Three independent samples from each animal were stained. Two pathologists blinded to the identity of the samples analyzed the samples for presence of Oil Red O‐positive fat droplets. Results Forty‐eight hours after T injection, all experimental animals exhibited large lipid droplets in the outer retina, indicated by the deep red Oil Red O staining. Lipid droplets were absent in retinas of saline injected controls. The lipid droplets typically span the outer segments, outer nuclear, and outer plexiform layers with some extending through the inner nuclear layer and into the inner plexiform layer. No lipid droplets observed in the inner retina or extending into the retinal ganglion cell layer. T‐treated rats also had the expected large fat droplets in the lungs, mostly in the alveoli with an inflammatory response in the parenchyma; while the saline treated animals showed only a small number of droplets. Conclusions Fat droplets were observed within the eyes in T‐injected rats at 48 hours following injection and were predominantly located within the outer retina. As previously described, the lungs has significant accumulation of fat droplets. This animal model could serve as a novel model for studying retinopathy subsequent to fat embolism in human patients. Future studies should include longitudinal analyses of fat embolism in the retina and resulting structural damage and functional impairment at different post injection intervals. It is proposed that the underlying pathogenesis may involve alterations in the renin‐angiotensin system as suggested for the lung. Support or Funding Information Supported by the Catherine T Geldmacher foundation, Saint Louis, MO. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .