Fat embolism: evolution of histopathological changes in the rat lung

Fat Embolism Does Not Alter Cardiac Structure or Induce Pathological Changes in a Rat Model

INTRODUCTION

Fat embolism (FE) encompasses conditions in which fatty substance becomes embedded in a tissue/organ. Fat emboli most commonly affect the lungs in a trauma setting. This can lead to both significant pathology locally and systemically including changes in structure, inflammatory response, activation of the renin-angiotensin system, and subsequent hypoxia. In fact, changes in skin, brain, lungs, and kidneys have been noted in FE syndrome. Because there is an extensive record of pathology reports on this condition without evidence of direct cardiac involvement, as well as our studies showing apparent complete recovery after the acute embolism, we hypothesized that structural changes similar to the lung and at the same time course would not be observed in the heart.

METHODS

We used a rat model of FE previously described by our group where we have documented significant lung pathology. In this study, we analyzed both pulmonary and cardiac structure, histology, and gene expression at 48 h and 10 wks post fat injection to mimic FE.

RESULTS

Despite severe inflammatory evidence and structural changes to the lung and vasculature up to 10 wks after FE, we found no significant alterations to cardiovascular morphometry including lumen patency ratio, adventitia/media ratio, fibrosis content, and heart chamber/wall dimensions in stained histological sections. Additionally, genetic markers of cardiac pathological hypertrophy were not significantly elevated 48 h or 10 wks after fat treatment. Oil Red O staining showed increased fat droplet content within lung and aorta tissue, but not in the myocardium.

CONCLUSIONS

Our study suggests that, in contrast to the lungs, the heart is more resistant to the inflammatory and remodeling responses that result from FE, possibly due to the organ-specific differences in fat retention.

Comparison of Three Histological Techniques for Fat Emboli Detection in Lung Cetacean's Tissue

Fat embolism is the mechanical blockage of blood vessels by circulating fat particles. It is frequently related to traumas involving soft tissues and fat-containing bones. Different techniques have been used for decades to demonstrate histologically fat emboli, being the extremely toxic post-fixation with osmium tetroxide one of the most used techniques in the last decades. In the present study, the osmium tetroxide technique was compared qualitatively and quantitatively, for the first time, with chromic acid and Oil Red O frozen techniques  for histological fat emboli detection in the lungs of eight sperm whales that died due to ship strikes. This was also the first time that chromic acid technique was tested in cetaceans. Results showed that the three techniques were valuable for the histological detection of fat embolism in cetaceans, even when tissues presented advanced autolysis and had been stored in formaldehyde for years. Although quantitative differences could not be established, the Oil Red O frozen technique showed the lowest quality for fat emboli staining. On the contrary, the chromic acid technique was proven to be a good alternative to osmium tetroxide due to its slightly lower toxicity, its equivalent or even superior capacity of fat emboli detection, and its significantly lower economic cost.

The renin inhibitor aliskiren protects rat lungs from the histopathologic effects of fat embolism

BACKGROUND

Fat embolism (FE) and the consequent FE syndrome occurring after trauma or surgery can lead to serious pulmonary injury, including ARDS and death. Current treatment of FE syndrome is limited to supportive therapy. We have shown in a rat model that the renin angiotensin system plays a significant role in the pathophysiology of FE because drugs interfering with the renin angiotensin system, captopril and losartan reduce the histopathologic pulmonary damage. The purpose of the current study was to determine if inhibition of renin by aliskiren, an FDA-approved drug for treating hypertension, would produce effective protection in the same model.

METHODS

The FE model used intravenous injection of the neutral fat triolein in unanesthetized rats. Intraperitoneal injections of saline or aliskiren at either 50 or 100 mg/kg were performed 1 hour after FE induction via triolein. Rats were euthanized at 48 hours, and various histologic stains were used to examine the lungs.

RESULTS

(1) Fibrosis: rats treated with triolein showed significant fibrotic changes with increased collagen and myofibroblast activation (p < 0.0001 for both trichrome and α-smooth muscle actin staining). Aliskiren blocked this inflammatory and profibrotic process to a level indistinguishable from the controls (p < 0.0001 for both trichrome and α-smooth muscle actin staining). (2) Fat: rats treated with triolein showed a statistically significant increase in fat (p = 0.0006). Subsequent aliskiren administration at both doses reduced the size, distribution, and amount of fat droplets (low dose, p = 0.0095; high dose, p = 0.0028). (3) Vessel patency: the low dose of aliskiren blocked the reduction of lumen patency observed after triolein administration (p = 0.0058).

CONCLUSIONS

Aliskiren protected the lungs of rats from gross and histopathologic FE-induced pulmonary damage at 48 hours. Clinical implications include the use of aliskiren both prophylactically (before certain orthopedic procedures) and therapeutically (after severe trauma) to prevent the consequent severe pulmonary pathologic sequelae.

Detection of pulmonary fat embolism with dual-energy CT: an experimental study in rabbits

OBJECTIVES

To evaluate the use of dual-energy CT imaging of the lung perfused blood volume (PBV) for the detection of pulmonary fat embolism (PFE).

METHODS

Dual-energy CT was performed in 24 rabbits before and 1 hour, 1 day, 4 days and 7 days after artificial induction of PFE via the right ear vein. CT pulmonary angiography (CTPA) and lung PBV images were evaluated by two radiologists, who recorded the presence, number, and location of PFE on a per-lobe basis. Sensitivity, specificity, and accuracy of CTPA and lung PBV for detecting PFE were calculated using histopathological evaluation as the reference standard.

RESULTS

A total of 144 lung lobes in 24 rabbits were evaluated and 70 fat emboli were detected on histopathological analysis. The overall sensitivity, specificity and accuracy were 25.4 %, 98.6 %, and 62.5 % for CTPA, and 82.6 %, 76.0 %, and 79.2 % for lung PBV. Higher sensitivity (p < 0.001) and accuracy (p < 0.01), but lower specificity (p < 0.001), were found for lung PBV compared with CTPA. Dual-energy CT can detect PFE earlier than CTPA (all p < 0.01).

CONCLUSION

Dual-energy CT provided higher sensitivity and accuracy in the detection of PFE as well as earlier detection compared with conventional CTPA in this animal model study.

KEY POINTS

• Fat embolism occurs commonly in patients with traumatic bone injury. • Dual-energy CT improves diagnostic performance for pulmonary fat embolism detection. • Dual-energy CT can detect pulmonary fat embolism earlier than CTPA.

The Effects of Aquaporin-1 in Pulmonary Edema Induced by Fat Embolism Syndrome

This study was designed to investigate the role of aquaporin1 (AQP1) in the pathologic process of pulmonary edema induced by fat embolism syndrome (FES) and the effects of a free fatty acid (FFA) mixture on AQP1 expression in pulmonary microvascular endothelial cells (PMVECs). In vivo, edema was more serious in FES mice compared with the control group. The expression of AQP1 and the wet-to-dry lung weight ratio (W/D) in the FES group were significantly increased compared with the control group. At the same time, inhibition of AQP1 decreased the pathological damage resulting from pulmonary edema. Then we performed a study in vitro to investigate whether AQP1 was induced by FFA release in FES. The mRNA and protein level of AQP1 were increased by FFAs in a dose- and time-dependent manner in PMVECs. In addition, the up-regulation of AQP1 was blocked by the inhibitor of p38 kinase, implicating the p38 MAPK pathway as involved in the FFA-induced AQP1 up-regulation in PMVECs. Our results demonstrate that AQP1 may play important roles in pulmonary edema induced by FES and can be regarded as a new therapy target for treatment of pulmonary edema induced by FES.

Pulmonary fat embolism and related effects during femoral intramedullary surgery: An experimental study in dogs

The aim of the present study was to develop an animal model of pulmonary fat embolism (PFE) caused by femoral intramedullary procedures, and to investigate the initial changes in the hemodynamics, cytokines and risk factors of PFE. Sixteen dogs were randomly divided into two groups: Group A (intramedullary reaming and bone cement injection, n=8) and Group B (surgical approach without opening the medullary cavity, n=8). The hemodynamics, arterial blood gases and relevant cytokines were evaluated, and the lungs were examined using Oil Red O staining. In the animals of Group A, the heart rate, central venous pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure and extravascular lung water (EVLW) were increased compared with the baseline levels, while the mean arterial pressure was decreased immediately following the reaming and bone cement infusion (P<0.05). Furthermore, there was a significant reduction in the pH and the arterial oxygen tension (PaO₂), and a significant increase in the arterial carbon dioxide tension (PaCO₂; P<0.05 for all) following the bilateral intramedullary surgery. The EVLW was correlated with the PaO₂ (P<0.001) and PaCO₂ (P=0.046). Following surgery, there was a significant increase in tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6 levels in Group A (P<0.05). However, there were no significant changes in these parameters in Group B. The parameters tested, with the exception of pH, were significantly different in Group A compared with those in Group B (P<0.05) following the bilateral intramedullary surgery. Oil Red O staining was positive for all animals in Group A and negative for those in Group B. Femoral intramedullary surgery may induce PFE and subsequently affect hemodynamics and arterial blood gases. EVLW was correlated with the PaO₂ (P<0.001) and the PaCO₂ (P=0.046). These results demonstrated that EVLW and cytokines may serve as predictors of the development of fat embolism syndrome (FES).

Dietary Flaxseed Oil Protects against Bleomycin-Induced Pulmonary Fibrosis in Rats

Bleomycin, a widely used antineoplastic agent, has been associated with severe pulmonary toxicity, primarily fibrosis. Previous work has shown a reduction in bleomycin-induced lung pathology by long-chain omega-3 fatty acids. Treatment by short-chain omega-3 fatty acids, α-linolenic acid, found in dietary flaxseed oil may also reduce lung fibrosis, as previously evidenced in the kidney. To test this hypothesis, 72 rats were divided between diets receiving either 15% (w/w) flaxseed oil or 15% (w/w) corn oil (control). These groups were further divided to receive either bleomycin or vehicle (saline) via an oropharyngeal delivery, rather than the traditional intratracheal instillation. Lungs were harvested at 2, 7, and 21 days after bleomycin or saline treatment. Animals receiving flaxseed oil showed a delay in edema formation (P = 0.025) and a decrease in inflammatory cell infiltrate and vasculitis (P = 0.04 and 0.007, resp.). At days 7 and 21, bleomycin produced a reduction in pulmonary arterial lumen patency (P = 0.01), but not in rats that were treated with flaxseed oil. Bleomycin-treated rats receiving flaxseed oil had reduced pulmonary septal thickness (P = 0.01), signifying decreased fibrosis. Dietary flaxseed oil may prove beneficial against the side effects of this highly effective chemotherapeutic agent and its known toxic effects on the lung.