Experimental fat embolism induces urine 2,3-dinor-6-ketoprostaglandin F1alpha and 11-dehydrothromboxane B2 excretion in pigs

Significance of urinary 11-dehydro-thromboxane B2 in age-related diseases: Focus on atherothrombosis

Platelet activation plays a key role in atherogenesis and atherothrombosis. Biochemical evidence of increased platelet activation in vivo can be reliably obtained through non-invasive measurement of thromboxane metabolite (TXM) excretion. Persistent biosynthesis of TXA₂ has been associated with several ageing-related diseases, including acute and chronic cardio-cerebrovascular diseases and cardiovascular risk factors, such as cigarette smoking, type 1 and type 2 diabetes mellitus, obesity, hypercholesterolemia, hyperhomocysteinemia, hypertension, chronic kidney disease, chronic inflammatory diseases. Given the systemic nature of TX excretion, involving predominantly platelet but also extraplatelet sources, urinary TXM may reflect either platelet cyclooxygenase-1 (COX-1)-dependent TX generation or COX-2-dependent biosynthesis by inflammatory cells and/or platelets, or a combination of the two, especially in clinical settings characterized by low-grade inflammation or enhanced platelet turnover. Although urinary 11-dehydro-TXB₂ levels are largely suppressed with low-dose aspirin, incomplete TXM suppression by aspirin predicts the future risk of vascular events and death in high-risk patients and may identify individuals who might benefit from treatments that more effectively block in vivo TX production or activity. Several disease-modifying agents, including lifestyle intervention, antidiabetic drugs and antiplatelet agents besides aspirin have been shown to reduce TX biosynthesis. Taken together, these aspects may contribute to the development of promising mechanism-based therapeutic strategies to reduce the progression of atherothrombosis. We intended to critically review current knowledge on both the pathophysiological significance of urinary TXM excretion in clinical settings related to ageing and atherothrombosis, as well as its prognostic value as a biomarker of vascular events.

Plasma levels of endothelin-1 after a pulmonary embolism of bone marrow fat

BACKGROUND

During orthopedic surgery, embolization of bone marrow fat can lead to potentially fatal, intra-operative cardiovascular deterioration. Vasoactive mediators may also be released from the bone marrow and contribute to these changes. Increased plasma levels of endothelin-1 (ET-1) have been observed after pulmonary air and thrombo-embolism. The role of ET-1 in the development of acute cardiovascular deterioration as a result of bone marrow fat embolization during vertebroplasty was therefore investigated.

METHODS

Bone cement was injected into three lumbar vertebrae of six sheep in order to force bone marrow fat into the circulation. Invasive blood pressures and heart rate were recorded continuously until 60 min after the last injection. Cardiac output, arterial and mixed venous blood gas parameters and plasma ET-1 concentrations were measured at selected time points. Post-mortem, lung biopsies were taken for analysis of intravascular fat.

RESULTS

Cement injections resulted in a sudden (within 1 min) and severe increase in pulmonary arterial pressure (>100%). Plasma concentrations of ET-1 started to increase after the second injection, but no significant changes were observed. Intravascular fat and bone marrow cells were present in all lung lobes.

CONCLUSION

Cement injections into vertebral bodies elicited fat embolism resulting in subsequent cardiovascular changes that were characterized by an increase in pulmonary arterial pressure. Cardiovascular complications as a result of bone marrow fat embolism should thus be considered in patients undergoing vertebroplasty. No significant changes in ET-1 plasma values were observed. Thus, ET-1 did not contribute to the acute cardiovascular changes after fat embolism.

Prostacyclin therapy increases right ventricular capillarisation in a model for flow-associated pulmonary hypertension

Pulmonary hypertension, and consequently right ventricular failure, complicates several congenital heart defects. Although intervention in the prostacyclin-thromboxane ratio is known to improve outcome, the underlying mechanism is not clear. Therefore, effects of acetyl salicylic acid and iloprost are studied in an animal model for flow-associated pulmonary hypertension. Male Wistar rats with flow-associated pulmonary hypertension, an aortocaval shunt in addition to monocrotaline induced pulmonary hypertension, were treated with low-dose aspirin (25 mg/kg/day) or iloprost (72 microg/kg/day). Effects on pulmonary hemodynamics and pulmonary vascular remodeling as well as right ventricular hemodynamics and remodeling were evaluated. Ninety percent (n=7/8) of the untreated pulmonary hypertensive rats developed dyspnea and pleural fluid, whereas this was seen in 50% (n=4/8, ns) and 10% (n=1/8, P<0.05 vs. untreated animals) of the aspirin and iloprost-treated rats, respectively. This could not be attributed to changes in pulmonary artery pressure, wall-lumen ratio of the pulmonary vasculature or right ventricular hypertrophy. However, both therapies restored reduced right ventricular capillary to myocyte ratio in pulmonary hypertensive rats (0.95+/-0.10 in untreated rats vs. 1.38+/-0.18 in control animals; P<0.05, and 1.32+/-0.11 in aspirin-treated and 1.29+/-0.9 in iloprost-treated rats; both P<0.05 vs. non-treated animals), which was associated with improved right ventricular contractility (iloprost). Thus, interventions in the prostacyclin-thromboxane metabolism improve outcome in rats with flow-associated pulmonary hypertension. However, these effects may be attributed to effects on cardiac rather than on pulmonary vascular remodeling.

Pathophysiological advantages of rinsing-suction-reaming (RSR) in a pig model for intramedullary nailing

Although reamed intramedullary nailing has been one of the greatest advances in modern fracture care, the concomitant increase in medullary cavity pressure leads to intravasation of bone marrow content into the blood stream, an effect that can evoke serious systemic reactions. A newly developed rinsing-suction-reamer (RSR) was able to substantially reduce the pressure and bone marrow intravasation content during experimental femoral nailing. We investigated the pathophysiological effects using the RSR, testing the hypothesis that by reducing marrow fat embolization, RSR would also reduce the activation of coagulation compared with the universal AO-Reamer (AOR) and comparable to external fixation. Twenty-two pigs were treated with either simulated external fixation or reamed femoral nailing using AOR or RSR. During surgery, the intramedullary pressure was measured and intravasation of medullary material was quantified. After surgery, the pigs were kept anaesthetised and monitored for 6 h. At defined intervals, serological, hematological, and hemodynamic parameters were evaluated. The RSR was significantly superior when compared to AOR with regard to the generation of intramedullary pressure and fat embolization; however, with external fixation the values were even lower. The evaluation of other parameters revealed no clear differences between the two reamers and the external fixator. The pig model showed that RSR led to a significant reduction of the intramedullary increase in pressure and fat intravasation compared to AOR. Although the reduction of fat embolism by RSR is not associated with pathophysiological changes, RSR can have advantages for the treatment of femoral fractures.

The pulmonary biology of isoprostanes

Isoprostanes were first recognized as convenient markers of oxidative stress, but their powerful effects on a variety of cell functions are now also being increasingly appreciated. This is particularly true of the lung, which is comprised of a wide variety of different cell types (smooth muscle, innervation, epithelium, lymphatics, etc.), all of which have been shown to respond to exogenously applied isoprostanes. In this review, we summarize these biological responses in the lung, and also consider the roles that isoprostanes might play in a range of pulmonary clinical disorders.

The pulmonary biology of isoprostanes

Isoprostanes are widely recognized as useful markers of membrane lipid peroxidation. It seems to be less well appreciated, however, that they also elicit important biological responses, even though this was first shown at the same time that they were introduced as markers of oxidative stress. The past several years have seen the list of cells/tissues which are sensitive to isoprostanes grow considerably: in fact, as we summarize here, there is now evidence that essentially every cell type in the lung responds in some pathologically relevant way to isoprostanes. In this sense, they might well be considered as not just markers of oxidative stress and inflammation, but also as a novel group of inflammatory mediators. Moreover, in addition to their pathological effects, we summarize here the evidence which has led us to hypothesize that isoprostanes could play an important role in vascular smooth muscle physiology as "endothelium-derived hyperpolarizing factors."

Modulation and roles of the endothelins in the pathophysiology of pulmonary embolism

Recent research on the endothelins (ETs) and their pathways in acute pulmonary embolism (APE) has led to significant advances in the understanding of this disease. ETs are potent vasoconstrictors and bronchoconstrictors found abundantly in the lung and can be released by stimuli such as endothelial injury, hypoxia, or thrombin, a key product in the coagulation cascade. Many studies using different approaches and methods of inducing pulmonary embolization, both in vitro and in vivo in various species, have mostly shown that ETs play an important role in the pathophysiology of APE. These results were obtained by comparing the hemodynamic data in the presence or absence of various ETs inhibitors, but also by assessing the modulation of the ET-related elements of this system by molecular, cell biology, and pharmacological methods. Based on the current understanding, a mechanism involving the ET pathway in the pathophysiology of APE is proposed for the reader's considerations. We postulate that ETs are primary mediators in APE based on the following: (i) their source from pulmonary endothelial cells where the primary injury takes place; (ii) their direct vasconstrictive, bronchoconstrictive, and promitogenic effects via distinct ET receptors; and (iii) their indirect effects associated with the secondary release of thromboxane and other mediators, which are released from inflammatory cells and platelets, which together can potentiate the overall hemodynamic response, most specifically the pulmonary vascular bed. Such combined effects of ETs on bronchomotor and vasomotor tone in the lung can adversely affect ventilation perfusion matching and lead to severe hypoxemia without causing significant changes in the chest X-ray of these patients. Thus, we may consider ET inhibitors as future current therapeutic agents in patients with PE.

Isoprostanes: an overview and putative roles in pulmonary pathophysiology

Isoprostanes are produced during peroxidation of membrane lipids by free radicals and reactive oxygen species. Initially, they were recognized as being valuable markers of oxidative stress, and in the past 10 years, dozens of disease states and experimental conditions with diverse etiologies have been shown to be associated with marked increases in urinary, plasma, and tissue levels of isoprostanes. However, they are not just mere markers; they evoke important biological responses on virtually every cell type found within the lung, and these responses exhibit compound-, tissue-, and species-related variations. In fact, the isoprostanes may mediate many of the features of the disease states for which they are used as indicators. In this review, I describe the chemistry, metabolism, and pharmacology of isoprostanes, with a particular emphasis on pulmonary cell types, and the possible roles of isoprostanes in pulmonary pathophysiology.

Fat embolism

Fat embolism syndrome is a collection of respiratory, haematological, neurological and cutaneous symptoms and signs associated with trauma and other disparate surgical and medical conditions. The incidence of the clinical syndrome is low (< 1% in retrospective reviews) whilst the embolisation of marrow fat appears to be an almost inevitable consequence of long bone fractures. There is debate over the pathogenesis of fat embolism syndrome and it seems a variety of factors interact to produce a spectrum of end organ damage. Many therapeutic interventions and prophylactic strategies have been tried with varying success. Current treatments are supportive and the condition is usually associated with a good outcome. The literature on fat embolism syndrome is extensive and this review aims to discuss the incidence, aetiology, pathophysiology, diagnosis and treatment of fat embolism.

Isoprostanes: generation, pharmacology, and roles in free-radical-mediated effects in the lung

Isoprostanes are produced during peroxidation of membrane lipids by free radicals and reactive oxygen species, and are currently used as markers of many disease states and experimental conditions in which oxidative stress is a prominent feature. A small number of reports have described the ability of some isoprostanes to evoke important biological effects in smooth muscle and other cell types. However, most of these studies were done using rat tissues, and only two specific isoprostanes - 8-iso-PGE(2)and 8-iso-PGF(2alpha)- were tested. In this review, we describe the generation of isoprostanes during oxidative stress, and their effects on smooth muscle, including our novel findings of their effects on human airway, pulmonary artery and pulmonary vein smooth muscles. Collectively, the data suggest that isoprostanes may not only be markers, but may in fact mediate the effects of free radicals and reactive oxygen species.

Combination therapy with inhaled nitric oxide and intravenous dobutamine during pulmonary hypertension in the rabbit

Combination therapy with an intravenous inovasodilator and inhaled nitric oxide (NO) may be appropriate in patients with pulmonary hypertension and associated right ventricular failure. We examined whether dobutamine and inhaled NO would have additive pulmonary vasodilator effects in experimental pulmonary hypertension. Pulmonary hypertension was produced in anesthetized, mechanically ventilated rabbits by infusion of U46619, a thromboxane analogue. Dobutamine was administered in increasing doses (2.5-20 microg/kg/min) with and without inhaled NO (40 ppm). Dobutamine produced dose-dependent decreases in pulmonary vascular resistance (PVR) and mean arterial pressure (MAP) and increases in cardiac output (CO). Inhaled NO alone decreased pulmonary artery pressure (PAP) and PVR with no effect on MAP or CO. The effects of dobutamine and inhaled NO were additive, so that at each dose of dobutamine, inhaled NO decreased PAP and PVR with no effect on systemic hemodynamics. This study suggests that the combination of dobutamine and inhaled NO should produce additive pulmonary vasodilation in patients with pulmonary hypertension and associated right ventricular dysfunction.

Fatal fat embolism syndrome: a case report

Fat embolism syndrome is a dire complication of long bone trauma. It is usually associated with neurological, hematological and respiratory involvement, the latter being the major cause of death. We present a case of severe fat embolism syndrome occurring 3 hours after a long bone injury, leading to permanent vegetative state and death without any respiratory signs. The diagnosis was confirmed by cytology of the bronchoalveolar lavage fluid. Clinical presentation of the puzzling fat embolism syndrome and diagnostic tests in suspected fat embolism syndrome are reviewed.

Inhalation of nebulized nitroglycerin in dogs with experimental pulmonary hypertension induced by U46619

BACKGROUND

Pulmonary hypertension (PH) causes mortality in some congenital and acquired heart and lung diseases. However, inhalation of NO gas requires complicated and expensive instruments and elaborate preparations to avoid toxic gas administration. We tested the effectiveness and safety of inhaled nebulized nitroglycerin (Neb-NTG) in dogs with experimental PH.

METHODS

Experimental PH was induced by continuous infusion of a thromboxane analog (U46619). The U46619 infusion rate was adjusted to maintain a systolic pulmonary artery pressure (PAP) at 40 mmHg in 10 anesthetized and mechanically ventilated dogs. Then, 20 micrograms/kg of NTG liquid nebulized by compressed air was inhaled.

RESULTS

After infusion of U46619, the systolic, diastolic and mean PAP increased by 119%, 228% and 169%, respectively, and the systolic, diastolic and mean systemic arterial pressures (SAP) increased by 19%, 29% and 23%, respectively. The systolic pulmonary to systemic pressure ratio (Pp/Ps) and mean Pp/Ps increased by 83% and 113%, respectively, and the pulmonary vascular resistance (PVR), systemic vascular resistance (SVR) and pulmonary to systemic resistance ratio (Rp/Rs) increased by 341%, 100% and 145%, respectively. After inhalation of Neb-NTG in dogs with experimental PH, systolic, diastolic and mean PAP and PVR decreased by 25 +/- 4, 26 +/- 11, 25 +/- 9 and 31 +/- 21%, respectively. There were no significant changes in systolic, diastolic and mean SAP, SVR, cardiac output and plasma methemoglobin concentrations. The systolic and mean Pp/Ps decreased by 18 +/- 7 and 20 +/- 7%, respectively. The Rp/Rs decreased by 25 +/- 13%.

CONCLUSIONS

The results of this study demonstrate that Neb-NTG is an effective and selective pulmonary vasodilator and may offer a new therapeutic option for PH.

Central hemodynamics during reamed intramedullary nailing of unilateral tibial fractures

BACKGROUND

Intramedullary nailing of a long-bone fracture results in intravasation of bone marrow contents into the right atrium and pulmonary vascular bed and, therefore, may alter cardiac and pulmonary hemodynamics.

METHODS

Central hemodynamic changes were recorded in 12 healthy adults with a unilateral simple tibial fracture undergoing intramedullary nailing. The patients were cannulated with a pulmonary artery catheter. Reamed intramedullary nailing was performed during general anesthesia. Preoperative and immediate postoperative hemodynamic variables were compared and intraoperative changes studied.

RESULTS

During the operation, the right ventricular preload as represented by central venous pressure and the right ventricular afterload as presented by mean pulmonary arterial pressure increased significantly. Preoperative and postoperative arterial oxygen tension values demonstrated hypoxia. Abnormal pulmonary shunting and increased oxygen consumption were observed as well.

CONCLUSION

Changes in cardiac and pulmonary hemodynamics are already present after the trauma and before the reamed intramedullary nailing procedure.

The effect of unreamed and reamed intramedullary nailing on the urinary excretion of prostacyclin and thromboxane A2 metabolites in patients with tibial shaft fractures

OBJECTIVE

To compare the effects of unreamed and reamed intramedullary nailing on the systemic production of prostacyclin and thromboxane A2 as assessed, respectively, by determinations of urinary 2,3-dinor-6-ketoprostaglandin F1alpha and 11-dehydrothromboxane B2 excretion.

METHODS

Ten otherwise healthy patients with closed and simple tibial shaft fractures were treated with unreamed intramedullary nailing, and 10 otherwise healthy patients with closed and simple tibial shaft fractures were treated with reamed intramedullary nailing. Urine was collected preoperatively and during the next 5 postoperative days. The samples were stored at -70 degrees C until assayed at the end of the study.

RESULTS

In the unreamed group, urinary 2,3-dinor-6-ketoprostaglandin F1alpha and 11-dehydrothromboxane B2 excretion remained stable and at a significantly lower levels compared with the reamed group during the entire study period (p < 0.021). In the reamed group, the alteration in urinary 2,3-dinor-6-ketoprostaglandin F1alpha excretion preoperatively and on the first postoperative day was nearly significant (p=0.075), and the increase in urinary 11-dehydrothromboxane B2 excretion was significant (p=0.020). The proportional increase compared with baseline, however, was 1.6 times greater for 11-dehydrothromboxane B2 than for 2,3-dinor-6-ketoprostaglandin F1alpha.

CONCLUSION

Only reamed intramedullary nailing elevates urinary 2,3-dinor-6-ketoprostaglandin F1alpha and 11-dehydrothromboxane B2 concentrations and their ratio (thromboxane A2/prostacyclin production) in patients with simple tibial shaft fractures.