Orthopedic trauma-induced pulmonary injury in the obese Zucker rat

Does Scheduled Low-Dose Short-Term NSAID (Ketorolac) Modulate Cytokine Levels After Orthopaedic Polytrauma? A Secondary Analysis of a Randomized Clinical Trial

OBJECTIVES

To determine whether scheduled low-dose, short-term ketorolac modulates cytokine concentrations in orthopaedic polytrauma patients.

METHODS

DESIGN

Secondary analysis of a double-blinded, randomized controlled trial.

SETTING

Single Level I trauma center from August 2018 to October 2022.

PATIENT SELECTION CRITERIA

Orthopaedic polytrauma patients between 18 and 75 years with a New Injury Severity Score greater than 9 were enrolled. Participants were randomized to receive 15 mg of intravenous ketorolac every 6 hours for up to 5 inpatient days or 2 mL of intravenous saline similarly.

OUTCOME MEASURES AND COMPARISONS

Daily concentrations of prostaglandin E2 and interleukin (IL)-1a, IL-1b, IL-6, and IL-10. Clinical outcomes included hospital and intensive care unit length of stay, pulmonary complications, and acute kidney injury.

RESULTS

Seventy orthopaedic polytrauma patients were enrolled, with 35 participants randomized to the ketorolac group and 35 to the placebo group. The overall IL-10 trend over time was significantly different in the ketorolac group ( P = 0.043). IL-6 was 65.8% higher at enrollment compared to day 3 ( P < 0.001) when aggregated over both groups. There was no significant treatment effect for prostaglandin E2, IL-1a, or IL-1b ( P > 0.05). There were no significant differences in clinical outcomes between groups ( P > 0.05).

CONCLUSIONS

Scheduled low-dose, short-term, intravenous ketorolac was associated with significantly different mean trends in IL-10 concentration in orthopaedic polytrauma patients with no significant differences in prostaglandin E2, IL-1a, IL-1b, or IL-6 levels between groups. The treatment did not have an impact on clinical outcomes of hospital or intensive care unit length of stay, pulmonary complications, or acute kidney injury.

LEVEL OF EVIDENCE

Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

A rat model of orthopedic injury-induced hypercoagulability and fibrinolytic shutdown

BACKGROUND

Postinjury hypercoagulability occurs in >25% of injured patients, increasing risk of thromboembolic complications despite chemoprophylaxis. However, few clinically relevant animal models of posttraumatic hypercoagulability exist. We aimed to evaluate a rodent model of bilateral hindlimb injury as a preclinical model of postinjury hypercoagulability.

METHODS

Forty Wistar rats were anesthetized with isoflurane: 20 underwent bilateral hindlimb fibula fracture, soft tissue and muscular crush injury, and bone homogenate injection intended to mimic the physiological severity of bilateral femur fracture. Twenty sham rats underwent anesthesia only. Terminal citrated blood samples were drawn at 0, 6, 12, and 24 hours (n = 5 per timed group) for analysis by native thromboelastography in the presence and absence of taurocholic acid to augment fibrinolysis. Plasminogen activator inhibitor 1 and α-2 antiplasmin levels in plasma were assessed via enzyme-linked immunosorbent assay.

RESULTS

Injured rats became hypercoagulable relative to baseline by 6 hours based on thromboelastography maximal amplitude (MA) and G (p < 0.005); sham rats became hypercoagulable to a lesser degree by 24 hours (p < 0.005). Compared with sham animals, injured rats were hypercoagulable by MA and G within 6 hours of injury, remained hypercoagulable by MA and G through at least 24 hours (all p < 0.01), and showed impaired fibrinolysis by taurocholic acid LY30 at 12 hours (p = 0.019) and native LY30 at 24 hours (p = 0.045). In terms of antifibrinolytic mediators, α-2 antiplasmin was elevated in trauma animals at 24 hours (p = 0.009), and plasminogen activator inhibitor 1 was elevated in trauma animals at 6 hours (p = 0.004) and 12 hours (p < 0.001) when compared with sham.

CONCLUSIONS

Orthopedic injury in rodents induced platelet and overall hypercoagulability within 6 hours and fibrinolytic impairment by 12 to 24 hours, mimicking postinjury hypercoagulability in injured patients. This rodent model of orthopedic injury may serve as a preclinical testing ground for potential therapies to mitigate hypercoagulability, maintain normal fibrinolysis, and prevent thromboembolic complications.

Early treatment with GLP-1 after severe trauma preserves renal function in obese Zucker rats

Early posttrauma hyperglycemia (EPTH) is correlated with later adverse outcomes, including acute kidney injury (AKI). Controlling EPTH in the prehospital setting is difficult because of the variability in the ideal insulin dosage and the potential risk of hypoglycemia, especially in those with confounding medical comorbidities of obesity and insulin resistance. Glucagon-like peptide-1 (GLP-1) controls glucose levels in a glucose-dependent manner and is a current target in antidiabetic therapy. We have shown that after orthopedic trauma, obese Zucker rats exhibit EPTH and a later development of AKI (within 24 h). We hypothesized that GLP-1 treatment after trauma decreases EPTH and protects renal function in obese Zucker rats. Obese Zucker rats (~12 wk old) were fasted for 4 h before trauma. Soft tissue injury, fibula fracture, and homogenized bone component injection were then performed in both hind limbs to induce severe extremity trauma. Plasma glucose levels were measured before and 15, 30, 60, 120, 180, 240, and 300 min after trauma. GLP-1 (3 μg·kg^-1·h^-1, 1.5 ml/kg total) or saline was continuously infused from 30 min to 5 h after trauma. Afterwards, rats were placed in metabolic cages overnight for urine collection. The following day, plasma interleukin (IL)-6 levels, renal blood flow (RBF), glomerular filtration rate (GFR), and renal oxygen delivery (Do₂) and consumption (V̇o₂) were measured. EPTH was evident within 15 min after trauma but was significantly ameliorated during the 5 h of GLP-1 infusion. One day after trauma, plasma IL-6 was markedly increased in the trauma group and decreased in GLP-1-treated animals. RBF, GFR, and Do₂ all significantly decreased with trauma, but renal V̇o₂ was unchanged. GLP-1 treatment normalized RBF, GFR, and Do₂ without affecting V̇o₂. These results suggest that GLP-1 decreases EPTH and protects against a later development of AKI. Early treatment with GLP-1 (or its analogs) to rapidly, effectively, and safely control EPTH may be beneficial in the prehospital care of obese patients after trauma.

Hyperglycemia-Mediated Oxidative Stress Increases Pulmonary Vascular Permeability

OBJECTIVE

Hyperglycemia in diabetes mellitus is associated with endothelial dysfunction as evidenced by increased oxidative stress and vascular permeability. Whether impaired glucose control in metabolic syndrome impacts pulmonary vascular permeability is unknown. We hypothesized that in metabolic syndrome, hyperglycemia increases lung vascular permeability through superoxide.

METHODS

Lung capillary Kf and vascular superoxide were measured in the isolated lungs of LZ and OZ rats. OZ were subjected to 4 weeks of metformin treatment (300 mg/kg/day orally) to improve insulin sensitivity. In a separate experiment, lung vascular permeability and vascular superoxide were measured in LZ exposed to acute hyperglycemia (30 mM).

RESULTS

As compared to LZ, OZ had impaired glucose and insulin tolerance and elevated vascular superoxide which was associated with an elevated lung Kf. Chronic metformin treatment in OZ improved glucose control and insulin sensitivity which was associated with decreased vascular oxidative stress and lung Kf. Acute hyperglycemia in isolated lungs from LZ increased lung Kf, which was blocked with the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, apocynin (3 mM). Apocynin also decreased baseline Kf in OZ.

CONCLUSIONS

These data suggest that hyperglycemia in metabolic syndrome exacerbates lung vascular permeability through increases in vascular superoxide, possibly through NADPH oxidase.

OBESITY AND CRITICAL ILLNESS: INSIGHTS FROM ANIMAL MODELS

Critical illness is a major cause of morbidity and mortality around the world. While obesity is often detrimental in the context of trauma, it is paradoxically associated with improved outcomes in some septic patients. The reasons for these disparate outcomes are not well understood. A number of animal models have been used to study the obese response to various forms of critical illness. Just as there have been many animal models that have attempted to mimic clinical conditions, there are many clinical scenarios that can occur in the highly heterogeneous critically ill patient population that occupies hospitals and intensive care units. This poses a formidable challenge for clinicians and researchers attempting to understand the mechanisms of disease and develop appropriate therapies and treatment algorithms for specific subsets of patients, including the obese. The development of new, and the modification of existing animal models, is important in order to bring effective treatments to a wide range of patients. Not only do experimental variables need to be matched as closely as possible to clinical scenarios, but animal models with pre-existing comorbid conditions need to be studied. This review briefly summarizes animal models of hemorrhage, blunt trauma, traumatic brain injury, and sepsis. It also discusses what has been learned through the use of obese models to study the pathophysiology of critical illness in light of what has been demonstrated in the clinical literature.

Distinct temporal phases of microvascular rarefaction in skeletal muscle of obese Zucker rats

Evolution of metabolic syndrome is associated with a progressive reduction in skeletal muscle microvessel density, known as rarefaction. Although contributing to impairments to mass transport and exchange, the temporal development of rarefaction and the contributing mechanisms that lead to microvessel loss are both unclear and critical areas for investigation. Although previous work suggests that rarefaction severity in obese Zucker rats (OZR) is predicted by the chronic loss of vascular nitric oxide (NO) bioavailability, we have determined that this hides a biphasic development of rarefaction, with both early and late components. Although the total extent of rarefaction was well predicted by the loss in NO bioavailability, the early pulse of rarefaction developed before a loss of NO bioavailability and was associated with altered venular function (increased leukocyte adhesion/rolling), and early elevation in oxidant stress, TNF-α levels, and the vascular production of thromboxane A2 (TxA2). Chronic inhibition of TNF-α blunted the severity of rarefaction and also reduced vascular oxidant stress and TxA2 production. Chronic blockade of the actions of TxA2 also blunted rarefaction, but did not impact oxidant stress or inflammation, suggesting that TxA2 is a downstream outcome of elevated reactive oxygen species and inflammation. If chronic blockade of TxA2 is terminated, microvascular rarefaction in OZR skeletal muscle resumes, but at a reduced rate despite low NO bioavailability. These results suggest that therapeutic interventions against inflammation and TxA2 under conditions where metabolic syndrome severity is moderate or mild may prevent the development of a condition of accelerated microvessel loss with metabolic syndrome.

Inhibition of NADPH oxidase prevents acute lung injury in obese rats following severe trauma

Lung capillary filtration coefficient (Kf) and impacts of oxidative stress have not been determined in the setting of severe trauma, especially in obese patients who exhibit increased lung injury. We hypothesized that severe trauma leads to a greater increase in lung Kf in obesity due to exacerbated production of and/or vulnerability to oxidative stress. Severe trauma was induced in lean and obese Zucker rats by muscle injury, fibula fracture, and bone component injection to both hindlimbs, with or without 24-h treatments of apocynin, a NADPH oxidase (NOX) inhibitor. Lung wet/dry weight ratios, lung vascular Kf, lung neutrophil counts, lung NOX and myeloperoxidase (MPO) activity, and plasma IL-6 levels were measured 24 h after trauma. In an additional study, lungs were isolated from nontrauma lean and obese rats to determine the acute effect of phenazime methosulfate, a superoxide donor, on pulmonary vascular Kf. After trauma, compared with lean rats, obese rats exhibited greater increases in lung capillary Kf, neutrophil accumulation, NOX and MPO activity, and plasma IL-6. The lung wet/dry weight ratio was increased in obese rats but not in lean rats. Apocynin treatment decreased lung Kf, neutrophil counts, NOX and MPO activities, wet/dry weight ratio, and plasma IL-6 in obese rats. Phenazime methosulfate treatment resulted in a greater increase in lung Kf in nontrauma obese rats compared with nontrauma lean rats. These results suggest that obese rats are susceptible to lung injury following severe trauma due to increased production of and responsiveness to pulmonary oxidative stress.

A novel experimental model of orthopedic trauma with acute kidney injury in obese Zucker rats

Obesity is associated with an increased risk of acute kidney injury (AKI) after blunt traumatic injury in humans. Because limitations exist in studying trauma in human patients, animal models are necessary to elucidate mechanisms of remote organ injury after trauma. We developed a model of severe orthopedic trauma in lean (LZ) and obese (OZ) Zucker rats, in which OZ develop greater kidney dysfunction after trauma than LZ. Orthopedic trauma was inflicted via bilateral hindlimb soft tissue injury, fibula fracture, and injection of homogenized bone components. Mean arterial pressure (MAP) and heart rate (HR) were measured for 6 h after trauma, and again at 24 h after trauma. Urine was collected for 24 h before and after trauma to measure urine albumin excretion. Glomerular filtration rate (GFR), renal plasma flow (RPF), plasma interleukin-6 (IL-6), and renal macrophage infiltration (ED-1 [CD68 Antibody] immunostaining) were measured in animals with and without trauma. MAP and HR were similar between LZ and OZ throughout the study, with the exception that OZ had a 18 mmHg lower pressure 24 h posttrauma. GFR and RPF were decreased significantly (∼50%), while urine albumin excretion, plasma IL-6, and renal ED-1-positive cells were increased in OZ 24 h after trauma compared to both OZ without trauma and LZ after trauma. In conclusion, these data are consistent with studies in humans that show that AKI develops more frequently in obese than in lean individuals. This model will be an important experimental tool to better understand the underlying mechanisms of poor outcomes after trauma in obese patients.

Impact of the body mass on complications and outcome in multiple trauma patients: what does the weight weigh?

Obesity is known as an independent risk factor for various morbidities. The influence of an increased body mass index (BMI) on morbidity and mortality in critically injured patients has been investigated with conflicting results. To verify the impact of weight disorders in multiple traumatized patients, 586 patients with an injury severity score >16 points treated at a level I trauma center between 2005 and 2011 were differentiated according to the BMI and analyzed regarding morbidity and outcome. Plasma levels of interleukin- (IL-) 6 and C-reactive protein (CRP) were measured during clinical course to evaluate the inflammatory response to the "double hit" of weight disorders and multiple trauma. In brief, obesity was the highest risk factor for development of a multiple organ dysfunction syndrome (MODS) (OR 4.209, 95%-CI 1.515-11.692) besides injury severity (OR 1.054, 95%-CI 1.020-1.089) and APACHE II score (OR 1.059, 95%-CI 1.001-1.121). In obese patients as compared to those with overweight, normal weight, and underweight, the highest levels of CRP were continuously present while increased systemic IL-6 levels were found until day 4. In conclusion, an altered posttraumatic inflammatory response in obese patients seems to determine the risk for multiple organ failure after severe trauma.

Impaired blood pressure recovery to hemorrhage in obese Zucker rats with orthopedic trauma

We have shown that obese Zucker rats with orthopedic trauma (OZT) exhibit a loss of arteriolar tone in skeletal muscle. We hypothesize that the loss of arteriolar tone in OZT blunts vasoconstrictor responses to hemorrhage, resulting in an impaired blood pressure recovery. Orthopedic trauma was induced with soft tissue injury and local injection of bone components in both hindlimbs in lean (LZT) and OZT (11-13 wk). One day after the orthopedic trauma, blood pressure responses following hemorrhage were measured in conscious control lean, control obese, LZT, and OZT. In another set of experiments, the spinotrapezius muscle of control and trauma animals was prepared for microcirculatory observation. Arteriolar responses to phenylephrine (PE) or hemorrhage were determined. Hemorrhage resulted in similar blood pressure responses in control animals and LZT, but the blood pressure recovery following hemorrhage was blunted in the OZT. In the spinotrapezius, OZT exhibited decreased arteriolar tone and blunted vasoconstrictor responses to PE and hemorrhage. Treatment with glibenclamide improved the blood pressure recovery in the conscious OZT and improved the arteriolar tone, and PE induced vasoconstriction in the spinotrapezius of the OZT. Thus, ATP-dependent K(+) channel-mediated loss of arteriolar tone in OZT blunts the arteriolar constriction to hemorrhage, resulting in impaired blood pressure recovery.

Ethyl pyruvate protects rats from phosgene-induced pulmonary edema by inhibiting cyclooxygenase2 and inducible nitric oxide synthase expression

Phosgene is a poorly water-soluble gas penetrating the lower respiratory tract which can induce acute lung injury characterized by a latent phase of fatal pulmonary edema. Pulmonary edema caused by phosgene is believed to be a consequence of oxidative stress and inflammatory responses. Ethyl pyruvate (EP) has been demonstrated to have anti-inflammatory and anti-oxidative properties in vivo and in vitro. The potential therapeutic role of EP in phosgene-induced pulmonary edema has not been addressed so far. In the present study, we aim to investigate the protective effects of EP on phosgene-induced pulmonary edema and the underlying mechanisms. Rats were administered with EP (40 mg kg(-1)) and RAW264.7 cells were also incubated with it (0, 2, 5 or 10 µm) immediately after phosgene (400 ppm, 1 min) or air exposure. Wet-to-dry lung weight ratio (W:D ratio), nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production, cyclooxygenase2 (COX-2) and inducible nitric oxide synthase (iNOS) expression, and mitogen-activated protein kinases activities (MAPKs) were measured. Our results showed that EP treatment attenuated phosgene-induced pulmonary edema and decreased the level of NO and PGE(2) dose-dependently. Furthermore, EP significantly reduced COX-2 expression, iNOS expression and MAPK activation induced by phosgene. Moreover, specific inhibitors of MAPKs reduced COX-2 and iNOS expression induced by phosgene. These findings suggested that EP has a protective role against phosgene-induced pulmonary edema, which is mediated in part by inhibiting MAPK activation and subsequently down-regulating COX-2 and iNOS expression as well as decreasing the production of NO and PGE(2).