Microthrombus formation may trigger lung injury after acute blood loss

Combination of aspirin and rosuvastatin for reduction of venous thromboembolism in severely injured patients: a double-blind, placebo-controlled, pragmatic randomized phase II clinical trial (The STAT Trial)

INTRODUCTION

Venous thromboembolism (VTE) remains a significant source of postinjury morbidity and mortality. Beta-hydroxy beta-methylglutaryl-CoA (HMG-CoA) reductase inhibitors (rosuvastatin) significantly reduced pathologic clotting events in healthy populations in a prior trial. Furthermore, acetylsalicylic acid (ASA) has been shown to be noninferior to prophylactic heparinoids for VTE prevention following orthopedic surgery. We hypothesized that a combination of rosuvastatin/ASA, in addition to standard VTE chemoprophylaxis, would reduce VTE in critically ill trauma patients.

METHODS

This was a double-blind, placebo-controlled, randomized trial, evaluating VTE rates in two groups: ASA + statin (Experimental) and identical placebos (Control). Injured adults, 18-65 years old, admitted to the surgical intensive care unit without contraindications for VTE prophylaxis were eligible. Upon initiation of routine VTE chemoprophylaxis (i.e. heparin/heparin-derivatives), they were randomized to the Experimental or Control group. VTE was the primary outcome.

RESULTS

Of 112 potentially eligible patients, 33% (n = 37, median new injury severity scale = 27) were successfully randomized, of whom 11% had VTEs. The Experimental group had no VTEs, while the Control group had 6 VTEs (4 PEs and 2 DVTs) in 4 (22%) patients (P = 0.046). The Experimental treatment was not associated with any serious adverse events. Due to the COVID-19 pandemic, the study was interrupted at the second interim analysis at <10% of the planned enrollment, with significance declared at P < 0.012 at that stage.

DISCUSSION

The combination of ASA and rosuvastatin with standard VTE prophylaxis showed a favorable trend toward reducing VTEs with no serious adverse events. An appropriately powered phase III multicenter trial is needed to further investigate this therapeutic approach.

LEVEL OF EVIDENCE

Level II, Therapeutic.

Intestinal Microbiota - An Unmissable Bridge to Severe Acute Pancreatitis-Associated Acute Lung Injury

Severe acute pancreatitis (SAP), one of the most serious abdominal emergencies in general surgery, is characterized by acute and rapid onset as well as high mortality, which often leads to multiple organ failure (MOF). Acute lung injury (ALI), the earliest accompanied organ dysfunction, is the most common cause of death in patients following the SAP onset. The exact pathogenesis of ALI during SAP, however, remains unclear. In recent years, advances in the microbiota-gut-lung axis have led to a better understanding of SAP-associated lung injury (PALI). In addition, the bidirectional communications between intestinal microbes and the lung are becoming more apparent. This paper aims to review the mechanisms of an imbalanced intestinal microbiota contributing to the development of PALI, which is mediated by the disruption of physical, chemical, and immune barriers in the intestine, promotes bacterial translocation, and results in the activation of abnormal immune responses in severe pancreatitis. The pathogen-associated molecular patterns (PAMPs) mediated immunol mechanisms in the occurrence of PALI via binding with pattern recognition receptors (PRRs) through the microbiota-gut-lung axis are focused in this study. Moreover, the potential therapeutic strategies for alleviating PALI by regulating the composition or the function of the intestinal microbiota are discussed in this review. The aim of this study is to provide new ideas and therapeutic tools for PALI patients.

Xanthine Oxidase-Induced Inflammatory Responses in Respiratory Epithelial Cells: A Review in Immunopathology of COVID-19

Xanthine oxidase (XO) is an enzyme that catalyzes the production of uric acid and superoxide radicals from purine bases: hypoxanthine and xanthine and is also expressed in respiratory epithelial cells. Uric acid, which is also considered a danger associated molecule pattern (DAMP), could trigger a series of inflammatory responses by activating the inflammasome complex path and NF-κB within the endothelial cells and by inducing proinflammatory cytokine release. Concurrently, XO also converts the superoxide radicals into hydroxyl radicals that further induce inflammatory responses. These conditions will ultimately sum up a hyperinflammation condition commonly dubbed as cytokine storm syndrome (CSS). The expression of proinflammatory cytokines and neutrophil chemokines may be reduced by XO inhibitor, as observed in human respiratory syncytial virus (HRSV)-infected A549 cells. Our review emphasizes that XO may have an essential role as an anti-inflammation therapy for respiratory viral infection, including coronavirus disease 2019 (COVID-19).

Obstructive apnea causes microvascular perfusion maldistribution in the lungs of rats

Obstructive sleep apnea (OSA) is associated with significant cardiovascular consequences, including pulmonary hypertension, yet little is known about its effects on pulmonary microvascular perfusion. To investigate effects of OSA on pulmonary microvascular perfusion, we clamped the tracheal cannulas of anesthetized, spontaneously breathing rats to simulate obstructive apnea. The clamp remained in place for 10 breaths before it was released to allow the animals to again breathe spontaneously. We repeated this protocol every 20 s until the rat experienced a total of five apneic episodes of 10 breaths each. We then infused into a femoral vein 10⁸ fluorescent latex particles (4 µm diameter), which became trapped within the pulmonary microcirculation. We removed the lungs, allowed them to air-dry, and quantified the particle distributions in sections of the lungs using dispersion index (DI) analysis, a method we developed previously. The log of the DI (logDI) is a measure of perfusion maldistribution. Greater log(DI) values correspond to greater maldistribution. Apneic lungs had average logDI values of 1.28 (SD 0.24). Rats not subjected to apnea had average logDI values of 0.85 (SD 0.08) ( P ≤ 0.05). Rats that received latex particles 10 min or 24 h after apnea had average logDI values of 0.97 (SD 0.31) and 0.84  (SD 0.38), respectively (not significant). Our results demonstrate, for the first time, that a few apneic events produced significant, but temporary, perfusion maldistribution within the pulmonary microcirculation. Repeated nightly episodes of apnea over months and years may explain why human patients with OSA suffer from significantly greater cardiovascular disease than those without OSA.

Interleukin-8, interleukin-1β and tumour necrosis factor-α in sequential units of packed red blood cells collected from retired racing Greyhounds

BACKGROUND

We hypothesised that concentrations of interleukin-8 (IL-8), interleukin-1β (IL-1β) and tumour necrosis factor-α (TNF-α) would increase during storage in the third sequential unit (U3) of canine packed red blood cells (PRBC) collected from terminal donors in haemorrhagic shock. We further hypothesised that leucoreduction would prevent cytokine accumulation in U3 and that cytokine concentrations in U3 would be higher than in the first units (U1) collected from the same dogs.

METHODS

U1 and U3 were each collected from 12 anaesthetised healthy Greyhounds. Removal of leucocytes from half of each PRBC unit produced one leucoreduced (LR) and one non-leucoreduced (NLR) unit. Canine IL-8, IL-1β and TNF-α concentrations were measured in samples collected from the units during storage on days 0, 10, 20, 30 and 37.

RESULTS

The IL-8 concentration in U3 NLR units was significantly higher on days 10, 20, 30 and 37 than on day 0 and was significantly higher than in the LR units at all time points. The IL-1β concentration in U3 did not change over time, or between LR and NLR units. TNF-α was not detected in any unit. There were no significant differences in IL-8 or IL-1β concentrations between U3 and U1 at any time point; however, some NLR U3 units had markedly elevated IL-8 concentrations at day 37 (2060-20,682 pg/mL) compared with NLR U1 units (3369-5280 pg/mL).

CONCLUSION

NLR U3 units collected from dogs in haemorrhagic shock showed a significant increase in IL-8 concentrations during storage. Leucoreduction was effective at preventing the accumulation of IL-8. There was no difference detected between U3 and U1.

Trauma-Related Acute Lung Injury Develops Rapidly Irrespective of Resuscitation Strategy in the Rat

BACKGROUND

Acute lung injury (ALI) has been observed clinically after severe trauma. We have recently developed a rat model of polytrauma that shows evidence of multi-organ failure and coagulopathy. In this study, we investigate whether ALI occurs after severe trauma and resuscitation, and the cellular mechanisms involved.

METHODS

Polytrauma and hemorrhage was induced in anesthetized Sprague-Dawley rats. Five groups were prepared: control, no resuscitation, and resuscitation with Lactated Ringer (LR), fresh whole blood or whole blood stored 7days at 4°C. Resuscitation was begun 1 hr after trauma. Lung injury was determined by lung wet/dry weight ratios.

RESULTS

Polytrauma and hemorrhage (no resuscitation) led to a significant increase in the number of neutrophils, monocytes, macrophages, platelets, and the levels of myeloperoxidase, pro-inflammatory cytokines (IL-6, IL-1α, IL-1β), anti-inflammatory Th2 cytokines (IL-4, IL-10, IL-13), and chemokines (MIP-1α, GRO KC) in the lung tissue. Resuscitation with LR, fresh whole blood or stored blood led to a significant change in the lung wet/dry ratio signifying fluid movement into the lungs. However, fluid did not move into the lungs in non-resuscitated controls.

CONCLUSION

This study shows that trauma related acute lung injury occurs early after polytrauma and hemorrhage in rat. This ALI is secondary to the trauma, and likely due to an elevation in leukocytes, platelets, inflammatory cytokines and myeloperoxidase in the lung tissue prior to any resuscitation. Resuscitation with either LR or whole blood demonstrated similar lung edema. Blood was neither more protective nor more damaging than LR during early resuscitation.

Emerging therapies for the prevention of acute respiratory distress syndrome

The development of acute respiratory distress syndrome (ARDS) carries significant risk of morbidity and mortality. To date, pharmacological therapy has been largely ineffective for patients with ARDS. We present our personal review aimed at outlining current and future directions for the pharmacological prevention of ARDS. Several available risk-stratification or prediction score strategies for identification of patients at risk of ARDS have been reported. Although not ready for clinical everyday use, they are and will be instrumental in the ongoing and future trials of pharmacoprevention of ARDS.Several systemic medications established the potential role in ARDS prevention based on the preclinical studies and observational data. Due to potential for systemic adverse effects to neutralize any pharmacological benefits of systemic therapy, inhaled medications appear particularly attractive candidates for ARDS prevention. This is because of their direct delivery to the site of proposed action (lungs), while the pulmonary epithelial surface is still functional.We postulate that overall morbidity and mortality rates from ARDS in the future will be contingent upon decreasing the overall incidence of ARDS through effective identification of those at risk and early application of proven supportive care and pharmacological interventions.

Inhaled thrombolytics reduce lung microclot and leukocyte infiltration after acute blood loss

We showed previously that a 30% blood loss in rats, without resuscitation, caused significant accumulation of microthrombi and leukocytes within the pulmonary circulation by 24 h. We hypothesized that the microthrombi formed spontaneously as a consequence of hemorrhage-induced stasis within the low-pressure pulmonary circuit and that the leukocytes were attracted to them. This suggested that elimination of the microthrombi, using an inhaled thrombolytic agent, could prevent the neutrophil sequestration after blood loss. To test this hypothesis, we removed 30% of the calculated blood volume from isoflurane-anesthetized, male Sprague-Dawley rats (350-500 g) over 5 min and allowed them to recover. Six hours later, we re-anesthetized the rats and nebulized tissue plasminogen activator (80 or 320 µg/kg), lactated Ringer's solution (LRS), or ipratropium bromide (i-bromide) into their lungs. We used i-bromide as a control after we discovered that nebulized LRS had thrombolytic properties. At 24 h, we removed and fixed the lungs and prepared sections for immunohistochemistry using antibodies against fibrinogen (microthrombi) and CD16 (leukocytes). Digital images of each section were obtained using a confocal microscope. Pixel counts of the images showed significantly less accumulation of microthrombi and leukocytes in lungs nebulized with tissue plasminogen activator or LRS than in non-nebulized lungs or in lungs nebulized with i-bromide (P ≤ 0.05). Lactated Ringer's solution becomes positively charged when nebulized (unlike i-bromide), suggesting that it eliminated microthrombi by fibrin depolymerization. We confirmed this using an in vitro assay. Our results demonstrate that lyses of microthrombi that accumulate in the lung after acute blood loss prevent subsequent leukocyte sequestration.

Isoflurane prevents acute lung injury through ADP-mediated platelet inhibition

BACKGROUND

Growing evidence suggests platelets are essential in posttraumatic, acute lung injury (ALI). Halogenated ethers interfere with the formation of platelet-granulocyte aggregates. The potential benefit of halogenated ethers has not been investigated in models of trauma/hemorrhagic shock (T/HS). Therefore, we hypothesized that isoflurane decreases T/HS-mediated ALI through platelet inhibition.

METHODS

Sprague-Dawley rats (n = 47) were anesthetized by either pentobarbital or inhaled isoflurane and placed into (1) control, (2) trauma (laparotomy) sham shock, (3) T/HS (mean arterial pressure, 30 mmHg × 45 min), (4) pretreatment with an ADP receptor antagonist, or (5) T/HS with isoflurane initiated during resuscitation groups. ALI was determined by protein and pulmonary immunofluorescence bronchoalveolar lavage (BAL) fluid. Platelet Mapping specifically evaluated thrombin-independent inhibition of the ADP and AA pathways of platelet activation.

RESULTS

Pretreatment with isoflurane abrogated ALI as measured by both BAL fluid protein and pulmonary immunofluorescence (P < .001). Platelet Mapping revealed specific inhibition of the platelet ADP-pathway with isoflurane (P < .001). Pretreatment with an ADP receptor antagonist decreased ALI to sham levels, confirming that specific platelet ADP inhibition decreases ALI. Isoflurane initiated during resuscitation also decreased ALI (P < .001).

CONCLUSION

Isoflurane attenuates ALI through an antiplatelet mechanism, in part, through inhibition of the platelet ADP pathway. Isoflurane given postinjury also protects against ALI, and highlights the potential applications of this therapy in various clinical scenarios of ischemia/reperfusion.

Activated platelets in heparinized shed blood: the "second hit" of acute lung injury in trauma/hemorrhagic shock models

The return of heparinized shed blood (SB) in trauma/hemorrhagic shock (T/HS) models remains controversial because of potential anti-inflammatory properties. Although ubiquitous as an anticoagulant, heparin is ineffective on cellular coagulation as an antithrombotic agent. Therefore, we hypothesized that returning heparinized SB would paradoxically enhance acute lung injury (ALI) after T/HS because of the infusion of activated platelets. Sprague-Dawley rats, anesthetized with pentobarbital, underwent laparotomy and hemorrhage-induced shock (MAP of 30 mmHg × 45 min). Animals were resuscitated with a combination of normal saline and returned SB. Shed blood was collected in either 80 U/kg of heparin, 800 U/kg of heparin, or citrate or diluted 1:8 with normal saline. An additional group of animals were pretreated with a platelet P2Y12 receptor antagonist (clopidogrel) before T/HS. Bronchoalveolar lavage, lung myeloperoxidase assays, pulmonary immunofluorescence, and blood smears were conducted. Bronchoalveolar lavage protein increased in animals resuscitated with heparinized SB (T/HS + 80 U/kg Hep 1.62 ± 0.29, T/HS + 800 U/kg Hep 1.30 ± 0.15 vs. T/SS 0.51 ± 0.16 and T/HS Citrate 0.7 ± 0.09) (P < 0.0001). Blood smears and platelet function assays revealed platelet aggregates and increased platelet activation. Animals pretreated with a platelet P2Y12 receptor antagonist were protected from postinjury ALI (P < 0.0001). Animals with return of SB had increased pulmonary polymorphonuclear leukocyte sequestration (P < 0.0001). Pulmonary immunofluorescence demonstrated microthrombi only in the T/HS group receiving heparinized SB (P < 0.0001). The return of heparinized SB functions as a "second hit" to enhance ALI, with activated platelets propagating microthrombi and pulmonary polymorphonuclear leukocyte recruitment.