Diagnostic performance and clinical implications for enhancing a hybrid quantitative flow ratio and fractional flow reserve revascularization decision making strategy

Background

Fractional flow reserve (FFR) adoption persists low mainly due to procedural and operator related factors as well as costs. An alternative for FFR, quantitative flow ratio (QFR) achieves a high accuracy mainly outside the intermediate zone without the need for hyperemia and wire-use. Currently, no outcome trials assess the role of QFR in the guidance of revascularization. Therefore, we evaluate a QFR-FFR hybrid strategy in which FFR is measured inside of the intermediate zone.

Methods

This retrospective multi-center study included consecutive patients who underwent both invasive coronary angiography and FFR in the participating centers. QFR was calculated for all vessels in which FFR was measured. Diagnostic performance of QFR was assessed using an FFR cut-off of 0.80 as reference standard. The QFR-FFR hybrid approach was modeled using the intermediate zone of 0.77 to 0.87 assuming that lesions within the intermediate zone follow the FFR binary cutoff.

Results

In total, 381 vessels in 289 patients were analyzed. The sensitivity, specificity and accuracy on a per vessel-based analysis were 84.6%, 86.3% and 85.6% for QFR and 91.1%, 95.3% and 93.4% for the QFR-FFR hybrid approach. The diagnostic accuracy of QFR-FFR hybrid strategy with invasive FFR measurement is 93.4% and results in a FFR reduction of 56.7%.

Conclusion

QFR has a good correlation and agreement with invasive FFR and a high diagnostic accuracy. A hybrid QFR-FFR approach could extend the use of QFR and reduces the proportion of invasive FFR-measurements needed while maintaining a high accuracy.

Hybrid QFR-FFR strategy

Funding Acknowledgement

Type of funding source: None

External validation of PRECISE-DAPT score and PARIS bleeding risk score in a real-world cohort of patients with acute coronary syndrome

Background

In patients with acute coronary syndrome (ACS) shortened duration of dual antiplatelet therapy (DAPT) should be considered in those at high risk of bleeding. Risk scores may be used to assess the bleeding risk, but their predictive value remains unclear.

Purpose

To externally validate and compare the PRECISE-DAPT and the PARIS bleeding risk scores in patients with ACS.

Methods

From January 2015 to June 2018, all patients admitted with ACS were consecutively included in a single center, observational, prospective registry with follow-up of at least one year. In all patients, the PRECISE-DAPT and the PARIS risk-score were retrospectively assessed. Primary endpoint was moderate or severe bleeding defined as Bleeding Academic Research Consortium (BARC) 3 or 5 bleeding within one year after ACS. Kaplan-Meier curves showed the probabilty of bleeding during follow-up as assessed by both scores. Score discrimination using c-statistic were calculated and calibration curves were visually assessed.

Results

2,729 patients were included for analysis. 93.6% were discharged with ≥2 antithrombotic drugs. At one year follow-up, the event rate of moderate or severe bleeding was 5.5%. High bleeding risk as stratified by both risk scores was associated with higher bleeding rates. Discriminative values for BARC 3 or 5 bleeding at one year were 0.67 [95% CI 0.61–0.72] for the PRECISE-DAPT score and 0.62 [95% CI 0.57–0.68] for the PARIS bleeding score (p=0.31).

Conclusion

The PRECISE-DAPT and the PARIS bleeding scores both showed adequate discriminative performances in predicting moderate or severe bleeding in this study.

Kaplan-meier and ROC-curves

Funding Acknowledgement

Type of funding source: None

The current treatment and predictors of outcome in elderly patients with non-ST-elevation myocardial infarction in an all comers population: the POPular Age registry

Background

Elderly patients form a large and growing part of the patients presenting with non-ST-elevation myocardial infarction (NSTEMI). Choosing the optimal antithrombotic treatment in these elderly patients is more complicated because they frequently have characteristics indicating both a high ischaemic and high bleeding risk.

Purpose

We describe the treatment of elderly patients (>75 years) admitted with NSTEMI, present the outcomes (major adverse cardiovascular events (MACE) and bleeding) and aim to find predictors for adverse events.

Methods

The POPular AGE registry is an investigator initiated, prospective, observational, multicentre study of patients aged 75 years or older presenting with NSTEMI. Patients were recruited between August 1st, 2016 and May 7th, 2018 at 21 sites in the Netherlands. The primary composite endpoint of MACE included cardiovascular death, non-fatal myocardial infarction and non-fatal stroke at one-year follow-up.

Results

A total of 757 patients were enrolled. During hospital stay 76% underwent coronary angiography, 34% percutaneous coronary intervention and 12% coronary artery bypass grafting (CABG). At discharge 78.6% received aspirin (non-users mostly because of the combination of oral anticoagulant and clopidogrel), 49.7% were treated with clopidogrel, 34.2% with ticagrelor and 29.6% were prescribed oral anticoagulation. Eighty-three percent of patients received dual antiplatelet therapy (DAPT) or dual therapy consisting of oral anticoagulation and at least one antiplatelet agent for a duration of 12 months. At one year, the primary outcome of cardiovascular death, myocardial infarction or stroke occurred in 12.3% of patients and major bleeding (BARC 3 or 5) occurred in 4.8% of the patients. The risk of MACE and major bleeding was highest during the first month and stayed high over time for MACE while the risk for major bleeding levelled off. Independent predictors for MACE were age, renal function, medical history of CABG, stroke and diabetes. The only independent predictor for major bleeding was haemoglobin level on admission.

Conclusion

In this all-comers registry, most elderly patients (≥75 years) with NSTEMI are treated with DAPT and undergoing coronary angiography the same way as younger NSTEMI patients from the SWEDEHEART registry. Aspirin use was lower as was the use of the more potent P2Y12 inhibitors compared to the SWEDEHEART which is very likely due to the concomitant use of oral anticoagulation in 30% of patients. The fact that ischemic risk stays constant over 1 year of follow-up, while the bleeding risk levels off after one month may suggest the need of dual antiplatelet therapy until at least one year after NSTEMI.

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): AstraZeneca

IABP and VA-ECMO is associated with better outcome than VA-ECMO alone in the treatment of cardiogenic shock in STEMI

Introduction

VA-ECMO is an upcoming technique in the treatment of cardiogenic shock in patients with STEMI however it increases afterload. IABP in addition to VA-ECMO has been suggested to reduce afterload and increase survival.

Methods

A multi-center in-hospital registry was kept on all patients undergoing VA-ECMO or VA-ECMO and additional IABP treatment for cardiogenic shock in STEMI. Patients were analyzed for baseline characteristics, coronary anatomy using the SYNTAX score, predicted survival using the SAVE-score, survival, neurological status and complications.

Results

Between 2011 and 2018 18 patients with STEMI underwent VA-ECMO +/− IABP treatment for cardiogenic shock. The majority was male (78% (14/18)) with a median age of 59 (47–75) years. All patients were in Killip class IV. VA-ECMO alone was performed in 61% (11/18) and VA-ECMO and IABP was performed in 39% (7/18). A cardiac arrest was observed 91% (10/11) of the patients in the VA-ECMO alone group vs 71% (5/7) in the VA-ECMO+IABP group (p=0.52).

The VA-ECMO+IABP group had more complex coronary anatomy, i.e. a higher amount of left main (LM) disease, LM + 3 vessel disease, and three vessel disease when compared to the ECMO alone group (ECMO+IABP 87% vs ECMO alone 18% vs p=0.03). The Syntax score was higher in the ECMO+IABP group (ECMO alone 22±14 vs ECMO+IABP 32±13). The SAVE score did not differ between the groups (ECMO alone −5.9±2.4 vs ECMO+IABP −6.1±2.6 p=0.88) and has a predicted survival of 25–35%.

Survival in the VA-ECMO+IABP group was 100% (7/7), survival in the VA-ECMO group was 55% (6/11) (p=0.035). Good neurological outcome was achieved in more patients in the ECMO+IABP group (ECMO alone 45% vs ECMO+IABP 100% p=0.037). There was no difference in leg ischemia between the VA-ECMO alone group vs the ECMO+IABP group (27% (2/11) vs 0% (0/7) p=0.55) or in bleeding complications (18% (2/11) vs 43% (3/7) p=0.28)

Conclusion

VA-ECMO can improve survival in patients with cardiogenic shock due to STEMI even when in cardiac arrest. VA-ECMO in combination with IABP is associated with better outcome than VA-ECMO alone.

Funding Acknowledgement

Type of funding source: None

Identifying high thrombotic risk in atrial fibrillation patients undergoing percutaneous coronary intervention: is there a benefit of triple therapy?

Introduction

Patients requiring concomittant use of oral anticoagulants for atrial fibrillation and dual antiplatelet therapy after percutaneous coronary intervention (PCI) are at increased risk of bleeding and mortality. Omittance of aspirin (dual antithrombotic therapy, DAT) reduces bleeding as compared to triple antithrombotic therapy (TAT), but might not ascertain antithrombotic efficacy, especially in high-risk patients.

Purpose

To identify a subgroup of patients at high thrombotic risk that might benefit most from TAT over DAT.

Methods

The study was performed in a combined cohort of two randomised controlled trials (WOEST, RE-DUAL PCI) comparing TAT versus DAT after PCI. A Cox proportional hazards model predictive for the composite thrombotic endpoint of cardiovascular death, myocardial infarction (MI), stent thrombosis, and ischaemic stroke was built by stepwise selection of plausible predictor variables. Area under the receiver operating curve (AUC) was obtained, and clinical outcomes (thrombotic endpoint, bleeding [BARC 2,3+5], and all-cause mortality) were compared between the highest quintile of predicted thrombotic risk (high risk) and the remainder of patients (low-intermediate risk). Within the different risk groups, effect of TAT versus DAT was compared.

Results

A total of 3288 patients in the combined WOEST and RE-DUAL cohorts were included in this analysis. Approximately half underwent PCI for acute coronary syndrome. In 250 patients (7.6%) the composite thrombotic endpoint occurred during the first year. The final Cox proportional hazards model predicting thrombotic events contained: left ventricular ejection fraction, 3-vessel disease, MI at index PCI, peripheral artery disease, prior stroke, left circumflex coronary artery stenting, a history of MI, PCI to a bypass graft, and platelet count. The discriminatory capacity of the ischaemic model was fair (AUC 0.68, 95% confidence interval 0.64–0.71). Incidence of thrombotic events and mortality was higher in the high-risk as compared to low-intermediate risk patients (15.8% vs 5.6%, and 8.4% vs 3.2%, respectively, both p<0.001), whereas bleeding was comparable (20.5% vs 19.6%, p=0.60). No statistically significant effect of TAT over DAT was seen with regards to the thrombotic endpoint in both high and low-intermediate risk patients (13.9% vs 17.0%, p=0.36, and 6.5% vs 5.0%, p=0.11, respectively). Bleeding was significantly reduced with DAT versus TAT in both high and low-intermediate risk patients (minus 12.8% and 8.1%, both p<0.02). For low-intermediate risk patients a statistically significant increase in mortality was found with TAT versus DAT (4.2% vs 2.5%, p=0.02), whereas this was not found in high-risk patients (7.2% vs 9.1%, p=0.47).

Conclusions

No significant antithrombotic advantage of TAT over DAT was found in high-risk patients. However, TAT increased bleeding risk in all patients, and increased mortality in low-intermediate risk patients.

Funding Acknowledgement

Type of funding source: None

Zymosan priming protects rats against pulmonary oxygen toxicity

OBJECTIVE

To determine whether zymosan priming protects rats against oxygen toxicity.

METHODS

37 rats were used with 6 treatment groups. 11 received zymosan priming (3 daily i. v. injections with 15 mg zymosan and 2 days rest) before 52 h exposure to either normobaric hyperoxia (ZP group, 5 rats) or air (ZPA group, 6 rats)]. Two other groups received saline (Saline group, 9 rats) or zymosan by i. p. injection (Zip group, 6 rats) before hyperoxia. A fifth group received a non-priming (NP) treatment with zymosan before hyperoxia (ZNP group, 6 rats, single i. v. injection) and a final group received no treatment (Air group, 5 rats). Pleural effusions and lung injury were then assessed.

RESULTS

Saline, Zip or ZNP rats developed massive, proteinaceous pleural effusions indicative of oxygen toxicity while ZP rats did not (0.02 +/- 0.01 ml). The ratios of effusion protein to plasma protein concentration and wet/dry lung weight were also significantly reduced in ZP rats following hyperoxia.

CONCLUSIONS

Zymosan priming protects rats against pulmonary oxygen toxicity.

Effects of S-nitrosation of hemoglobin on hypoxic pulmonary vasoconstriction and nitric oxide flux

Free hemoglobin (Hb) augments hypoxic pulmonary vasoconstriction (HPV), ostensibly by scavenging nitric oxide (NO). However, recent evidence suggests that Hb that is S-nitrosated may act as an NO donor and vasodilator. We studied the effects of oxyHb, Hb that is chemically modified to prevent heme binding or oxidation of NO (cyanometHb), and Hb that is S-nitrosated (SNO-Hb and SNO-cyanometHb) on HPV, expired NO (eNO), and perfusate S-nitrosothiol (SNO) concentration in isolated, perfused rabbit lungs. Perfusate containing either 4 microM oxyHb or SNO-Hb increased normoxic pulmonary artery pressure (Ppa), augmented HPV dramatically, and resulted in an 80% fall in eNO in comparison to perfusion with buffer, whereas 4 microM cyanometHb or SNO-cynanometHb had no effect on these variables. Excess glutathione (GSH) added to perfusate containing SNO-Hb resulted in a 20 to 40% fall in the perfusate SNO concentration, with a concomitant increase in metHb content, without affecting Ppa, HPV, or eNO. In conclusion, free Hb augments HPV by scavenging NO, an effect that is not prevented by S-nitrosation. NO released from SNO-Hb in the presence of GSH does not produce measurable vascular effects in the lung or changes in eNO because of immediate oxidation and metHb formation.

Hemoglobin and red blood cells alter the response of expired nitric oxide to mechanical forces

Expired nitric oxide (NO(e)) varies with hemodynamic or ventilatory perturbations, possibly due to shear stress- or stretch-stimulated NO production. Since hemoglobin (Hb) binds NO, NO(e) changes may reflect changes in blood volume and flow. To determine the role of blood and mechanical forces, we measured NO(e) in anesthetized rabbits, as well as rabbit lungs perfused with buffer, red blood cells (RBCs) or Hb following changes in flow, venous pressure (P(v)), and positive end-expiratory pressure (PEEP). In buffer-perfused lungs decreases in flow and P(v) reduced NO(e), but NO(e) rose when RBCs and Hb were present. These findings are consistent with changes in vascular NO production, whose detection is obscured in blood-perfused lungs by the more dominant effect of Hb NO scavenging. PEEP decreased NO(e) in all perfused lungs but increased NO(e) in live rabbits. The NO(e) fall with PEEP in isolated lungs is consistent with flow redistribution from alveolar septal capillaries to extra-alveolar vessels and decreased surface area or a direct, stretch-mediated depression of lung epithelial NO production. In live rabbits, increased NO(e) may reflect blood flow reduction and decreased Hb NO scavenging and/or autonomic responses that increase NO production. We conclude that blood and systemic responses render it difficult to use NO(e) changes as an accurate measure of lung tissue NO production.

Parathyroid hormone-related protein reduces alveolar epithelial cell proliferation during lung injury in rats

Parathyroid hormone-related protein (PTHrP) is a growth inhibitor for alveolar type II cells and could be a regulatory factor for alveolar epithelial cell proliferation after lung injury. We investigated lung PTHrP expression in rats exposed to 85% oxygen. Lung levels of PTHrP were significantly decreased between 4 and 8 days of hyperoxia, concurrent with increased expression of proliferating cell nuclear antigen and increased incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA in lung corner cells. PTHrP receptor was present in both normal and hyperoxic lung. To test whether the fall in PTHrP was related to cell proliferation, we instilled PTHrP into lungs on the fourth day of hyperoxia. Eight hours later, BrdU labeling in alveolar corner cells was 3.2 +/- 0.4 cells/high-power field in hyperoxic PBS-instilled rats compared with 0.5 +/- 0.3 cells/high-power field in PTHrP-instilled rats (P < 0. 01). Thus PTHrP expression changes in response to lung injury due to 85% oxygen and may regulate cell proliferation.

Effects of the RBC membrane and increased perfusate viscosity on hypoxic pulmonary vasoconstriction

Red blood cells (RBCs) augment hypoxic pulmonary vasoconstriction (HPV) in part by scavenging of nitric oxide (NO) by Hb (Deem S, Swenson ER, Alberts MK, Hedges RG, and Bishop MJ, Am J Respir Crit Care Med 157: 1181-1186, 1998). We studied the contribution of the RBC compartmentalization of Hb to augmentation of HPV and scavenging of NO in isolated perfused rabbit lungs. Lungs were initially perfused with buffer; HPV was provoked by a 5-min challenge with hypoxic gas (inspired O(2) fraction 0.05). Expired NO was measured continuously. Addition of free Hb to the perfusate (0.25 mg/ml) resulted in augmentation of HPV and a fall in expired NO that were similar in magnitude to those associated with a hematocrit of 30% (intracellular Hb of 100 mg/ml). Addition of dextran resulted in a blunting of HPV after free Hb but no change in expired NO. Blunting of HPV by dextran was not prevented by NO synthase inhibition with N(omega)-nitro-L-arginine and/or cyclooxygenase inhibition. RBC ghosts had a mild inhibitory effect on HPV but caused a small reduction in expired NO. In conclusion, the RBC membrane provides a barrier to NO scavenging and augmentation of HPV by Hb. Increased perfusate viscosity inhibits HPV by an undetermined mechanism.

Alveolar hypoxia increases gene expression of extracellular matrix proteins and platelet-derived growth factor-B in lung parenchyma

The walls of pulmonary capillaries are extremely thin, and wall stress increases greatly when capillary pressure rises. Alveolar hypoxia causes pulmonary vasoconstriction and hypertension, and if this is uneven, some capillaries may be exposed to high transmural pressure and develop stress failure. There is evidence that increased wall stress causes capillary remodeling. In this study we exposed Madison strain Sprague-Dawley rats to normobaric hypoxia (10% oxygen) for 6 h or 3 d (short-term group), and for 3 d or 10 d (long-term group). Peripheral lung tissue was then collected and messenger RNA (mRNA) levels were determined for extracellular matrix (ECM) proteins and growth factors. Collagen content (hydroxyproline) was also measured. Levels of mRNA for alpha2(IV) procollagen increased sixfold after 6 h of hypoxia and sevenfold after 3 d of hypoxia, and then decreased after 10 d exposure. Levels of mRNA for platelet-derived growth factor-B (PDGF-B) doubled after 6 h of hypoxia but returned to control values after 3 d. mRNA levels for alpha1(I) and alpha1(III) procollagens and fibronectin were increased after 3 d of hypoxia (by seven- to 12-fold, 1.6- to eightfold, and 12-fold, respectively), then decreased toward control values after 10 d. In contrast, neither levels of mRNA for vascular endothelial growth factor (VEGF) nor collagen content changed. These results suggest that alveolar hypoxia causes vascular remodeling in lung parenchyma, and are consistent with capillary wall remodeling in response to increased wall stress.

High lung inflation increases mRNA levels of ECM components and growth factors in lung parenchyma

Remodeling of pulmonary capillaries occurs after chronic increases in capillary pressure (e.g., mitral stenosis). Also, remodeling of pulmonary arteries begins within 4 h of increased wall stress and is endothelium dependent. We have previously shown that high lung inflation increases wall stress in pulmonary capillaries. This study was designed to determine whether high lung inflation induces remodeling of the extracellular matrix (ECM) in lung parenchyma. Open-chest rabbits were ventilated for 4 h with 9-cmH2O positive end-expiratory pressure (PEEP) on one lung and 1-cmH2O PEEP on the other (High-PEEP group), or with 2-cmH2O PEEP on both lungs (Low-PEEP group). An additional untreated control group was also included. We found increased levels of mRNA in both lungs of High-PEEP rabbits (compared with both the Low-PEEP and untreated groups) for alpha1(III) and alpha2(IV) procollagen, fibronectin, basic fibroblast growth factor, and transforming growth factor-beta1. In contrast, alpha2(I) procollagen and vascular endothelial growth factor mRNA levels were not changed. We conclude that high lung inflation for 4 h increases mRNA levels of ECM components and growth factors in lung parenchyma.

Comparison of two methods for INR determination in a pharmacist-based oral anticoagulation clinic

Warfarin is a commonly used oral anticoagulant that is usually initiated after the definitive diagnosis of a certain thromboembolic disorder or disease. Warfarin therapy will usually be prescribed for 6-12 weeks or more, and some patients may continue therapy throughout life, depending on the type of thromboembolic disorder. Major problems associated with warfarin therapy include adverse effects such as bleeding complications and drug-drug or drug-food interactions. In addition, thromboembolic complications may occur due to subtherapeutic dosages of warfarin. The laboratory reference standards for monitoring warfarin therapy are the prothrombin time (PT) and the International Normalized Ratio (INR). While both the PT or INR will reflect the clinical response in the patient, results reported as INR values have been shown to be more accurate than those reported as PT values. Thirty-two patients were enrolled in this study. Our objectives were to compare INR values measured by both the Coumatrak and conventional laboratory method, and to demonstrate the effects of pharmacist intervention on managing patients receiving warfarin therapy. Results from our study reveal that INR monitoring by Coumatrak is similar to the conventional laboratory method. In addition, our study indicates that patients receiving warfarin therapy can be monitored and managed effectively by pharmacists.

Response of alveolar macrophage-depleted rats to hyperoxia

Recently an alveolar macrophage (AM)-depleted rat model has been characterized and it has been demonstrated that AM are required for the endotoxin-induced tumor necrosis factor (TNF) release into the alveolar space (J Appl Physiol 1993;74:2812-2819). The current study investigated the response of AM-depleted rats to hyperoxia and evaluated the potential role of AM in the pathogenesis of pulmonary O2 toxicity. Rats were insufflated with Hanks' balanced salt solution (HBSS), liposome-encapsulated phosphate-buffered saline (PBS-liposomes), or liposome-encapsulated dichloromethylene diphosphonate (Cl2MDP-liposomes) and 2 days later exposed to 100% O2. The effect of hyperoxia was assessed by parameters of O2-induced lung injury (e.g., hematocrit value, pleural effusion volume, effusion protein to plasma protein ratio, and alveolar lavage fluid protein content), TNF release into the alveolar space, and survival. Insufflation of Cl2MDP-liposomes, but not HBSS or PBS-liposomes, caused a sustained depletion of > 70% AM, which was associated with a slight but significant increase in the number of lavageable neutrophils. Twenty percent of AM-depleted rats survived longer than 74 h of O2 exposure, while all rats insufflated with HBSS or PBS-liposomes died within 74 h (p < .05). No significant differences were detected in alveolar TNF release or in the extent of O2-induced lung injury.

Protection against oxygen toxicity by tracheal insufflation of endotoxin: role of Mn SOD and alveolar macrophages

Endotoxin and the cytokines, tumor necrosis factor and interleukin-1, are known to protect adult rats against O2 toxicity. However, whether the effect of endotoxin is mediated through its direct effect on lung cells or through cytokines is not clear. In this study, we demonstrated that endotoxin at a dosage of 5 micrograms/rat (14-20 micrograms/kg) attenuated O2-induced pulmonary injury and markedly prolonged the survival of rats exposed to 100% O2. Endotoxin was more protective when given by intratracheal insufflation or intravenous injection than by intraperitoneal injection. The endotoxin-induced O2 tolerance was associated with a selective enhancement of pulmonary manganese superoxide dismutase, but not Cu,Zn SOD, mRNA. In addition, depletion of 84% rat alveolar macrophages by liposome-encapsulated dichloromethylene diphosphonate, resulted in a marked reduction (86%) of endotoxin-induced release of tumor necrosis factor into the alveolar space. However, endotoxin was still protective in these alveolar macrophage-depleted animals.

Depletion of alveolar macrophages by liposome-encapsulated dichloromethylene diphosphonate

Alveolar macrophages (AM) play an important role in lung biology. In this study, we demonstrated that tracheal insufflation of liposome-encapsulated dichloromethylene diphosphonate (Cl2MDP-liposome) selectively depleted AMs in rats. Insufflation of a single dose of Cl2MDP-liposomes (80 microliters containing 1.34 mumol of Cl2MDP) but not liposomes containing phosphate-buffered saline resulted in > 70% depletion of AMs starting within 1 day and lasting for > 5 days after insufflation. There was a slight but significant intraalveolar inflammatory response. Insufflation of Cl2MDP also resulted in depletion of AMs; however, it caused cytoplasmic edema of alveolar epithelial cells as well. Depletion of AMs by Cl2MDP-liposomes markedly reduced the endotoxin-induced neutrophil (polymorphonuclear lymphocyte) recruitment and the release of tumor necrosis factor into the alveolar space, suggesting that endotoxin-induced neutrophil recruitment and tumor necrosis factor release were dependent on AMs. This AM-depleted animal model will be useful for studying the in vivo functions of AMs and their role in various physiological and pathological conditions.

Endotoxin extends survival of adult mice in hyperoxia

Research on endotoxin protection from oxygen toxicity is presently limited to the rat model since only rats have been protected by endotoxin. This study reports that endotoxin also extends survival of adult male mice in hyperoxia (greater than 99% oxygen at 1 ATA). Initially, 4-month-old male mice were treated with Boivin-extracted E. coli endotoxin and placed in hyperoxia. Zymosan-primed mice receiving 2 or 10 micrograms endotoxin, and unprimed mice receiving 10-40 micrograms endotoxin, showed moderate protection against hyperoxia; 11/15 Boivin-treated mice survived 120 hours exposure to hyperoxia with time-of-death in hyperoxia = 126.7 +/- 4.4 hours (mean +/- SEM, n = 15). This contrasts with untreated male mice; 0/4 survived 120 hours exposure to hyperoxia with mean survival = 103.5 +/- 3.5 hours. Mice receiving 20 or 60 micrograms Westphal-extracted endotoxin were not protected nor were older female mice receiving 20 micrograms Boivin-extracted endotoxin. This study suggests that age, sex, the extraction method used to obtain endotoxin, and possibly the time of year when endotoxin is administered, are important variables in allowing endotoxin to extend survival of mice in hyperoxia.

Endotoxin protection of rats from pulmonary oxygen toxicity: possible cytokine involvement

Treatment with endotoxin protects rats against lung injury during hyperoxia (greater than 98% oxygen at 1 atmosphere absolute for 60 h). This study demonstrates that serum from endotoxin-treated donor rats also protects recipients from oxygen toxicity. Rats treated with serum from saline-treated donors were not protected, and protection was not explained by residual endotoxin in protective sera. Unlike endotoxin-protected rats (where lung antioxidant enzyme activity is elevated after hyperoxia), postexposure superoxide dismutase (SOD) and catalase (CAT) activities in the lungs of serum-protected rats were not affected. Levels of tumor necrosis factor (TNF) and interleukin 1 (IL-1) in protective sera were increased. This study demonstrates that increases in lung SOD and CAT activity are not required for endotoxin protection from hyperoxia and suggests that TNF and IL-1 may participate in the mechanism of endotoxin protection.

Protection against hyperoxia by serum from endotoxin treated rats: absence of superoxide dismutase induction

Endotoxin greatly reduces lung injury and pleural effusions in adult rats exposed to normobaric hyperoxia (greater than 98% oxygen for 60 hours). This study reports that serum from endotoxin treated donor rats protects serum recipients against hyperoxic lung injury without altering lung superoxide dismutase (SOD) activity. Rats pretreated with endotoxin alone were protected and exhibited an increase in lung SOD activity as previously reported by others. Protection by serum was not due to the transfer of residual endotoxin or SOD. These results show that protection from oxygen toxicity can occur in rats without an increase in lung SOD and suggest that a serum factor may be involved.

Endotoxin protection of rats from pulmonary oxygen toxicity: lack of complement involvement

Endotoxin (1 mg/kg, I.P.) greatly reduces lung damage and pleural edema in rats exposed to greater than 99% oxygen. Endotoxin also activates and depletes complement in vitro. Prior in vivo complement depletion has been shown to protect rats from lung edema in some experimental models. This study was designed to evaluate the possibility that endotoxin may protect rats from oxygen toxicity by activating and thereby depleting complement. We found no significant changes in complement hemolytic activity in serum from endotoxin pretreated rats breathing greater than 99% oxygen at sea level for 60 hours. We also found that complement depletion prior to oxygen exposure failed to protect rats from the lung damage of oxygen toxicity. These results indicate that the mechanism of endotoxin protection from pulmonary oxygen toxicity does not involve complement.

Endotoxin protection of rats from O2 toxicity: chemiluminescence of lung neutrophils

Endotoxin (1 mg/kg body weight, I.P.) greatly reduces pulmonary permeability edema in rats breathing greater than 99% O2. Polymorphonuclear leukocytes (PMN's) have the potential to damage tissue by releasing free radicals or proteolytic enzymes and are needed to produce permeability edema in some models. This study evaluates the possibility that endotoxin protects rats from the pulmonary edema of O2 toxicity by inhibiting free radical release by lung PMN's. The potential of lavaged phagocytes to generate free radicals was determined using zymosan stimulated chemiluminescence (Cl). Values were then expressed as peak C1/10(6) PMN's. We found that PMN peak C1 fell progressively with time of O2 exposure. Peak C1 by PMN's from saline pretreated rats breathing O2 for 3 days was 80% lower than peak C1 by PMN's from paired rats pretreated with endotoxin. Assuming that peak C1 (measured in vitro) inversely reflects the level of free radical release by PMN's prior to lavage, the data suggest that endotoxin protects rats from O2 toxicity by inhibiting in vivo free radical release by lung PMN's.