Benjamin O. Anderson

Mechanisms of neutrophil-mediated tissue injury

Neutrophil-mediated tissue injury (NMTI) is a prominent mechanism of host autodestruction. It is defined by a sequence of events including neutrophil adherence and sequestration, diapedesis, activation, and secretion of toxic compounds. Knowledge of this sequence is valuable because it outlines points at which intervention may be sought. A limitation of these studies comes in the misunderstanding and misapplication of the tests used to analyze these events. We now realize that neutrophil adherence, sequestration, diapedesis, and secretion of toxic compounds can each occur alone without promoting generalized tissue injury. NMTI is a normally localized process that has gone systemically awry. Influencing this system must be selective and controlled because the inflammatory system is a critical component of host defense. As we gain insight into the pathophysiology of NMTI, we hope to find new avenues for therapeutic intervention in critical care.

Multiple organ failure: inflammatory priming and activation sequences promote autologous tissue injury.

Systemic inflammation promotes multiple organ failure through the induction of diffuse microvascular leak. Inflammatory cells such as neutrophils propagate this process. Tissue injury by neutrophils may be viewed as a normal process, inflammation, that has become uncontrolled and generalized. Multiple inflammatory stimuli synergistically promote neutrophil-mediated tissue injury in priming and activation sequences. In some settings, cellular priming is mediated by platelet-activating factor and can be prevented by platelet-activating factor antagonists. Inhibiting cellular priming could be efficacious in the therapy of multiple organ failure.

Neutrophils contribute to TNF induced myocardial tolerance to ischaemia

Sublethal endotoxin (ETX) pretreatment of rats induces protection from cardiac ischaemia-reperfusion injury. This protective state is associated with increased endogenous myocardial catalase activity. Since tumour necrosis factor (TNF) is one mediator of ETX effects, we hypothesized that (TNF) pretreatment of the rat (30 micrograms/kg ip) 36 h prior to cardiac ischaemia-reperfusion could induce myocardial protection. We found that TNF administration increased both myocardial tolerance to ischaemia reperfusion injury (modified Langendorff, buffer perfusion, global, normothermic ischaemia) and myocardial catalase activity at 36 h. Moreover, we found that 6 h after TNF administration, myocardial hydrogen peroxide (H2O2, assessed by aminotriazole-H2O2 inactivation of catalase) and myocardial neutrophil accumulation (assessed by histology) were both increased. When neutrophil function was inhibited either by neutrophil depletion (vinblastine) or by ibuprofen treatments of the rat before TNF, the protection previously apparent at 36 h was blocked. We conclude that TNF can induce myocardial resistance to ischaemia reperfusion injury. This protection is related to prior tissue neutrophil accumulation and concomitant increases in H2O2 levels.

Induction of endogenous tissue antioxidant enzyme activity attenuates myocardial reperfusion injury

Efforts to reduce reperfusion injury have focused on exogenous therapies; however, endogenous attenuation of reperfusion injury can be induced by a single sublethal dose of endotoxin (ETX) prior to ischemia. The purposes of this study were to investigate (i) the early neutrophil-endothelial (PMN-EC) adherence, (ii) the associated myocardial oxidant stress, (iii) the relationship of oxidant stress to antioxidant enzyme activity, and (iv) the correlation of increased antioxidant enzyme activity to myocardial recovery following ischemia/reperfusion (I-R) injury at 36 hr. Rats were administered a sublethal dose (2% of LD50) of endotoxin (500 micrograms/kg, ip, Salmonella typhimurium). At 6 hr, myocardial neutrophil accumulation (histology), hydrogen peroxide (H2O2) levels, and myocardial tissue glutathione (glutathione and oxidized glutathione) levels were determined. At 24 hr myocardial tissue glutathione levels and catalase (CAT) activity were assayed. At 36 hr, myocardial tissue superoxide dismutase, glutathione peroxidase, glutathione reductase, catalase, and glucose-6-phosphate dehydrogenase (G-6-PD) were assayed. At 36 hr, hearts were subjected to a standard (20 min, global, 37 degrees C) ischemic insult followed by reperfusion. At 40 min of reperfusion, ventricular function was assessed (ventricular balloon; ventricular developed pressure +dP/dt, and -dP/dt).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased serum catalase activity in rats subjected to thermal skin injury

We found that: rats subjected to thermal skin injury (burn) had increased serum hydrogen peroxide (H2O2) scavenging activity, serum catalase activity, erythrocyte (RBC) fragility, and edematous lung injury (lung leak) when compared to sham-treated rats. Serum H2O2 scavenging activity was inhibited by addition of sodium azide, a catalase inhibitor. Treatment of rats with the oxygen radical scavenger, dimethylthiourea (DMTU), decreased RBC fragility and lung leak but did not alter increased H2O2 scavenging or catalase activity of serum from rats subjected to skin burn. We conclude that increased serum catalase activity is a consequence of thermal skin injury and that increased serum catalase activity may be a mechanism that modulates H2O2-dependcnt processes following skin burn.

Primed neutrophils injure rat lung through a platelet-activating factor-dependent mechanism.

Bacterial lipopolysaccharide (LPS) promotes transient lung neutrophil sequestration. These LPS-primed neutrophils, when stimulated by an N-formyl peptide (FNLP), promote lung injury. We hypothesized that LPS-primed, FNLP-stimulated neutrophils promote lung injury through a platelet-activating factor (PAF)-dependent mechanism. Rats were pretreated with either saline or WEB2170, a PAF receptor antagonist (10 mg/kg po). One hour after pretreatment, rats were administered intraperitoneal LPS (salmonella typhimurium lipopolysaccharide, 500 micrograms/kg) followed 6 hr later by intravenous FNLP (250 micrograms/kg infused over 30 min). Two hours after the initiation of FNLP infusion, rats were sacrificed and assays were performed to measure: (1) lung neutrophil sequestration with myeloperoxidase (MPO) activity; (2) circulating neutrophil activation with nitroblue tetrazolium (NBT) staining, and (3) lung microvascular leak with 125I-albumin flux. We found that lung myeloperoxidase, circulating neutrophil NBT staining, and lung 125I-albumin flux were increased (P less than 0.05) in saline-pretreated LPS/FNLP rats, relative to control. While lung MPO remained increased (P less than 0.05) in WEB2170-pretreated LPS/FNLP rats, circulating neutrophil NBT and lung 125I-albumin flux were decreased (P less than 0.05) relative to those in saline-pretreated rats. We conclude that PAF mediates LPS/FNLP-induced neutrophil activation and lung injury, but is independent from lung neutrophil sequestration. Thus, lung neutrophil sequestration does not inevitably produce lung injury. Rather, neutrophils can accumulate in the lung without causing lung injury if neutrophil activation can be blocked.

Gut and liver coordinated metabolic response following major torso injury.

Major trauma provokes a stress response which is mediated, in part, via glucagon, catecholamines, and cortisol. These stress hormones modulate the choice of energy substrate for various tissues. While glucose and fatty acids are considered the preferred fuels, ketone bodies (26/ATP/mole) may be a viable alternative. In this study, we measured the concentrations of acetoacetate and beta-hydroxybutyrate (3-OHB) in the portal as well as systemic circulations of 10 critically injured patients (revised trauma score = 6.8 +/- 0.5, injury severity score = 27 +/- 3) during the first 5 postoperative days. At 6 hr postinjury, 3-OHB was elevated in the portal system (0.34 +/- 0.01 mM) while depressed systemically (0.09 +/- 0.02 mM), indicating that the gut was capable of ketogenesis. In contrast, at 24 hr, 3-OHB rose systemically (0.39 +/- 0.02 mM) while decreasing in portal blood (0.09 +/- 0.01 mM) implying gut ketone consumption. Moreover, the systemic ketone body ratio became elevated at 24 hr, suggesting an enhanced liver energy status. In summary, we believe ketogenesis is stimulated by major trauma. Initially, the gut supports ketone concentration in the systemic circulation, whereas, by 24 hr, the gut becomes a ketone consumer and the liver maintains circulating levels.

Platelet activating factor alters receptor-coupled function in the isolated perfused rat heart

Sepsis induces primary myocardial dysfunction. Yet, both hyper- and hypodynamic cardiac states characterize the sepsis syndrome, suggesting a modulatory role of septic mediators. Platelet activating factor (PAF), implicated in the pathogenesis of sepsis, is an endogenous phospholipid with diverse intracellular and extracellular effects. The purpose of this study was to investigate the influence of PAF (1) upon basal mechanical function of the heart, (2) upon receptor-coupled function of the heart, and (3) on basal and stimulated myocardial function at differing concentrations. In order to focus on the relationship between PAF and cardiac mechanical function, rat hearts were isolated and crystalloid perfused using a modified Langendorf preparation. Separate hearts received intracoronary vehicle (5% ethanol, 2.5% BSA) or PAF (20 or 40 microM) as a bolus, followed 10 min later by 0.25 microM isoproterenol (beta-receptor agonist) infusion over 3 min. Both 20 and 40 microM PAF produced a rapid decrease in rate pressure product (RPP = HR X LVDPmax) relative to control (P < 0.05). The depressive effect of PAF upon basal myocardial function did not persist and by 10 min RPP was not different (P > 0.05) among the groups. Isoproterenol infusion increased (P < 0.05) RPP in all groups. However, hearts pretreated with 20 microM PAF demonstrated a greater (P < 0.05) response to beta-adrenergic stimulation relative to vehicle-pretreated controls. This amplified response to isoproterenol was not observed with pretreatment at a higher concentration of PAF (40 microM, P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)