The effects of prostaglandin E1 on the adult respiratory distress syndrome in septic primates

Sepsis target validation for repurposing and combining complement and immune checkpoint inhibition therapeutics

Introduction: Sepsis is a disease that occurs due to an adverse immune response to infection by bacteria, viruses and fungi and is the leading pathway to death by infection. The hallmarks for maladapted immune reactions in severe sepsis, which contribute to multiple organ failure and death, are bookended by the exacerbated activation of the complement system to protracted T-cell dysfunction states orchestrated by immune checkpoint control. Despite major advances in our understanding of the condition, there remains to be either a definitive test or an effective therapeutic intervention.Areas covered: The authors consider a combinational drug therapy approach using new biologics, and mathematical modeling for predicting patient responses, in targeting innate and adaptive immune mediators underlying sepsis. Special consideration is given for emerging complement and immune checkpoint inhibitors that may be repurposed for sepsis treatment.Expert opinion: In order to overcome the challenges inherent to finding new therapies for the complex dysregulated host response to infection that drives sepsis, it is necessary to move away from monotherapy and promote precision for personalized combinatory therapies. Notably, combinatory therapy should be guided by predictive systems models of the immune-metabolic characteristics of an individual's disease progression.

Targeting of Pseudomonas aeruginosa in the bloodstream with bispecific monoclonal antibodies

We examined the ability of a bispecific mAb reagent, consisting of a mAb specific for the primate erythrocyte complement receptor cross-linked with an anti-bacterial mAb, to target bacteria in the bloodstream in an acute infusion model in monkeys. In vitro studies demonstrated a variable level of complement-mediated binding (immune adherence) of Pseudomonas aeruginosa (strain PAO1) to primate E in serum. In vivo experiments in animals depleted of complement revealed that binding of bacteria to E was <1% before administration of the bispecific reagent, but within 5 min of its infusion, >99% of the bacteria bound to E. In complement-replete monkeys, a variable fraction of infused bacteria bound to E. This finding may have significant implications in the interpretation of animal models and in the understanding of bacteremias in humans. Treatment of these complement-replete monkeys with the bispecific reagent led to >99% binding of bacteria to E. Twenty-four-hour survival studies were conducted; several clinical parameters, including the degree of lung damage, cytokine levels, and liver enzymes in the circulation, indicate that the bispecific mAb reagent provides a degree of protection against the bacterial challenge.

Dibutyryl cyclic AMP attenuates lung responses induced by endotoxin in conscious sheep

Dibutyryl cyclic AMP (DBcAMP) could inhibit the production of prostanoids and modulate the pulmonary vascular responses induced by endotoxin. Diffuse lung injury after endotoxemia in sheep is accompanied by the production of prostanoids and an increase in endothelial permeability. To determine whether exogenous DBcAMP could prevent the endotoxin responses, we measured pulmonary hemodynamics, gas exchange, and lung lymph responses to an intravenous infusion of Escherichia coli endotoxin (1.0 micrograms/kg over 30 min) in unanesthetized sheep in the presence and absence of DBcAMP (30 micrograms/kg/min) infused intravenously for 6 h beginning 1 h before endotoxin infusion or for 4.5 h after 30 min of treatment with endotoxin infusion. We also measured circulating leukocytes and lung lymph and plasma concentrations of thromboxane B2 (TXB2) and prostacyclin (6-keto-PGF1 alpha) metabolites by radioimmunoassay. DBcAMP infusion before endotoxin infusion decreased endotoxin-induced pulmonary hypertension and hypoxemia and markedly attenuated the increased lung lymph flow and lymph protein clearance. DBcAMP after endotoxin only attenuated the increased lung lymph flow and lymph protein clearance. DBcAMP treatment both before and after endotoxin infusion blocked endotoxin-induced increases in lung lymph and plasma TXB2 and 6-keto-PGF1 alpha. DBcAMP did not affect the number of circulating leukocytes. Although DBcAMP alone did not affect the pulmonary and systemic hemodynamics and lung lymph balance, the potential that DBcAMP directly modulates the pulmonary vascular responses to endotoxin as a vasodilator could be expected. We conclude that DBcAMP infusion attenuates lung dysfunction caused by endotoxemia, possibly by preventing prostanoid release and modulating the pulmonary vascular responses.

Concentration-dependent regulatory effects of prostaglandin E1 on human neutrophil function in vitro

Prostaglandin E1 (PGE1) has recently been used clinically as a purported modulator of activated neutrophils in certain forms of the adult respiratory distress syndrome (ARDS). We now report that PGE1 does not have a uniform inhibitory effect upon human neutrophil functions in vitro. Cells were first pretreated with PGE1 followed by incubation with either N-formyl-methionyl-leucyl-phenylalanine (FMLP), phorbol myristate acetate (PMA), or C5a. Lysosomal enzyme release (myeloperoxidase, lysozyme), superoxide anion generation, and chemotaxis were then quantitated. PGE1 alone lacked any appreciable effect on these neutrophil functions. However, neutrophils pretreated with PGE1 (50 to 100 microM) followed by stimulation with FMLP (50 nM) showed as much as 40% inhibition of lysosomal enzyme release compared with control values (p less than 0.0005). In contrast, 0.1 nM to 1 microM PGE1 enhanced FMLP-stimulated enzyme release as much as 50% above baseline control values (p less than 0.05). Preincubation with 0.1 nM PGE1 followed by stimulation with variable doses of FMLP also resulted in enhancement of lysosomal enzyme release by as much as 187 +/- 3% of control values. The enhancing but not inhibitory effects of PGE1 were reversible with serial washing of the neutrophil preparations. Enhancement of enzyme release was not observed when either PMA or C5a was used as a stimulus after PGE1 pretreatment. However, cells pretreated with PGE1 (50 to 100 microM) and subsequently stimulated with C5a showed as much as 40% inhibition of lysosomal enzyme release. Preincubation of neutrophils with PGE1 (1 microM) resulted in a slight (15%) enhancement of chemotaxis to FMLP, but it had no significant effect on C5a-induced chemotaxis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prostaglandin E1 on oxygen delivery and consumption in patients with the adult respiratory distress syndrome. Results from the prostaglandin E1 multicenter trial. The Prostaglandin E1 Study Group

We wanted to determine the long-term effects of a continuous infusion of PGE1 on DO2 and VO2 in patients with ARDS. Data were obtained from a randomized double-blind multicenter trial, which evaluated the effects of PGE1 on survival in patients with ARDS. Patients were stratified according to treatment and outcome: placebo-died (n = 8); PGE1-died (n = 12); placebo-survived (n = 9); and PGE1-survived (n = 8). In the placebo-died group, elevations occurred in VO2, which were associated with increases in O2ext and a constant DO2. In contrast, in the PGE1-died group, elevations in VO2 were associated with increases in DO2 and an unchanged O2ext. In the placebo-survived group, VO2 and DO2 decreased, whereas in the PGE1-survived group, VO2 and DO2 increased; however, O2ext decreased in both of these groups. Since impaired O2ext occurs in ARDS, PGE1-induced elevations in DO2, rather than compensatory increases in O2ext, may achieve better tissue oxygenation. We conclude that although the recently completed multicenter trial failed to show an enhancing effect of PGE1 on survival in patients with advanced ARDS, PGE1 may have important effects on oxygen transport and, therefore, may still have a role in the treatment of early manifestations of ARDS, either alone or in combination with other agents.

Kinetics of leukocyte sequestration in the lungs of acutely septic primates: a study using 111In-labeled autologous leukocytes

To further clarify the role of leukocytes in the pathogenesis of ARDS, we studied the localization and kinetics of leukocyte migration using 111In-labeled autologous white cell scans (111In wbc scans) in four primates made acutely septic with infusions of Escherichia coli. Whole body images were obtained with a gamma camera and were acquired on computer every 15 min beginning immediately after the E. coli infusion. Simultaneous measurements of C5a and peripheral blood leukocyte count were also obtained. Within 5 min of initiating sepsis, three major events occurred: complement activation as measured by the production of C5a, a profound fall in peripheral leukocyte count, and a significant increase in the sequestration of leukocytes in the lungs. The pulmonary sequestration reached a peak at 15 min with a mean of 152% of baseline activity. This sequestration consisted of a population that was predominantly neutrophils. Damage to the pulmonary capillary endothelium was demonstrated by an increase in extravascular lung water. The results support a role for neutrophils and complement as mediators in the pathogenesis of ARDS.

Multiple organ damage caused by tumor necrosis factor and prevented by prior neutrophil depletion

The effect of TNF on nonpulmonary multiple organ damage (MOD) was studied. Since polymorphonuclear leukocytes (PMN) are thought to play an important role in septic or TNF-induced MOD, we investigated both neutrophil sufficient (PMN+) and neutropenic (PMN-) guinea pigs. Sepsis was induced by Escherichia coli administration (2 x 10(9)/kg) or recombinant human TNF (1.4 x 10(6) U/kg) was infused into PMN+ and PMN- guinea pigs. During necropsy, the PMN+/TNF and PMN+/E coli animals exhibited marked damage in the adrenal glands, kidneys and liver as evidenced by hemorrhage, congestion, and PMN sequestration on histopathologic examination. There was also increased tissue albumin accumulation in the adrenal glands, kidneys, spleen, heart, and liver as demonstrated by 125I-labeled albumin determinations. In contrast, the PMN-/TNF group did not reveal histopathologic damage in any organ system and there was no abnormal organ accumulation of 125I-albumin. However, in PMN-/E coli animals, marked histopathologic damage in the adrenal glands and liver was evident. Furthermore, there were marked accumulations of 125I-albumin in the adrenals, heart, kidneys, liver, and spleen. Moreover, the PMN-/E coli guinea pigs had a much greater accumulation (p less than 0.01) of 125I-albumin in the kidneys than any other group including the PMN+/E coli group. Thus, nonpulmonary MOD in guinea pigs is caused by TNF administration and can be prevented by PMN depletion. However, while E coli administration also caused marked nonpulmonary MOD in neutrophil sufficient guinea pigs, equivalent or greater damage was produced in neutropenic animals. This suggests that while TNF-induced MOD may be primarily mediated by PMN, E coli-induced MOD seems to be mediated by more than PMN.

Prostaglandin E1 in the adult respiratory distress syndrome. Benefit for pulmonary hypertension and cost for pulmonary gas exchange

Prostaglandin E1 (PGE1) has been reported to improve survival in patients with the adult respiratory distress syndrome (ARDS). However, the effects of this pulmonary vasodilating compound on gas exchange have been little documented. We therefore measured hemodynamics, blood gases, and the distributions of ventilation-perfusion ratios (VA/Q), using the multiple inert gas elimination technique, at baseline and during infusion of PGE1 0.02 to 0.04 microgram.kg-1.min-1 in six patients with pulmonary hypertension secondary to ARDS ventilated with 10 cm H2O positive end-expiratory pressure. PGE1 decreased systemic arterial mean pressure (-16%) and pulmonary arterial mean pressure (-15%) and increased cardiac index (+20%) and heart rate (+11%). Arterial PO2 decreased from 99 +/- 6 to 77 +/- 8 mm Hg (p less than 0.01, mean +/- SEM) with no change in mixed venous PO2 and in O2 consumption. PGE1 increased true shunt from 21 +/- 4 to 32 +/- 5% of total blood flow (p less than 0.01) with no significant modification in the pattern of VA/Q distribution. Thus, in ARDS, pulmonary hypertension is reduced by PGE1 at the price of a deterioration in pulmonary gas exchange. The clinical relevance of these findings remains to be evaluated.

Granulocyte depletion prevents tumor necrosis factor-mediated acute lung injury in guinea pigs

To examine the role of polymorphonuclear neutrophils (PMN) and other granulocytes in the pathogenesis of acute lung injury caused by tumor necrosis factor alpha (TNF), we compared the permeability edema and pulmonary histopathology in normal (granulocyte sufficient) guinea pigs and in granulocytopenic guinea pigs treated with TNF. Circulating granulocytes were depleted with cyclophosphamide. Two groups of normal animals were treated with either saline (PMN+/Control) or 1.4 x 10(6) U/kg recombinant human TNF (PMN+/TNF). Three granulocytopenic groups were treated with either saline (PMN-/Control), TNF (PMN-/TNF), or intravenous infusion of 2 x 10(9) E. coli strain J96 (PMN-/Sepsis). We measured the amount of 125I-labeled albumin in bronchoalveolar lavage (BAL) fluid and whole lung tissue and the wet/dry lung weight ratio to assess pulmonary transvascular protein flux and edema. We also quantified PMN in BAL fluid and fixed lung tissue. There were no statistically significant differences in any of these parameters between the PMN+/Control, PMN-/Control, or PMN-/TNF groups, except that the PMN+/Control predictably had more PMN/alveolus than the PMN- groups. However, both the PMN+/TNF and the PMN-/Sepsis groups had increased amounts of 125I-labeled albumin in BAL fluid and lung tissue (p less than 0.01) and increased wet/dry lung weight ratios (p less than 0.05), compared to all other groups. Histopathologically, capillary congestion and moderate inflammation were seen in the PMN+/TNF group, and acute inflammation and gross alveolar hemorrhage were seen in the PMN-/Sepsis group.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of acute lung injury in septic guinea pigs by pentoxifylline

Pentoxifylline (PTXF), a drug demonstrated to improve intermittent claudication, is a methylxanthine that increases intracellular cyclic AMP (cAMP) and, unlike theophylline, has few side effects. Because increased cAMP levels have been associated with a decrease in lung injury, we examined the effects of PTXF on acute lung injury in a septic guinea pig model. Five groups of guinea pigs were studied over a period of 8 h. (Group I: saline control injected intravenously with 2 ml of saline; Group II: septic control injected intravenously with 2 x 10(9) Escherichia coli; Group III: E. coli septicemia plus PTXF bolus 20 mg/kg injected 5 min before E. coli injection; Group IV: E. coli septicemia plus PTXF continuous infusion, begun with bolus [20 mg/kg] followed by continuous infusion [20 mg/kg/h] started 60 min before injection of E. coli; Group V: PTXF continuous infusion [20 mg/kg/h] control). Arterial blood gases, arterial blood pressure, and blood WBC counts were monitored serially for 8 h. Lung water (wet-to-dry ratio), the concentration ratio of 125I-labeled albumin in bronchoalveolar lavage (BAL) fluid to that in plasma (albumin index; AI), total cell count in BAL fluid, thiobarbituric-acid-reactive material (TBARM), and the lysosomal enzyme beta-glucuronidase (beta-G) were examined. Lung tissue was studied histologically to assess neutrophil accumulation. Our results showed that E. coli septicemia caused significant peripheral neutropenia and histopathologic evidence of neutrophil alveolitis associated with an increased ratio of TBARM and beta-G in BAL fluid as compared with those in plasma (TBARM BAL ratio and beta-G BAL ratio).(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary vascular pressure-flow plots in canine oleic acid pulmonary edema. Effects of prostaglandin E1 and nitroprusside

We investigated the effects of prostaglandin E1 (PGE1) and of sodium nitroprusside (NP) on multipoint pulmonary arterial pressure (PAP)/cardiac index (Q) plots in 24 pentobarbital-anesthetized and ventilated dogs with pulmonary hypertension secondary to oleic acid lung injury. The PAP/Q plots were rectilinear in all experimental conditions. In control dogs (n = 8), PAP was increased over the entire range of Q studied, from 1 to 4 L/min.m2, 90 min after oleic acid 0.09 ml/kg, and remained so during 2 consecutive 5-point PAP/Q plots, each of them being constructed in about 30 min. Oleic acid increased the extrapolated pressure intercept (p less than 0.001) but not the slope of the PAP/Q plots. Infusion of PGE1 0.4 micrograms/kg.min intravenously (n = 8) reduced PAP at each level of Q, with a reduction of the extrapolated pressure intercept (p less than 0.01) and no change in slope of the PAP/Q plots. In contrast, NP 5 micrograms/kg.min intravenously (n = 8) slightly reduced PAP only at the highest Q studied, without any significant change in extrapolated pressure intercept or slope of PAP/Q plots. Systemic blood pressure was decreased by 21% after PGE1 and by 24% after NP. Neither drug affected Q nor blood gases after oleic acid. The results suggest that pulmonary hypertension secondary to oleic acid pulmonary edema may be due more to an increase in effective outflow pressure of the pulmonary circulation than to an increase in incremental vascular resistance, and that active vasoconstriction contributes to this type of pulmonary hypertension.

Tumor necrosis factor causes increased pulmonary permeability and edema. Comparison to septic acute lung injury

Tumor necrosis factor alpha (TNF), a monokine produced by mononuclear cells in response to bacterial endotoxin (LPS), creates a syndrome similar to septic shock in animal models. To study whether TNF could induce acute lung injury similar to that seen in gram-negative sepsis, we injected recombinant human TNF (rHuTNF alpha) into guinea pigs and monitored arterial blood gases, leukocyte counts, and left atrial (Pla), pulmonary artery (Ppa), and mean arterial pressures (MAP) serially for 8 h. Pulmonary histopathology was assessed microscopically, and cell counts and 125I-labeled albumin (125I-albumin) in bronchoalveolar lavage (BAL) fluid and lung wet/dry weight ratios were determined. Five groups of animals were studied; the 2 TNF groups received high (1.4 X 10(6) U/kg) or low (1.0 X 10(6) U/kg) doses of rHuTNF alpha, the sepsis group received 2 X 10(9) Escherichia coli/kg intravenously, and the control group received saline. An LPS control group receiving 40 ng/kg E. coli LPS was also included because the rHuTNF alpha contained a small amount of LPS as a contaminant. Pulmonary permeability was assessed by studying the Pla and the BAL fluid/plasma 125I-albumin ratio (permeability index). The permeability index was significantly increased in the high-dose TNF (0.0408 +/- 0.0041, p less than 0.05) and sepsis groups (0.0466 +/- 0.0068, p less than 0.01) relative to controls (0.0215 +/- 0.0028). The wet/dry lung weight ratios were also significantly increased in the high-dose TNF (6.07 +/- 0.29, p less than 0.05) and sepsis groups (6.22 +/- 0.30, p less than 0.05) relative to the control group (5.18 +/- 0.20).(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary edema after Escherichia coli peritonitis correlates with thiobarbituric-acid-reactive materials in bronchoalveolar lavage fluid

We developed a new model of acute lung injury caused by live Escherichia coli peritonitis in guinea pigs. Arterial blood gas determinations, arterial blood pressure, and white blood cell counts were monitored serially for 12 h after the injection of either 2 x 10(9) E. coli J96 or saline. Lung water, albumin concentration in bronchoalveolar lavage fluid (BALF) and in lung tissue, WBC counts in BALF, and thiobarbituric-acid-reactive materials (TBARM) in plasma, lung tissue, and BALF were examined. Increased TBARM might be associated with pulmonary injury and are produced either by the generation of lipoperoxides secondary to oxygen-free radicals or as metabolic byproducts of prostanoid metabolism. Lung tissue sections were studied by light microscopy. E. coli peritonitis, as compared with control animals, caused significant peripheral neutropenia, histopathologic evidence of lung inflammation, acidosis, and hypotension. The wet-to-dry lung ratio was increased in the peritonitis group when compared with that in the control group (p less than 0.01). Pulmonary edema in the peritonitis group was associated with significantly increased albumin concentrations in BALF and lung tissue. We report the new finding of increased TBARM concentrations in BALF after E. coli peritonitis (p less than 0.01 and p less than 0.05, respectively). In contrast, plasma TBARM concentrations were unchanged. The levels of TBARM in the BALF correlated significantly with both lung water (p less than 0.01) and lung tissue albumin concentration (p less than 0.01). The measurement of elevated TBARM in BALF may allow acute lung injury to be detected. We conclude that this model may be useful for further studies of acute lung injury caused by E. coli peritonitis.