Immediate Effects of Intravenous Endotoxin on Serotonin Concentrations and Blood Platelets

Role of Serotonergic System in Regulating Brain Tumor-Associated Neuroinflammatory Responses

Serotonin signaling regulates wide arrays of both neural and extra-neural functions. Serotonin is also found to affect cancer progression directly as well as indirectly by modulating the immune cells. In the brain, serotonin plays a key role in regulating various functions; disturbance of the normal activities of serotonin leads to various mental illnesses, including the neuroinflammatory response in the central nervous system (CNS). The neuroinflammatory response can be initiated in various psychological illnesses and brain cancer. Serotonergic signaling can impact the functions of both glial as well as the immune cells. It can also affect the tumor immune microenvironment and the inflammatory response associated with brain cancers. Apart from this, many drugs used for treatment of psychological illness are known to modulate serotonergic system and can cross the blood-brain barrier. Understanding the role of serotonergic pathways in regulating neuroinflammatory response and brain cancer will provide a new paradigm in modulating the serotonergic components in treating brain cancer and associated inflammation-induced brain damages.

Does time of CCI measurement affect the evaluation of platelet transfusion effectiveness?

The measurement of corrected count increment at 1-h post-transfusion (CCI-1 h) of platelet concentrate (PC) transfusion is recommended, but in the revised Japanese Guideline (2017) it was changed to "after 10-min to 1-h", following the revision of the guidelines from Western countries. Here, we aimed to investigate on the feasibility to apply the CCI measured at 10-min or 30-min post-transfusion as the surrogate of CCI-1 h. Peripheral blood was collected at 10-min, 30-min and 1-h post-transfusion of PC and the effectiveness of the transfusion was analyzed based on the CCI. In the period from December 2017 to February 2020, 8 patients, who received multiple PC transfusion (total 208) at our institution, were analyzed. We performed the univariate analyses to examine the relationship between CCI value and the categorical variables, p-value <0.1 was obtained for gender (p = 2.91 × 10^-19), fever after transfusion (p = 0.0163). The qualitative variables, namely measurement time (p = 0.0553), also showed p-value <0.1. Using these factors as covariates in the mixed effect model, we found that the measurement time (p = 0.0007) had a significant effect on the CCI value when looking at fixed effects. Although there is a tendency for decreased CCI values with time progression, the slope of the change in the mixed model was -0.00307, indicating that the CCI difference among the 3 measurements was small. Here we provide evidence that CCI measured at 10-min and 30-min post-transfusion give results comparable to those measured at 1-h post-transfusion, under the Japanese practice of platelet transfusion, which relies on 100 % single-donor apheresis PC, and ABO-identical whenever possible.

Non-Alloimmune Mechanisms of Thrombocytopenia and Refractoriness to Platelet Transfusion

Refractoriness to platelet transfusion is a common clinical problem encountered by the transfusion medicine specialist. It is well recognized that most causes of refractoriness to platelet transfusion are not a consequence of alloimmunization to human leukocyte, platelet-specific, or ABO antigens, but are a consequence of platelet sequestration and consumption. This review summarizes the clinical factors that result in platelet refractoriness and highlights recent data describing novel biological mechanisms that contribute to this clinical problem.

Serotonin (5-HT) Shapes the Macrophage Gene Profile through the 5-HT2B-Dependent Activation of the Aryl Hydrocarbon Receptor

Macrophages can either promote or resolve inflammatory responses, and their polarization state is modulated by peripheral serotonin (5-hydroxytryptamine [5-HT]). In fact, pro- and anti-inflammatory macrophages differ in the expression of serotonin receptors, with 5-HT_2B and 5-HT₇ expression restricted to M-CSF-primed monocyte-derived macrophages (M-MØ). 5-HT₇ drives the acquisition of profibrotic and anti-inflammatory functions in M-MØ, whereas 5-HT_2B prevents the degeneration of spinal cord mononuclear phagocytes and modulates motility of murine microglial processes. Because 5-HT_2B mediates clinically relevant 5-HT-related pathologies (valvular heart disease, pulmonary arterial hypertension) and is an off target of anesthetics, antiparkinsonian drugs, and selective serotonin reuptake inhibitors, we sought to determine the transcriptional consequences of 5-HT_2B engagement in human macrophages, for which 5-HT_2B signaling remains unknown. Assessment of the effects of specific agonists and antagonist revealed that 5-HT_2B engagement modifies the cytokine and gene signature of anti-inflammatory M-MØ, upregulates the expression of aryl hydrocarbon receptor (AhR) target genes, and stimulates the transcriptional activation of AhR. Moreover, we found that 5-HT dose dependently upregulates the expression of AhR target genes in M-MØ and that the 5-HT-mediated activation of AhR is 5-HT_2B dependent because it is abrogated by the 5-HT_2B-specific antagonist SB204741. Altogether, our results demonstrate the existence of a functional 5-HT/5-HT_2B/AhR axis in human macrophages and indicate that 5-HT potentiates the activity of a transcription factor (AhR) that regulates immune responses and the biological responses to xenobiotics.

In Vitro Thrombogenicity Testing of Biomaterials

The short- and long-term thrombogenicity of implant materials is still unpredictable, which is a significant challenge for the treatment of cardiovascular diseases. A knowledge-based approach for implementing biofunctions in materials requires a detailed understanding of the medical device in the biological system. In particular, the interplay between material and blood components/cells as well as standardized and commonly acknowledged in vitro test methods allowing a reproducible categorization of the material thrombogenicity requires further attention. Here, the status of in vitro thrombogenicity testing methods for biomaterials is reviewed, particularly taking in view the preparation of test materials and references, the selection and characterization of donors and blood samples, the prerequisites for reproducible approaches and applied test systems. Recent joint approaches in finding common standards for a reproducible testing are summarized and perspectives for a more disease oriented in vitro thrombogenicity testing are discussed.

Autocrine and paracrine regulatory functions of platelet serotonin

Platelets serotonin (5-hydroxytrytamine, 5-HT) uptake and storage in dense granules is tightly regulated by the serotonergic transport system in the blood. Several 5-HT transporters (5-HTTs) have been identified in the vasculature and blood cells, beyond them 5-HTT is the major 5-HT transporter in platelets. Abnormal 5-HT concentrations in the blood plasma or increased platelet 5-HT uptake or abnormal release contribute to the development of various diseases in the vasculature. Consequently, several clinical trials suggested the positive therapeutic effects of 5-HTT blockade in the circulation. Inhibition of 5-HT strongly attenuates autocrine and paracrine functions of platelets, influencing platelet aggregation, vascular contraction, permeability, tissue repair, wound healing, immunity and cancer. Here, we highlight the current state of basic biological research regarding the hemostatic and non-hemostatic functions of platelet-derived 5-HT in normal and disease conditions. We also describe the physiological consequences of targeting platelet 5-HT functions in thrombosis, stroke, inflammation and cancer to overcome common health problems.

The Effects of Serotonin in Immune Cells

Serotonin [5-hydroxytryptamine (5-HT)] plays an important role in many organs as a peripheral hormone. Most of the body’s serotonin is circulating in the bloodstream, transported by blood platelets and is released upon activation. The functions of serotonin are mediated by members of the 7 known mammalian serotonin receptor subtype classes (15 known subtypes), the serotonin transporter (SERT), and by covalent binding of serotonin to different effector proteins. Almost all immune cells express at least one serotonin component. In recent years, a number of immunoregulatory functions have been ascribed to serotonin. In monocytes/macrophages, for example, serotonin modulates cytokine secretion. Serotonin can also suppress the release of tumor necrosis factor-α and interleukin-1β by activating serotonin receptors. Furthermore, neutrophil recruitment and T-cell activation can both be mediated by serotonin. These are only a few of the known immunomodulatory roles of serotonin that we will review here.

Blockade of Thrombopoietin Reduces Organ Damage in Experimental Endotoxemia and Polymicrobial Sepsis

Background and Purpose

Thrombopoietin (TPO), a growth factor primarily involved in thrombopoiesis may also have a role in the pathophysiology of sepsis. In patients with sepsis, indeed, TPO levels are markedly increased, with disease severity being the major independent determinant of TPO concentrations. Moreover, TPO increases and correlates with ex vivo indices of platelet activation in patients with burn injury upon sepsis development, and may contribute to depress cardiac contractility in septic shock. Still, the role of TPO in sepsis pathophysiology remains controversial, given the protective role of TPO in other experimental disease models, for instance in doxorubicin-induced cardiotoxicity and myocardial ischemia/reperfusion injury. The aim of our study was to define the contribution of TPO in the development of organ damage induced by endotoxemia or sepsis, and to investigate the effects of inhibiting TPO in these conditions.

Methods

We synthesized a chimeric protein able to inhibit TPO, mTPOR-MBP, and studied its effect in two murine experimental models, acute endotoxemia and cecal ligation and puncture (CLP) model.

Results

In both models, TPO levels markedly increased, from 289.80±27.87 pg/mL to 465.60±45.92 pg/mL at 3 hours in the LPS model (P<0.01), and from 265.00±26.02 pg/mL to 373.70±26.20 pg/mL in the CLP model (P<0.05), respectively. Paralleling TPO levels, also platelet-monocyte aggregates increased, from 32.86±2.48% to 46.13±1.39% at 3 hours in the LPS model (P<0.01), and from 43.68±1.69% to 56.52±4.66% in the CLP model (P<0.05). Blockade of TPO by mTPOR-MBP administration reduced histological damage in target organs, namely lung, liver, and gut. In particular, neutrophil infiltration and lung septal thickening were reduced from a score of 1.86±0.34 to 0.60±0.27 (P<0.01) and from 1.43±0.37 to 0.40±0.16 (P<0.05), respectively, in the LPS model at 3 hours, and from a score of 1.75±0.37 to 0.38±0.18 (P<0.01) and from 1.25±0.31 to 0.13±0.13 (P<0.001), respectively, in the CLP model. Similarly, the number of hepatic microabscesses was decreased from 14.14±1.41 to 3.64±0.56 in the LPS model at 3 hours (P<0.001), and from 1.71±0.29 to 0.13±0.13 in the CLP model (P<0.001). Finally, the diameter of intestinal villi decreased from 90.69±3.95 μm to 70.74±3.60 μm in the LPS model at 3 hours (P<0.01), and from 74.29±4.29 μm to 57.50±1.89 μm in the CLP model (P<0.01). This protective effect was associated with the blunting of the increase in platelet-monocyte adhesion, and, on the contrary, with increased platelet-neutrophil aggregates in the circulation, which may be related to decreased neutrophil sequestration into the inflamed tissues. Conversely, circulating cytokine levels were not significantly changed, in both models, by mTPOR-MBP administration.

Conclusion

Our results demonstrate that TPO participates in the development of organ damage induced by experimental endotoxemia or polymicrobial sepsis via a mechanism involving increased platelet-leukocyte adhesion, but not cytokine release, and suggest that blocking TPO may be useful in preventing organ damage in patients affected by systemic inflammatory response or sepsis.

Role for platelet glycoprotein Ib-IX and effects of its inhibition in endotoxemia-induced thrombosis, thrombocytopenia, and mortality

OBJECTIVE

Poor prognosis of sepsis is associated with bacterial lipopolysaccharide (LPS)-induced intravascular inflammation, microvascular thrombosis, thrombocytopenia, and disseminated intravascular coagulation. Platelets are critical for thrombosis, and there has been increasing evidence of the importance of platelets in endotoxemia. The platelet adhesion receptor, the glycoprotein Ib-IX complex (GPIb-IX), mediates platelet adhesion to inflammatory vascular endothelium and exposed subendothelium. Thus, we have investigated the role of GPIb-IX in LPS-induced platelet adhesion, thrombosis, and thrombocytopenia.

APPROACH AND RESULTS

LPS-induced mortality is significantly decreased in mice expressing a functionally deficient mutant of GPIbα. Furthermore, we have developed a micellar peptide inhibitor, MPαC (C13H27CONH-SIRYSGHpSL), which selectively inhibits the von Willebrand factor -binding function of GPIb-IX and GPIb-IX-mediated platelet adhesion under flow without affecting GPIb-IX-independent platelet activation. MPαC inhibits platelet adhesion to LPS-stimulated endothelial cells in vitro and alleviates LPS-induced thrombosis in glomeruli in mice. Importantly, MPαC reduces mortality in LPS-challenged mice, suggesting a protective effect of this inhibitor during endotoxemia. Interestingly, MPαC, but not the integrin antagonist, Integrilin, alleviated LPS-induced thrombocytopenia.

CONCLUSIONS

These data indicate an important role for the platelet adhesion receptor GPIb-IX in LPS-induced thrombosis and thrombocytopenia, and suggest the potential of targeting GPIb as an antiplatelet strategy in managing endotoxemia.

Bidirectional crosstalk between platelets and monocytes initiated by Toll-like receptor: an important step in the early defense against fungal infections?

Monocytes are important in the defense against fungal infections due to their phagocytic and immunoregulatory functions. Platelets also contribute in such immune responses through their release of soluble mediators, including chemokines as well as several other soluble mediators. Both monocytes and platelets express several Toll-like receptors (TLRs) that can recognize fungal molecules and thus initiate intracellular signaling events. TLR ligation on monocytes and platelets may thereby be an early immunological event and function as an initiator of a local proinflammatory crosstalk between platelets and monocytes resulting in (i) monocyte-induced increase of platelet activation and (ii) platelet-associated enhancement of the monocyte activation/function. These effects may have clinical implications both for the efficiency of antifungal treatment and for the predisposition to fungal infections, for example, increased predisposition in patients with thrombocytopenia/monocytopenia due to chemotherapy- or disease-induced bone marrow failure.

Lipopolysaccharide signaling without a nucleus: kinase cascades stimulate platelet shedding of proinflammatory IL-1β-rich microparticles

Platelets contain unspliced heteronuclear IL-1β RNA, which is rapidly spliced and translated upon activation. LPS is a superior agonist for this atypical platelet response, but how LPS induces proinflammatory cytokine production in anucleate cells lacking NF-κB is unknown. Platelets express functional TLR4, and stimulation by LPS induced rapid splicing, translation, and secretion of mature IL-1β after caspase-1 processing. LPS stimulated microparticle shedding, and secreted IL-1β was exclusively present in these particles. Microparticles from LPS-stimulated platelets induced VCAM-1 production by cultured human endothelial cells, and blockade of endothelial IL-1β receptor with IL-1 receptor antagonist completely suppressed endothelial activation. Splicing was posttranscriptional as the SR kinase inhibitor TG003 blocked IL-1β RNA production by platelets, but not by monocytes, and was dependent on exogenous CD14--a property of platelets. We used a combination of small-molecule inhibitors, cell-penetrating chimeric peptide inhibitors, and gene-targeted animals to show splicing required MyD88 and TIRAP, and IRAK1/4, Akt, and JNK phosphorylation and activation. Traf6 couples MyD88 to the Akt pathway and, remarkably, a Traf6 interacting peptide-antennapedia chimera was more effective than LPS in stimulating IL-1β splicing. The Traf6 chimera did not, however, stimulate microparticle shedding, nor was IL-1β released. We conclude LPS-induced kinase cascades are sufficient to alter cellular responses, that three signals emanate from platelet TLR4, and that Akt and JNK activation are sufficient to initiate posttranscriptional splicing while another event couples microparticle shedding to TLR4 activation. Platelets contribute to the inflammatory response to LPS through production of microparticles that promote endothelial cell activation.

The role of inflammation in regulating platelet production and function: Toll-like receptors in platelets and megakaryocytes

Platelets have been extensively studied as hemostatic regulators, stopping uncontrolled flow of blood from an injured vessel and allowing for repair. However, multiple studies have shown that platelets can interact with bacterial proteins, particularly seen during sepsis and inflammation. Immune cells recognize pathogens through Toll-like Receptors (TLRs). These same receptors allow platelets to recognize bacterial proteins and regulate platelet immunity and function. This review examines the TLRs expressed on platelets and megakaryocytes and how these receptors affect the function of these cells. Through TLRs, platelets go beyond hemostatic regulation and play a pivotal role in inflammation and infection.

Lipopolysaccharide stimulates platelet secretion and potentiates platelet aggregation via TLR4/MyD88 and the cGMP-dependent protein kinase pathway

Bacterial LPS induces rapid thrombocytopenia, hypotension, and sepsis. Although growing evidence suggests that platelet activation plays a critical role in LPS-induced thrombocytopenia and tissue damage, the mechanism of LPS-mediated platelet activation is unclear. In this study, we show that LPS stimulates platelet secretion of dense and alpha granules as indicated by ATP release and P-selectin expression, and thus enhances platelet activation induced by low concentrations of platelet agonists. Platelets express components of the LPS receptor-signaling complex, including TLR (TLR4), CD14, MD2, and MyD88, and the effect of LPS on platelet activation was abolished by an anti-TLR4-blocking Ab or TLR4 knockout, suggesting that the effect of LPS on platelet aggregation requires the TLR4 pathway. Furthermore, LPS-potentiated thrombin- and collagen-induced platelet aggregation and FeCl(3)-induced thrombus formation were abolished in MyD88 knockout mice. LPS also induced cGMP elevation and the stimulatory effect of LPS on platelet aggregation was abolished by inhibitors of NO synthase and the cGMP-dependent protein kinase (PKG). LPS-induced cGMP elevation was inhibited by an anti-TLR4 Ab or by TLR4 deficiency, suggesting that activation of the cGMP/protein kinase G pathway by LPS involves the TLR4 pathway. Taken together, our data indicate that LPS stimulates platelet secretion and potentiates platelet aggregation through a TLR4/MyD88- and cGMP/PKG-dependent pathway.

In vivo effects of lipopolysaccharide and TLR4 on platelet production and activity: implications for thrombotic risk

Gram-negative bacteria release LPS, which activates Toll-like-receptor-4 (TLR4) in the host, initiating an inflammatory response to infection. Infection increases risk for thrombosis. Platelets contribute to defense from infection and to thrombosis. Experiments were designed to determine whether LPS, through TLR4 signaling, affects platelet phenotype. Platelet responses in wild-type (WT) mice and mice that lack the TLR4 gene (dTLR4) were compared following a single nonlethal injection of LPS (0.2 mg/kg iv). Compared with WT mice, mice without TLR4 had fewer circulating platelets with lower RNA content and were less responsive to thrombin-activated expression of P-selectin but were equally sensitive to aggregation or ATP secretion. One week following the LPS injection, the time it takes for the circulating platelet pool to turnover, the number of circulating platelets, thrombin-induced expression of P-selectin, and collagen-activated aggregation were increased comparably in both groups of mice. Therefore, the change of the platelet pool to an activated phenotype 1 wk after a single exposure to LPS appears to arise from a process that is independent of TLR4. The persistence of the effect 1 wk after the injection suggests that the changes reflect an action of LPS on megakaryocytes and their platelet progeny rather than on circulating platelets, which would have been cleared.

Complement-dependent accumulation and degradation of platelets in the lung and liver induced by injection of lipopolysaccharides

We found unique behaviors among platelets within a few minutes of the intravenous injection of lipopolysaccharide (LPS) into mice. Platelets accumulated primarily in the liver at lower doses of LPS, but at higher doses they accumulated largely in the lungs. When the platelets accumulated in these organs were degraded, there was a rapid anaphylactoid shock. The platelet response depended on the strain of mouse and on the source of LPS. Of various LPSs tested, the LPS from the smooth type of Klebsiella O3 (KO3-S LPS) was the most potent at inducing the platelet response and shock. K-76 monocarboxylic acid, an inhibitor of complement C5, effectively prevented the KO3-S LPS-induced degradation (but not accumulation) of platelets and the ensuing rapid shock in BALB/c mice. Moreover, in DBA/2 mice (which are deficient in complement C5), platelets accumulated in the lungs and liver in response to KO3-S LPS but soon returned to the circulation without degradation, and there was no rapid shock. The LPS from the rough type of KO3 induced an accumulation of platelets in the liver and lungs but not a degradation of platelets. On the basis of these results and those reported by other investigators, we propose that in the platelet response to LPS, the lectin pathway to form C3 convertase from C4 and C2 is involved in the rapid accumulation of platelets in the liver and lungs and that the pathway from C5 to C9 is involved in the destruction of platelets and the consequent anaphylactoid shock.

The antiplatelet activity of Escherichia coli lipopolysaccharide is mediated through a nitric oxide/cyclic GMP pathway

In this study, Escherichia coli LPS dose-dependently (100-500 microg/ml) and time-dependently (10-60 min) inhibited platelet aggregation in human and rabbit platelets stimulated by agonists. LPS also dose-dependently inhibited the intracellular Ca2+ mobilization in human platelets stimulated by collagen. In addition, LPS (200 and 500 microg/ml) significantly increased the formation of cyclic GMP but not cyclic AMP in platelets. LPS (200 microg/ml) significantly increased the production of nitrate within a 10-min incubation period. Furthermore, LPS also dose-dependently inhibited platelet aggregation induced by PDBu (30 nmol/l), a protein kinase C activator. These results indicate that the antiplatelet activity of E. coli LPS may be involved in the activation of a nitric oxide/cyclic GMP pathway in platelets, resulting in inhibition of platelet aggregation. Therefore, LPS-mediated alteration of platelet function may contribute to bleeding diathesis in septicemic and endotoxemic patients.

Effects of bacterial endotoxin on rabbit platelets. I. Platelet aggregation and release of platelet factors in vitro

Incubation of platelet-rich rabbit plasma with E. coli endotoxin at 37°C results in platelet aggregation and transfer of platelet 5-hydroxytryptamine to plasma. Release of 5HT is influenced by dose of endotoxin, type of anticoagulant, and temperature of incubation. A heat-labile plasma factor is necessary for the platelet-endotoxin interaction. Additional studies have shown that incubation of endotoxin with platelet-rich rabbit plasma also results in release of platelet phospholipid and bactericidins active against B. subtilis.

Mechanisms involved in the antiplatelet activity of Escherichia coli lipopolysaccharide in human platelets

In this study, Escherichia coli lipopolysaccharide (LPS) dose-dependently (100-300 microg/ml) and time-dependently (10-60 min) inhibited platelet aggregation in human platelets stimulated by agonists. LPS also dose-dependently inhibited the phosphoinositide breakdown and the intracellular Ca+2 mobilization in human platelets stimulated by collagen. LPS (300 microg/ml) also significantly inhibited the thromboxane A2 formation stimulated by collagen in human platelets. Moreover, LPS (100-300 microg/ml) dose-dependently decreased the fluorescence of platelet membranes tagged with diphenylhexatrience. In addition, LPS (200 and 300 microg/ml) significantly increased the formation of cyclic GMP but not cyclic AMP in platelets. LPS (200 microg/ml) also significantly increased the production of nitrate within a 30 min incubation period. Rapid phosphorylation of a platelet protein of Mr 47,000, a marker of protein kinase C activation, was triggered by phorbol-12-13-dibutyrate (PDBu, 50 nM). This phosphorylation was markedly inhibited by LPS (200 microg/ml) within a 30 min incubation period. These results indicate that the antiplatelet activity of LPS may be involved in two important pathways. (1) LPS may induce conformational changes in the platelet membrane, leading to change in the activity of phospholipase C. (2) LPS also activated the formation of nitric oxide (NO)/cyclic GMP in human platelets, resulting in inhibition of platelet aggregation. Therefore, LPS-mediated alteration of platelet function may contribute to bleeding diathesis in septicaemic and endotoxaemic patients.

Induction mechanism of small intestinal lesions caused by intravenous injection of endotoxin in rats

The pathogenesis of intestinal damage caused by bolus intravenous injection of endotoxin (ETX; 3 mg/kg) was investigated. Administration of ETX to rats induced reddish discoloration suggestive of bleeding, increased hemoglobin amounts, and leakage of plasma protein in the intestine. However, light microscopic examination of the intestine demonstrated blood congestion of the microvessels. Plasma accumulation was partially inhibited by combined pretreatment with a histamine H1 antagonist and a serotonin (5-HT) antagonist. Neither a 5-lipoxygenase inhibitor, a soybean trypsin inhibitor, nor atropine was observed to inhibit plasma accumulation. Both the intestinal leakage of plasma and the accumulation of hemoglobin were completely inhibited by indomethacin, a selective thromboxane A synthetase inhibitor (OKY 1581), and a stable PGI2 analogue (beraprost). Intravital microscopic observation of the microvessels of the small intestinal villi demonstrated microthrombus formation within several minutes after the injection of ETX, and pretreatment with OKY 1581 attenuated the formation of microthrombus. Platelet counts decreased significantly 10 min after ETX administration, and the decrease was not inhibited by pretreatment with either OKY 1581 or beraprost. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were not prolonged. These observations thus suggest that microcirculatory disturbances by platelet thrombus, which are mediated by thromboxane A2 at least in part, play an important role in ETX-induced intestinal damage.

Effects of bacterial endotoxin and platelet activating factor (PAF) on human platelet aggregation in native whole blood

The effect of bacterial endotoxins E. coli 0111:B4 or S. minnesota and platelet activating factor (1-0-alkyl-2-acetyl-SN-glycero-3-phosphorylcholine) on platelet aggregation in native whole blood (NWB) were evaluated by impedance aggregometry. In the absence of anticoagulants the patterns of impedance changes associated with aggregation were distinct from those of clotting. Both E. coli 0111:B4 and S. minnesota endotoxins shortened the time to clot formation, but impedance changes suggestive of accelerated platelet aggregation were minimal or absent. In contrast, PAF caused an increased impedance, with oscillations characteristic of aggregation, which in some instances was superseded by the smooth impedance change associated with clotting. E. coli 0111:B4 endotoxin blocked aggregation and delayed the onset of clotting after PAF, whereas S. minnesota endotoxin accelerated platelet aggregation by PAF in ten of thirteen experiments. Incubation of E. coli 0111:B4 endotoxin and PAF markedly enhanced aggregation by PAF, whereas the effect of S. minnesota was variable. Although E. coli 0111:B4 and S. minnesota endotoxins accelerated clotting but not platelet aggregation of human NWB in vitro, their interaction with PAF is complex, depending on the type of endotoxin and individual reactivity. The findings suggest that endotoxin could interact with PAF to significantly augment possible hemorrhagic and/or thrombotic complications of septic shock in humans.

Species variability in the cardiovascular and hematologic effects of zymosan-activated plasma infusion

The anaphylatoxins have been implicated in the pathogenesis of endotoxin shock and the adult respiratory distress syndrome. Both endotoxin and zymosan activate the complement pathway. Because there are marked species differences in the cardiovascular and hematologic effects of endotoxin infusion, the purpose of this study was to compare the effects of zymosan-activated plasma (ZAP) infusion in dogs, sheep, and baboons. ZAP was infused (0.11 ml/kg/min for 60 min) into dogs (n = 5), baboons (n = 5), and sheep (n = 3). The infusion of ZAP resulted in significant changes in heart rate (HR) (P less than 0.03), mean arterial pressure (MAP) (P less than 0.002), pulmonary artery pressure (PAP) (P less than 0.004), cardiac index (CI) (P less than 0.034), and extra vascular lung water (EVLW) (P less than 0.001). A specific difference between the species' response to ZAP infusion was present when evaluating the effect of ZAP on MAP (P less than 0.02), HR (P less than 0.003). EVLW (P less than 0.001), platelet count (P less than 0.01), and white blood cell count (P less than 0.01). The main species differences in the changes in MAP, HR, and platelet count were an increase in MAP, decrease in HR, and decrease in platelet count that occurred in dogs. The species difference in the WBC count was the result of ZAP-induced neutropenia in sheep versus a leukocytosis in dogs. Unlike dogs and baboons, sheep developed an increase in EVLW. Like endotoxin, the cardiovascular and hematologic effects of ZAP infusion are species dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Ibuprofen prevents Pasteurella hemolytica endotoxin-induced changes in plasma prostanoids and serotonin, and fever in sheep

Intravenous infusion of Pasteurella hemolytica endotoxin caused marked increases in the plasma levels of thromboxane B2 (TxB2), prostaglandins (PG) and serotonin in sheep. The control values for TxB2, 6-keto-PGF1 alpha, PGF2 alpha, and serotonin before endotoxin infusion averaged 283 +/- 53 (standard error of mean), 281 +/- 14 and 199 +/- 27 pg/ml and 57 +/- 3 ng/ml, respectively. At 50 min during endotoxin infusion, these values were increased to their maximum of 376, 339, 325 and 202% of control, respectively. Body temperature increased from the control value of 39.5 +/- 0.1 degrees C to a maximum of 41.5 +/- 0.1 degrees C at 200-300 min of infusion. In the second part of this study, we have examined the effects of ibuprofen on endotoxin-induced increases in plasma PG, TxB2, and serotonin levels and body temperature. The control values for TxB2, 6-keto-PGF1 alpha, PGF2 alpha, and temperature prior to ibuprofen and endotoxin infusion averaged 238 +/- 35, 335 +/- 44 and 248 +/- 28 pg/ml, 65 +/- 3 ng/ml and 40.1 +/- 0.2 degrees C, respectively. A loading dose (15 mg/kg) of ibuprofen was followed by infusion of endotoxin (12 micrograms/kg) and ibuprofen (43.3 mg/kg) over 500 min. Plasma levels of 6-keto-PGF1 alpha and serotonin increased only to 131 and 149% of control at 50 min of infusion, and levels of PGF2 alpha and TxB2 decreased to 50 and 80% of control at 100 and 150 min of infusion, respectively. Temperature remained unchanged. Ibuprofen effectively suppressed endotoxin-induced increases in the plasma levels of TxB2, 6-keto-PGF1 alpha, PGF2 alpha, and serotonin and body temperature. It was concluded from the present study that nonsteroidal anti-inflammatory drugs as an adjunct to antibiotic therapy might have a rational basis in treatment of endotoxin toxicity.

Thrombocytopenia and laboratory evidence of disseminated intravascular coagulation after shunts for ascites in malignant disease

Twenty-eight peritoneovenous shunts were placed to relieve ascites in 26 patients with a variety of underlying malignancies. Nine of the patients had documented liver metastases and hyperbilirubinemia. Severe thrombocytopenia with laboratory evidence of disseminated intravascular coagulation (DIC) occurred in four of these nine patients following shunt placement. Relative or absolute thrombocytopenia was also commonly observed in this series. Other complications included pulmonary edema, ventricular tachycardia, culture-negative fever, pneumonia, and late shunt occlusion. Good palliation, with relief of abdominal pain or respiratory compromise, was achieved in 57% of these patients. Our experience suggests that DIC following peritoneovenous shunts in patients with malignancy may be more common than previously reported, although not as frequent as the incidence of DIC associated with shunt placement for cirrhotic ascites. Platelet aggregation or Factor X activation by ascitic fluid and failure of the liver to inactivate activated clotting factors may play a role in this coagulopathy. Because of the risk of potentially fatal DIC, palliative peritoneovenous shunts should be considered with caution in patients with liver metastases and hyperbilirubinemia.

Endotoxin-mediated inhibition of human platelet aggregation

A variety of endotoxins, when added to human platelet-rich plasma (PRP) or to suspensions of washed platelets (WP), demonstrated an inhibitory effect on platelet aggregation induced by various aggregating agents. Endotoxin blocked the release of 14C serotonin from platelets but had no influence on cyclic AMP production. Endotoxin did not interfere with thromboxane generation by platelets. However, endotoxin-treated platelets failed to respond to added thromboxane. The inhibitory effect of endotoxin on platelet aggregation was more pronounced in the presence of ionophore A23187 as compared to other aggregating agents and was effectively reversed by calcium but not by magnesium, another divalent cation. Furthermore, endotoxin failed to inhibit the ristocetin-induced agglutination of formaldehyde-fixed platelets; a non-calcium dependent phenomenon. These findings appear to suggest that endotoxin-mediated inhibitory activity of platelet aggregation is related to the interference in the role of calcium. The antiaggregatory activity of endotoxin appears to be due to a direct and rapid action on platelets and not due to a non-specific binding, as the effect was not abolished by washing the endotoxin-incubated platelets. Endotoxin-mediated alteration of platelet function may contribute to bleeding diathesis in septecemic and endotoxemic patients.

Ultrastructural study on the release reaction of the platelet. Release I

The ultrastructural changes of human or rabbit platelets in response to release inducers I were studied by using isolated cells from the respective platelet rich plasma. The changes of platelets were more dynamic in ADP than those in epinephrine and endotoxin though common changes occurred in all cases. In the platelets on release reaction, there were well preserved alpha-granules and the disappearance of very dense granules accompanied by simultaneous appearance of round vesicles. The contraction wave of the microtubules rarely occurred and the microfibrils increased in amount in the cytoplasm of platelets. The canalicular system in response to ADP alone is morphologically interpreted as the open canalicular system. On the other hand, epinephrine and endotoxin did not cause obvious morphological changes of the open canalicular system. When the contents of very dense granules alone were discharged leaving the round vesicles behind in the release I, it seems likely that the microfibrils play a more important role than the microtubules. Furthermore, the author suggests that the dense tubular system or third canalicular system may play an essential role for the release I as a secretory pathway in place of the open canalicular system.

Endotoxic shock in the primate: effects of aspirin and dipyridamole administration

A primate model was utilized to study the cardiovascular and coagulation effects of endotoxic shock. The therapeutic effectiveness of drugs such as aspirin and dipyridamole, which diminish platelet aggregation and adherence, were evaluated. From the data, it appears that the kidney is a target organ in endotoxic shock, at least when a bolus injection of endotoxin is administered. The precipitate falls in the renal artery flow (p less than 0.01) and platelet count (p less than 0.01), which occur 3 minutes after the intravenous injection of endotoxin, can be prevented in part by pretreatment with aspirin (40 mg/kg of body weight). The changes in the coagulation profile were of less magnitude, and the fibrin degradation products appeared late in the group pretreated with aspirin as compared to the other groups. The combination of dipyridamole and aspirin was not as effective as aspirin alone in achieving the apparently protective effect. The study suggests that the administration of aspirin to patients with gram-negative infections may be beneficial.

Role of thromboxane and prostacyclin in pulmonary vasomotor changes after endotoxin in dogs

Cyclooxygenase inhibitors prevent the pulmonary vasomotor changes in response to low-dose endotoxin. We, therefore, explored the role of two highly vasoactive prostanoids, thromboxane A(2), a vasoconstrictor, and prostacyclin, a vasodilator, in the transient pulmonary vasoconstriction and subsequent loss of alveolar hypoxis vasoconstriction (AHPV) that follows endotoxin. AHPV was tested in the dog with a double-lumened endotracheal tube allowing ventilation of one lung with nitrogen as a hypoxic challenge while the other lung was ventilated with oxygen to maintain systemic oxygenation. Relative distribution of perfusion to the two lungs was assessed with intravenous (133)Xe and external scintillation detectors. The stable metabolites of thromboxane and prostacyclin, i.e., thromboxane B(2) and 6-keto-prostaglandin F(1alpha) were measured in plasma with radioimmunoassay. 15 mug/kg i.v. of endotoxin induced no rise in pulmonary vascular resistance (PVR), but prevented AHPV so that the initial 33% (+/-2 SEM) decrease in perfusion to the hypoxic lung became only a 2% (+/-1) decrease. Circulating levels of thromboxane and prostacyclin concurrently rose (P < 0.01) from nondetectable levels to 380 pg/ml (+/-40) and 360 pg/ml (+/-130). 150 mug/kg of endotoxin induced a transient rise in PVR from 4.09 to 9.00 mm Hg/liter per min in association (r = 0.89, P < 0.01) with a sharp rise in thromboxane levels to 4,460 pg/ml (+/-1,350) whereas prostacyclin levels were elevated less markedly to 550 pg/ml (+/-400). Prostaglandin F(2alpha), another vasoconstrictor, was not elevated. 30 min after endotoxin when PVR was again base line and AHPV lost, thromboxane fell significantly (P < 0.01) to 2,200 pg/ml (+/-1,100) whereas prostacyclin remained elevated at 360 pg/ml (+/-135), a level similar to that seen when 15 mug/kg of endotoxin induced loss of AHPV. Indomethacin prevented the rise in thromboxane and prostacyclin after endotoxin as well as the changes in pulmonary vasomotor tone. Thus, a complex interaction between thromboxane and prostacyclin is involved in the pulmonary vasomotor response to low-dose endotoxin.

Prostacyclin reversal of lethal endotoxemia in dogs

Severe endotoxemia, a condition where microembolization and intravascular coagulation are thought to play important roles, was treated experimentally with prostacyclin (PGI(2)). In a study of 24 dogs, 8 control animals injected with 1.75 mg.kg(-1) of endotoxin died within 24 h. Six animals given intravenous aspirin 100 mg/kg, 30 min after endotoxin died. 9 of 10 dogs infused with 100 ng PGI(2).kg(-1).min(-1) for 3 h, given 30 min after the injection of endotoxin survived 24 h (P < 0.025). Injection of endotoxin resulted in a: (a) maximal 62% fall in mean arterial pressure (P < 0.001); (b) transient doubling of mean pulmonary arterial pressure (P < 0.001); (c) initial 70% drop in cardiac index (P < 0.001); (d) decline in blood platelets from 213,700 to 13,700/mm(3) (P < 0.001), and leukocytes from 7,719 to < 750/mm(3) (P < 0.001); (e) depressed urine output (P < 0.001); (f) 34% decrease in blood fibrinogen (P < 0.01) and an increase in fibrin degradation products > 50 mug/ml (P < 0.001); (g) fivefold increase in circulating cathepsin D titer (P < 0.005) and (h) increase in blood norepinephrine (P < 0.005), dopamine (P < 0.005), and epinephrine (P < 0.001). Aspirin treatment led to an increase in mean arterial pressure (P < 0.001) and mean pulmonary arterial pressure (P < 0.005), but cardiac index, urine flow, platelets, leukocytes, fibrin degradation products, and cathepsin D levels remained similar to untreated controls. After infusion of PGI(2) there was a: (a) prompt increase of cardiac index to base-line levels; (b) late increase in mean arterial pressure (P < 0.005) after the discontinuation of PGI(2) treatment (c) restoration of urine output; (d) increase in circulating platelets to levels still below base line but above untreated control animals (P < 0.05); (e) no effect on circulating leukocyte levels; (f) fall in fibrin degradation products to 11.2 mug/ml (P < 0.05); (g) decline in cathepsin D levels to values 60% lower than the untreated controls (P < 0.025); and (h) reduction in plasma norepinephrine levels to base line at 4 h (P < 0.005). Although the mode of PGI(2) action is not clear, it is effective in the treatment of experimental endotoxemia.

Effect of gram-negative bacterial lipopolysaccharide-derived polysaccharides, glycolipids, and lipopolysaccharides on rabbit and human platelets in vitro

The in vitro effect of gram-negative bacterial LPS-derived polysaccharide (PS), glycolipid (GL), and lipopolysaccharide (LPS) was investigated both on rabbit and human platelets. Rabbit platelets aggregated when they were treated with either GL or LPS, but no aggregation occurred when PS was used. No aggregation occurred when human platelets were treated with LPS, PS, or GL. However, when either human or rabbit platelets were treated with LPS-antibody complexes (LPS-ab), aggregation took place. Guinea-pig serum inhibited the aggregation caused by LPS-ab, but had no effect on rabbit platelet aggregation caused by LPS or GL alone. The factor(s) in guinea-pig serum that inhibited aggregation was heat-stable. These results suggest that there may be two different mechanisms involved in rabbit platelet aggregation by endotoxin in vitro. Using human platelets, only one mechanism was observed.

Role of platelets in the pathogenesis of canine endotoxin shock

Endotoxin-platelet interactions are thought to be of major importance in the response of dogs and other species to bacterial endotoxin; the mechanisms postulated are: (i) the release of vasoactive substances, (ii) the formation of occlusive platelet aggregates, and (iii) induction of intravascular coagulation. The role of platelets in canine endotoxin shock was examined in animals with thrombocytopenia induced by estrogen pretreatment (less than 10,000 platelets/mm3) and in controls. After intravenously administered endotoxin, the hemodynamic responses, mortality, and gross necropsy findings were similar in both groups. These data indicate that endotoxin-platelet interactions are not determinative in the pathogenesis of canine endotoxin shock.

The early diagnosis of gram negative septicemia in the pediatric surgical patient

Ninety-three postoperative patients 1 day to 13 years of age had blood cultures, limulus lysate assay, determination of fibrin degradation products, white blood cell and platelet counts. Seven groups were studied. The limulus lysate assay was often positive (64%) in the presence of gram negative septicemia but there were false positives and negatives. The tests for fibrin degradation products were inconsistent. The white blood cell count was low in babies with gram negative septicemia. One hundred per cent of the infants with gram negative septicemia had a platelet count below 150,000; 71% below 100,000 (average 67,000 septic babies, 257,000 non-septic babies). The drop in platelet count with gram negative septicemia was abrupt---as much as 222,000 in 24 hours. Platelets increased when therapy was effective. Two children with gram negative septicemia had platelet counts of 50,000 and 20,000. The platelet count for patients with gram positive septicemia was 299,000, and above 150,000 in all children with ruptured and non-ruptured appendicitis and major surgery without gram negative septicemia. It was concluded that serial measurements of platelet count in the postoperative infant and child was a rapid and reliable method for early detection of gram negative septicemia and changes in platelet count in response to treatment was an indicator of the effectiveness of therapy.

Significane of intravascular coagulation in canine endotoxin shock

The contribution of disseminated fibrin clot formation to the pathogenesis of canine endotoxin shock was explored in control dogs and in those defibrinated with a purified fraction of Malayan pit viper venom. The hemodynamic and humoral responses after the administration of an intravenous challenge dose of Escherichia coli endotoxin were comparable as was mortality. It is concluded that, although the role of the coagulation sequence in canine endotoxin shock is unclear, it does not appear to be determinative.

Pulmonary effects of E. coli endotoxin: role of leukocytes and platelets

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Hemodynamic effects of isoproterenol in canine endotoxin shock

Myocardial function and peripheral hemodynamic alterations were measured through the late stages of canine endotoxin shock. 60 min postendotoxin paired animals were given infusions of either 5 ml/kg per hr of 5% dextrose or dextrose plus isoproterenol (0.25 mug/kg per min). Comparable blood lactic and pyruvic acid levels were determined, the excess lactic acid calculated, and pH values were obtained. During the initial stages the classic pattern of hemodynamic alterations was observed; an excess of lactic acid appeared and the pH decreased. Outstanding was evidence of markedly reduced myocardial function in the late stages of shock with progressive rise in left ventricular end diastolic pressure (LVEDP), low cardiac index, rise of central venous pressure, increased central blood volume, tachycardia, and declining arterial pressure. Analyses of left ventricular function curves also indicated myocardial failure. Infusion of dextrose alone failed to decrease mortality rate (10 of 18 dying), whereas the rate was significantly decreased with isoproterenol (2 of 18). Dextrose infusion did not benefit myocardial function. Isoproterenol resulted in a marked improvement in myocardial action with a significant increase in heart work associated with, yet very minor, increments of LVEDP. In addition, tachycardia subsided, peripheral resistance decreased, and the blood pressure stabilized. The prognostic value of excess lactic acid was doubtful but a progressive fall in later stages was associated with survival.