Complement-Dependent and Complement-Independent Interactions of Bacterial Lipopolysaccharides and Mucopeptides with Rabbit and Human Platelets

Effects of plasma collection systems and processing parameters on the quality of factor IX concentrate

Using pilot-scale production of our present factor IX (II and X) concentrate, we have studied the effects of starting plasma source and processing parameter on two in-vitro indicators of product quality - yield and thrombogenic potential. Plasma source did not affect factor IX yield but had a marked effect on thrombogenic potential. Factor IX concentrates produced from plasma derived through centrifugation-based technology showed significantly higher thrombogenic potential than products derived from plasma derived through a filtration-based system. Removal of Cohn fraction I prior to ion-exchange chromatography resulted in a drop in factor IX yield and thrombogenic potential, as did heat treatment to 80 degrees C for 72 h. We conclude that a membrane-filtration-based plasmapheresis system may be the preferred method of plasma procurement for factor IX concentrate production.

Mediators of pulmonary injury induced by inhalation of bacterial endotoxin

The purpose of this study has been to further define the pathophysiologic aspects of lung injury caused by the inhalation of endotoxin (LPS) using the morphometric approach to identify mediators that influence distal lung structure and function. Hamsters were divided into 3 groups 24 h prior to low dose LPS inhalation exposure (4 micrograms/m3 for 5 h): (1) pretreated with cobra venom factor to deplete complement in vivo, (2) pretreated with indomethacin to block prostaglandin production, and (3) untreated control group. Both pretreatments abolished LPS-induced decreases in lung volume as well as increases in capillary PMN and platelets seen in untreated control animals. Neither pretreatment had any effect on the LPS-induced decreases of other capillary leukocytes. Similarly, both methods of pretreatment failed to block increases in cellular interstitium of distal capillary septa induced with LPS alone. LPS provoked changes in capillary endothelium, especially seen as an increase in numerical density of endothelial pinocytotic vesicles. Decomplementation failed to alter this increase, but indomethacin pretreatment blocked the effect. Neither treatment had any effect on their size. Low dose LPS inhalation also altered pulmonary capillary permeability to a 125I-BSA probe, which was found in significantly greater amounts in LPS-exposed lungs than in those of saline aerosol control lungs, but was not present in the air space as evidenced by negligible counts in bronchoalveolar lavages. It is evident that endotoxin on the epithelial side of the air-blood barrier leads to changes on the other side of that barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood-platelets-damaging activity of some synthetic Streptococcus peptidoglycan subunits and analogues

A series of 25 synthetic subunits or analogues of streptococcal peptidoglycan was tested for their ability to damage rabbit blood platelets. The morphological changes of the platelets were studied on an ultrastructural level. Minimal subunit structure able to produce a complete lysis of the platelets was found to be muramyldipeptide (MDP). Comparable lysis of platelets was also caused by muramyltetrapeptide and MDP containing D-Ala instead of L-Ala. The lytic effect was dose-dependent and was exhibited rather after high doses of the substances used (up to 500 micrograms/ml). For the lytic reaction, the configuration of C3 and C4 in the muramyl residue of MDP was essential. Many substances produced only degranulation without lysis of the platelets and some of them did not influence the platelet ultrastructure at all. The paper presents some structure-to-function relationships of the compounds and shows that the platelet-damaging activity of peptidoglycan may be related to certain portions of the peptidoglycan molecule. This activity should be tested when the immunomodulatory substances derived from the bacterial peptidoglycan are searched for.

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.

Platelet activating factor (PAF) involvement in endotoxin-induced thrombocytopenia in rabbits: studies with FR-900452, a specific inhibitor of PAF

PAF (1 ug/kg) injected intravenously (i.v.) into anesthetized rabbits resulted in marked loss of circulating platelets and leukocytes. Administration of FR-900452 1-methyl-3-(1-(5-methylthiomethyl-6-oxo-3-(2-oxo-3-cyclopenten-1-y lidene)- 2-piperazinyl) ethyl)-2-indolinone, a specific PAF inhibitor, at a dose of 10 mg/kg i.v. with 10 min prior to the PAF injection significantly prevented both changes. On the other hand, PAF has been considered as a mediator of endotoxin shock. Therefore, in order to determine whether endogenous PAF contributes to the occurrence of thrombocytopenia or leukopenia in endotoxin shock, we assessed the effect of FR-900452 on the thrombocytopenia and the leukopenia following bolus i.v. injection of E.coli endotoxin (0.03 mg/kg) in rabbits. As a result, pretreatment with the compound (10 mg/kg, i.v.) significantly reduced the thrombocytopenia at 60 and 180 min after the endotoxin injection. In contrast, FR-900452 did not reduced the leukopenia at any time of after endotoxin. These results indicate that PAF might be involved in the occurrence of thrombocytopenia in rabbit endotoxemia and the contribution of PAF to the leukopenia is much less extent than that to the thrombocytopenia.

Aggregation of human platelets and adhesion of Streptococcus sanguis

Platelet vegetations or thrombi are common findings in subacute bacterial endocarditis. We investigated the hypothesis that human platelets selectively bind or adhere strains of Streptococcus sanguis and Streptococcus mutans and aggregate, as a result, into an in vitro thrombus. Earlier ultrastructural studies suggested that aggregation of platelets over time by Staphylococcus aureus was preceded in order by adhesion and platelet activation. We uncoupled the adhesion step from activation and aggregation in our studies by incubating streptococci with platelet ghosts in a simple, quantitative assay. Adhesion was shown to be mediated by protease-sensitive components on the streptococci and platelet ghosts rather than cell surface carbohydrates or dextrans, plasma components, or divalent cations. The same streptococci were also studied by standard aggregometry techniques. Platelet-rich plasma was activated and aggregated by certain isolates of S. sanguis. Platelet ghosts bound the same strains selectively under Ca2+- and plasma-depleted conditions. Fresh platelets could activate after washing, but Ca2+ had to be restored. Aggregation required fresh platelets in Ca2+-restored plasma and was inducible by washed streptococcal cell walls. These reactions in the binding and aggregometry assays were confirmed by transmission electron microscopy. Surface microfibrils on intact S. sanguis were identified. These appendages appeared to bind S. sanguis to platelets. The selectivity of adhesion of the various S. sanguis strains to platelet ghosts or Ca2+- and plasma-depleted fresh washed platelets was similar for all donors. Thus, the platelet binding site was expressed widely in the population and was unlikely to be an artifact of membrane aging or preparation. Since selective adhesion of S. sanguis to platelets was apparently required for aggregation, it is suggested that functionally defined receptors for ligands on certain strains of S. sanguis may be present on human platelets. Some differences in the selectivity and rate of the aggregation response were noted among platelet donors, although the meaning of the variability requires further study. Nonetheless, these interactions may contribute to platelet accretion in the initiation and development of vegetative lesions in the subacute bacterial endocarditis.

Contribution of complement activation to the rise in blood levels of 6-oxo-prostaglandin F1 alpha during endotoxin-induced hypotension in rabbits

Administration of endotoxin (lipopolysaccharide W E. coli O111 B4, 0.5 mg/kg i.v.) induced about 20% activation of the complement system (measured as CH50 and C3), a biphasic hypotension, thrombocytopenia and a significant rise in blood levels of 6-oxo-PGF1 alpha. Complement depletion (CH50 and C3 less than 3%) with Cobra Venom Factor significantly reduced the initial fall in blood pressure and the rise in 6-oxo-PGF1 alpha, and abolished the second phase of hypotension and the thrombocytopenia, due to subsequent injection of endotoxin. It is concluded that activation of about 20% of the complement system by endotoxin is a prerequisite for the occurrence of thrombocytopenia and secondary hypotension, and that it is involved in the increase in blood levels of 6-oxo-PGF1 alpha. The results of histamine determinations in rabbit blood and plasma indicate that, besides products derived from prostaglandin endoperoxides, other vasoactive substances, possibly released during complement-mediated adherence aggregation of platelets, might contribute to the endotoxin-induced hypotension.

Platelet aggregation and stimulation of leucocyte procoagulant activity by rickettsial lipopolysaccharides in rabbits and in man

The effects in vitro of 4 purified lipopolysaccharide (LPS) preparations from Rickettsiae on platelets and leucocytes were studied in rabbits and in man. All LPS induced aggregation in rabbit platelet-rich plasma but to differing degrees. This activity was abolished by inactivation of complement. None of the preparations induced aggregation of human platelets. Both rabbit and human leucocytes, when incubated with each of the rickettsial LPS preparations, generated a potent procoagulant activity (tissue factor). These findings add further support to the concept that rickettsial LPS behave as typical LPS from gram-negative bacteria and may be relevant to the understanding of the mechanism(s) responsible for triggering intravascular coagulation in rickettsial diseases.

Early increase of a new platelet coagulant activity in rats fed a thrombogenic diet

A recently described platelet coagulant activity (factor X activating activity), whose pathophysiological significance is as yet unknown, was studied in rats fed a fat-rich (thrombogenic) diet for 1, 2 and 7 weeks and compared to rats fed normal laboratory chow. Whatever the duration of the special feeding period, a highly significant shortening of the clotting time, used for measuring this activity, was observed. When the platelet coagulant activity of individual "fat-fed"rats was quantitated by reference to that of individual control animals, we found a mean increase of 350% (n = 9) after one week and 267% (n = 3) after two weeks of dietary treatment. Partial thromboplastin time, thrombin time and soluble fibrin monomer complexes did not differ in control and treated animals. It seems that platelet coagulant activity, as measured in our test system, is one of the first laboratory parameters to be modified by fat-rich diets. These findings may be relevant to an understanding of the role of platelet coagulant activities other than platelet factor 3 in thrombotic phenomena.