An off-the-shelf plasma-based material to prevent pacemaker pocket infection

Bacterial infection of subcutaneous “pockets” housing cardiovascular implantable electronic devices is a significant clinical complication. In this study, pacemakers encapsulated in a blood plasma-based material (PBM) composited with antibiotics were investigated for use as prophylactics against such infections. PBMs, which are made from pooled allogeneic plasma and platelets, are off-the-shelf biomaterials that can be manufactured in the form of complex 3D shapes, extrudable putties, or injectable pastes. In vitro studies with PBM pastes formulated with rifampicin and minocycline demonstrated antibiotic release over 6 days, activity against Escherichia coli, and reduced cytotoxic effects of the antibiotics on fibroblasts. The materials were also evaluated in vivo in a rabbit model in which pacemaker pockets were inoculated with methicillin-resistant Staphylococcus aureus (S. aureus) strain and examined 1 week later. The pockets containing the pacemaker plus S. aureus were grossly purulent and culture positive, whereas pockets into which PBM with antibiotics were injected around the pacemaker were free of purulence and culture negative (p < 0.001). None of the pockets into which PBM without antibiotics were placed demonstrated purulence, but 60% were culture positive. These results demonstrate the potential of PBMs to deliver antibiotics to diminish the incidence of pocket infections for pacemakers and other implantable devices.     

抗人血小板单克隆抗体SZ——47的功能研究

本文报道1株抑制型抗人血小板单克隆抗体 SZ—47。SZ—47能完全抑制 ADP 及肾上腺素诱导的血小板聚集;而对花生四烯酸,瑞斯托霉素诱导的血小板聚集无影响;对胶原诱导的血小板聚集无明显抑制作用。因此,推测单克隆抗体 SZ—47主要通过 ADP 途径来影响血小板的聚集功能。     

High- and low-affinity receptors regulate platelet responses to phorbol diesters and teleocidin

We examined binding of ³H-phorbol dibutyrate (³H-PDBu) to gel filtered human platelets (GFP) and discovered that GFP possess two classes of receptors for phorbol diesters (PDE). High-affinity (HA) receptors, approximately 5000/GFP, bound ³H-PDBu with an apparent dissociation constant (K_D) of approximately 12 nM. Low-affinity receptors were approximately 5 times more numerous (2.4 × 10⁴/GFP) and had a 10-fold lower affinity for ³H-PDBu (apparent K_D = 115 nM). The potencies of phorbol myristate acetate (PMA) and PDBu paralleled their binding affinities to the PDE receptors. Teleocidin (Tel), although structurally distinct from PDE, competed with ³H-PDBu for its HA-receptors (K_I Tel = 1.9 nM). Binding of PDE to HA- or LA- receptors was rapid, reversible, saturable and stereospecific. The HA- and LA-receptors modulated different platelet responses. HA-receptors regulated the secretion of β-thromboglobulin from -granules and the release of N-acetyl-β-D-hexosaminidases from lysosomes. LA-receptors mediated both platelet aggregation and the release of serotonin from dense granules. This is the first demonstration of two physiologically active classes of PDE/Tel receptors in human platelets, and demonstrates that particular platelet responses may be directed by distinct classes of receptors for specific agonists.     

Alcohol and Platelet Function

Epidemiological studies have shown that moderate consumption of alcoholic beverages is inversely related to the incidence of the complications of coronary artery disease. The protective effect of ethanol may be partially attributable to an inhibitory effect of ethanol on platelets. This article summarizes the experimental observations that ethanol inhibits platelet responses to specific physiological agonists. In alcoholics, various platelet defects have been observed, but these may be influenced by metabolic factors rather than the presence of ethanol alone. The acute effects of ethanol on platelet functions both in vivo and ex vivo will be reviewed. Evidence will be presented demonstrating that ethanol added acutely in vitro inhibits phospholipase A₂ in stimulated platelets. The interaction of ethanol with other signal transduction pathways will also be discussed.     

Evidence for intact V1-vasopressin receptors in congenital nephrogenic diabetes insipidus

The binding of tritium-labelled arginine vasopressin to human platelet vasopressin receptors was investigated in patients with congenital nephrogenic diabetes insipidus. Binding characteristics, that is receptor affinity and the maximum number of binding sites, were not significantly different from those found in normal control individuals. The findings confirm the concept of intact V₁ receptors in congenital nephrogenic diabetes insipidus. The defect in nephrogenic diabetes insipidus apparently only affects the cyclic adenosine monophosphate dependent V₂ receptors.     

Role of neutrophils in gastric damage induced by platelet activating factor

Summary Platelet-activating factor (PAF) has recently been shown to be a potent ulcerogenic agent in the stomach and intestinal mucosa. Its exact mechanism of action is not yet known although histological studies suggest that vasocongestion is an important feature of PAF-induced damage. We have therefore studied the activity of various agents with different modes of action toward PAF-induced gastrointestinal lesions in the rat (PAF 2 g/kg i.v. ; macroscopic lesions of tissues scored 20 min later; arbitrary scale from 0 to 4). Drugs were administered either i. m., s. c. (5 min) or orally (30 min) before PAF injection. PAF-induced gastric lesions were strongly inhibited by the natural PAF-antagonist BN 52021 as well as by atropine sulphate and cimetidine which implicates cholinergic stimulation in the ulcerogenic activity of PAF. The somatostatin analog BIM 23014 was also very potent against PAF, perhaps by reducing the parasympathetic stimulation in the gastric wall as described for somatostatin. Allopurinol, which is a free radical scavenger also almost totally inhibited PAF-induced gastric damage, suggesting that neutrophils are involved in the mucosal lesions. The considerable inhibition of the gastric effects of PAF found in neutrophil-depleted animal supports this hypothesis. Theophylline and disodium cromoglycate, mast cell stabilizing drugs which were also active in our model, could act by protecting mast cell degranulation induced by free radicals released from activated neutrophils. A multifunctional process seems to determine the mucosal gastric damage induced by PAF, but parasympathetic stimulation and neutrophil activation play a major role in this pathology.Send offprint requests to A. Etienne at the above address     

Factors affecting serotonin uptake into human platelets

Because of complexities in platelet serotonin uptake dynamics, we studied the influence of the time of day and year as well as the subject's age on uptake parameters. While the assay itself was quite reproducible, and the kinetic parameters of 5 HT uptake were stable over a few days, at a given time, within an individual, the variance was quite large when samples from different times of the day or year or from different individuals were compared. An inverse relationship between V _max (moles/cell number/time) and platelet number was found in data from a group of individuals, suggesting regulation of V _max not at the level of uptake capacity per cell, but in a manner that somehow takes into consideration the number of platelets in the subject's plasma. Indeed, expressing V _max in a new way (called total V _max), not based on V _max per cell or per 10⁷ cells but for the total number of platelets in the volume of PRP used, greatly reduced the scatter in the between-individuals and across-time data. While V _max (moles/cell number/time) exhibited only a trend toward reduction with age, for example, the decline in total V _max with subject age was statistically significant. It is suggested that total V _max (moles/time) may be a more physiologically relevant expression for an uptake function than V _max (moles/time/cell number).     

Protection of the ischemic myocardium from reperfusion injury by prostaglandin E1 inhibition of ischemia-induced neutrophil activation

Summary This study investigates the action of intravenous PGE₁ on myocardial reperfusion injury and the possible involvement of antineutrophil activities. Cats were subjected to 3 h of temporary ligation of the left anterior descending coronary artery, followed by 2 h of reperfusion. Animals were treated with PGE₁ (5 g/kg x min) or vehicle (saline solution), starting 0.5 h after coronary artery occlusion. Vehicle-treated cats exhibited a significant loss of cardiac creatine phosphokinase specific activity at 5 h, accompanied by a significant ischemia-induced rise in the ST segment of the ECG and development of a Q wave after starting reperfusion. All of these alterations were largely prevented by PGE₁ treatment. PGE₁ exerted some blood-pressurelowering activity at 5 h (P > 0.05) but did not reduce myocardial contractile force and oxygen consumption. PGE₁ modestly antagonized ischemia-induced formation of platelet aggregates. However, PGE₁ prevented the rise in peripheral white blood cell count during ischemia and reperfusion and inhibited the generation of reactive oxygen species (myeloperoxidase assay) from zymosan-stimulated whole blood ex vivo. The ratio of generation of reactive oxygen species/white blood count remained unchanged. It is concluded that PGE₁ protects the ischemic myocardium from acute reperfusion injury and that this effect involves an action of the compound on neutrophils, probably by improved myocardial tissue preservation, resulting in reduced formation of chemotactic products and, consequently, less local neutrophil accumulation and release of noxious metabolites.Parts of these results have been presented to the 29th Spring meeting of the Deutsche Gesellschaft für Pharmakologie und Toxikologie, Mainz, 1988 Send offprint requests to K. Schrör at the above address     

Degenerative neurological disorders associated with deficiency of glutamate dehydrogenase

Summary The activity of glutamate dehydrogenase, the enzyme of glutamate degradation, was measured in platelets of 27 healthy controls and 85 patients with different degenerative cerebellar and/or basal ganglia disorders. A group of 7 patients was selected with slowly progressive multiple-system atrophy, in whom a clinical diagnosis of olivopontocerebellar atrophy appeared tenable, with decreased activity of glutamate dehydrogenase (38% of the mean control value). In 4 patients data on inheritance were compatible with the genetic pattern of autosomal recessive inheritance, while 3 patients were sporadic cases. In an effort to define this group of patients more precisely, it is suggested that decreased activity of glutamate dehydrogenase induces an increase in extracellular glutamate levels in the central nervous system with subsequent development of excitotoxicity.     

N G-nitro-l-arginine antagonizes endothelium-dependent dilator responses by inhibiting endothelium-derived relaxing factor release in the isolated rabbit heart

The effects of a recently described inhibitor of endothelial NO synthesis, N ^G-nitro-l-arginine (l-NNA), on the vasomotor responses to endothelium-dependent and independent vasodilators, and on the release of endothelium-derived relaxing factor (EDRF), were studied in the isolated saline-perfused rabbit heart. Infusion of l-NNA (30 M) resulted in a 52±12% increase in basal coronary perfusion pressure. The vasomotor responses to 1 M acetylcholine (ACh) and serotonin after l-NNA became biphasic, showing a small transient dilation followed by a pronounced vasoconstriction. In contrast, the dilation observed with sodium nitroprusside was not affected by l-NNA. None of the above-mentioned effects was elicited by the Stereo-isomer d-NNA. Similarly, an increase in the basal coronary perfusion pressure by endothelin-1 (0.3 nM) to the same level as observed with l-NNA did not alter the vasomotor responses to ACh and sodium nitroprusside. The increase in cyclic GMP (cGMP) in platelets passing through the coronary vascular bed was used as an index of EDRF release. Platelet cGMP amounted to 0.50±0.10 pmol/mg protein after passage through the coronary bed of the unstimulated heart. When platelets were injected during an ACh infusion (1 M), a 2.7 fold increase in cGMP was observed (P<0.01). After a 30-min infusion with l-NNA, the cGMP content of platelets passing through the unstimulated heart was reduced by 62%. Likewise, the ACh-induced increase in platelet cGMP was totally blocked. These results show that l-NNA inhibits EDRF release, and is thus a potent and selective inhibitor of EDRF-mediated dilation in the isolated rabbit heart.