The ontogeny of aggregation-enhanced toxicity

Sensitivity to the lethal effects of methamphetamine was observed under grouped conditions relative to isolated conditions in rats 25 and 30 days old but not in rats 7, 10, 15, or 20 days of age. Results are interpreted in terms of the development of the central catecholaminergic systems through which methamphetamine is thought to induce toxicity.Supported by Searle Fellowship     

Comparative studies on thein vitro andin vivo morphology of clones of experimental CNS tumours in the rat

Summary Two sarcomas, one neurosarcoma and one polymorphous tumour of uncertain classification of the central nervous system of the rat induced by N-nitrosomethylurea or ethylnitrosourea were the source of 14 clones. The cytomorphology and the aggregation pattern of the clonesin vitro are described. The malignancy and histology were checked by homologous transplantation. All the clones formed sarcoma-like structuresin vivo, but it was difficult to decide whether these neoplasias were real sarcomas or very dedifferentiated glial tumours. The differences in cytology observedin vitro were greater than the histological differencesin vivo.     

Dual effect of thiopentone on human granulocyte activation. Non–intervention by ketamine and morphine

The immune system, defending our organism against infections, can also cause disease. Anaesthetics may impair immunological defence by modifying the number and functions of immunocompetent cells, including the polymorphonuclear leucocytes (PMN). We have studied the effects of thiopentone, ketamine and morphine on some stimulated PMN responses that presumably reflect their microbicidal activity, i.e. oxygen consumption, aggregation, and volume increase. Stimulators were N-formyl-methionyl-leucyl-phenylalanine (FMLP, affecting cells via specific membrane receptors) and phorbol-myristate-acetate (PMA, activating protein kinase C, thereby short-cutting intramembraneous steps in normal signal transmission, and presumably provoking near-maximal cell responses with the dose applied). Preincubation of PMN with low doses of thiopentone enhanced oxygen consumption in unstimulated cells as well as in response to FMLP, but not PMA. FMLP-stimulated volume and aggregation responses were not detectably affected. The highest concentration of thiopentone depressed both oxygen uptake and volume/aggregation responses in FMLP-stimulated PMN. The amount of oxygen consumed after PMA stimulation was not affected, but both the onset of increased consumption and the maximal response were delayed. The two other drugs investigated, ketamine and morphine, did not appreciably affect oxygen consumption or aggregation by PMN: neither the baseline values nor those obtained after FMLP or PMA stimulation.     

Platelet function in septic multiple organ dysfunction syndrome

Objective: Altered platelet function plays a role in the pathophysiology of multiple organ failure in sepsis. The purpose of the present study was to evaluate various aspects of platelet adhesive function in septic patients and its putative relevance for prognosis. Design: Prospective clinical study. Setting: Intensive Care Unit of the University Hospital. Patients and methods: A total of 41 patients admitted to the medical Intensive Care Unit were studied. On the day of admission, patients were evaluated by intensive care scoring systems (Elebute, APACHE II) to assess the severity of sepsis and multiple organ dysfunction syndrome (MODS), and platelet function tests were performed. All patients were observed for 28 days to assess their clinical outcomes. Eleven patients revealed septicemia without MODS (Elebute ≥12, APACHE II <20) and 20 septic patients suffered from MODS (Elebute ≥12, APACHE II ≥20). Ten non-septic patients without MODS served as a control group (Elebute <12, APACHE II <20). Flow cytometric determination of the activated fibrinogen (fg) receptor GPIIb-IIIa and as well as thrombospondin (TSP) on platelets and platelet-neutrophil adhesion (CD41 immunofluorescence) ex vivo was performed using monoclonal antibodies. The effect of plasma obtained from patients on normal platelet aggregation in vitro, and adhesion to cultured endothelial cells was evaluated. Results: The surface expression of TSP on platelets was increased in septic patients with MODS compared to controls (p<0.03). Platelet-neutrophil adhesion was not significantly altered in septicemia (p<0.09) but decreased significantly in the presence of MODS (p<0.05) when compared to controls. Logistic regression analysis showed that platelet-neutrophil adhesion was an independent predictor for poor clinical outcome (p<0.01). Plasma from septic patients sensitized normal platelets to hyperaggregate and to adhere to cultured endothelium (p<0.01). Conclusion: In septic patients platelets become activated and are hyperadhesive to other vascular cells including neutrophils and endothelium. This may induce sequestration of platelets and microcirculatory arrest, thus the development of MODS. Received: 6 June 1996 Accepted: 4 October 1996     

TPA诱导的血小板聚集的研究

应用不同浓度ＴＰＡ诱发血小板聚集，观察２０名正常人血小板的聚集率。结果显示：ＴＰＡ从５ｎｇ／ｍｌ到１０ｎｇ／ｍｌ之间，随着浓度的增加，血小板聚集率逐渐增加，最佳浓度为１０ｎｇ／ｍｌ。当ＴＰＡ浓度〉１０ｍｇ／ｍｌ时，继续增加ＴＰＡ浓度，血小板聚集率将不再升高，且于２０ｍｇ／ｍｌ时出现明显的解聚现象。     

Effects of 5-Hydroxytraptamine on Aggregation,Release Reaction and Mobilization of Cytosolic Free Calcium Concentration in Rabbit Normal and Washed Single Platelets

In rabbit platelet rich plasma (PRP), 5-hydroxytraptamine (5-HT,0.03～3μmol/L) induced decrease in light transmission (DLT) dose-de pendently with centralization, as revealed by electron microscopy. However, 5-HT did not induced platelet aggregation and release reaction. 5-HT-induced DLT was inhibited by methysergide (0.3～30μmol/L), indomethacin (0.3～10μmol/L) and PGE_1 (0.01～0.3μmol/L) in a dose-dependent manner, but not EGTA(0.3～3mmol/L). Collagen(Coll), arachidonic acid (AA), adenosine diphosphate (ADP) and a stable thromboxane A2 analoge(STA_2) also induced DLT before aggregation by themselves, which was also inhibited by PGE_1, but not inhibited by EGTA except for Coll However,Coll-, AA-, STA_2-and ADP-induced DLT were reduced by pretreatment of PRP with 5-HT dose-depen-dently. The duration of DLT by Coll and AA were decreased from 151.4±5.93 sec and 15(?)38±0.60sec to 45.44±4.04 sec and 9.00±1.25 sec respectively ((?)±s(?) P<0.01), but not by ADP and STA_2, 3μmol/L of ADP-and 0.3μmol/L of STA_2-induced aggregation which was not accompanied with release reaction were enhanced by 5-HT pretreatment, but in those (Coil 5μg/ml, AA 100～200μmol/L and STA_2 1～3 μmol/L) with release reaction, the amount of adenosine triphosphate(ATP)were suppressed significantly (P<0.001) by 5-HT pretreatment without the effect on the magnitude of aggregation, The mobilization of cytosolic free calcium concentration ([Ca~(2+)]i) was observed after 5-HT treatment in single washed platelet, the results indicated that the basic level of [Ca~(2+)] i was 64.78±3.24nmol/L and this level was increased dose-dependently and significantly at 30 sec after administration of 5-HT and the time of peak value of [Ca~(2+)] i was at 90～100 sec.The similar time courses of suppression of ATP released during aggregation, in cases of Coll(5μg/ml), AA (200μmol/L) and STA_2(3μmol/L), by 5-HT were also found in the present experiment.     

Age-dependent oxidation and aggregation of ZnT-1: A role for metal catalyzed oxidation?

Biological aging is associated with the oxidation and/or aggregation of a variety of proteins, which may contribute to the age-dependent loss of function. Protein modification can be caused by multiple chemical mechanisms, which may selectively target specific proteins. Here we show that the ZnT-1 isoform of the family of cation diffusion facilitators suffers age-dependent oxidation and covalent aggregation. Parallel in vitro experiments with a plasma membrane-rich fraction and recombinant ZnT-1 suggest that ZnT-1 aggregation may be caused by metal-catalyzed oxidation (MCO). The latter would be consistent with the known propensity of metal-binding proteins to suffer MCO.     

Delayed thrombin-induced platelet-fibrin clot generation by clopidogrel: a new dose-related effect demonstrated by thrombelastography in patients undergoing coronary artery stenting

BACKGROUND: We have previously demonstrated that clopidogrel reduces platelet activation and aggregation in patients undergoing stenting. However, the effect of the clopidogrel loading dose on the rate of thrombin-induced platelet-fibrin clot formation is unknown in this patient population. METHODS AND RESULTS: Using thrombelastography (TEG) we measured the time to platelet-fibrin clot formation (R), a marker of the speed of thrombin generation, in 120 patients undergoing elective coronary artery stenting treated with standard and high loading doses of clopidogrel. Platelet reactivity to adenosine diphosphate (ADP) by light transmittance aggregometry (LTA) was determined simultaneously. Measurements were made immediately before and at 24 h after clopidogrel treatment. Clopidogrel produced a prolongation in R (4.4+/-1.4 min pre vs. 5.4+/-1.7 min post, p<0.001) that directly correlated with the change in platelet aggregation (r=0.65, p<0.0001). Prolongation in R was greatest in patients treated with a high loading dose (p=0.004). CONCLUSIONS: Delayed thrombin-induced platelet-fibrin clot formation as measured by TEG is a newly reported dose-related effect of clopidogrel that may contribute to the overall antithrombotic properties of the drug in patients undergoing stenting. This effect was more marked in patients loaded with 600 mg, lending further mechanistic support for this dose of clopidogrel as a more effective antithrombotic regimen than the standard 300 mg dose. Measurement of R may serve as a new indicator of clopidogrel responsiveness.     

Mutual Stimulation of Beta-Amyloid Fibrillogenesis by Clioquinol and Divalent Metals

As reported by some authors, clioquinol (CQ), a 8-hydroxyquinoline derivative, has produced very encouraging results in the treatment of Alzheimer’s disease (AD). Its biological effects are most likely ascribed to complexation of specific metal ions, such as copper (II) and zinc (II), critically associated with β-amyloid (Aβ) aggregation/fibrillogenesis and degeneration processes in the brain. The present study was aimed at assessing the in vitro effects of CQ on the aggregation/fibrillogenesis properties of human Aβ either alone or complexed with Cu²⁺ and Zn²⁺. Surprisingly, our data indicated that CQ promoted rather than inhibited the formation of Aβ fibrillar aggregates when added metal ions were present. To understand whether the latter effects were related to the peptide amino acid sequence, we also investigated the aggregational profile of rat Aβ, which differs from the human homologous for three amino acidic substitutions. Such a sequence alteration drastically reduced the tendency of the peptide to undergo spontaneous aggregation/fibrillization. In the presence of CQ and metals, however, also rat Aβ showed a strong propensity to generate fibrillar aggregates. In agreement with the pro-aggregation effects observed in solution, studies with neuroblastoma cells demonstrated an impairment of cell functioning only in the presence of CQ + Aβ–metals. Based on the present findings, the literature data on the potential effectiveness of CQ-based chelation therapy in AD should be re-interpreted. An erratum to this article can be found at