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Biomedical subjects

A Ordinas

Publications and source records attributed to A Ordinas.

At least 163 records · Page 9Linked to original sources
PubMed1988

Platelet contribution to the formation of metastatic foci: the role of cancer cell-induced platelet activation.

Platelets are thought to be involved in the development of blood borne metastasis. Ultrastructural and experimental studies demonstrate that association between tumor cells and platelets with subsequent activation of the coagulation cascade takes place in malignancy. Several hypotheses have been proposed to explain the mechanisms by which tumor cells activate platelets including generation of thrombin, ADP release and involvement of arachidonate metabolism. Perfusion studies with human homologous systems showed that intact tumor cells and tumor cell microvesicles were able to induce platelet thrombogenicity under defined flow conditions. The presence of divalent cations and plasma factors was necessary for the cancer cells to exert their activating capacity. These results suggest a role for platelets in the development of secondary metastasis as well as in the thrombotic events of malignancy.

Adenosine Diphosphate↗
PubMed1987

Tumor-cell-induced platelet aggregation is a glycoprotein-dependent and lipoxygenase-associated process.

To characterize the platelet receptor sites and the platelet metabolic pathways involved in tumor-cell-induced platelet aggregation, we have used a homologous system consisting of human platelets and 2 tumor cell lines of human origin, which activate platelets through different mechanisms. Preincubation of platelets with an MAb against platelet glycoprotein Ib partially blocked tumor-cell-induced platelet aggregation, and preincubation of platelets with an MAb against the glycoprotein complex GPIIb/IIIa totally blocked the aggregation induced by the 2 tumor-cell lines. No inhibitory effect was found when platelets were treated with PAF-receptor antagonists or with specific peptides which block the platelet sites involved in bacterially induced platelet aggregation. Compounds which raised intra-platelet cAMP levels inhibited tumor-cell-induced platelet aggregation in a dose-related manner. Inhibition of cyclo-oxygenase by aspirin which blocked TxB2 formation by platelets did not inhibit platelet aggregation induced by tumor cells whereas the BW755 compound which inhibits cyclo- and lipoxygenase blocked platelet aggregation. These results demonstrate that tumor-cell-induced platelet aggregation is a glycoprotein-dependent and a lipoxygenase-associated phenomenon.

Aspirin↗
PubMed1987

Cell surface sialylation of two human tumor cell lines and its correlation with their platelet-activating activity.

The relationship between cell surface sialylation and platelet-activating activity was studied in two tumor cell lines of human origin, the SKNMC neuroblastoma line and the U87MG glioblastoma line. Their platelet-activating activity was evaluated in two different experimental systems, one that measures platelet aggregation and the other that quantifies platelet thrombus formation on vascular subendothelium under flow conditions. Our results demonstrate that, for the SKNMC line, the loss of 30% of surface sialic acid induced a significant reduction in its platelet-activating capacity. Upon recultivation desialylated SKNMC cells did not regenerate surface sialic acid and did not restore their initial values of platelet aggregation and platelet thrombus formation. Conversely, removal of 35% sialic acid from the surface of U87MG cells did not affect their pattern of platelet activation in either system tested. These results demonstrate that there is a correlation between cell surface sialylation and the capacity of SKNMC cells to activate platelets. The lack of effect of desialylation on U87MG-induced platelet activation indicates that different surface components may be the modulators of the interactions of these tumor cells with platelets. Our results support the hypothesis that heterologous mechanisms regulate platelet-tumor cell interactions and that tumor cell sialic acid may be only one of the aspects involved in such interactions.

Cell Line↗
PubMed1987

Ticlopidine inhibits platelet thrombus formation studied in a flowing system.

We have studied the effect of ticlopidine on platelet function. This effect was assessed by aggregation studies and by the Baumgartner perfusion system as an ex vivo approach to study modifications in the interaction of platelets with vascular subendothelium. Platelets from volunteers, that were given 250 mg of ticlopidine twice a day showed a significantly decreased aggregation of platelets induced by several agonists. In the perfusion studies a marked reduction in the parameters that measure platelet interaction with subendothelium was also observed. The decrease in thrombus formation, and the diminished size of platelet aggregates, clearly indicated that ticlopidine impaired platelet-platelet interaction in this experimental flowing system. Our results suggest that ticlopidine is a potent inhibitor of platelet function and that its antiplatelet activity might be related to the mechanisms that regulate the interaction between platelets at the membrane level.

Administration, Oral↗
PubMed1987

Fibronectin is required for platelet adhesion and for thrombus formation on subendothelium and collagen surfaces.

Fibronectin (FN) plays a role in several adhesion mediated functions including the interaction of platelets with subendothelium. We investigated the role of plasma FN in platelet adhesion and platelet thrombus formation under flow conditions. We used two different perfusion models: the annular chamber with alpha-chymotrypsin-treated rabbit vessel segments, and the flat chamber with coverslips coated with fibrillar purified human collagen type III. Perfusates consisted of washed platelets and washed RBCs, suspended in normal or FN-depleted plasma. Perfusions were carried out for ten minutes at shear rates of 300 or 1,300 s-1. Platelet deposition and thrombus dimensions were evaluated morphometrically by a computerized system. We found that depletion of plasma fibronectin significantly reduced the percentage of total coverage surface and percentage of platelet thrombus, at both shear rates studied, and in both perfusion systems (P less than .01) (P less than .01). The dimensions of the platelet thrombi formed in perfusions at high shear rate were also significantly reduced in perfusions carried out with FN depleted plasma (P less than .01). Addition of purified FN to FN-depleted perfusates restored all values to those measured in the control perfusions. These results indicate that plasma FN is required for platelet aggregate and thrombus formation following adhesion under flow conditions.

Aorta, Abdominal↗
PubMed1986

Sex-related differences in the effects of aspirin on the interaction of platelets with subendothelium.

Using the Baumgartner perfusion technique, marked sex-related differences in the extent of platelet-subendothelium interaction and in the effect of aspirin (ASA) have been observed. The administration of ASA (150 mg daily for 15 days) to two groups of healthy volunteers, one composed of males and the other of females, proved to block the generation of TXB2 in both cases. The basic pattern of platelet subendothelium interaction, however, was found to be markedly different in both groups studied. In men, aspirin treatment induced a significant reduction in the percentage of platelet thrombi, whereas in women, post ASA values remained at the same level as in control experiments. These results show that in the Baumgartner perfusion system women display a less thrombogenic tendency than men and that 150 mg of ASA administered daily are effective in reducing the extent of platelet-subendothelium interaction in the male group but not in the female group. These findings could explain the absence of benefit observed for women in clinical trials with aspirin.

Administration, Oral↗
PubMed1986

Platelet activation induced by a human neuroblastoma tumor cell line is reduced by prior administration of ticlopidine.

Ticlopidine (250 mg twice daily) was administered to human volunteers for seven days and the response of their heparinized platelet-rich plasma to SKNMC (ADP-dependent) human neuroblastoma cells was examined. The first wave of platelet aggregation, characteristic of ADP-dependent human tumor cell lines, was completely abolished but was replaced by a lag period prior to the onset of aggregation. In the Baumgartner perfusion apparatus there was a marked inhibition in the thrombus generated by the presence of SKNMC cells with a concomitant increase in the percentage of surface coverage. These results suggest that the administration of ticlopidine could be useful to prevent some of the steps of metastatic dissemination in which activated platelets may play a role.

Adenosine Diphosphate↗
PubMed1986

Development of a computer program to analyze the parameters of platelet-vessel wall interaction.

The use of the Baumgartner perfusion system allows the morphometric quantification of platelets interacting with vessel wall, however it presents the basic difficulties of morphometrical measurements. In order to facilitate the procedure of evaluation we developed a semiautomated method to avoid the complexity of the classical evaluation. Our system consists on an optical picture analysis system connected with a specially developed computer program which allows fast quantification. Simultaneously to the outlining of interacting platelets the computer program recognizes, corrects, selects and stores the information, in order to perform the final calculations as previously established. This system has been demonstrated to be as effective as the classical morphometric evaluation in the measure of platelets interacting with subendothelium. Potential sources of error such as subjectivity of the observers in selecting the class of interacting platelets are avoided. The use of this combined method opens the possibility to adapt the Baumgartner perfusion system to clinical routine and to the screening of drugs that modify platelet adherence.

Animals↗
PubMed1986

Defective platelet adhesion on vessel subendothelium in uremic patients.

Bleeding time, platelet retention on glass beads, and ristocetin-induced platelet agglutination (RIPA) in platelet-rich plasma were simultaneously determined for 20 patients with chronic renal failure and previous hemorrhagic history. In seven patients chosen at random out of a group of 16 in whom the three tests were abnormal, RIPA of uremic-isolated platelets in presence of normal platelet-poor plasma (PPP) and of normal platelets in presence of patient PPP were performed. In all cases, the first assay showed diminished agglutination, suggesting a platelet defect; however, uremic PPP did not inhibit the agglutination of normal platelets. In the same patients, the interaction of platelets with subendothelium was evaluated using Baumgartner's perfusion method. The subendothelial surface covered by platelets was significantly decreased in experiments with uremic whole blood when compared to normal controls. The interaction of platelets with subendothelium was also decreased when perfusions were carried out with platelet-plasma mixtures containing either normal washed platelets and uremic PPP or uremic washed platelets and normal PPP. These results show an impaired platelet adhesion caused both by a platelet and a plasmatic abnormality. Since uremic PPP decreased the adhesion of normal platelets to subendothelium but did not inhibit RIPA, it seems probable that the plasmatic defect could result in a defective binding between vWF and subendothelium. The influence of the red cell count on the platelet adhesion to subendothelium was reconfirmed by comparing perfusions of reconstituted blood with hematocrit values of 20% to 23% and 40% to 45%. In summary, a defective platelet adhesion to subendothelium has been postulated in uremic patients, caused by platelet and plasmatic alterations that are influenced by a low hematocrit.

Adult↗
PubMed1986

Morphometric evaluation of thrombogenesis by microvesicles from human tumor cell lines with thrombin-dependent (U87MG) and adenosine diphosphate-dependent (SKNMC) platelet-activating mechanisms.

The Baumgartner perfusion apparatus has been used for quantitative comparison of the interaction of platelets with subendothelium in the presence of microvesicles derived from SKNMC (human neuroblastoma) cells, which aggregate platelets by an adenosine diphosphate (ADP)-dependent mechanism, and U87MG (human glioblastoma) cells, which function by a thrombin-dependent mechanism. The derived microvesicles from each line were as effective as the intact cells in inducing thrombogenesis on both undigested and alpha-chymotrypsin-digested subendothelium. Thrombus size on digested vessels was greater than on undigested vessels by fivefold for SKNMC cells and microvesicles and by 20-fold for U87MG cells and sevenfold for U87MG microvesicles. The results show that microvesicles from both cell lines initiate interactions between platelets and subendothelium identical to those caused by intact tumor cells. The results also demonstrate that intact tumor cells in the circulation may not be necessary for the thromboembolic complications of malignancy.

Adenosine Diphosphate↗
PubMed1985

Inhibitory effects of dipyridamole on growth, nucleoside incorporation, and platelet-activating capability in the U87MG and SKNMC human tumor cell lines.

The effects of dipyridamole on tumor cell function were examined in cultures of two lines of human origin, the SKNMC neuroblastoma line that activates platelets by a mechanism which is dependent on the release of adenosine 5'-diphosphate and the U87MG glioblastoma line that induces platelet activation by the generation of thrombin. Cells grown in the presence of dipyridamole at 1 microM showed greater than 80% inhibition of uptake of adenosine, thymidine, and uridine with both lines. At 5 microM tumor cell growth was inhibited by 70% (U87MG) and 90% (SKNMC) but without concomitant cytotoxicity as determined by clonogenic assay (50% inhibitory concentration approximately 20 microM). At 10 microM dipyridamole cyclic adenosine 3':5'-monophosphate levels increased 150% with both cell lines but no changes above baseline values were seen at 2.5 microM. The two cell lines showed different responses to being cultured in the presence of dipyridamole in terms of their ability to subsequently activate platelets. U87MG cells cultured in 10 microM dipyridamole showed a doubling of the lag time as compared with cells grown in the absence of dipyridamole but with full aggregation; with SKNMC cells the aggregation rate was reduced and cells grown in 10 microM dipyridamole showed no reversible first wave, a 5-fold increase in lag time and a 75% inhibition in total aggregation. Since therapeutic doses of dipyridamole result in plasma concentrations of approximately 3.5 microM these results suggest that potential antimetastatic effects of dipyridamole could be direct arising from inhibition of important steps in tumor cell metabolism or indirect by suppressing one or more of the mechanisms involved in the ability of tumor cells to activate platelets.

Cell Division↗
PubMed1985

Effects of divalent cations on the interaction of platelets with tumor cells: aggregation and perfusion studies with two homologous human systems.

The effects of chelation of divalent cations in the interaction of platelets and tumor cells has been studied in a homologous human system using human platelet-rich plasma and two tumor cell lines of human origin: SKNMC (neuroblastoma) cells, which cause platelet aggregation by an adenosine diphosphate-dependent mechanism, and U87MG (glioblastoma) cells, which function by a thrombin-dependent mechanism. When added at zero time, citrate 14 mmol/L completely abolished aggregation in heparinized (5 U/ml) platelet-rich plasma by either cell line, but the degree of inhibition was reduced by later addition of the chelating agent. Calcium citrate 8 mmol/L reduced by only 10%, indicating that citrate anion was not responsible for the inhibition. Addition of Ca++ or Mg++ alone or in combination at concentrations up to 1.5 mmol/L did not reverse the inhibition. Addition of higher concentrations of Ca++ (2 mmol/L) caused immediate clotting, whereas concentrations of Mg++ up to 6 mmol/L were without effect. Inhibition could be reversed by washing the platelets free of citrate and resuspending in heparinized platelet-rich plasma. Aggregation by either cell line was inhibited by EDTA and EGTA. In the Baumgartner perfusion apparatus, platelet interaction with subendothelium was increased about 50-fold in the presence of SKNMC cells, but this effect was also abolished after addition of citrate. After addition of U87MG cells to heparinized PRP, there was a 400-fold increase in platelet interaction with subendothelium, and complex thrombi containing red cells, white cells, and fibrin were formed. This stimulation was reduced to control levels by addition of citrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Platelets↗
PubMed1984

Tissue factor in microvesicles shed from U87MG human glioblastoma cells induces coagulation, platelet aggregation, and thrombogenesis.

Microvesicles (diameter ca 200 nm) from the cell-free supernatant of U87MG human glioblastoma cell caused platelet aggregation and coagulation in a manner identical with that previously shown for the intact cells. Both activities were inhibited by dansylarginine -N-(3-ethyl-1,5-pentanediyl) amide (DAPA), confirming the thrombin-dependent nature of both activities. The specific activities per microgram of protein were 2-10 times greater in the microvesicles than in the plasma membrane fraction, suggesting localization in specific membrane domains. Sucrose density centrifugation gave a single protein peak (density 1.14) with congruent procoagulant and platelet aggregating activities. Both activities required the extrinsic pathway, as shown by studies with factor-deficient plasmas, and both were inhibited by heating (60 min/100 degrees C), by reduction and alkylation, and by incubation of the microvesicles with rabbit anti-bovine brain tissue factor antibody. These observations were confirmed using microvesicles from the HL-60 human promyelocytic leukemia cells, which are known to contain tissue factor activity. The results suggest that both procoagulant and proaggregating activities are causally related through the presence of tissue factor in the microvesicles. Studies with the Baumgartner perfusion apparatus showed that U87MG microvesicles increased the size of adherent thrombi nearly tenfold and that these thrombi were associated with nucleated cells from the blood. The increase in adherent thrombi did not occur if perfusion was carried out in the presence of DAPA, confirming the role of thrombin in their formation.

Antibodies↗