Biomedical subjects

P A Whiss

Publications and source records attributed to P A Whiss.

9 recordsLinked to original sources

PubMed2002

Divalent cations and the protein surface co-ordinate the intensity of human platelet adhesion and P-selectin surface expression.

At sites of blood vessel injury, platelets adhere to exposed vessel components, such as collagen, or immobilized fibrinogen derived from plasma or activated platelets. The divalent cations Mg(2+) and Ca(2+) are essential for platelet adhesion and activation, but Mg(2+) can also inhibit platelet activation. The present study evaluates, by an enzymatic method, the effects of various divalent cations on the adhesion of isolated human platelets to collagen, fibrinogen, albumin or plastic in vitro. By enzyme-linked immunosorbent assay, platelet surface expression of P-selectin was measured to estimate the state of activation on adherence. Mg(2+) increased platelet adhesion exclusively to collagen and fibrinogen at physiologically relevant concentrations. At higher concentrations, the adhesion declined. Ca(2+) induced a weak adhesion only to fibrinogen at physiological doses and a peak of increased adhesion to all protein-coated surfaces at 10 mmol/l. Mn(2+) elicited dose-dependent adhesion only to collagen and fibrinogen. Zn(2+), Ni(2+) and Cu(2+) increased the adhesion of platelets independently of the surface. Ca(2+) dose-dependently inhibited adhesion elicited by Mg(2+) to collagen and fibrinogen. No other combination of divalent cations elicited such an effect. Mg(2+)-dependent platelet adhesion to collagen and Ca(2+)-dependent adhesion to fibrinogen increased P-selectin expression. Thus, the present study shows that the outcome of the platelet adhesion depends on the surface and the access of divalent cations, which co-ordinate the intensity of platelet adhesion and P-selectin surface expression.

Acid Phosphatase↗

PubMed2001

CTC-11 (Teijin).

Teijin and Chemo-Sero are codeveloping CTC-111 as a treatment for disseminated intravascular coagulation (DIC) due to protein C deficiency. The drug was launched for the treatment of protein C deficiency in Japan on January 31, 2001 and as of October 2001 was awaiting approval for the treatment of DIC, also in Japan [426762]. CTC-111 was evaluated in a multicenter pharmacokinetic trial in venous thrombosis patients with inherited protein C deficiency. CTC-111 was effective in six of ten patients with venous thrombosis, six of seven patients with deep vein thrombosis and two of three patients with pulmonary embolism. Treatment was safe and effective and there were no serious adverse events [350149].

Journal Article↗

PubMed2000

Nitric oxide donors and angiotensin-converting enzyme inhibitors act in concert to inhibit human angiotensin-converting enzyme activity and platelet aggregation in vitro.

This study investigates the effects of exogenous and endogenous nitric oxide (NO) on human circulating and endothelial angiotensin-converting enzyme activity and platelet aggregation. The NO donor S-nitroso-N-acetylpenicillamine (10(-8)-10(-6) M) significantly and dose-dependently inhibited serum angiotensin-converting enzyme activity. The concomitant addition of S-nitroso-N-acetylpenicillamine to angiotensin-converting enzyme inhibitor-treated (captopril or enalaprilat) serum, further reduced angiotensin-converting enzyme activity. In cultured endothelial cells from human umbilical veins (HUVECs), both S-nitroso-N-acetylpenicillamine and 3-morpholinosydnonimine (SIN-1) significantly reduced angiotensin-converting enzyme activity. An additative effect was seen with a combined treatment of captopril and S-nitroso-N-acetylpenicillamine. Treatment with the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) did not affect angiotensin-converting enzyme activity. Thrombin inhibited endothelial angiotensin-converting enzyme activity, an effect that was abolished when cells were pretreated with L-NMMA. Adenosine 5'-diphosphate (ADP)-induced platelet aggregation was inhibited with S-nitroso-N-acetylpenicillamine, SIN-1 and nitroglycerine. Captopril did not affect aggregation, while a high concentration of enalaprilat (10(-4) M) reduced it. The concomitant addition of 10(-5) M angiotensin-converting enzyme inhibitor to NO donor-treated platelets resulted in a further reduction of platelet aggregation. This effect was most evident with SIN-1 and enalaprilat. In conclusion, both exogenous and endogenous NO inhibit human angiotensin-converting enzyme activity. NO donors and angiotensin-converting enzyme inhibitors act in concert to inhibit angiotensin-converting enzyme and platelet aggregation.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2000

Acute effects of nicotine infusion on platelets in nicotine users with normal and impaired renal function.

The role of platelets in cardiovascular disease associated with smoking is becoming more established, but the effects of nicotine on platelets are unclear. Nicotine therapy is used for smoking cessation in both health and disease. Consequently, the effects of nicotine on platelets are of particular significance in disorders such as renal disease, which is associated with defective platelet function, increased cardiovascular morbidity, and altered nicotine metabolism. Thus, the aim of the present study was to investigate the acute effects of nicotine infusion (NI) on platelets in seven healthy subjects (HS) and seven patients with renal failure (RF). All subjects were nicotine users and had refrained from using nicotine for 36 h before NI. Blood was collected before, immediately after, and 2 h after NI. The plasma concentrations of nicotine and its main metabolite cotinine were determined by gas chromatography. Platelet responsiveness was assessed by aggregometry and flow cytometry in whole blood (P-selectin surface expression, fibrinogen- and von Willebrand factor-binding), P-selectin expression in isolated platelets, and immunoassays of platelet release (beta-thromboglobulin, platelet factor 4, and soluble P-selectin) and nitric oxide (NO) products. The plasma levels of cotinine, but not nicotine, were significantly higher in RF compared to HS at all time points. In both groups, collagen-induced platelet aggregation was restrained immediately after NI, when the plasma concentration of nicotine was maximal, and was restored after 2 h. Two hours after NI, activation-dependent P-selectin surface expression in isolated platelets increased in both groups. This increased platelet responsiveness occurred simultaneously with a significant increase of plasma cotinine and a decrease of NO products. Thus, the present study suggests that nicotine, directly or through some secondary mechanism or metabolite, only slightly potentiates some of the platelet responses. Renal failure appears not to influence the effects of nicotine on platelets.

Blood Platelets↗

PubMed2000

Expression of platelet P-selectin and detection of soluble P-selectin, NPY and RANTES in patients with inflammatory bowel disease.

OBJECTIVE AND DESIGN: P-selectin, a membrane glycoprotein which is expressed on activated platelets and endothelial cells, plays a crucial role in the inflammatory response. The main action is adhesion of leukocytes, facilitation of diapedesis and induction of cytokine production from monocytes (MCP-1 and IL-8), mediated via RANTES released from activated platelets. An abnormal platelet activity has been reported in patients with ulcerative colitis (UC) and Crohn's disease (CD), jointly referred to as inflammatory bowel disease (IBD), which could have an aggravating influence on the inflammatory response. In addition, an up-regulation of platelet IL-8 receptors among patients with IBD has been reported. To reveal a presumptuous platelet dysfunction we analysed the expression of platelet surface P-selectin at resting state and after stimulation with thrombin, collagen, epinephrine and interleukin 8 (IL-8), and plasma levels of soluble P-selectin, neuropeptide Y (NPY) and RANTES in patients with IBD. SUBJECTS: Blood from twelve healthy subjects (control group) and twenty-one patients with IBD who had not taken any anti-platelet drugs or steroids were analysed. METHODS: Patients were sub-grouped according to disease entity, disease activity and 5ASA medication. Surface P-selectin expression on isolated human platelets and plasma P-selectin, NPY and RANTES were analysed with ELISA. All values are presented as mean +/- standard error of the mean (SEM). Mann-Whitney U test and Wilcoxon matched rank test were used for statistical analyses. RESULTS: Patients with IBD in remission (n = 9) had higher basal P-selectin expression, 0.38+/-0.04, compared to the control group (n = 12), 0.22+/-0.03,p < 0.01. UC patients (n = 16) showed down-regulation of P-selectin expression after stimulation with IL-8, 0.26+/-0.03 to 0.22+/-0.02, p < 0.05. No significant differences could be observed concerning soluble P-selectin and NPY in plasma. Patients with 5ASA (n = 12) had lower levels of plasma RANTES, 2.39+/-0.06 microg/l, compared to the control group (n = 12), 3.29+/-0.19 microg/l, p < 0.01, and patients without 5ASA (n = 9), 2.90+/-0.17 microg/l, p < 0.05. CONCLUSIONS: Patients with IBD in remission have higher basal platelet surface P-selectin expression. An exaggerated platelet activity with increased expression of platelet P-selectin and release of inflammatory mediators such as RANTES, which is chemotactic and induce chemokine production, could have a reinforcing and aggravating influence on the inflammatory response and increase the susceptibility to IBD. In addition IL-8 has a down-regulating effect on platelet surface P-selectin expression and 5ASA medication seems to lower plasma RANTES. If 5ASA is responsible for lowering the concentration of RANTES this could be one of the beneficial outcomes of 5ASA medication.

Adult↗

PubMed1999

Platelets enhance neutrophil locomotion: evidence for a role of P-selectin.

It has been suggested that the accumulation of platelets at sites of vascular damage and inflammation regulates the function of leukocytes. In this study, we investigated the effects of platelets on the transmigration of neutrophil granulocytes through microporous membranes. We demonstrate that platelets markedly enhance both the random and the chemotactic migration of neutrophils. Stimulatory effects were acquired by adding paraformaldehyde-fixed platelets or the supernatants of platelets; however, the effects were lower or significantly higher, respectively, compared with viable platelets. The increased neutrophil migration was associated with an amplified polymerization of actin filaments and expression of CD11b/CD18. Previous investigations indicate that the initial adhesion between platelets and neutrophils is mediated by P-selectin exposed on the surface of platelets. In this study, the following observations suggest a role for P-selectin in the platelet-induced enhancement of neutrophil motility: (i) platelet supernatants contained substantial amounts of P-selectin, (ii) filtration of platelet supernatants markedly reduced the content of P-selectin and simultaneously decreased the potentiating effects on neutrophil motility, (iii) inhibition of P-selectin-mediated cell cell adhesion with sialyl Lewis X or by incubation in calcium-free medium reduced the enhancing effects of platelets on neutrophil responses, and (iv) purified and recombinant P-selectin mimicked the effects of platelets on neutrophil locomotion. In conclusion, we propose that platelets through P-selectin promote accumulation and emigration of neutrophils during inflammatory and thrombotic processes.

Actins↗

PubMed1998

Kinetics of platelet P-selectin mobilization: concurrent surface expression and release induced by thrombin or PMA, and inhibition by the NO donor SNAP.

Activated platelets and endothelium surface express the cell adhesion molecule P-selectin (CD62P), which plays an important role in mediating interactions with leukocytes. Increased levels of a functional soluble form of P-selectin (sP-selectin) have been reported in several pathological states but it is not clear whether this circulating sP-selectin originates from platelets and/or endothelial cells. Here we describe the concurrent kinetics of intracellular storage, surface expression and release of platelet P-selectin induced by thrombin or the protein kinase C activator PMA. Platelet activation with submaximal concentrations of thrombin (0.1 U/ml) resulted in a rapid decrease of intracellular P-selectin. This decrease of intracellular P-selectin concurred with a gradual increase of surface expression and an initial increase of sP-selectin. Our results indicate that intracellular stores of P-selectin were only partly mobilized upon activation with submaximal concentrations of thrombin. A high concentration of thrombin (1.0 U/ml) induced a rapid and nearly total decrease of intracellular stores and a more pronounced, but transient, increase of surface expression. The release of P-selectin was fast and occurred during the initial activation phase. The NO donor SNAP inhibited both surface expression and release of platelet P-selectin in a similar manner. PMA (0.1-1.0 microM) mediated a more slow, gradual and sustained surface expression and release of P-selectin than thrombin. Thus, surface expression and release of platelet P-selectin show different kinetics depending on the mode of activation.

Blood Platelets↗

PubMed1997

Modulation of P-selectin expression on isolated human platelets by an NO donor assessed by a novel ELISA application.

Adhesion molecules such as P-selectin are potential markers for evaluating platelet activation and studying the role of cell-cell interactions in numerous biological processes related to hemostasis and inflammation. The expression of P-selectin and related molecules has previously been quantified with different techniques. As an alternative to the most common method. flow cytometry, we have developed a useful ELISA method to simultaneously analyse 96 samples for platelet expression of P-selectin. Samples may be stored for at least 7 days at 4 degrees C prior to analysis. The method is simple, reproducible, flexible and requires only standard equipment. Washed platelets (WP) from healthy male volunteers, at a concentration of 1 x 10(7)/microtiter plate well, were stimulated with various known platelet activators and fixed with 0.1% formaldehyde for 10 min. The fixed WP were centrifuged to form a confluent layer in the wells and then incubated with optimal dilutions of primary antibodies (1/2000) directed against P-selectin, CD41, CD9 and secondary antibodies conjugated with alkaline phosphatase. Our results show that P-selectin expression on WP increases significantly upon stimulation with thrombin (0.1-1.0 U/ml), ADP (10 microM) and epinephrine (100 microM). The induction of P-selectin expression by thrombin is fast and has different kinetics depending on the concentration of the agonist. Prior incubation with the nitric oxide donor SNAP (10 microM) inhibits the up-regulation of P-selectin induced by sub-maximal concentrations of thrombin (p < 0.05). This ELISA is suitable for studying the expression and regulation of P-selectin and other surface molecules on human platelets in various pathological states.

Adenosine Diphosphate↗

PubMedDate not supplied

Adenosine 5'-diphosphate-induced platelet aggregation in uremia shows resistance to inhibition by the novel nitric oxide donor GEA 3175 but not by S-nitroso-N-acetylpenicillamine.

Both bleeding and thrombosis are complications of uremia in patients on regular hemodialysis. An excessive endogenous formation of the vasodilator and platelet inhibitor nitric oxide (NO) has been proposed to contribute to the bleeding defect. Since exposure to pharmacological donors of NO, nitrovasodilators, can cause tolerance to NO, we investigated whether platelets from uremic patients on regular hemodialysis are influenced differently by NO donors than platelets from healthy subjects. A frequently used S-nitrosothiol, S-nitroso-N-acetylpenicillamine (SNAP), was compared to a recently synthezised mesoionic oxatriazole derivate, GEA 3175, regarding its capacity to inhibit adenosine 5'-diphosphate (ADP)-induced platelet aggregation in vitro. The final products of NO production, nitrite + nitrate, were found to be significantly increased in uremic patients. The capacity to inhibit platelet aggregation by SNAP was only slightly different between the groups. However, GEA 3175 showed a significantly marked and reduced capacity to inhibit aggregation of uremic platelets compared to controls. Interactions of erythropoietin (EPO) with NO have earlier been reported. Addition of EPO to platelets from healthy donors in vitro did not significantly influence the NO donor capacity to inhibit platelet aggregation, but showed a tendency to enhance the effect of SNAP while the effect of GEA 3175 was inhibited. These results suggest compound-specific resistance to NO donors in uremic platelet activation.

Adenosine Diphosphate↗