Aggregating human platelets stimulate the expression of thrombin receptors in cultured vascular smooth muscle cells via the release of transforming growth factor-beta1 and platelet-derived growth factorAB

Evaluation of Platelet Activation by HIV Protease Inhibitors - The HIV-PLA II Study

Background

In the past, protease inhibitors (PIs) and the reverse transcriptase inhibitor abacavir were identified increasing the risk for thromboembolic complications and cardiovascular events (CVE) of HIV infected patients taking a combination antiretroviral therapy (cART). Results of the previous HIV-PLA I-study lead to the assumption that platelet activation could play a substantial role in increasing CVE risks.

Methods

The open label, monocentric HIV-PLA II-study investigated HIV-1-infected, therapy-naïve adults (n=45) starting with cART, consisting either of boosted PI (atazanavir, n= 6, darunavir, n=11), NNRTI (efavirenz, n=14) or integrase inhibitor (raltegravir, n=14), each plus tenofovir/emtricitabine co-medication. Main exclusion criteria were tobacco smoking, the intake of NSAIDs or abacavir or past CVE. Platelet adhesive molecule p-selectin (CD62P) and FITC anti-human Integrin α-IIb/Integrin β-3 (CD41/CD61) antibody (PAC-1) binding, monocyte CD11b/monocyte-associated CD41 expression and the endogenous thrombin potential (ETP) were assessed ex vivo-in vitro at baseline, weeks 4, 12 and 24. Therapy regimens were blinded to the investigators for laboratory and statistical analyses.

Results

CD11b and ETP showed no significant changes or differences between all study groups. In contrast, the mean + SD mean fluorescence units (MFI) of CD62P and PAC-1 increased significantly in patients taking PI, indicating an enhanced potential for thrombocyte activation and aggregation.

Conclusion

CD62P expression, detecting the ɑ-platelet degranulation of pro-inflammatory and pro-thrombotic factors and adhesive proteins, and PAC-1 expression, representing a marker for conformation changes of the GIIb/IIIa receptor, increased significantly in patients taking HIV protease inhibitors. The findings of this study revealed a yet unknown pathway of platelet activation, possibly contributing to the increased risk for CVE under HIV protease inhibitor containing cART.

Clinical Trial Registration No.

DRKS00000288.

PAR2 (Protease-Activated Receptor 2) Deficiency Attenuates Atherosclerosis in Mice

OBJECTIVE

PAR2 (protease-activated receptor 2)-dependent signaling results in augmented inflammation and has been implicated in the pathogenesis of several autoimmune conditions. The objective of this study was to determine the effect of PAR2 deficiency on the development of atherosclerosis.

APPROACH AND RESULTS

PAR2 mRNA and protein expression is increased in human carotid artery and mouse aortic arch atheroma versus control carotid and aortic arch arteries, respectively. To determine the effect of PAR2 deficiency on atherosclerosis, male and female low-density lipoprotein receptor-deficient (Ldlr-/-) mice (8-12 weeks old) that were Par2+/+ or Par2-/- were fed a fat- and cholesterol-enriched diet for 12 or 24 weeks. PAR2 deficiency attenuated atherosclerosis in the aortic sinus and aortic root after 12 and 24 weeks. PAR2 deficiency did not alter total plasma cholesterol concentrations or lipoprotein distributions. Bone marrow transplantation showed that PAR2 on nonhematopoietic cells contributed to atherosclerosis. PAR2 deficiency significantly attenuated levels of the chemokines Ccl2 and Cxcl1 in the circulation and macrophage content in atherosclerotic lesions. Mechanistic studies using isolated primary vascular smooth muscle cells showed that PAR2 deficiency is associated with reduced Ccl2 and Cxcl1 mRNA expression and protein release into the supernatant resulting in less monocyte migration.

CONCLUSIONS

Our results indicate that PAR2 deficiency is associated with attenuation of atherosclerosis and may reduce lesion progression by blunting Ccl2- and Cxcl1-induced monocyte infiltration.

Genomic correlates of glatiramer acetate adverse cardiovascular effects lead to a novel locus mediating coronary risk

Glatiramer acetate is used therapeutically in multiple sclerosis but also known for adverse effects including elevated coronary artery disease (CAD) risk. The mechanisms underlying the cardiovascular side effects of the medication are unclear. Here, we made use of the chromosomal variation in the genes that are known to be affected by glatiramer treatment. Focusing on genes and gene products reported by drug-gene interaction database to interact with glatiramer acetate we explored a large meta-analysis on CAD genome-wide association studies aiming firstly, to investigate whether variants in these genes also affect cardiovascular risk and secondly, to identify new CAD risk genes. We traced association signals in a 200-kb region around genomic positions of genes interacting with glatiramer in up to 60 801 CAD cases and 123 504 controls. We validated the identified association in additional 21 934 CAD cases and 76 087 controls. We identified three new CAD risk alleles within the TGFB1 region on chromosome 19 that independently affect CAD risk. The lead SNP rs12459996 was genome-wide significantly associated with CAD in the extended meta-analysis (odds ratio 1.09, p = 1.58×10⁻¹²). The other two SNPs at the locus were not in linkage disequilibrium with the lead SNP and by a conditional analysis showed p-values of 4.05 × 10⁻¹⁰ and 2.21 × 10⁻⁶. Thus, studying genes reported to interact with glatiramer acetate we identified genetic variants that concordantly with the drug increase the risk of CAD. Of these, TGFB1 displayed signal for association. Indeed, the gene has been associated with CAD previously in both in vivo and in vitro studies. Here we establish genome-wide significant association with CAD in large human samples.

Vessel wall, not platelet, P2Y12 potentiates early atherogenesis

AIMS

Platelets have a fundamental role in atherothrombosis, but their role in early atherogenesis is unclear. The P2Y12 receptor is responsible for amplifying and sustaining platelet activation and P2Y12 inhibition is crucial in modulating the vessel wall response to injury. We therefore examined the role of platelet vs. vessel wall P2Y12 in early atherogenesis and considered the use of P2Y12 antagonists ticagrelor and clopidogrel in modulating this process.

METHODS AND RESULTS

ApoE(-/-) and ApoE(-/-)P2Y12 (-/-) male mice underwent bone marrow transplantation and were fed a western diet for 4 weeks before assessing atherosclerotic burden. Compared with ApoE(-/-) controls, platelet P2Y12 deficiency profoundly reduced platelet reactivity but had no effect on atheroma formation, whereas vessel wall P2Y12 deficiency significantly attenuated atheroma in the aortic sinus and brachiocephalic artery (both P < 0.001). ApoE(-/-) and ApoE(-/-)P2Y12 (-/-) male mice fed western diet plus either twice-daily doses of ticagrelor (100 mg/kg) or daily clopidogrel (20 mg/kg) for 4 weeks exhibited no significant reduction in atheroma compared with control mice fed mannitol. Attenuated P-selectin expression confirmed platelet P2Y12 inhibition in drug-treated mice.

CONCLUSIONS

Despite its major contribution to platelet reactivity, platelet P2Y12 has no effect on early atheroma formation, whereas vessel wall P2Y12 is important in this process. Ticagrelor and clopidogrel effectively reduced platelet reactivity but were unable to inhibit early atherogenesis, demonstrating that these P2Y12 inhibitors may not be effective in preventing early disease.

In vitro and in vivo evidence that thrombospondin-1 (TSP-1) contributes to stirring- and shear-dependent activation of platelet-derived TGF-beta1

Thrombospondin 1 (TSP-1), which is contained in platelet α-granules and released with activation, has been shown to activate latent TGF-β1 in vitro, but its in vivo role is unclear as TSP-1-null (Thbs1^−/−) mice have a much less severe phenotype than TGF-β1-null (Tgfb1^−/−) mice. We recently demonstrated that stirring and/or shear could activate latent TGF-β1 released from platelets and have now studied these methods of TGF-β1 activation in samples from Thbs1^−/− mice, which have higher platelet counts and higher levels of total TGF-β1 in their serum than wild type mice. After either two hours of stirring or shear, Thbs1^−/− samples demonstrated less TGF-β1 activation (31% and 54% lower levels of active TGF-β1 in serum and platelet releasates, respectively). TGF-β1 activation in Thbs1^−/− mice samples was normalized by adding recombinant human TSP-1 (rhTSP-1). Exposure of platelet releasates to shear for one hour led to near depletion of TSP-1, but this could be prevented by preincubating samples with thiol-reactive agents. Moreover, replenishing rhTSP-1 to human platelet releasates after one hour of stirring enhanced TGF-β1 activation. In vivo TGF-β1 activation in carotid artery thrombi was also partially impaired in Thbs1^−/− mice. These data indicate that TSP-1 contributes to shear-dependent TGF-β1 activation, thus providing a potential explanation for the inconsistent in vitro data previously reported as well as for the differences in phenotypes of Thbs1^−/− and Tgfb1^−/− mice.

Is thrombin a key player in the 'coagulation-atherogenesis' maze?

In addition to its established roles in the haemostatic system, thrombin is an intriguing coagulation protease demonstrating an array of effects on endothelial cells, vascular smooth muscle cells (VSMC), monocytes, and platelets, all of which are involved in the pathophysiology of atherosclerosis. There is mounting evidence that thrombin acts as a powerful modulator of many processes like regulation of vascular tone, permeability, migration and proliferation of VSMC, recruitment of monocytes into the atherosclerotic lesions, induction of diverse pro-inflammatory markers, and all of these are related to the progression of cardiovascular disease. Recent studies in transgenic mice models indicate that the deletion of the natural thrombin inhibitor heparin cofactor II promotes an accelerated atherogenic state. Moreover, the reduction of thrombin activity levels in apolipoprotein E-deficient mice, because of the administration of the direct thrombin inhibitor melagatran, attenuates plaque progression and promotes stability in advanced atherosclerotic lesions. The combined evidence points to thrombin as a pivotal contributor to vascular pathophysiology. Considering the clinical development of selective anticoagulants including direct thrombin inhibitors, it is a relevant moment to review the different thrombin-induced mechanisms that contribute to the initiation, formation, progression, and destabilization of atherosclerotic plaques.

In vitro and in vivo evidence for shear-induced activation of latent transforming growth factor-beta1

Transforming growth factor-beta1 (TGF-beta1) has potent physiologic and pathologic effects on a variety of cell types at subnanomolar concentrations. Platelets contain 40 times as much TGF-beta1 as other cells and secrete it as an inactive (latent) form in complex with latency-associated peptide (LAP), which is disulfide bonded via Cys33 to latent TGF-beta binding protein 1 (LTBP-1). Little is known about how latent TGF-beta1 becomes activated in vivo. Here we show that TGF-beta1 released from platelets or fibroblasts undergoes dramatic activation when subjected to stirring or shear forces, providing a potential mechanism for physiologic control. Thiol-disulfide exchange appears to contribute to the process based on the effects of thiol-reactive reagents and differences in thiol labeling of TGF-beta1 before and after stirring or shear. Activation required the presence of LTBP, as TGF-beta1 contained in complex with only LAP could not be activated by stirring when studied as either a recombinant purified protein complex or in the platelet releasates or sera of mice engineered to contain an LAP C33S mutation. Release and activation of latent TGF-beta1 in vivo was demonstrated in a mouse model 5 minutes after thrombus formation. These data potentially provide a novel mechanism for in vivo activation of TGF-beta1.

Modulation of mast cell proteinase-activated receptor expression and IL-4 release by IL-12

It has been recognized that protease-activated receptors (PARs), interleukin (IL)-4 and IL-6 are involved in the pathogenesis of allergic diseases, and that IL-12 plays a role in adaptive immune response. However, little is known of the effect of IL-12 on protease-induced cytokine release from mast cells. In the present study, we examined potential influence of IL-12 on mast cell PAR expression and IL-4 and IL-6 release. The results showed that IL-12 downregulated the expression of PAR-2 and upregulated expression of PAR-4 on P815 cells. It also downregulated expression of PAR-2 mRNA, and upregulated expression of PAR-1, PAR-3 and PAR-4 mRNAs. However, IL-12 enhanced trypsin- and tryptase-induced PAR-2 and PAR-2 mRNA expression. It was observed that IL-12 induced release of IL-4, but reduced trypsin- and tryptase-stimulated IL-4 secretion from P815 cells. PD98059, U0126 and LY294002 not only abolished IL-12-induced IL-4 release but also inhibited IL-12-induced phosphorylation of extracellular signal-regulated kinase and Akt. In conclusion, IL-12 may serve as a regulator in keeping the balance of Th1 and Th2 cytokine production in allergic inflammation.

Absence of proteinase-activated receptor-1 signaling affords protection from bleomycin-induced lung inflammation and fibrosis

Activation of the coagulation cascade is commonly observed in the lungs of patients with both acute and chronic inflammatory and fibrotic lung disorders, as well as in animal models of these disorders. The aim of this study was to examine the contribution of the major thrombin receptor, proteinase-activated receptor-1 (PAR-1), during the acute inflammatory and chronic fibrotic phases of lung injury induced by intratracheal instillation of bleomycin in mice. Inflammatory cell recruitment and increases in bronchoalveolar lavage fluid (BALF) protein were attenuated by 56 +/- 10% (P < 0.05) and 53 +/- 12% (P < 0.05), respectively, in PAR-1-deficient (PAR-1-/-) mice compared with wild-type (WT) mice. PAR-1-/- mice were also protected from bleomycin-induced pulmonary fibrosis with total lung collagen accumulation reduced by 59 +/- 5% (P < 0.05). The protection afforded by PAR-1 deficiency was accompanied by significant reductions in pulmonary levels of the potent PAR-1-inducible proinflammatory and profibrotic mediators, monocyte chemoattractant protein-1 (MCP-1), transforming growth factor-beta-1 (TGF-beta1), and connective tissue growth factor/fibroblast-inducible secreted protein-12 (CTGF/FISP12). In addition, PAR-1 was highly expressed in inflammatory and fibroproliferative lesions in lung sections obtained from patients with fibrotic lung disease. These data show for the first time that PAR-1 signaling plays a key role in experimentally induced lung injury, and they further identify PAR-1 as one of the critical receptors involved in orchestrating the interplay between coagulation, inflammation, and remodeling in response to tissue injury.

Physiology and Pathophysiology of Proteinase-Activated Receptors (PARs): Regulation of the Expression of PARs

The level of receptors expressed on the cell surface determines the cellular responsiveness to agonists. Proteinase-activated receptors (PARs) have been reported to be either up-regulated or down-regulated in response to various types of stimulation and pathological situations. In addition, the transcriptional regulation plays a major role in the alteration of the expression of PARs under pathological conditions, while post-translational mechanisms such as phosphorylation, arresting-binding, internalization, and lysosomal degradation, which desensitize activated PARs and terminate intracellular signaling, also play an important role in regulating the expression of PARs and the cellular responsiveness to the agonists. Elucidating the mechanisms related to the expression of PARs is a critical step to understand the pathophysiology of various diseases and establish new therapeutic strategies. However, the molecular mechanism regulating the expression of PARs still remains to be elucidated. This minireview discusses our current understanding of the mechanisms regulating the expression of PARs. The transcription factors and the regulatory elements in the promoter regions, and the proteins that interact with the receptors and thereby regulate their trafficking and desensitization are the main problems that need to be elucidated.

Insights into the redox control of blood coagulation: role of vascular NADPH oxidase-derived reactive oxygen species in the thrombogenic cycle

Various cardiovascular diseases including thrombosis, atherosclerosis, (pulmonary) hypertension and diabetes, are associated with disturbed coagulation. Alterations in the vessel wall common to many cardiovascular disorders have been shown to initiate the activity of the coagulation system, but also to be the result of an abnormal coagulation system. The primary link between the coagulation and the vascular system appears to be tissue factor (TF), which is induced on the surface of vascular cells and initiates the extrinsic pathway of the blood coagulation cascade, leading to the formation of thrombin. Thrombin can also interact with the vascular wall via specific receptors and can increase vascular TF expression. Such a "thrombogenic cycle" may be essentially involved in the pathogenesis of cardiovascular disorders associated with an abnormal coagulation. Therefore, the identification of the signaling pathways regulating this cycle and each of its relevant connecting links is of fundamental importance for the understanding of these disorders and their putative therapeutic potential. Reactive oxygen species (ROS) and the ROS-generating NADPH oxidases have been shown to play important roles as signaling molecules in the vasculature. In this review, we summarize the data supporting a substantial role of ROS in promoting a thrombogenic cycle in the vascular system.

Pharmacodynamic characterization of the interaction between the glycoprotein IIb/IIIa inhibitor YM337 and unfractionated heparin and aspirin in humans

AIMS

To investigate the pharmacodynamic interaction of unfractionated heparin (UFH) and acetylic salicylic acid (ASA) on YM337, a monoclonal humanized antibody of the platelet GPIIb/IIIa receptor.

METHODS

In a randomized, placebo-controlled study three treatment groups each with six healthy volunteers received the following medication: group 1, ASA (3 days) + UFH + YM337 (placebo); group 2, ASA (placebo) + UFH (placebo) + YM337; group 3, ASA + UFH + YM337. Assessments were made over 24 h and included bleeding time (BT), ADP (20 microm)- and collagen (5 microg ml-1)-induced platelet aggregation and PAC1 and CD62 expression measured by flow cytometry.

RESULTS

In group 3 BT was prolonged to 35 [median, 16-45 min (1,3 quartile)] after UFH administration, increasing to 45 [median, 42-45 min (1,3 quartile)] after YM infusion (6 h). BT remained elevated to 26 [median, 14-45 min (1,3 quartile)] at 24 h, while groups 1 and 2 returned to normal values. Collagen-induced aggregation was 73% [median, 70-80% (1,3 quartile)] under YM337 alone, 79% [median, 72-80% (1,3 quartile)] under ASA + UFH and reduced only in group 3 to 24% [median, 18-29% (1,3 quartile)]. In both groups receiving active YM337, PAC1 expression showed a reduction to < 20% after 6 h of infusion. CD62 expression was not significantly affected by any treatment.

CONCLUSION

UFH and YM337 have strong synergistic effects on BT, while coadministration of ASA strongly augments inhibitory effects of YM337 on collagen-induced platelet aggregation.

Activated platelets trigger an inflammatory response and enhance migration of aortic smooth muscle cells

OBJECTIVE

Exposure of the subendothelium to flowing blood following rupture of atherosclerotic lesions or during balloon angioplasty initiates platelet adhesion to the vascular wall. Because activated platelets release proinflammatory mediators (e.g., interleukin (IL)-1beta) and secrete growth factors, platelet adhesion to the subendothelial matrix might contribute to the recruitment of inflammatory cells and promote migration and proliferation of vascular smooth muscle cells (SMCs).

METHODS AND RESULTS

Here, we demonstrate that incubation of cultured monolayers of aortic SMCs with alpha-thrombin-activated platelets significantly enhances the secretion of monocyte chemoattractant protein-1 (MCP-1) (P<0.05) and promotes SMC migration (P<0.05). Platelet-induced secretion of MCP-1 was abolished by anti-IL-1alpha and beta monoclonal antibodies or the IL-1 receptor antagonist (IL-1RA). In contrast, platelet-mediated SMC migration was attenuated only by anti-platelet-derived growth factor (PDGF)-mAb but not by IL-1RA. Correspondingly, recombinant human interleukin-1 (rhIL-1) beta increased MCP release by SMCs but had no effect on SMC migration. Platelet-mediated MCP secretion by SMCs involved the activation and nuclear translocation of the transcription factor nuclear factor-kappaB (NF-kappaB).

CONCLUSION

Therefore, platelet adhesion to the subendothelium increases the chemotactic and migratory properties of SMC and is likely to contribute substantially to the process of atherosclerosis and vessel (re-)stenosis.

Prospective evaluation of hydroperoxide plasma levels and stable nitric oxide end products in patients subjected to angioplasty for coronary artery disease

BACKGROUND

Oxidative stress appears to be involved in several processes that contribute to atherogenesis and restenosis following vascular intervention.

METHODS

The aim of our study was to evaluate prospectively the plasma concentrations of a hydroperoxide (ROOH) and nitric oxide end product (NO(x)) in patients subjected to coronary angioplasty (PTCA) and routine control angiography 6 months after the initial procedure. We prospectively studied 48 consecutive patients (39 men, nine women, mean age 52 years) with stable angina who underwent successful elective angioplasty. A vascular segment was considered successfully treated when the residual luminal narrowing in the dilated segment immediately after angioplasty was <50%. Angiographic follow-up was obtained in all of the patients. Plasma samples were drawn at baseline (before angioplasty) and serially after angioplasty (1, 3 and 6 months afterwards). Hydroperoxides were determined by the FOX II assay (ferrous oxidation in xylenol orange, Pierce Rockford, IL). Nitrate was converted in the presence of NO3 reductase. The Griess reagent was used for the measurement of NO2.

RESULTS

The overall angiographic restenosis rate was 35%. There were no significant differences in clinical variables between the patients with or without restenosis. The baseline levels (0.8+/-0.09 vs. 0.6+/-0.2 micromol/l) as well as the concentrations of authentic lipid hydroperoxide in plasma after 1 month (0.7+/-0.09 vs. 1.0+/-0.2 micromol/l) and 6 months (0.8+/-0.1 vs. 1.0+/-0.2 micromol/l) were similar in both groups. Three months after the angioplasty a significant increase in the ROOH level was noticed in the patients with restenosis (0.9+/-0.1 vs. 1.4+/-0.2, P=0.04). Plasma levels of NO(x) were similar in both groups at baseline (23.6+/-2.1 vs. 22.7+/-2.6 micromol/l) and 1 month after procedure (24.4+/-2.2 vs. 23.4+/-3.3 micromol/l). However, in patients with restenosis significant decreases in stable NO end products were observed 3 and 6 months after PTCA (18.1+/-1.5 vs. 13.3+/-1.7, P=0.04; 14.2+/-1.0 vs. 8.7+/-1.3, P=0.02, respectively).

CONCLUSIONS

In patients with angiographic restenosis a significant increase in lipid peroxidation accompanied by a reduction in the stable end products of nitric oxide in plasma is observed several months after PTCA.

Close relationship between the platelet activation marker CD62 and the granular release of platelet-derived growth factor

The expression of CD62 on the surface of platelets is considered to be an indicator of platelet degranulation and secretion. We characterized the relationship between CD62 expression and platelet-derived growth factor (PDGF)(AB) and PDGF(BB) secretion in response to thrombin-receptor activating peptide (TRAP). The principal findings were 1) expression of CD62 as a constituent of platelet alpha-granule membrane and secretion of PDGF, an important ingredient of alpha-granules, can be stimulated by TRAP-induced activation in a dose-dependent fashion; 2) the activation marker and secretion product are closely correlated with each other; and 3) changes in the CD62 expression induced by a drug, namely clopidogrel, or by a disease, namely diabetes, are paralleled by changes in PDGF secretion. Although CD62 is perceived as an activation marker of platelets indicating enhanced aggregability and secretion of alpha-granular content, the proof that the CD62 status and its modifications reflect directly the actual secretion of the most important platelet mitogen, PDGF, has so far not been given. This ex vivo-in vitro study shows that at least for the activation pathway provided by the PAR-1 receptor for which TRAP is the selective agonist, CD62 expression on platelets could be a surrogate for their secretory activity.

Platelet CD62 expression and PDGFAB secretion in patients undergoing PTCA and treatment with abciximab

AIMS

To investigate a correlation of the platelet activation marker CD62 and secretion of the growth factor PDGF from platelets in coronary patients under therapy with the GPIIb/IIIa-inhibitor abciximab.

METHODS

Flow cytometric assessment of fibrinogen binding (GPIIb/IIIa-binding site) and CD62 expression, as well as PDGF release of human platelets (immunoassay) and platelet aggregation with 20 microM ADP and 2 microg ml(-1) collagen were evaluated in nine patients with stable coronary artery disease. Patients were undergoing elective balloon angioplasty and were treated with aspirin (100 mg day(-1)), heparin (ACT < 220 s) and abciximab (bolus and infusion over 12 h). Blood samples were obtained before initiation of abciximab therapy (under aspirin and heparin) (I), 3 h after angioplasty under abciximab (II) and 12 h after termination of abciximab infusion (III).

RESULTS

Compared with sample I before abciximab therapy, fibrinogen binding was reduced to 37% (+/- 34 s.d., P < 0.05) (II) and 55% (+/- 40 s.d., P < 0.05) (III). Reduced fibrinogen binding also led to a significant reduction of the aggregation response to ADP (down to 37% +/- 20) and collagen (down to 0%). Mean fluorescence intensity of CD62-expression was 78 units (+/- 20 s.d.) (I), 72 units (+/- 14 s.d.) (II) and 64 units (+/- 12 s.d., P < 0.05) (III). PDGF release from isolated, washed platelets was 99 (+/- 33 s.d.) ng/10(9) platelets at (I), 82 (+/- 31 s.d.) ng/10(9) platelets and 96 (+/- 30 s.d.) ng/10(9) platelets.

CONCLUSIONS

The results indicate that despite a strong reduction of GPIIb/IIIa-binding and platelet aggregation, CD62 as a marker of platelet secretion and the secretion product PDGF were only slightly reduced under abciximab treatment. No direct correlation between CD62 expression and PDGF release could be demonstrated.

Embolized ischemic lesions of toes in an afibrinogenemic patient: possible relevance to in vivo circulating thrombin

Fibrinogen plays a complex role in hemostasis, thrombosis, and vascular disease. Hyperfibrinogenemia is an independent vascular risk factor and dysfibrinogenemia can provoke thrombosis. Afibrinogenemia is usually responsible for hemorrhagic diathesis, and unexpected ischemic lesions are intriguing. We report the case of an afibrinogenemic patient, who at the age of 30 developed ischemic lesions of the feet related to severe stenosis of the iliac and hypogastric arteries. The biopsy of the iliac artery lesion showed an intense myointimal hyperplasia. We performed standard hemostatic analysis and analyzed the activation markers of platelets and coagulation factors and the kinetics of thrombin generation in the patient and in normal control plasmas treated or not with reptilase. Occlusive arterial lesions were attributed to a disruptive hematoma penetrating the vascular lumen. Thrombin concentration after calcium addition increase markedly in the afibrinogenemic patient and in defibrinated normal plasma, as compared to untreated normal plasma. Thrombin-antithrombin complexes (T-AT) were markedly enhanced while F1+2 prothrombin fragments stayed in the normal range. These results suggested activation of coagulation and in vivo circulating thrombin. Thrombin activates the platelets that secrete growth factors for smooth muscle cells and generate the intimal hyperplasia. Recurrent hemorrhage within the vessel wall might induce injury and local thrombin generation. Thrombin not trapped by the clot is available for platelet activation and smooth muscle cell migration and proliferation. The absence of a protective fibrin cap on the intima might account for intima vulnerability and embolization. Afibrinogenemia appears in this paradoxical situation as a vascular risk factor.

The GPIIIa (beta3 integrin) PlA polymorphism in the early development of coronary atherosclerosis

The GPIIIa (beta3 integrin) is an integral part of two glycoprotein receptors - the GP(IIb/IIIa) fibrinogen receptors in platelets and the GP(V/IIIa) vitronectin receptors in endothelium and vascular smooth muscle cells (vSMC). The PlA polymorphism of the gene for GPIIIa (beta3 integrin) has been suggested to play an important role in the progression of coronary artery disease (CAD) and in coronary thrombosis. Whether the action of the PlA polymorphism is due to differences in platelet aggregability or function of the vSMC and endothelial GPIIIa is not known. The association of the PlA polymorphism with the early, non-complicated atherosclerosis and CAD was studied in the Helsinki Sudden Death Study (HSDS) comprising two independent, autopsy series of altogether 700 middle-aged Caucasian Finnish men (33-70 year) suffering sudden out-of-hospital death. The burden of complicated lesions was greater in men with the A2 allele (heterozygotes or homozygotes for A2) (P=0.01) compared with PlA1/A1 homozygotes in the entire series. To further estimate the role of platelet-independent GPIIIa receptors, we excluded all cases with coronary thrombosis and thrombus-overlaid complicated lesions. In this subset of men, fibrous coronary lesions were more frequent (OR 2.9; P<0.01) in the coronary arteries of PlA1/A1 homozygotes compared with men with the PlA2 allele. Moreover, men with the PlA1/A1 genotype also had more stenotic coronary arteries (P<0.05) compared with men with the A2 allele at this early, non-complicated stage of atherosclerosis. The findings of this study suggest that Pl(A1/A1) homozygotes may be prone to early atherosclerosis and more rapid progression of stable CAD whereas carriers of the PlA2 allele are more prone to thrombotic complications. We hypothesize that the PlA polymorphism may account for the early atherosclerosis by affecting the function of endothelial and vSMC GP(V/IIIa) receptors, whereas the PlA polymorphism on platelet GP(IIb/IIIa) receptors may play a major role in coronary thrombosis.

Evidence that furin is an authentic transforming growth factor-beta1-converting enzyme

Transforming growth factor (TGF)-beta1 plays an essential role in cell growth and differentiation. It is also considered as a gatekeeper of immune homeostasis with gene disruption leading to autoimmune and inflammatory diseases. TGF-beta1 is produced as an inactive precursor polypeptide that can be efficiently secreted but correct proteolytic cleavage is an essential step for its activation. Assessment of the cleavage site has revealed a unique R-H-R-R sequence reminiscent of proprotein convertase (PC) recognition motifs and has previously demonstrated that this PC-like cleavage site is correctly cleaved by furin, a member of the PC family. Here we report that among PC members, furin more closely satisfies the requirements needed to fulfill the role of a genuine TGF-beta1 convertase. Even though six members of the PC family have the ability to cleave TGF-beta1, ectopic expression of alpha(1)-antitrypsin Portland (alpha(1)-AT-PDX), a potent furin inhibitor, blocked 80% of TGF-beta1 processing mediated by endogenous enzymes as demonstrated in an in vitro digestion assay. Genetic complementation of a furin-deficient LoVo cell line with the wild-type gene restores the production of mature and bioactivable TGF-beta1. Moreover, both furin and TGF-beta are coordinately expressed and regulated in vitro and in vivo in the hematopoietic and immune system, an important tissue target. These results demonstrate for the first time that furin is an authentic and adaptive TGF-beta1-converting enzyme whereas other members of the PC family might substitute or supplement furin activity. Our study advances our comprehension of the complexity of the TGF-beta system and should facilitate the development of therapeutically useful TGF-beta inhibitors.

A CD36 synthetic peptide inhibits bleomycin-induced pulmonary inflammation and connective tissue synthesis in the rat

Transforming growth factor (TGF)-beta1 is an important regulator of inflammation and fibrosis. TGF-beta1 is usually secreted as a biologically latent protein called latent TGF-beta1 (L-TGF-beta1). L-TGF-beta1 has no biologic effect unless L-TGF-beta1 is converted to its active form. Using a well-recognized model of lung injury induced by the antineoplastic antibiotic bleomycin (Blm), we demonstrated that 7 d after intratracheal Blm administration, total lung TGF-beta was maximally increased. This induction was due to TGF-beta1 production by alveolar macrophages that, when explanted, generated increased quantities of L-TGF-beta1 complexed with the glycoprotein thrombospondin (TSP)-1. The TSP-1/L-TGF-beta1 complex was associated with CD36, a receptor for TSP-1. The association of TSP-1/L-TGF-beta1 to CD36 was critical for plasmin-mediated release of mature TGF-beta1. In this paper we show that, compared with administration of Blm by itself, when a synthetic peptide of CD36 between amino acids 93 and 110 is given concomitantly with Blm to rats, alveolar macrophages generate markedly less active TGF-beta1, the rats gain weight more rapidly, and there is less inflammation, collagen I and III, and fibronectin synthesis. These findings demonstrate a novel in vivo mechanism of activation of L-TGF-beta1 in lung injury and the importance of alveolar macrophage- derived active TGF-beta1 in the pathogenesis of pulmonary inflammation and fibrosis.

Elevated plasma TGF-beta1 in renal diseases: cause or consequence?

We previously reported elevated levels of TGF-beta1 in patients with renal carcinoma. Certain aspects led us to ask whether they might be caused by chronic damage to the kidney(s). Here we report on an extended set of patients with various renal diseases, lung cancer, humoral immunodeficiency and controls. For latent TGF-beta1 in plasma, we find that the control, immunodeficiency, lung cancer and kidney transplant groups do not differ significantly (means, 7.0-8.8 ng/ml). Also, acute short-term renal stress (extracorporal lithotrypsy) does not lead to an increase of TGF-beta1. However, the pyelonephritis patients present with levels of 19.0 ng/ml, chronic extracorporal dialysis patients with 15.5 ng/ml, and renal cell carcinoma patients with 22.8 ng/ml. For active TGF-beta1 these findings are exactly recovered. For serum levels, only the renal carcinoma group presents with significantly elevated levels of TGF-beta1. Kidney transplantation seems to normalize TGF-beta1 levels, while in the kidney cancer patients surgery has an effect only in part of the group. We conclude that elevated plasma TGF-beta1 levels are common in at least two chronic renal disease conditions, and that it normalizes with restoration of renal function. It is tempting to speculate that chronic elevation of TGF-beta1 in these patients may be critically involved in these conditions predisposing to renal cancer.

Intracoronary collagen: effects on coronary collateral circulation and the role of thromboxane

This study investigated the effects of intravascular collagen on coronary collateral blood flow. Collateral vessel growth was stimulated in 11 dogs by embolizing the left anterior descending (LAD) coronary artery with a hollow stainless steel plug. Experiments were performed 41 +/- 7 days after coronary embolization when collateral vessels were moderately well developed. Under alpha-chloralose anesthesia, the LAD was cannulated, and retrograde blood flow was used as a measure of collateral flow. Collagen (10-100 microg/kg) injected into the left main coronary artery caused a decrease of coronary collateral blood flow that became maximal at 3 min after injection and subsided within 9 min. At peak effect intracoronary collagen decreased retrograde flow by 53 +/- 6% from 32.7 +/- 8.2 to 16.8 +/- 3.7 ml/min (p < 0.05) with no change in systemic hemodynamics. Selective thromboxane A2 (TxA2)-receptor blockade with SQ30,741 had no effect on collateral blood flow during basal conditions but attenuated the collateral constriction in response to collagen. Thus, after SQ30,741, collagen caused only a nonsignificant decrease retrograde flow from 35.9 +/- 9.0 to 31.7 +/- 9.62 ml/min. The findings indicate that intravascular collagen exerts a potent vasoconstrictor effect on coronary collateral vessels. Attenuation of this response by TxA2-receptor blockade suggests that thromboxane released by activated platelets is the principal mediator of this response.

Cardiopulmonary bypass decreases cytokine production in lipopolysaccharide-stimulated whole blood cells: roles of interleukin-10 and the extracorporeal circuit

OBJECTIVE

To determine whether cardiopulmonary bypass (CPB) alters the ex vivo cytokine production of whole blood cells stimulated by lipopolysaccharide (LPS) and to assess the roles of interleukin (IL)-10 and an extracorporeal circuit (ECC) in the alteration.

DESIGN

Prospective, controlled study.

SETTING

Biochemistry laboratory and surgical intensive care unit in a university hospital.

PATIENTS

Seventeen consecutive adult patients undergoing coronary artery bypass grafting or valve surgery with normothermic CPB and eight healthy volunteers.

INTERVENTIONS

Blood samples for cytokine measurement were drawn from patients before and during (at 60, 90, 120, 180 and 360 mins) CPB and were cultured with and without LPS and with and without anti-IL-10 antibodies. Blood was also drawn from healthy subjects and sampled for cytokine analysis before and during circulation in an isolated ECC.

MEASUREMENTS AND MAIN RESULTS

The concentrations of ex vivo tumor necrosis factor (TNF)-alpha, IL-6, IL-8, and IL-10, measured by enzyme-linked immunosorbent assay, were reduced in both experimental settings. In patients on CPB, LPS hyporesponsiveness was detected at 60 mins after the onset of CPB and was maximal at 120 mins (78% to 86% decreases from pre-CPB levels) but was transient, except for TNF-alpha. The plasma concentration of IL-10 peaked at 90 mins after the start of CPB, but the role of IL-10 in LPS hyporesponsiveness appears limited because anti-IL-10 antibodies significantly increased ex vivo production of IL-6 but not TNF-alpha or IL-8. In the isolated ECC study, no IL-10 was detected in plasma, yet the ex vivo production of the cytokines (except IL-8) was decreased (by 66% to 95%).

CONCLUSION

Our results demonstrate the following: a) CPB induces an early and transient LPS hyporesponsiveness of whole blood as measured by cytokine production; b) IL-10 seems only partly involved in this process, and its role is restricted to an in vivo situation; and c) contact of blood with an ECC is sufficient to induce LPS hyporesponsiveness.

Remodeling of coronary artery lesions due to Kawasaki disease: comparison of arteriographic and immunohistochemical findings

Since the original report of Kawasaki disease in 1967 more than 150,000 cases have been reported in Japan. Although there have been no nationwide epidemics in Japan since 1987, more than 6,000 newly diagnosed cases are reported every year, and the number has been increasing year by year despite the decreasing birth rate. The etiology of the disease is still unknown. High dose intravenous gammaglobulin is currently used during the acute phase in 84% of the patients in Japan with a concomitant decrease in coronary arterial sequelae. However, 7-13% of the patients still have persistent coronary artery aneurysms after the acute stage. The aneurysms are seen mostly in the proximal coronary arteries, and are often associated with aneurysms in the distal coronary artery segments (Figure 1A, 2A). Most of the patients show a decrease in the size of aneurysms soon after the acute phase (Figure 1B). However, the aneurysms may progress to obstructive lesions even after initial regression (Figures 1C, D, 2B). Such obstructive lesions may cause sudden death or myocardial infarction. Long term follow-up of coronary artery lesions has revealed several characteristic features, including progressive localized stenosis (Figure 1D), extensive recanalizations (Figure 2D) and development of collateral arteries. Progressive increases in aneurysm size and the appearance of new aneurysms in the late phase have also been reported. The basic mechanisms of the coronary arterial remodeling in Kawasaki disease have not yet been elucidated. Only recently has immunohistochemical staining in formalin-fixed specimens become feasible. This is a major technical breakthrough since it is almost impossible to obtain fresh frozen specimens of coronary artery lesions of Kawasaki discase. In this paper, we compare immunohistochemical findings in coronary artery lesions with the corresponding coronary angiographic findings, and attempt to make inferences as to the mechanism of remodeling both in early and late phases of the disease based on the expression of vascular growth factors.

Differential in vitro effects of the platelet glycoprotein IIb/IIIa inhibitors abixicimab or SR121566A on platelet aggregation, fibrinogen binding and platelet secretory parameters

The aim of this study was to compare fibrinogen binding, inhibition of platelet aggregation and secretory potential of the MAb abciximab (0.5-5 microg/mL) and the peptidomimetic compound SR121566A (15-250 ng/mL) in vitro in whole blood. Fibrinogen binding was followed by flow cytometry; platelet function was evaluated by light transmittance and by impedance aggregometry. Secretory functions of platelets were evaluated using ATP as marker for early secretion by dense granulae and P-selectin (CD62) for alpha-granular secretion as well as CD63 for lysosomal degranulation. Results showed that fibrinogen binding induced by 5 microM TRAP was maximally inhibited greater than 80% at 3 microg/mL abciximab or at 250 ng/mL SR121566A. At these concentrations of antagonists, platelet aggregation induced by 5 microM ADP or 2 microg/mL collagen was inhibited completely. Expression of CD62 was reduced 34% with abciximab or 15% with SR121566A; CD63 expression was reduced 22% with both agents. With both agents, the EC50 for inhibition of CD62 and CD63 expressions was in similar magnitudes than the EC50 for fibrinogen binding inhibition. With 3 microg/mL abciximab, ATP secretion was maximally reduced to 50% of the control, whereas SR121566A at 250 ng/mL had no inhibitory effect on this parameter. A slight increase in ATP secretion was seen with 0.5 microg/mL abciximab and with SR121566A in concentrations of less than 45 ng/mL. The data suggest a discoupling between the anti-aggregatory and the antisecretory effects of IIb/IIIa antagonists. Because it is not established to what extend CD62 or CD63 expression can be reduced by any means, the reduction by 20-30% obtained by 3 microg/mL abciximab or 250 ng/mL SR121566A might already be the maximum possible inhibition by these agents.

Gender differences and endothelium- and platelet-derived factors in the coronary circulation

1. Experiments were designed to determine whether or not interactions of platelets with coronary arteries are affected by gender or oestrogen-status. 2. Platelets and right coronary arteries were isolated from sexually mature male, female and ovariectomized pigs. Arteries were suspended in organ chambers for the measurement of isometric force. Responses of rings, with and without endothelium, were evaluated to aggregating platelets and the platelet products 5-hydroxytryptamine (5-HT) and adenosine diphosphate (ADP). 3. Release of 5-HT, thromboxane A2 (TXA2) and prostacyclin were measured from platelets. 4. Platelets caused relaxations of rings with endothelium from all pigs. However, in rings without endothelium, consistent contractions were observed only in rings from male pigs. 5. The release of 5-HT and prostacyclin was greatest from platelets of ovariectomized pigs compared with male and female pigs. Release of TXA2 was greatest from platelets of male pigs. 6. Endothelium-dependent relaxations to ADP and contractions to 5-HT were similar among the three groups. 7. These results suggest that there may be gender-specific differences in vasomotor responses to autogenous platelets but not to the platelet-derived products 5-HT and ADP. Furthermore, there are gender differences in platelets in the release of cyclo-oxygenase metabolites of arachidonic acid and 5-HT. These products could contribute to gender differences in response to injury in the coronary circulation.