Vascular permeation of platelet factor 4 after endothelial injury

The cross talk between type II diabetic microenvironment and the regenerative capacities of human adipose tissue-derived pericytes: a promising cell therapy

BACKGROUND

Pericytes (PCs) are multipotent contractile cells that wrap around the endothelial cells (ECs) to maintain the blood vessel's functionality and integrity. The hyperglycemia associated with Type 2 diabetes mellitus (T2DM) was shown to impair the function of PCs and increase the risk of diabetes complications. In this study, we aimed to investigate the deleterious effect of the diabetic microenvironment on the regenerative capacities of human PCs.

METHODS

PCs isolated from human adipose tissue were cultured in the presence or absence of serum collected from diabetic patients. The functionality of PCs was analyzed after 6, 14, and 30 days.

RESULTS

Microscopic examination of PCs cultured in DS (DS-PCs) showed increased aggregate formation and altered surface topography with hyperbolic invaginations. Compared to PCs cultured in normal serum (NS-PCs), DS-PCs showed more fragmented mitochondria and thicker nuclear membrane. DS caused impaired angiogenic differentiation of PCs as confirmed by tube formation, decreased VEGF-A and IGF-1 gene expression, upregulated TSP1, PF4, actin-related protein 2/3 complex, and downregulated COL21A1 protein expression. These cells suffered more pronounced apoptosis and showed higher expression of Clic4, apoptosis facilitator BCl-2-like protein, serine/threonine protein phosphatase, and caspase-7 proteins. DS-PCs showed dysregulated DNA repair genes CDKN1A, SIRT1, XRCC5 TERF2, and upregulation of the pro-inflammatory genes ICAM1, IL-6, and TNF-α. Further, DS-treated cells also showed disruption in the expression of the focal adhesion and binding proteins TSP1, TGF-β, fibronectin, and PCDH7. Interestingly, DS-PCs showed resistance mechanisms upon exposure to diabetic microenvironment by maintaining the intracellular reactive oxygen species (ROS) level and upregulation of extracellular matrix (ECM) organizing proteins as vinculin, IQGAP1, and tubulin beta chain.

CONCLUSION

These data showed that the diabetic microenvironment exert a deleterious effect on the regenerative capacities of human adipose tissue-derived PCs, and may thus have possible implications on the vascular complications of T2DM. Nevertheless, PCs have shown remarkable protective mechanisms when initially exposed to DS and thus they could provide a promising cellular therapy for T2DM.

Plasma and Urinary Platelet Factor 4 as Biomarkers for Cardiovascular Risk in Children with Chronic Kidney Disease

Children suffering from chronic kidney disease (CKD) have a high risk of cardiovascular disease (CVD). The early detection and diagnosis of subclinical CVD in pediatric CKD can reduce mortality later in life. Plasma factor 4 (PF4) is a chemokine released by activated platelets. We examined whether or not PF4 in the plasma and urine, its kidney function normalized ratio, and fractional excretion have differential associations with CVD risk markers in 139 youths aged 3 to 18 years old with CKD stages G1-G4. Significant negative correlations were observed between plasma PF4 and cardiovascular surrogate markers, such as the left ventricular mass index (LVMI), carotid intima-media thickness (cIMT), and pulse wave velocity (PWV). The plasma PF4/creatinine (Cr) ratio was lower in CKD children with a high daytime BP and 24 h BP, high BP load, and nocturnal non-dipping status. After adjusting for confounders, the plasma PF4 and plasma PF4/Cr ratio still independently predicted an abnormal ABPM profile. In addition, both the plasma PF4 and plasma PF4/Cr ratio presented a negative correlation with the L-arginine and asymmetric dimethylarginine ratio. These findings provide convincing evidence supporting the link between PF4 and CVD markers in pediatric CKD. Our study highlights the importance of further research to assess the performance of PF4-related biomarkers in predicting CVD events and CKD progression in children with CKD.

Differential Effects of Platelet Factor 4 (CXCL4) and Its Non-Allelic Variant (CXCL4L1) on Cultured Human Vascular Smooth Muscle Cells

Platelet factor 4 (CXCL4) is a chemokine abundantly stored in platelets. Upon injury and during atherosclerosis, CXCL4 is transported through the vessel wall where it modulates the function of vascular smooth muscle cells (VSMCs) by affecting proliferation, migration, gene expression and cytokine release. Variant CXCL4L1 is distinct from CXCL4 in function and expression pattern, despite a minor three-amino acid difference. Here, the effects of CXCL4 and CXCL4L1 on the phenotype and function of human VSMCs were compared in vitro. VSMCs were found to constitutively express CXCL4L1 and only exogenously added CXCL4 was internalized by VSMCs. Pre-treatment with heparin completely blocked CXCL4 uptake. A role of the putative CXCL4 receptors CXCR3 and DARC in endocytosis was excluded, but LDL receptor family members appeared to be involved in the uptake of CXCL4. Incubation of VSMCs with both CXCL4 and CXCL4L1 resulted in decreased expression of contractile marker genes and increased mRNA levels of KLF4 and NLRP3 transcription factors, yet only CXCL4 stimulated proliferation and calcification of VSMCs. In conclusion, CXCL4 and CXCL4L1 both modulate gene expression, yet only CXCL4 increases the division rate and formation of calcium-phosphate crystals in VSMCs. CXCL4 and CXCL4L1 may play distinct roles during vascular remodeling in which CXCL4 induces proliferation and calcification while endogenously expressed CXCL4L1 governs cellular homeostasis. The latter notion remains a subject for future investigation.

Platelet-derived chemokines in atherosclerosis

In atherosclerosis, activated platelets have been recently recognised not only to participate in thrombotic events but also to play an essential role in the development of atherosclerotic lesions. Upon their activation, platelets release several pro-inflammatory mediators including chemokines. Chemokines are key molecules in inflammation as they are able to recruit leukocytes, modulate their activation/differentiation and control their proliferation/apoptosis.

In this review we will discuss recent findings regarding the specific roles of chemokines released by platelets on leukocytes and their effects on atherosclerosis.

Platelet Factor 4 Binds to Vascular Proteoglycans and Controls Both Growth Factor Activities and Platelet Activation

Platelet factor 4 (PF4) is produced by platelets with roles in both inflammation and wound healing. PF4 is stored in platelet α-granules bound to the glycosaminoglycan (GAG) chains of serglycin. This study revealed that platelet serglycin is decorated with chondroitin/dermatan sulfate and that PF4 binds to these GAG chains. Additionally, PF4 had a higher affinity for endothelial-derived perlecan heparan sulfate chains than serglycin GAG chains. The binding of PF4 to perlecan was found to inhibit both FGF2 signaling and platelet activation. This study revealed additional insight into the ways in which PF4 interacts with components of the vasculature to modulate cellular events.

Generation and Characterization of a New Monoclonal Antibody Against CXCL4

CXCL4 plays important roles in numerous disease processes, which makes the CXCL4 signaling pathway a potential therapeutic target. In this study, we aimed to develop a neutralizing antibody against both human and mouse CXCL4. Rats were immunized with recombinant human CXCL4 (rhCXCL4). Hybridoma clones were created by fusion of the immunized rat spleen cells with mouse myeloma SP2/0 cells and screened using recombinant mouse CXCL4 (rmCXCL4) and rhCXCL4. The CXCL4 monoclonal antibody (CXCL4 MAb) produced by the 16D6-3 hybridoma clone was sequenced and characterized by Western blot and Biacore assays. It recognized both human and mouse CXCL4 with high affinity and neutralized the effect of rhCXCL4 in vitro. Thus, the antibody may be used in the studies of CXCL4 in murine disease models and as a template in the antibody humanization for clinical developments.

Serum biomarkers in uncontrolled no heart-beating donors may identify kidneys that will never work after transplantation

BACKGROUND/AIMS

Kidneys from uncontrolled non heart-beating donors achieve a good level of renal function after transplantation. However, a number of them will never function in the recipient. Our aim was to determine if serum biomarkers associated with platelet activity, inflammation and the nitric oxide system in uncontrolled non heart-beating donors may help to predict no renal function recovery after renal transplantation.

METHODS

Serum levels of interleukin (IL)-6, IL-10, intercellular cell adhesion molecule-1 (ICAM-1), cyclic guanosine monophosphate (cGMP), nitrite + nitrate and platelet factor-4 (PF4) were measured using enzyme-linked immunosorbent assay (ELISA) kits in 88 uncontrolled non heart-beating donors divided according to the renal functionality achieved in the recipients into functional (n = 76) and non functional (n = 12).

RESULTS

Kidneys from donors with higher IL-6 levels (>900 pg/ml) were functional after transplantation. Serum cGMP levels below 372.3 fmol/l were also associated with kidneys that recovered the renal function. However, serum levels of PF4 showed the best correlation with recovery of renal functional in the recipients since they were significantly lower in the donors whose kidneys functioned after transplantation.

CONCLUSIONS

Serum PF4 levels in uncontrolled non heart-beating donors may be a good predictor for kidneys that never will reach functional recovery. Some serum cGMP, IL-6 and IL-10 levels may simply help identify kidneys that will function after transplantation.

The role of the CXC chemokines platelet factor-4 (CXCL4/PF-4) and its variant (CXCL4L1/PF-4var) in inflammation, angiogenesis and cancer

Chemokines are chemotactic cytokines which recruit leukocytes to inflammatory sites. They also affect tumor development and metastasis by acting as growth factor, by attracting pro- or anti-tumoral leukocytes or by influencing angiogenesis. Platelet factor-4 (CXCL4/PF-4) was the first chemokine shown to inhibit angiogenesis. CXCL4L1/PF-4var, recently isolated from thrombin-stimulated platelets, differing from authentic CXCL4/PF-4 in three carboxy-terminally located amino acids, was found to be more potent than CXCL4/PF-4 in inhibiting angiogenesis and tumor growth. Both glycosaminoglycans (GAG) and CXCR3 are implicated in the activities of the PF-4 variants. This report reviews the current knowledge on the role of CXCL4/PF-4 and CXCL4L1/PF-4var in physiological and pathological processes. In particular, the role of CXCL4/PF-4 in cancer, heparin-induced thrombocytopenia and atherosclerosis is described.

Role of platelets in the development of atherosclerotic disease and possible interference with platelet inhibitor drugs

During the last two decades, significant advances have been made in the understanding of atherosclerotic disease. The pathogenesis of atherosclerosis appears to depend on a precise sequence of critical events based on the interaction of blood elements and lipids with the arterial wall. The major critical events and their sequence appears to be as follows: hemodynamic stress and endothelial injury; arterial wall-platelet interaction; smooth muscle cell proliferation; lipid entry and accumulation; significant arterial narrowing with fibrosis and development of thrombi; and complications in the form of calcification, ulceration, aneurysm, acute thrombotic occlusion and embolization. This sequence of critical events starts at a young age and in all geographic racial groups. Their evolution into advanced symptomatic lesions takes many years and varies in incidence and extent among different geographic and ethnic groups. It appears that in promoting and accelerating this process into the advanced stage of the disease, the presence at a young age of the so-called risk factors of atherosclerotic disease is most important. The recent advances in the understanding of the atherosclerotic process will be highlighted in this chapter with particular attention being focused on the role of platelets and thrombosis in the development of the disease and the possible role of platelet inhibitor drugs on the prevention of coronary atherosclerotic disease.

Platelet-derived growth factor: its potential roles in wound healing, atherosclerosis, neoplasia, and growth and development

Platelet-derived growth factor (PDGF) has been found to be derived not only from platelets that have been induced to release their contents, but also from a number of transformed cells (including cells transformed by both DNA and RNA viruses, spontaneous transformation, and cells from various human tumours), from activated macrophages, from embryonic rat aortic smooth muscle cells, and from rat aortic smooth muscle cells derived from experimentally induced intimal proliferative lesions. The studies discussed demonstrate the potential role of platelets and macrophages in atherosclerosis and in wound repair, and indicate the ability of anti-PDGF IgG to inhibit proliferative responses in vitro. With the demonstration that the transforming protein derived from the oncogene from the simian sarcoma virus is highly homologous with PDGF, it was possible to show that a number of transformed cells secrete PDGF and show markedly decreased binding of PDGF. The same is true for embryonic rat aortic smooth muscle cells and for cells from experimentally induced proliferative lesions in the rat carotid artery. All these findings point to the role of PDGF in the formation of these lesions and can be correlated with the capacity of the cells noted above, as well as injured endothelial cells, to secrete PDGF or PDGF-like molecules. The biological significance of these observations is discussed and a model for atherogenesis is proposed.

Mean platelet volume as marker of restenosis after percutaneous transluminal coronary angioplasty in patients with stable and unstable angina pectoris

INTRODUCTION

Several experimental and clinical studies have demonstrated that platelet size and function correlate since large platelets are hemostatically more reactive than platelets of normal size. Since platelets play a crucial role in vascular remodeling after percutaneous transluminal coronary angioplasty (PTCA), we investigated the influence of the mean platelet volume (MPV), a parameter of platelet size, on restenosis after PTCA.

METHODS

The retrospective study comprised 174 patients who underwent elective PTCA and follow-up angiography within 6 months thereafter. According to the follow-up angiograms, the patients were assigned to group A ("restenosis", n=74) or group B ("no restenosis", n=100). Both groups were compared in regard to pre-procedural hematological routine parameters including MPV, platelet count, hematocrit, white blood cell count and fibrinogen.

RESULTS

MPV was significantly increased in group A, compared with that in group B (8.75+/-0.99 fl vs. 8.04+/-0.74 fl, p<0.001). This difference in MPV was evident in patients with stable and unstable angina pectoris. In addition, MPV had an impact on the time-related incidence of angiographic restenosis, as early restenosis was associated with higher pre-procedural MPV values. Platelet count correlated inversely with MPV (r=-0.36, p<0.01) and was significantly lower in group A than in group B. The remaining hematological parameters were not different in both groups.

CONCLUSIONS

The MPV seems to be a marker of coronary restenosis in patients undergoing PTCA. Patients with high pre-procedural MPV values might benefit from an intensified antiplatelet therapy after coronary interventions.

Platelet factor 4 neutralizes heparan sulfate-enhanced antithrombin inactivation of factor Xa by preventing interaction(s) of enzyme with polysaccharide

Platelet factor 4 (PF4) is a heparin-binding protein which exhibits anti-heparin activities through the inhibition of antithrombin (AT)-dependent reactions with the serine proteases thrombin and factor Xa. PF4 also neutralizes heparan sulfate (HS), a glycosaminoglycan (GAG) present on the surface of endothelial cells, thereby possibly modulating an anticoagulant response. Previous models of PF4 mechanism did not distinguish whether PF4 causes steric hindrance of AT binding to fXa or of AT binding to the surface of the GAG chain. To shed light on the mechanism of PF4, studies of HS/heparin-catalyzed fXa inactivation by AT were undertaken. The results were consistent with PF4 directly interfering with AT binding to fXa rather than AT binding to the GAG chain, since PF4 did not prevent the heparin-dependent increase in AT intrinsic fluorescence. In fact, PF4 mechanism was competitive with respect to AT and non-competitive with respect to fXa, suggesting inhibition of important regulatory/catalytic interactions of fXa with the polysaccharide. Altogether, the results suggested a model by which PF4 bound to proximal (but distinct) sites to AT, resulting in steric interference of fXa binding to both polysaccharide and AT. It is proposed that PF4 inhibited the sequence of events recapitulated in the template mechanism describing heparin-dependent inhibition of fXa.

Platelet factor 4 enhances generation of activated protein C in vitro and in vivo

Platelet factor 4 (PF4), an abundant platelet alpha-granule protein, accelerates in vitro generation of activated protein C (APC) by soluble thrombin/thrombomodulin (TM) complexes up to 25-fold. To test the hypothesis that PF4 similarly stimulates endothelium-associated TM, we assessed the influence of human PF4 on thrombin-dependent APC generation by cultured endothelial monolayers. APC generated in the presence of 1 to 100 microg PF4 was up to 5-fold higher than baseline for human umbilical vein endothelial cells, 10-fold higher for microvascular endothelial cells, and unaltered for blood outgrowth endothelial cells. In an in vivo model, cynomolgus monkeys (n = 6, each serving as its own control) were infused with either PF4 (7.5 mg/kg) or vehicle buffer, then with human thrombin (1.0 microg/kg/min) for 10 minutes. Circulating APC levels (baseline 3 ng/mL) peaked at 10 minutes, when PF4-treated and vehicle-treated animals had APC levels of 67 +/- 5 ng/mL and 39 +/- 2 ng/mL, respectively (P <.001). The activated partial thromboplastin time (APTT; baseline, 28 seconds) increased maximally by 27 +/- 6 seconds in PF4-treated animals and by 9 +/- 1 seconds in control animals at 30 minutes (P <.001). PF4-dependent increases in circulating APC and APTT persisted more than 2-fold greater than that of controls from 10 through 120 minutes (P < or =.04). All APTT prolongations were essentially reversed by monoclonal antibody C3, which blocks APC activity. Thus, physiologically relevant concentrations of PF4 stimulate thrombin-dependent APC generation both in vitro by cultured endothelial cells and in vivo in a primate thrombin infusion model. These findings suggest that PF4 may play a previously unsuspected physiologic role in enhancing APC generation.

Platelet factor 4 enhances the binding of oxidized low-density lipoprotein to vascular wall cells

Accumulation of low-density lipoprotein (LDL)-derived cholesterol by macrophages in vessel walls is a pathogenomic feature of atherosclerotic lesions. Platelets contribute to lipid uptake by macrophages through mechanisms that are only partially understood. We have previously shown that platelet factor 4 (PF4) inhibits the binding and degradation of LDL through its receptor, a process that could promote the formation of oxidized LDL (ox-LDL). We have now characterized the effect of PF4 on the binding of ox-LDL to vascular cells and macrophages and on the accumulation of cholesterol esters. PF4 bound to ox-LDL directly and also increased ox-LDL binding to vascular cells and macrophages. PF4 did not stimulate ox-LDL binding to cells that do not synthesize glycosaminoglycans or after enzymatic cleavage of cell surface heparan and chondroitin sulfates. The effect of PF4 on binding ox-LDL was dependent on specific lysine residues in its C terminus. Addition of PF4 also caused an approximately 10-fold increase in the amount of ox-LDL esterified by macrophages. Furthermore, PF4 and ox-LDL co-localize in atherosclerotic lesion, especially in macrophage-derived foam cells. These observations offer a potential mechanism by which platelet activation at sites of vascular injury may promote the accumulation of deleterious lipoproteins and offer a new focus for pharmacological intervention in the development of atherosclerosis.

Platelet and fibrinogen turnover at the exposed subendothelium measured over 1 year after a balloon catheter de-endothelializing injury to the rabbit aorta: thrombotic eruption at the late re-endothelialization stage

Balloon catheter de-endothelialization of the rabbit aorta in vivo causes a rapid release of thrombin and a consequent hemostatic response at the surface of the exposed subendothelium. Previously, we have compared the net fluxes of several hemostatic proteins from plasma into the exposed aorta subendothelium for up to 600 days after injury. We now report the turnover of platelets, compared to fibrinogen, at the de-endothelialized aorta for up to 390 days after injury. Anesthetized NZW rabbits received either a de-endothelializing or a sham injury (controls) to their aortas. At a predetermined time (either 10 min before or up to 390 days after injury), each rabbit was infused with known quantities of rabbit (51)Cr-platelets and rabbit (125)I-fibrinogen; the radiolabels were allowed to circulate for 10 min before the rabbit was rapidly exsanguinated. Radioactivity measurements and tissue analysis revealed that at 10 min after balloon injury, approximately 165,000 platelets/mm(2) were associated with the aorta surface, and platelet turnover was 840/min/mm(2). Turnover had decreased to <200/min/mm(2) at 10-21 days but, from 65 to 390 days, had increased to approximately 1500/min/mm(2). In comparison, approximately 17 pmol of fibrinogen/cm(2) saturated the ballooned surface by 10 min after injury. Fibrinogen turnover at the aorta surface at 10 min after injury amounted to 0.2 pmol/min/cm(2), increasing to 0.7 at 10 days but decreasing to 0.25 at 21 days. Between 65 and 390 days, fibrinogen turnover increased slowly to 1.3 pmol/min/cm(2). Fibrinogen turnover at the surface of the aorta paralleled that within the intima-media over 390 days. Platelet and fibrin(ogen) deposits within the aorta wall increased over the 21-390 days interval as shown by immunostaining. The results are consistent with the re-endothelializing aorta tending to support thrombosis and ulceration in the late healing stage.

An iron-binding exochelin prevents restenosis due to coronary artery balloon injury in a porcine model

Background- Vascular smooth muscle cell (VSMC) proliferation is a critical factor in the neointima formation that causes restenosis after coronary angioplasty (PTCA). Desferri-exochelin 772SM (D-EXO), a highly diffusible, lipophilic iron chelator secreted by Mycobacterium tuberculosis, inhibits proliferation of VSMCs in culture. We hypothesized that treatment with D-EXO would inhibit neointima formation in balloon-injured vessels in vivo. Methods and Results- We subjected 24 pigs to overstretch coronary artery injury with standard PTCA balloons and then administered intramural injections of either D-EXO (n=14) or vehicle (n=10) through an Infiltrator catheter. Treatments were randomized, and the investigators were blinded with regard to treatment group until data analysis was completed. One month later, we euthanized the pigs, excised the injured coronary segments, made multiple sections of each segment, and identified the site of maximal neointima formation. An injury score based on the degree of disruption of the internal or external elastic lamina or media was assigned. D-EXO reduced stenosis index (neointima area divided by the area within the internal elastic lamina), adjusted for injury score, by 47%. Neointima thickness was also reduced. Conclusions- D-EXO, injected intramurally, substantially inhibited formation of neointima in a porcine vascular injury model.

Impaired fibrinolysis determines the outcome of percutaneus transluminal coronary angioplasty (PTCA)

BACKGROUND

Coronary artery stenosis lesions dilated by percutaneus transluminal coronary angioplasty (PTCA) show a disappointingly frequent recurrence of stenosis. We have investigated the possible role of fibrinolysis and various platelet-release factors - specifically in the locality of the affected vessel - by following 19 patients for 6 months after PTCA.

METHODS

PTCA was performed on 19 patients with a significant primary coronary stenosis, proven by quantitative CAAS analysis. Blood for measurement of local fibrinolysis and platelet activity was drawn from the aortic root and the coronary sinus, at three times: just before PTCA, 10 min after it, and 6 months later.

RESULTS

The incidence of restenosis at the 6 months follow-up was 37%. PTCA almost doubled the platelet-derived growth factor level (PDGF) in coronary sinus blood in all patients. The seven restenosis patients had a substantially higher tissue plasminogen activator inhibitor antigen (PAI-1ag) level in the aortic root before PTCA than the 12 who remained stenosis-free (mean 62.4 +/- 31.6 ng mL -1 compared with 33.1 + 25.3; P < 0.04) and a lower tissue plasminogen activator activity (t-PAac) level (mean 0.32 +/- 0.19 IU mL-1 compared with 0.68 +/- 0.34; P < 0.03). This was corroborated by the levels of tissue plasminogen activator inhibitor activity (PAI-1ac). At reassessment after 6 months, the restenosis patients had developed, in coronary sinus blood, a large rise of PAI-1ac (7.7 +/- 4.8 IU mL-1 rising to 15.7 +/- 13.9, P < 0.04) and a large rise of of PAI-1ag (48.8 +/- 31.3 ng mL-1 vs. 72.4 +/- 47.2; P < 0.03). But no such increase occurred in the patients who remained stenosis-free. Conclusion Our results indicate that the minor balloon injury, which is inseparable from PCTA, stimulates the local release of PDGF. We suggest that, in those patients whose fibrinolytic activity is inherently low, this rise of PDGF could be a major causative factor in restenosis. We also discuss the possibility that the preoperative level of PAI-1ac could provide a limited but useful prediction of the outcome of PTCA.

Platelet immunoregulatory factors

A number of soluble and membrane-associated proteins are known to mediate platelet:leukocyte interactions. Platelet-derived factors that have attracted the most attention to date include transforming growth factor beta, interleukin 1 and platelet factor 4. Recently, we have uncovered another protein within platelets that has leukocyte modulatory activity. It was previously characterized as an endometrial glycoprotein named placental protein 14 (PP14) with suppressive effects upon lymphocyte proliferation, pro-inflammatory cytokine production and natural killer cell function. The "hematopoietic" PP14 derived from cells of the megakaryocytic lineage shares this immunosuppressive property, as evaluated by two-way mixed lymphocyte cultures. Interestingly, two alternatively spliced hematopoietic PP14 mRNAs have been cloned which differ in their encoded proteins. Cell-free translation and transfection analyses have verified the translatability of both PP14 mRNA species and allowed for the analysis of their glycosylation properties. PP14, a member of the lipocalin structural superfamily of proteins, now offers an intriguing new link between the coagulation and immune systems.

[Anti-angiogenesis: a new approach to tumor therapy?]

BACKGROUND

The overall mortality due to metastatic cancer has not or only minimally been reduced in spite of intensive research and many innovations in the field of conventional antineoplastic therapy in the past decade. In the last years it has become a fact that tumor growth is angiogenesis-dependent. Therefore, inhibitors of angiogenesis are a new class of antineoplastic substances with a novel mechanism of action that might be a powerful complement to conventional cytostatic therapy. SUBSTANCES AND CLINICAL TRIALS: Inhibitors of tumor-angiogenesis which have entered clinical trials, with their results published until December 1998 are discussed here. Most results originate from phase-I or phase-II clinical trials. They are discussed and compared in respect to toxicity and response. Also some substances with high therapeutic potential which are still in preclinical testing are discussed.

RESULTS

Many of the investigated angiogenesis inhibitors demonstrated anti-tumor effects in phase-I or phase-II clinical trials. The commonest manifestation was stable disease, followed by partial remissions. In a few cases, complete remissions were observed. The toxicities of these substances differ both in type and degree of side effects.

CONCLUSION

Some antiangiogenic drugs appear to be promising candidates for a clinical use in the therapy of solid tumors. Further conclusions can only be drawn after evaluation of the results of ongoing phase-III clinical trials.

Platelet surface membranes are highly mitogenic for coronary artery smooth muscle cells--A novel mechanism for sustained proliferation after vessel injury?

The effects of isolated platelet surface membranes on DNA synthesis and proliferation of bovine coronary artery smooth muscle cells (SMC) were studied. Platelet membranes were very potent mitogens for SMC. The potency was about 10-fold higher than the maximum effects of platelet-derived growth factor-BB (PDGF). Platelet membrane-induced mitogenesis was inhibited by rapamycin, wortmannin or heating for 15 min at 70 degrees C but not by the PDGF receptor antagonist SCH 13.929 or by neutralizing PDGF antibodies. Only a partial (30%) inhibition was seen with PD 98059. In contrast, PDGF-induced SMC mitogenesis was heat-stable but sensitive to SCH 13. 929, PDGF antibodies, and PD 98059. These findings provide evidence for a novel mechanism for platelet-induced SMC proliferation that is independent of PDGF secretion. Platelet membranes, attached to or incorporated into the vessel wall, could maintain sustained SMC proliferation following injury.

Pretreatment of rabbits with either hirudin, ancrod, or warfarin significantly reduces the immediate uptake of fibrinogen and platelets by the deendothelialized aorta wall after balloon-catheter injury in vivo

Fibrinogen and platelets rapidly saturate the exposed subendothelium of a freshly deendothelialized aorta in vivo. As thrombin generated within the site of injury is largely responsible for fibrin(ogen) deposition, we questioned whether various anticoagulant treatments would inhibit uptake of both fibrinogen and platelets in vivo. Rabbits were anticoagulated by pretreatment with either Warfarin, Ancrod, or recombinant hirudin. Each anesthetized, anticoagulated (or saline-injected control) rabbit was injected i.v. with rabbit 51Cr-platelets and 125I-fibrinogen before a balloon-catheter deendothelializing (or sham) injury of the thoracic aorta. At 10 minutes after injury, the rabbit was exsanguinated and the aorta excised. Platelet adsorption by the deendothelialized aorta surface was substantially reduced in anticoagulated rabbits (controls, 2.2x10(5)/mm2; Warfarin-treated, 1.2x10(5)/mm2; Ancrod-treated, 5.3x10(4)/mm2; r-hirudin-treated [5 mg/kg], 5.3x10(4)/mm2), and a significant reduction of fibrinogen associated with the platelet layer (from 5.3 to 1 to 2 pmol/cm2) and within the underlying intima-media layer (from 16.9 to 5 to 6 pmol/cm2) was observed in the r-hirudin-and Warfarin-treated rabbits. The pattern of aorta-deposited 51Cr-platelets and 125I-fibrin in the anticoagulated rabbits corresponded well with an assessment by transmission electron microscopy of aortic tissue samples. We conclude that approximately 70% of fibrinogen uptake is thrombin dependent and that approximately 80% of platelet adsorption depends on codeposited fibrin(ogen) during the 10-minute interval after balloon injury. Pretreatment with an agent that interferes with either thrombin or fibrin production will inhibit the immediate interaction of fibrinogen and platelets with the freshly exposed subendothelium.

Coronary artery disease and polymorphisms in a receptor mediating shear stress-dependent platelet activation

BACKGROUND

Platelets play pivotal roles in coronary thrombosis, and antiplatelet therapies are widely used for coronary artery disease (CAD). However, the effects of genetic variation in platelets on CAD are poorly understood. We have assessed the association between CAD and polymorphisms in a platelet receptor for von Willebrand factor, the glycoprotein (GP) Ib/IX complex, which mediates shear stress-dependent platelet activation.

METHODS AND RESULTS

Genotypes of the alpha-chain of the receptor (GP Ib alpha, 145Thr/Met) were determined in 91 patients with myocardial infarction (MI) or angina pectoris whose lesions were confirmed by coronary angiography as well as in 105 individuals from the general population with no history of angina or other heart diseases and normal resting ECGs. There was no homozygote for Met/Met in either the control or patient groups. The prevalence of the Thr/Met genotype (T/M) in all patients was not significantly different from that in the control group. However, the frequency of T/M was significantly higher in patients aged < or = 60 years (31.8%) than in control subjects aged < or = 60 years (16.0%; P<.05, odds ratio=2.5). An association was also demonstrated between CAD and the other polymorphism of GP Ib alpha, a variable number of tandem repeats of a 13-amino acid sequence, which is known to be linked to the 145Thr/Met polymorphism. There was an association between the frequency of the T/M genotype and the angiographic severity of CAD: 11.1% for Gensini score < 40 versus 50.0% for Gensini score > or = 40 (P=.0015). There was no difference in the distribution of GP Ib alpha genotypes between patients with MI and those with angina pectoris.

CONCLUSIONS

This study suggests that the presence of the Met allele in GP Ib alpha is a risk factor for the prevalence and severity of CAD in individuals aged < or = 60 years. The results need to be confirmed in a large-scale study of incident case subjects and matching control subjects.

An overview of clinical trials involving inhibitors of angiogenesis and their mechanism of action

Angiogenesis is a biologic process whereby endothelial cells divide and migrate to form new blood vessels. This process is required in physiological conditions, but is also a necessary requirement for solid tumors to grow and metastasize. Over the last several years, the growth factors that have both a positive and negative influence on tumor angiogenesis have been delineated. Interfering with tumor angiogenesis was considered a potential therapeutic strategy 25 years ago, but only recently have compounds with an ability to interfere with angiogenesis entered clinical trials. This review will discuss the first generation of angiogenesis inhibitors, their mechanism of action and data from clinical trials.

Management of peripheral vascular disease: innovative approaches using radiation therapy

Despite the early successes at vascular recanalization with percutaneous transluminal angioplasty, vascular restenosis has emerged as a clinical problem of near epidemic proportions. Numerous pharmacologic and mechanical adjuncts have been tried with little success. Over the last few years, there have major advances in our understanding of the biology of the restenotic process. The process is now recognized as a proliferation disorder, and therapies akin to those used in the treatment of malignant diseases are being explored. Endovascular brachytherapy has shown strong potential in controlling this pathologic proliferative process in the laboratory and in early clinical studies. In this review we discuss some of the basic issues involved in vascular restenosis and the current status of endovascular brachytherapy.

Role of cimetidine in the prevention of intimal hyperplasia in rat carotid artery

In vitro studies have revealed that histamine increases smooth muscle cell proliferation and migration, an effect abolished by the H2 antagonist cimetidine. This study examined the effect of cimetidine on intimal hyperplasia in vivo. Thirty male Wistar rats underwent endothelial denudation of the left carotid artery; 15 received cimetidine 350 mg per kg per day for four weeks and 15 received vehicle only. Four weeks after injury the left carotid arteries were perfusion fixed and harvested. Morphometric analysis revealed that there was no significant difference between the intima:media ratio of rats treated with cimetidine (median (interquartile range (i.q.r.)) 1.69 (0.59)) and those treated with vehicle (median (i.q.r.) 1.59 (0.59), P = 0.28). Similarly, the percentage luminal reduction was not significantly different between the groups (median (i.q.r.) 54.7 (19.9) per cent and 45.8 (13.4) per cent respectively, P = 0.30). It is concluded that treatment with cimetidine does not reduce the formation of intimal hyperplasia in rat carotid arteries de-endothelialized with a balloon catheter.

Phenotypic modulation of smooth muscle cells during the formation of neointimal thickenings in the rat carotid artery after balloon injury: an electron-microscopic and stereological study

The formation of neointimal thickenings in the rat carotid artery after balloon injury was studied by a combination of electron-microscopic and stereological methods. All smooth muscle cells in the normal media had a contractile phenotype, the cytoplasm being dominated by myofilaments. Seven days after endothelial denudation, the smooth muscle cells in the innermost part of the media had assumed a synthetic phenotype by loss of myofilaments and formation of a large endoplasmic reticulum and Golgi complex. These cells moved through fine openings in the internal elastic lamina and gave rise to a growing neointima by proliferation and secretion of extracellular matrix components. Fourteen days after the operation, the neointima had almost reached its final size, and mitoses were no longer noted. Nevertheless, the cells maintained a synthetic phenotype with prominent secretory organelles, although myofilaments had started to become more abundant again. They were surrounded by an extracellular matrix made up of collagen fibrils and coalescing patches of elastin. Thirty-five days after the operation, an endothelial cell layer had reformed and covered most of the luminal vessel surface. In parallel, the smooth muscle cells in the neointima had returned to a contractile phenotype with a cytoplasm dominated by myofilaments. These findings provide a morphological basis for further analysis of the cellular and molecular interactions involved in the formation of neointimal thickenings after endothelial injury, and for the search for agents interfering with this process.

VCL, an antagonist of the platelet GP1b receptor, markedly inhibits platelet adhesion and intimal thickening after balloon injury in the rat

BACKGROUND

Arterial injury is immediately followed by platelet adhesion at the site of injury, a process that requires the interaction of subendothelial von Willebrand factor with the platelet GP1b receptor. VCL, a recombinant von Willebrand factor GP1b binding domain, inhibits platelet binding to von Willebrand factor. The aim of this study was to determine whether VCL inhibits platelet adhesion at the site of arterial injury and affects neointimal thickening after injury in rats.

METHODS AND RESULTS

Sprague-Dawley rats were randomized to receive VCL, 4 mg/kg bolus followed by a continuous infusion of 2 mg.kg-1.h-1 for 72 hours, or an identical volume of saline. Balloon injury of the femoral artery was performed 15 minutes after the initial bolus injection of VCL. Scanning electron microscopy performed 1 and 3 days after injury indicated that VCL-treated rats had > 80% reduction in the number of platelets adherent to the vessel wall at the site of injury compared with controls (P < .003). Histological examination at day 14 showed that, compared with controls, VCL-treated rats had a 60% reduction in the intima-media ratio (0.21 +/- 0.03 versus 0.53 +/- 0.06, P = .001) and a reduced luminal area stenosis (12 +/- 3% versus 38 +/- 10%, P = .04). At 28 days after injury, there was no rebound of neointimal thickening in VCL-treated rats (intima-media ratio, 0.19 +/- 0.04; luminal stenosis, 17 +/- 5%). The difference between VCL-treated rats and control rats persisted but was attenuated (intima-media ratio, 0.19 +/- 0.04 versus 0.28 +/- 0.1, P = .162; luminal stenosis, 17 +/- 5% versus 31 +/- 5%, P = .058) as neointimal thickening regressed in untreated rats. With the use of proliferating cell nuclear antigen immunohistochemistry on day 3, VCL had no effect on smooth muscle cell (SMC) proliferation.

CONCLUSIONS

Antagonism of the platelet GP1b receptor by VCL profoundly decreased platelet deposition at the site of balloon injury in the rat femoral artery. This effect was associated with a persistent reduction in neointimal thickening. The lack of effect of VCL on SMC proliferation suggests that the decrease in neointimal thickening may have been mediated through inhibition of SMC migration and/or modulation of the extracellular matrix.

Binding of platelet-derived growth factor and low density lipoproteins to glycosaminoglycan species produced by human arterial smooth muscle cells

The platelet-derived growth factor (PDGF) binds via a defined amino acid sequence to heparin (Fager et al., 1992, In Vitro Cell. Dev. Biol., 28A:176-180) and the protein moiety of low density lipoproteins (LDL; apo B-100) via a similar sequence to chondroitin sulfate (Camejo et al., 1988, Arteriosclerosis Thromb., 8:368-377). In this study, synthetic oligopeptides were used to explore the capacity of smooth muscle cell-derived glycosaminoglycans to bind to the critical sequences of PDGF and apo B-100. In vitro, proliferating human arterial smooth muscle cells synthesized twice as much proteoglycans as did quiescent cells. The dominating glycosaminoglycan side chains were chondroitin and heparan sulfates in secreted and cell-associated proteoglycans, respectively. The chondroitin sulfate-rich proteoglycans had a higher molecular size and were to a larger extent secreted into the culture medium than the heparan and dermatan sulfate-rich proteoglycans. Heparan, dermatan, and chondroitin sulfates bound to the PDGF-derived oligopeptide with affinities similar to those of heparin. However, while heparan and dermatan sulfates both inhibited DNA synthesis in human arterial smooth muscle cells, chondroitin sulfate had no such inhibitory effect. Like the PDGF-derived oligopeptide, the apo B-100-derived oligopeptide bound to these glycosaminoglycans. At the same time, both oligopeptides displaced bound LDL from chondroitin sulfate in vitro and released the block on DNA synthesis in smooth muscle cells that heparin induced in culture. Thus, chondroitin, dermatan, and heparan sulfates produced by arterial smooth muscle cells may bind LDL and PDGF competitively in atherogenesis but only heparan and dermatan sulfates inhibit cellular DNA synthesis. LDL and PDGF deposition may occur by binding to similar binding sites on glycosaminoglycans derived from smooth muscle cells within atherosclerotic lesions.

How do fish oils affect vascular function?

1. This is a review on the mechanisms by which fish oils affect vascular function and how such changes contribute to their documented cardioprotective effects. 2. Evidence that fish oils depress vascular responses to contractile agents will be examined. It is concluded that this effect of fish oils is mediated predominantly by alterations in prostanoid profile. 3. Effects of fish oils on arterial relaxation are discussed with particular emphasis on endothelium dependent relaxation. It is suggested that the functional impairment of endothelium dependent relaxation documented in a number of cardiovascular disease states can be reversed by dietary fish oils. 4. In addition, possible effects of fish oils on growth factors, inositol trisphosphate and lipid metabolism, the sympathetic nervous system, rheological and membrane properties and inducible nitric oxide are reviewed.

Platelet-induced vascular smooth muscle cell proliferation is modulated by the growth amplification factors serotonin and adenosine diphosphate

BACKGROUND

Platelet-mediated mechanisms have been implicated in intimal lesion formation following vascular injury. Although the participation of peptide growth factors has been suspected in this process, little has been known about the possible mitogenic role of other platelet factors that are released at sites of vascular injury.

METHODS AND RESULTS

We tested the hypothesis that platelet products, which are not peptide growth factors, are important modulators of the platelet-induced smooth muscle cell (SMC) proliferative response by acting as growth amplification factors. In these studies, cell proliferation was assessed by [3H]thymidine incorporation, flow cytometry, and direct cell counting. We examined the potential mitogenicity of several platelet products, including serotonin, ADP, norepinephrine, histamine, platelet-activating factor, the thromboxane A2 mimetic U46619, and bradykinin. Of the platelet products tested, serotonin and ADP induced a synergistic response with peptide growth factors. This synergy was greatest at low growth-factor concentrations. Addition of nonaggregated platelets to quiescent SMC cultures strongly stimulated cell proliferation. Since the addition of suramin to platelet-treated cultures markedly inhibited SMC proliferation, peptide growth factors are most likely the primary mitogens mediating this response. However, platelet-induced proliferation was also markedly reduced by the serotonin antagonists ketanserin and LY53857 (44%), and by the ADP antagonist apyrase (35%).

CONCLUSIONS

Therefore, serotonin and ADP contribute significantly, in synergy with peptide growth factors, to the platelet-induced SMC proliferative response. We propose that in vivo serotonin and ADP act as amplification factors for SMC proliferation at sites of vascular injury.

Platelet factor 4 modulates the mitogenic activity of basic fibroblast growth factor

Basic fibroblast growth factor (bFGF) has been shown to stimulate cell proliferation after vascular injury. The mitogenic activity of bFGF requires interactions with both a high affinity receptor and a cell-surface heparan sulfate proteoglycan. We tested the ability of platelet factor 4 (PF 4) and other platelet heparin-binding proteins to modulate bFGF-stimulated [3H]thymidine incorporation into fibroblasts. The supernatant of thrombin-stimulated platelets contained an inhibitor of bFGF-induced mitogenesis; this activity coeluted with PF 4 upon gel filtration, heparin-agarose, and ion-exchange chromatography. Purified thrombospondin and beta-thromboglobulin did not inhibit the mitogenic activity of bFGF. PF 4 inhibited the activity of 5 pM bFGF with 50% inhibitory concentration of 75 nM. Purified PF 4 also inhibited the basal incorporation of [3H]thymidine into 3T3 fibroblasts and the increased [3H]thymidine incorporation occurring after wounding of a cell monolayer. PF 4 did not affect the mitogenic activity of serum. Inhibition of bFGF activity by PF 4 could be overcome by exogenous heparin or chondroitin-4-sulfate, suggesting that inhibition of mitogenesis is caused by binding of PF 4 to cell-surface glycosaminoglycans. These results indicate that an important role of PF 4 released at sites of vascular injury and platelet activation is to control cellular proliferation caused by the release of bFGF from ruptured cells.

Review article: thromboxanes in inflammatory bowel disease--pathogenic and therapeutic implications

Recent work suggests that thromboxanes may play a major pathogenic role in inflammatory bowel disease. Thromboxanes are produced in excess not only in inflamed mucosa but also in Crohn's disease, by uninflamed bowel and by isolated intestinal and peripheral blood mononuclear cells. Their cellular source is likely to include platelets, neutrophils, endothelial and epithelial cells as well as mononuclear cells, possible stimuli to their overproduction being chemotactic peptides, lipopolysaccharide, leukotrienes, platelet activating factor, interleukin-1, bradykinin and angiotensin II. The pro-inflammatory effects of thromboxanes are both direct (diapedesis and activation of neutrophils, mucosal ulceration, reduction of suppressor T-cell activity) and indirect (vasoconstriction, platelet activation). Although corticosteroids and aminosalicylates inhibit thromboxane synthesis, this action does not necessarily explain their therapeutic effect in inflammatory bowel disease. Selective thromboxane synthesis inhibitors and receptor antagonists, however, ameliorate experimental colitis in animals. Picotamide and ridogrel are dual thromboxane pathway blockers already used in man. Drugs of this type could prove useful not only for the prevention of systemic thrombo-embolism but also for suppressing intestinal mucosal inflammation in patients with inflammatory bowel disease.

Influence of platelet size before coronary angioplasty on subsequent restenosis

Platelet size has been shown to reflect platelet activity. We prospectively measured the mean platelet volume (MPV) in 47 patients undergoing single vessel angioplasty for symptomatic angina. The patients underwent repeat angiography 4-8 months later irrespective of symptomatic status. Restenosis was assessed quantitatively by hand held calliper measurements of the lesion and qualitatively by a return of angina, ST segment changes on an exercise test and visual analysis of the lesion severity by two experienced angiographers. Twenty-four patients developed recurrent angina during the follow-up period, the MPV in the group with chest pain was 8.54 +/- 0.60 fl compared to 8.1 +/- 0.69 fl in the asymptomatic group (P = 0.04). Twenty two patients had significant ST segment changes at exercise. In this group the MPV was 8.6 +/- 0.56 fl compared to 8.0 +/- 0.70 fl for the group with a negative test (P = 0.002). Similarly visually assessed angiographic stenosis showed a significant increase in the restenotic group (8.6 +/- 0.56 vs. 8.0 +/- 0.61 fl, P = 0.001). The relative odds for developing clinically defined restenosis were 10.2 times greater if the pre-procedural MPV lay in the upper compared to the lowest quartile. There was a positive correlation between MPV and change in minimal luminal diameter between post angioplasty and follow-up angiography, assessed quantitatively, r = +0.56, P = 0.016. There was no association between clinical or angiographic definitions of restenosis and haemoglobin, red cell count, mean corpuscular volume, white cell count or platelet count. Platelet size may influence the development of restenosis after successful coronary angioplasty.

SIN-1 reduces platelet adhesion and platelet thrombus formation in a porcine model of balloon angioplasty

BACKGROUND

Nitric oxide inhibits platelet adhesion and platelet aggregation in vivo. In this study, we investigated the effects of the nitric oxide donor SIN-1 on platelet adhesion and platelet-thrombus formation following experimental angioplasty.

METHODS AND RESULTS

Bilateral carotid angioplasty was performed in 20 anesthetized pigs. Animals received either SIN-1 (3-morpholino-sydnonimine; 10 micrograms/kg/min; n = 8) or placebo (n = 8) before and during angioplasty. An additional control group of pigs received trimetaphan (n = 4), which induced hemodynamic changes similar to those that followed treatment with SIN-1. Platelet deposition was quantified by the injection of autologous 111In-labeled platelets. SIN-1 reduced platelet deposition after deep arterial injury compared with placebo (mean +/- SEM, 10.870 +/- 2.415 versus 40.326 +/- 9.889 platelets x 10(6)/cm2, p < 0.05). SIN-1 reduced platelet adhesion after superficial injury compared with both placebo and trimetaphan (2.231 +/- 0.333 versus 5.278 +/- 0.606 versus 5.022 +/- 1.136 platelets x 10(6)/cm2, respectively; p < 0.005). Scanning electron microscopy confirmed that platelets were deposited in the form of an adherent monolayer following superficial endothelial denudation and were reduced in number following treatment with SIN-1. The effects of SIN-1 on platelet function were associated with a significant increase in platelet cyclic GMP concentration from baseline (3.15 +/- 0.88 versus 1.58 +/- 0.73 pmol/10(9) platelets, p < 0.005).

CONCLUSIONS

SIN-1 reduces platelet adhesion and platelet-thrombus formation following experimental angioplasty. The antiadhesive effects of SIN-1 are independent of changes in systemic hemodynamics. These results imply that the administration of a nitric oxide donor may prove effective in modifying the pathophysiological response to angioplasty injury.

Inhibitory effects of a novel antiplatelet agent, E5510, on collagen-induced platelet-derived growth factor release and aggregation of human platelets in vitro

E5510, 4-cyano-5,5-bis(4-methoxyphenyl)-4-pentenoic acid, is a new anti-platelet-aggregation agent under development. We examined the inhibitory efficacy of E5510 on PDGF-release from washed human platelets. E5510 concentration-dependently inhibited collagen-induced PDGF release from human platelets. PDGF release was reduced to below the detection limit (0.47 ng/ml) by preincubation of platelets with 0.04 microM or higher concentrations of E5510. Total growth factor release from platelets was also measured by a bioassay with cultured smooth muscle cells. E5510 almost completely abolished the mitogenic effect of collagen-induced platelet releasates at concentrations of 0.04 microM or higher. Our data suggest that the release of PDGF and other growth factors was inhibited by E5510 at the same concentration that inhibited platelet aggregation.

Platelet-neutrophil interactions: their significance

In the vicinity of an acute inflammatory response both cellular and non-cellular elements may interact to modify the overall response. Evidence suggests that leukocytes may play an active role in the modulation of platelet function and vice-versa. This interaction may be abnormal in certain pathological states. Neutrophils have been found to alter platelet behaviour by several mechanisms. These include transcellular metabolism of eicosanoids. Neutrophils utilize platelet-derived arachidonate to increase leukotriene synthesis. Other arachidonate metabolites result from platelet-neutrophil interaction and these differ quantitatively and qualitatively from those arising from either cell-type alone. Another mechanism is the release of a nitric oxide-like factor by neutrophils. Nitric oxide inhibits platelet adhesion and aggregation via guanylate cyclase stimulation. Neutrophils, under different conditions, are potent inducers of platelet calcium flux, aggregation and secretion. This activity is mediated by a neutrophil-derived protease, most likely to be cathepsin G. The interaction of platelets with neutrophils may help to explain some of the pathophysiological events associated with different clinical states.

Platelet activation in the lung after antigen challenge in a model of allergic asthma

The purpose of this study was to investigate whether platelets are activated and release their products in the human lung after antigen challenge. Using subsegmental antigen challenge as a model of asthma, bronchoalveolar lavage fluids from ragweed-allergic asthmatic subjects were assayed for the alpha granule products, platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG), prior to challenge (baseline) and at 5 min and 19 h after challenge with ragweed antigen. Airway segments challenged with normal saline were used as controls. Five minutes after antigen challenge, levels of platelet products in BAL fluid were not elevated from baseline or normal saline control levels. However, 19 h after antigen challenge, a 10-fold increase in platelet products in BAL fluids was found. The mean PF4 levels increased from baseline and saline control values of less than 1.0 to 7.2 ng/ml (p less than 0.05) 19 h after antigen challenge. beta-TG increased from baseline and control levels of less than 1.0 to 6.6 ng/ml (p less than 0.05). Elevations in PF4 and beta-TG were highly correlated with each other (r = 0.98, p less than 0.0001). Levels of platelet products during the 19-h response correlated with albumin, with kinins, with the prostaglandins 6-keto-PGF1 alpha, PGE2, and PGF2 alpha, and with the eosinophil-derived proteins, eosinophil-derived neurotoxin and eosinophil peroxidase. We conclude that platelet activation in the lung is a feature of the late inflammatory response to antigen challenge and that platelets may play an important role in allergic inflammation and asthma.

Arterial response to mechanical injury: balloon catheter de-endothelialization

Coronary angioplasty has been used clinically for over a decade. Its initial promise as an alternative to coronary bypass surgery has only partially been fulfilled because of the high rate of post-operative restenosis. A number of animal models have been devised to study this phenomenon and although none is entirely satisfactory, they have, together with recent advances in molecular biology provided an insight into the cellular mechanisms that may contribute to this complication. This knowledge may ultimately lead to a means of therapeutic intervention. This review summarises our present understanding of the pathology of post-angioplasty re-stenosis as revealed by studies using the balloon catheter de-endothelialization model, and discusses some of the intervention strategies that have been attempted.

Ultrastructure appearance of atherosclerosis in human and experimentally-induced animal models

We describe here the basic structure of the aorta, the changes with aging and ultrastructural appearance of atherosclerosis of human and animal models. The architecture of the aortic wall is highly organized, for adaptation to changes of blood pressure. The main cells composing the vessel are endothelial cells and smooth muscle cells. They maintain the integrity and homeostasis of the aorta along with the extracellular matrix of collagen fibrils, elastic fibers and glycosaminoglycans. The structural changes with aging and atherogenesis are a compensative or degenerative phenomenon caused by many factors. Three major cells are the endothelial cell, smooth muscle cell and monocyte-derived macrophages (as well as platelets) all of which are involved in atherogenesis. Foam cells in atheromatous lesions are derived from macrophages and smooth muscle cells. Recently, the molecular biological nature and function of these cells and their derived-factors have been thoroughly investigated in cell culture and in experimental animal models caused by a mechanical injury of the endothelium or by a dietary induced hypercholesterolemia. However, the mechanism of the endothelial injury in vivo as well as formation of atheromatous cores of human atherosclerosis is not exactly understood. Some structural and functional changes inherent to the arterial wall during aging may play an important role in initiation or progression of human atherosclerosis.

Fish oils in the prevention of atherosclerosis

The hypothesis that oils derived from the flesh of fish and marine mammals inhibit the atherosclerotic process is critically reviewed. Populations consuming a diet rich in fish have low rates of coronary heart disease. Dietary fish oil is associated with changes in serum lipids, prostaglandin and leukotriene metabolism, enhanced endothelial function and effects on growth factors released from platelets, leukocytes and endothelial cells. Dietary fish oil supplementation has been associated with inhibition of atherosclerosis experimentally induced by dietary hyperlipidemia and balloon injury. Results of studies of the use of fish oil to inhibit postangioplasty restenosis in human subjects have been inconclusive.

Effect of PGI2 on platelet binding to partially denuded endothelial monolayer in vitro

We have developed a new model for the investigation of platelet interaction with injured vascular endothelium. This involves the quantitative detection of platelet binding to a partially denuded endothelial cell monolayer in vitro. Porcine arterial endothelial monolayer, cultured on collagen gel containing fibrinogen and fibronectin, was partially denuded and the binding of 51Cr-platelets was measured. A synergistic increase in platelet binding was observed in the presence of fibrinogen and fibronectin. A distinct aggregation of platelets along the edge of the denuded area of the endothelial monolayer was seen. Prostacyclin (PGI2) inhibited platelet aggregation, although adhesive platelets were still present at denuded sites.

Platelet secretory products may contribute to neuronal injury

BACKGROUND

We do not fully understand the mechanisms for neuronal damage following cerebral arterial occlusion by a thrombus that consists mainly of platelets. The view that certain endogenous substances, such as glutamate, may also contribute to neuronal injury is now reasonably well established. Blood platelets are known to contain and secrete a number of substances that have been associated with neuronal dysfunction. Therefore, we hypothesize that a high concentration (approximately several thousand-fold higher than in plasma, in our estimation) of locally released platelet secretory products derived from the causative thrombus may contribute to neuronal injury and promote reactive gliosis.

SUMMARY OF COMMENT

We have recently been able to report some direct support for this concept. When organotypic spinal cord cultures were exposed to platelet and platelet products, a significant reduction in the number and the size of the surviving neurons occurred in comparison with those in controls. We further observed that serotonin, a major platelet product, has neurotoxic properties. There may be other platelet components with similar effect.

CONCLUSIONS

The hypothesis of platelet-mediated neurotoxicity gains some support from these recent in vitro findings. The concept could provide a new area of research in stroke, both at the clinical and basic levels.

The role of platelets, thrombin and hyperplasia in restenosis after coronary angioplasty

Coronary angioplasty has become a successful and widely used treatment for patients with coronary artery disease since its first clinical application in 1977. The primary success rate has improved despite the increase in procedure and case complexity. However, acute reocclusion and late restenosis, which constitute the most important problems after successful angioplasty, continue to occur in about 5% and 35% of patients within 3 to 6 months, respectively. Angioscopic and pathologic observations have suggested that a multifactorial pathophysiologic process accounts for acute reocclusion, involving marked thrombosis, intimal dissection, medial and subintimal hemorrhage, vascular recoil and vasocontriction. In contrast, chronic restenosis involves the development of fibrocellular intimal hyperplasia within a milieu created by vascular injury, platelet activation, thrombin generation and the release of mitogens. Although current pharmacologic approaches, which involve antithrombotic and anticoagulant therapy, have been largely ineffective in eliminating acute reocclusion and chronic restenosis, recent advances in the research in thrombosis, platelet receptors and smooth muscle growth regulation have allowed new therapeutic options to be tested in the experimental setting, with subsequent potential clinical applications in patients.

Myointimal hyperplasia: pathogenesis and implications. 2. Animal injury models and mechanical factors

Arterial wall injury either by balloon catheter, drying, or scraping results in a denudation of endothelial cells (EC) and a subsequent proliferation of smooth-muscle cells (SMC). The degree of SMC proliferation appears to be dependent on the degree of initial injury and not to the loss of the overlying endothelium. Successful reendothelialization of denuded areas depends on the size of the denuded segment as well as SMC-EC interactions. Prolonged exposure of SMC to serum substances results in inhibition of EC regrowth, the production of prostacyclin by SMC, and the development of a thromboresistant surface. Heparin appears to inhibit SMC proliferation in vivo (as well as in vitro), an effect that is independent of platelet SMC interaction. EC-derived heparin in vivo may also result in inhibition of SMC proliferation. Platelets may play an important role in the early response to arterial injury and development of myointimal hyperplasia (MIH), but their long-term role appears to be minor. Antiplatelet agents have widely varying species-dependent effects on platelets and platelet-vessel wall interactions, but in specific circumstances they may inhibit MIH. The precise role of steroid drugs and immunosuppression on MIH in arterial injury models awaits further study. The role of lipoproteins in MIH is unclear; however, the inhibition of MIH by omega-3 fatty acids in vivo as well as their inhibition of platelet-derived growth factor production by EC in vitro implies a regulatory role. Acute hypertension results in a marked proliferation of EC and SMC in vivo and enhances the proliferative response to injury as well. Low wall shear stress, turbulence, and boundary layer separation all increase EC turnover, a likely influence on EC growth factor production. The compliance mismatch resulting from graft-artery anastomoses, injury, and endarterectomy results in locally increased cyclical stretch, which may predispose to SMC proliferation.

Pathogenesis of atherosclerosis: state of the art

The practical implementation of the results of large, well-controlled clinical and epidemiologic studies has led to substantial progress in the prevention of atherosclerosis. Now, daring and aggressive interventions, as well as a new understanding of cellular and molecular mechanisms of atherogenesis, also provide new possibilities of effective treatments at an advanced, symptomatic stage of the disease. An abundance of new information has come from an increasing number of seemingly unrelated scientific fields, ranging from laser optics to genetic engineering. This short study examines how some selected new findings and concepts fit into the traditional theories of atherogenesis: encrustation, infiltration, and response to injury. Endothelial and smooth muscle cells, platelets, and leukocytes are viewed in their dual capability of promoting as well as inhibiting the atherogenic process. Mechanisms of vascular healing and intimal hyperplasia after physical interventions are distinguished from those leading to complicated spontaneous atherosclerotic plaques, and the impact of some new ideas on potential pharmacologic interventions is brought to the reader's attention.