Disturbed blood flow induces erosive injury to smooth muscle cell-rich neointima and promotes thrombus formation in rabbit femoral arteries.

BACKGROUND: Plaque erosion is a cause of atherothrombosis that preferentially occurs on smooth muscle cell (SMC)- and proteoglycan-rich rather than lipid-rich plaques. However, its underlying mechanisms remain unknown. OBJECTIVE: To determine whether disturbed blood flow induces erosive injury and thrombus formation on SMC-rich neointima. METHODS: Three weeks after balloon injury, SMC-rich neointima with increased tissue factor (TF) activity developed in rabbit femoral arteries that were narrowed with a vascular occluder to disturb blood flow after stenosis. Neointimal injury and thrombus formation were assessed at 15, 30, and 180 min after the vascular narrowing. RESULTS: Endothelial detachment, platelet adhesion and neointimal cell apoptosis became evident at the post-stenotic regions of all femoral arteries (n = 5) within 15 min of narrowing. Mural thrombi composed of platelet and fibrin developed after 30 min, and then occlusive thrombi were generated in three out of five vessels after 180 min. The identical vascular narrowing of normal femoral arteries also induced endothelial detachment with small platelet thrombi at post-stenotic regions, but fibrin and occlusive thrombi did not develop. Computational simulation analysis indicated that oscillatory shear stress contributes to the development of erosive damage to the neointima. CONCLUSIONS: These results suggest that disturbed post-stenotic blood flow can induce erosive injury in SMC-rich plaques and promote thrombus formation that results in vascular events.

Serotonin induces vasoconstriction of smooth muscle cell-rich neointima through 5-hydroxytryptamine2A receptor in rabbit femoral arteries.

BACKGROUND: Smooth muscle cell (SMC)-rich intima is a morphological feature of atherosclerotic lesions that is observed in eroded plaque and spastic arteries. Arteries with SMC-rich intima are susceptible to vasoconstriction or vasospasm against some vasoactive agents. OBJECTIVE: The present study evaluates the contribution of SMC-rich intima to thrombogenic vasoconstriction. METHODS: We established SMC-rich neointima by damaging rabbit femoral arteries using balloons and then measured the isometric tension of the femoral strips against 5-hydroxytryptamine (5-HT), adenosine diphosphate, adenosine triphosphate and thrombin. RESULTS: Among these agents, only 5-HT induced a hypercontractile response of the injured arteries with SMC-rich neointima, compared with non-injured arteries. Smooth muscle cells of both the neointima and media expressed 5-HT(2A) receptor, and sarpogrelate, a selective 5-HT(2A) receptor antagonist significantly inhibited the hypercontraction. Furthermore, 5-HT induced contraction of separated neointima and hypercontraction of separated media compared with non-injured media. Sarpogrelate and fasudil, a specific Rho-kinase inhibitor, significantly suppressed such contraction of both the neointima and media of injured arteries. CONCLUSIONS: These results suggest that 5-HT plays a crucial role in thrombogenic vasoconstriction, and that SMC-rich intima as well as media directly contributes to the hypercontractile response of atherosclerotic vessels through the 5-HT(2A) receptor and the Rho-kinase pathway.

Medial and adventitial macrophages are associated with expansive atherosclerotic remodeling in rabbit femoral artery.

Expansive vascular remodeling is considered a feature of vulnerable plaques. Although inflammation is upregulated in the media and adventitia of atherosclerotic lesions, its contribution to expansive remodeling is unclear. We investigated this issue in injured femoral arteries of normo- and hyperlipidemic rabbits fed with a conventional (CD group; n=20) or a 0.5% cholesterol (ChD group; n=20) diet. Four weeks after balloon injury of the femoral arteries, we examined vascular wall alterations, localization of macrophages and matrix metalloproteases (MMP)-1, -2, -9, and extracellular matrix. Neointimal formation with luminal stenosis was evident in both groups, while expansive remodeling was observed only in the ChD group. Areas immunopositive for macrophages, MMP-1, -2 and -9 were larger not only in the neointima, but also in the media and/or adventitia in the injured arterial walls of the ChD, than in the CD group. Areas containing smooth muscle cells (SMCs), elastin and collagen were smaller in the injured arterial walls of the ChD group. MMP-1, -2 and -9 were mainly localized in infiltrating macrophages. MMP-2 was also found in SMCs and adventitial fibroblasts. Vasa vasorum density was significantly increased in injured arteries of ChD group than in those of CD group. These results suggest that macrophages in the media and adventitia play an important role in expansive atherosclerotic remodeling via extracellular matrix degradation and SMC reduction.

Factor XI contributes to thrombus propagation on injured neointima of the rabbit iliac artery.

BACKGROUND: Thrombus formation through the activation of tissue factor (TF) and factor (F) XI is a critical event in the onset of cardiovascular disease. TF expressed in atherosclerotic plaques and circulating blood is an important determinant of thrombogenicity that contributes to fibrin-rich thrombus formation after plaque disruption. However, the contribution of FXI to thrombus formation on disrupted plaques remains unclear. METHODS: A mouse monoclonal antibody against FXI and activated FXI (FXIa) (XI-5108) was generated by immunization with activated human FXI. Prothrombin time (PT), activated partial thromboplastin time (APTT), bleeding time, and ex vivo platelet aggregation in rabbits were measured before and after an intravenous bolus injection of XI-5108. We investigated the role of FXI upon arterial thrombus growth in the rabbit iliac artery in the presence of repeated balloon injury. RESULTS: The XI-5108 antibody reacted to the light chain of human and rabbit FXI/FXIa, and inhibited FXIa-initiated FXa and FXIa generation. Fibrin-rich thrombi developed on the injured neointima that was obviously immunopositive for glycoprotein IIb-IIIa, fibrin, TF, and FXI. Intravenous administration of XI-5108 (3.0 mg kg(-1)) remarkably reduced thrombus growth, and the APTT was significantly prolonged. However, PT, bleeding time and platelet aggregation were not affected. CONCLUSIONS: These results indicate that plasma FXI plays a potent role in thrombus growth on the injured neointima. Inhibition of plasma FXI activity might help to reduce thrombus growth on ruptured plaques without prolonging bleeding time.

Inhibition of 5-hydroxytryptamine receptor prevents occlusive thrombus formation on neointima of the rabbit femoral artery.

BACKGROUND: Thrombus propagation on disrupted plaque is a major cause of acute coronary events and serious complication after coronary intervention. 5-Hydroxytryptamine (5-HT) is a potent vasoactive and platelet-aggregating substance that is predominantly mediated by 5-HT2A receptor. However, the roles of 5-HT2A receptor in occlusive thrombus formation on disrupted plaque remain obscure. OBJECTIVE: We investigated the role of 5-HT2A receptor in thrombus formation using a rabbit model of repeated balloon-injury. METHODS: Three weeks after a first balloon-injury of the femoral arteries, luminal diameter, neointimal growth, and vasoconstriction by 5-HT in vitro were examined. Thrombus propagation and the role of 5-HT2A receptor after a second balloon-injury were evaluated using sarpogrelate, a selective 5-HT2A receptor antagonist. RESULTS: Three weeks after the first balloon-injury, luminal stenosis was evident in the femoral arteries, where the neointima expressed tissue factor and 5-HT2A receptor. The hypercontractile response of the stenotic arteries to 5-HT was significantly reduced by sarpogrelate. Balloon-injury of the neointima with substantially reduced blood flow promoted the formation of occlusive thrombus that was immunoreactive against glycoprotein IIb-IIIa, 5-HT2A receptor and fibrin. Intravenous injection of sarpogrelate significantly inhibited ex vivo platelet aggregation induced by adenosine 5'-diphosphate, thrombin and collagen alone as well as with 5-HT, and significantly prevented occlusive thrombus formation in vivo. CONCLUSIONS: The 5-HT2A receptor appears to play a crucial role in occlusive thrombus formation in diseased arteries via platelet aggregation and vasoconstriction. Inhibition of 5-HT2A receptor might help reduce the onset of acute coronary events and of acute coronary occlusion after the intervention.

[The effect of recombinant human granulocyte colony-stimulating factor (rG-CSF) on childhood neutropenias].

The clinical effect of recombinant human granulocyte colony-stimulating factor (rG-CSF), produced by Chinese hamster ovary cells, was studied in 27 patients with childhood neutropenias. The sample consisted of 8 patients with congenital neutropenia (Kostmann type), 9 with neutropenia with miscellaneous causes (5 chronic benign, 2 associated with hypogammaglobulinemia, 1 drug-induced, and 1 hypoplastic type), 3 with cyclic neutropenia, and 7 with severe aplastic anemia. The rG-CSF was given subcutaneously (or in a few cases intravenously) at a dose of 2 micrograms/kg/day for 7 days and 5 micrograms/kg/day for additional 7 to 28 days in cases with poor response. The rG-CSF was effective in 18 of 27 cases (67%). Patients with congenital neutropenia and aplastic anemia responded less frequently and poorly. The mean level of absolute neutrophil counts of 8 congenital neutropenia cases increased from 88/microliters to 2,718/microliters. That of 9 miscellaneous cases changed from 189/microliters to 7,224/microliters at a dose of 2 micrograms/kg/day. In 7 aplastic anemia cases pretreatment level of 220/microliters rose to 851/microliters, usually after increasing the dose up to 5 micrograms/kg/day. The rG-CSF was apparently effective in 3 cases of cyclic neutropenia. In any type of neutropenia, the effect was largely transient; after the discontinuation of rG-CSF, the absolute neutrophil counts tended to decrease to pretreatment levels within 1 to 2 weeks. The G-CSF was well tolerated, and only one case with mild lumbago and another with minimal elevation of transaminases were observed. We conclude that the rG-CSF can be effective for treating various types of childhood neutropenia.(ABSTRACT TRUNCATED AT 250 WORDS)

[Clinical evaluation of recombinant human G-CSF in children with cancer].

Recombinant human granulocyte colony-stimulating factor (rG-CSF), produced by Chinese hamster ovary cells, was administered in 69 chemotherapy-induced neutropenic pediatric patients (pts) with malignant tumors. Each pt received two cycles of the same chemotherapy and had neutropenia with absolute neutrophil counts (ANC) less than 500/microliter in the first cycle. Initiating 72 hours after termination of chemotherapy in the second cycle, rG-CSF (2 micrograms/kg/day) was given subcutaneously or intravenously to each pt for 10 days. rG-CSF significantly increased ANC at nadir; 72 +/- 14 vs. 206 +/- 40/microliter (data in the first cycle vs. data in the second cycle, respectively), and reduced the period of neutropenia with ANC less than 500/microliter; 9.7 +/- 0.6 vs. 5.1 +/- 0.6 days, and the period for restoration to ANC greater than or equal to 1,000/microliter after initiation of chemotherapy; 25.5 +/- 0.6 vs 17.5 +/- 0.9 days. rG-CSF did not affect other components of peripheral blood. The number of days with fever greater than or equal to 38 degrees C was significantly reduced by rG-CSF treatment. Neck pain and lumbago were observed in one pt, pollakisuria in one pt, and elevation of the serum levels of LDH and uric acid in one pt, however these were mild to moderate, transient, and resolved without any specific treatment. We concluded that rG-CSF was effective in neutropenia induced by intensive chemotherapy for malignant tumors without any serious side effects.