RESUMO
BACKGROUND: Lp(a) is a lipoparticle of unknown function mainly present in primates and humans. It consists of a low-density lipoprotein and apo(a), a polymorphic glycoprotein. Apo(a) shares sequence homology and fibrin binding with plasminogen, inhibiting its fibrinolytic properties. Lp(a) is considered a link between atherosclerosis and thrombosis. Marked inter-ethnic differences in Lp(a) concentration related to the genetic polymorphism of apo(a) have been reported in several populations. AIM: The study examined the structural and functional features of Lp(a) in three Native Mexican populations (Mayos, Mazahuas and Mayas) and in Mestizo subjects. METHODS: We determined the plasma concentration of Lp(a) by immunonephelometry, apo(a) isoforms by Western blot, Lp(a) fibrin binding by immuno-enzymatic assay and short tandem repeat (STR) polymorphic marker genetic analysis by capillary electrophoresis. RESULTS: Mestizos presented the less skewed distribution and the highest median Lp(a) concentration (13.25 mg dL(-1)) relative to Mazahuas (8.2 mg dL(-1)), Mayas (8.25 mg dL(-1)) and Mayos (6.5 mg dL(-1)). Phenotype distribution was different in Mayas and Mazahuas as compared with the Mestizo group. The higher Lp(a) fibrin-binding capacity was found in the Maya population. There was an inverse relationship between the size of apo(a) polymorphs and both Lp(a) levels and Lp(a) fibrin binding. CONCLUSION: There is evidence of significative differences in Lp(a) plasma concentration and phenotype distribution in the Native Mexican and the Mestizo group.
Assuntos
Etnicidade/genética , Indígenas Norte-Americanos/genética , Lipoproteína(a)/genética , Polimorfismo Genético , Feminino , Fibrina/metabolismo , Marcadores Genéticos , Genética Populacional , Humanos , Indígenas Norte-Americanos/etnologia , Lipoproteína(a)/sangue , Masculino , México/etnologia , Fenótipo , Isoformas de Proteínas/sangue , Isoformas de Proteínas/genéticaRESUMO
Fibrinogen Bicêtre II is a dysfibrinogenemia in which there is a substitution of Lys for Asn at gamma 308. We have studied the polymerization of this abnormal fibrinogen by measurement of turbidity and have characterized clot structure by scanning electron microscopy, permeation, and viscoelastic measurements. The results of these studies demonstrate that this amino acid substitution has substantial effects on the structure and properties of the clot, resulting in clots made up of thick fibers and large pores with greatly reduced stiffness and increased slippage of protofibrils.
Assuntos
Fibrinogênios Anormais/química , Fibrinogênios Anormais/metabolismo , Fibrinogênios Anormais/genética , Humanos , MutaçãoRESUMO
High plasma concentrations of lipoprotein (a) [Lp(a)] are now considered a major risk factor for atherosclerosis and cardiovascular disease. This effect of Lp(a) may be related to its composite structure, a plasminogen-like inactive serine-proteinase, apoprotein (a) [apo(a)], which is disulfide-linked to the apoprotein B100 of an atherogenic low-density lipoprotein (LDL) particle. Apo(a) contains, in addition to the protease region and a copy of kringle 5 of plasminogen, a variable number of copies of plasminogen-like kringle 4, giving rise to a series of isoforms. This structural homology endows Lp(a) with the capacity to bind to fibrin and to membrane proteins of endothelial cells and monocytes, and thereby inhibits binding of plasminogen and plasmin formation. This mechanism favors fibrin and cholesterol deposition at sites of vascular injury and impairs activation of transforming growth factor-beta (TGF-beta) that may result in migration and proliferation of smooth muscle cells into the vascular intima. It is currently accepted that this effect of Lp(a) is linked to its concentration in plasma, and an inverse relationship between apo(a) isoform size and Lp(a) concentrations that is under genetic control has been documented. Recently, it has been shown that inhibition of plasminogen binding to fibrin by apo(a) from homozygous subjects is also inversely associated with isoform size. These findings suggest that the structural polymorphism of apo(a) is not only inversely related to the plasma concentration of Lp(a), but also to a functional heterogeneity of apo(a) isoforms. Based on these pathophysiological findings, it can be proposed that the predictive value of Lp(a) as a risk factor for vascular occlusive disease in heterozygous subjects would depend on the relative concentration of the isoform with the highest affinity for fibrin.
Assuntos
Arteriosclerose/fisiopatologia , Lipoproteína(a)/fisiologia , Apolipoproteínas A/genética , Arteriosclerose/metabolismo , Homocisteína/sangue , Humanos , Lipoproteína(a)/sangue , Lipoproteína(a)/química , Inibidor 1 de Ativador de Plasminogênio/metabolismo , Polimorfismo Genético , Ativador de Plasminogênio Tecidual/metabolismoRESUMO
The fibrino(geno)lytic protein designated hementerin contained in crude extracts of the salivary complex of Haementeria depressa leeches was purified to apparent homogeneity by gel filtration, ion exchange chromatography and preparative SDS-PAGE. It is a single-chain 80 kDa, PhMeSO2F-resistant, calcium-dependent, metalloproteinase, which specifically degrades fibrin(ogen) through a plasminogen-independent pathway. The amino terminal sequence of 8 residues shows 80% similarity with hementin, another fibrino(geno)lytic protein purified from Haementeria ghilianii leeches. However, their activities differ somewhat in terms of kinetics and with regard to the structure of the fibrin(ogen) fragments they may produce. Cleavage by hementerin of fibrinogen Aalpha, gamma and Bbeta chains, in that order, produces 270 kDa to 67 kDa fragments which differ from those produced by plasmin. Hementerin was also able to degrade cross-linked fibrin although at a lower rate as compared to fibrinogen. In conclusion, hementerin is a plasminogen-independent fibrino(geno)lytic metalloproteinase that degrades fibrinogen faster than fibrin, prevents blood coagulation and destroys fibrin clots in vitro.
Assuntos
Fibrinogênio/metabolismo , Fibrinolíticos/farmacologia , Sanguessugas/enzimologia , Metaloendopeptidases/farmacologia , Extratos de Tecidos/farmacologia , Animais , Fibrinolíticos/isolamento & purificação , Humanos , Cinética , Metaloendopeptidases/isolamento & purificação , Análise de Sequência , Extratos de Tecidos/isolamento & purificaçãoAssuntos
Hemostasia , Adulto , Animais , Transtornos da Coagulação Sanguínea/sangue , Fatores de Coagulação Sanguínea/fisiologia , Feminino , Fibrinólise/fisiologia , Fibrinolíticos/uso terapêutico , Hemostasia/fisiologia , Humanos , Masculino , Agregação Plaquetária , Gravidez , Complicações Hematológicas na Gravidez/sangue , Trombose/fisiopatologiaAssuntos
Trombofilia , Animais , Animais Geneticamente Modificados , Fatores de Coagulação Sanguínea/genética , Fatores de Coagulação Sanguínea/fisiologia , Suscetibilidade a Doenças , Fibrinólise/fisiologia , Humanos , Lipoproteína(a)/genética , Lipoproteína(a)/fisiologia , Isquemia Miocárdica/genética , Deficiência de Proteína S/complicações , Fatores de Risco , Trombofilia/sangue , Trombofilia/congênito , Trombofilia/etiologia , Trombofilia/genética , Trombose/epidemiologia , Trombose/etiologiaRESUMO
Lipoprotein Lp(a) is a major and independent genetic risk factor for atherosclerosis and cardiovascular disease. The essential difference between Lp(a) and low density lipoproteins (LDL) is apolipoprotein apo(a), a glycoprotein structurally similar to plasminogen, the precursor of plasmin, the fibrinolytic enzyme. This structural homology endows Lp(a) with the capacity to bind to fibrin and to membrane proteins of endothelial cells and monocytes, and thereby to inhibit plasminogen binding and plasmin generation. The inhibition of plasmin generation and the accumulation of Lp(a) on the surface of fibrin and cell membranes favor fibrin and cholesterol deposition at sites of vascular injury. Moreover, insufficient activation of TGF-beta due to low plasmin activity may result in migration and proliferation of smooth muscle cells into the vascular intima. These mechanisms may constitute the basis of the athero-thrombogenic mode of action of Lp(a). It is currently accepted that this effect of Lp(a) is linked to its concentration in plasma. An inverse relationship between Lp(a) concentration and apo(a) isoform size, which is under genetic control, has been documented. Recently, it has been shown that inhibition of plasminogen binding to fibrin by apo(a) is also inversely associated with isoform size. Specific point mutations may also affect the lysine-binding function of apo(a). These results support the existence of functional heterogeneity in apolipoprotein(a) isoforms and suggest that the predictive value of Lp(a) as a risk factor for vascular occlusive disease would depend on the relative concentration of the isoform with the highest affinity for fibrin.
Assuntos
Arteriosclerose/fisiopatologia , Lipoproteína(a)/fisiologia , Trombose/fisiopatologia , Animais , Arteriosclerose/sangue , Humanos , Lipoproteína(a)/sangue , Macaca fascicularis , Camundongos , Camundongos Transgênicos , Coelhos , Fatores de Risco , Trombose/sangueRESUMO
Fibrinolysis triggered by t-PA bound to fibrin is one of the main antithrombotic mechanisms. Defects in the fibrinolytic system-decreased tissue-type plasminogen activator (t-PA) activity and elevated levels of plasminogen activator inhibitor (PAI-1), in patients with SLE have been associated with an increased tendency to thrombosis. In the present study, 43 patients with SLE fulfilling the ACR criteria for the disease, were studied for the presence of autoantibodies to fibrin-bound t-PA, i.e. the physiological active form of this plasminogen activator. A solution of 200 IU/ml of t-PA was incubated with solid-phase fibrin prepared as previously described (Anal Biochem 1986; 153; 201-210). Sera diluted 1:50 were incubated with fibrin-bound t-PA, the plates were then washed, and bound immunoglobulins were detected using a polyvalent peroxidase-labeled goat anti-human Ig. Plates coated with fibrin alone were used as controls. Sera were considered positive when A490/630 obtained with normal human sera in two independent test was greater than the mean plus 2 SD. Eleven of 43 (26%) SLE sera demonstrated antibody reactivity against fibrin-bound t-PA. Within the anti-t-PA positive group there was a higher proportion of SLE patients with severe Raynaud's phenomenon and thrombotic events when compared to the anti-t-PA negative group: 36% vs 6% and 18% vs 6% respectively. These results suggest that autoantibodies to fibrin-bound t-PA could play a role in the pathogenesis of vascular disease in some SLE patients.
Assuntos
Autoanticorpos/imunologia , Doenças Autoimunes/imunologia , Fibrina/metabolismo , Lúpus Eritematoso Sistêmico/imunologia , Doença de Raynaud/imunologia , Trombose/imunologia , Ativador de Plasminogênio Tecidual/imunologia , Adulto , Especificidade de Anticorpos , Doenças Autoimunes/complicações , Suscetibilidade a Doenças , Feminino , Fibrinólise/imunologia , Humanos , Lúpus Eritematoso Sistêmico/complicações , Masculino , Doença de Raynaud/etiologia , Trombose/etiologia , Ativador de Plasminogênio Tecidual/metabolismoRESUMO
Defective fibrinolysis due to decreased tissue-type plasminogen activator (t-PA) activity is a well-established finding in patients with systemic lupus erythematosus (SLE). The possibility that this decrease in t-PA activity may be related to the presence of autoantibodies directed against t-PA, and the possible role of these autoantibodies in the pathophysiology of fibrinolysis in SLE, were investigated. Serum samples from 115 SLE patients and 63 normal volunteers were analyzed for the presence of such antibodies. The search for antibodies to t-PA was performed by means of several systems, allowing for the identification of epitopes presented in different conformational physical states of t-PA: free or associated to its inhibitor (PAI-1) in plasma, specifically bound to fibrin surface, or passively adsorbed to solid supports. Antibodies in variable amounts were detected by all systems used; however, t-PA activity was not inhibited by the IgG fraction of the positive sera in a fibrin-agar fibrinolysis system. Moreover, the demonstration of serum anti-t-PA antibodies was not associated with clinical or laboratory abnormalities related to vasoocclusive episodes. These results indicate that, as in the case of other autoantibodies, their detection in serum does not imply their direct participation in the pathophysiology of thrombosis in SLE.