ABSTRACT
To elucidate some of the links between homocysteine and vascular disease, we have evaluated the effect of the amino acid on the formation (by kinetics studies), structure (by electron microscopy) and lysis of the fibrin network, using tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). We have studied whether homocysteine could alter the activity of the components involved in fibrinolysis (by amidolytic and thrombolytic methods). The results showed that homocysteine-associated networks were more compact and branched than controls (52 +/- 6 vs 44 +/- 5 fibers/field, P = 0.008), and were formed by shorter and thicker fibers. This clot proved to be more resistant to fibrinolysis with u-PA than control [lysis time 50%: 257 +/- 16 (homocysteine) vs 187 +/- 6 min (control); P < 0.004], but there were no differences with t-PA. Homocysteine did not affect the biological activities of plasmin, or plasminogen activation by t-PA and u-PA. Defective fibrinolysis with u-PA was therefore associated with homocysteine-fibrin structural alterations rather than the homocysteine effect on the biological activities of the fibrinolytic components evaluated. Results suggest that hyperhomocysteinemic patients could produce tight clots, were more resistant to lysis, and generated a procoagulant environment in situ. We believe that our findings may contribute to understanding the mechanisms involved in the homocysteine harmful effect.
Subject(s)
Fibrin/ultrastructure , Fibrinolysis/physiology , Homocysteine/metabolism , Plasma/metabolism , Blood Coagulation/physiology , Fibrin/chemistry , Fibrin/metabolism , Fibrinolysin/metabolism , Humans , Microscopy, Electron , Plasminogen Activator Inhibitor 1/metabolism , Plasminogen Activators/chemistry , Plasminogen Activators/metabolism , Plasminogen Inactivators/metabolismABSTRACT
Plasminogen activators are considered to be involved in several developmental events. The present work aims at characterizing the developmental pattern of expression of plasminogen activators in the chick cerebellum. Soluble fractions derived by ultracentrifugation from Triton X-100 treated membrane fractions were used for determination of the enzyme activity with a radial fibrinolytic assay. By using specific inhibitors and different anti-plasminogen activators antibodies it is shown that only one type of the enzyme, the urokinase-type plasminogen activator, is expressed during the cerebellum ontogeny. Our results show the existence of a bimodal pattern of enzyme activity with two peaks that temporally coincide with the processes of massive neuronal migration, neurite outgrowth and synapse formation and plasticity. It is proposed that plasminogen activator could play a role in these developmental events and that its pattern of variability is developmentally regulated.
Subject(s)
Cerebellum/metabolism , Plasminogen Activators/metabolism , Animals , Cerebellum/embryology , Chick Embryo , Optic Lobe, Nonmammalian/embryology , Optic Lobe, Nonmammalian/metabolism , Plasminogen Inactivators/metabolism , Time FactorsABSTRACT
Plasminogen activation is a widespread cellular mechanism for localized extracellular proteolysis that is postulated to participate in many diverse physiological and pathological phenomena. The present review in intended as an introduction to the subject, and is by no means comprehensive, except for the section on breast cancer. Seral extensive reviews are available that should be consulted by intersted readers (1-6).