Fibrinolysis in a lipid environment: modulation through release of free fatty acids.
BACKGROUND
Thrombolysis is conventionally regarded as dissolution of the fibrin matrix of thrombi by plasmin, but the structure of clots in vivo includes additional constituents (proteins, phospholipids) that modulate their solubilization.


OBJECTIVE
We examined the presence of free fatty acids in thrombi and their effects on distinct stages of fibrinolysis (plasminogen activation, plasmin activity).


RESULTS
Using the fluorescent probe acrylodated intestinal fatty acid-binding protein, variable quantities (up to millimolar concentrations) of free fatty acids were demonstrated in surgically removed human thrombi. Oleic acid at relevant concentrations reversibly inhibits more than 90% of the amidolytic activity of plasmin on a synthetic substrate (Spectrozyme PL), but only partially inhibits its fibrinolytic activity measured using turbidimetry. Chromogenic assays detecting the generated plasmin activity show that plasminogen activation by tissue-type plasminogen activator (t-PA) is completely blocked by oleic acid in the fluid phase, but is accelerated on a fibrin matrix. A recombinant derivative of t-PA (reteplase) develops higher fibrin specificity in the presence of oleic acid, because both the inhibition of plasminogen activation in free solution and its enhancement on fibrin template are stronger than with wild-type t-PA.


CONCLUSIONS
Through the stimulation of plasminogen activation on a fibrin template and the inhibition of plasminogen activators and plasmin in the fluid phase, free fatty acids confine the action of fibrinolytic proteases to the site of clotting, where they partially oppose the thrombolytic barrier function of phospholipids.
Rábai
G
G
Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.
Váradi
B
B
Longstaff
C
C
Sótonyi
P
P
Kristóf
V
V
Timár
F
F
Machovich
R
R
Kolev
K
K
D000818:Animals; D002417:Cattle; D050556:Fatty Acid-Binding Proteins; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005342:Fibrinolysis / Q000187:drug effects / Q000502:physiology*; D005456:Fluorescent Dyes; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D050356:Lipid Metabolism; D019301:Oleic Acid / Q000378:metabolism / Q000494:pharmacology; D010958:Plasminogen / Q000378:metabolism; D011994:Recombinant Proteins; D013927:Thrombosis / Q000378:metabolism
D050556:Fatty Acid-Binding Proteins; D005230:Fatty Acids, Nonesterified; D005456:Fluorescent Dyes; D011994:Recombinant Proteins; C079339:acrylodated intestinal fatty acid binding protein, recombinant; D019301:Oleic Acid; D010958:Plasminogen