Summary
Procarboxypeptidase U (proCPU) is the plasma precursor of carboxypeptidase U (CPU,
carboxypeptidase R, plasma carboxypeptidase B or activated thrombin-activatable fibrinolysis
inhibitor, TAFIa). CPU removes C-terminal lysine residues that act as plasminogen
binding sites from partially degraded fibrin, thereby down-regulating plasminogen
activation and fibrinolysis. The present study was carried out as a pilot study to
examine whether the plasma proCPU concentration is related to the presence of coronary
artery disease (CAD) and/or to levels of established risk indicators for CAD, in a
case-control study of 110 men requiring coronary artery bypass grafting (CABG) because
of stable angina pectoris. The preoperative plasma proCPU level in the CABG patients
was significantly higher than in population-based controls (1029 ± 154 vs. 974 ± 140
U/L, p <0.05). In addition, in a subset of the patients (n = 31) the proCPU concentration,
which was significantly lower on the third postoperative day (−17 ± 10%), had increased
significantly on the sixth day (+14 ± 12%) after surgery, compared with the preoperative
level. In both patients and controls, proCPU concentration was strongly and positively
associated with factor VII amidolytic activity and protein C activity, suggesting
a common mechanism modulating the plasma levels of these proteins. Otherwise, statistically
significant correlations with proCPU were group-specific. In the patients, proCPU
correlated significantly with plasma fibrinogen and protein S. In the controls, proCPU
correlated significantly with concentrations of cholesterol in plasma, VLDL and LDL.
In addition, proCPU correlated significantly with C-reactive protein and haptoglobin
levels in the controls only, indicating that also inflammatory mechanisms are involved
in the regulation of plasma proCPU. These results suggest that a mechanism exists
by which fibrinolytic function is impaired in a manner that is likely to result in
more stable fibrin deposits and increase the risk of precocious CAD as well as early
occlusion of venous bypass grafts.
Key words
Procarboxypeptidase U - TAFI - coronary artery disease - bypass surgery - fibrinolysis