Catheter-directed thrombolysis with microplasmin for acute peripheral arterial occlusion (PAO): an exploratory study

AIM

We performed an open-label, dose-ascending, single-centre, Phase IIa study to explore the safety and efficacy of catheter-directed thrombolysis (CDT) with microplasmin for infrainguinal arterial or bypass occlusions.

METHODS

Patients who presented with acute occlusions were subsequently treated with an intrathrombus infusion of five ascending doses of microplasmin: 0.3 mg/kg/h for 4 hours; 0.45 mg/kg/h for 4 hours; 0.6 mg/kg/h for 4 hours; 0.9 mg/kg/h for 4 hours or 0.6 mg/kg/h for 6 hours. Repeat angiograms were obtained to assess the degree of clot lysis. The primary outcome was complete thrombolysis defined as >95% thrombus volume reduction at the end of the microplasmin infusion. Safety evaluation included bleedings, adverse events and coagulation biomarkers.

RESULTS

Complete thrombolysis was obtained in 3 of the 19 treated patients at the end of microplasmin infusion. Thrombus volume reduction between 50% and 95% was achieved with all dosing regimens. Clinically significant distal embolization occurred in 8 patients. One major and two non-major bleedings occurred. Microplasmin depleted α2-anti-plasmin and decreased fibrinogen.

CONCLUSION

Intrathrombus infusion of microplasmin for 4 or 6 hours resulted in significant clot lysis. Distal embolization appeared the most important limitation.

Lipid peroxidation as the mechanism of modification of brain 5'-nucleotidase activity in vitro

The effect of lipid peroxidation on the Mg2(+)-independent and Mg2(+)-dependent activity of brain cell membrane 5'-nucleotidase was determined and the affinity of the active sites of Mg2(+)-dependent enzyme for 5'-AMP (substrate) and Mg2+ (activator) was examined. Brain cell membranes were peroxidized at 37 degrees C in the presence of 100 microM ascorbate and 25 microM FeCl2 (resultant) for 10 min. The activity of 5'-nucleotidase and lipid peroxidation products (thiobarbituric acid reactive substances) were determined. At 10 min, the level of lipid peroxidation products increased from 0.20 +/- 0.10 to 17.5 +/- 1.5 nmoles malonaldehyde/mg membrane protein. The activity of Mg2(+)-independent 5'-nucleotidase increased from 0.201 +/- 0.020 in controls to 0.305 +/- 0.028 mumol Pi/mg protein/hr in peroxidized membranes. In the presence of 10 mM Mg2+, the activity increased by 5.8-fold in the peroxidized membrane preparation in comparison to 14-fold in control. In peroxidized preparation, the affinity of active site of Mg2(+)-dependent 5'-nucleotidase for 5'-AMP tripled, as indicated by a significant decrease in Km (Km = 95 +/- 2 microM AMP for control; Km = 32 +/- 2 microM AMP for peroxidized). Vmax was significantly reduced from 3.35 +/- 0.16 in control to 1.70 +/- 0.9 mumoles Pi/mg protein in peroxidized membranes. The affinity of the active site for Mg2+ significantly increased (Km = 6.17 +/- 0.37 mM Mg2+ for control; Km = 4.0 +/- 0.31 peroxidized).(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid peroxidation as the mechanism of modification of the affinity of the Na+, K+-ATPase active sites for ATP, K+, Na+, and strophanthidin in vitro

The effect of lipid peroxidation on the affinity of specific active sites of Na+,K+-ATPase for ATP (substrate), K+ and Na+ (activators), and strophanthidin (a specific inhibitor) was investigated. Brain cell membranes were peroxidized in vitro in the presence of 100 microM ascorbate and 25 microM FeCl2 at 37 degrees C for time intervals from 0-20 min. The level of thiobarbituric acid reactive substances and the activity of Na+, K+-ATPase were determined. The enzyme activity decreased by 80% in the first min. from 42.0 +/- 3.8 to 8.8 +/- 0.9 mumol Pi/mg protein/hr and remained unchanged thereafter. Lipid peroxidation products increased to a steady state level from 0.2 +/- 0.1 to 16.5 +/- 1.5 nmol malonaldehyde/mg protein by 3 min. In peroxidized membranes, the affinity for ATP and strophanthidin was increased (two and seven fold, respectively), whereas affinity for K+ and Na+ was decreased (to one tenth and one seventh of control values, respectively). Changes in the affinity of active sites will affect the phosphorylation and dephosphorylation mechanisms of Na+, K+-ATPase reaction. The increased affinity for ATP favors the phosphorylation of the enzyme at low ATP concentrations whereas, the decreased affinity for K+ will not favor the dephosphorylation of the enzyme-P complex resulting in unavailability of energy for transmembrane transport processes. The results demonstrate that lipid peroxidation alters Na+, K+-ATPase function by modification at specific active sites in a selective manner, rather than through a non-specific destructive process.