The effect of complexation of Cu(II) with P6A peptide and its analogs on their thrombolytic activities

The complexation of Cu(II) with previously synthesized thrombolytic peptides, Pro-Ala-Lys (6), Arg-Pro-Ala-Lys (7), Ala-Arg-Pro-Ala-Lys (8), Gly-Arg-Pro-Ala-Lys (9) and Gln-Arg-Pro-Ala-Lys (10), resulted in the formation of complexes, Cu(II)-(Pro-Ala-Lys) (6-Cu), Cu(II)-(Arg-Pro-Ala-Lys) (7-Cu), Cu(II)-(Ala-Arg-Pro-Ala-Lys) (8-Cu), Cu(II)-(Gly-Arg-Pro-Ala-Lys) (9-Cu) and Cu(II)-(Gln-Arg-Pro-Ala-Lys) (10-Cu), which was confirmed by UV-Vis, circular dichroism and ESI-MS analyses. Complexes (6-10)-Cu in normal saline (NS) were found to be able to assemble into aggregates, and the size of the aggregates were measured for the next eight consecutive days. It was found that on the 8th day, the diameters of (6-10)-Cu aggregates ranged from 179.21 ± 38.33 nm to 293.46 ± 51.07 nm. The Zeta potentials of (6-10)-Cu aggregates in NS were also examined and it was found that aggregates of (6, 8, 10)-Cu were negatively charged, and 7-Cu and 9-Cu were positively charged. The powders of (6-10)-Cu were analyzed by transmission electron microscopy and were found to have mean particle sizes of 8-15 nm. The in vitro euglobulin lysis, vasodilation and thrombolytic assays indicated that complexation with Cu(II) resulted in a significant increase in the activities of 6-10. The in vivo thrombolytic assays revealed that complexation with Cu(II) resulted in a significant enhancement in the in vivo thrombolytic activities for 6, 7, 8 and 10 at 10 μmol/kg, and 9 at 1 μmol/kg and 0.1 μmol/kg, respectively. These findings suggested that the self-assembly of the Cu(II)-peptide complexes into nano-scale aggregates was beneficial in improving the thrombolytic activity of the peptides.