FIBRIN BINDING OF PLASMINOGEN COATED LIPOSOMES IN-VITRO

In this study, the fibrin binding properties of liposomes containing a number of plasminogen (Pig) molecules on the outside were compared to those of free (non-liposomal) Pig in an in vitro model system. Fibrin monolayer coated 96-wells plates were used, containing fibrin monomer at a density of around 3.4 to 3.9 x 10(-4) nmol/cm(2). These densitie s are similar to liposomal Pig-densities, thus allowing multivalent in teractions to occur. In the panel of experimental conditions that was chosen, binding of free Pig and liposomes with Pig showed three main d ifferences in characteristics. Firstly, in the fibrin binding of Plg-l iposomes not all Pig may be involved, but on the average 40% of the to tal amount of liposomal Pit. This was shown by lysing the liposomes af ter binding to the fibrin and estimation of truly bound Pig. With Pig- densities on the liposomes below the fibrin binding sites density, the maximal number of bound Pig molecules remains below the amount of ava ilable fibrin binding sites. Secondly, a higher binding rare by at lea st one order of magnitude was observed for liposomes with Pig compared to foe Plg. Thirdly, liposomes with Pig: exhibit a fibrin binding aff inity which increases with Pig-density, because of the multivalent cha racter of interaction. Liposomal Pig can successfully compete for fibr in binding sites with a 100 fold higher concentration of free Pit. The se in vitro findings indicate that in view of avid and rapid fibrin bi nding, liposomes with attached plasminogen may be suitable for in vivo targeting to fibrin based thrombi.