CHARACTERIZATION OF A FIBRIN GLUE-GDNF SLOW-RELEASE PREPARATION

One novel method to deliver trophic factor locally in the CNS is to mi x it into fibrin glue, In the present studies, [I-125]-labeled GDNF-co ntaining fibrin glue balls were used to determine binding and spread o f the trophic factor, First, the binding of different concentrations o f [I-125]-labeled GDNF in fibrin glue was determined in vitro., Within the six concentrations used (from 200 nM to 0.004 nM, 0 M as control) , there was a strong linear correlation between the [I-125]-GDNF conce ntration and the recovered radioactivity (r = 0.992), The mean bound r adioactivity in 16 samples with 4 nM [I-125]-GDNF was 71262 +/- 2710 C PM, and accounted for 89.8% of the mean initial count of free [I-I25]- GDNF (79369 +/- 3499 CPM). Second, [I-125]-GDNF-containing glue balls were implanted into the anterior chamber of adult rats, The implanted fibrin glue balls decreased in size with time, but could still be iden tified on the irises 2 wk after implantation, Radioactivity was concen trated at the implantation sites in the early stages with a distributi on in the surrounding iris tissue, which became separated into focal r adioactive spots at the third week, Counts of radioactivity were signi ficantly higher, in the [I-125]-GDNF glue ball-implanted irises than c ontrols until 14 days after implantation, A study of the [I-125] decay over time using least-squares linear regression demonstrated first-or der kinetics (r = -0.98, p <0.02) with k = 0.0091 and T 1/2 = 76 h., F inally, [I-I25]-GDNF-containing glue balls were implanted in the spina l cord of adult rats, Radioactivity was concentrated at the implantati on sites in the early stages and was later distributed more widely in the surrounding thoracic cord, The [I-125]-GDNF-containing glue. degra ded over time and became a porous meshwork. with decreasing radioactiv ity at the later time points; Radioactivity in the spinal cords subjec ted to implantation of [I-125]-GDNP-containing glue balls was higher t han iri controls for 14 days, Study of the [I-125] decay by time with least-squares linear regression demonstrated first-order kinetics (r = -0.97, p = 0.001) with T 1/2 = 75.6 h., We conclude that the trophic factor GDNF becomes bound in the fibrin glue matrix from which it is g radually released, Our results suggest that fibrin glue is an effectiv e substrate for keeping a trophic factor localized in situ for a finit e period, protected from the circulation, surrounding aqueous humor or CSF, (C) 1998 Elsevier Science Inc,.