Intravenous treatment of experimental Parkinson's disease in the mouse with an IgG-GDNF fusion protein that penetrates the blood-brain barrier

Abstract

Glial-derived neurotrophic factor (GDNF) is a trophic factor for the nigra-striatal tract in experimental Parkinson's disease (PD). The neurotrophin must be administered by intra-cerebral injection, because GDNF does not cross the blood-brain barrier (BBB). In the present study, GDNF was re-engineered to enable receptor-mediated transport across the BBB following fusion of GDNF to the heavy chain of a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and this fusion protein is designated cTfRMAb-GDNF. This fusion protein had been previously shown to retain low nM binding constants for both the GDNF receptor and the mouse TfR, and to rapidly enter the mouse brain in vivo following intravenous administration. Experimental PD in mice was induced by the intra-striatal injection of 6-hydroxydopamine, and mice were treated with either saline or the cTfRMAb-GDNF fusion protein every other day for 3 weeks, starting 1 h after toxin injection. Fusion protein treatment caused a 44% decrease in apomorphine-induced rotation, a 45% reduction in amphetamine-induced rotation, a 121% increase in the vibrissae-elicited forelimb placing test, and a 272% increase in striatal tyrosine hydroxylase (TH) enzyme activity at 3 weeks after toxin injection. Fusion protein treatment caused no change in TH enzyme activity in either the contralateral striatum or the frontal cortex. In conclusion, following fusion of GDNF to a BBB molecular Trojan horse, GDNF trophic effects in brain in experimental PD are observed following intravenous administration.

Figure 1

Rotation measurements following the administration of apomorphine for PD mice treated with either saline or the cTfRMAb-GDNF fusion protein. Data are mean ± S.E. (n=9 mice/group). Statistical differences from the saline treated animals at 2 and 3 weeks are p<0.05 (*).

Figure 2

Rotation measurements following the administration of amphetamine for PD mice treated with either saline or the cTfRMAb-GDNF fusion protein. Data are mean ± S.E. (n=9 mice/group). Statistical differences from the saline treated animals at 2 and 3 weeks are p<0.005 (*).

Figure 3

Vibrissae-elicited forelimb placing test scores for right side, which is ipsilateral to the toxin lesion, and the left side, which is contralateral to the toxin lesion, for the saline and cTfRMAb-GDNF fusion protein treated mice. All scores were measured at 3 weeks following toxin injection. Data are mean ± S.E. (n=9 mice/group). Statistical differences from the saline treated animals are p<0.05 (*).

Figure 4

Striatal TH enzyme activity on the lesioned side and the non-lesioned side in the striatum and in the frontal cortex in mice treated with either saline or the cTfRMAb-GDNF fusion protein. Brain TH activity was measured at 3 weeks after toxin administration. Data are mean ± S.E. (n=9 mice/group). Statistical differences from the saline treated animals in the right striatum are p<0.001(*).