CO R R E S P O N D E N C E

NATURE MEDICINE VOLUME 11 | NUMBER 7 | JULY 2005 703

Glial cell line–derived neurotrophic factor induces neuronal sprouting in human brain

To the editor:Intraputaminal delivery of glial cell line–derived neurotrophic factor (GDNF) causes sprouting of dopaminergic fibers and clinical improvement in experimental animal mod-els of Parkinson disease. We provide the first neuropathological evidence that infusion of GDNF into the posterior putamen causes similar sprouting of dopaminergic fibers in association with clinical improvement in idiopathic Parkinson disease in humans.

A 62-year-old man was one of five indi-viduals in a phase 1 study of GDNF (Amgen) infusion into the posterodorsal putamen, for treatment of idiopathic Parkinson disease1,2. He had a 5-year history of poorly controlled tremor-predominant left hemiparkinsonism. An intraparenchymal catheter was stereotacti-cally implanted in the right posterodorsal puta-men and connected to a SynchroMed pump (Medtronic). GDNF was infused continuously, at 14.4–43.2 mg/putamen/d, for 43 months.

Clinical assessments were based on the Core Assessment Program for Intracerebral Transplantations1–3. At 24 months, the Unified Parkinson’s Disease Rating Scale (UPDRS)-III motor score off-medication had improved by 38% (Fig. 1a). This was accompanied by an 18% increase in whole-putamen 18F-dopa uptake and increased uptake in the posterior putamen of 91%. In contrast, the noninfused side showed a 7.4% decrease in whole-putamen 18F-dopa uptake

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bFigure 1 UPDRS-III scores, 18F-dopa uptake and neuropathological findings. (a) Over the 43 months of infusion of GDNF, both ipsilateral (left) and contralateral (right) UPDRS-III motor scores showed initial improvement, but from 24 to 43 months contralateral scores remained relatively stable whereas motor performance ipsilateral to the infusion declined. (b) A PET scan just prior to commencement of GDNF infusion (top) shows low 18F-dopa uptake in the posterior part of the right putamen. 18F-dopa uptake has increased markedly in the posterior part of the right putamen (arrow in the bottom panel) but declined in the left putamen 18 months later. (c–f) Postmortem immunohistochemical findings in axial sections through posterior part of left (c) and right (d,e) putamen, and through the midbrain (f); c,d are viewed from above with anterior putamen to the right of the figure. Note the increased density of GFAP-immunopositive astrocytes around the end of the catheter track (arrow) in the posterior third of the right (d, left panel) compared with the left (c, left panel) putamen. Tyrosine hydroxylase–immunopositive structures occupy a much greater part of the right (d, right panel) than the left (c, right panel) putamen. (e) High magnification shows finely granular tyrosine hydroxylase labeling of neuritic processes and of some axonal swellings (arrow in left panel). An occasional neuron in the putamen is immunopositive for tyrosine hydroxylase; note the lack of tyrosine hydroxylase in intervening macrophages and astrocytes (right panel). (f) Less tyrosine hydroxylase is present in the ventrolateral tier in the right side of the brain (arrow, left panel) than the left substantia nigra but GAP43 labeling (right panel) is similar on the two sides.

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CO R R E S P O N D E N C E

704 VOLUME 11 | NUMBER 7 | JULY 2005 NATURE MEDICINE

(Fig. 1b)4. Between 24 and 43 months, the overall UPDRS-III motor score worsened ipsilateral to the infusion (Fig. 1a). The left-sided scores remained relatively stable. Use of the PDQ-39 (Parkinson disease Questionnaire) to monitor the impact of GDNF on quality of life indicated improve-ment in most domains, including 75% and 70% improvements in activities of daily liv-ing at 24 and 43 months, respectively.

GDNF infusion was stopped after 43 months on withdrawal of the drug by Amgen. The patient died of a myocardial infarct, 3 months later. Postmortem exami-nation showed severe coronary atheroma. The brain was fixed in formalin before being sliced axially. Gross examination showed a fine catheter track passing through the right parasagittal frontal cortex and white matter, the posterior part of the right putamen and internal capsule, and into the posterior one-third of the right putamen. The only other macroscopic findings of note were poor pig-mentation of the substantia nigra and locus ceruleus, and an incidental right frontal venous angioma. Histology confirmed the angioma and disclosed a focus of old, prob-ably ischemic, scarring in the watershed region of the cerebellum, and small neuronal heterotopias in the cerebellar white matter.

Histology and immunohistochemistry showed marked loss of neurons from the substantia nigra, particularly from the right ventrolateral tier, with associated astrocytic gliosis. Lewy bodies were present in sev-eral remaining nigral neurons. Labeling for α-synuclein showed Lewy bodies and neu-rites in the cerebral neocortex, substantia nigra, locus ceruleus and motor nucleus of the vagus. The cerebral cortex contained sparse neuritic and diffuse plaques and vas-cular deposits of β-amyloid protein. Tau-immunopositive neurofibrillary tangles and

neuropil threads were confined to the entorhinal cor-tex and subiculum (Braak tangle stage II). There was a very focal increase in astrocytic gliosis around the catheter track but no inflam-mation except at the tip of the track in the posterior putamen, where there were scanty perivascular cuffs of lympho-cytes, predominantly CD3+ T cells, and

CD68+ macrophages. Scattered macrophages and major histocompatibility class II anti-gen–positive microglia were present in the adjacent parenchyma up to 2–3 mm from the tip of the track. No lymphocytes or macro-phages were demonstrable in the left puta-men. Quantification5 of labeling of astrocytes labeled with antibody to glial fibrillary acidic protein (GFAP) showed them to occupy a greater area fraction in the posterior third of the right (17.4%) than the left putamen (15.9%) in the axial plane of the tip of the catheter (Fig. 1c,d and Table 1).

Dopaminergic fibers and neurons were identified with antibody to tyrosine hydroxylase. There was a more than fivefold greater area occupied by tyrosine hydroxy-lase–immunopositive structures in the pos-terior one-third of the right than the left putamen (area fraction 13.8% versus 2.6%; Fig. 1c,d and Table 1). The increase in tyrosine hydroxylase–immunopositive struc-tures extended up to 5 mm anteriorly, 7 mm posteriorly, 3 mm medially (into the poste-rior globus pallidus), 1 mm laterally and 10 mm superiorly. Most of the labeling was fine and granular, but there was also labeling of larger nerve fibers (including some axonal swellings) and an occasional cell body (Fig. 1e). In the midbrain, tyrosine hydroxy-lase labeling occupied about twice the area in the left substantia nigra (27.6%) than the right (13.6%), in keeping with the asymmetry of the Parkinson disease (Fig. 1f and Table 1). In the same section, the num-ber of nigral tyrosine hydroxylase–immu-nopositive neurons was 367 on the left and 286 on the right.

The amount of the synaptic protein syn-aptophysin was reduced in the immedi-ate vicinity of the catheter tip (i.e., in the region of gliosis and inflammation) but overall the labeled-area fraction in the

posterior putamen was only slightly less on the right (15.5%) than the left (17.9%; Table 1). Despite a similar reduction in label-ing for the sprout-associated protein growth-associated protein 43 (GAP43) around the catheter tip, overall this label occupied approximately one-third more of the pos-terior putamen on the right (22.6%) than the left (17.0%; Table 1). The figures for the right and left substantia nigra are shown in Table 1; the differences in the two sides in syn-aptophysin and GAP43 (Fig. 1f) were much less than the differences in disease severity and labeling for tyrosine hydroxylase.

The present findings indicate for the first time that infusion of GDNF into the poste-rior putamen causes a marked local increase in tyrosine hydroxylase–immunopositive nerve fibers. There may also be sprouting of fibers in the substantia nigra, as suggested by the relatively strong expression of GAP43 on the side of infusion. These observations parallel those in experimental models of Parkinson disease6–9. It remains unclear how much of the increase in tyrosine hydroxy-lase–immunopositive nerve fibers results from axonal sprouting and how much results from upregulation of tyrosine hydroxylase in spared but dysfunctional fibers9. In either case, however, the findings provide a possible substrate for the sustained clinical improve-ment and enhanced 18F-dopa uptake in humans receiving intraputaminal infusion of GDNF1,2.

ACKNOWLEDGMENTSWe thank C. Redman, R. Quilty, T. McLaren, M. Jennings and R. Barber for technical assistance. Amgen, Inc. supplied the GDNF for this trial.

Seth Love1, Puneet Plaha2, Nikunj K Patel2, Gary R Hotton3, David J Brooks3 & Steven S Gill2

Departments of 1Neuropathology and 2Neurosurgery, Institute of Clinical Neurosciences, Frenchay Hospital, Bristol BS16 1LE, UK. 3MRC Clinical Sciences Centre and Division of Neuroscience, Faculty of Medicine, Imperial College, Hammersmith Hospital, London W12 0NN, UK.e-mail: seth.love@bris.ac.uk

1. Patel, N.K. et al. Ann. Neurol. 57, 298–302 (2005).

2. Gill, S.S. et al. Nat. Med. 9, 589–595 (2003).3. Langston, J.W. et al. Mov. Disord. 7, 2–13 (1992).4. Patel, N.K. et al. Mov. Disord. 17 Suppl 9, 727

(2004).5. Chalmers, K., Wilcock, G.K. & Love, S. Neuropathol.

Appl. Neurobiol. 29, 231–238 (2003).6. Opacka-Juffry, J. et al. Neuroreport 7, 348–352

(1995).7. Tomac, A. et al. Nature 373, 335–339 (1995).8. Date, I., Aoi, M., Tomita, S., Collins, F. & Ohmoto, T.

Neuroreport 9, 2365–2369 (1998).9. Kirik, D., Georgievska, B. & Bjorklund, A. Nat.

Neurosci. 7, 105–110 (2004).

Table 1 Immunolabeling of posterior putamen and substantia nigra

Left Right (side of GDNF infusion)

Posterior putamen

GFAP 15.9a 17.4

Tyrosine hydroxylase 2.6 13.8

Synaptophysin 17.9 15.5

GAP43 17.0 22.6

Substantia nigra

Tyrosine hydroxylase 27.6 13.6

Synaptophysin 21.5 18.6

GAP43 28.2 27.9aPercent area immunopositive for relevant antigen in 7 µm paraffin section through posterior putamen in axial plane of tip of catheter, or in substantia nigra immediately below plane of exit of oculomotor nerves.

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