Implanted fibroblasts genetically engineered to produce brain-derived neurotrophic factor prevent 1-methyl-4-phenylpyridinium toxicity to dopaminergic neurons in the rat.

The trophism of brain-derived neurotrophic factor (BDNF) for dopaminergic cells in culture has led to significant interest in the role of BDNF in the etiology and potential treatment of Parkinson disease. Previous in vivo investigation of BDNF delivery to axotomized substantia nigra dopaminergic neurons in the adult rat has shown no protective effect. In this study, we produced nigral degeneration by infusing 1-methyl-4-phenylpyridinium (MPP+), a mitochondrial complex I inhibitor and the active metabolite of 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP), into the rat striatum. The subsequent loss of nigral neurons was presumably due to mitochondrial toxicity after MPP+ uptake and retrograde transport to the substantia nigra. We engineered immortalized rat fibroblasts to secrete human BDNF and implanted these cells near the substantia nigra 7 days before striatal MPP+ infusion. We found that BDNF-secreting fibroblasts markedly increased nigral dopaminergic neuronal survival when compared to control fibroblast implants. The observation that BDNF prevents MPTP-induced dopaminergic neuronal degeneration in the adult brain has significance for the treatment of neurodegenerative disorders, which may involve mitochondrial dysfunction, such as Parkinson disease.

The effects of megadose methylprednisolone and U-78517F on toxicity mediated by glutamate receptors in the rat neostriatum.

Mechanisms of neuronal death after acute insults are unknown but may involve energy depletion and resultant glutamate toxicity. One potential pathway leading to cell death is the formation of oxygen free radicals in an energy-depleted state. Megadoses of glucocorticoids as well as the lazaroid compounds (e.g., 21-aminosteroids and 2-methylaminochromans) have been shown to be potent antioxidants, capable of mitigating the effects of oxygen radicals on lipid membranes in vitro. The authors investigated the protective antioxidant effects of megadose methylprednisolone (MPSS) and the lazaroid 2-methylaminochroman (U-78517F) on the size of striatal lesions caused by quinolinic acid, an N-methyl-D-aspartate (NMDA) receptor agonist that mimics certain aspects of the secondary injury surrounding the pan-necrosis central to stroke or cerebral contusion. Treatment with MPSS (60 mg/kg/day) before quinolinate infusion and continuing through the first postoperative day caused a significant (P < 0.01) 56% increase in the size of striatal lesions. In contrast, treatment with MPSS given 2 to 6 hours after creation of the lesion did not affect lesion size. Animals treated with U-78517F also failed to exhibit any neuroprotective effects. The detrimental effect of pretreatment with megadose MPSS is likely the result of deleterious energy-depleting glucocorticoid effect of pretreatment with megadose MPSS is likely the result of deleterious energy-depleting glucocorticoid effects that outweight any positive antioxidant effects. We conclude that megadose MPSS, although found to be beneficial in the treatment of spinal cord injury, may not be beneficial in the treatment of intracranial insults involving glutamate toxicity.

Striatal degeneration induced by mitochondrial blockade is prevented by biologically delivered NGF.

Consistent with the notion that a defect in cellular energy metabolism is a cause of human neurodegenerative disease, systemic treatment with the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NPA) can model the striatal neurodegeneration seen in Huntington's disease. Previously, we have found that nerve growth factor (NGF), delivered biologically by the implantation of a genetically altered fibroblast cell-line, can protect locally against striatal degeneration induced by infusions of high doses of glutamate receptor agonists. We now report that implantation of NGF-secreting fibroblasts reduces the size of adjacent striatal 3-NPA lesions by an average of 64%. We conclude that biologically delivered NGF protects neurons against excitotoxicity and mitochondrial blockade--both energy-depleting processes--implying that appropriate neurotrophic support in the adult brain could protect against neurodegenerative diseases caused in part by energy depletion.

Effects of biologically delivered NGF, BDNF and bFGF on striatal excitotoxic lesions.

Immortalized rat fibroblasts, genetically altered to secrete NGF, BDNF, and bFGF, were implanted in rat brain near the striatum 7 days before striatal infusion of excitotoxic quantities of an NMDA-receptor agonist. Analysis of striatal damage 7 days after lesioning revealed that implantation of NGF-secreting cells reduced the size of the excitotoxic lesions by more than 80% when compared with control cells, while implanting of bFGF-secreting cells caused a 30% decrease in excitotoxic lesion size. BDNF-secreting fibroblasts caused no protective sparing in the striatum in this lesion model. This finding shows that biological delivery of NGF and bFGF by grafting of genetically altered cells protects against glutamate toxicity in the adult striatum while grafting of BDNF-producing cells does not. Such observations begin to define a spectrum of neurotrophic agents able to mitigate the cell loss seen in neurodegeneration.