Caspase inhibitors attenuate 1-methyl-4-phenylpyridinium toxicity in primary cultures of mesencephalic dopaminergic neurons.

Parkinson's disease is characterized by a loss of dopaminergic nigrostriatal neurons. This neuronal loss is mimicked by the neurotoxin 1-methyl-4-phenylpyridinium (MPP+). MPP+ toxicity is mediated through inhibition of mitochondrial complex I, decreasing ATP production, and upregulation of oxygen radicals. There is evidence that the cell death induced by MPP+ is apoptotic and that inhibition of caspases may be neuroprotective. In primary cultures of rat mesencephalic dopaminergic neurons, MPP+ treatment decreased the number of surviving dopaminergic neurons in the cultures and the ability of the neurons to take up [3H]dopamine ([3H]DA). Caspase inhibition using the broad-spectrum inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk) spared MPP+-treated dopaminergic neurons and increased somatic size. There was a partial restoration of neurite length in zVAD-fmk-treated cultures, but little restoration of [3H]DA uptake. Peptide inhibitors of caspases 2, 3, and 9, but not of caspase 1, caused significant neuroprotection. Two novel caspase inhibitors were tested for neuroprotection, a broad spectrum inhibitor and a selective caspase 3 inhibitor; both inhibitors increased survival to >90% of control. No neuroprotection was observed with an inactive control compound. MPP+ treatment caused chromatin condensation in dopaminergic neurons and increased expression of activated caspase 3. Inhibition of caspases with either zVAD-fmk or a selective caspase 3 inhibitor decreased the number of apoptotic profiles, but not expression of the active caspase. We conclude that MPP+ toxicity in primary dopaminergic neurons involves activation of a pathway terminating in caspase 3 activation, but that other mechanisms may underlie the neurite loss.

Small molecule Trk receptor agonists and other neurotrophic factor mimetics.

Nerve growth factor belongs to a small family of proteins whose binding at the Trk and p75(NTR) transmembrane receptors triggers a cascade of signaling events that give rise to neurotrophic responses in neuronal cells and in vivo. Following their robust effects in animal models of neurodegeneration, neurotrophins have been evaluated for therapy for several human neurodegenerative diseases. However, due mainly to the poor pharmacokinetic behavior of these proteins, they have largely met without success in the clinic, making it desirable to develop small molecule neurotrophin mimetics. A range of compounds is described that achieves some of the neurotrophic and neuroprotective effects attributed to neurotrophins through a variety of mechanisms. These small molecules are divided into the following functional categories: (1). compounds that activate Trk receptors directly; (2). compounds that potentiate the actions of neurotrophins on Trk receptors; (3). compounds that activate Trk indirectly; (4). compounds that influence neurotrophin expression or secretion; and (5). a broad class of compounds that act downstream of, or independently of, Trk receptors. Unfortunately, most of the compounds that have been reported suffer from either lack of specificity for the desired mechanism/effect(s) or lack of efficacy of the compounds in appropriate in vivo models, or both. This second limitation has been particularly severe for compounds designed to mimic the neurotrophins in their interaction with Trk receptors, an ongoing and formidable challenge. Nevertheless, a small subset of the compounds, acting on intracellular signaling pathways downstream of Trk receptors, shows promise for the future treatment of neurodegenerative diseases.

CEP-1347 promotes survival of NGF responsive neurones in primary DRG explants.

CEP-1347 inhibits the signalling pathway of c-jun-N-terminal kinase, and is neuroprotective in vivo and in vitro. Embryonic chick dorsal root ganglion neurones are dependent on NGF for survival and neurite outgrowth; NGF withdrawal results in apoptotic cell death. We examined the neuroprotective and neurite outgrowth promoting activity of CEP-1347 in dissociated DRG neurones and in primary DRG explants. CEP-1347 was as effective as NGF in promoting survival of dissociated DRG neurones, but caused only limited neurite outgrowth from DRG explants. When NGF was subsequently added to CEP-1347 treated explants, the outgrowth increased to a similar level to explants which had received NGF throughout. CEP-1347 may be a useful tool to maintain viable DRG explants to allow evaluation of neurite outgrowth promoting compounds and dissection of survival and neurite outgrowth signalling pathways.

Trk Neurotrophin Receptor Activators.

The neurotrophins are a small group of proteins whose binding at the tropomyosin related kinase (Trk) and p75 neurotrophin receptor transmembrane receptors triggers a cascade of signaling events that give rise to neurotrophic responses in neuronal cells and in vivo. Although neurotrophins have been evaluated for therapy for several human neurodegenerative diseases, their poor pharmacokinetic behavior has rendered their development largely unsuccessful. For this reason, several strategies are being explored to obtain small molecules that achieve the neurotrophic and neuroprotective effects attributed to neurotrophins. One strategy in which to achieve these effects is to develop compounds that affect Trk receptor activation. (c) 2002 Prous Science. All rights reserved.

MAPKs: new targets for neurodegeneration.

Neurodegenerative diseases remain a huge unmet pharmaceutical need. For some diseases such as Parkinson's disease, there are currently only palliative therapies, and for others such as Alzheimer's disease there are no proven therapies on the market that have any significant impact on disease progression. Recent work has suggested that cell death may play a key role in a number of neurodegenerative diseases, and halting this aberrant cell death may halt disease progression. Kinases identified in cell death pathways may be attractive targets for neurodegenerative diseases. In this review, the authors will focus on three families of related mitogen-activated protein kinases (MAPKs), namely, the extracellular signal-regulated protein kinases (ERKs), the c-Jun N-terminal kinases (JNKs) and the p38 MAPKs. The evidence for activation of each of these pathways in disease states and in models of neurodegenerative disorders will be examined. Effects of inhibitors, where available, will be discussed, and potential problems and side effects of kinase inhibitors as therapeutics will be addressed.