Laboratory standards in the assessment of the quality of care

On the relation of oxidative stress to neuroinflammation: lessons learned from the G93A-SOD1 mouse model of amyotrophic lateral sclerosis

The central nervous system (CNS) presents both challenges and opportunities to researchers of redox biochemistry. The CNS is sensitive to oxidative damage during aging or disease; excellent transgenic models of specific neurodegenerative diseases have been created that reproduce oxidative stress components of the corresponding human disorder. Mouse models of familial amyotrophic lateral sclerosis (ALS) based on overexpressed mutant human Cu, Zn-superoxide dismutase (SOD1) are cases in point. These animals experience predictably staged, age-dependent motor neuron degeneration with profound cellular and biochemical damage to nerve fibers and spinal cord tissue. Severe protein and lipid oxidation occurs in these animals, apparently as an indirect consequence of protein aggregation or cytopathic protein-protein interactions, as opposed to aberrant redox catalysis by the mutant enzyme. Recent studies of G93A-SOD1 mice and rats suggest that oxidative damage is part of an unmitigated neuroinflammatory reaction, possibly arising in combination from mitochondrial dysfunction plus pathophysiologic activation of both astrocytes and microglia. Lesions to redox signal-transduction pathways in mutant SOD1+ glial cells may stimulate broad-spectrum upregulation of proinflammatory genes, including arachidonic acid-metabolizing enzymes [e.g., cyclooxygenase-II (COX-II) and 5-lipoxygenase (5LOX)]; nitric oxide synthase (NOS) isoforms; cytokines (particularly tumor necrosis factor alpha, TNF-alpha); chemokines; and immunoglobulin Fc receptors (FcgammaRs). The integration of these processes creates a paracrine milieu inconsistent with healthy neural function. This review summarizes what has been learned to date from studies of mutant SOD1 transgenic animals and demonstrates that the G93A-SOD1 mouse in particular is a robust laboratory for the study of neuroinflammation and redox biochemistry.

Excitatory amino acid neurotransmission

In recent years great progress has been made in understanding the function of ionotropic and metabotropic glutamate receptors; their pharmacology and potential therapeutic applications. It should be stressed that there are already N-methyl-D-aspartate (NMDA) antagonists in clinical use, such as memantine, which proves the feasibility of their therapeutic potential. It seems unlikely that competitive NMDA receptor antagonists and high-affinity channel blockers will find therapeutic use due to limiting side-effects, whereas agents acting at the glycineB site, NMDA receptor subtype-selective agents and moderate-affinity channel blockers are far more promising. This is supported by the fact that there are several glycineB antagonists, NMDA moderate-affinity channel blockers and NR2B-selective agents under development. Positive and negative modulators of AMPA receptors such as the AMPAkines and 2,3-benzodiazepines also show more promise than e.g. competitive antagonists. Great progress has also been made in the field of metabotropic glutamate receptors since the discovery of novel, allosteric modulatory sites for these receptors. Selective agents acting at these transmembrane sites have been developed that are more drug-like and have a much better access to the central nervous system than their competitive counterparts. The chapter will critically review preclinical and scarce clinical experience in the development of new ionotropic and metabotropic glutamate receptor modulators according to the following scheme: rational, preclinical findings in animal models and finally clinical experience, where available.

The arachidonic acid 5-lipoxygenase inhibitor nordihydroguaiaretic acid inhibits tumor necrosis factor alpha activation of microglia and extends survival of G93A-SOD1 transgenic mice

Familial forms of amyotrophic lateral sclerosis (ALS) can be caused by mutations in copper, zinc-superoxide dismutase (SOD1). Mice expressing SOD1 mutants demonstrate a robust neuroinflammatory reaction characterized, in part, by up-regulation of tumor necrosis factor alpha (TNFalpha) and its primary receptor TNF-RI. In an effort to identify small molecule inhibitors of neuroinflammation useful in treatment of ALS, a microglial culture system was established to identify TNFalpha antagonists. Walker EOC-20 microglia cells were stimulated with recombinant TNFalpha, with or without inhibitors, and the cell response was indexed by NO2- output. Three hundred and fifty-five rationally selected compounds were included in this bioassay. The arachidonic acid 5-lipoxygenase (5LOX) and tyrosine kinase inhibitor nordihydroguaiaretic acid (NDGA), a natural dicatechol, was one of the most potent non-cytotoxic antagonists tested (IC50 8 +/- 3 microm). Investigation of the G93A-SOD1 mouse model for ALS revealed increased message and protein levels of 5LOX at 120 days of age. Oral NDGA (2500 p.p.m.) significantly extended lifespan and slowed motor dysfunction in this mouse, when administration was begun relatively late in life (90 days). NDGA extended median total lifespan of G93A-SOD1 mice by 10%, and life expectancy following start of treatment was extended by 32%. Disease-associated gliosis and cleaved microtubule-associated tau protein, an indicator of axon damage, were likewise reduced by NDGA. Thus, TNFalpha antagonists and especially 5LOX inhibitors might offer new opportunities for treatment of ALS.

Gene therapy for amyotrophic lateral sclerosis and other motor neuron diseases

There are several incurable diseases of motor neuron degeneration, including amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, hereditary spastic hemiplegia, spinal muscular atrophy, and bulbospinal atrophy. Advances in gene transfer techniques coupled with new insights into molecular pathology have opened promising avenues for gene therapy aimed at halting disease progression. Nonviral preparations and recombinant adenoviruses, adeno-associated viruses, herpesviruses, and lentiviruses may ultimately transduce sufficient numbers of cerebral, brainstem, and spinal cord neurons for therapeutic applications. This could be accomplished by direct injection, transduction of lower motor neurons via retrograde transport after intramuscular injection, or cell-based therapies. Studies using transgenic mice expressing mutant superoxide dismutase 1 (SOD1), a model for one form of ALS, established that several proteins were neuroprotective, including calbindin, bcl-2, and growth factors. These same molecules promoted neuronal survival in other injury models, suggesting general applicability to all forms of ALS. Potentially correctable genetic lesions have also been identified for hereditary spastic hemiplegia, bulbospinal atrophy, and spinal muscular atrophy. Finally, it may be possible to repopulate lost corticospinal and lower motor neurons by transplanting stem cells or stimulating native progenitor populations. The challenge ahead is to translate these basic science breakthroughs into workable clinical practice.