Neuroprotection by the selective iNOS inhibitor GW274150 in a model of Parkinson disease.

Neuroinflammation and the activation of inducible nitric oxide synthase (iNOS) have been proposed to play a role in the pathogenesis of Parkinson disease (PD). In this study we investigated the effects of the selective iNOS inhibitor GW274150 in the 6-OHDA model of PD. 6-OHDA administration was associated with increased numbers of cells expressing iNOS. Administration of the iNOS inhibitor twice daily for 7 days, beginning 2 days after the 6-OHDA lesioning, led to a significant neuroprotection as shown by assessment of the integrity of the nigrostriatal system by tyrosine hydroxylase immunocytochemistry and HPLC assessment of striatal dopamine content. However, GW274150 displayed a bell-shaped neuroprotective profile, being ineffective at high doses. 6-OHDA lesioning was associated with an increase in microglial activation as assessed by the MHC II antigen OX-6 and the number of matrix metalloproteinase 9 (MMP-9)-immunopositive cells. NO is a known modulator of MMP-9, and iNOS inhibition was associated with decreased numbers of MMP-9-immunopositive cells, culminating in a reduction in the numbers of reactive microglia. Withdrawal of GW274150 for a further 7 days negated any neuroprotective effects of iNOS inhibition, suggesting that the damaging effects of inflammation last beyond 7 days in this model and the continued administration of the drug may be required.

Relationship between microglial activation and dopaminergic neuronal loss in the substantia nigra: a time course study in a 6-hydroxydopamine model of Parkinson's disease.

Cellular interactions between activated microglia and degenerating neurons in in vivo models of Parkinson's disease are not well defined. This time course study assesses the dynamics of morphological and immunophenotypic properties of activated microglia in a 6-hydroxydopamine (6-OHDA) model of Parkinson's disease. Neurodegeneration in the substantia nigra pars compacta (SNc) was induced by unilateral injection of 6-OHDA into the medial forebrain bundle. Activated microglia, identified using monoclonal antibodies: clone of antibody that detects major histocompatibility complex (MHC) class II antigens (OX6) for MHC class II, clone of antibody that detects cell surface antigen-cluster of differentiation 11b - anti-complement receptor 3, a marker for complement receptor 3 and CD 68 for phagocytic activity. Activation of microglia in the lesioned SNc was rapid with cells possessing amoeboid or ramified morphology appeared on day 1, whilst antibody clone that detects macrophage-myeloid associated antigen immunoreactivity was observed at day 3 post-lesion when there was no apparent loss of tyrosine hydroxylase (TH)+ve dopaminergic (DA) SNc neurons. Thereafter, OX6 and antibody clone that detects macrophage-myeloid associated antigen activated microglia selectively adhered to degenerating axons, dendrites and apoptotic (caspase 3+ve) DA neurons in the SNc were observed at day 7. This was followed by progressive loss of TH+ve SNc neurons, with the peak of TH+ve cell loss (51%) being observed at day 9. This study suggests that activation of microglia precedes DA neuronal cell loss and neurons undergoing degeneration may be phagocytosed prematurely by phagocytic microglia.

Constraints on the efficacy of mucosal tolerance in treatment of human and animal arthritic diseases.

Mucosal administration of an autoantigen has been shown to be a powerful way of inducing tolerance in both animal and human arthritis clinical trials. Bovine or chicken type II collagen has been administered orally to rheumatoid arthritis patients, resulting in some, although in many cases rather limited, clinical improvement. Animal studies have revealed that the mechanisms that underlie induction of mucosal tolerance include clonal deletion, suppression of the proinflammatory Th1 cells, and the induction of regulatory T cells. These cells, defined as a persistently CD25-expressing subset of CD4(+) cells, are frequently anergic, may produce anti-inflammatory cytokines such as IL-10 and TGF-beta, and are likely to be agents of bystander suppression. A key feature that may affect the induction of these cells and other suppressive mechanisms is the dose of antigen administered. The results from human clinical trials suggest a daily dose of significantly less than 1 mg is optimal. Similarly data from collagen-induced arthritis studies reveal an optimal dose above and below which there is little or no immune suppression. Indeed, the incorrect dose can prime the immune response and aggravate disease. The timing and frequency of administration is also vital to the level of immune tolerance induced and the control of the pathological process. This and other findings derived from animal studies are discussed here in relation to the results from human clinical trials.