Dominic B. Rowe

An inflammatory review of Parkinson’s disease

The symptoms of Parkinsons disease (PD) were first described nearly two centuries ago and its characteristic pathology identified nearly a century ago, yet its pathogenesis is still poorly understood. Parkinsons disease is the most prevalent neurodegenerative movement disorder and research into its pathogenesis recently accelerated following the identification of a number of causal genetic mutations. The mutant gene products all cause dysfunction of the ubiquitin-proteosome system, identifying protein modification and degradation as critical for pathogenesis. Modified non-degraded intracellular proteins accumulate in certain neuronal populations in all forms of the disease. However, neuronal degeneration is more highly selective and associates with substantial activation of microglia, the inflammatory cells of the brain. We review the current change in thinking regarding the role of microglia in the brain in the context of Parkinsons disease and animal models of the disease. Comparison of the cellular tissue changes across a number of animal models using diverse stimuli to mimic Parkinsons disease reveals a consistent pattern implicating microglia as the effector for the selective degeneration of dopaminergic neurons. While previous reviews have concentrated on the intracellular neuronal changes in Parkinsons disease, we highlight the cell to cell interactions and immune regulation critical for neuronal homeostasis and survival in Parkinsons disease.

Microglial activation and dopaminergic cell injury: an in vitro model relevant to Parkinson's disease.

Microglial activation and oxidative stress are significant components of the pathology of Parkinsons disease (PD), but their exact contributions to disease pathogenesis are unclear. We have developed an in vitro model of nigral injury, in which lipopolysaccharide-induced microglial activation leads to injury of a dopaminergic cell line (MES 23.5 cells) and dopaminergic neurons in primary mesencephalic cell cultures. The microglia are also activated by PD IgGs in the presence of low-dose dopa-quinone- or H2O2-modified dopaminergic cell membranes but not cholinergic cell membranes. The activation requires the microglial FcγR receptor as demonstrated by the lack of activation with PD IgG Fab fragments or microglia from FcγR−/− mice. Although microglial activation results in the release of several cytokines and reactive oxygen species, only nitric oxide and H2O2appear to mediate the microglia-induced dopaminergic cell injury. These studies suggest a significant role for microglia in dopaminergic cell injury and provide a mechanism whereby immune/inflammatory reactions in PD could target oxidative injury relatively specifically to dopaminergic cells.

Neuroprotection by pramipexole against dopamine- and levodopa-induced cytotoxicity

Pramipexole, a novel non-ergoline dopamine (DA) agonist, has been applied successfully for treatment of Parkinsons disease (PD). We report here that pramipexole can protect dopaminergic cell line Mes23.5 against dopamine- and levodopa-induced cytotoxicity possibly through a mechanism related to antioxidant activity. In the MES 23.5 cultures, DA and L-DOPA induce a dose- and time-dependent cytotoxicity, as determined by tetrazolium salt and trypan blue assays. Furthermore, an in situ terminal deoxynucleotidyl transferase assay demonstrates that DA-induced cell death is apoptotic. Pretreatment with pramipexole in a concentration range (4-100 microM) significantly attenuates DA- or L-DOPA-induced cytotoxicity and apoptosis, an action which is not blocked by D3 antagonist U-99194 A or D2 antagonist raclopride. Pramipexole also protects MES 23.5 cells from hydrogen peroxide-induced cytotoxicity in a dose-dependent manner. In cell-free system, pramipexole can effectively inhibit the formation of melanin, an end product resulting from DA or L-DOPA oxidation. These results indicate that pramipexole exerts its neuroprotective effect possibly through a mechanism, which is independent of DA receptors but related to antioxidation or scavenging of free radicals (e.g. hydrogen peroxide). As a direct DA agonist and potentially neuroprotective agent, pramipexole remains attractive in the treatment of PD.

Genetic contributions to Parkinson's disease

Sporadic Parkinsons disease (PD) is a common neurodegenerative disorder, characterized by the loss of midbrain dopamine neurons and Lewy body inclusions. It is thought to result from a complex interaction between multiple predisposing genes and environmental influences, although these interactions are still poorly understood. Several causative genes have been identified in different families. Mutations in two genes [alpha-synuclein and nuclear receptor-related 1 (Nurr1)] cause the same pathology, and a third locus on chromosome 2 also causes this pathology. Other familial PD mutations have identified genes involved in the ubiquitin-proteasome system [parkin and ubiquitin C-terminal hydroxylase L1 (UCHL1)], although such cases do not produce Lewy bodies. These studies highlight critical cellular proteins and mechanisms for dopamine neuron survival as disrupted in Parkinsons disease. Understanding the genetic variations impacting on dopamine neurons may illuminate other molecular mechanisms involved. Additional candidate genes involved in dopamine cell survival, dopamine synthesis, metabolism and function, energy supply, oxidative stress, and cellular detoxification have been indicated by transgenic animal models and/or screened in human populations with differing results. Genetic variation in genes known to produce different patterns and types of neurodegeneration that may impact on the function of dopamine neurons are also reviewed. These studies suggest that environment and genetic background are likely to have a significant influence on susceptibility to Parkinsons disease. The identification of multiple genes predisposing to Parkinsons disease will assist in determining the cellular pathway/s leading to the neurodegeneration observed in this disease.

Assessment of disease progression in motor neuron disease

Motor neuron disease (MND) is characterised by progressive deterioration of the corticospinal tract, brainstem, and anterior horn cells of the spinal cord. There is no pathognomonic test for the diagnosis of MND, and physicians rely on clinical criteria-upper and lower motor neuron signs-for diagnosis. The presentations, clinical phenotypes, and outcomes of MND are diverse and have not been combined into a marker of disease progression. No single algorithm combines the findings of functional assessments and rating scales, such as those that assess quality of life, with biological markers of disease activity and findings from imaging and neurophysiological assessments. Here, we critically appraise developments in each of these areas and discuss the potential of such measures to be included in the future assessment of disease progression in patients with MND.

Antibodies from patients with Parkinson's disease react with protein modified by dopamine oxidation

To determine whether specific antibodies are present in PD, we used an enzyme‐linked immunosorbant assay (ELISA) that identifies increased immunoglobulin (IgG) levels towards a synthetic substrate prepared by incubating ovalbumin with dopamine and copper sulfate. Altered absorption spectrum and specific chemical detection demonstrated quinone modification of the ovalbumin. This modified protein was demonstrated to react with serial dilutions of PD sera. A threshold dilution of 1:500 was subsequently used to screen sera from patients with PD (n = 21), amyotrophic lateral sclerosis (n = 7), Alzheimers disease (n = 7) and other neurological disease controls (n = 7). The assay produced a positive result in 7/21 PD patients and 0/21 disease controls (P < 0.02, Kruskal–Wallis test). Further testing of sera from untreated PD patients (n = 6) identified one positive sample. Thus, a subset of Parkinsons disease (PD) patients has immunoglobulin (IgG) to ovalbumin modified by dopamine oxidation. The presence of antibody reactivity to quinone‐modified proteins could contribute to or amplify the inflammatory response in PD. J. Neurosci. Res. 53:551–558, 1998.

Reduced T helper and B lymphocytes in Parkinson's disease

Gene association with HLA suggests involvement of immune mediated mechanisms in the pathogenesis of Parkinsons disease (PD). Only a small number of studies have found differences between circulating leukocyte populations in PD patients compared to controls, with conflicting results. To clarify whether there is a circulating leukocyte PD phenotype, we assessed the numbers of T, B and natural killer cells, and monocytes and found a small reduction (15-25%) in CD4+ T and CD19+ B cells in PD. These findings suggest some compromise in immune cells in PD and have potential implications for immune function and the progression of PD.

Do polymorphisms in the familial Parkinsonism genes contribute to risk for sporadic Parkinson's disease?

Recent whole genome association studies provided little evidence that polymorphisms at the familial Parkinsonism loci influence the risk for Parkinsons disease (PD). However, these studies are not designed to detect the types of subtle effects that common variants may impose. Here, we use an alternative targeted candidate gene approach to examine common variation in 11 genes related to familial Parkinsonism. PD cases (n = 331) and unaffected control subjects (n = 296) were recruited from three specialist movement disorder clinics in Brisbane, Australia and the Australian Electoral Roll. Common genetic variables (76 SNPs and 1 STR) were assessed in all subjects and haplotype, genotype, and allele associations explored. Modest associations (uncorrected P < 0.05) were observed for common variants around SNCA, UCHL1, MAPT, and LRRK2 although none were of sufficient magnitude to survive strict statistical corrections for multiple comparisons. No associations were seen for PRKN, PINK1, GBA, ATP13A2, HTRA2, NR4A2, and DJ1. Our findings suggest that common genetic variables of selected PD‐related loci contribute modestly to PD risk in Australians.

Anti-melanin antibodies are increased in sera in Parkinson's disease

An increasing body of research suggests that a number of immune mechanisms play a role in degenerative pathways in Parkinsons disease (PD). In the current work we investigated a posited humoral immune response in this disorder. Sera from PD patients exhibited a significantly enhanced absorbance response on a novel ELISA for anti-melanin antibodies, compared to sera from age-matched control subjects. The enhanced ELISA absorbance response was specific for catecholamine-based melanins and was unrelated to antiparkinsonian dopaminergic medication. Further, the absorbance response was significantly and negatively correlated with disease duration. These data suggest that a specific humoral anti-melanin antibody response is present in PD and is more active in early disease. While the contribution of this novel immune response to the initiation and progression of this disorder is unclear, this finding supports the hypothesis that specific immune responses occurring in PD may respond to therapeutic interventions in this disorder.

Prevalence and Clinical Features of Common LRRK2 Mutations in Australians with Parkinson's Disease

We determined the prevalence of two common leucine‐rich repeat kinase 2 (LRRK2) gene mutations in Australian patients with Parkinsons disease (PD). Of 830 affected patients, eight were heterozygous for the G2019S mutation, and two were heterozygous for the R1441H (4,322 G > A) mutation. In addition, one familial patient had a novel A1442P (4,324 G > C) mutation. Haplotype analysis showed that all LRRK2 G2019S‐positive individuals carried the common founder haplotype 1 and a putative founder haplotype for the R1441H mutation carriers. Clinically, patients with LRRK2 mutations had typical levodopa responsive Parkinsonism with tremor being the commonest presenting feature. Patients with the G2019S mutation in our series had a similar age of onset of symptoms when compared with patients with other LRRK2 mutations or sporadic PD, although they were more likely to have a family history of PD (2.4% of Australian patients with familial PD and 0.3% of Australian patients with sporadic PD). Our results demonstrate that the G2019S mutation carriers share the same ancestors who migrated to Australia originally from Europe and that other LRRK2 mutations (R1441H and A1442P) can be found in this population.