A unique retinal epitheliopathy is associated with amyotrophic lateral sclerosis/Parkinsonism-Dementia complex of Guam

Brain health: Pathway to primary prevention of neurodegenerative disorders of environmental origin

While rising global rates of neurodegenerative disease encourage early diagnosis and therapeutic intervention to block clinical expression (secondary prevention), a more powerful approach is to identify and remove environmental factors that trigger long-latencybrain disease (primary prevention) by acting on a susceptible genotype or acting alone. The latter is illustrated by the post-World War II decline and disappearance of Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex (ALS/PDC), a prototypical often-familial neurodegenerative disease formerly present in very high incidence on the island of Guam. Lessons learned from 75 years of investigation on the etiology of ALS/PDC include: the importance of focusing field research on the disease epicenter and patients with early-onset disease; soliciting exposure history from patients, family, and community to guide multidisciplinary biomedical investigation; recognition that disease phenotype may vary with exposure history, and that familial brain disease may have a primarily environmental origin. Furthermore, removal from exposure to the environmental trigger effects primary disease prevention.

Western Pacific ALS-PDC: Evidence implicating cycad genotoxins

Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex (ALS-PDC) is a disappearing neurodegenerative disorder of apparent environmental origin formerly hyperendemic among Chamorros of Guam-USA, Japanese residents of the Kii Peninsula, Honshu Island, Japan and Auyu-Jakai linguistic groups of Papua-Indonesia on the island of New Guinea. The most plausible etiology is exposure to genotoxins in seed of neurotoxic cycad plants formerly used for food and/or medicine. Primary suspicion falls on methylazoxymethanol (MAM), the aglycone of cycasin and on the non-protein amino acid β-N-methylamino-L-alanine, both of which are metabolized to formaldehyde. Human and animal studies suggest: (a) exposures occurred early in life and sometimes during late fetal brain development, (b) clinical expression of neurodegenerative disease appeared years or decades later, and (c) pathological changes in various tissues indicate the disease was not confined to the CNS. Experimental evidence points to toxic molecular mechanisms involving DNA damage, epigenetic changes, transcriptional mutagenesis, neuronal cell-cycle reactivation and perturbation of the ubiquitin-proteasome system that led to polyproteinopathy and culminated in neuronal degeneration. Lessons learned from research on ALS-PDC include: (a) familial disease may reflect common toxic exposures across generations, (b) primary disease prevention follows cessation of exposure to culpable environmental triggers; and (c) disease latency provides a prolonged period during which to intervene therapeutically. Exposure to genotoxic chemicals ("slow toxins") in the early stages of life should be considered in the search for the etiology of ALS-PDC-related neurodegenerative disorders, including sporadic forms of ALS, progressive supranuclear palsy and Alzheimer's disease.

Etiology of Retinal and Cerebellar Pathology in Western Pacific Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex

Purpose

To reexamine the etiology of a unique retinal pathology (linear and vermiform sub-retinal tubular structures) described among subjects with and without neurodegenerative disease in former high-incidence foci of Western Pacific amyotrophic lateral sclerosis and parkinsonism-dementia complex (ALS/PDC) in Guam (USA) and the Kii peninsula of Honshu island (Japan).

Methods

Analysis of published and unpublished reports of 1) ALS/PDC and the retinal and cerebellar pathology associated therewith and 2) exogenous neurotoxic factors associated with ALS/PDC and the developing retina and cerebellum.

Results

ALS/PDC retinal and cerebellar pathology matches persistent retinal and cerebellar dysplasia found in laboratory animals given single in utero or postnatal systemic treatment with cycasin, the principal neurotoxic component in the seed of cycad plants traditionally used for food (Guam) or oral medicine (Kii-Japan), both of which have been linked to the human neurodegenerative disease.

Conclusion

ALS/PDC-associated retinal and cerebellar dysplasia could arise from in utero exposure to methylazoxymethanol, the genotoxic metabolite of cycasin that results from maternal ingestion of this azoxyglucoside. These results support the environmental toxic etiology of retinal and brain pathology in ALS/PDC.

Changes in Retinal OCT and Their Correlations with Neurological Disability in Early ALS Patients, a Follow-Up Study

BACKGROUND

To compare early visual changes in amyotrophic lateral sclerosis (ALS) patients with healthy controls in a baseline exploration, to follow-up the patients after 6 months, and to correlate these visual changes with neurological disability.

METHODS

All patients underwent a comprehensive neurological and ophthalmological examination. A linear mixed analysis and Bonferroni p-value correction were performed, testing four comparisons as follows: Control baseline vs. control follow-up, control baseline vs. ALS baseline, control follow-up vs. ALS follow-up, and ALS baseline vs. ALS follow-up.

RESULTS

The mean time from the diagnosis was 10.80 ± 5.5 months. The analysis of the optical coherence tomography (OCT) showed: (1) In ALS baseline vs. control baseline, a macular significantly increased thickness of the inner macular ring temporal and inferior areas; (2) in ALS follow-up vs. ALS baseline, a significant macular thinning in the inner and outer macular ring inferior areas; (3) in ALS follow-up vs. ALS baseline, a significant peripapillary retinal nerve fiber layer (pRNFL) thinning in the superior and inferior quadrants; and (4) ALS patients showed a moderate correlation between some OCT pRNFL parameters and Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) score.

CONCLUSION

The OCT showed retinal changes in patients with motoneuron disease and could serve as a complementary tool for studying ALS.

Dysfunction of Protein Quality Control in Parkinsonism-Dementia Complex of Guam

Guam parkinsonism–dementia complex (G-PDC) is an enigmatic neurodegenerative disease that is endemic to the Pacific island of Guam. G-PDC patients are clinically characterized by progressive cognitive impairment and parkinsonism. Neuropathologically, G-PDC is characterized by abundant neurofibrillary tangles, which are composed of hyperphosphorylated tau, marked deposition of 43-kDa TAR DNA-binding protein, and neuronal loss. Although both genetic and environmental factors have been implicated, the etiology and pathogenesis of G-PDC remain unknown. Recent neuropathological studies have provided new clues about the pathomechanisms involved in G-PDC. For example, deposition of abnormal components of the protein quality control system in brains of G-PDC patients indicates a role for proteostasis imbalance in the disease. This opens up promising avenues for new research on G-PDC and could have important implications for the study of other neurodegenerative disorders.

Cellular and Molecular Aspects of the β-N-Methylamino-l-alanine (BMAA) Mode of Action within the Neurodegenerative Pathway: Facts and Controversy

The implication of the cyanotoxin β-N-methylamino-l-alanine (BMAA) in long-lasting neurodegenerative disorders is still a matter of controversy. It has been alleged that chronic ingestion of BMAA through the food chain could be a causative agent of amyotrophic lateral sclerosis (ALS) and several related pathologies including Parkinson syndrome. Both in vitro and in vivo studies of the BMAA mode of action have focused on different molecular targets, demonstrating its toxicity to neuronal cells, especially motoneurons, and linking it to human neurodegenerative diseases. Historically, the hypothesis of BMAA-induced excitotoxicity following the stimulation of glutamate receptors has been established. However, in this paradigm, most studies have shown acute, rather than chronic effects of BMAA. More recently, the interaction of this toxin with neuromelanin, a pigment present in the nervous system, has opened a new research perspective. The issues raised by this toxin are related to its kinetics of action, and its possible incorporation into cellular proteins. It appears that BMAA neurotoxic activity involves different targets through several mechanisms known to favour the development of neurodegenerative processes.

Ophthalmologic Baseline Characteristics and 2-Year Ophthalmologic Safety Profile of Pramipexole IR Compared with Ropinirole IR in Patients with Early Parkinson's Disease

Background. Parkinson's disease (PD) progressively affects dopaminergic neurotransmission and may affect retinal dopaminergic functions and structures. Objective. This 2-year randomized, open-label, parallel-group, flexible-dose study, NCT00144300, evaluated ophthalmologic safety profiles of immediate-release (IR) pramipexole and ropinirole in patients with early idiopathic PD with ≤6 months' prior dopamine agonist exposure and without preexisting major eye disorders. Methods. Patients received labeled IR regimens of pramipexole (n = 121) or ropinirole (n = 125) for 2 years. Comprehensive ophthalmologic assessments (COA) included corrected acuity, Roth 28-color test, slit-lamp biomicroscopy, intraocular pressure, computerized visual field test, fundus photography, and electroretinography. Results. At baseline, we observed retinal pigmentary epithelium (RPE) hypopigmentation not previously reported in PD patients. The estimated relative risk of 2-year COA worsening with pramipexole versus ropinirole was 1.07 (95% CI: 0.71–1.60). Mean changes from baseline in Unified Parkinson's Disease Rating System parts II+III total scores (pramipexole: 1 year, −4.1 ± 8.9, and 2 years, −0.7 ± 10.1, and ropinirole: 1 year, −3.7 ± 8.2, and 2 years, −1.7 ± 10.5) and Hoehn–Yahr stage distribution showed therapeutic effects on PD symptoms. Safety profiles were consistent with labeling. Conclusions. The risk of retinal deterioration did not differ in early idiopathic PD patients receiving pramipexole versus ropinirole. RPE hypopigmentation at baseline was not previously reported in this population. This trial is registered with NCT00144300.