Introduction: In almost all degenerative diseases of the brain aggregation of proteins inside neurons or extracellulary, is a common pathological phenomenon regardless of etiology. It is assumed that the biochemical pathways leading to aggregation are more harmful than the aggregations themselves and most likely imply production of free oxygen radicals. This oxidative stress is in the body met by free radical scavengers in the form of specific chemical substances and antioxidative enzymes. It has therefore been postulated that defective free radical defense is a common pathway in most neurodegenerative diseases in humans as well as in other mammals.
Material and methods: The concentration of copper and the activity of two antioxidative copper containing enzymes, ceruloplasmin and superoxide dismutase (SOD 1), was analyzed in the blood. A series of case control studies were performed in Alzheimer s disease (AD), Parkinson s disease (PD) and amyotrophic lateral sclerosis (ALS) as well as in Down s syndrome and autism. Furthermore, a study in sheep was conducted in different areas with different risks of infection of scrapie. In that study, in addition, the activity of the selenium-containing enzyme, glutathione peroxidase, was determined as well as the concentration of manganese in blood.
Results: The oxidative activity of ceruloplasmin and SOD1 was shown to be significantly lowered in Alzheimer s disease without any signs of copper deficiency. In Parkinson s disease, the oxidative activity of ceruloplasmin was also on the whole shown to be signifcantly lowered, and furthermore, it decreased significantly as well as the SOD1 activity with duration of the disease. In ALS, the means of all of the determinations were shown to be the same, but the equality of variances differed significantly in the patients compared to their controls. In Down s syndrome past the age of 40, when Alzheimer s type changes appear in the brain, the SOD1 activity and the ceruloplasmin specific oxidative activity (activity in relation to concentration) was significantly lowered compared with the younger patients. In autism, a non-degenerative affection of the central nervous system, there was no difference between patients and their controls. In the sheep, the results indicated a relationship between decreased glutathione peroxidase activity, and possibly also SOD1 activity, and increased susceptibility to scrapie infection. No connection was found between ceruloplasmin oxidative activity and susceptibility to scrapie infection. Susceptibility to scrapie infection was apparantly not conntected with low levels of copper or high levels of manganese in blood of the animals.
Discussion: The results indicate that the oxidative defenses in four neurodegenerative diseases with different clinical features are defective as the activity of two copper containing antioxidative enzymes, ceruloplasmin and SOD1, was found defective in all of them. In a developmental syndrome (autism), where neither active degenerative changes nor aggregations are found, no such changes in enzyme activity were detected. The results thus support the idea that deranged oxidative defense is a common denominator in the pathogenesis of these diseases. As far as sheep is concerned, the results also indicate, that there is a defect in oxidative defense connected with increased susceptibility to scrapie infection in the form of lowered glutathione peroxidase activity.