Elevated plasma amyloid beta-peptide 1-42 and onset of dementia in adults with Down syndrome

Relationship between amyloid beta protein and melatonin metabolite in a study of electric utility workers

This study assessed the relationship between occupational magnetic field exposure, the urinary melatonin metabolite 6-hydroxymelatonin sulfate (6-OHMS), and concentrations of blood-borne soluble amyloid beta (A beta), a protein associated with the hallmark lesions of Alzheimer's disease (AD). Blood and urine samples were obtained from male electric utility workers (n = 60) to quantify two lengths of the protein in plasma, A beta (amino acids 1-40) and A beta (1-42), and the urinary concentrations of 6-OHMS. Average A beta levels were positively associated with categories of magnetic field exposure, but this relationship was weak and did not achieve statistical significance. The melatonin metabolite was inversely correlated with A beta (1-42) and the ratio of A beta (1-42) to A beta (1-40). This observation is consistent with recent in vitro data and provides a plausible mechanism for the association between magnetic field exposure and AD that has been observed in some studies.

Genetic and host factors for dementia in Down's syndrome

BACKGROUND

The high risk for dementia in adults with Down's syndrome has been attributed to triplication and overexpression of the gene for amyloid precursor protein (APP). But the wide variation in age at onset must be due to other risk factors.

AIMS

To identify factors which influence age at onset of dementia in Down's syndrome.

METHOD

Studies of factors which influence formation of beta-amyloid (Abeta) were reviewed, including atypical karyotypes, susceptibility genotypes, gender and oestrogen deficiency, and individual differences in Abeta peptide levels.

RESULTS

The apolipoprotein E epsilon4 allele, oestrogen deficiency and high levels of Abeta1-42 peptide are associated with earlier onset of dementia, while atypical karyotypes and the apolipoprotein E epsilon2 allele are associated with reduced mortality and reduced risk of dementia.

CONCLUSIONS

Factors which influence Abeta levels, rather than overexpression of APP, may account for the differences in age at onset of dementia in Down's syndrome.

Altered metabolism of the amyloid beta precursor protein is associated with mitochondrial dysfunction in Down's syndrome

Most Down's syndrome (DS) patients develop Alzheimer's disease (AD) neuropathology. Astrocyte and neuronal cultures derived from fetal DS brain show alterations in the processing of amyloid beta precursor protein (AbetaPP), including increased levels of AbetaPP and C99, reduced levels of secreted AbetaPP (AbetaPPs) and C83, and intracellular accumulation of insoluble Abeta42. This pattern of AbetaPP processing is recapitulated in normal astrocytes by inhibition of mitochondrial metabolism, consistent with impaired mitochondrial function in DS astrocytes. Intracellular Abeta42 and reduced AbetaPPs are also detected in DS and AD brains. The survival of DS neurons is markedly increased by recombinant or astrocyte-produced AbetaPPs, suggesting that AbetaPPs may be a neuronal survival factor. Thus, mitochondrial dysfunction in DS may lead to intracellular deposition of Abeta42, reduced levels of AbetaPPs, and a chronic state of increased neuronal vulnerability.