3-nitrotyrosine and Down-Syndrome

Down syndrome (DS) is the most common genetic cause of intellectual disability in children, and the number of adults with DS reaching old age is increasing. By the age of 40 years, virtually all people with DS have sufficient neuropathology for a postmortem diagnosis of Alzheimer disease (AD). Trisomy 21 in DS leads to an overexpression of many proteins, of which at least two are involved in oxidative stress and AD: superoxide dismutase 1 (SOD1) and amyloid precursor protein (APP). In this study, we tested the hypothesis that DS brains with neuropathological hallmarks of AD have more oxidative and nitrosative stress than those with DS but without significant AD pathology, as compared with similarly aged-matched non-DS controls. The frontal cortex was examined in 70 autopsy cases (n=29 control and n=41 DS). By ELISA, we quantified soluble and insoluble Aβ40 and Aβ42, as well as oligomers. Oxidative and nitrosative stress levels (protein carbonyls, 4-hydroxy-2-trans-nonenal (HNE)-bound proteins, and 3-nitrotyrosine) were measured by slot-blot. We found that soluble and insoluble amyloid beta peptide (Aβ) and oligomers increase as a function of age in DS frontal cortex. Of the oxidative stress markers, HNE-bound proteins were increased overall in DS. Protein carbonyls were correlated with Aβ40 levels. These results suggest that oxidative damage, but not nitrosative stress, may contribute to the onset and progression of AD pathogenesis in DS. Conceivably, treatment with antioxidants may provide a point of intervention to slow pathological alterations in DS.

Topics: Adolescent; Adult; Age Factors; Aldehydes; Alzheimer Disease; Amyloid beta-Peptides; Biomarkers; Down Syndrome; Female; Frontal Lobe; Humans; Male; Middle Aged; Nitrosation; Oxidation-Reduction; Oxidative Stress; Superoxide Dismutase; Superoxide Dismutase-1; Tyrosine

Patients with Down's syndrome (DS) show elevated levels of copper, zinc-containing superoxide dismutase (SOD1) and appear to have increased lipid peroxidation and oxidative damage to DNA as well as elevated glutathione peroxidase activity. Increasing SOD1 levels by gene transfection in NT-2 and SK-N-MC cell lines also led to a rise in glutathione peroxidase activity, but this was nevertheless accompanied by decreased proliferation rates, increased lipid peroxidation and protein carbonyls, and a trend to a rise in 8-hydroxyguanine and protein-bound 3-nitrotyrosine. Transfection of these cell lines with DNA encoding two mutant SOD1 enzymes (G37R and G85R) associated with familial amyotrophic lateral sclerosis (FALS), produced similar, but more severe changes, i.e. even lower growth rates, higher lipid peroxidation, 3-nitrotyrosine and protein carbonyl levels, decreased GSH levels, raised GSSG levels and higher glutathione peroxidase activities. Since G85R has little SOD activity, these changes cannot be related to increased O(2)(-) scavenging. In no case was SOD2 (mitochondrial Mn-SOD) level altered. Our cellular systems reproduce many of the biochemical changes observed in patients with DS or ALS, and in transgenic mice overexpressing mutant SOD1. They also show the potentially deleterious effects of SOD1 overexpression on cellular proliferation, which may be relevant to abnormal development in DS.

Topics: Aldehydes; Amyotrophic Lateral Sclerosis; Antioxidants; Cell Division; Cell Line; Cell Survival; Down Syndrome; Gene Expression; Glutathione; Glutathione Disulfide; Guanine; Humans; Ketones; Lipid Peroxidation; Mutation; Neuroblastoma; Oxidative Stress; Superoxide Dismutase; Superoxide Dismutase-1; Teratocarcinoma; Transfection; Tyrosine

The predictable chronological sequence of pathological events in Down syndrome (DS) provides the opportunity to rigorously investigate the relationship between oxidative stress and amyloid-beta (Abeta) deposition. In this study, we report a marked accumulation of oxidized nucleic acid, 8-hydroxyguanosine (8OHG), and oxidized protein, nitrotyrosine, in the cytoplasm of cerebral neurons in DS with the levels of nucleic acid and protein oxidation paralleling each other. Relative density measurements of neuronal 8OHG immunoreactivity showed that there was a significant increase (p < 0.02) in DS (n = 22, ages 0.3-65 yr) compared with age-matched controls (n = 10, ages 0.3-64 yr). As a function of age, 8OHG immunoreactivity increased significantly in the teens and twenties (p < 0.04), while Abeta burden only increased after age 30 (p < 0.0001). In 9 cases of DS bearing Abeta deposition, the extent of deposits of Abeta ending at amino acid 42 (Abeta42) was actually associated with a decrease in relative 8OHG (r = -0.79, p < 0.015) while Abeta40 was not. These findings suggest that in brains of patients with DS, increased levels of oxidative damage occur prior to the onset of Abeta deposition.

Topics: Adolescent; Adult; Aged; Amyloid beta-Peptides; Cerebral Cortex; Child; Child, Preschool; Down Syndrome; Guanosine; Humans; Middle Aged; Neurons; Oxidative Stress; Tyrosine