Effect of oxidative stress on DNA damage and beta-amyloid precursor proteins in lymphoblastoid cell lines from a Nigerian population

The accelerated aging phenotype: The role of race and social determinants of health on aging

The pursuit to discover the fundamental biology and mechanisms of aging within the context of the physical and social environment is critical to designing interventions to prevent and treat its complex phenotypes. Aging research is critically linked to understanding health disparities because these inequities shape minority aging, which may proceed on a different trajectory than the overall population. Health disparities are characteristically seen in commonly occurring age-associated diseases such as cardiovascular and cerebrovascular disease as well as diabetes mellitus and cancer. The early appearance and increased severity of age-associated disease among African American and low socioeconomic status (SES) individuals suggests that the factors contributing to the emergence of health disparities may also induce a phenotype of 'premature aging' or 'accelerated aging' or 'weathering'. In marginalized and low SES populations with high rates of early onset age-associated disease the interaction of biologic, psychosocial, socioeconomic and environmental factors may result in a phenotype of accelerated aging biologically similar to premature aging syndromes with increased susceptibility to oxidative stress, premature accumulation of oxidative DNA damage, defects in DNA repair and higher levels of biomarkers of oxidative stress and inflammation. Health disparities, therefore, may be the end product of this complex interaction in populations at high risk. This review will examine the factors that drive both health disparities and the accelerated aging phenotype that ultimately contributes to premature mortality.

Role of Resveratrol and Selenium on Oxidative Stress and Expression of Antioxidant and Anti-Aging Genes in Immortalized Lymphocytes from Alzheimer's Disease Patients

Oxidative damage is involved in the pathophysiology of age-related ailments, including Alzheimer's disease (AD). Studies have shown that the brain tissue and also lymphocytes from AD patients present increased oxidative stress compared to healthy controls (HCs). Here, we use lymphoblastoid cell lines (LCLs) from AD patients and HCs to investigate the role of resveratrol (RV) and selenium (Se) in the reduction of reactive oxygen species (ROS) generated after an oxidative injury. We also studied whether these compounds elicited expression changes in genes involved in the antioxidant cell response and other aging-related mechanisms. AD LCLs showed higher ROS levels than those from HCs in response to H2O2 and FeSO4 oxidative insults. RV triggered a protective response against ROS under control and oxidizing conditions, whereas Se exerted antioxidant effects only in AD LCLs under oxidizing conditions. RV increased the expression of genes encoding known antioxidants (catalase, copper chaperone for superoxide dismutase 1, glutathione S-transferase zeta 1) and anti-aging factors (sirtuin 1 and sirtuin 3) in both AD and HC LCLs. Our findings support RV as a candidate for inducing resilience and protection against AD, and reinforce the value of LCLs as a feasible peripheral cell model for understanding the protective mechanisms of nutraceuticals against oxidative stress in aging and AD.

Exploration of Environmental and Genetic Risk Factors for Alzheimer's Disease: The Value of Cross-Cultural Studies

Advances in molecular genetics have revolutionized epidemiological research. It is now possible to combine the techniques of population genetics with research on risk factors to construct genetic-environmental interactive models that explain geographic-ethnic variations in disease rates. Cross-cultural studies involving populations from developing and developed countries offer a unique opportunity for constructing these models by providing a wide diversity of environmental exposures. Results from a comparative Indianapolis-Ibadan study suggest that Alzheimer's disease incidence rates are lower in Yoruba than in African Americans and that these lower rates may be due to a combination of genetic and environmental, primarily dietary, influences.

Reactive oxygen species in the regulation of synaptic plasticity and memory

The brain is a metabolically active organ exhibiting high oxygen consumption and robust production of reactive oxygen species (ROS). The large amounts of ROS are kept in check by an elaborate network of antioxidants, which sometimes fail and lead to neuronal oxidative stress. Thus, ROS are typically categorized as neurotoxic molecules and typically exert their detrimental effects via oxidation of essential macromolecules such as enzymes and cytoskeletal proteins. Most importantly, excessive ROS are associated with decreased performance in cognitive function. However, at physiological concentrations, ROS are involved in functional changes necessary for synaptic plasticity and hence, for normal cognitive function. The fine line of role reversal of ROS from good molecules to bad molecules is far from being fully understood. This review focuses on identifying the multiple sources of ROS in the mammalian nervous system and on presenting evidence for the critical and essential role of ROS in synaptic plasticity and memory. The review also shows that the inability to restrain either age- or pathology-related increases in ROS levels leads to opposite, detrimental effects that are involved in impairments in synaptic plasticity and memory function.

The LEARn model: an epigenetic explanation for idiopathic neurobiological diseases

Neurobiological disorders have diverse manifestations and symptomology. Neurodegenerative disorders, such as Alzheimer's disease, manifest late in life and are characterized by, among other symptoms, progressive loss of synaptic markers. Developmental disorders, such as autism spectrum, appear in childhood. Neuropsychiatric and affective disorders, such as schizophrenia and major depressive disorder, respectively, have broad ranges of age of onset and symptoms. However, all share uncertain etiologies, with opaque relationships between genes and environment. We propose a 'Latent Early-life Associated Regulation' (LEARn) model, positing latent changes in expression of specific genes initially primed at the developmental stage of life. In this model, environmental agents epigenetically disturb gene regulation in a long-term manner, beginning at early developmental stages, but these perturbations might not have pathological results until significantly later in life. The LEARn model operates through the regulatory region (promoter) of the gene, specifically through changes in methylation and oxidation status within the promoter of specific genes. The LEARn model combines genetic and environmental risk factors in an epigenetic pathway to explain the etiology of the most common, that is, sporadic, forms of neurobiological disorders.

BACE1 gene promoter is differentially regulated: detection of a novel promoter region for its cell type-specific regulation

The amyloid-beta (Abeta) peptide, the proteolytic fragment of Abeta precursor protein (APP), aggregates and forms neuritic plaques, a major hallmark of Alzheimer's disease (AD). The limiting step in generating the Abeta peptide from APP is cleavage by the beta-secretase enzyme, BACE1. Regulation of the BACE1 gene is likely to play an important role in AD etiology and treatment. We therefore studied the activity of a 4.1-kb 5'-flanking region (-3765/+364, +1 being the transcription start site) of the BACE1 gene, both in 5'- and 3'-deletion series and through Northern blotting. We show that the BACE1 promoter has regulatory activity throughout the 4.1-kb length, both positive and negative, and that this activity can be quantitatively modeled according to promoter sequence length, with the specific model depending on the presence of negative regulatory elements as the 5'- most portion of the sequence. We also examined a previously identified 141-bp proximal fragment (+224/+364) of the BACE1 promoter and two constituent (91- and 50-bp) subfragments. We report that the 91-bp fragment (+224/+314) is the most likely seat of neuronal expression of the BACE1 gene and that it is the portion of the 141-bp fragment that accounts for observed DNA-protein interactions in brain extracts. The 50-bp fragment (+315/+364), which showed significant reporter gene activity from the empty vector, binds nuclear proteins in a cell type-specific manner and contains the AP2 site as shown by the electrophoretic mobility shift assay. Overall, the 141-bp fragment had no strong matches within GenBank, and the 91-bp fragment is predicted to have several potential stem-loop sites. Taken together, BACE1 gene promoter activity is differentially regulated, and the 91-bp fragment represents a novel promoter region for cell type-specific regulation. This fragment might be a useful target to regulate BACE1 expression leading to Abeta production and to understand the neuropathogenesis of AD.

Lessons learned from international comparative crosscultural studies on dementia

International and crosscultural comparative studies of Alzheimer disease (AD) offer significant advantages in elucidating risk factors for the disease by providing a wider diversity of environmental exposures as well as greater genetic diversity than do studies confined to a single ethnic group in a developed country. They also present with major methodological problems. The problems and their possible solutions are discussed in this article by describing three projects involving the Cree and English-speaking residents of Manitoba, blacks from Indianapolis, Indiana, and Yoruba from Ibadan and residents of Chinese villages. In this review, the development and harmonization of a culture fair screening instrument for dementia, the CSID, is described. The advantage of a scientific paradigm that can incorporate genetic and environmental factors as well as their interactions to explore the etiology of AD is presented. The importance of developing strategies for recruitment and retention in international community-based studies is emphasized as is the necessity of establishing academic partnerships between the countries. The unique opportunity provided by geopolitical and sociocultural influences to study environmental exposures is exemplified by the ongoing study of the influence of selenium levels on cognition in Chinese villagers. Results from the Indianapolis, Indiana-Ibadan dementia project are presented suggesting that the incidence of AD is lower in Yoruba than in blacks and that this lower rate may be the result of a combination of genetic and environmental factors.

Exposure to lead and the developmental origin of oxidative DNA damage in the aging brain

Oxidative damage to DNA has been associated with neurodegenerative diseases. Developmental exposure to lead (Pb) has been shown to elevate the Alzheimer's disease (AD) related beta-amyloid peptide (Abeta), which is known to generate reactive oxygen species in the aging brain. This study measures the lifetime cerebral 8-hydroxy-2'-deoxyguanosine (oxo8dG) levels and the activity of the DNA repair enzyme 8-oxoguanine DNA glycosylase (Ogg1) in rats developmentally exposed to Pb. Oxo8dG was transiently modulated early in life (Postnatal day 5), but was later elevated 20 months after exposure to Pb had ceased, while Ogg1 activity was not altered. Furthermore, an age-dependent loss in the inverse correlation between Ogg1 activity and oxo8dG accumulation was observed. The effect of Pb on oxo8dG levels did not occur if animals were exposed to Pb in old age. These increases in DNA damage occurred in the absence of any Pb-induced changes in copper/zinc-superoxide dismutase (SOD1), manganese-SOD (SOD2), and reduced-form glutathion (GSH). These data suggest that oxidative damage and neurodegeneration in the aging brain could be impacted by the developmental disturbances.

Alzheimer's disease, genes, and environment: the value of international studies

OBJECTIVE

To describe the construction of a disease model incorporating both genetic an environmental factors in the etiology of Alzheimer's disease (AD), using data generated from the Indianapolis-Ibadan dementia project (I-IDP).

METHOD

The I-IDP is a longitudinal comparative study of the prevalence and incidence o dementia in 2 communities: elderly African Americans living in Indianapolis, Indiana, an Yoruba living in Ibadan, Nigeria.

RESULTS

African Americans are more than twice as likely as Yoruba to develop AD. Possible explanations for this finding include genetic factors: the possession of the apolipoprotein E epsilon4 allele does not increase risk for AD among Yoruba but confers a sligh increase in AD risk for African Americans. As well, environmental factors may play a role: African Americans have a higher risk of vascular risk factors than do Yoruba.

CONCLUSIONS

International comparative studies, particularly those involving population from developing and developed countries, offer a unique opportunity for applying new in formation regarding population genetics to traditional AD risk factor research.

Effect of perchloroethylene, smoking, and race on oxidative DNA damage in female dry cleaners

Perchloroethylene (PERC) is used widely as an industrial dry cleaning solvent and metal degreaser. PERC is an animal carcinogen that produces increased incidence of renal adenomas, adenocarcinomas, mononuclear cell leukemia, and hepatocellular tumors. Oxidative DNA damage and lipid peroxidation were assessed in 38 women with (dry cleaners) or without (launderers) occupational exposure to PERC. PERC exposure was assessed by collecting breathing zone samples on two consecutive days of a typical work week. PERC levels were measured in blood drawn on the morning of the second day of breathing zone sample collection in dry cleaners and before a typical workday in launderers. Blood PERC levels were two orders of magnitude higher in dry cleaners compared to launderers. A significant correlation was noted between time weighted average (TWA) PERC and blood PERC in dry cleaners (r=0.7355, P<0.002). 8-Hydroxydeoxyguanosine (8-OHdG), ng/mg deoxyguanosine (dG) in leukocyte nuclear DNA was used as an index of steady-state oxidative DNA damage. Urinary 8-OHdG, microg/g creatinine was used as an index of oxidative DNA damage repair. Urinary 8-epi-prostaglandin F(2alpha) (8-epi-PGF), ng/g creatinine was used as an index of lipid peroxidation. The mean+/-S.D. leukocyte 8-OHdG in launderers was 16.0+/-7.3 and was significantly greater than the 8.1+/-3.6 value for dry cleaners. Urinary 8-OHdG and 8-epi-PGF were not significantly different between dry cleaners and launderers. Unadjusted Pearson correlation analysis of log transformed PERC exposure indices and biomarkers of oxidative stress indicated a significant association in launderers between blood PERC and day 1 urinary 8-OHdG (r=0.4661, P<0.044). No significant associations between exposure indices and biomarkers were evident in linear models adjusted for age, body mass index, race, smoking (urinary cotinine, mg/g creatinine) and blood levels of the antioxidants Vitamin E and beta-carotene. The mean+/-S.D. leukocyte 8-OHdG value in control white women was 17.8+/-7.4 and was significantly greater than the 11.8+/-5.9 in control black women. No significant differences by race were evident for the other biomarkers. Smoking status was not significantly associated with any of the oxidative damage indices. Results indicate a reduction in oxidative DNA damage in PERC exposed dry cleaners relative to launderers, but PERC could not clearly be defined as the source of the effect.

Altered glial fibrillary acidic protein content and its degradation in the hippocampus, cortex and cerebellum of rats exposed to constant light: reversal by melatonin

Reactive astrocytosis is a well-known phenomenon that occurs rapidly after physical or metabolic injury to the brain. One of the important events during astrocyte differentiation is the increased expression of glial fibrillary acidic protein (GFAP), a member of the family of intermediate filament structural proteins. Free radicals are neurotoxic and free radical scavengers have been shown to protect the brain against neurotoxic damage. In the present study, we examined the effect of melatonin on astrocytic reactivity by determining the expression of the glial marker, GFAP, in different brain regions. Rats were exposed to constant light to reduce endogenous melatonin production; half of the animals were injected with melatonin during the exposure to constant light for 7 days. Western blots showed increases in total and degraded GFAP content in the brain of rats exposed to constant light. Melatonin administration caused a reduction of degraded GFAP content. In addition, melatonin significantly reduced neural tissue lipid peroxidation while constant light significantly enhanced the breakdown of lipids in the brain. Brain glutathione levels decreased significantly as a result of constant light exposure; this reduction was reversed by melatonin administration. These results suggest that melatonin potentially protects both neurons and glial cells from free radicals; melatonin's protective actions are probably related to the antioxidant properties of the indole.