X. ISTERH CONFERENCE
Selenium status in elderly: Relation to cognitive decline

https://doi.org/10.1016/j.jtemb.2014.08.009Get rights and content

Abstract

Studies show that decreased antioxidant system is related to cognitive decline. Thus we aimed to measure selenium (Se) status in Alzheimer's disease (AD) and mild cognitive impairment (MCI) elderly and compared them with a control group (CG). 27 AD, 17 MCI and 28 control elderly were evaluated. Se concentration was determined in plasma and erythrocyte by using hydride generation atomic absorption spectroscopy. Erythrocyte Se concentration in AD group was lower than CG (43.73 ± 23.02 μg/L and 79.15 ± 46.37 μg/L; p = 0.001), but not statistically different from MCI group (63.97 ± 18.26 μg/L; p = 0.156). AD group exhibited the lowest plasma Se level (34.49 ± 19.94 μg/L) when compared to MCI (61.36 ± 16.08 μg/L; p = 0.000) and to CG (50.99 ± 21.06 μg/L; p = 0.010). It is observed that erythrocyte Se decreases as cognition function does. Since erythrocyte reflects longer-term nutritional status, the data point to the importance of the relation between Se exposure and cognitive function. Our findings suggest that the deficiency of Se may contribute to cognitive decline among aging people.

Introduction

Life expectancy is continuing to increase and population aging is a worldwide phenomenon that is related to the prevalence of chronic diseases and also to higher risk of dementia since cognitive impairment results from the physiological process of brain aging. Cognitive impairment is an important cause of disability which results in loss of autonomy and thus it is one of the major causes of institutionalization. Because the costs of dementia care include physician services, hospitalization, medications, as well as indirect costs associated with patient and caregiver productivity, it results in a great impact on public health policy [1], [2], [3].

Cognitive decline beyond that expected for corresponding age and education marks mild cognitive impairment (MCI) which represents an intermediate stage between the expected cognitive decline of normal aging and the more serious decline of dementia [4]. Although MCI does not significantly impact daily functioning, it is associated with higher risk of progressing to dementia as Alzheimer's disease (AD) [5], [6], which is the main cause of dementia in the elderly. This was showed by Mitchell and Shiri-Feshki [7] who observed in a meta-analysis of 13 clinical studies that the annual conversion rate from MCI to dementia was 9.6% and, over the natural observation period, 39.2% converted to dementia. AD is clinically characterized by progressive and irreversible cognitive deficits and behavioral alterations that affect memory and learning ability, activities of daily living and quality of life [8]. Although the greatest known risk factor for AD is advancing age, diabetes, hypertension, smoking, obesity, elevated lipid levels and cerebrovascular disease are also associated with dementia. On the other hand, higher education, mentally stimulating activities and engagement in mental, social, and productive activities are associated with lower rates of dementia [9], [10].

It is known that oxidative stress plays central role in cognitive decline and dementia as Alzheimer's disease. First, it is associated with increasing of protein oxidation, lipid peroxidation, DNA and mRNA oxidation, which leads to believe that the damage resulted from oxidative stress is the first event that precedes dementia. On the other hand, senile plaques and neurofibrillary tangles, which are structures observed in AD patients’ brains, generate reactive oxygen species (ROS), thus creating a vicious cycle of ROS generation that far exceeds the antioxidant defense system [11], [12], [13].

The brain is particularly vulnerable to oxidative damage because it presents (1) elevated oxygen utilization rate; (2) high content of polyunsaturated lipids that are very susceptible to lipid peroxidation; (3) accumulation of transition metals such as iron, copper and zinc, which are capable of catalyzing the formation of ROS; (4) relatively poor concentrations of antioxidants [12], [14], [15].

Selenium plays antioxidant role because it is the main constituent of antioxidant enzymes that are expressed in different tissues, including the brain. Thus, this mineral has an important role to the antioxidant system. This trace element is known for providing protection from ROS-induced cell damage and the proposed mechanisms mainly invoke the functions of glutathione peroxidase family and selenoprotein P [16].

Although some authors found increased levels of selenium in AD patients’ blood, others related blood levels of this mineral to cognition and thus the deficiency of selenium, even subclinical, would be a risk factor for disease [17], [18], [19], [20]. In this context, the present study aimed to evaluate nutritional status of selenium in AD and MCI elderly and compare them with healthy older adults.

Section snippets

Subjects

We enrolled twenty-seven patients diagnosed with probable AD according to the NINCDS-ADRDA criteria [21]. MCI group was composed by thirty-one MCI participants who fulfilled the criteria proposed by the International Working Group on Mild Cognitive Impairment [22], which includes the following: (1) the person is neither normal nor demented; (2) there is evidence of cognitive deterioration shown by subjective report in conjunction with objective cognitive deficits; and (3) activities of daily

Results and discussion

In the present study, 28 elderly (39.3% men and 60.7% women) in AD group, 31 MCI patients (30% men and 70% women) and 29 healthy elderly (34.5% men and 65.5% women) in C group were evaluated. There was no gender difference among groups; however, the AD group was older than MCI and C groups (80.6 ± 5.7, 77.7 ± 5.3 and 71.2 ± 6.2 years, AD, MCI and C groups, respectively). In order to verify if in our study age influenced selenium levels, we performed correlation analysis between selenium parameters

Conflicts of Interest

None declared.

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