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Copper, Zinc and Selenium in Elderly Persons

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Published: Tue, 22 May 2018

Evaluation of the Serum Levels of Oxidant/Antioxidant Status, Copper, Zinc and Selenium in Elderly Persons with and without Physical Disability

Abstract:

The growing population of old persons causes that scientific community increase focus on age related disease such as physical disability. In recent studies, has been shown that parameters include serum levels of oxidative stress, copper, zinc, selenium and bone mineral density(BMD) play important role in the development of physical disability. We aimed to investigate the relationship between aforementioned parameters and the physical disability.

Among 1616 elderly participants in the Amirkola health and aging project (AHAP), 44 subjects were determined according to the Katz ADL as patient with physical disability and 66 age-gender match subjects were selected among without physical disability subjects as control group. Serum selenium and copper measured with atomic absorption spectrometry, serum Zn level and oxidative stress parameters with spectrophotometery and the bone mineral density (BMD) with Dual-Energy X-ray Absorptiometry(DEXA). Then obtained data were statistically analyzed using SPSS version 16.0.

Our results indicate that patient subjects had lower serum Zn, Se and FRAP levels than the control group (47.53%, 25.51% and 69.99% vs. zero in controls, p<0.05) whereas serum TBARS level and Cu to Zn ratio (CZr) were higher (117.25% and 112.53% vs. zero in controls, p<0.05). We found a positive correlation between Zn, Se, FRAP and BMD.F with ADL score (r= 0.449, 0.275, 0.601 and 0.435; p<0.05), meanwhile negative correlation between Cu to Zn ratio (CZr) and TBARS with ADL score (r=-0.351 and -0.485; p<0.05). According to ROC analysis, areas under the curve for serum TBARS level and Cu to Zn ratio (CZr) were equal to 0.979 and 0.832 respectively and it seems that CZr is a reliable parameter for discriminating patient with physical disability.

The results of this study shows that situations of low serum Zn and Se levels and high Cu to Zn ratio (CZr), maybe leads to physical disability, meanwhile BMD deficiency and increasing oxidative stress also increase the severity of physical disability.

Keywords: Aging, Physical disability, Oxidative stress, Copper, Zinc, Selenium, BMD

Table 1: List of abbreviations

ADL

Activities of Daily Living

BMD

Bone Mineral Density

BMD.F

Femur Bone Mineral Density

BMD.S

Spine Bone Mineral Density

BMI

Body Mass Index

CZr

Cu to Zn Ratio

DEXA

Dual-Energy X-ray Absorptiometry

FRAP

Ferric Reducing Ability of Plasma

IADL

Instrumentals Activities of Daily Living

MDA

Malondialdehyde

OD

Optical Density

ROS

Reactive Oxygen Species

SD

Standard Deviation

TBARS

Thiobarbituric Acid Reactive Substances

1. Introduction

According to the national population census, the total population of Iran has been 75,149,669 (comprising 50.4 % male and 49.6% female) [1]. The proportion of people aged 60 years or older was about 7.3% in 2005 and it is predicted to increase to 11.6% in 2025 and 30.8% by 2050[2]. This demographic transition will be followed by a huge population of old people in the next decades [3]. Aging is an extremely complex and multi-factorial process and leads to disability and death[4].In older people, level of physical function is a good predictor of subsequent disability[5]. Physical disability is often characterized by the inability to independently carry out essential activities of daily living include bathing, dressing, transferring, walking, shopping, preparing meals, cleaning, and housework [6]. Trace element determinations in blood serum have become important to investigate their vital role in human metabolism [7]. Zinc and copper, are constituent components of many metalloproteins and metalloenzymes [8] and it seems that low serum level of copper and zinc, was important to predict the development of physical disability [9]. Zn and Se are potent antioxidants involved in cellular defense against oxygen free radicals and the risk of deficiency seems to increase in proportion to the age [10]. Oxidative stress is defined as a redox unbalance with an excess of oxidants or a defect in antioxidants [11]. Oxidative damage to DNA, proteins, and lipids in human skeletal muscle, increases with age and may contribute to the poor grip strength in older adults [12]. Oxidative stress also is involved in osteoblastogenesis, osteoclastogenesis and bone resorption [13]and several trace elements such as zinc and copper are essential for development of the skeleton in humans [14]. Individual studies performed for selenium (Se), zinc (Zn) and copper (Cu), demonstrated that deficiency in any of these trace elements can cause an increase in the risk of osteoporosis [15]by reduced bone mineral density(BMD) and changed bone micro-architecture[14]

Therefore, we aimed to assess serum levels of oxidative stress, Cu, Zn, and Se of elderly patients with physical disability and compare their levels to control group. In addition, we consider the relationships between bone mineral density (BMD) and physical disability in these subjects.

2. Subjects and methods

Among 1616 elderly participants in the Amirkola health and aging project (AHAP)[2], 44 subjects were determined according to the Katz ADL [16] as patient with physical disability and 66 age-gender match subjects were selected among without physical disability subjects as control group. In the Amirkola health and aging project (AHAP) [2], 15 ml fasting blood samples were collected from the 110 subjects (45 male and 65 female) aged 60–92 years (mean  S.D = 76.86 8.81). The resulted samples were immediately centrifuged and stored at −80°C until the final analysis of this study. Serum antioxidant and oxidant levels measured by FRAP and TBARS tests and The serum Zn level measured by zinc kite with spectrophotometery method. In the FRAP test, Reduction of ferric to ferrous ions in the presence of antioxidants in low PH cause the formation of colored complex ferrous-Tripyridyl-S-triazine (Fe(III)-TPTZ) and a blue solution is generated with a maximum absorbance at 593 nm[17]. In the TBARS method, reaction of MDA with two molecules of TBA (Thiobarbituric acid) and the elimination of two molecules of water, leads to the formation of a pink complex, with the maximum absorption at 532 nm. The results for FRAP and TBARS tests were reported as µmol/L and for the serum Zn level as µg/dl [18]. The serum Cu and Se levels measured using atomic absorption spectrometry(PG-990) equipped with a graphite furnace. In this method, the samples were first diluted with HNO3 provided from Merck and then 10 µL of the diluted samples was injected into the graphite furnace. The operating parameters were set for measuring serum Cu and Se levels as recommended by manufacture (wavelength 324.7 and 196 nm, bandwidth 0.4 nm, current 3 and 5 mA respectively). Bone mineral density (BMD) of the subjects measured using Dual Energy X-ray Absorptiometry (DEXA) with the Lexxos densitometer. The diagnosis of osteopenia and osteoporosis was based on spine and femur bone mineral density (BMD) measurements according to the WHO study group criteria[19] in which, T-score of -2.5 SD considered as osteoporosis, -2.5T-score-1.0 SD as osteopenia and T-score  -1.0 SD as normal.

3. Statistical Analysis

All statistical analyses were performed using SPSS version 16.0. Descriptive analyses were performed to provide information on general characteristics of the study population. Independent-Samples T-test was used to compare mean of all variables between control group and patient group. The data were presented as mean ± SD and statistical significance was defined as p<0.05. The associations between variables were evaluated using Pearson’s correlation test. Then p-value and Pearson’s coefficient were reported in table and corresponding graphs were plotted using Matrix Scatter. ROC curve were plotted to compare the physical disability diagnostic power of the parameters for the elderly patient and the area under the curve (AUC) and significance for each parameter were reported in table.

4. Results

The demographic and clinical characteristics of the control group and patient group are shown in Table 2. The control and the patient subjects were of similar age and There were no significant differences according to age and gender between patient and control groups (p>0.05). The average serum trace element and oxidative stress levels plus and minus standard deviation (mean ± SD) of the control and patient groups are shown in Table 3. Comparisons of serum trace element levels in the patient group vs. control group are shown in Fig. 1. As can be seen, the CZR and TBARS serum levels were higher (P<0.05) whereas Zn, Se and FRAP serum levels were lower in the patient group vs. control group (p<0.05). Serum Cu levels were higher in the patient group when compared to the control group, but the difference was not statistically significant (p>0.05). The results of correlation analysis between parameters and ADL score are shown in Figs. 2 and 3. We found a positive correlation between Zn, Se, FRAP and BMD.F with ADL score (p<0.05) and negative correlation between TBARS and ADL score (p<0.05). Receiver operating characteristic (ROC) curve analysis is shown in Fig 4 and related data are summarized in Table 4. Although TBARS has the maximum area under the curve but this parameter is affected easily with many of other factors such as lifestyle and nutrition. Area under the curve for CZr is equal to 0.832 and it seems that CZr is a reliable parameter for discriminating patient with physical disability and control group. Area under the curve for Cu is equal to 0.603 but was not statistically significant (p>0.05).

5- Discussion

In the present study, the serum Cu, Zn, Se, oxidative stress levels and bone mineral density (BMD) of elderly patient with physical disability were assessed and compared with control group. Present study shows that serum Zn level was 47.53% lower in patient group compared to control group (p<0.05). The decrease in serum zinc concentration is often accompanied by an increase in copper level and several studies have reported elevated serum copper levels during aging [8]. Accordingly, serum Cu level was 10.79% higher in patient group compared to control group but this difference was not statistically significant (p>0.05). However, trace element homeostasis may have an important role in physical performance. In fact, the serum level of Cu and Zn is strictly regulated by modulators and compensatory mechanisms that act to decrease serum Zn level while increasing serum Cu level [9].

Our results indicate that CZr level was 112.53% higher in patient group compared to control group (p<0.05). According to Eugenio et al. study [9] Cu to Zn ratio (CZr) displays significant and stronger relationships than Cu or Zn alone with physical performances and similarly Slimane et al.[16] study showed that An increased copper/zinc ratio was observed for all categories of diseases and it was more likely due to lower serum zinc levels than higher serum copper levels, they conclude that elderly patients are at elevated risk of low zinc values but not for copper[8]. According to ROC curve analysis, Area under the curve (AUC) for CZr was equal to 0.832 and consequently CZr is an acceptable parameter to predict physical disability, similar to several studies [9], [8], and [20]that showed Cu to Zn ratio (CZr) as biochemical marker in various diseases.

We found that serum Se level was 25.51% lower in patient group compared to control group (p<0.05). Also we found a positive correlation between serum Se level and ADL score (p<0.05). Low serum selenium has been shown to be associated with elevated interleukin (IL)-6. Elevated serumIL-6 levels have been linked with an increased risk of reduced physical function and sarcopenia as well as the development of disability. Thus, selenium may also play a role in muscle weakness due to its relationship with the upregulation of IL-6 [12]. Similarly Beneddera et al. [3]study showed that Low serum selenium level is significant and independent predictors of ADL disability among older women[3].

According to our study a positive correlation was between FRAP and ADL score (p<0.05) and negative correlation between TBARS and ADL score (p<0.05). It means that increasing oxidative stress and decreasing total anti-oxidant causes physical disability decline in patient group (p<0.001). Similarly Richard et al. study [21] showed that older women with higher oxidative stress are at higher risk of severe walking disability and this is maybe due to oxidative damage to DNA, protein, and lipids causes skeletal muscle atrophy and loss of muscle fibers[21].

Our study shows a positive correlation between Zn and Se with FRAP (p<0.05) and negative correlation with TBARS (p<0.05). Zinc and selenium are involved in many biochemical processes supporting life. The most important of these processes are cellular respiration, DNA and RNA reproduction, maintenance of cell membrane integrity, and sequestration of free radicals. Zinc and selenium are involved in destruction of free radicals through cascading enzyme systems. Superoxide radicals are reduced to hydrogen peroxide by superoxide dismutases in the presence of zinc cofactors. Hydrogen peroxide is then reduced to water by the selenium ±glutathione peroxidase couple. Efficient removal of these superoxide free radicals maintains the integrity of membranes, reduces the risk of cancer, and slows the aging process [10]. Selenium exerts important beneficial effects. In particular, the selenoprotein antioxidant enzymes. Low antioxidants may tip the balance between antioxidants and free radicals and allow increased oxidative stress [3]. Se functions in the antioxidant system are an essential component of a family of GPx enzymes. Deficiency of GPx may occur in the presence of severe Se deficiency [20].

Our study shows a positive correlation between BMD.F and BMD.S with ADL score (p<0.05). Similarly Eimear et al. study [22] showed that in the people with disability, there was a higher prevalence of osteopenia and osteoporosis than in the general young adult population and onset of disability and ambulatory status were the most important predictors of BMD deficiency [22].

Our findings show that serum Zn and Se levels decreases in patient group. Cu and Zn play important role in the bone metabolism to stimulate osteoblasts and inhibit osteoclasts [14]. Selenium plays a fundamental role in protection against oxidative damage and Se deficiency has been shown to affect bone tissue [15] as can be seen that BMD.F is lower in patient group compared with control group.

Our study shows a positive correlation between BMD.F with FRAP (p<0.05) and negative correlation with TBARS (p<0.05). Oxidative stress due to free radicals are involved in osteoblastogenesis, in apoptosis of osteoblasts and osteocytes and in osteoclastogenesis and therefore also in bone resorption. These experimental data clearly establish a biological link between oxidative stress and bone [13].

6- Conclusion

The results of this study shows that situations of low serum Zn and Se levels and high Cu to Zn ratio (CZr), maybe leads to physical disability, meanwhile BMD deficiency and increasing oxidative stress also increase the severity of physical disability. Among the parameters studied, it seems that CZr is a reliable parameter for discriminating patient with physical disability and control group.


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