Is there a link between functional ability and serum natural antioxidants in elderly?

Abstract

Ageing is an unavoidable complex biological process that is defined as a decline in intrinsic physiological and biochemical functions of the major systems, leading to an increase in the risk of disease and mortality [1]. It is assumed that with ageing, mitochondrial functions decline progressively and cause accumulation of reactive oxygen species (ROS) [2]. Oxidative stress, caused by imbalance between ROS and antioxidants, is responsible for various age-related diseases such as arteriosclerosis, malignancies and neurodegenerative diseases. Serum uric acid, albumin, and bilirubin are strong natural hydrophilic antioxidants, while gamma glutamyl transferase (cGT) is a marker of oxidative stress in body. Functional ability is one of the main components of successful ageing; in this context, activity of daily living (ADL) and instrumental activities of daily living (IADL) reflect the functional status of elderly people. We hypothesized that there may be an association between functional ability and natural serum oxidants and antioxidants. The patients with end stage renal disease, malignant disease, severe liver failure, neurodegenerative diseases such as Alzheimer’s disease and Parkinson were excluded from the study. A total of 1,418 elderly persons (48 % men) with a mean age of 69.4 were evaluated by comprehensive geriatric assessment. The age range of the men and women was 63–84 and 64–87, respectively. Functional status was measured by using the Barthel index [3] for basic ADL, while the Lawton–Brody index [4] was used for IADL. Laboratory tests including uric acid, albumin, bilirubin and cGT were performed by a hospital autoanalyzer. Spearman correlation analysis revealed a significant positive relationship between ADL and IADL scores with serum natural antioxidants as summarized in Table 1. In addition, a negative, weak correlation was found between ADL and IADL scores with serum cGT levels as oxidative stress marker (Table 1). We have also measured serum uric acid, albumin, bilirubin and cGT levels of a middle-aged group including 331 persons (51 % men) with a mean age 41.3 (29–51). In comparison with elderly group, serum bilirubin and albumin levels were significantly higher in middle-aged group (P = 0.03 and P \ 0.01). There was no difference in the levels of serum uric acid and cGT between two groups. There is a growing body of evidence linking oxidative stress and ageing. In this regard, two recent studies demonstrated that serum natural antioxidants were lower in elderly patients with Alzheimer’s disease and osteoporosis [5, 6]. Uric acid is a strong, endogenously produced watersoluble antioxidant and can scavenge numerous oxidants including superoxide, hydroxyl radical and peroxynitrite [7]. Emerging data indicate that bilirubin, end product of heme metabolism, has more potent antioxidant effect than other antioxidants, including a-tocopherol, superoxide dismutase and catalase [8]. Moreover, bilirubin also has immunomodulatory functions [9]. The main antioxidant role of albumin could be linked to its physiological properties including inhibition of lipid peroxidation and scavenging of oxygenand carbon-centered free radicals [10]. On the other hand, cGT is a prominent oxidative stress marker and cGT-induced glutathione cleavage results in the production of the superoxide anion and hydrogen peroxide [11]. Furthermore, serum free radicals were found to be higher in patients with diabetes mellitus, coronary heart Z. A. Ozturk (&) Y. Kepekci Division of Geriatric Medicine, Department of Internal Medicine, Faculty of Medicine, Gaziantep University, Sahinbey, 27100 Gaziantep, Turkey e-mail: zaodr79@yahoo.com