Abstract
The disruption of balance between production of reactive oxygen species and antioxidant systems in favor of the oxidants is termed oxidative stress (OS). To counteract the damaging effects of prooxidant free radicals, all aerobic organisms have antioxidant defense mechanisms that are aimed at neutralizing the circulating oxidants and repair the resulting injuries. Antioxidants are either endogenous (the natural defense mechanisms produced by the human body) or exogenous, found in supplements and foods. OS is present at the early stages of chronic kidney disease, augments progressively with renal function deterioration, and is further exacerbated by renal replacement therapy. End-stage renal disease patients, on hemodialysis (HD) or peritoneal dialysis (PD), suffer from accelerated OS, which has been associated with increased risk for mortality and cardiovascular disease. During HD sessions, the bioincompatibility of dialyzers and dialysate trigger activation of white blood cells and formation of free radicals, while a significant loss of antioxidants is also present. In PD, the bioincompatibility of solutions, including high osmolality, elevated lactate levels, low pH, and accumulation of advanced glycation end-products trigger formation of prooxidants, while there is significant loss of vitamins in the ultrafiltrate. A number of exogenous antioxidants have been suggested to ameliorate OS in dialysis patients. Vitamins B, C, D, and E, coenzyme Q10, L-carnitine, a-lipoic acid, curcumin, green tea, flavonoids, polyphenols, omega-3 polyunsaturated fatty acids, statins, trace elements, and N-acetylcysteine have been studied as exogenous antioxidant supplements in both PD and HD patients.
Highlights
Every substance that can accept electrons is defined as oxidant, while a compound donating electrons is considered a reductant
end-stage renal disease (ESRD) patients commonly have multiple comorbidities related to excessive production of prooxidants, like hypertension, dyslipidemia, diabetes mellitus (DM), vascular calcification, and old age [13]
Besides formation of prooxidant molecules, patients on renal replacement therapy (RRT) are characterized by significant depletion of antioxidant defense mechanisms, due to a number of reasons: both the traditional, strict dietary restrictions and the malnutrition status that usually accompanies ESRD patients are characterized by limited consumption of fruits and vegetables and poor intake of antioxidants such as vitamins C, D, and E [18], while treatment with both peritoneal dialysis (PD) or HD has been associated with loss of vitamins and trace elements [19,20,21]
Summary
Every substance that can accept electrons is defined as oxidant, while a compound donating electrons is considered a reductant. A chemical process that includes loss of electrons is defined as oxidation, while reduction is a chemical reaction in which a compound gains electrons. The disruption of balance between production of ROS and antioxidant systems is termed oxidative stress (OS) [2]. Based on this OS paradox, abundant antioxidants in a cellular environment might scavenge an excessive amount of ROS and inhibit their beneficial role in stimulating important biochemical reactions, crucial for cell homeostasis [3]. Disruption of balance of the redox state to either excessive reduction or oxidation results in injury and damage of the biological systems [4]. This review is aimed at presenting the available data regarding the exogenous administration of antioxidants and their possible protective effects on renal replacement therapy (RRT) patients
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