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      Oxidative Stress in Patients Undergoing Peritoneal Dialysis: A Current Review of the Literature

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          Abstract

          Peritoneal dialysis (PD) patients manifest excessive oxidative stress (OS) compared to the general population and predialysis chronic kidney disease patients, mainly due to the composition of the PD solution (high-glucose content, low pH, elevated osmolality, increased lactate concentration and glucose degradation products). However, PD could be considered a more biocompatible form of dialysis compared to hemodialysis (HD), since several studies showed that the latter results in an excess accumulation of oxidative products and loss of antioxidants. OS in PD is tightly linked with chronic inflammation, atherogenesis, peritoneal fibrosis, and loss of residual renal function. Although exogenous supplementation of antioxidants, such as vitamins E and C, N-acetylcysteine, and carotenoids, in some cases showed potential beneficial effects in PD patients, relevant recommendations have not been yet adopted in everyday clinical practice.

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          Most cited references 115

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          Klotho deficiency causes vascular calcification in chronic kidney disease.

          Soft-tissue calcification is a prominent feature in both chronic kidney disease (CKD) and experimental Klotho deficiency, but whether Klotho deficiency is responsible for the calcification in CKD is unknown. Here, wild-type mice with CKD had very low renal, plasma, and urinary levels of Klotho. In humans, we observed a graded reduction in urinary Klotho starting at an early stage of CKD and progressing with loss of renal function. Despite induction of CKD, transgenic mice that overexpressed Klotho had preserved levels of Klotho, enhanced phosphaturia, better renal function, and much less calcification compared with wild-type mice with CKD. Conversely, Klotho-haploinsufficient mice with CKD had undetectable levels of Klotho, worse renal function, and severe calcification. The beneficial effect of Klotho on vascular calcification was a result of more than its effect on renal function and phosphatemia, suggesting a direct effect of Klotho on the vasculature. In vitro, Klotho suppressed Na(+)-dependent uptake of phosphate and mineralization induced by high phosphate and preserved differentiation in vascular smooth muscle cells. In summary, Klotho is an early biomarker for CKD, and Klotho deficiency contributes to soft-tissue calcification in CKD. Klotho ameliorates vascular calcification by enhancing phosphaturia, preserving glomerular filtration, and directly inhibiting phosphate uptake by vascular smooth muscle. Replacement of Klotho may have therapeutic potential for CKD.
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            Relative contribution of residual renal function and peritoneal clearance to adequacy of dialysis: a reanalysis of the CANUSA study.

            Studies of the adequacy of peritoneal dialysis and recommendations have assumed that renal and peritoneal clearances are comparable and therefore additive. The CANUSA data were reanalyzed in an effort to address this assumption. Among the 680 patients in the original CANUSA study, 601 had all of the variables of interest for this report. Adequacy of dialysis was estimated from GFR (mean of renal urea and creatinine clearance) and from peritoneal creatinine clearance. The Cox proportional-hazards model was used to evaluate the time-dependent association of these independent variables with patient survival. For each 5 L/wk per 1.73 m(2) increment in GFR, there was a 12% decrease in the relative risk (RR) of death (RR, 0.88; 95% confidence interval [CI], 0.83 to 0.94) but no association with peritoneal creatinine clearance (RR, 1.00; 95% CI, 0.90 to 1.10). Estimates of fluid removal (24-h urine volume, net peritoneal ultrafiltration, and total fluid removal) then were added to the Cox model. For a 250-ml increment in urine volume, there was a 36% decrease in the RR of death (RR, 0.64; 95% CI, 0.51 to 0.80). The association of patient survival with GFR disappeared (RR, 0.99; 95% CI, 0.94 to 1.04). However, neither net peritoneal ultrafiltration nor total fluid removal was associated with patient survival. Although these results may be explained partly, statistically, by less variability in peritoneal clearance than in GFR, the latter seems to be physiologically more important than the former. The assumption of equivalence of peritoneal and renal clearances is not supported by these data. Recommendations for adequate peritoneal dialysis need to be reevaluated in light of these observations.
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              Uremic toxicity, oxidative stress, and hemodialysis as renal replacement therapy.

              Patients with uremia are subject to greatly increased cardiovascular risk that cannot be completely explained by traditional cardiovascular risk factors. An increase in oxidative stress and inflammation has been proposed as contributory nontraditional uremic cardiovascular risk factors. Oxidative stress reflects the balance between oxidant generation and antioxidant defense mechanisms. Reduction/oxidation (redox) reactions may result in a stochastic process leading to oxidation of neighboring macromolecules. However, in many instances the reactive oxygen species target particular amino acid residues or lipid moieties. This provides a mechanism by which increased oxidative stress and/or alteration of antioxidant mechanisms can alter cell signaling. In individuals with advanced chronic kidney disease, the redox balance is not in equilibrium and is tipped toward oxidation resulting in the dysregulation of cellular process with subsequent vascular and tissue injury. In this review, the major oxidant and antioxidant pathways and the biomarkers to assess redox status in uremia are discussed, as well as the data linking the pathogenesis of oxidative stress, inflammation, cardiovascular events, and the progressive loss of kidney function in chronic kidney disease.
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                Author and article information

                Contributors
                Journal
                Oxid Med Cell Longev
                Oxid Med Cell Longev
                OMCL
                Oxidative Medicine and Cellular Longevity
                Hindawi
                1942-0900
                1942-0994
                2017
                27 December 2017
                : 2017
                Affiliations
                1Division of Nephrology and Hypertension, 1st Department of Internal Medicine, AHEPA Hospital, School of Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece
                2Clinic of Nephrology and Hypertension, Diabetes and Endocrinology, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
                Author notes

                Academic Editor: Janusz Gebicki

                Article
                10.1155/2017/3494867
                5892210
                Copyright © 2017 Vassilios Liakopoulos et al.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Funding
                Funded by: Collaborative Research Centres (CRC)
                Funded by: Deutsche Forschungsgemeinschaft
                Award ID: Me1365/9-1
                Award ID: Me1365/7-2
                Categories
                Review Article

                Molecular medicine

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