No abstract

An increased oxidative stress is now considered one of the major risk factors in chronic renal failure (CRF) patients that may be exacerbated by dialysis. It has been postulated that this increased oxidative stress might cause an augmented red blood cell (RBC) membrane lipid peroxidation with the consequent alteration in membrane deformability. The aim of this study was to evaluate RBC susceptibility to an in vitro induced oxidative stress and RBC antioxidant potential in different groups of CRF patients undergoing different substitutive treatment modalities. Fifteen end-stage CRF patients were evaluated in conservative treatment, 23 hemodialysis (HD) patients, 15 continuous ambulatory peritoneal dialysis (CAPD) patients, 15 kidney transplanted patients, and 16 controls. Their RBCs were incubated with the oxidative stress-inducing agent tert-butylhydroperoxide both in the presence and in the absence of the catalase inhibitor sodium azide, and the level of malondialdehyde (MDA) (a product of lipid peroxidation), was measured at 0, 5, 10, 15, and 30 min of incubation. In addition, the RBC content of reduced glutathione (GSH) was measured by HPLC. As opposed to the controls, RBCs from end-stage CRF patients exhibited an increased sensitivity to oxidative stress induced in vitro, both in the absence and presence of a catalase inhibitor, as demonstrated by a significantly higher level of MDA production at all the incubation times (P < 0.05). Different substitutive treatments had different impacts on this phenomenon; CAPD and kidney transplantation were able to normalize this alteration while HD was not. GSH appeared to be related to the increase in RBC susceptibility to oxidative stress; its content being significantly elevated in end-stage CRF and HD patients as compared with CAPD and transplanted patients and controls (P < 0.05). No significant changes were observed in the RBC glutathione content during the HD session. The increase of GSH in RBCs of end-stage CRF and HD patients seems to indicate the existence of an adaptive mechanism under increased oxidative stress occurring in vivo. Unlike HD, the beneficial effect of CAPD on the anemia of dialysis patients might partly be due to a condition of lower oxidative stress that might in addition counterbalance the cardiovascular negative effects of dislipidemia of CAPD patients.

Activation of coagulation during hemodialysis (HD) is a relevant clinical problem, especially when patients at risk of bleeding are treated. However, little is known about the relative contribution of the various components of the circuit to the thrombotic process. Thus, an experimental model was developed that is aimed at evaluating biochemical markers of coagulation activation at different times and sites throughout the HD circuit. A HD blood-tubing set with integrated arterial and venous chambers (cartridge-line set) was used, which was added with the following sampling points: at the beginning of the arterial line (P1), before the blood pump (P2), after the blood pump (P3), and at the end of the venous line (P4). A bypass system allowed us to circulate the blood only into the blood lines for the first 20 min of the extracorporeal circulation. The extracorporeal circuit was rinsed with 1.7 L of heparinized saline (2,500 IU/L) that was completely discarded before patient connection. A continuous administration of unfractionated heparin (500-800 IU/h) without a starting bolus was adopted as a low heparin extracorporeal treatment. Samples were collected before the start of the extracorporeal circulation from the fistula needle (T0P0), after 5 (T1), 10 (T2), and 20 min (T3) from P1, P2, P3, and P4. After 20 min, the blood was returned to the patient using only saline and HD was then started, circulating the blood through the dialyzer. Further samples were obtained from P1 and P4 after 5 (T4) and 210 min (T5). Plasma levels of coagulation activation markers-thrombin-antithrombin complex (TAT) and prothrombin fragment 1 + 2 (F1 + 2)-were evaluated in all the samples in 12 stable HD patients. In each patient, the activated partial thromboplastin time (APTT) was measured at T0P0 and T1-T5 from P1. No significant changes were found at any time as far as F1 + 2 is concerned. However, TAT levels increased over time only after the start of HD, suggesting that the latter test could be more useful in order to detect coagulation activation during HD. The same experiments performed with nonheparin-primed extracorporeal circuit showed similar results. The blood lines used did not significantly activate coagulation during the first 20 min, whereas only 5 min of blood circulation throughout the whole circuit increased TAT values, which still remained lower than previous reports, even after 210 min of treatment.