Effetto dell'emodiafiltrazione con rigenerazione on-line dell'ultrafiltrato (HFR) sullo stress ossidativo nei pazienti con insufficienza renale terminale in dialisi cronica

Cardiovascular disease remains the most common cause for the excess of morbidity and mortality in end-stage renal disease (ESRD) patients. Increased oxidative stress (OxSt), inflammation and endothelial dysfunction are recognized non-traditional cardiovascular risk factors in these patients. These patients, in fact, have increased levels of inflammation-related proteins, such as interleukin-6 (IL-6) and C-reactive protein (PCR), as well as OxSt-related proteins, such as NAD(P)H oxidase, which lead to reduced nitric oxide (NO) availability and endothelial dysfunction. The cause(s) of inflammation in dialysis have been shown to be multi-factorial and to include both factors arising from dialysis as well as other non-dialysis- related factors. Unfortunately, during the last 20 years the mortality rate in ESRD patients treated with dialysis has remained high, which has prompted the exploration of multiple strategies such as anti-inflammatory treatment using either pharmacological or dialysis-based approaches, to improve outcomes in these patients. A novel dialysis technique, haemodiafiltration with online regeneration of ultrafiltrate (HFR), has recently been reported to reduce levels of inflammation-related proteins, such as tumour necrosis factor (TNF-?), IL-6 and PCR, counteracting the inflammatory state while no data are available on the effect of HFR on OxSt. HFR (double chamber HDF with reinfusion of ultrafiltrate regenerated through a charcoal-resin cartridge), combines the processes of diffusion, convection and adsorbance. During HFR, the ultrafiltrate derived from the convective section of the filter is processed in a charcoal-resin cartridge and the regenerated ultrafiltrate is reinfused into the bloodstream before the diffusive section of the filter. An additional feature is that the resin component of the cartridge adsorbs in particular pro-inflammatory cytokines. Given the important role played by OxSt and its associated molecules, including those related to inflammation in increasing cardiovascular disease (CVD) risk in end-stage renal disease (ESRD), HFR may be useful in reducing the levels of these molecules, and thereby, in reducing the morbidity and mortality of dialysis patients. The aim of the current study was to evaluate the effect of dialysis using HFR on OxSt as assessed by plasma markers of OxSt such as oxidized low density lipoproteins (LDL), an indicator of cardiovascular risk factor, as well as gene and protein expression levels of OxSt-related proteins in mononuclear cells such as p22phox, a 22 kDa subunit of cytochrome b558 included in the NADH/NADPH oxidase which is present both in leucocytes and in the vascular wall which functions as an integral subunit of the final electron transport from NAD(P)H to haeme and molecular oxygen in generating O2, plasminogen activator inhibitor (PAI)-1, a proatherothrombogenic factor; haeme-oxygenase-1 (HO-1), one of three different isoforms of HO, it acts on haeme, producing CO and biliverdin, which is further metabolized to bilirubin, a potent antioxidant itself. Eighteen patients from the Division of Nephrology II at the Padova University Hospital, age range 19-60 years, undergoing chronic dialysis treatment (210-240 min three times a week bicarbonate-dialysis) for at least 1 year (range 1-6 years), were recruited and randomized into a 1 year cross-over study. One group of patients was initially treated for 6 months with HFR (SG8 Plus-Bellco, Mirandola Italy) then followed by 6 months of low-flux bicarbonate dialysis with ultrapure dialysate, using a polysulphone dialyser 1.8m2 and the other group was first treated with low flux bicarbonate dialysis with ultrapure dialysate, using a polysulphone dialyser 1.8m2 for 6 months followed by 6 months of treatment using HFR. Treatment with HFR significantly reduced mononuclear cell p22phox mRNA level and protein expression compared with the treatment with BD. Also mononuclear cell PAI-1 mRNA level and protein expression was significantly reduced by the treatment with HFR compared with the treatment with BD. Whereas treatment with HFR did not modify gene and protein expression of HO-1 compared with the treatment with BD. Treatment with HFR compared with the treatment with BD significantly reduced the plasma level of OxLDL: -14 ± 19 ?% vs 1 ± 14, p<0.01. The results of this study indicate that the treatment with HFR has a much lower impact on OxSt, as the levels of expression of proteins related to and the level of markers of OxSt were lower than those seen with standard dialysis. The more plausible explanation may come from both the efficacy of HFR in reducing the level of pro-oxidant/proinflammatory cytokines such as TNF-?, IL-6, which are inducers of and involved in the OxSt and inflammatory response, and from a possible sparing effect of HFR on several water soluble antioxidants. These effects of HFR might contribute to reduce the oxidative status in dialysis patients in general and explain its effects compared with standard bicarbonate dialysis in reducing the gene and protein expression of the OxSt-related proteins. This lower impact on OxSt suggests that HFR is a more biocompatible system for dialysis. Given the very close relationships between OxSt and inflammation and the determinant role played by OxSt in the induction of inflammation-related mechanisms in ESRD patients, HFR treatment could have considerable clinical impact in reducing the risk of progressive atherosclerotic cardiovascular disease in dialysis patients, which is the main cause of death in these patients.