The Challenges of O2 Detection in Biological Fluids: Classical Methods and Translation to Clinical Applications.

Dissolved oxygen (DO) is deeply involved in preserving the life of cellular tissues and human beings due to its key role in cellular metabolism: its alterations may reflect important pathophysiological conditions. DO levels are measured to identify pathological conditions, explain pathophysiological mechanisms, and monitor the efficacy of therapeutic approaches. This is particularly relevant when the measurements are performed in vivo but also in contexts where a variety of biological and synthetic media are used, such as ex vivo organ perfusion. A reliable measurement of medium oxygenation ensures a high-quality process. It is crucial to provide a high-accuracy, real-time method for DO quantification, which could be robust towards different medium compositions and temperatures. In fact, biological fluids and synthetic clinical fluids represent a challenging environment where DO interacts with various compounds and can change continuously and dynamically, and further precaution is needed to obtain reliable results. This study aims to present and discuss the main oxygen detection and quantification methods, focusing on the technical needs for their translation to clinical practice. Firstly, we resumed all the main methodologies and advancements concerning dissolved oxygen determination. After identifying the main groups of all the available techniques for DO sensing based on their mechanisms and applicability, we focused on transferring the most promising approaches to a clinical in vivo/ex vivo setting.

Removal of Bilirubin with a New Adsorbent System: In Vitro Kinetics.

BACKGROUND/AIMS: Many potentially toxic molecules accumulate in the blood during hepatic dysfunction. In clinical practice, it is very difficult to remove bilirubin, the most widely studied toxin, and particularly the unconjugated form, strongly albumin-bound. The aim of this in vitro study was to assess irreversible bilirubin adsorption as a protein-bound compound marker, using Cytosorb® (Cytosorbents Corp.), a new hemoadsorption device designed to remove cytokines. METHODS: We performed 4 in vitro experiments, dynamic and static, with different albumin-bilirubin solutions. RESULTS: All experiments showed the resin's ability to break the albumin-bilirubin complex (Experiment 1, 2), leading to efficient bilirubin removal for 24 h (Removal Rate: 90% Experiment 3) with minimal albumin loss. No sign of bilirubin release from the charged resin was detected (Experiment 4). CONCLUSION: Cytosorb® seems a promising artificial liver support, thanks to its ability to adsorb bilirubin and its proven ability to modulate the cytokines involved in hepatic dysfunction.

Proteomic analisys of protein extraction during hemofiltration with on-line endogenous reinfusion (HFR) using different polysulphone membranes.

In end-stage renal disease patients, extracorporeal dialytic therapy is not able to prevent the accumulation of toxins related to the uremic syndrome, a severe complication that increases morbidity and mortality rate. In this paper, hemoFiltration with on-line Reinfusion (HFR) architecture is used to evaluate the effect of a more permeable membrane on the extraction of medium-high molecular weight molecules. The aim of this study was to compare two polysulphone membranes for convective chamber: polyphenylene High Flux (pHF) and polyphenylene Super High-Flux (pSHF). Fourteen patients were subjected to HFR with pHF and pSHF membranes and ultra filtrate (UF) samples were collected to evaluate molecular weight cut-off (MWCO) and to identify extracted proteins. Furthermore, image analysis software was used in order to evaluate change in protein extraction during the dialysis. The quantification of four proteins by immunoassay demonstrates a higher permeability of pSHF membrane. Two-dimensional electrophoresis (2-DE) gels showed, for both membranes, the greater number of protein spots at 235 min. Some of the identified proteins, involved in nephropathic disease complications, were compared to assess differences in extraction during dialytic treatment by PDQuest analysis. UF proteomic analysis demonstrated a different behavior for the two membranes; pHF membrane was more permeable at the beginning of HFR treatment (15 min), while pSHF membrane at the end of treatment (235 min). Proteomic analysis is a suitable approach to investigate the behavior of different membranes during dialysis. Results indicated that pSHF membrane offers the higher permeability, and showed higher efficiency in removal of middle molecules related to uremic syndrome.

Uremic Toxins and Blood Purification: A Review of Current Evidence and Future Perspectives.

Accumulation of uremic toxins represents one of the major contributors to the rapid progression of chronic kidney disease (CKD), especially in patients with end-stage renal disease that are undergoing dialysis treatment. In particular, protein-bound uremic toxins (PBUTs) seem to have an important key pathophysiologic role in CKD, inducing various cardiovascular complications. The removal of uremic toxins from the blood with dialytic techniques represents a proved approach to limit the CKD-related complications. However, conventional dialysis mainly focuses on the removal of water-soluble compounds of low and middle molecular weight, whereas PBTUs are strongly protein-bound, thus not efficiently eliminated. Therefore, over the years, dialysis techniques have been adapted by improving membranes structures or using combined strategies to maximize PBTUs removal and eventually prevent CKD-related complications. Recent findings showed that adsorption-based extracorporeal techniques, in addition to conventional dialysis treatment, may effectively adsorb a significant amount of PBTUs during the course of the sessions. This review is focused on the analysis of the current state of the art for blood purification strategies in order to highlight their potentialities and limits and identify the most feasible solution to improve toxins removal effectiveness, exploring possible future strategies and applications, such as the study of a synergic approach by reducing PBTUs production and increasing their blood clearance.

Efficacy of Divinylbenzenic Resin in Removing Indoxyl Sulfate and P-Cresol Sulfate in Hemodialysis Patients: Results From an In Vitro Study and An In Vivo Pilot Trial (xuanro4-Nature 3.2).

High serum levels of microbiota-derived uremic toxins, indoxyl sulfate (IS) and p-cresyl sulfate (PCS), are associated with chronic kidney disease (CKD) progression and cardiovascular complications. IS and PCS cannot be efficiently removed by conventional hemodialysis (HD), due to their high binding affinity for albumin. This study evaluates the efficacy of a divinylbenzene-polyvinylpyrrolidone (DVB-PVP) cartridge and a synbiotic to reduce uremic toxins in HD patients. First, the in vitro efficacy of DVB-PVP in adsorbing IS and PCS was evaluated. Second, a randomized, placebo-controlled pilot study in HD patients was carried out to establish whether the administration of a synbiotic, either individually and in association with DVB-PVP-HD, could reduce the production of uremic toxins. In vitro data showed that DVB-PVP resin removed a mean of 56% PCS and around 54% IS, after 6 h of perfusion. While, in the in vivo study, the DVB-PVP cartridge showed its adsorbing efficacy only for IS plasma levels. The combination of synbiotic treatment with DVB-PVP HD decreased IS and PCS both at pre- and post-dialysis levels. In conclusion, this study provides the first line of evidence on the synergistic action of gut microbiota modulation and an innovative absorption-based approach in HD patients, aimed at reducing plasma levels of IS and PCS.

A single dialysis session of hemodiafiltration with sorbent-regenerated endogenous ultrafiltrate reinfusion (HFR) removes hepcidin more efficiently than bicarbonate hemodialysis: a new approach to containing hepcidin burden in dialysis patients?

BACKGROUND: Most hemodialysis patients have high Hepcidin-25 levels, which may be involved in the pathogenesis of several uremic complications related to an altered iron biology. The hemodialysis procedure itself can influence Hepcidin-25 levels by removing Hepcidin-25 and maybe stimulating its production due to a pro-inflammatory effect. METHODS: To assess the relationship between dialysis-related inflammation and intradialysis changes in Hepcidin-25, we performed a crossover trial in 28 hemodialysis patients to compare the effects on serum levels of Hepcidin-25 and inflammatory markers activated during dialysis [Tumor Necrosis Factor-α (TNF-α), Interleukin-6, C-reactive protein (CRP), Pentraxin-3] of a single dialysis session using a technique capable of reducing inflammation, HFR (Hemo Filtrate Reinfusion: a hemodiafiltration system combining convection, diffusion and adsorption) or bicarbonate-dialysis using either the same low-flux membrane as in the diffusion stage of HFR (LFBD) or a high-flux membrane (HFBD). RESULTS: HFR achieved a greater reduction in Hepcidin-25 levels than both LFBD [-72% (95% CI: -11 to -133), p = 0.022] and HFBD [-137% (95% CI: -2 to -272), p = 0.047], conceivably due to both a greater removal (because of its convective/adsorptive component) and a lower inflammation-related Hepcidin-25 production. HFR also led to a greater decrease in TNF-α than LFBD [-277% (95% CI: -59 to -494), p = 0.014], while the two methods induced similar changes in Interleukin-6, CRP and Pentraxin-3 levels. CONCLUSIONS: Our findings suggest that a single bicarbonate-dialysis session can upregulate Hepcidin-25 synthesis and that HFR can fully overcome this effect, enabling a greater Hepcidin-25 removal during dialysis. Adequately-designed studies are needed, however, to establish whether the beneficial effect of HFR emerging from our study could reduce Hepcidin-25 (and TNF-α) burden and improve clinically-relevant outcomes. TRIAL REGISTRATION: ISRCTN15957905.