**3.2 Removal of free light chain (FLC)**

Monoclonal free light chains of immunoglobulin kappa or lambda isotype have a molecular weight of 22.5 kDa and 45 kDa, respectively. They are metabolized by the kidney and can be detected in blood or urine. These FLC can polymerize in the form of dimer or multimer and thus reach high molecular weights of up to 900 kilodaltons [8]. Recently, they have been identified as toxic molecules in uremic patients [27]. Serum FLC levels have been shown to be associated with increased mortality in end-stage renal disease [27]. Therefore, FLC could be biomarkers of medium and large molecules that can be eliminated by hemodialysis, especially since their

#### *Expanded Hemodialysis Therapy: From the Rational to the Delivery DOI: http://dx.doi.org/10.5772/intechopen.110262*

determination is not expensive and are available in most laboratories. In patients with dialysis-dependent myeloma cast nephropathy, early FLC removal by intensive hemodialysis (IHD) with an adsorbent polymethylmethacrylate membrane (IHD-PMMA) combined with chemotherapy was associated with high rates of renal recovery and survival [28]. In a multicenter randomized trial, including 172 hemodialysis patients showed that the reduction ratio of FLC kappa and lambda was significantly higher in the HDx group using Theranova membranes compared to the use of high flux dialysis with Elisio-17H dialyzers after 6 months. This reduction was maintained in HDx until subsequent dialysis sessions [29].

### **3.3 Chronic inflammation**

Chronic inflammation is a major and known complication during the end-stage renal disease. Among others, serum concentration of beta2-microglobulin and inflammatory mediators have been correlated with malnutrition-inflammationatherosclerosis and formation of amyloid deposits in bone, tendons, and joints [30]. Indeed, oxidative stress results from a disequilibrium between pre-oxidative and anti-oxidative products, several molecules of high and medium molecular weight have increased levels, particularly the pro-inflammatory cytokines interleukins 1β, 6, 18, and TNF-α with prolongation of their half-life due to the uremic state. The clinical consequences are malnutrition, increased cardiovascular risk, erythropoietin resistance, and increased all-cause mortality [31].

Studies have suggested a better removal of pro-inflammatory proteins with MCO membranes and HDx. In a study conducted on patients with acute kidney injury and sepsis suspected of having high cytokine levels, the use of MCO membrane in continuous veno-venous hemodialysis (CVVHD) had a modest clearance of most cytokines and demonstrated small to no adsorptive capacity despite a decline in plasma cytokine concentrations [32] while in the randomized crossover trial of 48 hemodialysis patients, comparing MCO dialysis to HF dialysis for 12 weeks, the authors showed a considerable reduction in the expression of cytokines -RNAm of IL2 and TNFα, in circulating leucocytes when using MCO, compared to HF dialyzers. This study showed that MCO could significantly reduce inflammatory mediators in the first weeks. This difference was absent when the study was extended to 12 weeks. There was a decrease in the initial albumin concentration with stabilization thereafter [33].

In a prospective study [34], the MCO dialysis membranes had a favorable outcome on inflammation with a decrease in C-reactive protein levels when compared to low-flow dialysis and high-flux membranes, without any effect on oxidative stress markers (paraoxonase-1, ischemia-modified albumin, total Thiol, disulfide bond, and native Thiol). In addition, in Cozzolino et al. study, there was a 50% reduction in infection rate that requires admission and systemic antibiotics in patients treated with expanded hemodialysis enabled by the medium cutoff membrane [35].

#### **3.4 Cardiovascular parameters**

It is well established that cardiovascular damage is the primary cause of morbidity and mortality in end-stage renal disease. Several factors are involved or may contribute to their aggravation (increased phospho-calcium product with vascular calcification, anemia, inflammation, and oxidative stress). Uremic toxins can induce platelet activation and aggregation, leading to the development of thrombi [36].

In a clinical trial comparing the reduction of vascular smooth muscle cell calcifications *in vitro* by MCO and HF membranes, vascular calcifications were significantly reduced *in vitro* by 24% after 4 weeks and by 33% after 12 weeks in the MCO group compared to the HF group. The concentration of calcification-associated proteins (Matrix GIa, osteopontin (OPN) and growth differentiation factor 15 (GDF-15)) was higher after incubation with HF compared to MCO. This suggests that expanded hemodialysis reduces the potential for calcifications in dialysis serum *in vitro*; these results remain to be proven *in vivo* [37]. Ciceri et al. performed a prospective, controlled, cross-over study, comparing HDx and conventional hemodialysis to analyze the pro-calcifying serum of uremic patients. Uremic serum of HDx-treated patients induced less vascular smooth muscle cells (VSMC) necrosis compared with uremic serum of HD patients. However, no differences were found between dialytic treatments in the serum potential to induce apoptosis and to modulate the expression of a panel of genes involved in VSMC simil-osteoblastic differentiation [38].

Regarding the clinical impact of HDx on cardiovascular parameters, a prospective randomized controlled trial enrolled 80 patients with HDX and HDF online. The first criterion evaluated was the changes in brachial-ankle pulse wave velocity, which did not differ between the HDX group with MCO and the HDF group. Echocardiographic parameters and cardiovascular mortality were comparable in the two groups with a tendency to increase the coronary artery calcium score in HDx [36]. HDx with MCO membranes could be a good alternative when online-HDF is not available.

### **3.5 Removal of proteins binding to uremic toxins (PBUT)**

Despite their small molecular weight, proteins bound to albumin are difficult to remove by conventional methods. Among these molecules homocysteine, which is three to four times higher in dialysis patients, can cause inflammation, endothelial lesions, and cardiovascular damage [39]. Other small molecules, such as 3-Carboxy4 methyl-5-propyl-2-furanpropionate (MPF), tryptophan and some of its metabolites, such as indoxyl sulfate (IS), 3 indol acetic acid, kynurenine, and p-cresulfate (p-CS), bind to albumin making their removal difficult. Theoretically, a decrease in albumin would allow the elimination of these PBUTs, but studies conducted to compare this clearance between HDx and conventional HD showed contradictory results regarding the elimination of these molecules [40]. A sub-study of the REMOVAL-HD trial, enlisting 89 participants, found no significant changes in total or free levels of IS or p-CS after 12 or 24 weeks of MCO membrane use compared to baseline, as no significant albumin loss was observed in this study. Whereas an open-label, controlled, cross-over study comparing HDx and conventional HD found a significant decrease in IS and other metabolites in the HDx group [38]. Further long-term, randomized studies are needed to prove whether PBUTs clearance by HDx is superior to other techniques and to evaluate its clinical impact.

#### **3.6 Quality of life**

The evaluation of health-related quality of life (QOL) in end-stage renal disease became more and more important. Patients on dialysis suffer from symptoms, such as fatigue, cramps, loss of appetite, and pruritus [41]. Those signs are mostly related to the accumulation of uremic toxins, anemia, and cardiovascular complications, which altered mental and physical health. A decrease in QOL is also associated with an increase in mortality [42].

#### *Expanded Hemodialysis Therapy: From the Rational to the Delivery DOI: http://dx.doi.org/10.5772/intechopen.110262*

Several studies aimed to compare the use of HDx with conventional hemodialysis or HDF in improving QOL parameters, using several scores (LEVIL, KDQOL -SF 36, PROM POS-S Renal Symptom questionnaire and the "Recovery time from last dialysis session) [43, 44]. The major items assessed were dialysis symptom index, restless legs syndrome, sleep, energy, and well-being. In a prospective multicenter observational study of the COREXH registry, 992 patients were switched from HF to HDx for one year. The results showed that the items' symptoms, effects of kidney disease, and burden of kidney disease, improved as well as restless leg syndrome, which decreased significantly over a 12-month monitoring period [45]. Multiple studies [24, 46] showed an upgrade in QOL in patients on HDx compared to HDF or conventional HD. Bolton et al., when switching from regular high-flux dialysis membrane to medium cutoff (MCO) membrane, and evaluating different symptoms burden by the POS-S Renal total symptom score, showed a decrease at 6 months. The fatigue and lack of energy improved constantly; the percentage of participants scoring its impact as "severe" decreased from 28% at baseline to 16% at 12 months [44]. Other studies using the KDQol-36 and the Edmonton symptom assessment system revised (ESAS-r), did not demonstrate any effect of HDx on QOL [29, 47]. Studies were conducted to evaluate biomarkers for the best use of the distinctive features and benefits of HDF, α 1-MG is one biomarker that could evaluate this removal performance. The authors concluded that hemodiafilter should provide an α 1-MG removal rate of 35%. An improvement in clinical manifestations can be expected by doing so, and it increases patients' QOL [48].

The HDx with MCO membranes can improve the QOL of patients. The use of this technique may be of use in the targeted selection of patients and assist in monitoring response. The study's results are encouraging and suggest the use of HDx even in patients who cannot benefit from convective techniques because of vascular access or intolerance to high volumes of exchange [49].

#### **3.7 Safety concerns**

#### *3.7.1 Albumin loss*

HDx allows the removal of large molecules (>45 k daltons), including albumin, due to its large pore size distribution [39]. In the studies that evaluated albumin removal by HDx, there was a controversy between those showing a significant decrease versus those where the level of albumin remained the same. Even when the decrease was significant, there were no clinical signs of hypoalbuminemia, some patients reported a better appetite after switching to the HDx therapy [29, 45]. This is probably due to better removal of leptin, obsestatin, and acyl ghrelin associated with a drop in appetite among dialysis patients [50].

In the large observational study from the COREXH registry, the observed variability from baseline and maximum average change in mean serum albumin levels were − 1.8% and − 3.5%, respectively. No adverse events were related to the MCO membrane [51].

On the other hand, a slight decrease in serum albumin might be beneficial for dialysis patients. HDx might induce a moderate removal of PBUTs, oxidized albumin, and carbamylated albumin along with the serum albumin loss [51].

#### *3.7.2 Pyrogene retention*

The larger pore sizes of MCO membranes have raised concerns about the potential for increased membrane permeability to pyrogens including endotoxins and other

bacterial contaminants that could be present in the dialysis fluid, which can contribute to the pathological features of uremia in patients receiving dialysis. Hulko et al. tested the capacity of low-fux, high-fux, MCO, and HCO dialyzer membranes with different pore sizes to prevent pyrogens crossing from dialysate to the blood side in a closed-loop test system, differentiating among lipopolysaccharides, peptidoglycans, and bacterial DNA using a toll-like receptor assay. Levels of lipopolysaccharides, peptidoglycans, and bacterial DNA in the blood-side samples were too low to identify potential differences in pyrogen permeability among the membranes [52].

In another study by Schepers et al., four dialysis membranes of comparable composition but with different pore sizes were tested for their permeability for endotoxins by exposing them during a 1 h *in vitro* dialysis session to dialysate contaminated with filtrates of two water-borne bacteria, *Pseudomonas aeruginosa* and *Pelomonas* saccharophila, at an endotoxin challenge at least four times the upper limit of endotoxin load (2 EU/ml) when using standard dialysis fluid. For the tested membranes, there was a nonsignificant difference in the number of the polyvinylpyrrolidone solutions, which contained a detectable amount of endotoxin after repetitive circulation through the dialyzer, be it close to the detection limit in the majority of cases [53].

These results suggest that MCO membranes are suitable for hemodialysis using ISO standard dialysis fluid quality [54], and retain endotoxins at a similar level as other membranes.

#### *3.7.3 Effects on medication clearance*

The question that comes to mind is whether the increased pore size in MCO membranes affects the retention of commonly used medications or coagulation factors in dialysis patients. Very few clinical studies have addressed this issue [55].

Using an *in vitro* model, removing erythropoietin, heparin, insulin, and several coagulation factors with HDx was comparable with HF and HDF therapy, suggesting that it is not necessary to change the medication dosing or anticoagulation protocols for dialysis patients receiving HDx therapy with MCO membranes. In the study published by Allawati et al., vancomycin clearance was higher in the MCO group compared to high-flux the group, but it was not statistically significant [56].

#### *3.7.4 Routine use evaluation of MCO membranes*

In the study by Florens et al., the authors evaluated the first routine use of HDx therapy in real-life conditions. Eighteen centers participated, and nurses and nephrologists answered by filling in a score regarding the use of MCO membranes. The assessment was related to packaging, priming, and rinsing of the dialyzers. Overall HDx therapy was easy to use in routine, and no adverse events were reported. However, nurses experienced some issues concerning poor de-aeration and the need for more anticoagulation. These problems could be prevented by training the medical staff [50].
