In vivo removal of high- and low-molecular-weight compounds in hemodiafiltration with on-line regeneration of ultrafiltrate

Reduction of protein-bound uraemic toxins in plasma of chronic renal failure patients: A systematic review

BACKGROUND

Protein-bound uraemic toxins (PBUTs) accumulate in patients with chronic kidney disease and impose detrimental effects on the vascular system. However, a unanimous consensus on the most optimum approach for the reduction of plasma PBUTs is still lacking.

METHODS

In this systematic review, we aimed to identify the most efficient clinically available plasma PBUT reduction method reported in the literature between 1980 and 2020. The literature was screened for clinical studies describing approaches to reduce the plasma concentration of known uraemic toxins. There were no limits on the number of patients studied or on the duration or design of the studies.

RESULTS

Out of 1274 identified publications, 101 studies describing therapeutic options aiming at the reduction of PBUTs in CKD patients were included in this review. We stratified the studies by the PBUTs and the duration of the analysis into acute (data from a single procedure) and longitudinal (several treatment interventions) trials. Reduction ratio (RR) was used as the measure of plasma PBUTs lowering efficiency. For indoxyl sulphate and p-cresyl sulphate, the highest RR in the acute studies was demonstrated for fractionated plasma separation, adsorption and dialysis system. In the longitudinal trials, supplementation of haemodialysis patients with AST-120 (Kremezin®) adsorbent showed the highest RR. However, no superior method for the reduction of all types of PBUTs was identified based on the published studies.

CONCLUSIONS

Our study shows that there is presently no technique universally suitable for optimum reduction of all PBUTs. There is a clear need for further research in this field.

Acute effect of one session of hemodiafiltration with endogenous reinfusion on uremic toxins and inflammatory mediators

Aims:

To investigate the acute effects of hemodiafiltration with endogenous infusion on the elimination of uremic toxins and inflammatory mediators in patients with end-stage renal disease.

Materials and methods:

A total of 37 end-stage renal disease patients undergoing chronic hemodialysis received a single hemodiafiltration with endogenous infusion dialysis treatment. The acute effects of one hemodiafiltration with endogenous infusion session on uremic toxins and inflammatory mediators were assessed by comparing the pre- and post-hemodiafiltration with endogenous infusion concentrations.

Results:

Hemoglobin and albumin were stable during hemodiafiltration with endogenous infusion therapy. The mean reduction ratios of β2-microglobulin, p-cresyl sulfate, and indoxyl sulfate were 43.60%, 40.91%, and 43.64%, respectively. Tumor necrosis factor-α also decreased significantly at a mean rate of 28.10%, while the concentrations of interleukin-6 and high-sensitivity C-reactive protein remained unchanged after one session of hemodiafiltration with endogenous infusion.

Conclusion:

The hemodiafiltration with endogenous infusion system is a new dialysis technique that combines diffusion, convection, and adsorption processes. It allows for extensive solute removal, including protein-bound uremic toxins and some pro-inflammatory cytokines, but does not cause nutrient loss and inflammatory response during the treatment. Although the effect after a single hemodiafiltration with endogenous infusion session is limited, it may be improved by repeated and long-term treatment.

Development and Validation of Residual Kidney Function Estimating Equations in Dialysis Patients

RATIONALE & OBJECTIVE

Measurement of residual kidney function is recommended for the adjustment of the dialysis prescription, but timed urine collections are difficult and prone to errors. Equations to calculate residual kidney function from serum concentrations of endogenous filtration markers and demographic parameters would simplify monitoring of residual kidney function. However, few equations to estimate residual kidney function using serum concentrations of small solutes and low-molecular-weight proteins have been developed and externally validated.

STUDY DESIGN

Study of diagnostic test accuracy.

SETTING & PARTICIPANTS

823 Chinese peritoneal dialysis (PD) patients (development cohort) and 826 PD and hemodialysis patients from the Netherlands NECOSAD study (validation cohort).

TESTS COMPARED

Equations to estimate residual kidney function (estimated clearance [eCl]) using serum creatinine, urea nitrogen, cystatin C, β2-microglobulin (B2M), β-trace protein (BTP), and combinations, as well as demographic variables (age, sex, height, and weight). Equations were developed using multivariable linear regression analysis in the development cohort and then tested in the validation cohort. Equations were compared with published validated equations.

OUTCOMES

Residual kidney function measured as urinary clearance (mCl) of urea nitrogen (mClUN) and average of creatinine and urea nitrogen clearance (mClUN-cr).

RESULTS

In external validation, bias (difference between mCl and eCl) was within ± 1.0 unit for all equations. Accuracy (percent of differences within ± 2.0 units) was significantly better for eClBTP, eClB2M, and eClBTP-B2M than eClUN-cr for both mClUN (78%, 80%, and 81% vs 72%; P < 0.05 for all) and mClUN-cr (72%, 78%, and 79% vs 68%; P < 0.05 for all). The area under the curve for predicting mClUN > 2.0 mL/min was highest for eClB2M (0.853) and eClBTP-B2M (0.848). Results were similar for other validated equations.

LIMITATIONS

Development cohort only consisted of PD patients, no gold-standard method for residual kidney function measurement.

CONCLUSIONS

These results confirm the validity and extend the generalizability of residual kidney function estimating equations from serum concentrations of low-molecular-weight proteins without urine collection.

Effect of hemodiafiltration with endogenous reinfusion on overt idiopathic chronic inflammation in maintenance hemodialysis patients: a multicenter longitudinal study

Chronic inflammation is widely diffuse in maintenance hemodialysis (MHD) patients and is associated with poor survival. Hemodiafiltration with endogenous reinfusion (HFR) is a dialysis technique, highly biocompatible, able to adsorb proinflammatory cytokines and to decrease amino acids and antioxidants loss. These features could be helpful in MHD patients affected by idiopathic chronic inflammation, but this issue remains to be elucidated. We performed a multicenter longitudinal study to assess the effect of the switching from bicarbonate HD to HFR in patients with serum C-reactive Protein (CRP) > 5 mg/L coupled with albumin <4.0 g/dL in the last 6 months. We enrolled 24/176 (14%) patients, of which 20 patients were assessed at 4 months and 18 completed the study. We excluded 11 patients with evident causes of inflammation. At baseline, serum levels of CRP (18.7[7.0-39.4] mg/L) and albumin (3.5[3.3-3.7] g/dL) were significantly correlated (r = -0.49; P = 0.028). The effect on CRP and albumin was almost evident in the first 4 months and remained stable until to eighth month. A strict correlation (R = -0.49; 0.040) between percentage change of CRP (-35%) and albumin (+14%) after 8 months of HFR. These effects were associated with the reduction of IL-6, IL-1β, and TNF-α and the increment of pre-albumin and leptin, whereas the serum levels of Branched Chain Amino Acid (BCAA) remained unchanged. In MHD patients affected by idiopathic chronic inflammation the switching from BHD to HFR is associated with improvement of inflammation. Whether these favorable effects may modify the outcomes of these high-risk patients needs to be confirmed by studies ad hoc.

Elimination of large uremic toxins by a dialyzer specifically designed for high-volume convective therapies

BACKGROUND

Unlike conventional hemodialysis treatments, which rely almost solely on diffusion-related mechanisms for solute removal, hemodiafiltration (HDF) allows more efficient removal of higher molecular weight toxins due to convective transport mechanisms. To facilitate the removal of these toxins in HDF treatment modalities, dialyzers with highly efficient high-flux membranes are necessary. This study assessed the large uremic toxin removal ability of a high-flux dialyzer (FX CorDiax 60) specifically designed to facilitate convective therapies compared with a standard high-flux dialyzer (FX 60).

METHODS

In an open, randomized, cross-over, single-center, controlled, prospective clinical study, 30 adult chronic hemodialysis patients were treated by post-dilution online HDF with the FX 60 or the FX CorDiax 60 dialyzer. All other dialysis parameters were kept constant in both study arms. The reduction rate (RR) of blood urea nitrogen, phosphate, β2-microglobulin (β2-m), myoglobin, prolactin, α1-microglobulin, α1-acid glycoprotein, albumin and total protein as well as the elimination into dialysate was intraindividually compared for the two dialyzer types.

RESULTS

For FX CorDiax 60 versus FX 60, the RR was significantly higher for blood urea nitrogen (86.23 ± 4.14 vs. 84.89 ± 4.59%, p = 0.015), β2-m (84.67 ± 3.79 vs. 81.30 ± 4.82%, p < 0.0001), myoglobin (75.23 ± 10.48 vs. 58.60 ± 12.1%, p < 0.0001), prolactin (72.96 ± 9.68 vs. 56.91 ± 13.01%, p < 0.0001) and α1-microglobulin (20.89 ± 18.27 vs. 13.60 ± 12.50%, p = 0.016). There were no significant differences in the RR for phosphate, α1-acid glycoprotein, albumin and total protein. Mass removal was significantly higher with the FX CorDiax 60 than with the FX 60 for β2-m (0.26 ± 0.09 vs. 0.24 ± 0.09 g, p = 0.0006), myoglobin (1.83 ± 0.89 vs. 1.51 ± 0.76 mg, p = 0.0017), prolactin (0.17 ± 0.13 vs. 0.14 ± 0.08 mg, p = 0.02) and albumin (4.25 ± 3.49 vs. 3.01 ± 2.37 g, p = 0.03).

CONCLUSIONS

This study demonstrates that treating patients with an FX CorDiax 60 instead of an FX 60 dialyzer in post-dilution HDF mode significantly increases the elimination of middle molecules.

Effect of hemodialysis and hemofiltration on plasma C.E.R.A. concentrations

C.E.R.A., a continuous erythropoietin receptor activator, is a long-acting erythropoiesis-stimulating agent approved for the treatment of anemia in patients with chronic kidney disease. Although the large molecular weight and the carbohydrate chain make it unlikely that C.E.R.A. could be removed during hemodialysis or hemofiltration, no such data have been published. In vitro studies were performed to assess the removal of C.E.R.A. during hemodialysis and hemofiltration, using both low-flux and high-flux membranes and parameters very similar to those used in clinical practice. Clinical pharmacokinetic studies of plasma C.E.R.A. concentrations in patients undergoing hemodialysis were also performed following subcutaneous injection of C.E.R.A. In the in vitro studies, plasma C.E.R.A. concentrations were not significantly different from baseline values in the primed blood reservoir over a 4-hour period during hemodialysis (P = 0.12). C.E.R.A. concentrations in the plasma obtained from the venous end of the hemofilter increased proportionally with the plasma total protein concentrations, reflecting the consequence of hemoconcentration and suggesting that C.E.R.A and plasma total proteins were retained by hemofiltration membranes to a similar degree. These in vitro studies showed that C.E.R.A. was not removed by simulated hemodialysis or hemofiltration either via transmembrane transport or adsorption to the membrane. The results were corroborated by the clinical pharmacokinetic data, which showed no detectable changes in plasma C.E.R.A. concentrations during hemodialysis using either low-flux or high-flux dialyzers. These results suggest that C.E.R.A. can be administered to patients at any time during hemodialysis or hemofiltration without appreciable loss in the extracorporeal circuit.

Normal and pathologic concentrations of uremic toxins

An updated review of the existing knowledge regarding uremic toxins facilitates the design of experimental studies. We performed a literature search and found 621 articles about uremic toxicity published after a 2003 review of this topic. Eighty-seven records provided serum or blood measurements of one or more solutes in patients with CKD. These records described 32 previously known uremic toxins and 56 newly reported solutes. The articles most frequently reported concentrations of β2-microglobulin, indoxyl sulfate, homocysteine, uric acid, and parathyroid hormone. We found most solutes (59%) in only one report. Compared with previous results, more recent articles reported higher uremic concentrations of many solutes, including carboxymethyllysine, cystatin C, and parathyroid hormone. However, five solutes had uremic concentrations less than 10% of the originally reported values. Furthermore, the uremic concentrations of four solutes did not exceed their respective normal concentrations, although they had been previously described as uremic retention solutes. In summary, this review extends the classification of uremic retention solutes and their normal and uremic concentrations, and it should aid the design of experiments to study the biologic effects of these solutes in CKD.

Effect of different dialysis modalities on microinflammatory status and endothelial damage

BACKGROUND AND OBJECTIVES

We studied the relationship between microinflammation and endothelial damage in chronic kidney disease (CKD) patients on different dialysis modalities.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Four groups of CKD stage 5 patients were studied: 1) 14 nondialysis CKD patients (CKD-NonD); 2) 15 hemodialysis patients (HD); 3) 12 peritoneal dialysis patients with residual renal function >1 ml/min (PD-RRF >1); and 4) 13 peritoneal dialysis patients with residual renal function <or=1 ml/min (PD-RRF <or=1). Ten healthy subjects served as controls. CD14(+)CD16(+) cells and apoptotic endothelial microparticles (EMPs) were measured by flow cytometry. Serum vascular endothelial growth factor (VEGF) was measured by ELISA.

RESULTS

CKD-NonD and HD patients had a higher percentage of CD14(+)CD16(+) monocytes than PD groups and controls. CD14(+)CD16(+) was similar in the PD groups, regardless of their RRF, and controls. The four uremic groups displayed a marked increase in apoptotic EMPs and VEGF compared with controls. Apoptotic EMPs and VEGF were significantly higher in HD patients than in CKD-NonD and both PD groups. However, there were no significant differences between CKD-NonD and the two PD groups. There was a correlation between CD14(+)CD16(+) and endothelial damage in CKD-NonD and HD patients, but not in PD and controls.

CONCLUSIONS

There was an increase in CD14(+)CD16(+) only in CKD-NonD and HD patients. In these patients, there was a relationship between increased CD14(+)CD16(+) and endothelial damage. These results strongly suggest that other factors unrelated to the microinflammatory status mediated by CD14(+)CD16(+) are promoting the endothelial damage in PD, regardless of their RRF.