In Vitro Assessment of Dialysis Membrane as an Endotoxin Transfer Barrier: Geometry, Morphology, and Permeability

The scientific principles and technological determinants of haemodialysis membranes

In most biological or industrial (including medical) separation processes, a membrane is a semipermeable barrier that allows or achieves selective transport between given compartments. In haemodialysis (HD), the semipermeable membrane is in a tubular geometry in the form of miniscule pipes (hollow fibres) and separation processes between compartments involve a complex array of scientific principles and factors that influence the quality of therapy a patient receives. Several conditions need to be met to accomplish the selective and desired removal of substances from blood in the inner cavity (lumen) of the hollow fibres and across the membrane wall into the larger open space surrounding each fibre. Current HD membranes have evolved and improved beyond measure from the experimental membranes available in the early developmental periods of dialysis. Today, the key functional determinants of dialysis membranes have been identified both in terms of their potential to remove uraemic retention solutes (termed ‘uraemic toxins’) as well subsidiary criteria they must additionally fulfill to avoid undesirable patient reactions or to ensure safety. The production of hundreds of millions of kilometres of hollow fibre membranes is truly a technological achievement to marvel, particularly in ensuring that the fibre dimensions of wall thickness and inner lumen diameter and controlled porosity—all so vital to core solute removal and detoxification functions of dialysis—are maintained for every centimetre length of the fragile fibres. Production of membranes will increase in parallel with the increase in the number of chronic kidney disease (CKD) patients expected to require HD therapies in the future. The provision of high-quality care entails detailed consideration of all aspects of dialysis membranes, as quality cannot in any way be compromised for the life-sustaining—like the natural membranes within all living organisms—function artificial dialysis membranes serve.

Exploring the Link Between Hepatic Perfusion and Endotoxemia in Hemodialysis

Introduction

The liver receives gut-derived endotoxin via the portal vein, clearing it before it enters systemic circulation. Hemodialysis negatively impacts the perfusion and function of multiple organs systems. Dialysate cooling reduces hemodialysis-induced circulatory stress and protects organs from ischemic injury. This study examined how hemodialysis disrupts liver hemodynamics and function, its effect on endotoxemia, and the potential protective effect of dialysate cooling.

Methods

Fifteen patients were randomized to receive either standard (36.5°C dialysate temperature) or cooled (35.0°C) hemodialysis first in a two-visit crossover trial. We applied computed tomography (CT) liver perfusion imaging to patients before, 3 hours into and after each hemodialysis session. We measured hepatic perfusion and perfusion heterogeneity. Hepatic function was measured by indocyanine green (ICG) clearance. Endotoxin levels in blood throughout dialysis were also measured.

Results

During hemodialysis, overall liver perfusion did not significantly change, but portal vein perfusion trended towards increasing (P = 0.14) and perfusion heterogeneity significantly increased (P = 0.038). In addition, ICG clearance decreased significantly during hemodialysis (P = 0.016), and endotoxin levels trended towards increasing during hemodialysis (P = 0.15) and increased significantly after hemodialysis (P = 0.037). Applying dialysate cooling trended towards abrogating these changes but did not reach statistical significance compared to standard hemodialysis.

Conclusion

Hemodialysis redistributes liver perfusion, attenuates hepatic function, and results in endotoxemia. Higher endotoxin levels in end-stage renal disease (ESRD) patients may result from the combination of decreased hepatic clearance function and increasing fraction of liver perfusion coming from toxin-laden portal vein during hemodialysis. The protective potential of dialysate cooling should be explored further in future research studies.

Utility Of An Automatic Limulus Amebocyte Lysate Kinetic Turbidimetric Test For Endotoxin Screening Of Dialysate Samples

Background

Endotoxin contamination of dialysate has serious adverse effects on patients undergoing hemodialysis. Therefore, endotoxin activity in dialysate is closely monitored. Limulus amebocyte lysate (LAL) has been used as a reagent to measure endotoxin activity. Here, we investigated the efficacy of an automatic LAL kinetic turbidimetric test (Toxinometer ET-mini) for screening endotoxin activity in dialysate.

Methods

In total, endotoxin activity was measured in 110 dialysate samples obtained from several sites within hemodialysis circuits between June 2012 and March 2018. The results were compared with those from a conventional chromogenic substrate LAL test conducted by a clinical examination laboratory.

Results

Both the automatic LAL test and the chromogenic substrate LAL test had a minimum detection level of 0.001 endotoxin units (EU)/mL. Endotoxin activity levels measured via the automatic LAL test showed a strongly positive correlation (concordance correlation coefficient: 0.9933; 95% CI: 0.9902–0.9954) and good agreement (mean difference: 0.00±0.01 EU/mL) with those obtained using the chromogenic substrate LAL test.

Conclusion

The results suggest that the automatic LAL test may be useful for endotoxin activity screening in hemodialysis facilities.

Endotoxin contamination, a potentially important inflammation factor in water and wastewater: A review

Endotoxins, also referred to as lipopolysaccharides or pyrogens, are major components embedded in the outer cell wall membrane of most Gram-negative bacteria and some cyanobacteria. As common pyrogens and strong immune stimulators, health hazards associated with endotoxins in water and wastewater have been attracting attention in recent years. In this paper, the characteristics, existing forms, and detection assays of endotoxins in water and wastewater are reviewed. Cellular response and pathophysiological effects, and main exposure tracts of endotoxins in water and wastewater are discussed. Levels of endotoxin contamination in water, wastewater, and their aerosols are presented. The removal effects of different water and wastewater treatment processes are summarized. Hence, it is important to: (i) Improve investigations into endotoxin contamination in water and wastewater in order to identify their source, occurrence, and fate. (ii) Implement water and wastewater treatment processes capable of ensuring low levels of endotoxins. This review aims to identify efficient water and wastewater treatment processes capable of ensuring the production of WTPs and WWTPs effluents with a low level of endotoxin activity, and to guarantee the reduction of endotoxin exposure risks to the consumers of water and wastewater.

In vitro assessment of mixed matrix hemodialysis membrane for achieving endotoxin-free dialysate combined with high removal of uremic toxins from human plasma

For a single hemodialysis session nearly 500 L of water are consumed for obtaining pyrogen-free dialysis fluid. However, many efforts are required to avoid biofilm formation in the system and risk of contamination can persist. Water scarcity and inadequate water purification facilities worsen contamination risk in developing countries. Here, we investigated the application of an activated carbon (AC)/polyethersulfone/polyvinylpyrrolidone mixed matrix membrane (MMM) for achieving for the first time endotoxin-free dialysate and high removal of uremic toxins from human plasma with a single membrane. The MMM, thanks to sorbent AC, can remove approximately 10 times more endotoxins from dialysis fluid compared to commercial fibers. Pyrogens transport through the MMM was investigated analyzing inflammation in THP-1 monocytes incubated with samples from the dialysis circuit, revealing safety-barrier properties of the MMM. Importantly, endotoxins from dialysate and protein-bound toxins from human plasma can be removed simultaneously without compromising AC adsorption capacity. We estimated that only 0.15 m² of MMM is needed to totally remove the daily production of the protein-bound toxins indoxyl sulfate and hippuric acid and to completely remove endotoxins in a wearable artificial kidney (WAK) device. Our results could open up new possibilities for dialysis therapy with low water consumption including WAK and where purity and scarcity of water are limiting factors for hemodialysis treatment. STATEMENT OF SIGNIFICANCE: Hemodialysis is a life-sustaining extracorporeal treatment for renal disease, however the production of pyrogen-free dialysate is very costly and water demanding. Biofilm formation in the system worsens bacteria contamination risk. Pyrogens could be transferred into the patients' blood and trigger inflammation. Here, we show for the first time that a mixed matrix membrane composed of polyethersulfone/polyvinylpyrrolidone and activated carbon can achieve simultaneous complete removal of endotoxins from dialysate and high removal of uremic toxins from human plasma without compromising activated carbon adsorption capacity. The mixed matrix membrane could find future applications for simultaneous blood purification and dialysate depyrogenation thus lowering water consumption as for wearable artificial kidney devices and where purity and scarcity of water hamper hemodialysis treatment.

Regulatory Considerations for Hemodiafiltration in the United States

Online hemodiafiltration provides greater removal of higher molecular weight uremic retention solutes than conventional high-flux hemodialysis. However, online hemodiafiltration is used sparsely in the United States in part because of a paucity of delivery systems cleared for clinical use by the US Food and Drug Administration. Although a pathway for regulatory approval exists in the United States, concerns remain, particularly regarding online production of the large volumes of sterile, nonpyrogenic substitution fluid infused directly into the bloodstream to maintain fluid balance. Clearly defined testing protocols, acceptable to Food and Drug Administration, will be useful to show that an online hemodiafiltration system is capable of routinely achieving a sterility assurance level of 10-6 and nonpyrogenic levels of endotoxin. Large-scale clinical experience has shown that systems providing this level of performance when combined with certain design features, such as redundancy, and an appropriate quality management process can routinely and safely produce substitution fluid for online hemodiafiltration.

The Effect of Intra-Dialytic Exercise on Inflammation and Blood Endotoxin Levels

Background: In healthy individuals, an acute inflammatory response occurs after intense exercise due to gut ischaemia and intestinal bacterial endotoxin translocation into the bloodstream. This process maybe exacerbated in patients who exercise during dialysis due to large volume shifts experienced by many during haemodialysis (HD). The acute effect of intra-dialytic exercise on blood endotoxins and inflammation is not known. Method: The effect of intra-dialytic exercise on blood endotoxin and inflammation was investigated in 10 patients and compared with resting haemodialysis. Blood was measured for endotoxin and inflammatory biomarkers before and after dialysis. Result: With the exception of one sample, all samples tested negative for endotoxin. Intra-dialytic exercise attenuated the rise of interleukin-6, tumour necrosis factor-α and high-sensitivity C-reactive protein after the HD procedure. Conclusion: Intra-dialytic exercise was not associated with an observable rise in blood endotoxin, although it may ameliorate the inflammatory effects of the HD procedure. Larger studies are needed to confirm this finding.

Endotoxemia in end-stage kidney disease

Chronic unexplained inflammation remains a prevalent and clinically significant problem for patients with end-stage kidney disease (ESKD), especially in the dialysis population. The causes of persistent inflammation are likely to be multifactorial, but the underlying mechanisms remain to be elucidated. Endotoxins are reported to play a significant role in the pathogenesis of inflammation in patients with ESKD. However, blood endotoxin measurement with the Limulus amoebocyte lysate (LAL) assay is difficult with current detection systems. The reported degree and prevalence of endotoxemia varies in the literature. There are questions as to whether endotoxemia is truly present; whether the varied findings are due to methodological issues with the LAL assay and whether any endotoxemia that might be present plays a role in chronic inflammation frequently observed in ESKD patients. This review will discuss the challenges of accurate blood endotoxin detection, the potential source of blood endotoxins, and the significance of endotoxemia to patient with ESKD.

Endotoxemia after high cutoff hemodialysis for treatment of patient with multiple myeloma can be prevented by using ultrapure dialysate: a case report

To report endotoxemia presented in a case with multiple myeloma (MM) treated by high cutoff hemodialysis (HCO-HD) being prevented by using ultrapure dialysate. A female inpatient with MM received six times HCO-HD (HCO 2100 dialyzer) within 3 weeks after initiation of a chemotherapy based on vincristine+epirubicin+dexamethasone protocol. Conventional dialysate was used in the first three times and then changed to ultrapure dialysate due to elevation of body temperature after HCO-HD. Free light chains (FLC) and endotoxin levels in blood and dialysate were monitored. After six times HCO-HD, her serum FLC λ decreased from 4689 mg/L to 492.7 mg/L, with a trend of decline of serum creatinine. The clearance, reduction ratio, and removal amount of FLC λ was 38.4 mL/min, 71.0-85.2%, and 9.06-18.02 g, respectively, in the setting of dialysate flow rate 500 mL/min, while in the setting of dialysate flow rate 200 mL/min, the removal efficacy of FLC λ was lower than the former. A rise of body temperature up to 38.5°C after treatment and endotoxemia (endotoxin levels 0.122 EU/mL) was found when using conventional dialysate (endotoxin levels 0.112-0.145 EU/mL), but not seen after changing to ultrapure dialysate. Combined with appropriate chemotherapy, HCO-HD can effectively remove and reduce blood FLC. Attention should be paid to the endotoxemia and the rise of temperature after treatment when conventional dialysate is used, which can be prevented by using ultrapure dialysate.