Sorbent Suspensions vs. Sorbent Columns for Extracorporeal Detoxification in Hepatic Failure

Non-Cell-Based Extracorporeal Artificial Liver Systems: Historic Perspectives, Approaches and Mechanisms, Current Applications, and Challenges

BACKGROUND

Liver disease is a growing burden. Transplant organs are scarce. Extracorporeal liver support systems (ELSS) are a bridge to transplantation for eligible patients. For transplant-ineligible patients the objective becomes liver recovery.

METHODS

We review seven decades of non-cell-based ELSS research in humans. Where possible, we emphasize randomized controlled trials (RCTs). When RCTs are not available, we describe the available human clinical data.

RESULTS

There are three broad cell-free approaches to remove protein-bound toxins (PBTs) and treat liver failure. The first is a dialysate binder suspension. A material that binds the PBT (the binder) is added to the dialysate. Binders include albumin, charcoal, and polystyrene sulfonate sodium. The unbound fraction of the PBT crosses the dialyzer membrane along a chemical gradient and binds to the binder. The second approach is using grains of sorbent fixed in a plastic housing to remove PBTs. Toxin-laden blood or plasma flows directly through the column. Toxins are removed by binding to the sorbent. The third approach is exchanging toxin-laden blood, or fractions of blood, for a healthy donor blood product. Most systems lack widespread acceptance, but plasma exchange (PE) is recommended in many guidelines. The large donor plasma requirement of PE creates demand for systems to complement or replace it.

CONCLUSIONS

Now that PE has become recommended in some, but not all, jurisdictions, we discuss the importance of reporting precise PE protocols and dose. Our work provides an overview of promising new systems and lessons from old technologies to enable ELSS improvement.

Recent trends in therapeutic application of engineered blood purification materials for kidney disease

Blood purification is a commonly used method to remove excess metabolic waste in the blood in renal replacement therapy. The sufficient removal of these toxins from blood can reduce complications and improve survival lifetime in dialysis patients. However, the current biological blood purification materials in clinical practice are not ideal, where there is an unmet need for producing novel materials that have better biocompatibility, reduced toxicity, and, in particular, more efficient toxin clearance rates and a lower cost of production. Given this, this review has carefully summarized newly developed engineered different structural biomedical materials for blood purification in terms of types and structure characteristics of blood purification materials, the production process, as well as interfacial chemical adsorption properties or mechanisms. This study may provide a valuable reference for fabricating a user-friendly purification device that is more suitable for clinical blood purification applications in dialysis patients.

Biocompatibility and Cytotoxic Evaluation of New Sorbent Cartridges for Blood Hemoperfusion

BACKGROUND/AIMS

The use of adsorption cartridges for hemoperfusion (HP) is rapidly evolving. For these devices, the potential induced cytotoxicity is an important issue. The aim of this study was to investigate potential in vitro cytotoxic effects of different sorbent cartridges, HA130, HA230, HA330, HA380 (Jafron, China), on U937 monocytes.

METHODS

Monocytes were exposed to the sorbent material in static and dynamic manners. In static test, cell medium samples were collected after 24 h of incubation in the cartridges. In dynamic test, HP modality has been carried out and samples at 30, 60, 90, and 120 min were collected.

RESULTS

Compared to control samples, there was no evidence of increased necrosis or apoptosis in monocytes exposed to the cartridges both in the static and dynamic tests.

CONCLUSION

Our in vitro testing suggests that HA cartridges carry an optimal level of biocompatibility and their use in HP is not associated with adverse reactions or signs of cytotoxicity.

Targeting Albumin Binding Function as a Therapy Goal in Liver Failure: Development of a Novel Adsorbent for Albumin Dialysis

Liver failure results in impaired hepatic detoxification combined with diminished albumin synthesis and is associated with secondary organ failure. The accumulation of liver toxins has shown to saturate albumin binding sites. This was previously demonstrated by an in vitro test for albumin binding capacity (ABiC) that has shown to inversely correlate with the established MELD (Model for End-Stage Liver Disease) score. In this study, we introduced a new adsorbent material for albumin dialysis treatments that improves albumin binding capacity. The new charcoal adsorbent was developed by an evolutionary test schedule. Batch testing of charcoals was performed as steady-state experiments. The charcoal reflecting the highest increase in albumin binding capacity was then introduced to kinetic models: Perfusion tests were designed to evaluate adsorption capacity and kinetics for liver failure marker toxins. A dynamic recirculation model for liver failure was used for upscaling and comparison against conventional MARS adsorbents as the gold standard in an albumin dialysis setting. Batch tests revealed that powdered activated Hepalbin charcoal displayed the highest ABiC score. Hepalbin charcoal also demonstrated higher adsorptive capacity and kinetics for liver failure marker toxins as determined by perfusion tests. These findings translated to tests of upscaled adsorbents in a dynamic model for liver failure: upscaled Hepalbin adsorbent removes bile acids, direct bilirubin and indirect bilirubin significantly better than MARS adsorbents and significantly increases ABiC. The novel adsorbent Hepalbin offers a significant improvement over both MARS adsorbents concerning liver failure marker toxin removal and ABiC improvement.

Alleviating liver failure conditions using an integrated hybrid cryogel based cellular bioreactor as a bioartificial liver support

Conventionally, some bioartificial liver devices are used with separate plasmapheresis unit to separate out plasma from whole blood and adsorbent column to detoxify plasma before it passes through a hepatocytes-laden bioreactor. We aim to develop a hybrid bioreactor that integrates the separate modules in one compact design improving the efficacy of the cryogel based bioreactor as a bioartificial liver support. A plasma separation membrane and an activated carbon cloth are placed over a HepG2-loaded cryogel scaffold in a three-chambered bioreactor design. This bioreactor is consequently connected extracorporeally to a rat model of acute liver failure for 3 h and major biochemical parameters studied. Bilirubin and aspartate transaminase showed a percentage decrease of 20-60% in the integrated bioreactor as opposed to 5-15% in the conventional setup. Urea and ammonia levels which showed negligible change in the conventional setup increase (40%) and decrease (18%), respectively in the integrated system. Also, an overall increase of 5% in human albumin in rat plasma indicated bioreactor functionality in terms of synthetic functions. These results were corroborated by offline evaluation of patient plasma. Hence, integrating the plasmapheresis and adsorbent units with the bioreactor module in one compact design improves the efficacy of the bioartificial liver device.

An adsorbent monolith device to augment the removal of uraemic toxins during haemodialysis

Adsorbents designed with porosity which allows the removal of protein bound and high molecular weight uraemic toxins may improve the effectiveness of haemodialysis treatment of chronic kidney disease (CKD). A nanoporous activated carbon monolith prototype designed for direct blood contact was first assessed for its capacity to remove albumin bound marker toxins indoxyl sulphate (IS), p-cresyl sulphate (p-CS) and high molecular weight cytokine interleukin-6 in spiked healthy donor studies. Haemodialysis patient blood samples were then used to measure the presence of these markers in pre- and post-dialysis blood and their removal by adsorbent recirculation of post-dialysis blood samples. Nanopores (20-100 nm) were necessary for marker uraemic toxin removal during in vitro studies. Limited removal of IS and p-CS occurred during haemodialysis, whereas almost complete removal occurred following perfusion through the carbon monoliths suggesting a key role for such adsorbent therapies in CKD patient care.

A novel approach for blood purification: mixed-matrix membranes combining diffusion and adsorption in one step

Hemodialysis is a commonly used blood purification technique in patients requiring kidney replacement therapy. Sorbents could increase uremic retention solute removal efficiency but, because of poor biocompatibility, their use is often limited to the treatment of patients with acute poisoning. This paper proposes a novel membrane concept for combining diffusion and adsorption of uremic retention solutes in one step: the so-called mixed-matrix membrane (MMM). In this concept, adsorptive particles are incorporated in a macro-porous membrane layer whereas an extra particle-free membrane layer is introduced on the blood-contacting side of the membrane to improve hemocompatibility and prevent particle release. These dual-layer mixed-matrix membranes have high clean-water permeance and high creatinine adsorption from creatinine model solutions. In human plasma, the removal of creatinine and of the protein-bound solute para-aminohippuric acid (PAH) by single and dual-layer membranes is in agreement with the removal achieved by the activated carbon particles alone, showing that under these experimental conditions the accessibility of the particles in the MMM is excellent. This study proves that the combination of diffusion and adsorption in a single step is possible and paves the way for the development of more efficient blood purification devices, excellently combining the advantages of both techniques.

Synthesis, in vitro macrophage response and detoxification of bamboo charcoal beads for purifying blood

Bamboo charcoal beads (BCBs) were formed by coprecipitating bamboo charcoal particles with chitosan in alkaline solution. The amount of chitosan in the BCBs and their surface properties were measured. When 13-52 mg BCBs were exposed to RAW 264.7 macrophages, the amount of nitric oxide released and the cell viability were close to those of the blank. The amount of cytokine IL-6 secreted by macrophages did not depend on the dose of BCBs but macrophages secreted more TNF-alpha in response to higher doses of BCBs. However, the cytokine levels were relatively low, suggesting the favorable biocompatibility of BCBs. In adsorption experiments, BCBs adsorbed and released bovine serum albumin at particular concentrations, whereas BCBs adsorbed L-phenylalanine without a sign of release. This difference is attributed to the hydrophilicity and the pore size of the BCBs. Finally, the potential of BCBs as biocompatible adsorbents in blood detoxification is considered.

Thermodynamic considerations in solid adsorption of bound solutes for patient support in liver failure

New detoxification modes of treatment for liver failure that use solid adsorbents to remove toxins bound to albumin in the patient bloodstream are entering clinical evaluations, frequently in head-to-head competition. While generally effective in reducing toxin concentration beyond that obtainable by conventional dialysis procedures, the solid adsorbent processes are largely the result of heuristic development. Understanding the principles and limitations inherent in competitive toxin binding, albumin versus solid adsorbent, will enhance the design process and, possibly, improve detoxification performance. An equilibrium thermodynamic analysis is presented for both the molecular adsorbent recirculating system (MARS) and fractionated plasma separation, adsorption, and dialysis system (Prometheus), two advanced systems with distinctly different operating modes but with similar equilibrium limitations. The Prometheus analysis also applies to two newer approaches: sorbent suspension reactor and microsphere-based detoxification system. Primary results from the thermodynamic analysis are that: (i) the solute-albumin binding constant is of minor importance to equilibrium once it exceeds about 10(5) L/mol; (ii) the Prometheus approach requires larger solid adsorbent columns than calculated by adsorbent solute capacity alone; and (iii) the albumin-containing recycle stream in the MARS approach is a major reservoir of removed toxin. A survey of published results indicates that MARS is operating under mass transfer control dictated by solute-albumin equilibrium in the recycle stream, and Prometheus is approaching equilibrium limits under current clinical protocols.