Permeability and Adsorption Capacity of Dialysis Membranes to Lipid A

Hemodialysis membranes were tested in vitro for possible penetration by low molecular weight endotoxins containing lipid A. Using lipid A from Escherichia coli as a model substance for this kind of pyrogen, different dialyzers (F4, E3, Acepal 1300, Altraflux, F 40, Polyflux 110, Filtral 12, F 60) were challenged by tangential filtration in aqueous medium. All membranes exhibited impermability to lipid A (as well as to LPS from Pseudomonas aeruginosa), which was proved by additional experiments using culture filtrates of Pseudomonas aeruginosa in bicarbonate dialysis fluid, as well as by employing miniaturized dialyzers with synthetic lipid A as a contaminant. Furthermore, the highest adsorption capacities were found for polysulfone and polyamide membranes.

A Simplified Procedure to Compute Dialysis Time and Frequency by Means of Urea Kinetics

A simplified urea model is presented based on the concept of the time-averaged deviation (TAD) of the blood urea concentration and the introduction of an effective urea generation rate. The increase in the interdialytic blood urea concentration Δc is specific for the individual patient and includes the urea generation rate, distribution volume and residual kidney clearance. By measuring Δc of the largest interdialytic interval of the week the treatment frequency and duration can be calculated. Even for larger residual clearances Kr ≤ 5 ml/min this calculated treatment time does not differ by more than 5 min from the result of the exact urea kinetics. In vivo estimation of the urea clearances versus blood flow for the dialyzer types used is necessary for the application of urea modelling in clinical practice.

Influence of Membranes on Generation of β2 M and Release of Leukocyte Lysosomal Enzymes

Normal leukocyte functional capacity was investigated by evaluation of phagocytosis of opsonised yeast cells in a radiometric test system. After incubation with dialysis membranes (different cellulosic membranes, polysulfon membrane (PS), polymethylmetacrylate membrane (PMMN), the phagocytosis index, expressed as percent decrease with respect to initial values without membrane, decreased by 10%–25%. The most pronounced effect was observed with PS, cuprophane, modified cellulose and PMMA. The results are not related to differences in the viability of PMN during the test procedure; dead PMN amounted to about 4–6.5%. A significant increase in β-NAG and β-Gluc activities was released in the supernatants of the phagocytosis suspensions. This increase activity can be explained by the phagocytosis of PMN but it was not influenced by membrane contact. There was no influence of membrane contact or phagocytosis activity of PMN on the β2M concentration in the supernatant demonstrating that no in vitro generation during incubation with either membrane exists.

Tc-99m-DTPA - a new Test Substance for Detoxification Devices

Tc99m labeled diethylenetriaminepentaacetic acid (Tc-99m-DTPA) is an appropriate in vivo test solute for all extracorporeal detoxification procedures. The molecular weight of the Tc-99m-DTPA complex is within the biologically relevant middle molecular range of 400 to 700 daltons. Tc-99m-DTPA is distributed in the extracellular space in the same way as inulin. Regarding its localization in the gel filtration spectra and plasma clearance, Tc-99m-DTPA corresponds to middle molecule peak 2.

The evaluation of elimination rate and plasma clearance CP of Tc-99m-DTPA is possible by measuring the pulse rates before and after the detoxification device. Taking into account the corrections for Ht and UFR, the Tc-99m-DTPA plasma clearances were calculated for different dialyzers, high flux dialyzers, hemofilters and a hemoperfusion device.

The continuous measurement of pulse rates and the use of a UFR-controller (A2008) allow an exact tracking of CP vs. time, the estimation of CP(QB), CP(UFR) and of the sieving coefficient. Examples are given for these cases.

It was shown that an increase in plasma clearance to more than about 100 ml/min does not greatly increase the Tc-99m-DTPA elimination rate.

Volumetrically Controlled Ultrafiltration. Current Experiences and Future Prospects

Exact control of ultrafiltration (UF) is a prerequisite for high flux dialysis and hemodiafiltration. Volumetric dialysate balancing is the best current method for the use of dialyzers with high water permeabilities. The precision of UF control by volumetric dialysate balancing is in agreement with all medical requirements. A positive influence of volumetric UF control on patients undergoing chronic hemodialysis can be shown by the frequencies of dialysis side effects. Volumetric UF control is only a first step towards an intelligent UF module to correlate water removal, solute removal and sodium balance.

Rotary Cell Culture System (RCCS): A new Method for Cultivating Hepatocytes on Microcarriers

The Rotary Cell Culture System (RCCS) is a new technology for growing anchorage dependent or suspension cells in the laboratory. The RCCS is a horizontally rotated, bubble free disposable culture vessel with diffusion gas exchange. The system provides a reproducible, complex 3D in vitro culture system with large cell masses. During cell growing the rotation speed can be adjusted to compensate for increased sedimentation rates. The unique environment of low shear forces, high mass transfer, and microgravity provides very good cultivating conditions for many cell types, cell aggregates or tissue particles in a standard tissue culture laboratory.

The system enables to culture HepG2 cells on Cytodex 3 microcarriers (mcs) to high densities. We inoculated 2 × 105/ml HepG2 cells and 200 mg Cytodex 3 mcs in 50 ml Williams E medium (incl. 10% FCS) allowing them to attach to the mcs in the rotating vessel (rotation rate 14–20 rpm). HepG2 cells readily attached to the mcs while the vessel was rotating. Attachment of HepG2 to the mcs was about 50% after 24 hrs and 100 % within 48 hrs. After 72 hrs of rotary culturing small aggregates of Hep G2 on mcs were built. HepG2 cells and the aggregates rotated with the vessel and did not settle within the vessel or collide with the wall of the vessel.

We conclude that this new RCCS is an excellent technology for culturing HepG2 cells on Cytodex 3 mcs. The system is easy to handle and enables to culture anchorage dependent cells to high densities in a short period.

Preclinical Evaluation of Haemosorbents

The selection of assessment procedures for the preclinical evaluation of haemosorbents and the relationship between such procedures and the intended application are exemplified by examination of the design and utilization of procedures based on the rat. Procedures are described for haemoperfusion and for membrane plasma separation followed by on-line sorbent treatment of plasma (plasma perfusion).

These procedures are suitable for single or repeated use, with the animal in an unrestrained and conscious state. The relevance to the intended application is demonstrated with respect to artificial liver support by the ability of rat extracorporeal circuits to provide information on the relationship between sorbent properties and liver regeneration as determined by the proliferative response following partial hepatectomy.

Microspheres Based Detoxification System: In Vitro Study and Mathematical Estimation of Filter Performance

Because of the closed plasma (secondary) circuit in the Microspheres based Detoxification System (MDS), a convective blood purification system, the same amount of filtrated plasma is backfiltrated into the blood circuit. Therefore, there is no direct way to determine the ultrafiltrate production rate, which is an important factor of efficiency. The only possible way to estimate the filtration properties of the filter is to consider pressure values. In this study the pressure distribution in the filter was investigated in vitro. To explain the results and to calculate inaccessible parameters, a mathematical model was estabilshed which also considered the asymmetric behaviour of the filter membrane. The result was a linear pressure gradient, agreement with the measurements was reasonably good (calculated primary pressure loss differes <13% from measured value when using mean measured filter resistance as model parameter). Linear pressure distribution offers the possibility of easily calculating the filtration length, a parameter which can be used to estimate the filter condition. The comparison between calculated filtration and backfiltration rates offers an instrument of control for these values.

Detection of Charges and their Distribution on Dialysis Membranes with Cationic/Anionic Dyes Using Confocal Laser Scanning Microscopy

Methods for the detection of positive or negative charges on the surface of biomaterials/membranes and inside a membrane are important for the characterisation of such materials. We tested different dyes and optimized staining procedures. Under standardized conditions negatively charged membranes were stained with cationic triarylmethane compounds such as crystal violet and positively charged membranes with the anionic anthraquinone dye anthralan blue B. There was no staining of uncharged cellulose membranes. The applicability of these methods was demonstrated on membranes coated to varying degrees with charged compounds such as heparin, these changes in charge being detectible quantitatively by photometry. The distribution of charges inside a membrane was detected by optical sectioning across the stained (FITC labelled poly-L-lysine) membrane using confocal laser scanning microscopy (LSM). LSM offers a completely new application possibility in biomaterial and biocompatibility research.

Monocyte Activation and Humoral Immune Response to Endotoxins in Patients Receiving On-Line Hemodiafiltration Therapy

With the on-line preparation of substitution fluid, an easy-to-operate and cost-effective alter-native to conventional hemodiafiltration (HDF) has been realized. The continuous filtration of dialysis fluid, furthermore, allows high volumes of exchange. Microbial contamination and subsequently endotoxins, however, may be present in dialysis fluid, and thus the microbiological safety has become a pivotal issue.

In this clinical study we evaluated the safety of the Fresenius Medical Care on-line HDF system which is based on a two-stage filtration of dialysis fluid with upstream DIASAFE® and downstream on-line HDF filter. During the three-month study period we failed to detect germs or endotoxins in the substitution fluid. Augmented plasma interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα) concentrations were found neither during the intradialytic period nor when pre-session values at study begin and study end were compared. In addition, changes in the anti-endotoxin core antibody levels and soluble CD14 (sCD14) concentration, or pyrogenic episodes were not observed.

On-line HDF with DIASAFE® and on-line HDF filter thus represents a safe treatment modality by effectively depleting dialysis fluid of cytokine-inducing substances.

A Novel Field Generator for Magnetic Stimulation in Cell Culture Experiments

A novel field generator specially designed to examine the influence of low frequency magnetic fields on specific cell material was constructed and characterized. The exposure unit described in this paper consists of a controller unit and three sets of coils. The field generator permits a precious definition of the revelant signal parameters and allows the superposition of alternating current (AC) and direct current (DC) magnetic fields. Critical system parameters were monitored continuously. The three sets of coils, each arranged in the Helmholtz Configuration were characterized. After data processing and visualization the results showed a constant and homogeneous field within the experimental area. The special coil design also allows their use in an incubator.

Protein a Carrying Monosize PMMA Microbeads for the Removal of HlgG from Human Plasma

Protein A-incorporated polymethylmethacrylate (PMMA) microbeads were investigated for specific removal of HlgG from human plasma. The microbeads were prepared by a phase inversion polymerization, and activated by periodate oxidation. Protein A was then incorporated by covalent binding onto these microbeads through hydroxyl groups coming from the stabilizer. The amount of incorporated protein A was controlled by the initial concentrations of protein A in the immobilization medium and pH. The maximum protein A immobilization of 0.615 mg protein A/g PMMA, was observed at a pH of 9.5 corresponding to an initial protein A concentration of 0.1 mg/ml. There was no HlgG adsorption onto the plain PMMA microbeads, while high HlgG adsorptions of up to 32 mg HlgG/g PMMA were achieved with human plasma.

The Microspheres based Detoxification System (MDS): A new extracorporeal blood purification technology based on recirculated microspherical adsorbent particles

Plasma sorption processes have so far been performed with filters and appropriate adsorption columns. In this paper, we introduce a newly developed plasma sorption system, which is based on the high adsorption capacity of microspheres in a recirculation system. The technology has been applied successfully in vitro to eliminate endotoxins, low density lipoproteins (LDL) and barbiturates from human plasma

Comparison of Specific Adsorbents for Tumor Necrosis Factor-α and Therapeutic Anti-Tumor Necrosis Factor-α Antibodies: An in Vitro Sepsis Model

Background

Tumor necrosis factor alpha (TNF-α), as a key mediator, represents a major point of attack in sepsis. Since it has been shown that systemic anti-TNF-α antibodies do not improve the situation of septic patients, the use of specific adsorption technology in the treatment of sepsis could have beneficial effects.

Methods

Magnetic beads coated with polyclonal or with monoclonal anti-TNF-α antibodies were investigated in vitro in order to analyze their ability to prevent TNF-α induced adhesion of peripheral blood mononuclear cells (PBMCs) at human umbilical vein endothelial cells (HUVECs). Additionally, therapeutical monoclonal anti-TNF-α antibodies were proofed for inhibitory effects of TNF-α mediated activation of HUVECs.

Results

We have shown, in vitro, that beads coated with polyclonal or monoclonal anti-TNF-α antibodies were able to significantly reduce monocyte adhesion. It was possible to decrease monocyte adhesion from nearly 9% to 3% within 2 hours and from 18% to 2% within 6 hours of TNF-α treatment by the simultaneous use of beads coated with polyclonal anti-TNF-α antibodies. Beads coated with monoclonal anti-TNF-α antibodies could even prevent monocyte adhesion within the first 2 hours, and reduced monocyte adhesion to 2% during 6 hours of incubation with TNF-α. On the other hand, application of therapeutic anti-TNF-α antibodies showed no significant difference compared to the measured monocyte adhesion values of activated endothelial cells.

Conclusion

Adsorption techniques using specific adsorbents, possibly used in MDS (Microspheres-Based Detoxification System), are efficient in specific reduction of TNF-α and pathophysiological consequences, since monocyte adhesion at activated HUVECs was shown to be reduced. (Int J Artif Organs 2006; 29: 1140–7)

In vitro assessment of charcoal and resin hemoadsorbents

An in vitro assessment has been made of the blood compatibility and efficiency of different charcoal and resin hemoadsorbents. The charcoals vary in source, shape, size, nature and amount of polymer coating. The resins are the macroreticular adsorbents XAD-4 and Y56 and a carbonized resin. The effect on Y56 of albumin coating has been studied. The assessment has demonstrated that a reduction in platelet drop is accompanied by a decrease in the adsorption of fibrinogen. The results confirm the potential advantages of spherical charcoal and that coating with an ultrathin layer of polymer or with albumin does not seriously reduce efficiency. For Y56 resin, treatment with an albumin solution of 1-2 g/100 ml appears to be a suitable procedure if clinical use is considered.

A target-orientated algorithm for regional citrate-calcium anticoagulation in extracorporeal therapies

BACKGROUND

Citrate anticoagulation offers several advantages in comparison to conventional anticoagulation. Most algorithms for regional citrate-calcium anticoagulation are based on citrate and calcium chloride infusion coupled in a fixed proportion to the blood flow without considering the hematocrit (Hct)/plasma flow or the filter clearance of citrate and calcium.

METHODS

The aim of this study was to develop an algorithm for optimized citrate anticoagulation in extracorporeal therapies such as dialysis. A mathematical model was developed to calculate the volume of citrate infusion required to achieve a desired ionized calcium (iCa) target level in the extracorporeal circuit and to restore the total calcium level to a physiological value.

RESULTS

The model was validated by correlation analyses for different blood Hct values and shows an excellent fit to the laboratory measurements.

CONCLUSION

The results for both iCa target concentrations, namely those after citrate and calcium infusion, proved that the software algorithm adapts well to variable treatment parameters.

Anticoagulation in combined membrane/adsorption systems

For extracorporeal blood purification treatments, an effective anticoagulation is needed to avoid contact activation via the intrinsic pathway of the blood-clotting system. While heparin is the standard anticoagulant in dialysis, it shows some disadvantages which have to be considered when it is used in membrane/adsorption-based blood purification systems. An alternative option for anticoagulation in these systems is citrate, which is effective as an anticoagulant by reducing the ionized calcium concentration in the extracorporeal circuit. However, to avoid citrate accumulation in the patient during treatment, the amount of citrate infusion and the citrate removal by the patient's metabolism as well as by dialysis have to be taken into consideration. The aim of this study was to elucidate the characteristics of heparin removal in membrane/adsorption-based blood purification systems, to find the correct way to pre-coat adsorbents in order to avoid excessive adsorption of heparin by anionic exchanging resins, and also to find an appropriate dosage of heparin for treatments with these systems to ensure patient safety. A further aim was to find the correct ionized calcium concentration to suppress complement activation, and to compare different dialysis filters regarding their citrate clearance in order to be able to recommend the correct dialysis setup to achieve appropriate citrate clearance. We were able to show that the adsorptive removal of heparin can be significantly reduced by pre-coating the adsorbents with heparin without a perceptible impact on the adsorption kinetics of bilirubin. Furthermore, we recommend the use of unfractionated heparin due to its lower sieving coefficient and therefore lower removal compared to fractionated heparins. Reducing the extracorporeal Ca(2+) concentration to 0.2 mmol/L by infusion of citrate solution to the extracorporeal circuit results in an effective suppression of the complement activation. To avoid citrate accumulation, we recommend the use of high flux filters when citrate anticoagulation is applied.

New methods for hemoglobin detection in a microparticle-plasma suspension

In the extracorporeal adsorption system, MDS (Microspheres based Detoxification System), micro-adsorbent particles measuring 1-25 micrometers circulate in a filtrate circuit for highly specific blood purification/adsorption. The MDS circuit containing the adsorbent microparticles is linked to the patient's blood line by a hollow fiber plasma filter. When the transmembrane pressure or the shear forces due to the red blood cells in the hollow fiber filter are too high, they can be damaged and hemoglobin will be released. In order to detect free hemoglobin (fHb) by optical means, we have designed a new flow-dynamic filter system, placed in the microadsorbent circuit for continuous separation of microparticles from the filtrate. In the flow dynamic filter, we use a high velocity liquid vortex to remove sedimentation and particle plugs on the filter membrane. In our investigations, 3 and 8 micron cellulose nitrate filter membranes for particle separation are used. The obtained particle free bypass filtrate flow rates are typically 0.5 and 0.8 ml/min respectively. The typical sensitivity for fHb detection by the applied noninvasive optical method is 0.15 g/dL. Medical safety regulations require a fail-safe mechanism for fHb detection which monitors the bypass filtrate flow in the flowdynamic filter and shuts down the system in case of membrane occlusion. The bypass filtrate flow is monitored by periodically occluding and releasing the bypass line by means of a clamp. The resulting back pressure profile gives information about the actual filtration rate. This safety principle was proven by statistical analysis and shows its clear functionality.

Detection of Fluorescently Labeled Microparticles in Blood

BACKGROUND

A microsphere-based detoxification system is an adsorption system, whereby microadsorbent particles having diameters of 1-20 microm circulate in an extracorporeal filtrate circle. A thin-wall hollow-fiber membrane filter separates the microparticle-plasma suspension from the bloodstream. For patient safety, it is necessary to have a means to detect membrane ruptures that could lead to a release of microparticles into the patient's bloodstream.

METHODS

An optical detection system was developed to monitor the venous bloodstream for the presence of microparticles from the filtrate circuit. For detection purposes, cellulose microspheres, both ferromagnetic and fluorescence labeled, were included with the microsphere adsorbant particles. In the case of a membrane rupture, the labeled particles would also be released into the bloodstream. By illuminating a small volume of blood with an excitation wavelength (590 nm) of the fluorescence marker, the particles can be detected by their emission light at 620 nm. The detector sensitivity is increased by collecting the ferromagnetic and fluorescently labeled microparticles using a magnetic trap. The efficiency of magnetic trap arrangements was tested by adjusting the magnet placements.

RESULTS

In vitro experiments were performed by pumping whole blood and labeled microparticles through the fluorescence detector. The efficiency of a magnetic trap arrangement was determined. With an optimal trap setup, 5-10 microl of labeled microparticles can be clearly detected in streaming whole blood.

CONCLUSION

An easy to handle microparticle detector was developed, ready for use in particle based blood detoxification systems. The microparticle detection system fulfills the medical and technical requirements to bring the MDS into clinical tests.

Patient safety technology for microadsorbent systems in extracorporeal blood purification

Alternative technologies for extracorporeal blood purification systems based on microadsorbents in suspension are discussed. Principally, microadsorbents offer higher efficiency and flexibility when compared to conventional column-based adsorption systems. Systems already clinically employed (e.g., BioLogic DT) or close to clinical application (e.g., the microspheres-based detoxification system, MDS) are described. The MDS technology, in particular, is characterized by efficiency and a high degree of flexibility with respect to both the use of different adsorbents as well as the combination with hemodialysis/hemofiltration therapy. It was designed for continuous use in intensive-care units, but enables also the removal of low-density lipoprotein, fibrinogen, autoimmune antibodies, immune complexes, and other pathophysiologically relevant substances. Alternative anticoagulation regimes and safety systems on fluorescence sensor technology have recently been developed for the MDS and are presented in this paper.

Cellular interleukin-1 receptor antagonist production in patients receiving on-line haemodiafiltration therapy

BACKGROUND

Repetitive exposure to cytokine-inducing substances (pyrogens) results in chronic inflammation, which may significantly contribute to some of the long-term complications in dialysis patients. On-line dialysis modalities, such as on-line haemodiafiltration (HDF), raise particular concerns because of the administration of infusate prepared from potentially contaminated dialysis fluid. Hence, great retention capability for pyrogens is of critical importance for the safe performance of on-line systems.

METHODS

The microbiological safety of a novel on-line system, ONLINEplus(TM), was assessed in clinical practice in five centres for 3 months. Infusate and dialysis fluid were regularly monitored for microbial counts, endotoxins, and cytokine-inducing activity. Levels of interleukin-1 receptor antagonist (IL-1Ra) were determined in supernatants of whole blood incubated either under pyrogen-free conditions (spontaneous cytokine production) or following low-dose endotoxin exposure (LPS-stimulated cytokine production).

RESULTS

We failed to detect microorganisms or endotoxin contamination of infusate during the entire study period. Moreover, neither infusate nor dialysis fluid demonstrated cytokine-inducing activity. Intradialytic IL-1Ra induction was not detected, as there was no difference between pre- and post-session values for both spontaneous and LPS-stimulated IL-1Ra production (115+/-26 vs 119+/-27 and 2445+/-353 vs 2724+/-362 pg/10(6) white blood cells (WBC), respectively). Neither the number of immunocompetent cells nor their capacity to produce IL-1Ra declined during this period, indicating that cells were not significantly stimulated during treatment. Spontaneous and LPS-induced exvivo IL-1Ra generation remained unchanged after 3 months of on-line HDF therapy as compared with the start of the study (71+/-30 pre- vs 48+/-14 post-study, and 2559+/-811 vs 2384+/-744 pg/10(6) WBC, respectively).

CONCLUSIONS

The present on-line system performed safely from a microbiological view-point as both the dialysis fluid and infusate were consistently free of microorganisms, endotoxins, and cytokine-inducing substances. As a result, on-line HDF therapy had no effect upon the chronic inflammatory responses in end-stage renal disease patients.

Development of affinity microparticles for extracorporeal blood purification based on crystalline bacterial cell surface proteins

In this article, the development of specific adsorbents for extracorporeal blood purification are described. Affinity microparticles were prepared by linking Protein A to crystalline cell surface layers (S-layers) from Thermoanaerobacter thermohydrosulfuricus 1111-69. S-layers were used in the form of cell wall fragments obtained by breaking whole cells by ultrasonification, resulting in cup-shaped structures (average size 0.5 x 1 microm) completely covered with S-layer protein. Protein A was covalently bound to carboxylic acid groups of the S-layer protein after activation with 1-ethyl-3,3'(dimethylamino)propylcarbodiimide. In batch adsorption experiments with fresh frozen human plasma, the resulting S-layer based affinity microparticles showed a high adsorption capacity for IgG (40 mg IgG were bound per g wet pellet of S-layer based affinity microparticles). Fractions eluted from the microparticles were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. They contained only IgG demonstrating that adsorption was specific. In biocompatibility tests, preparations of the S-layer microparticles showed no low-density lipoprotein-reactivity, no cytotoxicity, and no cytokine inducing activity.

Blood purification by a membrane technique--a new method for the effective removal of low-density lipoprotein cholesterol

A membrane plasma fractionation (MPS) technique is applied in order to obtain selective removal of pathological plasma components from the extracorporeal circuit. An effective plasma fractionation procedure should be characterized by the highest possible removal of the pathological plasma components and, equally as important, the lowest unwanted protein losses caused mainly by adsorption to the membrane structure. In order to obtain a higher efficiency of the MPS procedure (high selectivity between removal of pathological plasma components and unwanted losses mainly represented by albumin) several methods such as thermofiltration, application of pulsate flow at the end of secondary filter, etc. have been developed. Clinical verification of these methods led to some improvement in MPS procedure but these results did not seem to be optimal. The main objective of this paper is to present a new two-stage membrane system utilizing a high flow recirculation circuit developed particularly, but not only, for effective removal of low-density lipoprotein cholesterol. The designed and developed system has been tested in vitro using several different plasma fractionation membranes. The results obtained indicated the importance of the membrane structure and membrane material on the efficiency of the tested plasma fractionation procedure. It was also found that it is possible to obtain negligible protein losses for some selected membrane structures applied in the assessed system. Based on preliminary results, it seems that the new two-stage membrane system proposed could be characterized by a very low range of unwanted protein losses leading to high effectiveness of the plasma fractionation procedure.

A novel configuration of bioartificial liver support system based on circulating microcarrier culture

The purpose of this investigation is to initiate a new bioartificial liver support system that utilizes circulating microcarrier cultures in the extracapillary space of a hollow fiber cartridge. The material exchange occurs on the membranes of the hollow fiber. Toxins are metabolized by the circulating cells on the microcarriers driven by a centrifugal pump. We inoculated 2-3 x 10E8 Hep G2 cells on 2.5 grams of Cytodex 3 microcarriers, and allowed them flowing in the extracapillary space of a modified plasma filter. 10% FCS Medium was pumped through the capillaries at different rates. Cells keep morphological integrity and functionality during the circulation. These preliminary results suggest that this configuration of a bioartificial liver support system offers a future investigation.

Cytokine induction in patients undergoing regular online hemodiafiltration treatment

End-stage renal disease (ESRD) patients are known to suffer from chronic inflammation as the result of an ongoing subacute cytokine induction, which may contribute considerably to dialysis-related, long-term morbidity and mortality. Preparation of infusate from cytokine-inducing dialysis fluid and its administration in large quantities as well as the use of high-flux membranes bear the risk of aggravating the chronic inflammatory response among online hemodiafiltration (online HDF) patients. In order to assess the inflammatory risk associated with online HDF, we compared the cytokine induction profile of ESRD patients receiving either online HDF or low-flux hemodialysis (low-flux HD). Specifically, we measured spontaneous and lipopolysaccharide (LPS)-stimulated tumor necrosis factor alpha (TNFalpha) and interleukin-1 receptor antagonist (IL-1Ra) release during ex vivo incubation of whole blood. Ultrapure dialysis fluid and polysulfone membranes were used for both treatment modalities. LPS-stimulated release of TNFalpha and IL-1Ra was elevated for both online HDF and low-flux HD patients compared to healthy individuals (TNFalpha: 2,336 +/- 346 and 2,192 +/- 398 versus 1,218 +/- 224 pg/106 white blood cells [WBC]; IL-1Ra: 2,410 +/- 284 and 2,326 +/- 186 versus 1,678 +/- 219 pg/106 WBC). Likewise, spontaneous production of TNFalpha, but not IL-1Ra, was higher in online HDF and low-flux HD patients than in normal controls (37 +/- 32 and 22 +/- 19 versus 0.8 +/- 0.3 pg TNFalpha/106 WBC). There was no difference in spontaneous and LPS-stimulated cytokine release between both dialysis groups. In addition, intradialytic cytokine induction was not significant for either treatment modality as spontaneous and LPS-stimulated cytokine release were not increased postdialysis. These findings indicate that online HDF does not contribute to chronic leukocyte activation and, consequently, does not place ESRD patients at greater risk with respect to inflammatory morbidity and mortality.

Novel online infusate-assisted dialysis system performs microbiologically safely

Administration of adequate amounts of commercial infusion fluids renders modern convective dialysis modalities, such as hemodiafiltration, labor-intensive and costly. Preparation of infusate by cold sterilization of dialysis fluid, which is abundantly available, and its immediate (online) use, in contrast, enables a large volume fluid exchange in a cost-effective manner. Recent developments aimed at more hygienic and user-friendly online systems with increased operational flexibility. As a result the novel ONLINEplus system does not only provide online prepared infusate for convective dialysis therapy, but also for priming and rinsing of the extracorporeal blood circuit, for intradialytic bolus administration, and for re-infusion of patients' blood as well. Production of infusate from potentially impure dialysis fluid containing endotoxins and other pyrogens raises severe concerns of affecting the patients' well-being. To assess its safety, the online system was challenged with microbially contaminated dialysis fluid. Despite high levels of microbial counts (7.5 x 104 +/- 105 CFU/ml), endotoxin concentration (14.1 +/- 7.7 IU/ml and 9.265 +/- 3.000 IU/ml, as measured turbidimetrically and chromogenically, respectively) and cytokine-inducing activity (20,827 +/- 3,082 pg IL-1Ra/Mio WBC), we failed to detect contaminants in the final infusate during a 5 week laboratory testing period. In addition, infusate samples complied consistently with the European Pharmacopeia test for sterility. The present online system is comprehensive, operates user-friendly, and provides microbiologically safe infusate in large quantities. In this way, both patients and dialysis staff will benefit from improved dialysis therapy and reduced treatment-related labor burden, respectively. Moreover, convective dialysis modalities will become less expensive.

Can sterile and pyrogen-free on-line substitution fluid be routinely delivered? A multicentric study on the microbiological safety of on-line haemodiafiltration

BACKGROUND

Microbial contamination is characterized not only by the presence of bacteria, but also by high concentrations of biologically active by-products. They are potentially able to cross ultrafiltration and dialysis membranes and stimulate immunocompetent blood cells to synthesize cytokines. In turn, cytokine induction causes acute symptoms and has been incriminated in the long-term complications of haemodialysis patients. Infusion of large volumes of substitution fluids following ultrafiltration of microbially contaminated dialysis fluids may place patients on on-line therapies at particular risk.

METHODS

In this study we evaluated 30 machines with a two-stage ultrafiltration system in routine clinical haemodiafiltration settings in six centres for 6 months. Microbiological safety was assessed monthly and at the last use of the filters by determining microbial counts, endotoxin concentration and cytokine-inducing activity.

RESULTS

No pyrogenic episodes were observed during the study period. Double-filtration of standard dialysis fluid (range, <1-895 cfu/ml, 0.0028-4.6822 IU/ml) resulted in sterile substitution fluids with endotoxin concentrations well below the Ph.Eur. standard for haemofiltration solutions (range, 0.0014-0.0281 vs 0.25 IU/ml). Moreover, they did not differ from commercial haemofiltration solutions and depyrogenated saline. Likewise, there was no difference in the cytokine-inducing activity between the solutions tested. The high microbiological quality of the ultrafiltered dialysis fluid, which was in the same range as substitution fluid, translates into both the absence of cytokine induction by dialyser back-transport and a redundant safety mode of the on-line system by a second filtration step.

CONCLUSION

On-line HDF treatment can routinely be provided with ultra-pure dialysis fluids and sterile substitution fluids at pyrogen-free levels. The online preparation of substitution fluids thus can be considered microbiologically safe.

Rotary cell culture system (RCCS): a new method for cultivating hepatocytes on microcarriers

The Rotary Cell Culture System (RCCS) is a new technology for growing anchorage dependent or suspension cells in the laboratory. The RCCS is a horizontally rotated, bubble free disposable culture vessel with diffusion gas exchange. The system provides a reproducible, complex 3D in vitro culture system with large cell masses. During cell growing the rotation speed can be adjusted to compensate for increased sedimentation rates. The unique environment of low shear forces, high mass transfer, and microgravity, provides very good cultivating conditions for many cell types, cell aggregates or tissue particles in a standard tissue culture laboratory. The system enables to culture HepG2 cells on Cytodex 3 microcarriers (mcs) to high densities. We inoculated 2 x 10(5)/ml HepG2 cells and 200 mg Cytodex 3 mcs in 50 ml Williams E medium (incl. 10% FCS) allowing them to attach to the mcs in the rotating vessel (rotation rate 14-20 rpm). HepG2 cells readily attached to the mcs while the vessel was rotating. Attachment of HepG2 to the mcs was about 50% after 24 hrs and 100 % within 48 hrs. After 72 hrs of rotary culturing small aggregates of Hep G2 on mcs were built. HepG2 cells and the aggregates rotated with the vessel and did not settle within the vessel or collide with the wall of the vessel. We conclude that this new RCCS is an excellent technology for culturing HepG2 cells on Cytodex 3 mcs. The system is easy to handle and enables to culture anchorage dependent cells to high densities in a short period.

In vitro cell culture systems as the basis for an extracorporeal blood purification strategy in multiorgan failure treatment

Multiorgan failure (MOF) based on septic processes is very common but prognostically an extremely severe disease that has to be treated exclusively under intensive care conditions. Extracorporeal blood purification (ECBP) using specific and efficient systems such as the microspheres based detoxification system (MDS) (Artif Organs 1996;20:420) could improve significantly the situation of MOF in terms of the efficient removal of endotoxins as well as key mediators such as tumor necrosis factor alpha (TNF alpha). The purpose of the study was to test the effectiveness of endotoxin and cytokine removal to blunt cellular response. In terms of the in vitro principle methodology, isolated peripheral blood mononuclear cells (PBMC) were incubated with endotoxins and a selective endotoxin adsorbent, which was added at various times (immediately or 30, 60, 120, 240, or 360 min) after the onset of incubation. TNF alpha release of monocytes was measured following a standard procedure after 20 h. Human TNF alpha was incubated with cultured human endothelial cells with and without a specific TNF alpha adsorbent (polyclonal antibodies coated on polystyrene particles). The results showed that after the initial addition of endotoxins, the activation of monocytes can be stopped within 120 min by addition of endotoxin adsorbents. In addition, specific TNF alpha adsorbents are able to prevent intercellular adhesion molecule 1 (ICAM-1) expression of endothelial cells, therefore avoiding activation of endothelial cells. In conclusion, cell culture models are suitable to simulate cell interaction in MOF. Specific adsorbents are able to reduce or block pathophysiologically relevant cell interactions, and the time frame for effective ECBP seems to be very short, and therefore, efficiency must be high.

Microspheres based detoxification system: in vitro study and mathematical estimation of filter performance

Because of the closed plasma (secondary) circuit in the Microspheres based Detoxification System (MDS), a convective blood purification system, the same amount of filtrated plasma is backfiltrated into the blood circuit. Therefore, there is no direct way to determine the ultrafiltrate production rate, which is an important factor of efficiency. The only possible way to estimate the filtration properties of the filter is to consider pressure values. In this study the pressure distribution in the filter was investigated in vitro. To explain the results and to calculate inaccessible parameters, a mathematical model was established which also considered the asymmetric behaviour of the filter membrane. The result was a linear pressure gradient, agreement with the measurements was reasonably good (calculated primary pressure loss differs <13% from measured value when using mean measured filter resistance as model parameter). Linear pressure distribution offers the possibility of easily calculating the filtration length, a parameter which can be used to estimate the filter condition. The comparison between calculated filtration and backfiltration rates offers an instrument of control for these values.

Fractionated plasma separation and adsorption system: a novel system for blood purification to remove albumin bound substances

The removal of albumin bound substances has gained increasing interest in different diseases, especially in acute and chronic liver disease. Therefore, a new system, the fractionated plasma separation and adsorption (FPSA) system, was developed based on combined membrane and adsorbent blood purification techniques. The most important contribution to the FPSA system was the development of a new polysulfone hollow-fiber filter, which is characterized by a sieving coefficient of 0.89 for human serum albumin (HSA) but only of 0.17 for fibrinogen, and 0 (zero) for IgM immunoglobulins. Using a closed filtrate circuit connected to the new polysulfone filter which integrates 1 or 2 adsorption columns and also a high flux dialyzer adapted to a dialysis machine, the FPSA system opens excellent possibilities for the relatively specific removal of albumin bound substances from the blood such as albumin bound bilirubin or even tryptophan. In comparison to other systems (for example, the Molecular Adsorbent Recirculating System [MARS] and albumin dialysis systems), the FPSA system enables much higher elimination of strongly bound albumin substances. The first clinical investigations have recently started based on a modified dialysis machine designed with all necessary safety measures.

Monocyte activation and humoral immune response to endotoxins in patients receiving on-line hemodiafiltration therapy

With the on-line preparation of substitution fluid, an easy-to-operate and cost-effective alternative to conventional hemodiafiltration (HDF) has been realized. The continuous filtration of dialysis fluid, furthermore, allows high volumes of exchange. Microbial contamination and subsequently endotoxins, however, may be present in dialysis fluid, and thus the microbiological safety has become a pivotal issue. In this clinical study we evaluated the safety of the Fresenius Medical Care on-line HDF system which is based on a two-stage filtration of dialysis fluid with upstream DIASAFE and downstream on-line HDF filter. During the three-month study period we failed to detect germs or endotoxins in the substitution fluid. Augmented plasma interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) concentrations were found neither during the intradialytic period nor when pre-session values at study begin and study end were compared. In addition, changes in the anti-endotoxin core antibody levels and soluble CD14 (sCD14) concentration, or pyrogenic episodes were not observed. On-line HDF with DIASAFE and on-line HDF filter thus represents a safe treatment modality by effectively depleting dialysis fluid of cytokine-inducing substances.