Endotoxins adsorption

Samples should be collected aseptically in nonpyrogenic containers. Reused depyrogenate glassware or sterile, disposable polystyrene plastics are recommended to minimize adsorption of endotoxin. 

Due to the high DNA and endotoxin levels a second Q-step was added as a safety net. The pH was adjusted to 4.7, such that the vaccine product would flow through while the DNA and endotoxins would be retained. The low pH allowed sequential adsorption onto a carboxyl (C) membrane (Sartorius Corp.). A stepwise citrate pH gradient showed elution of the product at pH 5.5 (Fig. 11). 

Adsorption of inflammatory cytokines and endotoxin by mesoporous polymers and activated carbons... 

Adsorbents are used in medicine mainly for the treatment of acute poisoning, whereas other extracorporeal techniques based on physico-chemical principles, such as dialysis and ultrafiltration, currently have much wider clinical applications [1]. Nevertheless, there are medical conditions, such as acute inflammation, hepatic and multi-organ failure and sepsis, for which mortality rates have not improved in the last forty years. These conditions are usually associated with the presence of endotoxin - lipopolysaccharide (LPS) or inflammatory cytokines - molecules of peptide/protein nature [2]. Advantages of adsorption over other extracorporeal techniques include ability to adsorb high molecular mass (HMM) metabolites and toxins. Conventional adsorbents, however, have poor biocompatibility. They are used coated with a semipermeable membrane of a more biocompatible material to allow for a direct contact with blood. Respectively, ability of coated adsorbents to remove HMM solutes is dramatically reduced. In this paper, preliminary results on adsorption of LPS and one of the most common inflammatory cytokines, TNF-a, on uncoated porous polymers and activated carbons, are presented. The aim of this work is to estimate the potential of extracorporeal adsorption technique to remove these substances and to relate it to the porous structure of adsorbents. 

The PSDs calculated by the CONTIN procedure and the Micromeritics DFT are similar i.e., represented estimations of f(x) are quite reliable, which are in agreement with the structural parameters calculated by the DS method. Notice that the availability of broad mesopores x < 50 nm and transport pores at x > 50 nm (Fig. 1, a and b) is important with respect to adsorption of such biopol5mier molecules cis endotoxins or inflammatory c)nokines of peptide/protein nature. 

Hou, K.C. Zaniewski, R. The effect of hydrophobic interaction on endotoxin adsorption by polymeric affinity matrix. Biochem. Biophys. Acta 1991, 1073, 149-154. 

A number of studies have investigated interferences with the LAL assay and have attempted to optimize the assay (Douwes et al., 1995 Hollander et al., 1993 Thorne et al., 1997). These studies have demonstrated that results may vary depending upon the sample matrix, the extraction method and the assay method. Other constituents present in the sample may interfere with the LAL assay and cause inhibition or enhancement of the test or aggregation and adsorption of endotoxins, resulting in under- or over-estimation of the concentration. Techniques such as spiking with known quantities of purified endotoxin and analysis of dilution series of the same sample have been described to deal with these interferences (Hollander et al., 1993 Milton et al., 1990 Milton et al., 1992 Whitakker, 1988). Studies in the laboratories of the authors of this chapter have demonstrated within-Iaboratory coefficients of variation between 15 % and 20 % in routine assay work. When extra care is taken to optimize precision this can be reduced to under 5 % in the endpoint chromogenic assay (Thorne, unpublished data). Several interlaboratory comparison studies have been performed and demonstrate much greater variability. One in-depth comparison of two laboratories experienced in the LAL assay. 

MWCO may be able to prevent transport of antibodies, but it is not possible to block all components of the immune system while still allowing nutrient transport. Hydrophilic materials tend have a higher biocompatibility as they resist protein adsorption. Protein adsorption can initiate a cascade of events culminating in fibrotic encapsulation of the capsule as discussed in a recent review. The use of natural materials for the capsule increases the risk of triggering an immune response due to antigens in the material or insufficient removal of immunogenic compounds from the material such as endotoxin. 

Polyethyleneimine (PEI) (Scheme 3) was immobilized onto cellulose fibers by a crosslinking agent glutaraldehyde (21). 10-60 wt% of PEI was attached by varying the mass ratio of PEI to cellulose. The cellulose-PEI fibers with 20-60 wt% of PEI adsorbed up to 10 mg endotoxin per g of modified fibers and could remove 90-100% endotoxin from 500 ng/ml endotoxin solution at pH 7.0 and ionic strengths lower than 0.4. In addition, the cellulose-PEI fibers with 20 wt% PEI showed selective removal activity toward endotoxins from various protein solutions at pH 7 and 0.05 ionic strength. This selective adsorption was due to simultaneous effects of cationic properties of amino groups and... 

Sawada Y, Fuji R, Iqami I et al. The adsorption of endotoxin molecules in a microporous polyethylene hollow fiber membranes. J Hyg 1986 97 97-102. 

Fig. 13.6 Endotoxin adsorption at the inner layer of a membrane made of a polysulfone/poyl vinylpyrroUdone blend. This adsorption capacity prevents endotoxins possibly originating from contaminated dialysis fluid to enter the patient s blood stream...

Weber and coworkers were able to show in an in vitro model, that endotoxin adsorption depends both, on chemical composition and the manufacturing process of the membrane [30], In fact, hydrophobic parts of the lipopolysaccharide molecule (LPS, endotoxin) are considered to interact with hydrophobic entities within the pol-ysulfone structure thereby facilitating their removal [29] (Tables 13.3 and 13.4). 

As a summary, it is possible to improve both, blood compatibility and the adsorption of dialysate contaminants, such as endotoxins, through a chemical modification of the membrane poly-mer, as realized in some polysuHone dialysis membranes. 

Clinical parameters related to polymers apphed in dialyzers refer to blood compatibility and biostability. Membrane polymers should have adsorptive capacity for specific uremic retention products, even when these are unknown yet [59]. Adsorption of endotoxins [27-30] and of anaphyla-toxins, such as C3a and C5a [34] have considerably contributed to the safety and biocompalibility of dialysis treatments. 

Results are already available as some polymers used for dialysis membranes exhibit intrinsic and specific adsorptive features for endotoxins [27-30], complement proteins or even unknown peptides [59]. 

Nakatani, T., Tsuchida, K., Sugimura, K., Yoshimura, R., Takemoto, Y. Investigation of endotoxin adsorption with polyether polymer alloy dialysis membranes. Int. J. Mol. Med. 11, 195-197 (2003)... 

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