Endotoxin removal from aqueous solutions with dimethylamine-functionalized graphene oxide: Modeling study and optimization of adsorption parameters

Lysozyme-Immobilized Polyethersulfone Membranes with Satisfactory Hemocompatibility and High Enzyme Activity for Endotoxin Removal

Endotoxin adsorption has received extensive attention in the field of blood purification. However, developing highly efficient endotoxin adsorbents with excellent hemocompatibility remains challenging. In this study, we propose a new approach for developing the functional polyethersulfone (PES) membrane to remove endotoxins. First, the PES polymer is grafted with polyethylene glycol methyl acrylate (PEG-MA) in a homogeneous phase system via γ irradiation, and PES-g-PEG can be directly used to prepare the membrane by the phase inversion method. Then, polydopamine (PDA) is coated as an adhesive layer onto a PES-g-PEG membrane in an alkaline aqueous solution, and lysozyme (Lyz) is covalently immobilized with PDA through the Schiff base reaction. Lysozyme acts as an affinity adsorption ligand of endotoxin through charge and hydrophobic action. Our study reveals that the PEG branched chain and the PDA coating on the PES membrane can maintain the secondary structure of lysozyme, and thus, the immobilized Lyz can maintain high activity. The adsorption capacity of endotoxins for the PES-g-PEG/PDA/Lyz membrane is 1.28 EU/mg, with an equilibrium adsorption time of 6 h. Therefore, the PES-g-PEG/PDA/Lyz membrane shows great potential application in the treatment of endotoxemia.

Preparation of chitin/MXene/poly(L-arginine) composite aerogel spheres for specific adsorption of bilirubin

Currently, hemoperfusion is clinically the most rapid and effective treatment for removing toxins from the blood. The core of hemoperfusion is the sorbent inside the hemoperfusion device. Due to the complex composition of the blood, adsorbents tend to adsorb substances such as proteins in the blood (non-specific adsorption) while adsorbing toxins. Hyperbilirubinemia is caused by excessive levels of bilirubin in the human blood, causing irreversible damage to the patient's brain and nervous system, and even leading to death. High adsorption and high biocompatibility adsorbents with specific bilirubin adsorption are urgently needed to treat hyperbilirubinemia. Herein, poly(L-arginine) (PLA) which can specifically adsorb bilirubin, was introduced into chitin/MXene (Ch/MX) composite aerogel spheres. Ch/MX/PLA prepared by supercritical CO₂ technology had higher mechanical properties than Ch/MX and can withstand 50,000 times its own weight. The in vitro simulated hemoperfusion test showed that the adsorption capacity of Ch/MX/PLA was as high as 596.31 mg/g, which was 15.38 % higher than that of Ch/MX. Binary and ternary competitive adsorption tests showed that Ch/MX/PLA also had good adsorption capacity in the presence of a variety of interfering molecules. In addition, hemolysis rate testing and CCK-8 testing confirmed that Ch/MX/PLA had better biocompatibility and hemocompatibility. Ch/MX/PLA can meet the required properties of clinical hemoperfusion sorbents and has the ability to produce mass production. It has good application potential in the clinical treatment of hyperbilirubinemia.

Plant produced endotoxin binding recombinant proteins effectively remove endotoxins from protein samples

Lipopolysaccharides (LPS) are highly toxic compounds, even at a trace amount. When recombinant proteins are produced in E. coli, it is inevitable that LPS contaminates. However, LPS removal is still technically challenging and costly due to the high degree of solubility in a wide range of solvents. In this study, we explored the possibility of using the N-terminal region containing cysteine-rich, EGF-like, and sushi1–3 domains (CES3) of Factor C from the horseshoe crab Carcinoscorpius rotundicauda to develop a platform to remove LPS from recombinant proteins. We expressed CES3 as part of a recombinant protein, BiP:NT:CBM3:SUMO:CES3:His:HDEL, in Nicotiana benthamiana and found that purified or microcrystalline cellulose (MCC) bead-immobilised CES3 showed strong binding to LPS-containing E. coli. To produce CES3:CBM3 in an LPS-free environment, we generated Arabidopsis transgenic plants harbouring a recombinant gene, BiP:NT:SUMO:CES3:CBM3:HDEL, and found that transgenic plants mainly produce CES3:CBM3:His:HDEL, a truncated version of BiP:NT:SUMO:CES3:CBM3:HDEL via endogenous protease-mediated proteolytic processing in vivo. CES3:CBM3:HDEL purified from Arabidopsis plant extracts and immobilised onto MCC beads removed LPS contamination from protein samples. We propose that the CES3:CBM3 fusion protein produced in plants and immobilised on MCC beads can be a robust and easy platform for LPS removal from recombinant proteins.

Ultraporous Polyquaternium-Carboxylated Chitosan Composite Hydrogel Spheres with Anticoagulant, Antibacterial, and Rapid Endotoxin Removal Profiles for Sepsis Treatment

Hemoperfusion is an important method to remove endotoxins and save the lives of patients with sepsis. However, the current adsorbents for hemoperfusion have disadvantages of insufficient endotoxin adsorption capacity, poor blood compatibility, and so on. Herein, we proposed a novel emulsion templating (ET) method to prepare ultraporous and double-network carboxylated chitosan (CCS)-poly(diallyl dimethylammonium chloride) (PDDA) hydrogel spheres (ET-CCSPD), bearing both negative and positive charges. CCS was introduced to balance the strong positive charges of PDDA to improve hemocompatibility, and emulsion templates endowed the adsorbent with an ultraporous structure for enhanced adsorption efficacy. The ET-CCSPDs neither damaged blood cells nor activated complement responses. In addition, the activated partial thromboplastin time (APTT) was prolonged to 8.5 times, which was beneficial for reducing the injection of anticoagulant in patients. The ET-CCSPDs had excellent scavenging performance against bacteria and endotoxin, with removal ratios of 96.7% for E. coli and 99.8% for S. aureus, respectively, and the static removal ratio of endotoxin in plasma was as high as 99.1% (C₀ = 5.50 EU/mL, critical illness level). An adsorption cartridge filled with the ET-CCSPDs could remove 84.7% of endotoxin within 1 h (C₀ = 100 EU/mL in PBS). Interestingly, the ET-CCSPDs had a good inhibitory effect on the cytokines produced by endotoxin-mediated septic blood. By developing the ET method to prepare ultraporous and double-network adsorbents, the problems of low adsorption efficiency and poor blood compatibility of traditional endotoxin adsorbents have been solved, thus opening a new route to fabricate absorbents for blood purification.

Occurrence and fate of bacterial endotoxins in the environment (air, water, wastewater) and remediation technologies: An overview

Endotoxins as the outer membrane of most Gram-Negative Bacteria (GNB) and typical toxic biochemical produced by microorganisms are identified as one of the emerging pollutants. These microbial by-products are harmful compounds that can be present in various environments including air, water, soil, and other ecosystems which was discussed in detail in this review. Environmental and occupational exposure caused by endotoxin occurs in water and wastewater treatment plants, industrial plants, farming, waste recovery, and composting facilities. Even though the health risk related to endotoxin injection in intravenous and dialysis are well identified, the harmful effects of ingestion, inhalation, and other way of exposure are not well quantified and there is insufficient information on the potential health risks of endotoxins exposure in water environments, and another exposures. Because of limited studies, the outbreaks of diseases related to endotoxins in the various source of exposure not been well documented. Endotoxin removal from different environments are investigated in this review. The results of various studies have shown that conventional treatment methods have been unable to remove endotoxins from water and wastewater, therefore, monitoring the effectiveness of these processes in controlling this contaminant and also using the appropriate removal method is essential. However, management of water and wastewater treatment processes and the use of advanced processes such as Advanced Oxidation Processes (AOPs) can be effective in monitoring and reducing endotoxin levels during water and wastewater treatment. One of the limitations of endotoxin monitoring is the lack of sufficient information to develop monitoring levels. In addition, the lack of guidelinesand methods of controlling them at high levels may cause irreparable disaster.

Preparation and characterization of polymyxin B- and histidine-coupled magnetic nanoparticles for purification of biologics from acquired endotoxin contamination

Background

Endotoxin is a major process-related impurity that can act as a strong immunostimulant leading to fever and hypotensive shock. Thus, the US FDA and international quality standards strictly direct the biologics manufacturers to control the endotoxin contamination during the purification process. In this work, a developed method for biologics purification from acquired endotoxin contamination is introduced. This is accomplished by the preparation of dextran-coated magnetic nanoparticles using a facile rapid co-precipitation method.

Results

The resulting magnetic nanoparticles (MNPs) are characterized by dynamic light scattering, transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The dextran-coated magnetic nanoparticles are further coupled to either polymyxin B or histidine to provide a positively charged ligand which enhances the affinity to the negatively charged endotoxin. Both ligands-coupled MNPs are tested for purification efficiency using the chromogenic kinetic assay. The method conditions are optimized using a two-level factorial design to achieve best purification conditions of the contaminated biologics and indicated endotoxin removal percentage 85.12% and maximum adsorption capacity of 38.5 mg/g, for histidine-coupled MNPs.

Conclusions

This developed method is introduced to serve biologics manufacturers to improve their manufacturing processes through providing a simple purifying tool for biologics from acquired endotoxin contamination.

Graphical Abstract

Advances in the Development of Biomaterials for Endotoxin Adsorption in Sepsis

Sepsis, a life-threatening and intractable disease without any specific treatment, is activated by endotoxin. Some attempts at removing endotoxin to treat sepsis from the blood circulation using different hemoperfusion cartridges have been proposed recently, but they have failed to reduce the mortality of severe septic patients. This review summarizes the latest advances in the development of endotoxin adsorbents. In particular, we highlight two critical parameters for endotoxin adsorbents when they are applied in blood purification: the dissociation constant and the maximum adsorption capacity. We also discuss potential challenges and research directions for the future development of endotoxin adsorbents.

Surface Modification of Reduced Graphene Oxide Beads: Integrating Efficient Endotoxin Adsorption and Improved Blood Compatibility

As a pathogenic toxin, endotoxins are the culprit for endotoxemia and can be generally removed from the blood by hemoperfusion. Reduced graphene oxide (rGO) is a promising endotoxin sorbent for hemoperfusion owing to its excellent adsorption capacity, but it has the side effect of nonspecific adsorption and low blood compatibility. Polymyxin B (PMB) acts as an organic affinity ligand that can specifically bind endotoxins. As a natural anticoagulant, heparin (Hep) can reduce the risk of coagulation and improve the blood compatibility of materials. Herein, an rGO bead adsorbent was prepared by coupling with PMB and Hep and used for endotoxin adsorption; in this, polydopamine (pDA) served as an active coating for immobilization of PMB and further coupling with Hep. The physicochemical characteristics indicated that PMB and Hep were successfully immobilized on rGO beads with a hierarchical pore structure. PMB endowed rGO beads with higher adsorption capacity (143.84 ± 3.28 EU/mg) and good adsorption selectivity for endotoxins. Hep significantly improved the blood compatibility of rGO beads. These modified rGO beads also achieved good adsorption capacity and adsorption selectivity for endotoxins in plasma, serum, or blood. Therefore, rGO/pDA/PMB/Hep beads are potential adsorbents for endotoxins in hemoperfusion.

Magnetic carnosine-based metal-organic framework nanoparticles: fabrication, characterization and application as arsenic adsorbent

This study centers on the controllable synthesis, characterization, and application of a novel magnetic bio-metal-organic framework (Bio-MOF) for the adsorption and subsequent removal of arsenic from aqueous solutions. Zinc ions and carnosine (Car) were exploited to construct the Car-based MOF on the surface of magnetite (Fe₃O₄ NPs). The Magnetite precoating with Car led to an increase in the yield and the uniform formation of the magnetic MOF. The prepared magnetic Bio-MOF nanoparticles (Fe₃O₄-Car-MOF NPs) had semi-spherical shape with the size in the range of 35-77 nm, and the crystalline pattern of both magnetite and Car-based MOF. The NPs were employed as an adsorbent for arsenic (As) removal. The adsorption analyses revealed that all studied independent variables including pH, adsorbent dose, and initial arsenic concentration had a significant effect on the arsenic adsorption, and the adsorption data were well matched to the quadratic model. The predicted adsorption values were close to the experimental values confirming the validity of the suggested model. Furthermore, adsorbent dose and pH had a positive effect on arsenic removal, whereas arsenic concentration had a negative effect. The adsorption isotherm and kinetic studies both revealed that As adsorption fitted best to the Freundlich isotherm model. The maximum monolayer adsorption capacity (94.33 mg/g) was achieved at room temperature, pH of 8.5 and adsorbent dose of 0.4 g/L. Finally, the results demonstrated that the adsorbent could be efficiently applied for arsenic removal from aqueous environment.

pH-Dependent adsorption of aromatic compounds on graphene oxide: An experimental, molecular dynamics simulation and density functional theory investigation

This work provides a comprehensive understanding for the pH-dependent adsorption of aromatic compounds (ACs) on graphene oxide (GO). Isothermal and kinetics experiments indicated both adsorption capacity and adsorption rate were suppressed at higher pH, and the mechanisms were revealed by molecular dynamics simulations and density functional theory calculations. More specifically, π-π, hydrogen bond, vdWs, and water-mediated steric hindrance interactions were examined to reveal how pH affected the adsorption capacity, and microscopic dynamic adsorption process was captured to reveal how pH affected the adsorption rate. Results showed the reduced adsorption capacity at higher pH was mediated by increased electrostatic repulsion, weakened π-π interaction, and increased water-mediated steric hindrance. The pH-dependent behaviour of GO was responsible for the effect of pH on adsorption rate. Self-aggregation of GO at lower pH helped to capture ACs and created more favourable adsorption sites. Upon the adsorption of ACs on GO, GO/water/AC/water/GO sandwich-like structure formed, which was also mediated by solution pH. Overall, pH affects the adsorption of ACs on GO by regulating driving forces, adsorption process, and the configuration property of GOAC complex.

Current technologies to endotoxin detection and removal for biopharmaceutical purification

Endotoxins are the major contributors to the pyrogenic response caused by contaminated pharmaceutical products, formulation ingredients, and medical devices. Recombinant biopharmaceutical products are manufactured using living organisms, including Gram-negative bacteria. Upon the death of a Gram-negative bacterium, endotoxins (also known as lipopolysaccharides) in the outer cell membrane are released into the lysate where they can interact with and form bonds with biomolecules, including target therapeutic compounds. Endotoxin contamination of biologic products may also occur through water, raw materials such as excipients, media, additives, sera, equipment, containers closure systems, and expression systems used in manufacturing. The manufacturing process is, therefore, in critical need of methods to reduce and remove endotoxins by monitoring raw materials and in-process intermediates at critical steps, in addition to final drug product release testing. This review paper highlights a discussion on three major topics about endotoxin detection techniques, upstream processes for the production of therapeutic molecules, and downstream processes to eliminate endotoxins during product purification. Finally, we have evaluated the effectiveness of endotoxin removal processes from a perspective of high purity and low cost.

Correction to the calculation of Polanyi potential from Dubinnin-Rudushkevich equation

The Dubinin-Radushkevitch (D-R) adsorption isotherm model has been widely used to measure adsorption, and it can be used to value the mean free adsorption energy (E). In order to do this, the first step is to calculate the Polanyi adsorption potential (Ɛ). However, we find that the computational formula of Polanyi potential from the D-R equation has a dimensinal problem. Specifically, the units of the equilibrium concentration of solute (C_e) used in the Polanyi potential equation are in chaos. Accurate calculation is the basic characteristic of scientific papers. This comment highlighted the possible flaws related to the calculation of Polanyi potential and analyzed the evolution and application of Polanyi potential equation, and then provided the modified form of Polanyi potential equation. This note offers deeper insights into the Polanyi potential equation, and can help avoid misuse and propagation of the Polanyi potential equation in adsorption research.

A green biochar/iron oxide composite for methylene blue removal

Adsorbents that effectively remove dye substances from industrial effluents are needed for the protection of human health and the natural environment. However, adsorbent manufacture is associated with secondary environmental impacts. In this study, a green biochar/iron oxide composite was produced using a facile approach involving banana peel extract and FeSO₄. The modified biochar's capacity to adsorb methylene blue (MB) was considerably enhanced (Langmuir Q_max of 862 mg/g for MB when C₀ = 500 mg/L, pH = 6.1, T =313 K) compared to the unmodified banana peel biochar, and exhibited good performance for a wide range of pH values (pH 2.05-9.21). The Langmuir isotherm model and pseudo second-order kinetic model accurately describe the adsorption process. The material properties and corresponding adsorption mechanisms were investigated by various experimental techniques. Enhanced MB adsorption by the biochar/iron oxide composite is attributed to increased electronic attraction to MB molecules, as evidenced by XPS analysis. High adsorption capacity was retained after 5 regeneration cycles. This study suggests that biochar can be modified by a green synthesis approach to produce biochar/iron oxide composite with good MB removal capacity.