Bacterial Endotoxin Testing-Fast Endotoxin Masking Kinetics in the Presence of Lauryldimethylamine Oxide

The impact of LPS mutants on endotoxin masking in different detection systems

Endotoxin masking poses a potential risk to patient safety by rendering endotoxin undetectable. While research often focuses on international endotoxin standards (RSE), the effects of LPS mutants on Low Endotoxin Recovery (LER) are poorly understood. Our study investigated S. minnesota and E. coli mutants with incomplete O-antigen chains (rough LPS) using Limulus amebocyte lysate (LAL), recombinant Factor C (rFC) and the monocyte activation test (MAT). All tested methods detected the mutants, with variations in activity observed. Measurements over time in a common drug formulation (10 mM sodium citrate and 0.05 % (w/v) polysorbate 20) showed different masking kinetics for the mutants using different methods. We were able to show that LAL and rFC have comparable kinetics, whereas MAT showed improved recovery of masked endotoxin. The study showed that the mutation of LPS have an effect on masking, independent of the assay system. We propose that polysaccharide length affects masking susceptibility, with lower hydrophilic/hydrophobic ratios caused by the shortened polysaccharide chain (rough LPS) reducing masking. In addition, the stronger negative charge of the rough mutants increases cation affinity and is suggested to contribute to the stabilisation of supramolecular structures, making the rough mutants less susceptible to masking than the smooth mutants.

Advances in endotoxin analysis

The outer membrane of gram-negative bacteria is primarily composed of lipopolysaccharide (LPS). In addition to protection, LPS defines the distinct serogroups used to identify bacteria specifically. Furthermore, LPS also act as highly potent stimulators of innate immune cells, a phenomenon essential to understanding pathogen invasion in the body. The complex multi-step process of LPS binding to cells involves several binding partners, including LPS binding protein (LBP), CD14 in both membrane-bound and soluble forms, membrane protein MD-2, and toll-like receptor 4 (TLR4). Once these pathways are activated, pro-inflammatory cytokines are eventually expressed. These binding events are also affected by the presence of monomeric or aggregated LPS. Traditional techniques to detect LPS include the rabbit pyrogen test, the monocyte activation test and Limulus-based tests. Modern approaches are based on protein, antibodies or aptamer binding. Recently, novel techniques including electrochemical methods, HPLC, quartz crystal microbalance (QCM), and molecular imprinting have been developed. These approaches often use nanomaterials such as gold nanoparticles, quantum dots, nanotubes, and magnetic nanoparticles. This chapter reviews current developments in endotoxin detection with a focus on modern novel techniques that use various sensing components, ranging from natural biomolecules to synthetic materials. Highly integrated and miniaturized commercial endotoxin detection devices offer a variety of options as the scientific and technologic revolution proceeds.

Improved endotoxin removal using ecofriendly detergents for intensified plasmid capture

Increasing plasmid demand for both production of viral and gene therapies as well as nucleic acid based vaccines has highlighted bottlenecks in production. One bottleneck is traditional bead-based chromatography as a capture step. To meet the needs of fast-growing markets, new production solutions are needed. These solutions must enable efficient capture of a diverse range of plasmid types and excellent clearance of bacterial host impurities, such as endotoxin. Enhanced endotoxin clearance during chromatographic purification has previously been demonstrated with detergents such as Triton™ X-100. However, degradation products of Triton™ X-100 are known to have a negative environmental impact, and more sustainable, environmentally benign alternatives have been identified. This work establishes an efficient, intensified plasmid capture using convective anion exchange (AEX) chromatography. The feasibility of the intensified capture approach was assessed with different membrane and a monolith AEX supports. Various detergents from different physico-chemical classes were evaluated with different AEX technologies. Purification efficiency evaluated endotoxin and host cell protein (HCP) clearance, plasmid yield, potential interference of the detergents with analytical in-process control assays, and overall process compatibility. This comprehensive screening approach provides valuable insights to intensified plasmid production.

Low endotoxin recovery and its impact on endotoxin detection

Endotoxin exists on the outer membrane of Gram-negative bacteria and poses risks to human health by triggering a series of immune responses. Therefore, its accurate detection is essential. The Limulus amoebocyte lysate (LAL) test is the most pharmacopeia-recognized and popular technique for endotoxin detection. Despite its wide industry adoption, the low endotoxin recovery (LER) phenomenon can compromise the LAL test's reliability. This review summarizes the possible reasons attributing to the LER phenomenon from three different perspectives: the endotoxin standards used in hold time study, protein active pharmaceutical ingredients, and excipients. Potential mechanisms and strategies to mitigate the LER phenomenon are also discussed as presented by different research groups.