Automation of chromogenic substrate Limulus amebocyte lysate assay method for endotoxin by robotic system

Highly Sensitive Electrochemical Endotoxin Sensor Based on Redox Cycling Using an Interdigitated Array Electrode Device

The Limulus amebocyte lysate (LAL) reaction-based assay, the most commonly used endotoxin detection method, requires a skilled technician. In this study, to develop an easy-to-use and highly sensitive endotoxin sensor, we created an electrochemical endotoxin sensor by using an interdigitated array electrode (IDAE) device with advantages of amplifiable signals via redox cycling and portability. We added Boc-Leu-Gly-Arg-p-aminophenol (LGR-pAP) as an electrochemical substrate for an LAL reaction and detected p-aminophenol (pAP) released from LGR-pAP as a product of an endotoxin-induced LAL reaction via an IDAE device. The IDAE device showed a great redox cycling efficiency of 79.8%, and a 4.79-fold signal amplification rate. Then, we confirmed that pAP was detectable in the presence of LGR-pAP through chronoamperometry with the potential of the anode stepped from -0.3 to 0.5 V vs. Ag/AgCl while the cathode was biased at -0.3 V vs. Ag/AgCl. Then, we performed an endotoxin assay by using the IDAE device. Our endotoxin sensor detected as low as 0.7 and 1.0 endotoxin unit/L after the LAL reaction for 1 h and 45 min, respectively, and these data were within the cut-off value for ultrapure dialysis fluid. Therefore, our highly sensitive endotoxin sensor is useful for ensuring medical safety.

Gene Expression Changes Induced by Exposure of RAW 264.7 Macrophages to Particulate Matter of Air Pollution: The Role of Endotoxins

Despite the variable chemical and physical characteristics of particulate air pollutants, inflammation and oxidative stress have been identified as common mechanisms for cell damage and negative health influences. These effects are produced by organic components, especially by endotoxins. This study analyzed the gene expression profile after exposure of RAW 264.7 cells to the standard particulate matter (PM) material, NIST1648a, and PM with a reduced organic matter content, LAp120, in comparison to the effects of lipopolysaccharide (LPS). The selected parameters of cell viability, cell cycle progression, and metabolic and inflammatory activity were also investigated. Both forms of PM negatively influenced the parameters of cell activity. These results were generally reflected in the gene expression profile. Only NIST1648a, excluding LAp120, contained endotoxins and showed small but statistically significant pro-inflammatory activity. However, the gene expression profiling revealed strong pro-inflammatory cell activation induced by NIST1648a that was close to the effects of LPS. Changes in gene expression triggered by LAp120 were relatively small. The observed differences in the effects of NIST1648a and LAp120 were related to the content of organic matter in which bacterial endotoxins play an important role. However, other organic compounds and their interactions with other PM components also appear to be of significant importance.

Improved bioluminescence-based endotoxin measurement method using a salt-resistant luciferase mutant

Endotoxin is a component of the cell wall of gram-negative bacteria and causes fever and shock symptoms upon entering the bloodstream. We previously demonstrated that the bioluminescence-based Limulus amebocyte lysate test is highly sensitive and rapid for measuring endotoxin. However, as the firefly luciferase reaction is inhibited in the presence of sodium chloride, the endotoxin detection method did not meet the validation guidelines under medical dialysis conditions (range of 75-125% of the measured values tested in water). Here, we used a salt-resistant luciferase mutant, which met the criteria for validation of endotoxin measurement.

Miniaturization, Parallelization, and Automation of Endotoxin Detection by Centrifugal Microfluidics

We demonstrate microfluidic automation and parallelization of Limulus amebocyte lysate (LAL)-based bacterial endotoxin testing using centrifugal microfluidics. LAL is the standard reagent to test for endotoxin contaminations in injectable pharmaceuticals. The main features of the introduced system are more than 90% reduction of LAL consumption, from 100 μL/reaction to 9.6 μL/reaction, automated liquid handling to reduce opportunities for contamination and manual handling errors, and microfluidic parallelization by integrating 104 reactions into a single centrifugal microplate. In a single Eclipse microplate, 21 samples and their positive product controls are tested in duplicate. In addition, a standard curve with up to five points is generated, resulting in a total of 104 reactions. Test samples with a defined concentration of 0.5 endotoxin units per milliliter were tested, resulting in a coefficient of variation below 0.75%. A key feature for achieving a small coefficient of variation is ensuring the same path length along the microfluidic channels to the final reaction chambers for each sample and the reagent, so that any unspecific adsorption to the polymer surfaces does not affect the accuracy and precision. Analysis of a sample containing naturally occurring endotoxin with the developed microfluidic microplate yielded comparable results to the conventional testing method. A test with eight commercially available pharmaceuticals was found to pass all requirements for bacterial endotoxin testing as specified in the United States Pharmacopeia. The automated endotoxin testing system reveals specific advantages of centrifugal microfluidics for analytical biochemistry applications. Small liquid volumes are handled (metered, mixed, and aliquoted) in a very precise, highly integrated, and highly parallel manner within mass-fabricated microplates.

In Vitro Release of Bioactive Bone Morphogenetic Proteins (GDF5, BB-1, and BMP-2) from a PLGA Fiber-Reinforced, Brushite-Forming Calcium Phosphate Cement

Bone regeneration of sheep lumbar osteopenia is promoted by targeted delivery of bone morphogenetic proteins (BMPs) via a biodegradable, brushite-forming calcium-phosphate-cement (CPC) with stabilizing poly(l-lactide-co-glycolide) acid (PLGA) fibers. The present study sought to quantify the release and bioactivity of BMPs from a specific own CPC formulation successfully used in previous in vivo studies. CPC solid bodies with PLGA fibers (0%, 5%, 10%) containing increasing dosages of GDF5, BB-1, and BMP-2 (2 to 1000 µg/mL) were ground and extracted in phosphate-buffered saline (PBS) or pure sheep serum/cell culture medium containing 10% fetal calf serum (FCS; up to 30/31 days). Released BMPs were quantified by ELISA, bioactivity was determined via alkaline phosphatase (ALP) activity after 3-day exposure of different osteogenic cell lines (C2C12; C2C12BRlb with overexpressed BMP-receptor-1b; MCHT-1/26; ATDC-5) and via the influence of the extracts on the expression of osteogenic/chondrogenic genes and proteins in human adipose tissue-derived mesenchymal stem cells (hASCs). There was hardly any BMP release in PBS, whereas in medium + FCS or sheep serum the cumulative release over 30/31 days was 11-34% for GDF5 and 6-17% for BB-1; the release of BMP-2 over 14 days was 25.7%. Addition of 10% PLGA fibers significantly augmented the 14-day release of GDF5 and BMP-2 (to 22.6% and 43.7%, respectively), but not of BB-1 (13.2%). All BMPs proved to be bioactive, as demonstrated by increased ALP activity in several cell lines, with partial enhancement by 10% PLGA fibers, and by a specific, early regulation of osteogenic/chondrogenic genes and proteins in hASCs. Between 10% and 45% of bioactive BMPs were released in vitro from CPC + PLGA fibers over a time period of 14 days, providing a basis for estimating and tailoring therapeutically effective doses for experimental and human in vivo studies.

Bacterial contamination and health risks of drinking water from the municipal non-government managed water treatment plants

Water quality and bacterial contamination from 18 drinking water municipal plants in three locations at Giza governorate were investigated. The average total count of bacteria detected after four stages of treatments in the investigated plants was 32 CFU/1 mL compared to 2330 cfu/mL for raw water, with a reduction percentage of 98.6. Although there is a relatively high removal percent of bacterial contamination from the water sources, however, several bacterial pathogens were identified in the produced water prepared for drinking including Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, and Shigella spp. After 3 days of water incubation at 30 °C, the amount of bacterial endotoxins ranged from 77 to 137 ng/mL in the water produced from the municipal plants compared to 621-1260 ng/mL for untreated water. The main diseases reported from patients attending different clinics and hospitals during summer 2014 at the surveyed locations and assuredly due to drinking water from these plants indicated that diarrheas and gastroenteritis due to E. coli and Campylobacter jejuni constituted 65.7% of the total patients followed by bacillary dysentery or shigellosis due to Shigella spp. (7.9%) and cholera due to Vibrio cholera (7.2%). There was an increase in serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) as well as urea and creatinine values of guinea pigs consuming water produced from the non-governmental plants for 6 months indicating remarkable liver and kidney damages. Histological sections of liver and kidney from the tested animal revealed liver having ballooning degeneration of hepatocytes and distortion and fragmentation of the nuclei, while the section of the kidney showed irregularly distributed wrinkled cells, degenerated Bowman's capsule, congested blood vessels, and inflammatory cells.

A polymyxin B-silver nanoparticle colloidal system and the application of lipopolysaccharide analysis

Polymyxin B (PMB) is a small cyclic polycationic lipopeptide, which can be used as an antibiotic drug against Gram-negative bacteria. In this work, the interaction between citrate capped silver nanoparticles (AgNPs) and PMB is studied. Experimental results show that the association constant is extremely high and the binding event leads to a significant variation in the localized surface plasmon resonance (LSPR) of AgNPs. Moreover, the PMB-AgNP colloidal system can be further exploited as a sensitive analytical platform. Taking lipopolysaccharide (LPS) as an example, we demonstrate a facile colorimetric LPS detection method. LPS is a major constituent of the Gram-negative bacterial cell wall which is used as an optimal biomarker for some diseases like urinary tract infections and sepsis. In this study, target LPS is able to tightly bind to PMB, which effectively inhibits the PMB induced aggregation of AgNPs. By monitoring the UV-vis absorption spectra, the LPS concentration can be quantitatively determined with high sensitivity. The sensing strategy is quite simple, which allows effortless diagnosis of many diseases at different stages.

Preparation of a Peptide-Modified Electrode for Capture and Voltammetric Determination of Endotoxin

Endotoxin is the major structural constituent of the outer membrane of Gram-negative bacteria, which is a great threat to human health. Herein, a sensitive electrochemical biosensor for the detection of endotoxin is established by recording the voltammetric responses of the peptide-modified electrode. The utilized peptide has a high affinity for the target endotoxin, which ensures the high selectivity of this method. After the capture of endotoxin on the electrode surface, a negatively charged layer is formed, and the electron-transfer process is significantly hindered because of the increased steric hindrance and the electrostatic repulsion. The declined electrochemical signal could be used to indicate the concentration of endotoxin. This method is simple but effective, which requires limited reagents. Another highlight of this method is its user-friendly operation. Moreover, its applicability in human blood plasma promises its great potential utility in the near future.

A quartz crystal microbalance sensor for endotoxin assay by monitoring limulus amebocyte lysate protease reaction

Endotoxin is able to trigger strong innate immune responses by interacting with specific receptors on immune cells. Therefore, accurate and rapid detection of endotoxin is of primary importance. In this study, endotoxin induced viscosity variation of limulus amebocyte lysate (LAL) reagent is monitored by a quartz crystal microbalance (QCM) sensor with enhanced signal. Based on the analysis of the relationship between endotoxin concentration and QCM frequency shift with time, an effective sensing strategy is developed for endotoxin assay, which shows excellent sensitivity and specificity in the linear detection range from 0.005 to 10 EU mL^-1. Moreover, this QCM sensor could be reused after a simple regeneration procedure. Therefore, it has potential practical utility for endotoxin determination in various applications.

More than 70 Years of Pyrogen Detection: Current State and Future Perspectives

In the quality assurance of medical products, tests for sterility are essential. For parenteral pharmaceuticals, avoiding the presence of pyrogens is crucial. These fever-inducing substances (endotoxins and non-endotoxins) are not eliminated by standard sterilisation processes, and are biologically active once in the bloodstream, causing risks to human health, ranging from mild reactions (e.g. fever) to septic shock and death. Therefore, for injectable formulations, pyrogen testing is mandatory. Over the years, various pyrogen testing methods have been introduced, namely: in the 1940s, the rabbit pyrogen test, which is an in vivo test that measures the fever reaction as an endpoint; in the 1970s, the Limulus Amoebocyte Lysate (LAL) test, which is an in vitro test (with the haemolymph of the horseshoe crab) that specifically detects endotoxin; and in 2010, the Monocyte-Activation Test (MAT), which is a non-animal based in vitro pyrogen test that represents a full replacement of the rabbit test. Due to the ubiquity and biological significance of pyrogens, we are currently further developing the MAT so that it can be used for other applications. More specifically, our focus is on the detection of pyrogenic contamination on medical devices, as well as on the measurement of air quality. In addition, further improvements to permit the use of cryopreserved blood in the MAT, to overcome the limitations in the availability of freshly-drawn blood from human donors, are ongoing.

Comparison of endotoxin levels in previous studies on primary endodontic infections

BACKGROUND

This study was performed to determine which of the quantitative methods, namely, chromogenic endpoint, chromogenic kinetic, and turbidimetric kinetic ones, best fit for the analysis of primary endodontic infections.

METHODS

Twenty-one root canals with apical periodontitis were sampled with paper points. The same sample was analyzed by means of the endpoint chromogenic Limulus amebocyte lysate (LAL) assay (QCL), quantitative kinetic chromogenic LAL assay (KQCL), and kinetic turbidimetric LAL assay (Turbidimetric).

RESULTS

All three LAL methods were effective in the recovery of endotoxin from root canal infection. Regardless of the method tested, endotoxin was detected in 100% of the root canals (21/21). The KQCL assay yielded a median value of endotoxin of 7.49 EU/mL, close to and not significantly different from those for the turbidimetric test (9.19 EU/mL) (both kinetic methods) (p > 0.05). In contrast, the endpoint QCL showed a median value of 34.20 EU/mL (p < 0.05). The comparison of the three methods revealed that both turbidimetric and KQCL methods were more precise, with best reproducibility (the coefficient variation between analysis of the root canal and its duplicate was lower than 10%). The inhibition/enhancement assay indicated a good interaction between the root canal samples with the turbidimetric method.

CONCLUSION

This study has revealed that quantitative kinetic-turbidimetric and kinetic-chromogenic LAL methods are best fitted for the analysis of endotoxins in root canal infection, both being more precise and allowing better reproducibility compared with the endpoint-QCL assay.

Limulus amebocyte lysate assay for endotoxins by an adsorption method with polycation-immobilized cellulose beads

To assay lipopolysaccharides (LPSs) in solutions containing Limulus amebocyte lysate (LAL)-inhibiting or LAL-enhancing compounds, we developed a selective endotoxin (LPS) assay using poly(epsilon-lysine)-immobilized cellulose beads (PL-Cellufine) and LAL. The PL-Cellufine can adsorb LPSs in a solution containing certain compounds (NaCl, proteins and amino acids) at an ionic strength of mu = 0.05-0.4 at neutral pH. The LPSs adsorbed on the PL-Cellufine were separated from the compounds by centrifugation and then the PL-Cellufine was suspended in LPS-free water. The LPS activities of the suspension are directly assayed by a turbidimetric time assay with the LAL reagent. The accuracy of the adsorption method was high compared with those of common solution methods. As for the common method, the apparent recovery of LPS from the compounds was 40-95%. This suggests that these compounds inhibit the LAL procedure. By contrast, the adsorption method showed good LPS recovery (88-120%) in all cases, without being inhibited or enhanced by the compounds.

Endotoxin assay by bioluminescence using mutant firefly luciferase

The Limulus reaction is an application of the defense mechanism of horseshoe crab for endotoxin detection. Endotoxin is a component of the cell wall in the outer membrane of gram-negative bacteria, and causes fever or shock when it enters the human blood stream. For endotoxin detection, gel formation or turbidity of the coagulation factor chromogen or fluorescence-modified peptide is used. However, these conventional methods have problems with regard to their measurement time or sensitivity. We recently obtained a mutant firefly luciferase that has a luminescence intensity over 10-fold higher than that of the wild type. Therefore, we developed a new endotoxin detection method that combines the Limulus reaction and bioluminescence using mutant luciferase. The new method detects 0.0005EU/ml of endotoxin within 15min.

Novel endotoxin assay by laser light-scattering particle-counting method

Exposure of Limulus amoebocyte lysate to endotoxin under stirring produced light-reflective particles that appeared to be coagulin polymers. A laser light-scattering particle counter, the PA-200, detected these particles sensitively. The PA-200 detected endotoxin at a concentration as low as 0.00015 EU/ml in 71 min, whereas the minimum endotoxin concentration measured by a turbidimeter, ET-2000, was 0.0005 EU/ml in 138 min. Moreover, PA-200 was much less affected by the presence of colored substances and refractive materials than was ET-2000. We propose that the high sensitivity, speed, and high interference tolerance of the laser light-scattering particle-counting method make it more useful than the widely used turbidimetric method for quantitative endotoxin assay.

Single-step, chromogenic Limulus amebocyte lysate assay for endotoxin

A new reagent for the chromogenic Limulus amebocyte lysate (LAL) assay is described. LAL was formulated for optimal performance in either an endpoint procedure or a kinetic procedure with the chromogenic substrate, buffer, and LAL components colyophilized as a single reagent. The kinetic chromogenic method required an incubating microplate reader coupled to a computer for collection and analysis of data. The kinetic method had a longer incubation time than the endpoint method and spanned a range of over 3 orders of magnitude compared with the 1-order-of-magnitude range of the endpoint assay. The kinetic method was less subject to operator error, since readings were continuous and automatic. The endpoint test was more operator intensive, requiring both addition of acetic acid to stop the reaction and transfer of the sample to the reading device. A single-step chromogenic reagent was also prepared without lyophilization by mixing reconstituted gel clot LAL with a buffer and a chromogenic substrate. The reagent prepared in this manner performed as well as the colyophilized agent.

Comparison of a gelation and a chromogenic Limulus (LAL) assay for the detection of gram-negative bacteria, and the application of the latter assay to milk

When a chromogenic Limulus Amoebocyte Lysate (LAL) assay and a tube gelation LAL assay were compared for the detection of Gram-negative bacteria using a strain of Pseudomonas putida, the detection level (approximately 10(3) cfu/ml) and cost of the assays were approximately the same for both assays but the reading was more precise for the chromogenic substrate assay. A modified chromogenic assay was devised for detection of Ps. putida in milk.