Since the pharmaceutical industry produces injections of many kinds, testing for pyrogens is an absolute necessity. Pyrogens are substances that can cause fever, shock and in extreme cases even the death. Endotoxin is a pyrogen of Gram-negative bacteria. It is found as a natural component in the outer cell membrane and is released by cell lysis. Over 30 different biological activities of endotoxin are known, including macrophage activation, mitogenic activity and induction of interferon and colony-stimulating factors.
For a long time, the "Rabbit Pyrogen Test" was the drug of choice. In the 1970s, the LAL test (Limulus Amebocyte Lysate) was introduced. LAL comes from the amebocytes of the horseshoe crab Limulus polyphemus. Frederick Bang and Jack Levin observed that these amebocytes coagulate in the presence of Gram-negative bacteria. The technology for the endotoxin test was derived from this observation.
The Pyrogent Gel Clot Assay is a qualitative LAL test for endotoxins from Gram-negative bacteria. The assay is performed in glass tubes at 37°C. After one hour of incubation in a water bath or incubation block, the tubes are inverted 180°. If endotoxin contamination is present, a gel-like matrix will form and remain intact when the tube is inverted.
For a quantitative endotoxin determination, Lonza offers the Kinetic Turbidimetric LAL Assays. This method is performed in a microplate using an incubating absorbance plate reader at the wavelength 340nm and at 37°C. Using special software, the turbidity is monitored over time. Endotoxin-containing samples show a faster increase in OD than non-contaminated samples. Endotoxin concentrations of samples can be determined.
This method is carried out in tubes or in microplates. After a certain time, the reaction mixture turns yellow and can be measured with a photometer at 405-410 nm. Positive samples give a stronger discoloration, or higher OD value. Using the accompanying standard, sample values can be quantitatively calculated.
Similar to the Endpoint Chromogenic LAL Assay, this method uses an absorbance reading at 405-410 nm. These tests are particularly suitable for the quality control of biological products, e.g. vaccines or antibiotics. The sensitivity range is between 0.005 and 50 EU / mL.
The PyroGene assay is a reliable alternative to traditional endotoxin tests. It relies on the activation of recombinant Factor C, an endotoxin-sensitive protein that initiates the traditional LAL cascade. The measurement is carried out with a fluorescence reader (ex: 380 nm / em: 440 nm) in a microplate. Standards allow quantification of positive samples in the range 0.01-10 EU / mL.