What are endotoxins?
Endotoxins are lipopolysaccharides (LPS): molecules from the outer membrane of Gram-negative bacteria. They are very heat-stable and can survive processes that kill the bacteria themselves. That’s why they are tested separately from sterility.
Why they matter for in-vitro work
Many cell types, especially immune cells such as macrophages, respond strongly to LPS through the TLR4 receptor, even at very low concentrations. If a research compound carries endotoxin, the cells may react to the contamination rather than the compound. That can confound cytokine readouts, viability assays and signalling studies. A low endotoxin result helps make sure that what you observe comes from the compound.
How it’s measured: the LAL test
The standard method uses Limulus amebocyte lysate (LAL), which comes from horseshoe crab blood cells and clots in the presence of endotoxin. There are three common formats:
- Gel-clot: a pass/fail result at a set sensitivity.
- Turbidimetric: measures how cloudy the sample becomes over time.
- Chromogenic: measures a colour change, which allows precise quantification.
Some labs now use recombinant Factor C (rFC), a synthetic alternative that doesn’t use horseshoe crabs.
Reading the result
Results are reported in endotoxin units (EU) per ml or per mg. A result written as “<0.05 EU/ml” means the endotoxin level was below the method’s limit of detection. Lower is better. What counts as acceptable depends on the experiment, so compare the figure with your own assay’s sensitivity.
On Isla certificates
Most of our Bioviridian reports include an endotoxin result, and every one published so far is below 0.05 EU/ml. You can see each one in the COA Bank and in the Specifications section of each product page. Related reading: How to read a COA · HPLC vs mass spectrometry.
Research use only
Isla Longevity supplies research compounds for laboratory use only. They are not approved by the FDA for human or veterinary use and are not for human consumption. This article explains analytical testing and is not medical guidance.
