A new National Institute of
Standards and Technology (NIST) assay using a "glow or no glow"
technique may soon help the U.S. Department of Homeland Security (DHS) defend
the nation against a spectrum of biological weapons that could be used in a
terrorist attack. One very dangerous toxin on the list is ricin, a protein derived
from castor beans that is lethal in doses as small as 500 micrograms-about the
size of a grain of salt.
As part of its efforts to address the threat, DHS is working with NIST to create
a standardized ricin sample with a known potency. Such a standard is needed
both to check the accuracy of detection equipment, and, should an attack occur,
to confirm the success of decontamination procedures. A major step toward this
goal—the development of a rapid, reliable and precise assay of the potency
of a ricin sample—has now been achieved by NIST scientists.
As detailed in an article posted online this week in Assay and Drug Development
Technologies,* the new NIST assay uses a commercially available cell line genetically
engineered to produce large amounts of green fluorescent protein (GFP). Ricin
shuts down ribosomes—the protein manufacturing factories of a cell. Assay
cells exposed to the toxin will quickly stop synthesizing GFP. This, in turn,
will result in a measurable decrease in fluorescence—a drop that correlates
directly to the strength of the ricin present.
The NIST assay yields many advantages over traditional cytotoxicity measuring
systems, including: a highly sensitive response to ricin (as little as 1 nanogram
per milliliter) within six rather than 24 hours; detection of the toxin long
before significant cell death has occurred; results that are highly reproducible;
no need for the addition of any reagents; and the flexibility to measure the
potency of other ribosome inhibitors, even nanoparticles, with the same precision