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 as ricin.