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About FDA

April-June 2006


Critical Path — Automated Assays
The in vivo rodent erythrocyte micronucleus test is used in regulatory safety assessment to evaluate the potential of agents to cause chromosomal damage. The test is resource intensive requiring a separate bioassay protocol and expert microscopic evaluation of bone marrow.

NCTR led an intra- and inter-laboratory collaboration with rats to show that flow cytometry evaluation of chromosome damage using peripheral blood was both more efficient and precise than the traditional microscopic methods that use bone marrow. The flow cytometry method uses only a small amount of blood allowing multiple samples to be taken from the same animal, which also provides its own baseline values. This improved procedure for conducting the in vivo phase of the genetic toxicology battery provides not only a faster more precise analysis but also the possibility that the micronucleus endpoint can be evaluated in conjunction with other toxicological endpoints, thus improving the preclinical safety assessment.

For more information, contact Dr. Martha Moore, Director, Division of Genetic and Reproductive Toxicology, NCTR.


TSSRC Meeting — Study Protocols
On May 16-17, the Toxicology Study Selection and Review Committee (TSSRC) met at NCTR.

The TSSRC provides scientific oversight to the conceptual design and interim results of study protocols conducted under the NIEHS/FDA IAG for the FDA. The overall goal is to provide scientific information on which to base FDA regulatory decisions. The committee reviewed updates on current studies including: rodent and non-human primate studies of the anesthetic ketamine; neurotoxicology, PB/PK, mechanistic, and chronic studies of the food contaminant acrylamide; AIDS therapeutics; topical and oral studies of aloe vera; skin penetration of nanoscale-engineered material (quantum dots); and metabolic, physiologic, and developmental toxicology studies of the dietary supplement bitter orange (ephedra substitute).

The TSSRC also reviewed the protocol design for the plasticizer, diethyl-hexylpthalate; for usnic acid; for the dietary supplement glucosamine/chondritin studies in diabetic rats; and for permanent make-up. The TSSRC membership is composed of representatives from each FDA Center and from other governmental organizations, academia, and industry as required to review the specialized topics under discussion.

For further information, contact Dr. William T. Allaben, Associate Director for Scientific Coordination, NCTR.


Critical Path — New Mouse Model
Scientists from NCTR and the National Institute of Environmental Health Sciences have completed preliminary studies demonstrating their newly created transgenic mouse model (C3H/HeNTac x B6.129SvEv)F1+ -/Trp53tm1Brd) is robust. The model has good reproductive success and survivability for testing potential toxicity and carcinogenicity of compounds such as AZT and 3TC in short-term, 45-week studies.

Transgenic animals have held tremendous promise for toxicity testing through incorporation of critical genes (in this model a “+/-“, haplodeficient p53 tumor suppressor gene). However, many strains are not robust or express other non-desirable traits.

The new mouse model has overcome these difficulties, and preliminary histopathological findings suggest the model will be effective for screening antiretroviral drugs, administered through the placenta, for potential carcinogenicity with the use of a shortened bioassay.

For more information, contact Dr. Julian Leakey, Office of Research, NCTR.

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