RSESS March 18, 2008 Robert Osterberg MTD Debate RSESS March 18, 2008 Robert Osterberg

Biomarkers The NAS defines a biomarker as a xenobiotically induced alteration in cellular or biochemical components or processes, structures or functions that is measurable in a biological system. Selection of appropriate biomarkers is based on the knowledge of the mechanism of the toxicity and they should correlate with the toxicity. The exact mechanism may not be known thus nonspecific biomarkers may be used to predict toxicity.

Biomarkers The use of biomarkers could reduce the amount of animal toxicity testing or could lead to changes in the way studies are conducted or theoretically lead to the actual replacement of animals using other means. Why is this important?

Testing Concerns Constant animal welfare concerns for use of animals in toxicity testing. Reduce or avoid pain and suffering! Animal Welfare Acts → animal welfare committees (IUCUCs) 3-R’s of Russell: a) reduction b) refinement c) replacement Also-reason, reliability, respect, refrain, etc.

Reduction/Replacement Computational Toxicology-use of SAR to reduce the need for animal testing - Topkat - Multi-Case - Federal agency guidances-CFSAN, CVM, EPA a) used for prediction of in vivo toxicities: LD50, genetic tox, teratology, immunotox b) only as useful as the extent of the database

Replacement/Reduction Use of gene chips for expression profiling -identify the effects of chemicals on gene expression in tissues to identify potential targets. NCTR has a Center for Toxicoinformatics -ArrayTrack an integrated suite designed for the management, analysis and interpretation of microarray experiment data. The Toxicant and EDKB Libraries contain chemical structure with tox endpoints and can integrate tox data with genomics data.

Reduction/Replacement In Vitro methods for prediction of in vivo toxicity targets: a) pharmacology assays-heart, smooth muscle, nerve-muscle b) cell cultures-cardiac cells, skin cells, isolated cornea

Use of Biomarkers indicate exposure to a specific chemical and susceptibility to an adverse effect; the most sensitive indicate exposure in the absence of an immediate event-Cystatin C; biomarkers of early effects like frank clinical pathology arise as a function of exposure, response and time-TSH; valid biomarkers need to be examined in relation to toxicity.

Biomarkers and Dose Selection 1-In a small repeat dose animal test find the dose that produces some h-path, check for specific biomarkers, then select a lower dose for definitive test. Biomarkers could increase with time and with dose. OR

Biomarkers and dose Use SAR and/or toxicogenomics and/or in vitro assays to identify tissues at risk and select biomarkers for use if known. May still have to use a small animal test to confirm before conducting definitive animal test.

Biomarkers Are they always predictive of toxicity? - >Acyl-Co-A oxidase and Cyp 4A → PPAR-α - Cystatin C detects kidney and CV disease before symptoms and creatinine > appears - >PPAR-γ→cardiac damage and Troponin I -PPAR-α could increase 10-40X but no S/S in patients with rhabdomyolysis. -Increases in liver biomarkers could be transient. Better biomarkers? Profiles?