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to peroxisome proliferators. Current limitations involving speed of throughput are
being overcome by increasing automation and the development of new techniques.
The isotope-coded affi nity tag (ICAT) method appears particularly promising.
Toxicoproteomics involves the evaluation of protein expression for the under-
standing of toxic events. Transcriptional profi ling and proteomics are used to com-
pile toxicology predictors. Affi nity-based biosensor technology is being investigated
to profi le lead compound-protein interactions. Immobilized artifi cial membrane
chromatography is being evaluated to predict oral compound absorption. It is
expected that these efforts will deliver the tools to annotate screening libraries, hits
and leads with quality measures of ADME-tox characteristics. Computational
methods will then relate compounds and ADME-tox properties to performance in
actual clinical trials. Some examples of application of proteomics in toxicology are
given in the following sections.
Hepatotoxicity
Studies on the rodent liver proteome show that several compounds cause increased
proliferation of peroxisomes and liver tumors. Peroxisome proliferators are found to
induce protein expression changes as a distinct protein signature. Overdose of acet-
aminophen causes acute hepatotoxicity in rodents and humans. Experimental evi-
dence suggests that activation of acetaminophen and subsequent formation of
protein adducts are involved in hepatotoxicity. Most of the changes caused by acet-
aminophen occur in a subset of the proteins modifi ed by acetaminophen. Many of
the proteins that show changed expression levels are involved in the regulation of
mechanisms that are believed to drive acetaminophen-induced hepatotoxicity.
Complementary strategies of 2D gel electrophoresis, coupled either with database
spot mapping or protein isolation and amino acid sequencing, have successfully
identifi ed a subset of proteins from xenobiotic-damaged rodent livers, the expres-
sion of which differs from controls.
Lovastatin is a lipid-lowering agent that acts by inhibiting 3-hydroxy-3-
methylglutaryl-coenzyme A (HMG-CoA) reductase, a key regulatory enzyme in
cholesterol biosynthesis. Lovastatin treatment is associated with signs of toxicity as
refl ected by changes in a heterogeneous set of cellular stress proteins involved in
functions such as cytoskeletal structure, calcium homeostasis, protease inhibition,
cell signaling or apoptosis. These results present new insights into liver gene net-
work regulations induced by lovastatin and illustrate a yet unexplored application of
proteomics to discover new targets by analysis of existing drugs and the pathways
that they regulate.
In rat primary hepatocytes exposed to the compounds (acetaminophen, amioda-
rone, tetracycline and carbon tetrachloride) that are known to induce hepatotoxicity,
LDH release and mitochondrial respiration (WST-1 reduction assay) have been
used to detect cytotoxicity along with application of proteomic technologies for
estimating reliable as well as sensitive biomarkers. Cytotoxicity can be detected
6 Pharmacoproteomics