167earlier by measuring WST-1 than by measuring LDH release because the reduction
of mitochondrial respiration is an expression of earlier toxicity for cellular function,
whereas measured increase in LDH release occurs after failure of the cell mem-
brane. Mitochondrial respiration is a useful parameter of cytotoxicity for in vitro
hepatotoxicity screening, as cytotoxicity can be detected during an early stage of
exposure. In addition to the conventional biomarkers, several protein biomarkers,
which relate to oxidative stress and metabolism-regulation, can also be detected.
Further comprehensive analysis of defi ned proteins would be necessary to estimate
more sensitive toxicology biomarkers.
Nephrotoxicity
An example of dose-related nephrotoxicity is that caused by cyclosporine A which
has proven benefi cial effects in organ transplantation. Proteomic analysis using
2DE has demonstrated an association between calbinden-D 28 and cyclosporine
A-induced nephrotoxicity and is considered to be a marker for this adverse effect.
This shows that proteomics can provide essential information in mechanistic toxi-
cology. 2DE and NMR spectrometry was used to study nephrotoxicity in the rat
following exposure to puramycin aminonucleoside. Monitoring of proteins in the
urine enabled a more detailed understanding of the nature and progression of the
proteinuria associated with glomerular nephrotoxicity than was previously
possible.
Neurotoxicity
Neurotoxicant-induced changes in protein level, function, or regulation could have
a detrimental effect on neuronal viability. Direct oxidative or covalent modifi cations
of individual proteins by various chemicals or drugs are likely to lead to disturbance
of tertiary structure and a loss of function of neurons. The proteome and the func-
tional determinants of its individual protein components are, therefore, likely targets
of neurotoxicant action and resulting characteristic disruptions could be critically
involved in corresponding mechanisms of neurotoxicity. A variety of classic pro-
teomic techniques (e.g. LC/tandem mass spectroscopy, 2DG image analysis ) as
well as more recently developed approaches (e.g. two-hybrid systems, antibody
arrays, protein chips, isotope-coded affi nity tags, ICAT) are available to determine
protein levels, identify components of multiprotein complexes and to detect post-
translational changes. Proteomics, therefore, offers a comprehensive overview of
cell proteins, and in the case of neurotoxicant exposure, can provide quantitative
data regarding changes in corresponding expression levels and/or post-translational
modifi cations that might be associated with neuron injury.
Role of Proteomics in Clinical Drug Safety