Toxicology of Industrial Compounds

detecting DNA adducts are much more sensitive than the physicochemical
methods needed for structural characterisation. A number of strategies
have been adopted in attempts to solve this problem.
Protein adducts
Genotoxic chemicals that react with DNA also react with nucleophilic
centres in proteins and may also undergo ‘spontaneous’ and enzymecatalysed
reactions with glutathione leading to the excretion of the
corresponding mercapturic acids. Insofar as the formation of protein
adducts and mercapturic acids reflect the formation of the corresponding
DNA adducts, their detection may also furnish evidence of exposure to a
genotoxic carcinogen.
The potential for reaction of genotoxic chemicals with proteins (and
glutathione) is much greater than with DNA. Furthermore, human
proteins, e.g. haemoglobin, are available in much larger quantities and are
more accessible than human tissue DNA. These advantages have been
exploited, particularly in the pioneering work of Ehrenberg’s group, to
develop a range of procedures for the qualitative and quantitative analysis
of protein adducts (Osterman-Golkar et al., 1976; Calleman et al., 1978;
Ehrenberg and Osterman-Golkar, 1980). (For a review of the available
methods see Skipper and Naylor, 1991.) The most powerful and generic
approach is undoubtedly that developed by Törnqvist et al. (1986a). An
initial purification or enrichment step is key to any successful method for
the analysis of low levels of organic residues. The amino-groups of the Nterminal
valine residues of the α-and
β-chains of human haemoglobin are
major targets for reaction with a broad range of genotoxic chemicals.
Törnqvist achieved selective enrichment of adducted N-terminal valine
residues of haemoglobin by devising a modified Edman degradation which
resulted in the scission of adducted residues whilst leaving the nonadducted
N-terminal valines intact. This procedure provides the basis for
identifying the adducting moieties and their quantitation by GC/MS.
Applications of this technology have furnished evidence of background
exposures to a range of alkylating species. Protein adduct technology has
the potential for considerable further refinement. The possibility of using
immunoaffinity technology to enrich both known and unidentified protein
adducts is currently being explored.
DNA adducts and immunoenrichment
A.S.WRIGHT ET AL. 185
The need for effective enrichment technology for DNA adducts is even
more pressing than for protein adducts. Ideally, the enrichment procedure
should be applied at the earliest possible stage of analysis. The procedure