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Mechanisms and Biomarkers (WG 4) page 35
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oligonucleotides and bases respectively. Bases are excreted directly into the urine whereas the
oligonucleotides are further hydrolysed to nucleosides before excretion into the urine. The
presence of background levels of a wide variety of oxidised nucleosides in urine indicates that
DNA oxidation by RS is occurring constantly under non-pathological conditions. In principle
the best analytical approach would be to measure a wide range of DNA base damage products
by mass spectrometry to obtain a comprehensive and rigorous identification of the products.
However, a major problem with the use of GC-MS is the formation of artefacts by the acidic
hydrolysis and derivatisation procedures required by the conventional process (Dizdaroglu,
1998). An obvious choice for non-destructive analysis of products would be LC-MS, but this
technique is still in the development phase for DNA oxidation products. Since the
development of a simple electrochemical detection method linked to HPLC (Floyd et al.,
1986) urinary 8OHdG has become the most widely analysed chemical biomarker for
oxidative DNA damage, reviewed in Loft et al. (1998). Limitations of the use of 8OHdG are:
1. It is not a quantitative marker for the oxidative damage to DNA.
2. It is only a minor product of the attack on DNA by reactive nitrogen and chlorine species.
3. The redox state of the cell will effect the ratio of 8OHdG to FAPyG, as will the presence of
transition metals (Dizdaroglu, 1998). Theoretically one can measure a wide range of base
damage products by mass spectrometry, this would also measure the attack on DNA by
reactive nitrogen and chlorine species and would enable a rigorous identification of products,
since techniques to overcome the problems of artifactual hydrolysis and derivatisation for
GC-MS have recently been overcome.
Biological markers of DNA damage and cancer development
The current most important barrier to progress in the search for cancer biomarkers is the lack
of intermediate biomarkers for the major cancers of the lung, breast and pancreas. Significant
intermediate biomarkers of full-blown oral and cervical cancers have been identified as the
hyperplastic or dysplastic lesions of oral leukoplakia and cervical dysplasia, which identify
individuals at high risk for development of these diseases. Fortunately these conditions are
reversible by appropriate interventions.
Membrane Damage: a prelude to DNA damage
LDH release is a marker for gross membrane damage resulting in a loss of membrane
integrity, it is suggested that over 10% LDH release leads to irreversible changes and cell
death (Miyashita et al., 1997). Trypan blue uptake is a measure of membrane