Oxidative Stress and Species Differences in the Metabolism, Developmental Toxicity, and Carcinogenic Potential of Methanol and Ethanol - The Toxicology of Methanol - page 220

during the acid heating step of the assay by the decomposition of lipids,
which can result in a wide variety of radical-generating toxic products
(Gutteridge and Quinlan, 1983). This can be circumvented by measur-
ing MDA directly via high-performance liquid chromatography
(HPLC) or gas chromatography-mass spectrometry (GC-MS). Another
source of uncertainty in the TBARs assay is that several compounds can
react with TBA to form chromogens that absorb at 532 nm. Lastly,
assaying human body fluids can detect artifactual MDA produced
enzymatically during eicosanoid synthesis (Shimizu et al., 1981).
HNE is formed during the oxidation of n

6 PUFAs, which are fatty
acids that contain a double bond at the carbon-6 position, such as linoleic
acid and arachidonic acid (Esterbauer et al., 1991; Spiteller, 1998). Basal
cellular levels of HNE in healthy tissues are approximately 1

m

Mor
lower; however, under conditions of oxidative stress, HNE concentrations
can rise to between 2 and 20 m Mwhich is cytotoxic, leading to inhibition
of DNA and protein synthesis, cellular proliferation, and NER (Parola et
al., 1999; Feng et al., 2004). HNE can react rapidly with thiol and amino
groups on proteins (i.e., histidine, lysine) and amino groups on DNA
bases, with guanine being the preferred target (Halliwell and Gutteridge,
2007). HNE reacts with DNA to form an etheno adduct by adding an NH 2
group to the double bond of the aldehyde to yield 1,N 2 -propano-2 1 -
deoxyguanosine adducts (Schaur, 2003; Choudhury et al., 2004) (Figure
7.22). Asmentioned previously, HNE andMDA, the end products of lipid
peroxidation, are DNA-damaging aldehydes. As such, theymay facilitate
cancer development in several ways such as (1) mutagenic adduct
formation with DNA bases, (2) formation of subsequent ROS during
the peroxidation process which may directly oxidize DNA leading to
mutagenesis, or (3) oxidation of DNA repair proteins resulting in
decreased replication fidelity with a subsequent increase in the incidence
of mutations (Halliwell and Gutteridge, 2007).
Isoprostanes (IPs) are formed from PUFAs with at least three double
bonds, which include linolenic acid, arachidonic acid (F 2 -isoprostanes),
eicosapentanoic acid (EPA) (F 3 isoprostanes), and docosahexanoic acid
(DHA) (F 4 isoprostanes) (Fam and Morrow, 2003; Roberts and Fessel,
2004). IPs can form isoketals that quickly react with amino groups to
form adducts with lysine residues on membrane proteins, resulting in