The effect of malondialdehyde is modified by simian virus 40 transformation in human lung fibroblast cells

The effects of malondialdehyde (MDA), a product of oxidative stress, on normal lung fibroblast cells (MRC5) and transformed cells (MRC5 SV2) showed differing responses between the two cell lines. MRC5 cells showed lower viability at low MDA concentrations (<250 μM) but had better viability at higher concentrations than the transformed cells. Both cell lines showed an increase in the number of micronuclei, nuclear size and a relocation of p53 to the nucleus with increasing MDA. The expression of p53 was higher in the MRC5 cells at 24 h; 2-8 fold induction vs 1-2.5 fold in the MRC5 SV2 cells, but reduced to almost zero at 48 h in the MRC5 cells. Mutation sequencing of the PCR products of a 689 bp region (residues 4640-5328) of the TP53 gene revealed MRC5 had more mutations than MRC5 SV2 cells (n = 21 and 11 respectively) and that they were predominantly insertions (MRC5 81%, MRC5 SV2 100%). A common mutation was observed in both cell lines; a G insertion at residue 4724 (n = 7) which could prove to be a mutational hotspot. These results indicate that the transformed cells are slower to respond to oxidative stress and/or mutagenic compounds. The mutation spectrum of predominantly frameshift mutations (insertions) suggests that oxidative stress plays a minimal role in smoking related lung cancer, but could be of greater importance to other lung diseases and cancer caused by exposures such as passive smokers, passive vapers and atmospheric pollutants.

3-(2-deoxy-β-d-erythro-pentafuranosyl)pyrimido[1,2-α]purin-10(3H)-one deoxyguanosine adducts of workers exposed to asbestos fibers

Asbestos is the commercial name for a group of silicate minerals naturally occurring in the environment and widely used in the industry. Asbestos exposure has been associated with pulmonary fibrosis, mesothelioma, and malignancies, which may appear after a period of latency of 20-40 years. Mechanisms involved in the carcinogenic effects of asbestos are still not fully elucidated, although the oxidative stress theory suggests that phagocytic cells produce large amounts of reactive oxygen species, due to their inability to digest asbestos fiber. We have conducted a mechanistic study to evaluate the association between 3-(2-deoxy-β-d-erythro-pentafuranosyl)pyrimido[1,2-α]purin-10(3H)-one deoxyguanosine (M₁dG) adducts, a biomarker of oxidative stress and lipid peroxidation, and asbestos exposure in the peripheral blood of 327 subjects living in Tuscany and Liguria, Italy, stratified by occupational exposure to asbestos. Adduct frequency was significantly greater into exposed subjects with respect to the controls. M₁dG per 10⁸ normal nucleotides were 4.0±0.5 (SE) in 156 asbestos workers, employed in mechanic, naval, petrochemical, building industries, and in pottery and ceramic plants, versus a value of 2.3±0.1 (SE) in 171 controls (p<0.001). After stratification for occupational history, the effects persisted in 54 current asbestos workers, mainly employed in building renovation industry (2.9±0.3 (SE)), and in 102 former asbestos workers (4.5±0.7 (SE)), with p-values of 0.033, and <0.001, respectively. A significant effect of smoking on heavy smokers was found (p=0.005). Our study gives additional support to the oxidative stress theory, where M₁dG may reflect an additional potential mechanism of asbestos-induced toxicity.