Benzene-derived N2-(4-hydroxyphenyl)-deoxyguanosine adduct: UvrABC incision and its conformation in DNA

A DNA Cleavage Assay Using Synthetic Oligonucleotide Containing a Single Site-Directed Lesion for In Vitro Base Excision Repair Study

Many chemicals cause mutation or cancer in animals and humans by forming DNA lesions, including base adducts, which play a critical role in mutagenesis and carcinogenesis. A large number of such adducts are repaired by the DNA glycosylase-mediated base excision repair (BER) pathway, and some are processed by nucleotide excision repair (NER) and nucleotide incision repair (NIR). To understand what structural features determine repair enzyme specificity and mechanism in chemically modified DNA in vitro, we developed and optimized a DNA cleavage assay using defined oligonucleotides containing a single, site specifically placed lesion. This assay can be used to investigate novel activities against any newly identified derivatives from chemical compounds, substrate specificity and cleavage efficiency of repair enzymes, and quantitative structure-function relationships. Overall, the methodology is highly sensitive and can also be modified to explore whether a lesion is processed by NER or NIR activity, as well as to study its miscoding properties in translesion DNA synthesis (TLS).

Changes in cognitive function and related brain regions in chronic benzene poisoning: a case report

To discuss the changes in cognitive function and related brain regions in patients with chronic benzene poisoning. Few studies have explored the damage to cognitive function that occurs in benzene toxic encephalopathy. It is important to identify early in the course of disease whether cognitive dysfunction is caused by benzene poisoning so that disease prognosis and appropriate treatment can be determined. We reported on the chronic benzene poisoning of a 41-year-old Han Chinese woman. The patient had graduated from primary school, and she had a cheerful and diligent personality. She had performed painting work for more than five years, and her primary work involved painting swivel chairs. The primary reasons she attended the psychiatric clinic were loss of appetite, she had experienced fatigue for more than 2 months, and she had had memory loss for a month. These symptoms seriously impacted the patient’s daily life and ability to work. The patient’s husband expressed concern that she could not recognize acquaintances, could not find her way home, and had lost approximately 5 kg per month over two months. We analyzed changes in this chronic benzene poisoning patient’s cognitive function with cognitive function assessments and magnetic resonance imaging (MRI). Measurements were taken on presentation to hospital, during the patient’s hospitalization, and three months following discharge. Long-term exposure to benzene can damage the central nervous system. However, it is difficult to recognize when cognitive impairment is caused by chronic benzene poisoning, as it rarely presents with a decline in cognitive function as the primary clinical manifestation. Atypical symptoms, such as decreased immune function and gastrointestinal issues, may be the first symptoms to appear, and these atypical symptoms are difficult to detect in the early stages of disease. Regular screening of high-risk groups is required to significantly reduce the incidence of systemic damage caused by benzene poisoning.

Genetic Polymorphisms in XRCC1, CD3EAP, PPP1R13L, XPB, XPC, and XPF and the Risk of Chronic Benzene Poisoning in a Chinese Occupational Population

Objectives

Individual variations in the capacity of DNA repair machinery to relieve benzene-induced DNA damage may be the key to developing chronic benzene poisoning (CBP), an increasingly prevalent occupational disease in China. ERCC1 (Excision repair cross complementation group 1) is located on chromosome 19q13.2–3 and participates in the crucial steps of Nucleotide Excision Repair (NER); moreover, we determined that one of its polymorphisms, ERCC1 rs11615, is a biomarker for CBP susceptibility in our previous report. Our aim is to further explore the deeper association between some genetic variations related to ERCC1 polymorphisms and CBP risk.

Methods

Nine single nucleotide polymorphisms (SNPs) of XRCC1 (X-ray repair cross-complementing 1), CD3EAP (CD3e molecule, epsilon associated protein), PPP1R13L (protein phosphatase 1, regulatory subunit 13 like), XPB (Xeroderma pigmentosum group B), XPC (Xeroderma pigmentosum group C) and XPF (Xeroderma pigmentosum group F) were genotyped by the Snapshot and TaqMan-MGB^® probe techniques, in a study involving 102 CBP patients and 204 controls. The potential interactions between these SNPs and lifestyle factors, such as smoking and drinking, were assessed using a stratified analysis.

Results

An XRCC1 allele, rs25487, was related to a higher risk of CBP (P<0.001) even after stratifying for potential confounders. Carriers of the TT genotype of XRCC1 rs1799782 who were alcohol drinkers (OR = 8.000; 95% CI: 1.316–48.645; P = 0.022), male (OR = 9.333; 95% CI: 1.593–54.672; P = 0.019), and had an exposure of ≤12 years (OR = 2.612; 95% CI: 1.048–6.510; P = 0.035) had an increased risk of CBP. However, the T allele in PPP1R13L rs1005165 (P<0.05) and the GA allele in CD3EAP rs967591 (OR = 0.162; 95% CI: 0039~0.666; P = 0.037) decreased the risk of CBP in men. The haplotype analysis of XRCC1 indicated that XRCC1 rs25487^A, rs25489^G and rs1799782^T (OR = 15.469; 95% CI: 5.536–43.225; P<0.001) were associated with a high risk of CBP.

Conclusions

The findings showed that the rs25487 and rs1799782 polymorphisms of XRCC1 may contribute to an individual’s susceptibility to CBP and may be used as valid biomarkers. Overall, the genes on chromosome 19q13.2–3 may have a special significance in the development of CBP in occupationally exposed Chinese populations.

Association of genetic polymorphisms in ERCC1 and ERCC2/XPD with risk of chronic benzene poisoning in a Chinese occupational population

DNA damage induced by benzene and its metabolites is thought of as an important mechanism underlying benzene genotoxicity in chronic benzene poisoning (CBP). Therefore, genetic variation in DNA repair genes may contribute to susceptibility to CBP in the exposed population. Since benzene-induced DNA damages include DNA adducts, we hypothesized that the polymorphisms of ERCC1 (Excision repair cross complementation group 1) and ERCC2/XPD (Excision repair cross complementation group 2/xeroderma pigmentosum group D) are associated with the risk of CBP. A case-control study involving 102 benzene-poisoned patients and 204 none-benzene-poisoned controls occupationally exposed to benzene was carried out in the Northeast region of China. The polymorphisms of codon 118 (rs11615) and C8092A (rs3212986) of ERCC1, codon 751 (rs13181), 312 (rs1799793) and 156 (rs238406) of ERCC2/XPD were genotyped by TaqMan(®) Real-time PCR. The results showed that individuals carrying the ERCC1 codon 118 TT genotype had an increased risk of CBP (OR(adj)=3.390; 95%CI: 1.393-8.253; P=0.007) comparing with its CC genotype. After stratified by smoking, gender and exposure duration we found that the increased risk of CBP associated with the ERCC1 codon 118 TT genotype confined to nonsmokers (OR=3.214; 95% CI: 1.359-7.601; P=0.006), female (OR=3.049; 95% CI: 1.235-7.529; P=0.013) and exposure duration> 12 years (OR=3.750; 95% CI: 1.041-13.513; P=0.035). Since ERCC1 and ERCC2/XPD are both located on chromosome 19q13.3, haplotype analysis of all 5 SNPs was also conducted. However no correlations between the risks of CBP and other genotypes or haplotypes were found. Therefore, our findings suggest an important role of ERCC1 codon 118 polymorphisms for a biomarker to CBP in the Chinese occupational population.

C8-linked bulky guanosine DNA adducts: experimental and computational insights into adduct conformational preferences and resulting mutagenicity

Bulky DNA adducts are formed through the covalent attachment of aryl groups to the DNA nucleobases. Many of these adducts are known to possess conformational heterogeneity, which is responsible for the variety of mutagenic outcomes associated with these lesions. The present contribution reviews several conformational and mutagenic themes that are prevalent among the DNA adducts formed at the C8-site of the guanine nucleobase. The most important conclusions obtained (to date) from experiments are summarized including the anti/syn conformational preference of the adducts, their potential to inflict DNA mutations and mismatch stabilization, and their interactions with DNA polymerases and repair enzymes. Additionally, the unique role that computer calculations can play in understanding the structural properties of these adducts are highlighted.

Formation and repair of tobacco carcinogen-derived bulky DNA adducts

DNA adducts play a central role in chemical carcinogenesis. The analysis of formation and repair of smoking-related DNA adducts remains particularly challenging as both smokers and nonsmokers exposed to smoke are repetitively under attack from complex mixtures of carcinogens such as polycyclic aromatic hydrocarbons and N-nitrosamines. The bulky DNA adducts, which usually have complex structure, are particularly important because of their biological relevance. Several known cellular DNA repair pathways have been known to operate in human cells on specific types of bulky DNA adducts, for example, nucleotide excision repair, base excision repair, and direct reversal involving O⁶-alkylguanine DNA alkyltransferase or AlkB homologs. Understanding the mechanisms of adduct formation and repair processes is critical for the assessment of cancer risk resulting from exposure to cigarette smoke, and ultimately for developing strategies of cancer prevention. This paper highlights the recent progress made in the areas concerning formation and repair of bulky DNA adducts in the context of tobacco carcinogen-associated genotoxic and carcinogenic effects.