Use of Comet assay to assess DNA damage in patients infected by Helicobacter pylori: comparisons between visual and image analyses

Comet assay as a suitable biomarker for in vivo oral carcinogenesis: a systematic review

BACKGROUND AND OBJECTIVES

In order to detect genetic damage, different methods have been developed, such as micronuclei and comet assay. The comet assay presents some advantages when compared to the other aforementioned methods, including wide versatility, as any eukaryotic cell can be evaluated at an individual cellular level. In this context, the aim of this systematic review was designed to help further elucidate the following question: is the comet assay a suitable biomarker of in vivo oral carcinogenesis?

MATERIAL AND METHODS

The present systematic review was performed in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Full manuscripts from 18 studies were carefully selected in this setting.

RESULTS

A total of 15 studies demonstrated positive findings for genotoxicity in peripheral blood or oral cells in patients with pre-malignant lesions or oral cancer. In the quality assessment of studies, 1 was classified as Strong, 5 were considered as Moderate, and 12 were classified as Weak.

CONCLUSION

In summary, the comet assay can be a useful biomarker for oral carcinogenesis. However, further studies with more strict parameters are suggested (with less uncontrolled confounders) in order to increase findings reliability for diagnosis of oral potentially malignant lesions.

H. pylori infection alters repair of DNA double-strand breaks via SNHG17

Chronic infections can lead to carcinogenesis through inflammation-related mechanisms. Chronic infection of the human gastric mucosa with Helicobacter pylori is a well-known risk factor for gastric cancer. However, the mechanisms underlying H. pylori-induced gastric carcinogenesis are incompletely defined. We aimed to screen and clarify the functions of long noncoding RNAs (lncRNAs) that are differentially expressed in H. pylori-related gastric cancer. We found that lncRNA SNHG17 was upregulated by H. pylori infection and markedly increased the levels of double-strand breaks (DSBs). SNHG17 overexpression correlated with poor overall survival in patients with gastric cancer. The recruitment of NONO by overabundant nuclear SNHG17, along with the role of cytoplasmic SNHG17 as a decoy for miR-3909, which regulates Rad51 expression, shifted the DSB repair balance from homologous recombination toward nonhomologous end joining. Notably, during chronic H. pylori infection, SNHG17 knockdown inhibited chromosomal aberrations. Our findings suggest that spatially independent deregulation of the SNHG17/NONO and SNHG17/miR-3909/RING1/Rad51 pathways upon H. pylori infection promotes tumorigenesis in gastric cancer by altering the DNA repair system, which is critical for the maintenance of genomic stability. Upregulation of SNHG17 by H. pylori infection might be an undefined link between cancer and inflammation.

The Significance of 8-oxoGsn in Aging-Related Diseases

Aging is a common risk factor for the occurrence and development of many diseases, such as Parkinson’s disease, Alzheimer’s disease, diabetes, hypertension, atherosclerosis and coronary heart disease, and cancer, among others, and is a key problem threatening the health and life expectancy of the elderly. Oxidative damage is an important mechanism involved in aging. The latest discovery pertaining to oxidative damage is that 8-oxoGsn (8-oxo-7,8-dihydroguanosine), an oxidative damage product of RNA, can represent the level of oxidative stress. The significance of RNA oxidative damage to aging has not been fully explained, but the relationship between the accumulation of 8-oxoGsn, a marker of RNA oxidative damage, and the occurrence of diseases has been confirmed in many aging-related diseases. Studying the aging mechanism, monitoring the aging level of the body and exploring the corresponding countermeasures are of great significance for achieving healthy aging and promoting public health and social development. This article reviews the progress of research on 8-oxoGsn in aging-related diseases.

DNA damage assessment in the lymphocytes of construction painters by comet assay

BACKGROUND

Exposure to chemicals is inevitable for certain occupational groups, particularly in industrial countries. Some cytogenetic tests such as comet assay are effectively utilized to screen genotoxic effects of these chemicals in humans. The purpose of this study has been to assess the DNA damage in construction painters' lymphocytes using the comet assay.

METHODS

Fourteen male construction painters with 1 year of required work experience were randomly selected from the list of Painter Union in Gonabad city, Iran. In addition, 14 healthy male non-painters were randomly selected as controls. The DNA damage degree was determined using a fluorescence microscope and CometScore software. The obtained data were analyzed employing independent t-test using SPSS software v. 14 at the significant level of p < 0.05.

RESULTS

All participants were non-smokers and non-alcoholics. No significant differences were found between the two groups in terms of age, weight, height, body mass index, and systolic and diastolic blood pressure. The DNA damage in the painter group was significantly greater than that of the control group. Tail length (µm) was 12.63 ± 6.54 versus 2.90 ± 0.84, tail DNA (%) was 4.33 ± 1.84 versus 1.29 ± 0.43, and tail moment (µm) was 1.85 ± 0.98 versus 0.14 ± 0.20 in painter and control groups ( p < 0.001), respectively.

CONCLUSION

The chemicals used in oil paint may increase the DNA damage in painter blood lymphocytes.

Kinetic response of a genotoxicity biomarker in the three-spined stickleback and implication for environmental monitoring

The ultimate sink for the majority of anthropogenic compounds are the aquatic ecosystems, either through direct discharges or indirectly through hydrologic or atmospheric processes, possibly leading to long-term adverse effects in aquatic living resources. In order to assess exposure, fate and effects of chemical contaminants, aquatic ecotoxicologists have developed a large array of early-warning biomarkers proving that toxicants have entered organisms, have been distributed between organs and have triggered toxic effects regarding critical targets. However, optimal use of biomarkers in environmental studies previously requires in-depth knowledge of the kinetics of response of biomarkers. This work aimed to define as a first step of a validation process the kinetic response of a genotoxicity biomarker recently developed in the three-spined stickleback (Gasterosteus aculeatus). DNA damage was assessed in stickleback erythrocytes after in vivo exposure for 12 days to methylmethanesulfonate (MMS), an alkylating compound, followed by a 20 day-recovery period. Results show a dose-response relationship, time to maximal induction being reached after 6 days at the highest MMS concentration. No acclimation process was noticed during exposure whatever the MMS concentration, and genotoxicity decreased during the recovery phase only in fish exposed to the highest MMS concentration, suggesting more an effect of erythrocyte turn-over than of DNA repair system on the observed DNA damage level. Further field experiments are needed before including this genotoxicity biomarker in a battery of biochemical markers to monitor adverse effects of pollutants on fish health.

Multi-level stressor analysis from the DNA/biochemical level to community levels in an urban stream and integrative health response (IHR) assessments

The objectives of this study were to identify multi-level stressors at the DNA/biochemical level to the community level in fish in an urban stream and to develop an integrative health response (IHR) model for ecological health diagnosis. A pristine control site (S (c) ) and an impacted site (S (i) ) were selected from among seven pre-screened sites studied over seven years. Various chemical analyses indicated that nutrient enrichment (Nitrogen, Phosphorus) and organic pollution were significantly greater (t > 8.783, p < 0.01) at the S (i) site compared to the S (c) site. Single-cell gel electrophoresis (comet assays) of DNA-level impairment indicated significantly (t = 5.678, p < 0.01) greater tail intensity, expressed as % tail-DNA, at the S (i) site and genotoxic responses were detected in the downstream reach. Ethoxyresorufin-O-deethylase (EROD) assays, as a physiological bioindicator, were 2.8-fold higher (p < 0.05, NK-test after ANOVA) at the S (i) site. Tissue analysis using a necropsy-based health assessment index (NHAI) showed distinct internal organ disorders in three tissues, i.e., liver, kidney, and gill, at the S (i) site. Population-level analysis using the sentinel species Zacco platypus showed that the regression coefficient (b) was 3.012 for the S (i) site and 2.915 for the S (c) site, indicating population skewness in the downstream reach. Community-level health was impaired at the S (i) site based on an index of biological integrity (IBI), and physical habitat modifications were identified by a qualitative habitat evaluation index (QHEI). Overall, the model values for the integrative health response (IHR), developed using the star plot approach, were 3.22 (80.5%) at the S (c) site and 0.74 (18.5%) at the S (i) site, indicating that, overall, ecological health impairments were evident in the urban reach. Our study was based on multi-level approaches using biological organization and the results suggest that there is a pivotal point of linkage between mechanistic understanding and real ecological consequences of environmental stressors.

Avaliação da expressão tecidual do gene de reparo MLH1 e dos níveis de dano oxidativo ao DNA em doentes com câncer colorretal

O dano oxidativo ao DNA provocado por radicais livres de oxigênio representa um dos principais mecanismos responsáveis pelas etapas iniciais da carcinogênese colorretal. O estresse oxidativo ocasiona erros de pareamento de bases possibilitando o aparecimento de mutações em genes controladores do ciclo celular. As células possuem um sistema de defesa representado pelos genes de reparo do DNA que corrigindo os erros de pareamento impedem o desenvolvimento de mutações. Poucos estudos avaliaram a relação entre dano oxidativo ao DNA e a expressão tecidual do gene de reparo MLH1. OBJETIVO: O objetivo do presente estudo foi avaliar os níveis de estresse oxidativo ao DNA e a expressão tecidual do gene de reparo MLH1 nas células da mucosa cólica normal e neoplásica de doentes com câncer colorretal. MATERIAL E MÉTODO: Foram estudados 44 doentes com diagnóstico de adenocarcinoma colorretal. Foram excluídos os doentes com câncer colorretal hereditário, portadores de câncer relacionado às doenças inflamatórias intestinais e os submetidos à radioquimioterapia neoadjuvante. Para a avaliação dos níveis de dano oxidativo ao DNA utilizou-se a técnica da eletroforese alcalina em gel de célula isolada (ensaio do cometa) avaliando 100 células obtidas dos tecidos normal e neoplásico. Para a avaliação da expressão do gene MLH1 utilizou-se a técnica de reação de polimerase em cadeia em tempo real (RT-PCR) com primer especificamente desenhados para amplificação do gene. A comparação dos resultados encontrados para os níveis de estresse oxidativo ao DNA, e expressão do gene MLH1 nos tecidos normais e neoplásicos foi feito pelo teste t de Student, adotando-se nível de significância de 5% (p<0,05). RESULTADOS: Os níveis de dano oxidativo ao DNA no tecido neoplásico foram significativamente mais elevados quando comparados ao tecido normal (p=0,0001). A expressão tecidual do gene MLH1 no tecido neoplásico foi significativamente menor quando comparado ao tecido normal (p=0,02). CONCLUSÃO: O gene de reparo MLH1 encontra-se menos expresso no tecido neoplásico e inversamente relacionado aos níveis de dano oxidativo ao DNA.

Tomato-oleoresin supplement prevents doxorubicin-induced cardiac myocyte oxidative DNA damage in rats

Doxorubicin (DOX) is an efficient chemotherapeutic agent used against several types of tumors; however, its use is limited due to severe cardiotoxicity. Since it is accepted that reactive oxygen species are involved in DOX-induced cardiotoxicity, antioxidant agents have been used to attenuate its side effects. To determine tomato-oleoresin protection against cardiac oxidative DNA damage induced by DOX, we distributed Wistar male rats in control (C), lycopene (L), DOX (D) and DOX+lycopene (DL) groups. They received corn oil (C, D) or tomato-oleoresin (5mg/kg body wt. day) (L, DL) by gavage for a 7-week period. They also received saline (C, L) or DOX (4mg/kg body wt.) (D, DL) intraperitoneally at the 3rd, 4th, 5th, and at 6th week. Lycopene absorption was checked by HPLC. Cardiac oxidative DNA damage was evaluated by the alkaline Comet assay using formamidopyrimidine-DNA glycosylase (FPG) and endonuclease III (endo III). Cardiomyocyte levels of SBs, SBs FPG and SBs Endo III were higher in rats from D when compared to other groups. DNA damage levels in cardiomyocytes from DL were not different when compared to C and L groups. The viability of cardiomyocytes from D or DL was lower than C or L groups (p<0.01). Lycopene levels (mean+/-S.D.nmol/kg) in saponified hearts were similar between L (47.43+/-11.78) and DL (49.85+/-16.24) groups. Our results showed: (1) lycopene absorption was confirmed by its cardiac levels; (2) DOX-induced oxidative DNA damage in cardiomyocyte; (3) tomato-oleoresin supplementation protected against cardiomyocyte oxidative DNA damage.