Alu hypermethylation and high oxidative stress in patients with musculoskeletal tumors

Tumor DNA hypomethylation of LINE-1 is associated with low tumor grade of breast cancer in Tunisian patients

DNA hypomethylation of long interspersed repetitive DNA retrotransposon (LINE-1) and Alu repeats elements of short interspersed elements family (SINEs) is an early event in carcinogenesis that causes transcriptional activation and leads to chromosomal instability. In the current study, DNA methylation levels of LINE-1 and Alu repeats were analyzed in tumoral tissues of invasive breast cancer in a Tunisian cohort and its association with the clinicopathological features of patients was defined. DNA methylation of LINE-1 and Alu repeats were analyzed using pyrosequencing in 61 invasive breast cancers. Median values observed for DNA methylation of LINE-1 and Alu repeats were considered as the cut-off (59.81 and 18.49%, respectively). The results of the current study demonstrated a positive correlation between DNA methylation levels of LINE-1 and Alu repeats (rho=0.284; P<0.03). DNA hypomethylation of LINE-1 was also indicated to be associated with low grade (P=0.023). To the best of our knowledge, the current study is the first study regarding DNA methylation of LINE-1 and Alu repeats element in breast cancer of the Tunisian population. The results of the current study suggest that, since hypomethylation of LINE-1 is associated with low grade, it could be used as a biomarker for prognosis for patients with breast cancer.

Alu Methylation and Risk of Cancer: A Meta-analysis

BACKGROUND

The association between Alu methylation and risk of cancer remains uncertain. This meta-analysis was conducted to elucidate this issue.

MATERIALS AND METHODS

PubMed and Web of Science up to December 31, 2018, and the reference lists of studies, as well as those presented in relevant meta-analyses and reviews were systematically searched. Standardized mean difference (SMD) in Alu methylation level between cases and controls were pooled using random effects model and assessed heterogeneity between strata by stratified factors using meta-regression model. Sensitivity analysis and publication bias test were also conducted.

RESULTS

Twenty-five articles, including 2719 cases and 3018 controls were included in the meta-analysis. The significant difference in Alu methylation level between cancer cases and controls was greater in tissue (SMD = -1.89, 95% CI: -2.72, -1.05) than blood (SMD = -0.46, 95% CI: -0.82, -0.09), and heterogeneity was found in materials (P = 0.038). In tissue samples, Alu hypomethylation was found in carcinoma (SMD = -2.50, 95% CI: -3.51, -1.48), while not in non-carcinoma. The inverse associations were consistently found in subgroups stratified by data sources and quality score in tissue samples, and publication year was considered to be the potential source of between-study heterogeneity. Moreover, reduced Alu methylation level was found in the European subgroup, detection method of SIRPH and COBRA, and original data source in blood samples.

CONCLUSIONS

Alu hypomethylation was associated with increased risk of cancer, which could be a potential biomarker for cancer.

Relative telomere length and oxidative stress in musculoskeletal tumors

Telomeres are capped at the end of the chromosome and gradually shorten when the cell divides. When there is an oxidative stress, it can cause the DNA to be damaged. Hence, 8-hydroxy-2'-deoxyguanosine (8-OHdG) has been shown to be an indicator for oxidative DNA damage. This study aimed to determine the relative telomere length (RTL) and 8-OHdG levels in neoplastic tissues, adjacent non-neoplastic tissues, and blood leukocytes of musculoskeletal (MS) tumor patients. Neoplastic tissues were compared to adjacent non-neoplastic tissues in MS tumor patients (n = 46). Peripheral blood leukocytes (PBLs) of MS tumor subjects were compared to those of age-matched healthy controls (n = 107). RTL was evaluated by quantitative real-time polymerase chain reaction and 8-OHdG levels were quantified by enzyme-linked immunosorbent assay. The RTL in neoplastic tissues was significantly shorter than that in non-neoplastic tissues [1.12 (0.86-1.46) vs 1.45 (1.25-1.65), P = 0.001]. PBLs had lower RTL than non-neoplastic tissues in MS tumor patients [1.04 (0.85-1.13) vs 1.45 (1.25-1.65), P < 0.001]. However, there was no significant difference between RTL in PBLs and in neoplastic tissues. In addition, PBLs of MS tumor patients had higher RTL than those of the controls [1.04 (0.85-1.13) versus 0.78 (0.68-0.90), P < 0.001]. The 8-OHdG levels in neoplastic tissues were remarkably higher than those in non-neoplastic tissues [8.14 (6.81-11.37) nM/μg/μl vs. 3.79 (2.53-6.17) nM/μg/μl, P < 0.001]. Furthermore, plasma 8-OHdG levels in MS tumor patients were markedly greater than those in the controls [102.50 (73.16-133.50) nM vs. 41.09 (6.81-11.37) nM, P < 0.001]. Area under the curve (AUC) was 0.7536 (95% confident interval (CI) 0.6602-0.8469) when the cut-off value of RTL in PBLs was 0.97. Also, plasma 8-OHdG levels depicted that when the cut-off value was 38.67 nM, the AUC was 0.7723 (95% CI 0.6920-0.8527). Moreover, ROC curve analysis showed that both RTL and 8-OHdG appeared to improve the sensitivity (85.68%) and specificity (70.91%) with the AUC 0.8639 (95% CI 0.7500-0.9500). This study suggested that blood leukocyte RTL and plasma 8-OHdG could serve as promising non-invasive biomarkers to differentiate between MS tumor patients and healthy controls. Additionally, telomere attrition and increased oxidative DNA damage might play contributory roles in the pathogenesis of MS tumors.