Association of mitochondrial deoxyribonucleic acid mutation with polymorphism in CYP2E1 gene in oral carcinogenesis

Altered methyltransferase gene expression, mitochondrial copy number and 4977-bp common deletion in subfertile men with variable sperm parameters

Semen parameters have been found to predict reproductive success poorly and are the most prevalent diagnostic tool for male infertility. There are few conflicting reports regarding the correlation of DNMT genes expression, mitochondrial DNA copy number (mtDNAcn) and deletion (mtDNAdel) with different sperm parameters. To investigate DNMT mRNA level, mtDNAcn and deletion in infertile men, with different sperm parameters, compared with fertile men, semen samples from 30 men with unknown male infertility and normal sperm parameters (experimental group I), 30 infertile patients with at least two abnormal sperm parameters (experimental group II) and 30 fertile normozoospermic men (control group) were collected. After semen analysis, total RNA and DNA were extracted. The isolated DNA was used for assessing the respective mtDNAcn and the presence of common 4977 bp deletion in mtDNA by applying real-time quantitative PCR and multiplex PCR, respectively. Synthesized cDNA from total RNAs was used to quantify DNMT1, DNMT3A and DNMT3B transcripts in study groups by using real-time quantitative reverse-transcription PCR. Significantly higher proportions of mtDNAcn were found in experimental group II. DNMT1 was significantly downregulated in both experimental groups and 4977 bp deletion was not detected. Progressive motility and normal morphology were significantly and negatively correlated with mtDNAcn. A significant positive correlation was detected between sperm parameters and DNMT1 mRNA levels. In conclusion, infertile men with different sperm parameter qualities showed elevated mtDNA content. Abnormal sperm parameters associated with DNMT1 gene expression indicate the possibility of changes in some epigenetic aspects of spermatogenesis in subfertile men with different sperm parameters.

Correlation of Sperm Mitochondrial DNA 7345 bp and 7599 bp Deletions with Asthenozoospermia in Jordanian Population

Background:

Alterations in sperm mitochondrial DNA (mtDNA) affect the functions of some OXPHOS proteins which will affect sperm motility and may be associated with asthenozoospermia. The purpose of this study was to investigate the correlation between 7599-bp and 7345-bp sperm mtDNA deletions and asthenozoospermia in Jordan.

Methods:

Semen specimens from 200 men including 121 infertile and 79 healthy individuals were collected at the Royal Jordanian Medical Services In-vitro fertilization (IVF) units. The mtDNA was extracted followed by mtDNA amplification. Polymerase chain reaction (PCR) was conducted for the target sequences, then DNA sequencing was performed for the PCR products. Chi-square, Fisher’s and Spearman’s tests were used to calculate the correlation.

Results:

The results showed a significant correlation between the presence of 7599-bp mtDNA deletion and infertility where the frequency of the 7599-bp deletion was 63.6% in the infertile group compared to the fertile 34.2% (p<0.001, (OR=3.37, 95% CI=1.860 to 6.108)). Additionally, the sperm motility showed a significant association with the frequency of the 7599-bp deletion (p=0.001, r=−0.887). The 7345-bp mtDNA deletion showed no assoctiation with the infertility (p=0.65, (OR=0.837, 95% CI= 0.464–1.51)) or asthenozoospermia (p=0.98, r=0.008).

Conclusion:

We demonstrated a significant correlation between asthenozoospermia and the 7599-bp mtDNA deletion but not the 7345-bp mtDNA deletion in the infertile men in Jordan. Screening for deletions in sperm mtDNA can be used as a pre-diagnostic molecular marker for male infertility.

The Uprising of Mitochondrial DNA Biomarker in Cancer

Cancer is a heterogeneous group of diseases, the progression of which demands an accumulation of genetic mutations and epigenetic alterations of the human nuclear genome or possibly in the mitochondrial genome as well. Despite modern diagnostic and therapeutic approaches to battle cancer, there are still serious concerns about the increase in death from cancer globally. Recently, a growing number of researchers have extensively focused on the burgeoning area of biomarkers development research, especially in noninvasive early cancer detection. Intergenomic cross talk has triggered researchers to expand their studies from nuclear genome-based cancer researches, shifting into the mitochondria-mediated associations with carcinogenesis. Thus, it leads to the discoveries of established and potential mitochondrial biomarkers with high specificity and sensitivity. The research field of mitochondrial DNA (mtDNA) biomarkers has the great potential to confer vast benefits for cancer therapeutics and patients in the future. This review seeks to summarize the comprehensive insights of nuclear genome cancer biomarkers and their usage in clinical practices, the intergenomic cross talk researches that linked mitochondrial dysfunction to carcinogenesis, and the current progress of mitochondrial cancer biomarker studies and development.

Elevated exposure to polycyclic aromatic hydrocarbons (PAHs) may trigger cancers in Pakistan: an environmental, occupational, and genetic perspective

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic compounds which are emitted through incomplete combustion of organic materials, fossil fuels, consumption of processed meat, smoked food, and from various industrial activities. High molecular mass and mobility make PAHs widespread and lethal for human health. A cellular system in human detoxifies these toxicants through specialized enzymatic machinery called xenobiotic-metabolizing (CYP450) and phase-II (GSTs) enzymes (XMEs). These metabolizing enzymes include cytochromes P450 family (CYP1, CYP2), glutathione s-transferases, and ALDHs. Gene polymorphisms in XMEs encoding genes can compromise their metabolizing capacity to detoxify ingested carcinogens (PAHs etc.) that may lead to prolong and elevated exposure to ingested toxicants and may consequently lead to cancer. Moreover, PAHs can induce cancer through reprograming XMEs' gene functions by altering their epigenetic markers. This review article discusses possible interplay between individual's gene polymorphism in XMEs' genes, their altered epigenetic markers, and exposure to PAHs in cancer susceptibility in Pakistan.

Role of Mitochondrial DNA (mtDNA) Variations in Cancer Development: A Systematic Review

mtDNA is the closed circular, ds-DNA present in mitochondria of eukaryotic cells and are inherited maternally. Besides being the power house of the cell, mitochondria are also responsible for the regulation of redox homeostasis, signaling, metabolism, immunity, survival and apoptosis. Lack of a 'Systematic Review' on mtDNA variations and cancers encouraged us to perform the present study. Pubmed', 'Embase' and 'Cochrane Library' databases were searched using keywords 'Mitochondrial DNA' OR 'mtDNA' OR 'mDNA' AND 'polymorphism' AND 'cancer' AND 'risk' to retrieve literature. Polymorphisms occupy first rank among mtDNA variations followed by CNV, MSI, mutations and hold a great potential to emerge as key predictors for human cancers.

A comprehensive overview of mitochondrial DNA 4977-bp deletion in cancer studies

Mitochondria are cellular machines essential for energy production. The biogenesis of mitochondria is a highly complex and it depends on the coordination of the nuclear and mitochondrial genome. Mitochondrial DNA (mtDNA) mutations and deletions are suspected to be associated with carcinogenesis. The most described mtDNA deletion in various human cancers is called the 4977-bp common deletion (mDNA⁴⁹⁷⁷) and it has been explored since two decades. In spite of that, its implication in carcinogenesis still unknown and its predictive and prognostic impact remains controversial. This review article provides an overview of some of the cellular and molecular mechanisms underlying mDNA⁴⁹⁷⁷ formation and a detailed summary about mDNA⁴⁹⁷⁷ reported in various types of cancers. The current knowledges of mDNA⁴⁹⁷⁷ as a prognostic and predictive marker are also discussed.

Analysis of the role of rs2031920 and rs3813867 polymorphisms within the cytochrome P450 2E1 gene in the risk of squamous cell carcinoma

Background

To explore the genetic effect of rs2031920 and rs3813867 polymorphisms within the cytochrome P450 2E1 (CYP2E1) gene on the risk of squamous cell carcinoma (SCC), a meta-analysis was performed.

Methods

The eligible case–control studies were obtained by database searching and screening, and the specific statistical analysis was performed with STATA 12.0 software.

Results

After the process of database searching and screening, a total of 32 case–control studies with 7435 cases and 10,466 controls were ultimately included in our meta-analysis. With regard to the rs2031920 C/T polymorphism, in comparison to controls, a reduced risk in cases of esophageal squamous cell carcinoma (ESCC) was detected for the models of allele T vs. allele C [P = 0.025, odds ratio (OR) = 0.67], carrier T vs. carrier C (P = 0.014, OR = 0.70), TT vs. CC (P = 0.029, OR = 0.65), CT vs. CC (P = 0.040, OR = 0.56), CT + TT vs. CC (P = 0.035, OR = 0.58). Similarly, a decreased SCC risk was observed for the rs3813867 G/C polymorphism in the allele, carrier, homozygote, dominant, and recessive models of overall SCC meta-analysis and “ESCC” subgroup analysis (all P < 0.05, OR < 1) and in all genetic models of “Asian” and “population-based control (PB)” subgroup analysis (all P < 0.05, OR < 1). Additionally, for the rs2031920/rs3813867 haplotype, a decreased SCC risk was also detected in the overall SCC meta-analysis under the allele, carrier, homozygote and dominant model (all P < 0.05, OR < 1) and the subgroup analysis of “PB” under the allele, carrier, and dominant models (all P < 0.05, OR < 1).

Conclusions

Our meta-analysis supports the “T” allele carrier of the CYP2E1 rs2031920 C/T polymorphism and “C” allele carrier of the rs3813867 G/C polymorphism as protective factors for ESCC patients, especially in Asian populations.

Does CYP2E1 RsaI/PstI polymorphism confer head and neck carcinoma susceptibility?: A meta-analysis based on 43 studies

BACKGROUND

Previous reports showed that CYP2E1 RsaI/PstI polymorphism may be a risk factor for cancers. Published meta-analyses in 2010 and 2011, respectively, on the relationship of CYP2E1 RsaI/PstI polymorphisms with the susceptibility to head and neck carcinoma (HNC) have generated inconsistent results. Thus, this study aimed to conduct an updated meta-analysis involving published studies up to Nov 2015 to get a more confidential result.

METHODS

Eligible studies up to Nov 2015 were retrieved and screened. Data were extracted and a quantitative meta-analysis was conducted. Subgroup analyses on ethnicity, source of controls, sample size, genotyping method, smoking status, and drinking status were also performed.

RESULTS

Forty-one publications including a total of 43 case-control studies were selected for analysis. The overall data under a homozygote comparison model indicated a significant association of CYP2E1 RsaI/PstI polymorphisms with HNC risk (c2c2 vs c1c1: odds ratio [OR] = 1.97; 95% confidence interval [CI] = 1.53-2.53). Similar results were observed in the Asian subgroup (c2c2 vs c1c1: OR = 1.98; 95%CI = 1.51-2.60; c2 vs c1: OR = 1.20; 95%CI = 1.03-1.39) and mixed population (c2 vs c1: OR = 1.41; 95%CI = 1.06-1.86) when the data were stratified by ethnicities. Interestingly, increased cancer risk only was shown among never-smokers (c2c2+c1c2 vs c1c1: OR = 1.44; 95%CI = 1.05-1.98) but not ever-smokers.

CONCLUSION

CYP2E1 RsaI/PstI polymorphisms may modify the susceptibility to HNC, particularly among Asians, mixed population, and never-smokers. Future large and well-designed studies are needed to verify this conclusion.

Mitochondrial common deletion, a potential biomarker for cancer occurrence, is selected against in cancer background: a meta-analysis of 38 studies

Mitochondrial dysfunction has been long proposed to play a major role in tumorigenesis. Mitochondrial DNA (mtDNA) mutations, especially the mtDNA 4,977 bp deletion has been found in patients of various types of cancer. In order to comprehend the mtDNA 4,977 bp deletion status in various cancer types, we performed a meta-analysis composed of 33 publications, in which a total of 1613 cancer cases, 1516 adjacent normals and 638 healthy controls were included. When all studies were pooled, we found that cancerous tissue carried a lower mtDNA 4,977 bp deletion frequency than adjacent non-cancerous tissue (OR = 0.43, 95% CI = 0.20-0.92, P = 0.03 for heterogeneity test, I(2) = 91.5%) among various types of cancer. In the stratified analysis by cancer type the deletion frequency was even lower in tumor tissue than in adjacent normal tissue of breast cancer (OR = 0.19, 95% CI = 0.06-0.61, P = 0.005 for heterogeneity test, I(2)= 82.7%). Interestingly, this observation became more significant in the stratified studies with larger sample sizes (OR = 0.70, 95% CI = 0.58-0.86, P = 0.0005 for heterogeneity test, I(2) = 95.1%). Furthermore, when compared with the normal tissue from the matched healthy controls, increased deletion frequencies were observed in both adjacent non-cancerous tissue (OR = 3.02, 95% CI = 2.13-4.28, P<0.00001 for heterogeneity test, I(2)= 53.7%), and cancerous tissue (OR = 1.36, 95% CI = 1.04-1.77, P = 0.02 for heterogeneity test, I(2)= 83.5%). This meta-analysis suggests that the mtDNA 4,977 bp deletion is often found in cancerous tissue and thus has the potential to be a biomarker for cancer occurrence in the tissue, but at the same time being selected against in various types of carcinoma tissues. Larger and better-designed studies are still warranted to confirm these findings.