Associations between cigarette smoking and mitochondrial DNA abnormalities in buccal cells

A state-of-the-science review of using mitochondrial DNA copy number as a biomarker for environmental exposure

Mitochondria are bioenergetic, biosynthetic, and signaling organelles in eukaryotes, and contain their own genomes, mitochondrial DNA (mtDNA), to supply energy to cells by generating ATP via oxidative phosphorylation. Therefore, the threat to mitochondria' integrity and health resulting from environmental exposure could induce adverse health effects in organisms. In this review, we summarized the association between mtDNA copy number (mtDNAcn), and environmental exposures as reported in the literature. We conducted a literature search in the Web of Science using [Mitochondrial DNA copy number] and [Exposure] as two keywords and employed three selection criteria for the final inclusion of 97 papers for review. The consensus of data was that mtDNAcn could be used as a plausible biomarker for cumulative exposures to environmental chemical and physical agents. In order to furtherly expand the application of mtDNAcn in ecological and environmental health research, we suggested a series of algorithms aiming to standardize the calculation of mtDNAcn based on the PCR results in this review. We also discussed the pitfalls of using whole blood/plasma samples for mtDNAcn measurements and regard buccal cells a plausible and practical alternative. Finally, we recognized the importance of better understanding the mechanistic analysis and regulatory mechanism of mtDNAcn, in particular the signals release and regulation pathways. We believe that the development of using mtDNAcn as an exposure biomarker will revolutionize the evaluation of chronic sub-lethal toxicity of chemicals to organisms in ecological and environmental health research that has not yet been implemented.

Associations between mitochondrial biomarkers, urban residential exposures and childhood asthma outcomes over 6 months

Determining biomarkers of responses to environmental exposures and evaluating whether they predict respiratory outcomes may help optimize environmental and medical approaches to childhood asthma. Relative mitochondrial (mt) DNA abundance and other potential mitochondrial indicators of oxidative stress may provide a sensitive metric of the child's shifting molecular responses to its changing environment. We leveraged two urban childhood cohorts (Environmental Control as Add-on Therapy in Childhood Asthma (ECATCh); Columbia Center for Children's Environmental Health (CCCEH)) to ascertain whether biomarkers in buccal mtDNA associate with airway inflammation and altered lung function over 6 months of time and capture biologic responses to multiple external stressors such as indoor allergens and fine particulate matter (PM2.5). Relative mtDNA content was amplified by qPCR and methylation of transfer RNA phenylalanine/rRNA 12S (TF/RNR1), cytochrome c oxidase (CO1), and carboxypeptidase O (CPO) was measured by pyrosequencing. Data on residential exposures and respiratory outcomes were harmonized between the two cohorts. Repeated measures and multiple regression models were utilized to assess relationships between mitochondrial biomarkers, respiratory outcomes, and residential exposures (PM2.5, allergens), adjusted for potential confounders and time-varying asthma. We found across the 6 month visits, a 0.64 fold higher level of TF/RNR1 methylation was detected among those with asthma in comparison to those without asthma ((parameter estimate (PE) 0.64, standard error 0.28, p = 0.03). In prospective analyses, CPO methylation was associated with subsequent reduced forced vital capacity (FVC; PE -0.03, standard error 0.01, p = 0.02). Bedroom dust mouse allergen, but not indoor PM2.5, was associated with higher methylation of TF/RNR1 (PE 0.015, standard error 0.006, p = 0.01). Select mtDNA measures in buccal cells may indicate children's responses to toxic environmental exposures and associate selectively with asthma and lung function.

Histologic Analysis of Buccal Graft Quality Stratified by Tobacco Use in Patients Undergoing Substitution Urethroplasty

OBJECTIVE

To determine if there are histologic differences relative to tobacco exposure in buccal mucosa. Substitution urethroplasty outcomes may be worse in tobacco users and we investigate if the buccal graft is inherently damaged due to chronic tobacco exposure.

METHODS

Subjects undergoing substitution urethroplasty with buccal graft harvest were prospectively consented in this IRB approved study. Subjects with poor dentition were excluded. A detailed tobacco use history was obtained. Cotinine testing was performed day of surgery to confirm or exclude active tobacco use. Trimmed portions of harvested graft were sent for tissue processing. Standard hematoxylin and eosin staining was performed. A single blinded pathologist performed analysis of the slides. Using a scale of none, mild, moderate, or severe slides were analyzed for cytologic atypia, architectural complexity, inflammation, and keratinization. Evidence of vascular damage was noted and the type of inflammation if present was classified.

RESULTS

Twenty-five buccal grafts were analyzed. No evidence of vascular damage or cytologic atypia were noted in any grafts. While mild architectural complexity and mild inflammation, typically lymphocytic, were noted in several of the buccal mucosa sections, this did not appear to correlate with tobacco exposure. The majority of grafts demonstrating increased keratinization correlated with significant tobacco exposure, but this was not consistently noted in all those with tobacco use.

CONCLUSIONS

Buccal mucosa in patients with tobacco exposure did not show significant histologic alterations. Outcomes of substitution urethroplasty may be more impacted by persistent systemic exposure causing local ischemia as opposed to the graft tissue itself.

Saliva-based cell-free DNA and cell-free mitochondrial DNA in head and neck cancers have promising screening and early detection role

BACKGROUND

Cell-free DNA (cfDNA) and cell-free mitochondrial DNA (cf-mtDNA) have been postulated as potential diagnostic and prognostic biomarkers for different human malignancies. Early detection of head and neck malignancies is fundamental for optimal patient management. This study, therefore, aimed to assess the utility of saliva-based liquid biopsy as a noninvasive source of cfDNA and cf-mtDNA for detecting head and neck cancer (HNSCC).

METHODS

One hundred thirty-three patients diagnosed with either oral leukoplakia (OLK) or HNSCC were compared with 137 healthy volunteers. An unstimulated whole saliva sample was collected from each participant. The absolute copy numbers of salivary cf-mtDNA and cfDNA were quantified using Multiplex Quantitative PCR. Two diagnostic indices based on the investigated molecules were assessed for their ability to differentiate between different diagnostic categories.

RESULTS

The median scores of cfDNA and cf-mtDNA were statistically significantly higher among HNSCC patients (p < 0.05), revealing area under the curve values of 0.758 and 0.826, respectively. The associated accuracy for this test in discriminating HNSCC from other diagnostic categories was 77.37% for the cfDNA-based index and 80.5% for the cf-mtDNA-based index. The median score of cfDNA was statistically significantly higher for patients with severe epithelial dysplasia (OED) compared to those with epithelial keratosis with no OED and mild OED. However, there was no significant difference between controls and OLK individuals.

CONCLUSION

cfDNA and cf-mtDNA showed potential for use as precision medicine tools to detect HNSCC. Further multi-centre prospective studies are warranted to assess the prognostic utility of these molecules.

Lung mitochondrial DNA copy number, inflammatory biomarkers, gene transcription and gene methylation in vapers and smokers

BACKGROUND

Mitochondrial DNA copy number (mtCN) maintains cellular function and homeostasis, and is linked to nuclear DNA methylation and gene expression. Increased mtCN in the blood is associated with smoking and respiratory disease, but has received little attention for target organ effects for smoking or electronic cigarette (EC) use.

METHODS

Bronchoscopy biospecimens from healthy EC users, smokers (SM), and never-smokers (NS) were assessed for associations of mtCN with mtDNA point mutations, immune responses, nuclear DNA methylation and gene expression using linear regression. Ingenuity pathway analysis was used for enriched pathways. GEO and TCGA respiratory disease datasets were used to explore the involvement of mtCN-associated signatures.

FINDINGS

mtCN was higher in SM than NS, but EC was not statistically different from either. Overall there was a negative association of mtCN with a point mutation in the D-loop but no difference within groups. Positive associations of mtCN with IL-2 and IL-4 were found in EC only. mtCN was significantly associated with 71,487 CpGs and 321 transcripts. 263 CpGs were correlated with nearby transcripts for genes enriched in the immune system. EC-specific mtCN-associated-CpGs and genes were differentially expressed in respiratory diseases compared to controls, including genes involved in cellular movement, inflammation, metabolism, and airway hyperresponsiveness.

INTERPRETATION

Smoking may elicit a lung toxic effect through mtCN. While the impact of EC is less clear, EC-specific associations of mtCN with nuclear biomarkers suggest exposure may not be harmless. Further research is needed to understand the role of smoking and EC-related mtCN on lung disease risks.

FUNDING

The National Cancer Institute, the National Heart, Lung, and Blood Institute, the Food and Drug Administration Center for Tobacco Products, the National Center For Advancing Translational Sciences, and Pelotonia Intramural Research Funds.

Cannabis smoke condensate induces human gingival epithelial cell damage through apoptosis, autophagy, and oxidative stress

OBJECTIVES

This study aims to investigate the effects of cannabis smoke condensate (CSC) on the adhesion, growth, and signaling pathways of human gingival epithelial cells.

DESIGN

The effects of CSC on cell shape and adhesion, and viability were evaluated after 30 min, 60 min, 2 h, and 24 h of exposure using microscopic observation, cell metabolic activity, and lactate dehydrogenase activity assays. The effects of CSC on cell apoptosis, necrosis, autophagy, and oxidative stress were determined through flow cytometry, while apoptotic and autophagic gene expression were identified via an RT2-PCR array. Phosphorylated signaling pathway proteins were measured using flow cytometry.

RESULTS

CSC deregulated gingival epithelial cell shape and adhesion, decreased cell viability, and increased lactate dehydrogenase release. Its toxic effects included apoptosis, autophagy, and oxidative stress. Moreover, it modulated seven specific apoptotic and six autophagic genes. Furthermore, it decreased phosphorylation in signaling proteins, such as STAT5, ERK12, P38, and nuclear factor κB.

CONCLUSIONS

CSC has notable adverse effects on gingival epithelial cells. This finding indicates that cannabis smoke could impair gingival epithelial cell innate immune function, leading to gingivitis and periodontitis. Oral health professionals may need to document observed modifications in the oral cavity of patients who smoke cannabis and consider these potential changes during clinical care.

Effects of exposure to environmental pollutants on mitochondrial DNA copy number: a meta-analysis

Exposure to environmental pollutants has been associated with alteration on relative levels of mitochondrial DNA copy number (mtDNAcn). However, the results obtained from epidemiological studies are inconsistent. This meta-analysis aimed to evaluate whether environmental pollutant exposure can modify the relative levels of mtDNAcn in humans. We performed a literature search using PubMed, Scopus, and Web of Science databases. We selected and reviewed original articles performed in humans that analyzed the relationship between environmental pollutant exposure and the relative levels of mtDNAcn; the selection of the included studies was based on inclusion and exclusion criteria. Only twenty-two studies fulfilled our inclusion criteria. A total of 6011 study participants were included in this systematic review and meta-analysis. We grouped the included studies into four main categories according to the type of environmental pollutant: (1) heavy metals, (2) polycyclic aromatic hydrocarbons (PAHs), (3) particulate matter (PM), and (4) cigarette smoking. Inconclusive results were observed in all categories; the pooled analysis shows a marginal increase of relative levels of mtDNAcn in response to environmental pollutant exposure. The trial sequential analysis and rate confidence in body evidence showed the need to perform new studies. Therefore, a large-scale cohort and mechanistic studies in this area are required to probe the possible use of relative levels of mtDNAcn as biomarkers linked to environmental pollution exposure.

Alterations of Mitochondrial Network by Cigarette Smoking and E-Cigarette Vaping

Toxins present in cigarette and e-cigarette smoke constitute a significant cause of illnesses and are known to have fatal health impacts. Specific mechanisms by which toxins present in smoke impair cell repair are still being researched and are of prime interest for developing more effective treatments. Current literature suggests toxins present in cigarette smoke and aerosolized e-vapor trigger abnormal intercellular responses, damage mitochondrial function, and consequently disrupt the homeostasis of the organelle's biochemical processes by increasing reactive oxidative species. Increased oxidative stress sets off a cascade of molecular events, disrupting optimal mitochondrial morphology and homeostasis. Furthermore, smoking-induced oxidative stress may also amalgamate with other health factors to contribute to various pathophysiological processes. An increasing number of studies show that toxins may affect mitochondria even through exposure to secondhand or thirdhand smoke. This review assesses the impact of toxins present in tobacco smoke and e-vapor on mitochondrial health, networking, and critical structural processes, including mitochondria fission, fusion, hyper-fusion, fragmentation, and mitophagy. The efforts are focused on discussing current evidence linking toxins present in first, second, and thirdhand smoke to mitochondrial dysfunction.

A novel role for vaping in mitochondrial gene dysregulation and inflammation fundamental to disease development

We constructed and analyzed the whole transcriptome in leukocytes of healthy adult vapers (with/without a history of smoking), ‘exclusive’ cigarette smokers, and controls (non-users of any tobacco products). Furthermore, we performed single-gene validation of expression data, and biochemical validation of vaping/smoking status by plasma cotinine measurement. Computational modeling, combining primary analysis (age- and sex-adjusted limmaVoom) and sensitivity analysis (cumulative e-liquid- and pack-year modeling), revealed that ‘current’ vaping, but not ‘past’ smoking, is significantly associated with gene dysregulation in vapers. Comparative analysis of the gene networks and canonical pathways dysregulated in vapers and smokers showed strikingly similar patterns in the two groups, although the extent of transcriptomic changes was more pronounced in smokers than vapers. Of significance is the preferential targeting of mitochondrial genes in both vapers and smokers, concurrent with impaired functional networks, which drive mitochondrial DNA-related disorders. Equally significant is the dysregulation of immune response genes in vapers and smokers, modulated by upstream cytokines, including members of the interleukin and interferon family, which play a crucial role in inflammation. Our findings accord with the growing evidence on the central role of mitochondria as signaling organelles involved in immunity and inflammatory response, which are fundamental to disease development.

Electronic Cigarettes Induce Mitochondrial DNA Damage and Trigger TLR9 (Toll-Like Receptor 9)-Mediated Atherosclerosis

OBJECTIVE

Electronic cigarette (e-cig) use has recently been implicated in promoting atherosclerosis. In this study, we aimed to investigate the mechanism of e-cig exposure accelerated atherosclerotic lesion development. Approach and Results: Eight-week-old ApoE^-/- mice fed normal laboratory diet were exposed to e-cig vapor (ECV) for 2 hours/day, 5 days/week for 16 weeks. We found that ECV exposure significantly induced atherosclerotic lesions as examined by Oil Red O staining and greatly upregulated TLR9 (toll-like receptor 9) expression in classical monocytes and in the atherosclerotic plaques, which the latter was corroborated by enhanced TLR9 expression in human femoral artery atherosclerotic plaques from e-cig smokers. Intriguingly, we found a significant increase of oxidative mitochondria DNA lesion in the plasma of ECV-exposed mice. Administration of TLR9 antagonist before ECV exposure not only alleviated atherosclerosis and the upregulation of TLR9 in plaques but also attenuated the increase of plasma levels of inflammatory cytokines, reduced the plaque accumulation of lipid and macrophages, and decreased the frequency of blood CCR2⁺ (C-C chemokine receptor type 2) classical monocytes. Surprisingly, we found that cytoplasmic mitochondrial DNA isolated from ECV extract-treated macrophages can enhance TLR9 activation in reporter cells and the induction of inflammatory cytokine could be suppressed by TLR9 inhibitor in macrophages.

CONCLUSIONS

E-cig increases level of damaged mitochondrial DNA in circulating blood and induces the expression of TLR9, which elevate the expression of proinflammatory cytokines in monocyte/macrophage and consequently lead to atherosclerosis. Our results raise the possibility that intervention of TLR9 activation is a potential pharmacological target of ECV-related inflammation and cardiovascular diseases.

Increased telomere length and mtDNA copy number induced by multi-walled carbon nanotube exposure in the workplace

Carbon nanotubes (CNTs) except MWCNT-7 have been classified as Group 3 ["Not classifiable as to its carcinogenicity to humans"] by the IARC. Despite considerable mechanistic evidence in vitro/in vivo, the classification highlights a general lack of data, especially among humans. In our previous study, we reported epigenetic changes in the MWCNT exposed workers. Here, we evaluated whether MWCNT can also cause alterations in aging related features including relative telomere length (TL) and/or mitochondrial copy number (mtDNAcn). Relative TL and mtDNAcn were measured on extracted DNA from peripheral blood from MWCNT exposed workers (N = 24) and non-exposed controls (N = 43) using a qPCR method. A higher mtDNAcn and longer TL were observed in MWCNT exposed workers when compared to controls. Independent of age, sex, smoking behavior, alcohol consumption and BMI, MWCNT-exposure was associated with an 18.30 % increase in blood TL (95 % CI: 7.15-30.62 %; p = 0.001) and 35.21 % increase in mtDNAcn (95 % CI: 19.12-53.46 %). Our results suggest that exposure to MWCNT can induce an increase in the mtDNAcn and TL; however, the mechanistic basis or consequence of such change requires further experimental studies.

Lung cancer increases H2O2 concentration in the exhaled breath condensate, extent of mtDNA damage, and mtDNA copy number in buccal mucosa

We have shown that the H2O2 concentration in exhaled breath condensate (EBC) in lung cancer patients increases significantly compared to the EBC of healthy people and revealed the correlation between the H2O2 level in the EBC and amount of mtDNA damage in buccal mucosa cells. The H2O2 hyper-production may trigger mitochondrial biogenesis, thereby resulting in an increase in mtDNA copy number. However, we did not observe a significant difference in the studied parameters between smokers and non-smokers. Overall, our data suggest that H2O2 concentration in the EBC, the extent of mtDNA damage, and mtDNA copy number in buccal mucosa could be potential as an early diagnostic marker of lung cancer.

Early effects of cigarette smoke extract on human oral keratinocytes and carcinogenesis in head and neck squamous cell carcinoma

Background

Cigarette smoking is a major risk factor for head and neck squamous cell carcinoma. Still, the effect of cigarette smoke on the molecular level is unclear. The aim of the present study was to investigate the early effects of cigarette smoke on carcinogenesis of head and neck squamous cell carcinoma.

Methods

Human oral keratinocytes were exposed for 1 week to standardized cigarette smoke extract, and subsequently RT‐quantitative PCR array was performed. Protein expression of dysregulated genes was determined by immunohistochemistry in tissue samples of oral squamous cell carcinoma, oral leukoplakia, and tonsil mucosa.

Results

RT‐PCR revealed upregulation of ITGA‐2 and MMP‐1, whereas TEK receptor tyrosine kinase was downregulated in human oral keratinocytes. ITGA‐2 and MMP‐1 were significantly overexpressed in tissue samples of oral squamous cell carcinoma in comparison to normal mucosa (P <.01 in all experiments).

Conclusion

Upregulation of ITGA‐2 and MMP‐1 induced by cigarette smoke contributes significantly to oral carcinogenesis.

Early life tobacco exposure and children's telomere length: The HELIX project

Telomere length and mitochondrial DNA content are considered biomarkers of cellular aging, oxidative stress, and inflammation, but there is almost no information on their association with tobacco smoke exposure in fetal and early life. The aim of this study was to assess whether prenatal and childhood tobacco exposure were associated with leukocyte telomere length (LTL) and mitochondrial DNA (mtDNA) content in children. As part of a multi-centre European birth cohort study HELIX (Human Early-Life Exposome) (n = 1396) we assessed maternal smoking status during pregnancy through questionnaires, and through urinary cotinine levels that were then used to classify women as not exposed to smoking (<10 µg/L), exposed to secondhand smoke (SHS) (10-50 µg/L) and active smokers (>50 µg/L). When the children were around 8 years of age (range: 5.4-12.0 years), childhood SHS tobacco smoke exposure was assessed through an extensive questionnaire and through measurements of urinary cotinine (<3.03 µg/L non-detected, >3.03 µg/L detected). Leukocyte mtDNA content and LTL were measured in the children at 8 years employing real time polymerase chain reaction (qPCR). Effect estimates were calculated using multivariate linear regression models for prenatal and childhood exposures adjusted for potential confounders. Maternal cotinine levels indicative of SHS exposure during pregnancy were associated with a decrease of 3.90% in LTL in children (95% CI: -6.68, -0.91), compared with non-smoking, whereas the association for maternal cotinine levels indicative of active smoking did not reach statistical significance (-3.24%; 95% CI: -6.59, 0.21). Childhood SHS tobacco exposure was not associated with LTL in children. Global SHS exposure during childhood was associated with an increase of 3.51% (95% CI: 0.78, 6.27) in mtDNA content. Our findings suggest that tobacco smoke exposure during pregnancy, even at SHS levels, may accelerate telomere shortening in children and thus induce biological aging from an early age.

DNA Adducts as Biomarkers To Predict, Prevent, and Diagnose Disease-Application of Analytical Chemistry to Clinical Investigations

Characterization of the chemistry, structure, formation, and metabolism of DNA adducts has been one of the most significant contributions to the field of chemical toxicology. This work provides the foundation to develop analytical methods to measure DNA adducts, define their relationship to disease, and establish clinical tests. Monitoring exposure to environmental and endogenous toxicants can predict, diagnose, and track disease as well as guide therapeutic treatment. DNA adducts are one of the most promising biomarkers of toxicant exposure owing to their stability, appearance in numerous biological matrices, and characteristic analytical properties. In addition, DNA adducts can induce mutations to drive disease onset and progression and can serve as surrogate markers of chemical exposure. In this perspective, we highlight significant advances made within the past decade regarding DNA adduct quantitation using mass spectrometry. We hope to expose a broader audience to this field and encourage analytical chemistry laboratories to explore how specific adducts may be related to various pathologies. One of the limiting factors in developing clinical tests to measure DNA adducts is cohort size; ideally, the cohort would allow for model development and then testing of the model to the remaining cohort. The goals of this perspective article are to (1) provide a summary of analyte levels measured using state-of-the-art analytical methods, (2) foster collaboration, and (3) highlight areas in need of further investigation.

Mitochondrial DNA somatic mutation burden and heteroplasmy are associated with chronological age, smoking, and HIV infection

The gradual accumulation of mitochondrial DNA (mtDNA) mutations is implicated in aging and may contribute to the accelerated aging phenotype seen with tobacco smoking and HIV infection. mtDNA mutations are thought to arise from oxidative damage; however, recent reports implicate polymerase γ errors during mtDNA replication. Investigations of somatic mtDNA mutations have been hampered by technical challenges in measuring low-frequency mutations. We use primer ID-based next-generation sequencing to quantify both somatic and heteroplasmic blood mtDNA point mutations within the D-loop, in 164 women and girls aged 2-72 years, of whom 35% were smokers and 56% were HIV-positive. Somatic mutations and the occurrence of heteroplasmic mutations increased with age. While transitions are theorized to result from polymerase γ errors, transversions are believed to arise from DNA oxidative damage. In our study, both transition and transversion mutations were associated with age. However, transition somatic mutations were more prevalent than transversions, and no heteroplasmic transversions were observed. We also measured elevated somatic mutations, but not heteroplasmy, in association with high peak HIV viremia. Conversely, heteroplasmy was higher among smokers, but somatic mutations were not, suggesting that smoking promotes the expansion of preexisting mutations rather than de novo mutations. Taken together, our results are consistent with blood mtDNA mutations increasing with age, inferring a greater contribution of polymerase γ errors in mtDNA mutagenesis. We further suggest that smoking and HIV infection both contribute to the accumulation of mtDNA mutations, though in different ways.

Multi-walled carbon nanotubes upregulate mitochondrial gene expression and trigger mitochondrial dysfunction in primary human bronchial epithelial cells

Nanomaterials are a relatively new class of materials that acquire novel properties based on their reduced size. While these materials have widespread use in consumer products and industrial applications, the potential health risks associated with exposure to them remain to be fully characterized. Carbon nanotubes are among the most widely used nanomaterials and have high potential for human exposure by inhalation. These nanomaterials are known to penetrate the cell membrane and interact with intracellular molecules, resulting in a multitude of documented effects, including oxidative stress, genotoxicity, impaired metabolism, and apoptosis. While the capacity for carbon nanotubes to damage nuclear DNA has been established, the effect of exposure on mitochondrial DNA (mtDNA) is relatively unexplored. In this study, we investigated the potential of multi-walled carbon nanotubes (MWCNTs) to impair mitochondrial gene expression and function in human bronchial epithelial cells (BECs). Primary BECs were exposed to sub-cytotoxic doses (up to 3 μg/ml) of MWCNTs for 5 d and assessed for changes in expression of all mitochondrial protein-coding genes, heteroplasmies, and insertion/deletion mutations (indels). Exposed cells were also measured for cytotoxicity, metabolic function, mitochondrial abundance, and mitophagy. We found that MWCNTs upregulated mitochondrial gene expression, while significantly decreasing oxygen consumption rate and mitochondrial abundance. Confocal microscopy revealed induction of mitophagy by 2 hours of exposure. Mitochondrial DNA heteroplasmy and insertion/deletion mutations were not significantly affected by any treatment. We conclude that carbon nanotubes cause mitochondrial dysfunction that leads to mitophagy in exposed BECs via a mechanism unrelated to its reported genotoxicity.

Effects of obesity and weight loss on mitochondrial structure and function and implications for colorectal cancer risk

Colorectal cancer (CRC) is the third most common cancer globally. CRC risk is increased by obesity, and by its lifestyle determinants notably physical inactivity and poor nutrition. Obesity results in increased inflammation and oxidative stress which cause genomic damage and contribute to mitochondrial dysregulation and CRC risk. The mitochondrial dysfunction associated with obesity includes abnormal mitochondrial size, morphology and reduced autophagy, mitochondrial biogenesis and expression of key mitochondrial regulators. Although there is strong evidence that increased adiposity increases CRC risk, evidence for the effects of intentional weight loss on CRC risk is much more limited. In model systems, energy depletion leads to enhanced mitochondrial integrity, capacity, function and biogenesis but the effects of obesity and weight loss on mitochondria in the human colon are not known. We are using weight loss following bariatric surgery to investigate the effects of altered adiposity on mitochondrial structure and function in human colonocytes. In summary, there is strong and consistent evidence in model systems and more limited evidence in human subjects that over-feeding and/or obesity result in mitochondrial dysfunction and that weight loss might mitigate or reverse some of these effects.

Mitochondrial Stress Response in Neural Stem Cells Exposed to Electronic Cigarettes

Stem cells provide a sensitive model to study exposure to toxicants, such as cigarette smoke. Electronic cigarettes (ECs) are popular nicotine delivery devices, often targeted to youth and pregnant mothers. However, little is known about how chemicals in ECs might affect neural stem cells, and in particular their mitochondria, organelles that maintain cell functionality and health. Here we show that the mechanism underlying EC-induced stem cell toxicity is stress-induced mitochondrial hyperfusion (SIMH), a transient survival response accompanied by increased mitochondrial oxidative stress. We identify SIMH as a survival response to nicotine, now widely available in EC refill fluids and in pure form for do-it-yourself EC products. These observed mitochondrial alterations combined with autophagy dysfunction to clear damaged mitochondria could lead to faulty stem cell populations, accelerate cellular aging, and lead to acquired mitochondriopathies. Any nicotine-containing product may likewise stress stem cells with long-term repercussions for users and passively exposed individuals. VIDEO ABSTRACT.

Recent Studies on DNA Adducts Resulting from Human Exposure to Tobacco Smoke

DNA adducts are believed to play a central role in the induction of cancer in cigarette smokers and are proposed as being potential biomarkers of cancer risk. We have summarized research conducted since 2012 on DNA adduct formation in smokers. A variety of DNA adducts derived from various classes of carcinogens, including aromatic amines, polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines, alkylating agents, aldehydes, volatile carcinogens, as well as oxidative damage have been reported. The results are discussed with particular attention to the analytical methods used in those studies. Mass spectrometry-based methods that have higher selectivity and specificity compared to 32P-postlabeling or immunochemical approaches are preferred. Multiple DNA adducts specific to tobacco constituents have also been characterized for the first time in vitro or detected in vivo since 2012, and descriptions of those adducts are included. We also discuss common issues related to measuring DNA adducts in humans, including the development and validation of analytical methods and prevention of artifact formation.

Predictors of mitochondrial DNA copy number and damage in a mercury-exposed rural Peruvian population near artisanal and small-scale gold mining: An exploratory study

Mitochondrial DNA (mtDNA) copy number (CN) and damage in circulating white blood cells have been proposed as effect biomarkers for pollutant exposures. Studies have shown that mercury accumulates in mitochondria and affects mitochondrial function and integrity; however, these data are derived largely from experiments in model systems, rather than human population studies that evaluate the potential utility of mitochondrial exposure biomarkers. We measured mtDNA CN and damage in white blood cells (WBCs) from 83 residents of nine communities in the Madre de Dios region of the Peruvian Amazon that vary in proximity to artisanal and small-scale gold mining. Prior research from this region reported high levels of mercury in fish and a significant association between food consumption and human total hair mercury level of residents. We observed that mtDNA CN and damage were both associated with consumption of fruit and vegetables, higher diversity of fruit consumed, residential location, and health characteristics, suggesting common environmental drivers. Surprisingly, we observed negative associations of mtDNA damage with both obesity and age. We did not observe any association between total hair mercury or, in contrast to previous results, age, with either mtDNA damage or CN. The results of this exploratory study highlight the importance of combining epidemiological and laboratory research in studying the effects of stressors on mitochondria, suggesting that future work should incorporate nutritional and social characteristics, and caution should be taken when applying conclusions from epidemiological studies conducted in the developed world to other regions, as results may not be easily translated. Environ. Mol. Mutagen. 60: 197-210, 2019. © 2018 Wiley Periodicals, Inc.

Molecular alterations associated with chronic exposure to cigarette smoke and chewing tobacco in normal oral keratinocytes

Tobacco usage is a known risk factor associated with development of oral cancer. It is mainly consumed in two different forms (smoking and chewing) that vary in their composition and methods of intake. Despite being the leading cause of oral cancer, molecular alterations induced by tobacco are poorly understood. We therefore sought to investigate the adverse effects of cigarette smoke/chewing tobacco exposure in oral keratinocytes (OKF6/TERT1). OKF6/TERT1 cells acquired oncogenic phenotype after treating with cigarette smoke/chewing tobacco for a period of 8 months. We employed whole exome sequencing (WES) and quantitative proteomics to investigate the molecular alterations in oral keratinocytes chronically exposed to smoke/ chewing tobacco. Exome sequencing revealed distinct mutational spectrum and copy number alterations in smoke/ chewing tobacco treated cells. We also observed differences in proteomic alterations. Proteins downstream of MAPK1 and EGFR were dysregulated in smoke and chewing tobacco exposed cells, respectively. This study can serve as a reference for fundamental damages on oral cells as a consequence of exposure to different forms of tobacco.

Genetic variations related to maternal whole blood mitochondrial DNA copy number: a genome-wide and candidate gene study

We conducted genome-wide (GWAS) and candidate gene association studies of maternal mitochondrial DNA copy number. Maternal peripheral blood was collected during labor and delivery admission from 471 participants of a placental abruption case-control study conducted in Lima, Peru. Single nucleotide polymorphism (SNP) genotyping was performed using the Illumina Cardio-Metabo Chip. Whole blood mitochondrial DNA (mtDNA) copy number was measured using qRT-PCR techniques. We evaluated 119,629 SNPs in the GWAS and 161 SNPs (in 29 mitochondrial biogenesis and oxidative phosphorylation genes) in the candidate association study. Top hits from GWAS and the candidate gene study were selected to compute weighted genetic risk scores (wGRS). Linear regression models were used to calculate effect size estimates and related nominal p values. The top hit in our GWAS was chr19:51063065 in FOXA3 (empirical p values = 2.20e - 6). A total of 134 SNPs had p values < 0.001 including rs17111633 in CNNM1 (p values = 6.32e - 6) and chr19:51083059 in MYPOP (p values = 3.23e - 5). In the candidate association study, several SNPs in PPARG, PRKCA, SP1 and THRB were associated with mtDNA copy number (p values < 0.05). mtDNA copy number was significantly associated with wGRS based on top GWAS hits (β = 0.49, 95% CI:0.38-0.60, p < 0.001). Variations in nuclear DNA are potentially associated with maternal mtDNA copy number.

A prospective study of mitochondrial DNA copy number and the risk of prostate cancer

PURPOSE

Evidence suggests that mitochondrial DNA (mtDNA) copy number increases in response to DNA damage. Increased mtDNA copy number has been observed in prostate cancer (PCa) cells, suggesting a role in PCa development, but this association has not yet been investigated prospectively.

METHODS

We conducted a nested case-control study (793 cases and 790 controls) of men randomized to the screening arm of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) to evaluate the association between pre-diagnosis mtDNA copy number, measured in peripheral blood leukocytes, and the risk of PCa. We used logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI) and polytomous logistic regression to analyze differences in associations by non-aggressive (Stage I/II AND Gleason grade < 8) or aggressive (Stage III/IV OR Gleason grade ≥ 8) PCa.

RESULTS

Although mtDNA copy number was not significantly associated with PCa risk overall (OR 1.23, 95% CI 0.97-1.55, p = 0.089), increasing mtDNA copy number was associated with an increased risk of non-aggressive PCa (OR 1.29, 95% CI 1.01-1.65, p = 0.044) compared to controls. No association was observed with aggressive PCa (OR 1.02, 95% CI 0.64-1.63, p = 0.933). Higher mtDNA copy number was also associated with increased PSA levels among controls (p = 0.014).

CONCLUSIONS

These results suggest that alterations in mtDNA copy number may reflect disruption of the normal prostate glandular architecture seen in early-stage disease, as opposed to reflecting the large number of tumor cells seen with advanced PCa.

Prenatal exposure to tobacco smoke leads to increased mitochondrial DNA content in umbilical cord serum associated to reduced gestational age

We investigated if prenatal exposures to tobacco smoke lead to changes in mitochondrial DNA content (mtDNA) in cord serum and adversely affect newborns' health. Umbilical cord serum cotinine levels were used to determine in utero exposure to smoking. Cord serum mtDNA was measured by quantitative polymerase chain reaction analysis of the genes coding for cytochrome c oxidase1 (MT-CO1) and cytochrome c oxidase2 (MT-CO2). Log transformed levels of mtDNA coding for MT-CO1 and MT-CO2 were significantly higher among infants of active smokers with higher serum level of cotinine (p < 0.05) and inversely associated with gestational age (p = 0.08; p = 0.02). Structural equation modeling results confirmed a positive association between cotinine and MT-CO1 and2 (p < 0.01) and inverse associations with gestational age (p = 0.02) and IGF-1 (p < 0.01). We identified a dose-dependent increase in the level of MT-CO1 and MT-CO2 associated to increased cord serum cotinine and decreased gestational age.

Oral Cell DNA Adducts as Potential Biomarkers for Lung Cancer Susceptibility in Cigarette Smokers

This perspective considers the use of oral cell DNA adducts, together with exposure and genetic information, to potentially identify those cigarette smokers at highest risk for lung cancer, so that appropriate preventive measures could be initiated at a relatively young age before too much damage has been done. There are now well established and validated analytical methods for the quantitation of urinary and serum metabolites of tobacco smoke toxicants and carcinogens. These metabolites provide a profile of exposure and in some cases lung cancer risk, but they do not yield information on the critical DNA damage parameter that leads to mutations in cancer growth control genes such as KRAS and TP53. Studies demonstrate a correlation between changes in the oral cavity and lung in cigarette smokers, due to the field effect of tobacco smoke. Oral cell DNA is readily obtained in contrast to DNA samples from the lung. Studies in which oral cell DNA and salivary DNA have been analyzed for specific DNA adducts are reviewed; some of the adducts identified have also been previously reported in lung DNA from smokers. The multiple challenges of developing a panel of oral cell DNA adducts that could be routinely quantified by mass spectrometry are discussed.

Persistent alterations of gene expression profiling of human peripheral blood mononuclear cells from smokers

The number of validated biomarkers of tobacco smoke exposure is limited, and none exist for tobacco-related cancer. Additional biomarkers for smoke, effects on cellular systems in vivo are needed to improve early detection of lung cancer, and to assist the Food and Drug Administration in regulating exposures to tobacco products. We assessed the effects of smoking on the gene expression using human cell cultures and blood from a cross-sectional study. We profiled global transcriptional changes in cultured smokers' peripheral blood mononuclear cells (PBMCs) treated with cigarette smoke condensate (CSC) in vitro (n = 7) and from well-characterized smokers' blood (n = 36). ANOVA with adjustment for covariates and Pearson correlation were used for statistical analysis in this study. CSC in vitro altered the expression of 1 178 genes (177 genes with > 1.5-fold-change) at P < 0.05. In vivo, PBMCs of heavy and light smokers differed for 614 genes (29 with > 1.5-fold-change) at P < 0.05 (309 remaining significant after adjustment for age, race, and gender). Forty-one genes were persistently altered both in vitro and in vivo, 22 having the same expression pattern reported for non-small cell lung cancer. Our data provides evidence that persistent alterations of gene expression in vitro and in vivo may relate to carcinogenic effects of cigarette smoke, and the identified genes may serve as potential biomarkers for cancer. The use of an in vitro model to corroborate results from human studies provides a novel way to understand human exposure and effect. © 2015 Wiley Periodicals, Inc.

Placental telomere length and risk of placental abruption

OBJECTIVE

To investigate the associations of placental telomere length with placental abruption (PA) risk and interactions between placental telomere length and placental mitochondrial DNA (mtDNA) copy number on PA risk.

MATERIALS AND METHODS

Relative telomere length and mtDNA copy number in placental samples collected from 105 cases and 73 controls were measured in two batches using qRT-PCR. Mean differences in relative telomere length between PA cases and controls were examined. After creating batch-specific median cutoffs for relative telomere length (84.92 and 102.53) and mtDNA copy number (2.32 and 1.42), interaction between the two variables was examined using stratified logistic regression models.

RESULTS

Adjusted mean difference in relative telomere length between PA cases and controls was -0.07 (p > 0.05). Among participants with low mtDNA copy number, participants with short relative telomere length had a 3.07-fold higher odds (95% CI: 1.13-8.38) of PA as compared with participants with long relative telomere length (the reference group). Among participants with high mtDNA copy number, participants with short relative telomere length had a 0.71-fold lower odds (95% CI: 0.28-1.83) of PA as compared with the reference group (interaction p values = 0.03).

CONCLUSION

Findings suggest complex relationships between placental telomere length, mtDNA copy number and PA risk which warrant further larger studies.

From the Cover: Thirdhand Cigarette Smoke Causes Stress-Induced Mitochondrial Hyperfusion and Alters the Transcriptional Profile of Stem Cells

Thirdhand cigarette smoke (THS) was recently recognized as an environmental health hazard; however, little is known about it effects on cells. Mitochondria are sensitive monitors of cell health and report on environmentally induced stress. We tested the effects of low levels of THS extracted from terry cloth on mitochondrial morphology and function using stem cells with well-defined mitochondria. Concentrations of THS that did not kill cells caused stress-induced mitochondrial hyperfusion (SIMH), which was characterized by changes in mitochondrial morphology indicative of fusion, increased mitochondrial membrane potential (MMP), increased ATP levels, increased superoxide production, and increased oxidation of mitochondrial proteins. SIMH was accompanied by a decrease in Fis1 expression, a gene responsible for mitochondrial fission, and a decrease in apoptosis-related genes, including Aifm2, Bbc3, and Bid There was also down regulation of Ucp2, Ucp4, and Ucp5, genes that decrease MMP thereby reducing oxidative phosphorylation, while promoting glycolysis. These effects, which collectively accompany SIMH, are a prosurvival mechanism to rescue damaged mitochondria and protect cells from apoptosis. Prolonged exposure to THS caused a reduction in MMP and decreased cell proliferation, which likely leads to apoptosis.

Outcome of buccal mucosa and lingual mucosa graft urethroplasty in the management of urethral strictures: A comparative study

Objective:

The objective of the study was to compare the outcome of buccal and lingual mucosa graft (LMG) augmentation urethroplasty along with donor sites morbidities in anterior urethra stricture.

Subjects and Methods:

From September 2010 to January 2014, 125 patients underwent single stage augmentation urethroplasty. They were randomly divided into two groups to receive either buccal mucosa graft (BMG) or LMG. The patients were prospectively followed for complications and outcome.

Results:

Baseline characteristics such as mean age, etiology, stricture length, and location were comparable in both groups. Overall success rate for Group 1 and Group 2 were 69.2% and 80%, respectively. Mean follow-up periods were 28.2 and 25 months in Group 1 and Group 2, respectively.

Conclusions:

LMG provides the better outcome with fewer immediate and delayed complications as compared to BMG. The length of stricture and width of graft were main factors affecting the outcome.

Integrating mitochondriomics in children's environmental health

The amount of scientific research linking environmental exposures and childhood health outcomes continues to grow; yet few studies have teased out the mechanisms involved in environmentally-induced diseases. Cells can respond to environmental stressors in many ways: inducing oxidative stress/inflammation, changes in energy production and epigenetic alterations. Mitochondria, tiny organelles that each retains their own DNA, are exquisitely sensitive to environmental insults and are thought to be central players in these pathways. While it is intuitive that mitochondria play an important role in disease processes, given that every cell of our body is dependent on energy metabolism, it is less clear how environmental exposures impact mitochondrial mechanisms that may lead to enhanced risk of disease. Many of the effects of the environment are initiated in utero and integrating mitochondriomics into children's environmental health studies is a critical priority. This review will highlight (i) the importance of exploring environmental mitochondriomics in children's environmental health, (ii) why environmental mitochondriomics is well suited to biomarker development in this context, and (iii) how molecular and epigenetic changes in mitochondria and mitochondrial DNA (mtDNA) may reflect exposures linked to childhood health outcomes.

Nuclear and mitochondrial DNA alterations in newborns with prenatal exposure to cigarette smoke

Newborns exposed to maternal cigarette smoke (CS) in utero have an increased risk of developing chronic diseases, cancer, and acquiring decreased cognitive function in adulthood. Although the literature reports many deleterious effects associated with maternal cigarette smoking on the fetus, the molecular alterations and mechanisms of action are not yet clear. Smoking may act directly on nuclear DNA by inducing mutations or epigenetic modifications. Recent studies also indicate that smoking may act on mitochondrial DNA by inducing a change in the number of copies to make up for the damage caused by smoking on the respiratory chain and lack of energy. In addition, individual genetic susceptibility plays a significant role in determining the effects of smoking during development. Furthermore, prior exposure of paternal and maternal gametes to cigarette smoke may affect the health of the developing individual, not only the in utero exposure. This review examines the genetic and epigenetic alterations in nuclear and mitochondrial DNA associated with smoke exposure during the most sensitive periods of development (prior to conception, prenatal and early postnatal) and assesses how such changes may have consequences for both fetal growth and development.

Mitochondrial DNA copy number in peripheral blood cells declines with age and is associated with general health among elderly

The role of the mitochondria in disease, general health and aging has drawn much attention over the years. Several attempts have been made to describe how the numbers of mitochondria correlate with age, although with inconclusive results. In this study, the relative quantity of mitochondrial DNA compared to nuclear DNA, i.e. the mitochondrial DNA copy number, was measured by PCR technology and used as a proxy for the content of mitochondria copies. In 1,067 Danish twins and singletons (18-93 years of age), with the majority being elderly individuals, the estimated mean mitochondrial DNA copy number in peripheral blood cells was similar for those 18-48 years of age [mean relative mtDNA content: 61.0; 95 % CI (52.1; 69.9)], but declined by -0.54 mtDNA 95 % CI (-0.63; -0.45) every year for those older than approximately 50 years of age. However, the longitudinal, yearly decline within an individual was more than twice as steep as observed in the cross-sectional analysis [decline of mtDNA content: -1.27; 95 % CI (-1.71; -0.82)]. Subjects with low mitochondrial DNA copy number had poorer outcomes in terms of cognitive performance, physical strength, self-rated health, and higher all-cause mortality than subjects with high mitochondrial DNA copy number, also when age was controlled for. The copy number mortality association can contribute to the smaller decline in a cross-sectional sample of the population compared to the individual, longitudinal decline. This study suggests that high mitochondrial DNA copy number in blood is associated with better health and survival among elderly.

Mitochondrial dysfunction in cancer

Mitochondria are semi-autonomous organelles of eukaryotic cells. They perform crucial functions such as generating most of the cellular energy through the oxidative phosphorylation (OXPHOS) system and some other metabolic processes. In addition, mitochondria are involved in regulation of cell death and reactive oxygen species (ROS) generation. Also, mitochondria play important roles in carcinogenesis via altering energy metabolism, resistance to apoptosis, increase of production of ROS and mtDNA (mitochondrial genome) changes. Studies have suggested that aerobic glycolysis is high in malignant tumors. Probably, it correlates with high glucose intake of cancerous tissues. This observation is contrary to Warburg's theory that the main way of energy generation in cancer cells is non-oxidative glycolysis. Further studies have suggested that in tumor cells both oxidative phosphorylation and glycolysis were active at various rates.

An increase of intracellular oxidative stress induces damage of cellular structure and somatic mutations. Further studies confirmed that permanent activity of oxidative stress and the influence of chronic inflammation damage the healthy neighboring epithelium and may lead to carcinogenesis. For instance, chronic inflammatory bowel disease could be related to high risk of colon adenocarcinoma.

The data have shown a role of ROS generation, mtDNA or nDNA alterations and abnormal apoptotic machinery in endometrial cancer progress. Recent studies suggest that mtDNA mutations might play a potential role in endometrial cancer progress and indicate an increase of mitochondrial biogenesis in this cancer. The investigators suggested that MtCOI and MtND6 alteration has an influence on assembly of respiratory complexes in endometrial cancer.

In many human cancers, there is a deregulation of the balance between cell growth and death. The tumor cells can avoid apoptosis through a loss of balance between anti- and pro-apoptotic proteins, reduced caspase function and impaired death receptor signaling. Over-expression of the anti-apoptotic BCL-2 gene has also been identified in numerous cancers including colon, thyroid, breast and endometrial cancer. Most studies have found low BCL-2 family gene expression, which could be a sign of blocking apoptosis in breast and endometrial cancer. Moreover, BCL-2 gene expression is correlated with the degree of aggressiveness and differentiation in endometrial cancer. As a result, it could be a valuable predictor of disease progression.

Increased leukocyte mitochondrial DNA copy number is associated with oral premalignant lesions: an epidemiology study

Although changes in the mitochondrial DNA (mtDNA) copy number in peripheral blood leukocytes (PBLs) have been linked to increased susceptibility to several cancers, the relationship between the mtDNA copy number in PBLs and the risk of cancer precursors has not been investigated. In this study, we measured the relative mtDNA copy number in PBLs of 143 patients with histologically confirmed oral premalignant lesions (OPLs) and of 357 healthy controls that were frequency-matched to patients according to age, sex and race. OPL patients had a significantly higher mtDNA copy number than the controls (1.36 ± 0.74 versus 1.11 ± 0.32; P < 0.001). In analyses stratified by sex, race, alcohol consumption and smoking status, the mtDNA copy number was higher in the OPL patients than in the controls in all the strata. Using the median mtDNA copy number in the control group as a cutoff, we found that individuals with a high mtDNA copy number had significantly higher risk of having OPLs than individuals with a low mtDNA copy number (adjusted odds ratio, 1.93; 95% confidence interval, 1.23-3.05, P = 0.004). Analysis of the joint effect of alcohol consumption and smoking revealed even greater risk for OPLs. Our results suggest that high mtDNA copy number in PBLs is significantly associated with having OPLs. To our knowledge, this is the first epidemiologic study to show that the mtDNA copy number may indicate the risk of cancer precursors.

Simultaneous quantification of nucleoproteins and comparison of methyl green-pyronin Y and Feulgen staining in sections of oral squamous cell carcinoma, dysplastic lesions and normal mucosa

A fundamental difference between normal cells and tumor cells is the proliferative activity of the nucleus and nucleolus, which increases progressively from normal to oral dysplastic mucosa to oral squamous cell carcinoma (OSCC). This activity is evaluated routinely using hematoxylin and eosin (H & E) staining, but in some cases, inter-observer variability occurs among pathologists. We evaluated cellular proliferation by staining sections with the methyl green-pyronin Y procedure and the Feulgen reaction. We also compared the efficacy of methyl green-pyronin Y and Feulgen staining for studying nuclear and nucleolar features in oral dysplastic mucosa and in different grades of OSCC. Sections cut from formalin fixed, paraffin embedded blocks of five normal mucosa, 15 dysplastic mucosa, 10 well-differentiated OSCC, 10 moderately differentiated OSCC and five poorly differentiated OSCC cases were stained with Hematoxylin and Eosin, methyl green-pyronin Y and the Feulgen reaction. The mean diameters of the nuclei and number of nucleoli showed significant differences. A progressive increase in diameter of the nucleus and number of nucleoli was observed from normal mucosa through poorly differentiated OSCC. We observed that methyl green-pyronin Y stain is more useful than Feulgen and hematoxylin and eosin for simultaneous quantitative assessment of both RNA and DNA. The simplicity of this technique makes it a valuable tool even for daily routine examination.

Mitochondrial DNA copy number and exposure to polycyclic aromatic hydrocarbons

BACKGROUND

Increased mitochondrial DNA copy number (mtDNAcn) is a biologic response to mtDNA damage and dysfunction, predictive of lung cancer risk. Polycyclic aromatic hydrocarbons (PAHs) are established lung carcinogens and may cause mitochondrial toxicity. Whether PAH exposure and PAH-related nuclear DNA (nDNA) genotoxic effects are linked with increased mtDNAcn has never been evaluated.

METHODS

We investigated the effect of chronic exposure to PAHs on mtDNAcn in peripheral blood lymphocytes (PBLs) of 46 Polish male noncurrent smoking coke-oven workers and 44 matched controls, who were part of a group of 94 study individuals examined in our previous work. Subjects' PAH exposure and genetic alterations were characterized through measures of internal dose (urinary 1-pyrenol), target dose [anti-benzo[a]pyrene diolepoxide (anti-BPDE)-DNA adduct], genetic instability (micronuclei and telomere length), and DNA methylation (p53 promoter) in PBLs. mtDNAcn (MT/S) was measured using a validated real-time PCR method.

RESULTS

Workers with PAH exposure above the median value (>3 μmol 1-pyrenol/mol creatinine) showed higher mtDNAcn [geometric means (GM) of 1.06 (unadjusted) and 1.07 (age-adjusted)] compared with controls [GM 0.89 (unadjusted); 0.89 (age-adjusted); (P = 0.029 and 0.016)], as well as higher levels of genetic and chromosomal [i.e., anti-BPDE-DNA adducts (P < 0.001), micronuclei (P < 0.001), and telomere length (P = 0.053)] and epigenetic [i.e., p53 gene-specific promoter methylation (P < 0.001)] alterations in the nDNA. In the whole study population, unadjusted and age-adjusted mtDNAcn was positively correlated with 1-pyrenol (P = 0.043 and 0.032) and anti-BPDE-DNA adducts (P = 0.046 and 0.049).

CONCLUSIONS

PAH exposure and PAH-related nDNA genotoxicity are associated with increased mtDNAcn.

IMPACT

The present study is suggestive of potential roles of mtDNAcn in PAH-induced carcinogenesis.

Maternal blood mitochondrial DNA copy number and placental abruption risk: results from a preliminary study

Oxidative stress and impaired placental function - pathways implicated in the pathogenesis of placental abruption - have their origins extending to mitochondrial dysfunction. To the best of our knowledge, there are no published reports of associations of placental abruption with circulating mitochondrial DNA (mtDNA) copy number - a novel biomarker of systemic mitochondrial dysfunction. This pilot case-control study was comprised of 233 placental abruption cases and 238 non-abruption controls. Real-time quantitative polymerase chain reaction (PCR) was used to assess the relative copy number of mtDNA in maternal whole blood samples collected at delivery. Logistic regression procedures were used to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI). There was some evidence of an increased odds of placental abruption with the highest quartile of mtDNA copy number (P for trend = 0.09) after controlling for confounders. The odds of placental abruption was elevated among women with higher mtDNA copy number (≥336.9) as compared with those with lower values (<336.9) (adjusted OR = 1.60; 95% CI 1.04-2.46). Women diagnosed with preeclampsia and with elevated mtDNA copy number had a dramatically increased odds of placental abruption as compared with normotensive women without elevated mtDNA copy number (adjusted OR = 6.66; 95% CI 2.58-17.16). Maternal mitochondrial dysfunction appears to be associated with placental abruption in the presence of preeclampsia. Replication in other studies, particularly prospective cohort studies and those that allow for tissue specific assessment of mitochondrial dysfunction (e.g., the placenta) are needed to further understand cellular and genomic biomarkers of normal and abnormal placental function.

Mitochondria and the evolutionary roots of cancer

Cancer disease is inherent to, and widespread among, metazoans. Yet, some of the hallmarks of cancer such as uncontrolled cell proliferation, lack of apoptosis, hypoxia, fermentative metabolism and free cell motility (metastasis) are akin to a prokaryotic lifestyle, suggesting a link between cancer disease and evolution. In this hypothesis paper, we propose that cancer cells represent a phenotypic reversion to the earliest stage of eukaryotic evolution. This reversion is triggered by the dysregulation of the mitochondria due to cumulative oxidative damage to mitochondrial and nuclear DNA. As a result, the phenotype of normal, differentiated cells gradually reverts to the phenotype of a facultative anaerobic, heterotrophic cell optimized for survival and proliferation in hypoxic environments. This phenotype matches the phenotype of the last eukaryotic common ancestor (LECA) that resulted from the endosymbiosis between an α-proteobacteria (which later became the mitochondria) and an archaebacteria. As such, the evolution of cancer within one individual can be viewed as a recapitulation of the evolution of the eukaryotic cell from fully differentiated cells to LECA. This evolutionary model of cancer is compatible with the current understanding of the disease, and explains the evolutionary basis for most of the hallmarks of cancer, as well as the link between the disease and aging. It could also open new avenues for treatment directed at reestablishing the synergy between the mitochondria and the cancerous cell.

Opportunities and challenges for selected emerging technologies in cancer epidemiology: mitochondrial, epigenomic, metabolomic, and telomerase profiling

Remarkable progress has been made in the last decade in new methods for biologic measurements using sophisticated technologies that go beyond the established genome, proteome, and gene expression platforms. These methods and technologies create opportunities to enhance cancer epidemiologic studies. In this article, we describe several emerging technologies and evaluate their potential in epidemiologic studies. We review the background, assays, methods, and challenges and offer examples of the use of mitochondrial DNA and copy number assessments, epigenomic profiling (including methylation, histone modification, miRNAs, and chromatin condensation), metabolite profiling (metabolomics), and telomere measurements. We map the volume of literature referring to each one of these measurement tools and the extent to which efforts have been made at knowledge integration (e.g., systematic reviews and meta-analyses). We also clarify strengths and weaknesses of the existing platforms and the range of type of samples that can be tested with each of them. These measurement tools can be used in identifying at-risk populations and providing novel markers of survival and treatment response. Rigorous analytic and validation standards, transparent availability of massive data, and integration in large-scale evidence are essential in fulfilling the potential of these technologies.

Primer effect in the detection of mitochondrial DNA point heteroplasmy by automated sequencing

The correct detection of mitochondrial DNA (mtDNA) heteroplasmy by automated sequencing presents methodological constraints. The main goals of this study are to investigate the effect of sense and distance of primers in heteroplasmy detection and to test if there are differences in the accurate determination of heteroplasmy involving transitions or transversions. A gradient of the heteroplasmy levels was generated for mtDNA positions 9477 (transition G/A) and 15,452 (transversion C/A). Amplification and subsequent sequencing with forward and reverse primers, situated at 550 and 150 bp from the heteroplasmic positions, were performed. Our data provide evidence that there is a significant difference between the use of forward and reverse primers. The forward primer is the primer that seems to give a better approximation to the real proportion of the variants. No significant differences were found concerning the distance at which the sequencing primers were placed neither between the analysis of transitions and transversions. The data collected in this study are a starting point that allows to glimpse the importance of the sequencing primers in the accurate detection of point heteroplasmy, providing additional insight into the overall automated sequencing strategy.

Analysis of 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing DNA adducts in human exfoliated oral mucosa cells by liquid chromatography-electrospray ionization-tandem mass spectrometry

Quantitation of DNA adducts could provide critical information on the relationship between exposure to tobacco smoke and cancer risk in smokers. In this study, we developed a robust and sensitive liquid chromatography-tandem mass spectrometry method for the analysis of 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing DNA adducts in human oral cells, a noninvasive source of DNA for biomarker studies. Isolated DNA undergoes acid hydrolysis, after which samples are purified by solid-phase extraction and analyzed by LC-ESI-MS/MS. The developed method was applied to the analysis of samples obtained via collection with a commercial mouthwash from 30 smokers and 15 nonsmokers. In smokers, the levels of HPB-releasing DNA adducts averaged 12.0 pmol HPB/mg DNA (detected in 20 out of 28 samples with quantifiable DNA yield), and in nonsmokers, the levels of adducts averaged 0.23 pmol/mg DNA (detected in 3 out of 15 samples). For the 30 smoking subjects, matching buccal brushings were also analyzed, and HPB-releasing DNA adducts were detected in 24 out of 27 samples with quantifiable DNA yield, averaging 44.7 pmol HPB/mg DNA. The levels of adducts in buccal brushings correlated with those in mouthwash samples of smokers (R = 0.73, p < 0.0001). Potentially, the method can be applied in studies of individual susceptibility to tobacco-induced cancers in humans.

The awakening of an advanced malignant cancer: an insult to the mitochondrial genome

BACKGROUND

In only months-to-years a primary cancer can progress to an advanced phenotype that is metastatic and resistant to clinical treatments. As early as the 1900s, it was discovered that the progression of a cancer to the advanced phenotype is often associated with a shift in the metabolic profile of the disease from a state of respiration to anaerobic fermentation - a phenomenon denoted as the Warburg Effect.

SCOPE OF REVIEW

Reports in the literature strongly suggest that the Warburg Effect is generated as a response to a loss in the integrity of the sequence and/or copy number of the mitochondrial genome content within a cancer.

MAJOR CONCLUSIONS

Multiple studies regarding the progression of cancer indicate that mutation, and/or, a flux in the copy number, of the mitochondrial genome content can support the early development of a cancer, until; the mutational load and/or the reduction-to-depletion of the copy number of the mitochondrial genome content induces the progression of the disease to an advanced phenotype.

GENERAL SIGNIFICANCE

Collectively, evidence has revealed that the human cell has incorporated the mitochondrial genome content into a cellular mechanism that, when pathologically actuated, can de(un)differentiate a cancer from the parental tissue of origin into an autonomous disease that disrupts the hierarchical structure-and-function of the human body. This article is part of a Special Issue entitled: Biochemistry of Mitochondria.

Association of mitochondrial DNA content in peripheral blood leukocyte with hepatitis B virus-related hepatocellular carcinoma in a Chinese Han population

Increasing epidemiological evidence has indicated that inherited variations of mtDNA content could affect the genetic susceptibility of many malignancies in a tumor-specific manner. However, the association between mtDNA content and hepatocellular carcinoma (HCC) remains undetermined. In this study, mtDNA content of peripheral blood leukocytes was determined using quantitative real-time PCR in a case-control study consisting of 274 HCC cases, 126 non-cancer patient controls with chronic liver diseases (CLD), and 258 healthy controls. We found that HCC cases had a significant lower mtDNA content than CLD controls (median [range]: 0.77 [0.17-2.30] vs 0.84 [0.32-3.37]; P = 0.012) and healthy controls (0.77 [0.17-2.30] vs 0.84 [0.35-3.44]; P = 0.035). There was no difference in mtDNA content between CLD and healthy controls (0.84 [0.32-3.37] vs 0.84 [0.35-3.44]; P = 0.261). We further assessed the association between mtDNA content and HCC and found that, compared to individuals with high mtDNA content, those with low mtDNA content had a significantly increased risk of HCC when health controls (adjusted odds ratio [aOR] = 1.64, 95% confidence interval [CI] = 1.06-2.55), CLD controls (aOR = 1.57, 95% CI = 1.10-2.25) or combined controls (aOR = 1.55, 95% CI = 1.12-2.14) were used as reference. In addition, stratified analyses showed that the significant association was only evident in younger individuals, male individuals, ever-smokers, and never-drinkers. Collectively, our findings provided the first epidemiological evidence that mtDNA content in peripheral blood leukocytes is significantly associated with HCC, which warrants further validation in prospective studies.

Mitochondrial subversion in cancer

Mitochondria control essential cellular activities including generation of ATP via oxidative phosphorylation. Mitochondrial DNA (mtDNA) mutations in the regulatory D-loop region and somatic mtDNA mutations are common in primary human cancers. The biological impact of a given mutation may vary, depending on the nature of the mutation and the proportion of mutant mtDNAs carried by the cell. Identification of mtDNA mutations in precancerous lesions supports their early contribution to cell transformation and cancer progression. Introduction of mtDNA mutations in transformed cells has been associated with increased ROS production and tumor growth. Studies reveal that increased and altered mtDNA plays a role in the development of cancer but further work is required to establish the functional significance of specific mitochondrial mutations in cancer and disease progression. This review offers some insight into the extent of mtDNA mutations, their functional consequences in tumorigenesis, mitochondrial therapeutics, and future clinical application.