Leukocyte telomere length in a population-based case-control study of ovarian cancer: a pilot study

Elevated tissue status of omega-3 fatty acids protects against age-related telomere attrition in fat-1 transgenic mice

BACKGROUND & AIMS

Leukocyte telomere length (LTL) is a biomarker of aging that may be influenced by dietary factors. Omega-3 fatty acids (n-3 FA) have been suggested to affect LTL. However, research on this effect has been inconclusive. The aim of the study was to test the hypothesis about the positive effect of n-3 FA on LTL.

METHODS

Fat-1 transgenic mice, which can convert omega-6 fatty acids (n-6 FA) to n-3 FA and have elevated levels of endogenous n-3 FA in their tissues, were used to study the effects of n-3 FA on LTL at different ages. Blood samples from 10-month-old wild-type (WT) mice (n = 10) and fat-1 mice (n = 10) and 3-month-old WT mice (n = 5) and fat-1 mice (n = 5) were used to measure relative and absolute LTL. The levels of proteins critical for telomere maintenance were examined by Western blot analysis.

RESULTS

Fat-1 transgenic mice had longer leukocyte telomeres than their WT siblings, suggesting a slower rate of age-related telomere shortening in fat-1 mice. In animals aged 10 months, the LTL was significantly longer in fat-1 than in WT mice (mean ± SEM; relative LTL: WT = 1.00 ± 0.09 vs. fat-1: 1.25 ± 0.05, P = 0.031; absolute LTL: WT = 64.41 ± 6.50 vs. fat-1: 78.53 ± 3.86, P = 0.048). The difference in LTL observed in three-month-old mice was insignificant, however the mean LTL was still longer in fat-1 mice than in the WT mice. Fat-1 mice also had abundant levels of two shelterin proteins: TRF1 (27%, P = 0.028) and TRF2 (47%, P = 0.040) (telomeric repeat binding factor 1 and 2) compared to WT animals.

CONCLUSION

This study, for the first time in a unique animal model free of dietary confounders, has demonstrated that increased levels of n-3 FA in tissues can reduce telomere attrition. The data presented indicate the possibility of using omega-3 fatty acids to reduce accelerated telomere attrition and, consequently, counteract premature aging and reduce the risk of age-related diseases.

Telomere length and hTERT genetic variants as potential prognostic markers in multiple myeloma

Telomere dysfunction is a notable event observed in many cancers contributing to their genomic instability. A major factor controlling telomere stability is the human telomerase reverse transcriptase catalytic subunit (hTERT). Telomere shortening has been observed in multiple myeloma (MM), a plasma cell malignancy with a complex and heterogeneous genetic background. In the present study, we aimed to analyse telomere length and hTERT genetic variants as potential markers of risk and survival in 251 MM patients. We found that telomere length was significantly shorter in MM patients than in healthy individuals, and patients with more advanced disease (stage III according to the International Staging System) had shorter telomeres than patients with less advanced disease. MM patients with hTERT allele rs2736100 T were characterized with significantly shorter progression-free survival (PFS). Moreover, allele rs2736100 T was also found to be less common in patients with disease progression in response to treatment. hTERT rs2853690 T was associated with higher haemoglobin blood levels and lower C-reactive protein. In conclusion, our results suggest that telomere length and hTERT genetic variability may affect MM development and can be potential prognostic markers in this disease.

Role of telomere length in human carcinogenesis (Review)

Cancer is considered the most important clinical, social and economic issue regarding cause‑specific disability‑adjusted life years among all human pathologies. Exogenous, endogenous and individual factors, including genetic predisposition, participate in cancer triggering. Telomeres are specific DNA structures positioned at the end of chromosomes and consist of repetitive nucleotide sequences, which, together with shelterin proteins, facilitate the maintenance of chromosome stability, while protecting them from genomic erosion. Even though the connection between telomere status and carcinogenesis has been identified, the absence of a universal or even a cancer‑specific trend renders consent even more complex. It is indicative that both short and long telomere lengths have been associated with a high risk of cancer incidence. When evaluating risk associations between cancer and telomere length, a disparity appears to emerge. Even though shorter telomeres have been adopted as a marker of poorer health status and an older biological age, longer telomeres due to increased cell growth potential are associated with the acquirement of cancer‑initiating somatic mutations. Therefore, the present review aimed to comprehensively present the multifaceted pattern of telomere length and cancer incidence association.

Maternal age at last birth and leukocyte telomere length in a nationally representative population of perimenopausal and postmenopausal women

OBJECTIVE

The primary aim of this study was to evaluate if maternal age at birth of last child is associated with leukocyte telomere length in a nationally representative population of perimenopausal and postmenopausal women.

METHODS

We conducted a cross-sectional analysis of 1,232 women from the National Health and Nutrition Examination Survey to examine maternal age at last birth and telomere length, surveyed between 1999 and 2002. We included perimenopausal and postmenopausal women age 40 years and older. Maternal age at last live birth was self-reported, and leukocyte telomere length was measured using quantitative polymerase chain reaction. We calculated least-squares geometric mean telomere length across categories of maternal age adjusted for age, race/ethnicity, number of live births, survey cycle, and history of hysterectomy or oophorectomy. P trend < 0.05 was considered statistically significant. For hypothesis-generation, we explored modification by reproductive and sociodemographic factors.

RESULTS

Maternal age at last birth was positively associated with telomere length: the multivariable-adjusted least-squares geometric mean leukocyte telomere length across categories of age at last birth (<25, 25-29, 30-34, 35-39, ≥40 y) was 0.90, 0.93, 0.93, 0.95, and 0.96, respectively (P trend = 0.04). There was suggestive evidence this association may be restricted to those women with one or two live births or women who reported ever using oral contraceptives (P interaction <0.10 for both).

CONCLUSIONS

Later maternal age was associated with longer telomere length in a nationally representative population of women. These data provide new insight into the biological relationship between reproductive history and long-term health. : Video Summary:http://links.lww.com/MENO/A662.

Prognostic Value of Peripheral Blood Lymphocyte Telomere Length in Gynecologic Malignant Tumors

Background: Lymphocyte telomere length is strongly correlated with patient prognosis in several malignant tumor types and is thought to be related to tumor immunity. However, this correlation has not been studied in gynecological cancers. We determined the prognostic significance of peripheral blood lymphocyte telomere length in gynecologic cancers. Methods: Telomere length of lymphocytes from patients with gynecological malignant tumors (ovarian cancer (OC), N = 72; cervical cancer (CC), N = 63; endometrial cancer (EC), N = 87) was examined by quantitative reverse-transcription PCR of isolated mononuclear cells. Kaplan–Meier and Cox proportional hazard analyses were used to determine the association between lymphocyte telomere length and clinicopathological factors. Results: The overall survival (OS) and progression-free survival (PFS) of patients were based on the dichotomized lymphocyte telomere length using the median as a threshold (OC: 0.75, CC: 1.94, and EC: 1.09). A short telomere length was significantly correlated with residual tumors (≥1 cm) in OC and with advanced stage (III and IV) of CC. In OC and CC, patients with shorter relative lymphocyte telomere length (RLT) had significantly poorer OS and PFS than patients with longer RLT (p = 0.002, p = 0.003, and p = 0.001, p = 0.001, respectively). However, in EC, RLT was not significantly associated with OS or PFS (p = 0.567 and p = 0.304, log-rank test). Multivariate analysis showed that shorter RLT was a significant independent prognostic factor of PFS and OS for OC (p = 0.03 and p = 0.04, respectively) and CC (p = 0.02 and p = 0.03, respectively). Conclusions: Patients with OC and CC with shorter lymphocyte telomeres have significantly reduced survival; therefore, the peripheral blood lymphocyte telomere length is a prognostic biomarker in OC and CC.

DNA damage in obesity: Initiator, promoter and predictor of cancer

Epidemiological evidence linking obesity with increased risk of cancer is steadily growing, although the causative aspects underpinning this association are only partially understood. Obesity leads to a physiological imbalance in the regulation of adipose tissue and its normal functioning, resulting in hyperglycaemia, dyslipidaemia and inflammation. These states promote the generation of oxidative stress, which is exacerbated in obesity by a decline in anti-oxidant defence systems. Oxidative stress can have a marked impact on DNA, producing mutagenic lesions that could prove carcinogenic. Here we review the current evidence for genomic instability, sustained DNA damage and accelerated genome ageing in obesity. We explore the notion of genotoxicity, ensuing from systemic oxidative stress, as a key oncogenic factor in obesity. Finally, we advocate for early, pre-malignant assessment of genome integrity and stability to inform surveillance strategies and interventions.

Beginning at the ends: telomeres and human disease

Studies of rare and common illnesses have led to remarkable progress in the understanding of the role of telomeres (nucleoprotein complexes at chromosome ends essential for chromosomal integrity) in human disease. Telomere biology disorders encompass a growing spectrum of conditions caused by rare pathogenic germline variants in genes encoding essential aspects of telomere function. Dyskeratosis congenita, a disorder at the severe end of this spectrum, typically presents in childhood with the classic triad of abnormal skin pigmentation, nail dystrophy, and oral leukoplakia, accompanied by a very high risk of bone marrow failure, cancer, pulmonary fibrosis, and other medical problems. In contrast, the less severe end of the telomere biology disorder spectrum consists of middle-age or older adults with just one feature typically seen in dyskeratosis congenita, such as pulmonary fibrosis or bone marrow failure. In the common disease realm, large-scale molecular epidemiology studies have discovered novel associations between illnesses, such as cancer, heart disease, and mental health, and both telomere length and common genetic variants in telomere biology genes. This review highlights recent findings of telomere biology in human disease from both the rare and common disease perspectives. Multi-disciplinary collaborations between clinicians, basic scientists, and epidemiologist are essential as we seek to incorporate new telomere biology discoveries to improve health outcomes.

Altered expression of telomere-associated genes in leukocytes among BRCA1 and BRCA2 carriers

Telomere dysfunction resulting from telomere shortening and deregulation of shelterin components has been linked to the pathogenesis of age-related disorders, including cancer. Recent evidence suggests that BRCA1/2 (BRCA1 and BRCA2) tumor suppressor gene products play an important role in telomere maintenance. Although telomere shortening has been reported in BRCA1/2 carriers, the direct effects of BRCA1/2 haploinsufficiency on telomere maintenance and predisposition to cancer development are not completely understood. In this study, we assessed the telomere-associated and telomere-proximal gene expression profiles in peripheral blood leukocytes from patients with a BRCA1 or BRCA2 mutation, compared to samples from sporadic and familial breast cancer individuals. We found that 25 genes, including TINF2 gene (a negative regulator of telomere length), were significantly differentially expressed in BRCA1 carriers. Leukocyte telomere length analysis revealed that BRCA1/2 carriers had relatively shorter telomeres than healthy controls. Further, affected BRCA1/2 carriers were well differentiated from unaffected BRCA1/2 carriers by the expression of telomere-proximal genes. Our results link BRCA1/2 haploinsufficiency to changes in telomere length, telomere-associated as well as telomere-proximal gene expression. Thus, this work supports the effect of BRCA1/2 haploinsufficiency in the biology underlying telomere dysfunction in cancer development. Future studies evaluating these findings will require a large study population.

Physical activity and telomere length: Impact of aging and potential mechanisms of action

Telomeres protect the integrity of information-carrying DNA by serving as caps on the terminal portions of chromosomes. Telomere length decreases with aging, and this contributes to cell senescence. Recent evidence supports that telomere length of leukocytes and skeletal muscle cells may be positively associated with healthy living and inversely correlated with the risk of several age-related diseases, including cancer, cardiovascular disease, obesity, diabetes, chronic pain, and stress. In observational studies, higher levels of physical activity or exercise are related to longer telomere lengths in various populations, and athletes tend to have longer telomere lengths than non-athletes. This relationship is particularly evident in older individuals, suggesting a role of physical activity in combating the typical age-induced decrements in telomere length. To date, a small number of exercise interventions have been executed to examine the potential influence of chronic exercise on telomere length, but these studies have not fully established such relationship. Several potential mechanisms through which physical activity or exercise could affect telomere length are discussed, including changes in telomerase activity, oxidative stress, inflammation, and decreased skeletal muscle satellite cell content. Future research is needed to mechanistically examine the effects of various modalities of exercise on telomere length in middle-aged and older adults, as well as in specific clinical populations.

Leukocyte Telomere Length and Pancreatic Cancer Risk: Updated Epidemiologic Review

Many risk factors have been firmly established for pancreatic cancer (PC), but the molecular processes by which known risk factors influence susceptibility to PC are not clear. There has been a recent upsurge of interest in the role of telomere length (TL), the protective DNA sequence repeats at chromosome ends, in pancreatic carcinogenesis. Given this heightened interest, we performed an in-depth, focused, and up-to-date review of the epidemiological evidence linking leukocyte TL (LTL) with PC risk. We searched MEDLINE, Embase, and the Cochrane Library databases for all published studies on LTL and PC risk, up to May 2017. Five studies were identified for review: 4 nested case-control studies and 1 retrospective case-control study. Two studies found opposite associations between LTL and PC risk: 1 found a dose-response positive association and the other found a dose-response inverse association. Two studies also found a "U-shaped" association, whereas another reported a weak nonlinear relationship. We offer potential reasons for the conflicting findings including variation in study design, biospecimen characteristics, and differences in interlaboratory measurements of TL. Future studies should carefully control for risk factors of PC that are associated also with telomere attrition and investigate the role of genetic variation in TL maintenance.

Chromosome Abnormalities and Absolute Telomere Lengths of Leukocytes from Silk Weavers with Emphasis on Potential Genotoxicity and Mutagenicity of Silk Dyes

Objectives:

This study is aimed to assess the possible genotoxicity and mutagenicity of silk dyes on silk weavers.

Methods:

Peripheral blood leukocytes were obtained from 24 silk weavers and 24 age- and sex-matched controls in northeastern Thailand. After mitogen stimulation in culture, chromosome abnormalities were examined using Giemsa banding and the absolute telomere length (aTL) was measured with SYBR green qRT-PCR. To confirm genotoxic and mutagenic effects of silk dyes, leukocytes from one each of healthy male and female volunteers were cultured with various concentrations of 3 dark red silk dyes under the presence of mitogen. Chromosome abnormalities and the telomere length were determined as above.

Results:

The proportion of normal metaphase in the silk weaving workers was significantly lower than that in controls. The frequency of chromosome aberrations was higher in the silk weavers than in control group. Polyploidy was detected only in the silk weavers. The aTL was significantly shorter in the silk weavers than in control group (p < 0.05). When leukocytes from normal volunteers were stimulated with mitogen under the presence of various concentrations of 3 silk dyes, suppressed the mitotic index (MI) and normal metaphase, whereas the proportion of prophase and the incomplete chromosome forming increased significantly. All dyes induced polyploidy. Dye #CA5 induced structural changes in male leukocytes, whereas #30 induced the changes in female leukocytes. The #CA5 increased aTL of normal leukocytes in a dose-dependent manner.

Conclusions:

All dyes, especially #CA5, have high genotoxicity and mutagenicity to induce chromosome aberrations and telomeric instability. Taken all those results together, regular health checking of silk weavers who have been exposed to those dyes is critically necessary to prevent various chemical-induced carcinogenesis.

Telomere length, ATM mutation status and cancer risk in Ataxia-Telangiectasia families

Recent studies have linked constitutive telomere length (TL) to aging-related diseases including cancer at different sites. ATM participates in the signaling of telomere erosion, and inherited mutations in ATM have been associated with increased risk of cancer, particularly breast cancer. The goal of this study was to investigate whether carriage of an ATM mutation and TL interplay to modify cancer risk in ataxia-telangiectasia (A-T) families.The study population consisted of 284 heterozygous ATM mutation carriers (HetAT) and 174 non-carriers (non-HetAT) from 103 A-T families. Forty-eight HetAT and 14 non-HetAT individuals had cancer, among them 25 HetAT and 6 non-HetAT were diagnosed after blood sample collection. We measured mean TL using a quantitative PCR assay and genotyped seven single-nucleotide polymorphisms (SNPs) recurrently associated with TL in large population-based studies.HetAT individuals were at increased risk of cancer (OR = 2.3, 95%CI = 1.2-4.4, P = 0.01), and particularly of breast cancer for women (OR = 2.9, 95%CI = 1.2-7.1, P = 0.02), in comparison to their non-HetAT relatives. HetAT individuals had longer telomeres than non-HetAT individuals (P = 0.0008) but TL was not associated with cancer risk, and no significant interaction was observed between ATM mutation status and TL. Furthermore, rs9257445 (ZNF311) was associated with TL in HetAT subjects and rs6060627 (BCL2L1) modified cancer risk in HetAT and non-HetAT women.Our findings suggest that carriage of an ATM mutation impacts on the age-related TL shortening and that TL per se is not related to cancer risk in ATM carriers. TL measurement alone is not a good marker for predicting cancer risk in A-T families.

Social-demographics, health behaviors, and telomere length in the Mexican American Mano a Mano Cohort

In the current study, we examined cross-sectional associations among social-demographics, lifestyle behaviors, and relative telomere length (RTL) in peripheral blood leukocytes, as well as longitudinal relationships among major chronic diseases, weight gain, and RTL, among 12,792 Mexican Americans aged 20 to 85 years in the Mano-A-Mano, the Mexican American Cohort. As expected, RTL was inversely correlated with age (ρ=-0.15, ρ<0.001). In the multivariate analysis, we found that RTL was positively correlated with levels of education (ρ=0.021), self-insurance (ρ=0.041), body mass index (BMI) (ρ<0.001), and sleeping time per day (ρ for trend<0.001), and RTL was inversely correlated with sitting time per day (ρ for trend =0.001). In longitudinal analysis, we found that longer RTL was modestly but positively associated with increased risks of overall cancer (adjusted hazard ratio (adj.HR)=1.05, 95% conference interval (95%CI)=1.02-1.09). In quartile analysis, 4^th quartile (longest RTL) was associated with 1.53-fold increased risk of overall cancer (adj.HR=1.53, 95%CI=1.11-2.10), compared to 1^st quartile (shortest RTL). RTL was reversely associated with the risk of type-2 diabetes (adj.HR=0.89, 95%CI=0.82-0.94). In quartile analysis, 4^th quartile (longest RTL) was associated with 48% decreased risk of typle-2 diabetes (adj.HR=0.52, 95%CI=0.32-0.70), compared to 1^st quartile (shortest RTL). In addition, longer RTL was a positive predictor of at least 10% weight gain (adj.HR=1.03, 95%CI=1.00-1.05). In summary, our results in Mexican Americans support the notion that telomere length is a biological mechanism by which social demographics and health behaviors “get under the skin” to affect health.

Prediagnosis Leukocyte Telomere Length and Risk of Ovarian Cancer

Background: The associations between telomere length and cancer risk are equivocal, and none have examined the association between prediagnosis leukocyte telomere length (LTL) and the risk of developing ovarian cancer.Methods: We prospectively measured LTL collected from 442 ovarian cancer cases and 727 controls in the Nurses' Health Studies and the Northern Sweden Health and Disease Study. Cases were matched to one or two controls on age, menopausal status, and date of blood collection. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using conditional logistic regression.Results: LTL was measured a median of 9.5 years before ovarian cancer diagnosis among cases. We observed a decreased risk of ovarian cancer with longer LTL. In multivariable models, women in the top quartile of LTL had an OR for ovarian cancer of 0.67 (95% CI, 0.46-0.97) compared with those in the bottom quartile. Inverse associations were stronger for nonserous cases (OR_{quartile 4 vs. quartile 1 of LTL} = 0.55, 95% CI, 0.33-0.94) and rapidly fatal cases (i.e., cases who died within 3 years of diagnosis; OR_{quartile 4 vs. quartile 1 of LTL} = 0.55, 95% CI, 0.32-0.95).Conclusions: Our prospective findings suggest that longer circulating LTL may be associated with a lower ovarian cancer risk, especially for nonserous and rapidly fatal cases. The evaluation of LTL in relation to ovarian cancer risk by tumor subtypes is warranted in larger prospective studies.Impact: Prediagnosis LTL may reflect an early event in the ovarian cancer development and could serve as a biomarker to predict future risk. Cancer Epidemiol Biomarkers Prev; 26(3); 339-45. ©2017 AACR.

Telomerase and telomere biology in hematological diseases: A new therapeutic target

Telomeres are structures confined at the ends of eukaryotic chromosomes. With each cell division, telomeric repeats are lost because DNA polymerases are incapable to fully duplicate the very ends of linear chromosomes. Loss of repeats causes cell senescence, and apoptosis. Telomerase neutralizes loss of telomeric sequences by adding telomere repeats at the 3' telomeric overhang. Telomere biology is frequently associated with human cancer and dysfunctional telomeres have been proved to participate to genetic instability. This review covers the information on telomerase expression and genetic alterations in the most relevant types of hematological diseases. Telomere erosion hampers the capability of hematopoietic stem cells to effectively replicate, clinically resulting in bone marrow failure. Furthermore, telomerase mutations are genetic risk factors for the occurrence of some hematologic cancers. New discoveries in telomere structure and telomerase functions have led to an increasing interest in targeting telomeres and telomerase in anti-cancer therapy.

Genetic variants in telomere-maintenance genes are associated with ovarian cancer risk and outcome

Most ovarian cancer patients present at an advanced stage with poor prognosis. Telomeres play a critical role in protecting chromosomes stability. The associations of genetic variants in telomere maintenance genes and ovarian cancer risk and outcome are unclear. We genotyped 137 single nucleotide polymorphisms (SNPs) in telomere-maintenance genes in 417 ovarian cancer cases and 417 matched healthy controls to evaluate their associations with cancer risk, survival and therapeutic response. False discovery rate Q-value was calculated to account for multiple testing. Eleven SNPs from two genes showed nominally significant associations with the risks of ovarian cancer. The most significant SNP was TEP1: rs2228026 with participants carrying at least one variant allele exhibiting a 3.28-fold (95% CI: 1.72-6.29; P < 0.001, Q = 0.028) increased ovarian cancer risk, which remained significant after multiple testing adjusting. There was also suggested evidence for the associations of SNPs with outcome, although none of the associations had a Q < 0.05. Seven SNPs from two genes showed associations with ovarian cancer survival (P < 0.05). The strongest association was found in TNKS gene (rs10093972, hazard ratio = 1.88; 95% CI: 1.20-2.92; P = 0.006, Q = 0.076). Five SNPs from four genes showed suggestive associations with therapeutic response (P < 0.05). In a survival tree analysis, TEP1:rs10143407 was the primary factor contributing to overall survival. Unfavourable genotype analysis showed a cumulative effect of significant SNPs on ovarian cancer risk, survival and therapeutic response. Genetic variations in telomere-maintenance genes may be associated with ovarian cancer risk and outcome.

Identification of recurrent focal copy number variations and their putative targeted driver genes in ovarian cancer

BACKGROUND

Genomic regions with recurrent DNA copy number variations (CNVs) are generally believed to encode oncogenes and tumor suppressor genes (TSGs) that drive cancer growth. However, it remains a challenge to delineate the key cancer driver genes from the regions encoding a large number of genes.

RESULTS

In this study, we developed a new approach to CNV analysis based on spectral decomposition of CNV profiles into focal CNVs and broad CNVs. We performed an analysis of CNV data of 587 serous ovarian cancer samples on multiple platforms. We identified a number of novel focal regions, such as focal gain of ESR1, focal loss of LSAMP, prognostic site at 3q26.2 and losses of sub-telomere regions in multiple chromosomes. Furthermore, we performed network modularity analysis to examine the relationships among genes encoded in the focal CNV regions. Our results also showed that the recurrent focal gains were significantly associated with the known oncogenes and recurrent losses associated with TSGs and the CNVs had a greater effect on the mRNA expression of the driver genes than that of the non-driver genes.

CONCLUSIONS

Our results demonstrate that spectral decomposition of CNV profiles offers a new way of understanding the role of CNVs in cancer.

The association between telomere length and cancer risk in population studies

Telomeres are crucial in the maintenance of chromosome integrity and genomic stability. A series of epidemiological studies have examined the association between telomere length and the risk of cancers, but the findings remain conflicting. We performed literature review and meta-analysis to demonstrate the relationship between telomere length and cancer risk. A total of 23,379 cases and 68,792 controls from 51 publications with 62 population studies were included in this meta-analysis to assess the association between overall cancer or cancer-specific risk and telomere length. General association and dose-response relationship were evaluated based on two and three groups, respectively. The estimates of association were evaluated with odds ratios and 95% confidence intervals by the random-effects or fixed-effects model based on heterogeneity test. We observed a non-significant association between short telomeres and overall risk of cancer. Convincing evidence was observed for the association of short telomeres with an increased risk of gastrointestinal tumor and head and neck cancer. Significant dose-response associations were also observed for gastrointestinal tumor and head and neck cancer. Our findings indicate that telomeres may play diverse roles in different cancers, and short telomeres may be risk factors for the tumors of digestive system.

Telomere length, genetic variants and risk of squamous cell carcinoma of the head and neck in Southeast Chinese

Telomere dysfunction participates in malignant transformation and tumorigenesis. Previous studies have explored the associations between telomere length (TL) and cancer susceptibility; however, the findings are inconclusive. The associations between genetic variants and TL have been verified by quite a few genome-wide association studies (GWAS). Yet, to date, there was no published study on the relationship between TL, related genetic variants and susceptibility to squamous cell carcinoma of the head and neck (SCCHN) in Chinese. Hence, we detected relative telomere length (RTL) by using quantitative PCR and genotyped seven selected single nucleotide polymorphisms by TaqMan allelic discrimination assay in 510 SCCHN cases and 913 controls in southeast Chinese. The results showed that RTL was significantly associated with SCCHN risk [(adjusted odds ratio (OR) = 1.19, 95% confidence interval (CI) = 1.08–1.32, P = 0.001]. Furthermore, among seven selected SNPs, only G allele of rs2736100 related to RTL in Caucasians was significantly associated with both the decreased RTL (P = 0.002) and the increased susceptibility to SCCHN in Chinese (additive model: adjusted OR = 1.17, 95%CI = 1.00–1.38, P = 0.049). These findings provide evidence that shortened TL is a risk factor for SCCHN, and genetic variants can contribute to both TL and the susceptibility to SCCHN in southeast Chinese population.

Genetic determinants of telomere length and risk of common cancers: a Mendelian randomization study

Epidemiological studies have reported inconsistent associations between telomere length (TL) and risk for various cancers. These inconsistencies are likely attributable, in part, to biases that arise due to post-diagnostic and post-treatment TL measurement. To avoid such biases, we used a Mendelian randomization approach and estimated associations between nine TL-associated SNPs and risk for five common cancer types (breast, lung, colorectal, ovarian and prostate cancer, including subtypes) using data on 51 725 cases and 62 035 controls. We then used an inverse-variance weighted average of the SNP-specific associations to estimate the association between a genetic score representing long TL and cancer risk. The long TL genetic score was significantly associated with increased risk of lung adenocarcinoma (P = 6.3 × 10(-15)), even after exclusion of a SNP residing in a known lung cancer susceptibility region (TERT-CLPTM1L) P = 6.6 × 10(-6)). Under Mendelian randomization assumptions, the association estimate [odds ratio (OR) = 2.78] is interpreted as the OR for lung adenocarcinoma corresponding to a 1000 bp increase in TL. The weighted TL SNP score was not associated with other cancer types or subtypes. Our finding that genetic determinants of long TL increase lung adenocarcinoma risk avoids issues with reverse causality and residual confounding that arise in observational studies of TL and disease risk. Under Mendelian randomization assumptions, our finding suggests that longer TL increases lung adenocarcinoma risk. However, caution regarding this causal interpretation is warranted in light of the potential issue of pleiotropy, and a more general interpretation is that SNPs influencing telomere biology are also implicated in lung adenocarcinoma risk.

Telomere length and common disease: study design and analytical challenges

Telomeres, the repetitive sequences that protect the ends of chromosomes, help to maintain genomic integrity and are of key importance to human health. The aim here is to give an overview of the evidence for the importance of telomere length (TL) to the risk of common disease, considering the strengths and weaknesses of different epidemiological study designs. Methods for measuring TL are described, all of which are subject to considerable measurement error. TL declines with age and varies in relation to factors such as smoking and obesity. It is also highly heritable (estimated heritability of ~40 to 50%), and genome-wide studies have identified a number of associated genetic variants. Epidemiological studies have shown shorter TL to be associated with risk of a number of common diseases, including cardiovascular disease and some cancers. The relationship with cancer appears complex, in that longer telomeres are associated with higher risk of some cancers. Prospective studies of the relationship between TL and disease, where TL is measured before diagnosis, have numerous advantages over retrospective studies, since they avoid the problems of reverse causality and differences in sample handling, but they are still subject to potential confounding. Studies of the genetic predictors of TL in relation to disease risk avoid these drawbacks, although they are not without limitations. Telomere biology is of major importance to the risk of common disease, but the complexities of the relationship are only now beginning to be understood.

Leukocyte telomere length: a novel biomarker to predict the prognosis of glioma patients

PURPOSE

Epidemiological studies have demonstrated that leukocyte telomere length is associated with the developing risk of various malignancies, including glioma. However, its prognostic value in glioma patients has never been investigated.

METHODS

Relative telomere length (RTL) of peripheral blood leukocytes from 301 glioma patients were examined using a real-time PCR-based method. Kaplan-Meier curves and Cox proportional hazards regression model were used to assess the association of RTL with clinical outcomes of patients. To explore the potential mechanism, the immune phenotype of peripheral blood mononuclear cells (PBMCs) and concentrations of several cytokines from another 20 glioma patients were detected by flow cytometry and enzyme-linked immunosorbent assay (ELISA), respectively. The relationship between RTL and immunological characteristics of PBMCs were further analyzed.

RESULTS

Patients with short RTL showed both poorer overall survival (OS) and progression-free survival (PFS) than those with long RTL. Multivariate Cox regression analysis demonstrated that RTL was an independent prognostic factor for both OS and PFS in glioma patients. Moreover, the effects of RTL on the prognosis of patients exhibited a dose-dependent manner. Stratified analysis showed that the prognostic value of RTL was not affected by host characteristics except for age. In addition, flow cytometry and ELISA analyses indicated that there was no significant association between RTL and frequency of different immune cell subsets or plasma cytokine concentrations.

CONCLUSIONS

Our study for the first time demonstrates that leukocyte RTL is an independent prognostic marker for glioma patients. The potential mechanism needs further investigation.

Leukocyte telomere length-related rs621559 and rs398652 genetic variants influence risk of HBV-related hepatocellular carcinoma

Recent genome-wide association studies (GWAS) have identified eleven leukocyte telomere length (LTL)-related single nucleotide polymorphisms (SNPs). Since LTL has been associated with risk of many malignancies, LTL-related SNPs may contribute to cancer susceptibility. To test this hypothesis in hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC), we genotyped these eleven LTL-related SNPs in a case-control set including 1186 HBV-related HCC cases, 508 chronic HBV carriers and 1308 healthy controls at the discovery stage. The associations of HCC risk with these SNPs were further confirmed in an independent case-control set. We found that 1p34.2 rs621559 and 14q21 rs398652 were significantly associated with HBV-related HCC risk (both P<0.005 after Bonferroni corrections). There was no significant difference of either rs621559 or rs398652 genotypes between chronic HBV carriers and healthy controls, demonstrating that the association was not due to predisposition to HBV infection. In the pooled analyses (1806 HBV-related HCC cases and 1954 controls), we observed a decreased HCC risk, 0.72-times, associated with the 1p34.2 rs621559 AA genotype compared to the GG genotype (P = 1.6×10⁻⁶). Additionally, there was an increased HCC risk, 1.27-fold, associated with the rs398652 GG genotype (P = 3.3×10⁻⁶). A statistical joint effect between the rs621559 GG and rs398652 GG genotypes may exist in elevating risk of HBV-related HCC. We show, for the first time, that rs398652 and rs621559 might be marker genetic variants for risk of HBV-related HCC in the Chinese population.

A retrospective examination of mean relative telomere length in the Tasmanian Familial Hematological Malignancies Study

Telomere length has a biological link to cancer, with excessive telomere shortening leading to genetic instability and resultant malignant transformation. Telomere length is heritable and genetic variants determining telomere length have been identified. Telomere biology has been implicated in the development of hematological malignancies (HMs), therefore, closer examination of telomere length in HMs may provide further insight into genetic etiology of disease development and support for telomere length as a prognostic factor in HMs. We retrospectively examined mean relative telomere length in the Tasmanian Familial Hematological Malignancies Study using a quantitative PCR method on genomic DNA from peripheral blood samples. Fifty-five familial HM cases, 191 unaffected relatives of familial HM cases and 75 non-familial HM cases were compared with 758 population controls. Variance components modeling was employed to identify factors influencing variation in telomere length. Overall, HM cases had shorter mean relative telomere length (P=2.9×10⁻⁶) and this was observed across both familial and non-familial HM cases (P=2.2×10⁻⁴ and 2.2×10⁻⁵, respectively) as well as additional subgroupings of HM cases according to broad subtypes. Mean relative telomere length was also significantly heritable (62.6%; P=4.7×10⁻⁵) in the HM families in the present study. We present new evidence of significantly shorter mean relative telomere length in both familial and non-familial HM cases from the same population adding further support to the potential use of telomere length as a prognostic factor in HMs. Whether telomere shortening is the cause of or the result of HMs is yet to be determined, but as telomere length was found to be highly heritable in our HM families this suggests that genetics driving the variation in telomere length is related to HM disease risk.

Telomere length and mortality following a diagnosis of ovarian cancer

BACKGROUND

Telomeres are essential for the maintenance of chromosomal integrity. Telomere shortening leads to genomic instability, which is hypothesized to play a role in cancer development and prognosis. No studies to date have evaluated the prognostic significance of telomere length for ovarian cancer.

METHODS

We examined whether relative telomere length in peripheral blood leukocytes was associated with survival following a diagnosis of ovarian cancer. We analyzed data from a large population-based study of incident ovarian cancer conducted in Ontario between 1995 and 2004. Telomere length was measured using the quantitative PCR-based relative telomere length assay and vital status was determined by computerized record linkage and by chart review (n = 1,042). Proportional hazard models were used to estimate ovarian cancer-specific survival HRs and 95% confidence intervals (CI) associated with quartiles of telomere length z score.

RESULTS

We found no significant relationship between telomere length and ovarian cancer-specific mortality (P log-rank test = 0.55). Compared with women in the lowest quartile of telomere length z score, the HR for women in the highest three quartiles of telomere length z score combined was 0.88 (95% CI, 0.77-1.10). The corresponding estimates for serous and nonserous tumors were 0.68 (95% CI, 0.66-1.13) and 1.13 (95% CI, 0.71-1.79), respectively.

CONCLUSIONS

Our data provide preliminary evidence that telomere length likely does not predict outcome after a diagnosis of ovarian cancer.

IMPACT

This represents the first study to suggest no prognostic role of telomere length for ovarian cancer.

Telomere length in peripheral blood leukocytes is associated with risk of colorectal cancer in Chinese population

Background

Human telomeres, tandem repeats of TTAGGG nucleotides at the ends of chromosomes, are essential for maintaining genomic integrity and stability. Results of previous epidemiologic studies about the association of telomere length with risk of colorectal cancer (CRC) have been conflicting.

Methods

A case-control study was conducted in a Han population in Wuhan, central China. The relative telomere length (RTL) was measured in peripheral blood leukocytes (PBLs) using quantitative real-time polymerase chain reaction (PCR) in 628 CRC cases and 1,256 age and sex frequency matched cancer-free controls. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using unconditional logistic regression models to evaluate the association between RTL and CRC risk.

Results

Using median RTL in the controls as the cutoff, individuals with shorter RTL were associated with a significantly increased risk of CRC (adjusted OR = 1.27, 95%CI: 1.05–1.55). When participants were further categorized into 3 and 4 groups according to the tertile and quartile RTL values of controls, significant relationships were still observed between shorter RTL and increased CRC risk (OR per tertile = 1.13, 95%CI: 1.00–1.28, P_trend = 0.045; OR per quartile = 1.12, 95%CI: 1.03–1.23, P_trend = 0.012). In stratified analyses, significant association between shorter RTL and increased CRC risk was found in females, individuals younger than 60 years old, never smokers and never drinkers.

Conclusions

This study suggested that short telomere length in PBLs was significantly associated with an increased risk of CRC in Chinese Han population. Further validation in large prospective studies and investigation of the biologic mechanisms are warranted.

Association between leukocyte telomere length and glioma risk: a case-control study

BACKGROUND

Compelling epidemiological evidence indicates that alterations of telomere length are associated with risks of many malignancies in a tumor-specific manner, such as lung cancer, breast cancer, and non-Hodgkin's lymphoma. However, the association between leukocyte telomere length and glioma risk has not been investigated.

METHODS

Relative telomere length (RTL) of peripheral blood leukocytes from 467 glioma patients and 467 healthy controls, matched by age and sex, was measured using the real-time PCR-based method in a case-control study. An unconditional multivariate logistic regression model was applied to estimate the association between RTL and glioma risk.

RESULTS

Glioma patients showed notably longer RTL than controls (median, 0.555 vs 0.444; P > .04). RTL was negatively correlated with age in both cases (ρ = -0.430; P < .001) and controls (ρ = -0.388; P < .001). After adjusting for age, sex, smoking status and family history of cancer, multivariate logistic regression analysis showed that there was a U-shaped association between RTL and glioma risk (P for nonlinearity <.001). Compared with individuals in the second tertile of RTL, the odds ratios (95% CI) for participants in the first and third tertiles were 2.16 (range, 1.52-3.09) and 3.51 (range, 2.45-5.00), respectively. Stratified analysis showed that the association between RTL and glioma risk was not modulated by major host characteristics.

CONCLUSIONS

Our study demonstrates for the first time that either shorter or longer RTL in peripheral blood leukocytes is associated with increased glioma risk, which warrants further investigation in the future.

Telomere length varies by DNA extraction method: implications for epidemiologic research

BACKGROUND

Both shorter and longer telomeres in peripheral blood leukocyte (PBL) DNA have been associated with cancer risk. However, associations remain inconsistent across studies of the same cancer type. This study compares DNA preparation methods to determine telomere length from patients with colorectal cancer.

METHODS

We examined PBL relative telomere length (RTL) measured by quantitative PCR (qPCR) in 1,033 patients with colorectal cancer and 2,952 healthy controls. DNA was extracted with phenol/chloroform, PureGene, or QIAamp.

RESULTS

We observed differences in RTL depending on DNA extraction method (P < 0.001). Phenol/chloroform-extracted DNA had a mean RTL (T/S ratio) of 0.78 (range 0.01-6.54) compared with PureGene-extracted DNA (mean RTL of 0.75; range 0.00-12.33). DNA extracted by QIAamp yielded a mean RTL of 0.38 (range 0.02-3.69). We subsequently compared RTL measured by qPCR from an independent set of 20 colorectal cancer cases and 24 normal controls in PBL DNA extracted by each of the three extraction methods. The range of RTL measured by qPCR from QIAamp-extracted DNA (0.17-0.58) was less than from either PureGene or phenol/chloroform (ranges, 0.04-2.67 and 0.32-2.81, respectively).

CONCLUSIONS

RTL measured by qPCR from QIAamp-extracted DNA was less than from either PureGene or phenol/chloroform (P < 0.001).

IMPACT

Differences in DNA extraction method may contribute to the discrepancies between studies seeking to find an association between the risk of cancer or other diseases and RTL.

Telomere length, telomere-related genes, and breast cancer risk: the breast cancer health disparities study

Telomeres are involved in maintaining genomic stability. Previous studies have linked both telomere length (TL) and telomere-related genes with cancer. We evaluated associations between telomere-related genes, TL, and breast cancer risk in an admixed population of US non-Hispanic white (1,481 cases, 1,586 controls) and U.S. Hispanic and Mexican women (2,111 cases, 2,597 controls) from the Breast Cancer Health Disparities Study. TL was assessed in 1,500 women based on their genetic ancestry. TL-related genes assessed were MEN1, MRE11A, RECQL5, TEP1, TERC, TERF2, TERT, TNKS, and TNKS2. Longer TL was associated with increased breast cancer risk [odds ratio (OR) 1.87, 95% confidence interval (CI) 1.38, 2.55], with the highest risk (OR 3.11, 95% CI 1.74, 5.67 p interaction 0.02) among women with high Indigenous American ancestry. Several TL-related single nucleotide polymorphisms had modest association with breast cancer risk overall, including TEP1 rs93886 (OR 0.82, 95% CI 0.70,0.95); TERF2 rs3785074 (OR 1.13, 95% CI 1.03,1.24); TERT rs4246742 (OR 0.85, 95% CI 0.77,0.93); TERT rs10069690 (OR 1.13, 95% CI 1.03,1.24); TERT rs2242652 (OR 1.51, 95% CI 1.11,2.04); and TNKS rs6990300 (OR 0.89, 95% CI 0.81,0.97). Several differences in association were detected by hormone receptor status of tumors. Most notable were associations with TERT rs2736118 (ORadj 6.18, 95% CI 2.90, 13.19) with estrogen receptor negative/progesterone receptor positive (ER-/PR+) tumors and TERT rs2735940 (ORadj 0.73, 95% CI 0.59, 0.91) with ER-/PR- tumors. These data provide support for an association between TL and TL-related genes and risk of breast cancer. The association may be modified by hormone receptor status and genetic ancestry.

Blood and dried blood spot telomere length measurement by qPCR: assay considerations

Measurement of telomere length is crucial for the study of telomere maintenance and its role in molecular pathophysiology of diseases and in aging. Several methods are used to measure telomere length, the choice of which usually depends on the type and size of sample to be assayed, as well as cost and throughput considerations. The goal of this study was to investigate the factors that may influence the reliability of qPCR-based relative telomere length measurements in whole blood. Day to day intra-individual variability, types of blood anticoagulant, sample storage conditions, processing and site of blood draw were investigated. Two qPCR-based methods to measure telomere length (monoplex vs. multiplex) were also investigated and showed a strong correlation between them. Freezing and thawing of the blood and storage of the blood at 4°C for up to 4 days did not affect telomere length values. Telomere lengths in dried blood spots were significantly higher than both whole blood and peripheral mononuclear blood cells, and were highly correlated with both. We found that telomere length measurements were significantly higher in dried blood spots collected directly from fingertip prick compared to dried blood spots prepared with anticoagulated whole blood collected from the finger, and non-blotted whole blood taken from both finger and arm venipuncture. This suggests that DNA from cells blotted on paper is not equivalent to that collected from venipuncture whole blood, and caution should be taken when comparing between blood sample types.

Telomere length and pancreatic cancer: a case-control study

BACKGROUND

Telomeres, the ends of chromosomes, are critical for maintaining genomic stability and grow shorter with age. Shortened telomeres in pancreatic tissue play a key role in the pathogenesis of pancreatic cancer, and shorter telomeres in peripheral blood leukocytes (PBL) have been associated with increased risk for several cancer types. We hypothesized that shorter blood telomeres are associated with higher risk for pancreatic cancer.

METHODS

Telomere length was measured in PBLs using quantitative real-time PCR in 499 cases with pancreatic cancer and 963 cancer-free controls from the Mayo Clinic. ORs and confidence intervals (CI) were computed using logistic generalized additive models (GAM) adjusting for multiple variables.

RESULTS

In multivariable adjusted models, we observed a significant nonlinear association between telomere length in peripheral blood samples and the risk for pancreatic cancer. Risk was lower among those with longer telomeres compared with shorter telomeres across a range from the 1st percentile to 90th percentile of telomere length. There was also some evidence for higher risk among those with telomeres in the longest extreme.

CONCLUSIONS

Short telomeres in peripheral blood are associated with an increased risk for pancreatic cancer across most of the distribution of length, but extremely long telomeres may also be associated with higher risk.

IMPACT

Although the temporality of this relationship is unknown, telomere length may be useful as either a marker of pancreatic cancer risk or of the presence of undetected pancreatic cancer. If telomere shortening precedes cancer incidence, interventions to preserve telomere length may be an effective strategy to prevent pancreatic cancer.

Genetic and lifestyle influence on telomere length and subsequent risk of colon cancer in a case control study

BACKGROUND

Telomeres cap the ends of chromosomes and help maintain genomic stability and integrity. Telomere length (TL) has been linked to a number of diseases, including a variety of cancers; however, the association between TL and risk for colorectal cancer is unclear.

METHODS

We investigate the association between genetic, diet, and lifestyle factors and TL and the association between TL and colorectal cancer using data from a population-based case-control study of colon (249 cases and 371 controls) and rectal cancer (276 cases and 372 controls) conducted in Utah. DNA samples came from immortalized cell lines for colon cancer and directly from whole blood for rectal cancer. We genotyped 11 single nucleotide polymorphisms in five genes associated with telomeres, TERT, MEN1, MRE11A, RECQL5, and TNKS.

RESULTS

TL was measured using quantitative PCR. TERT rs2853676 (p=0.044) and RECQL5 rs820152 (p=0.001) were associated with TL at <0.05 level of significance. After adjusting for age and sex, BMI and cigarette smoking were significantly inversely associated with TL among controls. Use of aspirin/NSAIDs interacted significantly with TERT rs10069690 and rs2242652 to alter TL. Longer TL was significantly associated with reduced colon cancer risk after adjusting for age and sex (OR = 0.94 95% confidence intervals 0.89-0.99 per decile of TL). Further adjustment for BMI and cigarette smoking attenuated the association so that it was no longer significant.

CONCLUSIONS

In summary several genetic and lifestyle factors were observed to influence TL. These factors also appear to confound associations between TL and colon cancer.

Telomeres and immune competency

Telomeres are essential for the integrity of chromosomes and for cellular replication. Attrition of telomeres occurs during DNA replication owing to the inability of conventional DNA polymerase to replicate chromosomal termini and the insufficient compensation for telomere loss by telomerase, an enzyme that synthesizes telomeric DNA. A number of genetic defects have been described in humans and in animal models that cause accelerated telomere attrition, in turn leading to severe phenotypes of hematopoietic and other proliferating cells. Telomere length, most frequently measured as an average value in heterogeneous peripheral blood leukocyte populations in humans, has been associated with a wide range of health conditions and diseases of immune and non-immune cells. Here, I review recent studies of telomere length dynamics with particular relevance to immune function.

Genetic variants in telomere-maintenance genes and bladder cancer risk

Telomeres are critical in maintaining genomic stability. Genetic variants in telomere pathway genes may affect telomere and telomerase function, and subsequently cancer risk. We evaluated 126 SNPs from 10 genes related to telomere regulation in relation to bladder cancer risk. Five SNPs, 4 from TEP1 gene and 1 from PINX1 gene, were found to be highly significant (P<0.01). Out of these, the most significant association was found in rs2228041 of TEP1 (OR 1.66, 95% CI 1.19–2.31) while rs1469557 of PINX1 had a protective effect (OR 0.75, 95% CI 0.61–0.93). Haplotype analysis showed that a TEP1 haplotype consisting of the variant alleles of 7 SNPs exhibited a 2.28 fold increased risk (95% CI 1.13–4.60). We then performed cumulative analysis of multiple risk variants, as well as Classification and Regression Tree (CART) to look for gene-gene interactions. In cumulative effect analysis, the group with 4–5 risk variants had an OR of 2.57 (95% CI = 1.62–4.09) versus the reference group with 0 risk variants. The CART analysis categorized individuals into five subgroups with different bladder cancer risk profiles based on their distinct genotype background. To our knowledge, this is one of the largest, most comprehensive studies on bladder cancer risk concerning telomere-regulating pathway gene SNPs and our results support that genetic variations of telomere maintenance modulate bladder cancer risk individually and jointly.

Surrogate tissue telomere length and cancer risk: shorter or longer?

Telomeres play a critical role in chromosome stability. Telomere length (TL) shortening is a risk factor for cancers. Measuring TL in surrogate tissues that can be easily collected may provide a potential tool for early detection of cancers. A number of studies on surrogate tissue TL and cancer risks have been conducted and results are inconsistent, including positive, negative, or null associations. In this article, we reviewed the published data on surrogate tissue TL in relation to cancer risks, discussed the possible reasons for the differences in the results and future directions and challenges for this line of research.

Telomere length and genetic variation in telomere maintenance genes in relation to ovarian cancer risk

BACKGROUND

Telomeres protect chromosomal ends, shorten with cellular division, and signal cellular senescence, but unchecked telomere attrition can lead to telomere dysfunction, upregulation of telomerase, and carcinogenesis. Shorter telomeres in peripheral blood leukocytes (PBL) have been associated with elevated cancer risk. Furthermore, genetic variants in and around the TERT gene have been implicated in carcinogenesis.

METHODS

We measured relative telomere length (RTL) in PBLs of 911 cases and 948 controls from the New England case-control (NECC) study, a population-based study of ovarian cancer. In addition, we assessed germ line genetic variation in five telomere maintenance genes among 2,112 cases and 2,456 controls from the NECC study and the Nurses' Health Study, a prospective cohort study. ORs and 95% CIs were estimated by logistic regression.

RESULTS

Overall, we observed no differences in telomere length between cases and controls. Compared with women with RTL in the longest tertile, women with RTL in the shortest tertile had no increase in risk (OR = 1.01, 95% CI: 0.80-1.28). However, several SNPs in the TERT gene, including rs2736122, rs4246742, rs4975605, rs10069690, rs2736100, rs2853676, and rs7726159, were significantly associated with ovarian cancer risk. We observed a significant gene-level association between TERT and ovarian cancer risk (P = 0.00008).

CONCLUSION

Our observations suggest that genetic variation in the TERT gene may influence ovarian cancer risk, but the association between average telomere length in PBLs and ovarian cancer remains unclear.

IMPACT

The role of telomeres in ovarian carcinogenesis remains unsettled and warrants further investigation.

Telomere length is a biomarker of cumulative oxidative stress, biologic age, and an independent predictor of survival and therapeutic treatment requirement associated with smoking behavior

Globally, tobacco use is associated with 5 million deaths per annum and is regarded as one of the leading causes of premature death. Major chronic disorders associated with smoking include cardiovascular diseases, several types of cancer, and chronic obstructive pulmonary disease (lung problems). Cigarette smoking (CS) generates a cumulative oxidative stress, which may contribute to the pathogenesis of chronic diseases. Mainstream and side stream gas-phase smoke each have about the same concentration of reactive free radical species, about 1 × 10(16) radicals per cigarette (or 5 × 10(14) per puff). This effect is critical in understanding the biologic effects of smoke. Several lines of evidence suggest that cigarette smoke constituents can directly activate vascular reactive oxygen species production. In this work we present multiple evidence that CS provide the important risk factors in many age-related diseases, and is associated with increased cumulative and systemic oxidative stress and inflammation. The cited processes are marked by increased white blood cell (leucocytes, WBCs) turnover. The data suggest an alteration of the circulating WBCs by CS, resulting in increased adherence to endothelial cells. Telomeres are complex DNA-protein structures located at the end of eukaryotic chromosomes. Telomere length shortens with biologic age in all replicating somatic cells. It has been shown that tobacco smoking enhances telomere shortening in circulating human WBCs. Telomere attrition (expressed in WBCs) can serve as a biomarker of the cumulative oxidative stress and inflammation induced by smoking and, consequently, show the pace of biologic aging. We originally propose that patented specific oral formulations of nonhydrolized carnosine and carcinine provide a powerful tool for targeted therapeutic inhibition of cumulative oxidative stress and inflammation and protection of telomere attrition associated with smoking. The longitudinal studies of the clinical population groups described in this study including elderly support the hypothesis that telomere length is a predictor of survival and therapeutic treatment requirement associated with smoking behavior.

The genetics and clinical manifestations of telomere biology disorders

Telomere biology disorders are a complex set of illnesses defined by the presence of very short telomeres. Individuals with classic dyskeratosis congenita have the most severe phenotype, characterized by the triad of nail dystrophy, abnormal skin pigmentation, and oral leukoplakia. More significantly, these individuals are at very high risk of bone marrow failure, cancer, and pulmonary fibrosis. A mutation in one of six different telomere biology genes can be identified in 50–60% of these individuals. DKC1, TERC, TERT, NOP10, and NHP2 encode components of telomerase or a telomerase-associated factor and TINF2, a telomeric protein. Progressively shorter telomeres are inherited from generation to generation in autosomal dominant dyskeratosis congenita, resulting in disease anticipation. Up to 10% of individuals with apparently acquired aplastic anemia or idiopathic pulmonary fibrosis also have short telomeres and mutations in TERC or TERT. Similar findings have been seen in individuals with liver fibrosis or acute myelogenous leukemia. This report reviews basic aspects of telomere biology and telomere length measurement, and the clinical and genetic features of those disorders that constitute our current understanding of the spectrum of illness caused by defects in telomere biology. We also suggest a grouping schema for the telomere disorders.

The potential utility of telomere-related markers for cancer diagnosis

The role telomeres and telomerase play in the initiation and progression of human cancers has been extensively evaluated. Telomeres are nucleoprotein complexes comprising the hexanucleotide DNA repeat sequence, TTAGGG and numerous telomere-associated proteins, including the six member Shelterin complex. The main function of the telomere is to stabilize the ends of the chromosomes. However, through multiple mechanisms, telomeres can become dysfunctional, which may drive genomic instability leading to the development of cancer. The majority of human cancers maintain, or actively lengthen, telomeres through up-regulation of the reverse transcriptase telomerase. Because there are significant differences in telomere length and telomerase activity between malignant and non-malignant tissues, many investigations have assessed the potential to utilize these molecular markers for cancer diagnosis. Here, we critically evaluate whether measurements of telomere lengths and telomerase levels may be clinically utilized as diagnostic markers in solid tumours, with emphasis on breast and prostate cancer as representative examples. Future directions focusing on the direct detection of dysfunctional telomeres are explored. New markers for telomere dysfunction may eventually prove clinically useful.

Telomere attrition and decreased fetuin-A levels indicate accelerated biological aging and are implicated in the pathogenesis of colorectal cancer

PURPOSE

Increasing chronological age is a risk factor for many types of cancer including colorectal. An understanding of the biology of aging and factors which regulate it may provide insight into cancer pathogenesis. The role of telomere biology in both the cancer and aging process could prove useful in this regard.

EXPERIMENTAL DESIGN

Using quantitative PCR, we determined telomere length in the peripheral blood leukocytes of 64 colorectal cancer (CRC) patients and 1,348 controls. We also measured telomere length in 32 colorectal tumor samples and matched normal tissue. We aimed to assess whether telomere lengths were reflected in circulating mediators of inflammation and redox control factors, including fetuin-A, a circulating modulator of calcium homeostasis.

RESULTS

CRC patients had shorter telomeres [adjusted mean ratio of relative telomere repeat copy number to single-copy gene number (RelT/S) = 0.61] compared with chronologically older controls (mean age = 75, adjusted mean RelT/S = 0.70; ANCOVA, P = 0.004). Telomere length in tumor tissue [median = 0.43, interquartile range (IQR) = 0.40] was significantly shorter than adjacent normal tissue (median = 0.65, IQR = 0.28; P = 0.004). Patients with low fetuin-A levels were shown to have significantly shorter telomeres (P = 0.041). Patients with rectal tumors had significantly higher levels of fetuin-A than those with colonic tumors (P = 0.045).

CONCLUSIONS

We have observed that patients with CRC display clear evidence of telomere attrition compared with controls. This is congruent with accelerated biological aging in the pathogenesis of CRC. An imbalance in redox control mechanisms and calcium homeostasis may be a contributing factor to telomere dynamics in our patients. Furthermore, fetuin-A levels can be used to distinguish between colon and rectal cancers.

Epidemiologic evidence for a role of telomere dysfunction in cancer etiology

Telomeres, the dynamic nucleoprotein structures at the ends of linear chromosomes, maintain the genomic integrity of a cell. Telomere length shortens with age due to the incomplete replication of DNA ends with each cell division as well as damage incurred by oxidative stress. Patterns of telomere shortening, genomic instability, and telomerase expression in many cancer tissues compared to adjacent normal tissue implicate telomere crisis as a common crucial event in malignant transformation. In order to understand the role of telomere length in cancer etiology, most epidemiologic studies have measured average telomere length of peripheral blood or buccal cell DNA as a surrogate tissue biomarker of telomere dysfunction and cancer risk. In this review, we present the results from epidemiologic investigations conducted of telomere length and cancer risk. We note differences in reported associations based on study design, which may be due to biases intrinsic to retrospective studies. Finally, we conclude with study design considerations as future investigations are needed to elucidate the relationship between telomere length and a number of cancer sites.

Shortened telomere length is associated with increased risk of cancer: a meta-analysis

BACKGROUND

Telomeres play a key role in the maintenance of chromosome integrity and stability, and telomere shortening is involved in initiation and progression of malignancies. A series of epidemiological studies have examined the association between shortened telomeres and risk of cancers, but the findings remain conflicting.

METHODS

A dataset composed of 11,255 cases and 13,101 controls from 21 publications was included in a meta-analysis to evaluate the association between overall cancer risk or cancer-specific risk and the relative telomere length. Heterogeneity among studies and their publication bias were further assessed by the χ(2)-based Q statistic test and Egger's test, respectively.

RESULTS

The results showed that shorter telomeres were significantly associated with cancer risk (OR = 1.35, 95% CI = 1.14-1.60), compared with longer telomeres. In the stratified analysis by tumor type, the association remained significant in subgroups of bladder cancer (OR = 1.84, 95% CI = 1.38-2.44), lung cancer (OR = 2.39, 95% CI = 1.18-4.88), smoking-related cancers (OR = 2.25, 95% CI = 1.83-2.78), cancers in the digestive system (OR = 1.69, 95% CI = 1.53-1.87) and the urogenital system (OR = 1.73, 95% CI = 1.12-2.67). Furthermore, the results also indicated that the association between the relative telomere length and overall cancer risk was statistically significant in studies of Caucasian subjects, Asian subjects, retrospective designs, hospital-based controls and smaller sample sizes. Funnel plot and Egger's test suggested that there was no publication bias in the current meta-analysis (P = 0.532).

CONCLUSIONS

The results of this meta-analysis suggest that the presence of shortened telomeres may be a marker for susceptibility to human cancer, but single larger, well-design prospective studies are warranted to confirm these findings.

Telomerase expression and telomere length in breast cancer and their associations with adjuvant treatment and disease outcome

Introduction

Telomere length plays important roles in maintaining genome stability and regulating cell replication and death. Telomerase has functions not only to extend telomere length but also to repair DNA damage. Studies have shown that telomerase may increase cancer cell resistance to DNA-damaging anticancer agents; tamoxifen may suppress telomerase expression in breast cancer cells. This study aimed to investigate the role of telomere length and telomerase activity in breast cancer prognosis.

Methods

qPCR and qRT-PCR were used to analyze telomere length and telomerase expression, respectively, in tumor samples of 348 breast cancer patients. Cox regression analysis was performed to examine telomere length and telomerase expression in association with disease-free survival and cause-specific mortality.

Results

Telomere length had no relation to tumor features or disease outcomes. Telomerase expression was detected in 53% of tumors. Larger tumors or aggressive disease were more likely to have telomerase expression. Among patients treated with chemotherapy, high telomerase was found to be associated with increased risk of death (hazard ratio (HR) = 3.15; 95% CI: 1.34 to 7.40) and disease recurrence (HR = 2.04; 95% CI: 0.96 to 4.30) regardless of patient age, disease stage, tumor grade, histological type or hormone receptor status. Patients treated with endocrine therapy had different results regarding telomerase: high telomerase appeared to be associated with better survival outcomes. Telomerase expression made no survival difference in patients who received both chemotherapy and endocrine therapy.

Conclusions

Overall, telomerase expression was not associated with disease outcome, but this finding may be masked by adjuvant treatment. Patients with high telomerase expression responded poorly to chemotherapy in terms of disease-free and overall survival, but fared better if treated with endocrine therapy.