Sex-Specific and Time-Varying Associations Between Cigarette Smoking and Telomere Length Among Older Adults

Proteomic Mendelian randomization to identify protein biomarkers of telomere length

Shortening of telomere length (TL) is correlated with many age-related disorders and is a hallmark of biological aging. This study used proteome-wide Mendelian randomization to identify the protein biomarkers associated with telomere length. Protein quantitative trait loci (pQTL) were derived from two studies, the deCODE Health study (4907 plasma proteins) and the UK Biobank Pharma Proteomics Project (2923 plasma proteins). Summary data from genome-wide association studies (GWAS) for TL were obtained from the UK Biobank (472,174 cases) and GWAS Catalog (418,401 cases). The association between proteins and TL was further assessed using colocalization and summary data-based Mendelian randomization (SMR) analyses. The protein-protein network, druggability assessment, and phenome-wide MR were used to further evaluate the potential biological effects, druggability, and safety of the target proteins. Proteome-wide MR analysis identified 22 plasma proteins that were causally associated with telomere length. Five of these proteins (APOE, SPRED2, MAX, RALY, and PSMB1) had the highest evidence of association with TL and should be prioritized. This study revealed telomere length-related protein biomarkers, providing new insights into the development of new treatment targets for chronic diseases and anti-aging intervention strategies.

Leukocyte telomere length and memory circuitry and cognition in early aging: Impact of sex and menopausal status

Telomere length (TL) is an important cellular marker of biological aging impacting the brain and heart. However, how it is related to the brain (e.g., cognitive function and neuroanatomic architecture), and how these relationships may vary by sex and reproductive status, is not well established. Here we assessed the association between leukocyte TL and memory circuitry regional brain volumes and memory performance in early midlife, in relation to sex and reproductive status. Participants (N = 198; 95 females, 103 males; ages 45-55) underwent structural MRI and neuropsychological assessments of verbal, associative, and working memory. Overall, shorter TL was associated with smaller white matter volume in the parahippocampal gyrus and dorsolateral prefrontal cortex. In males, shorter TL was associated with worse working memory performance and corresponding smaller white matter volumes in the parahippocampal gyrus, anterior cingulate cortex, and dorsolateral prefrontal cortex. In females, the impact of cellular aging was revealed over the menopausal transition. In postmenopausal females, shorter TL was associated with poor associative memory performance and smaller grey matter volume in the right hippocampus. In contrast, TL was not related to memory performance or grey and white matter volumes in any memory circuitry region in pre/perimenopausal females. Results demonstrated that shorter TL is associated with worse memory function and smaller volume in memory circuitry regions in early midlife, an association that differs by sex and reproductive status. Taken together, TL may serve as an early indicator of sex-dependent brain abnormalities in early midlife.

Association between modifiable lifestyle factors and telomere length: a univariable and multivariable Mendelian randomization study

BACKGROUND

Telomere length has long been recognized as a valuable biomarker of aging and is inversely correlated with chronological age. Various lifestyle factors have been implicated in telomere shortening or preservation; however, the association between lifestyle factors and telomere length remains controversial. To address this issue, we conducted a Mendelian randomization (MR) analysis to investigate the potential causal associations between multiple lifestyle factors and telomere length.

METHODS

Independent genetic variants strongly associated with lifestyle factors (tobacco smoking, sleep duration, insomnia, and physical activity) were selected as instrumental variables from corresponding genome-wide association studies (GWASs). Summary-level data for telomere length was obtained from a GWAS comprising 472,174 European ancestries. Univariable and multivariable MR analyses were performed to assess the relationships.

RESULTS

The genetic liability to lifetime smoking was robustly associated with shorter telomere length (odd ratio [OR]: 0.882; 95% confidence interval [CI]: 0.847-0.918). Genetically predicted insomnia was also linked to shorter telomere length (OR: 0.972; 95% CI: 0.959-0.985), while no significant association was observed between sleep duration and telomere length. Furthermore, a suggestive association was found between moderate-to-vigorous physical activity and longer telomere length (OR: 1.680; 95% CI: 1.115-2.531). In multivariable MR analyses, adjusting for potential mediators such as body mass index, type 2 diabetes, alcohol consumption, and alcohol use disorder, the associations of lifetime smoking and insomnia with telomere length remained robust.

CONCLUSION

Our findings suggest that smoking and insomnia may contribute to telomere shortening, while physical activity may play a role in telomere length maintenance. These findings underscore the importance of managing positive risk factors and adopting a healthy lifestyle to promote telomere health.

Targeting accelerated pulmonary ageing to treat chronic obstructive pulmonary disease-induced neuropathological comorbidities

Chronic obstructive pulmonary disease (COPD) is a major incurable health burden, ranking as the third leading cause of death worldwide, mainly driven by cigarette smoking. COPD is characterised by persistent airway inflammation, lung function decline and premature ageing with the presence of pulmonary senescent cells. This review proposes that cellular senescence, a state of stable cell cycle arrest linked to ageing, induced by inflammation and oxidative stress in COPD, extends beyond the lungs and affects the systemic circulation. This pulmonary senescent profile will reach other organs via extracellular vesicles contributing to brain inflammation and damage, and increasing the risk of neurological comorbidities, such as stroke, cerebral small vessel disease and Alzheimer's disease. The review explores the role of cellular senescence in COPD-associated brain conditions and investigates the relationship between cellular senescence and circadian rhythm in COPD. Additionally, it discusses potential therapies, including senomorphic and senolytic treatments, as novel strategies to halt or improve the progression of COPD.

Involvement of Inheritance in Determining Telomere Length beyond Environmental and Lifestyle Factors

All linear chromosomal ends have specific DNA-protein complexes called telomeres. Telomeres serve as a "molecular clock" to estimate the potential length of cell replication. Shortening of telomere length (TL) is associated with cellular senescence, aging, and various age-related diseases in humans. Here we reviewed the structure, function, and regulation of telomeres and the age-related diseases associated with telomere attrition. Among the various determinants of TL, we highlight the connection between TL and heredity to provide a new overview of genetic determinants for TL. Studies across multiple species have shown that maternal and paternal TL influence the TL of their offspring, and this may affect life span and their susceptibility to age-related diseases. Hence, we reviewed the linkage between TL and parental influences and the proposed mechanisms involved. More in-depth studies on the genetic mechanism for TL attrition are needed due to the potential application of this knowledge in human medicine to prevent premature frailty at its earliest stage, as well as promote health and longevity.

MEG3 polymorphisms associated with leukocyte telomere length in workers exposed to polycyclic aromatic hydrocarbons

Long non-coding RNA maternally expressed gene 3 (MEG3) has been revealed to be involved in telomere length (TL) maintenance and homeostasis. However, it is unknown whether single-nucleotide polymorphisms (SNPs) in MEG3 could regulate TL in populations exposed to polycyclic aromatic hydrocarbons (PAHs). This study aimed to explore the effect of MEG3 genetic polymorphisms on TL in PAH-exposed populations. This study recruited 544 coke oven workers and 238 controls using random cluster sampling. The concentrations of four urinary OH-PAHs were measured by employing high-performance liquid chromatography. TL was measured by a quantitative polymerase chain reaction assay. The MEG3 genetic polymorphisms were detected using a Sequenom MassARRAY matrix-assisted laser desorption/ionization-time of flight mass spectrometry platform. The concentrations of four urinary OH-PAHs in the exposure group were significantly higher than those in the control group (P < 0.001). TL in the exposure group (4.57 ± 0.84) was significantly lower than in the control (5.00 ± 0.75), and TL had a negative correlation with OH-PAHs. The generalized linear model found that PAH exposure [β(95% CI) = -0.409(-0.537, -0.282), P < 0.001] and the CT+TT genotype in MEG3 rs10132552 [β(95% CI) = -0.299(-0.582, -0.017), P = 0.038] were associated with the decreased TL. In conclusion, PAH exposure and the CT+TT genotype in MEG3 rs10132552 may be the risk factors for TL reduction.

Lifetime exposure to smoking, epigenetic aging, and morbidity and mortality in older adults

BACKGROUND

Cigarette smoke is a major public health concern. Epigenetic aging may be an important pathway by which exposure to cigarette smoke affects health. However, little is known about how exposure to smoke at different life stages affects epigenetic aging, especially in older adults. This study examines how three epigenetic aging measures (GrimAge, PhenoAge, and DunedinPoAm38) are associated with parental smoking, smoking in youth, and smoking in adulthood, and whether these epigenetic aging measures mediate the link between smoke exposure and morbidity and mortality. This study utilizes data from the Health and Retirement Study (HRS) Venous Blood Study (VBS), a nationally representative sample of US adults over 50 years old collected in 2016. 2978 participants with data on exposure to smoking, morbidity, and mortality were included.

RESULTS

GrimAge is significantly increased by having two smoking parents, smoking in youth, and cigarette pack years in adulthood. PhenoAge and DunedinPoAm38 are associated with pack years. All three mediate some of the effect of pack years on cancer, high blood pressure, heart disease, and mortality and GrimAge and DunedinPoAm38 mediate this association on lung disease.

CONCLUSIONS

Results suggest epigenetic aging is one biological mechanism linking lifetime exposure to smoking with development of disease and earlier death in later life. Interventions aimed at reducing smoking in adulthood may be effective at weakening this association.

Association between the Oxidative Balance Score and Telomere Length from the National Health and Nutrition Examination Survey 1999-2002

Purpose. Leukocyte telomere length (LTL) is an important biomarker of aging. The oxidative balance score (OBS) is used to assess the oxidative stress-related exposures of diet and lifestyle. This study is aimed at exploring if the OBS was associated with LTL. Methods. 3220 adults were included in this study from the National Health and Nutrition Examination Survey (NHANES) 1999-2002. LTL was assayed from leukocyte DNA. Twenty dietary and lifestyle factors were selected to score the OBS. Survey-based multivariable linear regression was conducted to assess the association between the OBS and log-transformed LTL. Results. The association between the OBS and log-transformed LTL was positive in females but not males. For females, compared with the lowest OBS category as a reference, the multivariable-adjusted beta estimate (95% confidence interval, CI) for the highest OBS category was 0.0701 (0.0205–0.1197) ( $p$ for $\text{trend}<0.01$ ), and the multivariable-adjusted beta estimate (95% CI) of the continuous OBS was 0.0039 (0.0014–0.0065). There was also the gender difference in the correlations of the dietary OBS and the lifestyle OBS with log-transformed LTL. Conclusion. There was a positive association between the OBS and LTL in females. This result suggested that diet and lifestyle might affect LTL by regulating oxidative balance.

Effect of Physical Activity, Smoking, and Sleep on Telomere Length: A Systematic Review of Observational and Intervention Studies

Aging is a risk factor for several pathologies, restricting one’s health span, and promoting chronic diseases (e.g., cardiovascular and neurodegenerative diseases), as well as cancer. Telomeres are regions of repetitive DNA located at chromosomal ends. Telomere length has been inversely associated with chronological age and has been considered, for a long time, a good biomarker of aging. Several lifestyle factors have been linked with telomere shortening or maintenance. However, the consistency of results is hampered by some methodological issues, including study design, sample size, measurement approaches, and population characteristics, among others. Therefore, we aimed to systematically review the current literature on the effects of three relevant lifestyle factors on telomere length in human adults: physical activity, smoking, and sleep. We conducted a qualitative systematic review of observational and intervention studies using the Preferred Reporting Item for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The systematic literature search covered articles published in MEDLINE and EMBASE databases (from 2010 to 2020). A total of 1400 studies were identified; 83 were included after quality control. Although fewer sedentary activities, optimal sleep habits, and non- or ex-smoker status have been associated with less telomere shortening, several methodological issues were detected, including the need for more targeted interventions and standardized protocols to better understand how physical activity and sleep can impact telomere length and aging. We discuss the main findings and current limitations to gain more insights into the influence of these lifestyle factors on the healthy aging process.

The correlation of salivary telomere length and single nucleotide polymorphisms of the ADIPOQ, SIRT1 and FOXO3A genes with lifestyle-related diseases in a Japanese population

Background

It has been reported that genetic factors are associated with risk factors and onset of lifestyle-related diseases, but this finding is still the subject of much debate.

Objective

The aim of the present study was to investigate the correlation of genetic factors, including salivary telomere length and three single nucleotide polymorphisms (SNPs) that may influence lifestyle-related diseases, with lifestyle-related diseases themselves.

Methods

In one year at a single facility, relative telomere length and SNPs were determined by using monochrome multiplex quantitative polymerase chain reaction and TaqMan SNP Genotyping Assays, respectively, and were compared with lifestyle-related diseases in 120 Japanese individuals near our university.

Results

In men and all participants, age was inversely correlated with relative telomere length with respective p values of 0.049 and 0.034. In men, the frequency of hypertension was significantly higher in the short relative telomere length group than in the long group with unadjusted p value of 0.039, and the difference in the frequency of hypertension between the two groups was of borderline statistical significance after adjustment for age (p = 0.057). Furthermore, in men and all participants, the sum of the number of affected lifestyle-related diseases, including hypertension, was significantly higher in the short relative telomere length group than in the long group, with p values of 0.004 and 0.029, respectively. For ADIPOQ rs1501299, men’s ankle brachial index was higher in the T/T genotype than in the G/G and G/T genotypes, with p values of 0.001 and 0.000, respectively. For SIRT1 rs7895833, men’s body mass index and waist circumference and all participants’ brachial-ankle pulse wave velocity were higher in the A/G genotype than in the G/G genotype, with respective p values of 0.048, 0.032 and 0.035. For FOXO3A rs2802292, women’s body temperature and all participants’ saturation of peripheral oxygen were lower in the G/T genotype than in the T/T genotype, with respective p values of 0.039 and 0.032. However, relative telomere length was not associated with physiological or anthropometric measurements except for height in men (p = 0.016). ADIPOQ rs1501299 in men, but not the other two SNPs, was significantly associated with the sum of the number of affected lifestyle-related diseases (p = 0.013), by genotype. For each SNPs, there was no significant difference in the frequency of hypertension or relative telomere length by genotype.

Conclusion

Relative telomere length and the three types of SNPs determined using saliva have been shown to be differentially associated with onset of and measured risk factors for lifestyle-related diseases consisting mainly of cardiovascular diseases and cancer.

Modifiable mediators associated with the relationship between adiposity and leukocyte telomere length in US adults: The National Health and Nutrition Examination Survey

Obesity is associated with age-related health conditions and telomere attrition - a marker of cellular aging. Obesity is attributable to adverse modifiable lifestyle factors. Little is known about the mediation effect of lifestyle factors associated with the relationship between obesity and telomere length. Our objective was to examine this association in the US. Pack years smoked, drinking level per day, physical activity (PA) per week and diet based on Healthy Eating Index (HEI) were assessed as mediators associated with the relationship between adiposity measures and leukocyte telomere length (LTL); adiposity measures included body mass index (BMI), % total body fat (TBF) and waist circumference (WC). Separate adjusted linear regressions and mediation analysis were conducted on a total of 4919 respondents aged 20-84 years using cross-sectional 1999-2002 data from the US National Health and Nutrition Examination Survey. Inadequate PA correlated with 1.28% shorter LTL and was a factor accounting for 35% of the relationship between BMI and LTL (β = -0.0128, 95% CI = 0.0259, 0.0004, p = .05). Smoking 30-≥59 pack years correlated with 4% shorter LTL and accounted for 21% of the relationship between %TBF and LTL (β = -0.0386, 95% CI = -0.0742, -0.0030, p = .03). Improvement in diet correlated with 0.11% longer LTL and contributed 25% of the association between %TBF and LTL (β = 0.0011, 95%CI =0.0004, 0.0018, p = .01). Diet correlated with 0.11% longer LTL and correspond to 28% of the relationship between WC and LTL (β = 0.0011, 95%CI = 0.0004, 0.0018, p = .03). Interventions to improve modifiable behaviors may ameliorate cellular aging and aging related health conditions due to obesity among US adults.

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.

Cell senescence and fibrotic lung diseases

Idiopathic pulmonary fibrosis (IPF) is a progressive fatal lung disorder with an unknown etiology and very limited therapeutic options. The incidence and severity of IPF increase with advanced age, suggesting that aging is a major risk factor for IPF. The mechanism underlying the aging-related susceptibility to IPF, however, remains unclear. Cellular senescence, a permanent arrest of cell growth, has been increasingly recognized as an important contributor to aging and aging-related diseases, including IPF. Senescent cells have been identified in IPF lungs and in experimental lung fibrosis models. Removal of senescent cells pharmacologically or genetically improves lung function and reverses pulmonary fibrosis induced by different stimuli in experimental fibrosis models. Treatment with senolytic drugs also improves clinical symptoms in IPF patients. These intriguing findings suggest that cellular senescence contributes importantly to the pathogenesis of fibrotic lung diseases and targeting senescent cells may represent a novel approach for the treatment of fibrotic lung disorders. In this mini review, we summarize the recent advance in the field regarding the role of cellular senescence in fibrotic lung diseases, with a focus on IPF.

Suppression effect of body weight on the association between cigarette smoking and telomere length: the Bogalusa Heart Study

This study aimed to dissect the direct effect of smoking and its indirect effect through body mass index (BMI) on leukocyte telomere length (LTL) and to distinguish the mediation and suppression effects of BMI. The study cohort included 1,037 adults (729 Whites and 308 African Americans; 42.1% males; mean age: 40.3 years) with LTL measurements by Southern blotting. General third variable models were used to distinguish the mediation and suppression effects of BMI on the smoking-LTL association. After adjusting for age, race, sex and alcohol drinking, the total effect of smoking on LTL was significant (standardized regression coefficient, β= -0.061, p=0.034) without BMI included in the model. With additional adjustment for BMI, the indirect effect of smoking on LTL through BMI was estimated at β= 0.011 (p=0.023), and the direct effect of smoking on LTL was strengthened to β= -0.072 (p=0.012). The results were similar when pack-years of smoking was used. The effect parameters did not differ significantly between race and sex groups. These results suggest that BMI has a suppression effect, not a mediation effect, on the smoking-LTL association, which potentially contributes to previous inconsistencies in the effect of smoking on LTL.

Holocaust history is not reflected in telomere homeostasis in survivors and their offspring

Telomeres, nucleoprotein structures at the ends of eukaryotic chromosomes, are crucial for the maintenance of genome integrity. While the lengths of telomeres at birth are determined genetically, many factors including environmental and living conditions affect the telomere lengths during a lifespan. In this context, extreme and long-term stress has been shown to negatively impact telomeres and their protective function, with even offspring being influenced by the stress experienced by parents. Using quantitative PCR, the relative lengths of telomeres of survivors of the Holocaust during World War II and two generations of their offspring were analyzed. These data were related to those of control groups, persons of comparable age without a strong life stress experience. In contrast to previous studies of other stress-exposed groups, the relative lengths of telomeres were comparable in groups of persons exposed to Holocaust-related stress and their progenies, and in control groups. Interestingly, shorter telomeres of Holocaust survivors of the age under 12 in the year 1945 compared to Holocaust survivors of the age above 12 were detected. Our results are discussed with respect to certain exceptionality of persons having been able to cope with an extreme stress more than 70 years ago and living to a very old age.

Associations of smoking indicators and cotinine levels with telomere length: National Health and Nutrition Examination Survey

The influence of smoking exposure on telomere length with a focus on the impact of race has rarely been discussed. We performed a cross sectional analysis into the associations of smoking indicators with leukocyte telomere length (LTL) by race among 5864 nationally representative sample of US adults (≥20 years). Data from 1999 to 2002 National Health and Nutrition Examination Survey was used for the analysis. Smoking indicators were assessed by interviews and serum cotinine levels. LTL was quantified by polymerase chain reaction. Multiple linear regressions were used to assess the association with adjustment for covariates, sample weights and design effects separately for Whites, Blacks and Mexican Americans. The intensity of smoking, measured by the average number of cigarettes consumed per day, was negatively associated with LTL among Whites (β: −3.87, 95% CI: −5.98 to −1.21) and among Blacks (β: −15.46, 95% CI: −29.79 to −2.12) participants. Compared with cotinine level < 0.05 ng/ml, cotinine level ≥3 ng/ml was associated with shorter LTL (β: −77.92, 95% CI = −143.05 to −11.70) among Whites, but not among Blacks. We found increased number of cigarette consumption to be associated with shorter LTL in both Blacks and Whites, indicating that the impact of smoking on life-shortening diseases could partly be explained by telomere biology. Increased cotinine concentration however, was associated with shorter LTL only among Whites, not among Blacks. This differential relationship that we observed may have implications in interpreting cotinine as an objective biomarker of smoking exposure across races and warrant additional prospective investigation.

•

Higher cigarette consumption was related to shorter telomere in Blacks and Whites.

•

The impact of smoking on diseases could partly be explained by telomere biology.

•

Cotinine concentration was associated with reduced telomere length only among Whites.

•

We observed a differential impact of biomarker cotinine on telomere length by race.

•

This questions cotinine's role as an objective biomarker of smoking exposure across races.

Stress and Salivary Telomere Length in the Second Half of Life: A Comparison of Life-course Models

Background

Previous research has explored the relationship between childhood and adulthood stressful life events (SLEs) and adult salivary telomere length (TL), but no research to date has tested different life-course models in which stress in adulthood may fully, partly, or not mediate the relationship between childhood stress and adult TL.

Methods

To fill this gap, we elaborate over previous work by Puterman et al. (2016) and other standard models that do not account for the temporal order of stressors in childhood and adulthood, by using structural equation modeling (SEM) for a sample of 5,754 Health and Retirement Study (HRS) participants to compare the fit of three nested life-course models-social trajectory, early critical period, and cumulative risk.

Results

Results indicated that the social trajectory model, in which the association between childhood SLEs and TL in later adulthood is fully mediated by adulthood SLEs, fit the data better than the early critical period (no mediation) and cumulative risk (partial mediation) models.

Conclusion

In the social trajectory model, childhood SLEs are related to TL in later life only through adulthood SLEs. The direct physiological effect of childhood SLEs on TL in later life would be overestimated if adulthood SLEs are overlooked.

Does Telomere Length Indicate Biological, Physical, and Cognitive Health Among Older Adults? Evidence from the Health and Retirement Study

Telomere length (TL) has been suggested as a biomarker that can indicate individual variability in the rate of aging. Yet, it remains unclear whether TL is related to recognized indicators of health in an aging, older nationally representative sample. We examine whether TL is associated with 15 biological, physical, and cognitive markers of health among older adults ages 54+. TL was assayed from saliva using quantitative polymerase chain reaction (T/S ratio) in the 2008 Health and Retirement Study (n = 4,074). We estimated probability of high-risk levels across indictors of health by TL and age-singly and jointly. TL was associated with seven indicators of poor functioning: high-density lipoprotein and total cholesterol, cystatin C, pulse pressure, body mass index, lung function, and walking speed. However, after adjusting for age, associations were substantially attenuated; only associations with cholesterol and lung function remained significant. Additionally, findings show TL did not add to the predictive power of chronological age in predicting poor functioning. While TL may not be a useful clinical marker of functional aging in an older adult population, it may still play an important role in longitudinal studies in young and middle aged populations that attempt to understand aging.

A study of telomere length, arsenic exposure, and arsenic toxicity in a Bangladeshi cohort

BACKGROUND

Chronic arsenic exposure is associated with increased risk for arsenical skin lesions, cancer, and other adverse health outcomes. One potential mechanism of arsenic toxicity is telomere dysfunction. However, prior epidemiological studies of arsenic exposure, telomere length (TL), and skin lesion are small and cross-sectional. We investigated the associations between arsenic exposure and TL and between baseline TL and incident skin lesion risk among individuals participating in the Health Effects of Arsenic Longitudinal Study in Bangladesh (2000-2009).

METHODS

Quantitative PCR was used to measure the average TL of peripheral blood DNA collected at baseline. The association between baseline arsenic exposure (well water and urine) and TL was estimated in a randomly-selected subcohort (n = 1469). A nested case-control study (466 cases and 464 age- and sex-matched controls) was used to estimate the association between baseline TL and incident skin lesion risk (diagnosed < 8 years after baseline).

RESULTS

No association was observed between arsenic exposure (water or urine) and TL. Among incident skin lesion cases and matched controls, we observed higher skin lesion risk among individuals with shorter TL (P_trend = 1.5 × 10^-5) with odds ratios of 2.60, 1.59, and 1.10 for the first (shortest), second, and third TL quartiles compared to the fourth (longest).

CONCLUSIONS

Arsenic exposure was not associated with TL among Bangladeshi adults, suggesting that leukocyte TL may not reflect a primary mode of action for arsenic's toxicity. However, short TL was associated with increased skin lesion risk, and may be a biomarker of arsenic susceptibility modifying arsenic's effect on skin lesion risk.

The association of sarcopenia, telomere length, and mortality: data from the NHANES 1999-2002

BACKGROUND/OBJECTIVES

Sarcopenia is defined as the loss of muscle mass or function with aging and is associated with adverse outcomes. Telomere shortening is associated with mortality, yet its relationship with sarcopenia is unknown.

SUBJECTS/METHODS

Adults ≥60 years from the 1999-2002 NHANES with body composition measures were identified. Sarcopenia was defined using the two Foundation for the National Institute of Health definitions: appendicular lean mass (ALM) (men <19.75; women <15.02 kg); or ALM divided by body mass index (BMI) (ALM:BMI, men <0.789; women <0.512). Telomere length was assessed using quantitative PCR. Regression models predicted telomere length with sarcopenia (referent = no sarcopenia).

RESULTS

We identified 2672 subjects. Mean age was 70.9 years (55.5% female). Prevalence of ALM and ALM:BMI sarcopenia was 29.2 and 22.1%. Deaths were higher in persons with sarcopenia as compared to those without sarcopenia (ALM: 46.4 vs. 33.4%, p < 0.001; ALM:BMI: 46.7 vs. 33.2%, p < 0.001). No adjusted differences were observed in telomere length in those with/without sarcopenia (ALM: 0.90 vs. 0.92, p = 0.74, ALM:BMI 0.89 vs. 0.92, p = 0.24). In men with ALM:BMI-defined sarcopenia, adjusted telomere length was significantly lower compared to men without sarcopenia (0.85 vs. 0.91, p = 0.013). With sarcopenia, we did not observe a significant association between telomere length and mortality (ALM: HR 1.11 [0.64,1.82], p = 0.68; ALM:BMI: HR 0.97 [0.53,1.77], p = 0.91), but noted significance in those without sarcopenia with mortality (ALM: HR 0.59 [0.40,0.86], p = 0.007; ALM:BMI: HR 0.62 [0.42,0.91]; p = 0.01).

CONCLUSIONS

We observed a potentially inverse relationship between telomere length and mortality in those without sarcopenia but did not observe a significant relationship between telomere length and mortality in the presence of sarcopenia.

Cigarette smoking and telomere length: A systematic review of 84 studies and meta-analysis

BACKGROUND

Cigarette smoking is a risk factor for ageing-related disease, but its association with biological ageing, indicated by telomere length, is unclear.

METHODS

We systematically reviewed evidence evaluating association between smoking status and telomere length. Searches were performed in MEDLINE (Ovid) and EMBASE (Ovid) databases, combining variation of keywords "smoking" and "telomere". Data was extracted for study characteristics and estimates for association between smoking and telomere length. Quality of studies was assessed with a risk of bias score, and publication bias was assessed with a funnel plot. I2 test was used to observe heterogeneity. Meta-analysis was carried out to compare mean difference in telomere length by smoking status, and a dose-response approach was carried out for pack-years of smoking and telomere length. A sensitivity analysis was carried out to examine sources of heterogeneity.

RESULTS

A total of 84 studies were included in the review, and 30 among them were included in our meta-analysis. Potential bias was addressed in half of included studies, and there was little evidence of small study bias. Telomere length was shorter among ever smokers compared to never smokers (summary standard mean difference [SMD]: -0.11 (95% CI -0.16 to -0.07)). Similarly, shorter telomere length was found among smokers compared to non-smokers, and among current smokers compared to never or former smokers. Dose-response meta-analysis suggested an inverse trend between pack-years of smoking and telomere length. However, heterogeneity among some analyses was observed.

CONCLUSION

Shorter telomeres among ever smokers compared to those who never smoked may imply mechanisms linking tobacco smoke exposure to ageing-related disease.

The Association of Telomere Length in Peripheral Blood Cells with Cancer Risk: A Systematic Review and Meta-analysis of Prospective Studies

The association between telomere length (TL) in peripheral blood cells and cancer risk remains inconclusive. We carried out a meta-analysis on prospective studies. The study-specific RR estimates were first transformed to a common comparable scale and then were pooled by a random-effects model. The dataset was composed of 13,894 cases and 71,672 controls from 28 studies in 25 articles. In the comparison of the longest versus shortest third of TL, we observed a marginally positive association between longer TL and higher risk of total cancers [OR = 1.086; 95% confidence interval (CI), 0.952-1.238]. Subgroup analyses showed that the association was stronger in lung cancer (n = 3; OR = 1.690; 95% CI, 1.253-2.280), in men (n = 6; OR = 1.302; 95% CI, 1.120-1.514) and in studies with more precise methods for DNA extraction (phenol-chloroform, salting-out or magnetic bead, n = 6, OR = 1.618; 95% CI, 1.320-1.985) and TL measurement (multiplex Q-PCR, n = 8; OR = 1.439; 95% CI, 1.118-1.852). Our meta-analysis suggested longer TL in peripheral blood cells is a likely risk factor for lung cancer or cancers in men. Accurate DNA extraction and TL measurement methods make it more liable to find significant associations between TL and cancer risk and thus should be taken into consideration in future epidemiologic studies. Cancer Epidemiol Biomarkers Prev; 26(9); 1381-90. ©2017 AACR.