Association of serum cotinine levels and lung cancer mortality in non-smokers

Lung cancer risk in never-smokers: An overview of environmental and genetic factors

Lung cancer is the leading cause of cancer-related mortality globally, accounting for 1.8 million deaths in 2020. While the vast majority are caused by tobacco smoking, 15%-25% of all lung cancer cases occur in lifelong never-smokers. The International Agency for Research on Cancer (IARC) has classified multiple agents with sufficient evidence for lung carcinogenesis in humans, which include tobacco smoking, as well as several environmental exposures such as radon, second-hand tobacco smoke, outdoor air pollution, household combustion of coal and several occupational hazards. However, the IARC evaluation had not been stratified based on smoking status, and notably lung cancer in never-smokers (LCINS) has different epidemiological, clinicopathologic and molecular characteristics from lung cancer in ever-smokers. Among several risk factors proposed for the development of LCINS, environmental factors have the most available evidence for their association with LCINS and their roles cannot be overemphasized. Additionally, while initial genetic studies largely focused on lung cancer as a whole, recent studies have also identified genetic risk factors for LCINS. This article presents an overview of several environmental factors associated with LCINS, and some of the emerging evidence for genetic factors associated with LCINS. An increased understanding of the risk factors associated with LCINS not only helps to evaluate a never-smoker's personal risk for lung cancer, but also has important public health implications for the prevention and early detection of the disease. Conclusive evidence on causal associations could inform longer-term policy reform in a range of areas including occupational health and safety, urban design, energy use and particle emissions, and the importance of considering the impacts of second-hand smoke in tobacco control policy.

Serum cotinine levels and nicotine addiction potential of e-cigarettes: an NHANES analysis

This study aims to compare serum cotinine levels in e-cigarette and combustible cigarette smokers, in an attempt to quantify the potential chronic nicotine addiction risk that e-cigarettes pose. We analyzed 428 participants in 2015-2016 NHANES: 379 (87.03%) smoked combustible cigarettes alone and 49 (12.97%) smoked e-cigarettes. Serum cotinine levels were measured by isotope-dilution high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometric method with a detection limit of 0.015 ng/ml. Electronic cigarette smokers were younger than combustible cigarette smokers (mean age 36.79 versus 42.69 years, P = 0.03), more likely to be male (64.93% versus 48.32%, P = 0.09) and significantly less likely to live with other smokers (50.17% versus 90.07%, P < 0.01). Serum cotinine levels increased linearly with self-reported days of smoking in both electronic cigarette and combustible cigarette smokers, after accounting for living with a smoker. The analysis of the subgroup who reported daily use show non-statistically significantly higher serum cotinine levels in electronic cigarette smokers versus combustible cigarette smokers (β adj = 52.50, P = 0.10). This analysis of recent US data demonstrates that electronic cigarettes expose users to nicotine levels proportionate to, and potentially higher than combustible cigarettes, and thus pose a serious risk of chronic nicotine addiction. This could be particularly relevant in otherwise tobacco naive individuals; future risk of tobacco-related dependence, addiction and relapse, as well as of tobacco-related cancers in these subjects needs to be investigated.

Biomarker-assessed passive smoking in relation to cause-specific mortality: pooled data from 12 prospective cohort studies comprising 36 584 individuals

AIMS

While investigators have typically quantified the health risk of passive (secondhand) smoking by using self-reported data, these are liable to measurement error. By pooling data across studies, we examined the prospective relation of a biochemical assessment of passive smoking, salivary cotinine, with mortality from a range of causes.

METHODS

We combined data from 12 cohort studies from England and Scotland initiated between 1998 and 2008. A total of 36 584 men and women aged 16-85 years of age reported that they were non-smoking at baseline, provided baseline salivary cotinine and consented to mortality record linkage.

RESULTS

A mean of 8.1 years of mortality follow-up of 36 584 non-smokers (16 792 men and 19 792 women) gave rise to 2367 deaths (775 from cardiovascular disease, 779 from all cancers and 289 from smoking-related cancers). After controlling for a range of covariates, a 10 ng/mL increase in salivary cotinine was related to an elevated risk of total (HRs; 95% CI) (1.46; 1.16 to 1.83), cardiovascular disease (1.41; 0.96 to 2.09), cancer (1.49; 1.00 to 2.22) and smoking-related cancer mortality (2.92; 1.77 to 4.83).

CONCLUSIONS

Assessed biomedically, passive smoking was a risk factor for a range of health outcomes known to be causally linked to active smoking.

All-in-one platform for salivary cotinine detection integrated with a microfluidic channel and an electrochemical biosensor

Medical disorders caused by second-hand smoke are a major public health concern worldwide. To estimate the level of second-hand smoke exposure, salivary diagnostics for cotinine analysis is a compelling alternative in conventional diagnostics using bio-fluids, such as blood and urine, owing to its simple and non-invasive collection method. However, there are several critical issues, such as tedious multisteps, demand for expertise, and field unavailability to collect and transport the purified saliva for further analysis. Here, an all-in-one platform is presented to simply collect real human saliva and directly deliver it onto the biosensing surface. The platform consists of a commercial cotton-swab-type collector, 3D-printed housing, and microfluidic channel integrated with an electrochemical competitive immunosensor to evaluate the level of salivary cotinine. The immunosensor is based on a competitive binding assay between cotinine-conjugated horseradish peroxidase (C-HRP) and cotinine for anti-cotinine binding sites. The current responses obtained from the HRP-thionine-H₂O₂ system decreased proportionally to the cotinine concentration. This immunosensor successfully detected its target over a range of 1 × 10^-1 to 1 × 10⁴ pg ml^-1 with a low limit of detection of 6 × 10^-2 pg ml^-1 and a limit of quantification of 1 × 10^-1 pg ml^-1. In addition, the platform is applicable to various commercial cotton-swab-type saliva collectors and can successfully transfer the saliva in wide flow rates ranging from 0.1 to 30 ml min^-1 without leakage or damage to the sensing surface. Furthermore, the practicality of the proposed platform was evaluated by measuring cotinine in real human saliva from eight non-smokers. The concentration of cotinine was from 45.7 to 890.8 pg ml^-1, which was in good agreement with that measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The introduced all-in-one platform represented a reliable performance delivering simple and practical steps in salivary diagnostics.

Relationships of Long-Term Smoking and Moist Snuff Consumption With a DNA Methylation Age Relevant Smoking Index: An Analysis in Buccal Cells

INTRODUCTION

Currently, there is no widely accepted, non-self-report measure that simultaneously reflects smoking behaviors and is molecularly informative of general disease processes. Recently, researchers developed a smoking index (SI) using nucleated blood cells and a multi-tissue DNA methylation-based predictor of chronological age and disease (DNA methylation age [DNAm-age]). To better understand the utility of this novel SI in readily accessible cell types, we used buccal cell DNA methylation to examine SI relationships with long-term tobacco smoking and moist snuff consumption.

METHODS

We used a publicly available dataset composed of buccal cell DNA methylation values from 120 middle-aged men (40 long-term smokers, 40 moist snuff consumers, and 40 nonsmokers). DNAm-age (353-CpGs) and SI (66-CpGs) were calculated using CpG sites measured using the Illumina HumanMethylation450 BeadChip. We estimated associations of tobacco consumption habits with both SI and DNAm-age using linear regression models adjusted for chronological age, race, and methylation technical covariates.

RESULTS

In fully adjusted models with nonsmokers as the reference, smoking (β = 1.08, 95% CI = 0.82 to 1.33, p < .0001) but not snuff consumption (β = .06, 95% CI = -0.19 to 0.32, p = .63) was significantly associated with SI. SI was an excellent predictor of smoking versus nonsmoking (area under the curve = 0.92, 95% CI = 0.85 to 0.98). Four DNAm-age CpGs were differentially methylated between smokers and nonsmokers including cg14992253 [EIF3I], which has been previously shown to be differentially methylated with exposure to long-term fine-particle air pollution (PM2.5).

CONCLUSIONS

The 66-CpG SI appears to be a useful tool for measuring smoking-specific behaviors in buccal cells. Still, further research is needed to broadly confirm our findings and SI relationships with DNAm-age.

IMPLICATIONS

Our findings demonstrate that this 66-CpG blood-derived SI can reflect long-term tobacco smoking, but not long-term snuff consumption, in buccal cells. This evidence will be useful as the field works to identify an accurate non-self-report smoking biomarker that can be measured in an easily accessible tissue. Future research efforts should focus on (1) optimizing the relationship of the SI with DNAm-age so that the metric can maximize its utility as a tool for understanding general disease processes, and (2) determining normal values for the SI CpGs so that the measure is not as study sample specific.