Aspirin May Slow the Aging Clocks of Colon Cells, Study Suggests

For decades, aspirin has been one of medicine’s most humble workhorses, a cheap pill taken for headaches and heart health. But a growing body of evidence suggests the familiar drug may have a far more remarkable talent: it could help keep the cells of the colon biologically young. A new analysis published in Epigenetics Communications adds a striking layer to that story, showing that long-term aspirin use is associated with a measurable slowdown of so-called epigenetic mitotic clocks in healthy colon tissue. The finding, drawn from a decade of follow-up in a unique cohort of Polish women, offers fresh clues about how aspirin might protect against one of the world’s most common cancers.

Colorectal cancer is the third most frequently diagnosed cancer worldwide, with an estimated 1.8 million new cases each year. Randomized controlled trials have already shown that aspirin can reduce colorectal cancer incidence in certain populations, and the United States Preventive Services Task Force has recommended low-dose aspirin for primary prevention in adults aged 50 to 59 who carry a ten-year cardiovascular disease risk of at least 10 percent. Yet questions of long-term adherence, contraindications, and the sheer scale of the disease mean screening and surveillance will remain essential. That is why researchers are increasingly interested in novel biomarkers that could flag cancer risk earlier and more precisely, and epigenetic aging measures are among the most promising candidates.

Epigenetic clocks are mathematical models that estimate biological age from patterns of DNA methylation, the chemical tags that attach to DNA and switch genes on or off without altering the underlying sequence. The best-known clocks, developed by Steven Horvath and Gregory Hannum in 2013, capture aging signals that are largely independent of cell division. But cancer is intimately a disease of uncontrolled mitosis, and that is where a newer family of biomarkers comes in. Mitotic clocks, including EpiTOC, EpiTOC2, and MiAge, are designed to estimate the cumulative number of cell divisions a tissue has undergone. EpiTOC tracks methylation gains at CpG sites within Polycomb group target genes that are typically unmethylated in fetal tissue but accumulate methylation with age, effectively counting stem cell replication errors. EpiTOC2 goes further, estimating the total number of stem cell divisions in a tissue, while MiAge represents the lifetime tally of cell divisions and has been found universally accelerated across thirteen cancer types, including colon adenocarcinoma.

Previous work on this same cohort, published in 2020 by Noreen and colleagues, reported that long-term aspirin users showed deceleration of conventional epigenetic age measures, specifically the Hannum, Horvath, and PhenoAge metrics, in the proximal colon but not the distal colon. What that study could not answer was whether aspirin’s effect extended to cell proliferation itself. Because the widely used clocks capture aging signals independent of mitosis, it was possible that aspirin’s relationship with epigenetic aging was entirely proliferation-independent. The new study, led by Jamaji C. Nwanaji-Enwerem of Emory University and the University of California, Berkeley, together with Chijioke Nze and Andres Cardenas, set out to close that gap by applying three mitotic clocks to the same decade-spanning dataset.

The data came from a publicly available NCBI Gene Expression Omnibus dataset comprising DNA methylation profiles from healthy colon mucosa biopsies collected at two timepoints, baseline and a ten-year follow-up. The researchers analyzed 112 samples from 28 healthy Polish women, 11 of whom never used aspirin and 17 of whom were long-term users, defined as taking aspirin at least twice per week for at least two years. Three participants who crossed over from non-use to long-term use during the study were excluded to keep the longitudinal comparison clean. Each participant had provided both proximal, or cecal, and distal, or sigmoid, colon biopsies at both timepoints, allowing the team to examine whether effects differed along the length of the colon. Genome-wide methylation was profiled using the Illumina Infinium MethylationEPIC BeadChip, and the mitotic clocks were computed from the normalized methylation values using published R code.

The statistical approach was deliberately careful. Because the mitotic clocks correlate strongly with chronological age, the researchers calculated age-independent intrinsic rates by dividing each clock value by the participant’s age, then derived residuals from linear mixed effects models adjusted for body mass index, polyp status, and DNA methylation batch, with a random intercept for each participant to account for repeated measures. They then used paired Wilcoxon signed rank tests to compare baseline and follow-up values within each aspirin group. All three clocks correlated significantly with chronological age, with coefficients ranging from 0.41 to 0.63, and the clocks correlated strongly with one another, with r values above 0.79 in both colon regions and an especially tight relationship between EpiTOC and EpiTOC2 exceeding 0.99.

The headline result was unambiguous. In the proximal colon of long-term aspirin users, the intrinsic rates of all three mitotic clocks decelerated significantly over the ten-year period: EpiTOC by a median of 0.0004 DNAm units, EpiTOC2 by roughly 16 cell divisions, and MiAge by about 3 cell divisions, with P values of 0.008, 0.009, and 0.002 respectively. No such deceleration was observed in non-users. In the distal colon, only MiAge showed a significant deceleration among long-term users. When the researchers compared the ten-year changes between the two groups directly, long-term users showed more negative median differences in the proximal colon for all three clocks, though these between-group comparisons did not reach statistical significance, likely a consequence of the small sample size and the unpaired nature of that analysis.

The findings dovetail neatly with the earlier report of aspirin-linked deceleration of Horvath, Hannum, and PhenoAge measures in the proximal colon, and they suggest that cell proliferation may indeed be part of the mechanism by which aspirin influences epigenetic aging. The proximal-distal split is itself intriguing. The right and left colon differ in embryonic origin and in the molecular pathways that drive tumor initiation: mismatch repair mutations are more common in right-sided tumors, while chromosomal instability dominates on the left. Some chemopreventive interventions, including aspirin, appear more robust in the proximal colon. The authors argue that future epigenetic aging studies of colorectal cancer should routinely report colon location-specific results rather than pooling the two regions.

Beyond the aspirin story, the paper issues a broader call to standardize a young and somewhat fragmented field. The Horvath and PhenoAge clocks were built from roughly 8,000 and 10,000 samples respectively, whereas EpiTOC was developed from just over 650 samples, and MiAge and EpiTOC2 from around 4,000 and 3,000. Differences in training data may explain why different clocks show different sensitivity to biological processes, a pattern the authors have observed elsewhere, including in a study of simulated long-duration space travel where only PhenoAge deceleration remained statistically significant. They recommend that future colorectal cancer epigenetic studies include, at minimum, the traditional Hannum, Horvath, and PhenoAge measures alongside the mitotic clocks MiAge, EpiTOC, and EpiTOC2, to allow the field to converge on which markers best capture cancer-relevant biology and to enable meaningful meta-analyses.

The authors also urge caution on the social dimensions of epigenetic aging. Racial disparities in colorectal cancer are well documented, and one recent study reported epigenetic age acceleration in the right colons of African Americans alongside deceleration in European American peers. Yet when Devall and colleagues analyzed differentially methylated positions by race, 18.4 percent overlapped with markers of ancestry, and lifestyle and social factors were largely absent from the discussion. Given that epigenetic aging has been linked to diet, racial discrimination, neighborhood deprivation, and exposure to violence, the researchers recommend that future studies explicitly distinguish the effects of racism and social environment from ancestry itself. The study carries clear limitations: it was observational, involved only Polish women, lacked aspirin dose information, and adjusted for a limited set of covariates, so causality cannot be established, and immune-mediated mechanisms remain possible. Still, the convergence of three independent mitotic clocks on the same signal in the proximal colon of long-term aspirin users is a compelling hint that a century-old drug may be quietly slowing the cellular clockwork of the gut, and it sets a template for the larger, more diverse, and better standardized studies that must now follow.

Subject of Research: Epigenetic mitotic clock analysis of long-term aspirin use and colorectal cancer risk in healthy colon mucosa

Article Title: Long-term aspirin use and epigenetic mitotic clocks for cancer risk prediction: findings in healthy colon mucosa and recommendations for future epigenetic aging studies

Article References: Nwanaji-Enwerem, J. C., Nze, C., & Cardenas, A. (2021). Long-term aspirin use and epigenetic mitotic clocks for cancer risk prediction: findings in healthy colon mucosa and recommendations for future epigenetic aging studies. Epigenetics Communications, 1(1), Article 5. https://doi.org/10.1186/s43682-021-00004-4

Image Credits: AI Generated

DOI: 10.1186/s43682-021-00004-4

Keywords: aspirin, epigenetic clocks, mitotic clocks, colorectal cancer, DNA methylation, EpiTOC, EpiTOC2, MiAge, colon mucosa, chemoprevention, epigenetic aging, cancer risk prediction