Non-Steroidal Anti-Inflammatory Drugs, Chronic Inflammation and Colorectal Cancer Risk

Substantial experimental and epidemiological evidence shows that long-term use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) are protective against colorectal cancer (CRC). However, the underlying chemopreventive mechanisms of NSAIDs are not fully understood, and whether there are specific subgroups of the population for whom the benefits of NSAIDs clearly outweigh the risk remains unknown. Using information from 11,894 cases and 15,999 controls from the Genetics and Epidemiology of Colorectal Cancer Consortium (GECCO) and the Colon Cancer Family Registry (CCFR), we systematically evaluated the interactions between regular use of NSAIDs (aspirin and non-aspirin NSAIDs) and other lifestyle and dietary factors in relation to CRC risk (Aim 1). NSAIDs were also reported to reduce the concentration of C-reactive protein (CRP), a biomarker of low-grade chronic inflammation that has been moderately associated with the risk of CRC. We used Mendelian randomization analysis to investigate whether the relationship between circulating CRP level and CRC risk were causal among 30,480 CRC cases and 22,844 controls from 33 observational studies (Aim 2). In addition to CRP-related pathways, several other inflammatory or carcinogenic pathways have been found to be involved in chemopreventive effect of aspirin. However, no trial has been carried out to systematically explore the biological mechanisms of aspirin in healthy humans. We assessed the difference in plasma protein levels after 60 days of regular dose aspirin (325 mg/day) compared to placebo in a randomized double-blinded crossover trial of 44 healthy non-smoking men and women, aged 21-45 years (Aim 3). In Aim 1, we found that the association between aspirin and CRC risk statistically significantly differed by smoking status after adjusting for other risk factors (P-interaction=0.048). Regular aspirin use was associated with a 29% lower risk of CRC among non-smokers (OR=0.71; 95% CI: 0.64, 0.79), whereas it was associated with 19% and 17% lower risk of CRC among smokers of pack-years below median (OR=0.81; 95% CI: 0.71, 0.92) and above median (OR=0.83; 95% CI: 0.74, 0.94), respectively. There was a suggestive interaction between regular use of any NSAID and body mass index (BMI) (P-interaction=0.075), where the association of any NSAID on CRC risk was attenuated with increasing BMI (normal: OR=0.69; 95% CI: 0.63, 0.77; overweight: OR=0.76; 95% CI: 0.70, 0.83; obese: OR=0.85; 95% CI: 0.75, 0.96). We did not observe interactions between non-aspirin NSAIDs and other CRC risk factors. In Aim 2, two of the 19 selected SNPs were significantly associated with CRC risk, where rs1260326 was significantly associated with higher risk of CRC (p=7.5×10-4), and rs6734238 was associated with lower CRC risk (p=0.003). Using all selected SNPs as instrumental variables, we found that a genetically predicted one-unit increase in the log-transformed CRP (mg/L) level was associated with a non-significant 4% higher risk of CRC (OR=1.04; 95% CI: 0.97, 1.12; p=0.256). Genetically elevated CRP was also not associated with CRC risk among subgroups of the population stratified by other risk factors. In Aim 3, among the 3,000 antibodies analyzed, statistically significant differences in plasma protein levels were observed for nine antibodies after adjusting for false discoveries (FDR adjusted p-value<0.1). The most significant protein was succinate dehydrogenase subunit C (SDHC), a key enzyme complex of the mitochondrial tricarboxylic acid (TCA) cycle. The other statistically significant proteins (NR2F1, MSI1, MYH1, FOXO1, KHDRBS3, NFKBIE, LYZ and IKZF1) are involved in multiple pathways, including DNA base-pair repair, inflammation and oncogenic pathways. However, none of the 258 KEGG and 1,139 GO pathways was found to be statistically significant after FDR adjustment. Our results suggest that the association between regular use of NSAIDs, primarily driven by aspirin, and CRC risk may be modified by smoking status and BMI. The beneficial effect of aspirin on CRC risk appears to be attenuated, rather than enhanced, among those with greater CRC risk due to obesity and heavy smoking, making it unlikely that these groups would benefit from use of aspirin. In addition, we observed no association between genetically elevated CRP levels and CRC risk, suggesting that circulating CRP is unlikely to play a causal role in the development of CRC. However, several other proteins may be involved in the chemopreventive mechanisms of aspirin on CRC risk, but larger and confirmatory studies are needed.