WESTPORT, Jun 02 (Reuters Health) - Investigators have identified a link between high levels of prostaglandin E2 in the rectal mucosa and high body mass index (BMI), a known risk factor for colon cancer, according to results from a study published today in the June 2nd issue of the Journal of the National Cancer Institute.
The Arizona group also found low prostaglandin E2 levels in the rectal mucosa in study subjects who reported high levels of physical activity.
According to the researchers, these findings might help explain why higher BMI and a sedentary lifestyle are consistently associated with an increase in colon cancer risk.
Dr. Maria Elena Martinez and co-investigators at the University of Arizona, in Tucson, obtained two sets of rectal biopsy samples, taken 8 weeks apart, from 63 patients between the ages of 42 and 78 years. The patients had one or more adenomatous colorectal polyps and were participating in a clinical trial of piroxicam.
The investigators found that for every 10 year-increase in age, prostaglandin E2 levels in rectal mucosa increased by 24%. "Likewise, a change in BMI from 24.2 to 28.8...was associated with a 27% increase in rectal mucosa [prostaglandin E2] concentration."
Compared with patients who were mostly sedentary, patients who engaged in the equivalent of a 30-minute daily jog or a 60-minute daily walk had 28% lower prostaglandin E2 concentrations, Dr. Martinez's team reports.
The research team speculates "...that the risk-enhancing effect of BMI and activity levels on [prostaglandin E2] is mediated through insulin or [insulin-like growth factor I] synthesis or that [prostaglandin E2] serves as a marker of insulin levels."
"Although it is likely that [prostaglandin E2] in the upper rectum is reflective of [prostaglandin E2] levels in the colon, this requires further study," the researchers acknowledge.
They conclude that in either case, the findings "...are supportive of the potential for [prostaglandin E2] playing a role in the protective mechanism of physical activity or BMI on risk of colon cancer."
The authors caution that "...the study population comprised nonusers of aspirin or other [nonsteroidal anti-inflammatory drugs]: it is not known whether similar effects would be observed among users of these agents."
In an interview with Reuters Health, Dr. Martinez noted that following intervention with piroxicam, a nonsteroidal anti-inflammatory, had close to the same effect on reducing prostaglandin synthesis in the colon as did an increase in physical activity.