Inhibition of Prostaglandins May Be Mechanism by Which Aspirin Protects Against Certain Cancers

New research suggests that the reason aspirin may protect againstcertain cancers is its ability to inhibit prostaglandins, chemicalsnaturally produced by the body that are suspected of playing arole in colorectal and lung cancer.

Prostaglandins are chemical messengers that send signals in thebody, stimulating various activities, including blood clottingand neurotransmission. Prostaglandins are also immune suppressors,and their inhibition might improve the body's ability to fightcancer cells.

Scientists were led to study aspirin because anecdotal evidencehas suggested that adults who take the drug on a regular basisfor other maladies are less likely to die of colorectal cancer.

Now, preliminary research by Mack T. Ruffin IV, MD, of the Universityof Michigan Medical School, Ann Arbor, suggests that as littleas 80 mg of acetylsalicylic acid (ASA), the dosage of a baby aspirintablet, taken each day can lead to significant prostaglandin suppression.By comparison, a person with a headache might take two adult-strengthtablets of approximately 325 mg ASA per tablet, as many as sixtimes a day.

Speaking at the annual meeting of the American Association forCancer Research (AACR), Dr. Ruffin described his study of 65 healthyadults given 14 days of a single daily dose of ASA or a placebo.The doses of ASA were 40, 80, 160, or 640 mg. Rectal tissue biopsieswere taken to monitor changes in prostaglandin levels.

Dr. Ruffin said that 80 mg/day was the lowest effective dose andthat prostaglandin production remained suppressed up to 3 daysafter the last dose. In addition, the research team observed thatwomen produce significantly less prostaglandin than men. "Womenalso have a lower incidence of colorectal cancer," Dr. Ruffinsaid, suggesting a possible link.

Aspirin and Lung Cancer

In his AACR presentation, André Castonguay, PhD, of LavalUniversity, Quebec City, Canada, reported on a study of the abilityof various nonsteroidal anti-inflammatory drugs (NSAIDs) to suppressthe development of lung cancer in mice given NNK, a powerful carcinogenfound in cigarette smoke.

He found that mice who received unprocessed, nonformulated ASAhad 60% fewer lung tumors, compared with the control group. Inmice fed the aspirin form of ASA, tumors were reduced by 63%.Sulindac, an NSAID arthritis medication, suppressed tumor growthby 52%, he said, and buffered aspirin did not demonstrate anysignificant protection from tumors.

Avoid 'Cavalier' Use

Even though ASA is available over-the-counter, Dr. Ruffin warnedthat it should not be used in a cavalier manner, and should beconsidered an experimental cancer drug. ASA has many potentialside effects, including stomach pain, bleeding ulcers, nausea,diarrhea, and vomiting.

As many as 4% of the population cannot tolerate normal doses ofASA because of side effects. In addition, some people are allergicto ASA, and the drug may interfere with other medications.

"It is ironic that in this era of high-tech medicine, researchersare taking a second look at this old standby," Dr. Ruffinsaid. "Scientists are rediscovering it, and may find thatit has a potential impact beyond even what we speculate now."

Dr. Ruffin also stressed that ASA should not be used as a "magicbullet" to prevent cancer instead of following a healthydiet and lifestyle. Colorectal cancer is believed to be relatedto the high-fat, low-fiber North American diet, and he also suspectsthat there may be a relationship between prostaglandin levelsand diet.