-ASA is in the salicylic acid family, so it seems like aspirin could be a good thing.
NSAIDs and 5-ASA are chemically similar but act very differently within the body then each other. A few subtle changes in the chemical structure can make drastic differences in what a compound does within the body, and this is a good example of that. Chemically, NSAIDs are known as ASA, while mesalamine is known as 5-ASA; similar.
NSAIDs are COX-1 and COX-2 inhibitors, which is their desired affect. 5-ASA is a very weak COX-inhibitor and not very effective at all for that purpose.
I believe the desired affect of 5-ASA is this. The U-M researchers discovered that mesalamine targets a bacterial stress response system that otherwise may help microorganisms survive in an environment of chronic inflammation. The microorganisms’ stress response system produces a substance called polyphosphate. Bacteria that are unable to make polyphosphate are less virulent, defective in forming antibiotic-resistant biofilms, less able to colonize the gut and are more sensitive to inflammatory oxidants, which are produced by our bodies to combat harmful bacteria. In other words, those bacteria are an easy, weakened target for the immune system to attack. After a period of time—up to seven hours after treatment—the researchers took samples from the participants’ gastrointestinal tracts. In the samples that did not show mesalamine, the study participants showed stable levels of polyphosphate. But that changed once mesalamine became detectable. “The moment we could detect mesalamine, the polyphosphate levels dropped dramatically,” Dahl said./news.umich.edu/u-m-researchers-discover-what-makes-drug-for-ulcerative-colitis-tick/