Mechanism of Action of Aminosalicylates

This animation explains the mechanism of action of aminosalicylates used for the treatment of inflammatory bowel disease (IBD).Aminosalicylates include sulfasalazine and 5-aminosalicylic acid (5-ASA).Sulfasalazine, a sulfa drug, inhibits folic acid synthesis. As such, folic acid supplements should be taken with sulfasalazine to reduce the risk of neural tube defects. Sulfasalazine exhibits anti-inflammatory properties when split by gut bacterium into its metabolites: sulfapyridine and 5-ASA (mesalamine).The anti-inflammatory benefits of sulfasalazine, are chiefly derived from 5-ASA, which has fewer side effects than sulfapyridine. As such, administration of 5-ASA alone may be preferred over sulfasalazine.5-ASA is poorly absorbed by the intestines and systemic circulation, thus most remains in the terminal ileum and colon or is passed in the stool. 5-ASA within the lumen primarily exhibits a topical effect on the colonic epithelium.

Absorbed 5-ASA is extensively metabolized to N-acetyl-5-ASA by N-acetyltransferase 1 (NAT1). N-acetyl-5-ASA then binds PPAR-gamma (peroxisome proliferator-activated receptor gamma) a nuclear hormone receptor.Binding of N-acetyl-5-ASA induces the translocation of PPAR-gamma from the cytoplasm to the cell nucleus and a conformational change in PPAR-gamma.This modification permits the recruitment of the co-activator, vitamin D3 receptor-interacting protein (DRIP), which interacts directly with PPAR-gamma.Heterodimerization with the retinoid X receptor (RXR) occurs, resulting in formation of the PPAR-RXR complex, a transcriptional regulator. The PPAR-RXR heterodimer controls transcription by binding a regulatory PPAR-gamma response element (PPRE) and modulating the expression of genes involved in the inflammation process.PPAR-RXR downregulates the nuclear factor kappa B (NF-kappaB) and mitogen-activated protein kinase (MAPK) to reduce production of pro-inflammatory cytokines. This complex also reduces COX-2 activity, leading to a reduction in prostaglandins involved in inflammation.Novel agents with similar mechanisms to 5-ASA, but which target PPAR-gamma more efficiently and report a reduction of adverse events, are currently under investigation. For example the compound, GED-0507-34, exhibits a 100- to 150-fold greater anti-inflammatory effect than 5-ASA.A new generation of 5-ASA, balsalazide, is able to bypass the small intestine and release a high concentration of 5-ASA in the colon.