Gastroprotective agents for the prevention of NSAID-induced gastropathy

Over 30 million people in the world take non-steroidal anti-inflammatory drugs (NSAID's). A large percentage of these individuals will develop gastric ulcers and related complications, a condition known as "NSAID gastropathy". NSAID gastropathy differs from classic peptic ulcer disease in many ways, and traditional peptic ulcer therapy is largely ineffective in preventing NSAID-induced gastropathy. The prostaglandin misoprostol has been shown to be effective and is approved for the prevention of NSAID gastropathy. However, misoprostol has side effects that limit its general use. For this reason, considerable effort throughout the 1990's has focused on the identification of new gastroprotective molecules. Some synthetic studies have been aimed at the preparation of new prostaglandins, prostacyclin mimetics, and thromboxane antagonists. New histamine H2 receptor antagonists have also been developed which, unlike cimetidine or ranitidine, now appear to couple true gastroprotective activity with antisecretory properties. One new H2 antagonist, ebrotidine, has shown clinical utility in preventing NSAID gastropathy. Many other types of structures (flavonoids, peptides, terpenoids, xanthines, others), as well as compounds displaying certain pharmacological actions (5-hydroxytryptamine receptor binding, adrenergic receptor binding, mast cell stabilization, others) have been linked in some way to gastroprotection. This article reviews many of these recent gastroprotection findings, with emphasis on those of potential use for prevention of NSAID gastropathy.

Synthesis and biological evaluation of substituted flavones as gastroprotective agents

Flavone (1) was found to protect against ethanol-induced gastric damage in rats; however, it is known that certain compounds in the flavone class, including flavone itself, are inducers of hepatic drug metabolizing enzymes. With the hope of identifying gastroprotective flavones that have minimal effects on drug metabolizing enzymes, we have synthesized and evaluated selected flavone analogs. Gastroprotective potency in the ethanol model was retained by methoxy substitution in the 5-position (4) and by methoxy (12) or methyl (14) substitution in the 7-position. A number of substituted analogs of the potent molecule 5-methoxyflavone (4) were also synthesized, and in many cases, these substitutions provided gastroprotective molecules. In order to assess liver enzyme induction potential, two of the gastroprotective flavones, 7-methoxyflavone (12) and 5-methoxy-4'-fluoroflavone (26), were examined for their effect on liver microsomal cytochrome P450 and 7-ethoxyresorufin O-dealkylase (CYP1A) activity. These two compounds caused minimal changes in the cytochrome P450 concentration and were considerably less potent than beta-naphthoflavone as inducers of CYP1A enzyme activity. Furthermore, following oral administration to rats, 5-methoxy-4'-fluoroflavone (26) was found to protect against indomethacin-induced gastric damage. These results indicate that, through appropriate substitution, flavones can be obtained that are gastroprotective but have minimal effects on drug-metabolizing enzymes.