May 12, 2006
Understanding the role of free radicals in thrombosis could lead to new therapy

In cardiovascular diseases arteries can become blocked by thrombosis, which is the formation of blood clots. Non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin are used as anti-thrombotic agents in preventing heart disease and stroke.

Oxygen free radicals play a role in the induction of thrombosis. Free radicals are reactive species involved in a range of normal biological processes, such as skin ageing, and in the pathogenesis of diseases. A greater understanding of the biochemical reactions of these oxygen free radicals could lead to the development of an improved therapeutic agent for treating and preventing cardiovascular diseases.
Scientists from the Royal College of Surgeons in Ireland (RCSI), which include CSCB researchers Dr Marc Devocelle and Professor Kevin Nolan, and Professor Des Fitzgerald, now Vice-President for Research at UCD, have recently synthesised some derivates of anthranilic hydroxamic acid (AHA). These AHA compounds have the potential to be developed as therapeutic agents for inhibiting the free radical activity that can contribute to cardiovascular diseases.

Discovering new therapeutic agents takes many years and chemists will often begin by making libraries of compounds which they then screen for biological activity.

"Jean Lee, one of the RCSI chemists involved in this research, used solid phase synthesis to facilitate and speed up the process," explains Dr Devocelle. "Although this technique required some initial optimisation, it allowed us to synthesise a large number of derivatives in sufficient quantities for the subsequent biological evaluation and to prepare compounds not easily obtained by traditional techniques."

NSAIDs act by interfering with the release of chemicals called prostaglandins, which are hormones produced by our bodies. The biosynthetic process of producing prostaglandins starts with the biotransformation of arachidonic acid by an enzyme called prostaglandin H2 synthase (PGHS). This enzyme is known to act at two sites - the cyclooxygenase (COX) site and the peroxidase (POX) site. Aspirin inhibits the COX site activity of this enzyme but does not act at the POX site.

"Peroxidases are very powerful enzymes capable of generating highly damaging free radicals. The enzyme we are working on shows up in a number of major diseases, including atherosclerosis or hardening of the arteries," says Professor Fitzgerald. "Indeed, the first of our series of compounds slowed the development of atherosclerosis in the lab in a mouse model."

Oxygen free radicals are generated at the POX site so synthesising compounds that inhibit the POX site activity of the PGHS enzyme could open up a way forward to developing anti-inflammatory agents with improved therapeutic profiles. In vitro testing of 29 AHA derivatives was carried out by Anthony Chubb in the RCSI and the results showed that these derivatives are true inhibitors of POX activity.

"There is no current therapeutic agent in clinical use for inhibiting POX site activity," says Dr Devocelle. "Since the COX site activity is dependent on the POX site activity, these AHA derivatives could potentially inhibit both sites and have a greater therapeutic value than NSAIDs."

About eight of the novel compounds showed significant biological activity, with one promising lead compound. The scientists then went on to synthesise and evaluate a second generation of AHA.

"Two of these new second generation compounds show superior activity compared to the best inhibitors from the original 29 compounds," concludes Professor Nolan. "We are now in the process of carrying out more in vitro testing on these second generation compounds in the hope of progressing towards clinical development."

Publication reference:
Lee, J.; Chubb, A. J.; Moman, E.; McLoughlin, B. M.; Sharkey, C. T.; Kelly, J. G.; Nolan, K. B.; Devocelle, M.; Fitzgerald, D. J. Org. Biomol. Chem. 2005, 3, 3678-3685.


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