IJUP08 - Universidade do Porto

Interactions of sulindac and its metabolites with phospholipid
membranes: an explanation for the peroxidation protective effect
of the bioactive metabolite
F. Santos 1 , L. Teixeira 1 , M. Lúcio 1 , J. L. F. C 1 . Lima and S. Reis 1
1 Serviço de Química-Física, Faculdade de Farmácia Universidade do Porto, Portugal.
Non-steroidal anti-inflammatory drugs (NSAIDs) are the most important therapeutic
agents used in the treatment of inflammatory processes. Although the most prominent
action of NSAIDs is due to their inhibitory activity against cycloxygenase (COX) enzymes
that catalyse the formation of prostaglandins there are also other important nonprostaglandin-mediated
effects. These include the NSAIDs antioxidant effect against lipid
peroxidation induced by reactive species which are implicated in several
pathophysiological processes such as inflammation, cell injury, cancer and death. Since
both inflammatory and lipid peroxidation processes are cell-surface phenomena, the
possible effects of NSAIDs on model membrane systems were investigated.
Sulindac is a sulfoxide prodrug of the therapeutic class of NSAIDs. Following oral
administration, it is reduced by the colonic flora to the pharmacologically active sulfide
form, which in turn is oxidized to the pharmacologically inactive sulfoxide and sulfone
metabolites. Different experiments performed in liposomes and aqueous solution were
compared and used to evaluate the protective effect of sulindac and metabolites in lipid
peroxidation induced by the peroxyl radical (ROO•) derived from 2,2’-azobis(2amidinopropane)
dihydrochloride (AAPH) and using fluorescence probes with distinct
lipophilic properties. Lipid peroxidation using the hydrophilic probe fluorescein was
evaluated in lipid and aqueous media. Lipid systems labelled with the fluorescent probe
diphenylhexatriene propionic acid (DPH-PA) were used to assess the effects of the drugs
on membrane peroxidation simultaneously by fluorescence intensity decay and changes in
membrane fluidity by steady-state anisotropy measurements. The location of sulindac and
its metabolites within lipid membrane models was determined by fluorescence quenching
using the probe (DPH-PA) inserted across the lipid bilayer. In addition, zeta-potential
measurements were made to evaluate changes in membrane surface resulting from its
interaction with sulindac and metabolites. Steady-state anisotropy measurements were also
made to determine possible membrane fluidity changes induced by the drugs assayed.
The use of different probes and liposomes as membrane mimetic systems allowed to
conclude that membrane lipoperoxidation, is not only related to the scavenging
characteristics of the antioxidants, but also to their ability to interact with lipid bilayers.
Results indicate that the antioxidant efficiency is linked to the proximity of the antioxidant
to the oxy-radical. The active NSAID studied (sulindac sulfide) can penetrate into the lipid
bilayer being accessible to protect membrane against oxy-radicals. In contrast the inactive
forms studied (sulindac and sulindac sulfone) do not present significant membrane effects
and are more able to scavenge radicals in the aqueous media.
176