SINGLET OXYGEN (O-2((1)DELTA(G))) PRODUCTION BY PHOTOSENSITIZING DRUGS IN MICROHETEROGENEOUS SYSTEMS

Photosensitization is a relatively common side-effect induced by some drugs. Non steroidal antiinflammatory drugs (NSAID) deserve special at tention because of various reasons: 1) these drugs are currently used to treat several human diseases, 2) their photosensitizing behaviour i n vivo is a well-documented phenomenon and 3) short-lived species, amo ng them singlet oxygen(O-1(2)), have been claimed to be involved in th e development of this side-effect [1]. We have measured the quantum yi eld of singlet oxygen production (Phi(Delta)) in anionic microemulsion s by a series of NSAID which have been found to behave as photosensiti zing agents in several in vitro and in vivo models. Microemulsions hav e been chosen as reaction media, because they may be considered as sim plest models to mimic organized microenvironments (ie., cellular membr anes) [2]. By monitoring the O-1(2) luminescence at 1270 nm upon irrad iation of the drugs, it has been possible to establish that NSAID are efficient O-1(2) sensitizers in microheterogeneous systems, some of th em exhibiting rather high Phi(Delta)(app) (0.86 for tiaprofenic acid). Although extrapolation of the data to more complicated systems is ext remely complex, we have found that NSAID are able to produce O-1(2) in microheterogeneous systems composed of hydrophobic and hydrophilic mi crodomains with a higher efficiency than in homogeneous aqueous soluti on.