Photosensitivity to Triflusal: Formation of a Photoadduct with Ubiquitin Demonstrated by Photophysical and Proteomic Techniques

Abstract

Triflusal is a platelet aggregation inhibitor chemically related to acetylsalicylic acid, which is used for the prevention and/or treatment of vascular thromboembolisms, which acts as a prodrug. Actually, after oral administration it is absorbed primarily in the small intestine, binds to plasma proteins (99%) and is rapidly biotransformed in the liver into its deacetylated active metabolite 2-hydroxy-4-trifluoromethylbenzoic acid (HTB). In healthy humans, the half-life of triflusal is ca. 0.5 h, whereas for HTB it is ca. 35 h. From a pharmacological point of view, it is interesting to note that HTB is itself highly active as a platelet anti-aggregant agent. Indeed, studies on the clinical profile of both drug and metabolite have shown no significant differences between them. It has been evidenced that HTB displays ability to induce photoallergy in humans. This phenomenon involves a cell-mediated immune response, which is initiated by covalent binding of a light-activated photosensitizer (or a species derived therefrom) to a protein. In this context, small proteins like ubiquitin could be appropriate models for investigating covalent binding by means of MS/MS and peptide fingerprint analysis. In previous work, it was shown that HTB forms covalent photoadducts with isolated lysine. Interestingly, ubiquitin contains seven lysine residues that could be modified by a similar reaction. With this background, the aim of the present work is to explore adduct formation between the triflusal metabolite and ubiquitin as model protein upon sunlight irradiation, combining proteomic and photophysical (fluorescence and laser flash photolysis) techniques. Photophysical and proteomic analysis demonstrates monoadduct formation as the major outcome of the reaction. Interestingly, addition can take place at any of the ε-amino groups of the lysine residues of the protein and involves replacement of the trifluoromethyl moiety with a new amide function. This process can in principle occur with other trifluoroaromatic compounds and may be responsible for the appearance of undesired photoallergic side effects.

Drug and chemical induced photosensitivity from a clinical perspective

“…The initial investigations in vitro would involve establishing absorption spectra and understanding the underlying mechanisms and the molecular structure of drug and whether metabolites and photoproducts are likely. Mass spectrometry may be of use in demonstrating photodegradation, as with sparfloxacin following UVA irradiation (135,136). Drug-induced phototoxicity should be investigated in vitro and photoclastogenicity, photomutagenicity and photocarcinogenicity studies may be considered, although the International Genotoxicity Testing Working Group concluded that photogenotoxicity studies were not recommended as part of standard photosafety evaluation, based on an expert panel workshop assessment that these studies were of negligible additional value (130).…”

Chemical Modifications of Globular Proteins Phototriggered by an Endogenous Photosensitizer

“…1 A large number of exogenous photoallergenic agents have been investigated. 2,3,4,5 However, up to now the potential role of some endogenous compounds as photoallergens has not been fully established.…”

Mechanisms Underlying the Anti-Inflammatory Activity of Bergamot Essential Oil and Its Antinociceptive Effects

“…Bergamot fruits are mainly exploited for the extraction of bergamot essential oil (BEO), whereas the juice (BJ), considered formerly a by-product, has recently been appreciated for its relevant biological activities. Indeed, different in vitro and in vivo studies have demonstrated its antimicrobial [ 11 ] and anticancer [ 12 , 13 ] properties, which seem to be due to the flavonoids it contains, since the flavonoid-rich fraction of BJ shows antioxidant and anti-inflammatory capabilities [ 14 , 15 , 16 , 17 , 18 ] and also reduces cancer formation [ 19 ]. BEO is broadly used by fragrance industries and in aromatherapy [ 20 ].…”