Luis Arboledas Martínez

PHOTODYNAMIC LIPID PEROXIDATION BY THE PHOTOSENSITIZING NONSTEROIDAL ANTIINFLAMMATORY DRUGS SUPROFEN AND TIAPROFENIC ACID

Abstract The photochemistry of the photosensitizing nonsteroidal antiinflammatory drugs tiaprofenic acid and suprofen involves the intermediacy of short‐lived species (i.e. radicals). The data obtained in the present work strongly suggest that such intermediates may be responsible for the phototoxicity of 2‐arylpropionic acids by inducing photodynamic lipid peroxidation at drug concentrations likely to be reached in the skin. This has been investigated using linoleic acid as a model lipid and determining the amount of hydroperoxides by measuring the spectrophotometric absorption at 233 nm, associated with the formation of dienic hydroperoxides. The major photoproducts of tiaprofenic acid and suprofen are derivatives bearing an ethyl side chain. Photoproducts of this type, due to the lack of polar moieties, are highly lipophilic and likely to accumulate in the lipid bilayer of cell membranes. Taking into account their ability to induce photodynamic lipid peroxidation and their marked photostability, it is conceivable that such photoproducts can participate in many catalytic cycles, playing a significant role in the mechanism of photosensitizatinn by tiprofenic acid and suprofen.

Time-Resolved Near Infrared Studies on Singlet Oxygen Production by the Photosensitizing 2-Arylpropionic Acids†

Abstract— Time‐resolved near infrared emission studies have been carried out on a series of nonsteroidal anti inflammatory 2‐arylpropionic acids, in order to assess their ability to photosensitize the production of singlet molecular oxygen O2(1Δg). Benoxaprofen, naproxen, tiaprofenic acid, suprofen, ketoprofen and carprofen showed quantum yields for this process (φΔ) in the range 0.2‐0.7 in acetonitrile. Deprotonation of the propionic acid moiety in mixtures of acetonitrile‐ethanol (4:1) basified with KOH produced a systematic decrease in φΔ for all compounds with the exception of naproxen. This effect was even more dramatic in D2O‐based phosphate buffer, where no singlet oxygen could be detected for benoxaprofen, ketoprofen or carprofen. The above results are consistent with the occurrence of competing photochemical reactions of 2‐arylpropionic acids in different media and particularly with the enhanced photodecarboxylation from the carboxylate anions.

Involvement of drug-derived peroxides in the phototoxicity of naproxen and tiaprofenic acid.

Photodegradation of naproxen and tiaprofenic acid in aqueous buffered solutions leads to decarboxylated products with ethyl, 1‐hydroxyethyl and/or acetyl side chains. The photomixtures obtained in the presence of oxygen were clearly more toxic to cultured hepatocytes than those obtained under anaerobic conditions. This effect was more noticeable in the case of naproxen. Based on the composition of the oxygenated photomixtures and the relative toxicity of the different photoproducts, it is possible to account for most of the observed toxicity in the case of tiaprofenic acid but not in the case of naproxen. This is explained as a result of the presence of drug‐derived peroxidic species in the photomixtures and their contribution to the observed toxicity. Peroxides were determined by the peroxidase‐catalyzed oxidation of dichlorodihydrofluorescein to its fluorescent analog. The amount of peroxides present in naproxen photomixtures was much higher than in the case of tiaprofenic acid. A dose‐dependent depletion of intracellular glutathione was observed when hepatocytes were incubated with peroxide‐containing naproxen photomixtures. This effect was prevented by the addition of catalase or jV‐acetylcysteine to the culture medium.

Evaluation of ketoprofen (R,S and R/S) phototoxicity by a battery of in vitro assays.

Abstract The various enantiomers of ketoprofen (S and R) and its racemic form ( R S ) exhibited comparable phototoxicities when examined by the following in vitro test systems: (a) effects of pre-irradiated drugs on cultured hepatocytes; (b) co-irradiation of drugs with hepatocytes or fibroblasts; (c) photohaemolysis sensitized by the various ketoprofen steroisomers; (d) drug-photosensitized formation of linoleic acid hydroperoxides. Inhibition of photohaemolysis and photodynamic lipid peroxidation by butylated hydroxyanisole and reduced glutathione suggests that the phototoxicity of ketoprofen is associated with a radical chain (type I) peroxidation of membrane lipids, leading to cell lysis In view of the above results it could be advantageous to use the pharmacologically active S(+) enantiomer instead of the R/S form, since the lower doses required would result in a diminished phototoxic potential.

Strategies and tactics for free radical carbocyclization: synthesis of polyfunctionalized cyclopentanoid molecules from carbohydrates

Abstract The tributyltin hydride + azobisisobutyronitrile (AIBN) mediated free radical carbocyclization of precursors 1–9, 48 and 49 is described. The resulting carbocycles have been obtained in moderate yield and good diastereoselectivity. These polyfunctionalized, enantiomerically pure cyclopentane derivatives are useful intermediates for further manipulation.

Uncoupling of EphA/ephrinA Signaling and Spontaneous Activity in Neural Circuit Wiring

Classic studies have proposed that genetically encoded programs and spontaneous activity play complementary but independent roles in the development of neural circuits. Recent evidence, however, suggests that these two mechanisms could interact extensively, with spontaneous activity affecting the expression and function of guidance molecules at early developmental stages. Here, using the developing chick spinal cord and the mouse visual system to ectopically express the inwardly rectifying potassium channel Kir2.1 in individual embryonic neurons, we demonstrate that cell-intrinsic blockade of spontaneous activity in vivo does not affect neuronal identity specification, axon pathfinding, or EphA/ephrinA signaling during the development of topographic maps. However, intrinsic spontaneous activity is critical for axon branching and pruning once axonal growth cones reach their correct topographic position in the target tissues. Our experiments argue for the dissociation of spontaneous activity from hard-wired developmental programs in early phases of neural circuit formation.

Photobinding of drugs to cells as an indicator of potential photoallergy.

The photobinding of drugs to cells has been investigated as a possible indicator of the photoallergic potential. Tiaprofenic acid (TA), carprofen (CP), benoxaprofen (BP) and ibuprofen (IP) were selected as test substances and human fibroblasts as model biological system. Radioactive labelling of the drugs was achieved through alkaline exchange of the alpha-carboxyl hydrogens by tritium, using (3)H(2)O as solvent. When the labelled compounds were co-irradiated with fibroblasts, TA gave rise to the highest amount of radioactivity covalently bound to cells. This also occurred, albeit to a lower extent, with CP and BP; by contrast, no effect was observed for IP. The observed rank order is in agreement with the available in vivo data. The time course of the process was determined for TA, distinguishing between covalent and non-covalent binding. The results, together with gas Chromatographie analyses of the irradiation mixtures and binding studies with TA and its major photoproduct decarboxytiaprofenic acid (decarboxy-TA) in the dark, indicated that most of the observed photobinding might be due to the photoproduct rather than to the parent drug. It is conceivable that hydrogen abstraction by the excited ketone could take place with proteins as reaction partners. This process would lead to the generation of a radical pair, whose coupling would result in the formation of a covalent bond. The contribution of this mechanistic pathway to the in vivo photobinding has to be considered when a lipophilic photoproduct is formed which, as for decarboxy-TA, still contains an active chromophore.

In vitro photoperoxidation as an indicator of the potential phototoxicity of non-steroidal anti-inflammatory 2-arylpropionic acids.

The photochemical behaviour of 2-arylpropionic acids involves the intermediacy of short-lived species such as drug-derived peroxides and/or free radicals. Although peroxides are expected to undergo very rapid breakdown, this study shows that they can be detected in the photomixtures by the peroxidase-catalysed oxidation of dichlorodihydrofluorescein to its fluorescent analogue. Their possible contribution to phototoxicity has been evaluated by red blood cell membrane lysis. The shorter lives of organic free radicals prevent their direct determination in the irradiation mixtures; however, the results strongly suggest that these intermediates have a key role in the phototoxicity of 2-arylpropionic acids, through induction of photodynamic lipid peroxidation. This has been determined using linoleic acid as a model lipid, and measuring the spectrophotometric absorption at 233 nm associated with the formation of dienic hydroperoxides. It is probable that a similar process is responsible for the photochemically induced damage to cell membranes observed in the photohaemolysis assays.

Carbocycles from carbohydrates: a free radical route to aminocyclitol derivatives

Abstract Some derivatives of (1R,2R,3R,4S,5R) and 1R,2R,3R,4R,5S)-5-amino-1,2,3,4-cyclohexanetetrol have been synthesized from acyclic carbohydrate intermediates via 6-exo free radical cyclization.

Mechanism of Lipid Peroxidation Photosensitized by Tiaprofenic Acid: Product Studies Using Linoleic Acid and 1,4-Cyclohexadienes as Model Substrates¶

Abstract A careful study of the linoleic acid hydroperoxide (LOOH) profile obtained upon peroxidation of linoleic acid (LA) photosensitized by tiaprofenic acid (TPA) and analogous ketones has been undertaken to distinguish between type-I and type-II photoperoxidation mechanisms. 1,4-Cyclohexadiene and 1,2-dimethylcyclohexa-2,5-dienecarboxylic acid (CHDCA) have also been used as models for LA since they also have double allylic systems. Coirradiation of LA with TPA and decarboxytiaprofenic acid (DTPA) in acetonitrile and micellar media produced significant amounts of conjugated dienic LOOH. The cis,trans to trans,trans ratio depended on the irradiation time; thus, this parameter is an ambiguous tool for mechanistic assignment. An interesting finding was the decrease of the LOOH level after long irradiation times in mixtures photooxidized by DTPA, which is attributed to quenching of the DTPA triplet by the generated dienic LOOH. High-performance liquid chromatography analyses confirmed that the main pathway operating in photodynamic lipid peroxidation sensitized by (D)TPA is a type-I mechanism. However, product studies using CHDCA have clearly shown that a type-II mechanism is also operating and might contribute to the overall photooxidation process in a significant way.