Photosensitizing properties of 6-methoxy-2-naphthylacetic acid, the major metabolite of the phototoxic non-steroidal anti-inflammatory and analgesic drug nabumetone.

The photobiological properties of 6-methoxy-2-naphthylacetic acid (6-MNAA) were studied using a variety of in vitro phototoxicity assays: photohemolysis, photoperoxidation of linoleic acid, photosensitized degradation of histidine and thymine and the Candida phototoxicity test. 6-MNAA was phototoxic in vitro. 6-MNAA reduced nitro blue tetrazolium (NBT) when irradiated with lambda > or = 300 nm in deoxygenated aqueous buffer solution (pH 7.4). NBT can be reduced by reaction with the excited state of 6-MNAA subject to interference with molecular oxygen. The photohemolysis rate was inhibited by the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO), sodium azide (NaN3) and reduced glutathione (GSH). Photoperoxidation of linoleic acid and photosensitized degradation of histidine and thymine were significantly inhibited by sodium azide and reduced glutathione. 6-MNAA was phototoxic to C. albicans, C. lipolytica and C. tropicalis. A mechanism involving singlet oxygen, radicals, and electron transfer reactions is suggested for the observed phototoxicity.

Isolation and identification of the photodegradation products of the photosensitizing antidepressant drug clomipramine. Phototoxicity studies on erythrocytes.

The isolation and identification of the photodegradation products of clomipramine (CIP) in phosphate buffered saline (PBS pH 7.4 and 6.0) solution and methanol under aerobic conditions were studied. Six compounds were identified and four of them were isolated and characterized by spectroscopic methods. A radical mechanism with the participation of the solvent is proposed for the photodegradation of CIP which undergoes homolytic cleavage of the carbon-chlorine bond and also photooxidation of the amine group. CIP was able to induce photohemolysis when it was irradiated in PBS pH 7.4 and in PBS pH 6.0 containing a suspension of human red blood cells (RBCs). The photohemolysis experiments in the presence of additives DABCO and GSH showed nearly total inhibition of drug-induced photohemolysis. The efficient inhibition of photohemolysis by the radical scavenger GSH compared with the inhibition show by DABCO suggests a moderate effect by singlet oxygen. Clomipramine-N-oxide was the unique photoproduct able to induce hemolysis and photohemolysis when it was incubated and irradiated with RBCs for 1 h. A mechanism involving singlet oxygen, radicals and photoproducts is suggested for the reported phototoxicity.

Photobiological properties of nabumetone (4-[6-methoxy-2-naphthalenyl]-2-butanone), a novel non-steroidal anti-inflammatory and analgesic agent.

The photolability of nabumetone (NB, 1, 4-[6-methoxy-2-naphthalenyl]-2-butanone) and its photobiological properties were studied under aerobic and anaerobic conditions using a variety of in vitro phototoxicity assays: photohemolysis, photoperoxidation of linoleic acid, and photosensitized degradation of histidine and thymine. The photodegradation rate of NB in methanol and phosphate buffered saline (PBS) was enhanced under oxygenated media. NB was phototoxic in vitro. The photohemolysis rate was enhanced by deuterium oxide and inhibited by the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO), butylated hydroxyanisole (BHA), sodium azide (NaN3) and reduced gluthathione (GSH). The induced photoperoxidation of linoleic acid was inhibited significantly by sodium azide and reduced gluthathione. Histidine and thymine were photodegraded by a photosensitized reaction induced by NB. A mechanism involving singlet oxygen, radicals and photoproducts is suggested for the observed photoxicity.

A photophysical and photochemical study of 6-methoxy-2-naphthylacetic acid, the major metabolite of the phototoxic nonsteroidal antiinflammatory drug nabumetone.

Nabumetone is a phototoxic nonsteroidal antiinflammatory drug used for the treatment of osteoarthritis. However, nabumetone is considered a prodrug with its metabolite 6-methoxy-2-naphthylacetic acid the active form. Photophysical and photochemical studies on this metabolite have been undertaken. It undergoes photodecarboxylation in aerated aqueous and organic solvents. In addition to the accepted photodegradation pathway for related molecules, a new mechanism that implies generation of the naphthalene radical cation from the excited singlet and addition of O2 prior to the decarboxylation process has been demonstrated. Evidence for the involvement of the excited singlet state in this mechanism have been obtained by steady-state and time-resolved fluorescence experiments. The fluorescence quenching by O2 and the shorter singlet lifetime in aerated solvents support this assignment. Laser flash photolysis also supports this mechanism by showing the noninvolvement of the triplet in the formation of the naphthalene radical cation. Finally, the well-known electron acceptor CCl4 acts as an efficient singlet quencher, enhancing the route leading to the radical cation, preventing intersystem crossing to the triplet and thus resulting in a dramatic increase in the yield of 6-methoxy-2-naphthaldehyde, the major oxidative decarboxylation product; this constitutes unambiguous proof in favor of the new mechanistic proposals.

Photodegradation of bezafibrate in aqueous media. Studies of its in vitro phototoxicity.

Aqueous solutions of the antihyperlipoproteinemic drug bezafibrate (CAS 41859-67-0) are photolabile towards UV-B light under aerobic conditions. Two compounds were isolated and identified spectroscopically as well as by alternative synthesis as the only photoproducts formed. Their formation involves primary cleavage of the aryloxy-carbon bond and decarboxylation followed by hydrogen abstraction or dimerization. Bezafibrate is phototoxic in vitro as indicated by the photohemolysis test. Furthermore bezafibrate photo-sensitizes peroxidation of linoleic acid as monitored by the UV detection of dienic hydroperoxides. Partial inhibition of these processes on addition of butylated hydroxyanisole (BHA), reduced glutathione (GSH), sodium azide (NaN3) or 1,4-diazabicyclo [2.2.2] octane (DABCO) suggests the involvement of type I as well as type II mechanisms.

[Mechanism of phototoxicity induced by drugs]. / Elucidación de los mecanismos de fototoxicidad inducida por fármacos.

First of all some general concepts are given on phototoxic activity of pharmaceutical products which full fill the structural characteristics required to decompose by light and to cause biological damage, either themselves, their photoproducts or the products of their metabolism. These considerations are important due to the fact that this field of research is fairly new. Next, a review is given on recent research carried out in this laboratory on the photochemistry and phototoxicity of fibric acid and their derivatives and finally a review is made as well on the photochemistry and phototoxicity of antibacterial quinolones. Mechanisms are postulated for the photochemical decomposition of the substances investigated and possible mechanism for the in vitro activity at cellular level are also presented.

Photosensitization by fenofibrate. II. In vitro phototoxicity of the major metabolites.

Fenofibric acid, the major metabolite of fenofibrate, was found to be photolabile. Its irradiation in aqueous solution gave rise to two photoproducts, whose formation involves photodecarboxylation of the dissociated acid to an aryloxy-substituted carbanion, which is directly protonated or, alternatively, undergoes a Wittig rearrangement. A comparative in vitro phototoxicity study has been carried out on the anti-hyperlipoproteinemic drug fenofibrate, its metabolites and the photoproducts of fenofibric acid. Fenofibrate, fenofibric acid and its two photoproducts were found to be active when examined by the photohemolysis test and were able to photosensitize peroxidation of linoleic acid, as evidenced by the UV monitoring of dienic hydroperoxides. In summary, the major metabolite of fenofibrate (fenofibric acid), as well as its photoproducts, are phototoxic in vitro. This behavior can be attributed to the fact that the four compounds retain the benzophenone chromophore present in fenofibrate and is indicative of free radical-mediated photosensitization. In agreement with this rationalization, the metabolites with a reduced ketone functionality exhibit no detectable in vitro phototoxicity.

Photolability and photohemolytic studies of fibrates.

Fenofibrate (1), gemfibrozil (2), clofibric acid (3), benzafibrate (4) and clofibrate (5) were found to be photolabile by UV-B (290-320 nm) light under aerobic conditions. The drugs 1, 2, 3 and 4 were phototoxic in vitro when examined by the photohemolysis test both under oxygen and argon atmosphere, although the photohemolysis rate was markedly lower under anaerobic conditions. Based on the inhibition of this process upon addition of butylated hydroxyanisole (BHA) and reduced glutathione (GSH), a radical chain (type I) mechanism appears to operate. Inhibition was seen in the presence of sodium azide (NaN3) and 1,4-diazabicyclo[2.2.2]octane (DABCO) as also in D2O induced-photohemolysis. No photohemolysis was evident for clofibrate (5) under these conditions. In summary, fenofibrate, gemfibrozil, clofibric acid and bezafribrate are phototoxic in vitro. This behavior can be explained through the involvement of free radicals, singlet oxygen and stable photoproducts.

In vitro phototoxicity of clofibrate. Photochemical and photohemolytic studies on its metabolite clofibric acid.

Aqueous or methanolic solutions of clofibrate and clofibric acid are photolabile towards UVB light under aerobic as well as anaerobic conditions. Nine photoproducts have been identified; their formation involves primary cleavage of the carbon-halogen bond or of the aryloxy-carbon bond, followed by hydrogen abstraction and/or radical recombination. Clofibric acid is phototoxic in vitro as indicated by the photohemolysis test, under both oxygen and argon atmospheres, although the photohemolysis rate is markedly higher under aerobic conditions. Partial inhibition of this process on addition of butylated hydroxyanisole (BHA), reduced glutathione (GSH), sodium azide (NaN3) or 1,4-diazabicyclo[2.2.2]octane (DABCO) suggests the involvement of type I as well as type II mechanisms.

Photodegradation and in vitro phototoxicity of fenofibrate, a photosensitizing anti-hyperlipoproteinemic drug.

The phototoxic anti-hyperlipoproteinemic drug fenofibrate was found to be photolabile under aerobic and anaerobic conditions. Irradiation under argon of a methanol solution of this drug produced the photoproducts isopropyl 4-(1-[4-chlorophenyl]-1,2-dihydroxy)ethylphenoxyisobutyrate, 1,2-bis(4-chlorophenyl)-1,2bis (4-[isopropoxycarbonylisopropoxy]phenyl)ethane-1,2-diol and 4-(4-chlorobenzoyl)phenol, while under oxygen the photoproducts were 4-chloroperbenzoic acid, methyl 4-chlorobenzoate, 4-chlorobenzoic acid and singlet oxygen, as evidenced by trapping with 2,5-dimethylfuran. These results can be rationalized through hydrogen abstraction by excited fenofibrate, to afford a free radical as key intermediate. Biologically active antioxidants such as glutathione and cysteine efficiently reduced 4-chloroperbenzoic acid to 4-chlorobenzoic acid. The involvement of an electron transfer mechanism is suggested by detection (UV-vis spectrophotometry) of the radical cation TMP+. during the oxidation of tetramethylphenylenediamine (TMP) with 4-chloroperbenzoic acid. Fenofibrate was phototoxic in vitro when examined by the photohemolysis test, both under oxygen and argon atmosphere, although the photohemolysis rate was markedly lower under anaerobic conditions. The photoproducts 4-(1-[4-chlorophenyl]-1,2-dihydroxy)ethylphenoxyisobutyrate and 4-chloroperbenzoic acid induced hemolysis in the dark; however, this effect was quantitatively less important than photohemolysis by fenofibrate. On the other hand, fenofibrate photosensitized peroxidation of linoleic acid, monitored by the UV detection of dienic hydroperoxides. Based on the inhibition of this process upon addition of butylated hydroxyanisole, a radical chain (type I) mechanism appears to operate. In summary, fenofibrate is phototoxic in vitro. This behavior can be explained through the involvement of free radicals, singlet oxygen and stable photoproducts.

Formation of a perbenzoic acid derivative in the photodegradation of fenofibrate: phototoxicity studies on erythrocytes.

The phototoxic antihyperlipoproteinemic drug fenofibrate (1) is photolabile under aerobic conditions. Irradiation of a methanol solution of 1 produces, under oxygen, photoproducts 2, 3, and 4. A peroxidic photoproduct 2 was isolated and identified. The biologically active antioxidants glutathione and cysteine efficiently reduce 2 to its acid. This photoproduct was also capable of efficiently oxidizing tetramethyl phenylendiamine (TMP) through an electron transfer mechanism, detecting a TMP+ species by UV-visible spectrometry. Fenofibrate was screened in vitro at different concentrations for UV-visible-induced phototoxic effects in a photohemolysis test, under oxygen as well as argon. The photohemolysis rate was low under anaerobic conditions. No hemolysis occurred without irradiation. The isolated photoproduct 2 induced hemolysis without irradiation.