Photodynamic lipid peroxidation by the photosensitizing nonsteroidal antiinflammatory drugs suprofen and tiaprofenic acid

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 photosensitization by tiaprofenic acid and suprofen.

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.

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 N-acetylcysteine to the culture medium.

Photosensitivity induced by fibric acid derivatives and its relation to photocontact dermatitis to ketoprofen

BACKGROUND

Photosensitivity reactions to fibric acid derivatives are not well understood and have been rarely reported.

OBJECTIVE

The aim of this study was to describe two cases of photosensitivity, one induced by fenofibrate and one by bezafibrate; to study the in vivo photosensitizing potential of these drugs; and to evaluate the possibility of cross-reactivity between fenofibrate and ketoprofen.

METHODS

Patch and photopatch tests with fibric acid derivatives and ketoprofen were performed in the patients, in 12 normal volunteers, and in 7 patients with photopatch-proven photocontact dermatitis to ketoprofen. Phototesting studies were performed both while the patients were taking the drugs and after withdrawal of them, as well as in a group of 18 hyperlipemic volunteers without history of photosensitivity who were taking therapeutic doses of fenofibrate or bezafibrate for 2 to 3 months.

RESULTS

Positive photopatch test responses to ketoprofen and to fenofibrate were obtained only in the first patient, who also had a weaker positive ordinary patch test response to the latter. Five patients photosensitized to ketoprofen also had a positive patch test to fenofibrate. Phototesting studies were abnormal in both patients but normal in all volunteers.

CONCLUSION

An association between systemic photosensitivity to fenofibrate and photocontact sensitivity to ketoprofen seems to exist. The structural similarities of these chemicals favor cross-reactivity.

Oxidative decarboxylation of naproxen

The decarboxylation of naproxen (1H) and its salt (1-) was achieved by means of chemical [Ce(IV) or S2O8(2-)] and electrochemical oxidation. The product patterns were compatible with mechanisms involving single-electron transfer from the pi-system or the carboxylate moiety. The results are discussed in connection with the involvement of electron-transfer processes in the reported phototoxicity of naproxen.

Phototoxicity of non-steroidal anti-inflammatory drugs: in vitro testing of the photoproducts of Butibufen and Flurbiprofen

In this work, the phototoxicity of two non-steroidal anti-inflammatory drugs, Butibufen and Flurbiprofen, was examined. Both were unstable to light, to give several photoproducts which were isolated and identified. The different photoproducts were formed by a primary photochemical mechanism which involves an initial cleavage of the C-C bond alpha to the carbonyl group, followed by several secondary processes. The cytotoxic effects of the xenobiotics were evaluated using two well-established biological in vitro tests: (a) enzyme leakage lactate dehydrogenase and glutamate-oxaloacetate transaminase from cultured fibroblasts and (b) lysis of red blood cells. The benzylic alcohols caused extensive leakage from cultured fibroblasts at the different concentrations assayed. The alcohol obtained from Butibufen was a potent lytic agent for human red blood cells. The other photoproducts, Butibufen and Flurbiprofen did not produce observable toxic effects on cells.

Oxicam-induced photosensitivity. Patch and photopatch testing studies with tenoxicam and piroxicam photoproducts in normal subjects and in piroxicam-droxicam photosensitive patients

BACKGROUND

The mechanism of piroxicam-induced photosensitivity is unknown. It was first attributed to metabolites of the drug produced in vivo but further photochemical studies disclosed that piroxicam was not stable to light, forming at least two photoproducts. Photosensitivity reactions to droxicam and tenoxicam have been not reported.

OBJECTIVE

The aim of this study was to determine whether piroxicam photoproducts contribute to the light reactions induced by this drug, to describe a case of droxicam-induced photosensitivity and to study the in vivo photosensitizing potential of tenoxicam.

METHODS

Patch and photopatch tests with two major photoproducts of piroxicam, with different preparations of UVA-preirradiated piroxicam, and with low and high concentrations of tenoxicam were performed in normal volunteers and in piroxicam-photosensitive patients. Phototesting studies were also performed before and after the oral administration of tenoxicam in both groups of subjects.

RESULTS

Positive patch test responses were obtained in piroxicam-photosensitive patients only with the preirradiated piroxicam preparations. Phototesting studies with tenoxicam were normal in both groups.

CONCLUSION

Minor or intermediate piroxicam photoproducts are more likely to be responsible for the photosensitivity reactions induced by this drug.

Photochemistry of tiaprofenic acid, a nonsteroidal anti-inflammatory drug with phototoxic side effects

The phototoxic nonsteroidal anti-inflammatory drug tiaprofenic acid (1) is photolabile under aerobic conditions. Irradiation of a methanol solution of 1 under oxygen produces the photoproducts 2, 3, 4, and 5, and also produces a singlet oxygen as evidenced by trapping with 2,5-dimethylfuran.

Photodegradation of nalidixic and tiaprofenic acids and nifedipine in aerobic conditions

Since nalidixic acid had been previously studied in acidic and basic media, nifedipine had been investigated in anaerobic conditions and under ultraviolet light and tiaprofenic acid had not been studied at all, their photodegradation was carried out in this laboratory under milder conditions, with methanol as the solvent and using visible light. The role of oxygen was demonstrated and the photoproducts were isolated and identified spectroscopically.

Piroxicam-induced photosensitivity and contact sensitivity to thiosalicylic acid

A photocontact dermatitis developed in three patients after the application of gel containing 0.5% piroxicam. Patch tests were positive to thiomersal and thiosalicylic acid. Photopatch tests with piroxicam at several concentrations were positive in the three patients but negative in 62 normal volunteer subjects. Patch tests performed on 14 patients with proved systemic photosensitivity to piroxicam were positive for thiomersal and thiosalicylic acid. Nine of 12 patients previously sensitized to thiosalicylic acid and with no history of exposure to piroxicam showed positive photopatch test reactions to this chemical. These results support a relation between piroxicam-induced photosensitivity and contact sensitivity to thiosalicylic acid. Contact allergic sensitivity to the latter is a marker for patients with a high risk of developing photosensitivity reactions to piroxicam. These reactions may be due to photoproducts of the drug rather than metabolites.

Photolytic degradation of benorylate: effects of the photoproducts on cultured hepatocytes

The photodegradation of benorylate [4'-(acetamido)phenyl-2-acetoxybenzoate], a drug frequently used in rheumatoid arthritis therapy, has been examined under different sets of experimental conditions. Several photoproducts have been isolated and identified on the basis of their IR, NMR, and MS spectra. The most significant photochemical process is the photo-Fries rearrangement of benorylate, leading to 5-acetamido-2'-acetoxy-2-hydroxybenzophenone (1). This compound undergoes a rapid transacylation to the isomeric 5'-acetamido-2'-acetoxy-2-hydroxybenzophenone (2). A primary culture of rat hepatocytes has been used to evaluate the possible toxicity of these two benzophenones, keeping in mind the following criteria: leakage of cytosolic enzymes, attachment index to culture plates, gluconeogenesis from lactate and fructose, glycogen balance, and albumin synthesis. At the concentrations assayed, neither of the two major photoproducts of benorylate (benzophenones 1 and 2) had significant toxic effects on liver cells in culture.

Toxic effects of the photoproducts of chlorpromazine on cultured hepatocytes

The photodegradation of chlorpromazine, a drug frequently used in psychotherapy, was examined under different sets of experimental conditions. A primary culture of rat hepatocytes was used to evaluate the possible hepatotoxicity of the chlorpromazine photoproducts, keeping in mind the following criteria: leakage of cytosolic enzymes; attachment index to culture plates, and albumin synthesis. Cells exposed to concentrations greater than 10(-4) M of the photomixtures showed extensive leakage of GOT and GPT into the culture medium and, at the same time, the cell attachment was seriously impaired. A concentration of 10(-7) M of the photoproducts proved capable of inhibiting the synthesis of albumin (20%). Photoproducts obtained after aerobic irradiations were as toxic for hepatocytes as those found in anaerobic conditions. The implications of our results in connection with the relevance of oxygen-dependent photoreactions of chlorpromazine to its phototoxicity, and the possible appearance of hepatic alterations in patients treated with the drug after exposure to the sunlight, are discussed.