Phototoxic potential of quinolones.

The photohaemolytic potentials of the quinolones oxolinic acid, pipemidic acid, rosoxacin, norfloxacin, ciprofloxacin and M-193324 (synthesis intermediary) were evaluated and compared with the photohaemolysis induced by nalidixic acid. Quinolones with a piperazine group in position 7 (pipemidic acid, norfloxacin and ciprofloxacin) did not induce photohaemolysis. However, oxolinic acid, rosoxacin and M-193324 produced a concentration- and oxygen-dependent photohaemolysis. Ascorbic acid, histidine and thiourea inhibited the photohaemolysis induced by oxolinic acid, rosoxacin and M-193324, suggesting a photodynamic mechanism similar to that found with nalidixic acid. In addition, deuterium oxide increased the photohaemolysis induced by photohaemolytic quinolones, indicating that this process is mediated by singlet oxygen.     

Phototoxic effects of Hypericum extract in cultures of human keratinocytes compared with those of psoralen

Extracts of Hypericum perforatum (St. John's wort) are used in the treatment of depression. They contain the plant pigment hypericin and hypericin derivates. These compounds have light-dependent activities. In order to estimate the potential risk of phototoxic skin damage during antidepressive therapy, we investigated the phototoxic activity of hypericin extract using cultures of human keratinocytes and compared it with the effect of the well-known phototoxic agent psoralen. The absorbance spectrum of our Hypericum extract revealed maxima in the whole UV range and in parts of the visible range. We cultivated human keratinocytes in the presence of different Hypericum concentrations and irradiated the cells with 150 mJ/cm2 UVB, 1 J/cm2 UVA or 3 h with a white light of photon flux density 2.6 mumol m-2 s-1. The determination of the bromodeoxyuridine incorporation rate showed a concentration- and light-dependent decrease in DNA synthesis with high hypericin concentrations (> or = 50 micrograms/mL) combined with UVA or visible light radiation. In the case of UVB irradiation a clear phototoxic cell reaction was not detected. We found phototoxic effects even with 10 ng/mL psoralen using UVA with the same study design as in the case of the Hypericum extract. These results confirm the phototoxic activity of Hypericum extract on human keratinocytes. However, the blood levels that are to be expected during antidepressive therapy are presumably too low to induce phototoxic skin reactions.     

Phototoxic and photochemical properties of sanguinarine.

Sanguinarine, a commercial drug exhibiting antimicrobial and antitumor properties, was studied with respect to its basic photochemical characteristics and also with regard to its phototoxicity to mosquito larvae (Aedes atropalpus). Sanguinarine proved to be clearly phototoxic to larvae, with an LD50 of 0.096 mg/mL with near UV exposure as compared with 23.3 mg/mL without. Flash photolysis experiments enabled the study of the triplet state of sanguinarine to be undertaken. Quenching by oxygen occurs with a rate constant of 6 x 10(9) M-1s-1 and time-resolved emission studies indicate that sanguinarine produces a significant amount of singlet oxygen (phi delta = 0.16) as does the isoquinoline alkaloid, berberine (phi delta = 0.25). These values represent the first direct quantitative measurements of photosensitization parameters of these compounds. Additionally, sanguinarine exhibits efficient electron donation properties, undergoing reaction with methyl viologen with a rate constant greater than 10(10) M-1s-1, but is a poor electron acceptor. Phototoxicity of sanguinarine can thus be explained in terms of its photosensitization properties.     

pH effects on the reduction of bilirubin in aqueous media

The electrochemical reduction of bilirubin at the mercury electrode was studied in aqueous media embracing an extended pH range; a variety of electrochemical techniques was used. Reduction in neutral solution results in three waves—the first a reversible adsorption prewave, followed by a pH dependent, reversible, two electron wave and finally by a one electron irreversible wave. In basic solution, only two waves are discernable: the reversible adsorption prewave, followed by a three electron wave resulting from the coalescence of the second and third waves seen in neutral solution. Familiarity with the detailed electrochemistry of bilirubin reduction provides the prerequisite basis for developing a sensitive analytical method for its determination.     

The Phototoxic Potential of the Flavonoids,Taxifolin and Quercetin

Quercetin, one of the most abundant polyphenols in the plant kingdom has been shown to be photodegraded on exposure to UV light. Despite the fact, it is a component of several dermatological preparations. Its phototoxic potential has not been evaluated to date. The aim of this study was to assess whether photo‐induced degradation of quercetin is linked to phototoxic effects on living cells. Its dihydro derivative, taxifolin, was included in the study. For evaluation, the 3T3 Neutral Red Uptake Phototoxicity Test according to OECD TG 432 was used. To better approximate human skin, HaCaT keratinocytes, normal human epidermal keratinocytes and dermal fibroblasts were used, apart from the Balb/c 3T3 cell line. Quercetin showed a dose‐dependent photodegradation in aqueous and organic environments and a phototoxic effect on all used cells. Quercetin pretreatment and following UVA exposure resulted in increased reactive oxygen species production and intracellular glutathione level depletion in human dermal fibroblasts. Taxifolin was found completely nonphototoxic and photostable. As only in vitro methodology was used, further studies using 3D skin models and/or human volunteers are needed to confirm whether exposure to sunlight, tanning sunbeds and/or phototherapy in people using cosmetics containing quercetin is a health risk.     

Isopimpinellin Is Not Phototoxic in a Chick Skin Assay

Abstract— Synthetic isopimpinellin (5,8-dimethoxypsoralen), confirmed to contain as impurities only trace quantities at most of psoralen, bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen), is not phototoxic when tested in a chick skin bioassay system. These findings are at variance with earlier studies showing isopimpinellin to be phototoxic against chick skin and support the conclusion that isopimpinellin is photobiologically inactive. As recently proposed by others, the several reports of isopimpinellin photoactivity are most likely attributable to contamination by small amounts of highly active psoralens such as bergapten or xanthotoxin.     

Toxic and Phototoxic Properties of the Protozoan Pigments Blepharismin and Oxyblepharismin*

Abstract— The toxic and phototoxic properties of blepharismin and oxyblepharismin that were purified from the pigments of a ciliated protozoan, Blepharisma japonicum, by thin-layer chromatography, were investigated in detail. The toxicity was tested against the ciliated protozoan Dileptus margaritifer, which is relatively sensitive to blepharismin. Although oxyblepharismin has been believed to be neither toxic nor phototoxic, it was found that oxyblepharismin is toxic in the dark and is also phototoxic. This shows that oxyblepharismin can act as a photosensitizer. The toxicity and phototoxicity of these pigments were compared with those of hypericin, which is known to be a typical, strong photosensitizer from plants. It was concluded that blepharismin and oxyblepharismin have strong intrinsic toxicities in the dark compared with hypericin, but their phototoxicities are slightly weaker than that of hypericin. This strong intrinsic toxicity supports our proposal that blepharismin acts as a defensive device against predators in the dark as well as in the light. The decrease in the defensive ability and the increase in the resistance to photokilling of Blepharisma concomitant with its color change from red to blue-purple in response to weak illumination can be explained by the decrease in toxicity and phototoxicity of the pigment itself and by the decrease in amount of the pigment.     

Toward an amphiphilic bilirubin: the crystal structure of a bilirubin e-isomer

A new bilirubinoid analog (1) with two methoxy beta-substituents on the lactam ring of each dipyrrinone was synthesized and examined spectroscopically. It is more soluble in CH3OH and CHCl3 than bilirubin, which is insoluble in CH3OH but soluble in CHCl3. The solubility of 1 is approximately 10 microg/mL in CH3OH (vs < or =1 microg/mL for bilirubin) and approximately 3 mg/mL in CHCl3 (vs approximately 0.6 mg/mL for bilirubin). Vapor pressure osmometry indicates that 1, like bilirubin, is monomeric in CHCl3, and NMR studies show that the most stable structure has the syn-4Z,syn-15Z configuration, with the pigment's dipyrrinones engaged in intramolecular hydrogen bonding to the propionic acid carboxyl groups. And, like bilirubin, Z,Z-1 adopts a conformation that is bent in the middle into a ridge-tile shape. For the first time, a crystal structure of a bilirubin E-isomer has been obtained. Crystallization of 1 under dim room lighting gave an X-ray quality crystal of the anti-4E,syn-15Z-(photo) isomer, in which only the Z-dipyrrinone half is engaged in intramolecular hydrogen bonding to a propionic acid. Hydrogen bonding is nearly completely disengaged in the E-dipyrrinone half; yet, the ridge-tile conformation persists.     

Facile Synthesis of a Phototoxic Monofunctionalized Tetraarylporphyrin as Scaffold for Porphyrin-Quinone Conjugates

A new carboxy-monofunctionalized tertraarylporphyrin has been tested for cytotoxicity toward OV2008 human ovarian cancer cells. This compound acutely inhibits growth of ovarian cancer cells upon exposure to ambient light while suppresses long-term clonogenic survival of cells under both dark and light stimulated conditions. Because of the variable length of the linkage between the anthraquinone and porphyrin moieties, the synthesized monocarboxylated porphyrin presents a versatile scaffold for fine-tuning of the photoelectron transfer in the quinone-porphyrin conjugate. To demonstrate its synthetic value, we converted the carboxy derivative to its amino counterpart.     

Solvation and crystal effects in bilirubin studied by NMR spectroscopy and density functional theory

The open-chain tetrapyrrole compound bilirubin was investigated in chloroform and dimethyl sulfoxide solutions by liquid-state NMR and as solid by (1)H, (13)C, and (15)N magic-angle spinning (MAS) solid-state NMR spectroscopy. Density functional theory (DFT) calculations were performed to interpret the data, using the B3LYP exchange-correlation functional to optimize geometries and to compute NMR chemical shieldings by the gauge-including atomic orbital method. The dependence of geometries and chemical shieldings on the size of the basis sets was investigated for the reference molecules tetramethylsilane, NH(3), and H(2)O, and for bilirubin as a monomer and in clusters consisting of up to six molecules. In order to assess the intrinsic errors of the B3LYP approximation in calculating NMR shieldings, complete basis set estimates were obtained for the nuclear shielding values of the reference molecules. The experimental liquid-state NMR data of bilirubin are well reproduced by a monomeric bilirubin molecule using the 6-311+G(2d,p) basis set for geometry optimization and for calculating chemical shieldings. To simulate the bilirubin crystal, a hexameric model was required. It was constructed from geometry-optimized monomers using information from the X-ray structure of bilirubin to fix the monomeric entities in space and refined by partial optimization. Combining experimental (1)H-(13)C and (1)H-(15)N NMR correlation spectroscopy and density functional theory, almost complete sets of (1)H, (13)C, and (15)N chemical shift assignments were obtained for both liquid and solid states. It is shown that monomeric bilirubin in chloroform solution is formed by 3-vinyl anti conformers, while bilirubin crystals are formed by 3-vinyl syn conformers. This conformational change leads to characteristic differences between the liquid- and solid-state NMR resonances.     

High-performance liquid chromatographic separation of bilirubin conjugates: the effects of change in molarity and pH

A fast, sensitive high-performance liquid chromatographic method has been developed for the separation and quantitation of biliary bile pigments; this utilizes a C18 reversed-phase column with two solvents, a buffer and an organic solvent, which were changed in a linear gradient from a polar to a less polar combination. Nine glycosidic conjugates of bilirubin as well as unconjugated bilirubin and a suitable internal standard, unconjugated mesobilirubin IX alpha, were all separated to baseline by gradient elution; the species eluted in a polar to less polar fashion. Increasing the molarity of the solvent decreased the binding of non-glucuronide pigments to the column, with a decrease in their retention times, whereas for bilirubin monoglucuronide they increased. Decrease in pH, similarly, preferentially increased bilirubin monoglucuronide retention times.     

A new photoisomerization of bilirubin

Photoirradiation of solutions of natural (4Z,15Z)-bilirubin-IX alpha in chloroform with approximately 366 nm UV light leads rapidly to a new photoisomer that has been characterized by NMR spectroscopy and by its (ground-state reaction) adducts with methanol and other protic nucleophiles. Unlike the previously described Z-->E geometric isomerization important in phototherapy of neonatal jaundice, the new photoisomerization involves regiospecific photoautomerization to afford 2-ethenyl-18-ethylidene- 1,10,19,22,24-pentahydro-2,7,13,17-tetramethyl-1,19- dioxo-21H-biline-8,12-dipropanoic acid.     

A novel diacetylenic bilirubin

An etiobilirubin‐IIβ analog with the central C(10) CH₂ group replaced by a diacetylene unit ( 1 ) was synthesized by base‐catalyzed condensation of bis‐[3‐methyl‐4‐ethyl‐5‐formylpyrrol‐2‐yl]‐diacetylene ( 3 ) with 3‐methyl‐4‐ethyl‐5‐p‐toluenesulfonyl‐2‐pyrrolinone ( 10 ). Diacetylenic rubin 1 is a dark red solid, giving orange solutions with uv‐visible absorption maxima near 460 nm.     

Novel synthesis of bilirubin mono-esters

A rapid, efficient procedure for the preparation of mono esters by reaction of bilirubin bis-tetra-n-butylammonium salt with alkyl iodides, methanesulfonates or p-toluenesulfonates in acetone is described.     

Tautomerism of azopigments derivedfrom bilirubin

¹H and ¹³C n.m.r. data indicate that bilirubin azopigments exist predominantly as phenylhydrazone rather than azobenzene tautomers. Whereas 0-lactim ethers derived from the azopigments exist predominantly as the azobenzene tautomers.     

Identification of Phototoxic Polycyclic Aromatic Hydrocarbons in Sediments Through Sample Fractionation and QSAR Analysis

Abstract

The toxicity of certain polycyclic aromatic hydrocarbons (PAHs) can be greatly increased by simultaneous exposure of test organisms to ultraviolet (UV) wavelengths present in sunlight. This phenomenon, commonly termed photoinduced toxicity, had been evaluated extensively in laboratory settings where only one chemical of concern was present. However, more recent studies have demonstrated that complex mixtures of PAHs present, for example in sediments, also can cause phototoxicity to a variety of aquatic species when the samples are tested in simulated sunlight. Unfortunately, because these types of samples can contain thousands of substituted and unsubstituted PAHs it is difficult, if not impossible, to use conventional analytical techniques to identify those responsible for photoinduced toxicity. The objective of the present study was to link two powerful ecotoxicology tools, toxicity-based fractionation techniques and QSAR models, to identify phototoxic chemicals in a sediment contaminated with PAHs emanating from an oil refinery. Extensive chromatographic fractionation of pore water from the sediment, in conjunction with toxicity testing, yielded a simplified set of sample fractions containing 12 PAHs that were identified via mass spectroscopy. Evaluation of these compounds using a recently developed QSAR model revealed that, based upon their HOMO-LUMO gap energies, about half were capable of producing photoinduced toxicity. We further evaluated the phototoxic potential of the reduced set of PAHs by determining their propensity to bioaccumulate in test organisms, through calculation of octanol-water partition coefficients for the chemicals. These studies represent a novel linkage of sample fractionation methods with QSAR models for conducting an ecological risk assessment.     

Modulation of Melanogenesis and Antioxidant Status of Melanocytes in Response to Phototoxic Action of Doxycycline

Doxycycline is a commonly used tetracycline antibiotic showing the broad spectrum of antibacterial action. However, the use of this antibiotic is often connected with the risk of phototoxic reactions that lead to various skin disorders. One of the factors influencing the photosensitivity reactions is the melanin content in melanocytes. In this study, the impact of doxycycline and UVA irradiation on cell viability, melanogenesis and antioxidant defense system in cultured normal human epidermal melanocytes (HEMn‐DP) was examined. The exposure of cells to doxycycline and UVA radiation resulted in concentration‐dependent loss in melanocytes viability and induced melanin biosynthesis. Significant changes were stated in cellular antioxidant enzymes activity: SOD, CAT and GPx, which indicates alterations of antioxidant defense system. The results obtained in vitro may explain the mechanisms of phototoxic reactions that occur in normal human epidermal melanocytes in vivo after exposure of skin to doxycycline and UVA radiation.     

Porphyrins and Related Compounds as Photoactivatable Insecticides. 2. Phototoxic Activity of Meso-Substituted Porphyrins

We have recently proposed the use of porphyrin sensitizers as photoinsecticidal agents. Our present findings show that the phototoxic efficiency of porphyrins toward the Mediterranean fruit fly Ceratitis capitata is strongly dependent on their chemical structure. Thus, two highly hydrophilic porphyrins, such as a tetraanionic and a te-tracationic meso-substituted derivative, show a very low photoactivity even upon prolonged irradiation with full-spectrum visible light. The phototoxicity increases upon increasing the hydrophobicity of the porphyrin molecule; out of the compounds examined by us, the highest pho-tocidal activity is exhibited by a dicationic amphophilic porphyrin, namely cis-(JV-methyl-piridyl), c/s-diphenyl-porphine, which causes 100% mortality upon 1 h irradiation with a fluence rate of 1220 μ.E s^-lm^-2even at a concentration as low as 0.85 mM. The differences in photoactivity are not related to differences in the photo-physical and photobiological properties or to differences in the rate of porphyrin uptake and clearance by the flies.