Photooxidation of Tryptophan and Tyrosine Residues in Human Serum Albumin Sensitized by Pterin: A Model for Globular Protein Photodamage in Skin.

Human serum albumin (HSA) is the most abundant protein in the circulatory system. Oxidized albumin was identified in the skin of patients suffering from vitiligo, a depigmentation disorder in which the protection against ultraviolet (UV) radiation fails because of the lack of melanin. Oxidized pterins, efficient photosensitizers under UV-A irradiation, accumulate in the skin affected by vitiligo. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to induce structural and chemical changes in HSA under UV-A irradiation. Our results showed that Ptr is able to photoinduce oxidation of the protein in at least two amino acid residues: tryptophan (Trp) and tyrosine (Tyr). HSA undergoes oligomerization, yielding protein structures whose molecular weight increases with irradiation time. The protein cross-linking, due to the formation of dimers of Tyr, does not significantly affect the secondary and tertiary structures of HSA. Trp is consumed in the photosensitized process, and N-formylkynurenine was identified as one of its oxidation products. The photosensitization of HSA takes place via a purely dynamic process, which involves the triplet excited state of Ptr. The results presented in this work suggest that protein photodamage mediated by endogenous photosensitizers can significantly contribute to the harmful effects of UV-A radiation on the human skin.

Mechanistic Studies on the Photoallergy Mediated by Fenofibric Acid: Photoreactivity with Serum Albumins.

The photoreactivity of fenofibric acid (FA) in the presence of human and bovine serum albumins (HSA and BSA, respectively) has been investigated by steady-state irradiation, fluorescence, and laser flash photolysis (LFP). Spectroscopic measurements allowed for the determination of a 1:1 stoichiometry for the FA/SA complexes and pointed to a moderate binding of FA to the proteins; by contrast, the FA photoproducts were complexed more efficiently with SAs. Covalent photobinding to the protein, which is directly related to the photoallergic properties of the drug, was detected after long irradiation times and was found to be significantly higher in the case of BSA. Intermolecular FA-amino acid and FA-albumin irradiations resulted in the formation of photoproducts arising from coupling between both moieties, as indicated by mass spectrometric analysis. Mechanistic studies using model drug-amino acid linked systems indicated that the key photochemical step involved in photoallergy is formal hydrogen atom transfer from an amino acid residue to the excited benzophenone chromophore of FA or (more likely) its photoproducts. This results in the formation of caged radical pairs followed by C-C coupling to give covalent photoaducts.

Effects of γ-Irradiation on the Molecular Structures and Functions of Human Serum Albumin.

In this paper, we use spectroscopic methods (fluorescence spectroscopy, UV absorption spectroscopy, and circular dichroism (CD) spectroscopy) to elucidate the effects of reactive oxygen species generated by γ-irradiation on the molecular properties of human serum albumin (HSA). The results of fluorescence spectroscopy indicated that oxidation by γ-irradiation can lead to conformational changes of HSA. Data of CD spectra suggested that with the increase of radiation dose the percentage of α-helix in HSA has decreased. The determination of protein hydrophobicity showed that the effective hydrophobicity of HSA decreased up to 62% compared to the native HSA solution due to the exposure to the γ-irradiation. Furthermore, small changes in the esterase-like activity of HSA were introduced because of oxidation. The content of bityrosine increased markedly, suggesting that the oxidized HSA was aggregated. Moreover, there was no obvious change in the molecular properties of HSA with low γ-irradiation dose. Changes happened when the irradiation dose exceeded 200 Gy.

Determination of Singlet Oxygen and Electron Transfer Mediated Mechanisms of Photosensitized Protein Damage by Phosphorus(V)porphyrins.

The mechanism of photosensitized protein damage byphosphorus(V) tetraphenylporphyrin derivatives (P(V)TPPs) wasquantitatively clarified. P(V)TPPs bound to human serum albumin(HSA), a water-soluble protein, and damaged its tryptophan residueduring photoirradiation. P(V)TPPs photosensitized singlet oxygen ((1)O(2))generation, and the contribution of (1)O(2) to HSA damage was confirmedby the inhibitory effect of sodium azide, a (1)O(2) quencher. However,sodium azide could not completely inhibit HSA damage, suggesting thecontribution of an electron transfer mechanism to HSA damage. Thedecrement in the fluorescence lifetime of P(V)TPPs by HSA supportedthe electron transfer mechanism. The contribution of these processes could be determined by the kinetic analysis of the effect ofsodium azide on the photosensitized protein damage by P(V)TPPs.

Design of Albumin-Coated Microbubbles Loaded With Polylactide Nanoparticles.

OBJECTIVES: A protocol was designed to produce albumin-coated microbubbles (MBs) loaded with functionalized polylactide (PLA) nanoparticles (NPs) for future drug delivery studies. METHODS: Microbubbles resulted from the sonication of 5% bovine serum albumin and 15% dextrose solution. Functionalized NPs were produced by mixing fluorescent PLA and PLA-polyethylene glycol-carboxylate conjugates. Nanoparticle-loaded MBs resulted from the covalent conjugation of functionalized NPs and MBs. Three NP/MB volume ratios (1/1, 1/10, and 1/100) and unloaded MBs were produced and compared. Statistical evaluations were based on quantitative analysis of 3 parameters at 4 time points (1, 4, 5, and 6 days post MB fabrication): MB diameter using a circle detection routine based on the Hough transform, MB number density using a hemocytometer, and NP-loading yield based on MB counts from fluorescence and light microscopic images. Loading capacity of the albumin-coated MBs was evaluated by fluorescence. RESULTS: Loaded MB sizes were stable over 6 days after production and were not significantly different from that of time-matched unloaded MBs. Number density evaluation showed that only 1/1 NP/MB volume ratio and unloaded MB number densities were stable over time, and that the 1/1 MB number density evaluated at each time point was not significantly different from that of unloaded MBs. The 1/10 and 1/100 NP/MB volume ratios had unstable number densities that were significantly different from that of unloaded MBs (P < .05). Fluorescence evaluation suggested that 1/1 MBs had a higher NP-loading yield than 1/10 and 1/100 MBs. Quantitative loading evaluation suggested that the 1/1 MBs had a loading capacity of 3700 NPs/MB. CONCLUSIONS: A protocol was developed to load albumin MBs with functionalized PLA NPs for further drug delivery studies. The 1/1 NP/MB volume ratio appeared to be the most efficient to produce stable loaded MBs with a loading capacity of 3700 NPs/MB.

Influence of MLS laser radiation on erythrocyte membrane fluidity and secondary structure of human serum albumin.

The biostimulating activity of low level laser radiation of various wavelengths and energy doses is widely documented in the literature, but the mechanisms of the intracellular reactions involved are not precisely known. The aim of this paper is to evaluate the influence of low level laser radiation from an multiwave locked system (MLS) of two wavelengths (wavelength = 808 nm in continuous emission and 905 nm in pulsed emission) on the human erythrocyte membrane and on the secondary structure of human serum albumin (HSA). Human erythrocytes membranes and HSA were irradiated with laser light of low intensity with surface energy density ranging from 0.46 to 4.9 J cm(-2) and surface energy power density 195 mW cm(-2) (1,000 Hz) and 230 mW cm(-2) (2,000 Hz). Structural and functional changes in the erythrocyte membrane were characterized by its fluidity, while changes in the protein were monitored by its secondary structure. Dose-dependent changes in erythrocyte membrane fluidity were induced by near-infrared laser radiation. Slight changes in the secondary structure of HSA were also noted. MLS laser radiation influences the structure and function of the human erythrocyte membrane resulting in a change in fluidity.

Dose optimization for near-infrared fluorescence sentinel lymph node mapping in patients with melanoma.

BACKGROUND: Regional lymph node involvement is the most important prognostic factor in cutaneous melanoma. As only 20% of patients with melanoma have occult nodal disease and would benefit from a regional lymphadenectomy, the sentinel lymph node (SLN) biopsy was introduced. Near-infrared (NIR) fluorescence has been hypothesized to improve SLN mapping. OBJECTIVES: To assess the potential of intraoperative NIR fluorescence imaging to improve SLN mapping in patients with melanoma and to examine the optimal dose of indocyanine green adsorbed to human serum albumin (ICG:HSA). METHODS: Fifteen consecutive patients with cutaneous melanoma underwent the standard SLN procedure using (99m) technetium-nancolloid and patent blue. In addition, intraoperative NIR fluorescence imaging was performed after injection of 1·6 mL of 600, 800, 1000 or 1200 µmolL(-1) of ICG: HSA in four quadrants around the primary excision scar. RESULTS: NIR fluorescence SLN mapping was successful in 93% of patients. In one patient, no SLN could be identified using either conventional methods or NIR fluorescence. A total of 30 SLNs (average 2·0, range 1-7) were detected, 30 radioactive (100%), 27 blue (73%) and 30 NIR fluorescent (100%). With regard to the effect of concentration on signal-to-background ratios a trend (P=0·066) was found favouring the 600, 800 and 1000 µmol L(-1) groups over the 1200 µmol L(-1) group. CONCLUSION: This study demonstrates feasibility and accuracy of SLN mapping using ICG: HSA. Considering safety, cost and pharmacological characteristics, an ICG: HSA concentration of 600 µmolL(-1) appears optimal for SLN mapping in cutaneous melanoma, although lower doses need to be assessed.

The modified action of triphenyllead chloride on UVB-induced effects in albumin and lipids.

Previously we have shown a toxic effect of the organometallic compound triphenyllead (TPhPb) on cells. In the present study we evaluated the destructive effect of TPhPb on model systems--serum albumin and liposome membranes--alone and under UVB irradiation. UVB irradiation of bovine serum albumin results in protein S-S bond reduction, free SH- and CO- group formation and decrease in fluorescence intensity of tryptophans. Triphenyllead chloride alone and under UVB irradiation did not induce protein oxidation, measured as formation of carbonyl groups, in serum albumin; however, it decreased the content of SH- groups in both cases (alone and under UVB radiation) in a dose-dependent manner. It was found that triphenyllead chloride alone did not induce lipid peroxidation of liposomes but increased their fluidity. However, under UVB irradiation TPhPb dramatically enhances the pro-oxidant action of UVB in a manner dependent on concentration and intensity of radiation, and these effects were suppressed by Trolox. These results suggest that the toxicity of TPhPb under UVB irradiation is due to formation of radical forms of the compound and its disordered effects on the membrane structure.

Fluorescent study of human blood plasma albumin alterations induced by ionizing radiation.

The use of hydrophobic fluorescent probe ABM (benzanthrone derivative) and albumin autofluorescence allowed show conformational alterations in Chernobyl clean-up workers blood plasma. Results obtained in 1996-1997 suggest that acidic expansion of plasma albumin takes place. Latest data (2006-2008) result in splitting of albumin alterations onto two stages - acidic expansion and N-F transition. The N-F transition is accompanied by the blue shift of fluorescence spectra and dehydration of tryptophanyl region of albumin molecule. In 2007 obtained.patterns of ABM spectra had never been previously seen in examined healthy individuals or patients with tuberculosis, multiple sclerosis, rheumatoid arthritis, etc. Patterns of ABM fluorescence spectra are associated with conformational changes of blood plasma albumin. The use of probe ABM and albumin auto-fluorescence allowed show conformational alterations in albumin of Chernobyl clean-up workers blood plasma. It is necessary to note that all investigated parameters significantly differ in observed groups of patients. These findings reinforce our understanding that the blood plasma albumin is a significant biological target of radiation. It may be concluded that fluorescence characteristics are representative of radiation induced albumin alterations and its carrier function.

Management of phototherapy for neonatal hyperbilirubinemia: is a new radiometer applicable for all wavelengths and light source types?

BACKGROUND: To evaluate the clinical effects of phototherapy for neonatal hyperbilirubinemia, it is necessary to measure the rate of cyclobilirubin production, which represents the main photochemical pathway of bilirubin metabolism. Since the Atom Phototherapy Analyzer can be used to calculate the theoretical relative light energy of irradiance as a means of assessing the cyclobilirubin production rate for each wavelength spectrum, the clinical effect of phototherapy can be evaluated regardless of the light source type. Using the Atom Phototherapy Analyzer, the correlation between the irradiance of various light sources with different peak wavelengths and the rate of cyclobilirubin production was investigated in vitro. We also investigated the utility of green LED in vitro. METHODS: A bilirubin-albumin complex solution was prepared, poured into tubes, and irradiated using various light sources. All light sources used were bed-type phototherapy devices; that is, green and blue LED and green and blue fluorescence tubes. The concentrations of photoisomers were measured after irradiation and compared with the irradiance of the light sources. RESULTS: The irradiance measured by the Atom Phototherapy Analyzer decreased in the following order: blue fluorescence tube > green LED > blue LED > green fluorescence tube. The cyclobilirubin production rates and irradiance values of the light sources were significantly positively correlated (R(2) = 0.93, P < 0.05). CONCLUSION: Our data indicate that the Atom Phototherapy Analyzer can be used to objectively evaluate the effects of phototherapy using various light sources. Further, the effects of green LED were similar to those of other light sources in vitro.

Characteristics of bilirubin photochemical changes under green light-emitting diodes in humans compared with animal species.

Phototherapy using light-emitting diodes (LEDs) centered on the green spectrum, which has a high cyclobilirubin production rate, was as effective as that centered on the blue spectrum for neonatal hyperbilirubinemia. There are no reports of species differences in bilirubin photochemical changes in this spectrum, and the characteristics of bilirubin photochemical changes in humans must be elucidated to proceed with the development of new light sources that include these spectra. This report describes the characteristic photochemical kinetics of bilirubin under green-spectrum LEDs in human, rat, rabbit, dog, pig, sheep, bovine and chicken serum albumin and rhesus monkey serum. These albumin-bilirubin complex solutions were irradiated by green LEDs, and the time-course changes in bilirubin photoisomers were measured by high-performance liquid chromatography. The cyclobilirubin production rates in humans, pigs, and monkeys were significantly higher than those in other species. The rate constant of (EZ)-cyclobilirubin production from (EZ)-bilirubin 'k' was significantly higher in humans and monkeys than in other species. In conclusion, bilirubin photochemical kinetics under green spectrum LEDs in humans were characterized by a high cyclobilirubin production rate at a low substrate concentration. The bilirubin photochemical kinetics in monkeys were similar to those in humans.

Effect of processing methods on colouration of human serum albumin preparations.

Human serum albumin is a well tolerated therapeutic for the treatment of hypovolemia. Despite all commercial human albumin preparations being derived from plasma, these products can have a highly variable colour. Albumin samples derived from ethanol precipitation and chromatographic fractionation procedures were evaluated for bilirubin and biliverdin levels and by spectrophotometry. It was shown that albumin derived from a chromatographic process, which had a bilirubin:albumin ratio similar to that observed in plasma, had a vibrant yellow appearance. The albumin derived from ethanol precipitation had undetectable levels of bilirubin, and the amber colour of this product was attributed mainly to residual haem. The presence of bilirubin during pasteurisation led to oxidation to biliverdin, with a resultant colour change from yellow to yellow/green. Given that the antioxidant properties of bilirubin are well established, it is possible that bilirubin helps protect albumin from oxidation during the pasteurisation step.

Hepatotoxicity and renal toxicity induced by gamma-radiation and the modulatory protective effect of Ficus carica in male albino rats.

It is well-known that gamma radiation initiates generation of free radicals which prompting serious cellular damages in biological systems. In the present study, we investigated the role of Ficus carica, a natural antioxidant substance, in modulating changes in liver and kidney functions, antioxidant enzyme's gene expression, and apoptosis, in male albino rats exposed to gamma radiation. A total of 40 rats were used in this experiment and divided equally into 4 groups: Group 1, rats administered distilled H2O (Control); Group 2, rats administered F. carica; Group 3, rats irradiated; and Group 4, rats treated with F. carica and irradiated. Groups 3 and 4 were exposed to whole-body gamma radiations at a dose level of 8 Gy and with a dose rate of 0.762 Gy/min. F. carica was administered to rats by gavage, for 3 consecutive weeks, before exposure to radiation. Five rats were sacrificed from each group at intervals of 24 and 72 h after cessation of treatment. The results revealed marked increases in alanine aminotransferase and aspartate aminotransferase levels in liver, a decrease in albumin level and increase in urea level in kidney. Irradiation resulted in cytotoxic effects as indicated by elevation in antioxidant enzyme's gene expression at 24 h, the opposite was observed at 72 h. Immunohistochemical analysis revealed that cytochrome c and p53 expressions significantly increased following exposure to radiation. Oral administration of F. carica pre-irradiation as a natural product plays a modulatory protective and anti-apoptotic role against cells damaged by free radicals induced by whole-body irradiation.

Suture-free laser-assisted vessel repair using CO2 laser and liquid albumin solder.

Numerous studies have shown that the use of proteinic solders during laser-assisted vascular anastomosis (LAVA) and repair (LAVR) can significantly increase welding strength, but these studies combined solder-mediated LAVA/R with the use of stay sutures, thereby defeating its purpose. In an in vitro study, we examined the leaking point pressures (LPPs) and histological damage profile of porcine carotid arteries following albumin solder-mediated CO(2) LAVR without the use of sutures. Longitudinal arteriotomies (9.1+/-0.8 mm in length) were sheathed with 25% liquid bovine serum albumin solder, and LAVR was performed using a micromanipulator-controlled CO(2) laser operating at 170-mW power and 1.25-mm spot size in continuous wave mode. The welding regime consisted of a transversal zigzag pass followed by one or two longitudinal zigzag passes, producing an irradiance of 13.9 W/cm(2) and energies of 10.5 J and 11.3 J per mm weld, respectively. LPPs were measured by the fluid infusion technique, and histological analysis was performed with light, fluorescence, and polarization microscopy. The LPP of the two-pass welds was 351+/-158 mmHg versus 538+/-155 mmHg for the three-pass welds. Thermal damage was confined primarily to the adventitial layers, with limited heat diffusion into the media below the solder around the coaptation interface.

Inactivation of chosen dehydrogenases by the products of water radiolysis and secondary albumin and haemoglobin radicals.

PURPOSE: Inactivation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) by products of water radiolysis and by secondary radicals localized on haemoglobin (Hb) and human albumin (HSA) was studied. MATERIALS AND METHODS: Aqueous solutions of ADH, GAPDH and LDH were irradiated under air and under nitrous oxide (N2O) in the absence and in the presence of Hb or HSA. In order to determine the effectiveness of inactivation of the enzymes by radicals localized on Hb and HSA, the inactivation efficiency determined experimentally was compared with that calculated under assumption that only hydroxyl radicals are responsible for the enzyme inactivation. RESULTS: In the absence of other proteins, under air, GAPDH showed the highest radiation sensitivity, followed by ADH and LDH. The sequence was reverse under anaerobic atmosphere. Oxygen increased considerably the inactivation of GAPDH and ADH. Secondary albumin and haemoglobin radicals brought about considerable inactivation of GAPGH and ADH. Albumin radicals (HSA) generated under N2O inactivated GAPDH and ADH more effectively than haemoglobin radicals (Hb). Under air, however, inactivation of GAPDH and ADH by haemoglobin peroxyl radicals was higher than by albumin peroxyl radicals. LDH was resistant to inactivation by haemoglobin and albumin radicals, and peroxides of these proteins. CONCLUSIONS: In the light of these results and literature data, the observed differences in the effectiveness of inactivation of the dehydrogenases studied by secondary protein radicals depend on the amino acid residues present at the active site and in its close neighborhood and on the number of amino acid residues available on the protein surface.

Influence of Gamma Irradiation on Porcine Serum Albumin Structural Properties and Allergenicity.

Pork provides an ideal source of food energy; however, pork can elicit an allergic reaction, and porcine serum albumin (PSA) has been identified as a major allergen. This study examined the impact of gamma irradiation on the allergenicity and structural qualities of PSA; the PSA solution was gamma-irradiated at 1, 2, 4, 6, and 8 kGy. Allergenicity was investigated by immunoblotting and competitive indirect ELISA using serum from patients who are allergic to pork, and conformational changes in irradiated PSA were measured by circular dichroism, sulfhydryl group detection, and fluorescence emission spectra. The secondary and tertiary structures of gamma-irradiated PSA were altered, and the allergenicity of PSA was lowered by boosting the amount of irradiation. In addition, there is high correlation between depletion in the α-helix and immunoglobulin E-binding capability of PSA. The results show a new possibility in using gamma irradiation to reduce the allergenicity of pork products.

Short-term measurement of catabolic rates using iodine-labeled plasma protein.

Fractional catabolic rates of iodine-labeled plasma albumins and fibrinogens have been measured in experiments of a few hours duration in adult rabbits. The method used which is based on release of labeled iodide from the protein gives accurate estimates of catabolic rates (expressed as fractions of the plasma protein pool catabolized per day) after 36 hr without the need for urine collections. At earlier times and using undenatured albumin, fractional catabolic rates increased steadily from approximately 10% per day in the first few hours to a constant 20-25% per day after 24 hr. Fibrinogen values which started at 15% plateaued after 24 hr at 30-35% per day. The fractional synthesis rate of albumin, measured with (14)C-labeled carbonate in the first 6 hr when the short-term fractional catabolic rate was 10.2% agreed with the 36 hr plateau value of 29% per day. The presence of traces of denatured or polymerized proteins was revealed by high initial fractional catabolic rates, and in a few experiments biological screening in another animal was not fully effective in removing them. On the other hand, some labeled albumins showed no traces of denatured protein even without biological screening. Fibrinogen polymer was catabolized rapidly and behaved like denatured or incipiently clotted fibrinogen. Irradiation of albumin produced a marked increase in early fractional catabolic rates, and some proteins after prolonged storage and labeling behaved similarly. Alternative theories to explain the low fractional catabolic rates in the first 24 hr are considered. Since radioautographic experiments failed to provide evidence for retention of labeled proteins or their nondiffusible breakdown products inside catabolic cells, preference is given to the view that catabolism occurs in a pool of significant protein content which is either a subunit of the extravascular pool or is independent and sandwiched between the plasma and extravascular pools. Earlier hypotheses concerning small catabolic pools in which protein specific activities approximate closely to plasma values at the same time are considered to be no longer tenable.

Stereodifferentiating drug-biomolecule interactions in the triplet excited state: studies on supramolecular carprofen/protein systems and on carprofen-tryptophan model dyads.

Stereoselective interaction between a chiral nonsteroidal antiinflammatory drug, namely carprofen (CP), and human serum albumin (HSA) was studied, and the results were compared with those obtained with model dyads. In the presence of albumin the same triplet-triplet transition was detected for both CP stereoisomers; however, time-resolved measurements revealed a remarkable stereodifferentiation in the CP/HSA interaction. For each stereoisomer, the decay dynamics evidenced the presence of two components with different lifetimes that can be correlated with complexation of CP to the two possible albumin binding sites (site I and site II). This assignment was confirmed by using ibuprofen, a site II displacer. Thus, the shorter lived components, for which stereodifferentiation was more important (tauR/tauS ca. 4), were ascribed to the CP triplet state in site I; the lifetime shortening can be attributed to electron-transfer quenching by the only tryptophan (Trp) of the protein. Laser flash photolysis of model dyads containing covalently linked CP and Trp revealed formation of the expected Trp radical cation, providing support for such a mechanism. Moreover, significant stereodifferentiation was observed between the (R)- and (S)-CP-Trp dyads. In the case of CP/HSA complexes, as well as in the model compounds, the stereodifferentiation detected in the decays is in good agreement with that observed in the formation of the only CP photoproduct, resulting from a photodehalogenation process. Moreover, stereodifferentiation was also found to occur for the photobinding of CP to the protein.

Photosensitizing activity of advanced glycation endproducts on tryptophan, glucose 6-phosphate dehydrogenase, human serum albumin and ascorbic acid evaluated at low oxygen pressure.

A comparative study of the photosensitizing activity of advanced glycation endproducts (AGEs) prepared by incubating glucose (Glc), threose (Threo) and ascorbate (AH-) in the presence of lysine (Lys) was performed. Photochemical activity was evaluated under low oxygen pressure with the aim to simulate the conditions of the eye lens. AGE-sensitized tryptophan and AH- photodecomposition and glucose 6-phosphate dehydrogenase inactivation were studied. In all systems, glucose-derived AGEs showed the highest photosensitizing efficiency, followed by ascorbate and threose. The presence of different sensitizers in glycation products mixtures was investigated. For this purpose, Trp decomposition quantum yields were determined at 344 and 367 nm. The values obtained at 344 nm are between three and six times higher than those observed at 367 nm, confirming the presence of at least two compounds with different photosensitizing activities in the mixtures. The chemiluminescence associated with the AGE-mediated oxidation of free Trp and Trp residues in human serum albumin was also studied, and a good correlation between the emission of light and the extent of Trp decomposition was found. In conclusion, it is demonstrated that glucose derived AGEs, which can be formed in vivo in the eye lens of diabetic patients and are accumulated in elderly lenses, have a higher photosensitizing efficiency, at low oxygen pressure, than those arising from ascorbate and threose. This high efficiency is especially significant when proteins are employed as photochemical targets, indicating that protein-sensitizer interaction and the local environment around the sensitizers play an important role.

Photodegradation and in vitro phototoxicity of aceclofenac.

Aceclofenac (Airtal) (1) is a photoallergic and phototoxic anti-inflammatory and analgesic agent. This drug is photolabile under aerobic and anaerobic conditions. Irradiation of an ethanol-solution of aceclofenac under oxygen or argon at 290-320 nm affords via decarboxlation compound 2 as the main isolated and spectroscopically identified photoproduct, besides hydroxylamine derivates 3 and 4. A radical intermediate was evidenced spectrophotometrically with GSH and DTNB, as well as by the dimerization of cysteine. Red blood cell lysis photosensitized by 1-4 was investigated. Furthermore, in a lipid-photoperoxidation test with linoleic acid the in vitro phototoxicity of aceclofenac was also verified. The photoinduced generation of peroxide by compound 1 was determined during the irradiation in presence of NADPH by chemiluminescence. In relation to the photoallergic activity of this drug, the interaction of aceclofenac with human serum albumin (HSA) has been studied through fluorescence spectroscopy. No photoinduced binding was observed after irradiation of compounds 1 in the presence of human serum albumin.