Production of cis-syn thymine-thymine cyclobutane dimer oligonucleotide in the presence of acetone photosensitizer

Characteristics of LED light-induced geometrical isomerization and degradation of astaxanthin and improvement of the color value and crystallinity of astaxanthin utilizing the photoisomerization

The effects of light-emitting diode (LED) irradiation characterized by different emission wavelengths on the E/Z-isomerization and degradation of astaxanthin were investigated. LED irradiation slightly promoted Z-isomerization of astaxanthin, whereas the all-E-isomerization was highly efficiently promoted at specific wavelengths, especially at 365 nm. Astaxanthin isomers did not degrade significantly when dissolved in ethanol and subjected to LED irradiation conditions for 300 min. However, significant degradation was achieved when ethyl acetate was used for dissolution, and the samples were irradiated at the wavelength of 405 nm. The addition of α-tocopherol suppressed the photodegradation of astaxanthin. LED irradiation significantly affected the physical properties of astaxanthin Z-isomers. Irradiation with 365, 405, and 470 nm LEDs enhanced the color value (redness) and crystallinity of the Z-isomers via an all-E-isomerization reaction. These findings can contribute to the development of technologies that can arbitrarily control the E/Z-isomer ratio and physical properties of astaxanthin.

Lignin Nanoparticles Deliver Novel Thymine Biomimetic Photo-Adducts with Antimelanoma Activity

We report here the synthesis of novel thymine biomimetic photo-adducts bearing an alkane spacer between nucleobases and characterized by antimelanoma activity against two mutated cancer cell lines overexpressing human Topoisomerase 1 (TOP1), namely SKMEL28 and RPMI7951. Among them, Dewar Valence photo-adducts showed a selectivity index higher than the corresponding pyrimidine-(6-4)-pyrimidone and cyclobutane counterpart and were characterized by the highest affinity towards TOP1/DNA complex as evaluated by molecular docking analysis. The antimelanoma activity of novel photo-adducts was retained after loading into UV photo-protective lignin nanoparticles as stabilizing agent and efficient drug delivery system. Overall, these results support a combined antimelanoma and UV sunscreen strategy involving the use of photo-protective lignin nanoparticles for the controlled release of thymine dimers on the skin followed by their sacrificial transformation into photo-adducts and successive inhibition of melanoma and alert of cellular UV machinery repair pathways.

Simultaneously monitoring UVC-induced DNA damage and photoenzymatic repair of cyclobutane pyrimidine dimers by electrochemical impedance spectroscopy

Cyclobutane pyrimidine dimers (CPDs) are the major DNA photoproducts of thymine-thymine dinucleotides upon ultraviolet (UV) irradiation. Failure in the repair of damaged DNA may lead to DNA replication errors, DNA mutations, and even cell death. Photoreactivation can mediate the repair of UV-induced DNA lesions by photolyases upon UVA (315-400 nm) or blue light (400-500 nm) irradiation. Herein, the UVC (254 nm)-induced DNA damage and photoenzymatic repair of the CPD products were simultaneously monitored by electrochemical impedance spectroscopy (EIS). The UVC-damaged dT₂₀ was first immobilized on the gold electrode, and the specific recognition by the anti-CPD antibody leads to significantly increased EIS signals. The electron transfer resistance (R_et) values were linearly proportional to the concentrations of damaged dT₂₀ ranging from 0.005 to 0.1 μM, and a detection limit of 3.06 nM was achieved. Using surface plasmon resonance, the equilibrium dissociation constant (K_D) between the CPDs in dT₂₀ and anti-CPD antibody was estimated to be (3.32 ± 0.31) × 10^-12 M, indicating the strong binding affinity. Evidenced by EIS, the CPDs in the damaged dT₂₀ could be repaired by the attached DNA photolyase under UVA (365 nm) photoexcitation, and the detachment of the photolyase from the DNA strand was accomplished after completion of the repair process. The repair efficiency was calculated to be 70.0% by EIS, being consistent with that of 71.4% by UV spectroscopy. The electrochemical method is simple, sensitive and straightforward, holding great potential for assaying other types of DNA lesions and their repair processes.

The effect of flanking bases on direct and triplet sensitized cyclobutane pyrimidine dimer formation in DNA depends on the dipyrimidine, wavelength and the photosensitizer

Cyclobutane pyrimidine dimers (CPDs) are the major products of DNA produced by direct absorption of UV light, and result in C to T mutations linked to human skin cancers. Most recently a new pathway to CPDs in melanocytes has been discovered that has been proposed to arise from a chemisensitized pathway involving a triplet sensitizer that increases mutagenesis by increasing the percentage of C-containing CPDs. To investigate how triplet sensitization may differ from direct UV irradiation, CPD formation was quantified in a 129-mer DNA designed to contain all 64 possible NYYN sequences. CPD formation with UVB light varied about 2-fold between dipyrimidines and 12-fold with flanking sequence and was most frequent at YYYR and least frequent for GYYN sites in accord with a charge transfer quenching mechanism. In contrast, photosensitized CPD formation greatly favored TT over C-containing sites, more so for norfloxacin (NFX) than acetone, in accord with their differing triplet energies. While the sequence dependence for photosensitized TT CPD formation was similar to UVB light, there were significant differences, especially between NFX and acetone that could be largely explained by the ability of NFX to intercalate into DNA.

An Ethenoadenine FAD Analog Accelerates UV Dimer Repair by DNA Photolyase

Reduced anionic flavin adenine dinucleotide (FADH^- ) is the critical cofactor in DNA photolyase (PL) for the repair of cyclobutane pyrimidine dimers (CPD) in UV-damaged DNA. The initial step involves photoinduced electron transfer from *FADH^- to the CPD. The adenine (Ade) moiety is nearly stacked with the flavin ring, an unusual conformation compared to other FAD-dependent proteins. The role of this proximity has not been unequivocally elucidated. Some studies suggest that Ade is a radical intermediate, but others conclude that Ade modulates the electron transfer rate constant (k_ET ) through superexchange. No study has succeeded in removing or modifying this Ade to test these hypotheses. Here, FAD analogs containing either an ethano- or etheno-bridged Ade between the AN1 and AN6 atoms (e-FAD and ε-FAD, respectively) were used to reconstitute apo-PL, giving e-PL and ε-PL respectively. The reconstitution yield of e-PL was very poor, suggesting that the hydrophobicity of the ethano group prevented its uptake, while ε-PL showed 50% reconstitution yield. The substrate binding constants for ε-PL and rPL were identical. ε-PL showed a 15% higher steady-state repair yield compared to FAD-reconstituted photolyase (rPL). The acceleration of repair in ε-PL is discussed in terms of an ε-Ade radical intermediate vs superexchange mechanism.

Divalent Cations Increase DNA Repair Activities of Bacterial (6-4) Photolyases

The (6-4) photolyases of the FeS-BCP group can be considered as the most ancient type among the large family of cryptochrome and photolyase flavoproteins. In contrast to other photolyases, they contain an Fe-S cluster of unknown function, a DMRL chromophore, an interdomain loop, which could interact with DNA, and a long C-terminal extension. We compared DNA repair and photoreduction of two members of the FeS-BCP family, Agrobacterium fabrum PhrB and Rhodobacter sphaeroides RsCryB, with a eukaryotic (6-4) photolyase from Ostreococcus, OsCPF, and a member of the class III CPD photolyases, PhrA from A. fabrum. We found that the low DNA repair effectivity of FeS-BCP proteins is largely stimulated by Mg²⁺ and other divalent cations, whereas no effect of divalent cations was observed in OsCPF and PhrA. The (6-4) repair activity in the presence of Mg²⁺ is comparable with the repair activities of the other two photolyases. The photoreduction, on the other hand, is negatively affected by Mg²⁺ in PhrB, but stimulated by Mg²⁺ in PhrA. A clear relationship of Mg²⁺ dependency on DNA repair with the evolutionary position conflicts with Mg²⁺ dependency of photoreduction. We discuss the Mg²⁺ effect in the context of structural data and DNA binding.

DNA damage spectra induced by photosensitization

DNA damage induced by photosensitization is not only responsible for the genotoxic effects of various types of drugs in the presence of light, but is also relevant for some of the adverse effects of sunlight, in particular in the UVA and visible range of the spectrum. The types of DNA modifications induced are very diverse and include pyrimidine dimers, covalent adducts, various base modifications generated by oxidation, single-strand breaks and (regular and oxidized) sites of base loss. The ratios in which the various modifications are formed (damage spectra) can be regarded as a fingerprint of the damaging mechanism. Here, we describe the damage spectra of various classes of photosensitizers in relation to the underlying damaging mechanisms. In mammalian cells irradiated with solar radiation, damage at wavelengths <400 nm is characteristic for a (not yet identified) endogenous type-I or type-II photosensitizer. In the UVA range, however, both direct DNA excitation and photosensitized damage appear to be relevant, and there are indications that other chromophore(s) are involved than in the visible range.