The adduct formation between the thioguanine-polyamine ligands and DNA with the AP site under UVA irradiated and non-irradiated conditions

Evaluation of Skin Damage Under UV Exposure

Photosensitivity disorder caused by sunlight, including ultraviolet (UV) rays, often occurs in connective tissue diseases such as lupus erythematosus. In addition, UVA (320-400 nM) and UVB (280-320 nM) trigger the progression of skin inflammation in the patients. Therefore, it is crucial to evaluate skin damage under UV exposure using experimental animals to clarify the relationship between connective tissue disease and photosensitivity disorder. In this chapter, our original protocol for evaluating UVA-dependent skin damage, which is known as photoaging via oxidative stress, is described.

2,6-Disubstituted 7-(naphthalen-2-ylmethyl)-7H-purines as a new class of potent antitubercular agents inhibiting DprE1

Phenotypic screening of an in-house library of small molecule purine derivatives against Mycobacterium tuberculosis (Mtb) led to the identification of 2-morpholino-7-(naphthalen-2-ylmethyl)-1,7-dihydro-6H-purin-6-one 10 as a potent antimycobacterial agent with MIC₉₉ of 4 μM. Thorough structure-activity relationship studies revealed the importance of 7-(naphthalen-2-ylmethyl) substitution for antimycobacterial activity, yet opened the possibility of structural modifications at positions 2 and 6 of the purine core. As the result, optimized analogues with 6-amino or ethylamino substitution 56 and 64, respectively, were developed. These compounds showed strong in vitro antimycobacterial activity with MIC of 1 μM against Mtb H₃₇Rv and against several clinically isolated drug-resistant strains, had limited toxicity to mammalian cell lines, medium clearance with respect to phase I metabolic deactivation (27 and 16.8 μL/min/mg), sufficient aqueous solubility (>90 μM) and high plasma stability. Interestingly, investigated purines, including compounds 56 and 64, lacked activity against a panel of Gram-negative and Gram-positive bacterial strains, indicating a specific mycobacterial molecular target. To investigate the mechanism of action, Mtb mutants resistant to hit compound 10 were isolated and their genomes were sequenced. Mutations were found in dprE1 (Rv3790), which encodes decaprenylphosphoryl-β-d-ribose oxidase DprE1, enzyme essential for the biosynthesis of arabinose, a vital component of the mycobacterial cell wall. Inhibition of DprE1 by 2,6-disubstituted 7-(naphthalen-2-ylmethyl)-7H-purines was proved using radiolabelling experiments in Mtb H₃₇Rv in vitro. Finally, structure-binding relationships between selected purines and DprE1 using molecular modeling studies in tandem with molecular dynamic simulations revealed the key structural features for effective drug-target interaction.

Intermittent environmental exposure to hydrogen prevents skin photoaging through reduction of oxidative stress

AIM

Molecular hydrogen is not only expected to be used as an energy-generating resource, but also to have preventive effects on a variety of clinical manifestations related to oxidative stress through scavenging radicals or regulating gene expression. In the current study, we investigated the influence of intermittent environmental exposure to hydrogen gas at a safe concentration (1.3%) on photoaging using an ultraviolet A (UVA)-irradiated murine model.

METHODS

To mimic the expected human daily activity cycle, UVA exposure in the daytime and hydrogen exposure in the night-time, an original design, UVA-transmission, hydrogen-exposure system was established. Mice were bred under experimental conditions of UVA irradiation and normal air for 8 h (outdoor time 09.00-17.00 hours), and UVA non-irradiation and inhalation of hydrogen gas for 16 h (indoor time 17.00-09.00 hours), and the daily cycle was continued for up to 6 weeks. The progression of photoaging, including morphological changes, collagen degradation and UVA-related DNA damage, was evaluated.

RESULTS

Intermittent administration of hydrogen gas by our system prevented UVA-induced epidermal signs, such as hyperplasia, melanogenesis and appearance of senescence cells, and UVA-induced dermal signs, such as collagen degradation. In addition, we detected attenuation of DNA damage in the hydrogen exposure group as indirect evidence that intermittent exposure to hydrogen gas reduced oxidative stress.

CONCLUSIONS

Our findings support the notion that long-term, intermittent environmental exposure to hydrogen gas in daily life has a beneficial effect on UVA-induced photoaging. Geriatr Gerontol Int 2023; ••: ••-••.

Selective Chemical Modification to the Higher-Order Structures of Nucleic Acids

DNA and RNA can adopt a variety of stable higher-order structural motifs, including G-quadruplex (G4 s), mismatches, and bulges. Many of these secondary structures are closely related to the regulation of gene expression. Therefore, the higher-order structure of nucleic acids is one of the candidate therapeutic targets, and the development of binding molecules targeting the higher-order structure of nucleic acids has been pursued vigorously. Furthermore, as one of the methodologies for detecting the higher-order structures of these nucleic acids, developing techniques for the selective chemical modification of the higher-order structures of nucleic acids is also underway. In this personal account, we focus on the following higher-order structures of nucleic acids, double-stranded DNA containing the abasic site, T-T/U-U mismatch structure, and G-quadruplex structure, and describe the development of molecules that bind to and chemically modify these structures.

Reconsidering the Chemical Nature of Strand Breaks Derived from Abasic Sites in Cellular DNA: Evidence for 3'-Glutathionylation

The hydrolytic loss of coding bases from cellular DNA is a common and unavoidable reaction. The resulting abasic sites can undergo β-elimination of the 3'-phosphoryl group to generate a strand break with an electrophilic α,β-unsaturated aldehyde residue on the 3'-terminus. The work reported here provides evidence that the thiol residue of the cellular tripeptide glutathione rapidly adds to the alkenal group on the 3'-terminus of an AP-derived strand break. The resulting glutathionylated adduct is the only major cleavage product observed when β-elimination occurs at an AP site in the presence of glutathione. Formation of the glutathionylated cleavage product is reversible, but in the presence of physiological concentrations of glutathione, the adduct persists for days. Biochemical experiments provided evidence that the 3'-phosphodiesterase activity of the enzyme apurinic/apyrimidinic endonuclease (APE1) can remove the glutathionylated sugar remnant from an AP-derived strand break to generate the 3'OH residue required for repair via base excision or single-strand break repair pathways. The results suggest that a previously unrecognized 3'glutathionylated sugar remnant─and not the canonical α,β-unsaturated aldehyde end group─may be the true strand cleavage product arising from β-elimination at an abasic site in cellular DNA. This work introduces the 3'glutathionylated cleavage product as the major blocking group that must be trimmed to enable repair of abasic site-derived strand breaks by the base excision repair or single-strand break repair pathways.

A base-repair based electrochemiluminescent genotoxicity sensor that detects abasic sites in double-stranded DNA films

A novel genotoxicity sensor was developed based on the base repair process associated with the electrochemiluminescence (ECL) detection of abasic sites in a double-stranded DNA monolayer. This is the first time that an ECL sensor with the ability to identify the removed nucleobases in a DNA duplex has been studied. The successful detection of abasic sites created by DNA glycosylase indicates its further applications for examining some other specific types of DNA damage.