Genotoxicity of ultraviolet light and sunlight in the bacterium Caulobacter crescentus: Wavelength-dependence.

The ultraviolet (UV) component of sunlight can damage DNA. Although most solar UV is absorbed by the ozone layer, wavelengths > 300 nm (UVA and UVB bands) can reach the Earth's surface. It is essential to understand the genotoxic effects of UV light, particularly in natural environments. Caulobacter crescentus, a bacterium widely employed as a model for cell cycle studies, was selected for this study. Strains proficient and deficient in DNA repair (uvrA-) were used to concurrently investigate three genotoxic endpoints: cytotoxicity, SOS induction, and gene mutation, using colony-formation, the SOS chromotest, and RifR mutagenesis, respectively. Our findings underscore the distinct impacts of individual UV bands and the full spectrum of sunlight itself in C. crescentus. UVC light was highly genotoxic, especially for the repair-deficient strain. A UVB dose equivalent to 20 min sunlight exposure also affected the cells. UVA exposure caused a significant response only at high doses, likely due to activation of photorepair. Exposure to solar irradiation resulted in reduced levels of SOS induction, possibly due to decreased cell survival. However, mutagenicity is increased, particularly in uvrA- deficient cells.

Recombinant production of a highly efficient photolyase from Thermus thermophilus.

Ultraviolet (UV) radiation from sunlight can damage DNA, inducing mutagenesis and eventually leading to skin cancer. Topical sunscreens are used to avoid the effect of UV irradiation, but the topical application of DNA repair enzymes, such as photolyase, can provide active photoprotection by DNA recovery. Here we produced a recombinant Thermus thermophilus photolyase expressed in Escherichia coli, evaluated the kinetic parameters of bacterial growth and the kinetics and stability of the enzyme. The maximum biomass (𝑋𝑚𝑎𝑥 ) of 2.0 g L-1 was reached after 5 h of cultivation, corresponding to 𝑃X  = 0.4 g L-1 h. The µð‘šð‘Žð‘¥ corresponded to 1.0 h-1 . Photolyase was purified by affinity chromatography and high amounts of pure enzyme were obtained (3.25 mg L-1 of cultivation). Two different methods demonstrated the enzyme activity on DNA samples and very low enzyme concentrations, such as 15 µg mL-1 , already resulted in 90% of CPD photodamage removal. We also determined photolyase kM of 9.5 nM, confirming the potential of the enzyme at very low concentrations, and demonstrated conservation of enzyme activity after freezing (-20°C) and lyophilization. Therefore, we demonstrate T. thermophilus photolyase capacity of CPD damage repair and its potential as an active ingredient to be incorporated in dermatological products.

DNA Damage Induced by Late Spring Sunlight in Antarctica.

Sunlight ultraviolet (UV) radiation constitutes an important environmental genotoxic agent that organisms are exposed to, as it can damage DNA directly, generating pyrimidine dimers, and indirectly, generating oxidized bases and single-strand breaks (SSBs). These lesions can lead to mutations, triggering skin and eye disorders, including carcinogenesis and photoaging. Stratospheric ozone layer depletion, particularly in the Antarctic continent, predicts an uncertain scenario of UV incidence on the Earth in the next decades. This research evaluates the DNA damage caused by environmental exposure to late spring sunlight in the Antarctic Peninsula, where the ozone layer hole is more pronounced. These experiments were performed at the Brazilian Comandante Ferraz Antarctic Station, at King's George Island, South Shetlands Islands. For comparison, tropical regions were also analyzed. Samples of plasmid DNA were exposed to sunlight. Cyclobutane pyrimidine dimers (CPDs), oxidized base damage and SSBs were detected using specific enzymes. In addition, an immunological approach was used to detect CPDs. The results reveal high levels of DNA damage induced by exposure under the Antarctic sunlight, inversely correlated with ozone layer thickness, confirming the high impact of ozone layer depletion on the DNA damaging action of sunlight in Antarctica.

Cuban flora species as a potential source of DNA protective compounds / Especies de la flora cubana cómo fuente potencial de compuestos protectores del DNA

Environmental exposure to genotoxic agents represents a major health concern for modern society. DNA damage could lead to mutations, which accumulative effect is closely related to degenerative and lethal diseases, such as cancer. Because of their structural and chemical diversity natural products play a fundamental role in pharmaceutical sciences for novel drug discovery. The present review article focuses on pre-clinical studies done with some species from Cuban flora that have been tested with positive antigenotoxic properties against different genotoxins. Special emphasis regarding molecular mechanisms suggested, from antioxidant activity to DNA repair modulation, a critical discussion of the state of art and the perspectives in the use of these plants as a new and promising strategy for genoprotection in the 21st Century are included.

La exposición ambiental a agentes genotóxicos representa un problema de salud significativo en la sociedad actual. El daño al ADN puede generar mutaciones, cuyo efecto acumulativo se encuentra estrechamente relacionado con enfermedades degenerativas y letales como el cáncer. Debido a su diversidad estructural y química los productos naturales juegan un papel fundamental en las ciencias farmacéuticas en el descubrimiento de nuevas drogas. El presente artículo de revisión puntualiza estudios pre-clínicos realizados con determinadas especies de la flora cubana que han sido estudiadas con una respuesta antioxidante positiva frente a diferentes genotoxinas. Se enfatizan especialmente los mecanismos moleculares sugeridos, desde actividad antioxidante hasta modulación de la reparación del ADN, así como una discusión crítica del estado del arte y las perspectivas en el empleo de estas plantas como una estrategia nueva y prometedora para la genoprotección en el siglo 21.

El extracto acuoso de Cymbopogon citratus protege al ADN plasmídico del daño inducido por radiación UVC / Cymbopogon citratus aqueous extract protects plasmid DNA from UVC-induced damage

Objetivo: Evaluar el efecto protector del extracto acuoso de Cymbopogon citratus (DC) Stapf, ante el daño inducido por las radiaciones UVC. Material y Métodos: Para evaluar si el extracto acuoso de C. citratus era capaz de inducir roturas de cadenas en el ADN, moléculas de plásmido pBluescript SK II fueron tratadas con diferentes concentraciones del extracto (0,01 - 4,0 mg/mL), en los tiempos de exposición: 30, 60 y 90 min. El efecto fotoprotector fue evaluado aplicando el extracto vegetal antes, durante, y después de la irradiación del ADN plasmídico con 200 J/m2 de UVC. La actividad enzimática de T4 endonucleasa V fue empleada para detectar formación de CPDs. Las formas superenrollada y relajada de las moléculas de plásmido fueron separadas electroforéticamente en gel de agarosa. Adicionalmente, se midió la transmitancia del extracto acuoso a la DO de 254 nm. Resultados: Ninguna de las concentraciones evaluadas resultó genotóxica con 30 min de tratamiento. Las concentraciones ≥ 2 mg/mL indujeron roturas de cadenas a los 90 min de incubación. El extracto de C. citratus a concentraciones ≥ 0,5 mg/mL protegió al ADN frente a las radiaciones UVC. Conclusiones: En nuestras condiciones experimentales, el extracto acuoso de C. citratus protege al ADN frente a la genotoxicidad inducida por la luz UVC, previniendo la generación de CPDs, pero no es capaz de eliminarlas una vez formadas

Aim: to evaluate the photoprotective effect of aqueous extract of Cymbopogon citratus (DC) Stapf against UVC-induced damage to ADN. Material and methods: In the experimental procedure, samples of plasmid pBluescript SK II solutions were exposed to C. citratus aqueous extract in 0.01-4.0 mg/mL concentrations during 30, 60 and 90 min. In order to evaluate the photoprotective effect, the vegetal extract was applied before, during and after UVC radiation at 200 J/m2 doses. DNA repair enzymes T4 endonuclease V was employed in order to discriminate CPDs damage. Then, supercoiled and relaxed forms of DNA were separated after electrophoretic migration in agarose gels. Also aqueous extract transmittance was measure at 254 nm OD. Results: None of the concentrations tested were genotoxic in 30 min of exposition. Concentrations ≥ 2 mg/mL induced strand breaks at 90 min of incubation. The C. citratus extract at concentrations ≥ 0.5 mg/ mL protect DNA in front of UVC radiation. Conclusions: In our experimental conditions, C. citratus extract protects DNA from the genotoxicity induced by light UVC, preventing the CPDs generation, but is not able to eliminate DNA damage once formed