UVA-induced carbon-centred radicals in lightly pigmented cells detected using ESR spectroscopy

Seasonal Phenolic Profile, Antioxidant, and Photoprotective Activities of Psidium guajava L. Leaves

This study aimed to evaluate the phytochemicals from extracts of Psidium guajava L. leaves (P. guajava extract [PGE]) and its antioxidant and photoprotective effects. PGE showed constant production of total phenolics and maintained high antioxidant capacity across seasons and years. Liquid chromatography-mass spectrometry (LC-MS/MS) analysis revealed the phenolic compounds quercetin, catechin, gallic acid, epicatechin, vanillic acid, and syringic acid, as well as two new compounds, syringaldehyde and ferulic acid. The high sun protection factor (SPF) was observed in all seasons. The phytochemicals ferulic acid, syringic acid, and quercetin were correlated with cloudiness and humidity. Antioxidant activity was correlated with vanillic acid, ascorbic acid, flavonoids, and tannins, and SPF with temperature, antioxidant activity, flavonoids, vanillic acid, gallic acid, and catechin. The formulations containing UVA/UVB filters or not, plus aqueous autumn extract, showed an increase in SPF. Therefore, the results suggested that PGE has potential photoprotective and antioxidant agents for the production of new sunscreen formulations with environmental and health benefits.

Comparison of the mechanisms of DNA damage following photoexcitation and chemiexcitation

In this review, we compare the mechanisms and consequences of electronic excitation of DNA via photon absorption or photosensitization, as well as by chemically induced generation of excited states. The absorption of UV radiation by DNA is known to produce cyclobutane pyrimidine dimers (CPDs) and thymine pyrimidone photoproducts. Photosensitizers are known to enable such transformations using UV-A and visible light by generating triplet species able to transfer energy to DNA. Conversely, chemiexcitation of DNA is a process related to the formation of high energy peroxides whose decomposition leads to triplet excited species. In practice, both photoexcitation and chemiexcitation produce reactive excited species able to promote some DNA nucleobases to their excited state. We discuss the effect of epigenetic methylation modifications of DNA and the role of endogenous and exogenous photosensitizers on the formation of DNA photoproducts via triplet-triplet energy transfer as well as oxidative DNA damages. The mechanisms of pathogenic pathway involving the generation of CPDs via chemiexcitation (namely dark CPDs, dCPDs) are discussed and compared with photoexcitation considering their spatiotemporal characteristics. Recognition of the multifaceted noxious effects of UV radiation opens new horizons for the development of effective electronically excited quenchers, thereby providing a crucial step toward mitigating DNA photodamage.

Myricetin: a Multifunctional Flavonol in Biomedicine

PURPOSE OF REVEIW

The root cause of many diseases like CVD, cancer, and aging is free radicals which exert their effect by interfering with different metabolic pathways. The sources of free radicals can be exogenous, like UV rays from sunlight, and endogenous due to different metabolic by-products.In our body, there are defense mechanisms present, such as antioxidant enzymes and antioxidant molecules to combat these free radicals, but if there is an overload of these free radicals in our body, the defense system may not be sufficient to neutralize these free radicals. In such situations, we are exposed to a chronic low dose of oxidants creating oxidative stress, which is responsible for eliciting different diseases.

RECENT FINDINGS

Pubmed and Google Scholar are the search engines used to sort out relevant papers on myricetin and its role in combating many diseases. Myricetin is present in many fruits and vegetables and is a known antioxidant. It can elevate the antioxidant enzyme levels; reduces the lipid peroxidation; and is known to protect against cancer. In the case of myocardial dysfunction, myricetin has been shown to suppress the inflammatory cytokines and reduced the mortality rate. Myricetin has also been found to reduce platelet aggregation and control the viral infections by interfering in the DNA replication pathways.

SUMMARY

In this paper, we have briefly reviewed about the different type and site of free radicals and the role of myricetin in addressing the ROS and different diseases.

COVID-19 and the ethnicity link - is there a photochemical link?

A hypothesis is proposed to explain the increased detrimental effect of COVID-19 for Black, Asian and Minority Ethnic (BAME) men and women compared to Caucasian individuals. This is based on the differing photochemistry of phaeomelanin in fair skin and eumelanin in dark/black skin. It is suggested that a range of reactive oxygen species, including, singlet oxygen and the superoxide radical anion, derived via direct photolysis of phaeomelanin, may escape the melanocyte and cause subsequent damage to the SARS-CoV-2 virus. It is further suggested that (large) carbon and sulphur peroxy radicals, from oxygen addition to radicals formed by carbon–sulphur bond cleavage, may assist via damage to the cell membranes. It is also speculated that light absorption by phaeomelanin and the subsequent C-S bond cleavage, leads to release of pre-absorbed reactive oxygen species, such as singlet oxygen and free radicals, which may also contribute to an enhanced protective effect for fair-skinned people.