It is well established that exposure of DNA to high-energy radiation results in a variety of physical and chemical changes in DNA including strand breakage, mutation, and DNA damage.1-16 Initially, high-energy radiation randomly ionizes or excites DNA components (base, sugar, and phosphate backbone) as well as the surrounding water molecules, which are an integral part of the DNA structure. Holes produced quickly shed excess energy and result in ground-state cation radicals.12-15,17,18 Secondary electrons with kinetic energy are produced in a large quantity (4 × 104 per MeV of energy deposited)19 along the tracks of the ionizing radiation and have been recently shown to produce singleand doublestrand breaks in DNA.20-26 Only a small fraction of the secondary electrons are able to cause DNA damage. Most secondary electrons undergo collisional loss of energy with the medium and thermalize within picoseconds. They then either recombine with holes or are captured by the pyrimidines (thymine (T) and cytosine (C)) to form DNA radical anions T•and C•-.27 Holes produced during the initial ionizing event in DNA for the most part transfer to the base with the lowest ionization potential. Guanine (G) has the lowest ionization potentials of the four DNA bases (adenine (A), T, G, and C),28-31 and as a consequence, guanine becomes the locus for hole trapping in DNA.32-34 Ionization of the sugar phosphate backbone initiates two competitive reactions for the hole formed: (i) deprotonation from sugar ring carbon sites to form neutral sugar radicals34-39 and (ii) hole transfer to a neighboring DNA base that after base-tobase hole transfer would end up on guanine.37,38,39b Figure 1 gives an overview of the processes that lead from radiationinduced hole and secondary electron generation in DNA to hole and electron transfer, proton transfer processes, and subsequent molecular product formation such as 8-oxo-G from G•+.32-34 Proton-coupled electron and hole transfer is an important feature of the radiation damage process. An example is the equilibrium shown in Figure 1, left side, in which protonation of the cytosine anion radical at N3 results in transfer of electrons from thymine to cytosine. Coupling of these prototropic equilibria to charge transfer of radiationproduced ion radicals is the focus of this review.

Proton-coupled electron transfer in DNA on formation of radiation-produced ion radicals.

5′,8-Cyclo-2′-deoxyadenosine and 5′,8-cyclo-2′-deoxyguanosine in their 5′R and 5′S diastereomeric forms are tandem-type lesions observed among the DNA modifications and identified in mammalian cellular DNAin vivo. These lesions result from the chemistry of the C5′ radicals generated by the attack of HO˙ radicals to 2-deoxyribose units. Quantitative determination of these lesions in biological samples as biomarkers of free radical damage is a challenge. Results reported for irradiated samples of calf thymus DNA have been critically reviewed, underlining the need of further research for the potential involvement of these lesions in human health (76 references).

Purine 5′,8-cyclonucleoside lesions: chemistry and biology

Cistanche deserticola Y. C. Ma (C. deserticola, "Rou Cong Rong" in Chinese) is an officinal plant that grows in arid or semi-arid areas. The dried fleshy stem of C. deserticola has been generally used as a tonic in China and Japan for many years. Modern pharmacology studies have since demonstrated that C. deserticola possesses broad medicinal functions, especially for use in hormone regulation, aperient, immunomodulatory, neuroprotective, antioxidative, anti-apoptotic, anti-nociceptive, anti-inflammatory, anti-fatigue activities and the promotion of bone formation. The phenylethanoid glycosides (PhGs) presented in C. deserticola have been identified as the major active components. This review summarizes the up-to-date and comprehensive information on C. deserticola covering the aspects of the botany, traditional uses, phytochemistry, and pharmacology.

Cistanche deserticola Y. C. Ma, "Desert ginseng": a review.

Protective effect of verbascoside on 1-methyl-4-phenylpyridinium ion-induced neurotoxicity in PC12 cells

The ubiquitous compound 4-hydroxy-3-methoxycinnamic acid, also known as ferulic acid (FA), constitutes a bioactive ingredient of many foods that may offer beneficial effects against disorders related to oxidative stress, including cancer, diabetes, and neurodegenerative diseases. This review discusses the antioxidant properties of FA, establishing relationships to several biological activities already described for this natural product. Next, 387 naturally occurring compounds, all isolated from plants and published between 1990 and 2015, the structures of which bear 1 or more feruloyl moieties, are covered in this review along with their structural formulas, botanical sources, and bioactivities. The compounds' distribution, structural patterns, bioactivities, and perspectives on food research are also succinctly discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12266

Ferulic Acid and Naturally Occurring Compounds Bearing a Feruloyl Moiety: A Review on Their Structures, Occurrence, and Potential Health Benefits

This tutorial review highlights the mechanism of a novel non-enzymatic fast repair of DNA damage, which refers exclusively to repair DNA radicals including DNA-OH* adducts, DNA radical cations and anions by various endogenous, natural and synthetic compounds. The repair rate constants are as high as 10(9) M(-1) s(-1). In cells, when the enzymatic repair system was inhibited or before the enzymatic repair mechanism was initiated, DNA oxidative damage was significantly reduced by natural polyphenols. This decrease of DNA damage is assigned to the fast repair. Fast repair takes place through an electron transfer process, and docking of polyphenol into the DNA minor groove could be the essential step.

Yimin Shi

Papers

Fast repair of DNA radicals

Fast repair of deoxynucleotide radical cations by phenylpropanoid glycosides (PPGs) and their analogs.

Fast repair of deoxythymidine radical anions by two polyphenols: rutin and quercetin.

Fast repair of hydroxy radical purine deoxynucleotide adducts by phenylpropanoid glycosides and their derivatives from Chinese herbs.

Fast repair activities of quercetin and rutin toward dGMP hydroxyl radical adducts