Role of hydroxyl radicals and singlet oxygen in the formation of primary radicals in unsaturated lipids: a solid state electron paramagnetic resonance study

Epoxides: an underestimated lipid oxidation product

Immense gains in understanding of mechanisms and effects of lipid oxidation have been achieved in the nearly 90 years over which lipid oxidation has been an active research focus. Even so, the substantial questions still being raised about lipid oxidation in this special issue show clearly that missing pieces remain and must be considered for full accounting of this important reaction in any system. In this context, epoxides are spotlighted as a critical overlooked product of lipid autoxidation - underestimated in analysis, underestimated in presence as a functionally active and competitive intermediate and product of lipid oxidation, and underestimated in potential contributions to impact of lipid oxidation on other molecules and cell functions. Logical reasons for ignoring or not finding epoxides are offered in historical development of lipid oxidation knowledge. Reactions generating lipid epoxides in autoxidation are reviewed, limitations in detecting and tracking epoxides are outlined to explain why epoxides may not be detected when they should be present, and justifications for increased research and analysis of epoxides are argued. The main goal is to provide a context for recognizing epoxides as critical products that must be accounted for in determining the state rather than extent of lipid oxidation and in tracking its consequences in oils, foods, personal care products, and tissues. A secondary goal is to stimulate new research using contemporary analyses to fill in the gaps of knowledge about epoxide formation, structure, and reactions in lipid autoxidation.

Shelf-Life Optimisation of Plasma Polymerised (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPOpp) Coatings; A New Possible Approach to Tackle Infections in Chronic Wounds

Chronic wounds fail to heal and are accompanied by an ongoing infection. They cause suffering, shorten lifespans, and their prevalence is increasing. Unfortunately, the medical treatment of chronic wounds has remained unchanged for decades. A novel approach to break the biological vicious cycle is the long-lived radical (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO). TEMPO can be plasma polymerised (TEMPOpp) into thin coatings that have antimicrobial properties. However, due to its radical nature, quenching causes it to lose effectiveness over time. Our aim in this study was to extend the shelf-life of TEMPOpp coatings using various storage conditions: Namely, room temperature (RT), room temperature & vacuum sealed (RTV), freezer temperature & vacuum sealed (FTV). We have analysed the coatings' quality via the surface analytical methods of X-Ray Photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR); finding marked differences among the three storage conditions. Furthermore, we have compared the antimicrobial efficacy of the stored coatings against two major bacterial pathogens, Staphylococcus aureus and Staphylococcus epidermidis, commonly found in chronic wounds. We did so both qualitatively via live/dead staining, as well as quantitatively via (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium (XTT) viability assay for up to 15 weeks in 5 weeks increments. Taken all together, we demonstrate that samples stored under FTV conditions retain the highest antimicrobial activity after 15 weeks and that this finding correlates with the retained concentration of nitroxides.

Impact of binding to the multidrug resistance regulator protein LmrR on the photo-physics and -chemistry of photosensitizers

Light activated photosensitizers generate reactive oxygen species (ROS) that interfere with cellular components and can induce cell death, e.g., in photodynamic therapy (PDT). The effect of cellular components and especially proteins on the photochemistry and photophysics of the sensitizers is a key aspect in drug design and the correlating cellular response with the generation of specific ROS species. Here, we show the complex range of effects of binding of photosensitizer to a multidrug resistance protein, produced by bacteria, on the formers reactivity. We show that recruitment of drug like molecules by LmrR (Lactococcal multidrug resistance Regulator) modifies their photophysical properties and their capacity to induce oxidative stress especially in 1O2 generation, including rose bengal (RB), protoporphyrin IX (PpIX), bodipy, eosin Y (EY), riboflavin (RBF), and rhodamine 6G (Rh6G). The range of neutral and charged dyes with different exited redox potentials, are broadly representative of the dyes used in PDT.

In-vitro effect of flavonoids from Solidago canadensis extract on glutathione S-transferase

Solidago canadensis is typical of a flavonoid-rich herb and the effect of an aqueous ethanol extract on glutathione-S-transferase (GST) activity using HepG2 cells was compared with those of the flavonol quercetin and its glycosides quercitrin and rutin, found as major constituents. The composition of the extract was determined by HPLC and rutin was found to be the major flavonoidal component of the extract. Total GST activity was assessed using 1-chloro-2,4-dinitrobenzene as a substrate. The glycosides rutin and quercitrin gave dose-dependent increases in GST activity, with a 50% and 24.5% increase at 250 mm, respectively, while the aglycone quercetin inhibited the enzyme by 30% at 250 mm. The total extract of the herb gave an overall dose-dependent increase, the fractions corresponding to the flavonoids showed activating effects while those containing caffeic acid derivatives were inhibitory. The activity observed corresponds to that reported for similar compounds in-vivo using rats, thus the HepG2 cell line could serve as a more satisfactory method of assessing the effects of extracts and compounds on GST.

Singlet oxygen quenching by anthocyanin's flavylium cations

The quenching of singlet molecular oxygen ((1)O(2)) by the flavylium cation form of six widespread anthocyanin derivatives: cyanidin 3-glucoside (CG), cyanidin 3-rutinoside (CR), cyanidin 3-galactoside (CGL), malvidin (M), malvidin 3-glucoside (MG) and malvidin 3,5-diglucoside (MDG) was studied in 1% HCl methanol solution by time-resolved phosphorescence detection (TRPD) of (1)O(2) and photostationary actinometry using perinaphthenone and methylene blue as sensitizers, respectively. The average value of the total (k(0)) and chemical (k(c)) quenching rate constants were approximately 4 x 10(8) M(-1) s(-1) and 3 x 10(6) M(-1) s(-1), respectively, indicating the good performance of the studied anthocyanins as catalytic quenchers of (1)O(2). The quenching efficiency was larger for malvidin than for cyanidin derivatives, probably by the extra electron-donating methoxy group in ring B of the malvidin derivatives; and it was also dependent on the number and type of glycosylated substitution. As observed for other phenolic-like derivatives, the quenching of (1)O(2) by anthocyanins was mediated by a charge-transfer mechanism, which was modulated by the total number of -OR substituents that increases the electron-donating ability of these compounds.