Oxidative stress is associated with the increased production of reactive oxygen species or with a significant decrease in the effectiveness of antioxidant enzymes and nonenzymatic defense. The penetration of oxygen and free radicals in the hydrophobic interior of biological membranes initiates radical disintegration of the hydrocarbon “tails” of the lipids. This process is known as “lipid peroxidation”, and the accumulation of the oxidation products as peroxides and the aldehydes and acids derived from them are often used as a measure of oxidative stress levels. In total, 40 phenolic antioxidants were selected for a comparative study and analysis of their chain-breaking antioxidant activity, and thus as modulators of oxidative stress. This included natural and natural-like ortho-methoxy and ortho-hydroxy phenols, nine of them newly synthesized. Applied experimental and theoretical methods (bulk lipid autoxidation, chemiluminescence, in silico methods such as density functional theory (DFT) and quantitative structure–activity relationship ((Q)SAR) modeling) were used to clarify their structure–activity relationship. Kinetics of non-inhibited and inhibited lipid oxidation in close connection with inhibitor transformation under oxidative stress is considered. Special attention has been paid to chemical reactions resulting in the initiation of free radicals, a key stage of oxidative stress. Effects of substituents in the side chains and in the phenolic ring of hydroxylated phenols and biphenols, and the concentration were discussed.

The general approach disclosed herein opens the new possibilities of exploiting the oxidation processes followed by chemiluminescence (CL) emission for the assessment of an antioxidant potential of natural lipid materials and enables determination of the amount and strength of lipid-borne antioxidants in one experiment. The reliability of the analytical procedure is completely unaffected by an inevitable entering of oxidizable lipid portions into the probe chemiluminescent mixture, which is exemplarily illustrated for the case of vegetable oils which served as sources of antioxidant-containing lipids. As a matter of fact, the difference in the effective radical-scavenging rate constants, determined for the antioxidative constituents of the sunflower and corn oils, perfectly matches the distinction of their qualitative tocopherol contents. In addition to the antiradical activity of lipid samples, the antioxidant potential of the latter may be modified by their influence on hydroperoxide stability, as it has been also demonstrated in the present work.

Extracts from tissues of the holothuria Eupentacta fraudatrix suppress the oxy-chemiluminescence of ethylbenzene in chlorobenzene initiated by azobisisobutyronitrile thermolysis and enhanced by energy transfer to 9,10-dibromoanthracene. The decrease of the chemiexcitation rate in the reaction between peroxyl radicals is caused by radical interception by the antioxidants contained in the extracts. The concentrations of the antioxidants in the extracts and the rate constants of their reactions with peroxyl radicals have been estimated from chemiluminescence kinetics.

Background: Through measurements of the heart rate variability (HRV) accompanied by the pertinent biomarker assays, the effects of nicotine and byproducts derived from alternative nicotine delivery systems (ANDS) on the autonomic nervous system (ANS) and hormonal system have been investigated. Methods: HRV was studied in a group of volunteers (17 people), involving non-smokers, i.e., who never smoked before (11), ex-smokers (4) and active smokers (2). ANDS and smoking simulators, including regular, nicotine-free and electronic cigarettes; tobacco heating systems; chewing gums and nicotine packs of oral fixation (nic-packs), were used. Blood pressure, levels of stress hormones in saliva and catecholamines in the blood were also monitored. Results: HRV analysis showed relatively small changes in HRV and in the other studied parameters with the systemic use of nic-packs with low and moderate nicotine contents (up to 6 mg) compared to other ANDS. Conclusions: The HRV method is proven to be a promising technique for evaluation of the risks associated with smoking, dual use of various ANDS and studying the biomedical aspects of smoking cessation. Nic-packs are shown to be leaders in biological safety among the studied ANDS. A sharp surge in the activity of the sympathetic division of the ANS within the first minutes of the use of nicotine packs implies that nicotine begins to act already at very low doses (before entering the blood physically in any significant amount) through fast signal transmission to the brain from the nicotinic and taste buds located in the mouth area.