Effect of phosphatidylcholine chlorohydrins on human erythrocytes

Computational Investigations of Reaction Mechanisms and Transformation Products of Olefins with Hypochlorous Acid

Hypochlorous acid (HOCl) as the main component in chlorination and also as the innate immune factor relevant to immune defense has attracted considerable attention. Electrophilic addition reaction of olefins with HOCl, one of the most important prototype of chemical reactions, has been intensively studied for a long time; however, it has not been fully understood yet. In this study, addition reaction mechanisms and transformation products of model olefins with HOCl were systematically investigated by the density functional theory method. The results indicate that the traditionally believed stepwise mechanism with a chloronium-ion intermediate is only suitable for olefins substituted with electron-donating groups (EDGs) and weak electron-withdrawing groups (EWGs) but it is a carbon-cation intermediate that is favorable for EDGs featuring p-π or π-π conjugation with the C═C moiety. Moreover, olefins substituted with moderate or/and strong EWGs prefer the concerted and nucleophilic addition mechanisms, respectively. Epoxide and truncated aldehyde as the main transformation products can be generated from chlorohydrin through a series of reactions involving hypochlorite; however, their generation is kinetically not as feasible as the formation of chlorohydrin. The reactivity of three chlorinating agents (HOCl, Cl₂O, and Cl₂) and the case study of chlorination and degradation of cinnamic acid were also explored. Additionally, APT charge on the double-bond moiety in olefin and energy gap (ΔE) between the highest occupied molecular orbital (HOMO) energy of olefin and the lowest unoccupied molecular orbital (LUMO) energy of HOCl were found to be good parameters to distinguish the regioselectivity of chlorohydrin and reactivity of olefin, respectively. The findings of this work are helpful in further understanding the chlorination reactions of unsaturated compounds and identifying complicated transformation products.

ROS from Physical Plasmas: Redox Chemistry for Biomedical Therapy

Physical plasmas generate unique mixes of reactive oxygen and nitrogen species (RONS or ROS). Only a bit more than a decade ago, these plasmas, operating at body temperature, started to be considered for medical therapy with considerably little mechanistic redox chemistry or biomedical research existing on that topic at that time. Today, a vast body of evidence is available on physical plasma-derived ROS, from their spatiotemporal resolution in the plasma gas phase to sophisticated chemical and biochemical analysis of these species once dissolved in liquids. Data from in silico analysis dissected potential reaction pathways of plasma-derived reactive species with biological membranes, and in vitro and in vivo experiments in cell and animal disease models identified molecular mechanisms and potential therapeutic benefits of physical plasmas. In 2013, the first medical plasma systems entered the European market as class IIa devices and have proven to be a valuable resource in dermatology, especially for supporting the healing of chronic wounds. The first results in cancer patients treated with plasma are promising, too. Due to the many potentials of this blooming new field ahead, there is a need to highlight the main concepts distilled from plasma research in chemistry and biology that serve as a mechanistic link between plasma physics (how and which plasma-derived ROS are produced) and therapy (what is the medical benefit). This inevitably puts cellular membranes in focus, as these are the natural interphase between ROS produced by plasmas and translation of their chemical reactivity into distinct biological responses.

Chlorinated Phospholipids and Fatty Acids: (Patho)physiological Relevance, Potential Toxicity, and Analysis of Lipid Chlorohydrins

Chlorinated phospholipids are formed by the reaction of hypochlorous acid (HOCl), generated by the enzyme myeloperoxidase under inflammatory conditions, and the unsaturated fatty acyl residues or the head group. In the first case the generated chlorohydrins are both proinflammatory and cytotoxic, thus having a significant impact on the structures of biomembranes. The latter case leads to chloramines, the properties of which are by far less well understood. Since HOCl is also widely used as a disinfecting and antibacterial agent in medicinal, industrial, and domestic applications, it may represent an additional source of danger in the case of abuse or mishandling. This review discusses the reaction behavior of in vivo generated HOCl and biomolecules like DNA, proteins, and carbohydrates but will focus on phospholipids. Not only the beneficial and pathological (toxic) effects of chlorinated lipids but also the importance of these chlorinated species is discussed. Some selected cleavage products of (chlorinated) phospholipids and plasmalogens such as lysophospholipids, (chlorinated) free fatty acids and α-chloro fatty aldehydes, which are all well known to massively contribute to inflammatory diseases associated with oxidative stress, will be also discussed. Finally, common analytical methods to study these compounds will be reviewed with focus on mass spectrometric techniques.

MALDI-TOF MS to monitor the kinetics of phospholipase A2-digestion of oxidized phospholipids

Free fatty acids (FFA) are released through phospholipase A2 (PLA2), which cleaves the fatty acyl residue at the sn-2 position of phospholipids (PL). During inflammatory diseases, reactive oxygen species (such as HOCl) lead to the formation of oxidatively modified PL (e.g., chlorohydrin generation). It is still widely unknown to which extent the oxidation of PL influences their digestibility by PLA2. Additionally, investigations on the impact of the position of the unsaturated fatty acyl residue (sn-1 versus sn-2 position) and modifications of the headgroup (for instance phosphatidylcholine (PC) versus phosphatidylethanolamine (PE)) are also lacking. Therefore, the aim of this study is the investigation of these aspects using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry to elucidate the PL/lysophospholipid (LPL) ratios as measures of the PLA2 digestibility. We will show that oxidative modifications of PL by HOCl have a considerable impact on the PLA2 digestibility, i.e., oxidation of the unsaturated fatty acyl residues leads to a reduced digestibility of both PC and PE. Besides, it will be shown that MALDI MS is a convenient and reliable tool to investigate the related changes.

Stabilization of erythrocytes against oxidative and hypotonic stress by tannins isolated from sumac leaves (Rhus typhina L.) and grape seeds (Vitis vinifera L.)

Erythrocytes are constantly exposed to ROS due to their function in the organism. High tension of oxygen, presence of hemoglobin iron and high concentration of polyunsaturated fatty acids in membrane make erythrocytes especially susceptible to oxidative stress. A comparison of the antioxidant activities of polyphenol-rich plant extracts containing hydrolysable tannins from sumac leaves (Rhus typhina L.) and condensed tannins from grape seeds (Vitis vinifera L.) showed that at the 5-50 μg/ml concentration range they reduced to the same extent hemolysis and glutathione, lipid and hemoglobin oxidation induced by erythrocyte treatment with 400 μM ONOO(-) or 1 mM HClO. However, extract (condensed tannins) from grape seeds in comparison with extract (hydrolysable tannins) from sumac leaves stabilized erythrocytes in hypotonic NaCl solutions weakly. Our data indicate that both hydrolysable and condensed tannins significantly decrease the fluidity of the surface of erythrocyte membranes but the effect of hydrolysable ones was more profound. In conclusion, our results indicate that extracts from sumac leaves (hydrolysable tannins) and grape seeds (condensed tannins) are very effective protectors against oxidative damage in erythrocytes.

Detection of 3-chlorinated tyrosine residues in human cells by flow cytometry

Hypochlorite is a strong oxidant, generated under pathological conditions, with the potency to introduce chlorine atom into a number of molecules. 3-Chloro- and 3,5-dichlorotyrosine are documented to be generated by this oxidant and their elevated levels were found in many diseases. Thus, we decided to check the possibility of use of FITC-conjugated antibodies for flow cytometric detection of 3-chlorotyrosine residues in human cells (A549, MCF-7, HUVEC-ST) exposed to the action of hypochlorite. Additionally, we compared the effects of chlorohydrins and N-chloroamino acids as chlorine donors. Cell fixation and permeabilization was followed by incubation with rabbit polyclonal anti-3-chlorotyrosine primary antibody and subsequent staining with goat anti-rabbit FITC-labeled secondary antibody. For antibody isotypic control, normal rabbit IgG was employed. Hypochlorite appeared to be the most efficient from the chlorocompounds analyzed in chlorotyrozine generation in all cell lines. Statistically significant increase of fluorescence corresponding to the level of 3-chlorotyrosine residues was found in cells treated with hypochlorite even at non-toxic concentrations (<5μM). This effect was not observed in cells exposed to the action of chlorinated amino acids or chlorohydrins. The use of anti-3-chlorotyrosine antibodies in conjunction with fluorophore-conjugated secondary antibodies analysis allows for detection of 3-chlorotyrosine residues by flow cytometry in cells treated with low doses of hypochlorite.

Lipid oxidation by hypochlorous acid: chlorinated lipids in atherosclerosis and myocardial ischemia

Leukocytes, containing myeloperoxidase (MPO), produce the reactive chlorinating species, HOCl, and they have important roles in the pathophysiology of cardiovascular disease. Leukocyte-derived HOCl can target primary amines, alkenes and vinyl ethers of lipids, resulting in chlorinated products. Plasmalogens are vinyl ether-containing phospholipids that are abundant in tissues of the cardiovascular system. The HOCl oxidation products derived from plasmalogens are α-chlorofatty aldehyde and unsaturated molecular species of lysophosphatidylcholine. α-chlorofatty aldehyde is the precursor of both α-chlorofatty alcohol and α-chlorofatty acid. Both α-chlorofatty aldehyde and α-chlorofatty acid accumulate in activated neutrophils and have disparate chemotactic properties. In addition, α-chlorofatty aldehyde increases in activated monocytes, human atherosclerotic lesions and rat infarcted myocardium. This article addresses the pathways for the synthesis of these lipids and their biological targets.