Effect of monochlorohydrins of linoleic acid on guinea-pig cardiac papillary muscles

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.

Effect of phosphatidylcholine chlorohydrins on human erythrocytes

Hypochlorite generated in vivo under pathological conditions is a known oxidant and chlorinating agent, able to react with proteins and lipids, which affects the stability of biological membranes. Reaction with unsaturated fatty acyl chains in glycerophospholipids such as phosphatidylcholine results in the formation of chlorohydrins. The aim of this study was to determine the effects of chlorohydrins formed by the reaction of hypochlorite with 1-stearoyl-2-oleoyl-, 1-stearoyl-2-linoleoyl-, and 1-stearoyl-2-arachidonylphosphatidylcholine on biophysical properties of bilayers and their effects on human erythrocytes. Using electrospray mass spectrometry we observed complete conversion of the lipids into chlorohydrins, which resulted in a decrease in the rotational correlation time and an increase in the order parameter of liposomes. Unilamellar chlorohydrin liposomes had a lower permeation coefficient for calcein than liposomes made of parent lipids. Flow cytometry demonstrated fast incorporation of uni and multilamellar chlorohydrin liposomes labeled with NBD-phosphatidylethanolamine into erythrocytes. This effect was accompanied by changes in erythrocyte shape (echinocyte formation) and aggregation. Similar but less pronounced effects were noticed for parent lipids only after longer incubation. Chlorohydrins showed also a stronger hemolytic action, proportional to the lipid:erythrocyte ratio. These results are important for understanding the effects of HOCl on mammalian cells, such as might occur in inflammatory pathology.

Identification of lysophosphatidylcholine-chlorohydrin in human atherosclerotic lesions

Lysophosphatidylcholine (LysoPtdCho) levels are elevated in sera in patients with atherosclerosis and in atherosclerotic tissue. Previous studies have shown that reactive chlorinating species attack plasmalogens in human coronary artery endothelial cells (HCAEC), forming lysoPtdCho and lysoPtdCho-chlorohydrin (lysoPtdCho-ClOH). The results herein demonstrate for the first time that lysoPtdCho-ClOH is elevated over 60-fold in human atherosclerotic lesions. In cultured HCAEC, 18:0 lysoPtdCho-ClOH led to a statistically significant increase in P-selectin cell-surface expression, but unlike 18:1 lysoPtdCho did not lead to cyclooxygenase-2 protein expression. These data show that 18:0 lysoPtdCho-ClOH is elevated in atherosclerotic tissue and may have unique pro-atherogenic properties compared to lysoPtdCho.

Phospholipid chlorohydrin induces leukocyte adhesion to ApoE-/- mouse arteries via upregulation of P-selectin

HOCl-modified low-density lipoprotein (LDL) has proinflammatory effects, including induction of inflammatory cytokine production, leukocyte adhesion, and ROS generation, but the components responsible for these effects are not completely understood. HOCl and the myeloperoxidase-H(2)O(2)-halide system can modify both protein and lipid moieties of LDL and react with unsaturated phospholipids to form chlorohydrins. We investigated the proinflammatory effects of 1-stearoyl-2-oleoyl-sn-3-glycerophosphocholine (SOPC) chlorohydrin on artery segments and spleen-derived leukocytes from ApoE(-/-) and C57 Bl/6 mice. Treatment of ApoE(-/-) artery segments with SOPC chlorohydrin, but not unmodified SOPC, caused increased leukocyte-arterial adhesion in a time- and concentration-dependent manner. This could be prevented by pretreatment of the artery with P-selectin or ICAM-1-blocking antibodies, but not anti-VCAM-1 antibody, and immunohistochemistry showed that P-selectin expression was upregulated. However, chlorohydrin treatment of leukocytes did not increase expression of adhesion molecules LFA-1 or PSGL-1, but caused increased release of ROS from PMA-stimulated leukocytes by a CD36-dependent mechanism. The SOPC chlorohydrin-induced adhesion and ROS generation could be abrogated by pretreatment of the ApoE(-/-) mice with pravastatin or a nitrated derivative, NCX 6550. These findings suggest that phospholipid chlorohydrins formed in HOCl-treated LDL could contribute to the proinflammatory effects observed for this modified lipoprotein in vitro.

Chlorinated lipids and fatty acids: an emerging role in pathology

Although the existence of halogenated lipids in lower organisms has been known for many years, it is only since the 1990s that interest in their occurrence in mammalian systems has developed. Chlorinated (and other halogenated) lipids can arise from oxidation by hypohalous acids, such as HOCl, which are products of the phagocytic enzyme myeloperoxidase and are generated during inflammation. The major species of chlorinated lipids investigated to date are chlorinated sterols, fatty acid and phospholipid chlorohydrins, and alpha-chloro fatty aldehydes. While all of these chlorinated lipids have been shown to be produced in model systems from lipoproteins to cells subjected to oxidative stress, as yet only alpha-chloro fatty aldehydes, such as 2-chlorohexadecanal, have been detected in clinical samples or animal models of disease. alpha-Chloro fatty aldehydes and chlorohydrins have been found to have a number of potentially pro-inflammatory effects ranging from toxicity to inhibition of nitric oxide synthesis and upregulation of vascular adhesion molecules. Thus evidence is building for a role of chlorinated lipids in inflammatory disease, although much more research is required to establish the contributions of specific compounds in different disease pathologies. Preventing chlorinated lipid formation and indeed other HOCl-induced damage, via the inhibition of myeloperoxidase, is an area of growing interest and may lead in the future to antimyeloperoxidase-based antiinflammatory therapy. However, other chlorinated lipids, such as punaglandins, have beneficial effects that could offer novel therapies for cancer.

Studies of phospholipid oxidation by electrospray mass spectrometry: from analysis in cells to biological effects

The oxidation of lipids is important in many pathological conditions and lipid peroxidation products such as 4-hydroxynonenal (HNE) and other aldehydes are commonly measured as biomarkers of oxidative stress. However, it is often useful to complement this with analysis of the original oxidized phospholipid. Electrospray mass spectrometry (ESMS) provides an informative method for detecting oxidative alterations to phospholipids, and has been used to investigate oxidative damage to cells, and low-density lipoprotein, as well as for the analysis of oxidized phosphatidylcholines present in atherosclerotic plaque material. There is increasing evidence that intact oxidized phospholipids have biological effects; in particular, oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycerophosphocholine (PAPC) have been found to cause inflammatory responses, which could be potentially important in the progression of atherosclerosis. The effects of chlorohydrin derivatives of lipids have been much less studied, but it is clear that free fatty acid chlorohydrins and phosphatidylcholine chlorohydrins are toxic to cells at concentrations above 10 micromolar, a range comparable to that of HNE and oxidized PAPC. There is some evidence that chlorohydrins have biological effects that may be relevant to atherosclerosis, but further work is needed to elucidate their pro-inflammatory properties, and to understand the mechanisms and balance of biological effects that could result from oxidation of complex mixtures of lipids in a pathophysiological situation.

Effects of linoleic acid metabolites on electrical activity in adult rat ventricular myocytes

Leukotoxin (Lx), an epoxide derivative of linoleic acid, has been suggested to be a toxic mediator of multiple organ failure in burn patients and of acute respiratory distress syndrome. Lx production was recently shown during myocardial ischemia/reperfusion. However, a recent study suggested that to be toxic Lx must be metabolized to Lx-diol. In the present study, isolated adult rat ventricular myocytes were studied with the whole-cell patch-clamp technique to determine the effects of these compounds on cardiac electrical activity. Measurements of action potentials showed that neither linoleic acid nor Lx (100 microM) caused any significant changes in action potential properties. However, Lx-diol in the range of 10-100 microM produced a dose dependent increase in duration and a decrease in overshoot of the action potential. Subsequent voltage clamp experiments isolating Na current (INa) and transient outward K current (Ito) revealed that Lx-diol inhibited INa and Ito by about 80% at 100 microM, while linoleic acid and Lx had no effect on these currents at the same concentration. While Lx-diol produced the same inhibition of INa and Ito at 100 microM, its effects were more potent on Ito with significant inhibition at 10 microM. Lx-diol also hastened the activation kinetics of Ito but not INa. The action of Lx-diol was rapid (reaching steady state in 3-5 min) and was reversible in 5-10 min following washout. Thus, Lx-diol could favor arrhythmias or cardiac arrest in intact heart and may be responsible for the cardiac problems seen in systemic inflammatory response syndrome. These results further support the suggestion that Lx is not toxic in the heart but rather must be metabolized to Lx-diol to produce toxic effects on cardiac muscle.

Calcium is required for quasi-lipoxygenase activity of hemoproteins

Bovine and guinea pig heart homogenates, porcine leukocyte homogenate, and human hemolysate were found to vigorously oxidize linoleic acid, with lipoxygenase-like activity, to its hydroperoxy, epoxy, hydroxy-epoxy, and keto compounds in the presence of calcium chloride. In the absence of calcium, the reaction was significantly reduced. Attempts to characterize this quasi-lipoxygenase activity revealed that calcium potentiated the quasi-lipoxygenase activities of hemoproteins (hemoglobin, myoglobin, myeloperoxidase, catalase, cytochrome c) and hemin at the physiological pH of 7.5. Lipid peroxidation by hemoproteins was inhibited by albumin and erythrocyte membranes in blood, as well as by a low concentration of calcium in cells. However, it seems possible that in extracellular fluid, which contains a high concentration of calcium and a low concentration of albumin, hemoprotein released from damaged cells could oxidize unsaturated fatty acids derived by phospholipase-A2 from phospholipids of damaged cellular membranes. In a model of quasi-lipoxygenase activation under such conditions, lipids of erythrocyte membranes were oxidized by hemoglobin in the presence of phospholipase-A2 and calcium. The effect of nitrogen oxide, paraquat, and bleomycin on oxidation by hemoproteins and hemin was also discussed.

Calcium ions potentiate lipoxygenase activity of cytochrome c at the physiological pH

Cytochrome c oxidized linoleic acid, with lipoxygenase-like activity, to 9-hydroperoxy-10,12-octadecadienoic acid (9-HpODE), 13-hydroperoxy-9,11-octadecadienoic acid (13-HpODE), 13-keto-9,11-octadecadienoic acid (13-KODE), and hydroxy-epoxy-octadecenoic acids (HEPOs) in the presence of calcium chloride at the physiological pH of 7.5. In the absence of calcium, the reaction was remarkably reduced. Statistically significant increase of 13-KODE was observed 1 min after the reaction was started by adding calcium. Calcium chloride at concentrations as low as 30 microM caused statistically significant increase of 13-KODE production in the presence of 1 microM cytochrome c, and cytochrome c at concentrations as low as 10 nM caused statistically significant increase of 13-KODE production in the presence of 2 mM calcium. The addition of bleomycin enhanced the reaction, and the addition of adriamycin attenuated the reaction. The same oxidized linoleic acid products were found in the submitochondrial particles which were hydrolyzed by phospholipase-A2 in the presence of calcium. Lipoxygenase activity potentiated by calcium may be involved in the lipid peroxidation in the submitochondrial particles hydrolyzed by phospholipase-A2.