Differential Effects of Linoleic Acid Metabolites on Cardiac Sodium Current

Abstract

9,10-Epoxy-12-octadecenoic acid (EOA), a metabolite of linoleic acid, causes cardiac arrest in dogs. Other metabolites of linoleic acid also have toxic effects. This study investigates the mechanism of action of four of these compounds on cardiac Na ϩ current (I Na ). The whole-cell patch-clamp technique was used to investigate the effects of EOA, 9,10-dihydroxy-12-octadecenoic acid (DHOA), and their corresponding methyl esters (9,10-epoxy-12-octadecenoic methyl ester, EOM; and 9,10-dihydroxy-12-octadecenoic methyl ester, DHOM) on I Na in isolated adult rat ventricular myocytes. Extracellular application of each compound elicited a concentration-dependent inhibition of I Na . The dose-response curve yielded 50% inhibition concentrations of 301 Ϯ 117 M for DHOA, 41 Ϯ 6 M for DHOM, 34 Ϯ 5 M for EOA, and 160 Ϯ 41 M for EOM. Although there was no effect on activation, 50 M DHOM, EOA, and EOM significantly hyperpolarized the steady-state inactivation curve by approximately Ϫ6 mV. Furthermore, EOM significantly increased the slope of the steady-state inactivation curve. These compounds also seemed to stabilize the inactivated state because the time for recovery from inactivation was significantly slowed from a control value of 12.9 Ϯ 0.5 ms to 30.5 Ϯ 3.3, 31.4 Ϯ 1.4, and 20.5 Ϯ 1.0 ms by 50 M DHOM, EOA, and EOM, respectively. These compounds have multiple actions on Na ϩ channels and that despite their structural similarities their actions differ from each other. The steady-state block of I Na suggests that either the pore is being blocked or the channels are prevented from gating to the open state. In addition, these compounds stabilize the inactivated state and promote increased population of a slower inactivated state.The role of fatty acids in signaling processes is becoming increasingly important. Various fatty acids have been shown to alter several ion currents, including Na ϩ (Xiao et al., 1995;Kang and Leaf, 1996), Ca 2ϩ (Huang et al., 1992;Hashimoto et al., 1999) Bogdanov et al., 1998;Crumb et al., 1999), and Cl Ϫ (Ordway et al., 1991). Arachidonic acid (C20:4) has been widely studied for the actions of the parent compound as well as the extensive metabolic pathways, including the prostaglandins and leukotrienes. Although less widely studied, linoleic acid (C18:2) is a major component of cell membrane phospholipids and is subject to some of the same metabolic pathways. A linoleic acid metabolite (LAM) of interest is 9,10-epoxy-12-octadecenoic acid (EOA), also known as leukotoxin. EOA is formed by lipid autoxidation in the lungs (Sevanian et al., 1979) and by spontaneous reaction of oxygen radicals with linoleic acid in neutrophil membranes (Hayakawa et al., 1996) (Fig. 1). Although undetectable in normal patients (Hayakawa et al., 1990), EOA has been associated with acute respiratory distress syndrome in burn patients where it can reach plasma concentrations up to 300 M (mean peak plasma concentration of 99 Ϯ 25 M) (Kosaka et al., 1994). EOA has also been shown to cause cardiac arrest in dogs (Fukush...

Dihydroxyoctadecamonoenoate esters inhibit the neutrophil respiratory burst

“…This effect can be largely blocked by administration of an sEH inhibitor (Smith et al 2005). The DiHOMEs exert a number of effects on mammalian cells including stimulating MCF-7 cell proliferation and acting as an endocrine disrupter (Markaverich et al 2005), modulating the sodium cation current in cardiac cells (Harrell and Stimers 2002), and increasing cellular oxidative stress (Viswanathan et al 2003). In mammalian cells, the DiHOMEs specifically inhibit mitochondrial function (Sisemore et al 2001;Moran et al 1997), suggesting one possible mechanism underlying EpOME-associated toxicity.…”

Salt Loading Increases Urinary Excretion of Linoleic Acid Diols and Triols in Healthy Human Subjects

“…Although cardiac and epithelial sodium channels are structurally unrelated, the data on cardiac sodium channels might point toward the distal tubule epithelial sodium channel as a possible target for inhibition by LA diols and triols. 19,20 Although the biological role and synthesis of LA-derived triols are uncharacterized in mammals, these metabolites are present in the urine 17 and are likely generated by the enzymatic rearrangement of linoleate hydroperoxides. 30 Other relevant findings suggesting associations between octadecanoids and hypertension have been reported recently.…”

“…[1][2][3][4][5][6][7]10 In addition, in vitro studies have demonstrated that LA metabolites inhibit cardiac sodium channels. 19,20 Several studies in rats have shown the development of salt-sensitive hypertension with the inability to excrete an acute salt load after dietary LA acid deprivation that is corrected by administration of LA, suggesting that LA is intimately involved with renal sodium handling. 8,9 The results we report here reveal an increase in urinary excretion of LA diols and triols during intravenous salt loading that correlate with sodium excretion.…”

“…19 Moreover, EpOMEs and DiHOMEs have been shown to stabilize the inactivated state of the inward cardiac Na ϩ current in isolated rat ventricular myocytes. 20 Therefore, it must be considered that evidence arguing for linkage between CYP-dependent arachidonate metabolism and sodium handling may also apply directly to linoleate metabolism, with modulation of membrane ion transport in the kidney forming a plausible link between the physiological regulation of Na ϩ balance and LA metabolism. To investigate this linkage, we conducted salt loading/depletion studies in human subjects and investigated the influence of this regimen on the urinary excretion of various oxygenated metabolites of linoleate and arachidonate.…”

Metabolomics reveals increased isoleukotoxin diol (12,13-DHOME) in human plasma after acute Intralipid infusion

“…Although it was once thought that sEH acted to render the leukotoxins safe by converting them to their diols, it now appears that the diols (including 12,13-DHOME) are the morepotent cytotoxins ( 29 ). Thus, inhibition of sEH ameliorates many of the toxic effects of the leukotoxins ( 39 ), whereas 12,13-DHOME adversely affects the electrophysiology of cells including oligodendrocytes ( 40 ) and cardiac myocytes ( 41 ). In addition, both 12(13)-and 9(10)-EpOME can be metabolized to the THF-diols ( Fig.…”