Kasem Nithipatikom

Superoxide reacts with hydroethidine but forms a fluorescent product that is distinctly different from ethidium: Potential implications in intracellular fluorescence detection of superoxide

Hydroethidine (HE) or dihydroethidium (DHE), a redox-sensitive probe, has been widely used to detect intracellular superoxide anion. It is a common assumption that the reaction between superoxide and HE results in the formation of a two-electron oxidized product, ethidium (E+), which binds to DNA and leads to the enhancement of fluorescence (excitation, 500-530 nm; emission, 590-620 nm). However, the mechanism of oxidation of HE by the superoxide anion still remains unclear. In the present study, we show that superoxide generated in several enzymatic or chemical systems (e.g., xanthine/xanthine oxidase, endothelial nitric oxide synthase, or potassium superoxide) oxidizes HE to a fluorescent product (excitation, 480 nm; emission, 567 nm) that is totally different from E+. HPLC measurements revealed that the HE/superoxide reaction product elutes differently from E+. This new product exhibited an increase in fluorescence in the presence of DNA. Mass spectral data indicated that the molecular weight of the HE/superoxide reaction product is 330, while ethidium has a molecular weight of 314. We conclude that the reaction between superoxide and HE forms a fluorescent marker product that is different from ethidium. Potential implications of this finding in intracellular detection and imaging of superoxide are discussed.

Production of 20-HETE and Its Role in Autoregulation of Cerebral Blood Flow

In the brain, pressure-induced myogenic constriction of cerebral arteriolar muscle contributes to autoregulation of cerebral blood flow (CBF). This study examined the role of 20-HETE in autoregulation of CBF in anesthetized rats. The expression of P-450 4A protein and mRNA was localized in isolated cerebral arteriolar muscle of rat by immunocytochemistry and in situ hybridization. The results of reverse transcriptase-polymerase chain reaction studies revealed that rat cerebral microvessels express cytochrome P-450 4A1, 4A2, 4A3, and 4A8 isoforms, some of which catalyze the formation of 20-HETE from arachidonic acid. Cerebral arterial microsomes incubated with [(14)C]arachidonic acid produced 20-HETE. An elevation in transmural pressure from 20 to 140 mm Hg increased 20-HETE concentration by 6-fold in cerebral arteries as measured by gas chromatography/mass spectrometry. In vivo, inhibition of vascular 20-HETE formation with N-methylsulfonyl-12, 12-dibromododec-11-enamide (DDMS), or its vasoconstrictor actions using 15-HETE or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), attenuated autoregulation of CBF to elevations of arterial pressure. In vitro application of DDMS, 15-HETE, or 20-HEDE eliminated pressure-induced constriction of rat middle cerebral arteries, and 20-HEDE and 15-HETE blocked the vasoconstriction action of 20-HETE. Taken together, these data suggest an important role for 20-HETE in the autoregulation of CBF.

Epoxy-Keto Derivative of Linoleic Acid Stimulates Aldosterone Secretion

Abstract—Plasma levels of aldosterone are not always predictable from the activity of renin and the concentration of potassium. Among the unexplained are elevated levels of aldosterone in some obese humans. Obesity is characterized by increased plasma fatty acids and oxidative stress. We postulated that oxidized fatty acids stimulate aldosteronogenesis. The most readily oxidized fatty acids are the polyunsaturated, and the most abundant of those is linoleic acid. We tested oxidized derivatives of linoleic acid for effects on rat adrenal cells. One derivative, 12,13-epoxy-9-keto-10(trans)-octadecenoic acid (EKODE), was particularly potent. EKODE stimulated aldosteronogenesis at concentrations from 0.5 to 5 &mgr;mol/L, and inhibited aldosteronogenesis at higher doses. EKODE’s stimulatory effect was most prominent when angiotensin and potassium effects were submaximal. The lipid’s mechanism of action was on the early pathway leading to pregnenolone; its action was inhibited by atrial natriuretic peptide. Plasma EKODE was measured by liquid chromatography/mass spectrometry. All human plasmas tested contained EKODE in concentrations ranging from 10−9 to 5×10−7 mol/L. In samples from 24 adults, levels of EKODE correlated directly with aldosterone (r =0.53, P =0.007). In the 12 blacks in that cohort, EKODE also correlated with body mass index and systolic pressure. Those other correlations were not seen in white subjects. The results suggest that oxidized derivatives of polyunsaturated fatty acids other than arachidonic are biologically active. Compounds like EKODE, derived from linoleic acid, may affect adrenal steroid production in humans and mediate some of the deleterious effects of obesity and oxidative stress, especially in blacks.

Bimakalim, an ATP-Sensitive Potassium Channel Opener, Mimics the Effects of Ischemic Preconditioning to Reduce Infarct Size, Adenosine Release, and Neutrophil Function in Dogs

BACKGROUND The primary goal of the present study was to determine whether the infarct size-reducing effect of preconditioning is associated with an increase in adenosine release from the ischemic myocardium during a prolonged occlusion period or the subsequent reperfusion period and by a decrease in neutrophil infiltration. A second objective was to determine whether bimakalim, a KATP channel opener, mimics the effects of ischemic preconditioning. METHODS AND RESULTS Barbital-anesthetized open-chest dogs were subjected to 60 minutes of left anterior descending coronary artery (LAD) occlusion followed by 3 hours of reperfusion. In the preconditioning group, 5 minutes of LAD occlusion followed by 10 minutes of reperfusion was elicited before the 60-minute occlusion period. In two other groups, bimakalim 1 microgram/kg bolus followed by a 0.05 micrograms.kg-1.min-1 infusion or an equivalent volume of saline was administered intravenously 15 minutes before occlusion and continued until the time of reperfusion. In a final group, bimakalim was administered 10 minutes before reperfusion and continued until the end of the experiment. To measure the release of adenosine from the ischemic region, coronary venous blood samples were collected at various times during ischemia and after reperfusion, and the concentration of adenosine was measured. Myocardial infarct size was determined by triphenyl tetrazolium chloride; transmural myocardial blood flow, by radioactive microspheres. Transmural myeloperoxidase (MPO) activity, an index of neutrophil infiltration in the area at risk, was also measured. Preconditioning produced a marked reduction in infarct size (9.8 +/- 3.0% versus 28.6 +/- 5.2% in the control group, mean +/- SEM); adenosine release at 5, 10, 15, and 30 minutes of the 3-hour reperfusion period; and transmural MPO activity in the risk area. Similarly, pretreatment with bimakalim resulted in reductions in infarct size, adenosine release, and transmural MPO activity to an extent almost identical to that of preconditioning. When bimakalim was administered 10 minutes before reperfusion, the drug also produced a significant reduction in infarct size and transmural MPO activity; however, no significant reduction in coronary venous adenosine concentrations was observed. There were no significant differences in collateral blood flow between groups. CONCLUSIONS These results indicate that myocardial preconditioning in the canine heart produced by a short period of ischemia or a KATP channel opener is not mediated by an increase in adenosine release, as measured by coronary venous adenosine concentrations, during 60 minutes of occlusion or the initial 30 minutes of reperfusion. A significant reduction in transmural MPO activity in the ischemic area also appears to result from KATP channel activation and may play a role, at least in part, in the reduction in infarct size observed, particularly when a KATP channel opener is administered just before reperfusion.

The general anesthetic propofol increases brain N‐arachidonylethanolamine (anandamide) content and inhibits fatty acid amide hydrolase

Propofol (2,6‐diisopropylphenol) is widely used as a general anesthetic and for the maintenance of long‐term sedation. We have tested the hypothesis that propofol alters endocannabinoid brain content and that this effect contributes to its sedative properties. A sedating dose of propofol in mice produced a significant increase in the whole‐brain content of the endocannabinoid, N‐arachidonylethanolamine (anandamide), when administered intraperitoneally in either Intralipid or emulphor‐ethanol vehicles. In vitro, propofol is a competitive inhibitor (IC50 52 μM; 95% confidence interval 31, 87) of fatty acid amide hydrolase (FAAH), which catalyzes the degradation of anandamide. Within a series of propofol analogs, the critical structural determinants of FAAH inhibition and sedation were found to overlap. Other intravenous general anesthetics, including midazolam, ketamine, etomidate, and thiopental, do not affect FAAH activity at sedative‐relevant concentrations. Thiopental, however, is a noncompetitive inhibitor of FAAH at a concentration of 2 mM. Pretreatment of mice with the CB1 receptor antagonist SR141716 (1 mg kg−1, i.p.) significantly reduced the number of mice that lost their righting reflex in response to propofol. Pretreatment of mice with the CB1 receptor agonist, Win 55212‐2 (1 mg kg−1, i.p.), significantly potentiated the loss of righting reflex produced by propofol. These data indicate that CB1 receptor activity contributes to the sedative properties of propofol. These data suggest that propofol activation of the endocannabinoid system, possibly via inhibition of anandamide catabolism, contributes to the sedative properties of propofol and that FAAH could be a novel target for anesthetic development.

Membrane Potential-Dependent Inhibition of Platelet Adhesion to Endothelial Cells by Epoxyeicosatrienoic Acids

Objective—Epoxyeicosatrienoic acids (EETs) are potent vasodilators produced by endothelial cells. In many vessels, they are an endothelium-derived hyperpolarizing factor (EDHF). However, it is unknown whether they act as an EDHF on platelets and whether this has functional consequences. Methods and Results—Flow cytometric measurement of platelet membrane potential using the fluorescent dye DiBac4 showed a resting potential of −58±9 mV. Different EET regioisomers hyperpolarized platelets down to −69±2 mV, which was prevented by the non-specific potassium channel inhibitor charybdotoxin and by use of a blocker of calcium-activated potassium channels of large conductance (BKCa channels), iberiotoxin. EETs inhibited platelet adhesion to endothelial cells under static and flow conditions. Exposure to EETs inhibited platelet P-selectin expression in response to ADP. Stable overexpression of cytochrome P450 2C9 in EA.hy926 cells (EA.hy2C9 cells) resulted in release of EETs and a factor that hyperpolarized platelets and inhibited their adhesion to endothelial cells. These effects were again inhibited by charybdotoxin and iberiotoxin. Conclusions—EETs hyperpolarize platelets and inactivate them by inhibiting adhesion molecule expression and platelet adhesion to cultured endothelial cells in a membrane potential-dependent manner. They act as an EDHF on platelets and might be important mediators of the anti-adhesive properties of vascular endothelium.

Inhibition of Cytochrome P450ω-Hydroxylase A Novel Endogenous Cardioprotective Pathway

Cytochrome P450s (CYP) and their arachidonic acid (AA) metabolites have important roles in regulating vascular tone, but their function and specific pathways involved in modulating myocardial ischemia–reperfusion injury have not been clearly established. Thus, we characterized the effects of several selective CYP&ohgr;-hydroxylase inhibitors and a CYP&ohgr;-hydroxylase metabolite of AA, 20-hydroxyeicosatetraenoic acid (20-HETE), on the extent of ischemia–reperfusion injury in canine hearts. During 60 minutes of ischemia and particularly after 3 hours of reperfusion, 20-HETE was produced at high concentrations. A nonspecific CYP inhibitor, miconazole, and 2 specific CYP&ohgr;-hydroxylase inhibitors, 17-octadecanoic acid (17-ODYA) and N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), markedly inhibited 20-HETE production during ischemia–reperfusion and produced a profound reduction in myocardial infarct size (expressed as a percent of the area at risk) (19.6±1.7% [control], 8.4±2.5% [0.96 mg/kg miconazole], 5.9±2.2% [0.28 mg/kg 17-ODYA], and 10.8±1.8% [0.40 mg/kg DDMS], P<0.05, respectively). Conversely, exogenous 20-HETE administration significantly increased infarct size (26.9±1.9%, P<0.05). Several CYP&ohgr;-hydroxylase isoforms, which are known to produce 20-HETE such as CYP4A1, CYP4A2, and CYP4F, were demonstrated to be present in canine heart tissue and their activity was markedly inhibited by incubation with 17-ODYA. These results indicate an important endogenous role for CYP&ohgr;-hydroxylases and in particular their product, 20-HETE, in exacerbating myocardial injury in canine myocardium. The full text of this article is available online at http://circres.ahajournals.org.

2-Arachidonoylglycerol: A Novel Inhibitor of Androgen-Independent Prostate Cancer Cell Invasion

Endocannabinoids have been implicated in cancer. Increasing endogenous 2-arachidonoylglycerol (2-AG) by blocking its metabolism inhibits invasion of androgen-independent prostate cancer (PC-3 and DU-145) cells. Noladin ether (a stable 2-AG analog) and exogenous CB1 receptor agonists possess similar effects. Conversely, reducing endogenous 2-AG by inhibiting its synthesis or blocking its binding to CB1 receptors with antagonists increases the cell invasion. 2-AG and noladin ether decrease protein kinase A activity in these cells, indicating coupling of the CB1 receptor to downstream effectors. The results suggest that cellular 2-AG, acting through the CB1 receptor, is an endogenous inhibitor of invasive prostate cancer cells.

Identification of the 11,14,15- and 11,12,15-Trihydroxyeicosatrienoic Acids as Endothelium-derived Relaxing Factors of Rabbit Aorta

A number of endothelium-derived relaxing factors have been identified including nitric oxide, prostacyclin, and the epoxyeicosatrienoic acids. Previous work showed that in rabbit aortic endothelial cells, arachidonic acid was metabolized by a lipoxygenase to vasodilatory eicosanoids. The identity was determined by the present study. Aortic homogenates were incubated in the presence of [U-14C]arachidonic acid, [U-14C]arachidonic acid plus 15-lipoxygenase (soybean lipoxidase), or [U-14C]15-hydroxyeicosatetraenoic acid (15-HPETE) and analyzed by reverse phase high pressure liquid chromatography (RP-HPLC). Under both experimental conditions, there was a radioactive metabolite that migrated at 17.5–18.5 min on RP-HPLC. When the metabolite was isolated from aortic homogenates, it relaxed precontracted aortas in a concentration-dependent manner. Gas chromatography/mass spectrometry (GC/MS) of the derivatized metabolite indicated the presence of two products; 11,12,15-trihydroxyeicosatrienoic acid (THETA) and 11,14,15-THETA. A variety of chemical modifications of the metabolite supported these structures and confirmed the presence of a carboxyl group, double bonds, and hydroxyl groups. With the combination of 15-lipoxygenase, arachidonic acid, and aortic homogenate, an additional major radioactive peak was observed. This fraction was analyzed by GC/MS. The mass spectrum was consistent with this peak, containing both the 11-hydroxy-14,15-epoxyeicosatrienoic acid (11-H-14,15-EETA) and 15-H-11,12-EETA. The hydroxyepoxyeicosatrienoic acid (HEETA) fraction also relaxed precontracted rabbit aorta. Microsomes derived from rabbit aortas also synthesized 11,12,15- and 11,14,15-THETAs from 15-HPETE, and pretreatment with the cyctochrome P450 inhibitor, miconazole, blocked the formation of these products. The present studies suggest that arachidonic acid is metabolized by 15-lipoxygenase to 15-HPETE, which undergoes an enzymatic rearrangement to 11-H-14,15-EETA and 15-H-11,12-EETA. Hydrolysis of the epoxy group results in the formation of 11,14,15- and 11,12,15-THETA, which relaxed rabbit aorta. Thus, the 15-series THETAs join prostacyclin, nitric oxide, and epoxyeicosatrienoic acids as new members of the family of endothelium-derived relaxing factors.

Effects of nicorandil and glyceryl trinitrate on infarct size, adenosine release, and neutrophil infiltration in the dog

OBJECTIVE The major aim of this study was to determine if nicorandil, a potassium channel opener nitrate, produces a reduction in myocardial infarct size at a non-hypotensive dose in dogs and to determine if this effect is the result of an increase in adenosine release or reduction in neutrophil infiltration into the ischaemic area. Glyceryl trinitrate was used for purposes of comparison. METHODS Barbitone anaesthetised dogs were subjected to 60 min of left anterior descending coronary artery occlusion followed by 3 h of reperfusion. Nicorandil (100 microgram.kg-1 bolus followed by a 10 microgram.kg-1.min-1 infusion; NC/pre group), glyceryl trinitrate (10 microgram.kg-1 bolus followed by a 1 microgram.kg-1.min-1 infusion; GTN/pre group), or an equivalent volume of saline (control group) were given intravenously 15 min before occlusion and continued to the time of reperfusion. In two other groups, nicorandil (NC/post group) or glyceryl trinitrate (GTN/post group) were given 10 min before reperfusion and continued until the end of the experiment. To measure the release of adenosine from the ischaemic region, coronary venous blood samples were collected before occlusion, during occlusion, and at various times following reperfusion. Myocardial infarct size was determined by triphenyltetrazolium chloride and transmural myocardial blood flow by radioactive microspheres. Transmural myeloperoxidase activity, an index of neutrophil infiltration, was measured in biopsies obtained from the area at risk. RESULTS Pretreatment with nicorandil and glyceryl trinitrate caused a marked reduction in myocardial infarct size expressed as percent of the area at risk [NC/pre group, 7.8(SEM 1.6)%; GTN/pre group, 11.9(2.3)%; control group, 31.0(5.6)%]. When nicorandil and glyceryl trinitrate were given before reperfusion, both drugs still produced a significant reduction in infarct size [NC/post group, 13.8(2.0)%; GTN/post group, 18.9(4.3)%]. Coronary venous adenosine concentrations during reperfusion were significantly lower in both nicorandil and glyceryl trinitrate pretreated groups, but not in the post-treated groups. Transmural myeloperoxidase activity was significantly lower in both nicorandil treated groups. CONCLUSIONS Pretreatment with a non-hypotensive dose of nicorandil or glyceryl trinitrate markedly reduces myocardial infarct size and adenosine release from the ischaemic-reperfused area. These agents were also effective, but to a lesser degree, when given just before reperfusion. The cardioprotective actions of nicorandil appear to be related not only to its potassium channel opening activity but also in part to its nitrate activity.