Determination of 20-hydroxyeicosatetraenoic acid in microsomal incubates using high-performance liquid chromatography-mass spectrometry (HPLC-MS)

A microsomal based method to detect aromatase activity in different brain regions of the rat using ultra performance liquid chromatography-mass spectrometry

Aromatase (ARO) is a cytochrome P450 enzyme that accounts for local estrogen production in the brain. The goal of this study was to develop a microsomal based assay to sensitively and reliably detect the low levels of ARO activity in different brain regions. Enzyme activity was detected based on the conversion of testosterone to estradiol. Quantity of estradiol was measured using ultra performance liquid chromatography-mass spectrometry. Detection was linear over a range of 2.5-200pg/ml estradiol, and was reproducible with intra- and inter-assay coefficients of variation (CV) <15%. Estradiol production using isolated microsomes was linear with time up to 30min as well as linearly related to amount of microsome. Substrate concentration curves revealed enzymatic kinetics (hippocampus: Vmax and Km: 0.57pmol estradiol/h per mg microsome and 48.58nM; amygdala: Vmax and Km: 1.69pmol estradiol/h per mg microsome and 48.4nM; preoptic area: Vmax and Km: 0.96pmol estradiol/h per mg microsome and 44.31nM) with testosterone used at a saturating concentration of 400nM. Anastrozole treatment blocked ARO activity in hippocampal and ovarian microsomes, indicating that the assay is specific for ARO. Also, we showed that the distribution of the long form ARO mRNA (CYP19A1) in different regions of the brain is correlated with ARO activity, with highest levels in the amygdala, followed by preoptic area and hippocampus. In the frontal cortex, very little long form ARO mRNA, and little to no ARO activity, were detected. These findings demonstrate that the microsomal incubation (MIB) assay is a sensitive and reliable method for quantifying ARO activity in discrete brain regions.

Exploratory investigation reveals parallel alteration of plasma fatty acids and eicosanoids in coronary artery disease patients

Fatty acids and eicosanoids are two important classes of signaling lipid molecules involved in the pathogenesis of cardiovascular diseases. To investigate the physiological functions and interplay between fatty acids and eicosanoids in coronary artery disease (CAD) patients, we developed an analytical approach for parallel quantitative analysis of plasma fatty acids and eicosanoids, using gas chromatography-tandem mass spectrometry (GC-MS/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this study, 26 fatty acids and 12 eicosanoids were confidently detected in 12 patients with confirmed coronary artery disease and 11 healthy subjects. Pattern recognition analysis (principal components analysis, orthogonal partial least-square discriminate analysis, and hierarchical clustering analysis) demonstrated that the plasma lipid profile of fatty acids and eicosanoids enabled robust discrimination of CAD patients versus healthy subjects. Significant differences in six fatty acids and five eicosanoids were noted among CAD patients and healthy subjects. The development of cardiovascular disease-induced metabolic change of fatty acids and eicosanoids, such as eicosapentaenoic acid, docosahexaenoic acid, arachidonic acid, hydroxyeicosatetraenoic acids and hydroxyoctadecadienoic acid, were consistent with previous isolated observations. Moderate-strong correlations between three plasma fatty acids and three eicosanoids from arachidonic acid metabolism were also observed. In brief, findings from this exploratory study offered a new insight on the roles of various bioactive lipid molecules in the development of coronary artery disease biomarkers.

Cerebrospinal fluid 20-HETE is associated with delayed cerebral ischemia and poor outcomes after aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Delayed cerebral ischemia (DCI) is a major complication after aneurysmal subarachnoid hemorrhage (aSAH); it is manifested by changes in cerebral blood flow accompanied by neurological decline, and it results in long-term functional and neuropsychological impairment. Preclinical evidence has demonstrated that the arachidonic acid metabolite, 20-hydroxyeicosatetraenoic acid (20-HETE), affects cerebral microvascular tone and cerebral blood flow after aSAH. The purpose of this study was to determine whether cerebrospinal fluid 20-HETE levels were associated with DCI and long-term neuropsychological outcomes in aSAH patients.

METHODS

Cerebrospinal fluid samples were collected twice daily through 14 days after hemorrhage on 108 acute, adult, aSAH patients. Samples were analyzed for 20-HETE via HPLC MSQ single quadrupole mass spectrometry. DCI was defined as the presence of impaired cerebral blood flow (angiographic vasospasm, elevated transcranial Dopplers, abnormal computed tomography or magnetic resonance perfusion scans) accompanied by neurological deterioration. Outcomes, including death and neuropsychological testing, were completed at 3 months after hemorrhage.

RESULTS

Detectable 20-HETE levels were observed in 31% of patient samples and were associated with severity of hemorrhage (Hunt & Hess [HH], P=0.04; Fisher, P=0.05). Detection of 20-HETE was not associated with angiographic vasospasm (P=0.34); however, detectable 20-HETE was significantly associated with DCI (P=0.016). Our data also suggest that detectable 20-HETE was associated with decreased performance in 5 neuropsychological domains.

CONCLUSIONS

These results provide the first clinical evidence that cerebrospinal fluid 20-HETE concentrations are associated with DCI and poor outcomes, and this provides impetus for future studies to elucidate the clinical utility of inhibiting 20-HETE formation as a novel therapeutic intervention in patients with aSAH.

Ultra-pressure liquid chromatography/tandem mass spectrometry targeted profiling of arachidonic acid and eicosanoids in human colorectal cancer

Cumulative evidence shows that eicosanoids such as prostaglandins, leukotrienes, thromboxanes and hydroxy eicosatetraenoic acids play an important role in associating inflammation with human colorectal cancer (CRC). In this study an ultra-pressure liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed and validated for the targeted profiling of eight relevant eicosanoids and the major metabolic precursor, arachidonic acid (AA), in human colon. Multiple reaction monitoring (MRM) experiments were performed in negative electrospray ionization mode. The metabolites were separated using a C(18) column consisting of 1.7 µm ethylene-bridged hybrid particles (100 × 2.1 mm i.d.) and gradient elution (50 to 95% of solvent B) with a mobile phase comprising water (0.1% formic acid) [solvent A] and acetonitrile (0.1% formic acid) [solvent B] at a flow rate of 0.4 mL/min. The analysis time for each sample was 5.5 min. Our UPLC/MS/MS method demonstrated satisfactory validation results in terms of selectivity, sensitivity, matrix effect, linearity, extraction efficiency, intra- and inter-day precision, accuracy and autosampler stability. The method was applied for the clinical profiling of matched pairs of cancerous and normal colon mucosae obtained from eight colorectal cancer patients. Endogenous levels of AA and selected eicosanoids such as prostaglandin E(2) (PGE(2)), prostacyclin (PGI(2)) [assayed as its stable hydrolytic product 6-keto-prostaglandin(1α) (6-k PGF(1α))] and 12-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12-HETE) were found to be significantly different (p <0.05; paired t-test) between cancerous and normal mucosae.

Rapid, simultaneous quantitation of mono and dioxygenated metabolites of arachidonic acid in human CSF and rat brain

Currently, there are few biomarkers to predict the risk of symptomatic cerebral vasospasm (SV) in subarachnoid hemorrhage (SAH) patients. Mono and dioxygenated arachidonic acid metabolites, involved in the pathogenesis of ischemic injury, may serve as indicators of SV. This study developed a quantitative UPLC-MS/MS method to simultaneously measure hydroxyeicosatetraenoic acid (HETE), dihydroxyeicosatrienoic acid (DiHETrE), and epoxyeicosatrienoic acid (EET) metabolites of arachidonic acid in cerebrospinal fluid (CSF) samples of SAH patients. Additionally, we determined the recovery of these metabolites from polyvinylchloride (PVC) bags used for CSF collection. Linear calibration curves ranging from 0.208 to 33.3 ng/ml were validated. The inter-day and intra-day variance was less than 15% at most concentrations with extraction efficiency greater than 73%. The matrix did not affect the reproducibility and reliability of the assay. In CSF samples, peak concentrations of 8,9-DiHETrE, 20-HETE, 15-HETE, and 12-HETE ranged from 0.293 to 24.9 ng/ml. In rat brain cortical tissue samples, concentrations of 20-, 15-, 12-HETE, 8,9-EET, and 14,15-, 11,12-DiHETrE ranged from 0.57 to 23.99 pmol/g wet tissue. In rat cortical microsomal incubates, all 10 metabolites were measured with formation rates ranging from 0.03 to 7.77 pmol/mg/min. Furthermore, 12-HETE and EET metabolites were significantly altered by contact with PVC bags at all time points evaluated. These data demonstrate that the simultaneous measurement of these compounds in human CSF and rat brain can be achieved with a UPLC-MS/MS system and that this method is necessary for evaluation of these metabolites as potential quantitative biomarkers in future clinical trials.

Microsomal omega-hydroxylated metabolites of N-arachidonoyl dopamine are active at recombinant human TRPV1 receptors

N-Arachidonoyl dopamine (NADA) is an endogenous lipid that modulates signal transduction in neuronal and immune pathways. NADA activates the non-selective cation channel, transient receptor potential vanilloid type 1 (TRPV(1)) and cannabinoid receptor 1. That NADA is comprised of an arachidonic acid (AA) backbone suggests that it may be metabolized through many of the enzymes that act upon AA such as the other AA-derived signaling lipids, the endogenous cannabinoids. To investigate the metabolism of NADA through the cytochrome P450 (CYP450) metabolic pathway, we studied the in vitro rat liver microsomal production of hydroxylated metabolites and their activity at recombinant human TRPV(1) receptors. We showed that following microsomal activation in the presence of NADA, omega and (omega-1) hydroxylated metabolites (19- and 20-HETE-DA) were formed. These metabolites were active at recombinant human TRPV(1) receptors, inducing a dose-dependent calcium influx. Both metabolites exhibited lower potency compared to NADA. We conclude that CYP450 enzymes are capable of metabolizing this signaling lipid forming a larger family of potential neuromodulators.

A liquid chromatography/mass spectrometric method for simultaneous analysis of arachidonic acid and its endogenous eicosanoid metabolites prostaglandins, dihydroxyeicosatrienoic acids, hydroxyeicosatetraenoic acids, and epoxyeicosatrienoic acids in rat brain tissue

A sensitive, specific, and robust liquid chromatography/mass spectrometric (LC/MS) method was developed and validated that allows simultaneous analysis of arachidonic acid (AA) and its cyclooxygenase, cytochrome P450, and lipoxygenase pathway metabolites prostaglandins (PGs), dihydroxyeicosatrienoic acids (DiHETrEs), hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs), including PGF(2alpha), PGE(2), PGD(2), PGJ(2), 14,15-DiHETrE, 11,12-DiHETrE, 8,9-DiHETrE, 5,6-DiHETrE, 20-HETE, 15-HETE, 12-HETE, 9-HETE, 8-HETE, 5-HETE, 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET in rat brain tissues. Deuterium labeled PGF(2alpha)-d(4), PGD(2)-d(4), 15(S)-HETE-d(8), 14,15-EET-d(8), 11,12-EET-d(8), 8,9-EET-d(8), and AA-d(8) were used as internal standards. Solid phase extraction was used for sample preparation. A gradient LC/MS method using a C18 column and electrospray ionization source under negative ion mode was optimized for the best sensitivity and separation within 35 min. The method validation, including LC/MS instrument qualification, specificity, calibration model, accuracy, precision (without brain matrix and with brain matrix), and extraction efficiency were performed. The linear ranges of the calibration curves were 2-1000 pg for PGs, DiHETrEs, HETEs, and EETs, 10-2400 pg for PGE(2) and PGD(2), and 20-2000 ng for AA, respectively.

Protective effect of the 20-HETE inhibitor HET0016 on brain damage after temporary focal ischemia

Cytochrome P450 metabolism of arachidonic acid produces the potent vasoconstrictive metabolite, 20-hydroxyeicosatetraenoic acid (20-HETE). Recent studies have implicated 20-HETE as a vasoconstrictive mediator in hemorrhagic stroke. The purpose of this study was to determine the effect of the 20-HETE inhibitor, HET0016, on lesion volume and cerebral blood flow (CBF) after temporary middle cerebral artery occlusion (MCAO) in rats. Plasma pharmacokinetics and tissue concentrations of HET0016 were determined after a 10 mg/kg intraperitoneal dose. Separate rats were treated with HET0016 or vehicle before 90 mins of MCAO. Lesion volume was assessed by 2,3,5-triphenyl-tetrazolium-chloride and cerebral flow was determined using laser Doppler flow. The effect of MCAO on in vitro microsomal formation of mono-oxygenated arachidonic acid metabolites was also determined. Results show that HET0016 has a short biologic half-life, distributes into the brain, and is associated with a 79.6% reduction in 20-HETE concentration in the cortex. Lesion volume was greatly reduced in HET0016-treated (9.1%+/-4.9%) versus vehicle-treated (57.4%+/-9.8%; n=6; P<0.001) rats. An attenuation of the observed decrease in CBF was observed in HET0016-treated (180 mins 89.2%+/-6.2%; 240 mins 88.1%+/-5.7% of baseline flow) versus vehicle control (180 mins 57.6%+/-19.0%; 240 mins 53.8%+/-20.0% of baseline flow; n=6; P<0.05). Brain cortical microsomal formation rate of 20-HETE was also reduced at 24 h in the ipsilateral hemisphere after MCAO. These data support a significant role for 20-HETE in the pathogenesis of ischemic stroke.

Identification and quantification of the hydroxyeicosatetraenoic acids, 20-HETE and 12-HETE, in the cerebrospinal fluid after subarachnoid hemorrhage

PURPOSE

The monohydroxylated metabolite of arachidonic acid, 20-hydroxyeicosatetraenoic acid (20-HETE), is a potent vasoconstrictor of cerebral microvessels. 20-HETE formation is substantially elevated in the cerebral spinal fluid (CSF) in the rat subarachnoid hemorrhage (SAH) model. The presence of 20-HETE in human CSF has not been demonstrated. Therefore, it was the purpose of this study to determine if HETE metabolites are present in human CSF after SAH.

METHODS

CSF samples were collected daily from four SAH patients over 15 days. HETE metabolites were separated by HPLC with identification by ion-trap MS/MS and quantification via single quadrupole MS operating in negative single ion monitoring mode.

RESULTS

Two major metabolites were identified as 12-HETE and 20-HETE. 20-HETE maximal concentrations were 2.9 and 0.7 ng/ml at approximately 70 h in the two patients with symptomatic cerebral vasospasm (SV) after SAH. Concentrations of 12-HETE in these patients peaked at 21.9 ng/ml and 2.8 ng/ml. Concentrations of 20-HETE and 12-HETE were non-detectible in the majority of the samples obtained from two matched SAH patients without SV.

CONCLUSIONS

This study is the first to demonstrate that 20-HETE and 12-HETE are present in the CSF of SAH patients at physiologically relevant concentrations. Based on this information future prospective studies will allow for the delineation of the role of these metabolites in the pathogenesis of SAH.

The effect of isoniazid on CYP2E1- and CYP4A-mediated hydroxylation of arachidonic acid in the rat liver and kidney

Cytochrome P450 (P450) bioactivation of arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) has been reported to be isoform- and tissue-specific. To determine whether altered P450 expression affects the production of these metabolites, the formation of HETEs after isoniazid-mediated CYP2E1 induction was evaluated in the rat liver and kidney. Male Sprague-Dawley rats received isoniazid (200 mg/kg) or saline intraperitoneally once daily for 5 days. Chlorzoxazone, lauric acid, and arachidonic acid hydroxylation was measured in liver and kidney microsomes with and without preincubation with the specific CYP2E1 inhibitor, trans-1,2-dichloroethylene (DCE). P450 isoform content and tissue HETE metabolite concentrations were also determined. Isoniazid increased CYP2E1 protein, and the 6-hydroxychlorzoxazone formation rate was increased by 2.7 +/- 0.3- and 2.2 +/- 0.5-fold in liver and kidney, respectively. Formation of 19-HETE and 11-hydroxylauric acid was induced 2.3 +/- 0.6-fold and 2.2 +/- 0.4-fold in the liver, respectively, with no difference in the kidney. All of the induced activities were attenuated by DCE. An unanticipated decrease in liver CYP4A expression and in vitro 20-HETE formation rate was observed after isoniazid administration. Isoniazid decreased liver and kidney 20-HETE content to 34 +/- 10% and 15.6 +/- 5.3% of control, respectively, without significantly altering tissue 19-HETE concentration. Based on these findings, we conclude that under induced conditions, CYP2E1 is a primary enzyme involved in liver, but not kidney, formation of 19-HETE. In addition, formation of both CYP4A and 20-HETE is reduced in the liver by isoniazid. It was also demonstrated that tissue concentrations parallel in vitro inhibited formation rates for 20-HETE, but not the induced 19-HETE formation in the liver.