Quantification of 6-nitrodopamine in Krebs-Henseleit's solution by LC-MS/MS for the assessment of its basal release from Chelonoidis carbonaria aortae in vitro

6-Nitrodopamine is an endogenous mediator of the rabbit corpus cavernosum relaxation

BACKGROUND

6-Nitrodopamine (6-ND) is a novel endogenous catecholamine that has a potent relaxant action on vascular smooth muscle in vitro.

OBJECTIVES

To evaluate the basal release of 6-ND and noradrenaline from rabbit-isolated corpus cavernosum (RbCC) and its relaxing action on this tissue.

METHODS

Rabbit corpus cavernosa were dissected and suspended in a 5-mL organ bath containing oxygenated Krebs-Henseleit's solution. 6-ND and noradrenaline release was quantified by liquid chromatography coupled to tandem mass spectrometry. The relaxant activity of 6-ND was assessed in RbCC strips pre-contracted with endothelin-1 (10 nM).

RESULTS

Rabbit corpus cavernosum presented basal release of both 6-ND (2.9 ± 0.8 ng/mL, n = 12) and noradrenaline (1.7 ± 1.3 ng/mL, n = 12). The 6-ND release was reduced by pre-treatment with Nω-nitro-l-arginine methyl ester (l-NAME) (100 µM), whereas that of noradrenaline was unaffected. Tetrodotoxin (TTX, 1 µM) abolished the noradrenaline release but had no effect on 6-ND release, indicating a non-neurogenic origin for 6-ND. 6-ND and the selective dopamine D2-agonist L-741,626 caused concentration-dependent RbCC relaxations (pEC50 of 11 ± 0.15 and 11.15 ± 0.28, respectively). Pre-treatment with either l-NAME or the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-on (ODQ) (100 µM) caused a rightward shift of the concentration-response curve to 6-ND, without affecting the L-741,626 responses. In TTX (100 nM)-pre-treated preparations, neither l-NAME nor ODQ shifted the 6-ND concentration-response curve. Dopamine, noradrenaline, and adrenaline caused concentration-dependent RbCC contractions. Pre-incubation with 6-ND concentration-dependently inhibited the dopamine-induced contractions, without affecting those induced by either noradrenaline or adrenaline.

DISCUSSION AND CONCLUSION

6-Nitrodopamine is the most potent endogenous relaxant agent in RbCC ever described and represents a novel mechanism by which NO causes corpus cavernosum smooth muscle relaxation. The finding that 6-ND acts as a truly selective dopamine D2-receptor antagonist indicates that the balance of dopamine and 6-ND release/synthesis may be the main mechanism that modulates corpus cavernosum smooth muscle tonus in vivo.

Impact of biochar on the degradation rates of three pesticides by vegetables and its effects on soil bacterial communities under greenhouse conditions

A 28 days pesticide degradation experiment was conducted for broccoli (Brassica oleracea L. var. italica Planch) and pakchoi (Brassica chinensis L.) with three pesticides (chlorantraniliprole (CAP), haloxyfop-etotyl (HPM), and indoxacarb (IXB)) to explore the effects of biochar on pesticide environmental fate and rhizosphere soil diversity. Rice straw biochar (RB) was applied to soil at a 25.00 t ha-1 dosage under greenhouse conditions, and its effects on the degradation of three pesticides in vegetables and in soil were investigated individually. Overall, RB application effectively facilitated CAP and HPM degradation in broccoli by 13.51-39.42% and in broccoli soil by 23.80-74.10%, respectively. RB application slowed the degradation of CAP, HPM and IXB in pakchoi by 0.00-57.17% and slowed the degradation of CAP in pakchoi by 37.32-43.40%. The results showed that the effect of RB application on pesticide degradation in crops and soil was related to biochar properties, pesticide solubility, plant growth status, and soil characteristics. Rhizosphere soil microorganisms were also investigated, and the results showed that biochar application may be valuable for altering bacterial richness and diversity. The effect of biochar application on pesticide residues in crops and soil was influenced by the vegetable variety first, and the second was pesticide characteristics. RB applied to soil at a 25.00 t ha-1 dosage under greenhouse conditions is recommended for broccoli production to ensure food safety. Our results suggested that biochar application in soil could reduce pesticide non-point source pollution, especially for highly soluble pesticides, and could affect soil microorganisms.

A LC-MS/MS method for the simultaneous determination of 6-cyanodopamine, 6-nitrodopamine, 6-nitrodopa, 6-nitroadrenaline and 6-bromodopamine in human plasma and its clinical application in patients with chronic kidney disease

The aim of this study was to develop a high-performance liquid chromatography-tandem mass spectrometry method for the determination of 6-cyanodopamine, 6-nitrodopamine, 6-nitrodopa, 6-nitroadrenaline and 6-bromodopamine in human plasma samples. Strata-X 33 μm solid-phase extraction cartridges were used for the extraction of the catecholamines from human plasma samples. The catecholamines were separated in a 150 × 3 mm Shim-pack GIST C18-AQ column with 3 μm particle size, placed in an oven at 40°C and perfused with 82% mobile phase A (acetonitrile-H2O; 90:10, v/v) + 0.4% acetic acid and 18% mobile phase B (deionized H2O) + 0.2% formic acid at a flow rate of 340 μl/min in isocratic mode. The injected volume was 4 μl and the run lasted 4 min. The method was linear from 0.1 to 20 ng/ml and the lower limit of quantification was 0.1 ng/ml for all analytes. The method was applied to evaluate the plasma levels of catecholamines in plasma of patients with chronic kidney disease and allowed the detection for the first time of circulating levels of the novel catecholamines 6-bromodopamine and 6-cyanodopamine.

GKT137831 and hydrogen peroxide increase the release of 6-nitrodopamine from the human umbilical artery, rat-isolated right atrium, and rat-isolated vas deferens

Introduction: The human umbilical artery (HUA), rat-isolated right atrium, and rat-isolated vas deferens present a basal release of 6-nitrodopamine (6-ND). The basal release of 6-ND from these tissues was significantly decreased (but not abolished) when the tissues were pre-incubated with Nω-nitro-L-arginine methyl ester (L-NAME). Methods: In this study, the effect of the pharmacological modulation of the redox environment on the basal release of 6-ND was investigated. The basal release of 6-ND was measured using Liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results and Discussion: Pre-incubation (30 min) of the tissues with GKT137831 (1 μM) caused a significant increase in the basal release of 6-ND from all tissues. In the HUA, pre-incubation with diphenyleneiodonium (DPI) (100 μM) also caused significant increases in the basal release of 6-ND. Preincubation of the HUA with hydrogen peroxide (H2O2) (100 μM) increased 6-ND basal release, whereas pre-incubation with catalase (1,000 U/mL) significantly decreased it. Pre-incubation of the HUA with superoxide dismutase (SOD) (250 U/mL; 30 min) also significantly increased the basal release of 6-ND. Preincubation of the HUA with either allopurinol (100 μM) or uric acid (1 mM) had no effect on the basal release of 6-ND. Pre-treatment of the HUA with L-NAME (100 μM) prevented the increase in the basal release of 6-ND induced by GKT137831, diphenyleneiodonium, and H2O2. The results obtained indicate a major role of endogenous H2O2 and peroxidases as modulators of 6- ND biosynthesis/release and a lack of peroxynitrite contribution.

Endothelium-Derived Dopamine and 6-Nitrodopamine in the Cardiovascular System

The review deals with the release of endothelium-derived dopamine and 6-nitrodopamine (6-ND) and its effects on isolated vascular tissues and isolated hearts. Basal release of both dopamine and 6-ND is present in human isolated umbilical cord vessels, human popliteal vessels, nonhuman primate vessels, and reptilia aortas. The 6-ND basal release was significantly reduced when the tissues were treated with Nω-nitro-l-arginine methyl ester and virtually abolished when the endothelium was mechanically removed. 6-Nitrodopamine is a potent vasodilator, and the mechanism of action responsible for this effect is the antagonism of dopamine D2-like receptors. As a vasodilator, 6-ND constitutes a novel mechanism by which nitric oxide modulates vascular tone. The basal release of 6-ND was substantially decreased in endothelial nitric oxide synthase knockout (eNOS-/-) mice and not altered in neuronal nitric oxide synthase knockout (nNOS-/-) mice, indicating a nonneurogenic source for 6-ND in the heart. Indeed, in rat isolated right atrium, the release of 6-ND was not affected when the atria were treated with tetrodotoxin. In the rat isolated right atrium, 6-ND is the most potent endogenous positive chronotropic agent, and in Langendorff's heart preparation, it is the most potent endogenous positive inotropic agent. The positive chronotropic and inotropic effects of 6-ND are antagonized by β1-adrenoceptor antagonists at concentrations that do not affect the effects induced by noradrenaline, adrenaline, and dopamine, indicating that blockade of the 6-ND receptor is the major modulator of heart chronotropism and inotropism. The review proposes that endothelium-derived catecholamines may constitute a major mechanism for control of vascular tone and heart functions, in contrast to the overrated role attributed to the autonomic nervous system.

6-Nitrodopamine Is the Most Potent Endogenous Positive Inotropic Agent in the Isolated Rat Heart

BACKGROUND

6-nitrodopamine released from rat isolated atria exerts positive chronotropic action, being more potent than noradrenaline, adrenaline, and dopamine. Here, we determined whether 6-nitrodopamine is released from rat isolated ventricles (RIV) and modulates heart inotropism.

METHODS

Catecholamines released from RIV were quantified by LC-MS/MS and their effects on heart inotropism were evaluated by measuring left ventricular developed pressure (LVDP) in Langendorff's preparation.

RESULTS

6-nitrodopamine was the major released catecholamine from RIV. Incubation with L-NAME (100 µM), but not with tetrodotoxin (1 µM), caused a significant reduction in 6-nitrodopamine basal release. 6-nitrodopamine release was significantly reduced in ventricles obtained from L-NAME chronically treated animals. 6-nitrodopamine (0.01 pmol) caused significant increases in LVDP and dP/dtmax, whereas dopamine and noradrenaline required 10 pmol, and adrenaline required 100 pmol, to induce similar increases in LVDP and dP/dtmax. The infusion of atenolol (10 nM) reduced basal LVDP and blocked the increases in LVDP induced by 6-ND (0.01 pmol), without affecting the increases in LVDP induced by 10 nmol of dopamine and noradrenaline and that induced by adrenaline (100 nmol).

CONCLUSIONS

6-nitrodopamine is the major catecholamine released from rat isolated ventricles. It is 1000 times more potent than dopamine and noradrenaline and is selectively blocked by atenolol, indicating that 6-ND is a main regulator of heart inotropism.

Measurement of 6-cyanodopamine, 6-nitrodopa, 6-nitrodopamine and 6-nitroadrenaline by LC-MS/MS in Krebs-Henseleit solution. Assessment of basal release from rabbit isolated right atrium and ventricles

This study presents the validation of a sensitive method for the determination of 6-nitrodopa, 6-nitrodopamine, 6-nitroadrenaline and 6-cyanodopamine in Krebs-Henseleit solution by LC-MS/MS with ESI+ . HRMS was used to precisely characterize the structures of the fragment ions. The method was applied to investigate the catecholamine basal release from rabbit isolated atria and ventricles. The atria and ventricles were suspended separately in a 5 ml organ bath containing Krebs-Henseleit solution with ascorbic acid (3 mM), gassed (95%O2 /5%CO2 ) at 37°C for 30 min. Strata-X 33 μm SPE cartridges were employed for the extraction of the catecholamines and the internal standard 6-nitrodopamine-d4 . The catecholamines were separated employing a 150 × 3 mm Shim-pack GIST C18-AQ (3 mm particle size), placed in an oven at 40°C and perfused by 65% of mobile phase A (MeCN/H2 O; 90/10, v/v) + 0.4% CH3 COOH and 35% mobile phase B (deionized H2 O) + 0.2% CH2 O2 at 320 μl/min in isocratic mode. The method was linear at 0.1-20 ng/ml. The method was used to identify for the first-time basal release of the three nitrocatecholamines mentioned above and a member of a novel class of catecholamines, the cyanocatecholamines.

Investigation on the positive chronotropic action of 6-nitrodopamine in the rat isolated atria

6-Nitrodopamine (6-ND) is released from rat isolated atria being 100 times more potent than noradrenaline and adrenaline, and 10,000 times more potent than dopamine as a positive chronotropic agent. The present study aimed to investigate the interactions of 6-ND with the classical catecholamines, phosphodiesterase (PDE)-3 and PDE4, and the protein kinase A in rat isolated atria. Atrial incubation with 1 pM of dopamine, noradrenaline, or adrenaline had no effect on atrial frequency. Similar results were observed when the atria were incubated with 0.01 pM of 6-ND. However, co-incubation of 6-ND (0.01 pM) with dopamine, noradrenaline, or adrenaline (1 pM each) resulted in significant increases in atrial rate, which persisted over 30 min after washout of the agonists. The increased atrial frequency induced by co-incubation of 6-ND with the catecholamines was significantly reduced by the voltage-gated sodium channel blocker tetrodotoxin (1 µM, 30 min), indicating that the positive chronotropic effect of 6-ND is due in part to activation of nerve terminals. Pre-treatment of the animals with reserpine had no effect on the positive chronotropic effect induced by dopamine, noradrenaline, or adrenaline; however, reserpine markedly reduced the 6-ND (1 pM)-induced positive chronotropic effect. Incubation of the rat isolated atria with the protein kinase A inhibitor H-89 (1 µM, 30 min) abolished the increased atrial frequency induced by dopamine, noradrenaline, and adrenaline, but only attenuated the increases induced by 6-ND. 6-ND induces catecholamine release from adrenergic terminals and increases atrial frequency independently of PKA activation.

Relaxation of thoracic aorta and pulmonary artery rings of marmosets (Callithrix spp.) by endothelium-derived 6-nitrodopamine

6-Nitrodopamine is a novel catecholamine released by vascular tissues, heart, and vas deferens. The aim of this study was to investigate whether 6-nitrodopamine is released from the thoracic aorta and pulmonary artery rings of marmosets (Callithrix spp.) and to evaluate the relaxing and anti-contractile actions of this catecholamine. Release of 6-nitrodopamine, dopamine, noradrenaline, and adrenaline was assessed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The relaxations induced by 6-nitrodopamine and by the selective dopamine D2 receptor antagonist L-741,626 were evaluated on U-46619 (3 nM)-pre-contracted vessels. The effects of 6-nitrodopamine and L-741,626 on the contractions induced by electric-field stimulation (EFS), dopamine, noradrenaline, and adrenaline were also investigated. Both aorta and pulmonary artery rings exhibited endothelium-dependent release of 6-nitrodopamine, which was significantly reduced by the NO synthesis inhibitor L-NAME. Addition of 6-nitrodopamine or L-741,626 caused concentration-dependent relaxations of both vascular tissues, which were almost abolished by endothelium removal, whereas L-NAME and the soluble guanylate cyclase inhibitor ODQ had no effect on 6-nitrodopamine-induced relaxations. Additionally, pre-incubation with 6-nitrodopamine antagonized the dopamine-induced contractions, without affecting the noradrenaline- and adrenaline-induced contractions. Pre-incubation with L-741,626 antagonized the contractions induced by all catecholamines. The EFS-induced contractions were significantly increased by L-NAME, but unaffected by ODQ. Immunohistochemical assays showed no immunostaining of the neural tissue markers S-100 and calretinin in either vascular tissue. The results indicated that 6-nitrodopamine is the major catecholamine released by marmoset vascular tissues, and it acts as a potent and selective antagonist of dopamine D2-like receptors. 6-nitrodopamine release may be the major mechanism by which NO causes vasodilatation.

Synthesis, Chiral Resolution and Enantiomers Absolute Configuration of 4-Nitropropranolol and 7-Nitropropranolol

We recently identified 6-nitrodopamine and other nitro-catecholamines (6-nitrodopa, 6-nitroadrenaline), indicating that the endothelium has the ability to nitrate the classical catecholamines (dopamine, noradrenaline, and adrenaline). In order to investigate whether drugs could be subject to the same nitration process, we synthesized 4-nitro- and 7-nitropropranolol as probes to evaluate the possible nitration of the propranolol by the endothelium. The separation of the enantiomers in very high yields and excellent enantiopurity was achieved by chiral HPLC. Finally, we used Riguera's method to determine the absolute configuration of the enantiomers, through double derivatization with MPA and NMR studies.

6-nitrodopamine is a major endogenous modulator of human vas deferens contractility

BACKGROUND

Rat isolated vas deferens releases 6-nitrodopamine (6-ND), and the spasmogenic activity of this novel catecholamine is significantly reduced by tricyclic compounds such as amitriptyline, desipramine, and carbamazepine and by antagonists of the α₁ -adrenergic receptors such as doxazosin, tamsulosin, and prazosin.

OBJECTIVES

To investigate the liberation of 6-ND by human epididymal vas deferens (HEVDs) and its pharmacological actions.

METHODS

The in vitro liberation of 6-ND, dopamine, noradrenaline, and adrenaline from human vas deferens was evaluated by LC-MS/MS. The contractile effect of the catecholamines in HEVDs was investigated in vitro. The action of tricyclic antidepressants was evaluated on the spasmogenic activity ellicited by the catecholamines and by the electric-field stimulation (EFS). The tissue was also incubated with the inhibitor of nitric oxide (NO) synthase L-NAME and the release of catecholamines and the contractile response to EFS were assessed.

RESULTS

6-ND is the major catecholamine released from human vas deferens and its synthesis/release is inhibited by NO inhibition. The spasmogenic activity elicited by EFS in the human vas deferens was blocked by tricyclic antidepressants only at concentrations that selectively antagonize 6-ND induced contractions of the human vas deferens, without affecting the spasmogenic activity induced by dopamine, noradrenaline, and adrenaline in this tissue. Incubation of the vas deferens with L-NAME reduced both the 6-ND release and the contractions induced by EFS.

DISCUSSION AND CONCLUSION

6-ND should be considered a major endogenous modulator of human vas deferens contractility and possibly plays a pivotal role in the emission process of ejaculation. It offers a novel and shared mechanism of action for tricyclic antidepressants and α₁ -adrenergic receptor antagonists.

β1- and β1/β2-adrenergic receptor antagonists block 6-nitrodopamine-induced contractions of the rat isolated epididymal vas deferens

6-Nitrodopamine (6-ND) is an endogenous modulator of the contractility in the rat isolated epididymal vas deferens (RIEVD) and considered to be the main peripheral mediator of the emission process. Use of selective and unselective β-adrenergic receptor antagonists has been associated with ejaculatory failure. Here, the effects of selective β₁- and β₁/β₂-adrenergic receptor antagonists on RIEVD contractions induced by 6-ND, dopamine, noradrenaline, adrenaline, and electric-field stimulation (EFS) were investigated. The selective β₁-adrenergic receptor antagonists atenolol (0.1 and 1 µM), betaxolol (1 µM), and metoprolol (1 µM) and the unselective β₁/β₂-adrenergic receptor antagonists propranolol (1 and 10 µM) and pindolol (10 µM) caused significant rightward shifts of the concentration-response curve to 6-ND (pA₂ 6.41, 6.91, 6.75, 6.47, and 5.74; for atenolol, betaxolol, metoprolol, propranolol, and pindolol), but had no effect on dopamine-, noradrenaline-, and adrenaline-induced contractions. The effects of selective β₁- and β₁/β₂-adrenergic receptor antagonists at a higher concentration (atenolol 1 µM, betaxolol 1 µM, metoprolol 1 µM, propranolol 10 µM, and pindolol 10 µM) also reduced the EFS-induced RIEVD contractions in control, but not in RIEVD obtained from L-NAME-treated animals. The selective β₁-adrenoceptor agonist RO-363, the selective β₂-adrenoceptor agonist salbutamol, and the selective β₃-adrenoceptor agonist mirabegron, up to 300 µM, had no effect on the RIEVD tone. The results demonstrate that β₁- and β₁-/β₂-adrenoceptor receptor antagonists act as 6-ND receptor antagonists in RIEVD, further confirming the main role of 6-ND in the RIEVD contractility.

6-Nitrodopamine is an endogenous mediator of rat isolated epididymal vas deferens contractions induced by electric-field stimulation

6-nitrodopamine (6-ND) is released from human umbilical cord vessels and modulates vascular reactivity by acting as a dopamine antagonist. Here we investigate whether 6-ND is released by the rat isolated vas deferens and its effect on this tissue. Dopamine, noradrenaline, adrenaline and 6-ND levels were quantified in rat isolated vas deferens by LC-MS-MS. Electric-field stimulation (EFS) and concentration-response curves to 6-ND, noradrenaline, dopamine and adrenaline were performed in the absence and in the presence (30 min) of L-NAME, SCH-23390, haloperidol, PG-01037, sonepiprazole, desipramine, clomipramine, amitriptyline, cyclobenzaprine, carbamazepine, maprotiline, paroxetine, oxcarbazepine and ketanserin in the rat isolated epididymal vas deferens (RIEVD). Basal releases of 6-ND and noradrenaline were detected from the rat isolated vas deferens. 6-ND release was reduced by tissue incubation with L-NAME and from the vas deferens obtained from L-NAME-treated rats. SCH-23390 caused leftward shifts on concentration-response curves to 6-ND without affecting dopamine- or EFS-induced RIEVD contractions. Haloperidol, PG-01037 and sonepiprazole caused significant rightward shifts on concentration-response curves to dopamine but had no effect on either the 6-ND or EFS-induced RIEVD contractions. The tricyclic compounds desipramine, clomipramine, amitriptyline, cyclobenzaprine and carbamazepine induced rightward shifts on 6-ND concentration-response curve but did not reduce the noradrenaline, dopamine and adrenaline contractile responses. They also reduced the EFS-induced RIEVD contractions in control but not in tissues obtained from L-NAME-treated animals. Maprotiline, oxcarbazepine, paroxetine and ketanserin had no effect in either 6-ND or EFS-induced RIEVD contractions. Thus, 6-ND modulates RIEVD contractility, and desipramine, clomipramine, amitriptyline, cyclobenzaprine and carbamazepine act as selective 6-ND receptor antagonists.