Pressor response to intravenous tyramine is a marker of cardiac, but not vascular, adrenergic function

Reappraisal of the mechanism of cardiovascular responses to sympathomimetic amines in anaesthetised rats: dual α1-adrenoceptor and trace amine receptor mechanisms

Established dogma is that sympathomimetic amines, including β-phenylethylamine (PEA), increase blood pressure by releasing noradrenaline from sympathetic neurons. Recent evidence allowing longer contact with isolated immersed tissues indicates other mechanisms. The present study re-evaluates the mechanism of pressor responses to PEA in anaesthetised rats with longer exposure to infusions. Blood pressure and heart rate were monitored by cannulating a common carotid artery of anaesthetised male Sprague-Dawley rats. Drugs were administered by bolus doses or by 20-min infusions via a cannulated jugular vein. Increases in blood pressure by bolus doses of the α-adrenoceptor agonist, phenylephrine, were converted to depressor responses by prazosin and therefore α-adrenoceptor-mediated. Pressor responses to bolus doses of PEA were reduced. PEA infusions yielded four-phase responses: An initial increase in pressure (phase 1) blocked by prazosin was due to α-adrenoceptor vasoconstriction and a secondary fall in pressure (phase 2) due to vasodilatation by nitric oxide release. A later pressure increase (phase 3), further elevated after infusion stopped (phase 4), was not attenuated by prazosin and therefore non-adrenergic. This study showed for the first time that the sympathomimetic amine, β-phenylethylamine, increases blood pressure by two mechanisms. The established indirect sympathomimetic mechanism applies to bolus dose administration. However, with prolonged exposure to infusions, an additional slow-onset sustained non-adrenergic blood pressure increase occurs, most likely mediated via trace amine-associated receptors (TAAR-1). This response will dominate with prolonged exposures in clinical practice. These results prompt a re-evaluation of established dogma on the indirect sympathomimetic mechanisms of these amines.

The trace amine theory of spontaneous hypertension as induced by classic monoamine oxidase inhibitors

The classic monoamine oxidase inhibitors (MAOIs) tranylcypromine (TCP) and phenelzine (PLZ) are powerful antidepressants that come with an equally powerful stigma, and are thus rarely prescribed-despite their well-established effectiveness. Some of these preconceptions appear to stem from unclarity, as the etiology of a rare but important side effect, 'spontaneous hypertension' (SH)-a significant increase in blood pressure absent dietary tyramine ingestion-remains improperly elucidated. This paper aims at uprooting some of the stigma surrounding MAOIs by advancing the trace amine (TA) theory as the causative underpinning of SH. This theory posits that SH results from the considerable influx of TAs observed following TCP- or PLZ-administration. TAs are known, albeit at greatly supraphysiological levels, to raise blood pressure on account of their propensity to exert potent indirect sympathomimetic effects; additionally, some research posits that TAs may induce vasoconstrictive effects partly or wholly separate therefrom, which would then constitute a second hypertensive mechanism. TAs are endogenous to the human body in low quantities. Both TCP and PLZ cause marked elevations of 2-phenylethylamine (PEA), meta- and para-tyramine (m-/p-TYR), octopamine (OA), and tryptamine (TRYP), following both acute and (sub)chronic administration. This paper holds that TYR plays a pivotal role in causing SH, due to its strong pressor effect. Cautious treatment of SH is advised, given its typically self-limiting nature. The risk of hypotensive overshoots must be taken into account. For severe cases, this paper urges reconsideration, following suitable confirmation trials, of antipsychotics (notably risperidone) as these agents may reduce striatal p-TYR levels.

A reassessment of the safety profile of monoamine oxidase inhibitors: elucidating tired old tyramine myths

This review appraises over 150 recent original papers reporting data that demonstrate the greatly reduced tyramine content of modern-day 'foods', about which the medical literature has a paucity of information. It discusses the cardiovascular pharmacology of tyramine and the characteristics, extent, risks, and treatment of the blood pressure increases that sometimes result from tyramine ingestion (the pressor response). In past decades, cheese was the only food associated with documented fatalities resulting from hypertension. Today, few foods contain problematically high tyramine levels, which is a result of changes in international food production techniques (especially the use of starter cultures), and hygiene regulations. Nowadays, even 'matured' cheeses are usually safe in healthy-sized portions. The mechanism by which tyramine may be produced in foods (by certain micro-organisms) is explained and hundreds of recent estimations of cheeses are reviewed. Numerous other previously inadequately documented foods are reviewed, including fish and soy sauces, salami-type sausages, dried meats, beers, wines, and various condiments. Evidence that the risk of harm from the pressor response has previously been overstated is reviewed, and the iatrogenic harms from hasty and aggressive treatment of hypertensive urgency are re-evaluated. Evidence now suggests that MAOIs are of comparable safety to many newer drugs and are straightforward to use. Previously held concerns about MAOIs are misplaced and some are of over-estimated consequence. The variability of pressor sensitivity to tyramine between individuals means that the knowledge and judgement of doctors, and some care, are still required.

Synthesis and Biological Evaluation of Pyrimidine-oxazolidin-2-arylimino Hybrid Molecules as Antibacterial Agents

Pyrimidine-1,3-oxazolidin-2-arylimino hybrids have been synthesized as a new class of antibacterial agents. The synthetic approach exploits a Cu(II)-catalyzed intramolecular halkoxyhalogenation of alkynyl ureas, followed by a Suzuki coupling reaction with 2,4-dimethoxypyrimidin-5-boronic acid. Biological screenings revealed that most of the compounds showed moderate to good activity against two Gram-positive (B. subtilis, S. aureus) and three Gram-negative (P. aeruginosa, S. typhi, K. pneumonia) pathogenic strains. A molecular docking study, performed in the crystal structure of 50S ribosomal unit of Haloarcula marismortui, indicated that pyrimidine-oxazolidin-2-arylimino hybrids 8c and 8h exhibited a high binding affinity (−9.65 and −10.74 kcal/mol), which was in agreement with their good antibacterial activity. The obtained results suggest that the combination of pyrimidine and oxazolidone moieties can be considered as a valid basis to develop new further modifications towards more efficacious antibacterial compounds.

The hemostatic effect study of Cirsium setosum on regulating α1-ARs via mediating norepinephrine synthesis by enzyme catalysis

BACKGROUND

Cirsium setosum (CS) is the aboveground part of Cephalanoplos segetum Kitam. Although it has been used as a hemostatic treatment for thousands of years and is still in use today, the mechanism of CS on regulating ARs is still not clear.

PURPOSE

In this study, we aimed to clarify the mechanism of CS on regulating ARs.

METHODS

We developed a simple method based on UPLC/Q-TOF MS combined adrenergic receptor dual-luciferase reporter assay systems for the rapid determination of active constituents in CS. The mechanism of tyramine, the main active component for regulating ARs, was further investigated by an in vitro norepinephrine biotransformation test and in vivo vaso activity tests.

RESULTS

Two phenethylamine ARs regulators (tyramine and N-methyltyramine) in CS were characterized, and it was found that tyramine could induce vasoconstriction via regulation of α1-ARs by mediating norepinephrine synthesis.

CONCLUSION

The hemostatic effect of CS is associated with tyramine and N-methyltyramine, via regulation of α1-ARs, and the mechanism of tyramine is related to mediating norepinephrine synthesis by enzyme catalysis.

Oxazolidinone antimicrobials: a patent review (2012-2015)

INTRODUCTION

Antimicrobial resistance in Gram-positive bacteria is a major health care issue. This review summarizes patent publications from 2012 to 2015 that divulged novel oxazolidinones as antibacterial agents.

AREAS COVERED

A total of 25 patents obtained from Espacenet, WIPO Patentscope and FreePatentsOnline, and AcclaimIP search engines were reviewed. The patents were scrutinized based on the novelty of the compounds, their antibacterial activity (MIC, µg/mL), and the process of preparation. The oxazolidinones with promising antibacterial activity were classified according to the following structural diversities, as biaryl heterocyclic, fused heteroaryl rings containing oxazolidinones, and others. The biaryl heterocyclic, fused heteroaryl, benzoxazine, and the 1H-pyrazol-1-yl containing oxazolidinone derivatives demonstrated potent antibacterial activities superior to linezolid against Gram-positive bacteria. Some derivatives were effective against standard strains of Gram-negative bacteria, namely Moraxella catarrhalis ATCC A894, and Escherichia coli ATCC 25922. In addition, a patent disclosed a structural isomer of linezolid with marginal activity against the aerobic Gram-negative bacteria MDR Stenotrophomonas (Xanthomonas) maltophilia, while linezolid and vancomycin did not inhibit growth. Finally, some derivatives showed activity against respiratory infectious diseases' causative agents, such as B. anthracis, B. mallei, Y. pestis, and M. pneumoniae.

EXPERT OPINION

Overall, there is limited in vivo data to support the potential clinical advancement of the currently reported novel derivatives.

Synthesis and biological evaluation of novel 5-(hydroxamic acid)methyl oxazolidinone derivatives

Research activities on the oxazolidinone antibacterial class of compounds continue to focus on developing newer derivatives with improved potency, broad-spectrum activity and safety profiles superior to linezolid. Among the safety concerns with the oxazolidinone antibacterial agents is inhibition of monoamine oxidases (MAO) resulting from their structural similarity with toloxatone, a known MAO inhibitor. Diverse substitution patterns at the C-5 position of the oxazolidinone ring have been shown to significantly affect both antibacterial activity and MAO inhibition to varying degrees. Also, the antibacterial activity of compounds containing iron-chelating functionalities, such as the hydroxamic acids, 8-hydroxyquinolines and catechols have been correlated to their ability to alter iron intake and/or metabolism. Hence a series of novel 5-(hydroxamic acid)methyl oxazolidinone derivatives were synthesized and evaluated for their antibacterial and MAO-A and -B inhibitory activities. The compounds were devoid of significant antibacterial activity but most demonstrated moderate MAO-A and -B inhibitory activities. Computer modeling studies revealed that the lack of potent antibacterial activity was due to significant steric interaction between the hydroxamic acid N-OH oxygen atom and one of the G2540 5'-phosphate oxygen atoms at the bacterial ribosomal binding site. Therefore, the replacement of the 5-acetamidomethyl group of linezolid with the 5-(N-hydroxyacetamido)methyl group present in the hydroxamic acid oxazolidinone derivatives was concluded to be detrimental to antibacterial activity. Furthermore, the 5-(hydroxamic acid)methyl oxazolidinone derivatives were also less active as MAO-A and -B inhibitors compared with linezolid and the selective inhibitors clorgyline and pargyline. In general, the 5-(hydroxamic acid)methyl oxazolidinone derivatives demonstrated moderate but selective MAO-B inhibitory activity.

Evaluation of the monoamine oxidases inhibitory activity of a small series of 5-(azole)methyl oxazolidinones

Oxazolidinone class of compounds continue to generate interest as promising agents effective against sensitive and resistant Gram-positive pathogenic bacteria strains. Recent focus is to develop new potent derivatives with improved broad-spectrum activity and safety profile superior to linezolid. An important toxicity issue for this class of compounds arises from the structural similarity with toloxatone, a known MAO inhibitor. Herein, we report the evaluation of a small series of 5-(1H-1,2,3-triazolyl)-, 5-(4-methyl-1H-1,2,3-triazolyl)-, 5-(5-methyl-1H-1,2,3-triazolyl)- and 5-imidazolyl-methyl oxazolidinone analogs with and without antibacterial activity for their effects as inhibitors of monoamine-A and -B (MAO-A and -B) oxidases. Substitutions at the oxazolidinone C-5 position significantly affected antibacterial activity and MAO inhibition. The N-substituted-glycinyl 1H-1,2,3-triazolyl methyl oxazolidinones with potent antibacterial activity demonstrated only weak to moderate affinity for MAO-A and -B, supporting further investigation for this group of compounds.

VIBRATIONAL DYNAMICS AND POTENTIAL ENERGY DISTRIBUTION OF TWO WELL-KNOWN NEUROTRANSMITTER RECEPTORS: TYRAMINE AND DOPAMINE HYDROCHLORIDE

This work deals with the theoretical study on the molecular structure of two well-known neurotransmitter receptors tyramine hydrochloride and dopamine hydrochloride. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities, and Raman scattering activities were calculated by the density functional B3LYP method employing 6-311G(d,p) as the basis set and the vibrational studies were interpreted in terms of the potential energy distribution (P.E.D.). The internal coordinates were optimized repeatedly to maximize the P.E.D. contributions. A detailed interpretation of the infrared and Raman spectra of tyramine and dopamine hydrochloride is reported in the present work. The similarities and differences between the vibrational spectra of the two molecules studied have been highlighted. The scaled theoretical wave numbers are in perfect agreement with the experimental values. The thermodynamic calculations related to the title compounds were also performed at B3LYP/6-311G(d,p) level of theory. The FT-Raman and FT-IR spectra of tyramine and dopamine hydrochloride have been taken from literature.

Advances pertaining to the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors

Recent advances clarifying the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors that have not been considered in depth lately are discussed. These new data elucidate aspects of enzyme inhibition and pharmacokinetic interactions involving amine oxidases, cytochrome P450 enzymes, aminotransferases (transaminases), and decarboxylases (carboxy-lyases) and the effects of tyramine. Phenelzine and tranylcypromine remain widely available, and many publications have data relevant to this review. Their effect on CYP 450 enzymes is less than many newer drugs. Tranylcypromine only inhibits CYP 450 2A6 (selectively and potently). Phenelzine has no reported interactions, but, like isoniazid, weakly and irreversibly inhibits CYP 450 2C19 and 3A4 in vitro. It might possibly be implicated in interactions (as isoniazid is). Phenelzine has some clinically relevant inhibitory effects on amine oxidases, aminotransferases, and decarboxylases, and it lowers pyridoxal phosphate levels. It commonly causes pyridoxal deficiency, weight gain, sedation, and sexual dysfunction, but only rarely causes hepatic damage and failure, or neurotoxicity. The adverse effects and difficulties with monoamine oxidase inhibitors are less than previously believed or estimated, including a lower risk of hypertension, because the tyramine content in foods is now lower. Potent norepinephrine reuptake inhibitors have a strong protective effect against tyramine-induced hypertension. The newly discovered trace amine-associated receptors probably mediate the pressor response. The therapeutic potential of tranylcypromine and L-dopa in depression and Parkinson disease is worthy of reassessment. Monoamine oxidase inhibitors are not used to an extent proportionate with their benefits; medical texts and doctors' knowledge require a major update to reflect the evidence of recent advances.

Selective inhibitors of monoamine oxidase type B and the "cheese effect"

Potentiation of the cardiovascular and other effects of dietary tyramine by monoamine oxidase (MAO) inhibitors (cheese effect) has been a major limitation to clinical use of these drugs. The discovery that MAO exists in two distinct isoforms, MAO-A and MAO-B, together with the development of selective inhibitors of each isoform, enabled the understanding that selective inhibition of MAO-A, or inhibition of both isoforms, will cause cheese effect, but selective inhibition of MAO-B can be elicited without dangerous pressor reaction. This development has permitted the introduction of selective MAO-B inhibitors to clinical medicine for treatment of Parkinson's disease. This review describes the basic mechanisms involved in cheese effect, as well as providing information on tyramine levels in a variety of foodstuff, and surveys clinical information from tyramine pressor testing with the selective MAO-B inhibitors, selegiline and rasagiline.

Generalized and neurotransmitter-selective noradrenergic denervation in Parkinson's disease with orthostatic hypotension

Patients with Parkinson's disease (PD) often have manifestations of autonomic failure. About 40% have neurogenic orthostatic hypotension (NOH), and among PD+NOH patients virtually all have evidence of cardiac sympathetic denervation; however, whether PD+NOH entails extra-cardiac noradrenergic denervation has been less clear. Microdialysate concentrations of the main neuronal metabolite of norepinephrine (NE) and dihydroxyphenylglycol (DHPG) were measured in skeletal muscle, and plasma concentrations of NE and DHPG were measured in response to i.v. tyramine, yohimbine, and isoproterenol, in patients with PD+NOH, patients with pure autonomic failure (PAF), which is characterized by generalized catecholaminergic denervation, and control subjects. Microdialysate DHPG concentrations were similarly low in PD+NOH and PAF compared to control subjects (163 +/- 25, 153 +/- 27, and 304 +/- 27 pg/mL, P < 0.01 each vs. control). The two groups also had similarly small plasma DHPG responses to tyramine (71 +/- 58 and 82 +/- 105 vs. 313 +/- 94 pg/mL; P < 0.01 each vs. control) and NE responses to yohimbine (223 +/- 37 and 61 +/- 15 vs. 672 +/- 130 pg/mL, P < 0.01 each vs. control), and virtually absent NE responses to isoproterenol (20 +/- 34 and 14 +/- 15 vs. 336 +/- 78 pg/mL, P < 0.01 each vs. control). Patients with PD+NOH had normal bradycardia responses to edrophonium and normal epinephrine responses to glucagon. The results support the concept of generalized noradrenergic denervation in PD+NOH, with similar severity to that seen in PAF. In contrast, the parasympathetic cholinergic and adrenomedullary hormonal components of the autonomic nervous system seem intact in PD+NOH.

Functional effects of cardiac sympathetic denervation in neurogenic orthostatic hypotension

BACKGROUND

Diseases characterized by neurogenic orthostatic hypotension (NOH), such as Parkinson disease (PD) and pure autonomic failure (PAF), are associated with cardiac sympathetic denervation, as reflected by low myocardial concentrations of 6-[(18)F]fluorodopamine-derived radioactivity. We studied the impact of such denervation on cardiac chronotropic and inotropic function.

METHODS

Cardiac inotropic function was assessed by the pre-ejection period index and the systolic time ratio index in response to the directly acting beta-adrenoceptor agonist, isoproterenol, and to the indirectly acting sympathomimetic amine, tyramine, in patients with PD+NOH or PAF (PD+NOH/PAF group, N=13). We compared the results to those in patients with multiple system atrophy, which usually entails NOH with normal cardiac sympathetic innervation (MSA, N=15), and in normal control subjects (N=5).

RESULTS

The innervated and denervated groups did not differ in baseline mean pre-ejection period index or systolic time ratio index. Tyramine increased cardiac contractility in the MSA patients and controls but not in the PD+NOH/PAF group. For similar heart rate responses, the PD+NOH/PAF group required less isoproterenol (p<0.01) and had lower plasma isoproterenol levels (p<0.01) than did the MSA group.

CONCLUSIONS

Among patients with NOH those with cardiac sympathetic denervation have an impaired inotropic response to tyramine and exaggerated responses to isoproterenol. This pattern suggests that cardiac denervation is associated with decreased ability to release endogenous norepinephrine from sympathetic nerves and with supersensitivity of cardiac beta-adrenoreceptors.

Ranbezolid, a novel oxazolidinone antibacterial: In vivo characterisation of monoamine oxidase inhibitory potential in conscious rats

Ranbezolid, a novel oxazolidinone antibacterial, competitively inhibits monoamine oxidase-A (MAO-A), in vitro. The consequences of MAO-A inhibition was evaluated in vivo, by testing interaction of Ranbezolid with tyramine (in solution or mixed with feed), and amine containing cold remedies on pressor response in conscious rats. Single and repeat doses of Ranbezolid (50 mg/kg, p.o.) did not affect pressor response to tyramine (5 or 15 mg/kg), but potentiated the same after a single dose of 100 mg/kg. Co-administration of Ranbezolid with tyramine in feed or with cold remedies also did not potentiate the respective pressor responses. These results suggest that Ranbezolid exhibits minimal cardiovascular liability associated with MAO-A inhibition.

Antianxiety effects of riparin I fromAniba riparia (Nees) Mez (Lauraceae) in mice

This work presents the behavioral effects of riparin I (methyl ether of N-benzoyl tyramine) from unripe fruit of Aniba riparia (Lauraceae) on the elevated plus maze, open field, rota rod and hole board tests in mice. Riparin I was administered acutely by intraperitoneal (i.p.) and oral routes to male mice at doses of 25 and 50 mg/kg. The results showed that riparin I (25 and 50 mg/kg, i.p. and per os) increased the number of entries and the time of permanence in the open arms in the plus maze test. Similarly, in the hole board test, riparin I in both routes increased the number of head dips. Riparin I with both doses and routes had no effects on spontaneous motor activity in mice or in the rota rod test, but decreased the number of groomings. These results showed that riparin I by both administration routes has effects on the central nervous system with antianxiety effects on the plus maze and hole board tests. The substance is devoid of myorelaxant effects.