Studies of the in vitro human plasma degradation of methionine-enkephalin

Mosnaim, Aron D.; Puente, Javier; Wolf, Marion E.; Callaghan, Owen; Busch, Randall; Diamond, Seymour

doi:10.1016/0306-3623(88)90137-1

Cited by 23 publications

(24 citation statements)

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“…These findings follow a similar pattern than those already reported for the in vitro human plasma MET and LEU degradation kinetics [15][16][17][18]24]. In an effort to keep the peptide concentration as close to its physiological levels as possible, our experimental conditions call for using the smaller MET concentration achievable and still be able to confidently measure peptide degradation products; whether the use of higher MET concentrations would also result in the formation of DPPs and/or PDDPs catalyzed metabolites needs to be explored [25].…”

Section: Discussionsupporting

confidence: 89%

In vitro Methionine5-Enkephalin Degradation Kinetics by Human Brain Preparations

et al. 2007

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Incubation of [3H]-tyrosine methionine5-enkephalin (MET) with human brain preparations (100,000g supernatant; sections of the limbic system, thalamus, basal ganglia, cerebellum, and cortex) results in its rapid and complete degradation; over 95% of the initial labeled tyrosine is recovered as the free aminoacid within 10 min. Results show a considerable range in the peptide initial velocity (Iv) and half-life (t1/2) degradation values obtained from different brain sections of individual brains, either from the same or from different main brain areas. This relatively wide range of values was scattered, failing to identify consistent differences between the various brains areas studied. Differences in brain tissue storage time or repeated sample freezing and thawing failed to alter significantly either of these kinetic parameters of MET metabolism. Peptide degradation rate (optimum pH and temperature of 7.4 and 37 degrees C, respectively) was concentration-dependent inhibited by known aminopeptidase inhibitors (puromycin, bacitracin, and bestatin, and to a lesser extent by thioridazine). However, it was not significantly affected by either N-carboxymethyl phenyl leucine, captopril or thiorphan [dipeptidyl peptidase(s) or peptidyl dipeptidase(s) inhibitors, respectively]. A better understanding of the mechanisms regulating brain MET metabolism may contribute to the rational design of pharmacological strategies based in the modulation of its bioavailability.

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Section: Discussionsupporting

confidence: 89%

In vitro Methionine5-Enkephalin Degradation Kinetics by Human Brain Preparations

et al. 2007

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“…Quantitatively, tyrosine-glycine amide bond hydrolysis ( fig. 1) is the predominant step for LEU, and MET, in vitro degradation by samples obtained from various human tissues and fluids [11][12][13]. Under experimental conditions designed to mimic the physiological environment as closely as technically possible, incubation of human plasma with [ 3 H]-tyrosine LEU results in rapid and complete peptide degradation.…”

Section: Discussionmentioning

confidence: 99%

“…The possible biological importance of LEU circulating levels, which mostly reflect the active interaction between its rate of synthesis, a process taking place mainly in the adrenal medulla chromaffin granules, and its rate of degradation [1,12,13], is still not well understood. However, identifying substances able to significantly alter such levels may be of significance in the better understanding of the pathophysiology of various diseases, and to the rational devise of pharmacological strategies based in the modulation of their bioavailability.…”

Section: Discussionmentioning

confidence: 99%

“…due redissolved in buffer (200 Ìl) and after counting an aliquot, unchanged LEU and labeled LEU metabolites (if any) were identified (TLC) and individually quantitated [12,13]. Chemical tested included various clinically used antipsychotic drugs representing significantly different chemical structures e.g., chlorpromazine, fluphenazine, prochlorperazine, thioridazine, trifluoperazine, haloperidol, sulpiride, thiothixene, loxapine, clozapine and molindone.…”

Section: Methodsmentioning

confidence: 99%

“…1), and MET; H-Tyr-Gly-Gly-PheMe-OH, YGGFM, respectively] are involved in the regulation of various physiological and behavioral processes, and appear to play a role in the pathophysiology of various diseases [1][2][3][4][5][6][7][8][9][10]. Whereas little is known regarding the in vivo kinetics of LEU metabolism in humans, in vitro studies show that incubation of this peptide with plasma results in its rapid and complete degradation, mostly as a result of tyrosine-glycine amide bond hydrolysis [11,12,13]. Consistently, and irrespective of gender, age, race, length of frozen plasma storage time, or repeated sample freezing and thawing, over 95% of the initially added [ 3 H]-tyrosine LEU is recovered as the free labeled-aminoacid (after 30 min reaction; pH 7.4 and 37°C), with little formation of any of the other possible LEU degradation fragments [13].…”

Section: Introductionmentioning

confidence: 99%

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In vitro Human Plasma Leucine<sup>5</sup>-Enkephalin Degradation Is Inhibited by a Select Number of Drugs with the Phenothiazine Molecule in Their Chemical Structure

Mosnaim¹,

Puente²,

Saavedra³

et al. 2002

Pharmacology

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A number of drugs with the phenothiazine molecule in their chemical structure inhibit in a dose-dependent manner human plasmatic aminopeptidase leucine⁵-enkephalin (LEU) metabolism. Half-life peptide degradation was significantly increased by thioridazine > fluphenazine > As-1397 [10-(α-diethylaminopropionyl)phenothiazine] ≧ promethazine ≧ chlorpromazine (final drug conc. 10^–4M); t1/2 (± SD) 21.2 ± 1.1, 19.6 ± 1.0, 17.2 ± 0.9, 17.1 ± 1.0, and 17.1 ± 1.1 min, respectively. Control and bacitracin (known aminopeptidase inhibitor) values were 11.8 ± 1.0 and 31.3 ± 1.7 min, respectively. These drugs significantly decreased (listed in the same order) LEU degradation initial velocity; Iv (± SD) 0.77 ± 0.2, 0.82 ± 0.2, 0.92 ± 0.3, 0.93 ± 0.2, 0.94 ± 0.3 pg LEU/min, respectively. Control and bacitracin 1.10 ± 0.3 and 0.20 ± 0.1 pg LEU/min, respectively. Values represent results from 5 samples, each obtained by pooling 6 individual plasmas (4 male and 2 female; n = 30 healthy, drug-free volunteers). However, neither the phenothiazines ethopropazine, methotrimeprazine, prochlorperazine and trifluoperazine nor the various commonly used heterocyclic antipsychotics tested, e.g., molindone, loxapine, clozapine, haloperidol, sulpiride and thiothixene inhibited plasma LEU degradation kinetics. Our results failed to show correlations between chemical structure, antipsychotic properties and ability to inhibit plasmatic aminopeptidase LEU degradation. Whereas, presence of the phenothiazine molecule appears to be necessary for enzyme inhibition, only five out of nine substituted phenothiazines tested exhibited this effect. Furthermore, there was a lack of correlation between phenothiazines antipsychotic properties and their capacity to inhibit aminopeptidase activity, a property shown by promethazine (antihistaminic) and As-1397 (selective butyrylcholinesterase inhibitor) but lacking in prochlorperazine and trifluoperazine. Our results provide information which could lead to the rational design of agents capable to modulate the bioavailability of enkephalin and other endogenous aminopeptidase-degraded peptides believed to be involved in the etiology and/or pathophysiology associated with various disease conditions. Whether their development could find useful pharmacological applications remains to be explored.

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Determination of methionine-enkephalin and leucine-enkephalin by LC-MS in human plasma: Study of pre-analytical stability

Özalp

Barroso

Meijer

et al. 2018

Analytical Biochemistry

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Studies of the in vitro human plasma degradation of methionine-enkephalin

Cited by 23 publications

References 22 publications

In vitro Methionine5-Enkephalin Degradation Kinetics by Human Brain Preparations

In vitro Methionine5-Enkephalin Degradation Kinetics by Human Brain Preparations

In vitro Human Plasma Leucine<sup>5</sup>-Enkephalin Degradation Is Inhibited by a Select Number of Drugs with the Phenothiazine Molecule in Their Chemical Structure

Determination of methionine-enkephalin and leucine-enkephalin by LC-MS in human plasma: Study of pre-analytical stability

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