Monoamine Oxidase Inhibitors Selegiline Research Articles

Possible synergies between isatin, an endogenous MAO inhibitor, and antiparkinsonian agents on the dopamine release from striatum of freely moving rats.

Isatin is an endogenous indole that inhibits monoamine oxidase (MAO). When exogenously administered, it increases the striatal dopamine and acetylcholine levels and presents neuroprotective effects in the brain. Previous studies show that intrastriatal administration of isatin increased the in vivo dopamine release from striatum in a concentration-dependent form. In the present work, we investigated the effects of combined administration of isatin together with other substances actually used in antiparkinsonian pharmacotherapy on in vivo dopamine overflow. For this, we co-administered isatin with the MAO inhibitors selegiline and clorgyline, l-DOPA, the catechol-o-methyl-transferase (COMT) inhibitors tropolone and dinitrocatechol, with the dopaminergic agonist ropinirole, and with the psychostimulant caffeine, in order to evaluate possible synergies between these substances to increase the dopamine extracellular levels in freely moving rats. Intrastriatal administration of isatin (10 mM, 60 min) significantly increased dopamine release to 1164 ± 152%, compared to the baseline. Co-administration of isatin together with selegiline (1 mM) or clorgyline (1 mM) alone or in combinations showed a similar profile to increase in vivo dopamine release. Intrastriatal infusion of isatin together with antiparkinsonian drugs l-DOPA (25 μM), tropolone (1 mM), dinitrocatechol (100 μM), amantadine (5 mM) and caffeine (5 mM) significantly elevated extracellular dopamine levels more than any single drug, showing a good neurochemical synergy by improving the effect of isatin on the extracellular dopamine levels in the striatum. Infusion of isatin + ropinirole (5 mM) did not change the isatin-induced increase in dopamine overflow. These results could be useful to carry out further investigations with a possible clinical application.

Three Paths to Better Tyrosine Kinase Inhibition Behind the Blood-Brain Barrier in Treating Chronic Myelogenous Leukemia and Glioblastoma with Imatinib

Chronic myelogenous leukemia (CML) can be controlled for years with the tyrosine kinase inhibitor imatinib but because imatinib poorly penetrates the blood-brain barrier (BBB), on occasion, the CML clone will thrive and evolve to an accelerated phase in the resulting imatinib sanctuary within the central nervous system. In this, CML resembles glioblastoma in that imatinib, which otherwise may be effective, cannot get to the tumor. Although a common street drug of abuse, methamphetamine is Food and Drug Administration-approved and marketed as a pharmaceutical drug to treat attention-deficit disorders. It has shown the ability to open the BBB in rodents. We have some clinical hints that it may do so in humans as well. This short note presents three new points potentially leading to better tyrosine kinase inhibition behind the BBB: 1) Pharmaceutical methamphetamine may have a useful role in treating both CML and glioblastoma by allowing higher imatinib concentrations behind the BBB. 2) The old antidepressant and monoamine oxidase inhibitor selegiline, used to treat Parkinson disease, is catabolized to methamphetamine. Selegiline, as a nonscheduled drug,may therefore be an easier way to open the BBB, allowing more effective chemotherapy with tyrosine kinases. 3) Dasatinib is a tyrosine kinase inhibitor with a spectrum of inhibition only partially overlapping that of imatinib and a mechanism of tyrosine kinase inhibition that is different from that of imatinib. The two should be additive. In addition, dasatinib crosses the BBB poorly, and it can therefore be expected to benefit from methamphetamine-assisted entry.

Prevention of psychiatric illness in the elderly, I: Path to prevention of dementia

Prevention of psychiatric illness in the elderly, I: Path to prevention of dementia

Novel Transdermal Delivery Formulation of the Monoamine Oxidase Inhibitor Selegiline Nearing Release for Treatment of Depression

4However, the unique therapeutic properties of the MAOIs for patients with so-called atypical depressive features (i.e., hypersomnolence, increased appetite, and weight gain) 6 coupled with the lack of progress in developing effective and welltolerated medications with truly unique mechanisms of action have led to continued efforts to develop safer and easier-to-use MAOIs. The holy grail of this search for a better MAOI has been identification of a drug that (1) did not require a special diet, (2) has a tolerability and ease-of-use profile comparable to the selective serotonin reuptake inhibitors (SSRIs), and (3) is as effective as tranylcypromine or phenelzine. Two aspects of the pharmacology of the older MAOIs—lack of selectivity for the 2 subtypes of MAO (i.e., type A and type B) and the irreversibility of inhibitory effect— have been targets for drug development. The subtyping of the 2 types of MAO is based on the preferred substrates of enzymatic activity. The A type of enzyme, which is found in the gut, liver, and brain, metabolizes norepinephrine, serotonin, and tyramine. Thus, it is inhibition of MAO A

Neuroprotection in Parkinson's disease: an elusive goal.

Parkinson's disease is a chronic progressive condition that causes disability and reduction of quality of life. Symptomatic treatments are effective in the early disease; however, with time, most patients develop motor complications. Neuroprotective therapies are those that can slow disease progression; unfortunately, these agents are not available. Advances in the knowledge of the possible pathogenic events that can lead to nigral cell death have increased dramatically. These mechanisms include oxidative stress, mitochondrial dysfunction, inflammation, excitotoxicity, alterations in protein degradation, and ultimately apoptosis. Based on these laboratory scientific findings, a number of agents have been studied in clinical trials. However, how to assess disease evolution and establish reliable endpoints is still an unresolved issue. The monoamine oxidase inhibitors selegiline and rasagiline have been shown to be neuroprotective in vitro and in animal models, but so far this property was not demonstrated in clinical trials. Other agents have been studied and still others are undergoing clinical investigation. These include antiexcitotoxicity drugs like riluzole, the bioenergetic agent coenzyme Q10, trophic factors, and antiapoptotic drugs. Laboratory and clinical data suggest that dopamine agonists may have a neuroprotective action, but this has yet to be proven. However, as our basic and clinical knowledge on Parkinson's disease increases, it is likely that a neuroprotective drug will be found.

Determination of 4-hydroxy-3-methoxyphenylethylene glycol 4-sulfate in human urine using liquid chromatography-tandem mass spectrometry.

A major metabolite of norepinephrine (NE) in brain is 4-hydroxy-3-methoxyphenylethylene glycol (MHPG). In many species, a large fraction of MHPG formed in brain is converted to the sulfate conjugate. Consequently, MHPG sulfate has been proposed as a biomarker for NE metabolism in the central nervous system. As part of the clinical trials of the monoamine oxidase inhibitor selegiline for treating cocaine addiction, we required a method for measuring urine concentrations of MHPG sulfate. Using a deuterium-labeled analogue as an internal standard, we developed a liquid chromatography-electrospray ionization tandem mass spectrometry (LC-MS/ MS) method for determination of MHPG sulfate in human urine. Sample preparation involves simply diluting 50 microL of urine with 1 mL of ammonium formate buffer and adding the internal standard. The sample is centrifuged, the supernate is transferred to an autosampler vial, and 10 microL is injected into the LC-MS/MS system. Standard curves from 50 to 10,000 ng/mL are generated. Only one sample of 277 clinical samples analyzed had a concentration outside of this range. Precision (coefficient of variation) ranged from 1.9 to 9.7%, and accuracy ranged from 97 to 103% of expected values for controls prepared by spiking sulfatase-treated urine with MHPG sulfate.

Selegiline induces dopamine release through ATP-sensitive potassium channels in the rat caudate-putamen in vitro

We used superfusion chambers to investigate the role of ATP-sensitive potassium (K ATP) channels in dopamine (DA) release elicited by the monoamine oxidase inhibitor selegiline in the rat caudate-putamen in vitro. Selegiline (R[−]-deprenyl), but not the S[+] enantiomer, concentration-dependently induced increases in extracellular concentrations of DA, with a maximal increase to 185% in comparison to basal outflow at 0.1 mM selegiline. Since in our experimental conditions exclusive MAO inhibition does not lead to an enhancement of extracellular DA levels, the effect of selegiline on DA levels seems not to be related to MAO inhibition. Butanedione (0.1 mM), a specific K ATP channel blocker, also significantly enhanced extracellular DA levels in the rat caudate-putamen to approx. 260%. Selegiline only led to an additional increase of DA outflow, when added to submaximal concentrations of butanedione or tolbutamide, implying that selegiline is acting on identical sites. When the K ATP channel opener cromakalim was added to the incubation medium, basal as well as butanedione-enhanced DA levels markedly decreased to about 40% when compared to baseline values. Selegiline-activated DA release was also antagonized by cromakalim. The selegiline effect was neither modulated by preincubation with the uptake inhibitor nomifensine nor by the DA agonist quinpirole and antagonist sulpiride. In conclusion these results suggest that selegiline is able to modulate K ATP channels in the caudate-putamen of the rat in vitro resulting in an enhancement of striatal DA release.

Tyramine kinetics and pressor sensitivity during monoamine oxidase inhibition by selegiline

The effect of the monoamine oxidase inhibitor selegiline on tyramine metabolism and intravenous and oral tyramine pressor sensitivity was studied in healthy subjects. After oral doses of tyramine, which caused systolic blood pressure to increase by 30 mm Hg, we determined plasma concentrations of p-hydroxyphenylacetic acid (HPAA) and of conjugated and unconjugated tyramine. When 20 mg/day of selegiline was administered, the AUCspec of HPAA decreased from 86% to 64% and the AUCspec of conjugated tyramine increased from 13% to 35% of the sum of total tyramine and HPAA. Pressor sensitivity was enhanced more with oral administration of tyramine than with intravenous administration of tyramine. After the drug was discontinued, initial values were reached within 4 days (one subject) and 2 weeks (two subjects). Fifty-five percent of the selegiline dose was eliminated in urine as amphetamine and methamphetamine. The findings support the assumption that selegiline does not selectively inhibit monoamine oxidase-B (MAO-B) when administered in doses of 20 mg/day and higher.