Erin M. MacKenzie

An update on amine oxidase inhibitors: Multifaceted drugs

Although not used as extensively as other antidepressants for the treatment of depression, the monoamine oxidase (MAO) inhibitors continue to hold a niche in psychiatry and to have a relatively broad spectrum with regard to treatment of psychiatric and neurological disorders. Experimental and clinical research on MAO inhibitors has been expanding in the past few years, primarily because of exciting findings indicating that these drugs have neuroprotective properties (often independently of their ability to inhibit MAO). The non-selective and irreversible MAO inhibitors tranylcypromine (TCP) and phenelzine (PLZ) have demonstrated neuroprotective properties in numerous studies targeting elements of apoptotic cascades and neurogenesis. l-Deprenyl and rasagiline, both selective MAO-B inhibitors, are used in the management of Parkinsons disease, but these drugs may be useful in the treatment of other neurodegenerative disorders given that they demonstrate neuroprotective/neurorescue properties in a wide variety of models in vitro and in vivo. Although the focus of studies on the involvement of MAO inhibitors in neuroprotection has been on MAO-B inhibitors, there is a growing body of evidence demonstrating that MAO-A inhibitors may also have neuroprotective properties. In addition to MAO inhibition, PLZ also inhibits primary amine oxidase (PrAO), an enzyme implicated in the etiology of Alzheimers disease, diabetes and cardiovascular disease. These multifaceted aspects of amine oxidase inhibitors and some of their metabolites are reviewed herein.

The relevance of neuroactive steroids in schizophrenia, depression, and anxiety disorders.

1. Neuroactive steroids are steroid hormones that exert rapid, nongenomic effects at ligand-gated ion channels. There is increasing awareness of the possible role of these steroids in the pathology and manifestation of symptoms of psychiatric disorders. The aim of this paper is to review the current knowledge of neuroactive steroid functioning in the central nervous system, and to assess the role of neuroactive steroids in the pathophysiology and treatment of symptoms of schizophrenia, depression, and anxiety disorders. Particular emphasis will be placed on GABAA receptor modulation, given the extensive knowledge of the interactions between this receptor complex, neuroactive steroids, and psychiatric illness.2. A brief description of neuroactive steroid metabolism is followed by a discussion of the interactions of neuroactive steroids with acute and chronic stress and the HPA axis. Preclinical and clinical studies related to psychiatric disorders that have been conducted on neuroactive steroids are also described.3. Plasma concentrations of some neuroactive steroids are altered in individuals suffering from schizophrenia, depression, or anxiety disorders compared to values in healthy controls. Some drugs used to treat these disorders have been reported to alter plasma and brain concentrations in clinical and preclinical studies, respectively.4. Further research is warranted into the role of neuroactive steroids in the pathophysiology of psychiatric illnesses and the possible role of these steroids in the successful treatment of these disorders.

Monoamine oxidase inhibitors and neuroprotection: a review.

Monoamine oxidase inhibitors have been available for more than 50 years, initially developed as antidepressants but currently used in a variety of psychiatric and neurological conditions. There has been a recent surge of interest in monoamine oxidase inhibitors because of their reported neuroprotective and/or neurorescue properties. Interestingly, it seems that often these properties are independent of their ability to inhibit monoamine oxidase. This review article presents an overview of the neuroprotective/neurorescue properties of these multifaceted drugs and focuses on phenelzine, (-)-deprenyl, rasagiline, ladostigil, tranylcypromine, moclobemide, and clorgyline and their possible neuroprotective mechanisms.

d-serine and schizophrenia: an update

Considering the lengthy history of pharmacological treatment of schizophrenia, the development of novel antipsychotic agents targeting the glutamatergic system is relatively new. A glutamatergic deficit has been proposed to underlie many of the symptoms typically observed in schizophrenia, particularly the negative and cognitive symptoms (which are less likely to respond to current treatments). d-serine is an important coagonist of the glutamate NMDA receptor, and accumulating evidence suggests that d-serine levels and/or activity may be dysfunctional in schizophrenia and that facilitation of d-serine transmission could provide a significant therapeutic breakthrough, especially where conventional treatments have fallen short. A summary of the relevant animal data, as well as genetic studies and clinical trials examining d-serine as an adjunct to standard antipsychotic therapy, is provided in this article. Together, the evidence suggests that research on the next generation of antipsychotic agents should include studies on increasing brain levels of d-serine or mimicking its action on the NMDA receptor.

The pharmacology and formulation of paliperidone extended release.

Paliperidone, or 9-hydroxyrisperidone (Invega®, Janssen, Antwerp, Belgium) is the major active metabolite of the atypical antipsychotic risperidone (Risperdal®, Janssen). It possesses a similar, though not identical, receptor pharmacology to the parent molecule. There are additional differences in terms of its predominant renal metabolism, lower protein binding and decreased inhibition of P-glycoprotein leading to decreased potential for drug–drug interactions. Paliperidone is approved as an extended release (ER) tablet based on an osmotic-controlled release oral Push–Pull™ delivery system (Oral Osmotic System, OROS®, Alza Corporation) for the treatment of schizophrenia. The ER formulation results in decreased fluctuations in plasma drug levels and allows for once-daily administration with initial tolerability that permits treatment initiation at a clinically effective dose without the need for titration. This achieves therapeutic levels rapidly and simplifies dosing regimens, leading to potentially better adherence and improved outcome. The present review focuses on the clinical implications of the pharmacology and formulation of paliperidone ER.

Phenelzine: An Old Drug That May Hold Clues to The Development of New Neuroprotective Agents

5 OZET: Fenelzin: Eski bir ilac, yeni noroprotektif ajanlar›n gelifltirilmesine ipuclar› tutabilir Panik bozukluk ve sosyal anksiyete bozukluu gibi anksiye- te bozukluklar›n›n tedavisinde kullan›lan monoamin oksi- daz (MAO) inhibitoru bir antidepresan olan fenelzinin geci- ci onbeyin iskemisi olan bir hayvan modelinde noroprotek- tif etkileri olduu gosterilmifltir. Fenelzinin MAO inhibisyo- nu etkisi yan› s›ra farmakolojik ve terapotik profiline ekle- nebilir cok say›da etkisi vard›r. Bu etkiler GABA transamina- z›n inhibisyonuyla beyin GABA duzeylerini artt›rmas›, glu- tamat›n ifllevsel durumu uzerine etkileri, reaktif aldehitlerin tutulumu, primer amin oksidaz inhibisyonu ve beyin kay- nakl› norotrofik faktor (BDNF) uzerindeki etkilerin inhibe edilmesidir. 2-Feniletilidenehidrazin, fenelzinin onemli bir metabolit olup GABA beyin duzeylerini artt›rd›¤› gosteril- mifltir ve gecici onbeyin iskemisi modelinde reaktif aldehit- lerin tutulumu ve noroprotektif etkileri keflfedilmifltir. Fe- nelzin ve feniletilidenehidrazin bu etkileri nedeniyle ozel- likle norodejenerasyon iceren psikiyatrik ve norolojik bo- zukluklar›n tedavisi icin gelecekte ilac tasar›m› yonunden goz onunde tutulmal›d›r. ABSTRACT: Phenelzine: An old drug that may hold clues to the development of new neuroprotective agents The monoamine oxidase (MAO)-inhibiting antidepressant phenelzine (PLZ) is also used in the treatment of anxiety disorders such as panic disorder and social anxiety disorder and has been shown to have neuroprotective actions in an animal model of transient forebrain ischemia. Phenelzine has multiple actions in addition to inhibition of MAO that may contribute to its pharmacological and therapeutic profile. These actions include inhibition of GABA transaminase and elevation of brain levels of GABA, effects on functional availability of glutamate, sequestration of reactive aldehydes, inhibition of primary amine oxidase and effects on brain-derived neurotrophic factor (BDNF). 2- Phenylethylidenehydrazine (PEH) has been identified as a major metabolite of PLZ and has also been shown to elevate brain levels of GABA, to sequester reactive aldehydes and to exert neuroprotective effects in a transient forebrain ischemia model. The actions of PLZ and PEH should be considered when designing future drugs for the treatment of psychiatric and neurologic disorders, particularly those involving neurodegeneration.

Comparison of phenelzine and geometric isomers of its active metabolite, β-phenylethylidenehydrazine, on rat brain levels of amino acids, biogenic amine neurotransmitters and methylamine

Phenelzine is a monoamine oxidase (MAO) inhibitor used in treatment of depression and anxiety disorders. It also elevates brain levels of γ-aminobutyric acid (GABA) and inhibits primary amine oxidase (PrAO), an enzyme whose activity and/or expression has been reported to be increased in diabetes mellitus, Alzheimer’s disease and cardiovascular disorders. Phenelzine is not only an inhibitor of, but also a substrate for, MAO and it has been suggested that an active metabolite, namely β-phenylethylidenehydrazine (PEH), is responsible for phenelzine’s effects on amino acids. PEH is also a strong inhibitor of PrAO but has weak effects on MAO. PEH has a double bond and can thus exist as (E)- and (Z)-geometric isomers, but to date the two isomers have not been compared with regard to their neurochemical effects. We have investigated the effects of phenelzine, (E)- and (Z)-PEH on rat whole brain levels of amino acids, biogenic amine neurotransmitters and methylamine (an endogenous substrate of PrAO). Under the conditions used in the study, (E)- and (Z)-PEH appear to be equivalent in their neurochemical properties. Both PEH isomers and phenelzine produced marked increases in rat brain levels of GABA and alanine while decreasing brain levels of glutamine. Phenelzine increased brain levels of biogenic amine neurotransmitters (noradrenaline, dopamine and serotonin), whereas neither PEH isomer altered levels of these neurotransmitters to a considerable extent. All three drugs significantly increased rat brain levels of methylamine, with (E)- and (Z)-PEH causing a greater increase than phenelzine. These results are discussed in relation to the possible therapeutic applications of these drugs.

Inhibition of p53 attenuates ischemic stress-induced activation of astrocytes.

In cerebral ischemia, studies of cell death have focused primarily on neurons, but recent work indicates that ischemia also causes damage to astrocytes. Activation of astrocytes is a typical brain response to stress stimuli and is evidenced by changes in cellular function and morphology, as well as upregulation of glial fibrillary acidic protein. The tumor-suppressor transcription factor p53 has recently been implicated as a mediator of ischemia-induced neuronal death, but very little is known about its role in the activation or the death of astrocytes. The present study investigated the role of p53 in astrocyte and neuronal toxicity using in-vitro and in-vivo ischemic stroke models. We showed that p53 is activated in ischemic brains and in oxygen–glucose deprivation (OGD)-induced cell death in neurons and astrocytes. Inhibition of p53 activity using either pifithrin-&agr; or small interference RNA interference reduced OGD-induced cell death and pifithrin-&agr; reversed OGD-induced impairment of glutamate uptake in astrocytes, suggesting that p53 might play a key role in mediating neurotoxicity and gliotoxicity in ischemic brain injury. This study shows that p53 is activated in astrocytes during ischemia and that inhibition of the activity of this molecule prevents not only OGD-induced neuronal and astrocytic death but also astrocyte activation and impaired glutamate uptake. These findings suggest that p53 may be a valuable therapeutic target in ischemic brain injury.

N-Propynyl analogs of β-phenylethylidenehydrazines: Synthesis and evaluation of effects on glycine, GABA, and monoamine oxidase

A group of beta-phenylethylidenehydrazines possessing a variety of substituents (Me, OMe, Cl, F, and CF(3)) at the ortho-, meta-, or para-positions of the phenyl ring, in conjunction with either a N-bis-(2-propynyl) or a N-mono-(2-propynyl) moiety, were synthesized and compared to the novel neuroprotective drug beta-phenylethylidenehydrazine (PEH) with regard to their ability to inhibit the enzymes GABA-transaminase (GABA-T) and monoamine oxidase (MAO)-A and -B in vitro in brain tissue. Two of the analogs synthesized (mono- and bis-N-propynylPEH) were also studied exvivo in rats to compare their effects to those of PEH with regard to ability to inhibit GABA-T and MAO and to change brain levels of several important amino acids. Unlike PEH, none of the new drugs inhibited GABA-T in vitro at 10 or 100 microM, and all of the drugs (including PEH) were poor inhibitors (at 10 microM) of MAO-A and -B invitro. The two analogs studied exvivo inhibited GABA-T to a lesser extent than PEH, unlike PEH that did not elevate brain levels of GABA, and inhibited MAO-A and -B more potently than PEH. Interestingly, unlike PEH, the two analogs caused marked increases in brain levels of glycine; because of the current interest in drugs that increase glycine availability in the brain as potential antipsychotic drugs, these two analogs now warrant further investigation.