K. Magyar

Novel (-)deprenyl-derived selective inhibitors of B-type monoamine oxidase. The relation of structure to their action

Abstract A structure-activity relationship study has revealed the importance of the aromatic ring and the optimum length of the chain between the aromatic ring and the nitrogen for the selective inhibition of MAO-B. Among the (−)deprenyl derived new compounds described in this study N -methyl- N -propargyl-(2-furyl-1-methyl)-ethylammonium. HCl(U-1424) seems to be the most promising selective inhibitor of MAO-B.

Activated MAO-B in the brain of Alzheimer patients, demonstrated by [11C]-L-deprenyl using whole hemisphere autoradiography

In the human brain the monoaminooxidase-B enzyme or MAO-B is highly abundant in astrocytes. As astrocyte activity and, consequently, the activity of the MAO-B enzyme, is up-regulated in neuroinflammatory processes, radiolabelled analogues of deprenyl may serve as an imaging biomarker in neuroinflammation and neurodegeneration, including Alzheimers disease. In the present study [(11)C]-L-deprenyl, the PET radioligand version of L-deprenyl or selegiline®, a selective irreversible MAO-B inhibitor was used in whole hemisphere autoradiographic experiments in human brain sections in order to test the radioligands binding to the MAO-B enzyme in human brain tissue, with an eye on exploring the radioligands applicability as a molecular imaging biomarker in human PET studies, with special regard to diagnostic detection of reactive astrogliosis. Whole hemisphere brain sections obtained from Alzheimer patients and from age matched control subjects were examined. In control brains the binding of [(11)C]-L-deprenyl was the highest in the hippocampus, in the basal ganglia, the thalamus, the substantia nigra, the corpus geniculatum laterale, the nucleus accumbens and the periventricular grey matter. In Alzheimer brains significantly higher binding was observed in the temporal lobes and the white matter. Furthermore, in the Alzheimer brains in the hippocampus, temporal lobe and white matter the binding negatively correlated with Braak stages. The highest binding was observed in Braak I-II, whereas it decreased with increasing Braak grades. The increased regional binding in Alzheimer brains coincided with the presence of an increased number of activated astrocytes, as demonstrated by correlative immunohistochemical studies with GFAP in adjacent brain slices. Deprenyl itself as well as the MAO-B antagonist rasagiline did effectively block the binding of the radioligand, whereas the MAO-A antagonist pirlindole did not affect it. Compounds with high affinity for the PBR system did not block the radioligand binding either, providing evidence for the specificity of [(11)C]-L-deprenyl for the MAO-B enzyme. In conclusion, the present observations indicate that [(11)C]-L-deprenyl may be a promising and selective imaging biomarker of increased MAO-B activity in the human brain and can therefore serve as a prospective PET tracer targeting neuroinflammation and neurodegeneration.

Semicarbazide-Sensitive Amine Oxidase: Current Status and Perspectives

Semicarbazide-sensitive amine-oxidase (SSAO) is present in various human tissues and in plasma. Oxidative deamination of short-chain aliphatic amines is catalyzed by this enzyme to afford the corresponding aldehydes, ammonia and hydrogen peroxide. Methylamine and aminoacetone have been recognized to be physiological substrates for SSAO. There are several pathological states where increased serum SSAO activity have been found, such as diabetes mellitus, congestive heart failure, multiple types of cerebral infarction, uraemia, and hepatic cirrhosis. The role of SSAO in pathophysiology of diabetes has been most extensively investigated. The elevated formation of the potentially cytotoxic products of the enzyme may contribute to the endothelial injury of blood vessels, resulting in the early development of severe atherosclerosis; it may also contribute to the pathogenesis of diabetic angiopathy. It is now suggested that SSAO inhibitors may prevent the development of atherosclerosis and diabetic complications as well. Inhibitors can be conveniently subdivided into the main groups of hydrazine derivatives, arylalkylamines, propenyl- and propargylamines, oxazolidinones, and haloalkylamines. Of them, aryl(alkyl)hydrazines, and 3-halo-2-phenylallylamines are generally very strong SSAO inhibitors. Most of these inhibitors of SSAO have been originally developed for other purposes, or they are simple chemical reagents with highly reactive structural element(s); these compounds have not been able to fulfil all criteria of high potency, selectivity, and acceptable toxicity. New potent compounds with selectivity and low toxicity are needed, which may prove useful tools for understanding the roles and function of SSAO, or they may even be valuable substances for treatment of various diseases.

Does the B form selective monoamine oxidase inhibitor lose selectivity by long term treatment

Abstract Rats were treated subcutaneously with different doses of the “B form” selective monoamine oxidase (MAO) inhibitors deprenyl (phenylisopropylmethylpropargylamine), U-1424 (N-methyl-N-propargyl-[2-furyl-1-methyl]-ethylammonium) and J-508 (N-methyl-N-propargyl-[1-indenyl]-ammonium. HCl) in order to study the changes of their selectivity during 21 days of treatment. When the daily dose of (−) deprenyl and U-1424 was 0.05 or 0.25 mg/kg body wt (similar to the human dosage of deprenyl in clinical trials), in spite of their repeated administration, a fairly selective inhibition pattern was maintained. In this case at a low rate of oxidation of beta-phenylethylamine (MAO-B form specific substrate) the conversion of serotonin (MAO-A form specific substrate) was near to the untreated value. When 1.0 mg/kg of these inhibitors were repeatedly administered they also inhibited the A form of MAO. As J-508 is a more potent MAO inhibitor than deprenyl and U-1424. even the lowest dose (0.05 mg/kg) used in this study proved to inhibit MAO-A. All the compounds tested were less effective on liver than on brain MAO; thus their selectivity was more pronounced on liver homogenate.

Pharmacological aspects of (-)-Deprenyl

Deprenyl, the selective irreversible inhibitor of monoamine oxidase-B (MAO-B), has been synthesised as a potential antidepressant, however, due to its dopamine potentiating capacity, became a registered drug in the treatment of Parkinsons disease. Deprenyl possesses a wide range of pharmacological activities; some of them are not related to its MAO-B inhibitory potency. Beside its dopamine potentiating effect, it renders protection against a number of dopaminergic, cholinergic and noradrenergic neurotoxins with a complex mechanism of action. By inducing antioxidant enzymes and decreasing the formation of reactive oxygen species, deprenyl is able to combat an oxidative challenge implicated as a common causative factor in neurodegenerative diseases. In a dose substantially lower than required for MAO-B inhibition (10(-9)-10(-13) M), deprenyl interferes with early apoptotic signalling events induced by various kinds of insults in cell cultures of neuroectodermal origin, thus protecting cells from apoptotic death. Deprenyl requires metabolic conversion to a hitherto unidentified metabolite to exert its antiapoptotic effect, which serves to protect the integrity of the mitochondrion by inducing transcriptional and translational changes. Pharmacokinetic and metabolism studies have revealed that deprenyl undergoes intensive first pass metabolism, and its major metabolites also possess pharmacological activities. The ratio of the parent compound and its metabolites reaching the systemic circulation and the brain are highly dependent on the routes of administration. Therefore, in the treatment of neurodegenerative diseases, reconsideration of the dosing schedule, by lowering the dose of deprenyl and choosing the most appropriate route of administration, would diminish undesired adverse effects, with unaltered neuroprotective potency.

The neuroprotective and neuronal rescue effects of (-)-deprenyl

The pharmacological effects of (-)-deprenyl is multi-fold in its nature (dopamine sparing activity, neuroprotective and neuronal rescue effects), which cannot be explained solely by the irreversible MAO-B inhibitory action of the substance. Deprenyl slightly inhibits the re-uptake of noradrenaline and dopamine, but methylamphetamine, the metabolite of the inhibitor, by one order of magnitude is more potent in this respect, than the parent compound. Neither the metabolite nor (-)-deprenyl acts on the uptake of serotonin. The inhibitor has an intensive first pass metabolism after oral treatment. The in vivo pharmacokinetic studies with (-)-deprenyl, using the double labelled radioisotope technique (1.5 mg/kg; orally) in rats revealed that the molar concentration of methylamphetamine can reach the level suitable to induce a significant inhibition of amine uptake. Deprenyl, but especially methylamphetamine pre-treatment can prevent the noradrenaline release induced by the noradrenergic neurotoxin DSP-4. The uptake inhibitory effect of (-)-deprenyl and the metabolites is reversible. After repeated administration of (-)-deprenyl (1.5 mg/kg daily, for 8 days) sustained concentration of its metabolites was detected, compared to that of the acute studies. This can at least partly explain why (-)deprenyl should be administered daily to evoke therapeutic effects in Parkinsons disease. Administration of (-)-deprenyl in a low dose, following the toxic insult, can rescue the damaged neurones. The neuronal rescue effect of the drug was studied on M-1 human melanoma cells in tissue culture. The inhibitor reduced the apoptosis of serum-deprived M-1 cells, but the (+)-isomer failed to exert this effect. The (+/-)-desmethyl-deprenyl almost lacks the property to inhibit apoptosis. For neuroprotection and neuronal rescue an optimal dose of (-)-deprenyl should be administered, because to reach a well balanced concentration of the metabolites in tissues is critical.

Prostacyclin mediates antiaggregatory and hypotensive actions of endothelin in anaesthetized beagle dogs.

The effects of endothelin on blood pressure and in vivo aggregation of platelets were studied in anaesthetized beagle dogs. Intravenous administration of endothelin (0.03‐0.3 nmol kg−1) resulted in a dose‐dependent transient hypotension followed by a long‐lasting hypertension and inhibition of platelet aggregation. These changes were accompanied by dose‐dependent elevation of plasma 6‐keto prostaglandin F1α levels. Pretreatment of the animals with acetylsalicylic acid significantly attenuated both the vascular and antiaggregatory responses to endothelin. These data provide evidence for in vivo release of prostacyclin by endothelin in anaesthetized dogs.

Semicarbazide-Sensitive Amine Oxidase/Vascular Adhesion Protein 1: Recent Developments Concerning Substrates and Inhibitors of a Promising Therapeutic Target

SSAO/VAP-1 is not only involved in the metabolism of biogenic and xenobiotic primary amines and in the production of metabolites with cytotoxic effects or certain physiological actions, but also plays a role, for example, as an adhesion molecule, in leukocyte trafficking, in regulating glucose uptake and in adipocyte homeostasis. Interest in the enzyme has been stimulated by the findings that the activities of the SSAOs are altered (mostly increased) in various human disorders, including diabetes, congestive heart failure, liver cirrhosis, Alzheimers disease and several inflammatory diseases, although the underlying causes are often unknown. On the basis of their insulin-mimicking effect, SSAO substrates are possibly capable of ameliorating metabolic changes in diabetes, while SSAO inhibitors (somewhat of a contradiction) are of potential benefit in preventing diabetes complications, atherosclerosis and oxidative stress contributing to several disorders or modulating inflammation, and hence may be of substantial therapeutic value. Great efforts have been made to develop novel compounds which may lead to future drugs useful in therapy, based on their effects on SSAO/VAP-1, and some of the results relating to novel substrates and inhibitors are surveyed in the present review.

Serum semicarbazide-sensitive amine oxidase (SSAO) activity is an independent marker of carotid atherosclerosis.

BACKGROUND Clinical and experimental studies suggest that increased activity of semicarbazide-sensitive amine oxidase (SSAO) and the production of cytotoxic metabolites (e.g., formaldehyde and hydrogen peroxide) may play an important role in the pathogenesis of atherosclerosis. The present study was designed to assess the relationship between the increased activity of the enzyme and the severity of atherosclerosis in diabetic and control subjects. METHODS The study included 29 patients with type 2 diabetes mellitus and 25 control subjects. Human serum SSAO activity was determined by using 14C-benzylamine as substrate. Mean common carotid intima-media thickness (IMT), Crouse score and Bogousslawsky score was evaluated by color-coded, high-resolution duplex carotid sonography. RESULTS Serum SSAO activity was significantly increased in patients with type 2 diabetes compared to controls. Carotid plaque score (Crouse score), total cholesterol level and age-corrected intima-media thickness showed positive correlation with enzyme activity in control subjects. In patients with diabetes, serum SSAO activity correlated with the severity of carotid stenosis (Bogousslawsky score) as well as the carotid plaque score. CONCLUSIONS Determination of serum SSAO activity might be a candidate biochemical marker of early atherosclerosis and diabetic macrovascular complications.

Urinary excretion of deprenyl metabolites

(+)-Deprenyl metabolites in rats urine, such as nordeprenyl. methamphetamine amphetamine and p-hydroxy. methamphetamine were identified by HPLC-MS. After oral administration of 10 mg of pure (-)- and (+)-deprenyl to human volunteers, their urine was analyzed by gas chromatography. The concentration of methamphetamine was found to be overwhelming in the case of the (-)-isomer, while amphetamine and methamphetamine were excreted in equal amounts when (+)-deprenyl was administered. The metabolic processes of deprenyl resulted in metabolites possessing different lipophilicity, as it has been shown by planar displacement chromatography.