l-Deprenyl Prevents Lipid Peroxidation and Memory Deficits Produced by Cerebral Ischemia in Rats

Type-B monoamine oxidase inhibitors in neurological diseases: clinical applications based on preclinical findings

Type-B monoamine oxidase inhibitors, encompassing selegiline, rasagiline, and safinamide, are available to treat Parkinson's disease. These drugs ameliorate motor symptoms and improve motor fluctuation in the advanced stages of the disease. There is also evidence supporting the benefit of type-B monoamine oxidase inhibitors on non-motor symptoms of Parkinson's disease, such as mood deflection, cognitive impairment, sleep disturbances, and fatigue. Preclinical studies indicate that type-B monoamine oxidase inhibitors hold a strong neuroprotective potential in Parkinson's disease and other neurodegenerative diseases for reducing oxidative stress and stimulating the production and release of neurotrophic factors, particularly glial cell line-derived neurotrophic factor, which support dopaminergic neurons. Besides, safinamide may interfere with neurodegenerative mechanisms, counteracting excessive glutamate overdrive in basal ganglia motor circuit and reducing death from excitotoxicity. Due to the dual mechanism of action, the new generation of type-B monoamine oxidase inhibitors, including safinamide, is gaining interest in other neurological pathologies, and many supporting preclinical studies are now available. The potential fields of application concern epilepsy, Duchenne muscular dystrophy, multiple sclerosis, and above all, ischemic brain injury. The purpose of this review is to investigate the preclinical and clinical pharmacology of selegiline, rasagiline, and safinamide in Parkinson's disease and beyond, focusing on possible future therapeutic applications.

Pharmacological aspects of the neuroprotective effects of irreversible MAO-B inhibitors, selegiline and rasagiline, in Parkinson's disease

The era of MAO-B inhibitors dates back more than 50 years. It began with Kálmán Magyar's outstanding discovery of the selective inhibitor, selegiline. This compound is still regarded as the gold standard of MAO-B inhibition, although newer drugs have also been introduced to the field. It was revealed early on that selective, even irreversible inhibition of MAO-B is free from the severe side effect of the non-selective MAO inhibitors, the potentiation of tyramine, resulting in the so-called 'cheese effect'. Since MAO-B is involved mainly in the degradation of dopamine, the inhibitors lack any antidepressant effect; however, they became first-line medications for the therapy of Parkinson's disease based on their dopamine-sparing activity. Extensive studies with selegiline indicated its complex pharmacological activity profile with MAO-B-independent mechanisms involved. Some of these beneficial effects, such as neuroprotective and antiapoptotic properties, were connected to its propargylamine structure. The second MAO-B inhibitor approved for the treatment of Parkinson's disease, rasagiline also possesses this structural element and shows similar pharmacological characteristics. The preclinical studies performed with selegiline and rasagiline are summarized in this review.

Effects of HIV/TAT protein expression and chronic selegiline treatment on spatial memory, reversal learning and neurotransmitter levels in mice

Neurotoxic viral protein TAT may contribute to deficits in dopaminergic and cognitive function in individuals infected with human immunodeficiency virus. Transgenic mice with brain-specific doxycycline-induced TAT expression (TAT+, TAT- control) show impaired cognition. However, previously reported TAT-induced deficits in reversal learning may be compromised by initial learning deficits. We investigated the effects of TAT expression on memory retention/recall and reversal learning, and neurotransmitter function. We also investigated if TAT-induced effects can be reversed by improving dopamine function with selegiline, a monoamine oxidase inhibitor. Mice were tested in the Barnes maze and TAT expression was induced after the task acquisition. Selegiline treatment continued throughout behavioral testing. Dopamine, serotonin and glutamate tissue levels in the prefrontal/orbitofrontal cortex, hippocampus and caudate putamen were measured using high performance liquid chromatography. Neither TAT expression nor selegiline altered memory retention. On day 2 of reversal learning testing, TAT+ mice made fewer errors and used more efficient search strategies than TAT- mice. TAT expression decreased dopamine turnover in the caudate putamen, increased serotonin turnover in the hippocampus and tended to increase the conversion of glutamate to glutamine in all regions. Selegiline decreased dopamine and serotonin metabolism in all regions and increased glutamate levels in the caudate putamen. In the absence of impaired learning, TAT expression does not impair spatial memory retention/recall, and actually facilitates reversal learning. Selegiline-induced increases in dopamine metabolism did not affect cognitive function. These findings suggest that TAT-induced alterations in glutamate signaling, but not alterations in monoamine metabolism, may underlie the facilitation of reversal learning.

Reactive oxygen species in the regulation of synaptic plasticity and memory

The brain is a metabolically active organ exhibiting high oxygen consumption and robust production of reactive oxygen species (ROS). The large amounts of ROS are kept in check by an elaborate network of antioxidants, which sometimes fail and lead to neuronal oxidative stress. Thus, ROS are typically categorized as neurotoxic molecules and typically exert their detrimental effects via oxidation of essential macromolecules such as enzymes and cytoskeletal proteins. Most importantly, excessive ROS are associated with decreased performance in cognitive function. However, at physiological concentrations, ROS are involved in functional changes necessary for synaptic plasticity and hence, for normal cognitive function. The fine line of role reversal of ROS from good molecules to bad molecules is far from being fully understood. This review focuses on identifying the multiple sources of ROS in the mammalian nervous system and on presenting evidence for the critical and essential role of ROS in synaptic plasticity and memory. The review also shows that the inability to restrain either age- or pathology-related increases in ROS levels leads to opposite, detrimental effects that are involved in impairments in synaptic plasticity and memory function.

The effects of hypoxia/reoxygenation on the physiological behaviour of U373-MG astrocytes

Nerve cells are very susceptible to hypoxia responsive for mitochondrial dysfunctions involved in the subsequent oxidative stress, apoptosis and necrosis. In this paper, we examined the effect of 12 h incubation of U-373 MG astrocytes in hypoxic environment (73% N(2): 2% O(2): 5% CO(2), v:v) by evaluating cell proliferation, modifications of NO and ATP production, intracellular Ca(2+) concentration [Ca(2+)](i), membrane potential, desferoxamine-chelatable free iron, esterified F2-isoprostanes levels and the production of phosphorylated ERK. The same parameters were evaluated also after a following re-oxygenation period of 24 h. Immediately after hypoxia the NO concentration increased significantly and returned to values similar to those of controls after the re-oxygenation period. At the same time, ATP levels remained similar to controls and the cell proliferation significantly decreased. This involved a significant increase of [Ca(2+)](i) immediately after hypoxia and the value remained significantly elevated after the following re-oxygenation period. Moreover, after hypoxia, astrocytes were slightly although not significantly depolarized. Indeed iron and F2-isoprostanes levels increased significantly after hypoxia. Finally ERK proteins increased slowly and not significantly after hypoxia and the same trend was observed after the re-oxygenation period. On the whole, our results indicate that 2% O(2) hypoxia induces a moderate oxidative stress, well tolerated by U-373 MG cells, remaining the ATP production, mitochondrial membrane potential and activated ERK proteins, similar to the values of controls.

Antioxidant Effects of SelegilIne in Oxidative Stress Induced by Iron Neonatal Treatment in Rats

Increased levels of iron in specific brain regions have been reported in neurodegenerative disorders. It has been postulated that iron exerts its deleterious effects on the nervous system by inducing oxidative damage. In a previous study, we have shown that iron administered during a particular period of the neonatal life induces oxidative damage in brain regions in adult rats. The aim of the present study was to evaluate the possible protective effect of selegiline, a monoamino-oxidase B (MAO-B) inhibitor used in pharmacotherapy of Parkinson's disease, against iron-induced oxidative stress in the brain. Results have shown that selegiline (1.0 and 10.0 mg/kg), when administered early in life was able to protect the substantia nigra as well as the hippocampus against iron-induced oxidative stress, without affecting striatum. When selegiline (10.0 mg/kg) was administered in the adult life to iron-treated rats, oxidative stress was reduced only in the substantia nigra.

Acceleration after-effects on learning and memory in rats: +10 Gz or +6 Gz for 3 min

High sustained positive Gz (+Gz) exposures have been shown to have a pathophysiological impact on the brain in rats. However, the consequence for brain function such as learning and memory remains elusive. In the present study, we investigated locomotor activity, learning ability and memory in rats over 6 days (d) following +6 Gz/3 min and +10 Gz/3 min exposures. In an open field test, rats treated with +10 Gz showed a significant increase in the time spent in the center square immediately and 2d after exposure compared with control rats. In contrast, the number of grid crosses and number of rears of rats decreased significantly immediately after +6 Gz and +10 Gz exposures. In addition, a Y-maze test revealed that +Gz exposures reduced the number of correct responses and increased total reaction time in rats, and the number of correct responses was negatively correlated with the total reaction time in all groups throughout the period of study. Moreover, the passive avoidance test exhibited that the latency increased significantly on 0 d and decreased significantly on 6 d after +Gz exposures compared with control. Thus, +6 Gz/3 min and +10 Gz/3 min exposures may transiently decrease locomotor activity, impair learning, and induce a deficit in memory retention in rats.

L-deprenyl protects against rotenone-induced, oxidative stress-mediated dopaminergic neurodegeneration in rats

The present study investigated oxidative damage and neuroprotective effect of the antiparkinsonian drug, L-deprenyl in neuronal death produced by intranigral infusion of a potent mitochondrial complex-I inhibitor, rotenone in rats. Unilateral stereotaxic intranigral infusion of rotenone caused significant decrease of striatal dopamine levels as measured employing HPLC-electrochemistry, and loss of tyrosine hydroxylase immunoreactivity in the perikarya of ipsilateral substantia nigra (SN) neurons and their terminals in the striatum. Rotenone-induced increases in the salicylate hydroxylation products, 2,3- and 2,5-dihydroxybenzoic acid indicators of hydroxyl radials in mitochondrial P2 fraction were dose-dependently attenuated by L-deprenyl. L-deprenyl (0.1-10mg/kg; i.p.) treatment dose-dependently attenuated rotenone-induced reductions in complex-I activity and glutathione (GSH) levels in the SN, tyrosine hydroxylase immunoreactivity in the striatum or SN as well as striatal dopamine. Amphetamine-induced stereotypic rotations in these rats were also significantly inhibited by deprenyl administration. The rotenone-induced elevated activities of cytosolic antioxidant enzymes superoxide dismutase and catalase showed further significant increase following L-deprenyl. Our findings suggest that unilateral intranigral infusion of rotenone reproduces neurochemical, neuropathological and behavioral features of PD in rats and L-deprenyl can rescue the dopaminergic neurons from rotenone-mediated neurodegeneration in them. These results not only establish oxidative stress as one of the major causative factors underlying dopaminergic neurodegeneration as observed in Parkinson's disease, but also support the view that deprenyl is a potent free radical scavenger and an antioxidant.

Low dose (-)deprenyl is cytoprotective: it maintains mitochondrial membrane potential and eliminates oxygen radicals

Hypoxia leads to a collapse in mitochondrial transmembrane potential (Deltapsi(M)), a fall in the ATP/ADP ratio, and finally cell death. Since (-)deprenyl directly modulates Deltapsi(M) and production of reactive oxygen species (ROS) by altering the respiratory function of mitochondria, we were interested in the dose-response relations of these effects. The changes in JC-1 red/green signal ratios {mitochondrial transmembrane potential}, and the changes in the cerium staining (intracellular ROS) in hypoxic and normoxic PC12 cell cultures were measured following 1 h of Argon hypoxia and 24 h of re-oxygenation in the absence and in the presence of various concentrations of (-)deprenyl. Deltapsi(M) shifted to lower values following hypoxia/re-oxygenation and all cells had decreased and uniform Deltapsi(M) levels. The amount of ROS increased. Following 24 h of treatment with various concentrations of (-)deprenyl during the re-oxygenation period, survival increased, the Deltapsi(M) shift caused by oxygen deprivation was reversed and the peroxy radical levels decreased except for at 10(-3) M.

Electroacupuncture prevents cognitive deficits in pilocarpine-epileptic rats

Here we investigated the effects of electroacupuncture over the cognitive deficits in the pilocarpine model of epilepsy in rats. Acupuncture stimulation was provided at acupoints located in either the midline of the back and of the head [HD]: Gv-20 (Baihui), Gv-14 (Dazhui), Gv-2 (Yaoshu) and M-HN-3 (Yin Tang); or acupoints located in the limbs [LB]: St-36 (Zusanli) and Sp-6 (Sanyinjiao). In the elevated T-maze test, electroacupuncture at HD and LB acupoints produced an improvement in the acquisition and retention parameters. Retention in the inhibitory avoidance test was seen only in short-term retention and only for animals stimulated at HD. At histology it was found that electroacupuncture at HD acupoints abolished tissue shrinkage in dorsal hippocampus, basolateral nucleus of the amygdala, substantia nigra and perirhinal cortex, whereas stimulation of LB acupoints prevented tissue shrinkage in all of the above structures except dorsal hippocampus. Administration of p-chlorophenylalanine, a serotonergic releaser, abolished both behavioral and part of the histological changes in these animals. We conclude that electroacupuncture at HD and LB acupoints prevents atrophy of some limbic structures and improves cognitive deficits in pilocarpine-epileptic rats and that this effect is dependent on the serotonergic system.