Deprenyl induces the tyrosine hydroxylase enzyme in the rat dopaminergic nigrostriatal system

Comparison of selegiline and levodopa combination therapy versus levodopa monotherapy in the treatment of Parkinson's disease: a meta-analysis

BACKGROUND

Selegiline or levodopa treatment has been suggested as a therapeutic method for Parkinson's disease (PD) in many clinical trial reports. However, the combined effects of two drugs still remain controversial. The aim of this report was to evaluate the clinical efficacy and safety of selegiline plus levodopa (S + L) combination therapy in the treatment of PD compared to that of L monotherapy, to provide a reference resource for rational drug use.

METHODS

Randomized controlled trials (RCTs) of S + L for PD published up to September, 2018 were searched. Mean difference (MD), odds ratio (OR), and 95% confidence interval (CI) were calculated and heterogeneity was assessed with the I² test. Sensitivity analysis was also performed. The outcomes measured were as follows: the unified Parkinson's disease rating scale (UPDRS) scores, modified Webster score, adverse events and mortality.

RESULTS

Fourteen RCTs with 2008 participants were included. Compared with L monotherapy, the pooled effects of S + L combination therapy on UPDRS score were (eleven trials; MD - 7.00, 95% CI - 8.35 to - 5.65, P < 0.00001) for total UPDRS score (nine trials; MD - 5.74, 95% CI - 7.71 to - 3.77, P < 0.00001) for motor UPDRS score (seven trials; MD - 1.61, 95% CI - 2.18 to - 1.04, P < 0.00001) for activities of daily living UPDRS score (three trials; MD - 0.38, 95% CI - 0.61 to - 0.14, P = 0.002) for mental UPDRS score. The Webster score showed significant decrease in the S + L combination therapy compared to L monotherapy (four trials; MD - 5.71, 95% CI - 7.11 to - 4.32, P < 0.00001). Compared with L monotherapy, S + L combination therapy did not increase the number of any adverse events significantly in PD patients (ten trials; OR 1.58, 95% CI 0.83-3.00, P = 0.16).

CONCLUSIONS

S + L combination therapy is superior to L monotherapy for the improvement of clinical symptoms in PD patients. Moreover, the safety profile of S + L combination therapy is comparable with that of L monotherapy.

Purinergic Antagonism Prevents Mitochondrial Dysfunction and Behavioral Deficits Associated with Dopaminergic Toxicity Induced by 6-OHDA in Rats

Purinoceptors are present in neurons, microglia and oligodendrocytes and regulate dopamine (DA) release, striatal-related function and striatal neuronal and DA cells damage. Therefore, purinoceptors may be involved in the pathology of Parkinson's disease (PD) and purinergic antagonism may show neuroprotective effect. The study investigated the role of the non-selective purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2^', 4^'-disulfonic acid (PPADS) and a selective purinergic receptor P2X7 receptor antagonist Brilliant Blue G (BBG) against 6-OHDA induced dopaminergic neurotoxicity in rats; while adenosine triphosphate (ATP) was used as a P2X receptor agonist. Behavioral parameters like spontaneous motor activity, narrow beam walk, footprint, bar catalepsy, grip strength and rotarod tests were performed to evaluate motor deficits in PD. Striatal DA contents were estimated as neurochemical measures of PD. Mitochondrial studies and oxidative status were assessed to investigate the mechanism of purinergic system antagonists. Involvement of purinergic receptors in apoptosis was assessed by expressing cytochrome-C, caspase-9 and caspase-3. Both the antagonists not only attenuated 6-OHDA induced motor deficits but also protected against 6-OHDA induced DA depletion in the striatum. Oxidative stress, mitochondrial integrity and dysfunction were attenuated by purinergic antagonists. Further, they attenuated mitochondrial-linked apoptosis as observed by a decrease in expression of cytochrome-C, caspase-9 and caspase-3. Therefore, purinoceptor antagonism shows neuroprotective effect in 6-OHDA induced dopamine toxicity through preservation of mitochondrial bioenergetics and anti-apoptotic activities.

MAO-B inhibitors: multiple roles in the therapy of neurodegenerative disorders?

Monoamine oxidases play a central role in catecholamine catabolism in the central nervous system. The biochemical and pharmacological properties of inhibitors of the monoamine oxidase type B are reviewed. The evidence for biochemical activities distinct from their ability to inhibit MAO-B is discussed, including possible antioxidative and antiapoptotic activities of these agents. The significance of these properties for the pharmacological management of Parkinson's disease and the evidence for a neuroprotective effect of one such agent (selegiline) is also discussed.

Ginkgo biloba extract enhances noncontact erection in rats: the role of dopamine in the paraventricular nucleus and the mesolimbic system

Penile erection is essential for successful copulation in males. Dopaminergic projections from the paraventricular nucleus (PVN) to the ventral tegmental area (VTA) and from the VTA to the nucleus accumbens (NAc) are thought to exert a facilitatory effect on penile erection. Our previous study showed that treatment with an extract of Ginkgo biloba leaves (EGb 761) enhances noncontact erection (NCE) in male rats. However, the relationship between NCE and dopaminergic activity in the PVN, VTA, and NAc remains unknown. The present study examined the relationship between NCE and central dopaminergic activity following EGb 761 treatment. We report here that, in comparison with the controls, there was a significant increase in the number of NCEs in rats after treatment with 50 mg/kg of EGb 761 for 14 days. EGb 761-treated rats also showed more NCEs than the same group before EGb 761 treatment. A significant increase in the expression of catecholaminergic neurons in the PVN and the VTA was seen by means of tyrosine hydroxylase immunohistochemistry, and tissue levels of dopamine and 3,4-dihydroxyphenylacetic acid in the NAc were also markedly increased in the EGb 761-treated animals. However, the norepinephrine tissue levels in the PVN and the NAc in the EGb 761-treated group were not significantly different from those in the controls. Together, these results suggest that administration of EGb 761 increases dopaminergic activity in the PVN and the mesolimbic system to facilitate NCE in male rats.

Semichronic Inhibition of Glutathione Reductase Promotes Oxidative Damage to Proteins and Induces both Transcription and Translation of Tyrosine Hydroxylase in the Nigrostriatal System

We have evaluated the effect of N,N-bis (2-chloroethyl)-N-nitrosourea (BCNU), an inhibitor of glutathione reductase (GR), on the oxidative status along with the integrity of the nigrostriatal dopaminergic system of the rat. The oxidative status was studied by the quantification of carbonyl groups coupled to protein homogenates. Moreover, the specific oxidations in glial fibrillary acidic protein (GFAP) and neurofilament-200 (NF-200) were also measured. The results show that oxidative damage in proteins in the nigrostriatal system is confined to the striatum. Specific carbonyl groups coupled to native NF-200 and GFAP were also increased. These changes were accompanied by reactive astrocytosis in striatum but not in substantia nigra. In substantia nigra, decreased levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were observed following BCNU treatment. In contrast, DA levels were increased in the striatum along with an overall decrease in the ratios of DA metabolites to DA. We also studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra following BCNU treatment, which was consistent with significant elevations in TH enzyme amount and activity and unchanged DA uptake in striatum. All these results support the DA free radical hypothesis and the key role of the striatal glutathione system in protecting the striatal system against oxidative stress.

Selegiline Induces Neuronal Phenotype and Neurotrophins Expression in Embryonic Stem Cells

The antiaging effect of selegiline was reported by several investigators; therefore, there is a growing interest in the potential use of stem cell therapy in aging. In this investigation, selegiline was used to induce neuronal differentiation in undifferentiated pluripotent embryonic stem cells (ESCs). The results show that selegiline can induce neuronal phenotype associated with neurotrophic factor expression. Morphologic and immunohistochemical techniques were used to evaluate the differentiation of the CCE cells, Cresyl violet for the morphologic study, anti-synaptophysin and antityrosine hydroxylase antibodies for characterizing the neuronal phenotype of ESCs, and RT-PCR to study the neurotrophins. The results showed that selegiline can induce dose-dependent ESC differentiation into neurons. Moreover, selegiline can induce neurotrophin expression. This study suggests the potential use of combined selegiline and stem cell therapy to improve deficits in neurodegenerative diseases in aging.

Acute effects of moclobemide and deprenyl on 5-HT synthesis rates in the rat brain: An autoradiographic study

Serotonin (5-HT), norepinephrine (NE) and dopamine (DA) released from nerve terminals in the brain are primarily removed from the synaptic cleft by a reuptake mechanism. In part, the homeostasis is maintained by monoamine oxidase (MAO) deamination achieved primarily intracellularly. The present study's aim was to examine the effect of the acute administration of the MAO inhibitors, moclobemide (a MAO-A inhibitor) and deprenyl (a MAO-B inhibitor), on 5-HT synthesis rates, measured in discrete regions of the rat brain by an autoradiographic method, using alpha-[14C]methyl-l-tryptophan as a tracer. MAO inhibitors have different effects on 5-HT synthesis rates in the cell bodies and areas of the nerve terminals. Moclobemide (10 mg/kg, i.p. 30 min before the tracer injection) and deprenyl (3 mg/kg, i.p. 2 h before the tracer injection) decreased the 5-HT synthesis rates in the dorsal (-18% and -22%) and median (-22% and -33%) raphe, respectively. Moclobemide also significantly decreased 5-HT synthesis in the entire nerve terminal areas investigated. The reductions were between 23% (cingulate cortex) and 50% (locus coeruleus). Deprenyl did not significantly affect 5-HT synthesis in the nerve terminals. The present results suggest that MAO-A, and to a lesser extent, MAO-B, are involved in the regulation of 5-HT synthesis in the rat brain. The mechanism(s) of MAO inhibitors' action on 5-HT synthesis in the raphe nuclei are probably related to an increase in the extraneuronal 5-HT concentration and also to the interaction between the serotonergic and catecholaminergic neurons. The reduction of 5-HT synthesis in the raphe nuclei likely occurs by an action of extracellular 5-HT via the dendritic autoreceptors with a possible contribution from the action of extracellular DA and NE. In the terminal regions, the most likely mechanism is via the presynaptic autoreceptors through which elevated extraneuronal 5-HT acts on synthesis control. However, there is also a possibility that the elevation in intraneuronal 5-HT directly inhibits its synthesis, especially following deprenyl treatment. A great influence of moclobemide on 5-HT synthesis could be related to its antidepressant action.

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.

Deprenyl enhances the striatal neuronal damage produced by quinolinic acid

We have tested the effect of deprenyl on the neurotoxicity induced by the injection of quinolinic acid within the striatum. Deprenyl was unable to prevent these quinolinic acid-induced damages, but enhanced the loss of several gamma-aminobutyric acid (GABA) positive subpopulations, the loss of the astroglial population and the activation of microglia produced by quinolinic acid. These effects are produced by deprenyl potentiation of dopamine actions since dopamine depletion produced by previous injection of the dopaminergic toxin 6-hydroxydopamine within the medial forebrain bundle overcomes deprenyl effects and the involvement of dopamine in the quinolinic acid-induced toxicity in striatum. In these conditions, quinolinic acid toxic action in striatum is significantly lower and similar in the animals treated with or without deprenyl. All these data justify why deprenyl worsen some pathological signals of disorders involving excitotoxicity. This also may be involved in other secondary effects described for deprenyl.

D-deprenyl protects nigrostriatal neurons against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurotoxicity

Selegiline (L-deprenyl) is believed to render protection against l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-neurotoxicity to a significant extent via a free radical scavenging mechanism, which is independent of its ability to inhibit monoamine oxidase-B (MAO-B) in the brain. We investigated the hydroxyl radical (.OH) scavenging action and neuroprotective effect of D-deprenyl, its less active isomer, in MPTP-induced dopaminergic neurotoxicity in mice to test whether the chemical structure of the molecule or its biological effects contribute to this property. To achieve this goal we studied the effects of D-deprenyl on: (1).OH production in a Fenton reaction; (2) MPTP-induced.OH generation and dopamine (DA) depletion in vivo, employing a sensitive HPLC-electrochemical procedure; and (3) formation of MPP(+) in vivo in the striatum following systemic administration of MPTP, employing an HPLC-photodiode array detection system. D-deprenyl inhibited ferrous citrate-induced.OH in vitro (0.45 microM) and MPTP-induced.OH in vivo in substantia nigra (SN) and in the striatum (1.0 mg/kg, i.p.). D-deprenyl did not, but L-deprenyl (0.5 mg/kg dose) did significantly inhibit formation of MPP(+) in the striatum 90 min following systemic MPTP injection. It failed to affect MAO-B activity at 0.5 mg/kg in the striatum, but effectively blocked MPTP-induced striatal DA depletion. The potency of D-deprenyl to scavenge MPTP-induced.OH in vivo and to render protection against the dopaminergic neurotoxicity without affecting dopamine turnover, MAO-B activity, or formation of MPP(+) in the brain indicates a direct involvement of.OH in the neurotoxic action of MPTP and antioxidant effect in the neuroprotective action of deprenyl.

Decreased messenger RNA expression of key markers of the nigrostriatal dopaminergic system following vitamin E deficiency in the rat

We have evaluated the effect of a vitamin E-deficient diet on the rat nigrostriatal dopaminergic system. After 15 days of deficient diet, the amount and activity of striatal and nigral tyrosine hydroxylase increased, which contrasted with a decreased messenger RNA expression for tyrosine hydroxylase and the dopamine transporter in the ventral mesencephalon. When we prolonged the deficiency of vitamin E for 30 days, dopamine levels did not differ in both areas. In contrast, messenger RNA levels for tyrosine hydroxylase and the dopamine transporter were markedly reduced in 30-day deficient rats. In addition, the number of oxidatively modified proteins significantly increased in the striatal and nigral areas studied. Overall, we propose that these changes suggest an important role of vitamin E in maintaining the normal equilibrium of the dopaminergic nigrostriatal system.

Low selenium diet induces tyrosine hydroxylase enzyme in nigrostriatal system of the rat

We have studied the effect of a selenium-deficient diet on the nigrostriatal dopaminergic system for 15 and 30 days. The neurochemical analysis demonstrated significant elevations in nigral DA levels after 15 and 30 days of selenium deficiency. The most significant change in striatum was an elevation in dopamine (DA) in 30-day-deficient animals. As a further step, we measured the levels of activity and mRNA expression of tyrosine hydroxylase (TH) and dopamine transporter (DAT). There were significant elevations in all of these parameters in the nigrostriatal system following selenium deficiency at the two time-points studied except for the striatal DA uptake at day 30, which dropped to control levels. Altogether, our results suggest that the decrease in antioxidant capacity due to a selenium deficiency promotes an increase in DA synthesis and turnover, which are clearly associated to the induction of TH. This effect may trigger a positive feed-forward mechanism that could increase the oxidative stress considering the capacity of DA to generate free radicals.

Perinatal asphyxia induces region-specific long-term changes in mRNA levels of tyrosine hydroxylase and dopamine D(1) and D(2) receptors in rat brain

To study the effects of neonatal asphyxia on gene expression of the dopaminergic systems, we determined quantitatively the mRNA levels of tyrosine hydroxylase, dopamine transporter, dopamine D(1) and D(2) receptors in substantia nigra/ventral tegmental area, striatum and limbic area. The mRNA levels were determined at one and 4 weeks after asphyxia by a quantitative reverse transcription polymerase chain reaction method. Spontaneously and Caesarean section born rats showed similar mRNA levels with the exception of an increase of tyrosine hydroxylase mRNA levels in the limbic area of 4-week-old animals. Five min of asphyxia did not change the mRNA levels in any region compared to that in the spontaneously born rats. Fifteen and twenty min of asphyxia induced region-specific alterations in mRNA levels. In SN/VTA an increase of tyrosine hydroxylase mRNA levels in the 1-week-old rats and in striatum an increase of D(1) and D(2) dopamine receptor mRNA levels in the 4-week-old rats were observed. Fifteen min of asphyxia induced a selective increase of D(1) and D(2) dopamine receptor mRNA levels in the limbic area of 4-week-old rats. These observations indicate that neonatal asphyxia triggers a cascade of gene expressions for tyrosine hydroxylase and D(1) and D(2) dopamine receptors. In 1-week-old rats, the gene expression of tyrosine hydroxylase increased in the cell body region substantia nigra/ventral tegmental area. This change may increase the D(1) and D(2) dopamine receptor expression in the target regions striatum and limbic area during further development.

Effects of L-deprenyl treatment on noradrenergic innervation and immune reactivity in lymphoid organs of young F344 rats

Sympathetic noradrenergic (NA) neuronal activities in the thymus, spleen and mesenteric lymph nodes (MLN) and immune responses in the spleen were examined in young male F344 rats treated daily with 0, 0.25 mg, or 2.5 mg/kg body weight of L-deprenyl, an irreversible monoamine oxidase-B (MAO-B) inhibitor. Rats were treated daily for 1, 15, or 30 days, and sacrificed 7 days after the last deprenyl treatment. Deprenyl treatment increased norepinephrine (NE) content in the spleen without modifying the pattern and density of NA innervation in the splenic white pulp. The concentration of NE was unaltered in the thymus, but it was increased in the MLN of deprenyl-treated rats. One day of treatment with deprenyl decreased splenic NK cell activity while 15 days of deprenyl treatment enhanced splenic NK cell activity. Deprenyl elevated Con A-induced T lymphocyte proliferation following 30 days of treatment, but did not alter spleen cell Con A-induced IL-2 production or the percentage of CD5 + T cells in the spleen. A moderate decrease in the percentage of sIgM + B cells was observed in the spleens of 15- and 30-day deprenyl-treated rats. These results suggest that deprenyl has sympathomimetic action on sympathetic NA nerve fibers in the spleen; the enhancement of NA neuronal activity may contribute to the modulation of immune responses in the spleen.

Region-specific alterations in the concentrations of catecholamines and indoleamines in the brains of young and old F344 rats after L-deprenyl treatment

The effects of L-deprenyl, a monoamine oxidase-B (MAO-B) inhibitor, on the concentrations of norepinephrine (NE), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-hydroxytryptamine), and 5-hydroxyindoleacetic acid (5-HIAA) in medial basal hypothalamus (MBH), substantia nigra (SN), striatum (Str), and nucleus accumbens (NAc) of young (3 month) and old (21 month) male F344 rats were examined after a 7-day wash-out period following 1, 15, or 30 days of deprenyl treatment in young rats and a 9-day wash-out period after a 10-week deprenyl treatment in old rats. The brain areas were microdissected and the concentrations of neurotransmitters were measured by High Performance liquid chromatography with electrochemical detection (HPLC-EC). Deprenyl administration following the drug wash-out period increased the concentrations of DOPAC in the SN, Str, and in the NAc of young rats but it was decreased in the NAc of old rats. The concentration of HVA was lower in the Str of young deprenyl-treated rats, and in the Str and NAc of old deprenyl-treated rats, but it was higher in the SN of young deprenyl-treated rats. The concentration of 5-HIAA was increased in the MBH, SN, and in the NAc of young deprenyl-treated rats, but it was decreased in the Str and NAc of old deprenyl-treated rats. The concentration of NE was increased in the MBH, SN, Str, and in the NAc of young rats treated with deprenyl and in the MBH of old deprenyl-treated rats. The concentration of 5-HT was increased in the SN of young deprenyl-treated rats. The concentration of DA increased in the Str of both young and old deprenyl-treated rats. We concluded that a drug wash-out period after deprenyl treatment differentially affects the metabolism of catecholamines and indoleamine depending on the region of the brain and that this effect may be due to variation in the kinetics of MAO inhibition.

Tyrosine hydroxylase and Parkinson's disease

A consistent neurochemical abnormality in Parkinson's disease (PD) is degeneration of dopaminergic neurons in substantia nigra, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-DOPA, the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Similarly, some patients with hereditary L-DOPA-responsive dystonia, a neurological disorder with clinical similarities to PD, have mutations in the TH gene and decreased TH activity and/or stability. Thus, a logical and efficient treatment strategy for PD is based on correcting or bypassing the enzyme deficiency by treatment with L-DOPA, DA agonists, inhibitors of DA metabolism, or brain grafts with cells expressing TH. A direct pathogenetic role of TH has also been suggested, as the enzyme is a source of reactive oxygen species (ROS) in vitro and a target for radical-mediated oxidative injury. Recently, it has been demonstrated that L-DOPA is effectively oxidized by mammalian TH in vitro, possibly contributing to the cytotoxic effects of DOPA. This enzyme may therefore be involved in the pathogenesis of PD at several different levels, in addition to being a promising candidate for developing new treatments of this disease.

(-)-Deprenyl treatment restores serum insulin-like growth factor-I (IGF-I) levels in aged rats to young rat level

We studied the effects of treatment with (-)-deprenyl, a monoamine oxidase B inhibitor, on plasma levels of insulin-like growth factor-I (IGF-I) (as indicator of growth hormone (GH) secretion), levels of monoamines and their metabolites, and the activity and content of tyrosine hydroxylase - the rate-limiting enzyme in the biosynthesis of catecholamines - in the hypothalamus and hypophysis of old male rats. Male Wistar rats (22 months old) were treated with 2 mg deprenyl/kg body weight s.c. three times a week for 2 months. At the end of the treatment period, blood was collected for measurement of plasma IGF-I levels by radioimmunoassay (RIA). The concentrations of dopamine, serotonin (5-HT) and their main metabolites were determined by high performance liquid chromatography (HPLC) with electrochemical detection, and the tyrosine hydroxylase content in hypothalamus and hypophysis was determined by enzyme-linked immunoabsorbent assay (ELISA). (-)-Deprenyl treatment produced a pronounced increase in dopamine and 5-HT in both the hypothalamus and hypophysis (P < 0.01). The main dopaminergic metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), decreased in hypothalamus but not in hypophysis, and treatment had no effect on the concentration of 5-hydroxyindole-3-acetic acid (5-HIAA). The tyrosine hydroxylase activity and tyrosine hydroxylase content increased in hypothalamus and hypophysis (P < 0.05). In the hypophysis the increase in tyrosine hydroxylase activity was consistent with the increase in tyrosine hydroxylase amount. Moreover, (-)-deprenyl treatment restored the IGF-I plasma levels in old rats to a concentration similar to those found in young animals. Postulated anti-aging effects of (-)-deprenyl could hence be due to restoration of hypothalamic hormones such as GH.