Depletion of nigrostriatal and forebrain tyrosine hydroxylase by S-adenosylmethionine: a model that may explain the occurrence of depression in Parkinson's disease

Behind the Mask: Parkinson's Disease and Depression

Parkinson's disease (PD) is a common, prevalent neurodegenerative disease. It is mainly characterized by motor symptoms such as rigidity, tremors, and bradykinesia, but it can also manifest with non-motor symptoms, of which depression is the most frequent. The latter can impair the quality of life, yet it gets overlooked and goes untreated because of the significant overlap in their clinical features, hence making the diagnosis difficult. Furthermore, there is limited data on the availability of appropriate criteria for making the diagnosis of depression in PD patients, as it can occur with varying expressions throughout the course of PD or it can also precede it. This review article has included a brief discussion on the diagnosis of depression in PD patients and their overlapped clinical manifestations. Understanding the mechanisms underlying the disease processes of PD and depression and the pathways interconnecting them gives better knowledge on devising treatment options for the patients. Only studies from Pubmed were included and all other databases were excluded. Studies from the last 50 years were included. Suitable references included in these studies were also extracted. Thus, depression in PD and PD in depression, along with their pharmacological and non-pharmacological treatment options, have been discussed.

Prenatal exposure to methanol as a dopamine system sensitization model in C57BL/6J mice

AIMS

In this study, the effects of prenatal exposure to methanol (MeOH) on the nigrostriatal dopamine (NSDA) system were examined to determine if the interaction could sensitize this system, and serve as an underpinning for Parkinson's disease (PD) like changes that occur later in life. Methanol was studied because its toxicity resembles the symptoms of PD and the symptoms are relieved by L-dopa meaning that MeOH targets the NSDA system. Since fermentation and wood combustion are major sources for MeOH, the incidence of human encounters with MeOH is high. As a superior solvent and the precursor for formaldehyde, MeOH has a powerful and sometimes, irreversible impact on chemical processes, such as cross-linking proteins and nucleic acids. It may cause subthreshold changes that sensitizes the NSDA system to PD, that occur during aging.

MAIN METHODS

To study the prenatal effects of MeOH, pregnant C57BL/6J mice were administered 40 mg/kg MeOH by oral gavage during gestation days 8-12, twice daily. Twelve weeks after birth, behavior impairments were recorded. The striatum was dissected for the determination of tyrosine hydroxylase (TH), L-aromatic amino acid decarboxylase (LAAD), α-synuclein and levels of dopamine (DA) and its metabolites.

KEY FINDINGS

MeOH reduced striatal TH and LAAD protein by 47% and 57% respectively and DA by 32%.

SIGNIFICANCE

The results mean that in utero exposure to toxins similar to MeOH could sensitize the striatal system to changes that cause PD. This study may help identify strategies to block this type of in utero toxicity.

5-HTP efficacy and contraindications

L-5-hydroxytryptophan (5-HTP) is the immediate precursor of serotonin. It is readily synthesized into serotonin without biochemical feedback. This nutrient has a large and strong following who advocate exaggerated and inaccurate claims relating to its effectiveness in the treatment of depression and a number of other serotonin-related diseases. These assertions are not supported by the science. Under close examination, 5-HTP may be contraindicated for depression in some of the very patients for whom promoters of 5-HTP advocate its use.

Amino acid management of Parkinson's disease: a case study

An extensive list of side effects and problems are associated with the administration of l-dopa (l-3, 4-dihydroxyphenylalanine) during treatment of Parkinson's disease. These problems can preclude achieving an optimal response with l-dopa treatment.

PURPOSE

To present a case study outlining a novel approach for the treatment of Parkinson's disease that allows for management of problems associated with l-dopa administration and discusses the scientific basis for this treatment.

PATIENTS AND METHODS

The case study was selected from a database containing 254 Parkinson's patients treated in developing and refining this novel approach to its current state. The spectrum of patients comprising this database range from newly diagnosed, with no previous treatment, to those who were diagnosed more than 20 years before and had virtually exhausted all medical treatment options. Parkinson's disease is associated with depletion of tyrosine hydroxylase, dopamine, serotonin, and norepinephrine. Exacerbating this is the fact that administration of l-dopa may deplete l-tyrosine, l-tryptophan, 5-hydroxytryptophan (5-HTP), serotonin, and sulfur amino acids. The properly balanced administration of l-dopa in conjunction with 5-HTP, l-tyrosine, l-cysteine, and cofactors under the guidance of organic cation transporter functional status determination (herein referred to as "OCT assay interpretation") of urinary serotonin and dopamine, is at the heart of this novel treatment protocol.

RESULTS

When 5-HTP and l-dopa are administered in proper balance along with l-tyrosine, l-cysteine, and cofactors under the guidance of OCT assay interpretation, the long list of problems that can interfere with optimum administration of l-dopa becomes controllable and manageable or does not occur at all. Patient treatment then becomes more effective by allowing the implementation of the optimal dosing levels of l-dopa needed for the relief of symptoms without the dosing value barriers imposed by side effects and adverse reactions seen in the past.

Prenatal lipopolysaccharide does not accelerate progressive dopamine neuron loss in the rat as a result of normal aging

We previously demonstrated that in utero exposure to the bacteriotoxin lipopolysaccharide (LPS) led to the birth of rat pups with fewer than normal dopamine (DA) neurons. These animals exhibited significant neuroinflammation in the nigrostriatal pathway creating the possibility that they could exhibit further, progressive DA neuron loss over their lives. To study this possibility, we injected gravid female rats i.p. at 10,000 endotoxin units (EUs) of LPS per kg or saline at embryonic (E) day 10.5 and assigned pups to sacrifice groups at 4, 14 and 17 months such that littermates were sacrificed at each end point. The effects of prenatal LPS on DA cell counts and striatal DA were significantly reduced relative to controls whereas DA activity and numbers of activated microglia (OX-6ir cell) were statistically increased. However, the progressive DA neuron loss was parallel to that of the controls suggesting that prenatal LPS does not produce an accelerated rate of DA neuron loss. Interestingly, locomotor activity was increased after 3 months in animals exposed to LPS prenatally, but by 16 months, was significantly reduced relative to controls. Additionally, animals exposed to LPS prenatally exhibited Lewy body-like inclusions that were first seen in 14 month old animals. These data broadly support previous studies demonstrating that prenatal exposure to LPS, as frequently occurs in humans as part of Bacterial Vaginosis, leads to the birth of animals with fewer than normal DA neurons. The progressive DA neuron loss seen in these animals is, however, primarily a result of normal aging.

Acute intranigral homocysteine administration produces stereotypic behavioral changes and striatal dopamine depletion in Sprague–Dawley rats

Homocysteine has been considered a major risk factor for cardiovascular diseases, and patients with hyperhomocystinemia exhibit neurological and psychological abnormalities. Elevated level of this molecule in the blood of Parkinson's disease patients receiving long-term l-DOPA therapy prompted us to investigate whether homocysteine is neurotoxic to the nigrostriatal dopaminergic system in Sprague-Dawley rats. Animals infused unilaterally with different doses of homocysteine (0.25-1 micromol in 1 microl) intranigrally exhibited significant and dose-dependent decrease in dopamine levels in the ipsilateral striatum as assayed employing an HPLC coupled with electrochemical detector, 19 days post-infusion. While 3,4-dihydroxyphenylacetic acid level in the striatum showed a dose-dependent decrease, homovanillic acid was found to be inhibited only for the highest dose. Amphetamine administration in these animals on the 14th day caused stereotypic turning behavior ipsilateral to the side of infusion. Apomorphine challenge on the 16th day elicited stereotypic contralateral circling behavior. Neurotransmitter levels in the serotonergic perikarya or terminals were unaltered 19 days following intraraphe infusion of homocysteine, which suggested the specificity of its action to dopaminergic neurons. These results indicate nigrostriatal lesions similar to that observed following intranigral infusion of the dopaminergic neurotoxin, 6-hydroxydopamine and suggest its closeness to the parkinsonian animal model. Furthermore, these findings provide evidence for the neurotoxic nature of homocysteine to dopaminergic neurons and suggest that elevated level of this molecule in parkinsonian patients may be conducive to accelerate the progression of the disease.

Inhibition mechanism of S-adenosylmethionine-induced movement deficits by prenylcysteine analogs

We previously showed that S-adenosylmethionine (SAM) induces movement impairments similar to those observed in Parkinson's disease (PD) apparently by prenylated protein methylation; 5 kDa molecules being methylated and the symptoms being inhibited by prenylcysteine (PC) analogs. In the present study, we explore the biochemical mechanism of action of the PC analogs. N-acetylgeranylcysteine (AGC), N-acetylfarnesylcysteine (AFC), N-acetylgeranylgeranylcysteine (AGGC), farnesylthioacetic acid (FTA), farnesyl-2-ethanesulfonic acid (FTE) and farnesylsuccinic acid (FMS), but not farnesylthiotriazole (FTT) and farnesylthiolactic acid (FTL), inhibited the SAM-induced motor impairments. Incubation of the respective analogs with rat brain membranes containing prenylated protein methyltransferase (PPMTase) resulted in the methylation of AGC, AFC and AGGC. FTA, FTE, FMS and FTT, but not FTL, inhibited the enzyme activity. A single injection of the active analogs remained effective for at least 3 days against repeated injections of 1 micromol SAM. Amphetamine-induced hyperactivity in rats was inhibited by SAM but potentiated by FTE. During 60 min, the movement time for amphetamine-treated rats was 1477 s compared with 633 and 1664 s for amphetamine+SAM- and amphetamine+FTE-treated rats, respectively. The total distance for amphetamine+FTE-treated rats was 82% higher than for amphetamine. The horizontal activity was 30,728 (amphetamine), 15,430 (FTE), 18,526 (amphetamine+SAM), 41,736 (amphetamine+FTE) and 7004 (SAM) as compared to the PBS control (4726). The intricate relationship between the actions of SAM, which speeds up prenylated protein methylation and impairs movement, amphetamine, which increases synaptic dopamine levels and movement, and the PC analogs, which prevent the SAM-induced movement impairments, suggests a SAM-induced defect on dopamine signaling as the likely cause of the symptoms. The data reveal that interaction of PC analogs with PPMTase may not be an indicator of anti-PD-like activity.

Depression in Parkinson's disease

Depression in Parkinson's disease (PD) is a common complication, with a major impact on quality of life. Failure to recognize and treat depression can lead to premature and inappropriate discontinuation of antiparkinsonian therapies. Cited frequency for depression in PD varies between 2.7 and 70%. Methodological differences account for much of the disparity. The aetiology of depression in PD is complex, with 'tonic' (slowly changing and persistent) and 'phasic' (short-lived and fluctuating) components. Both depression and anxiety may predate the onset of the motor disorder by some years. Hedonistic homeostatic dysregulation is a cyclical mood disorder associated with excessive intake of dopaminergic therapies, inappropriate for the motor state. Negative affective symptoms occur on attempted reduction of medication, reinforcing the abnormal medication pattern. The Montgomery-Asberg Depression Rating Scale and the Hamilton Rating Scale for Depression have good diagnostic sensitivity and specificity for assessing depression in PD. There is a dearth of sizeable, placebo-controlled studies for evaluating drug treatment of depression in PD. Dopaminergic drugs have variable antidepressant properties. Selective serotonin reuptake inhibitors are currently the most commonly prescribed group of antidepressants in the depressed PD patient. Depression in the PD patient may be associated with a more rapid deterioration in cognitive and motor functions.

S-adenosyl-methionine-induced apoptosis in PC12 cells

Our previous studies showed that S-adenosyl-methionine (SAM) induced Parkinson's disease-like changes in rat. It caused death to dopamine neurons in the substantia nigra, which appeared shrunken and fragmented, indicative of apoptosis-like changes (Charlton and Crowell [1995] Mol. Chem. Neuropathol. 26:269-284; Charlton [1997] Life Sci. 61:495-502). In this study, we investigated whether SAM causes apoptosis in both undifferentiated PC12 (PC12) cells and nerve growth factor (NGF)-differentiated PC12 (D-PC12) cells. S-adenosyl-homocysteine (SAH), the nonmethyl analog of SAM, was also tested. SAM and SAH (1.0 nM to 10.0 microM) caused lactate dehydrogenase (LDH) release from the PC12 cells and D-PC12 cells; cells with morphological changes and fluorescent DNA fragmentation staining were detected among both PC12 cell and D-PC12 cell. Compared with the PC12 cell, the D-PC12 cell, a postmitotic cell, was more sensitive to the toxic effects of SAM or SAH and presented much greater LDH release, suggesting a lethal effect; surprisingly, the amounts of apoptotic cells did not differ significantly between the two kinds of cells. In medium deprived of exogenous methionine, a decline in LDH release was observed in PC12 and D-PC12 cells. Also, lower levels of intracellular SAM and SAH were observed in the methionine-deleted media, which were reversed by the addition of either SAM or SAH. An antivitamin B(12) monoclonal antibody was added to methionine-depleted medium, resulting in deficiency of both endogenous and exogenous methionine, which caused further decreases in LDH release and reduction in the levels of intracellular SAM and SAH. The preliminary data showed different sensitivities to SAM or SAH between PC12 cell and D-PC12 cells, which suggests that PC12 cell may be more stable as a metabolic model. Apoptosis of PC12 cells was also assessed by PARP cleavage detection, Western blot analysis of Bax and Bcl-2 proteins, and DNA laddering on agarose gel electrophoresis. The proapoptoic protein Bax was dominantly expressed, whereas Bcl-2 was slightly down-regulated by SAM. SAH weakly induced the expression of Bax and slightly decreased Bcl-2 levels. The effects of SAM and its analog, SAH, were demonstrated conclusively to induce apoptosis in PC12 cells.

Beyond the iron mask: towards better recognition and treatment of depression associated with Parkinson's disease

This review examines the frequency of depression complicating Parkinson's disease (PD), its aetiology and clinical features, and also how it may be recognised and treated. Studies investigating the frequency of depression in PD have yielded figures ranging between 2.7% and 70%. Methodological differences account for much of the disparity. The aetiology of depression in PD is complex, and probably relates to both biological and exogenous factors. Dysfunction of multiple neurotransmitter systems, including the serotonergic system, may be involved. Mood disturbances resulting from deep brain stimulation of the subthalamic nucleus may provide a fruitful area for future research, and assist our understanding of the neural networks involved in mediating depression. Several recent studies have confirmed that depression in the PD patient is a major determinant of quality of life and that this is closely related to dysfunction in other clinically important health areas. The validity for many existing scales in the screening, diagnosis, and monitoring of depression in the PD patient has not been established. The Montgomery-Asberg Depression Rating Scale and the Hamilton Rating Scale for Depression appear to have good diagnostic sensitivity and specificity when compared with DSM-IV criteria. Recommendations for the optimal drug treatment of depression in PD are difficult to give, due to an inexplicable dearth of sizeable, placebo-controlled studies. A majority of physicians would probably now opt for a selective serotonin reuptake inhibitor in the depressed PD patient. There is no good evidence that these drugs are associated with a worsening of motor features, but they should probably not be coprescribed with selegiline, because of the risk of causing a potentially serious serotonin syndrome. Several studies have suggested that depression in the PD patient is associated with a more rapid deterioration in cognitive and motor functions, perhaps as a surrogate marker for more extensive brainstem cell loss.

L-dopa upregulates the expression and activities of methionine adenosyl transferase and catechol-O-methyltransferase

High nonphysiological doses of l-dopa are administered to Parkinson's disease (PD) patients, to replenish the depleted dopamine (DA). A large portion of the administered L-dopa and the newly formed DA undergoes methylation by reacting with S-adenosyl-L-methionine (SAM). In the process SAM, as well as L-dopa and DA, is utilized and great demands are placed on the transmethylation system. In this study we investigated whether L-dopa increases the transmethylation process by inducing methionine adenosyl transferase (MAT), the enzyme that produces SAM, and catechol-O-methyl transferase (COMT), the enzyme that transfers the methyl group from SAM to L-dopa and DA. Swiss Webster mice were injected with L-dopa, four times/day, for 1 to 16 days. Brain DA, 3-O-methyldopa (3-OMD), SAM, S-adenosylhomocysteine (SAH), MAT, and COMT were measured following a 24-h withdrawal period. An increase of 264% of brain DA occurred at days 2 and 3 after which it tapered to about 164% of control. The brain level of 3-OMD increased to 870% of the control. SAM was increased by 44% after the sixth day and SAH level was about double after the second day. After day 3, MAT activity was increased by about 35%. Western blot analysis showed that MAT is more clearly characterized in 10% mercaptoethanol reducing buffer in which 31.5-, 38- (beta), and 48-kDa (alpha1/alpha2) subunits were distinctly revealed. The induction of the 38-kDa and, more prominently, the 48-kDa subunits of MAT and the potential transactivator proteins of MAT, c-Jun/AP-1, was evident by day 6. The 31.5-kDa subunit was downregulated. COMT was detected as 24.7-, 30-, and 47.5-kDa bands in the brain, consistent with the membrane-bound COMT I (MB-COMT) and the dimeric COMT II. The 24.7- and the 30-kDa MB-COMT bands were induced in the brain by day 6 and peaked on day 9. The highlight of the study is the fact that L-dopa induces the enzymes MAT and COMT. In addition, the downturn in brain DA after the sixth day coincides with the increase in SAM and the 48-kDa MAT protein. Thus, during PD treatment with L-dopa the induction of MAT and COMT is likely to occur and in turn increase the methylation and reduction of L-dopa and DA that may help cause the tolerance or the wearing-off effect developed to L-dopa.

Quantification of S-adenosylmethionine-induced tremors: a possible tremor model for Parkinson's disease

Tremor is the most visible symptom of Parkinson's Disease (PD), and should be the appropriate parameter in models for its evaluation. Lack of reliable PD tremor models and methods to distinguish tremors from nontremor movements means that nontremor behavior such as rotation following basal ganglia damage are mostly used. Our laboratory has shown that S-adenosyl-methionine (SAM) injections into the brain of rats reliably produced tremors, rigidity, hypokinesia, and abnormal posture. Thus, SAM-induced tremors, when distinguished from nontremor activities, has the potential as a model for testing anti-PD agents. Tremor Monitor-recorded activity profiles of the rats injected with SAM showed low-amplitude signals interlaced with high-amplitude bursts of tremor episodes. Control activities were of low-medium amplitudes with no such patterns. The number of real and apparent episodes detected over 20 min were 92 +/- 12 and 84 +/- 14 lasting 470 +/- 50 and 210 +/- 50 s, indicating mean durations of 5.1, and 2.4 s, frequencies of 12 +/- 0.1 and 11 +/- 0.2 Hz, cycles (waves) per episode of 54 +/- 6 and 19 +/- 2 and amplitudes of 42.3 +/- 5 and 19.8 +/- 1 for the SAM-treated and control rats, respectively. The nontremor activities of rats injected with phosphate-buffered saline were distinguished and eliminated by raising the minimum amplitude and number of cycles to 20. This procedure is being enhanced for screening antitremor agents and for elucidating the possible mechanism for Parkinsonism.

The effect of long-term levodopa therapy on depression level in de novo patients with Parkinson's disease

20) became non-depressed, while five patients (22%) among 23 initially non-depressed became depressed. With long-term levodopa therapy, the UPDRS-motor score significantly improved (35+/-15. 7-18+/-7.6), but the BDI score was unchanged (18+/-9.3-19+/-9.2). The initial BDI score was significantly and inversely correlated to the parkinsonian motor symptoms, but their percentage changes were not correlated to each other. These results provide strong support to previous observations that levodopa therapy does not alter parkinsonian depression as well as providing additional evidence to support the role of non-dopaminergic mechanisms in parkinsonian depression.