Is there a difference in gastric emptying between Parkinson’s disease patients under long-term <Emphasis Type="SmallCaps">l</Emphasis>-dopa therapy with and without motor fluctuations? An analysis using the <Superscript>13</Superscript>C-acetate breath test

The mechanism underlying the motor fluctuations that develop after long-term l-dopa therapy is not fully known. It has been speculated that malabsorption of l-dopa from the small intestine occurs. It was reported that gastric retention in Parkinson’s disease (PD) patients with motor fluctuations is increased as compared with that in PD without fluctuations. Because l-dopa therapy may worsen the symptoms of delayed gastric emptying (GE), it was not clear whether the delayed GE of PD patients with motor fluctuation was affected by l-dopa therapy. We assessed GE in PD patients with and without motor fluctuations. We investigated GE in 40 patients with PD under long-term l-dopa therapy, 20 fluctuators with “delayed-on” and “no-on” phenomena, 20 nonfluctuators, and 20 healthy volunteers. GE was examined by the ¹³C-acetate breath test (¹³C-ABT) [the half emptying time (HET), the peak time of the ¹³C-%-dose-excess curve (T _max)], with expirations collected for 4 h after a test meal and analyzed for ¹³CO₂ using an infrared (IR) spectrophotometer. The T _max of GE as assessed using the ¹³C-ABT was significantly delayed in all PD patients as compared with controls (P = 0.002). The HET was significantly delayed in all PD patients as compared with controls (P < 0.001). The T _max and HET were not significantly delayed in PD patients with motor fluctuations as compared with PD patients without motor fluctuations. These results demonstrated that GE is commonly delayed in PD patients with long-term l-dopa therapy. Delayed GE does not differ between PD patients with and without motor fluctuations. This finding demonstrated that the motor fluctuation in PD may not be influenced by GE.     

Deletion of N-terminus of human tyrosine hydroxylase type 1 enhances stability of the enzyme in AtT-20 cells

Wildtype human tyrosine hydroxylase (TH) type 1 and 4 mutants (del-52, a form with the first 52 amino acid residues deleted; del-157, one with the first 157 amino acid residues deleted; RR-EE, one in which Arg37-Arg38 was replaced by Glu37-Glu38; and S40D, one in which Ser40 was replaced by Asp40) were expressed in AtT-20 mouse neuroendocrine cells in order to clarify how deeply the N-terminus of TH is involved in the efficient production of dopamine (DA) in mammalian cells. The amounts of DA that accumulated in AtT-20 cells expressing these human TH type 1 (hTH1) phenotypes were in the following order: del-52 = del-157 = RR-EE > S40D > wildtype, although the enzyme activities of del-52 and del-157 were lower than those of wildtype, RR-EE, and S40D. The observation on immunoblot analyses that the N-terminus-deleted hTH1 mutants were much more stable than wildtype can reconcile the discrepant results. Computer-assisted analysis of the spatial configuration of hTH1 identified five newly recognized PEST motifs, one of which was located in the N-terminus sequence of Met1-Lys12 and predicted that deletion of the N-terminus region would alter the secondary structure within the catalytic domain. Collectively, the high stability of the N-terminus-deleted hTH1 mutants can be generated by the loss of a PEST motif in their N-termini and the structural change in the catalytic domain, which would promise an efficient production of DA in mammalian cells expressing N-terminus deleted hTH1.     

The particular relationship between Parkinson’s disease and malignancy: a focus on skin cancers

Although the risk for most cancers appears to be relatively low in patients with Parkinson’s disease (PD), skin cancers and melanomas occur more frequently in the PD population as compared to controls. This article summarizes the findings of cohort studies on skin cancer in Parkinson’s disease. Given that melanoma may precede use of l-dopa, the increased risk of melanoma for PD patients cannot be attributed to l-dopa. On the basis of these observations it may be reasonable to recommend that all patients with PD, whether treated with l-dopa or not, should undergo regular dermatological screening for neoplastic or pre-neoplastic skin lesions, especially melanoma.     

Chronic high dose l-dopa treatment does not alter the levels of dopamine D-1, D-2 or D-3 receptor in the striatum of normal monkeys: an autoradiographic study

Summary. To assess the role of dopamine receptors in the genesis of dyskinesia, we have used quantitative autoradiography to determine the effect of chronic l-dopa administration on dopamine D-1 (using [³H]SCH 23390), D-2 (using [³H]spiperone) and D-3 (using [³H]7-OH-DPAT) receptor binding levels in the striatum of dyskinetic or non-dyskinetic monkeys. Total and subregional striatal analysis showed no difference in D-1, D-2 or D-3 receptor binding in the caudate and putamen between monkeys receiving high dose l-dopa treatment with marked dyskinesia and those without dyskinesia compared to untreated animals. It thus appears unlikely that changes in dopamine receptor expression are a primary cause of l-dopa induced dyskinesia. Rather, a functional dissociation of D-2 receptor coupling to co-expressed enkephalin/adenosine-2a receptor activity in the striato-GPe indirect pathway may be more important in the development or expression of l-dopa-induced involuntary movements. Received July 3, 2000; accepted March 13, 2001     

The dopamine D2 receptor partial agonist aplindore improves motor deficits in MPTP-treated common marmosets alone and combined with l-dopa

Dopamine replacement therapy in Parkinson’s disease (PD) using l-dopa is invariably associated with a loss of drug efficacy (“wearing off”) and the onset of dyskinesia. The use of dopamine receptor partial agonists might improve therapeutic benefit without increased dyskinesia expression but may antagonise the effects of l-dopa. We now examine the effects of the novel high affinity, dopamine D₂ receptor partial agonist, aplindore alone and in combination with l-dopa in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmoset. In non-dyskinetic MPTP treated animals, aplindore (0.05–1.0 mg/kg p.o.) produced a dose-dependent reversal of motor disability and an increase in locomotor activity that was maximal at doses of 0.2 mg/kg and above. In animals previously exposed to l-dopa to induce dyskinesia, escalating and repeated dosing of aplindore (0.05–0.5 mg/kg p.o.) produced a sustained, dose-related improvement in motor disability and an increase in locomotor activity. The effects were maximal at a dose of 0.1 mg/kg and above and not different from those produced by l-dopa (12.5 mg/kg plus carbidopa 12.5 mg/kg p.o.). Aplindore administration also led to dose-dependent expression of dyskinesia but at 0.1 mg/kg, this was significantly less intense than that produced by l-dopa. Administration of aplindore (1.0 mg/kg p.o.) in combination with l-dopa (2.5 mg/kg plus carbidopa 12.5 mg/kg p.o.) did not inhibit the reversal of motor deficits but improved motor disability and increased both locomotor activity and dyskinesia expression equivalent to that produced by l-dopa (12.5 mg/kg plus carbidopa 12.5 mg/kg p.o.). These data suggest that dopamine receptor partial agonists would be effective in the treatment of Parkinson’s disease and would not inhibit the beneficial actions of l-dopa.     

Treatment of idiopathic parkinsonism with l-dopa in the absence and presence of decarboxylase inhibitors: effects on plasma levels of l-dopa,dopa decarboxylase,catecholamines and 3-O-methyl-dopa

Summary The effect of levodopa (l-dopa), alone or in combination with a peripheral decarboxylase inhibitor (PDI), on plasma levels of aromatic-l-amino acid decarboxylase (ALAAD, = dopa decarboxylase), l-dopa, 3-O-methyl-dopa (3-OMD), dopamine (DA), noradrenaline, adrenaline and dopamine beta-hydroxylase has been studied. In healthy subjects and in patients with parkinsonism plasma ALAAD level fell after administration of l-dopa + benserazide, but returned to previous levels within 90 min. In a cross-sectional study blood was obtained, 2 h after dosing, from 104 patients with idiopathic parkinsonism, divided into four groups: no l-dopa treatment (group 1), l-dopa alone (group 2), l-dopa + benserazide (Madopar) (group 3) and l-dopa + carbidopa (Sinemet) (group 4). Plasma ALAAD, which was normal in groups 1 and 2, was increased 3-fold in groups 3 and 4, indicating that there was induction of ALAAD by the co-administration of PDI. Despite this induction of ALAAD, in groups 3 and 4, with half the daily l-dopa dose compared with group 2, plasma l-dopa and 3-OMD levels were 5 times higher, while plasma DA levels were not different. The DA/l-dopa ratio was decreased 5-fold in group 2 and 16-fold in groups 3 and 4 as compared with group 1. Neither 3-OMD levels nor 3-OMD/l-dopa ratios correlated with the occurrence of on-off fluctuations. In a longitudinal study of three patients started on Madopar treatment the induction of plasma ALAAD was found to occur gradually over 3–4 weeks. Further detailed pharmacokinetic studies in plasma and cerebrospinal fluid are required in order to elucidate whether the ALAAD induction by PDI may be related to the loss of clinical efficacy of combination therapy in some patients and how it is related to end-of-dose deterioration and on-off phenomena.     

Effects of unilateral pedunculopontine stimulation on electromyographic activation patterns during gait in individual patients with Parkinson’s disease

In Parkinson’s disease (PD), the effects of deep brain stimulation of the pedunculopontine nucleus (PPTg-DBS) on gait has been object of international debate. Some evidence demonstrated that, in the late swing-early stance phase of gait cycle, a reduced surface electromyographic activation (sEMG) of tibialis anterior (TA) is linked to the striatal dopamine deficiency in PD patients. In the present study we report preliminary results on the effect of PPTg-DBS on electromyographic patterns during gait in individual PD patients. To evaluate the sEMG amplitude of TA, the root mean square (RMS) of the TA burst in late swing-early stance phase (RMS-A) was normalized as a percent of the RMS of the TA burst in late stance-early swing (RMS-B). We studied three male patients in the following conditions: on PPTg-DBS/on l-dopa, on PPTg-DBS/off l-dopa, off PPTg-DBS/on l-dopa, off PPTg-DBS/off l-dopa. For each assessment the UPDRS III was filled in. We observed no difference between on PPTg-DBS/off l-dopa and off PPTg-DBS/off l-dopa in UPDRS III scores. In off PPTg-DBS/off l-dopa, patient A (right implant) showed absence of the right and left RMSA, respectively, in 80% and 83% of gait cycles. Patient B (right implant) showed absence of the right RMS-A in 86% of cycles. RMS-A of the patient C (left implant) was bilaterally normal. In on PPTg- DBS/off l-dopa, no patient showed reduced RMS-A. Although the very low number of subjects we evaluated, our observations suggest that PPTg plays a role in modulating TA activation pattern during the steady state of gait.     

Continuous drug delivery in early- and late-stage Parkinson’s disease as a strategy for avoiding dyskinesia induction and expression

The treatment of the motor symptoms of Parkinson’s disease (PD) is dependent on the use of dopamine replacement therapy in the form of l-dopa and dopamine agonist drugs. However, the development of dyskinesia (chorea, dystonia, athetosis) can become treatment limiting. The initiation of dyskinesia involves a priming process dependent on the presence of nigral dopaminergic cell loss leading to alterations in basal ganglia function that underlie the expression of involuntary movements following the administration of each drug dose. Once established, dyskinesia is difficult to control and it is even more difficult to reverse the priming process. Dyskinesia is more commonly induced by l-dopa than by dopamine agonist drugs. This has been associated with the short duration of l-dopa causing pulsatile stimulation of postsynaptic dopamine receptors compared to the longer acting dopamine agonists that cause more continuous stimulation. As a result, the concept of continuous dopaminergic stimulation (CDS) has arisen and has come to dominate the strategy for treatment of early PD. However, CDS has flaws that have led to the general acceptance that continuous drug delivery (CDD) is key to the successful treatment of PD. Studies in both experimental models of PD and in clinical trials have shown CDD to improve efficacy, but reduce dyskinesia induction, and to reverse established involuntary movements. Two key clinical strategies currently address the concept of CDD: (1) in early-, mid- and late-stage PD, transdermal administration of rotigotine provides 24 h of drug delivery; (2) in late-stage PD, the constant intraduodenal administration of l-dopa is utilized to improve control of motor symptoms and to diminish established dyskinesia. This review examines the rationale for CDD and explores the clinical benefit of using such a strategy for the treatment of patients with PD.     

Increased vulnerability to l-DOPA toxicity in dopaminergic neurons from VMAT2 heterozygote knockout mice

Parkinson’s disease (PD) is characterized by a preferential loss of dopaminergic neurons in the substantia nigra pars compacta. The etiology of PD remains unclear; however, generation of reactive oxygen species during oxidation of free dopamine (DA) in the cytoplasm might be one of the causes of selective dopaminergic neuron loss in PD. Vesicular monoamine transporter type 2 (VMAT2) proteins in nerve terminals take up and partition DA from neuronal cytoplasm into synaptic vesicles. Alterations of VMAT2 function might therefore cause cytoplasmic accumulation of free DA, which is toxic for dopaminergic neurons. We showed that dopaminergic neurons from VMAT2 heterozygous knockout mice were more vulnerable to the toxic effect of l-3,4-dihydroxyphenylalanine (l-DOPA, a DA precursor) than those from wild-type mice. Our results suggest that reduction of VMAT2 activity might attenuate the efficacy of l-DOPA therapy for patients with PD.     

Effects of dopaminergic stimulation on peripheral markers of apoptosis: relevance to Parkinson’s disease

Abstract. We investigated the effects of dopaminergic stimulation on anti-apoptotic protein Bcl-2, pro-apoptotic enzyme caspase- 3, and anti-oxidant/anti-apoptotic enzyme Cu/Zn superoxide dismutase (SOD) in human lymphocytes exposed to dopamine (DA). The same determinations were also carried out in parkinsonian patients treated with L-dopa. Caspase-3 activity and Cu/Zn SOD levels tended to increase when lymphocytes were exposed to low or intermediate doses of DA, while a decrease was observed, particularly in caspase-3 activity, with the higher DA dose. Bcl-2 levels were unaffected. In patients, we observed a negative correlation between Cu/Zn SOD levels and daily intake of L-dopa, which also tended to be negatively correlated with caspase-3 activity, but not with Bcl- 2. Our results show that dopaminergic stimulation is associated with complex changes in regulatory proteins of apoptosis.     

Effects of perinatal exposure to Δ9-tetrahydrocannabinol on the fetal and early postnatal development of tyrosine hydroxylase-containing neurons in rat brain

The exposure of pregnant rats to Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive constituent ofCannabis sativa, during the perinatal period affects the gene expression and the activity of tyrosine hydroxylase (TH) in the brains of their offspring at peripubertal and adult ages. In the present work we explored whether these effects also appear during fetal and early neonatal periods, when TH expression plays an important role in neural development. To this end, the mRNA amounts for TH and the amounts and activity of this enzyme, in addition to catecholamine (CA) contents, were analyzed in the brain of fetuses at different gestational days (GD) and of newborns at two postnatal ages, which had been daily exposed to Δ⁹-THC or vehicle from d 5 of gestation. Results were as follows. The exposure to Δ⁹-THC markedly affected the expression of the TH gene in the brain of fetuses at GD 14. Thus, the amounts of its mRNA at this age were higher in Δ⁹-THC-exposed fetuses than in controls. This corresponded with a marked rise in the amounts of TH protein and in the activity of this enzyme at this age. Normalization was found in these parameters at GD16. However, a marked sexual dimorphism in the response of TH gene to cannabinoid exposure appeared from GD18 and was particularly evident at GD21, when TH-mRNA amounts increased in developing female brains, but decreased in developing male brains exposed to Δ⁹-THC, effects that were mostly prolonged to early postnatal ages. However, these changes did not correspond always with parallel changes in the amounts and activity of TH and in CA contents, as occurred in GD14, suggesting that Δ⁹-THC would not be affecting the basal capability to synthesize CAs in TH-containing neurons, but would affect the responsiveness of TH gene. We found only a marked increase in the production ofl-3,4-dihydroxyphenylacetic acid, the main intraneuronal dopamine metabolite, in female newborns exposed to Δ⁹-THC. Collectively, our results support the belief that the perinatal exposure to Δ⁹-THC affects the expression of the TH gene and, sometimes, the activity of this enzyme in brain catecholaminergic neurons in certain critical periods of fetal and early neonatal brain development. These results support the notion that cannabinoids are able to affect the gene expression of specific key proteins for catecholaminergic development, and that these alterations might be the origin of important long-term neurobehavioral effects caused by perinatal cannabinoid exposure at peripubertal and adult ages. Part of this work has been previously presented in abstract form and published in the Proceedings of the International Cannabis Research Society (July 21–23, 1994, L’Esterel, Quebec, Canada).     

Efficacy and tolerability of dopamine agonists in a parkinsonian population

A clinical retrospective study was carried out in a population of 366 Parkinson's disease (PD) outpatients, to analyse the efficacy and tolerability of nonergoline and ergoline dopamine agonist (DA), in monotherapy or in combination with L-dopa. Safety was comparable in both groups except for higher occurrence of gastrointestinal symptoms in ergoline group and somnolence in nonergoline group. No significant difference concerning efficacy and tolerability was found during DA monotherapy. Mean age at PD onset was slightly higher in patients withdrawing DA monotherapy for adverse events comparing to patients who needed the addition of L-dopa (60.36±7.53 versus 54.88±:10.75; p<0.05), suggesting that older age at the onset of the disease increases the risk for adverse events during DA monotherapy. The follow-up of the remaining patients still in monotherapy with DA will allow a better evaluation of these aspects.     

A possible pathophysiological role of tyrosine hydroxylase in Parkinson’s disease suggested by postmortem brain biochemistry: a contribution for the special 70th birthday symposium in honor of Prof. Peter Riederer

Postmortem brain biochemistry has revealed that the main symptom of movement disorder in Parkinson’s disease (PD) is caused by a deficiency in dopamine (DA) at the nerve terminals of degenerating nigro-striatal DA neurons in the striatum. Since tyrosine hydroxylase (TH) is the rate-limiting enzyme for the biosynthesis of DA, TH may play an important role in the disease process of PD. DA regulated by TH activity is thought to interact with α-synuclein protein, which results in intracellular aggregates called Lewy bodies and causes apoptotic cell death during the aging process. Human TH has several isoforms produced by alternative mRNA splicing, which may affect activation by phosphorylation of serine residues in the N-terminus of TH. The activity and protein level of TH are decreased to cause DA deficiency in the striatum in PD. However, the homo-specific activity (activity/enzyme protein) of TH is increased. This increase in TH homo-specific activity suggests activation by increased phosphorylation at the N-terminus of the TH protein for a compensatory increase in DA synthesis. We recently found that phosphorylation of the N-terminal portion of TH triggers proteasomal degradation of the enzyme to increase TH turnover. We propose a hypothesis that this compensatory activation of TH by phosphorylation in the remaining DA neurons may contribute to a further decrease in TH protein and activity in DA neurons in PD, causing a vicious circle of decreasing TH activity, protein level and DA contents. Furthermore, increased TH homo-specific activity leading to an increase in DA may cause toxic reactive oxygen species in the neurons to promote neurodegeneration.     

TH基因修饰细胞脑内移植治疗猴帕金森病的实验研究

目的 评价包囊化酪氨酸羟化酶（tyrosine hydroylase,TH）基因修饰的基因工程细胞脑内移植治疗帕金森病的疗效。方法 将pcDNA3/hTH质粒转染人神经母细胞瘤细胞系SYTY细胞，筛选出阳性克隆，微包囊化处理后的含有TH基因修饰细胞植入PD猴模型脑内，观察其行为、CSF中DA含量的变化，用免疫组化法检查移植细胞的存活情况。结果 （1）pcDNA3/hTH基因经亚克隆，提取纯化的质粒，经ECORI酶切后产生1.9Kb和5.5Kb的片段。转基因后的SY5Y细胞免疫细胞化学染色显示TH染色强阳性；（2）移植后PD猴症状明显改善，脑脊液中DA含量升高；（3）SABC免疫组化发现移植区存在大量TH阳／性细胞。结论 构建的TH基因工程细胞体外和体内均表达人类TH基因；微包囊化处理后的基因工程细胞在PD猴脑内存活并发挥治疗作用。     

The assays of activities and function of TH, AADC, and GCH1 and their potential use in ex vivo gene therapy of PD

In the past decades, there have been numerous studies in the gene therapy for Parkinson's disease (PD), especially in delivering genes of enzymes for dopamine (DA) synthesis. Gene therapy in PD appears to be at the brink of the clinical study phase. However, there are many questions that need to be solved before this approach can be contemplated clinically, especially the question about the control of DA production because too much DA could cause toxicity. Until recently, few studies have investigated the relation between DA production and PD improvement and respective expressed human tyrosine hydroxylase (hTH), human GTP-cyclohydrolase 1 (hGCH1), and human aromatic acid decarboxylase (hAADC) in ex vivo gene therapy for PD. Now, we have developed a simple, fast, and reliable method to assay the activities of TH and AADC and have provided the possibility of ex vivo gene therapy for PD by genetically modifying cells with separate hTH, hGCH1, and hAADC genes. Using the method, we found though hTH, hGCH1, and hAADC genes were expressed, respectively, they could fulfil the function of DA synthesis by incubating together in vitro, and more DA was synthesized in vitro when hTH, hGCH1, and hAADC genes were expressed together rather than hTH and hAADC genes expressed or hTH expressed. The result suggests that we could easily control DA production in ex vivo gene therapy before transplantation. By combining this method and microdialysis, we also could further investigate the DA production in vitro and in vivo and then decide the optimal number and ratio of different transduced cells to improve the therapy of PD. Thus, the method has potential use in ex vivo gene therapy of PD.     

Controlled-release levodopa/benserazide (Madopar HBS): clinical observations and levodopa and dopamine plasma concentrations in fluctuating parkinsonian patients

Summary In five levodopa (l-dopa)-treated patients with Parkinson's disease with severe fluctuations of motor performance, plasma l-dopa as well as dopamine levels were measured during 2 days, first under optimal standard l-dopa with peripheral decarboxylase inhibitor (PDI) and then after a dose adjustment period using slow-release l-dopa/benserazide (Madopar HBS) in an open inpatient trial. Three patients benefited from the slow-release preparation; two patients deteriorated with a tendency to have an unpredictable response, a delay to turn on with the first dose in the morning, as well as an increase in dyskinesia corresponding to l-dopa cumulation during the day. These problems were subsequently also seen during the follow-up period of 1 year in those patients who benefited from Madopar HBS as inpatients. This might indicate that patient compliance is more difficult with the new formulation. After 1 year all patients had returned to their previous standard l-dopa/PDI treatment. l-Dopa levels continued to fluctuate, but to a lesser degree with Madopar HBS. The equivalent l-dopa dosage had to be increased by 56% (29–100%) with Madopar HBS while mean dopamine levels increased in four patients (by 47–257%) without the occurrence of peripheral side-effects. This implies that with the new formulation more l-dopa is metabolized to dopamine and explains the necessity to increase the equivalent l-dopa dosage.     

Reduced L-dopa absorption and increased clinical fluctuations in Helicobacter pylori-infected Parkinson's disease patients

We report that the area under the cure of L-dopa plasma concentration, following the administration of a single 250 mg L-dopa dose, is augmented after Helicobacter pylori (HP) eradication in six Parkinson's disease (PD) patients showing high IgG antibody titer against HP. A prolongation of L-dopa clinical benefit was also observed. We suggest that HP infection-activated gastric alterations may be responsible, at least in part, for the reported erratic efficacy or oral L-dopa therapy in some advanced PD patients. Given the high percentage of HP-positivity in the age cohorts including the largest prevalence of PD patients, we propose that HP eradication be recommended in all PD patients under L-dopa therapy.     

Gait variability in Parkinson’s disease: an indicator of non-dopaminergic contributors to gait dysfunction?

Gait variability has potential utility as a predictive measure of dysfunction in Parkinson’s disease (PD). Current understanding implicates non-dopaminergic pathways. This study investigated the explanatory characteristics of gait variability in PD on and off medication under single and dual task conditions. Fifty people with PD were assessed twice at home (on and off l-dopa) whilst walking under single and dual task conditions, and variability (coefficient of variation, CV) was calculated for stride time and double limb support (DLS) time. Hierarchical regression analysis was used to identify predictors. The first block of variables included age, gait speed, depression (Hospital Anxiety and Depression Scale) and fatigue (Multidimensional Fatigue Inventory), and the second block included motor severity (UPDRS III), executive function (Hayling and Brixton) and attention (Test of Everyday Attention). Motor severity predicted stride time variability and DLS time variability independent of l-dopa during single task gait. Dual task gait yielded a more complex picture. Depression made a unique contribution of 9.0% on medication and 5.0% off medication to stride time variability, and visual attention and younger age contributed to DLS variability on medication, explaining 3% and 2%, respectively. Motor severity predicted DLS variability off medication, explaining 74% of variance. Different characteristics explain the two measures of gait variability, pointing to different control mechanisms.     

No increased chromosomal damage in l-DOPA-treated patients with Parkinson’s disease: a pilot study

Parkinson’s disease (PD) is a neurodegenerative movement disorder affecting about 2% of the human population in old age. l-3,4-Dihydroxyphenylalanine (l-DOPA) in combination with a peripheral aromatic amino acid decarboxylase inhibition has been the most frequently prescribed drug for alleviating symptoms of PD, but a potential contribution of l-DOPA therapy to further neurodegeneration via oxidative stress is still debated. We report that the specific oxidative stress biomarker 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) level in peripheral blood lymphocyte DNA was elevated to 8.1 ± 1.7 8-oxodG/10⁶dG in 17 chronically l-DOPA-treated PD patients, compared to 4.6 ± 1.2 8-oxodG/10⁶dG in 12 controls. However, the total antioxidative capacity of plasma was increased to 1113 ± 237 μM in the PD patients compared to 941 ± 254 μM in controls. The frequency of micronuclei, a subgroup of chromosomal aberrations, in peripheral blood lymphocytes was not elevated compared to healthy age-matched individuals. In vitro, in a cell-free assay, dopamine and its precursor l-DOPA exhibited antioxidative capacity. On the other hand, the 8-oxodG concentration in cultured PC 12 cells was enhanced after dopamine treatment. This elevation may be below a threshold for manifestation as chromosomal damage.     

In VivoL-DOPA Production by Genetically Modified Primary Rat Fibroblast or 9L Gliosarcoma Cell Grafts via Coexpression of GTPcyclohydrolase I with Tyrosine Hydroxylase

To investigate the biochemical requirements forin vivoL-DOPA production by cells genetically modifiedex vivoin a rat model of Parkinson's disease (PD), rat syngeneic 9L gliosarcoma and primary Fischer dermal fibroblasts (FDFs) were transduced with retroviral vectors encoding the human tyrosine hydroxylase 2 (hTH2) and human GTP cyclohydrolase I (hGTPCHI) cDNAs. As GTPCHI is a rate-limiting enzyme in the pathway for synthesis of the essential TH cofactor, tetrahydrobiopterin (BH₄), only hTH2 and GTPCHI cotransduced cultured cells produced L-DOPA in the absence of added BH₄. As striatal BH₄levels in 6-hydroxydopamine (6-OHDA)-lesioned rats are minimal, the effects of cotransduction with hTH2 and hGTPCHI on L-DOPA synthesis by striatal grafts of either 9L cells or FDFs in unilateral 6-OHDA-lesioned rats were tested. Microdialysis experiments showed that those subjects that received cells cotransduced with hTH2 and hGTPCHI produced significantly higher levels of L-DOPA than animals that received either hTH2 or untransduced cells. However, animals that received transduced FDF grafts showed a progressive loss of transgene expression until expression was undetectable 5 weeks after engraftment. In FDF-engrafted animals, no differential effect of hTH2 vs hTH2 + hGTPCHI transgene expression on apomorphine-induced rotation was observed. The differences in L-DOPA production found with cells transduced with hTH2 alone and those cotransduced with hTH2 and hGTPCHI show that BH₄is critical to the restoration of the capacity for L-DOPA production and that GTPCHI expression is an effective means of supplying BH₄in this rat model of PD.