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Levodopa and 3-OMD levels in Parkinson patients treated with Duodopa
European Neuropsychopharmacology (2010) 20, 683–687
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Levodopa and 3-OMD levels in Parkinson patients treated with Duodopa A. Antonini a,c , G. Bondiolotti b , F. Natuzzi a , S.R. Bareggi b,⁎ a
Ist. Clinici Perfezionamento, Parkinson Institute, Milan, Italy Dept. of Pharmacology, University of Milan, Milan, Italy c IRCCS San Camillo, Venezia, Italy b
Received 9 February 2010; received in revised form 26 April 2010; accepted 30 April 2010
KEYWORDS Duodopa; Levodopa levels; OMD levels; Dyskinesia
Abstract We studied 19 patients (14 men, 5 women, Hoehn and Yahr (H&Y) ≥ 3) with advanced Parkinson's disease (PD) attending the Parkinson Institute, Milan, whose motor fluctuations and dyskinesia were not controlled by oral medications. After all oral PD medications had been withdrawn, they received a duodenal levodopa infusions (Duodopa, Solvay Pharmaceuticals) for 14 h/day through a transabdominal port; levodopa boluses were administered in the morning and during “off” periods. The patients were evaluated by means of the UPDRS in the morning (“off”) and 60–120 min after the infusion (“on”) at baseline and for a mean follow-up of 13.5 ± 12.5 months (up to 36 months in 10 patients:). Levodopa (L-DOPA) and its metabolites were determined by HPLC with electrochemical detection. L-DOPA concentrations tended to higher in the afternoon (2008± 345 vs 1713± 274 ng/mL) and correlated with the daily dose. O-methyldopa (OMD) levels correlated with L-DOPA levels, and the OMD/L-DOPA ratios were stable over the day. There was a relationship between decreasing UPDRS III scores and decreasing OMD/L-DOPA ratios. Dyskinesia (UPDRS IV, items 32–34) showed a clear improvement over time but there was no clear relationship with L-DOPA and OMD levels, or the OMD/L-DOPA ratio. The L-DOPA/dose ratio was stable over time, whereas OMD levels and the OMD/LDOPA ratio decreased. It is conceivable that continuous infusion decreases metabolism possibly due to a reduction in methyl donor availability, as demonstrated by the increase in total homocysteine levels. Our results do not support the development of tolerance even after several months of continuous infusion, and indicate that pharmacodynamic factors play a role in afternoon off periods. © 2010 Elsevier B.V. and ECNP All rights reserved.
⁎ Corresponding author. Dept. of Pharmacology, University of Milan, Via Vanvitelli 32, 20129 Milano, Italy. Tel.: +39 02 5031 6946. E-mail address: [email protected] (S.R. Bareggi). 0924-977X/$ - see front matter © 2010 Elsevier B.V. and ECNP All rights reserved. doi:10.1016/j.euroneuro.2010.04.010
684
1. Introduction Parkinson's disease (PD) is a progressive neurodegenerative disease whose main clinical features of motor dysfunction are the result of a loss of dopaminergic neurons in the substantia nigra pars compacta. Dopamine replacement therapy in the form of levodopa, dopamine agonists or monoamine oxidase B inhibitors is effective in treating these symptoms and improving the quality and duration of life (Clarke et al., 1995; Karlsen et al., 2000; Shapira, 2007). Levodopa is the most potent drug in this respect, but its use is associated with the development of motor complications that include ‘wearing-off’ and dyskinesias. These develop at a rate of approximately 10% per year, but more rapidly in patients with young-onset PD, in whom their 3-year prevalence is 70% (Kostic et al., 1991). However, levodopa is still the most widely used agent in the treatment of PD patients. It reaches its site of effect crossing the blood/brain barrier by means of an active transport system and, in brain tissues, it is decarboxylated to dopamine, which is normally stored in the presynaptic terminals of striatal neurons. The pathogenesis of the decline in motor response and onset of motor fluctuations during long-term treatment with levodopa has not been precisely defined but is related to the intermittent stimulation of dopamine receptors in a denervated striatum (Olanow et al., 2000). This means that oral levodopa, which has a half-life of approximately 90 min, is a potent cause whereas continuous levodopa infusion can be used to treat fluctuations (Shoulson et al., 1975; Kurth et al., 1993). Furthermore, it has been shown that long-acting dopamine agonists such as pramipexole or ropinirole lead to a significantly lower risk of dyskinesia (Rascol et al., 2000; Holloway et al., 2004). Consequently, in addition to combining levodopa with dopamine agonists, patients with motor fluctuations are also managed by prolonging the action of individual levodopa doses (Shoulson et al., 1975; Kostic et al., 1991). This is done by using extended-release levodopa formulations, inhibiting the metabolic pathways of levodopa or dopamine degradation such as decarboxylase, monoamine oxidase and catechol-O-methyltransferase (COMT) (Shoulson et al., 1975; Kostic et al., 1991; Parkinson Study Group, 1997; Piccini et al., 2000), or administering intraduodenal infusions (Duodopa) (Antonini et al., 2007). The effective management of motor complications is significantly challenging in many patients with advanced PD because their clinical condition becomes dependent on their short-term response to oral levodopa (Karlsen et al., 2000). In addition to the “wearing-off” effect of levodopa (Clarke et al., 1995), the onset of dyskinesia causes additional “on” time disability (Kostic et al., 1991). The currently available strategies in these patients include deep brain stimulation and apomorphine infusion, whereas intravenous levodopa infusion can only be sustained for a few days (Fabbrini et al., 1988). Continuous levodopa delivery by enteral infusion represents a novel approach that ensures more continuous plasma levels than oral treatment, thus leading to the effective control of motor complications and improving the patients' quality of life (Nyholm et al., 2005). However, experience with this technique has so far been limited to short-term trials and there are no published data concerning its use in a
A. Antonini et al. routine clinical setting. Furthermore, little is known about the pharmacokinetics of Duodopa infusion, and there are no published data concerning levodopa metabolism and 3-Omethyldopa (3-OMD) accumulation. Levodopa is administered with dopa decarboxylase inhibitors (DDI) in order to prevent its peripheral degradation. This increases the conversion of levodopa to 3-Omethyldopa (3-OMD) by catechol-O-methyltransferase (COMT) in blood, peripheral tissue and nigrostriatal neurons (Müller and Kuhn, 2006). COMT requires Mg2+ as a co-factor and the methyl donor S-adenosylmethionine (SAM), which is synthesised from adenosintriphosphate and methionine (MET) (Müller and Kuhn, 2006). The O-methylation of levodopa to 3-OMD is therefore associated with the conversion of SAM to S-adenosylhomocysteine (SAH) and subsequently total homocysteine (tHcys), which can be considered an index of methylation. As OMD is an amino acid, it competes with L-DOPA at the blood/brain barrier, which decreases the penetration of levodopa into the central nervous system (CNS) and therefore its effectiveness. However, the effects of L-DOPA can be improved by administering COMT inhibitors (entacapone or tolcapone) to reduce OMD levels (Bet et al., 2008). As all of the data concerning L-DOPA kinetics have been obtained after short-term Duodopa infusion (Stocchi et al., 2005), the main aim of this study was to determine the concentrations of L-DOPA and its metabolites (mainly OMD) after medium- and long-term infusion. We also measured plasma tHcys levels as there are no published data concerning tHcys after medium- or long-term treatment. The final aim was to describe the clinical condition and quality of life of 19 PD patients who underwent continuous duodenal infusion of levodopa/carbidopa because of severe motor complications and were followed up for a mean period of 13.5 ± 12.5 months (up to 36 months in 10 patients).
2. Patients and methods We studied 19 patients (14 men, 5 women, Hoehn and Yahr (H&Y) ≥ 3) with advanced PD attending the Parkinson Institute, Milan, Italy, whose motor fluctuations and dyskinesia were not controlled by oral medications. After all oral PD medications had been withdrawn, all of the patients received duodenal levodopa infusions (Duodopa, Solvay Pharmaceuticals) for 14 h/day through a transabdominal port; with levodopa boluses being administered in the morning and during “off” periods. All of the patients gave their informed consent to participate in the study, which was approved by the local Ethics Committee and conducted in accordance with the principles of good clinical practice.
2.1. Assessments The clinical assessments throughout the study were based on the administration of the UPDRS (Fahn et al., 1987) in the morning (“off”), and 60–120 min after the beginning of the infusion (“on”) at baseline and for a mean follow-up of 13.5±12.5 months (up to 36 months in 10 patients). Blood samples for the determination of plasma levodopa and 3OMD levels were drawn in the morning and afternoon.
Levodopa and 3-MD levels in Parkinson patients treated with Duodopa
685
2.2. Levodopa and total homocysteine assay Levodopa and its metabolites, dopamine, 3-O-methyl-Dopa (OMD), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were determined by means of HPLC using amperometric detection (ESA, Bedford, MA, USA) as described by Wikberg (1991) with minor modifications: 0.5 mL of ice-cold perchloric acid 0.6 N with sodium disulfite 1% were added to 0.5 mL of plasma and, after centrifuging for 20 min at 30,000 g in a Sorvall centrifuge (Thermo Electron Corporation, Waltham, MA, USA), 50 μl of the supernatant were injected into the chromatograph. Total homocysteine (tHcys) was determined by means of HPLC using coulometric detection, a simple and reliable procedure based on a chemical reductant and direct measurement on porous graphite electrodes. The isocratic system consisted of a pump (Shimadzu LC 6A), an autosampler (Shimadzu SIL 9A) and a Coulochem II (ESA) detector coupled with a5014A microdialysis cell. The mobile phase consisted of a sodium citrate/sodium phosphate buffer, EDTA, octansulfonic acid and 7% of methanol, pH 3.2, delivered at 0.5 mL/min; the column (Ascentis Express C18, 100 mm × 4.6 mm, 2.7 µm) was kept at 40 °C, the injection volume was 10 µl, and the retention times were 5.3 min for homocysteine and 10.9 min for penicillamine (IS).
2.3. Sample preparation A plasma sample (100 µl) was mixed with 5 µl of internal standard solution (penicillamine), and the disulfides were completely reduced by the addition of 5 µl of 1 M L-dithiothreitol, which was allowed to react at room temperature for 15 min. The proteins were precipitated by the addition of 20 µl of 90% trichloroacetic acid, mixed and, after 10 min centrifugation at 13,000 g, 100 µl of the clear supernatant were transferred to an autosampler vial.
2.4. Pharmacokinetic and statistical analyses The levels of levodopa, its COMT-related metabolites (OMD, HVA) and clinical response were compared using repeated measures (RM) ANOVA with Tukey's test for multiple comparisons (Sigmastat, USA).
Figure 1 Relationships between levodopa daily dose and concentrations.
There was a relationship between the decrease in UPDRS III scores and the decrease in OMD/L-DOPA ratios (r = 0.44, p b 0.05; Fig. 4). The 15 patients with dyskinesia showed a clear improvement in dyskinesia (UPDRS IV, items 32 and 33) and the proportion of “off” periods (item 39) over time (Table 2), but there was no clear relationship with L-DOPA or OMD levels, or the OMD/LDOPA ratio. The L-DOPA/dose ratio was also stable over time, whereas OMD levels and the OMD/L-DOPA ratio decreased (Fig. 5). It is therefore conceivable that continuous infusion leads to a decrease in metabolism possibly due to a reduction in methyl donor availability because our data show a decrease in tHcys over time (Fig. 5) that can be considered an index of the decrease in methylation as a decrease in SAM levels has been found after a single oral administration of oral levodopa (Müller et al., 2001). Minor adverse events occurred in six patients: four cases of tube occlusion and two cases of tube dislocation, all requiring tube replacement.
4. Conclusions 3. Results Levodopa concentrations were similar in the morning and afternoon, but tended to be slightly higher in the afternoon (Table 1) and correlated with the daily dose (Fig. 1); OMD levels and OMD/L-DOPA ratios were stable over the day (Table 1), and OMD levels correlated with LD levels (Fig. 2: r=0.54, pb 0.02). Total Hcys levels at the beginning of Duodopa therapy were much higher than those observed in patients receiving oral levodopa (Müller et al., 2001), and correlated with levodopa levels (Fig. 3).
Our results clearly indicate that L-DOPA and OMD levels are high after Duodopa infusion, but remain stable during the day. This
Table 1 L-DOPA, OMD concentrations (ng/ml) and OMD/LDOPA ratios in the morning and afternoon at the first observation (n = 19, values are not significantly different).
L-DOPA
3-OMD OMD/DOPA
Morning
Afternoon
1892.74 ± 723.11 12195.91 ± 6061.86 6.27 ± 2.31
1948.83 ± 868.57 12959.04 ± 5941.01 8.30 ± 9.11
Figure 2 Relationships between levodopa and OMD concentrations (r = 0.54, p b 0.02).
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A. Antonini et al. Table 2 Scores on items 32, 33, and 39 of UPDRS IV after different times of Duodopa treatment (M ± S.D.; (range)). Weeks
0
1–20
21–50
51–100
101–200
n = 15
n=8
n=5
n=4
n=4
Item 32
2.51 ± 0.61 1.81 ± 0.80 1.55 ± 0.60 (1–3)
1.25 ± 0.92 0.75± 1.50 0.75 ± 0.71 (0–2)
1.40 ± 0.60 0.60 ± 0.61* 1.00 ± 0.10 (1)
1.51 ± 0.62 1.75 ± 0.95 0.75 ± 0.50 (0–1)
1.00 ± 0.01* 0.70 ± 0.51* 0.50 ± 0.49* (0–1)
Item 33 Item 39
*p b 0.05 vs basal values. RM ANOVA, Tukey's test.
Figure 3 Relationships between levodopa and total homocysteine concentrations(r = 0.52, p b 0.05).
favours good motor control and decreases dyskinesia over time, thus improving the patients' quality of life as previously described (Antonini et al., 2007). They also confirm previous findings (Bet et al., 2008) that higher OMD levels decrease the efficacy of L-DOPA. The mechanism underlying “wearing-off” and the development of dyskinesia is still unclear, but it is likely that both are influenced by disease progression and the pulsatility of oral levodopa. Our findings are consistent with previous data demonstrating that, in comparison with oral levodopa, Duodopa infusion decreases the fluctuations in levodopa levels (Stocchi et al., 2005). As the half-life of OMD is much longer than that of LDOPA, it could be expected that OMD accumulates over time. However, this is not the case because the metabolism of L-DOPA in the presence of DDI is completely governed by COMT and a sort of self-limiting step occurs due to the consumption of the methyl donor (SAM). The concentrations of OMD therefore decrease in parallel with tHomocysteine levels, which can be considered an index of decreasing methylation as lower SAM levels have been found even after
Figure 4 Relationships between OMD/levodopa concentrations and improvement (% over basal values) on the UPDRS III (r = 0.45, p b 0.05) at the time of the final assessment.
a single oral administration of levodopa (Müller et al., 2001). A similar decrease has been described after the administration of the COMT inhibitor, tolcapone (Müller and Kuhn, 2006). Our results do not support the hypothesis of the development of tolerance even after several months of continuous infusion, and indicate that pharmacodynamic factors may play a role in afternoon “off” periods.
Figure 5 A) decrease of OMD/LD ratio over time (r = 0.59, p b 002); B) decrease of tHcys over time (r = 0.55 p b 0.05).
Levodopa and 3-MD levels in Parkinson patients treated with Duodopa
Role of the funding source University funding.
Contributors A. Antonini, G. Bondiolotti, F. Natuzzi, S.R. Bareggi.
Conflict of interest None of the authors has any conflict of interest.
Acknowledgement We thank Prof. G. Pezzoli for its supervision of the research.
References Antonini, A., Isaias, I.U., Canesi, M., Zibetti, M., Mancini, F., Manfredi, L., Dal Fante, M., Lopiano, L., Pezzoli, G., 2007. Duodenal levodopa infusion for advanced Parkinson's disease: 12month treatment outcome. Mov. Disord. 22, 1145–1149. Bet, L., Bareggi, S.R., Pacei, F., Bondiolotti, G., Meola, G., Schapira, A.H., 2008. Bimodal administration of entacapone in Parkinson's disease patients improves motor control. Eur. J. Neurol. 15, 268–273. Clarke, C.E., Zobkiw, R.M., Gullaksen, E., 1995. Quality of life and care in Parkinson's disease. Br. J. Clin. Pract. 49, 288–293. Fabbrini, G., Mouradian, M.M., Juncos, J.L., Schlegel, J., Mohr, E., Chase, T.N., 1988. Motor fluctuations in Parkinson's disease: central pathophysiological mechanisms, Part 1. Ann. Neurol. 24, 366–371. Fahn, S., Elton, R.L., the UPDRS Development Committee, 1987. Unified Parkison's disease rating scale. In: Fahn, S., Mardsen, C. D., Goldstein, M., Calne, D. (Eds.), Recent Developments in Parkinson's Disease. MacMillan Healthcare Information, Florham Park, NJ, pp. 153–163. Holloway, R.G., Shoulson, I., Fahn, S., et al., 2004. Pramipexole vs levodopa as initial treatment for Parkinson disease: a 4-year randomized controlled trial. Arch. Neurol. 61, 1044–1053. Karlsen, K.H., Tandberg, E., Arsland, D., Larsen, J.P., 2000. Health related quality of life in Parkinson's disease: a prospective longitudinal study. J. Neurol. Neurosurg. Psychiatry 69, 584–589.
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Kostic, V., Przedborski, S., Flaster, E., Sternic, N., 1991. Early development of levodopa-induced dyskinesias and response fluctuations in young-onset Parkinson's disease. Neurology 41, 202–205. Kurth, M.C., Tetrud, J.W., Tanner, C.M., Irwin, I., Stebbins, G.T., Goetz, C.G., et al., 1993. Double-blind, placebo-controlled, crossover study of duodenal infusion of levodopa/carbidopa in Parkinson's disease patients with ‘on-off’ fluctuations. Neurology 43, 1698–1703. Müller, T., Kuhn, W., 2006. Tolcapone decrease plasma levels of Sadenosyl-L-homocysteine and homocystiene in treated Parkinson's disease patients. Eur. J. Clin. Pharmacol. 62, 447–450. Müller, T., Woitalla, D., Hauptmann, B., Fowler, B., Kuhn, W., 2001. Decrease of methionine and S-adenosylmethionine and increase of homocysteine in treated patients with Parkinson's disease. Neurosci. Lett. 308, 54–56. Nyholm, D., Nilsson Remahl, A.I., Dizdar, N., et al. , 2005. Duodenal levodopa infusion monotherapy vs oral polypharmacy in advanced Parkinson disease. Neurology 64, 216–223. Olanow, W., Schapira, A.H., Rascol, O., 2000. Continuous dopaminereceptor stimulation in early Parkinson's disease. Trends Neurosci. 23 (10 suppl), S117–S126. Parkinson Study Group, 1997. Entacapone improves motor fluctuations in levodopa-treated Parkinson's disease patients. Ann. Neurol. 42 (5), 747–755. Piccini, P., Brooks, D.J., Korpela, K., Pavese, N., Karlsson, M., Gordin, A., 2000. The catechol-O-methyltransferase (COMT) inhibitor entacapone enhances the pharmacokinetic and clinical response to Sinemet CR in Parkinson's disease. J. Neurol. Neurosurg. Psychiatry 68, 589–594. Rascol, O., Brooks, D.J., Korczyn, A.D., De Deyn, P.P., Clarke, C.E., Lang, A.E., 2000. A five-year study of the incidence of dyskinesia in patients with early Parkinson's disease who were treated with ropinirole or levodopa. 056 Study Group. N Engl J. Med. 342, 1484–1491. Shapira, A.H., 2007. Treatment options in the modern management of Parkinson disease. Arch. Neurol. 64, 1083–1088. Shoulson, I., Glaubiger, G.A., Chase, T.N., 1975. On-off response. Clinical and biochemical correlations during oral and intravenous levodopa administration in parkinsonian patients. Neurology 25 (12), 1144–1148. Stocchi, F., Vacca, L., Ruggieri, S., Olanow, W., 2005. Intermittent versus continuous levodopa administration in patients with advanced Parkinson's disease. Arch. Neurol. 62, 905–910. Wikberg, T., 1991. Simultaneous determination of levodopa, its main metabolites and carbidopa in plasma by liquid chromatography. J. Pharm. Biomed. Anal. 9, 167–176.
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Levodopa and 3-OMD levels in Parkinson patients treated with Duodopa A. Antonini a,c , G. Bondiolotti b , F. Natuzzi a , S.R. Bareggi b,⁎ a
Ist. Clinici Perfezionamento, Parkinson Institute, Milan, Italy Dept. of Pharmacology, University of Milan, Milan, Italy c IRCCS San Camillo, Venezia, Italy b
Received 9 February 2010; received in revised form 26 April 2010; accepted 30 April 2010
KEYWORDS Duodopa; Levodopa levels; OMD levels; Dyskinesia
Abstract We studied 19 patients (14 men, 5 women, Hoehn and Yahr (H&Y) ≥ 3) with advanced Parkinson's disease (PD) attending the Parkinson Institute, Milan, whose motor fluctuations and dyskinesia were not controlled by oral medications. After all oral PD medications had been withdrawn, they received a duodenal levodopa infusions (Duodopa, Solvay Pharmaceuticals) for 14 h/day through a transabdominal port; levodopa boluses were administered in the morning and during “off” periods. The patients were evaluated by means of the UPDRS in the morning (“off”) and 60–120 min after the infusion (“on”) at baseline and for a mean follow-up of 13.5 ± 12.5 months (up to 36 months in 10 patients:). Levodopa (L-DOPA) and its metabolites were determined by HPLC with electrochemical detection. L-DOPA concentrations tended to higher in the afternoon (2008± 345 vs 1713± 274 ng/mL) and correlated with the daily dose. O-methyldopa (OMD) levels correlated with L-DOPA levels, and the OMD/L-DOPA ratios were stable over the day. There was a relationship between decreasing UPDRS III scores and decreasing OMD/L-DOPA ratios. Dyskinesia (UPDRS IV, items 32–34) showed a clear improvement over time but there was no clear relationship with L-DOPA and OMD levels, or the OMD/L-DOPA ratio. The L-DOPA/dose ratio was stable over time, whereas OMD levels and the OMD/LDOPA ratio decreased. It is conceivable that continuous infusion decreases metabolism possibly due to a reduction in methyl donor availability, as demonstrated by the increase in total homocysteine levels. Our results do not support the development of tolerance even after several months of continuous infusion, and indicate that pharmacodynamic factors play a role in afternoon off periods. © 2010 Elsevier B.V. and ECNP All rights reserved.
⁎ Corresponding author. Dept. of Pharmacology, University of Milan, Via Vanvitelli 32, 20129 Milano, Italy. Tel.: +39 02 5031 6946. E-mail address: [email protected] (S.R. Bareggi). 0924-977X/$ - see front matter © 2010 Elsevier B.V. and ECNP All rights reserved. doi:10.1016/j.euroneuro.2010.04.010
684
1. Introduction Parkinson's disease (PD) is a progressive neurodegenerative disease whose main clinical features of motor dysfunction are the result of a loss of dopaminergic neurons in the substantia nigra pars compacta. Dopamine replacement therapy in the form of levodopa, dopamine agonists or monoamine oxidase B inhibitors is effective in treating these symptoms and improving the quality and duration of life (Clarke et al., 1995; Karlsen et al., 2000; Shapira, 2007). Levodopa is the most potent drug in this respect, but its use is associated with the development of motor complications that include ‘wearing-off’ and dyskinesias. These develop at a rate of approximately 10% per year, but more rapidly in patients with young-onset PD, in whom their 3-year prevalence is 70% (Kostic et al., 1991). However, levodopa is still the most widely used agent in the treatment of PD patients. It reaches its site of effect crossing the blood/brain barrier by means of an active transport system and, in brain tissues, it is decarboxylated to dopamine, which is normally stored in the presynaptic terminals of striatal neurons. The pathogenesis of the decline in motor response and onset of motor fluctuations during long-term treatment with levodopa has not been precisely defined but is related to the intermittent stimulation of dopamine receptors in a denervated striatum (Olanow et al., 2000). This means that oral levodopa, which has a half-life of approximately 90 min, is a potent cause whereas continuous levodopa infusion can be used to treat fluctuations (Shoulson et al., 1975; Kurth et al., 1993). Furthermore, it has been shown that long-acting dopamine agonists such as pramipexole or ropinirole lead to a significantly lower risk of dyskinesia (Rascol et al., 2000; Holloway et al., 2004). Consequently, in addition to combining levodopa with dopamine agonists, patients with motor fluctuations are also managed by prolonging the action of individual levodopa doses (Shoulson et al., 1975; Kostic et al., 1991). This is done by using extended-release levodopa formulations, inhibiting the metabolic pathways of levodopa or dopamine degradation such as decarboxylase, monoamine oxidase and catechol-O-methyltransferase (COMT) (Shoulson et al., 1975; Kostic et al., 1991; Parkinson Study Group, 1997; Piccini et al., 2000), or administering intraduodenal infusions (Duodopa) (Antonini et al., 2007). The effective management of motor complications is significantly challenging in many patients with advanced PD because their clinical condition becomes dependent on their short-term response to oral levodopa (Karlsen et al., 2000). In addition to the “wearing-off” effect of levodopa (Clarke et al., 1995), the onset of dyskinesia causes additional “on” time disability (Kostic et al., 1991). The currently available strategies in these patients include deep brain stimulation and apomorphine infusion, whereas intravenous levodopa infusion can only be sustained for a few days (Fabbrini et al., 1988). Continuous levodopa delivery by enteral infusion represents a novel approach that ensures more continuous plasma levels than oral treatment, thus leading to the effective control of motor complications and improving the patients' quality of life (Nyholm et al., 2005). However, experience with this technique has so far been limited to short-term trials and there are no published data concerning its use in a
A. Antonini et al. routine clinical setting. Furthermore, little is known about the pharmacokinetics of Duodopa infusion, and there are no published data concerning levodopa metabolism and 3-Omethyldopa (3-OMD) accumulation. Levodopa is administered with dopa decarboxylase inhibitors (DDI) in order to prevent its peripheral degradation. This increases the conversion of levodopa to 3-Omethyldopa (3-OMD) by catechol-O-methyltransferase (COMT) in blood, peripheral tissue and nigrostriatal neurons (Müller and Kuhn, 2006). COMT requires Mg2+ as a co-factor and the methyl donor S-adenosylmethionine (SAM), which is synthesised from adenosintriphosphate and methionine (MET) (Müller and Kuhn, 2006). The O-methylation of levodopa to 3-OMD is therefore associated with the conversion of SAM to S-adenosylhomocysteine (SAH) and subsequently total homocysteine (tHcys), which can be considered an index of methylation. As OMD is an amino acid, it competes with L-DOPA at the blood/brain barrier, which decreases the penetration of levodopa into the central nervous system (CNS) and therefore its effectiveness. However, the effects of L-DOPA can be improved by administering COMT inhibitors (entacapone or tolcapone) to reduce OMD levels (Bet et al., 2008). As all of the data concerning L-DOPA kinetics have been obtained after short-term Duodopa infusion (Stocchi et al., 2005), the main aim of this study was to determine the concentrations of L-DOPA and its metabolites (mainly OMD) after medium- and long-term infusion. We also measured plasma tHcys levels as there are no published data concerning tHcys after medium- or long-term treatment. The final aim was to describe the clinical condition and quality of life of 19 PD patients who underwent continuous duodenal infusion of levodopa/carbidopa because of severe motor complications and were followed up for a mean period of 13.5 ± 12.5 months (up to 36 months in 10 patients).
2. Patients and methods We studied 19 patients (14 men, 5 women, Hoehn and Yahr (H&Y) ≥ 3) with advanced PD attending the Parkinson Institute, Milan, Italy, whose motor fluctuations and dyskinesia were not controlled by oral medications. After all oral PD medications had been withdrawn, all of the patients received duodenal levodopa infusions (Duodopa, Solvay Pharmaceuticals) for 14 h/day through a transabdominal port; with levodopa boluses being administered in the morning and during “off” periods. All of the patients gave their informed consent to participate in the study, which was approved by the local Ethics Committee and conducted in accordance with the principles of good clinical practice.
2.1. Assessments The clinical assessments throughout the study were based on the administration of the UPDRS (Fahn et al., 1987) in the morning (“off”), and 60–120 min after the beginning of the infusion (“on”) at baseline and for a mean follow-up of 13.5±12.5 months (up to 36 months in 10 patients). Blood samples for the determination of plasma levodopa and 3OMD levels were drawn in the morning and afternoon.
Levodopa and 3-MD levels in Parkinson patients treated with Duodopa
685
2.2. Levodopa and total homocysteine assay Levodopa and its metabolites, dopamine, 3-O-methyl-Dopa (OMD), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were determined by means of HPLC using amperometric detection (ESA, Bedford, MA, USA) as described by Wikberg (1991) with minor modifications: 0.5 mL of ice-cold perchloric acid 0.6 N with sodium disulfite 1% were added to 0.5 mL of plasma and, after centrifuging for 20 min at 30,000 g in a Sorvall centrifuge (Thermo Electron Corporation, Waltham, MA, USA), 50 μl of the supernatant were injected into the chromatograph. Total homocysteine (tHcys) was determined by means of HPLC using coulometric detection, a simple and reliable procedure based on a chemical reductant and direct measurement on porous graphite electrodes. The isocratic system consisted of a pump (Shimadzu LC 6A), an autosampler (Shimadzu SIL 9A) and a Coulochem II (ESA) detector coupled with a5014A microdialysis cell. The mobile phase consisted of a sodium citrate/sodium phosphate buffer, EDTA, octansulfonic acid and 7% of methanol, pH 3.2, delivered at 0.5 mL/min; the column (Ascentis Express C18, 100 mm × 4.6 mm, 2.7 µm) was kept at 40 °C, the injection volume was 10 µl, and the retention times were 5.3 min for homocysteine and 10.9 min for penicillamine (IS).
2.3. Sample preparation A plasma sample (100 µl) was mixed with 5 µl of internal standard solution (penicillamine), and the disulfides were completely reduced by the addition of 5 µl of 1 M L-dithiothreitol, which was allowed to react at room temperature for 15 min. The proteins were precipitated by the addition of 20 µl of 90% trichloroacetic acid, mixed and, after 10 min centrifugation at 13,000 g, 100 µl of the clear supernatant were transferred to an autosampler vial.
2.4. Pharmacokinetic and statistical analyses The levels of levodopa, its COMT-related metabolites (OMD, HVA) and clinical response were compared using repeated measures (RM) ANOVA with Tukey's test for multiple comparisons (Sigmastat, USA).
Figure 1 Relationships between levodopa daily dose and concentrations.
There was a relationship between the decrease in UPDRS III scores and the decrease in OMD/L-DOPA ratios (r = 0.44, p b 0.05; Fig. 4). The 15 patients with dyskinesia showed a clear improvement in dyskinesia (UPDRS IV, items 32 and 33) and the proportion of “off” periods (item 39) over time (Table 2), but there was no clear relationship with L-DOPA or OMD levels, or the OMD/LDOPA ratio. The L-DOPA/dose ratio was also stable over time, whereas OMD levels and the OMD/L-DOPA ratio decreased (Fig. 5). It is therefore conceivable that continuous infusion leads to a decrease in metabolism possibly due to a reduction in methyl donor availability because our data show a decrease in tHcys over time (Fig. 5) that can be considered an index of the decrease in methylation as a decrease in SAM levels has been found after a single oral administration of oral levodopa (Müller et al., 2001). Minor adverse events occurred in six patients: four cases of tube occlusion and two cases of tube dislocation, all requiring tube replacement.
4. Conclusions 3. Results Levodopa concentrations were similar in the morning and afternoon, but tended to be slightly higher in the afternoon (Table 1) and correlated with the daily dose (Fig. 1); OMD levels and OMD/L-DOPA ratios were stable over the day (Table 1), and OMD levels correlated with LD levels (Fig. 2: r=0.54, pb 0.02). Total Hcys levels at the beginning of Duodopa therapy were much higher than those observed in patients receiving oral levodopa (Müller et al., 2001), and correlated with levodopa levels (Fig. 3).
Our results clearly indicate that L-DOPA and OMD levels are high after Duodopa infusion, but remain stable during the day. This
Table 1 L-DOPA, OMD concentrations (ng/ml) and OMD/LDOPA ratios in the morning and afternoon at the first observation (n = 19, values are not significantly different).
L-DOPA
3-OMD OMD/DOPA
Morning
Afternoon
1892.74 ± 723.11 12195.91 ± 6061.86 6.27 ± 2.31
1948.83 ± 868.57 12959.04 ± 5941.01 8.30 ± 9.11
Figure 2 Relationships between levodopa and OMD concentrations (r = 0.54, p b 0.02).
686
A. Antonini et al. Table 2 Scores on items 32, 33, and 39 of UPDRS IV after different times of Duodopa treatment (M ± S.D.; (range)). Weeks
0
1–20
21–50
51–100
101–200
n = 15
n=8
n=5
n=4
n=4
Item 32
2.51 ± 0.61 1.81 ± 0.80 1.55 ± 0.60 (1–3)
1.25 ± 0.92 0.75± 1.50 0.75 ± 0.71 (0–2)
1.40 ± 0.60 0.60 ± 0.61* 1.00 ± 0.10 (1)
1.51 ± 0.62 1.75 ± 0.95 0.75 ± 0.50 (0–1)
1.00 ± 0.01* 0.70 ± 0.51* 0.50 ± 0.49* (0–1)
Item 33 Item 39
*p b 0.05 vs basal values. RM ANOVA, Tukey's test.
Figure 3 Relationships between levodopa and total homocysteine concentrations(r = 0.52, p b 0.05).
favours good motor control and decreases dyskinesia over time, thus improving the patients' quality of life as previously described (Antonini et al., 2007). They also confirm previous findings (Bet et al., 2008) that higher OMD levels decrease the efficacy of L-DOPA. The mechanism underlying “wearing-off” and the development of dyskinesia is still unclear, but it is likely that both are influenced by disease progression and the pulsatility of oral levodopa. Our findings are consistent with previous data demonstrating that, in comparison with oral levodopa, Duodopa infusion decreases the fluctuations in levodopa levels (Stocchi et al., 2005). As the half-life of OMD is much longer than that of LDOPA, it could be expected that OMD accumulates over time. However, this is not the case because the metabolism of L-DOPA in the presence of DDI is completely governed by COMT and a sort of self-limiting step occurs due to the consumption of the methyl donor (SAM). The concentrations of OMD therefore decrease in parallel with tHomocysteine levels, which can be considered an index of decreasing methylation as lower SAM levels have been found even after
Figure 4 Relationships between OMD/levodopa concentrations and improvement (% over basal values) on the UPDRS III (r = 0.45, p b 0.05) at the time of the final assessment.
a single oral administration of levodopa (Müller et al., 2001). A similar decrease has been described after the administration of the COMT inhibitor, tolcapone (Müller and Kuhn, 2006). Our results do not support the hypothesis of the development of tolerance even after several months of continuous infusion, and indicate that pharmacodynamic factors may play a role in afternoon “off” periods.
Figure 5 A) decrease of OMD/LD ratio over time (r = 0.59, p b 002); B) decrease of tHcys over time (r = 0.55 p b 0.05).
Levodopa and 3-MD levels in Parkinson patients treated with Duodopa
Role of the funding source University funding.
Contributors A. Antonini, G. Bondiolotti, F. Natuzzi, S.R. Bareggi.
Conflict of interest None of the authors has any conflict of interest.
Acknowledgement We thank Prof. G. Pezzoli for its supervision of the research.
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