Unique Hydrolysis of an Ester-Type Prodrug of Levodopa in Human Plasma: Relay-Type Role Sharing between Alpha-1 Acid Glycoprotein and Human Serum Albumin.

ONO-2160 is a newly developed oral ester-type prodrug of levodopa for removing the problems in use of levodopa. It has a structure in which two of the same substituents are bound to levodopa. It is important to understand the pharmacokinetics and metabolic pathway for new drug candidate compounds. The aim of this study was to identify the major enzymes that contribute to the metabolism of ONO-2160 in human plasma. ONO-2160 was hydrolyzed by human serum albumin (HSA) and α1-acid glycoprotein (AGP) in human plasma, although the hydrolysis was not inhibited by various reported esterase inhibitors. The value of the intrinsic clearance per milliliter of plasma of ONO-2160 in AGP solution was greater than that in HSA solution and was comparable to that in human plasma. Therefore, AGP is responsible for the hydrolysis of ONO-2160 in human plasma. ONO-M, which is an intermediate metabolite of ONO-2160, has a structure in which one substituent is removed from ONO-2160 and was mainly generated in AGP solution, but not in human plasma or HSA solution. The hydrolysis of ONO-M by HSA was much greater than by AGP. These results indicate that ONO-M, which is mainly generated from ONO-2160 by AGP, is rapidly hydrolyzed by HSA, and that ONO-2160 generates levodopa via ONO-M in a relay-type reaction through AGP and HSA in human plasma. It has not been reported that AGP has esterase-like activity. These findings could be useful information for drug development of the ester-type prodrug.

Tremella-like graphene-Au composites used for amperometric determination of dopamine.

Electrochemical detection of dopamine (DA) plays an important role in medical diagnosis. In this paper, tremella-like graphene-Au (t-GN-Au) composites were synthesized by a one-step hydrothermal method for selective detection of DA. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were used to characterize as-prepared t-GN-Au composites. The t-GN-Au composites were directly used for the determination of DA via cyclic voltammetry (CV) and the chronoamperometry (CA) technique. CA measurement gave a wide linear range from 0.8 to 2000 µM, and the detection limit of 57 nM (S/N = 3) for DA. The mechanism and the heterogeneous electron transfer kinetics of the DA oxidation were discussed in the light of rotating disk electrode (RDE) experiments. Moreover, the modified electrode was applied to the determination of DA in human urine and serum samples.

ß-Cyclodextrin functionalised gold nanoclusters as luminescence probes for the ultrasensitive detection of dopamine.

A novel luminescence probe based on mono-6-amino-ß-cyclodextrin (NH2-ß-CD) functionalised gold nanoclusters (ß-CD-AuNC) was designed for dopamine (DA) detection. The NH2-ß-CD molecules were conjugated onto the surface of 11-mercaptoundecanoic acid capped AuNCs (11-MUA-AuNC) via a carbodiimide coupling reaction. The integrity of the ß-CD cavities was preserved on the surface of AuNCs and they retained their capability for molecular DA host-guest recognition. DA could be captured by the ß-CD cavities to form an inclusion complex in which the oxidised DA could quench the fluorescence of the ß-CD-AuNC probe by electron transfer. The probe could be used to quantify DA in the range of 5-1000 nM with a detection limit of 2 nM. This sensitivity was 1-2 orders of magnitude higher than that in previously reported methods. Interference by both ascorbic acid (AA) and uric acid (UA) was not observed. Therefore, the ß-CD-AuNC probe could be directly used to determine the DA content in biological samples without further separation. This strategy was successfully applied to a DA assay in spiked human serum samples and it exhibited remarkable accuracy, sensitivity and selectivity.

Two-photon excited quantum dots with compact surface coatings of polymer ligands used as an upconversion luminescent probe for dopamine detection in biological fluids.

Water-soluble multidentate polymer coated CdTe quantum dots (QDs) were prepared via a stepwise addition of raw materials in a one-pot aqueous solution under ambient conditions. Just by adjusting the compositions of raw materials, different sized CdTe QDs were achieved within a short time. The as-prepared QDs showed compact surface coating (1.6-1.8 nm) of polymer ligands and photoluminescence (PL) emitted at 533-567 nm, as well as high colloidal/photo-stability and quantum yields (58-67%). Moreover, these QDs exhibited significant upconversion luminescence (UCL) upon excitation using an 800 nm femtosecond laser. Experimental results confirm that the UCL was ascribed to the two-photon assisted process via a virtual energy state. Then, the two-photon excited QDs were further developed as a novel UCL probe of dopamine (DA) due to self-assembled binding of DA molecules with QDs via non-covalent bonding. As a receptor, the DA attached onto the QD surface induced an electron transfer from QDs to DA, triggering UCL quenching of QDs. This UCL probe of DA presented a low limit of detection (ca. 5.4 nM), and high selectivity and sensitivity in the presence of potential interferences. In particular, it was favorably applied to the detection of DA in biological fluids, with quantitative recoveries (96.0-102.6%).

Impact of CYP2D6 and CYP3A4 genetic polymorphism on combined cholinesterase inhibitors and memantine treatment in mild to moderate Alzheimer's disease.

AIM: The impact of CYP2D6 and CYP3A4 polymorphism on the steady-state plasma concentrations and therapeutic outcome of donepezil monotherapy and combination therapy in Alzheimer's disease (AD) patients. METHODS: A total of 38 patients for donepezil and 17 patients for donepezil and memantine therapy, aged ≥ 55 years, were recruited meeting inclusion and exclusion criteria. Polymerase chain reaction-restriction fragment length polymorphism was performed. The liquid chromatography-tandem mass spectrometry method was used for estimation of drug levels of donepezil and memantine. RESULTS: Significant allele frequency was observed for CYP2D6*3 polymorphism in patients on donepezil monotherapy and combination therapy. Significant allele frequency for CYP2D6*4 was observed in the patients on donepezil monotherapy. CONCLUSION: CYP2D6 polymorphism, though not significant, might partially be involved in the plasma concentration of AD drug.

Pharmacokinetic and tolerability profile of pridopidine in healthy-volunteer poor and extensive CYP2D6 metabolizers, following single and multiple dosing.

Pridopidine is being developed for the treatment of impaired motor function associated with Huntington's disease and belongs to a new class of compounds known as dopidines, which act as dopaminergic stabilizers. In vitro studies have shown that pridopidine is a substrate for the P450 cytochrome 2D6 enzyme (CYP2D6), and clinical data show that the half-life of pridopidine is different following single dosing versus at steady state. To further investigate the pharmacokinetic profile of pridopidine and to establish whether dose adjustment is needed in poor CYP2D6 metabolizers, a single-centre, open-label, multiple-dose study in healthy volunteers was performed. In total, 24 extensive CYP2D6 metabolizers (EMs) and 12 poor CYP2D6 metabolizers (PMs) were enrolled. Both groups received 45 mg pridopidine twice daily (b.i.d.). Plasma samples were taken during the first day of b.i.d. dosing (Day 1) and at steady state, following 14 days of b.i.d. dosing. At Day 1, total exposure in PMs was almost three times higher than those in EMs (AUC0-∞ = 11,192 and 3,782 h·ng/mL, respectively; PM/EM ratio = 2.96; p < 0.001). However, at steady state, PMs and EMs had comparable exposure due to a reduction in pridopidine elimination in EMs over time. Thus, at steady-state peak (C max) and total (AUC0-24) exposures were only 1.24 and 1.29 times higher, respectively, in PMs than EMs. These results support that pridopidine is a CYP2D6 auto-inhibitor. Pridopidine was well tolerated in both EMs and PMs. The slightly higher exposure level in PMs at steady state does not indicate a need for dose adjustment or genotyping for CYP2D6 metabolizer status.

Levodopa treatment and mood fluctuation in dementia with Lewy bodies: a case report.

L-3,4-dihydroxyphenylalanine (L-dopa) has been the gold standard for pharmacotherapy for parkinsonism in patients with dementia with Lewy bodies (DLB). While L-dopa treatment is related to visual hallucinations, its relationship to mood fluctuation in DLB is poorly understood. Herein, we report the improvement of behavioural and psychological symptoms of dementia through the adjustment of L-dopa treatment in a 78-year-old woman with probable DLB. Her marked mood swings were improved by changing L-dopa administration from three to five times per day while maintaining the same total daily dosage. This observation suggests that there may be an association between plasmatic L-dopa levels and mood fluctuation in patients with DLB. This pharmacological approach may be useful in the management of behavioural and psychological symptoms of dementia without the use of antipsychotic agents to avoid severe neuroleptic sensitivity, which is one of the suggestive clinical features in the Third Consortium on DLB clinical criteria.

The effect of different dosing regimens of levodopa/carbidopa/entacapone on plasma levodopa concentrations.

BACKGROUND: Repeated dosing of levodopa/carbidopa/entacapone (LCE) has shown a favourable pharmacokinetic (PK) profile compared with levodopa/carbidopa (LC), but increases maximum plasma levodopa concentrations (C(max)) during the day. High levodopa concentrations are associated with peak-dose dyskinesias. PURPOSE: To determine whether administering LCE 75/18.5/200 and 125/31.5/200 mg (LCE 75 and LCE 125) following a morning dose of LCE 100/25/200 and 150/37.5/200 mg (LCE 100 and LCE 150), respectively, would avoid the increase in levodopa C(max) values observed during multiple dosing of LCE 100 and LCE 150. METHODS: This was an open, randomized, three-period, crossover PK trial in healthy volunteers (n = 19). Subjects were randomized to Group 1 or 2. Group 1 received in random sequence: LCE 150 followed by LCE 125 three times daily (tid); LCE 150 four times daily (qid); LC 150 qid. Group 2 received in random sequence: LCE 100 followed by LCE 75 tid; LCE 100 qid; LC 100 qid. Levodopa C(max), minimum plasma concentration (C(min)), area under the curve (AUC(0-14)) and peak-trough fluctuation (PTF) were calculated up to 14 h after the first dose. RESULTS: Levodopa C(max) was not increased when the LCE dose was decreased by 25 mg after the morning dose. In comparison to LC, levodopa C(min) levels and AUC(0-14) values for LCE were significantly higher, while the levodopa PTF was significantly smaller. CONCLUSIONS: Reducing the dose of LCE by 25 mg following the first morning dose results in a more consistent levodopa C(max) profile, avoiding levodopa accumulation while maintaining significantly higher C(min) levels and AUC(0-14) values compared with LC.

High-performance liquid chromatographic determination of memantine hydrochloride in rat plasma using sensitive fluorometric derivatization.

In this study, we investigated a simple, sensitive and reliable liquid chromatography-fluorescence detection method for the determination of memantine hydrochloride in rat plasma which was based on derivatization with 9-fluorenylmethyl chloroformate (FMOC-Cl). For the first time, FMOC-Cl was introduced into derivatization of memantine hydrochloride in rat plasma. The amino groups of memantine hydrochloride and amantadine hydrochloride (internal standard) were trapped with FMOC-Cl to form memantine hydrochloride-FMOC-Cl and amantadine hydrochloride-FMOC-Cl compositions, which can be very compatible for LC-FLD. Precipitation of plasma proteins by acetonitrile was followed by vortex mixing and centrifugation. Chromatographic separation was performed on a C(18) column (DIAMONSIL 150 × 4.6 mm, id 5 µm) with a mobile phase consisting of acetonitrile and water at a flow rate of 1.0 mL/min. The retention times of memantine hydrochloride-FMOC-Cl and amantadine hydrochloride-FMOC-Cl compositions were 23.69 and 40.27 min, respectively. Optimal conditions for the derivatization of memantine hydrochloride were also described. The limit of quantification (LOQ) was 25 ng/mL for memantine hydrochloride in plasma, the linear range was 0.025-5.0 µg/mL in plasma with a correlation coefficient (r) of 0.9999. The relative standard deviations (RSDs) of intra-day and inter-day assays were 4.46-12.19 and 5.23-11.50%, respectively. The validated method was successfully applied to the determination of memantine hydrochloride in rat plasma samples.

Dopamine, paranormal belief, and the detection of meaningful stimuli.

Dopamine (DA) is suggested to improve perceptual and cognitive decisions by increasing the signal-to-noise ratio. Somewhat paradoxically, a hyperdopaminergia (arguably more accentuated in the right hemisphere) has also been implied in the genesis of unusual experiences such as hallucinations and paranormal thought. To test these opposing assumptions, we used two lateralized decision tasks, one with lexical (tapping left-hemisphere functions), the other with facial stimuli (tapping right-hemisphere functions). Participants were 40 healthy right-handed men, of whom 20 reported unusual, "paranormal" experiences and beliefs ("believers"), whereas the remaining participants were unexperienced and critical ("skeptics"). In a between-subject design, levodopa (200 mg) or placebo administration was balanced between belief groups (double-blind procedure). For each task and visual field, we calculated sensitivity (d') and response tendency (criterion) derived from signal detection theory. Results showed the typical right visual field advantage for the lexical decision task and a higher d' for verbal than facial stimuli. For the skeptics, d' was lower in the levodopa than in the placebo group. Criterion analyses revealed that believers favored false alarms over misses, whereas skeptics displayed the opposite preference. Unexpectedly, under levodopa, these decision preferences were lower in both groups. We thus infer that levodopa (1) decreases sensitivity in perceptual-cognitive decisions, but only in skeptics, and (2) makes skeptics less and believers slightly more conservative. These results stand at odd to the common view that DA generally improves signal-to-noise ratios. Paranormal ideation seems an important personality dimension and should be assessed in investigations on the detection of signals in noise.

High levodopa plasma concentration after oral administration predicts levodopa-induced dyskinesia in Parkinson's disease.

INTRODUCTION: In patients with Parkinson's disease (PD), pulsatile dopaminergic stimulation may be a primary cause of levodopa-induced dyskinesia (LID). We aimed to investigate the correlation between levodopa pharmacokinetics (PK) and LID in PD. METHODS: We retrospectively reviewed the consecutive series of 255 PD patients without LID who underwent PK assessments with 100 mg levodopa. The type of peripheral decarboxylase inhibitor used in the PK assessments was determined by the usual prescription of the formulations of levodopa (10 mg carbidopa [n = 185] and 25 mg benserazide [n = 70]). RESULTS: During a median follow-up of 32 months (IQR, 16-49 months), 73 patients (29%) developed LID. Compared with patients who did not develop LID (PD-LID-), those who developed LID (PD-LID+) were younger (p = 0.003) and had significantly higher maximum levodopa concentration (Cmax) (p = 0.002) and area under the curve (p < 0.001), LEDD (p < 0.001), and improvement of motor symptoms (p = 0.009). In the multivariate Cox proportional hazards models, Cmax and AUC were associated with incident LID (Hazard Ratio [HR] 1.11, 95% confidence interval [CI] 1.03-1.19 and HR 1.13, 95% CI 1.03-1.24, respectively). In addition, younger age, benserazide use, LEDD, and MAOBI use were associated with incident LID. CONCLUSION: High levodopa plasma concentration after oral administration was associated with incident LID in patients with PD.

Effects of daily L-dopa administration on learning and brain structure in older adults undergoing cognitive training: a randomised clinical trial.

Cognitive aging creates major individual and societal burden, motivating search for treatment and preventive care strategies. Behavioural interventions can improve cognitive performance in older age, but effects are small. Basic research has implicated dopaminergic signalling in plasticity. We investigated whether supplementation with the dopamine-precursor L-dopa improves effects of cognitive training on performance. Sixty-three participants for this randomised, parallel-group, double-blind, placebo-controlled trial were recruited via newspaper advertisements. Inclusion criteria were: age of 65-75 years, Mini-Mental State Examination score >25, absence of serious medical conditions. Eligible subjects were randomly allocated to either receive 100/25 mg L-dopa/benserazide (n = 32) or placebo (n = 31) prior to each of twenty cognitive training sessions administered during a four-week period. Participants and staff were blinded to group assignment. Primary outcomes were latent variables of spatial and verbal fluid intelligence. Compared to the placebo group, subjects receiving L-dopa improved less in spatial intelligence (-0.267 SDs; 95%CI [-0.498, -0.036]; p = 0.024). Change in verbal intelligence did not significantly differ between the groups (-0.081 SDs, 95%CI [-0.242, 0.080]; p = 0.323). Subjects receiving L-dopa also progressed slower through the training and the groups displayed differential volumetric changes in the midbrain. No statistically significant differences were found for the secondary cognitive outcomes. Adverse events occurred for 10 (31%) and 7 (23%) participants in the active and control groups, correspondingly. The results speak against early pharmacological interventions in older healthy adults to improve broader cognitive functions by targeting the dopaminergic system and provide no support for learning-enhancing properties of L-dopa supplements in the healthy elderly. The findings warrant closer investigation about the cognitive effects of early dopamine-replacement therapy in neurological disorders. This trial was preregistered at the European Clinical Trial Registry, EudraCT#2016-000891-54 (2016-10-05).

Gold electrode incorporating corrole as an ion-channel mimetic sensor for determination of dopamine.

Here, we report on an ion-channel mimetic sensor using self-assembly monolayers deposited onto gold electrodes for electrochemical determination of dopamine. The different compositions of the modification solution consist of corrole-SH and other thiol derivatives used as the "background compounds" such as 1-dodecanethiol (DDT), 6-mercapto-1-hexanol (HS(CH(2))(6)OH), or 11-mercapto-1-undecanol (HS(CH(2))(11)OH) were explored to find the best self-assembled monolayer (SAM) suitable for dopamine determination. Among them, the mixed SAM consisting of corroles with the -SH group and 6-mercapto-1-hexanol (HS(CH(2))(6)OH) in the molar ratio 1:10 was the most sensitive. The signals generated by the formation of a complex between the corrole host and the dopamine guest were measured by Osteryoung square-wave voltammetry (OSWV) and electrochemical impedance spectroscopy (EIS) with [Ru(NH(3))(6)](3+) as an electroactive marker. The developed sensor was free of interferences of components of human plasma such as ascorbic acid, creatinine, creatine, and uric acid. The detection limits observed by EIS in buffer solution and in the presence of centrifuged human plasma 80 times diluted with a 0.9% NaCl containing 0.01 M borate buffer solution of pH 7.0 were 3.3 x 10(-12) and 5.3 x 10(-12) M, respectively.

Using Spontaneous Eye-blink Rates to Predict the Motor Status of Patients with Parkinson's Disease.

Objective Assessing daily motor fluctuations is an important part of the disease management for patients with Parkinson's disease (PD). However, the frequent recording of subjective and/or objective assessments is not always feasible, and easier monitoring methods have been sought. Previous studies have reported that the spontaneous eye-blink rate (EBR) is correlated with the dopamine levels in the brain. Thus, the continuous monitoring of the EBR may be useful for predicting the motor status in patients with PD. Methods Electrooculograms (EOGs) were recorded for up to 7.5 hours from three PD patients using a wearable device that resembled ordinary glasses. An receiver operating characteristic (ROC) analysis was performed to compare the ability of the EBR estimates at each time-point (Blink Index) and the plasma levodopa levels to predict the motor status. Results The Blink Index was correlated with the plasma levodopa levels. When an indicator for the first hour of the observation period was included in the model, the Blink Index discerned wearing-off and dyskinesia as accurately as the plasma levodopa level. Conclusion Our study provides preliminary evidence regarding the utility of continuous EBR monitoring for the non-invasive evaluation of the motor status in patients with PD.

Effect of Dopaminergic Medications on Blood Oxygen Level-Dependent Variability and Functional Connectivity in Parkinson's Disease and Healthy Aging.

Both functional connectivity (FC) and blood oxygen level-dependent (BOLD) signal variability (SDBOLD) are methods that are used for examining the physiological state of the brain. Although they are derived from signal changes and are related, a few studies have explored their relationship. Here, we examined the relationship between SDBOLD and FC within the default mode network (DMN) in healthy aging participants and those with Parkinson's disease (PD) ON and OFF dopaminergic medications. Dopaminergic medications had profound effects on both DMN FC and SDBOLD measured separately in PD. Analyzing DMN FC and SDBOLD in a joint independent component analysis, we identified joint components of DMN FC and SDBOLD that were separately associated with measurements of motor and cognitive impairment in PD and qualitatively similar to those in healthy aging. Dopaminergic medications had a differential effect on these components depending on these measures of disease severity, "normalizing" the relationships. Importantly, we show that dopaminergic medication status matters in imaging PD, and it can affect both connectivity and SDBOLD. Imaging PD ON may lead to inflated estimates of SDBOLD and diminish the ability to measure changes associated with declining motor and cognitive capacities.

Dose-proportional pharmacokinetics of d-threo-methylphenidate after a repeated-action release dosage form.

A bimodal extended-release formulation of d-methylphenidate (d-MPH) has been developed to enable fast onset of action and once-daily administration in patients with attention deficit hyperactivity disorder. The authors studied the dose proportionality of extended-release d-MPH pharmacokinetics. Twenty-five healthy adult volunteers received 5, 10, 20, 30, and 40 mg d-MPH in a crossover study with 7 days between doses. All doses were well tolerated. Dose proportionality was shown for all dose-dependent pharmacokinetic parameters. Geometric means (%gCV) for the first Cmax peak, Cmax0-4, were 3.25 (29.0%), 6.05 (27.1%), 12.6 (31.9%), 18.5 (31.9%), and 25.2 ng/mL (29.3%) for d-MPH 5, 10, 20, 30, and 40 mg, respectively. Geometric means (%gCV) for Cmax4-10 were 3.18 (27.5%), 5.84 (27.7%), 12.5 (31.7%), 17.7 (31.6%), and 23.6 ng/mL (29.0%), respectively. Geometric means for AUC(0-infinity) were 24.3 (30.7%), 45.9 (30.2%), 96.4 (35.5%), 144 (33.3%), and 195 ng x h/mL (30.9%), respectively. The pharmacokinetics of once-daily extended-release d-MPH are proportional to the dose.

The "motor complication syndrome" in rats with 6-OHDA lesions treated chronically with L-DOPA: relation to dose and route of administration.

L-DOPA-induced motor complications can be modelled in rats with 6-hydroxydopamine (6-OHDA) lesions by chronic injections of L-DOPA. We have compared the sensitisation and duration of rotational responses, and the occurrence of dose-failure episodes and abnormal involuntary movements (AIMs) in 6-OHDA-lesioned rats with regard to the dose and route of administration of L-DOPA. Rats were treated with either low (6mg/kg) or high (25mg/kg) doses of L-DOPA twice daily for 21 days whereas control animals received injections of either saline or bromocriptine (2.5mg/kg). A dose-dependent and gradual development of AIMs and contralateral turning was observed in rats treated chronically with l-DOPA. Rats treated with bromocriptine exhibited rotational sensitisation but no AIMs. A shortening of motor response duration was not seen in any of the drug-treated groups. In contrast, dose-failure episodes occurred frequently in both L-DOPA- and bromocriptine-treated animals. Changing the route of L-DOPA administration from intraperitoneal to subcutaneous completely abolished failures in motor response without affecting the development of dyskinesia. Based on the hypothesis that higher doses of L-DOPA may be toxic to dopaminoceptive structures, we compared the total number of neurons and the levels of activated microglia in the striatum. No signs of neurodegenerative changes could be seen in any of the treatment groups. In conclusion, both body AIMs and rotations were dose-dependently evoked by L-DOPA. Only AIMs, however, provided a specific measure of dyskinesia since rotations also were induced by bromocriptine, a drug with low dyskinesiogenic potential. Dose-failure episodes were not specific to L-DOPA treatment and could be attributed to erratic drug absorption from the peritoneal route.

Age-related differences in levodopa dynamics in Parkinson's: implications for motor complications.

Treatment-related motor complications in Parkinson's disease have been previously linked to disease-induced pre-synaptic alterations: dopaminergic denervation and changes in dopamine (DA) release patterns. The occurrence of such complications is also known to be partly dependent on the age of disease onset, occurring more frequently in patients with disease onset at a younger age. Using positron emission tomography (PET) and 4-h-long 18F-fluorodopa (FD) scans we have investigated in vivo an age dependence of disease-induced changes in DA turnover as a possible contributing factor to the age-related differences in treatment-related motor complications. We evaluated the relative changes in DA turnover (measured by its direct inverse, effective DA distribution volume--EDV) and DA synthesis and vesicular storage capacity (quantified by the plasma input uptake rate constant Ki) in Parkinson's disease patients as a function of age (n = 27, age range 38-79 years). After correcting for disease severity, a significant negative correlation was found between age and magnitude of disease-induced decrease in EDV and in Ki in the putamen (P < 0.001, P = 0.02, respectively). However, the difference between the disease-induced decrease in EDV and that in Ki also exhibited an age dependence (P < 0.001), indicating a relatively higher disease-induced increase in DA turnover (inverse of EDV) compared with the decrease in DA synthesis and storage rate in patients of younger age compared with older patients. This finding implies that DA turnover in younger-onset patients undergoes a relatively greater alteration and thus likely contributes to a greater imbalance between DA synthesis, storage and release, which could lead to larger swings in synaptic DA levels. It has indeed been suggested on theoretical grounds that such imbalance may contribute to the greater propensity for motor fluctuations. These results provide one possible explanation for the age-dependent occurrence of complications and support the existence of a pre-synaptic contribution to the occurrence of motor complications.

Amantadine as an additive treatment in patients suffering from drug-resistant unipolar depression.

The paper describes the effect of amantadine addition to imipramine therapy in patients suffering from treatment-resistant unipolar depression who fulfilled DSM IV criteria for major (unipolar) depression. Fifty patients were enrolled in the study on the basis of their histories of illness and therapy. After a 2-week drug-free period, 25 subjects belonging to the first group were treated only with imipramine twice daily (100 mg/day) for 12 weeks, and 25 subjects belonging to the second group were treated with imipramine twice daily (100 mg/day) for 6 weeks and then amantadine was introduced (150 mg/day, twice daily) and administered jointly with imipramine for the successive 6 weeks. Hamilton Depression Rating Scale (HDRS) was used to assess the efficacy of antidepressant therapy. Imipramine did not change the HDRS score after 3, 6 or 12 weeks of treatment when compared with the washout (before treatment). The addition of amantadine to the classic antidepressant reduced HDRS scores after 6-week joint treatment. Moreover, the obtained pharmacokinetic data indicated that amantadine did not significantly influence the plasma concentration of imipramine and its metabolite desipramine in patients treated jointly with imipramine and amantadine, which suggests lack of a pharmacokinetic interaction. The obtained results indicate that joint therapy with an antidepressant and amantadine may be effective in treatment-resistant unipolar depression.

Quantitation of levodopa and carbidopa in rat plasma by LC-MS/MS: The key role of ion-pairing reversed-phase chromatography.

A simple and selective bioanalytical method was developed for simultaneous determination of levodopa and carbidopa in rat plasma by LC-MS/MS. Levodopa and carbidopa are small polar molecules, posing challenges in the development of selective and efficient chromatography conditions. Perfluoropentanoic acid (PFPA), a volatile ion-pairing agent, was utilized to enhance chromatographic characteristics of both compounds in the reversed-phase mechanism. The ion-pairing chromatography played an essential role in mitigating matrix effects and achieving adequate separation between interfering background peaks and those of the analytes of interest, especially for levodopa. A 96-well based, automated liquid-liquid extraction, via the use Hamilton NIMBUS liquid handlers, was developed. Butyl alcohol, when mixed with ethyl acetate, greatly increased the recovery of both levodopa and carbidopa. The addition of PFPA further enhanced recovery for both analytes. Sodium metabisulfite, an antioxidant, was used to stabilize levodopa and carbidopa in rat plasma. The method was validated in the ranges of 50-10,000ng/mL and 25-5000ng/mL for levodopa and carbidopa, respectively, using levodopa-d3 and carbidopa-d3 as internal standards. The validated method was successfully applied to analyze rat plasma samples from in-life studies.