Assay of R-apomorphine, S-apomorphine, apocodeine, isoapocodeine and their glucuronide and sulfate conjugates in plasma and urine of patients with Parkinson's disease

Prolonged Delivery of Apomorphine Through the Buccal Mucosa, Towards a Noninvasive Sustained Administration Method in Parkinson's Disease: In Vivo Investigations in Pigs

In the current work, prolonged systemic delivery of apomorphine via buccal mucosa was shown to be a promising treatment for Parkinson's disease as a substitute for clinically utilized subcutaneous infusions. Due to extensive 'first-pass' metabolism, apomorphine is administered parenterally to bypass liver metabolism. Drawbacks of parenteral administration cause low patient compliance and adherence to treatment. On the other hand, while also bypassing the liver, delivery through buccal mucosa has a superior safety profile, is less costly, lacks pain and discomfort, and possesses excellent accessibility, overall augmenting patient compliance. Current in vivo study in pigs showed: (1) steady plateau levels of apomorphine in plasma were obtained 30 min following administration and remained constant for 8 h until a delivery device was removed, (2) bioavailability of apomorphine was 55%-80% as opposed to <2% peroral and (3) simulation of the pharmacokinetic profile obtained in pigs predicted therapeutically relevant levels of apomorphine in human. Furthermore, antipyrine was incorporated as a permeation marker to enable mechanistic investigation of apomorphine release from the delivery device and its permeation through the buccal mucosa. In addition, limitations of an Ussing diffusion chamber as an ex vivo research tool were also discussed.

Making methods rugged for regulated bioanalysis

Methods started in discovery are optimized as they progress through preclinical and clinical development. Making a robust assay includes testing individual steps for consistency and points of failure. Assays may be transferred, optimized and revalidated several times. A rugged assay will not only meet regulatory requirements, but will execute with a low failure rate and confirm results under repeat analysis. Challenging aspects such as differential recovery, sample stabilization, resolution of isomers or conjugate analysis must be tackled and made routine. The proper selection of the IS can overcome limitations. It is best to know the potential points of failure before a study has started, but lessons learned from each study also provide invaluable insights to improve assay ruggedness.

Concerted actions of the catechol O-methyltransferase and the cytosolic sulfotransferase SULT1A3 in the metabolism of catecholic drugs

Catecholic drugs had been reported to be metabolized through conjugation reactions, particularly methylation and sulfation. Whether and how these two Phase II conjugation reactions may occur in a concerted manner, however, remained unclear. The current study was designed to investigate the methylation and/or sulfation of five catecholic drugs. Analysis of the spent media of HepG2 cells metabolically labeled with [(35)S]sulfate in the presence of individual catecholic drugs revealed the presence of two [(35)S]sulfated metabolites for dopamine, epinephrine, isoproterenol, and isoetharine, but only one [(35)S]sulfated metabolite for apomorphine. Further analyses using tropolone, a catechol O-methyltransferase (COMT) inhibitor, indicated that one of the two [(35)S]sulfated metabolites of dopamine, epinephrine, isoproterenol, and isoetharine was a doubly conjugated (methylated and sulfated) product, since its level decreased proportionately with increasing concentrations of tropolone added to the labeling media. Moreover, while the inhibition of methylation resulted in a decrease of the total amount of [(35)S]sulfated metabolites, sulfation appeared to be capable of compensating the suppressed methylation in the metabolism of these four catecholic drugs. A two-stage enzymatic assay showed the sequential methylation and sulfation of dopamine, epinephrine, isoproterenol, and isoetharine mediated by, respectively, the COMT and the cytosolic sulfotransferase SULT1A3. Collectively, the results from the present study implied the concerted actions of the COMT and SULT1A3 in the metabolism of catecholic drugs.

Apomorphine in the treatment of Parkinson's disease

Motor fluctuations, refractory to conventional medical management, are one of the most troubling aspects of Parkinson's disease. Apomorphine is a dopaminergic agent that has been known to the medical community for more than a century, but has only recently been developed to treat such motor fluctuations. In this article, the authors review the historical background, structure, mechanism of action, pharmacologic properties, clinical trials, indications and side effects, as well as avenues of further research, of apomorphine.

Determination of apomorphine in canine plasma by liquid chromatography–electrospray ionization mass spectrometry and its application to a pharmacokinetic study

An LC-ESI-MS method was developed and validated for the assay of apomorphine in canine plasma using one-step liquid-liquid extraction. The analytes were separated on a Phenomenex Gemini C18 (150 mm x 2.0 mm id 3 microm) column and determined by MS in the positive ion mode. The linear range was 0.4-40 ng/mL with an LOD of 0.2 ng/mL for apomorphine in plasma. The intraday and interday precision and accuracy of quality control samples were < 5.9% RSD and < 7.5% bias for apomorphine. Extraction recoveries were > 80%. The validated method was successfully applied to analyze canine plasma samples in a pharmacokinetic study of apomorphine in dogs and detailed pharmacokinetic parameters were calculated.

Sensitive Quantification of Apomorphine in Human Plasma Using a LC-ESI-MS-MS Method

An analytical method based on liquid chromatography coupled with ion trap mass spectrometry (MS) detection with electrospray ionization interface has been developed for the identification and quantification of apomorphine in human plasma. Apomorphine was isolated from 0.5 mL of plasma using a liquid-liquid extraction with diethyl ether and boldine as internal standard, with satisfactory extraction recoveries. Analytes were separated on a 5-microm C18 Highpurity (Thermohypersil) column (150 mm x 2.1 mm I.D.) maintained at 30 degrees C, coupled to a precolumn (C18, 5-microm, 10 mm x 2.0 mm I.D., Thermo). The elution was achieved isocratically with a mobile phase of 2 mM NH4COOH buffer pH 3.8/acetonitrile (50/50, vol/vol) at a flow rate of 200 microL per minute. Data were collected either in full-scan MS mode at m/z 150 to 500 or in full-scan tandem mass spectrometry mode, selecting the [M+H]ion at m/z 268.0 for apomorphine and m/z 328.0 for boldine. The most intense daughter ion of apomorphine (m/z 237.1) and boldine (m/z 297.0) were used for quantification. Retention times were 2.03 and 2.11 minutes for boldine and apomorphine, respectively. Calibration curves were linear in the 0.025 to 20 ng/mL range. The limits of detection and quantification were 0.010 ng/mL and 0.025 ng/mL, respectively. Accuracy and precision of the assay were measured by analyzing 54 quality control samples for 3 days. At concentrations of 0.075, 1.5, and 15 ng/mL, intraday precisions were less than 10.1%, 5.3%, and 3.8%, and interday precisions were less than 4.8%, 6.6%, and 6.5%, respectively. Accuracies were in the 99.5 to 104.2% range. An example of a patient who was given 6 mg of apomorphine subcutaneously is shown, with concentrations of 14.1 ng/mL after 30 minutes and 0.20 ng/mL after 6 hours. The method described enables the unambiguous identification and quantification of apomorphine with very good sensitivity using only 0.5 mL of sample, and is very convenient for therapeutic drug monitoring and pharmacokinetic studies.

Improved assay for R(−)-apomorphine with application to clinical pharmacokinetic studies in Parkinson's disease

A high performance liquid chromatographic assay for the quantitative determination of apomorphine in human plasma is described. Sample clean-up and concentration was optimised using solid-phase extraction on C18 cartridges, enabling rapid and sensitive determination of apomorphine and potential metabolites. The limit of apomorphine quantification, using fluorescence detection, was 0.5 ng/mL. The assay was stability-indicating, and allowed the detection of analytes in the presence of commonly co-administered anti-Parkinsonian drugs. Apomorphine was stable in frozen plasma containing 0.14% (w/v) ascorbic acid for 98 days, and through four freeze-thaw cycles. The assay has been used in clinical pharmacokinetic studies of apomorphine in patients with Parkinson's disease, and in preliminary studies of novel apomorphine delivery devices in volunteers.

Development of a sensitive and rapid liquid chromatography/tandem mass spectrometry method for the determination of apomorphine in canine plasma

A sensitive, rapid and specific quantitative liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination of apomorphine (APO) in canine plasma. The analytes were prepared using one-step liquid-liquid extraction, and analyzed on a Waters Symmetry C(18) column interfaced with triple quadrupole tandem mass spectrometer. A mixture of methanol/0.1% formic acid in water (70: 30, v/v) was employed as the isocratic mobile phase. Positive electrospray ionization was utilized as the ionization source. The analyte and clenbuterol (internal standard) were both detected using multiple reaction monitoring (MRM) mode. The limit of detection (LOD) obtained was 0.03 ng/mL. The assay was linear over the concentration range of 0.1-100 ng/mL, and provided good precision (RSD) and good accuracy (RE). The analyte was stable by using antioxidants throughout the whole study. The experimental results show that LC/MS/MS is a rapid and sensitive method to analyze APO in plasma. Finally, the proposed method was successfully applied to a pharmacokinetic study of APO after intranasal administration of 0.5 mg apomorphine to 10 healthy beagle dogs.

Development of a gas chromatographic/mass spectrometric method to quantify R(-)-apomorphine, R(-)-apocodeine and R(-)-norapomorphine in human plasma and urine

A method was developed and validated for the analysis of R(-)-apomorphine, (R-)-apocodeine and R(-)-norapomorphine in human plasma and urine with N-propylnorapomorphine as internal standard using gas chromatography/mass spectrometry (GC/MS) and single-ion monitoring after a single liquid-liquid extraction and silylation of compounds. The quantification limits were 1 ng/ml for apomorphine and apocodeine and 25 ng/ml for norapomorphine. Calibration curves were linear, within the range 1-100 ng/ml. Variation in intraday and interday precision was below 10%. This method was applied to study apomorphine bioavailability in nine patients with Parkinson's disease before and after coadministration of a catechol-O-methyl transferase inhibitor.

Transdermal apomorphine permeation from microemulsions: a new treatment in Parkinson's disease

We studied absorption, efficacy, and tolerability in Parkinson's disease (PD) of a new preparation of apomorphine included in a microemulsion and administered by transdermal route (Apo-MTD). Twenty-one PD patients were treated with levodopa plus oral dopamine-agonists (T0), with levodopa alone (T1), finally with levodopa plus Apo-MTD (T2). Apo-MTD provided therapeutic plasma levels for many hours, improved Unified Parkinson's Disease Rating Scale III scores, and reduced total duration of off periods compared to T0 and T1. We concluded that Apo-MTD is absorbed and demonstrates clinical efficacy and long action. Therefore, it seems a promising add-on treatment for uncontrolled prolonged off phases in PD patients, but chronic tolerability needs further study.

Chiral capillary electrophoretic method for quantification of apomorphine

A new method for chiral determination of apomorphine enantiomers was developed and validated. Seven different neutral and charged cyclodextrins were tested for enantioselectivity on R,S-apomorphine. Sulfobutylether-beta-cyclodextrin was found to offer the best resolution, but with this system, four peaks were detected from a solution of the two enantiomers, which was suggested to be the result of different forms of the complex between the selector and apomorphine. A complexation constant was estimated for a complex of 1:1 ratio for the second and the fourth peak, whereas the other two peaks were fitted to a model ratio of 1:2 (analyte-selector). To avoid this phenomenon, hydroxypropyl-beta-cyclodextrin was then chosen as the chiral selector. An optimisation study was performed on three factors: concentration of the chiral selector, pH of the buffer, and applied voltage. Optimum conditions were: 14 mM of hydroxypropyl-beta-cyclodextrin, pH 3.0, and 16 kV. UV detection was at 200 nm. The method was validated at the chosen conditions, offering a limit of detection of 0.2 microM and a limit of quantification of 0.5 microM. The validated method was applied for the determination of R,S-apomorphine in a transport study with an in vitro cell culture model of the intestinal mucosa (Caco-2).

Subcutaneous Apomorphine

Apomorphine, a short-acting dopamine D1 and D2 receptor agonist, was the first dopamine receptor agonist used to treat Parkinson's disease. Subcutaneous apomorphine is currently used for the management of sudden, unexpected and refractory levodopa-induced 'off' states in fluctuating Parkinson's disease either as intermittent rescue injections or continuous infusions. Other indications include the challenge test for determining the dopaminergic responsiveness and finding the appropriate dose of the drug in intermittent subcutaneous administration. Except for a rapid on- and offset of the antiparkinsonian response with subcutaneous apomorphine, the magnitude and pattern of the motor response to single dose of subcutaneously administered apomorphine is qualitatively comparable to that of oral levodopa. Seventy-five percent of patients achieve a clinically significant improvement with a dose of apomorphine 4mg. The efficacy of intermittent subcutaneous apomorphine injections as an add-on to levodopa therapy in advanced Parkinson's disease was explored in one short-term, randomised, double-blind, placebo-controlled trial, one short-term and six long-term, open-label, uncontrolled studies, including a total of 195 patients. These studies provide evidence that this mode of administration was successful in aborting 'off' periods and improving Parkinson's disease motor scores, but tended to increase dyskinesias. No levodopa-sparing effect was observed. Eleven long-term, open-label, uncontrolled studies, including a total of 233 patients evaluated the efficacy of continuous subcutaneous apomorphine infusions in monotherapy or as an add-on to levodopa therapy in advanced Parkinson's disease. These studies proved that subcutaneous apomorphine infusions are successful in aborting 'off' periods, reducing dyskinesias and improving Parkinson's disease motor scores with the added benefit of a substantial levodopa-sparing effect. The apomorphine challenge test has at least 80% overall predictive ability to clinically diagnose Parkinson's disease across the different stages of the disease and parkinsonian syndromes. Similarly, those data also indicate that the apomorphine challenge test has a >80% ability to predict dopaminergic responsiveness across all stages of Parkinson's disease. Adverse events are usually mild and consist predominantly of cutaneous reactions and neuropsychiatric adverse effects. The incidence of adverse effects is higher in patients receiving continuous infusion than in those receiving intermittent pulsatile administration. Based on the results of these studies it is recommended that subcutaneous apomorphine either as intermittent injections or continuous infusions should be offered to any suitable Parkinson's disease patient who has difficulties in his/her management with conventional therapy. Low-dose levodopa therapy in combination with waking-day hours subcutaneous apomorphine infusion would probably be the most efficient treatment. Continuous subcutaneous apomorphine infusions should be evaluated before more invasive measures or neurosurgical interventions are contemplated.

Comparison of electrospray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization in the identification of apomorphine, dobutamine, and entacapone phase II metabolites in biological samples

The applicability of different ionization techniques, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and a novel atmospheric pressure photoionization (APPI), were tested for the identification of the phase II metabolites of apomorphine, dobutamine, and entacapone in rat urine and in vitro incubation mixtures (rat hepatocytes and human liver microsomes). ESI proved to be the most suitable ionization method; it enabled detection of 22 conjugates, whereas APCI and APPI showed only 12 and 14 conjugates, respectively. Methyl conjugates were detected with all ionization methods. Glucuronide conjugates were ionized most efficiently with ESI. Only some of the glucuronides detected with ESI were detected with APCI and APPI. Sulfate conjugates were detected only with ESI. MS/MS experiments showed that the site of glucuronidation or sulfation could not be determined, since the primary cleavage was a loss of the conjugate group (glucuronic acid or SO3), and no site-characteristic product ions were formed. However, it may be possible to determine the site of methylation, since methylated products are more stable than glucuronides or sulfates. Furthermore, the loss of CH3 is not necessarily the primary cleavage, and site characteristic products may be formed. Identification and comparison of conjugates formed from the current model drugs were successfully analyzed in different biological specimens of common interest to biomedical research. A fairly good relation was obtained between the data from in vivo and in vitro models of drug metabolism.

Mechanisms of apomorphine cytoxicity towards rat glioma C6 cells: protection by bovine serum albumin and formation of apomorphine-protein conjugates

Apomorphine cytotoxicity towards rat glioma C6 cells was recently demonstrated to be time- and concentration-dependent. In the present work, the mechanism of cytotoxicity of apomorphine was further studied in the C6 cell line. We showed that bovine serum albumin partially protects C6 cells against apomorphine cytotoxicity. However, serum albumin did not prevent apomorphine autoxidation and melanin formation, suggesting that this protein scavenges apomorphine reactive products formed during its oxidation. The use of radioactive tracers, fluorimetry and protein electrophoresis showed that apomorphine autoxidation products covalently and nonspecifically bind to serum albumin and to rat liver microsomes. L-Cysteine, which is a thiol reagent that inhibits apomorphine autoxidation also prevented the formation of apomorphine-serum albumin adducts. These results suggest that quinone derivatives formation and oxidative stress should be responsible for apomorphine cytotoxicity.

An integrated pharmacokinetic-pharmacodynamic approach to optimization of R-apomorphine delivery in Parkinson's disease

R-apomorphine is a mixed dopamine D(1)/D(2) receptor agonist which is potentially useful in the management of Parkinson's disease. The delivery of R-apomorphine is complicated however by a number of pharmacokinetic and pharmacodynamic factors. This review describes the development of a transdermal iontophoretic delivery system for R-apomorphine on the basis of integrated pharmacokinetic-pharmacodynamic (PK/PD) investigations in patients with idiopathic Parkinson's disease. The pharmacokinetics and metabolic pathways of R-apomorphine were determined following intravenous infusion of 30 µg kg(-1) in 15 min in 10 patients. A stepwise infusion protocol was used to determine the therapeutic window. A wide interindividual variability in both pharmacokinetics and pharmacodynamics and a narrow therapeutic concentration range were observed. This shows the need for individualized and carefully controlled delivery of R-apomorphine in Parkinson's disease. Transdermal iontophoretic transport was studied both in vitro in human stratum corneum and dermatomed full skin and in vivo in patients with Parkinson's disease. These studies showed that the delivery of R-apomorphine by transdermal iontophoresis is feasible and furthermore that the rate of delivery can be carefully controlled by variation of the current density. It is concluded that the delivery of R-apomorphine by transdermal iontophoresis may be an attractive tool in future clinical pharmacological investigations in patients with Parkinson's disease aiming at characterization of the influence of chronic treatment and disease progression on the pharmacokinetics and pharmacodynamics. Ultimately these studies may result in a system which is suitable for clinical application.

Iontophoretic delivery of apomorphine. I: In vitro optimization and validation

PURPOSE

To investigate the feasibility of transdermal iontophoretic delivery of apomorphine in patients with Parkinson's disease, transdermal transport rates were optimized and validated across human stratum corneum and freshly dermatomed human skin in vitro.

METHODS

In all experiments R-apomorphine hydrochloride was applied in the anodal compartment. The effect on the flux of the following parameters was studied, using a flow through transport cell current density, pH, concentration, ionic strength, osmolarity, buffer strength, temperature and skin type.

RESULTS

Transdermal transport of apomorphine was directly controlled by the presence or absence of current. Passive delivery was minimal and no depot effect was observed. A linear relationship was found between current density and steady-state flux. At room temperature the lag time was 30 to 40 minutes. A maximal steady-state flux was obtained when the donor concentration approached maximum solubility. By increasing the temperature of the acceptor chamber to 37 degrees C the steady-state flux was increased by a factor of 2.3 and the lag time decreased to +/- 3 minutes. No effect of osmolarity and buffer strength and only a small effect of ionic strength and pH on the transport rate were observed. The flux through dermatomed human skin was decreased compared to stratum corneum. This effect was shown not to be caused by skin metabolism.

CONCLUSIONS

The results obtained in vitro indicate that the iontophoretic delivery of apomorphine can be controlled and manipulated accurately by the applied current. The in vitro flux furthermore depends on the donor composition, temperature and skin type. Under optimized conditions, transport rates resulting in therapeutically effective plasma concentrations are feasible, assuming a one to one in vitro/in vivo correlation.

Iontophoretic delivery of apomorphine. II: An in vivo study in patients with Parkinson's disease

PURPOSE

Transdermal transport rates of the dopamine agonist R-apomorphine were determined in patients with idiopathic Parkinson's disease (IPD). Apomorphine was applied by iontophoresis at two current densities.

METHODS

In ten patients apomorphine was applied passively for one hour. Thereafter, in the first five patients, a current density of 250 microA.cm-2 was applied for one hour and a current density of 375 microA.cm-2 in the second group. The individual pharmacokinetic parameters were obtained separately following a 15-minute zero-order intravenous infusion of 30 micrograms.kg-1. Skin resistance was measured during current delivery. Current-induced irritation was measured by Laser Doppler Flowmetry (LDF). The pharmacodynamics were quantified by a unilateral tapping score. Qualitative clinical improvements (decreased tremor, rigidity or cramp) were also recorded.

RESULTS

In all patients increasing plasma concentrations of R-apomorphine were found during the interval of current application. The maximum concentrations that were attained were related to the applied current density: 1.3 +/- 0.6 ng.ml-1 at 250 microA.cm-2 and 2.5 +/- 0.7 ng.ml-1 at 375 microA.cm-2. When the current was switched off all concentrations returned to baseline values in about 90 minutes. By mathematical deconvolution of the profiles it was shown that steady-state fluxes were reached within the one-hour interval of current driven transport Steady-state fluxes were calculated to be 69 +/- 30 nmol.cm-2.h-1 at 250 microA.cm-2 and 114 +/- 34 nmol.cm-2.h-1 at 375 microA.cm-2. Individual drug input rates were inversely related to the overall resistance. Significantly elevated LDF values were found after patch removal, indicating mild current induced erythema. Only subtherapeutic plasma concentrations were obtained in all patients except for one.

CONCLUSIONS

The results show that current-dependent delivery of apomorphine is possible in vivo at acceptable levels of skin irritation. Excellent correlation was found between the calculated in vivo transport rates and the rates that were previously obtained in vitro.