The pharmacology and clinical pharmacokinetics of apomorphine SL

Male DAT Val559 Mice Exhibit Compulsive Behavior under Devalued Reward Conditions Accompanied by Cellular and Pharmacological Changes

Identified across multiple psychiatric disorders, the dopamine (DA) transporter (DAT) Ala559Val substitution triggers non-vesicular, anomalous DA efflux (ADE), perturbing DA neurotransmission and behavior. We have shown that DAT Val559 mice display a waiting impulsivity and changes in cognitive performance associated with enhanced reward motivation. Here, utilizing a within-subject, lever-pressing paradigm designed to bias the formation of goal-directed or habitual behavior, we demonstrate that DAT Val559 mice modulate their nose poke behavior appropriately to match context, but demonstrate a perseverative checking behavior. Although DAT Val559 mice display no issues with the cognitive flexibility required to acquire and re-learn a visual pairwise discrimination task, devaluation of reward evoked habitual reward seeking in DAT Val559 mutants in operant tasks regardless of reinforcement schedule. The direct DA agonist apomorphine also elicits locomotor stereotypies in DAT Val559, but not WT mice. Our observation that dendritic spine density is increased in the dorsal medial striatum (DMS) of DAT Val559 mice speaks to an imbalance in striatal circuitry that might underlie the propensity of DAT Val559 mutants to exhibit compulsive behaviors when reward is devalued. Thus, DAT Val559 mice represent a model for dissection of how altered DA signaling perturbs circuits that normally balance habitual and goal-directed behaviors.

Induction of emesis with apomorphine using a novel gingival administration method in dogs

OBJECTIVE

To describe a novel method of inducing emesis in the dog using gingival administration of apomorphine, compare the efficacy of inducing emesis with gingival apomorphine to conjunctival apomorphine, and describe adverse effects associated with the gingival route.

DESIGN

Retrospective study from January 2017 to September 2018.

SETTING

Independent all-hours primary and secondary emergency and critical care referral center.

ANIMALS

Five hundred fifty-eight client-owned dogs.

MEASUREMENTS AND MAIN RESULTS

The medical records of dogs presenting for induction of emesis were searched. Dogs receiving either gingival or conjunctival apomorphine were included in the study. A short online survey was sent to clients whose dogs received gingival apomorphine. Apomorphine was administered conjunctivally in 430 (77.1%) dogs and gingivally in 128 (22.9%) dogs. There was no difference between route of administration and success of emesis (p = 0.29). A total of 14 clients responded to the survey, and diarrhea, lethargy, hyperactivity, and sedation were reported as adverse effects of gingival apomorphine administration. No clients sought veterinary attention for any of the adverse effects reported.

CONCLUSIONS

Gingival administration of apomorphine is easy, appears to be safe, and is an effective method of inducing emesis in the dog. Gingival administration of apomorphine may be considered in cases where parenteral administration is not feasible and could replace conjunctival administration in compliant dogs.

Pharmacokinetics and Comparative Bioavailability of Apomorphine Sublingual Film and Subcutaneous Apomorphine Formulations in Patients with Parkinson's Disease and "OFF" Episodes: Results of a Randomized, Three-Way Crossover, Open-Label Study

Introduction

In a pivotal study, apomorphine sublingual film (APL; KYNMOBI^®) was an effective and generally well-tolerated on-demand treatment of “OFF” episodes in patients with Parkinson’s disease (PD), approved across the dose range of 10–30 mg. Pharmacokinetics and comparative bioavailability of APL and two subcutaneous (SC) apomorphine formulations (SC-APO [APOKYN^®] and SC-APO-GO [APO-go^® PEN]) were evaluated in a randomized, three-way crossover, open-label study (NCT03292016).

Methods

Patients with PD and “OFF” episodes received an open-label randomized sequence of single doses of SC-APO and SC-APO-GO at the currently prescribed dose (2/3/4/5 mg) and APL doses with similar plasma exposure (15/20/25/30 mg) with ≥ 1-day washout between formulations. Plasma pharmacokinetics of apomorphine and apomorphine sulfate (major inactive metabolite) were measured 0–6 h postdose.

Results

Median time to maximum plasma concentration (t_max) of apomorphine was 0.63–0.75 h for APL and 0.25–0.38 h for SC-APO and SC-APO-GO. Geometric mean maximum plasma concentration (C_max) of apomorphine was 4.31–11.2 ng/ml across APL doses and was generally lower compared with SC apomorphine formulations within dose groups. Area under the concentration-time curve from time 0 to infinity (AUC_∞) was similar across apomorphine formulations within most dose groups. Relative bioavailability of APL was ~ 17% of SC apomorphine by AUC_∞; SC-APO and SC-APO-GO had similar bioavailability (98% and 83% by AUC_∞ and C_max, respectively). Apomorphine sulfate exposure was ~ three-fold higher for APL versus SC-APO and SC-APO-GO by AUC_∞ and C_max.

Conclusion

In patients with PD and “OFF” episodes, APL demonstrated lower C_max and relative bioavailability but similar exposures (AUCs) versus SC apomorphine within the approved dose range.

Trial Registration

ClinicalTrials.gov, NCT03292016.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-021-00251-6.

Population pharmacokinetic analysis of apomorphine sublingual film or subcutaneous apomorphine in healthy subjects and patients with Parkinson's disease

Apomorphine is an on-demand treatment of "OFF" episodes in patients with Parkinson's disease (PD). A joint parent-metabolite population pharmacokinetic (PK) model characterized apomorphine and apomorphine-sulfate following administration of apomorphine sublingual film (APL) and two formulations of subcutaneous apomorphine. Overall, 2485 samples from 87 healthy subjects and 71 patients with PD and "OFF" episodes were analyzed using nonlinear mixed-effects modeling. Apomorphine PK was adequately described by a two-compartment model with first-order transit absorption via both routes of administration and first-order metabolism to apomorphine-sulfate with one-compartment disposition and first-order elimination. Bioavailability of apomorphine sublingual film was ~ 18% relative to subcutaneous apomorphine. Among covariates tested, only body weight had a large effect on apomorphine exposure (maximum plasma concentration and area under the concentration-time curve [AUC_0-∞ ]), with greater weight resulting in lower exposure. Model-predicted apomorphine exposure was similar between apomorphine sublingual film 30 mg and subcutaneous apomorphine 5 mg (median AUC_0-24 , 66.7 ng•h/mL, geometric mean ratio of 0.99; 90% confidence interval [CI], 0.96-1.03) and was comparable between apomorphine sublingual film 35 mg and subcutaneous apomorphine 6 mg (median AUC_0-24 , 75.4 and 80.0 ng•h/mL, respectively; geometric mean ratio of 0.94; 90% CI, 0.90-0.97) administered every 2 h for a maximum of 5 doses per day. In a typical patient with PD, predicted apomorphine exposure increased with increasing doses of apomorphine sublingual film; however, the increase was less than dose proportional. Similar apomorphine exposure was predicted in patients with mild renal impairment versus normal renal function. PK properties of apomorphine sublingual film support its administration for a wide range of patients with PD and "OFF" episodes, regardless of demographic and clinical characteristics.

Apomorphine for Parkinson's Disease: Efficacy and Safety of Current and New Formulations

Satisfactory management of Parkinson's disease is a challenge that requires a tailored approach for each individual. In the advanced phase of the disease, patients may experience motor complications despite optimized pharmacological therapy. Apomorphine, a short-acting D₁- and D₂-like receptor agonist, is the only drug proven to have an efficacy equal to that of levodopa, albeit with a shorter time to onset and effect duration. Clinical trials have shown that intermittent apomorphine injections provide rapid and effective relief from unpredictable "off" periods. Continuous apomorphine infusion reduced around 50% of the daily "off" time in several studies. Dopaminergic side effects such as nausea, somnolence and hypotonia, as well as administration site reactions, are often mild or treatable, but somnolence and skin reactions in particular can sometimes be reasons for premature discontinuation. We provide an overview of the pharmacological mechanism of action of the drug in light of its effects on Parkinson's disease symptoms. We then summarize the evidence regarding the efficacy and tolerability of apomorphine, both in its established formulations (subcutaneous intermittent injection and continuous infusion) and in the new preparations currently under investigation.

Controlling Sulfuryl-Transfer Biology

In humans, the cytosolic sulfotransferases (SULTs) catalyze regiospecific transfer of the sulfuryl moiety (-SO3) from 3'-phosphoadenosine 5'-phosphosulfate to thousands of metabolites, including numerous signaling small molecules, and thus regulates their activities and half-lives. Imbalances in the in vivo set points of these reactions leads to disease. Here, with the goal of controlling sulfonation in vivo, molecular ligand-recognition principles in the SULT and nuclear receptor families are integrated in creating a strategy that can prevent sulfonation of a compound without significantly altering its receptor affinity, or inhibiting SULTS. The strategy is validated by using it to control the sulfonation and estrogen receptor (ER) activating activity of raloxifene (a US Food and Drug Administration-approved selective estrogen receptor modulator) and its derivatives. Preventing sulfonation is shown to enhance ER-activation efficacy 10(4)-fold in studies using Ishikawa cells. The strategy offers the opportunity to control sulfuryl transfer on a compound-by-compound basis, to enhance the efficacy of sulfonated drugs, and to explore the biology of sulfuryl transfer with unprecedented precision.

The allosteric binding sites of sulfotransferase 1A1

Human sulfotransferases (SULTs) comprise a small, 13-member enzyme family that regulates the activities of thousands of compounds-endogenous metabolites, drugs, and other xenobiotics. SULTs transfer the sulfuryl-moiety (-SO3) from a nucleotide donor, PAPS (3'-phosphoadenosine 5'-phosphosulfate), to the hydroxyls and primary amines of acceptors. SULT1A1, a progenitor of the family, has evolved to sulfonate compounds that are remarkably structurally diverse. SULT1A1, which is found in many tissues, is the predominant SULT in liver, where it is a major component of phase II metabolism. Early work demonstrated that catechins and nonsteroidal anti-inflammatory drugs inhibit SULT1A1 and suggested that the inhibition was not competitive versus substrates. Here, the mechanism of inhibition of a single, high affinity representative from each class [epigallocatechin gallate (EGCG) and mefenamic acid] is determined using initial-rate and equilibrium-binding studies. The findings reveal that the inhibitors bind at sites separate from those of substrates, and at saturation turnover of the enzyme is reduced to a nonzero value. Further, the EGCG inhibition patterns suggest a molecular explanation for its isozyme specificity. Remarkably, the inhibitors bind at sites that are separate from one another, and binding at one site does not affect affinity at the other. For the first time, it is clear that SULT1A1 is allosterically regulated, and that it contains at least two, functionally distinct allosteric sites, each of which responds to a different class of compounds.

Paradigms of sulfotransferase catalysis: the mechanism of SULT2A1

Human cytosolic sulfotransferases (SULTs) regulate the activities of thousands of signaling small molecules via transfer of the sulfuryl moiety (-SO3) from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the hydroxyls and primary amines of acceptors. Sulfonation controls the affinities of ligands for their targets, and thereby regulates numerous receptors, which, in turn, regulate complex cellular responses. Despite their biological and medical relevance, basic SULT mechanism issues remain unresolved. To settle these issues, and to create an in-depth model of SULT catalysis, the complete kinetic mechanism of a representative member of the human SULT family, SULT2A1, was determined. The mechanism is composed of eight enzyme forms that interconvert via 22 rate constants, each of which was determined independently. The result is a complete quantitative description of the mechanism that accurately predicts complex enzymatic behavior. This is the first description of a SULT mechanism at this resolution, and it reveals numerous principles of SULT catalysis and resolves previously ambiguous issues. The structures and catalytic behaviors SULTs are highly conserved; hence, the mechanism presented here should prove paradigmatic for the family.

Comparison of the MK-801-induced increase in non-rewarded appetitive responding with dopamine agonists and locomotor activity in rats

Systemic administration of the noncompetitive N-methyl-D-aspartate (NMDA)- receptor antagonist, MK-801, has been proposed to model cognitive deficits similar to those seen in patients with schizophrenia. Evidence has shown that MK-801 increases the probability of operant responding during extinction, possibly modeling perseveration, as would be seen in patients with schizophrenia. This MK-801-induced behavioral perseveration is reversed by dopamine receptor antagonism. To further explore the role of dopamine in this behavioral change, the current study sought to determine if the MK-801-induced increase in non-rewarded operant responding could be mimicked by dopamine agonism and determine how it was related to locomotor activity. Male Long Evans rats were treated systemically with MK-801, cocaine, GBR12909 or apomorphine (APO) and given a single trial operant extinction session, followed by a separate assessment of locomotor activity. Both MK-801 (0.05 mg/kg) and cocaine (10 mg/kg) significantly increased responding during the extinction session and both increased horizontal locomotor activity. No dose of GBR-12909 (5, 10 or 20 mg/kg) was found to effect non-rewarded operant responding or locomotor activity. APO (0.05, 0.5, 2 or 5 mg/kg) treatment produced a dose-dependent decrease in both operant responding and locomotor activity. These results suggest the possibility that, rather than a primary influence of increased dopamine concentration on elevating bar-pressing responses during extinction, other neurotransmitter systems may be involved.

Inhibition of human drug metabolizing cytochrome P450 enzymes by plant isoquinoline alkaloids

The human cytochrome P450 (CYP) enzymes play a major role in the metabolism of endobiotics and numerous xenobiotics including drugs. Therefore it is the standard procedure to test new drug candidates for interactions with CYP enzymes during the preclinical development phase. The purpose of this study was to determine in vitro CYP inhibition potencies of a set of isoquinoline alkaloids to gain insight into interactions of novel chemical structures with CYP enzymes. These alkaloids (n=36) consist of compounds isolated from the Papaveraceae family (n=20), synthetic analogs (n=15), and one commercial compound. Their inhibitory activity was determined towards all principal human drug metabolizing CYP enzymes: 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4. All alkaloids were assayed in vitro in a 96-well plate format using pro-fluorescent probe substrates and recombinant human CYP enzymes. Many of these alkaloids inhibited the CYP3A4 form, with 30/36 alkaloids inhibiting CYP3A4 with at least moderate potency (IC₅₀ < 10 μM) and 15/36 inhibiting CYP3A4 potently (IC₅₀ < 1 μM). Among them corydine, parfumine and 8-methyl-2,3,10,11-tetraethoxyberbine were potent and selective inhibitors for CYP3A4. CYP2D6 was inhibited with at least moderate potency by 26/34 alkaloids. CYP2C19 was inhibited by 15/36 alkaloids at least moderate potently, whereas CYP1A2, CYP2B6, CYP2C8, and CYP2C9 were inhibited to a lesser degree. CYP2A6 was not significantly inhibited by any of the alkaloids. The results provide initial structure-activity information about the interaction of isoquinoline alkaloids with major human xenobiotic-metabolizing CYP enzymes, and illustrate potential novel structures as CYP form-selective inhibitors.

Inhalation device allows novel administration of apomorphine in men with erectile dysfunction-efficacy and safety findings

INTRODUCTION

Erectile dysfunction (ED) treatment is greatly influenced by patient preference, and currently available oral therapies do not meet all patients' needs. New therapies and formulations are therefore being investigated.

AIM

The aim of this article is to assess the clinical efficacy and safety of inhaled apomorphine, VR004, in men with mild to severe ED.

MAIN OUTCOME MEASURES

Efficacy outcomes were the change in the proportion of positive responses to sexual encounter profile questions, International Index of Erectile Function (IIEF) scores and onset of therapeutic effect. Safety outcomes included a change in vital signs at an orthostatic challenge and adverse events (AEs).

METHODS

Two consecutive, multicenter trials each comprised a 4-week no-treatment period and a 12-week "at home" treatment period with regular clinic visits. Patients (N = 211 and N = 389) were randomized to receive one of three set doses of VR004 (100-300 microg) or matching placebo in each trial. VR004 was administered by a dry-powder inhaler at least once a week.

RESULTS

Efficacy was generally dose dependent. The proportion of per-protocol patients maintaining an erection long enough for successful intercourse increased in all VR004 groups vs. placebo. IIEF scores were higher in the VR004 groups compared with placebo, and the majority of responders achieved an erection within 10 minutes of dosing. The safety profile of VR004 was generally similar to that of placebo, and AEs were mild or moderate in severity. The incidence of treatment-related AEs was dose dependent. Few patients (4%) withdrew because of treatment-related AEs, and the majority of these withdrawals occurred on the day of the stringent orthostatic challenge.

CONCLUSIONS

The VR004 system administers low apomorphine doses that are well tolerated without compromising efficacy. This route of administration ensures a rapid onset of action and reproducible efficacy and safety profiles. Inhaled apomorphine is therefore a potential first-line treatment for ED.

Addiction to apomorphine: a clinical case-centred discussion

AIM

To report the case of a patient, who in the context of an anti-Parkinsonian therapy, developed addiction to apomorphine.

METHODS

Clinical case description.

RESULTS

Apomorphine is a dopaminergic agonist that acts directly on D2 receptors. It has been used in alcoholism, male sexual dysfunction and with diagnostic and therapeutic purposes in Parkinson's disease (PD).

CONCLUSIONS

The present work describes the case of a woman with PD who developed a loss of control over the consumption of apomorphine that resulted in a significant impairment of her functioning. PD patients with high frequency develop different psychiatric symptoms. Conversely, anti-Parkinsonian drugs also generate psychiatric symptoms that can be experienced by the patient as pleasant sensations ('alerting', 'awakening', 'activating', hypomania and hypersexuality). In spite of this, addiction to these drugs in patients with PD is a very rare phenomenon. Currently, the prescription of apomorphine has been extended to patients with erectile dysfunction, which may increase the prevalence of addiction cases or of severe psychiatric symptoms.

A comparative review of apomorphine formulations for erectile dysfunction : recommendations for use in the elderly

Erectile dysfunction (ED) is a common medical condition that affects the sexual life of millions of men worldwide. First-line oral therapy for ED includes the use of phosphodiesterase type 5 inhibitors (sildenafil, tadalafil and vardenafil) and sublingual apomorphine. Apomorphine is a dopamine D(1) and D(2) receptor agonist that has been approved for marketing in Europe. Different apomorphine formulations have been tested, such as sublingual, subcutaneous and intranasal. However, the sublingual formulation has shown the best results in terms of efficacy, safety and tolerability, especially the 2mg and 3mg doses. Although clinical studies of the efficacy and tolerability of apomorphine sublingual (SL) have included older patients, who are more likely to have ED, no study has specifically assessed the efficacy and tolerability of different doses of apomorphine SL in aging men. Therefore, a MEDLINE search was conducted from January 1987 to November 2005 to identify studies of the efficacy, safety (in particular cardiovascular safety) and tolerability of different apomorphine formulations and doses as treatments for ED in the subcohort of aging men. On the basis of the most recent peer-reviewed publications, the first part of this article critically evaluates data regarding the epidemiology of ED in the aging population. The second part of the article focuses on the mechanism of action and pharmacokinetics of apomorphine both in the general and the elderly population. Finally, a critical analysis of the efficacy and safety of different apomorphine formulations and doses for the treatment of ED is reported. Apomorphine represents a first-line oral treatment for ED. Available formulations include only sublingual administration. Few studies have assessed the efficacy and safety of apomorphine in the elderly population. However, in clinical practice, older patients with multiple vascular risk factors and systematic vascular damage show poor overall response to apomorphine SL for the treatment of ED.

Comparison of the Effect of Sildenafil and Apomorphine SL on Nocturnal Erections in Healthy Volunteers: A Placebo-Controlled Study

OBJECTIVE

To compare the effects of sildenafil and sublingual (sl) apomorphine on nocturnal erections.

METHODS

In a prospective, single-blinded, placebo-controlled at-home study we compared the effect of apomorphine sl and sildenafil on sleep-related erectile activity in 30 healthy potent volunteers (mean age, 26.4 years; range, 23-35 years; Erectile Function domain of the International Index of Erectile Function > or =26), not reporting any subjective sleep abnormality during 4 consecutive nights with rigidity monitoring (NPTR) with the RigiScantrade mark device. After the first night of adaptation, they were randomized to receive placebo or apomorphine sl 2mg or sildenafil 50mg taken at bedtime during the following 3 consecutive nights.

RESULTS

Sildenafil increased the mean+/-SE number of erections, overall length of erectile events, and the time of erections with rigidity >60% at both tip and base, as compared to placebo. The same parameters were reduced after administration of apomorphine sl. Similar findings were observed with regards to Rigidity Activity Units and Tumescence Activity Units.

CONCLUSIONS

Our results confirm that sildenafil taken at bedtime might increase nocturnal erectile activity also in young potent men as compared to placebo. Apomorphine sl taken at bedtime seems to have the opposite effect.

PROSPECTIVE, RANDOMIZED, CROSSOVER COMPARISON OF SUBLINGUAL APOMORPHINE (3 mg) WITH ORAL SILDENAFIL (50 mg) FOR MALE ERECTILE DYSFUNCTION

PURPOSE

We established the efficacy and safety of sublingual apomorphine compared with oral sildenafil in comparable groups of patients with erectile dysfunction (ED).

MATERIALS AND METHODS

This prospective, randomized, crossover study included 77 heterosexual men with ED of various etiologies and severities. A total of 62 men were randomized but only 34 were evaluable for efficacy and tolerability. The study started with a run-in period of 2 to 4 weeks. The first 4 weeks of treatment were followed by a washout period of 4 weeks, after which patients changed to the alternate treatment for an additional 4-week period. The sequence of the 2 treatments was established by a randomization list in blocks in closed packets. The primary efficacy end point was the percent of attempts resulting in erection firm enough for intercourse. Additional variables were the percent of attempts resulting in intercourse and improvement in ED, as evaluated by the erectile function domain score of the International Index of Erectile Function questionnaire.

RESULTS

Sildenafil was significantly more effective than apomorphine in regard to the percent of attempts resulting in erection firm enough for intercourse (85% vs 44%, p <0.0001) and actually resulting in intercourse (81% vs 43%, p <0.0001) as well as erectile function evaluated by the erectile function domain score of the International Index of Erectile Function (p <0.001). The incidence of adverse events was not significantly different for the 2 drugs. Although the number of patients was small, this study had strong statistical power due to the striking difference in results.

CONCLUSIONS

Sildenafil was significantly more effective than apomorphine for ED. No statistical difference in adverse events was noted.

Placebo-controlled study on efficacy and safety of daily apomorphine SL intake in premenopausal women affected by hypoactive sexual desire disorder and sexual arousal disorder

OBJECTIVES

To verify whether apomorphine SL is effective in premenopausal women affected by arousal disorder with hypoactive sexual desire disorder.

METHODS

Sixty-two volunteer women, aged 26 to 45 years, affected by arousal disorders and hypoactive sexual desire disorder participated in the study, which consisted of two parts. The first was 4 weeks of a taken-as-needed, open-label, dose-escalation regimen starting at 2 or 3 mg of apomorphine SL. The second part of the study was for the nonresponders, who were randomly allocated to treatment in one of six possible sequences of three 2-week double-blind, crossover study periods with apomorphine 2 mg or 3 mg, washout, and placebo. Efficacy was assessed with the Personal Experiences Questionnaire using the 5-point Likert scale. The Personal Experiences Questionnaire quantified subjective arousal, desire, orgasm, enjoyment, and frequency of sexual relationships.

RESULTS

Fifty women completed the 4-week "as required" drug regimen, and 6 of them benefited from this treatment regimen (P <0.05). The 44 women who reported no change with respect to baseline participated in the double-blind crossover part of the study. Six women stopped taking the drug because of a fear of problems (two each during the 2-mg apomorphine, 3-mg apomorphine, and placebo periods). Adverse events were mild or moderate, both occurred during the "as required" part (10 patients) and during daily usage (6 patients) and were mainly nausea, vomiting, dizziness, or headache. However, during the placebo period, 2 women had adverse events, mainly headache. The daily intake of the drug was effective with both the 2-mg and 3-mg dosages compared with placebo for arousal and desire (P <0.05). The effects of 3 mg of apomorphine were better than those obtained with 2 mg (P <0.05). The orgasm, enjoyment, and satisfied by frequency scores improved during treatment with daily apomorphine compared with baseline and placebo.

CONCLUSIONS

The results of our study suggest that daily apomorphine SL may improve the sexual life of women affected by sexual difficulties. Additional studies are needed to define the daily use of apomorphine SL in large subgroups of women on the basis of etiology and the severity of sexual dysfunction.

Sulfation of apomorphine by human sulfotransferases: evidence of a major role for the polymorphic phenol sulfotransferase, SULT1A1

1. The relative roles of various members of the human sulfotransferase (SULT) enzyme family in the metabolism of apomorphine, a dopamine receptor antagonist used in the treatment of Parkinson's disease and, more recently, erectile dysfunction, were examined. In humans, sulfation is the major route of metabolism of this drug. 2. Using recombinant SULTs expressed in Escherichia coli, R(--)-apomorphine sulfation was studied using the universal barium precipitation assay in the presence of [35S] 3'-phosphoadenosine 5'-phosphosulfate and SULTs 1A1, 1A2, 1A3, 1B1, 1C2, 1E1 and 2A1. It was shown that SULTs 1A1, 1A2, 1A3 and 1E1 all sulfated apomorphine to varying extents. Low activity with SULT1B1 was only seen at the highest concentration (100 microM) and no activity with SULT1C2 or SULT2A1 was observed. 3. Kinetic analysis using purified recombinant SULTs showed that 1A1, 1A3 and 1E1 all had similar Vmax/Km values, although SULT1E1 had a slightly lower Km at around 1 microM compared with approximately 4 microM for the other SULTs. 4. By correlating apomorphine sulfation (at 10 microM) in a bank of 28 liver cytosols with SULT activity towards 10 microM 4-nitrophenol (SULT1A1) and 0.2 microM 17beta-oestradiol (SULT1E1), a strong correlation with SULT1A1 activity was clearly demonstrated, suggesting this enzyme was primarily responsible for hepatic apomorphine sulfation. 5. These findings were confirmed using immuno-inhibition experiments with antibodies against SULT1A and SULT1E1, which showed preferential inhibition of apomorphine sulfation in human liver cytosol by anti-SULT1A. 6. The results strongly implicate SULT1A1 as the major enzyme responsible for hepatic apomorphine metabolism. As SULT1A1 is subject to a common functional polymorphism, sulfation phenotype may be an important determinant of susceptibility to side-effects of apomorphine and/or efficacy of treatment.

Apomorphine-induced brain modulation during sexual stimulation: a new look at central phenomena related to erectile dysfunction

It is well recognized that sexual stimulation leading to penile erection is controlled by different areas in the brain. Animal erection studies have shown that apomorphine (a D2>D1 dopamine receptors nonselective agonist) seems to act on neurons located within the paraventricular nucleus and the medial preoptic area of the hypothalamus. Yet, only recently, was a centrally acting agent, apomorphine sublingual, approved for the treatment of erectile dysfunction. The present functional magnetic resonance imaging placebo-controlled study presents the first in vivo demonstration of the apomorphine-induced modulation of cortical and subcortical brain structures in patients with psychogenic erectile dysfunction. Noteworthy, patients in comparison with potent controls, showed an increased activity in frontal limbic areas that was downregulated by apomorphine. This suggests that psychogenic impotence may be associated with previously unrecognized underlying functional abnormalities of the brain.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.

Central mechanisms of erectile dysfunction: what a clinician may want to know

The interplay between peripheral and central mechanisms of erectile function are not fully elucidated although basic science is moving ahead in this area. It is important from a clinical point of view to understand these mechanisms so that we may begin to make further therapeutic advances in the treatment of erectile dysfunction (ED). It is now widely understood that central disinhibition plays a crucial role in the induction of erectile responses and this has led to the development of the central initiator, apomorphine SL (Ixense ) [apo SL]. Apo SL acts in the paraventricular nucleus of the hypothalamus as a dopamine receptor agonist. It works as a proerectile conditioner at this level to increase the responses of the erectile pathway following appropriate sexual stimulation. This unique central mode of action of apo SL has thus proved efficacious in approximately 70% of ED patients although persistence may be required to produce a robust effect for the maximum number of patients.

Interactions between drugs for erectile dysfunction and drugs for cardiovascular disease

The association of erectile dysfunction (ED) and cardiovascular disease is well-documented in the literature and both conditions share risk factors. Therefore, it is difficult to distinguish the effect of underlying disease and adverse effects of the drugs and/or interactions between ED drugs and drugs implemented for cardiovascular disease. The known interactions of systemic administered drugs for ED with drugs for cardiovascular disease are mainly pharmacodynamic. Thus, nitrates enhance the production of cyclic GMP and combined with phosphodiesterase type-5 inhibitors this can lead to severe hypotension. The same is the case for the treatment with phentolamine in patients treated with beta-adrenoceptor antagonists. Due to increased partial thromboplastin time, the risk of bleeding is enhanced for intracavernous alprostadil injection in heparin-treated patients. Pharmacokinetic interactions of clinical importance have been described for ED drugs with other therapeutic groups such as sildenafil with the antifungal drug, ketoconazole, and apomorphine with the antiparkinson drug, entacapon. Although sildenafil and antihypertensive dihydropyridines like amlodipine are metabolized by the same cytochrome P450 enzyme, CYP3A4 in the liver, the combination of these drugs does not exhibit a synergistic blood pressure lowering action. Unfortunately documentation concerning drug interactions is often poor and occasional.