Challenges and trends in apomorphine drug delivery systems for the treatment of Parkinson's disease

Parkinson's disease(PD) is a chronic debilitating disease affecting approximately 1% of the population over the age of 60. The severity of PD is correlated to the degree of dopaminergic neuronal loss. Apomorphine has a similar chemical structure as the neurotransmitter dopamine and has been used for the treatment of advanced PD patients. In PD patients,apomorphine is normally administered subcutaneously with frequent injections because of the compound's extensive hepatic first-pass metabolism. There is, hence, a large unmet need for alternative administrative routes for apomorphine to improve patient compliance.The present review focuses on the research and development of alternative delivery of apomorphine, aiming to highlight the potential of non-invasive apomorphine therapy in PD,such as sublingual delivery and transdermal delivery.

Apomorphine effects on the hippocampus

Apomorphine is a non-specific dopamine receptor agonist that has been used in the treatment of some diseases and mental disorders. Its use has particularly well documented in Parkinson＇s disease（PD）. The dopaminergic agonists like apomorphine are related to oxidative processes that could induce cell damage and the functional impairment of some structures in the brain. However, most information about apomorphine in literature is focused on the improvement of the motor problems characteristic of PD, but little is known about the effects on cognitive behaviors and brain structures indirectly related to motor function. The presence of dopaminergic receptors in the hippocampus has recently been discovered, in connection with cognitive behaviors like learning and memory, these receptors are needed in neuronal plasticity. There has been a growing interest to know if this structure could be compromised by the effect of apomorphine and elucidate if part of the cognitive impairment present in the PD is due to the effect of apomorphine. In this mini-review, we summarized how apomorphine has been used since its creation, we discuss the latest information about its effect on the hippocampus and also the future perspectives to fully understand the effects of this compound.

Involvement of CRH Receptors in the Neuroprotective Action of R-Apomorphine in the Striatal 6-OHDA Rat Model

The dopamine D1-D2 receptor agonist, R-apomorphine, has been shown to be neuroprotective in different models of Parkinson’s disease. Different mechanisms of action for this effect have been proposed, but not verified in the striatal 6-hydroxydopamine rat model. In this study, the expression of a set of genes involved in 1) signaling, 2) growth and differentiation, 3) neuronal regeneration and survival, 4) apoptosis and 5) inflammation in the striatum was measured after a subchronic R-apomorphine treatment (10 mg/kg/day, subcutaneously, during 11 days) in the striatal 6-hydroxydopamine rat model. The expression of 84 genes was analysed by using the rat neurotrophins and receptors RT2 ProfilerTM PCR array. The neuroprotective effects of R-apomorphine in the striatal 6-hydroxydopamine model were confirmed by neurochemical and behavioural analysis. The expression data suggest the observed neuroprotection involved the alteration of the gene and the protein expression levels of the anti-inflammatory corticotropin releasing hormone receptor (CRHR) 1 and the pro-inflammatory CRHR2 receptor confirming its potential anti-inflammatory action.

Potentiation of apomorphine effect on sildenafil-induced penile erection in conscious rabbits

Aim: To investigate a possible potentiation effect of apomorphine (APO) on sildenafil-induced penile erection in the conscious rabbit. Methods: Erection of male New Zealand White rabbits (3.5-4.0 kg, n=12) was assessed by measuring the length of the uncovered penile mucosa and the duration of erection before and after intravenous administration of agents. After injection of APO (0, 0.05, 0.1 and 0.4 mg/kg), sildenafil was administered intravenously in a dose-response manner (0.5, 1 and 5 mg/kg). In additional experiments, the effect of increasing doses of sildenafil in combination with APO on systemic blood pressure was evaluated. Results: Systemic administration of sildenafil induced a dose-dependent increase in the penile length. Intravenous injection of APO alone did not produce any change in the penile length, while significantly enhanced the penile erection induced by sildenafil. The co-administration of 0.1 mg/kg of APO and 1 mg/kg of sildenafil was found to be the most effective combination in producing penile erection. Intravenous administration of sildenafil caused a concentration-dependent decrease in systemic blood pressure, but no additional decrease was observed with co-administration of APO. Conclusion: APO enhances the penile erection induced by sildenafil in the conscious rabbit without causing an additional decrease in blood pressure.

The Effect of Aging on Erectile Function Induced by Apomorphine and Electric Field Stimulation to Rat

Objective To explore the effect and mechanism of aging on erection by using rat model. Materials & Methods Forty male SD rats of 3, 9, 18 and 24 months old were divided into 4 groups equally according to their age. Apomorphine given subcutaneously and cavernous nerve electric field stimulation was used to induce erection of rats. Results The successful erection rate, number of erection times, and intracavernous pressure (ICP) in the rats of 18 and 24 month old was significantly lower than that of 3 and 9 month old. Conclusion The erectile function in aging rats is deteriorated. The damage mechanism with aging might be related to dopaminergic system in central nerves.

液相色谱-串联质谱法测定人血浆中阿扑吗啡

盐酸阿扑吗啡(apomorphine hydrochloride)为吗啡的衍生物,系中枢多巴胺D2受体激动剂,其舌下片制剂是目前用于治疗男性勃起机能障碍的新药[1,2].为了研究该制剂中阿扑吗啡的药代动力学特性,我们建立了阿扑吗啡血药浓度测定的液相色谱-串联质谱法.测定了28名健康志愿者口服阿扑吗啡舌下片后阿扑吗啡的血药浓度.……

多巴胺对长爪沙鼠贮食行为的影响

长爪沙鼠的贮食行为具有高低二型性。禁食诱导的贮食行为可能与中脑多巴胺(Dopamine,DA)系统有关,但尚乏证据。本文通过Fos标记相关脑区的活性,酪氨酸羟化酶(TH)标记DA神经元,以免疫组化方法观察对高贮食组长爪沙鼠腹腔注射DA拮抗剂haloperidol(1 mg/kg)和对低贮食组长爪沙鼠腹腔注射DA激动剂apomorphine(0.3 mg/kg)的行为和神经变化,验证中枢DA对贮食行为的调节。结果显示,haloperidol抑制了禁食诱导的沙鼠的贮食行为,这种抑制刺激了伏隔核和尾壳核Fos-ir阳性细胞表达,但却降低了黑质区Fos-ir和Fos-ir/TH-ir的细胞表达。Apomorphine增加了禁食诱导的沙鼠的贮食行为,降低伏隔核和尾壳核Fos-ir阳性细胞表达。这些结果表明,中脑DA系统参与调节了禁食条件下长爪沙鼠的贮食行为。

Value of mink vomit model in study of anti-emetic drugs

AIM： To establish a new, reliable vomit model of minks METHODS： Adult male minks were randomly divided into 8 groups （n=6）： cisplatin （7.5 mg/kg） intraperitoneal injection （ip） group, copper sulfate （40 mg/kg） intragastric injection （ig） group, apomorphine （1.6 mg/kg） subcutaneous injection （sc） group, and 18 Gy whole-body X-irradiation group, ondansetron injection group （2 mg/kg ip） 30 min later followed by cisplatin （7.5 mg/kg） ip, normal saline （NS） ip injection control group, metoclopramide injection group （4 mg/kg ip） 30 rain later followed by apomorphine （1.6 mg/kg） sc, NS ig control group. The frequency of retching and vomiting was calculated. After behavioral experiment, distribution of 5-HT in the ileum was detected by immunohistologic method. RESULTS： Cisplatin, apomorphine, copper sulfate and X-irradiation administered to minks evoked a profound emetic response in the animals. However, retching and vomiting were significantly inhibited by pretreatment with ondansetron and metoclopramide in cisplatin and copper sulfate groups （P=0.018）. Immunohistologic result showed that 5-HT released from enterochromaffin cells （EC cells） was involved in vomiting mechanism. CONCLUSION： Mink vomit model has a great value in studying the vomiting mechanism and screening new antiemetic drugs.

New oral agents for erectile dysfunction: what is changing in our practice?

Erectile dysfunction (ED) is a highly prevalent disorder affecting an estimated 152 million men worldwide and isassociated with a variety of behavioral risk factors, such as cigarette smoking and excessive alcohol consumption, aswell as numerous age - related medical conditions, notably type-2 diabetes mellitus and cardiovascular disease. A ratio-nal step - wise approach which includes comprehensive medical and sexual history, a focused physical examination andessential laboratory tests such as fasting glucose, lipid profile and testosterone assay is to be preferred. Current diagnos-tic work - up does not recommend any of the specialized tests which were previously considered mandatory-i. e. penilepharmacotesting, Duplex ultrasound and nocturnal penile tumescence. Hormonal replacement therapy is appropriate onlyin the hypogonadal male with ED. Prior to direct intervention, the physician should consider altering modifiable riskfactors or causes, although frequently insufficient to reverse ED completely. When indicated, oral therapy with newmolecules (phosphodiesterase inhibitors or apomorphine) is the first - line treatment for the majority of patients becauseof potential benefits and lack of invasiveness. (Asian J Androl 2001 Sep; 3: 175-179 )

P2X4 receptor participates in autophagy regulation in Parkinson’s disease

Dysfunctional autophagy often occurs during the development of neurodegenerative diseases,such as Parkinson’s disease,Huntington’s disease,and Alzheimer’s disease.The purinergic P2X4 receptor is an ATP-gated ion channel that is widely expressed in the microglia,astrocytes,and neurons of the central and peripheral nervous systems.P2X4R is involved in the regulation of cellular excitability,synaptic transmission,and neuroinflammation.However,the role played by P2X4R in Parkinson’s disease remains poorly understood.Rat models of Parkinson’s disease were established by injecting 6-hydroxydopamine into the substantia nigra pars compacta.P2X4R-targeted small interfering RNA(siRNA)was injected into the same area 1 week before injury induction to inhibit the expression of the P2X4 receptor.The results showed that the inhibition of P2X4 receptor expression in Parkinson’s disease model rats reduced the rotation behavior induced by apomorphine treatment,increased the latency on the rotarod test,and upregulated the expression of tyrosine hydroxylase,brain-derived neurotrophic factor,LC3-II/LC3-I,Beclin-1,and phosphorylated tropomyosin receptor kinase B(TrkB)in brain tissue,while simultaneously reducing p62 levels.These findings suggest that P2X4 receptor activation might inhibit neuronal autophagy through the regulation of the brain-derived neurotrophic factor/TrkB signaling pathway,leading to dopaminergic neuron damage in the substantia nigra and the further inhibition of P2X4 receptor-mediated autophagy.These results indicate that P2X4 receptor might serve as a potential novel target for the treatment of Parkinson’s disease.This study was approved by the Animal Ethics Committee of Affiliated Hospital of Qingdao University(approval No.QYFYWZLL26119)on April 12,2016.

Degree of dopaminergic degeneration measured by ^(99m)Tc-TRODAT-1 SPECT/CT imaging

To prevent and treat Parkinson＇s disease in its early stages,it is essential to be able to detect the degree of early dopaminergic neuron degeneration.Dopamine transporters（DAT） in the striatum regulate synaptic dopamine levels,and striatal ^99mTc-TRODAT-1 single-photon emission computed tomography（-SPECT） imaging is a marker for presynaptic neuronal degeneration.However,the association between the degree of dopaminergic degeneration and in vivo ^99mTc-TRODAT-1 SPECT imaging is unknown.Therefore,this study investigated the association between the degree of 6-hydroxydopamine（6-OHDA）-induced dopaminergic degeneration and DAT imaging using^99mTc-TRODAT-1 SPECT in rats.Different degrees of nigrostriatal dopamine depletion were generated by injecting different doses of 6-OHDA（2,4,and 8 μg） into the right medial forebrain bundle.The degree of nigrostriatal dopaminergic neuron degeneration was assessed by rotational behavior and immunohistochemical staining.The results showed that striatal ^99mTc-TRODAT-1 binding was significantly diminished both in the ipsilateral and the contralateral sides in the 4 and 8 μg 6-OHDA groups,and that DAT ^99mTc-TRODAT-1 binding in the ipsilateral striatum showed a high correlation to apomorphine-induced rotations at 8 weeks post-lesion（r = –0.887,P 〈 0.01）.There were significant correlations between DAT ^99mTc-TRODAT-1 binding in the ipsilateral striatum and the amount of tyrosine hydroxylase immunoreactive neurons in the ipsilateral substantia nigra in the 2,4,and 8 μg 6-OHDA groups at 8 weeks post-lesion（r = 0.899,P 〈 0.01）.These findings indicate that striatal DAT imaging using ^99mTc-TRODAT-1 is a useful technique for evaluating the severity of dopaminergic degeneration.

Reduced normogastric electrical activity associated with emesis:A telemetric study in ferrets

AIM： To characterize the gastric myoelectric activity （GMA） and intra-abdominal pressure changes induced by emetic stimuli （apomorphine and cisplatin） in the ferret. METHODS： GMA and intra-abdominal pressure were recorded in conscious, unrestrained ferrets surgically implanted with radiotelemetry transmitters. Animals were challenged with apomorphine （0.25 mg/kg sc） and cisplatin （10 mg/kg ip）, and the emetic response was quantified via direct observation and intra-abdominal pressure recording for 1 and 4 h, respectively. The GMA was analyzed by spectral analysis; the parameters used to characterize the GMA were the dominant frequency （DF） and the repartition of spectral power in the bradygastric, normogastric and tachygastric frequency ranges. RESULTS： Retches were identified on the intraabdominal pressure trace as peaks 0.30 ± 1.01 s in duration and 59.57 ± 2.74 mmHg in amplitude, vomit peaks were longer （0.82 ± 0.06 s, P 〈 0.01） and reached a higher pressure （87.73 ± 8.12 mmHg, P 〈 0.001）. The number of retches and vomits quantified via direct observation [apomorphine： 65.5 ± 11.8 retches ± vomits （R＋V）, cisplatin： 202.6 ± 64.1 R＋V] and intra-abdominal pressure （apomorphine： 68.3± 13.7 R＋V, n = 8; cisplatin： 219.0 ± 69.2 R＋V, n = 8） were correlated （r = 0.97, P 〈 0.0001） and the timing of emesis was consistent between the 2 methods. Apomorphine induced a decrease in normogastria from 45.48% ± 4.35% to 36.70 ± 4.34% （n = 8, P 〈 0.05） but the DF of the slow waves was not changed [8.95 ± 0.25 counts/rain （cpm） vs 8.68 ± 0.35 cpm, n = 8, P 〉 0.05]. Cisplatin induced a decrease in normogastria from 55.83% ± 4.30% to 29.22% ± 5.16% and an increase in bradygastria from 14.28% ± 2.32% to 31.19% ± 8.33% （n = 8, P 〈 0.001） but the DF （9.14 ± 0.13 cpm） remained unchanged （P 〉 0.05）. The GMA changes induced by cisplatin preceded the emetic response as normogastria was reduced for 1 h before the onset of emesis （57.61% ± 5.66% to 39.91% ± 5.74%, n = 6, P 〈 0.05）. Peri-emesis analysis revealed that the GMA was significantly disturbed during and immediately after, but not immediately before, the emetic episodes. CONCLUSION： The induction of emesis is reliably associated with a disrupted GMA, but changes may also occur prior to and following the emetic response.

Roles of dopaminergic receptors in bladder and erectile function at the spinal level

1 Introduction At the spinal level, the dopaminergic, the α1adrenergic and the neurokinin receptors play definite roles in the micturition control. From the anatomical point of view, the spinal center of micturition is located close to the center of erectile function. Recently, apomorphine is used for the treatment of erectile dysfunction and its mechanism of action is considered to be mainly through the central nervous system. 2 Dopaminergic receptors and bladder function at the spinal level

Why do‘OFF’periods still occur during continuous drug delivery in Parkinson’s disease?

Continuous drug delivery(CDD)is used in moderately advanced and late-stage Parkinson’s disease(PD)to control motor and non-motor fluctuations(‘OFF’periods).Transdermal rotigotine is indicated for early fluctuations,while subcutaneous apomorphine infusion and levodopa-carbidopa intestinal gel are utilised in advanced PD.All three strategies are considered examples of continuous dopaminergic stimulation achieved through CDD.A central premise of the CDD is to achieve stable control of the parkinsonian motor and non-motor states and avoid emergence of‘OFF’periods.However,data suggest that despite their efficacy in reducing the number and duration of‘OFF’periods,these strategies still do not prevent‘OFF’periods in the middle to late stages of PD,thus contradicting the widely held concepts of continuous drug delivery and continuous dopaminergic stimulation.Why these emergent‘OFF’periods still occur is unknown.In this review,we analyse the potential reasons for their persistence.The contribution of drug-and device-related involvement,and the problems related to site-specific drug delivery are analysed.We propose that changes in dopaminergic and non-dopaminergic mechanisms in the basal ganglia might render these persistent‘OFF’periods unresponsive to dopaminergic therapy delivered via CDD.