Pharmacokinetic and pharmacodynamic analyses, based on dopamine D2-receptor occupancy of bromocriptine, of bromocriptine-induced contralateral rotations in unilaterally 6-OHDA-lesioned rats

Sleep and local field potential effect of the D2 receptor agonist bromocriptine during the estrus cycle and postpartum period in female rats

BACKGROUND

Pituitary lactotrophs are under tonic dopaminergic inhibitory control and bromocriptine treatment blocks prolactin secretion.

METHODS

Sleep and local field potential were addressed for 72 h after bromocriptine treatments applied during the different stages of the estrus cycle and for 24 h in the early- and middle postpartum period characterized by spontaneously different dynamics of prolactin release in female rats.

RESULTS

Sleep changes showed strong dependency on the estrus cycle phase of the drug application. Strongest increase of wakefulness and reduction of slow wave sleep- and rapid eye movements sleep appeared during diestrus-proestrus and middle postpartum treatments. Stronger sleep-wake effects appeared in the dark phase in case of the estrus cycle treatments, but in the light phase in postpartum treatments. Slow wave sleep and REM sleep loss in case of estrus cycle treatments was not compensated at all and sleep loss seen in the first day post-injection was gained further later. In opposition, slow wave sleep loss in the light phase after bromocriptine injections showed compensation in the postpartum period treatments. Bromocriptine treatments resulted in a depression of local field potential delta power during slow wave sleep while an enhancement in beta and gamma power during wakefulness regardless of the treatment timing.

CONCLUSIONS

These results can be explained by the interplay of dopamine D2 receptor agonism, lack of prolactin release and the spontaneous homeostatic sleep drive being altered in the different stages of the estrus cycle and the postpartum period.

Micro- and Nanosized Carriers for Nose-to-Brain Drug Delivery in Neurodegenerative Disorders

Neurodegenerative disorders (NDs) have become a serious health problem worldwide due to the rapid increase in the number of people that are affected and the constantly aging population. Among all NDs, Alzheimer’s and Parkinson’s disease are the most common, and many efforts have been made in the development of effective and reliable therapeutic strategies. The intranasal route of drug administration offers numerous advantages, such as bypassing the blood–brain barrier and providing a direct entrance to the brain through the olfactory and trigeminal neurons. The present review summarizes the available information on recent advances in micro- and nanoscale nose-to-brain drug-delivery systems as a novel strategy for the treatment of Alzheimer’s and Parkinson’s disease. Specifically, polymer- and lipid-base micro- and nanoparticles have been studied as a feasible approach to increase the brain bioavailability of certain drugs. Furthermore, nanocomposites are discussed as a suitable formulation for administration into the nasal cavity.

Pilot study assessing the use of cabergoline for the treatment of cats with hypersomatotropism and diabetes mellitus

OBJECTIVES

An affordable and effective treatment is needed to manage feline hypersomatotropism. The aim of this study was to assess whether treatment with oral cabergoline for 90 days in cats with hypersomatotropism and diabetes mellitus improved diabetic and insulin-like growth factor 1 (IGF-1) control.

METHODS

This was a prospective cohort non-blinded pilot study enrolling client-owned cats with spontaneously occurring diabetes mellitus and hypersomatotropism. Cats received oral cabergoline (5-10 µg/kg q24h) for 90 consecutive days. Serum IGF-1 and fructosamine concentrations were measured on days 1, 30 and 90. Quality of life was determined using the DIAQoL-pet questionnaire on days 1 and 90.

RESULTS

Nine cats were enrolled and eight completed the study. There was no significant change in the following: IGF-1 (day 1 median 2001 ng/ml [range 890-2001 ng/ml]; day 30 median 2001 ng/ml [range 929-2001 ng/ml]; day 90 median 1828 ng/ml [range 1035-2001 ng/ml]; χ2(2) = 0.667, P = 0.805); fructosamine (day 1 median 499 µmol/l [range 330-887 µmol/l], day 30 median 551 µmol/l [range 288-722 µmol/l], day 90 median 503 [range 315-851 µmol/l]; χ2(2) = 0.581, P = 0.764); or DIAQoL-pet score (median on day 1 -2.79 [range -4.62 to -0.28], median on day 90 -3.24 [range -4.41 to -0.28]; P = 0.715). There was a significant change of insulin dose (χ2(2) = 8.667, P = 0.008) with cats receiving higher insulin doses at day 90 compared with day 1 (median on day 1 was 0.98 [range 0.63-1.49] and median on day 90 was 1.56 [range 0.49-2.55] units/kg q12h; P = 0.026).

CONCLUSIONS AND RELEVANCE

Cabergoline did not improve diabetic control or normalise insulin-like growth factor concentration, or improve patient quality of life.

Predicting the dopamine D2 receptor occupancy of ropinirole in rats using positron emission tomography and pharmacokinetic-pharmacodynamic modeling

1. The purpose of this study was to measure dopamine D_2/3 receptor occupancy (RO) as a marker of the clinical efficacy of ropinirole in rats via positron emission tomography (PET) using ¹⁸F-fallypride as the radiotracer and to explore the relationship between dopamine RO and the plasma concentration of ropinirole via pharmacokinetic-pharmacodynamic modeling. 2. Plasma was collected from 16 rats treated with one of four doses of ropinirole. For the time-dependent study, the data of 16 rats in the 15 mg/kg dose group at four time points were averaged, and another 24 rats were divided into three dose groups (5 mg/kg, 30 mg/kg and 60 mg/kg) for the dose-dependent study; the animals were assessed via ¹⁸F-fallypride PET scans. The correlation between dopamine RO and the ropinirole plasma concentration was investigated, and a pharmacokinetic-pharmacodynamic (PK-PD) model was established with WinNonlin 6.3 software. Both the plasma concentration and the binding potential changed in a time- and dose-dependent manner, and the plasma concentration that induces 50% RO (EC₅₀) as calculated by the PK-PD model was 1391 ng/mL. 3. ¹⁸F-fallypride appeared to be a suitable radiotracer for ropinirole imaging, and its binding to the dopamine D₂ receptor has time- and concentration-dependent characteristics. A theory-based PK-PD model was developed to describe the relationship between the plasma ropinirole concentration and RO, providing a methodological foundation for noninvasive and in vivo clinical evaluations of ropinirole treatment.

Theory-based analysis of clinical efficacy of triptans using receptor occupancy

BACKGROUND

Triptans, serotonin 5-HT1B/1D receptor agonists, exert their action by targeting serotonin 5-HT1B/1D receptors, are used for treatment of migraine attack. Presently, 5 different triptans, namely sumatriptan, zolmitriptan, eletriptan, rizatriptan, and naratriptan, are marketed in Japan. In the present study, we retrospectively analyzed the relationships of clinical efficacy (headache relief) in Japanese and 5-HT1B/1D receptor occupancy (Φ1B and Φ1D). Receptor occupancies were calculated from both the pharmacokinetic and pharmacodynamic data of triptans.

METHODS

To evaluate the total amount of exposure to drug, we calculated the area under the plasma concentration-time curve (AUCcp) and the areas under the time curves for Ф1B and Ф1D (AUCФ1B and AUCФ1D). Moreover, parameters expressing drug transfer and binding rates (Acp, AФ1B, AФ1D) were calculated.

RESULTS

Our calculations showed that Фmax1B and Фmax1D were relatively high at 32.0-89.4% and 68.4-96.2%, respectively, suggesting that it is likely that a high occupancy is necessary to attain the clinical effect. In addition, the relationships between therapeutic effect and AUCcp, AUCΦ1B, AUCΦ1D, and Acp · AUCcp differed with each drug and administered form, whereas a significant relationship was found between the therapeutic effect and AΦ1B · AUCΦ1B or AΦ1D · AUCΦ1D that was not affected by the drug and the form of administration.

CONCLUSIONS

These results suggest that receptor occupancy can be used as a parameter for a common index to evaluate the therapeutic effect. We considered that the present findings provide useful information to support the proper use of triptans.

Effects of noradrenergic denervation by anti-DBH-saporin on behavioral responsivity to L-DOPA in the hemi-parkinsonian rat

Dopamine (DA) replacement with l-DOPA remains the most effective pharmacotherapy for motor symptoms of Parkinson's disease (PD) including tremor, postural instability, akinesia, and bradykinesia. Prolonged L-DOPA use frequently leads to deleterious side effects including involuntary choreic and dystonic movements known as L-DOPA induced dyskinesias (LID). DA loss in PD is frequently accompanied by concomitant noradrenergic (NE) denervation of the locus coeruleus (LC); however, the effects of NE loss on L-DOPA efficacy and LID remain controversial and are often overlooked in traditional animal models of PD. The current investigation examined the role of NE loss in L-DOPA therapy by employing the NE specific neurotoxin anti-DA-beta hydroxylase saporin (αDBH) in a rat model of PD. Rats received unilateral 6-hydroxydopamine lesions of the medial forebrain bundle to deplete nigral DA and intraventricular injection of vehicle (DA lesioned rats) or αDBH (DANE lesioned rats) to destroy NE neurons bilaterally. Results indicated that αDBH infusion drastically reduced NE neuron markers within the LC compared to rats that received vehicle treatment. Behaviorally, this loss did not alter the development or expression of L-DOPA- or DA agonist-induced dyskinesia. However, rats with additional NE lesions were less responsive to L-DOPA's pro-motor effects. Indeed, DANE lesioned animals rotated less and showed less attenuation of parkinsonian stepping deficits following high doses of L-DOPA than DA lesioned animals. These findings suggest that severe NE loss may reduce L-DOPA treatment efficacy and demonstrate that degradation of the NE system is an important consideration when evaluating L-DOPA effects in later stage PD.

Hypothyroidism stimulates D2 receptor-mediated breathing in response to acute hypoxia and alters D2 receptors levels in carotid bodies and brain

Hypothyroidism can depress breathing and alter dopamine D2 receptor expression and function. We hypothesized that relative to euthyroid hamsters (EH), hypothyroid hamsters (HH) contain increased D2 receptors in brain regions associated with breathing and carotid bodies (CB), and that stimulation of D2 receptors would decease ventilation more in the HH compared to the EH. Hamsters were treated with vehicle, carmoxirile (peripherally acting D2 receptor agonist), or bromocriptine (central and peripherally acting D2 receptor agonist) and breathing was evaluated during exposure to air, hypoxia, and then air. HH exhibited increased D2 receptor protein levels in the striatum and CB, but decreased levels in the paraventricular hypothalamic nucleus. Relative to vehicle, carmoxirole and bromocriptine stimulated ventilation in the HH during and following exposure to hypoxia. Only bromocriptine depressed ventilation in the EH during and after exposure to hypoxia. Thus, hypothyroidism impacts the expression of D2 receptors in the carotid body, PVN and striatum, and D2 stimulation affects ventilation remarkably differently than in EH.

Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis

Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.