Cabergoline: Pharmacology, ocular hypotensive studies in multiple species, and aqueous humor dynamic modulation in the Cynomolgus monkey eyes

Identifying new drugs and targets to treat rapidly elevated intraocular pressure for angle closure and secondary glaucomas to curb visual impairment and prevent blindness

A multitude of pharmacological compounds have been shown to lower and control intraocular pressure (IOP) in numerous species of animals and human subjects after topical ocular dosing or via other routes of administration. Most researchers have been interested in finding drug candidates that exhibit a relatively long duration of action from a chronic therapeutic use perspective, for example to treat ocular hypertension (OHT), primary open-angle glaucoma and even normotensive glaucoma. However, it is equally important to seek and characterize treatment modalities which offer a rapid onset of action to help provide fast relief from quickly rising IOP that occurs in certain eye diseases. These include acute angle-closure glaucoma, primary angle-closure glaucoma, uveitic and inflammatory glaucoma, medication-induced OHT, and other secondary glaucomas induced by eye injury or infection which can cause partial or complete loss of eyesight. Such fast-acting agents can delay or prevent the need for ocular surgery which is often used to lower the dangerously raised IOP. This research survey was therefore directed at identifying agents from the literature that demonstrated ocular hypotensive activity, normalizing and unifying the data, determining their onset of action and rank ordering them on the basis of rapidity of action starting within 30-60 min and lasting up to at least 3-4 h post topical ocular dosing in different animal species. This research revealed a few health authority-approved drugs and some investigational compounds that appear to meet the necessary criteria of fast onset of action coupled with significant efficacy to reduce elevated IOP (by ≥ 20%, preferably by >30%). However, translation of the novel animal-based findings to the human conditions remains to be demonstrated but represent viable targets, especially EP2-receptor agonists (e.g. omidenepag isopropyl; AL-6598; butaprost), mixed activity serotonin/dopamine receptor agonists (e.g. cabergoline), rho kinase inhibitors (e.g. AMA0076, Y39983), CACNA2D1-gene product inhibitors (e.g. pregabalin), melatonin receptor agonists, and certain K+-channel openers (e.g. nicorandil, pinacidil). Other drug candidates and targets were also identified and will be discussed.

Evaluation of the effects of duloxetine treatment on anterior segment parameters by optical coherence tomography

PURPOSE

To evaluate the effects of Duloxetine on anterior segment parameters and intraocular pressure (IOP) in open angle eyes.

METHODS

38 eyes of 38 patients with fibromyalgia who had open or wide open angles according to the Shaffer classification. Anterior segment optic coherence tomography was performed before and after (month 3) Duloxetine treatment. IOP, central corneal thickness (CCT), corneal endothelial cell density (CECD) and anterior chamber depth (ACD) were also recorded and evaluated.

RESULTS

No statistically significant difference was determined in IOP, CCT and CECD (p > 0.05). However, a statistically significant decrease was determined in both the temporal and nasal anterior chamber angle, angle opening distance, nasal trabecular-iris space area and ACD values between the baseline and month 3 (p < 0.001).

DISCUSSION

We think that the short term use of Duloxetine does not lead to clinically significant changes despite their statistically significant effects on the anterior chamber parameters.

Therapeutic Drugs and Devices for Tackling Ocular Hypertension and Glaucoma, and Need for Neuroprotection and Cytoprotective Therapies

Damage to the optic nerve and the death of associated retinal ganglion cells (RGCs) by elevated intraocular pressure (IOP), also known as glaucoma, is responsible for visual impairment and blindness in millions of people worldwide. The ocular hypertension (OHT) and the deleterious mechanical forces it exerts at the back of the eye, at the level of the optic nerve head/optic disc and lamina cribosa, is the only modifiable risk factor associated with glaucoma that can be treated. The elevated IOP occurs due to the inability of accumulated aqueous humor (AQH) to egress from the anterior chamber of the eye due to occlusion of the major outflow pathway, the trabecular meshwork (TM) and Schlemm’s canal (SC). Several different classes of pharmaceutical agents, surgical techniques and implantable devices have been developed to lower and control IOP. First-line drugs to promote AQH outflow via the uveoscleral outflow pathway include FP-receptor prostaglandin (PG) agonists (e.g., latanoprost, travoprost and tafluprost) and a novel non-PG EP2-receptor agonist (omidenepag isopropyl, Eybelis^®). TM/SC outflow enhancing drugs are also effective ocular hypotensive agents (e.g., rho kinase inhibitors like ripasudil and netarsudil; and latanoprostene bunod, a conjugate of a nitric oxide donor and latanoprost). One of the most effective anterior chamber AQH microshunt devices is the Preserflo^® microshunt which can lower IOP down to 10–13 mmHg. Other IOP-lowering drugs and devices on the horizon will be also discussed. Additionally, since elevated IOP is only one of many risk factors for development of glaucomatous optic neuropathy, a treatise of the role of inflammatory neurodegeneration of the optic nerve and retinal ganglion cells and appropriate neuroprotective strategies to mitigate this disease will also be reviewed and discussed.

The prolactin receptor long isoform regulates nociceptor sensitization and opioid-induced hyperalgesia selectively in females

Pain is more prevalent in women for reasons that remain unclear. We have identified a mechanism of injury-free nociceptor sensitization and opioid-induced hyperalgesia (OIH) promoted by prolactin (PRL) in females. PRL signals through mutually inhibitory long (PRLR-L) and short (PRLR-S) receptor isoforms, and PRLR-S activation induces neuronal excitability. PRL and PRLR expression were higher in females. CRISPR-mediated editing of PRLR-L promoted nociceptor sensitization and allodynia in naïve, uninjured female mice that depended on circulating PRL. Opioids, but not trauma-induced nerve injury, decreased PRLR-L promoting OIH through activation of PRLR-S in female mice. Deletion of both PRLR-L and PRLR-S (total PRLR) prevented, whereas PRLR-L overexpression rescued established OIH selectively in females. Inhibition of circulating PRL with cabergoline, a dopamine D2 agonist, up-regulated PRLR-L and prevented OIH only in females. The PRLR-L isoform therefore confers protection against PRL-promoted pain in females. Limiting PRL/PRLR-S signaling pharmacologically or with gene therapies targeting the PRLR may be effective for reducing pain in a female-selective manner.

Discovery to Launch of Anti-allergy (Emadine; Patanol/Pataday/Pazeo) and Anti-glaucoma (Travatan; Simbrinza) Ocular Drugs, and Generation of Novel Pharmacological Tools Such as AL-8810

The eye and eyesight are exquistly designed and are precious, and yet we often take them for granted. Good vision is critical for our long-term survival and for humanity's enduring progress. Unfortunately, since ocular diseases do not culminate in life-and-death scenarios, awareness of the plight of millions of people suffering from such eye ailments is not publicized as other diseases. However, losing eyesight or falling victim to visual impairment is a frightening outlook for most people. Glaucoma, a collection of chronic optic neuropathies, of which the most prevalent form, primary open-angle glaucoma (POAG), is the second leading cause of irreversible blindness. POAG currently afflicts >70 million people worldwide and is an insidious, progressive, silent thief of sight that is asymptomatic. On the other hand, allergic conjunctivitis (AC), and the associated rhinitis ("hay-fever"), frequently victimizes a huge number of people worldwide, especially during seasonal changes. While not life-threatening, sufferers of AC soon learn the value of drugs to treat their signs and symptoms of AC as they desire rapid relief to overcome the ocular itching/pain, redness, and tearing AC causes. Herein, I will describe the collective efforts of many researchers whose industrious, diligent, and dedicated team work resulted in the discovery, biochemical/pharmacological characterization, development and eventual launch of drugs to treat AC (e.g., olopatadine [Patanol/Pataday/Pazeo] and emedastine [Emedine]), and for treating ocular hypertension and POAG (e.g., travoprost [Travatan ] and Simbrinza). This represents a personal perspective.

The risk of glaucoma and serotonergic antidepressants: A systematic review and meta-analysis

BACKGROUND

The aim of current study was to conduct a systematic review and meta-analysis to explore the relationship between antidepressant use and glaucoma.

METHODS

Eight major electronic databases were searched from inception until March 19th, 2018 to obtain relevant studies that evaluated associations of antidepressants [including selective serotonin reuptake inhibitors (SSRIs) and serotonin norepinephrine reuptake inhibitors (SNRIs)] treatment and the risk of primary open-angle glaucoma (POAG) or primary angle-closure glaucoma (PACG) as well as intraocular pressure (IOP), and related anterior chamber parameters compared to participants not exposed to antidepressant treatment. A random-effects meta-analysis was conducted.

RESULTS

Six case-control studies and one cohort study were eligible (N = 801,754). The use of SSRIs was not associated with a higher risk of glaucoma (k = 7, pooled adjusted odds ratio (pAOR) = 0.956, 95% confidence interval (CI) = 0.807 to 1.133, p = 0.604). In addition, IOP was lower in participants exposed to antidepressants (SSRIs and SNRIs) (k = 4, Hedges' g = -0.519, 95% CI = -0.743 to -0.296, p < 0.001). Finally, pupillary diameter was higher in participants exposed to antidepressant treatment (k = 4, Hedges' g = 0.681, 95% CI = 0.462 to 0.900, p < 0.001).

LIMITATIONS

High heterogeneity of included studies limit the establishment of causal inferences.

CONCLUSIONS

This meta-analysis indicates that a putative association between the use of SSRIs and a higher risk of glaucoma remains to be proven. However, antidepressant drug treatment may be associated with significantly lower IOP and higher pupillary diameter. The mechanisms underpinning these associations deserve further investigation.

How Does Usage of Serotonin Noradrenaline Reuptake Inhibitors Affect Intraocular Pressure in Depression Patients?

PURPOSE

To evaluate anterior segment parameters and intraocular pressure (IOP) modifications in patients using serotonin noradrenaline reuptake inhibitors (SNRIs) due to major depressive disorder.

METHODS

This cross-sectional study included 170 eyes of 85 subjects. All subjects were divided into three groups: group 1 included 44 healthy control subjects, group 2 included 22 patients receiving antidepressants for 1 week to 6 months, and group 3 included 19 patients receiving antidepressants for >6 months. All subjects underwent a detailed ophthalmologic examination, including gonioscopy. Anterior segments of all subjects were evaluated with the Scheimpflug system and pupil diameter (PD), central corneal thickness, anterior chamber depth (ACD), anterior chamber volume, and anterior chamber angle (ACA) measurements were enrolled.

RESULTS

The median IOP was significantly lower in patients using antidepressants [16.0 (11.0-21.0) mmHg] than the control group [17.5 (12.0-21.0) mmHg] (P = 0.041). The PD was significantly larger in patients using antidepressants [3.56 (2.29-5.60) mm] than the control group [2.95 (2.00-4.40) mm] (P = 0.000). In the study group, PD was also significantly larger in patients using SNRIs for ≥6 months [3.67 (2.38-5.08) mm] than <6 months [3.31 (2.29-5.60) mm] (P = 0.000). The median ACD was significantly lower in patients using antidepressants for ≥6 months [3.21 (2.52-4.06) mm] than the control group [3.44 (2.63-4.29) mm] (P = 0.000). ACAs were measured between 25° and 55° by Scheimpflug imaging.

CONCLUSIONS

Treatment of SNRIs causes mydriasis and decrease in width of ACD. These changes may not increase IOP as long as the patient has an open angle. SNRIs lead to decrease in IOP particularly in long-term usage.

Serotonin-2B/2C Receptors Mediate Bovine Ciliary Muscle Contraction: Role in Intraocular Pressure Regulation

PURPOSE

To study the pharmacological profile of the serotonin (5-hydroxytryptamine [5-HT]) receptor subtype mediating contractions in bovine isolated ciliary muscles.

METHODS

Ciliary muscle strips were isolated from bovine eyeballs and mounted in organ baths containing aerated (95% O₂, 5% CO₂) Krebs buffer solution maintained at 37°C. Each muscle strip was attached at 1 end to a Grass Force-displacement Transducer connected to a Polyview Computer System for recording changes in isometric tension. After an equilibration period, ciliary muscle strips were exposed to selective agonists and antagonists of 5-HT receptors.

RESULTS

Both selective and nonselective agonists for 5-HT produced concentration-dependent contractions of isolated ciliary muscles with the following rank order of potency: BW723C86>α-methyl-5-HT>MK-212>>8-hydroxy-DPAT>quipazine>R-DOI>>5-HT>>tryptamine. The selective 5-HT₂ receptor antagonists, M-100907 (5-HT_2A), RS-127445 (5-HT_2B), and RS-102221 (5-HT_2C), produced noncompetitive inhibition of the contractile effects of selective agonists yielding antagonist potency (pK_B) values of 251 ± 27.2 nM (n = 4), 52.5 ± 6.3 nM (n = 4), and 79.4 ± 9.5 nM (n = 4), respectively.

CONCLUSION

On the basis of the profile of activity of selective agonists and antagonists, we conclude that the 5-HT_2B and 5-HT_2C receptor subtypes appear to be the predominant serotonin receptors that mediate the contractile action of this amine in bovine isolated ciliary muscles.

iDrugs and iDevices Discovery Research: Preclinical Assays, Techniques, and Animal Model Studies for Ocular Hypotensives and Neuroprotectants

Discovery ophthalmic research is centered around delineating the molecular and cellular basis of ocular diseases and finding and exploiting molecular and genetic pathways associated with them. From such studies it is possible to determine suitable intervention points to address the disease process and hopefully to discover therapeutics to treat them. An investigational new drug (IND) filing for a new small-molecule drug, peptide, antibody, genetic treatment, or a device with global health authorities requires a number of preclinical studies to provide necessary safety and efficacy data. Specific regulatory elements needed for such IND-enabling studies are beyond the scope of this article. However, to enhance the overall data packages for such entities and permit high-quality foundation-building publications for medical affairs, additional research and development studies are always desirable. This review aims to provide examples of some target localization/verification, ocular drug discovery processes, and mechanistic and portfolio-enhancing exploratory investigations for candidate drugs and devices for the treatment of ocular hypertension and glaucomatous optic neuropathy (neurodegeneration of retinal ganglion cells and their axons). Examples of compound screening assays, use of various technologies and techniques, deployment of animal models, and data obtained from such studies are also presented.

Human ciliary muscle cell responses to kinins: Activation of ERK1/2 and pro-matrix metalloproteinases secretion

AIM

To study activation of extracellular signal-regulated kinase-1/2 (ERK1/2) and pro-matrix metalloproteinases (pro-MMPs) secretion from isolated primary human ciliary muscle (h-CM) cells in response to bradykinin (BK) and other agonists.

METHODS

Serum-starved h-CM cells were challenged with vehicle, BK agonists or antagonists. Cell lysates were evaluated for phosphorylated ERK1/2 using homogeneous time-resolved fluorescence technology based on a sandwich immunoassay. Rabbit polyclonal anti-pro-MMP antibodies were used to measure pro-MMPs using immunoblot analysis.

RESULTS

A 10 min incubation time using 5 × 10⁴ h-CM cells/well was optimum condition for studying stimulation of ERK1/2 phosphorylation. BK (100 nmol/L) caused a 1.86 ± 0.26 fold (n = 3) increase in ERK1/2 phosphorylation above baseline. BK analogs, Met-Lys-BK and RMP-7 (100 nmol/L), also stimulated ERK1/2 phosphorylation by 1.57 ± 0.04 and 1.55 ± 0.09 fold, respectively. However, Des-Arg⁹-Bradykinin, a B₁ receptor-selective agonist (0.1-1 μmol/L), was essentially inactive. HOE-140 or WIN-64338 (B₂-antagonists) appreciably blocked phosphorylation of ERK1/2 induced by various BK agonists. Pre-treatment of cells with a prostaglandin (PG) synthase inhibitor (bromfenac; 1 μmol/L) failed to alter kinin-induced ERK1/2 activation. BK and a non-peptide BK agonist (FR-190997) (10 nmol/L-1 μmol/L) also enhanced pro-MMPs secretion (pro-MMP-1 > pro-MMP-3 > pro-MMP-2; 1.45-1.75-fold over baseline) from h-CM cells.

CONCLUSION

These collective data suggest that B₂ kinin receptors initiate signaling in h-CM cells by a relatively rapid mechanism (within minutes) involving ERK1/2 activation which in turn regulates MMPs production (within hours). The latter process does not involve PGs.

An explicit-solvent conformation search method using open software

Computer modeling is a popular tool to identify the most-probable conformers of a molecule. Although the solvent can have a large effect on the stability of a conformation, many popular conformational search methods are only capable of describing molecules in the gas phase or with an implicit solvent model. We have developed a work-flow for performing a conformation search on explicitly-solvated molecules using open source software. This method uses replica exchange molecular dynamics (REMD) to sample the conformational states of the molecule efficiently. Cluster analysis is used to identify the most probable conformations from the simulated trajectory. This work-flow was tested on drug molecules α-amanitin and cabergoline to illustrate its capabilities and effectiveness. The preferred conformations of these molecules in gas phase, implicit solvent, and explicit solvent are significantly different.

Novel potential treatment modalities for ocular hypertension: focus on angiotensin and bradykinin system axes

Despite the availability of modern surgical procedures, new drug delivery techniques, health authority-approved single topical ocular drugs, and combination products thereof, there continues to be an unmet medical need for novel treatment modalities for preserving vision. This is especially true for the treatment of glaucoma and the high risk factor often associated with this ocular disease, elevated intraocular pressure (IOP). Undesirable local or systemic side effects, frequency of dosing, lack of sustained IOP lowering, and lack of prevention of diurnal IOP spikes are among the greatest challenges. The very recent discovery, characterization, and publication of 2 novel IOP-lowering agents that pertain to the renin-angiotensin and kallikrein-kinin axes potentially offer novel means to treat and control ocular hypertension (OHT). Here, some contextual introductory information is provided first, followed by more detailed discussion of the properties and actions of diminazene aceturate (DIZE; a novel angiotensin-converting enzyme-2 activator) and FR-190997 (a nonpeptide bradykinin receptor-2 agonist) in relation to their anti-OHT activities in rodent and cynomolgus monkey eyes, respectively. It is anticipated that these compounds will pave the way for future discovery, development, and marketing of novel drugs to treat glaucoma and thus help save sight for millions of people afflicted with this slow progressive optic neuropathy.

Color Doppler analysis of uterine, spiral, and intraovarian artery blood flow before and after treatment with cabergoline in hyperprolactinemic patients

Prolactin (PRL) may have stimulatory effects on vascular resistance. We aimed to analyze uterine, spiral, and intraovarian artery blood flow by Doppler ultrasonography in hyperprolactinemic patients prior to and after treatment with cabergoline. The study was conducted in Sisli Etfal Training and Research Hospital gynecology outpatient clinic between 1 March 2010 and 30 September 2011. Twenty-four women with symptomatic hyperprolactinemia in reproduction age were included in the study. All hyperprolactinemic patients were studied prior to and following the suppression of circulating PRL levels by cabergoline. Patients were examined by standard B-mod and color transvaginal ultrasonography. Pulsality index (PI), resistance index (RI), and systolic/diastolic ratio (S/D) were recorded. The median PRL value was 86 (62-120) ng/ml before treatment and 4.0 (2.5-6.4) ng/ml after the treatment (p < 0.001). We found a significant association among PRL, uterine, spiral, and intraovarian artery RI with linear regression analysis (p < 0.001 for all three arteries). Uterine, spiral, and intraovarian artery PI (p = 0.021, p < 0.001, and p < 0.001, respectively) and RI (p = 0.001, p < 0.001, and p < 0.001, respectively) significantly decreased after cabergoline treatment. In conclusion, this is a pilot study which shows for the first time that PRL increases the uterine, endometrial, and intraovarian vascular resistance and cabergoline reverses this effect.

Preclinical pharmacology, ocular tolerability and ocular hypotensive efficacy of a novel non-peptide bradykinin mimetic small molecule

We sought to characterize the ocular pharmacology, tolerability and intraocular pressure (IOP)-lowering efficacy of FR-190997, a non-peptidic bradykinin (BK) B2-receptor agonist. FR-190997 possessed a relatively high receptor binding affinity (Ki = 27 nM) and a high in vitro potency (EC50 = 18.3 ± 4.4 nM) for inositol-1-phosphate generation via human cloned B2-receptors expressed in host cells with mimimal activity at B1-receptors. It also mobilized intracellular Ca2+ in isolated human trabecular meshwork (h-TM), ciliary muscle (h-CM), and in immortalized non-pigmented ciliary epithelial (h-iNPE) cells (EC50s = 167-384 nM; Emax = 32-86% of BK-induced response). HOE-140, a selective B2-receptor antagonist, potently blocked the latter effects of FR-190997 (e.g., IC50 = 7.3 ± 0.6 nM in h-CM cells). FR-190997 also stimulated the release of prostaglandins (PGs) from h-TM and h-CM cells (EC50s = 60-84 nM; Emax = 29-44% relative to max. BK-induced effects). FR-190997 (0.3-300 μg t.o.) did not activate cat corneal polymodal nociceptors and did not cause ocular discomfort in Dutch-Belted rabbits, but it was not well tolerated in New Zealand albino rabbits and Hartley guinea pigs. A single topical ocular (t.o.) dose of 1% FR-190997 in Dutch-Belted rabbits and mixed breed cats did not lower IOP. However, FR-190997 efficaciously lowered IOP of conscious ocular hypertensive cynomolgus monkey eyes (e.g., 34.5 ± 7.5% decrease; 6 h post-dose of 30 μg t.o.; n = 8). Thus, FR-190997 is an unexampled efficacious ocular hypotensive B2-receptor non-peptide BK agonist that activates multiple signaling pathways to cause IOP reduction.

FR-190997, a nonpeptide bradykinin B2-receptor partial agonist, is a potent and efficacious intraocular pressure lowering agent in ocular hypertensive cynomolgus monkeys

Preclinical Research FR-190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl) cinnaminoacetyl]-N-methylamino]benzyloxy]-2-methyl-4- (2-pyridylmethoxy) quinoline), a nonpeptide bradykinin (BK) B2-receptor-selective agonist, represents a novel class of ocular hypotensive agents. FR-190997 exhibited a high affinity for the human cloned B2-receptor (Ki = 9.8 nM) and a relatively high potency (EC50 = 155 nM) for mobilizing intracellular Ca(2+) ([Ca(2+)]i) in human ocular cells from nonpigmented ciliary epithelium; trabecular meshwork [h-TM]; ciliary muscle [h-CM] that are involved in regulating intraocular pressure (IOP). Unlike BK, FR-190997 behaved as a partial agonist (Emax = 38-80%) in these cells and its [Ca(2+)]i-mobilizing effects were blocked by the B2-receptor-selective antagonists (HOE-140, Ki = 0.8-7 nM; WIN-64338, Ki = 157-425 nM). FR-190997 stimulated the production of prostaglandins (PGs) in h-CM and h-TM cells (EC50 = 15-19 nM; Emax = 27-33%); an effect that was reduced by the cyclooxygenase-2 inhibitor bromfenac, and by HOE-140. FR-190997 also induced pro-matrix metalloproteinase (MMP)-1 and MMP-3 release from h-CM cells. FR-190997 significantly lowered IOP (37% [P < 0.001] with 30 μg, 24 h post-topical ocular dosing) in ocular hypertensive eyes of conscious Cynomolgus monkeys. This effect was reduced by bromfenac and completely blocked by a B2-antagonist. FR-190997 primarily stimulated uveoslceral outflow (UVSO) of aqueous humor (2.6 to 3.9-fold above baseline). In conclusion, FR-190997 is a B2-receptor selective partial agonist that activates phospholipase C, mobilizes [Ca(2+)]; induces PG and pro-MMP production, and that profoundly lowers IOP by promoting UVSO in ocular hypertensive Cynomolgus monkey eyes.

Predictive in silico studies of human 5-hydroxytryptamine receptor subtype 2B (5-HT2B) and valvular heart disease

Serotonin (5-hydroxytryptamine, 5-HT) receptors are neuromodulator neurotransmitter receptors which when activated trigger a signal transduction cascade within cells resulting in cell-cell communication. 5-hydroxytryptamine receptor 2B (5-HT2B) is a subtype of the seven members of 5-hydroxytrytamine receptors family which is the largest member of the super family of 7-transmembrane G-protein coupled receptors (GPCRs). Not only do 5-HT receptors play physiological roles in the cardiovascular system, gastrointestinal and endocrine function as well as the central nervous system, but they also play a role in behavioral functions. In particular 5-HT2B receptor is widely spread with regards to its distribution throughout bodily tissues and is expressed at high levels in the lungs, peripheral tissues, liver, kidneys and prostate, just to name a few. Hence 5-HT2B participates in multiple biological functions including CNS regulation, regulation of gastrointestinal motality, cardiovascular regulation and 5-HT transport system regulation. While 5-HT2B is a viable drug target and has therapeutic indications for treating obesity, psychosis, Parkinson's disease etc. there is a growing concern regarding adverse drug reactions, specifically valvulopathy associated with 5-HT2B agonists. Due to the sequence homology experienced by 5-HT2 subtypes there is also a concern regarding the off-target effects of 5-HT2A and 5-HT2C agonists. The concepts of sensitivity and subtype selectivity are of paramount importance and now can be tackled with the aid of in silico studies, especially cheminformatics, to develop models to predict valvulopathy associated toxicity of drug candidates prior to clinical trials. This review has highlighted three in silico approaches thus far that have been successful in either predicting 5-HT2B toxicity of molecules or identifying important interactions between 5-HT2B and drug molecules that bring about valvulopathy related toxicities.

Regulation of intraocular pressure in mice: structural analysis of dopaminergic and serotonergic systems in response to cabergoline

Elevated intraocular pressure (IOP) is the main recognized risk factor of glaucoma. To investigate the contribution of dopaminergic and serotonergic systems in IOP regulation, we used cabergoline, a mixed dopamine and serotonin agonist, in C57BL/6J WT and dopamine D₃ receptor knock-out (D₃R⁻/⁻) mice with normal eye pressure or steroid-induced ocular hypertension. Furthermore, we studied the structural basis of the cabergoline-mediated activation of the dopaminergic and serotonergic systems by molecular modeling. Topical application of cabergoline, significantly decreased, in a dose-dependent manner, the intraocular pressure in WT mice, both in an ocular normotensive group (-9, -5 and -2 mmHg with 5%, 1%, and 0.1%, respectively) and an ocular hypertensive group, with a prolonged effect in this latter group. No change of intraocular pressure was observed after topical application of cabergoline in D₃R⁻/⁻ mice. We modeled and optimized, with molecular dynamics, structures of hD₃, h5HT(1A) and h5HT(2A-C) receptors; thereafter we carried out molecular docking of cabergoline. Docking revealed that binding of cabergoline into D₃ and 5HT(1A) receptors is associated with a better desolvation energy in comparison to 5HT(2A-C) binding. In conclusion, the present study support the hypothesis that dopaminergic system is pivotal to regulate IOP and that D₃R represents an intriguing target in the treatment of glaucoma. Furthermore, the structure-based computational approach adopted in this study is able to build and refine structure models of homologous dopaminergic and serotonergic receptors that may be of interest for structure-based drug discovery of ligands, with dopaminergic selectivity or with multi-pharmacological profile, potentially useful to treat optic neuropathies.

Dopamine D₂ receptor modulation of human response inhibition and error awareness

Response inhibition, comprising action cancellation and action restraint, and error awareness are executive functions of considerable clinical relevance to neuropsychiatric disorders. Nevertheless, our understanding of their underlying catecholamine mechanisms, particularly regarding dopamine, is limited. Here, we used the dopamine D2 agonist cabergoline to study its ability to improve inhibitory control and modulate awareness of performance errors. A randomized, double-blind, placebo-controlled, crossover design with a single dose of cabergoline (1.25 mg) and placebo (dextrose) was employed in 25 healthy participants. They each performed the stop-signal task, a well-validated measure of action cancellation, and the Error Awareness Task, a go/no-go measure of action restraint and error awareness, under each drug condition. Cabergoline was able to selectively reduce stop-signal RT, compared with placebo, indicative of enhanced action cancellation (p < .05). This enhancement occurred without concomitant changes in overall response speed or RT variability and was not seen for errors of commission on the Error Awareness Task. Awareness of performance errors on the go/no-go task was, however, significantly improved by cabergoline compared with placebo (p < .05). Our results contribute to growing evidence for the dopaminergic control of distinct aspects of human executive ability, namely, action cancellation and error awareness. The findings may aid the development of new, or the repurposing of existing, pharmacotherapy that targets the cognitive dysfunction of psychiatric and neurological disorders. They also provide further evidence that specific cognitive paradigms have correspondingly specific neurochemical bases.

Dopamine receptor agonists for the treatment of early or advanced Parkinson's disease

Dopamine receptor agonists are indicated for the symptomatic treatment of early, moderate or advanced Parkinson's disease as well as for the reduction of levodopa-related motor complications. Ergolinic dopamine agonists, such as bromocriptine or pergolide, were initially developed and marketed, and then non-ergolinic dopamine agonists, such as pramipexole and ropinirole, were introduced, reducing the risk of drug-induced fibrotic reactions. Once-daily, controlled-release oral and transdermal formulations have been developed aiming at providing more stable 24-hour plasma drug concentrations and more convenient administration. A disease-modifying effect of dopamine agonists has not been demonstrated clinically. As with any other drug, dopamine agonists can also cause adverse drug reactions, which can be related or unrelated to dopaminergic hyperactivation. Dopaminergic reactions include nausea, hallucinations, confusion and orthostatic hypotension, among others, which were readily identified in pre-marketing clinical trials. During post-marketing surveillance, important adverse reactions were identified, such as daytime somnolence, impulse-control disorders and heart valve fibrosis. Other issues, including the efficacy of dopamine agonists for the treatment of non-motor symptoms, remain under evaluation.