Serotonin 5-HT3 Receptor Research Articles

Efficacy of Prucalopride in bowel cleansing before colonoscopy: Results of a pilot study

Colonoscopy is a crucial diagnostic instrument for colorectal cancer screening and an adequate bowel preparation is definitely decisive for the success of the procedure. Especially in elderly patients, bowel cleansing is considered a big issue, because it is often poorly tolerated for many reasons (like inability to swallow large volume of liquids or unlikable taste); this can cause a suboptimal preparation that may lead to miss a neoplastic lesion. There is relatively little data about how to improve preparation tolerability. The purpose of our pilot study was to analyze the effect of prucalopride (Resolor®), a highly selective serotonin 5HT4 receptor agonist used for chronic constipation for its ability to stimulate gastrointestinal peristalsis, undertaken the day before colonoscopy, followed by half volume of polyethylene glycol solution. We found that this can be a good and safe method to achieve an adequate and better-tolerated colon cleansing.

MiR-16 and miR-103 impact 5-HT4 receptor signalling and correlate with symptom profile in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a gut-brain disorder involving alterations in intestinal sensitivity and motility. Serotonin 5-HT4 receptors are promising candidates in IBS pathophysiology since they regulate gut motor function and stool consistency, and targeted 5-HT4R selective drug intervention has been proven beneficial in subgroups of patients. We identified a single nucleotide polymorphism (SNP) (rs201253747) c.*61 T > C within the 5-HT4 receptor gene HTR4 to be predominantly present in diarrhoea-IBS patients (IBS-D). It affects a binding site for the miR-16 family and miR-103/miR-107 within the isoforms HTR4b/i and putatively impairs HTR4 expression. Subsequent miRNA-profiling revealed downregulation of miR-16 and miR-103 in the jejunum of IBS-D patients correlating with symptoms. In vitro assays confirmed expression regulation via three 3′UTR binding sites. The novel isoform HTR4b_2 lacking two of the three miRNA binding sites escapes miR-16/103/107 regulation in SNP carriers. We provide the first evidence that HTR4 expression is fine-tuned by miRNAs, and that this regulation is impaired either by the SNP c.*61 T > C or by diminished levels of miR-16 and miR-103 suggesting that HTR4 might be involved in the development of IBS-D.

Blockade of 5-HT3 receptors with granisetron does not affect trigeminothalamic nociceptive transmission in rats: Implication for migraine.

One way to expand the existing range of anti-migraine drugs seems to be the search for pharmacological agents with anti-cephalalgic properties among medicines approved for clinical indications other than migraine. Numerous experimental and clinical data imply that selective serotonin 5-HT3 receptor antagonists can be considered as potential anti-migraine agents. Therefore, the objective of our work was to examine the impact of selective 5-HT3 receptor blockade with granisetron on migraine-related nociceptive transmission within the spinal trigeminal nucleus (STN) and the ventroposteromedial nucleus of the thalamus (VPM). Using an electrophysiological model of trigemino-durovascular nociception in anaesthetised male Wistar rats, we evaluated the effects of intravenous administration of granisetron on ongoing firing and dural electrical stimulation-evoked responses of the spinal trigeminal and thalamic cells. Granisetron did not substantially affect responses of the STN and VPM neurons to electrical stimulation of the dura mater as well as did not cause steady changes in ongoing firing of the spinal trigeminal cells. The results obtained argue against the use of 5-HT3 receptor antagonists for treating migraine. These data also lead to the conclusion that in the absence of sustained sensitisation of neurons along the trigemino-thalamo-cortical pathway the role of 5-HT3 receptor-dependent mechanisms in serotonergic modulation of trigeminovascular nociceptive transmission can hardly be considered crucial.

Outpatient Co-prescription of Ondansetron With Other QT-Prolonging Drugs in a Large Community-Based Health System: A Warning Ignored

Introduction: Ondansetron is a 5HT-3 serotonin receptor antagonist that is commonly used to treat nausea and vomiting. The FDA has warned of QT-prolonging effects of ondansetron, especially when combined with other QT-prolonging drugs, or in patients with known cardiac disease. Electronic medical records with warning systems for drug-drug interactions have been promoted for patient safety. We present a review of de-identified data from a large community-based health system to determine how providers responded to electronic warnings when prescribing ondansetron combined with other QT-prolonging drugs. Methods: All prescriptions for ondansetron in combination with QT-prolonging drugs at NorthShore University HealthSystem between January and March 2016 were included in the initial database as part of a quality improvement project. Inpatient orders and IV ondansetron orders were removed. The name and class of co-prescribed QT-prolonging drugs, warning severity, response to the warning by prescribing practitioner (over-ride warning and prescribe, or cancel order), reason for the warning over-ride, patient age and gender were evaluated. Results: There were a total of 9203 episodes of co-prescription of ondansetron and another QT-prolonging drug in 2739 adult patients during the study time period. After filtering, there were 770 outpatient co-prescriptions in 500 patients. Mean patient age was 46.2 years (range 18 to 90 years). Orders were for 592 females (76.8%) and 178 males (33.2%). All warnings were considered “major interactions”. Most orders, 651 (84.5%) prescriptions were administered, while only 119 (15.5%) orders were canceled. The most common classes of co-prescribed QT-prolonging drugs were macrolide antibiotics (40.0%), flouroquinolone antibiotics (17.0%), SARI antidepressants (13.4%), and SSRI antidepressants (9.9%), (Table 1). There were nine (1.4%) cases of co-prescriptions with antiarrhythmic drugs (amioderone and flecainide). The most commonly co-prescribed QT-prolonging medications were azithromycin, levofloxacin, and trazadone (Table 2). Reasons for warning overrides were “benefit outweighs risk” in 266 (40.8%) and “not clinically significant” in 116 cases (17.7%).Table: Table. Classes of Drugs Co-Prescribed with OndansentronTable: Table. List of Drugs Co-Prescribed with OndansetronConclusion: After viewing warnings, practitioners still prescribed ondansetron with other QT-prolonging drugs 85% of the time. This form of co-prescription with ondansetron neglects FDA recommendations and could put patients at risk for cardiac arrhythmias.

Laminar and Cellular Distribution of Monoamine Receptors in Rat Medial Prefrontal Cortex.

The prefrontal cortex (PFC) is deeply involved in higher brain functions, many of which are altered in psychiatric conditions. The PFC exerts a top-down control of most cortical and subcortical areas through descending pathways and is densely innervated by axons emerging from the brainstem monoamine cell groups, namely, the dorsal and median raphe nuclei (DR and MnR, respectively), the ventral tegmental area and the locus coeruleus (LC). In turn, the activity of these cell groups is tightly controlled by afferent pathways arising from layer V PFC pyramidal neurons. The reciprocal connectivity between PFC and monoamine cell groups is of interest to study the pathophysiology and treatment of severe psychiatric disorders, such as major depression and schizophrenia, inasmuch as antidepressant and antipsychotic drugs target monoamine receptors/transporters expressed in these areas. Here we review previous reports examining the presence of monoamine receptors in pyramidal and GABAergic neurons of the PFC using double in situ hybridization. Additionally, we present new data on the quantitative layer distribution (layers I, II–III, V, and VI) of monoamine receptor-expressing cells in the cingulate (Cg), prelimbic (PrL) and infralimbic (IL) subfields of the medial PFC (mPFC). The receptors examined include serotonin 5-HT1A, 5-HT2A, 5-HT2C, and 5-HT3, dopamine D1 and D2 receptors, and α1A-, α1B-, and α1D-adrenoceptors. With the exception of 5-HT3 receptors, selectively expressed by layers I–III GABA interneurons, the rest of monoamine receptors are widely expressed by pyramidal and GABAergic neurons in intermediate and deep layers of mPFC (5-HT2C receptors are also expressed in layer I). This complex distribution suggests that monoamines may modulate the communications between PFC and cortical/subcortical areas through the activation of receptors expressed by neurons in intermediate (e.g., 5-HT1A, 5-HT2A, α1D-adrenoceptors, dopamine D1 receptors) and deep layers (e.g., 5-HT1A, 5-HT2A, α1A-adrenoceptors, dopamine D2 receptors), respectively. Overall, these data provide a detailed framework to better understand the role of monoamines in the processing of cognitive and emotional signals by the PFC. Likewise, they may be helpful to characterize brain circuits relevant for the therapeutic action of antidepressant and antipsychotic drugs and to improve their therapeutic action, overcoming the limitations of current drugs.

Serotonin 5-HT6 receptors affect cognition in a mouse model of Alzheimer\u2019s disease by regulating cilia function

BackgroundSerotonin receptor 5-HT6 is involved in cognition and Alzheimer’s disease (AD) development. However, the mechanism of 5-HT6 in AD pathology is not clear.MethodsSince 5-HT6 is almost exclusively expressed in the primary cilia, using immunostaining we examined the number of cilia in the hippocampus of AD animal model APP/PS1 mice. By overexpressing and knocking down 5-HT6 in the primary cultured hippocampal neurons, we investigated the roles of 5-HT6 in alternating ciliary morphology. Furthermore, 5-HT6 antagonist was applied to confirm its roles in cognition using the Morris water maze test, Y maze, and fear conditioning.ResultsIn the present study, we found that the primary cilia were elongated in the hippocampus of APP/PS1 mice compared with WT mice. 5-HT6 regulated cilia length, influenced cilia and axon initial segment (AIS) morphology, and affected localization of ARL13B and AnkG. We also found that, by changing cilia morphology, the AIS was elongated, branched, and more proximal to the cell body in both WT and APP/PS1 mouse neurons. Alterations of cilia also decreased the axonal length in WT and APP/PS1 neurons. Furthermore, in the water maze test, Y maze, and fear conditioning test, 5-HT6 antagonist SB271046 recovered the cognitive impairment of APP/PS1 mice.ConclusionWe suggest that 5-HT6 plays a critical role in AD development through regulating the morphology and function of neuronal primary cilia, which is possibly related to the AIS and axon alterations in AD development.

Ondansetron Does Not Reduce Withdrawal in Patients With Physical Dependence on Chronic Opioid Therapy.

Individuals taking opioids for an extended period of time may become physically dependent, and will therefore experience opioid withdrawal should they stop taking the medication. Previous work in animal and human models has shown that the serotonin (5-HT3) receptor may be implicated in opioid withdrawal. In this study, we investigated if ondansetron, a 5-HT3-receptor antagonist, could reduce the symptoms of opioid withdrawal after chronic opioid exposure in humans. In this double-blinded, randomized, crossover study, 33 chronic back pain patients (N = 33) were titrated onto sustained-release oral morphine for 30 days. After titration, participants attended 2 study sessions, 1 week apart, in which opioid withdrawal was induced with intravenous naloxone, with or without 8 mg intravenous ondansetron pretreatment. Opioid withdrawal symptoms were assessed by a blinded research assistant (objective opioid withdrawal score [OOWS]) and by the research participant (subjective opioid withdrawal score [SOWS]). Clinically significant signs of withdrawal were observed during both the ondansetron (ΔOOWS = 3.58 ± 2.22, P < 0.0001; ΔSOWS = 12.48 ± 11.18, P < 0.0001) and placebo sessions (ΔOOWS = 3.55 ± 2.39, P < 0.0001; ΔSOWS = 12.21 ± 10.72, P < 0.0001), but no significant differences were seen between the treatment sessions in either the OOWS or SOWS scores. We hypothesized that ondansetron would reduce opioid withdrawal symptoms in human subjects, but found no difference in withdrawal severity between ondansetron and placebo sessions. These findings suggest that more investigation may be necessary to determine if 5-HT3-receptor antagonists are suitable treatment options for opioid withdrawal.

Different Role of CA1 5HT3 Serotonin Receptors on Memory Acquisition Deficit Induced by Total (TSD) and REM Sleep Deprivation (RSD).

Serotonin receptors such as 5-HT3 plays critical role in regulation of sleep, wake cycle and cognitive process. Thus, we investigated the role of CA1 5HT3 serotonin receptors in memory acquisition deficit induced by total sleep deprivation (TSD; for 24 hour) and REM sleep deprivation (RSD; for 24 hour). Pain perception and locomotor activity were also assessed as factors that may affect the memory process. Modified water box and multi-platform apparatus were used to induce TSD or RSD, respectively. Passive avoidance, hot plate and open field devices were used for assessment of memory acquisition, pain and locomotor activity, respectively. Totally, 152 male Wistar rats were used in the study. Pre-training, intra-CA1 injection of 5-HT3 receptor agonist Chlorophenylbiguanide (Mchl; 0.01 and 0.001 µg/rat; P < 0.001) and antagonist Y-25130 (0.1 µg/rat; P < 0.001) reduced memory acquisition and did not alter pain response, while higher dose of both drugs increased locomotor activity in normal rats. Both TSD and RSD reduced memory acquisition (P < 0.001) and did not alter locomotor activity, while TSD (P < 0.001) but not RSD induced analgesia effect. The amnesia induced by TSD was restored by subthreshold dose of Y25130 (0.001 µg/rat; P < 0.001) but not Mchl (0.0001 µg/rat), while both drugs reversed TSD-induced analgesia effect (P < 0.01 for Mchl and P < 0.05 for Y25130), and Y25130 increased locomotor activity in TSD rats (P < 0.05). In RSD rats, subthreshold dose of both drugs did not alter memory acquisition deficit and increased locomotor activity (P < 0.001 for Mchl and P < 0.01 for Y25130), while the Y25130 (P < 0.001), but not Mchl induced analgesia in the RSD rats. Based on the above data, CA1 5HT3 receptors seem to play a critical role in cognitive and non-cognitive behaviors induced by TSD and RSD.

Do patients receiving pelvic radiation and anti-emetics experience diarrhea and/or constipation?

Pelvic radiation may cause radiation enteritis, which commonly manifests as diarrhea. Radiation to the abdomen or pelvis may also cause radiation-induced nausea and vomiting (RINV) which is often treated with anti-emetics such as serotonin (5-HT3) receptor antagonists (RA). However, a common side effect of these anti-emetic medications is constipation. Both diarrhea and constipation can have a significant impact on patient quality of life (QOL). The objective of this study was to assess the prevalence of diarrhea and constipation in patients receiving pelvic radiation and anti-emetics. Patients undergoing pelvic radiation between January 2011 and March 2017 at Sunnybrook Odette Cancer Centre were enrolled in three prospective clinical trials studying the efficacy of various anti-emetics for RINV prophylaxis. Patients completed QOL questionnaires which included a single question about severity of constipation at baseline, day 5 and 10 during radiation if applicable, and day 5 and 10 after completion of radiation; severity was measured on a 4-point Likert scale ranging from 1= "not at all" to 4= "very much". Patients also recorded severity of diarrhea throughout baseline, treatment, and 10 days follow-up via daily diaries; responses were qualitative ranging from "no diarrhea" to "severe diarrhea" on a 4-point scale. Fifty-nine patients received pelvic radiation across the three trials. The average constipation score at baseline was 1.69 [standard deviation (SD) 0.93], and increased up to 2.33 (SD 1.03) at day 10 during treatment. Following treatment, the average score decreased to 1.61 (SD 0.80) at day 10 follow-up with the majority of patients reporting no constipation at this time (57.7%). The average diarrhea score at baseline was 1.03 (SD 0.18) and remained stable throughout treatment and follow-up. A vast majority of patients reported no diarrhea after day 10 follow-up (96.4%). Constipation was more prevalent than diarrhea during radiation treatment and up to day 10 after radiation to the pelvis. Approximately 42% of patients will have constipation on day 10 post radiation. Further research is needed to assess the causes of constipation including analgesics, and the effect on QOL during and shortly after palliative radiation to the pelvis.

Cyclic AMP-regulated opposing and parallel effects of serotonin and dopamine on phototaxis in the Marmorkrebs (marbled crayfish).

Phototactic behaviours are observed from prokaryotes to amphibians and are a basic form of orientation. We showed that the marbled crayfish displays phototaxis in which the behavioural response reversed from negative to positive depending on external light conditions. Animals reared in a 12-L/12-D light cycle showed negative phototaxis during daytime and positive phototaxis during night-time. Animals reared under constant light conditioning showed negative phototaxis during day- and night-time, while animals reared under constant dark conditioning showed positive phototaxis during day- and night-time. Injection of serotonin leads to a reversal of negative to positive phototaxis in both light/dark-reared and light/light-reared animals while injection of dopamine induced reversed negative phototaxis in dark/dark-reared animals. Four hours of dark adaptation were enough for light/dark-reared animals to reverse phototaxis from negative to positive. Injection of a serotonin 5HT1 receptor antagonist blocked the reverse phototaxis while serotonin 5HT2 receptor antagonists had no effects. Similarly, dark/dark-reared animals reversed to showing negative phototaxis after 4h of light adaptation. Injection of a dopamine DA1 receptor antagonist blocked this reverse phototaxis, while dopamine DA2 receptor antagonists had no effects. Injection of a cAMP analogue into light/dark-reared animals blocked reverse phototaxis after dark adaptation, while adenylate cyclase inhibitor in dark/dark-reared animals blocked reverse phototaxis after light adaptation. These results strongly suggest that serotonin mediates positive phototaxis owing to decreased cAMP levels, while dopamine-mediated negative phototaxis occurs due to increased cAMP levels. Supporting this, the ratio of serotonin to dopamine in the brain was much higher in dark/dark-reared than light/dark-reared animals.

Characterization and Reliability of [18F]2FNQ1P in Cynomolgus Monkeys as a PET Radiotracer for Serotonin 5-HT6 Receptors.

Brain serotonin-6 receptor (5-HT6R) is the one of the most recently identified serotonin receptors. Accumulating evidence suggests that it is a potent therapeutic target for psychiatric and neurological diseases. Since [18F]2FNQ1P was recently proposed as the first fluorinated positron emission tomography (PET) radioligand for this receptor, the objective of the present study was to demonstrate its suitability for 5-HT6R neuroimaging in primates. [18F]2FNQ1P was characterized by in vitro autoradiography and in vivo PET imaging in cynomolgus monkeys. Following in vivo PET imaging, tracer binding indices were computed using the simplified reference tissue model and Logan graphical model, with cerebellum as reference region. The tracer binding reproducibility was assessed by test–retest in five animals. Finally, specificity was assessed by pre-injection of a 5-HT6R antagonist, SB258585. In vitro, results showed wide cerebral distribution of the tracer with specificity toward 5-HT6Rs as binding was effectively displaced by SB258585. In vivo brain penetration was good with reproducible distribution at cortical and subcortical levels. The automated method gave the best spatial normalization. The Logan graphical model showed the best tracer binding indices, giving the highest magnitude, lowest standard deviation and best reproducibility and robustness. Finally, 5-HT6R antagonist pre-injection significantly decreased [18F]2FNQ1P binding mainly in the striatum and sensorimotor cortex. Taken together, these preclinical results show that [18F]2FNQ1P is a good candidate to address 5-HT6 receptors in clinical studies.

Preliminary safety and efficacy profile of prucalopride in the treatment of systemic sclerosis (SSc)-related intestinal involvement: results from the open label cross-over PROGASS study

BackgroundProkinetics are used to treat enteric dismotility symptoms in systemic sclerosis (SSc) patients, but they often lack adequate efficacy. The most effective prokinetics belonging to the serotonin (5-HT4) receptor agonists class were withdrawn due to cardiac toxicity in relation to modest 5-HT4 receptor affinity. Prucalopride is a high-affinity 5-HT4 receptor agonist with no major cardiac issues, for which the efficacy in SSc has not yet been assessed.MethodsForty patients with self-reported mild to moderately severe enteric symptoms were enrolled in a cross-over 2 × 2 study. Subjects were randomized 1:1 to prucalopride 2 mg/day or no treatment for one month and vice versa after a 2-week washout period. Before and after each sequence the patients compiled the University of California Los Angeles gastrointestinal tract (UCLA GIT) 2.0 questionnaire and the numbers of complete intestinal movements were recorded. Oro-cecal transit time (OCTT) was evaluated by lactulose breath test in a subgroup of patients. Data were evaluated by mixed linear models corrected for the number of laxatives used during the study periods.ResultsThere were 29 subjects who completed the study; 7 subjects withdrew due to side-effects and 4 subjects were not compliant with the study procedures. As compared to dummy treatment, prucalopride was associated with more intestinal evacuations (p < 0.001), improvement of UCLA GIT constipation (-0.672 ± 0.112 vs 0.086 ± 0.115; p < 0.001), reflux (-0.409 ± 0.094 vs 0.01 ± 0.096; p < 0.005) and bloating (-0.418 ± 0.088 vs -0.084 ± 0.09; p = 0.01) scores. Treatment was ranked moderately to more than moderately effective by 22 patients (72.4%). OCTT was significantly reduced during prucalopruide consumption (prucalopride: -20.1 ± 20.1 vs no treatment: 45.8 ± 21.3 minutes; treatment effect = -65.9 minutes; p = 0.035).ConclusionsThe safety profile of prucalopride in SSc is similar to what is known from the literature. In patients with mild to severe gastrointestinal problems, prucalopride may be effective in treating dismotility symptoms, increasing the number of complete bowel movements and improving bowel transit, reducing reflux disease and bloating.Trial registrationEU Clinical Trial Registry, EudraCT2012-005348-92. Registered on 19 February 2013.

Ephedrine Versus Ondansetron in the Prevention of Hypotension During Cesarean Delivery: A Randomized, Double-blind, Placebo-controlled Trial

(Int J Obstet Anesth. 2016;27:25–31) Maternal hypotension is a common complication of spinal anesthesia for cesarean delivery. This can lead to bothersome side effects such as nausea and vomiting as well as more serious consequences like fetal hypoxia and acidosis. Phenylephrine and ephedrine are typically administered for the prevention and/or treatment of spinal-induced hypotension. However, some studies in the past few years have shown that ondansetron, a serotonin (5-HT3) receptor antagonist, was effective at preventing spinal-induced hypotension. It has been hypothesized that ondansetron prevents hypotension by inhibition of the Bezold-Jarisch reflex. This current randomized, double-blind study compared the efficacy of ephedrine and ondansetron for the prevention of maternal hypotension in parturients receiving spinal anesthesia for elective cesarean delivery.

The anti-asthmatic drug pranlukast suppresses the delayed-phase vomiting and reverses intracellular indices of emesis evoked by cisplatin in the least shrew (Cryptotis parva)

The introduction of second generation serotonin 5-HT3 receptor (5-HT3) antagonist palonosetron combined with long-acting substance P neurokinin NK1 receptor (NK1) antagonists (e.g. netupitant) has substantially improved antiemetic therapy against early- and delayed-phases of emesis caused by highly emetogenic chemotherapeutics such as cisplatin. However, the improved efficacy comes at a cost that many patients cannot afford. We introduce a new class of antiemetic, the antiasthmatic leukotriene CysLT1 receptor antagonist pranlukast for the suppression of cisplatin-evoked vomiting. Pranlukast (10mg/kg) by itself significantly reduced the mean frequency of vomits (70%) and fully protected least shrews from vomiting (46%) during the delayed-phase of cisplatin (10mg/kg)-evoked vomiting. Although, pranlukast tended to substantially reduce both the mean frequency of vomits and the number of shrews vomiting during the early-phase, these reductions failed to attain significance. When combined with a first (tropisetron)- or a second (palonosetron)-generation 5-HT3 receptor antagonist, pranlukast potentiated their antiemetic efficacy during both phases of vomiting. In addition, pranlukast by itself prevented several intracellular signal markers of cisplatin-evoked delayed-vomiting such as phosphorylation of ERK1/2 and PKA. When pranlukast was combined with either palonosetron or tropisetron, these combinations suppressed the evoked phosphorylation of: i) ERK1/2 during both acute- and delayed-phase, ii) PKCα/β at the peak acute-phase, and iii) PKA at the peak delayed-phase. The current and our published findings suggest that overall behavioral and intracellular signaling effects of pranlukast via blockade of CysLT1 receptors generally appear to be similar to the NK1 receptor antagonist netupitant with some differences.

1-(4-[18F]Fluorobenzyl)-4-[(tetrahydrofuran-2-yl)methyl]piperazine: A Novel Suitable Radioligand with Low Lipophilicity for Imaging σ1 Receptors in the Brain.

We have designed and synthesized novel piperazine compounds with low lipophilicity as σ1 receptor ligands. 1-(4-Fluorobenzyl)-4-[(tetrahydrofuran-2-yl)methyl]piperazine (10) possessed a low nanomolar σ1 receptor affinity and a high selectivity toward the vesicular acetylcholine transporter (>2000-fold), σ2 receptors (52-fold), and adenosine A2A, adrenergic α2, cannabinoid CB1, dopamine D1, D2L, γ-aminobutyric acid A (GABAA), NMDA, melatonin MT1, MT2, and serotonin 5-HT1 receptors. The corresponding radiotracer [18F]10 demonstrated high brain uptake and extremely high brain-to-blood ratios in biodistribution studies in mice. Pretreatment with the selective σ1 receptor agonist SA4503 significantly reduced the level of accumulation of the radiotracer in the brain. No radiometabolite of [18F]10 was observed to enter the brain. Positron emission tomography and magnetic resonance imaging confirmed suitable kinetics and a high specific binding of [18F]10 to σ1 receptors in rat brain. Ex vivo autoradiography showed a reduced level of binding of [18F]10 in the cortex and hippocampus of the senescence-accelerated prone (SAMP8) compared to that of the senescence-accelerated resistant (SAMR1) mice, indicating the potential dysfunction of σ1 receptors in Alzheimer's disease.

Development of assay for determination of eletriptan hydrobromide in loaded PLGA nanoparticles

Eletriptan Hydrobromide is a serotonin 5-HT1 receptor agonist and it used for the treatment of migraine headaches with or without aura. Even if the drug is well absorbed after oral administration, it has some drawbacks like first pass metabolism and decrease in bioavailability after migraine attacks. Encapsulation of drug into polymeric nanoparticles is one of the methods for protecting the drug against degradation. The present work described a preparation of Eletriptan Hydrobromide loaded poly (d,l-lactide-co-glycolide) nanoparticles prepared using o/w single emulsion solvent evaporation method. In order to determine the factors affecting the physicochemical properties of the nanoparticles on the particle size of poly (d,l-lactide-co-glycolide) nanoparticles, D-Optimal design is used. Moreover, novel, simple, sensitive, selective, and fully validated chromatographic technique for the quantification of Eletriptan Hydrobromide from Eletriptan Hydrobromide loaded poly(d,l-lactide-co-glycolide) nanoparticles was developed. Poly(d,l-lactide-co-glycolide) concentration, sonication time and sonication energy were found as significant factors (p<0.05) on particle size of nanoparticles. Limit of detection and limit of quantification values were calculated as 0.28μgmL−1and 0.86μgmL−1, respectively.

Patent highlights December 2016-January 2017.

Patent highlights December 2016-January 2017.

Synaptic Remodeling Depends on Signaling between Serotonin Receptors and the Extracellular Matrix

Rewiring of synaptic circuitry pertinent to memory formation has been associated with morphological changes in dendritic spines and with extracellular matrix (ECM) remodeling. Here, we mechanistically link these processes by uncovering a signaling pathway involving the serotonin 5-HT7 receptor (5-HT7R), matrix metalloproteinase 9 (MMP-9), the hyaluronan receptor CD44, and the small GTPase Cdc42. We highlight a physical interaction between 5-HT7R and CD44 (identified as an MMP-9 substrate in neurons) and find that 5-HT7R stimulation increases local MMP-9 activity, triggering dendritic spine remodeling, synaptic pruning, and impairment of long-term potentiation (LTP). The underlying molecular machinery involves 5-HT7R-mediated activation of MMP-9, which leads to CD44 cleavage followed by Cdc42 activation. One important physiological consequence of this interaction includes an increase in neuronal outgrowth and elongation of dendritic spines, which might have a positive effect on complex neuronal processes (e.g., reversal learning and neuronal regeneration).

Allosteric Inhibition of Serotonin 5-HT7 Receptors by Zinc Ions

The allosteric regulation of G protein-coupled receptors (GPCRs) is a well-known phenomenon, but there are only a few examples of allosteric modulation within the metabotropic serotonergic receptor family. Recently, we described zinc non-competitive interactions toward agonist binding at serotonin 5-HT1A receptors, in which biphasic effects, involving potentiation at sub-micromolar concentrations (10 μM) and inhibition at sub-millimolar concentrations (500 μM) of Zn2+ in radioligand binding assays, were consistent with both the agonist and antagonist-like effects of zinc ions observed in in vivo studies. Here, we showed new data demonstrating zinc allosteric inhibition of both agonist and antagonist binding at human recombinant 5-HT7 receptors stably expressed in HEK293 cells as observed by radioligand binding studies as well as zinc neutral antagonism displayed by the concentration of 10 μM in the functional LANCE assay. The allosteric nature of the effect of Zn on 5-HT7 receptors was confirmed (1) in saturation studies in which zinc inhibited the binding of potent orthosteric 5-HT7 receptor radioligands, the agonist [3H]5-CT, and the two antagonists [3H]SB-269970 and [3H]mesulergine, showing ceiling effect and differences in the magnitude of negative cooperativity (α = 0.15, 0.06, and 0.25, respectively); (2) in competition experiments in which 500 μM of zinc inhibited all radioligand displacements by non-labeled orthosteric ligands (5-CT, SB-269970, and clozapine), and the most significant reduction in affinity was observed for the 5-CT agonist (4.9–16.7-fold) compared with both antagonists (1.4–3.9-fold); and (3) in kinetic experiments in which 500 μM zinc increased the dissociation rate constants for [3H]5-CT and [3H]mesulergine but not for [3H]SB-269970. Additionally, in the functional LANCE test using the constitutively active HEK293 cell line expressing the 5-HT7 receptor, 10 μM zinc had features of neutral antagonism and increased the EC50 value of the 5-CT agonist by a factor of 3.2. Overall, these results showed that zinc can act as a negative allosteric inhibitor of 5-HT7 receptors. Given that the inhibiting effects of low concentrations of zinc in the functional assay represent the most likely direction of zinc activity under physiological conditions, among numerous zinc-regulated proteins, the 5-HT7 receptor can be considered a serotonergic target for zinc modulation in the CNS.

The computer-aided discovery of novel family of the 5-HT6 serotonin receptor ligands among derivatives of 4-benzyl-1,3,5-triazine

The work describes a discovery of new chemical family of potent ligands for the 5-HT6 serotonin receptors. During the search for new histamine H4 receptor antagonists among 1,3,5-triazine derivatives, compound 2 (4-benzyl-6-(4-methylpiperazin-1-yl)-1,3,5-triazin-2-amine) was found. Compound 2, weakly active for the H4 receptor but fitted in 3/4 of pharmacophore features of the 5-HT6R ligand, occurred to be a moderate 5-HT6R agent, useful as a lead structure for further modifications. A series of new derivatives (3–19) of the lead 2 was synthesized, evaluated in the radioligand binding assay (RBA) and explored in comprehensive molecular modelling, including both pharmacophore- and structure-based approaches with docking to the homology model of 5-HT6R. The most active compounds displayed a potent affinity for the 5-HT6R in the nanomolar range (Ki = 20–30 nM), some of them (4, 11 and 19) were tested in the rat forced swim test that revealed their antidepressant-like effect. SAR-analysis on the basis of both, RBA and docking results, indicated that action on the receptor is related to the hydrophobicity and the size of aromatic moiety substituted by a methylene linker at the position 4 of 1,3,5-triazine.