5-HT4 receptor agonists treatment reduces tau pathology and behavioral deficit in the PS19 mouse model of tauopathy

Background

Accumulation of tau in synapses in the early stages of Alzheimer's disease (AD) has been shown to cause synaptic damage, synaptic loss, and the spread of tau pathology through trans-synaptically connected neurons. Moreover, synaptic loss correlates with a decline in cognitive function, providing an opportunity to investigate therapeutic strategies to target synapses and synaptic tau to rescue or prevent cognitive decline in AD. One of the promising synaptic targets is the 5-HT4 serotonergic receptor present postsynaptically in the brain structures involved in the memory processes. 5-HT4R stimulation exerts synaptogenic and pro-cognitive effects involving synapse-to-nucleus signaling essential for synaptic plasticity. However, it is not known whether 5-HT4R activation has a therapeutic effect on tau pathology.

Methods

The goal of this study was to investigate the impact of chronic stimulation of 5-HT4R by two agonists, prucalopride and RS-67333, in PS19 mice, a model of tauopathy. We utilized gradient assays to isolate pre- and post-synaptic compartments, followed by biochemical analyses for tau species and ubiquitinated proteins in the synaptic compartments and total brain tissue. Next, we performed kinetic assays to test the proteasome's hydrolysis capacity in treatment conditions. Moreover, behavioral tests such as the open field and non-maternal nest-building tests were used to evaluate anxiety-like behaviors and hippocampal-related cognitive functioning in the treatment paradigm.

Results

Our results show that 5-HT4R agonism reduced tauopathy, reduced synaptic tau, increased proteasome activity, and improved cognitive functioning in PS19 mice. Our data suggest that enhanced proteasome activity by synaptic mediated signaling leads to the enhanced turnover of tau initially within synapses where the receptors are localized, and over time, the treatment attenuated the accumulation of tau aggregation and improved cognitive functioning of the PS19 mice.

Conclusion

Therefore, stimulation of 5-HT4R offers a promising therapy to rescue synapses from the accumulation of toxic synaptic tau, evident in the early stages of AD.

Tegaserod for the Treatment of Irritable Bowel Syndrome

Background: Tegaserod (Zelnorm®) is a 5-hydroxytryptamine (serotonin) type 4 receptor agonist for the treatment of hypomotility disorders of the lower gastrointestinal tract associated with the irritable bowel syndrome with constipation (IBS-C).

Objective: The authors provide the reader with a better understanding on tegaserod mechanism of action, on its pharmacodynamics and pharmacokinetic properties, on safety and tolerability, with a summary of the key published clinical trials conducted in patients with irritable bowel syndrome (IBS). Its effects on colon inflammation have also been described.

Results: Tegaserod was withdrawn in 2007 due to increased risks of cardiovascular adverse effects. The manufacturer denied this, because pre-existing cardiovascular disease or risk factors were attributed to all affected patients. Thus, no causal relationship between tegaserod use and cardiovascular events was clearly shown. A matched case-control study of tegaserod-treated with untreated patients found no association between tegaserod and adverse cardiovascular outcomes. Despite its adverse effects, tegaserod resulted to be effective in treating chronic constipation in adult women aged < 65 years with IBS-C, while the safety and effectiveness of tegaserod in men with IBS-C have not been established.

Conclusion: Tegaserod was resubmitted to the Food and Drug Administration in 2018 for use in a low-risk population. Moreover, tegaserod has also been shown to improve symptoms, enhance gastric accommodation and significantly attenuate visceral pain arising from the colon in functional dyspepsia patients. Treatment with tegaserod seems also to exert a protective effect in inflamed colons, reducing the severity of colitis in animal models.

Patient considerations in the management of chronic constipation: focus on prucalopride

Chronic constipation is a common condition that significantly impacts health care utilization, productivity, and quality of life. Laxatives are commonly used, although often insufficient in restoring normal bowel function or providing adequate relief. There remains a significant need for the development of novel agents to optimize treatment of this condition. This review provides an overview of the preclinical and clinical trial data, supporting the efficacy and safety of prucalopride, a highly selective 5-HT4 receptor agonist that has been approved by the European Medicine Agency for the treatment of chronic constipation in adults who have failed standard laxative therapy. Unlike older 5-HT4 agonists, prucalopride has not been associated with adverse cardiovascular side effects or QT prolongation owing to its high selectivity and affinity for the 5-HT4 receptor without clinically significant cross-reactivity at the human ether-à-go-go-related gene (hERG) potassium channel or 5-HT receptor subtypes that have previously been implicated in adverse cardiovascular events and arrhythmias. Careful safety assessments have documented the relative safety and tolerability of this agent in various patient groups. Focus has also been placed on demonstrating efficacy with regard to bowel function, symptoms, and patient-reported outcomes such as the Patient Assessment of Constipation-Symptoms and the Patient Assessment of Constipation Quality of Life scores to support the use of prucalopride as a safe and effective therapeutic option for the management of chronic constipation.

Efficacy and safety of oral prucalopride in women with chronic constipation in whom laxatives have failed: an integrated analysis

BACKGROUND

Prucalopride is a selective, high-affinity, 5-hydroxytryptamine (serotonin) type 4 (5-HT4) receptor agonist with gastrointestinal prokinetic activities. This integrated analysis of data from three double-blind phase III trials (ClinicalTrials.gov: NCT00488137, NCT00483886, NCT00485940) compared the efficacy and safety of prucalopride 2 mg once daily in women with chronic constipation [≤2 spontaneous complete bowel movements (SCBM) per week] in whom laxatives had failed to provide adequate relief with that in the all-patient (AP) population of men and women with chronic constipation who had or had not obtained relief from laxatives.

METHODS

Patients received prucalopride 2 mg or placebo once-daily for 12 weeks. Efficacy endpoints included an average of ≥3 SCBM/week and average increases of ≥1 SCBM/week and ≥1 SBM/week over this period. A response on any of these three endpoints was considered to be clinically relevant, and an overall response rate was derived for patients satisfying any of these endpoints.

RESULTS

Of the AP population (n = 1318), 936 were women in whom laxatives had failed to provide adequate relief (WLF). More patients on prucalopride 2 mg than placebo had an average of ≥3 SCBM/week (AP 24.4 vs 11.0%; WLF 24.7 vs 9.2%), an average increase of ≥1 SCBM/week (AP 43.5 vs 24.8%; WLF 44.2 vs 22.6%), and an average increase of ≥1 SBM/week (AP 66.7 vs 38.4%; WLF 68.3 vs 37.0%) (all p < 0.001). Significant differences from placebo were evident in week 1 and sustained thereafter. Overall response rates in the AP and WLF populations, respectively, were 69.7 and 71.0% with prucalopride 2 mg and 44.5 and 41.6% with placebo (p < 0.001). Early (weeks 1-4) response predicted ultimate response over time. Common (>10%) adverse events were abdominal pain, nausea, diarrhoea, and headache.

CONCLUSIONS

Prucalopride 2 mg once daily is effective in WLF. The efficacy and safety profile observed in WLF was similar to that in the total evaluated population of patients with chronic constipation who had or had not obtained adequate relief from laxatives.

Prucalopride: the evidence for its use in the treatment of chronic constipation

Introduction:

Chronic constipation is a common condition that is difficult to treat. Existing options for the treatment of patients with different subgroups of constipation are limited. A new efficacious and safe drug is needed to limit the frequently observed adverse effects induced by laxatives, to improve general wellbeing and quality of life, and to provide an alternative for enemas or even resectional surgery in patients in whom stimulant laxatives cause disabling adverse effects or fail to increase bowel movement frequency.

Aims:

The purpose of this article is to assess the current evidence supporting the use of the selective and high affinity serotonin-4 (5-HT₄) receptor agonist prucalopride in the management of chronic constipation.

Evidence review:

There are now convincing data from phase II and multicenter phase III randomized, double-blind, placebo-controlled trials that prucalopride treatment results in a clinically meaningful increase in the number of spontaneous complete bowel movements, a reduction of perceived severity of symptoms and improved disease-related quality of life in a significant proportion of patients. There is a rapid onset of the effect and the improvement is maintained for at least 12 weeks.

Prucalopride in a dose of up to 4 mg per day appeared generally well tolerated and devoid of serious cardiac events. Adverse events, most frequently headache and nausea, are usually mild or moderate and occur mainly during the first days of treatment. Prucalopride should be used with prudence and with careful assessment of the benefit-risk ratio until more clinical and electrophysiologic data become available, because relatively few patients have been exposed to the drug for long periods of time.

Place in therapy:

Prucalopride 1–2 mg once daily may be given to patients suffering from chronic constipation for whom laxatives do not provide adequate relief of their symptoms. Patients with severe constipation and slow transit, who frequently develop tolerance to stimulant laxatives, are also eligible for prucalopride treatment.

Role of prucalopride, a serotonin (5-HT(4)) receptor agonist, for the treatment of chronic constipation

Constipation affects up to a quarter of the population in developed countries and is associated with poor quality of life and significant economic burden. Many patients with chronic constipation are dissatisfied with current therapy due to lack of long-term efficacy or side effects. Previous nonselective 5-hydroxytryptamine receptor 4 (5-HT₄) agonists have been associated with significant interactions with other receptors (5-HT_1B, 5-HT_1D, and 5-HT_2B for tegaserod; hERG for cisapride), leading to adverse cardiovascular events resulting in withdrawal of these drugs from the market. Prucalopride is a novel gastrointestinal prokinetic agent. It acts as a high affinity, highly-selective 5-HT₄ agonist. Its efficacy in patients with chronic constipation has been demonstrated in several phase II and phase III clinical trials showing significant improvements in bowel transit, bowel function, gastrointestinal symptoms, and quality of life, with benefit maintained for up to 24 months in open label, multicenter, follow-up studies. Prucalopride’s high selectivity for the 5-HT₄ receptor may explain its favorable safety and tolerability profiles, even in elderly subjects with stable cardiovascular disease. Prucalopride is a well tolerated and efficacious prokinetic medication that should enhance the treatment of chronic constipation unresponsive to first-line treatments.