Substance P potentiates 5-HT3 receptor-mediated current in rat trigeminal ganglion neurons

Ferric Citrate Hydrate Has Little Impact on Hyperplasia of Enterochromaffin Cells in the Rat Small Intestine Compared to Sodium Ferrous Citrate

INTRODUCTION

The most detrimental factor preventing the use of oral iron in the treatment of iron deficiency anemia is gastrointestinal side effects accompanied by nausea and vomiting. Anorexia is a known secondary effect of nausea and vomiting. The important gastrointestinal signaling molecule 5-hydroxytryptamine (5-HT) is critically involved in not only physiological function but also nausea and vomiting. The present study was designed to compare the effects of the administration of sodium ferrous citrate (SF) and ferric citrate hydrate (FC) to rats on anorexia and hyperplasia of enterochromaffin cells, which mainly synthesize and store 5-HT.

METHODS

Rats received either SF (3 or 30 mg/kg/day) or FC (30 mg/kg/day) orally for 4 days. Food and water intakes were measured every 24 h during the study. At 96 h after the first administration of the oral iron preparation, the duodenal and jejunal tissues were collected for analysis. Enterochromaffin cells were detected by immunohistochemical analysis.

RESULTS

Administration of 3 mg/kg SF had no effect on anorexia but led to increased hyperplasia of enterochromaffin cells in the duodenum (p < 0.1). Administration of 30 mg/kg SF significantly decreased food and water intakes and significantly increased hyperplasia of enterochromaffin cells in the duodenum and jejunum. Alternatively, administration of 30 mg/kg FC had no significant effect on food and water intakes or hyperplasia of enterochromaffin cells.

CONCLUSION

The lower impact on the hyperplasia of enterochromaffin cells of FC compared to SF may contribute to the maintenance of rats' physical condition.

Involvement of 5-Serotonin and Substance p Pathways in Dichroa Alkali Salt-Induced Acute Pica in Rats

Dichroa alkali salt (DAS) is the active ingredient of Changshan, a traditional Chinese antimalarial medicine. However, owing to its vomiting side effects, its clinical use is limited. Recently, DAS-induced vomiting has attracted broad attention; however, the mechanisms involved have not yet been elucidated. The present study aimed to explore DAS induced vomiting and decipher the potential role of the 5-serotonin (5-HT) and substance p (SP) signaling pathways. We used a combination of approaches in the context of a rat pica model, such as immunoblot analysis, HPLC-ECD, ELISA, quantitative real-time PCR, pharmacological inhibition, and immunohistochemistry assays. We demonstrated that DAS contributed to Changshan-induced vomiting via the activation of the 5-HT and SP signaling pathways. DAS could induce a dose-dependent kaolin intake in the rat pica model. Moreover, DAS caused a similar profile as Cisplatin (DDP): “low-dose double-peak, high-dose single-peak pica phenomenon”. Interestingly, treatment with DAS stimulated the peripheral ileum and central medulla oblongata and augmented the release of 5-HT, SP, and preprotachykinin-A and the expression of 5-HT₃ and NK₁ receptors in the two issues in acute phase. Additionally, the 5-HT₃ and NK₁ receptor antagonists effectively alleviated DAS-induced kaolin intake and significantly reduced DAS-induced 5-HT and SP levels in the two issues in acute phase. Similar responses were not observed in the context of dopamine receptor inhibition. This study innovatively revealed that the 5-HT and SP-mediated vomiting network plays an important role in DAS-induced acute vomiting; of note, ondansetron, and aprepitant can effectively antagonize DAS-induced vomiting. Our results suggest a potential therapeutic strategy (based on drugs approved for human use) to prevent the DAS-associated adverse reactions.

Severity of constipation related to palonosetron during first-line chemotherapy: a retrospective observational study

PURPOSE

Palonosetron, a long-acting 5-HT₃ receptor antagonist, is an effective antiemetic agent for chemotherapy-induced nausea and vomiting; however, it sometimes causes severe constipation. The aim of the present study was to evaluate the severity of palonosetron-related constipation.

METHODS

We retrospectively analyzed the incidence and severity of constipation after intravenous administration of 0.75-mg palonosetron in 150 chemotherapy-naïve patients who received first-line chemotherapy at Saga University Hospital. Constipation was classified into grades 1-5 according to the Common Terminology Criteria for Adverse Events version 5.0. Multiple logistic regression analysis was performed to identify factors associated with palonosetron-related worsening of constipation to grade 2 or higher.

RESULTS

Palonosetron significantly increased the incidence and severity of constipation (incidence: before vs. after palonosetron, 35.4% vs. 74.0%, p < 0.0001, and severity: before vs. after palonosetron, 26.7% and 8.7% in grades 1 and 2, respectively, vs. 46.7%, 23.3%, and 4.0% in grades 1, 2, and 3, respectively, p < 0.0001). Despite the use of laxatives, 4.0% of patients had grade 3 constipation requiring manual evacuation. Combination treatment with aprepitant (odds ratio (OR), 10.9; 95% confidence interval (CI), 1.3-90.0; p = 0.026) and older age (OR, 1.25; 95% CI, 1.01-1.57; p = 0.039) were factors associated with the severity of constipation.

CONCLUSION

Constipation was more severe in patients receiving combination treatment with aprepitant than in those treated with palonosetron alone. Older age was also associated with increased risk of severe palonosetron-related constipation. Identification of risk factors can help target risk-based laxative therapy.

An Integrated In Silico and In Vivo Approach to Identify Protective Effects of Palonosetron in Cisplatin-Induced Nephrotoxicity

Cisplatin is widely used to treat various types of cancers, but it is often limited by nephrotoxicity. Here, we employed an integrated in silico and in vivo approach to identify potential treatments for cisplatin-induced nephrotoxicity (CIN). Using publicly available mouse kidney and human kidney organoid transcriptome datasets, we first identified a 208-gene expression signature for CIN and then used the bioinformatics database Cmap and Lincs Unified Environment (CLUE) to identify drugs expected to counter the expression signature for CIN. We also searched the adverse event database, Food and Drug Administration. Adverse Event Reporting System (FAERS), to identify drugs that reduce the reporting odds ratio of developing cisplatin-induced acute kidney injury. Palonosetron, a serotonin type 3 receptor (5-hydroxytryptamine receptor 3 (5-HT3R)) antagonist, was identified by both CLUE and FAERS analyses. Notably, clinical data from 103 patients treated with cisplatin for head and neck cancer revealed that palonosetron was superior to ramosetron in suppressing cisplatin-induced increases in serum creatinine and blood urea nitrogen levels. Moreover, palonosetron significantly increased the survival rate of zebrafish exposed to cisplatin but not to other 5-HT3R antagonists. These results not only suggest that palonosetron can suppress CIN but also support the use of in silico and in vivo approaches in drug repositioning studies.

Capsaicin Is a Negative Allosteric Modulator of the 5-HT3 Receptor

In this study, effects of capsaicin, an active ingredient of the capsicum plant, were investigated on human 5-hydroxytryptamine type 3 (5-HT₃) receptors. Capsaicin reversibly inhibited serotonin (5-HT)-induced currents recorded by two-electrode voltage clamp method in Xenopus oocytes. The inhibition was time- and concentration-dependent with an IC₅₀ = 62 μM. The effect of capsaicin was not altered in the presence of capsazepine, and by intracellular BAPTA injections or trans-membrane potential changes. In radio-ligand binding studies, capsaicin did not change the specific binding of the 5-HT₃ antagonist [³H]GR65630, indicating that it is a noncompetitive inhibitor of 5-HT₃ receptor. In HEK-293 cells, capsaicin inhibited 5-HT₃ receptor induced aequorin luminescence with an IC₅₀ of 54 µM and inhibition was not reversed by increasing concentrations of 5-HT. In conclusion, the results indicate that capsaicin acts as a negative allosteric modulator of human 5-HT₃ receptors.

Expression Analysis of Serotonin Receptors, Serotonin Transporter and l-Amino Acid Decarboxylase in the Mouse Sphenopalatine Ganglion by RT-PCR, Northern Blot Analysis and In Situ Hybridization

The sphenopalatine ganglion (SPG) is a gathering of the cell bodies of parasympathetic fibers that dominate the nasal gland, lacrimal gland and cerebral blood vessels. The SPG controls nasal secretions, tears, and the dilation of cerebral blood vessels. However, it is unclear how serotonin regulates SPG functions. In this study, we investigated the expression of genes involved in the serotonergic system in the mouse SPG. We examined the mRNA expression levels of 5-HT_1A, 5-HT_1B, 5-HT_1D, 5-HT_1F, 5-HT_2A, 5-HT_2B, 5-HT_2C, 5-HT_3A, 5-HT_3B, 5-HT₄, 5-HT_5A, 5-HT_5B, 5-HT₆ and 5-HT₇ receptors, as well as serotonin transporter, tryptophan hydroxylases 1 and 2, and L-amino acid decarboxylase (AADC) by RT-PCR. It revealed that the 5-HT_3A and 5-HT_3B ionotropic receptors and AADC were likely to be highly expressed in the SPG, as measured by RT-PCR. We next performed in situ hybridization on the SPG to examine the expression of these three genes at the cellular level after validating the specificity of each cRNA probe by northern blotting. The 5-HT_3A receptor, 5-HT_3B receptor, and AADC were expressed in 96.5% ± 1.0%, 29.7% ± 10.7%, and 57.4% ± 2.9% of neuronal cell bodies in the SPG, respectively, indicating that the 5-HT_3A receptor was virtually expressed in all SPG neurons. Our results on the expression of these critical serotonin system genes in the parasympathetic SPG provide insight into the pathogenetics of rhinitis, conjunctivitis and headache. Furthermore, our findings suggest that targeting the 5-HT_3A receptor might have therapeutic potential in the treatment of these ailments.

Feature Article: Selective modulation of tonically active GABAA receptor functional subgroups by G-proteins and protein kinase C

IMPACT STATEMENT

Here we study intracellular mechanisms which regulate inhibitory signaling delivered through continuously (tonically) open ionotropic receptors of γ-aminobutyric acid (GABA) of dentate gyrus granule cells (DGCs). We found that, apart of classical GABA-A receptors (GABA_ARs) which can be activated by GABA binding, a significant part of tonic inhibitory current is delivered by newly discovered spontaneously opening GABA_ARs (s-GABA_ARs), which enter active state without binding of GABA. We have also found that conventional GABA_ARs and s-GABA_ARs are regulated by different intracellular mechanisms, which may overlap and thus induce various signaling repercussions. Our results demonstrate that s-GABA_ARs play a key role in the mechanism that implements DGCs functional role in the brain. On top of that, since regulatory mechanisms under study are affected in a number of pathological states, our results may have broad implications for treatment of neurological disorders.

Tropisetron attenuates lipopolysaccharide induced neuroinflammation by inhibiting NF-κB and SP/NK1R signaling pathway

Tropisetron, an antagonist of serotonin type 3 receptors (5-HT₃Rs), has been investigated in colonic inflammatory process. Since substance P/neurokinin 1 receptor (SP/NK1R) signaling pathway plays a key role in several sensory neuronal inflammatory. We evaluated the anti-inflammatory activity of tropisetron in mice cerebral cortex, and discovered that it was a potential inhibitor in LPS-mediated neuron inflammation through SP/NK1R signaling pathway. We found that tropisetron significantly reduced the increased number of iba-1 positive microglia, down-regulated the gene transcription and protein expression of IL-1β,IL-6 and TNF-α in LPS stimulated cerebral cortex. To characterize the inhibitory mechanism of tropisetron at the SP response in inflammation, we further examined the effect of tropisetron on NF-κB and SP/NK1R signaling pathway in the process of mice cerebral cortex inflammation. We found that tropisetron inhibited the gene transcription and protein expression of NF-κB, SP, NK1R via inhibiting 5-HT₃R activity. These findings might provide new insights into the anti-inflammatory activities of 5-HT₃R inhibitor tropisetron, which would be the interaction of serotonin receptor signaling and SP/NK1R pathway. These might highlight their potential to design novel therapeutic strategies to manage inflammatory diseases.

NK1R/5-HT1AR interaction is related to the regulation of melanogenesis

Substance P (SP) is a candidate mediator along the brain-skin axis and can mimic the effects of stress to regulate melanogenesis. Previously, we and others have found that the regulation of SP for pigmentary function was mediated by neurokinin 1 receptor (NK1R). Emerging evidence has accumulated that psychologic stress can induce dysfunction in the cutaneous serotonin 5-hydroxytryptamine (5-HT)-5-HT1A/1B receptor system, thereby resulting in skin hypopigmentation. Moreover, NK1R and 5-HTR (except 5-HT3) belong to GPCR. The present study aimed at assessing the possible existence of NK1R-5-HTR interactions and related melanogenic functions. Western blot and PCR detection revealed that SP reduced expression of 5-HT1A receptor via the NK1 receptor. Biochemical analyses showed that NK1R and 5-HT1AR could colocalize and interact in a cell and in the skin. When the N terminus of the NK1R protein was removed NK1R surface targeting was prevented, the interaction between NK1R-5-HT1AR decreased, and the depigmentation caused by SP and WAY100635 could be rescued. Importantly, pharmaceutical coadministration of NK1R agonist (SP) and 5-HT1A antagonist (WAY100635) enhanced the NK1-5-HT1A receptor coimmunoprecipitation along with the depigmentary response. SP and WAY100635 cooperation elicited activation of a signaling cascade (the extracellular, regulated protein kinase p-JNK signaling pathway) and inhibition of p70S6K1 phosphorylation and greatly reduced melanin production in vitro and in vivo in mice and zebrafish. Moreover, the SP-induced depigmentation response did not be occur in 5-htr1aa^+/- zebrafish embryos. Taken together, the results of our systemic study increases our knowledge of the roles of NK1R and 5-HT1AR in melanogenesis and provides possible, novel therapeutic strategies for treatment of skin hypo/hyperpigmentation.-Wu, H., Zhao, Y., Huang, Q., Cai, M., Pan, Q., Fu, M., An, X., Xia, Z., Liu, M., Jin, Y., He, L., Shang, J. NK1R/5-HT1AR interaction is related to the regulation of melanogenesis.

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.

2',3'-O-Substituted ATP derivatives as potent antagonists of purinergic P2X3 receptors and potential analgesic agents

Blocking membrane currents evoked by the activation of purinergic P2X3 receptors localized on nociceptive neurons represents a promising strategy for the development of agents useful for the treatment of chronic pain conditions. Among compounds endowed with such antagonistic action, 2',3'-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP) is an ATP analogue, whose inhibitory activity on P2X receptors has been previously reported. Based on the results of molecular modelling studies performed with homology models of the P2X3 receptor, novel adenosine nucleotide analogues bearing cycloalkyl or arylalkyl substituents replacing the trinitrophenyl moiety of TNP-ATP were designed and synthesized. These new compounds were functionally evaluated on native P2X3 receptors from mouse trigeminal ganglion (TG) sensory neurons using patch clamp recordings under voltage clamp configuration. Our data show that some of these molecules are potent (nanomolar range) and reversible inhibitors of P2X3 receptors, without any apparent effect on trigeminal GABAA and 5-HT3 receptors, whose membrane currents were unaffected by the tested compounds.

Synergistic effect of 5-hydroxytryptamine 3 and neurokinin 1 receptor antagonism in rodent models of somatic and visceral pain

Synergistic activity has been observed between serotonergic 5-hydroxytryptamine 3 (5-HT3) and tachykinergic neurokinin 1 (NK1) receptor-mediated responses. This study investigated the efficacy of a 5-HT3 antagonist, palonosetron, and a NK1 antagonist, netupitant, alone or in combination in rodent models of somatic and visceral colonic hypersensitivity. In a rat model of experimental neuropathic pain, somatic hypersensitivity was quantified by the number of ipsilateral paw withdrawals to a von Frey filament (6g). Electrophysiologic responses were recorded in the dorsal horn neurons after mechanical or thermal stimuli. Acute colonic hypersensitivity was induced experimentally in rats by infusing dilute acetic acid (0.6%) directly into the colon. Colonic sensitivity was assessed by a visceromotor behavioral response quantified as the number of abdominal contractions in response to graded isobaric pressures (0-60 mm Hg) of colorectal distension. Palonosetron or netupitant was administered alone or in combination via oral gavage. When dosed alone, both significantly reduced somatic sensitivity, decreased the evoked response of spinal dorsal horn neurons to mechanical or thermal stimulation, and caused significant (P < 0.05) inhibition of colonic hypersensitivity in a dose-dependent manner. The combined administration of palonosetron and netupitant at doses that were ineffective alone significantly reduced both somatic and visceral sensitivity and decreased the evoked response of spinal dorsal horn neurons to mechanical or thermal stimulation. In summary, the combination of palonosetron with a NK1 receptor antagonist showed synergistic analgesic activity in rodent models of somatic and visceral hypersensitivity, and may prove to be a useful therapeutic approach to treat pain associated with irritable bowel syndrome.

Netupitant and palonosetron trigger NK1 receptor internalization in NG108-15 cells

Current therapy for chemotherapy-induced nausea and vomiting includes the use of both 5-HT₃ and NK₁ receptor antagonists. Acute emesis has largely been alleviated with the use of 5-HT₃ receptor antagonists, while an improvement in preventing delayed emesis has been achieved with NK₁ receptor antagonists. Delayed emesis, however, remains a problem with a significant portion of cancer patients receiving highly emetogenic chemotherapy. Like other drugs in its class, palonosetron, a 5-HT₃ receptor antagonist, has shown efficacy against acute emesis. However, palonosetron has also shown consistent improvement in the suppression of delayed emesis. Since both 5-HT₃ and NK₁ receptor antagonists are often simultaneously administered to patients, the question remains if palonosetron’s effect on delayed emesis would remain distinct when co-administered with an NK₁ receptor antagonist. Recent mechanistic studies using NG108-15 cells have shown that palonosetron and netupitant, an NK₁ receptor antagonist currently in phase 3 clinical trials, exhibited synergistic effects when inhibiting the substance P response. The present studies showed that both netupitant and palonosetron-induced NK₁ receptor internalization in NG108-15 cells and that when used together receptor internalization was additive. Palonosetron-induced NK₁ receptor internalization was dependent on the presence of the 5-HT₃ receptor. Results provide a possible explanation for palonosetron’s enhancement of the inhibition of the SP response and suggest that the effect of palonosetron and NK₁ receptor antagonists on prevention of delayed emesis could be additive.

Current pharmacotherapy for chemotherapy-induced nausea and vomiting in cancer patients

INTRODUCTION

Nausea and vomiting are two of the most frequent and troubling side effects patients experience during chemotherapy, interfering with compliance with cancer therapies and quality of life. While newly available treatments have improved our ability to manage nausea and vomiting, anticipatory and delayed nausea and vomiting are still major problems for patients receiving chemotherapy. Many cancer patients consider delaying future chemotherapy cycles and some contemplate stopping chemotherapy altogether because of their fear of experiencing further nausea and vomiting.

AREAS COVERED

The purpose of this article is to provide an overview of the pathopsychophysiology of chemotherapy-induced nausea and vomiting (CINV), the recommended guidelines for treatment, and current agents in late-stage clinical trials, and future research needs to address the continued challenges of treatment-related nausea and vomiting.

EXPERT OPINION

Despite advances in pharmaceutical and behavioral therapies, and the provision of standard clinical guidelines for effectively managing CINV, patients continue to experience it. Moreover, control of nausea, acute and delayed, and anticipatory nausea and vomiting remains an important, unmet need among cancer patients. It is critical to focus attention on better understanding the mechanisms underlying nausea, anticipatory symptoms and delayed symptoms.

Palonosetron for the prevention of chemotherapy-induced nausea and vomiting

Chemotherapy-induced nausea and vomiting (CINV) remains both a feared side effect of cancer treatment and a focus of many supportive care initiatives/guidelines. The class of medications known as serotonin receptor antagonists (5-HT3RAs) are integral in the prevention of CINV from both moderately and highly emetogenic chemotherapy. Palonosetron (ALOXI(®)), a second-generation 5-HT3RA, has a higher affinity for the 5-HT3 receptor, has a longer half-life and has unique interactions with the 5-HT3 receptor compared with the current first-generation 5-HT3RA such as ondansetron, granisetron, dolasetron and tropisetron. This may allow palonosetron an advantage in control of CINV. This review article examines the available evidence, the pharmacokinetics and the safety and tolerability of palonosetron in the prevention of CINV.

Inhibition of substance P-mediated responses in NG108-15 cells by netupitant and palonosetron exhibit synergistic effects

Netupitant is a potent and selective NK(1) receptor antagonist under development in combination with a fixed dose of palonosetron for the prevention of chemotherapy induced nausea and vomiting. Palonosetron is a 5-HT(3) receptor antagonist approved for both the prevention of acute and delayed chemotherapy induced nausea and vomiting after moderately emetogenic chemotherapy. Accumulating evidence suggests that substance P (SP), a ligand acting largely on tachykinin (NK(1)) receptors, is the dominant mediator of delayed emesis. Interestingly, palonosetron does not bind to the NK(1) receptor so that the mechanism behind palonosetron's unique efficacy against delayed emesis is not clear. Palonosetron exhibits a distinct ability among 5-HT(3) receptor antagonists to inhibit crosstalk between NK(1) and 5-HT(3) receptor signaling pathways. The objective of the current work was to determine if palonosetron's ability to inhibit receptor signaling crosstalk would influence netupitant's inhibition of the SP-mediated response when the two drugs are dosed together. We first studied the inhibition of SP-induced Ca(2+) mobilization in NG108-15 cells by palonosetron, ondansetron and granisetron. Unexpectedly, in the absence of serotonin, palonosetron inhibited the SP-mediated dose response 15-fold; ondansetron and granisetron had no effect. Netupitant also dose-dependently inhibited the SP response as expected from an NK1 receptor antagonist. Importantly, when both palonosetron and netupitant were present, they exhibited an enhanced inhibition of the SP response compared to either of the two antagonists alone. The results further confirm palonosetron's unique pharmacology among 5-HT(3) receptor antagonists and suggest that it can enhance the prevention of delayed emesis provided by NK(1) receptor antagonists.

Palonosetron: An Evidence-Based Choice in Prevention of Nausea and Vomiting Induced by Moderately Emetogenic Chemotherapy

Aims and background

In 2003, the second-generation, 5-HT3 receptor antagonist (5-HT3 RA) palonosetron was approved by the FDA for the prevention of nausea and vomiting associated with highly and moderately emetogenic chemotherapy. We reviewed the current knowledge on the role of palonosetron against acute and delayed emesis in patients with solid tumors undergoing single-day moderately emetogenic chemotherapy regimens.

Methods

A literature review in PubMed was performed to update currently available preclinical and clinical evidence on palonosetron, prioritizing randomized clinical trials.

Results

The distinct pharmacology of palonosetron provides a rationale behind the improved efficacy observed with the drug in prevention of delayed symptoms. This may be explained by allosteric binding properties and by palonosetron-triggered receptor internalization, which result in prolonged inhibition of the 5-HT3 receptor function. Very recent pharmacology experiments have also suggested that palonosetron would be able to differentially inhibit 5-HT3/neurokinin 1 (NK-1) receptor signaling cross-talk. In two recent meta-analyses, palonosetron was shown to be more effective than other available 5-HT3 RAs in preventing acute and delayed nausea and vomiting for both HEC and MEC. Recent findings also suggest that a single-day regimen of palonosetron plus dexamethasone (both drugs administered intravenously) may provide a reasonable therapeutic alternative to reduce the total dexamethasone dose administered in patients undergoing moderately emetogenic chemotherapy.

Conclusions

On the basis of accumulating data, the evidence-based international guidelines devised from the major organizations have been recently updated to recommend the use of palonosetron plus 3-day dexamethasone for the optimal prevention of nausea and vomiting due to moderately emetogenic chemotherapy. There is still a need to investigate the efficacy of palonosetron in combination with an NK-1 receptor antagonist and dexamethasone in well-designed randomized trials.

Pharmacological mechanisms of 5-HT₃ and tachykinin NK₁ receptor antagonism to prevent chemotherapy-induced nausea and vomiting

Nausea and vomiting are among the most common and distressing consequences of cytotoxic chemotherapies. Nausea and vomiting can be acute (0-24h) or delayed (24-72 h) after chemotherapy administration. The introduction of 5-HT(3) receptor antagonists in the 90s was a major advance in the prevention of acute emesis. These receptor antagonists exhibited similar control on acute emesis but had no effect on delayed emesis. These findings led to the hypothesis that serotonin plays a central role in the mechanism of acute emesis but a lesser role in the pathogenesis of delayed emesis. In contrast, delayed emesis has been largely associated with the activation of neurokinin 1 (NK(1)) receptors by substance P. However, in 2003, a new 5-HT(3) receptor antagonist was introduced into the market; unlike first generation 5-HT(3) receptor antagonists, palonosetron was found to be effective in preventing both acute and delayed chemotherapy induced nausea and vomiting. Recent mechanistic studies have shown that palonosetron, in contrast to first generation receptor antagonists, exhibits allosteric binding to the 5-HT(3) receptor, positive cooperativity, persistent inhibition of receptor function after the drug is removed and triggers 5-HT(3) receptor internalization. Further, in vitro and in vivo experiments have shown that palonosetron can inhibit substance P-mediated responses, presumably through its unique interactions with the 5-HT(3) receptor. It appears that the crossroads of acute and delayed emeses include interactions among the 5-HT(3) and NK(1) receptor neurotransmitter pathways and that inhibitions of these interactions lend the possibility of improved treatment that encompasses both acute and delayed emeses.

Synergistic antiemetic interactions between serotonergic 5-HT3 and tachykininergic NK1-receptor antagonists in the least shrew (Cryptotis parva)

Significant electrophysiological and biochemical findings suggest that receptor cross-talk occurs between serotonergic 5-HT(3)- and tachykininergic NK(1)-receptors in which co-activation of either receptor by ineffective doses of their corresponding agonists (serotonin (5-HT) or substance P (SP), respectively) potentiates the activity of the other receptor to produce a response. In contrast, selective blockade of any one of these receptors attenuates the increase in abdominal vagal afferent activity caused by either 5-HT or SP. This interaction has important implications in chemotherapy-induced nausea and vomiting (CINV) since 5-HT(3)- and NK(1)-receptor antagonists are the major classes of antiemetics used in cancer patients receiving chemotherapy. The purpose of this study was to demonstrate whether the discussed interaction produces effects at the behavioral level in a vomit-competent species, the least shrew. Our results demonstrate that pretreatment with either a 5-HT(3) (tropisetron)- or an NK(1) (CP99,994)-receptor specific antagonist, attenuates vomiting caused by a selective agonist (2-methyl 5-HT or GR73632, respectively) of both emetic receptors. In addition, relative to each antagonist alone, their combined doses were 4-20 times more potent against vomiting caused by each emetogen. Moreover, combined sub-maximal doses of the agonists 2-methyl 5-HT and GR73632, produced 8-12 times greater number of vomits relative to each emetogen tested alone. However, due to large variability in vomiting caused by the combination doses, the differences failed to attain significance. The antiemetic dose-response curves of tropisetron against both emetogens were U-shaped probably because larger doses of this antagonist behave as a partial agonist. The data demonstrate that 5-HT(3)- and NK(1)-receptors cross-talk to produce vomiting, and that synergistic antiemetic effects occur when both corresponding antagonists are concurrently used against emesis caused by each specific emetogen.

The antiemetic 5-HT3 receptor antagonist Palonosetron inhibits substance P-mediated responses in vitro and in vivo

Palonosetron is the only 5-HT(3) receptor antagonist approved for the treatment of delayed chemotherapy-induced nausea and vomiting (CINV) in moderately emetogenic chemotherapy. Accumulating evidence suggests that substance P (SP), the endogenous ligand acting preferentially on neurokinin-1 (NK-1) receptors, not serotonin (5-HT), is the dominant mediator of delayed emesis. However, palonosetron does not bind to the NK-1 receptor. Recent data have revealed cross-talk between the NK-1 and 5HT(3) receptor signaling pathways; we postulated that if palonosetron differentially inhibited NK-1/5-HT(3) cross-talk, it could help explain its efficacy profile in delayed emesis. Consequently, we evaluated the effect of palonosetron, granisetron, and ondansetron on SP-induced responses in vitro and in vivo. NG108-15 cells were preincubated with palonosetron, granisetron, or ondansetron; antagonists were removed and the effect on serotonin enhancement of SP-induced calcium release was measured. In the absence of antagonist, serotonin enhanced SP-induced calcium-ion release. After preincubation with palonosetron, but not ondansetron or granisetron, the serotonin enhancement of the SP response was inhibited. Rats were treated with cisplatin and either palonosetron, granisetron, or ondansetron. At various times after dosing, single neuronal recordings from nodose ganglia were collected after stimulation with SP; nodose ganglia neuronal responses to SP were enhanced when the animals were pretreated with cisplatin. Palonosetron, but not ondansetron or granisetron, dose-dependently inhibited the cisplatin-induced SP enhancement. The results are consistent with previous data showing that palonosetron exhibits distinct pharmacology versus the older 5-HT(3) receptor antagonists and provide a rationale for the efficacy observed with palonosetron in delayed CINV in the clinic.

Palonosetron plus 3-day aprepitant and dexamethasone to prevent nausea and vomiting in patients receiving highly emetogenic chemotherapy

BACKGROUND

The combination of a neurokinin-1 receptor antagonist, dexamethasone, and a 5-HT(3) receptor antagonist is currently the standard antiemetic treatment in patients receiving cisplatin-based high emetogenic chemotherapy (HEC). The aim of this study was to evaluate the efficacy of a combination of palonosetron, a unique second-generation 5-HT(3) receptor antagonist, aprepitant, the only approved neurokinin-1 receptor antagonist, and dexamethasone as antiemetic prophylaxis in patients receiving HEC (cisplatin ≥50 mg/mq).

METHODS

Chemotherapy-naïve adult patients, receiving cisplatin-based HEC, were treated with palonosetron 0.25 mg/i.v., dexamethasone 20 mg/i.v., and aprepitant 125 mg/p.o., 1-h before chemotherapy. Aprepitant 80 mg/p.o. and dexamethasone 4 mg p.o. were administered on days 2-3. Primary end point was complete response (CR; no vomiting and no use of rescue medication), during the overall study period (0-120 h). Secondary end points were complete control (CR and no more than mild nausea), emesis-free rate, and nausea-free rate during the acute (0-24 h), delayed (24-120 h), and overall (0-120 h) periods. Safety was also evaluated.

RESULTS

A total of 222 patients were included in the study. Median age was 62 years, 76.6% were male and 23.4% female, and most common tumors were lung (66.7%) and head and neck (15.8%); 70.3% of patients achieved CR during the overall study period. Complete control, emesis-free rate, and nausea-free rate were 70.3%, 92.8%, and 59.9%, respectively, during the overall phase. The most commonly reported side effects were constipation (39% of patients) and headache (5%).

CONCLUSIONS

This study shows that palonosetron in combination with aprepitant and dexamethasone is effective to prevent chemotherapy-induced nausea and vomiting in patients treated with cisplatin-based HEC.

Impact of the 5-HT3 receptor channel system for insulin secretion and interaction of ginger extracts

The relevance of serotonin and in particular that of 5-HT(3) receptors is unequivocal with respect to emetic/antiemetic effects, but it is controversial with respect to antidiabetic effects. The effects of tropisetron (5-HT(3) receptor antagonist) and various ginger (Zingiber officinale) extracts (known to interact with the 5-HT(3) receptor channel system) were investigated. Serotonin (32 to 500 microM) inhibits insulin release (RIA) from INS-1 cells which is reversed by tropisetron (10 to 100 microM) and two different ginger extracts (spissum and an oily extract). Their effects are obvious even in the absence of serotonin but are more pronounced in its presence (doubled to tripled). Specific 5-HT(3) binding sites are present in INS-1 cells using 0.4 nM [3H] GR65630 in displacement experiments. The in vitro data with respect to ginger are corroborated by in vivo data on glucose-loaded rats showing that blood glucose (Glucoquant) is decreased by approximately 35% and plasma insulin (RIA) is increased by approximately 10%. Both the spissum extract and the oily ginger extract are effective in two other models: they inhibit [(14)C] guanidinium uptake into N1E-115 cells (model of 5-HT(3) effects) and relax rat ileum both directly and as a serotonin antagonistic effect. Other receptors addressed by ginger are 5-HT(2) receptors as demonstrated by using methysergide and ketanserin. They weakly antagonize the serotonin effect as well. It may be concluded that serotonin and in particular the 5-HT(3) receptor channel system are involved in modulating insulin release and that tropisetron and various ginger extracts can be used to improve a diabetic situation.

5-Hydroxytryptamine directly inhibits neuronal nicotinic acetylcholine receptors in rat trigeminal ganglion neurons

In the present study, whole-cell patch clamp recording technique was used to investigate the action of 5-hydroxytryptamine (5-HT) on the function of native neuronal nicotinic acetylcholine receptors expressed in the rat trigeminal ganglion neurons. Inward currents (I(nic)) caused by externally-applied nicotine were observed in majority of the examined neurons, which were mediated by alpha-bungarotoxin-insensitive nicotinic acetylcholine receptors. We found that 5-HT could reversibly inhibit I(nic) in a concentration-dependent manner, and the inhibition did not involve 5-HT receptors. Other serotonergic agents, such as 2-methyl-5-HT, alpha-methyl-5-HT, sumatriptan and ICS-205,930, also had similar inhibitory effects on I(nic). 5-HT inhibited nicotinic acetylcholine receptors in a non-competitive manner, as 5-HT decreased the maximal current response to nicotine but had no effect on the threshold and EC(50). The inhibition of I(nic) by 5-HT was voltage-dependent and became stronger at hyperpolarized potentials. These results indicated that 5-HT directly inhibited nicotinic acetylcholine receptors in the trigeminal ganglion neurons. As a local modulator of the nicotinic acetylcholine receptor, 5-HT might play a role in the modulation of sensory information.

Hyperpolarization-activated channels in trigeminal ganglia innervating healthy and pulp-exposed teeth

AIM

To use immunocytochemistry for determining the expression of HCN1, HCN2 and HCN3 (three subunits of the hyperpolarization-activated cyclic nucleotide-gated current channel) in rodent trigeminal ganglia (TG) that innervate healthy teeth and determine if expression of HCN subunits is increased in TG following pulp exposure.

METHODOLOGY

Pulps were exposed in right maxillary incisors of male Sprague-Dawley rats. After fixation, TG were removed, cryostat sectioned, and immunocytochemistry was utilized to study the expression of HCN1-3 subunits. Immunoreactivity of individual neurons from the maxillary region of the TG was determined with ImageJ software. Differences in the number immunopositive neurons amongst groups were tested for statistical significance with either a Yates or Pearson's chi-square or Fisher's exact probability tests depending on neuron sample size. Differences in the intensity of immunoreactivity between groups were tested for statistical significance with a Student's t-test.

RESULTS

The majority of TG neurons were immunopositive for HCN1-3. Moreover, statistically significant increases in the number of TG neurons immunopositive for HCN1 and the intensity of HCN1-3 immunoreactivity were observed within hours of exposing the tooth pulp.

CONCLUSIONS

HCN1-3 expression, as determined by immunocytochemistry, is increased within hours after injury. Given that I(h) can facilitate neuronal excitability, results of the current study suggest that antagonists to HCN1-3 subunits could work as analgesics in the alleviation of orofacial pain.

New approaches to chemotherapy-induced nausea and vomiting: from neuropharmacology to clinical investigations

Nausea and vomiting are considered to be among the most distressing consequences of cytotoxic chemotherapies. Currently, there are several novel 5-HT(3) receptor antagonists for the treatment of chemotherapy-induced nausea and vomiting (CINV), including ondansetron, granisetron, and dolasetron. These agents provide significant improvement in the management of acute emesis but are ineffective at preventing delayed emesis. In 2003, a new 5-HT(3) receptor antagonist, palonosetron HCL (Aloxi), was introduced to the U.S. market. Palonosetron was found to be effective in preventing delayed CINV. Indeed, palonosetron was the first and only 5-HT(3) receptor antagonist approved by the FDA for the prevention of both acute and delayed CINV. More recently, studies on the role of substance P in the emetic process led to the development of aprepitant (Emend) for the prevention of delayed emesis in combination with 5-HT(3) receptor antagonists. Despite these major advances, CINV remains uncontrolled in some patients. Current efforts are focused on treating refractory emesis and include both the clinical evaluation of compounds marketed for other indications and the preclinical evaluation of novel molecules targeting other transmitters in the emetic pathway. Ongoing work in pharmacogenomics has postulated several candidate genes that could be involved in emetic sensitivity and responsiveness to antiemetic therapy. Investigations into the pharmacogenomics of CINV may someday be able to aid in the identification of high risk patients and patients unlikely to respond to conventional therapies.

Bradykinin potentiates 5-HT3 receptor-mediated current in rat trigeminal ganglion neurons

AIM

To explore the modulatory effect of bradykinin (BK) on 5-HT(3 )receptor-mediated current in trigeminal ganglion (TG) neurons in rats.

METHODS

The whole-cell patch-clamp technique was used to record 5-HT-activated currents (I(5-HT)) in neurons freshly dissociated from rat TG. Drugs were applied by rapid solution exchange.

RESULTS

The majority of the neurons examined responded to 5-HT applied externally with an inward current (76.3%, 74/97) that could be blocked by the 5-HT(3 )receptor antagonist, ICS-205,930 (10(-6) mol/L). In 66 of the 74 cells sensitive to 5-HT (89.2%), pretreatment for 30 s with BK (10(-6)-10(-10) mol/L) could potentiate I(5-HT) with the maximal modulatory effect occurring at 10(-7) mol/L BK (71.6%+/-4.9%). BK shifted the 5-HT concentration-response curve upwards with an increase of 68.9%+/-7.2% in the maximal current response, but with no significant change in the EC(50) value (19.1+/-3.2 mumol/L vs 20.9+/-3.5 micromol/L; t-test, P>0.05; n=8). BK potentiated I(5-HT) in a holding potential-independent manner and did not alter the reverse potential of I(5-HT). This BK-induced potentiation of I(5-HT) was almost completely blocked by Hoe 140 (5*10(-7) mol/L), a selective B2 BK receptor antagonist, and was removed after intracellular dialysis of GF-109203X (2 micromol/L), a selective protein kinase C (PKC) inhibitor, with the re-patch clamp.

CONCLUSION

Pre-application of BK exerts an enhancing effect on I(5-HT) via a PKC-dependent pathway in rat TG neurons, which may explain the peripheral mechanism of pain and hyperalgesia caused by, for example, tissue damage and inflammation.