Neurokinin 3 Receptor Antagonism Reveals Roles for Neurokinin B in the Regulation of Gonadotropin Secretion and Hot Flashes in Postmenopausal Women

Transfer of preclinical study data on the influence of cimicifuga racemosaon functional changes in the hippocampus during menopause

Menopausal transition in women involves complex neurobiochemical changes linked to ovarian dysfunction, resulting in symptoms like vasomotor symptoms (VMS), sleep disturbances, anxiety, and cognitive impairments. Hormone replacement therapy is the first-line treatment. However, many women are reluctant to use HRT or have contraindications toward HRT and seek for alternatives. Non-hormonal therapies with extracts of Cimicifuga racemosa rhizomes like the isopropanolic extract (iCR, black cohosh) offer a promising alternative. A preclinical pilot study exploring iCR's effects on gene expression in the hippocampus and hypothalamus of ovarectomized (OVX) rats mimicking menopausal conditions identified important signaling pathways and CNS-based contributions to the multitargeted modes of action of iCR. Especially in the hippocampus, iCR compensated effects of OVX on gene expression profiles. These changes are reflected by the genes AVPR1A, GAL, CALCA, HCRT, PNOC, ESR1, ESR2 and TAC3 contributing to the formation of hot flushes or thermoregulation as well as to secondary effects such as blood pressure, metabolism, hormonal regulation, homeostasis, mood regulation, neuroendocrine modulation, regulation of sleep and arousal, and in learning, memory and cognition. To understand the mechanisms in the brain of estrogen-depressed animals (OVX) and subsequent iCR treatment we combined the results of the pilot study with those of up-to-date literature and tried to transfer the current knowledge to humans during menopausal transition and adaptation. Focus was laid on changes in the hippocampal function, that is disturbed by hormonal fluctuations, but can also be brought back into balance by iCR.

Population pharmacokinetic-pharmacodynamic model of elinzanetant based on integrated clinical phase I and II data

Elinzanetant is a potent and selective dual neurokin-1 (NK-1) and -3 (NK-3) receptor antagonist that is currently developed for the treatment of women with moderate-to-severe vasomotor symptoms (VMS) associated with menopause. Here, we report the development of a population pharmacokinetic (popPK) model for elinzanetant and its principal metabolites based on an integrated dataset from 366 subjects (including 197 women with VMS) collected in 10 phase I or II studies. The pharmacokinetics of elinzanetant and its metabolites could be well described by the popPK model. Within the investigated dose range of 40-160 mg, the oral bioavailability of elinzanetant was dose independent and estimated to be 36.7%. The clearance of elinzanetant was estimated to be 7.26 L/h and the central and peripheral distribution volume were 23.7 and 168 L. No intrinsic or extrinsic influencing factors have been identified in the investigated population other than the effect of a high-fat breakfast on the oral absorption of elinzanetant. The popPK model was then coupled to a pharmacodynamic model to predict occupancies of the NK-1 and NK-3 receptors. After repeated once-daily administration of the anticipated therapeutic dose of 120 mg elinzanetant, the model-predicted median receptor occupancies are >99% for NK-1 and >94.8% for NK-3 during day and night-time, indicating sustained and near-complete inhibition of both target receptors during the dosing interval.

Restoring function to inactivating G protein-coupled receptor variants in the hypothalamic-pituitary-gonadal axis1

G protein-coupled receptors (GPCRs) are central to the functioning of the hypothalamic-pituitary-gonadal axis (HPG axis) and include the rhodopsin-like GPCR family members, neurokinin 3 receptor, kappa-opioid receptor, kisspeptin 1 receptor, gonadotropin-releasing hormone receptor, and the gonadotropin receptors, luteinizing hormone/choriogonadotropin receptor and follicle-stimulating hormone receptor. Unsurprisingly, inactivating variants of these receptors have been implicated in a spectrum of reproductive phenotypes, including failure to undergo puberty, and infertility. Clinical induction of puberty in patients harbouring such variants is possible, but restoration of fertility is not always a realisable outcome, particularly for those patients suffering from primary hypogonadism. Thus, novel pharmaceuticals and/or a fundamental change in approach to treating these patients are required. The increasing wealth of data describing the effects of coding-region genetic variants on GPCR function has highlighted that the majority appear to be dysfunctional as a result of misfolding of the encoded receptor protein, which, in turn, results in impaired receptor trafficking through the secretory pathway to the cell surface. As such, these intracellularly retained receptors may be amenable to 'rescue' using a pharmacological chaperone (PC)-based approach. PCs are small, cell permeant molecules hypothesised to interact with misfolded intracellularly retained proteins, stabilising their folding and promoting their trafficking through the secretory pathway. In support of the use of this approach as a viable therapeutic option, it has been observed that many rescued variant GPCRs retain at least a degree of functionality when 'rescued' to the cell surface. In this review, we examine the GPCR PC research landscape, focussing on the rescue of inactivating variant GPCRs with important roles in the HPG axis, and describe what is known regarding the mechanisms by which PCs restore trafficking and function. We also discuss some of the merits and obstacles associated with taking this approach forward into a clinical setting.

Effectiveness and safety of fezolinetant in alleviating vasomotor symptoms linked to Menopause.: A systematic review and Meta-Analysis

BACKGROUND & OBJECTIVE

Vasomotor symptoms (VMS) are the most common symptoms during menopause including hot flushes and night sweats. They are highly disruptive to the quality of life. Fezolinetant is an FDA-approved non-hormonal selective neurokinin3 receptor antagonist for the treatment of VMS. In this study, we aim to assess the efficacy and safety of fezolinetant for VMS associated with menopause.

METHODS

Databases were searched until September 2023 for relevant studies comparing fezolinetant against placebo. Data was extracted into an online form and analyzed using RevMan (Version 5.4.1). The GRADE approach was conducted to evaluate the quality of evidence regarding efficacy outcomes. We included randomized controlled trials (RCTs) comparing fezolinetant to placebo in postmenopausal women experiencing VMS. Exclusion criteria comprised studies involving participants with contraindications to fezolinetant or those evaluating its efficacy for indications other than VMS associated with menopause.

RESULTS

Six studies were included in this study involving 3301 patients. Compared to placebo, fezolinetant reduced the frequency of VMS episodes from baseline (SMD = -0.64, 95 % CI [-0.77, -0.5]) and (SMD = -0.63, 95 % CI [-0.72, -0.53] at weeks 4 and 12 respectively. Additionally, fezolinetant reduced VMS severity score (SMD = -0.59, 95 %CI [-0.77, -0.42]) and (SMD = -0.4, 95 % CI [-0.54, -0.27]) at weeks 4 at 12 respectively. These reductions were positively reflected on Menopause specific quality of life score (SMD = -0.46, 95 %CI [-57, -0.34]), (SMD = -0.37, 95 %CI [-0.48, -0.25]) at weeks 4 and 12 respectively. Regarding safety analysis, fezolinetant showed increased risk for drug-related TEAEs (RR = 1.47, 95 %CI [1.06,2.04]), serious TEAEs (RR = 1.67, 95 %CI [1.09,2.55]), fatigue (RR = 4.05, 95 %CI [1.27,12.88]), arthralgia (RR = 2.83, 95 %CI [1.02,7.8]) and ALT or AST > 3 times (RR = 2, 95 %CI [1.12,3.57]), with no other statistically significant difference regarding other safety terms.

CONCLUSION

Fezolinetant has demonstrated efficacy in reducing the frequency and severity of VMS in postmenopausal women, leading to an improvement in their quality of life. These findings suggest that Fezolinetant may serve as a viable alternative to hormonal therapy for managing VMS.

Fezolinetant for the treatment of vasomotor symptoms associated with menopause: a meta-analysis

This systematic review and meta-analysis investigated the efficacy and safety of fezolinetant for the treatment of moderate-to-severe vasomotor symptoms (VMS) associated with menopause. PubMed, Cochrane Library, Embase and Web of Science were searched for randomized controlled trials (RCTs) published from inception to June 2023, comparing fezolinetant to placebo in postmenopausal women suffering from moderate-to-severe VMS. The mean difference and risk ratio were calculated for continuous and binary outcomes, respectively. R software was used for the statistical analysis, and RoB-2 (Cochrane) to assess the risk of bias. We performed subgroup analysis based on different dosing regimens. Five RCTs comprising 3302 patients were included. Compared with placebo, at 12-week follow-up, fezolinetant significantly reduced the daily frequency of moderate-to-severe VMS (weighted mean difference [WMD] - 2.36; 95% confidence interval [CI] - 2.92, -1.81) and daily severity of moderate-to-severe VMS (WMD -0.22; 95% CI -0.31, -0.13). Also, fezolinetant significantly improved the quality of life (WMD -0.42; 95% CI -0.58, -0.26) and sleep disturbance (WMD -1.10; 95% CI -1.96, -0.24). There were no significant differences between groups in adverse events. These findings support the efficacy and safety of fezolinetant for the treatment of VMS related to menopause.

Elinzanetant, a new combined neurokinin-1/-3 receptor antagonist for the treatment of postmenopausal vasomotor symptoms

INTRODUCTION

In many postmenopausal women, quality of life is decreased due to vasomotor symptoms. Efficient and well-tolerated non-hormonal treatment options are needed.

AREAS COVERED

The present review summarizes what is known about the etiology of postmenopausal vasomotor symptoms as a rationale for the mechanism of action of Elinzanetant, a new neurokinin (NK)-1/-3 receptor antagonist, as well as its efficacy and side effect profile.

EXPERT OPINION

Elinzanetant likely exerts an antagonistic effect on the NK-3 receptor in the preoptic thermoregulatory zone, but also an additional antagonistic effect on the NK-1 receptor possibly leading to a reduction in vasodilatation and heat-sensing neuro-activity. Elinzanetant's reported peak drug concentrations are reached within one hour and the terminal elimination half-life is approximately 15 hours. Two phase IIb clinical trials evaluated the safety profile and efficacy of several doses. There were no serious adverse events, which also included a lack of evidence of drug-related hepatotoxicity. Overall, Elinzanetant seems to be well-tolerated. In the SWITCH-1 study, the 120 mg/day and 160 mg/day regimen showed good efficacy for the treatment of vasomotor symptoms and led to significant improvements in quality of life. Thus, 120 mg oral Elinzanetant/day was used in phase III trials, whose results have not yet been published.

New advances in menopause symptom management

Vasomotor symptoms (VMS) are characteristic of menopause experienced by over 75% of postmenopausal women with significant health and socioeconomic implications. Although the average duration of symptoms is seven years, 10% of women experience symptoms for more than a decade. Although menopausal hormone therapy (MHT) remains an efficacious and cost-effective treatment, its use may not be suitable in all women, such as those at an increased risk of breast cancer or gynaecological malignancy. The neurokinin B (NKB) signaling pathway, together with its intricate connection to the median preoptic nucleus (MnPO), has been postulated to provide integrated reproductive and thermoregulatory responses, with a central role in mediating postmenopausal VMS. This review describes the physiological hypothalamo-pituitary-ovary (HPO) axis, and subsequently the neuroendocrine changes that occur with menopause using evidence derived from animal and human studies. Finally, data from the latest clinical trials using novel therapeutic agents that antagonise NKB signaling are reviewed.

Elinzanetant: a phase III therapy for postmenopausal patients with vasomotor symptoms

INTRODUCTION

Menopausal vasomotor symptoms (VMS) are experienced by most women and are often debilitating and can last for years. While hormone replacement therapy is effective, it carries risks that have impacted its wider use, and it can be contraindicated. There is a large unmet need for a safe, effective non-hormonal therapy.

AREAS COVERED

The importance of the neurokinin (NK) system in the hypothalamic regulation of the vasomotor center has become clear. NK antagonists, previously developed for other indications, have therefore been investigated for the treatment of VMS. Elinzanetant is a potent antagonist at both NK1 (endogenous ligand Substance P) and NK3 (neurokinin B) receptors, whereas other related drugs in development are selective NK3 antagonists. Elinzanetant has been investigated in 2 Phase II trials for menopausal VMS, demonstrating rapid onset and dose-dependant efficacy for the relief of VMS and improvement in quality of life for up to 12 weeks. Phase III trials are underway in women both with physiological menopause and after treatment for breast cancer.

EXPERT OPINION

Elinzanetant is a very promising non-hormonal approach to a highly prevalent symptom constellation, with rapid onset and high efficacy. Wider indications are being explored in current Phase III trials.

KNDy neurones and GnRH/LH pulse generation: Current understanding and future aspects

Uncovering the central mechanism underlying mammalian reproduction is warranted to develop new therapeutic approaches for reproductive disorders in humans and domestic animals. The present study focused on the role of arcuate kisspeptin neurones (also known as KNDy neurones) as an intrinsic gonadotropin-releasing hormone (GnRH) pulse generator, which plays a fundamental role in mammalian reproduction via the stimulation of pituitary gonadotropin synthesis and release and thereby in gametogenesis and steroidogenesis in the gonads of mammals. We also discuss the mechanism that inhibits pulsatile GnRH/gonadotropin release under a negative energy balance, considering that reproductive disorders often occur during malnutrition in humans and livestock.

Role of Neurokinin B in gametogenesis and steroidogenesis of freshwater catfish, Clarias batrachus

Neurokinin B (NKB), a recently discovered neuropeptide, plays a crucial role in regulating the kiss-GnRH neurons in vertebrate's brain. NKB is also characterized in gonadal tissues; however, its role in gonads is poorly understood. Therefore, in the present study, the effects of NKB on gonadal steroidogenesis and gametogenesis through in vivo and in vitro approaches using NKB antagonist MRK-08 were evaluated. The results suggest that the NKB antagonist decreases the development of advanced ovarian follicles and germ cells in the testis. In addition, MRK-08 further reduces the production of 17β-estradiol in the ovary and testosterone in the testis under both in vivo and in vitro conditions in a dose-dependent manner. Furthermore, the in vitro MRK-08 treatment of gonadal explants attenuated the expression of steroidogenic marker proteins, i.e., StAR, 3β-HSD, and 17β-HSD dose-dependently. Moreover, the MAP kinase proteins, pERK1/2 & ERK1/2 and pAkt & Akt were also downregulated by MRK-08. Thus, the study suggests that NKB downregulates steroidogenesis by modulating the expressions of steroidogenic marker proteins involving ERK1/2 & pERK1/2 and Akt/pAkt signalling pathways. NKB also appears to regulate gametogenesis by regulating gonadal steroidogenesis in the catfish.

Structural insights into neurokinin 3 receptor activation by endogenous and analogue peptide agonists

Neurokinin 3 receptor (NK3R) is a tachykinin receptor essential for the hypothalamic-pituitary-gonadal axis. The endogenous peptide agonist neurokinin B (NKB) preferentially activates NK3R, while substance P (SP) binds preferentially to NK1R. In addition, the SP analogue senktide more potently activates NK3R than NKB and SP. However, the mechanisms of preferential binding of peptide and NK3R activation remain elusive. Herein, we determined the cryogenic electron microscopy (cryo-EM) structures of the NK3R-G_q complex bound to NKB, SP and senktide. The three NK3R-G_q/peptide complexes utilize a class of noncanonical receptor activation mechanisms. Combining the structural analysis and functional assay illustrated that the consensus C-termini of the three peptide agonists share a conserved binding mode to NK3R, while the divergent N-termini of the peptides confer the preferential binding of the agonist to NK3R. In addition, the specific interactions between the N-terminus of senktide and the N-terminus and extracellular loops (ECL2 and ECL3) of NK3R lead to the improved activation displayed by senktide compared to SP and NKB. These findings pave the way to understand tachykinin receptor subtype selectivity and provide ideas to rationally develop drugs targeting NK3R.

Neurokinin 1/3 receptor antagonists for menopausal women: A current systematic review and insights into the investigational non-hormonal therapy

BACKGROUND

Over 75% of menopausal women experience vasomotor symptoms (VMS), such as night sweats and hot flashes. Despite the prevalence of these symptoms, there is limited data on non-hormonal therapies to alleviate them.

METHODS

PubMed, Cochrane, Scopus, Ovid, Web of Science, and ClinicalTrials.Gov were searched for relevant studies. The search was performed using the following keywords, which were customized to suit the specific databases/registers: menopause, women, neurokinin 3, and/or Fezolinetant. The search was conducted until December 20, 2022. This systematic review was conducted in compliance with the PRISMA Statement 2020 guidelines.

RESULTS

A total of 326 records were found, with 10 studies (enrolling 1993 women) selected for inclusion. The women received 40-mg doses of NK1/3 receptor antagonists twice daily, with follow-ups at 1 to 3 weeks. Moderately strong evidence was found suggesting that NK1/3 receptor antagonists can help limit the frequency and severity of hot flashes in menopausal women.

CONCLUSION

While the results should be interpreted with caution until further clinical trials validate the efficacy and safety of NK1/3 receptor antagonists among menopausal women, these findings suggest that they are promising targets for future pharmacological and clinical studies in addressing vasomotor symptoms.

Management of Menopause Symptoms and Quality of Life during the Menopause Transition

Some women experience bothersome symptoms around the time of menopause that may have a negative impact on their quality of life and prompt them to seek treatments. Menopausal hormone therapy was historically the treatment of choice. However, medical contraindications and personal preference for nonhormonal therapy have prompted the evaluation of a range of nonhormonal pharmacologic and non-pharmacologic therapies. This review provides an update focusing on the latest evidence-based approach for the management of bothersome symptoms of menopause.

Advances in clinical applications of kisspeptin-GnRH pathway in female reproduction

BACKGROUND

Kisspeptin is the leading upstream regulator of pulsatile and surge Gonadotrophin-Releasing Hormone secretion (GnRH) in the hypothalamus, which acts as the key governor of the hypothalamic-pituitary-ovary axis.

MAIN TEXT

Exogenous kisspeptin or its receptor agonist can stimulate GnRH release and subsequent physiological gonadotropin secretion in humans. Based on the role of kisspeptin in the hypothalamus, a broad application of kisspeptin and its receptor agonist has been recently uncovered in humans, including central control of ovulation, oocyte maturation (particularly in women at a high risk of ovarian hyperstimulation syndrome), test for GnRH neuronal function, and gatekeepers of puberty onset. In addition, the kisspeptin analogs, such as TAK-448, showed promising agonistic activity in healthy women as well as in women with hypothalamic amenorrhoea or polycystic ovary syndrome.

CONCLUSION

More clinical trials should focus on the therapeutic effect of kisspeptin, its receptor agonist and antagonist in women with reproductive disorders, such as hypothalamic amenorrhoea, polycystic ovary syndrome, and endometriosis.

Review of human genetic and clinical studies directly relevant to GnRH signalling

GnRH is the pivotal hormone in controlling the hypothalamic-pituitary gonadal (HPG) axis in humans and other mammalian species. GnRH function is influenced by a multitude of known and still unknown environmental and genetic factors. Molecular genetic studies on human families with hypogonadotropic hypogonadism over the past two decades have been instrumental in delineating the kisspeptin and neurokinin B signalling, which integrally modulates GnRH release from the hypothalamus. The identification of kisspeptin and neurokinin B ligand-receptor gene pair mutations in patients with absent puberty have paved the way to a greater understanding of the central regulation of the HPG cascade. In this article, we aim to review the literature on the genetic and clinical aspects of GnRH and its receptor, as well as the two ligand-receptor sets directly pertinent to the function of GnRH hormone signalling, kisspeptin/ kisspeptin receptor and NKB/NK3R.

The roles of kisspeptin and neurokinin B in GnRH pulse generation in humans, and their potential clinical application

The delivery of gonadotropin-releasing hormone (GnRH) in a pulsatile mode to the gonadotropes has long been known to be essential for normal reproductive function. There have been numerous studies aimed at dissecting out the mechanisms underlying GnRH pulse generation. The discovery of kisspeptin as an upstream regulator of GnRH attracted the possibility that pulsatile kisspeptin governed the pulsatile secretion of GnRH. Subsequent studies have shown the importance of the neurokinin B (NKB) system in modulating kisspeptin secretion and this GnRH. A number of studies in laboratory rodents have supported this notion. By contrast, we present data from clinical studies in men and women, in a range of contexts, showing that continuous infusion of kisspeptin 10 at receptor-saturating levels gives rise to an increase in luteinizing hormone (LH) (GnRH) pulse frequency. This has been demonstrated in normal healthy and hypogonadal men, in normal women during the mid-cycle LH surge, in men and women with mutations in the genes encoding NKB or its receptor, neurokinin 3 receptor (NK3R), in women with polycystic ovary syndrome treated with NK3R antagonist, and in women treated with NK3R antagonist during the LH surge. These finds indicate that pulsatile secretion and action of kisspeptin on GnRH neurons is not required for the generation of LH (GnRH) pulses in humans. We also report that there is an absence of desensitization in humans exposed to continuous infusion of kisspeptin-10 at receptor-saturating concentrations over 22 h and briefly review GnRH, kisspeptin and NKB analogs and their clinical application.

Tachykinins, new players in the control of reproduction and food intake: A comparative review in mammals and teleosts

In vertebrates, the tachykinin system includes tachykinin genes, which encode one or two peptides each, and tachykinin receptors. The complexity of this system is reinforced by the massive conservation of gene duplicates after the whole-genome duplication events that occurred in vertebrates and furthermore in teleosts. Added to this, the expression of the tachykinin system is more widespread than first thought, being found beyond the brain and gut. The discovery of the co-expression of neurokinin B, encoded by the tachykinin 3 gene, and kisspeptin/dynorphin in neurons involved in the generation of GnRH pulse, in mammals, put a spotlight on the tachykinin system in vertebrate reproductive physiology. As food intake and reproduction are linked processes, and considering that hypothalamic hormones classically involved in the control of reproduction are reported to regulate also appetite and energy homeostasis, it is of interest to look at the potential involvement of tachykinins in these two major physiological functions. The purpose of this review is thus to provide first a general overview of the tachykinin system in mammals and teleosts, before giving a state of the art on the different levels of action of tachykinins in the control of reproduction and food intake. This work has been conducted with a comparative point of view, highlighting the major similarities and differences of tachykinin systems and actions between mammals and teleosts.

Gene expression analyses on multi-target mode of action of black cohosh in menopausal complaints - a pilot study in rodents

PURPOSE

This study aimed at assessing gene expression profiles in hippocampus and hypothalamus of ovariectomized (OVX) rats with or without treatment with an isopropanolic extract of Cimicifuga racemosa rhizomes (iCR) in comparison to intact rats.

METHODS

Exploration of hippocampal (Hi) and hypothalamic (Hy) tissue from Sprague Dawley rats: without OVX (NHi = NHy = 4), tissues 3 months after OVX (NHi = 4, NHy = 3), or tissues of rats after their treatment with iCR for 3 months after OVX (NHi = NHy = 2). Gene expression profiles in these tissues were investigated by RNA-microarray-analysis and subsequent verification by qPCR.

RESULTS

4812 genes were differentially regulated when comparing the three groups in hippocampus and hypothalamus. iCR compensated the effects of OVX in 518 genes. This compensatory effect was most prominent in hippocampal signalling pathways, thereof genes (GAL, CALCA, HCRT, AVPR1A, PNOC, etc.) involved in thermoregulation, regulation of sleep and arousal, blood pressure regulation, metabolism, nociception, hormonal regulation, homeostasis, learning and cognition, mood regulation, neuroendocrine modulation, etc.. In the hypothalamus, iCR compensated OVX-effects at TAC3 and OPRM1 but not at KISS1. These genes are involved in the pathophysiology of hot flashes.

CONCLUSIONS

Our pilot study findings support a multifaceted mode of action of iCR in menopausal complaints on a tissue-specific brain gene expression level.

Inhibiting Kiss1 Neurons With Kappa Opioid Receptor Agonists to Treat Polycystic Ovary Syndrome and Vasomotor Symptoms

CONTEXT

Recent evidence suggests that vasomotor symptoms (VMS) or hot flashes in the postmenopausal reproductive state and polycystic ovary syndrome (PCOS) in the premenopausal reproductive state emanate from the hyperactivity of Kiss1 neurons in the hypothalamic infundibular/arcuate nucleus (KNDy neurons).

OBJECTIVE

We demonstrate in 2 murine models simulating menopause and PCOS that a peripherally restricted kappa receptor agonist (PRKA) inhibits hyperactive KNDy neurons (accessible from outside the blood-brain barrier) and impedes their downstream effects.

DESIGN

Case/control.

SETTING

Academic medical center.

PARTICIPANTS

Mice.

INTERVENTIONS

Administration of peripherally restricted kappa receptor agonists and frequent blood sampling to determine hormone release and body temperature.

MAIN OUTCOME MEASURES

LH pulse parameters and body temperature.

RESULTS

First, chronic administration of a PRKA to bilaterally ovariectomized mice with experimentally induced hyperactivity of KNDy neurons reduces the animals' elevated body temperature, mean plasma LH level, and mean peak LH per pulse. Second, chronic administration of a PRKA to a murine model of PCOS, having elevated plasma testosterone levels and irregular ovarian cycles, suppresses circulating levels of LH and testosterone and restores normal ovarian cyclicity.

CONCLUSION

The inhibition of kisspeptin neuronal activity by activation of kappa receptors shows promise as a novel therapeutic approach to treat both VMS and PCOS in humans.

Menopause review: Emerging treatments for menopausal symptoms

Vasomotor symptoms (VMS) affect 2 out of 3 women during menopause and are highly disruptive and intolerable. They exert a negative impact on a woman's physical and mental well-being and are considered a high clinical priority requiring effective treatment. Although hormone therapy remains the gold-standard treatment for hot flushes, it is associated with several side effects and contraindications. Furthermore, alternative treatments for VMS are currently less efficacious and have limited availability; therefore, a new medication to treat VMS would benefit millions of women worldwide. Neurokinin 3 receptor (NK3R) antagonists have recently been developed as novel therapeutic agents for the amelioration of VMS through their action on NK3 receptors within the hypothalamus and consequent regulation of the thermoregulatory centre. So far, three NK3R antagonists have been studied in menopausal women, which have demonstrated significant reductions in VMS frequency and severity and have shown their ability to transform patients' quality of life.

The Effects of Estrogens on Neural Circuits That Control Temperature

Declining and variable levels of estrogens around the time of menopause are associated with a suite of metabolic, vascular, and neuroendocrine changes. The archetypal adverse effects of perimenopause are vasomotor symptoms, which include hot flashes and night sweats. Although vasomotor symptoms are routinely treated with hormone therapy, the risks associated with these treatments encourage us to seek alternative treatment avenues. Understanding the mechanisms underlying the effects of estrogens on temperature regulation is a first step toward identifying novel therapeutic targets. Here we outline findings in rodents that reveal neural and molecular targets of estrogens within brain regions that control distinct components of temperature homeostasis. These insights suggest that estrogens may alter the function of multiple specialized neural circuits to coordinate the suite of changes after menopause. Thus, defining the precise cells and neural circuits that mediate the effects of estrogens on temperature has promise to identify strategies that would selectively counteract hot flashes or other negative side effects without the health risks that accompany systemic hormone therapies.

Hypothalamic neurokinin signalling and its application in reproductive medicine

The discovery of the essential requirement for kisspeptin and subsequently neurokinin B signalling for human reproductive function has sparked renewed interest in the neuroendocrinology of reproduction. A key discovery has been a population of cells co-expressing both these neuropeptides and dynorphin in the hypothalamus, directly regulating gonadotropin hormone releasing hormone (GnRH) secretion and thus pituitary secretion of gonadotropins. These neurons also project to the vasomotor centre, and their overactivity in estrogen deficiency results in the common and debilitating hot flushes of the menopause. Several antagonists to the neurokinin 3 receptor, for which neurokinin B is the endogenous ligand, have been developed, and are entering clinical studies in human reproductive function and clinical trials. Even single doses can elicit marked declines in testosterone levels in men, and their use has elicited evidence of the regulation of ovarian follicle growth in women. The most advanced indication is the treatment of menopausal vasomotor symptoms, where these drugs show remarkable results in both the degree and speed of symptom control. A range of other reproductive indications are starting to be explored, notably in polycystic ovary syndrome, the most common endocrinopathy in women.

Elinzanetant (NT-814), a Neurokinin 1,3 Receptor Antagonist, Reduces Estradiol and Progesterone in Healthy Women

CONTEXT

The ideal therapy for endometriosis (EM) and uterine fibroids (UFs) would suppress estrogenic drive to the endometrium and myometrium, while minimizing vasomotor symptoms and bone loss associated with current treatments. An integrated neurokinin-kisspeptin system involving substance P and neurokinin B acting at the neurokinin (NK) receptors 1 and 3, respectively, modulates reproductive hormone secretion and represents a therapeutic target.

OBJECTIVE

This work aimed to assess the effects of the novel NK1,3 antagonist elinzanetant on reproductive hormone levels in healthy women.

METHODS

A randomized, single-blinded, placebo-controlled study was conducted in 33 women who attended for 2 consecutive menstrual cycles. In each cycle blood samples were taken on days 3 or 4, 9 or 10, 15 or 16, and 21 or 22 to measure serum reproductive hormones. In cycle 2, women were randomly assigned to receive once-daily oral elinzanetant 40, 80, 120 mg, or placebo (N = 8 or 9 per group).

RESULTS

Elinzanetant dose-dependently lowered serum luteinizing hormone, estradiol (120 mg median change across cycle: -141.4 pmol/L, P = .038), and luteal-phase progesterone (120 mg change from baseline on day 21 or 22: -19.400 nmol/L, P = .046). Elinzanetant 120 mg prolonged the cycle length by median of 7.0 days (P = .023). Elinzanetant reduced the proportion of women with a luteal-phase serum progesterone concentration greater than 30 nmol/L (a concentration consistent with ovulation) in a dose-related manner in cycle 2 (P = .002). Treatment did not produce vasomotor symptoms.

CONCLUSION

NK1,3 receptor antagonism with elinzanetant dose-dependently suppressed the reproductive axis in healthy women, with the 120-mg dose lowering estradiol to potentially ideal levels for UFs and EM. As such, elinzanetant may represent a novel therapy to manipulate reproductive hormone levels in women with hormone-driven disorders.

Effects of NT-814, a dual neurokinin 1 and 3 receptor antagonist, on vasomotor symptoms in postmenopausal women: a placebo-controlled, randomized trial

OBJECTIVES

To evaluate the safety, pharmacokinetics, and preliminary efficacy of NT-814, a dual neurokinin 1,3 antagonist, in postmenopausal women with vasomotor symptoms (hot flashes).

METHODS

We completed a double-blind, randomized, placebo-controlled trial in three US clinical research units in 76 postmenopausal women with moderate/severe hot flashes. Participants were randomized to 14 days of once-daily NT-814 or placebo within each of four sequential dose cohorts; 50, 100, 150, and 300 mg. Participants completed diaries of hot flash frequency and severity and waking due to night sweats before (baseline) and during treatment.

RESULTS

All prespecified efficacy parameters (24-h hot flash frequency and severity, frequency of waking due to night sweats) decreased in all groups (including placebo). Mean reduction from baseline at week 2 in moderate/severe hot flash frequency was 37% in the placebo group and, respectively, 24% (P = 0.048 vs placebo), 59% (P = 0.155), 84% (P < 0.001) and 66% (P = 0.022) in the 50 mg, 100 mg, 150 mg, and 300 mg NT-814 groups; in waking due to night sweats reduction was 20% (P = 0.059), 55% (P = 0.135), 81% (P < 0.001), and 63% (P = 0.031) in the NT-814 groups and 32% in the placebo group. The improvement with NT-814 ≥150 mg was also evident in the first week of treatment. The most common treatment-related adverse events were mild somnolence and headache, more frequently in the 300 mg group. Safety monitoring identified no concerns.

CONCLUSIONS

Once-daily NT-814 (≥150 mg/d) resulted in a rapid, marked improvement in hot flashes and waking due to night sweats. No safety concerns were identified. Doses up to 300 mg were well tolerated.

Neurokinin 3 receptor antagonists - prime time?

Vasomotor symptoms (hot flushes, flashes, night sweats) occur in the majority of menopausal women, and are reported as being of the highest symptom priority as they often persist over many years and can be highly disruptive. Hormone therapy is the most effective available treatment but is not without risk if taken long term, and is sometimes contraindicated; for example, in women with a personal or family history of breast cancer, which is the most common female cancer worldwide. Other treatment alternatives are not as efficacious, can cause side effects, and/or are not widely available. A new, effective, targeted treatment could therefore benefit millions of women worldwide. This became possible to investigate after accumulated evidence from both animal and human models implicated heightened signaling of a hypothalamic neuropeptide together with its receptor (neurokinin B/NK3R) in the etiology of sex-steroid-deficient vasomotor symptoms. Four clinical trials of three chemically distinct oral NK3R antagonists for the treatment of menopausal flushes have since completed and published, which consistently demonstrate efficacy and tolerability of these agents. These suggest great promise to change practice in the future if ongoing further larger-scale studies of longer duration confirm the same; as, estrogen exposure will no longer be required to effectively and safely treat vasomotor symptoms.

The neuroendocrinology of the preoptic area in menopause: Symptoms and therapeutic strategies

The preoptic area of the hypothalamus is the central hub of thermoregulation in mammals, coordinating autonomic heat-effector pathways in response to sensory information from the ambient and internal environment. This aims to maintain temperature homeostasis at a predetermined thermoregulatory set-point. However, hormonal and neuronal changes during the menopause, including estrogen deficiency, disrupt these normal thermoregulatory responses. This results in abnormal activation of heat dissipation effectors, manifesting clinically as hot flush symptoms. Neurokinin B (NKB) signaling via the neurokinin-3 receptor (NK3R) within the preoptic area is thought to play an important role in the pathophysiology of hot flushes. Therefore attenuation of the NKB/NK3R signaling pathway has garnered much interest as a novel therapeutic target for the amelioration of menopausal hot flushes. Recent clinical trials have demonstrated that NK3R antagonists can produce rapid and sustained improvements in hot flush frequency, severity, and quality of life, without the need for estrogen exposure. Therefore NK3R antagonists are fast emerging as a safe and efficacious alternative to hormone replacement therapy, the current gold standard of treatment.

Gonadotropin-releasing hormone analogs: Mechanisms of action and clinical applications in female reproduction

Extra-hypothalamic GnRH and extra-pituitary GnRH receptors exist in multiple human reproductive tissues, including the ovary, endometrium and myometrium. Recently, new analogs (agonists and antagonists) and modes of GnRH have been developed for clinical application during controlled ovarian hyperstimulation for assisted reproductive technology (ART). Additionally, the analogs and upstream regulators of GnRH suppress gonadotropin secretion and regulate the functions of the reproductive axis. GnRH signaling is primarily involved in the direct control of female reproduction. The cellular mechanisms and action of the GnRH/GnRH receptor system have been clinically applied for the treatment of reproductive disorders and have widely been introduced in ART. New GnRH analogs, such as long-acting GnRH analogs and oral nonpeptide GnRH antagonists, are being continuously developed for clinical application. The identification of the upstream regulators of GnRH, such as kisspeptin and neurokinin B, provides promising potential to develop these upstream regulator-related analogs to control the hypothalamus-pituitary-ovarian axis.

Pharmacodynamic Activity of the Novel Neurokinin-3 Receptor Antagonist SJX-653 in Healthy Men

CONTEXT

SJX-653 is a novel neurokinin 3 receptor (NK3R) antagonist. The NK3 pathway is a central regulator of gonadotropin releasing hormone (GnRH) secretion and has also been implicated in the generation of hot flashes. Therefore, decreases of luteinizing hormone (LH) and testosterone in men serve as sensitive pharmacodynamic (PD) markers of central NK3 antagonism.

OBJECTIVE

To characterize the safety, tolerability, pharmacokinetics, and pharmacodynamic activity of SJX-653 in healthy men.

DESIGN

A randomized, placebo-controlled, double-blind, single ascending dose study.

SETTING

Phase 1 unit.

PATIENTS OR OTHER PARTICIPANTS

Seven cohorts of 6 healthy men 18-45 years of age (4:2 randomization to SJX-653/placebo per cohort).

INTERVENTION(S)

Single oral doses of 0.5-90 mg SJX-653.

MAIN OUTCOME MEASURE(S)

Safety assessments and serial pharmacokinetic (PK)/PD measurements.

RESULTS

SJX-653 was well tolerated at all dose levels. Cmax and AUC0-24 increased in a dose-proportional manner. The terminal elimination half-life ranged between 9.8 and 12.5 hours independent of dose. A statistically significant, dose-dependent, reversible reduction of LH and testosterone was observed with near maximal effect after 15 mg and little to no effect at 4.5 mg. Maximal LH reduction was 70 ± 7% (mean ± sd) at 6 hours after 30 mg SJX-653 versus 10 ± 43% for placebo (P = 0.0006); maximal T reduction was of 68 ± 5% at 8 hours after 60 mg SJX-653 versus 18 ± 11% for placebo (P < 0.0001). The plasma IC50 for LH reduction was 33 ng/mL.

CONCLUSIONS

These data demonstrate clinical proof-of-mechanism for SJX-653 as a potent centrally-acting NK3R antagonist.

Tachykinin signaling in the control of puberty onset

The tachykinin family of peptides has emerged as a critical component of the central control of the reproductive axis. Mounting evidence suggests that neurokinin B (NKB) plays an essential role in sexual maturation and fertility by directly stimulating the release of kisspeptin, with the contribution of additional tachykinins (neurokinin A [NKA] and substance P [SP]) in the fine tuning of the activity of Kiss1 neurons. The expression of tachykinins increases in the hypothalamus before puberty and, therefore, they are considered as initiators of pubertal development by stimulating the awakening of Kiss1 neurons. This is supported by studies showing delayed or absent puberty onset in humans and mice devoid of tachykinin signaling, and the advancement of puberty onset in rodents subjected to chronic activation of tachykinin receptors. This review compiles the current knowledge on the role of tachykinins in the control of puberty onset.

Kisspeptin and neurokinin B interactions in modulating gonadotropin secretion in women with polycystic ovary syndrome

STUDY QUESTION

What is the role of the hypothalamic neuropeptide neurokinin B (NKB) and its interaction with kisspeptin on GnRH/LH secretion in women with polycystic ovary syndrome (PCOS)?

SUMMARY ANSWER

Administration of neurokinin 3 receptor antagonist (NK3Ra) for 7 days reduced LH and FSH secretion and LH pulse frequency in women with PCOS, whilst the stimulatory LH response to kisspeptin-10 was maintained.

WHAT IS KNOWN ALREADY

PCOS is characterized by abnormal GnRH/LH secretion. NKB and kisspeptin are master regulators of GnRH/LH secretion, but their role in PCOS is unclear.

STUDY DESIGN, SIZE, DURATION

The NK3Ra MLE4901, 40 mg orally twice a day, was administered to women with PCOS for 7 days (n = 8) (vs no treatment, n = 7). On the last day of NK3Ra administration or the equivalent day in those not treated, women were randomized to 7-h kisspeptin-10 (4 µg/kg/h i.v.) or vehicle infusion. This was repeated with the alternate infusion in a subsequent cycle.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Subjects were women with PCOS, studied in a Clinical Research Facility. Reproductive hormones were measured before and after NK3Ra administration. On the last day of NK3Ra administration (or the equivalent cycle day in untreated women), all women attended for an 8-h frequent blood sampling to allow analysis of the pulsatile LH secretion.

MAIN RESULTS AND THE ROLE OF CHANCE

NK3Ra reduced LH secretion (4.0 ± 0.4 vs 6.5 ± 0.8 IU/l, P < 0.05) and pulse frequency (0.5 ± 0.1 vs 0.8 ± 0.1 pulses/h, P < 0.05); FSH secretion was also reduced (2.0 ± 0.3 vs 2.5 ± 0.4 IU/l, P < 0.05). Without NK3Ra pre-treatment, kisspeptin-10 increased LH secretion (5.2 ± 0.5 to 7.8 ± 1.0 IU/L, P < 0.05), with a positive relationship to oestradiol concentrations (r2 = 0.59, P < 0.05). After NK3Ra administration, the LH response to kisspeptin-10 was preserved (vehicle 3.5 ± 0.3 vs 9.0 ± 2.2 IU/l with kisspeptin-10, P < 0.05), but the positive correlation with oestradiol concentrations was abolished (r2 = 0.07, ns. after NK3Ra). FSH secretion was increased by kisspeptin-10 after NK3Ra treatment, but not without NK3Ra treatment.

LIMITATIONS, REASONS FOR CAUTION

The study did not explore the dose relationship of the effect of NK3R antagonism. The impact of obesity or other aspects of the variability of the PCOS phenotype was not studied due to the small number of subjects.

WIDER IMPLICATIONS OF THE FINDINGS

These data demonstrate the interactive regulation of GnRH/LH secretion by NKB and kisspeptin in PCOS, and that the NKB system mediates aspects of oestrogenic feedback.

STUDY FUNDING/COMPETING INTEREST(S)

Wellcome Trust through Scottish Translational Medicine and Therapeutics Initiative (102419/Z/13/A) and MRC grants (G0701682 to R.P.M. and R.A.A.) and MR/N022556/1 to the MRC Centre for Reproductive Health. This work was performed within the Edinburgh Clinical Research Facility. J.T.G. has undertaken consultancy work for AstraZeneca and Takeda Pharmaceuticals and is an employee of Boehringer Ingelheim. R.P.M. has consulted for Ogeda and was CEO of Peptocrine. R.A.A. has undertaken consultancy work for Merck, Ferring, NeRRe Therapeutics and Sojournix Inc. J.D.V. and K.S. have nothing to disclose.

TRIAL REGISTRATION NUMBER

N/A.

Kisspeptin and neurokinin B analogs use in gynecological endocrinology: where do we stand?

BACKGROUND

Recent studies have found that kisspeptin/neurokinin B/dynorphin neurons (KNDy neurons) in the infundibular nucleus play a crucial role in the reproductive axis. Analogs, both agonists and antagonists, of kisspeptin and neurokinin B (NKB) are particularly important in explaining the physiological role of KNDy in the reproductive axis in animals. The use of kisspeptin and NKB analogs has helped elucidate the regulators of the hypothalamic reproductive axis.

PURPOSE

This review describes therapeutic uses of Kiss-1 and NKB agonists, most obviously the use of kisspeptin agonists in the treatment for infertility and the induction of ovulation. Kisspeptin antagonists may have potential clinical applications in patients suffering from diseases associated with enhanced LH pulse frequency, such as polycystic ovary syndrome or menopause. The inhibition of pubertal development using Kiss antagonists may be used as a therapeutic option in precocious puberty. Kisspeptin antagonists have been found capable of inhibiting ovulation and have been proposed as novel contraceptives. Hypothalamic amenorrhea and delayed puberty are conditions in which normalization of LH secretion may potentially be achieved by treatment with both kisspeptin and NKB agonists. NKB antagonists are used to treat vasomotor symptoms in postmenopausal women, providing rapid relief of symptoms while supplanting the need for exogenous estrogen exposure.

CONCLUSIONS

There is a wide spectrum of therapeutic uses of Kiss-1 and NKB agonists, including the management of infertility, treatment for PCOS, functional hypothalamic amenorrhea or postmenopausal vasomotor symptoms, as well as contraceptive issues. Nevertheless, further research is needed before kisspeptin and NKB analogs are fully incorporated in clinical practice.

Treatment of Menopausal Vasomotor Symptoms With Fezolinetant, a Neurokinin 3 Receptor Antagonist: A Phase 2a Trial

CONTEXT

The thermoregulatory center in the hypothalamus is stimulated by neurokinin 3 receptor (NK3R) activation and inhibited by estrogen-negative feedback. This balance is disrupted in menopause, producing vasomotor symptoms (VMSs).

OBJECTIVE

To evaluate safety and efficacy of the NK3R antagonist fezolinetant in menopausal VMSs.

DESIGN

Twelve-week, double-blind, randomized, placebo-controlled study.

SETTING

Eight Belgian centers from September 2015 to October 2016.

PARTICIPANTS

Generally healthy menopausal women aged 40 to 65 years with moderate/severe VMSs.

INTERVENTIONS

Subjects were randomized (1:1) to 90 mg of fezolinetant twice daily or placebo for 12 weeks.

MAIN OUTCOME MEASURES

Subjects captured VMS severity and frequency using an electronic diary. The primary outcome was change from baseline to week 12 in total VMS score with fezolinetant vs placebo. Secondary outcomes included timing of changes in frequency and severity of moderate/severe VMSs and quality-of-life assessments at weeks 4, 8, and 12. Pharmacodynamic and pharmacokinetic effects were assessed, as were safety and tolerability.

RESULTS

Of 122 subjects screened, 87 were randomized and 80 (92%) completed the study. At week 12, fezolinetant significantly reduced total VMS score vs placebo (-26.5 vs -12.2, P < 0.001) and decreased mean frequency of moderate/severe VMSs by five episodes per day vs placebo. Severity and frequency of moderate/severe VMSs were reduced from the first day of treatment. Improvements were achieved in all quality-of-life measures. Fezolinetant was well tolerated. The most common fezolinetant-related adverse event was gastrointestinal disorder (n = 6).

CONCLUSIONS

Fezolinetant rapidly and significantly reduced moderate/severe VMSs, supporting its potential as an effective nonhormonal treatment option for menopausal women.

Neurokinin 3 Receptor Antagonists Do Not Increase FSH or Estradiol Secretion in Menopausal Women

Background

Neurokinin 3 receptor (NK3R) antagonism is a promising novel treatment for menopausal flashes. However, to avoid adverse hormonal effects it is clinically important to first confirm whether gonadotropin and estradiol concentrations change as a result of their administration.

Methods

Single-center, randomized, double-blind, placebo-controlled, crossover trial of an oral NK3R antagonist (MLE4901) in 28 women aged 40 to 62 years, experiencing >7 hot flashes/24 h; some bothersome or severe (Clinicaltrials.gov, NCT02668185). Weekly serum gonadotropins and estradiol levels were measured using commercially available automated immunoassays a priori. Serum estradiol was also measured post hoc using a highly sensitive direct assay by liquid chromatography tandem mass spectrometry. Hormone levels were compared by the paired sample t tests or by the Wilcoxon matched-pairs signed rank test, as appropriate for the distribution of the data.

Results

Mean (standard deviation) serum follicle-stimulating hormone (FSH) concentration was not significantly increased when taking MLE4901 (72.07 ± 19.81 IU/L) compared to placebo (70.03 ± 19.56 IU/L), P = .26. Serum estradiol was also not significantly altered, irrespective of which assay method was used (median interquartile range of serum estradiol by immunoassay: placebo 36 ± 3 pmol/L, MLE4901 36 ± 1 pmol/L, P = .21; median serum highly sensitive estradiol: placebo 12 ± 16 pmol/L, MLE4901 13 ± 15 pmol/L, P = .70). However, mean (standard deviation) serum luteinizing hormone concentration significantly decreased with MLE4901 (27.63 ± 9.76 IU/L) compared to placebo (30.26 ± 9.75 IU/L), P = .0024.

Implication

NK3R antagonists do not increase serum estradiol or FSH despite their reduction in hot flashes. This is clinically significant and highly reassuring for women who have a contraindication to conventional hormone therapy such as prior/existing breast cancer and/or thromboembolism.

Severity of hot flushes is inversely associated with dietary intake of vitamin B6 and oily fish

Objectives: This study investigated the links between the severity of vasomotor symptoms (VMS) and the dietary consumption of a variety of nutrients. Method: A cross-sectional analysis of the first-visit records of 262 women aged 40-65 years was conducted. The severity of their hot flushes (HF) and night sweats (NS) and their dietary consumption of nutrients were evaluated using the Menopausal Health-Related Quality of Life Questionnaire and the brief-type self-administered Diet History Questionnaire, respectively. The relationships between severity of HF/NS and dietary intake were analyzed separately for 43 major nutrients. We then evaluated different food items as sources of the nutrients. Results: After adjustment for age, body mass index, menopausal status, and background factors significantly related to VMS, only vitamin B₆ (VB₆) was significantly related to severity of HF (adjusted odds ratio per 10 μg/MJ in VB₆ intake, 0.92; 95% confidence interval, 0.86-0.97). Moreover, a significant inverse relationship was found between the consumption of oily fish as a source of VB₆ and the severity of HF. Conclusions: VB₆ and oily fish intake is inversely associated with the severity of HF in middle-aged women. Therefore, increased intake of VB₆ could help attenuate HF.

Glutamatergic Neurokinin 3 Receptor Neurons in the Median Preoptic Nucleus Modulate Heat-Defense Pathways in Female Mice

We have proposed that arcuate neurons coexpressing kisspeptin, neurokinin B, and dynorphin (KNDy neurons) contribute to hot flushes via projections to neurokinin 3 receptor (NK3R)-expressing neurons in the median preoptic nucleus (MnPO). To characterize the thermoregulatory role of MnPO NK3R neurons in female mice, we ablated these neurons using injections of saporin toxin conjugated to a selective NK3R agonist. Loss of MnPO NK3R neurons increased the core temperature (TCORE) during the light phase, with the frequency distributions indicating a regulated shift in the balance point. The increase in TCORE in the ablated mice occurred despite changes in the ambient temperature and regardless of estrogen status. We next determined whether an acute increase in ambient temperature or higher TCORE would induce Fos in preoptic enhanced green fluorescent protein (EGFP)-immunoreactive neurons in Tacr3-EGFP mice. Fos activation was increased in the MnPO but no induction of Fos was found in NK3R (EGFP-immunoreactive) neurons. Thus, MnPO NK3R neurons are not activated by warm thermosensors in the skin or viscera and are not warm-sensitive neurons. Finally, RNAscope was used to determine whether Tacr3 (NK3R) mRNA was coexpressed with vesicular glutamate transporter 2 or vesicular γ-aminobutyric acid (GABA) transporter mRNA, markers of glutamatergic and GABAergic neurotransmission, respectively. In the MnPO, 94% of NK3R neurons were glutamatergic, but in the adjacent medial preoptic area, 97% of NK3R neurons were GABAergic. Thus, NK3R neurons in the MnPO are glutamatergic and play a role in reducing TCORE but are not activated by warm thermal stimuli (internal or external). These findings suggest that KNDy neurons modulate thermosensory pathways for heat defense indirectly via a subpopulation of glutamatergic MnPO neurons that express NK3R.

Neurokinin 3 Receptor Antagonism: A Novel Treatment for Menopausal Hot Flushes

Menopause is associated with significant symptomatic burden, with approximately two-thirds of postmenopausal women suffering from vasomotor symptoms, hot flushes, and night sweats. The mainstay of treatment for hot flushes continues to be hormone replacement therapy. However, as hormone replacement therapy is contraindicated in some cases, alternative, efficacious treatment options are also required. Hot flushes are thought to arise as a result of significant changes in the neuroendocrine circuitry underpinning the reproductive axis during menopause. This includes reduced circulating ovarian oestrogens, hypersecretion of gonadotropins, and increased expression of kisspeptin and neurokinin B (NKB) within the infundibular nucleus of the hypothalamus. In recent years, NKB, predominantly acting via the neurokinin 3 receptor (NK3R), has emerged as an important player in the development of menopausal hot flushes. Antagonism of NK3R has garnered much interest as a novel therapeutic target to help ameliorate hot flush symptoms. Improvements in hot flush frequency, severity, and quality of life have been demonstrated in a number of clinical trials using novel NK3R antagonists in postmenopausal women. Within this review, we will explore the growing body of evidence supporting antagonism of NK3R as a potentially promising treatment for menopausal hot flushes.

Gonadotropins and Their Analogs: Current and Potential Clinical Applications

The gonadotropin receptors LH receptor and FSH receptor play a central role in governing reproductive competency/fertility. Gonadotropin hormone analogs have been used clinically for decades in assisted reproductive therapies and in the treatment of various infertility disorders. Though these treatments are effective, the clinical protocols demand multiple injections, and the hormone preparations can lack uniformity and stability. The past two decades have seen a drive to develop chimeric and modified peptide analogs with more desirable pharmacokinetic profiles, with some displaying clinical efficacy, such as corifollitropin alfa, which is now in clinical use. More recently, low-molecular-weight, orally active molecules with activity at gonadotropin receptors have been developed. Some have excellent characteristics in animals and in human studies but have not reached the market-largely as a result of acquisitions by large pharma. Nonetheless, such molecules have the potential to mitigate risks currently associated with gonadotropin-based fertility treatments, such as ovarian hyperstimulation syndrome and the demands of injection-based therapies. There is also scope for novel use beyond the current remit of gonadotropin analogs in fertility treatments, including application as novel contraceptives; in the treatment of polycystic ovary syndrome; in the restoration of function to inactivating mutations of gonadotropin receptors; in the treatment of ovarian and prostate cancers; and in the prevention of bone loss and weight gain in postmenopausal women. Here we review the properties and clinical application of current gonadotropin preparations and their analogs, as well as the development of novel orally active, small-molecule nonpeptide analogs.

The role of kisspeptin/neurokinin B/dynorphin neurons in pathomechanism of vasomotor symptoms in postmenopausal women: from physiology to potential therapeutic applications

Women during perimenopausal period experience a range of symptoms, which interfere with physical, sexual, and social life. About 65-75% of symptoms connected with postmenopausal period are vasomotor symptoms (VMS), such as hot flushes and night sweats. Hot flushes are subjective sensation of heat associated with cutaneous vasodilatation and drop in core temperature. It is suspected that VMS are strongly correlated with pulsatile oversecretion of gonadotropin-releasing hormone (GnRH) and subsequently luteinizing hormone (LH). Evidence has accumulated in parallel showing that lack of negative feedback of steroid hormones synthesized in ovary causes overactivation of hypertrophied kisspeptin/neurokinin B/dynorphin (KNDy) neurons, located in infundibular nucleus. Oversecretion of both kisspeptin (KISS1) and neurokinin B (NKB), as well as downregulation of dynorphin, plays dominant role in creation of GnRH pulses. This in turn causes VMS. Administration of senktide, highly potent and selective NK3R agonist, resulted in increase of serum LH concentration, induction of VMS, increase in heart rate, and skin temperature in postmenopausal women. These finding suggest that modulation of KNDy neurons may become new therapeutic approach in the treatment of VMS.

Gonadotropin-releasing hormone analog therapeutics

Dysregulation at any level of the hypothalamic-pituitary-gonadal (HPG) axis results in, or aggravates, a number of hormone-dependent diseases such as delayed or precocious puberty, infertility, prostatic and ovarian cancer, benign prostatic hyperplasia, polycystic ovarian syndrome, endometriosis, uterine fibroids, lean body mass, as well as metabolism and cognitive impairment. As gonadotropin-releasing-hormone (GnRH) is an essential regulator of the HPG axis, agonist and antagonist analogs are efficacious in the treatment of these conditions. GnRH analogs also play an important role in assisted reproductive therapies. This review highlights the current and future therapeutic potential of GnRH analogs and upstream regulators of GnRH secretion.

Estradiol alters body temperature regulation in the female mouse

Hot flushes are due to estrogen withdrawal and characterized by the episodic activation of heat dissipation effectors. Recent studies (in humans and rats) have implicated neurokinin 3 (NK₃) receptor signaling in the genesis of hot flushes. Although transgenic mice are increasingly used for biomedical research, there is limited information on how 17β-estradiol and NK₃ receptor signaling alters thermoregulation in the mouse. In this study, a method was developed to measure tail skin temperature (T_SKIN) using a small data-logger attached to the surface of the tail, which, when combined with a telemetry probe for core temperature (T_CORE), allowed us to monitor thermoregulation in freely-moving mice over long durations. We report that estradiol treatment of ovariectomized mice reduced T_CORE during the light phase (but not the dark phase) while having no effect on T_SKIN or activity. Estradiol also lowered T_CORE in mice exposed to ambient temperatures ranging from 20 to 36°C. Unlike previous studies in the rat, estradiol treatment of ovariectomized mice did not reduce T_SKIN during the dark phase. Subcutaneous injections of an NK₃ receptor agonist (senktide) in ovariectomized mice caused an acute increase in T_SKIN and a reduction in T_CORE, consistent with the activation of heat dissipation effectors. These changes were reduced by estradiol, suggesting that estradiol lowers the sensitivity of central thermoregulatory pathways to NK₃ receptor activation. Overall, we show that estradiol treatment of ovariectomized mice decreases T_CORE during the light phase, reduces the thermoregulatory effects of senktide and modulates thermoregulation differently than previously described in the rat.