Increasing LH pulsatility in women with hypothalamic amenorrhoea using intravenous infusion of Kisspeptin-54

HormoneBayes: A novel Bayesian framework for the analysis of pulsatile hormone dynamics

The hypothalamus is the central regulator of reproductive hormone secretion. Pulsatile secretion of gonadotropin releasing hormone (GnRH) is fundamental to physiological stimulation of the pituitary gland to release luteinizing hormone (LH) and follicle stimulating hormone (FSH). Furthermore, GnRH pulsatility is altered in common reproductive disorders such as polycystic ovary syndrome (PCOS) and hypothalamic amenorrhea (HA). LH is measured routinely in clinical practice using an automated chemiluminescent immunoassay method and is the gold standard surrogate marker of GnRH. LH can be measured at frequent intervals (e.g., 10 minutely) to assess GnRH/LH pulsatility. However, this is rarely done in clinical practice because it is resource intensive, and there is no open-access, graphical interface software for computational analysis of the LH data available to clinicians. Here we present hormoneBayes, a novel open-access Bayesian framework that can be easily applied to reliably analyze serial LH measurements to assess LH pulsatility. The framework utilizes parsimonious models to simulate hypothalamic signals that drive LH dynamics, together with state-of-the-art (sequential) Monte-Carlo methods to infer key parameters and latent hypothalamic dynamics. We show that this method provides estimates for key pulse parameters including inter-pulse interval, secretion and clearance rates and identifies LH pulses in line with the widely used deconvolution method. We show that these parameters can distinguish LH pulsatility in different clinical contexts including in reproductive health and disease in men and women (e.g., healthy men, healthy women before and after menopause, women with HA or PCOS). A further advantage of hormoneBayes is that our mathematical approach provides a quantified estimation of uncertainty. Our framework will complement methods enabling real-time in-vivo hormone monitoring and therefore has the potential to assist translation of personalized, data-driven, clinical care of patients presenting with conditions of reproductive hormone dysfunction.

Quantifying the variability in the assessment of reproductive hormone levels

OBJECTIVE

To quantify how representative a single measure of reproductive hormone level is of the daily hormonal profile using data from detailed hormonal sampling in the saline placebo-treated arm conducted over several hours.

DESIGN

Retrospective analysis of data from previous interventional research studies evaluating reproductive hormones.

SETTING

Clinical Research Facility at a tertiary reproductive endocrinology centre at Imperial College Hospital NHS Foundation Trust.

PATIENTS

Overall, 266 individuals, including healthy men and women (n = 142) and those with reproductive disorders and states (n = 124 [11 with functional hypothalamic amenorrhoea, 6 with polycystic ovary syndrome, 62 women and 32 men with hypoactive sexual desire disorder, and 13 postmenopausal women]), were included in the analysis.

INTERVENTIONS

Data from 266 individuals who had undergone detailed hormonal sampling in the saline placebo-treated arms of previous research studies was used to quantify the variability in reproductive hormones because of pulsatile secretion, diurnal variation, and feeding using coefficient of variation (CV) and entropy.

MAIN OUTCOME MEASURES

The ability of a single measure of reproductive hormone level to quantify the variability in reproductive hormone levels because of pulsatile secretion, diurnal variation, and nutrient intake.

RESULTS

The initial morning value of reproductive hormone levels was typically higher than the mean value throughout the day (percentage decrease from initial morning measure to daily mean: luteinizing hormone level 18.4%, follicle-stimulating hormone level 9.7%, testosterone level 9.2%, and estradiol level 2.1%). Luteinizing hormone level was the most variable (CV 28%), followed by sex-steroid hormone levels (testosterone level 12% and estradiol level 13%), whereas follicle-stimulating hormone level was the least variable reproductive hormone (CV 8%). In healthy men, testosterone levels fell between 9:00 am and 5:00 pm by 14.9% (95% confidence interval 4.2, 25.5%), although morning levels correlated with (and could be predicted from) late afternoon levels in the same individual (r2 = 0.53, P<.0001). Testosterone levels were reduced more after a mixed meal (by 34.3%) than during ad libitum feeding (9.5%), after an oral glucose load (6.0%), or an intravenous glucose load (7.4%).

CONCLUSION

Quantification of the variability of a single measure of reproductive hormone levels informs the reliability of reproductive hormone assessment.

[Endocrine and psychosomatic disorders in patients with amenorrhea]

The article presents data on the relationship of pathogenetic mechanisms for the development of menstrual disorders of functional and organic origin in connection with mental disturbances from the point of view of the psychosomatic concept. According to the latter, functional disorders of the menstrual cycle are considered as psychosomatic, in which gynecological pathology develops as a result of psychopathological illness. A striking example of such a disorder is functional hypothalamic amenorrhea. At the same time, endocrinopathies, such as polycystic ovary syndrome and premature ovarian insufficiency, can also be considered in the paradigm of psychosomatic illnesses of ovarian function due to the high prevalence of anxiety and depressive disorders in this cohort of patients. This review highlights the importance of interdisciplinary collaboration between a gynecologist and a psychiatrist for the most effective reproductive rehabilitation of patients with amenorrhea. Literature search was carried out in national (eLibrary, CyberLeninka.ru) and international (PubMed, Cochrane Library) databases in Russian and English. The priority was free access to the full text of articles. The choice of sources was prioritized for the period from 2018 to 2023.However, taking into account the insufficient knowledge of the chosen topic, the choice of sources dates back to 1985.

The Emerging Therapeutic Potential of Kisspeptin and Neurokinin B

Kisspeptin (KP) and neurokinin B (NKB) are neuropeptides that govern the reproductive endocrine axis through regulating hypothalamic gonadotropin-releasing hormone (GnRH) neuronal activity and pulsatile GnRH secretion. Their critical role in reproductive health was first identified after inactivating variants in genes encoding for KP or NKB signaling were shown to result in congenital hypogonadotropic hypogonadism and a failure of pubertal development. Over the past 2 decades since their discovery, a wealth of evidence from both basic and translational research has laid the foundation for potential therapeutic applications. Beyond KP's function in the hypothalamus, it is also expressed in the placenta, liver, pancreas, adipose tissue, bone, and limbic regions, giving rise to several avenues of research for use in the diagnosis and treatment of pregnancy, metabolic, liver, bone, and behavioral disorders. The role played by NKB in stimulating the hypothalamic thermoregulatory center to mediate menopausal hot flashes has led to the development of medications that antagonize its action as a novel nonsteroidal therapeutic agent for this indication. Furthermore, the ability of NKB antagonism to partially suppress (but not abolish) the reproductive endocrine axis has supported its potential use for the treatment of various reproductive disorders including polycystic ovary syndrome, uterine fibroids, and endometriosis. This review will provide a comprehensive up-to-date overview of the preclinical and clinical data that have paved the way for the development of diagnostic and therapeutic applications of KP and NKB.

Endocrine profile of the kisspeptin receptor agonist MVT-602 in healthy premenopausal women with and without ovarian stimulation: results from 2 randomized, placebo-controlled clinical tricals

BACKGROUND

Kisspeptin is an essential regulator of hypothalamic gonadotropin-releasing hormone release and is required for physiological ovulation. Native kisspeptin-54 can induce oocyte maturation during in vitro fertilization treatment, including in women who are at high risk of ovarian hyperstimulation syndrome. MVT-602 is a potent kisspeptin receptor agonist with prospective utility to treat anovulatory disorders by triggering oocyte maturation and ovulation during medically assisted reproduction (MAR). Currently, the endocrine profile of MVT-602 during ovarian stimulation is unreported.

OBJECTIVE

To determine the endocrine profile of MVT-602 in the follicular phase of healthy premenopausal women (phase-1 trial), and after minimal ovarian stimulation to more closely reflect the endocrine milieu encountered during MAR (phase-2a trial).

DESIGN

Two randomized, placebo-controlled, parallel-group, dose-finding trials.

SETTING

Clinical trials unit.

PATIENTS

Healthy women aged 18-35 years, either without (phase-1; n = 24), or with ovarian stimulation (phase-2a; n = 75).

INTERVENTIONS

Phase-1: single subcutaneous dose of MVT-602 (0.3, 1.0, or 3.0 μg) or placebo, (n = 6 per dose). Phase-2a: single subcutaneous dose of MVT-602 (0.1, 0.3, 1.0, or 3.0 μg; n = 16-17 per dose), triptorelin 0.2 mg (n = 5; active comparator), or placebo (n = 5).

MAIN OUTCOME MEASURES

Phase-1: safety/tolerability; pharmacokinetics; and pharmacodynamics (luteinizing hormone [LH] and other reproductive hormones). Phase-2a: safety/tolerability; pharmacokinetics; pharmacodynamics (LH and other reproductive hormones); and time to ovulation assessed by transvaginal ultrasound.

RESULTS

In both the trials, MVT-602 was safe and well tolerated across the entire dose range. It was rapidly absorbed and eliminated, with a mean elimination half-life of 1.3-2.2 hours. In the phase-2a trial, LH concentrations increased dose dependently; mean maximum change from baseline of 82.4 IU/L at 24.8 hours was observed after administration of 3 μg MVT-602 and remained >15 IU/L for 33 hours. Time to ovulation after drug administration was 3.3-3.9 days (MVT-602), 3.4 days (triptorelin), and 5.5 days (placebo). Ovulation occurred within 5 days of administration in 100% (3 μg), 88% (1 μg), 82% (0.3 μg), and 75% (0.1 μg), of women after MVT-602, 100% after triptorelin and 60% after placebo.

CONCLUSIONS

MVT-602 induces LH concentrations of similar amplitude and duration as the physiological midcycle LH surge with potential utility for induction of oocyte maturation and ovulation during MAR.

CLINICAL TRIAL REGISTRATION NUMBER

EUDRA-CT: 2017-003812-38, 2018-001379-20.

KNDy Neurons of the Hypothalamus and Their Role in GnRH Pulse Generation: an Update

There is considerable evidence that synchronized activity within a reciprocally connected population of cells in the arcuate nucleus (ARC) coexpressing kisspeptin, neurokinin B (NKB), and dynorphin (KNDy cells) is crucial for the generation of gonadotrophin-releasing hormone (GnRH) pulses in mammals. The initial "KNDy hypothesis" proposed that pulsatile GnRH secretion is elicited by episodic kisspeptin release from KNDy cells following synchronized activation and termination of the population by NKB and dynorphin, respectively. Since then, the role of KNDy cells as a critical component of the pulse generator has been further supported by studies at the single-cell level, demonstrating that the population is both necessary and sufficient for pulsatility. In addition, there have been considerable modifications and expansion of the original hypothesis, including work demonstrating the critical role of glutamate in synchronization of the KNDy cell network, functional interactions with other ARC subpopulations, and the existence of species differences in the role of dynorphin in pulse generation. Here we review these recent changes and discuss how the translation of these findings has led to the development of new therapies for disorders related to pulse generation. We also outline critical gaps in knowledge that are currently limiting the application of KNDy research in the clinic, particularly regarding the role of dynorphin in pulse generation in primates.

Neuroendocrine disturbances in women with functional hypothalamic amenorrhea: an update and future directions

Functional hypothalamic amenorrhea (FHA) is one of the most common causes of both primary and secondary amenorrhea in women of reproductive age. It is characterized by chronic anovulation and the absence of menses that appear as a result of stressors such as eating disorders, excessive exercise, or psychological distress. FHA is presumed to be a functional disruption in the pulsatile secretion of hypothalamic gonadotropin-releasing hormone, which in turn impairs the release of gonadotropin. Hypoestrogenism is observed due to the absence of ovarian follicle recruitment. Numerous neurotransmitters have been identified which play an important role in the regulation of the hypothalamic-pituitary-ovarian axis and of which the impairment would contribute to developing FHA. In this review we summarize the most recent advances in the identification of contributing neuroendocrine disturbances and relevant contributors to the development of FHA.

Functional Hypothalamic Amenorrhea: Recognition and Management of a Challenging Diagnosis

Functional hypothalamic amenorrhea is responsible for approximately a third of the cases of secondary amenorrhea. The condition is a result of disturbances in gonadotropin-releasing hormone pulsatile secretion at the level of the hypothalamus, which in turn disrupts gonadotropin secretion. It is due to psychosocial stress, disordered eating, and/or excessive exercise. Often, however, it is a combination of more than one etiology, with a possible role for genetic or epigenetic predisposition. The dysfunctional gonadotropin-releasing hormone release leads to the cessation of ovarian function, resulting in amenorrhea, infertility, and a long-term impact on affected women's bone health, cardiovascular risk, cognition, and mental health. Functional hypothalamic amenorrhea is a diagnosis of exclusion, and treatment involves identifying and reversing the underlying cause(s). The aim of this concise review is to summarize the current knowledge of functional hypothalamic amenorrhea, review its pathophysiology and the adverse health consequences, and provide recommendations for diagnosis and management of this condition. Furthermore, this review will emphasize the gaps in research on this common condition impacting women of reproductive age all over the world.

Optogenetics studies of kisspeptin neurons

Optical systems and genetic engineering technologies have made it possible to control neurons and unravel neuronal circuit behavior with high temporal and spatial resolution. The application of optogenetic strategies to understand the physiology of kisspeptin neuronal circuits has evolved in recent years among the neuroendocrine community. Kisspeptin neurons are fundamentally involved in controlling mammalian reproduction but also are implicated in numerous other physiological processes, including but not limited to feeding, energy expenditure, core body temperature and behavior. We conducted a review aiming to shed light on the novel findings obtained from in vitro and in vivo optogenetic studies interrogating kisspeptin neuronal circuits to date. Understanding the function of kisspeptin networks in the brain can greatly inform a wide range of clinical studies investigating infertility treatments, gender identity, metabolic disorders, hot flushes and psychosexual disorders.

Current pharmacotherapy and future directions for neuroendocrine causes of female infertility

INTRODUCTION

Infertility is recognized as a major global health issue, often associated with significant psychological distress for affected couples. Causes of female infertility include endocrine conditions leading to oligo/anovulation, in addition to structural causes such as tubal, uterine, or peritoneal disorders. Pharmacological treatments, targeting pathways in the hypothalamic-pituitary-ovarian axis, can improve rates of ovulation, conception, pregnancy, and birth. Some existing therapeutic options are hindered by limited efficacy or by a non-physiological mechanism, which can risk excessive stimulation and treatment-related adverse effects. Therefore, there is a continued need for novel therapies to improve care for patients suffering with infertility.

AREAS COVERED

In this review, the authors focus on endocrine causes of oligo/anovulation in women and on advances in assisted reproductive technology. Current pharmacological treatments and putative future therapeutic avenues in development to aid fertility in women are outlined.

EXPERT OPINION

A deeper understanding of the reproductive neuroendocrine network governing hypothalamic gonadotropin-releasing hormone release can offer novel therapeutic targets for the treatment of female subfertility, leading to improved clinical outcomes, less invasive routes of administration, and decreased treatment-related side-effects. The ultimate aim of development in female subfertility is to offer therapeutic interventions that are effective, reproducible, associated with minimal risks, and have an acceptable route of administration.

Hypothalamic-Pituitary-Gonadal Axis Disorders Impacting Fertility in Both Sexes and the Potential of Kisspeptin-Based Therapies to Treat Them

Impaired function of the hypothalamic-pituitary-gonadal (HPG) axis can lead to a vast array of reproductive disorders some of which are inherited or acquired, but many are of unknown etiology. Among the clinical consequences of HPG impairment, infertility is quite common. According to the latest report from the World Health Organization, the global prevalence of infertility during a person's lifetime is a staggering 17.5% which translate into 1 out of every 6 people experiencing it. In both sexes, infertility is associated with adverse health events, and if unresolved, infertility can cause substantial psychological stress, social stigmatization, and economic strain. Even though significant advances have been made in the management and treatment of infertility, low or variable efficacy of treatments and medication adverse effects still pose a significant problem. However, the discovery that in humans inactivating mutations in the gene encoding the kisspeptin receptor (Kiss1R) results in pubertal failure and infertility has expanded our understanding of the mechanisms underlying the neuroendocrine control of reproduction, opening up potential new therapies for the treatment of infertility disorders. In this chapter we provide an overview of common infertility disorders affecting men and women, their recommended treatments, and the potential of kisspeptin-based pharmacotherapies to treat them.

Stress, kisspeptin, and functional hypothalamic amenorrhea

Functional hypothalamic amenorrhea (FHA) is the most common cause of secondary amenorrhea in women of reproductive age. FHA is predominantly caused by stress, decreased caloric intake, excessive exercise, or a combination thereof. These physical, psychological, and metabolic stressors cause aberration in the pulsatile release of gonadotropin-releasing hormone (GnRH) and subsequently impair function of the hypothalamic-pituitary-ovarian (HPO) axis. Various neurotransmitters acting in the central nervous system are involved in control of the HPO axis and of these, kisspeptin is one of the most important. Corticotropin-releasing hormone (CRH), also inhibits the pulsatile secretion of GnRH and also acts as an intermediary between stress factors and the reproductive system. One of the main ongoing concerns in patients with FHA is chronic hypoestrogenism, a condition, which is associated with sexual dysfunction and infertility. It may also lead to osteoporosis, and predispose to neurodegenerative and cardiovascular diseases. Treatment of FHA requires the elimination of causative factors, however, making the necessary lifestyle changes is not always easy to initiate and maintain. Broadening our knowledge of the complex neural mechanisms regulating reproductive function in which kisspeptin plays a key role can help in the development of new treatment options such as the potential of kisspeptin receptor agonists for patients with FHA.

Quantitative approaches in clinical reproductive endocrinology

Understanding the human hypothalamic-pituitary-gonadal (HPG) axis presents a major challenge for medical science. Dysregulation of the HPG axis is linked to infertility and a thorough understanding of its dynamic behaviour is necessary to both aid diagnosis and to identify the most appropriate hormonal interventions. Here, we review how quantitative models are being used in the context of clinical reproductive endocrinology to: 1. analyse the secretory patterns of reproductive hormones; 2. evaluate the effect of drugs in fertility treatment; 3. aid in the personalization of assisted reproductive technology (ART). In this review, we demonstrate that quantitative models are indispensable tools enabling us to describe the complex dynamic behaviour of the reproductive axis, refine the treatment of fertility disorders, and predict clinical intervention outcomes.

Novel therapeutic avenues for kisspeptin

Kisspeptin is a hypothalamic neuropeptide that acts via the hypothalamus to stimulate hypothalamic gonadotrophin-releasing hormone secretion and downstream gonadotrophin release. In health, kisspeptin induces normal puberty and modulates ovulation in healthy women. Hypothalamic kisspeptin expression is reduced in several functional reproductive disorders; thus, treating such conditions with kisspeptin is conceptually attractive. Recent studies have demonstrated that kisspeptin can induce a more physiological degree of oocyte maturation during in vitro fertilisation treatment that can reduce the risk of potentially life-threatening complications such as ovarian hyperstimulation syndrome seen with human chorionic gonadotrophin. Furthermore, chronic use of kisspeptin could potentially restore reproductive health in females with hypothalamic amenorrhoea, treat hyposexual drive disorder in otherwise healthy males and has potential indications in polycystic ovary syndrome, osteoporosis and metabolic dysfunction-associated fatty liver disease. Finally, kisspeptin analogues could potentially overcome some of the pharmacological challenges associated with the natural forms of kisspeptin such as short duration of action and development of tachyphylaxis.

Invited review: Translating kisspeptin and neurokinin B biology into new therapies for reproductive health

The reproductive neuropeptide kisspeptin has emerged as the master regulator of mammalian reproduction due to its key roles in the initiation of puberty and the control of fertility. Alongside the tachykinin neurokinin B and the endogenous opioid dynorphin, these peptides are central to the hormonal control of reproduction. Building on the expanding body of experimental animal models, interest has flourished with human studies revealing that kisspeptin administration stimulates physiological reproductive hormone secretion in both healthy men and women, as well as patients with common reproductive disorders. In addition, emerging therapeutic roles based on neurokinin B for the management of menopausal flushing, endometriosis and uterine fibroids are increasingly recognised. In this review, we focus on kisspeptin and neurokinin B and their potential application as novel clinical strategies for the management of reproductive disorders.

The role of Kisspeptin signaling in Oocyte maturation

Kisspeptins (KPs) secreted from the hypothalamic KP neurons act on KP receptors (KPRs) in gonadotropin (GPN) releasing hormone (GnRH) neurons to produce GnRH. GnRH acts on pituitary gonadotrophs to induce secretion of GPNs, namely follicle stimulating hormone (FSH) and luteinizing hormone (LH), which are essential for ovarian follicle development, oocyte maturation and ovulation. Thus, hypothalamic KPs regulate oocyte maturation indirectly through GPNs. KPs and KPRs are also expressed in the ovarian follicles across species. Recent studies demonstrated that intraovarian KPs also act directly on the KPRs expressed in oocytes to promote oocyte maturation and ovulation. In this review article, we have summarized published reports on the role of hypothalamic and ovarian KP-signaling in oocyte maturation. Gonadal steroid hormones regulate KP secretion from hypothalamic KP neurons, which in turn induces GPN secretion from the hypothalamic-pituitary (HP) axis. On the other hand, GPNs secreted from the HP axis act on the granulosa cells (GCs) and upregulate the expression of ovarian KPs. While KPs are expressed predominantly in the GCs, the KPRs are in the oocytes. Expression of KPs in the ovaries increases with the progression of the estrous cycle and peaks during the preovulatory GPN surge. Intrafollicular KP levels in the ovaries rise with the advancement of developmental stages. Moreover, loss of KPRs in oocytes in mice leads to failure of oocyte maturation and ovulation similar to that of premature ovarian insufficiency (POI). These findings suggest that GC-derived KPs may act on the KPRs in oocytes during their preovulatory maturation. In addition to the intraovarian role of KP-signaling in oocyte maturation, in vivo, a direct role of KP has been identified during in vitro maturation of sheep, porcine, and rat oocytes. KP-stimulation of rat oocytes, in vitro, resulted in Ca2+ release and activation of the mitogen-activated protein kinase, extracellular signal-regulated kinase 1 and 2. In vitro treatment of rat or porcine oocytes with KPs upregulated messenger RNA levels of the factors that favor oocyte maturation. In clinical trials, human KP-54 has also been administered successfully to patients undergoing assisted reproductive technologies (ARTs) for increasing oocyte maturation. Exogenous KPs can induce GPN secretion from hypothalamus; however, the possibility of direct KP action on the oocytes cannot be excluded. Understanding the direct in vivo and in vitro roles of KP-signaling in oocyte maturation will help in developing novel KP-based ARTs.

Kisspeptin Modulation of Reproductive Function

Kisspeptin is a peptide expressed mainly in the infundibular nucleus of the hypothalamus. Kisspeptin plays a crucial role in the regulation of reproductive functions. It is regarded as the most important factor responsible for the control of the hypothalamic–pituitary–gonadal axis, the onset of puberty, and the regulation of menstruation and fertility. Kisspeptin activity influences numerous processes such as steroidogenesis, follicular maturation, ovulation, and ovarian senescence. The identification of kisspeptin receptor mutations that cause hypogonadotropic hypogonadism has initiated studies on the role of kisspeptin in puberty. Pathologies affecting the neurons secreting kisspeptin play a major role in the development of PCOS, functional hypothalamic amenorrhea, and perimenopausal vasomotor symptoms. Kisspeptin analogs (both agonists and antagonists), therefore, may be beneficial as therapy in those afflicted with such pathologies. The aim of this review is to summarize the influence of kisspeptin in the physiology and pathology of the reproductive system in humans, as well as its potential use in therapy.

Bone Perspectives in Functional Hypothalamic Amenorrhoea: An Update and Future Avenues

One of the most important and potentially long-lasting detrimental consequences of Functional Hypothalamic Amenorrhoea (FHA) is on skeletal homeostasis. Beyond oestrogen deficiency, FHA is associated with a cascade of additional neuro-endocrine and metabolic alterations, some adaptive, but which combine to disrupt skeletal homeostasis. Ultimately, this leads to a two-fold increased risk of fractures in women with FHA compared to healthy eumenorrhoeic women. Although the cornerstone of management of FHA-related bone loss remains recovery of menses via restoration of metabolic/psychological balance, there is rapidly developing evidence for hormonal manipulations (with a particular emphasis on route of administration) and other pharmacological treatments that can protect or improve skeletal homeostasis in FHA. In this mini-review, we provide an update on the pathophysiology, clinical management and future avenues in the field from a bone perspective.

Kisspeptin Variations in Patients with Polycystic Ovary Syndrome-A Prospective Case Control Study

Background and objectives: Kisspeptin, also named metastin, showed important roles in initiating the secretion of gonadotropin-releasing hormone (GnRH) and is an essential factor in the development of polycystic ovaries syndrome (PCOS). Several research studies noticed associations between kisspeptin levels and patients with anovulatory cycles due to PCOS with an increased LH/FSH ratio. The aim of our study was to bring scientific evidence regarding the correlation between high kisspeptin and luteinizing hormone values in subfertile women due to PCOS. Materials and Methods: A prospective case-control study was conducted in “Elena Doamna” Hospital of Obstetrics and Gynecology between 4 January 2021 and 1 March 2022. All patients agreed to participate in our study, had ages between 18 and 45 years old, and had a body mass index between 18.5 and 30 kg/m². The study group consisted of subfertile patients with PCOS and menstrual disturbances, including amenorrhea or oligomenorrhea. The control group consisted of healthy patients with ovulatory cycles and no other reproductive or endocrinology pathologies. During the follicular phase of their menstrual cycle, patients had blood samples taken with the dosage of kisspeptin, LH, FSH, estradiol, insulin, glycemic levels, testosterone, and prolactin. Pelvic ultrasounds and clinical examinations were performed as well. Results: Significant differences were observed in kisspeptin, LH, FSH, and estradiol levels between patients with PCOS and the control group. After the univariate analysis, PCOS was significantly associated with increased kisspeptin, increased LH, and decreased FSH. There was no significant association between PCOS, estradiol, prolactin, and insulin. Conclusions: kisspeptin serum values are higher in subfertile PCOS patients, supporting the hypothesis that an over-stimulation of the KISS1 system might cause the hyper-stimulation of the HPG-axis.

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.

Acute Effects of Kisspeptin Administration on Bone Metabolism in Healthy Men

CONTEXT

Osteoporosis results from disturbances in bone formation and resorption. Recent nonhuman data suggest that the reproductive hormone kisspeptin directly stimulates osteoblast differentiation in vitro and thus could have clinical therapeutic potential. However, the effects of kisspeptin on human bone metabolism are currently unknown.

OBJECTIVE

To assess the effects of kisspeptin on human bone metabolism in vitro and in vivo.

METHODS

In vitro study: of Mono- and cocultures of human osteoblasts and osteoclasts treated with kisspeptin. Clinical study: Randomized, placebo-controlled, double-blind, 2-way crossover clinical study in 26 men investigating the effects of acute kisspeptin administration (90 minutes) on human bone metabolism, with blood sampling every 30 minutes to +90 minutes. Cells for the in vitro study were from 12 male blood donors and 8 patients undergoing hip replacement surgery. Twenty-six healthy eugonadal men (age 26.8 ± 5.8 years) were included in the clinical study. The intervention was Kisspeptin (vs placebo) administration. The main outcome measures were changes in bone parameters and turnover markers.

RESULTS

Incubation with kisspeptin in vitro increased alkaline phosphatase levels in human bone marrow mesenchymal stem cells by 41.1% (P = .0022), and robustly inhibited osteoclastic resorptive activity by up to 53.4% (P < .0001), in a dose-dependent manner. Kisspeptin administration to healthy men increased osteoblast activity, as evidenced by a 20.3% maximal increase in total osteocalcin (P = .021) and 24.3% maximal increase in carboxylated osteocalcin levels (P = .014).

CONCLUSION

Collectively, these data provide the first human evidence that kisspeptin promotes osteogenic differentiation of osteoblast progenitors and inhibits bone resorption in vitro. Furthermore, kisspeptin acutely increases the bone formation marker osteocalcin but not resorption markers in healthy men, independent of downstream sex steroid levels. Kisspeptin could therefore have clinical therapeutic application in the treatment of osteoporosis.

A customized long acting formulation of the kisspeptin analog C6 triggers ovulation in anestrus ewe

The modulation of the kisspeptin system holds promise as a treatment for human reproductive disorders and for managing livestock breeding. The design of analogs has overcome some unfavorable properties of the endogenous ligands. However, for applications requiring a prolongation of drug activity, such as ovulation induction in the ewe during the non-breeding season, additional improvement is required. To this aim, we designed and tested three formulations containing the kisspeptin analog C6. Two were based on polymeric nanoparticles (NP1 and NP2) and the third was based on hydrogels composed of a mixture of cyclodextrin polymers and dextran grafted with alkyl side chains (MD/pCD). Only the MD/pCD formulation prolonged C6 activity, as shown by monitoring luteinizing hormone (LH) plasma concentration (elevation duration 23.4 ± 6.1, 13.7 ± 4.7 and 12.0 ± 2.4 h for MD/pCD, NP1 and NP2, respectively). When compared with the free C6 (15 nmol/ewe), the formulated (MD/pCD) doses of 10, 15 and 30 nmol/ewe, but not the 90 nmol/ewe dose, provided a more gradual release of C6 as shown by an attenuated LH release during the first 6 h post-treatment. When tested during the non-breeding season without progestogen priming, only, the formulated 30 nmol/ewe dose triggered ovulation (50% of ewes). Hence, we showed that a formulation with an adapted action time would improve the efficacy of C6 with respect to inducing ovulation during the non-breeding season. This result suggests that formulations containing a kisspeptin analog might find applications in the management of livestock reproduction but also point to the possibility of their use for the treatment of some human reproductive pathologies.

Neuropeptides as regulators of the hypothalamus-pituitary-gonadal (HPG) axis activity and their putative roles in stress-induced fertility disorders

Neuropeptides being regulators of the hypothalamus-pituitary-adrenal (HPA) axis activity, also affect the function of the hypothalamus-pituitary-gonadal (HPG) axis by regulating gonadotrophin-releasing hormone (GnRH) secretion from hypothalamic neurons. Here, we review the available data on how neuropeptides affect HPG axis activity directly or indirectly via their influence on the HPA axis. The putative role of neuropeptides in stress-induced infertility, such as polycystic ovary syndrome, is also described. This review discusses both well-known neuropeptides (i.e., kisspeptin, Kp; oxytocin, OT; arginine-vasopressin, AVP) and more recently discovered peptides (i.e., relaxin-3, RLN-3; nesfatin-1, NEFA; phoenixin, PNX; spexin, SPX). For the first time, we present an up-to-date review of all published data regarding interactions between the aforementioned neuropeptide systems. The reviewed literature suggest new pathophysiological mechanisms leading to fertility disturbances that are induced by stress.

Kiss1 expression in the hypothalamic arcuate nucleus is lower in dairy cows of reduced fertility

We tested the hypothesis that divergent genetic merit for fertility of dairy cows is due to aberrant reproductive neuroendocrine function. The kisspeptin status of non-pregnant cows of either positive (POS) or negative (NEG) breeding values (BVs) for fertility was studied in three groups (n = 8), based on their previous post-partum period: POS cows, which had spontaneous ovarian cycles (POS-CYC) and NEG cows, which either cycled (NEG-CYC) or did not cycle (NEG-NONCYC). Ovarian cycles were synchronized, blood samples were taken to define endocrine status, and the animals were slaughtered in an artificial follicular phase. The brains and the pituitary glands were collected for quantitative polymerase chain reaction (qPCR) and in situ hybridization of hypothalamic GNRH1, Kiss1, TAC3, and PDYN and pituitary expression of LHB and FSHB. Gonadotropin releasing hormone (GnRH) and kisspeptin levels were quantified in snap frozen median eminence (ME). GNRH1 expression and GnRH levels in the ME were similar across groups. Kiss1 expression in the preoptic area of the hypothalamus was also similar across groups, but Kiss1 in the arcuate nucleus was almost 2-fold higher in POS-CYC cows than in NEG groups. TAC3 expression was higher in POS-CYC cows. The number of pituitary gonadotropes and the level of expression of LHB and FSHB were similar across groups. We conclude that the lower levels of Kiss1 and TAC3 in NEG cows with low fertility status and may lead to deficient GnRH and gonadotropin secretion.

Kisspeptin-neuron control of LH pulsatility and ovulation

Feedback from oestradiol (E2) plays a critical role in the regulation of major events in the physiological menstrual cycle including the release of gonadotrophins to stimulate follicular growth, and the mid-cycle luteinising hormone (LH) surge that leads to ovulation. E2 predominantly exerts its action via oestrogen receptor-alpha (ERα), however, as gonadotrophin releasing hormone (GnRH) neurons lack ERα, E2-feedback is posited to be indirectly mediated via upstream neurons. Kisspeptin (KP) is a neuropeptide expressed in hypothalamic KP-neurons that control GnRH secretion and plays a key role in the central mechanism regulating the hypothalamic-pituitary-gonadal (HPG) axis. In the rodent arcuate (ARC) nucleus, KP is co-expressed with Neurokinin B and Dynorphin; and thus, these neurons are termed 'Kisspeptin-Neurokinin B-Dynorphin' (KNDy) neurons. ARC KP-neurons function as the 'GnRH pulse generator' to regulate GnRH pulsatility, as well as mediating negative feedback from E2. A second KP neuronal population is present in the rostral periventricular area of the third ventricle (RP3V), which includes anteroventral periventricular (AVPV) nucleus and preoptic area neurons. These RP3V KP-neurons mediate positive feedback to induce the mid-cycle luteinising hormone (LH) surge and subsequent ovulation. Here, we describe the role of KP-neurons in these two regions in mediating this differential feedback from oestrogens. We conclude by considering reproductive diseases for which exploitation of these mechanisms could yield future therapies.

Kisspeptin Levels in Girls with Precocious Puberty: A Systematic Review and Meta-Analysis

BACKGROUND/AIMS

Kisspeptin (KP) is a key player in the regulation of the release of gonadotropin-releasing hormone (GnRH), which increases the secretion of gonadotropin during puberty to establish reproductive function and regulate the hypothalamic-pituitary-gonadal axis. Premature activation of GnRH secretion leads to idiopathic/central gonadotropin-dependent precocious puberty (CPP). We aimed to compare the blood KP concentrations in girls with CPP and healthy controls.

METHODS

A systematic review and meta-analysis was performed. We searched MEDLINE, EMBASE, The Cochrane Library, and SciELO. Random-effects model and standardized mean difference (SMD) were used. Heterogeneity was assessed through I2. Meta-regression considered patient age, KP fraction, and analytical method for KP measurement.

RESULTS

The 11 studies included comprised 316 CPP patients and 251 controls. Higher KP levels in the CPP group were found (SMD 1.53; CI 95% = 0.56-2.51). Subgroup analysis revealed association with patient age (p = 0.048), indicating a positive correlation between elevation in KP concentration and age in CPP group. A group of patients with precocious thelarche (PT) from 5 of the included studies comprising 121 patients showed higher levels of KP (1.10; -0.25-2.45: CI 95%) and high heterogeneity (I2 = 91%). The CPP/PT ratio for KP level indicates KP 36% higher on CPP than PT patients.

CONCLUSIONS

A consistent difference in KP levels between girls with CPP and controls was identified. While there are important limitations in KP assays which argue against its use as a diagnostic tool, the KP levels in CPP versus control and PT children are consistent with the predicted mechanisms and pathophysiology of CPP.

The role of polymorphism in various potential genes on polycystic ovary syndrome susceptibility and pathogenesis

Polycystic ovary syndrome (PCOS) is the most common endocrinopathies affecting the early reproductive age in women, whose pathophysiology perplexes many researchers till today. This syndrome is classically categorized by hyperandrogenism and/or hyperandrogenemia, menstrual and ovulatory dysfunction, bulky multi follicular ovaries on Ultrasonography (USG), and metabolic abnormalities such as hyperinsulinemia, dyslipidemia, obesity. The etiopathogenesis of PCOS is not fully elucidated, but it seems that the hypothalamus-pituitary-ovarian axis, ovarian, and/or adrenal androgen secretion may contribute to developing the syndrome. Infertility and poor reproductive health in women's lives are highly associated with elevated levels of androgens. Studies with ovarian theca cells taken from PCOS women have demonstrated increased androgen production due to augmented ovarian steroidogenesis attributed to mainly altered expression of critical enzymes (Cytochrome P450 enzymes: CYP17, CYP21, CYP19, CYP11A) in the steroid hormone biosynthesis pathway. Despite the heterogeneity of PCOS, candidate gene studies are the widely used technique to delineate the genetic variants and analyze for the correlation of androgen biosynthesis pathway and those affecting the secretion or action of insulin with PCOS etiology. Linkage and association studies have predicted the relationship between genetic variants and PCOS risk among families or populations. Several genes have been proposed as playing a role in the etiopathogenesis of PCOS, and the presence of mutations and/or polymorphisms has been discovered, which suggests that PCOS has a vital heritable component. The following review summarizes the influence of polymorphisms in crucial genes of the steroidogenesis pathway leading to intraovarian hyperandrogenism which can result in PCOS.

Deficiency of arcuate nucleus kisspeptin results in postpubertal central hypogonadism

Kisspeptin (encoded by Kiss1), a neuropeptide critically involved in neuroendocrine regulation of reproduction, is primarily synthesized in two hypothalamic nuclei: the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC). AVPV kisspeptin is thought to regulate the estrogen-induced positive feedback control of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH), and the preovulatory LH surge in females. In contrast, ARC kisspeptin neurons, which largely coexpress neurokinin B and dynorphin A (collectively named KNDy neurons), are thought to mediate estrogen-induced negative feedback control of GnRH/LH and be the major regulators of pulsatile GnRH/LH release. However, definitive data to delineate the specific roles of AVPV versus ARC kisspeptin neurons in the control of GnRH/LH release is lacking. Therefore, we generated a novel mouse model targeting deletion of Kiss1 to the ARC nucleus (Pdyn-Cre/Kiss1fl/fl KO) to determine the functional differences between ARC and AVPV kisspeptin neurons on the reproductive axis. The efficacy of the knockout was confirmed at both the mRNA and protein levels. Adult female Pdyn-Cre/Kiss1fl/fl KO mice exhibited persistent diestrus and significantly fewer LH pulses when compared with controls, resulting in arrested folliculogenesis, hypogonadism, and infertility. Pdyn-Cre/Kiss1fl/fl KO males also exhibited disrupted LH pulsatility, hypogonadism, and variable, defective spermatogenesis, and subfertility. The timing of pubertal onset in males and females was equivalent to controls. These findings add to the current body of evidence for the critical role of kisspeptin in ARC KNDy neurons in GnRH/LH pulsatility in both sexes, while directly establishing ARC kisspeptin's role in regulating estrous cyclicity in female mice, and gametogenesis in both sexes, and culminating in disrupted fertility. The Pdyn-Cre/Kiss1fl/fl KO mice present a novel mammalian model of postpubertal central hypogonadism.NEW & NOTEWORTHY We demonstrate through a novel, conditional knockout mouse model of arcuate nucleus (ARC)-specific kisspeptin in the KNDy neuron that ARC kisspeptin is critical for estrous cyclicity in female mice and GnRH/LH pulsatility in both sexes. Our study reveals that ARC kisspeptin is essential for normal gametogenesis, and the loss of ARC kisspeptin results in significant hypogonadism, impacting fertility status. Our findings further confirm that normal puberty occurs despite a loss of ARC kisspeptin.

A review of the pathophysiology of functional hypothalamic amenorrhoea in women subject to psychological stress, disordered eating, excessive exercise or a combination of these factors

INTRODUCTION

Functional hypothalamic amenorrhoea (FHA) is a common form of secondary amenorrhoea without an identifiable structural cause. Suppression of gonadotrophin-releasing hormone (GnRH) pulsatility results in reduced luteinizing hormone (LH) levels, with subsequent reduction in oestradiol, anovulation and cessation of menstruation. GnRH pulsatility suppression is a recognized complication of psychological stress, disordered eating, low body weight, excessive exercise or a combination of these factors.

PATHOPHYSIOLOGY OF FHA

Individuals with FHA demonstrate low energy availability (EA), body fat percentage and energy expenditure. Documented adipocytokine changes notably, raised adiponectin, ghrelin, PYY, and decreased leptin, are associated with GnRH suppression. Other endocrine responses seen in this low EA state include low insulin levels, low total T3, increased basal cortisol levels and a reduced response to corticotrophin-releasing hormone (CRH) administration. FHA is associated with raised growth hormone (GH) and low insulin-like growth factor (IGF-1), suggesting relative GH resistance. Kisspeptins are a group of polypeptides, recently discovered to play a major role in the regulation of the reproductive axis through influencing GnRH release. KNDy (kisspeptin/neurokinin B/dynorphin) act on GnRH neurons and a multitude of factors result in their release.

IMPLICATIONS FOR FUTURE TREATMENT

Management of FHA is imperative to prevent adverse outcomes in bone density, cardiovascular risk profile, psychological well-being and fertility. Outwith modification of nutritional intake and exercise, limited therapeutic strategies are currently available for women with FHA. Advancements in the understanding of the pathophysiological basis of this under-recognized and under-treated clinical entity will aid management and may result in the development of novel therapeutic approaches.

Kisspeptin modulates gamma-aminobutyric acid levels in the human brain

Gamma-aminobutyric acid (GABA) is a key inhibitory neurotransmitter that has been implicated in the aetiology of common mood and behavioural disorders. By employing proton magnetic resonance spectroscopy in man, we demonstrate that administration of the reproductive neuropeptide, kisspeptin, robustly decreases GABA levels in the limbic system of the human brain; specifically the anterior cingulate cortex (ACC). This finding defines a novel kisspeptin-activated GABA pathway in man, and provides important mechanistic insights into the mood and behaviour-altering effects of kisspeptin seen in rodents and humans. In addition, this work has therapeutic implications as it identifies GABA-signalling as a potential target for the escalating development of kisspeptin-based therapies for common reproductive disorders of body and mind.

Clinical Potential of Kisspeptin in Reproductive Health

Kisspeptins are a family of hypothalamic neuropeptides that are essential for the regulation of reproductive physiology. Their importance in reproductive health became apparent in 2003, when loss-of-function variants in the gene encoding the kisspeptin receptor were reported to result in isolated congenital hypogonadotropic hypogonadism (CHH). It has since been ascertained that hypothalamic kisspeptin neurons regulate gonadotropin-releasing hormone (GnRH) secretion to thus stimulate the remainder of the reproductive endocrine axis. In this review, we discuss genetic variants that affect kisspeptin receptor signaling, summarize data on KISS1R agonists, and posit possible clinical uses of native and synthetic kisspeptin receptor agonists for the investigation and treatment of reproductive disorders.

Kisspeptin receptor agonist has therapeutic potential for female reproductive disorders

BACKGROUNDKisspeptin is a key regulator of hypothalamic gonadotropin-releasing hormone (GnRH) neurons and is essential for reproductive health. A specific kisspeptin receptor (KISS1R) agonist could significantly expand the potential clinical utility of therapeutics targeting the kisspeptin pathway. Herein, we investigate the effects of a KISS1R agonist, MVT-602, in healthy women and in women with reproductive disorders.METHODSWe conducted in vivo and in vitro studies to characterize the action of MVT-602 in comparison with native kisspeptin-54 (KP54). We determined the pharmacokinetic and pharmacodynamic properties of MVT-602 (doses 0.01 and 0.03 nmol/kg) versus KP54 (9.6 nmol/kg) in the follicular phase of healthy women (n = 9), and in women with polycystic ovary syndrome (PCOS; n = 6) or hypothalamic amenorrhea (HA; n = 6). Further, we investigated their effects on KISS1R-mediated inositol monophosphate (IP1) and Ca2+ signaling in cell lines and on action potential firing of GnRH neurons in brain slices.RESULTSIn healthy women, the amplitude of luteinizing hormone (LH) rise was similar to that after KP54, but peaked later (21.4 vs. 4.7 hours; P = 0.0002), with correspondingly increased AUC of LH exposure (169.0 vs. 38.5 IU∙h/L; P = 0.0058). LH increases following MVT-602 were similar in PCOS and healthy women, but advanced in HA (P = 0.004). In keeping with the clinical data, MVT-602 induced more potent signaling of KISS1R-mediated IP1 accumulation and a longer duration of GnRH neuron firing than KP54 (115 vs. 55 minutes; P = 0.0012).CONCLUSIONTaken together, these clinical and mechanistic data identify MVT-602 as having considerable therapeutic potential for the treatment of female reproductive disorders.TRIAL REGISTRATIONInternational Standard Randomised Controlled Trial Number (ISRCTN) Registry, ISRCTN21681316.FUNDINGNational Institute for Health Research and NIH.

Functions of galanin, spexin and kisspeptin in metabolism, mood and behaviour

The bioactive peptides galanin, spexin and kisspeptin have a common ancestral origin and their pathophysiological roles are increasingly the subject of investigation. Evidence suggests that these bioactive peptides play a role in the regulation of metabolism, pancreatic β-cell function, energy homeostasis, mood and behaviour in several species, including zebrafish, rodents and humans. Galanin signalling suppresses insulin secretion in animal models (but not in humans), is potently obesogenic and plays putative roles governing certain evolutionary behaviours and mood modulation. Spexin decreases insulin secretion and has potent anorectic, analgesic, anxiolytic and antidepressive-like effects in animal models. Kisspeptin modulates glucose-stimulated insulin secretion, food intake and/or energy expenditure in animal models and humans. Furthermore, kisspeptin is implicated in the control of reproductive behaviour in animals, modulation of human sexual and emotional brain processing, and has antidepressive and fear-suppressing effects. In addition, galanin-like peptide is a further member of the galaninergic family that plays emerging key roles in metabolism and behaviour. Therapeutic interventions targeting galanin, spexin and/or kisspeptin signalling pathways could therefore contribute to the treatment of conditions ranging from obesity to mood disorders. However, many gaps and controversies exist, which must be addressed before the therapeutic potential of these bioactive peptides can be established.

The human hypothalamic kisspeptin system: Functional neuroanatomy and clinical perspectives

In mammals, kisspeptin neurons are the key components of the hypothalamic neuronal networks that regulate the onset of puberty, account for the pulsatile secretion of gonadotropin-releasing hormone (GnRH) and mediate negative and positive estrogen feedback signals to GnRH neurons. Being directly connected anatomically and functionally to the hypophysiotropic GnRH system, the major kisspeptin cell groups of the preoptic area/rostral hypothalamus and the arcuate (or infundibular) nucleus, respectively, are ideally positioned to serve as key nodes which integrate various types of environmental, endocrine, and metabolic signals that can influence fertility. This chapter provides an overview of the current state of knowledge on the anatomy, functions, and plasticity of brain kisspeptin systems based on the wide literature available from different laboratory and domestic species. Then, the species-specific features of human hypothalamic kisspeptin neurons are described, covering their topography, morphology, unique neuropeptide content, plasticity, and connectivity to hypophysiotropic GnRH neurons. Some newly emerging roles of central kisspeptin signaling in behavior and finally, clinical perspectives, are discussed.

Using Aptamers as a Novel Method for Determining GnRH/LH Pulsatility

Aptamers are a novel technology enabling the continuous measurement of analytes in blood and other body compartments, without the need for repeated sampling and the associated reagent costs of traditional antibody-based methodologies. Aptamers are short single-stranded synthetic RNA or DNA that recognise and bind to specific targets. The conformational changes that can occur upon aptamer–ligand binding are transformed into chemical, fluorescent, colour changes and other readouts. Aptamers have been developed to detect and measure a variety of targets in vitro and in vivo. Gonadotropin-releasing hormone (GnRH) is a pulsatile hypothalamic hormone that is essential for normal fertility but difficult to measure in the peripheral circulation. However, pulsatile GnRH release results in pulsatile luteinizing hormone (LH) release from the pituitary gland. As such, LH pulsatility is the clinical gold standard method to determine GnRH pulsatility in humans. Aptamers have recently been shown to successfully bind to and measure GnRH and LH, and this review will focus on this specific area. However, due to the adaptability of aptamers, and their suitability for incorporation into portable devices, aptamer-based technology is likely to be used more widely in the future.

The kisspeptin system in domestic animals: what we know and what we still need to understand of its role in reproduction

The discovery of the kisspeptin (Kp) system stirred a burst of research in the field of reproductive neuroendocrinology. In the last 15 yr, the organization and activity of the system, including its neuroanatomical structure, its major physiological functions, and its main pharmacological properties, were outlined. To this endeavor, the use of genetic tools to delete and to restore Kp system functionality in a specific tissue was essential. At present, there is no question as to the key role of the Kp system in mammalian reproduction. However, easily applicable genetic manipulations are unavailable for domestic animals. Hence, many essential details on the physiological mechanisms underlying its action on domestic animals require further investigation. The potentially different effects of the various Kp isoforms, the precise anatomical localization of the Kp receptor, and the respective role played by the 2 main populations of Kp cells in different species are only few of the questions that remain unanswered and that will be illustrated in this review. Furthermore, the application of synthetic pharmacologic tools to manipulate the Kp system is still in its infancy but has produced some interesting results, suggesting the possibility of developing new methods to manage reproduction in domestic animals. In spite of a decade and a half of intense research effort, much work is still required to achieve a comprehensive understanding of the influence of the Kp system on reproduction. Furthermore, Kp system ramifications in other physiological functions are emerging and open new research perspectives.

Kisspeptin-52 partially rescues the activity of the hypothalamus-pituitary-gonadal axis in underweight male rats dosed with an anti-obesity compound

Energy metabolism and reproduction are closely linked and reciprocally regulated. The detrimental effect of underweight on reproduction complicates the safety evaluation of anti-obesity drugs, making it challenging to distinguish pathological changes mediated through the intended drug-induced weight loss from direct drug effects on reproductive organs. Four-weeks dosing of normal weight Sprague Dawley rats with a glucagon-like peptide 1 (GLP-1)/glucagon receptor co-agonist induced a robust weight loss, accompanied by histological findings in prostate, seminal vesicles, mammary glands, uterus/cervix and vagina. Characterization of the hypothalamus-pituitary-gonadal (HPG) axis in male rats revealed reduced hypothalamic Kiss1 mRNA levels and decreased serum luteinizing hormone (LH) and testosterone concentrations following co-agonist dosing. These alterations resemble hypogonadotropic hypogonadism typically seen in adverse energy deprived conditions, like chronic food restriction. Concomitant daily administration of kisspeptin-52 from day 21 to the end of the four-week co-agonist dosing period evoked LH and testosterone responses without normalizing histological findings. This incomplete rescue by kisspeptin-52 may be due to the rather short kisspeptin-52 treatment period combined with a desensitization observed on testosterone responses. Concomitant leptin treatment from day 21 did not reverse co-agonist induced changes in HPG axis activity. Furthermore, a single co-agonist injection in male rats slightly elevated LH levels but left testosterone unperturbed, thereby excluding a direct acute inhibitory effect on the HPG axis. Our data suggest that the reproductive phenotype after repeated co-agonist administration was driven by the intended weight loss, however, we cannot exclude a direct organ related effect in chronically treated rats.

Acute Effects of Glucagon on Reproductive Hormone Secretion in Healthy Men

CONTEXT

Glucagon increases energy expenditure; consequently, glucagon receptor agonists are in development for the treatment of obesity. Obesity negatively affects the reproductive axis, and hypogonadism itself can exacerbate weight gain. Therefore, knowledge of the effects of glucagon receptor agonism on reproductive hormones is important for developing therapeutics for obesity; but reports in the literature about the effects of glucagon receptor agonism on the reproductive axis are conflicting.

OBJECTIVE

The objective of this work is to investigate the effect of glucagon administration on reproductive hormone secretion in healthy young men.

DESIGN

A single-blinded, randomized, placebo-controlled crossover study was conducted.

SETTING

The setting of this study was the Clinical Research Facility, Imperial College Healthcare NHS Trust.

PARTICIPANTS

Eighteen healthy eugonadal men (mean ± SEM: age 25.1 ± 1.0 years; body mass index 22.5 ± 0.4 kg/m2; testosterone 21.2 ± 1.2 nmol/L) participated in this study.

INTERVENTION

An 8-hour intravenous infusion of 2 pmol/kg/min glucagon or rate-matched vehicle infusion was administered.

MAIN OUTCOME MEASURES

Luteinizing hormone (LH) pulsatility; LH, follicle-stimulating hormone (FSH), and testosterone levels were measured.

RESULTS

Although glucagon administration induced metabolic effects (insulin area under the curve: vehicle 1065 ± 292 min.µU/mL vs glucagon 2098 ± 358 min.µU/mL, P < .001), it did not affect LH pulsatility (number of LH pulses/500 min: vehicle 4.7 ± 0.4, glucagon 4.2 ± 0.4, P = .22). Additionally, there were no significant differences in circulating LH, FSH, or testosterone levels during glucagon administration compared with vehicle administration.

CONCLUSIONS

Acute administration of a metabolically active dose of glucagon does not alter reproductive hormone secretion in healthy men. These data are important for the continued development of glucagon-based treatments for obesity.

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.

Effects of Glucagon-like Peptide-1 on the Reproductive Axis in Healthy Men

CONTEXT

Glucagon-like peptide-1 (GLP-1) potently reduces food intake and augments glucose-stimulated insulin secretion. Recent animal data suggest that GLP-1 may also influence reproduction. As GLP-1 receptor agonists are currently widely used in clinical practice to treat obesity/type 2 diabetes, it is necessary to determine the effects of GLP-1 on the reproductive system in humans.

OBJECTIVE

To investigate the effects of GLP-1 administration on the reproductive axis in humans.

DESIGN

Single-blind, randomized, placebo-controlled crossover study.

SETTING

Clinical Research Facility, Imperial College Healthcare NHS Trust.

PARTICIPANTS

Eighteen healthy men (mean age 24.7 ± 0.1years, mean BMI 22.1 ± 0.4kg/m2).

INTERVENTION

Eight-hour intravenous infusion of 0.8 pmol/kg/min GLP-1 or rate-matched vehicle infusion.

MAIN OUTCOME MEASURES

Number of luteinizing hormone (LH) pulses, LH, follicle-stimulating hormone (FSH), and testosterone levels.

RESULTS

The number of LH pulses (number of LH pulses/500 min: vehicle 4.2 ± 0.4, GLP-1 4.5 ± 0.3, P = 0.46), LH area under the curve (AUC) (vehicle 1518 ± 88min.IU/L, GLP-1 1524 ± 101min.IU/L, P = 0.95), follicle-stimulating hormone AUC (vehicle 1210 ± 112 min IU/L, GLP-1 1216 ± 112 min IU/L, P = 0.86), and testosterone AUC (vehicle 10893 ± 615 min nmol/L, GLP-1 11088 ± 792 min nmol/L, P = 0.77) did not significantly differ during vehicle and GLP-1 administration. Glucagon-like peptide-1 significantly reduced food intake (vehicle 15.7 ± 1.3 kcal/kg, GLP-1 13.4 ± 1.3 kcal/kg, P = 0.01).

CONCLUSIONS

In contrast to the animal literature, our data demonstrate that acute GLP-1 administration does not affect reproductive hormone secretion in healthy men.

Effects of Peptide YY on the Hypothalamic-Pituitary-Gonadal Axis in Healthy Men

CONTEXT

Central and peripheral administration of peptide YY (PYY) has potent anorectic effects, and PYY analogs are under development as antiobesity treatments. Recent animal data suggest PYY may also influence the reproductive axis; however the effects of PYY on the human reproductive system are unknown.

OBJECTIVE

To investigate the effects of PYY administration on the reproductive axis in healthy young men.

DESIGN

Single-blind, randomized, placebo-controlled crossover study.

SETTING

Clinical Research Facility, Imperial College Healthcare NHS Trust.

PARTICIPANTS

Eighteen healthy eugonadal men (mean age 24.1 ± 0.9 years, mean body mass index 22.2 ± 0.4 kg/m2).

INTERVENTION

Eight-hour intravenous infusion of 0.4 pmol/kg/min PYY3-36 or rate-matched vehicle infusion.

MAIN OUTCOME MEASURES

Number of luteinizing hormone (LH) pulses, LH, follicle stimulating hormone (FSH), and testosterone levels.

RESULTS

The number of LH pulses (mean number of LH pulses/8 hours: PYY 4.4 ± 0.3 vs vehicle 4.4 ± 0.4, P > .99), LH area under the curve (AUC) (PYY 1503 ± 79 IU.min/L vs vehicle 1574 ± 86 IU.min/L, P = .36), FSH AUC (PYY 1158 ± 513 IU.min/L vs vehicle 1199 ± 476 IU.min/L, P = .49) and testosterone AUC (PYY 10 485 ± 684 IU.min/L vs vehicle 11 133 ± 803 IU.min/L, P = .24) were similar during PYY and vehicle infusions.

CONCLUSIONS

Acute intravenous infusion of 0.4 pmol/kg/min PYY does not affect the reproductive axis in healthy men.

Kisspeptin enhances brain responses to olfactory and visual cues of attraction in men

Successful reproduction is a fundamental physiological process that relies on the integration of sensory cues of attraction with appropriate emotions and behaviors and the reproductive axis. However, the factors responsible for this integration remain largely unexplored. Using functional neuroimaging, hormonal, and psychometric analyses, we demonstrate that the reproductive hormone kisspeptin enhances brain activity in response to olfactory and visual cues of attraction in men. Furthermore, the brain regions enhanced by kisspeptin correspond to areas within the olfactory and limbic systems that govern sexual behavior and perception of beauty as well as overlap with its endogenous expression pattern. Of key functional and behavioral significance, we observed that kisspeptin was most effective in men with lower sexual quality-of-life scores. As such, our results reveal a previously undescribed attraction pathway in humans activated by kisspeptin and identify kisspeptin signaling as a new therapeutic target for related reproductive and psychosexual disorders.

Kisspeptin enhances brain processing in response to olfactory and visual cues of attraction and is most effective in men with lower sexual quality of life.

Neuroendocrine mechanisms of reproduction

The neuroendocrinology of reproduction focuses on the neuromodulation of gonadotropin-releasing hormone (GnRH), the ontogeny of the hypothalamic-pituitary-gonadal axis, and common reproductive events and conditions, namely, puberty, the menstrual cycle, and disorders of reproductive function. The core concept underpinning the neuroendocrinology of reproduction is neuroregulation of hypothalamic GnRH drive. In both men and women, reproductive function requires that GnRH input elicit appropriate secretion of follicle-stimulating hormone and luteinizing hormone from the anterior pituitary and that the gonads respond to such input appropriately. Moreover, insufficient GnRH drive causes hypothalamic hypogonadism and secondary insufficiency of gonadal sex steroid hormone synthesis and release in both sexes. Alterations in GnRH drive also reflect gonadal conditions such as dysgenesis, hyperandrogenism, gonadotropin mutations, and aging and loss or absence of oocytes or Sertoli cells. The most common cause of insufficient GnRH drive is functional, that is, due to the endocrine effects of psychologic or behavioral variables. Rarely does reduced GnRH drive reflect organic or congenital causes such as developmental defects, brain tumors, or celiac disease. Despite a common neuropathogenesis the heterogeneity of behavioral variables associated with reduced GnRH drive has resulted in a variety of names, including functional hypothalamic amenorrhea, stress-induced anovulation, and psychogenic amenorrhea.

Current understanding of hypothalamic amenorrhoea

Hypothalamic amenorrhoea (HA) accounts for approximately 30% of cases of secondary amenorrhoea in women of reproductive age. It is caused by deficient secretion of hypothalamic gonadotrophin-releasing hormone, which in turn leads to failure of pituitary gonadotrophin and gonadal steroid release. Functional HA (FHA) is defined as HA occurring in the absence of a structural lesion and is predominantly caused by significant weight loss, intense exercise or stress. Treatment of FHA is crucial in avoiding the long-term health consequences on fertility and bone health, in addition to reducing psychological morbidity. This article summarises our understanding of the mechanisms underlying FHA, the evidence base for its clinical management and emerging therapies.

The Origin of GnRH Pulse Generation: An Integrative Mathematical-Experimental Approach

Fertility critically depends on the gonadotropin-releasing hormone (GnRH) pulse generator, a neural construct comprised of hypothalamic neurons coexpressing kisspeptin, neurokoinin-B and dynorphin. Here, using mathematical modeling and in vivo optogenetics we reveal for the first time how this neural construct initiates and sustains the appropriate ultradian frequency essential for reproduction. Prompted by mathematical modeling, we show experimentally using female estrous mice that robust pulsatile release of luteinizing hormone, a proxy for GnRH, emerges abruptly as we increase the basal activity of the neuronal network using continuous low-frequency optogenetic stimulation. Further increase in basal activity markedly increases pulse frequency and eventually leads to pulse termination. Additional model predictions that pulsatile dynamics emerge from nonlinear positive and negative feedback interactions mediated through neurokinin-B and dynorphin signaling respectively are confirmed neuropharmacologically. Our results shed light on the long-elusive GnRH pulse generator offering new horizons for reproductive health and wellbeing.SIGNIFICANCE STATEMENT The gonadotropin-releasing hormone (GnRH) pulse generator controls the pulsatile secretion of the gonadotropic hormones LH and FSH and is critical for fertility. The hypothalamic arcuate kisspeptin neurons are thought to represent the GnRH pulse generator, since their oscillatory activity is coincident with LH pulses in the blood; a proxy for GnRH pulses. However, the mechanisms underlying GnRH pulse generation remain elusive. We developed a mathematical model of the kisspeptin neuronal network and confirmed its predictions experimentally, showing how LH secretion is frequency-modulated as we increase the basal activity of the arcuate kisspeptin neurons in vivo using continuous optogenetic stimulation. Our model provides a quantitative framework for understanding the reproductive neuroendocrine system and opens new horizons for fertility regulation.

Kisspeptin/Neurokinin B/Dynorphin (KNDy) cells as integrators of diverse internal and external cues: evidence from viral-based monosynaptic tract-tracing in mice

Neurons in the hypothalamic arcuate nucleus (ARC) that co-express kisspeptin, neurokinin B and dynorphin (KNDy cells) are essential for mammalian reproduction as key regulators of gonadotropin-releasing hormone (GnRH) secretion. Although multiple endogenous and exogenous signals act indirectly via KNDy neurons to regulate GnRH, the identity of upstream neurons that provide synaptic input to this subpopulation is unclear. We used rabies-mediated tract-tracing in transgenic Kiss1-Cre mice combined with whole-brain optical clearing and multiple-label immunofluorescence to create a comprehensive and quantitative brain-wide map of neurons providing monosynaptic input to KNDy cells, as well as identify the estrogen receptor content and peptidergic phenotype of afferents. Over 90% of monosynaptic input to KNDy neurons originated from hypothalamic nuclei in both male and female mice. The greatest input arose from non-KNDy ARC neurons, including proopiomelanocortin-expressing cells. Significant female-dominant sex differences in afferent input were detected from estrogen-sensitive hypothalamic nuclei critical for reproductive endocrine function and sexual behavior in mice, indicating KNDy cells may provide a unique site for the coordination of sex-specific behavior and gonadotropin release. These data provide key insight into the structural framework underlying the ability of KNDy neurons to integrate endogenous and environmental signals important for the regulation of reproductive function.

Reversible male hypogonadotropic hypogonadism due to energy deficit

CONTEXT

Calorie restriction and overtraining are increasingly seen in young men who suffer from increasing societal pressure to attain a perceived ideal male body image. The resulting energy deficit can lead to multiple endocrine consequences, including suppression of the male gonadal axis.

DESIGN

We reviewed the literature, including two unpublished cases.

RESULTS

We identified 23 cases, aged median (range) 20 years (16-33), with a body mass index of 15.9 kg/m² (12.5-20.5). Total testosterone was 3.0 nmol/L (0.6-21.3), and luteinizing hormone (LH) 1.2 mIU/L (<0.2-7.5), with 91% of cases demonstrating hypogonadotropic hypogonadism. Associated findings included evidence of growth hormone resistance (increased growth hormone in 57% and low insulin-like growth factor-1 in 71%), hypercortisolaemia (50%) and a nonthyroidal illness picture (67%). In cases with longitudinal measurements following weight regain, serum testosterone (n = 14) increased from median [interquartile range] 3.2 nmol/L [1.9-5.1] to 14.3 nmol/L [9.3-21.2] (P < 0.001), and LH (n = 8) from 1.2 IU/L [0.8-1.8] to 3.5 IU/L [3.3-4.3] (P = 0.008).

CONCLUSIONS

Hypogonadotropic hypogonadism can occur in the context of energy deprivation in young otherwise healthy men and may be underrecognized. The evidence suggests that gonadal axis suppression and associated hormonal abnormalities represent an adaptive response to increased physiological stress and total body energy deficit. The pathophysiology likely involves hypothalamic suppression due to dysregulation of leptin, ghrelin and pro-inflammatory cytokines. The gonadal axis suppression is functional, because it can be reversible with weight gain. Treatment should focus on reversing the existing energy deficit to achieve a healthy body weight, including psychiatric input where required.

The neurobiological mechanism underlying hypothalamic GnRH pulse generation: the role of kisspeptin neurons in the arcuate nucleus

This review recounts the origins and development of the concept of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator. It starts in the late 1960s when striking rhythmic episodes of luteinizing hormone secretion, as reflected by circulating concentrations of this gonadotropin, were first observed in monkeys and ends in the present day. It is currently an exciting time witnessing the application, primarily to the mouse, of contemporary neurobiological approaches to delineate the mechanisms whereby Kiss1/NKB/Dyn (KNDy) neurons in the arcuate nucleus of the hypothalamus generate and time the pulsatile output of kisspeptin from their terminals in the median eminence that in turn dictates intermittent GnRH release and entry of this decapeptide into the primary plexus of the hypophysial portal circulation. The review concludes with an examination of questions that remain to be addressed.

The neurobiological mechanism underlying hypothalamic GnRH pulse generation: the role of kisspeptin neurons in the arcuate nucleus

This review recounts the origins and development of the concept of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator. It starts in the late 1960s when striking rhythmic episodes of luteinizing hormone secretion, as reflected by circulating concentrations of this gonadotropin, were first observed in monkeys and ends in the present day. It is currently an exciting time witnessing the application, primarily to the mouse, of contemporary neurobiological approaches to delineate the mechanisms whereby Kiss1/NKB/Dyn (KNDy) neurons in the arcuate nucleus of the hypothalamus generate and time the pulsatile output of kisspeptin from their terminals in the median eminence that in turn dictates intermittent GnRH release and entry of this decapeptide into the primary plexus of the hypophysial portal circulation. The review concludes with an examination of questions that remain to be addressed.