Pineda et al.
Endocrinology. 2010 Feb;151(2):722-30.
Kisspeptins (Kp) have recently emerged as master regulators of the reproductive axis and among the most potent elicitors of GnRH-gonadotropin secretion. Despite their paramount importance in reproductive physiology and their potential therapeutic implications, development of Kp antagonists has remained elusive, and only recently has the first compound with the ability to block Kp actions in vitro and in vivo, namely p234, been reported. However, previous in vivo studies all used acute central injections, whereas characterization of the effects of the antagonist after continuous or systemic administration, which poses pharmacological challenges, is still pending. We report herein a comprehensive series of analyses on the impact of continuous intracerebroventricular infusion of p234 on puberty onset and the preovulatory surge of gonadotropins in the female rat. In addition, the effects of systemic (ip) administration of a tagged p234-penetratin, with a predicted higher permeability at the blood-brain barrier, on Kp-10 induced gonadotropin secretion were evaluated. Central infusion of p234 to pubertal females delayed vaginal opening and decreased uterine and ovarian weights at the expected time of puberty, without affecting body weight. Likewise, chronic intracerebroventricular administration of p234 for 4 d prevented the preovulatory surges of LH and FSH. In addition, systemic (ip) administration of p234-penetratin significantly attenuated acute LH and FSH responses to Kp-10, either after intracerebroventricular or ip injection of Kp. Our data document the validity of p234 for antagonizing Kp actions in vivo and provide direct experimental evidence for the important role of Kp signaling in the key events of female reproduction, such as puberty onset and the preovulatory surge of gonadotropins.
Pineda et al.
Endocrinology. 2010 Feb;151(2):722-30.
Neurons that produce gonadotropin-releasing hormone (GnRH) are the final common pathway by which the brain regulates reproduction. GnRH neurons are regulated by an afferent network of kisspeptin-producing neurons. Kisspeptin binds to its cognate receptor on GnRH neurons and stimulates their activity, which in turn provides an obligatory signal for GnRH secretion, thus gating down-stream events supporting reproduction. We have developed kisspeptin antagonists to facilitate the direct determination of the role of kisspeptin neurons in the neuroendocrine regulation of reproduction. In vitro and in vivo studies of analogues of kisspeptin-10 with amino substitutions have identified several potent and specific antagonists. A selected antagonist was shown to inhibit the firing of GnRH neurons in the brain of the mouse and to reduce pulsatile GnRH secretion in female pubertal monkeys; the later supporting a key role of kisspeptin in puberty onset. This analog also inhibited the kisspeptin-induced release of luteinizing hormone (LH) in rats and mice and blocked the postcastration rise in LH in sheep, rats, and mice, suggesting that kisspeptin neurons mediate the negative feedback effect of sex steroids on gonadotropin secretion in mammals. The development of kisspeptin antagonists provides a valuable tool for investigating the physiological and pathophysiological roles of kisspeptin in the regulation of reproduction and could offer a unique therapeutic agent for treating hormone-dependent disorders of reproduction, including precocious puberty, endometriosis, and metastatic prostate cancer.
Roseweir et al. J Neurosci. 2009 Mar 25;29(12):3920-9.
Substitution of Leu8 with D-Trp in combination with Ser5 substitution with Gly created potent antagonists (see supplemental Table S1, available at www.jneurosci.org as supplemental material). Additional substitution of Tyr1 with D-Ala (234 shown here) enhanced this (*p < 0.05, **p < 0.01, ***p < 0.001). Peptide 234 alone had no intrinsic IP stimulation. Bars show mean ± SEM of five experiments.
Roseweir et al. J Neurosci. 2009 Mar 25;29(12):3920-9.
A, Two infusions of 15 nmol of
peptide 234 inhibit the elevated LH levels of castrated male mice. B, Dose–response graph for castrated male mice given two infusions of peptide 234 indicates that all three doses tested are
able to inhibit the postcastration rise in LH. C, Likewise, a single infusion of 5 or 15 nmol of
peptide 234 potently inhibits LH levels of castrated mice.D, Exogenously administered kisspeptin
(100 fmol) is unable to stimulate LH levels in intact male mice when 100 pmol peptide 234 is
infused 5 min beforehand (n6–8). Bars show meanSEM (*p0.05).
Roseweir et al. J Neurosci. 2009 Mar 25;29(12):3920-9.
