A kisspeptin-10 analog with greater in vivo bioactivity than kisspeptin-10.

The kisspeptins are neuropeptides that stimulate the hypothalamo-pituitary-gonadal (HPG) axis. The smallest endogenous kisspeptin, kisspeptin-10 (KP-10), binds to the receptor KISS1R with a similar affinity to the full-length peptide, kisspeptin-54 (KP-54), but is less effective in vivo, possibly because of increased enzymatic breakdown or clearance. The kisspeptin system may have therapeutic potential in the treatment of reproductive disorders and endocrine cancers. We have rationally modified the structure of KP-10 and tested the binding affinity of these analogs for the KISS1R. Those analogs that bound with relatively high affinity to KISS1R were tested for ability to stimulate ERK1/2 phosphorylation in vitro and for their ability to stimulate the HPG axis in vivo. One analog, [dY](1)KP-10, bound to KISS1R with lower affinity to KP-10 and exhibited similar bioactivity in vitro. However, in vivo peripheral administration of [dY](1)KP-10 increased plasma LH and testosterone more potently than KP-10 itself at 20 min postinjection in mice. In addition, 60 min postinjection, 0.15 nmol [dY](1)KP-10 significantly increased total testosterone levels in mice whereas the same dose of KP-10 had no significant effect. Should manipulation of the kisspeptin/KISS1R signaling system prove therapeutically useful, long-lasting analogs such as [dY](1)KP-10 may have greater therapeutic potential than endogenous forms of kisspeptin.

Peripheral and central administration of xenin and neurotensin suppress food intake in rodents.

Xenin is a 25-amino acid peptide highly homologous to neurotensin. Xenin and neurotensin are reported to have similar biological effects. Both reduce food intake when administered centrally to fasted rats. We aimed to clarify and compare the effects of these peptides on food intake and behavior. We confirm that intracerebroventricular (ICV) administration of xenin or neurotensin reduces food intake in fasted rats, and demonstrate that both reduce food intake in satiated rats during the dark phase. Xenin reduced food intake more potently than neurotensin following ICV administration. ICV injection of either peptide in the dark phase increased resting behavior. Xenin and neurotensin stimulated the release of corticotrophin-releasing hormone (CRH) from ex vivo hypothalamic explants, and administration of alpha-helical CRH attenuated their effects on food intake. Intraperitoneal (IP) administration of xenin or neurotensin acutely reduced food intake in fasted mice and ad libitum fed mice in the dark phase. However, chronic continuous or twice daily peripheral administration of xenin or neurotensin to mice had no significant effect on daily food intake or body weight. These studies confirm that ICV xenin or neurotensin can acutely reduce food intake and demonstrate that peripheral administration of xenin and neurotensin also reduces food intake. This may be partly mediated by changes in hypothalamic CRH release. The lack of chronic effects on body weight observed in our experiments suggests that xenin and neurotensin are unlikely to be useful as obesity therapies.

Chronic subcutaneous administration of kisspeptin-54 causes testicular degeneration in adult male rats.

The kisspeptins are KiSS-1 gene-derived peptides that signal through the G protein-coupled receptor-54 (GPR54) and have recently been shown to be critical regulators of reproduction. Acute intracerebroventricular or peripheral administration of kisspeptin stimulates the hypothalamic-pituitary-gonadal (HPG) axis. This effect is thought to be mediated via the hypothalamic gonadotropin-releasing hormone (GnRH) system. Chronic administration of GnRH agonists paradoxically suppresses the HPG axis after an initial agonistic stimulation. We investigated the effects of continuous peripheral kisspeptin administration in male rats by use of Alzet minipumps. Initially we compared the effects of acute subcutaneous administration of kisspeptin-10, -14, and -54 on the HPG axis. Kisspeptin-54 produced the greatest increase in plasma LH and total testosterone at 60 min postinjection and was used in the subsequent continuous administration experiments. Chronic subcutaneous long-term administration of 50 nmol kisspeptin-54/day for 13 days decreased testicular weight. Histological examination showed degeneration of the seminiferous tubules associated with a significant decrease in the circulating levels of the testes-derived hormone, inhibin B. Plasma free and total testosterone were also lower, although these changes did not reach statistical significance. Further studies examined the effects of shorter periods of continuous kisspeptin administration. Subcutaneous administration of 50 nmol kisspeptin-54 for 1 day increased plasma LH and testosterone. This effect was lost after 2 days of administration, suggesting a downregulation of the HPG axis response to kisspeptin following continuous administration. These findings indicate that kisspeptin may provide a novel tool for the manipulation of the HPG axis and spermatogenesis.