Single-dose pharmacokinetics of Nestorone, a potential female-contraceptive

Metabolism of progestogens used for contraception and menopausal hormone therapy

A variety of progestogens are widely used by women for contraception and menopausal hormone therapy. The progestogens undergo extensive metabolism by oral and parenteral routes of administration to form many metabolites. Although a small number of metabolites have been shown to be biologically active, most have not been tested for biologic activity. The present review shows that we know most about progesterone metabolism, followed by the metabolism of levonorgestrel and norethindrone. Very few studies have been carried out on metabolism of most of the progestogens. The clinical significance of this deficiency is that those progestogen metabolites that bind to the progesterone receptors may also bind to other steroid receptors and be responsible for some of the well-documented side effects of administered progestogens. We also discuss how obesity and genetic polymorphisms alter progestogen metabolism, and how development of oral progestogen formulations that are targeted to the colon, where the concentration of steroid-metabolizing enzymes is much lower than in the proximal gut, may have a beneficial effect on progestogen metabolism.

Nestorone (segesterone acetate) effects on neuroregeneration

Nestorone® (segesterone acetate) is a progestin with a chemical structure closely related to progesterone with high affinity and selectivity for the progesterone receptor without significant interaction with other steroid receptors. It has been developed for female and male contraception and is FDA-approved in a first long-acting contraceptive vaginal system for female contraception. Its safety has been extensively demonstrated in both preclinical and clinical studies for contraceptive indications. Nestorone was found to display neuroprotective and neuroregenerative activity in animal models of various central nervous system diseases, including multiple sclerosis, stroke, and amyotrophic lateral sclerosis. Reviewed herein are neuroprotective and myelin- regenerating properties of Nestorone in various animal models and its translational potential as a therapeutic agent for debilitating neurological diseases for which limited therapeutic options are available (Table 1).

Evaluations of memory, anxiety, and the growth factor IGF-1R after post-surgical menopause treatment with a highly selective progestin

Progestogens are a key component of menopausal hormone therapies. While some progestogens can be detrimental to cognition, there is preclinical evidence that progestogens with a strong progesterone-receptor affinity benefit some molecular mechanisms believed to underlie cognitive function. Thus, a progestin that maximizes progesterone-receptor affinity and minimizes affinities to other receptors may be cognitively beneficial. We evaluated segesterone-acetate (SGA), a 19-norprogesterone derivative with a strong progesterone-receptor affinity and no androgenic or estrogenic-receptor activity, hypothesizing that it would enhance cognition. Middle-aged rats underwent Sham or Ovariectomy (Ovx) surgery followed by administration of medroxyprogesterone-acetate (MPA; used as a positive control as we have previously shown MPA-induced cognitive deficits), SGA (low or high dose), or vehicle (one Sham and one Ovx group). Spatial working and reference memory, delayed retention, and anxiety-like behavior were assessed, as were memory- and hormone- related protein assays within the frontal cortex, dorsal hippocampus, and entorhinal cortex. Low-dose SGA impaired spatial working memory, while high-dose SGA had a more extensive detrimental impact, negatively affecting spatial reference memory and delayed retention. Replicating previous findings, MPA impaired spatial reference memory and delayed retention. SGA, but not MPA, alleviated Ovx-induced anxiety-like behaviors. On two working memory measures, IGF-1R expression correlated with better working memory only in rats without hormone manipulation; any hormone manipulation or combination of hormone manipulations used herein altered this relationship. These findings suggest that SGA impairs spatial cognition after surgical menopause, and that surgical menopause with or without progestin administration disrupts relationships between a growth factor critical to neuroplasticity.

Pharmacokinetics, metabolism and serum concentrations of progestins used in contraception

Many different forms of hormonal contraception are used by millions of women worldwide. These contraceptives differ in the dose and type of synthetic progestogenic compound (progestin) used, as well as the route of administration and whether or not they contain estrogenic compounds. There is an increasing awareness that different forms of contraception and different progestins have different side-effect profiles, in particular their cardiovascular effects, effects on reproductive cancers and susceptibility to infectious diseases. There is a need to develop new methods to suit different needs and with minimal risks, especially in under-resourced areas. This requires a better understanding of the pharmacokinetics, metabolism, serum and tissue concentrations of progestins used in contraception as well as the biological activities of progestins and their metabolites via steroid receptors. Here we review the current knowledge on these topics and identify the research gaps. We show that there is a paucity of research on most of these topics for most progestins. We find that major impediments to clear conclusions on these topics include a lack of standardized methodologies, comparisons between non-parallel clinical studies and variability of data on serum concentrations between and within studies. The latter is most likely due, at least in part, to differences in intrinsic characteristics of participants. The review highlights the importance of insight on these topics in order to provide the best contraceptive options to women with minimal risks.

Progesterone receptor activation regulates seizure susceptibility

OBJECTIVE

Progesterone is a potent neuromodulator that exerts effects on the brain through neurosteroids, progesterone receptors (PRs), and other molecules. Whether PR activation regulates seizures is not known. We determined whether PR activation increased seizure susceptibility.

METHODS

Adult female rats that developed epilepsy following lithium-pilocarpine-induced status epilepticus (SE) were used. Seizures were recorded by continuous-video EEG and read by an individual blinded to the treatment of the animals. The animals were treated for a week with progesterone (50 mg/kg per day), and the effect of progesterone withdrawal on seizure frequency was assessed during the subsequent week. During the week of progesterone treatment, the animals were treated with PR antagonist RU-486 (10 mg/kg per day) or a vehicle control, which was administered 30 min before progesterone. In another set of animals, we determined the effect of the PR agonist Nestorone (3 mg/kg per day) on seizure frequency. The animals were treated with Nestorone or vehicle for a week, and seizure frequencies at baseline and during the treatment week were compared.

RESULTS

Progesterone withdrawal induced twofold increase in seizures in 57% of animals (n = 14). RU-486 treatment in combination with progesterone, prevented this increase, and a smaller fraction of animals (17%) experienced withdrawal seizures (n = 13). The specific activation of PRs by Nestorone also increased the seizure frequency. Forty-six percent (n = 14) of Nestorone-treated animals experienced at least a 50% increase in seizures compared to only 9% of the vehicle-treated animals (n = 11).

INTERPRETATION

PR activation increased seizure frequency in epileptic animals. Thus, PRs may be novel targets for treating catamenial epilepsy.

Differential metabolism of clinically-relevant progestogens in cell lines and tissue: Implications for biological mechanisms

Steroid hormones regulate a variety of physiological processes, including reproductive function, and are widely used in hormonal therapy. Synthetic progestogens, or progestins, were designed to mimic progesterone (P₄) for use in contraception and hormonal replacement therapy in women. Medroxyprogesterone acetate (MPA) and norethisterone (NET) are the most widely used injectable contraceptives in the developing world, while other progestins such as levonorgestrel (LNG), etonogestrel (ETG) and nestorone (NES) are used in or being developed for other forms of contraception. As concerns remain about the most appropriate choice of progestin and dosage, and the associated side-effects, the mechanisms and biological effects of progestins are frequently investigated in various in vitro mammalian cell line and tissue models. However, whether progestogens are differentially metabolised in different cell types in vivo or in vitro is unknown. For nine mammalian cell lines commonly used to investigate progestogen mechanisms of action, we developed and validated an ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) protocol for simultaneously quantifying the metabolism of the above-mentioned steroids. We show for the first time that, while 50-100% of P₄ was metabolised within 24 h in all cell lines, the metabolism of the progestins is progestin- and cell line-specific. We also show that MPA and NET are significantly metabolised in human cervical tissue, but to a lesser extent than P₄. Taken together, our findings suggest that differential progestogen metabolism may play a role in cell-specific therapeutic and side-effects. Relative affinities for binding to steroid receptors as well as potencies, efficacies and biocharacters for transcriptional activity of progestins, relative to P₄, are most frequently determined using some of the cell lines investigated. Our results, however, suggest that differential metabolism of progestins and P₄ may confound these results. In particular, metabolism may under-estimate the receptor-mediated intrinsic in vitro binding and dose-response values and predicted endogenous physiological effects of P₄.

Contraceptives with novel benefits

INTRODUCTION

Progesterone receptor (PR) agonists (progestins) and antagonists are developed for female contraceptives. However, non-contraceptive applications of newer progestins and PR modulators are being given more attention.

AREAS COVERED

The newer PR agonists including drospirenone, nomegestrol, trimegestone, dienogest and nestorone are being evaluated as contraceptives with health benefits because of their unique pharmacological properties. The selective PR modulators (SPRM; PR antagonists with PR agonistic properties) are under development not only for emergency contraception but also for other health benefits such as the treatment of endometritis and leiomyoma. After searching the literature from PubMed, clinicaltrials.gov and patent database, this review focuses on the effects and mechanisms of these progestins, and SPRMs as contraceptives with other health benefits.

EXPERT OPINION

PR agonists and antagonists that have novel properties may generate better contraceptive effects with other health benefits.