Progesterone improves functional outcomes after transient focal cerebral ischemia in both aged male and female rats

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).

A Pilot Systematic Review and Meta-analysis of Neuroprotective Studies in Female Rodent Models of Ischemic Stroke

Most ischemic stroke (IS) patients go untreated due to limited treatment windows, restrictive eligibility criteria, and poor availability of current clinical therapies. Neuroprotective treatments targeting protracted neurodegeneration are needed yet keep failing in clinical trials. Over half of IS patients are female, and the scarcity of neuroprotective studies using female animals hinders translational success. This pilot review and meta-analysis assessed the relationship between the risk of bias and efficacy of studies testing post-ischemic neuroprotective therapies using female rodent models of IS. We carried out a systematic search of the PubMed database for studies published between 1999 and May 2022, used the CAMARADES checklist to evaluate study quality, and extracted data pertaining to lesion volume and behavioral assessment. We found that 34 studies met our inclusion criteria, with pooled effect sizes depicting a significant treatment effect. However, researchers used mostly healthy young females, administered therapies within short time windows, ignored hormonal influences, and did not assess long-term outcomes. Interestingly, studies failing to report factors impacting internal validity, such as blinding and random allocation, had inflated effect sizes or did not reach statistical significance. There was also a relationship between low study quality and larger effect sizes for functional outcome, stressing the need to follow the existing translational design, reporting, and data analysis guidelines. In this review, we cover previous recommendations and offer our own in hopes that rigorous and meticulous research using female animal models of IS will increase our chances of successful bench-to-bedside translation.

Neuroprotective-Neurorestorative Effects Induced by Progesterone on Global Cerebral Ischemia: A Narrative Review

Progesterone (P4) is a neuroactive hormone having pleiotropic effects, supporting its pharmacological potential to treat global (cardiac-arrest-related) cerebral ischemia, a condition associated with an elevated risk of dementia. This review examines the current biochemical, morphological, and functional evidence showing the neuroprotective/neurorestorative effects of P4 against global cerebral ischemia (GCI). Experimental findings show that P4 may counteract pathophysiological mechanisms and/or regulate endogenous mechanisms of plasticity induced by GCI. According to this, P4 treatment consistently improves the performance of cognitive functions, such as learning and memory, impaired by GCI. This functional recovery is related to the significant morphological preservation of brain structures vulnerable to ischemia when the hormone is administered before and/or after a moderate ischemic episode; and with long-term adaptive plastic restoration processes of altered brain morphology when treatment is given after an episode of severe ischemia. The insights presented here may be a guide for future basic research, including the study of P4 administration schemes that focus on promoting its post-ischemia neurorestorative effect. Furthermore, considering that functional recovery is a desired endpoint of pharmacological strategies in the clinic, they could support the study of P4 treatment for decreasing dementia in patients who have suffered an episode of GCI.

Progesterone attenuates neurological deficits and exerts a protective effect on damaged axons via the PI3K/AKT/mTOR-dependent pathway in a mouse model of intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating event with high disability and fatality rates. However, there is a lack of effective treatments for this condition. We aimed to investigate the neuroprotective and axonal regenerative effects of progesterone after ICH. For this purpose, an ICH model was established in adult mice by injecting type VII collagenase into the striatum; the mice were then treated with progesterone (8 mg/kg). Hematoma absorption, neurological scores, and brain water content were evaluated on days one, three, and seven after the ICH. The effect of progesterone on inflammation and axonal regeneration was examined on day three after the ICH using western blotting, immunohistochemistry, immunofluorescence, as well as hematoxylin-eosin, Nissl, and Luxol fast blue staining. In addition, we combined progesterone with the phosphoinositide 3-kinase/serine/threonine-specific protein kinase (PI3K/AKT) inhibitor, LY294002, to explore its potential neuroprotective mechanisms. Administration of progesterone attenuated the neurological deficits and expression of inflammatory cytokines and promoted axonal regeneration after ICH, this effect was blocked by LY294002. Collectively, these results suggest that progesterone could reduce axonal damage and produced partial neuroprotective effects after ICH through the PI3K/AKT/mTOR pathway, providing a new therapeutic target and basis for the treatment of ICH.

Progress in progestin-based therapies for neurological disorders

Hormone therapy, primarily progesterone and progestins, for central nervous system (CNS) disorders represents an emerging field of regenerative medicine. Following a failed clinical trial of progesterone for traumatic brain injury treatment, attention has shifted to the progestin Nestorone for its ability to potently and selectively transactivate progesterone receptors at relatively low doses, resulting in robust neurogenetic, remyelinating, and anti-inflammatory effects. That CNS disorders, including multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), spinal cord injury (SCI), and stroke, develop via demyelinating, cell death, and/or inflammatory pathological pathways advances Nestorone as an auspicious candidate for these disorders. Here, we assess the scientific and clinical progress over decades of research into progesterone, progestins, and Nestorone as neuroprotective agents in MS, ALS, SCI, and stroke. We also offer recommendations for optimizing timing, dosage, and route of the drug regimen, and identifying candidate patient populations, in advancing Nestorone to the clinic.

Sexual dimorphism following in vitro ischemia in the response to neurosteroids and mechanisms of injury

Background

Cerebral ischemic stroke is a significant cause of morbidity and mortality. Sex differences exist following stroke in terms of incidence, symptoms, outcomes and response to some treatments. Importantly, molecular mechanisms of injury, activated following ischemia may differ between the sexes and if so may account, at least in part, for sex differences seen in treatment response. Here we aimed to determine, using single-sex organotypic hippocampal slice cultures, whether the effectiveness of a potential treatment option, i.e. sex steroids, exhibited any sexual dimorphism and whether sex affected the mechanisms of apoptosis activated following ischemia.

Results

Following exposure to ischemia, male-derived tissue exhibited higher levels of cell death than female-derived tissue. Various sex steroid hormones, i.e. progesterone, allopregnanolone, and estradiol, were protective in terms of reducing the amount of cell death in male- and female-derived tissue whereas medoxyprogesterone acetate (MPA) was only protective in female-derived tissue. The protective effect of progesterone was abolished in the presence of finasteride, a 5α-reductase inhibitor, suggesting it was largely mediated via its conversion to allopregnanolone. To test the hypothesis that sex differences exist in the activation of specific elements of the apoptotic pathway activated following ischemia we administered Q-VD-OPH, a caspase inhibitor, or PJ34, an inhibitor of poly (ADP ribose) polymerase (PARP). Caspase inhibition was only effective, in terms of reducing cell death, in female-derived tissue, whereas PARP inhibition was only protective in male-derived tissue. However, in both sexes, the protective effects of progesterone and estradiol were not observed in the presence of either caspase or PARP inhibition.

Conclusions

Sex differences exist in both the amount of cell death produced and those elements of the cell death pathway activated following an ischemic insult. There are also some sex differences in the effectiveness of steroid hormones to provide neuroprotection following an ischemic insult—namely MPA was only protective in female-derived tissue. This adds further support to the notion sex is an important factor to consider when investigating future drug targets for CNS disorders, such as ischemic stroke.

Reproductive Senescence and Ischemic Stroke Remodel the Gut Microbiome and Modulate the Effects of Estrogen Treatment in Female Rats

Our previous work has shown that reproductively senescent (or middle-aged; 10-12-month-old) Sprague-Dawley female rats, that are naturally estrogen-deficient, have worse stroke outcomes as compared to normally estrous-cycling adult (5-6-month-old) females. Paradoxically, estrogen replacement to this middle-aged group exacerbates stroke outcomes, while it is neuroprotective in adult females. Recent studies reveal an important role for the gut microbiome and gut metabolites in cardiovascular health, including stroke outcomes. To determine whether gut dysbiosis underlies stroke severity in reproductive senescent females, and underlies the anomalous effects of estrogen on stroke, we compared the gut microbiota and gut metabolites pre and post stroke in (a) gonadally intact adult and middle-aged females, (b) in ovariectomized and estrogen-treated (OVX+E) adult and OVX+E middle-aged females, and (c) in middle-aged OVX+E females after fecal microbiome transfer. Our data show significant gut dysbiosis in reproductive senescent females at baseline and after stroke as indicated by an elevated ratio of the major phyla, Firmicutes/Bacteroidetes (F:B), reduced alpha diversity, and significant shifts in beta diversity as compared with adult females. Specific bacterial families were also altered as a result of reproductive aging, as well as gut metabolites, including elevated serum endotoxin levels and decreased short-chain fatty acids (SCFAs), with a concomitant increase in IL-17A, indicating that reproductive senescence significantly affects gut communities under pathologic conditions. Despite the differences in gonadally intact adult and middle-aged females, estrogen-treated ovariectomized (OVX+E) females of either age group displayed no differences in the major phyla, but there was increased abundance in specific bacterial taxa, including Prevotella and Lactobacillus. The SCFA butyrate was significantly reduced at baseline in the middle-aged OVX+E females, while circulating endotoxin LPS were elevated in this group after stroke, suggesting that gut metabolites were differently affected by estrogen treatment in the two age groups. A fecal transfer from adult OVX+E females to middle-aged OVX+E females significantly reduced infarct volume, improved behavioral recovery and transiently reduced IL-17A expression. These data provide the first evidence that microbial gut communities and metabolites are altered by reproductive senescence in female rats at baseline and after stroke, and suggest that estrogen may impact stroke recovery differently in adult and reproductive senescent females due to an age-specific effect on gut microbiota and metabolites.

Progesterone treatment in rats after severe global cerebral ischemia promotes hippocampal dentate gyrus neurogenesis and functional recovery

OBJECTIVE

Rats treated with progesterone (P4) after ischemia show an adequate functional performance despite a significant loss of hippocampal pyramidal neurons, suggesting that P4 could favour a permissive microenvironment for cerebral plasticity mechanisms. The possibility of P4 treatment promoting the survival of newly generated hippocampal neurons, in relation to the performance of ischemic rats in a spatial learning task, was assessed in this study.

METHODS

Adult male rats were subjected to a severe global cerebral ischemia episode (30 min) and treated with P4 or its vehicle at 15 min, 2, 6, 24, 48 and 72 h of reperfusion. From day 4 to 8 post-ischemia 5-bromo-2-deoxyuridine (BrdU) was administered to label proliferating cells. Twenty-one days post-ischemia, the rats were exposed to the Morris water maze to assess behavioral parameters of spatial learning and memory. Subsequently, the brain was perfusion-fixed and immunofluorescence procedures were performed to quantify the number of new mature neurons (BrdU⁺/NeuN⁺) in the dentate gyrus (DG) of the hippocampus.

RESULTS

Rats subjected to severe global cerebral ischemia and treated with P4 had a significantly better performance in spatial learning-memory tests, than those treated with vehicle, and a significantly higher number of new mature neurons (BrdU⁺/NeuN⁺) in the DG.

CONCLUSION

These findings show that post-ischemia P4 treatment, following an episode of severe global cerebral ischemia, promotes the survival of newly generated hippocampal neurons in the DG, which may be one of the mechanisms of cerebral plasticity induced by the hormone, that underlie a successful functional performance in learning and memory tests.