Progesterone and allopregnanolone improves stroke outcome in male mice via distinct mechanisms but neither promotes neurogenesis

Emerging Pro-neurogenic Therapeutic Strategies for Neurodegenerative Diseases: A Review of Pre-clinical and Clinical Research

The neuroscience community has largely accepted the notion that functional neurons can be generated from neural stem cells in the adult brain, especially in two brain regions: the subventricular zone of the lateral ventricles and the subgranular zone in the dentate gyrus of the hippocampus. However, impaired neurogenesis has been observed in some neurodegenerative diseases, particularly in Alzheimer's, Parkinson's, and Huntington's diseases, and also in Lewy Body dementia. Therefore, restoration of neurogenic function in neurodegenerative diseases emerges as a potential therapeutic strategy to counteract, or at least delay, disease progression. Considering this, the present study summarizes the different neuronal niches, provides a collection of the therapeutic potential of different pro-neurogenic strategies in pre-clinical and clinical research, providing details about their possible modes of action, to guide future research and clinical practice.

Sex differences in the cerebroprotection by Nestorone intranasal delivery following stroke in mice

Our previous studies showed that intranasal delivery of progesterone offers a good bioavailability and neuroprotective efficacy after experimental stroke. We have also demonstrated that progesterone receptors (PR) are essential for cerebroprotection by endogenous progesterone and by progesterone treatment. The identification of PR as a potential drug target for stroke therapy opens new therapeutic indications for selective synthetic progestins. Nestorone® (16-methylene-17α-acetoxy-19-nor-pregn-4-ene-3, 20-dione, also known as segesterone acetate) is a 19-norprogesterone derivative that more potently targets PR than progesterone. The objective of this study was to evaluate the cerebroprotective efficiency of intranasal administration of Nestorone after middle cerebral occlusion (MCAO) in mice. We show here that intranasal administration is a very efficient route to achieve a preferential delivery of Nestorone to the brain and confers a slow elimination and a sustained bioavailability. Furthermore, intranasal administration of Nestorone (at 0.08 mg/kg) improved the functional outcomes and decreased the ischemic lesion in male but not in female mice at 48 h post MCAO. Use of PR^NesCre mice, selectively lacking expression of PR in neural cells, and their control PR^loxP/loxP littermates showed that the cerebroprotective effects of Nestorone in male mice depended on neural PR as they were not observed in PR^NesCre mice. Our findings show that intranasal delivery of Nestorone may be an efficient strategy to promote recovery after stroke in males and confirm the key role of PR in cerebroprotection. Furthermore, they point to sex differences in the response to Nestorone treatment and emphasize the necessity to include males and females in experimental studies.

Neurosteroids: A novel promise for the treatment of stroke and post-stroke complications

Stroke is the primary reason for death and disability worldwide, with few treatment strategies to date. Neurosteroids, which are natural molecules in the brain, have aroused great interest in the field of stroke. Neurosteroids are a kind of steroid that acts on the nervous system, and are synthesized in the mitochondria of neurons or glial cells using cholesterol or other steroidal precursors. Neurosteroids mainly include estrogen, progesterone (PROG), allopregnanolone, dehydroepiandrosterone (DHEA), and vitamin D (VD). Most of the preclinical studies have confirmed that neurosteroids can decrease the risk of stroke, and improve stroke outcomes. In the meantime, neurosteroids have been shown to have a positive therapeutic significance in some post-stroke complications, such as epilepsy, depression, anxiety, cardiac complications, movement disorders, and post-stroke pain. In this review, we report the historical background, modulatory mechanisms of neurosteroids in stroke and post-stroke complications, and emphasize on the application prospect of neurosteroids in stroke therapy.

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.

Progesterone in the Brain: Hormone, Neurosteroid and Neuroprotectant

Progesterone has a broad spectrum of actions in the brain. Among these, the neuroprotective effects are well documented. Progesterone neural effects are mediated by multiple signaling pathways involving binding to specific receptors (intracellular progesterone receptors (PR); membrane-associated progesterone receptor membrane component 1 (PGRMC1); and membrane progesterone receptors (mPRs)) and local bioconversion to 3α,5α-tetrahydroprogesterone (3α,5α-THPROG), which modulates GABA_A receptors. This brief review aims to give an overview of the synthesis, metabolism, neuroprotective effects, and mechanism of action of progesterone in the rodent and human brain. First, we succinctly describe the biosynthetic pathways and the expression of enzymes and receptors of progesterone; as well as the changes observed after brain injuries and in neurological diseases. Then, we summarize current data on the differential fluctuations in brain levels of progesterone and its neuroactive metabolites according to sex, age, and neuropathological conditions. The third part is devoted to the neuroprotective effects of progesterone and 3α,5α-THPROG in different experimental models, with a focus on traumatic brain injury and stroke. Finally, we highlight the key role of the classical progesterone receptors (PR) in mediating the neuroprotective effects of progesterone after stroke.

Corticosterone and progesterone differentially regulate HPA axis and neuroimmune responses to stress in male rats

In response to stressor exposure, expression of the inflammatory cytokine interleukin-1β (IL-1) is increased within the paraventricular nucleus of the hypothalamus (PVN). Surgical removal of the adrenal glands (ADX) potentiated stress-induced IL-1 expression, suggesting a role for adrenal-derived hormones in constraining stress-evoked increases in IL-1. While corticosterone (CORT) is a primary factor inhibiting IL-1 expression, progesterone (PROG) is also released by the adrenal glands in male rats in response to stress and also has potent anti-inflammatory properties. This series of studies first established doses of CORT and PROG that adequately recapitulate the normal stress-induced rise, and then tested for individual and combined roles of CORT and PROG in mitigating stress-induced expression of inflammatory genes. We found that CORT injection alone attenuated ADX-induced increases in IL-1 expression and normalized the HPA axis response to stress. In general, PROG replacement had little effect on changes in HPA axis responsivity or stress-induced inflammatory measures. When CORT and PROG were co-administered, a small effect on expression of the decoy receptor, IL-1R2 was observed, suggestive of an anti-inflammatory response. Overall, these results suggest that although CORT is likely to be the primary stress-related hormone responsible for constraining cytokine expression evoked by stress, CORT and PROG may exert certain combined actions that temper stress-induced neuroinflammation.LAY SUMMARYExposure to stress promoted expression of inflammation-related genes in the PVN and BNST. This inflammation was mainly suppressed by the adrenal hormone corticosterone, whereas progesterone had a smaller role in mitigating post-stress inflammation.

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.

Cerebroprotection by progesterone following ischemic stroke: Multiple effects and role of the neural progesterone receptors

Treatment with progesterone limits brain damage after stroke. However, the cellular bases of the cerebroprotective effects of progesterone are not well documented. The aims of this study were to determine neural cells and functions that are affected by progesterone treatment and the role of neural progesterone receptors (PR) after stroke. Adult male PR^NesCre mice, selectively lacking PR in the central nervous system, and their control PR^loxP/loxP littermates were subjected to transient ischemia by middle cerebral artery occlusion (MCAO) for 30 min. Mice received either progesterone (8 mg/kg) or vehicle at 1-, 6- and 24- hrs post-MCAO and outcomes were analyzed at 48 h post-MCAO. In PR^loxP/loxP mice, progesterone exerted multiple effects on different neural cell types, improved motor functional outcomes and reduced total infarct volumes. In the peri-infarct, progesterone increased the density of neurons (NeuN⁺ cells), of cells of the oligodendroglial lineage (Olig2⁺ cells) and of oligodendrocyte progenitors (OP, NG2⁺ cells). Progesterone decreased the density of activated astrocytes (GFAP⁺ cells) and reactive microglia (Iba1⁺ cells) coexpressing the mannose receptor type 1 CD206 marker. Progesterone also reduced the expression of aquaporin 4 (AQP4), the water channel involved in both edema formation and resorption. The beneficial effects of progesterone were not observed in PR^NesCre mice. Our findings show that progesterone treatment exerts beneficial effects on neurons, oligodendroglial cells and neuroinflammatory responses via PR. These findings demonstrate that progesterone is a pleiotropic cerebroprotective agent and that neural PR represent a therapeutic target for stroke cerebroprotection.

Therapeutic progestin segesterone acetate promotes neurogenesis: implications for sustaining regeneration in female brain

OBJECTIVE

Neurogenesis is the principal regenerative mechanism to sustain the plasticity potential in adult brains. Decreased neurogenesis parallels the cognition decline with aging, and has been suggested as a common hallmark in the progression of many neurodegeneration diseases. We previously reported that acute exposure to segesterone acetate (ST-1435; Nestorone), alone or in combination with 17β-estradiol (E2), increased human neural stem cells proliferation and survival both in vitro and in vivo. The present study expanded our previous findings to investigate the more clinical related chronic exposure in combination with E2 on the regenerative capacity of adult brain.

METHODS

To mimic the chronic contraception exposure in women, 3-month old female mice (n = 110) were treated with ST-1435, with or without co-administration of E2, for 4 weeks. Neural cell proliferation and survival, and oligodendrocyte generation were assessed. The involvement of insulin-like growth factor 1 signaling was studied.

RESULTS

Our results demonstrated that chronic ST-1435 and E2 alone or in combination increased neurogenesis by a comparable magnitude, with minimum to no antagonistic or additive effects between ST-1435 and E2. In addition, chronic exposure of ST-1435 or ST-1435 + E2 stimulated oligodendrocyte generation, indicating potential elevated myelination. Insulin-like growth factor-1 (IGF-1) and IGF-1 receptor (IGF-1R) were also up-regulated after chronic ST-1435 and E2 exposure, suggesting the involvement of IGF-1 signaling as the potential underlined regulatory pathway transducing ST-1435 effect.

CONCLUSION

These findings provide preclinical evidence and mechanistic insights for the development of ST-1435 as a neuroregenerative therapy to promote intrinsic regenerative capacity in female brains against aging and neurodegenerative disorders.

The 5α-Reductase Inhibitor Finasteride Exerts Neuroprotection Against Ischemic Brain Injury in Aged Male Rats

Progesterone (P4) exerts potent neuroprotection both in young and aged animal models of stroke. The neuroprotection is likely to be mediated by allopregnanolone (ALLO) metabolized from P4 by 5α-reductase, since the neuroprotection is attenuated by the 5α-reductase inhibitor finasteride, which was done only with young animals though. Thus, we do not know the contribution of ALLO to the P4-induced neuroprotection in aged animals. We examined effects of finasteride on the P4-induced neuroprotection in aged (16-18-month-old) male rats subjected to transient focal cerebral ischemia. Transient focal cerebral ischemia was induced by left middle cerebral artery occlusion (MCAO) and occlusion of the bilateral common carotid arteries. MCAO rats were given an 8 mg/kg P4 6 h after MCAO followed by the same treatment once a day for successive 3 days. Finasteride, a 5α-reductase inhibitor, at 20 mg/kg was intraperitoneally injected 30 min prior to the P4-injections. P4 markedly reduced neuronal damage 72 h after MCAO, and the P4-induced neuroprotection was apparently suppressed by finasteride in the aged animals. However, post-ischemic administration of finasteride alone (20 mg/kg) significantly prevented neuronal damage and the impairment of Rotarod performance after MCAO in aged male rats, but not in young ones. The androgen receptor antagonist flutamide markedly suppressed the neuroprotection of finasteride in the cerebral cortex, but not in the striatum, suggesting the androgen receptor-dependent mechanism of the finasteride-induced neuroprotection in the cerebral cortex. Our findings suggested, for the first time, the potential of finasteride as a therapeutic agent in post-ischemic treatment of strokes in aged population.

Sex steroids and neurogenesis

The brain has long been known as a dimorphic organ and as a target of sex steroids. It is also a site for their synthesis. Sex steroids in numerous ways can modify cerebral physiology, and along with many processes adult neurogenesis is also modulated by sex steroids. This review will focus on the effects of the main steroids, estrogens, androgens and progestogens, and unveil some aspects of their partly disclosed mechanisms of actions. Gonadal steroids act on different steps of neurogenesis: cell proliferation seems to be increased by estrogens only, while androgens and progestogens favor neuronal renewal by increasing cell survival; differentiation is a common target. Aging is characterized by a cognitive deficiency, paralleled by a decrease in the rate of neuronal renewal and in the levels of circulating gonadal hormones. Therefore, the effects of gonadal hormones on the aging brain are important to consider. The review will also be expanded to related molecules which are agonists to the nuclear receptors. Sex steroids can modify adult neuronal renewal and the extensive knowledge of their actions on neurogenesis is essential, as it can be a leading pathway to therapeutic perspectives.

Progesterone improves long-term functional and histological outcomes after permanent stroke in older rats

Previous studies have shown progesterone to be beneficial in animal models of central nervous system injury, but less is known about its longer-term sustained effects on recovery of function following stroke. We evaluated progesterone's effects on a panel of behavioral tests up to 8 weeks after permanent middle cerebral artery occlusion (pMCAO). Male Sprague-Dawley rats 12m.o. were subjected to pMCAO and, beginning 3h post-pMCAO, given intraperitoneal injections of progesterone (8mg/kg) or vehicle, followed by subcutaneous injections at 8h and then every 24h for 7 days, with tapering of the last 2 treatments. The rats were then tested on functional recovery at 3, 6 and 8 weeks post-stroke. We observed that progesterone-treated animals showed attenuation of infarct volume and improved functional outcomes at 8 weeks after stroke on grip strength, sensory neglect, motor coordination and spatial navigation tests. Progesterone treatments significantly improved motor deficits in the affected limb on a number of gait parameters. Glial fibrillary acidic protein expression was increased in the vehicle group and considerably lowered in the progesterone group at 8 weeks post-stroke. With repeated post-stroke testing, sensory neglect and some aspects of spatial learning performance showed spontaneous recovery, but on gait and grip-strength measres progesterone given only in the acute stage of stroke (first 7 days) showed sustained beneficial effects on all other measures of functional recovery up to 8 weeks post-stroke.

Embracing failure: What the Phase III progesterone studies can teach about TBI clinical trials

Background: Despite positive preclinical studies and two positive Phase II clinical trials, two large Phase III clinical trials of progesterone treatment of acute traumatic brain injury (TBI) recently ended with negative results, so a 100% failure rate continues to plague the field of TBI trials.

Methods: This paper reviews and analyses the trial structures and outcomes and discusses the implications of these failures for future drug and clinical trial development. Persistently negative trial outcomes have led to disinvestment in new drug research by companies and policy-makers and disappointment for patients and their families, failures which represent a major public health concern. The problem is not limited to TBI. Failure rates are high for trials in stroke, sepsis, cardiology, cancer and orthopaedics, among others.

Results: This paper discusses some of the reasons why the Phase III trials have failed. These reasons may include faulty extrapolation from pre-clinical data in designing clinical trials and the use of subjective outcome measures that accurately reflect neither the nature of the deficits nor long-term quantitative recovery.

Conclusions: Better definitions of injury and healing and better outcome measures are essential to change the embrace of failure that has dominated the field for over 30 years. This review offers suggestions to improve the situation.