Neurosteroids as regenerative agents in the brain: therapeutic implications.
ABSTRACT Regenerative therapeutics hold the promise of self-renewal and repair. Ageing and age-associated neurodegenerative diseases are marked by a decline in self-renewal and repair, but a capacity for regeneration is retained. The challenge faced by researchers developing molecular therapeutics to promote self-renewal in the nervous system is to activate regenerative and repair pathways often in the context of progressive degeneration. Neurosteroids regulate both regeneration and repair systems in the brain, and among this class of molecules, allopregnanolone has been broadly investigated for its role to promote regeneration in both the central and peripheral nervous systems. In the brain, allopregnanolone induced generation and survival of new neurons in the hippocampus of both aged mice and mice with Alzheimer disease, accompanied by restoration of associative learning and memory function. In the brain of mice with Alzheimer disease, allopregnanolone increased liver X receptor and pregnane X receptor expression, reduced amyloid-β and microglial activation, and increased markers of myelin and white matter generation. Therapeutic windows for efficacy of allopregnanolone were evident in the brains of mice with both normal ageing and Alzheimer disease. Allopregnanolone dose and a regenerative treatment regimen of intermittent allopregnanolone exposure were determining factors regulating therapeutic efficacy. Allopregnanolone serves as proof of concept for therapeutics that target endogenous regeneration, windows of therapeutic opportunity for regeneration, and critical system biology factors that will determine the efficacy of regeneration.
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ABSTRACT: Allopregnanolone (Allo), a neurosteroid, has emerged as a promising promoter of endogenous regeneration in brain. In a mouse model of Alzheimer's disease, Allo induced neurogenesis, oligodendrogenesis, white matter generation and cholesterol homeostasis while simultaneously reducing β-amyloid and neuroinflammatory burden. Allo activates signaling pathways and gene expression required for regeneration of neural stem cells and their differentiation into neurons. In parallel, Allo activates systems to sustain cholesterol homeostasis and reduce β-amyloid generation. To advance Allo into studies for chronic human neurological conditions, we examined translational and clinical parameters: dose, regimen, route, formulation, outcome measures, and safety regulations. A treatment regimen of once per week at sub-sedative doses of Allo was optimal for regeneration and reduction in Alzheimer's pathology. This regimen had a high safety profile following chronic exposure in aged normal and Alzheimer's mice. Formulation of Allo for multiple routes of administration has been developed for both preclinical and clinical testing. Preclinical evidence for therapeutic efficacy of Allo spans multiple neurological diseases including Alzheimer's, Parkinson's, multiple sclerosis, Niemann-Pick, diabetic neuropathy, status epilepticus, and traumatic brain injury. To successfully translate Allo as a therapeutic for multiple neurological disorders, it will be necessary to tailor dose and regimen to the targeted therapeutic mechanisms and disease etiology. Treatment paradigms conducted in accelerated disease models in young animals have a low probability of successful translation to chronic diseases in adult and aged humans. Gender, genetic risks, stage and burden of disease are critical determinants of efficacy. This review focuses on recent advances in development of Allo for Alzheimer's disease (AD) that have the potential to accelerate therapeutic translation for multiple unmet neurological needs.Frontiers in Cellular Neuroscience 07/2014; 8:203. DOI:10.3389/fncel.2014.00203 · 4.18 Impact Factor
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ABSTRACT: A growing number of studies indicate that 3-alpha reduced neurosteroids are remarkable analgesics in various pain states. This is the case for allopregnanolone (AP), one of the most potent endogenous positive allosteric modulators of GABAA receptor function. From the pioneering work of Hans Selye, who described the sedative properties of steroids, synthetic compounds resembling the progesterone metabolite AP have been developed. If some of them have been used as anesthetics, it seems difficult to propose them as a therapeutic option for pain since they display several adverse side effects such as sedation, amnesia and functional tolerance. An alternative strategy, chosen by few laboratories around the world, is aimed at stimulating the local production of 3-alpha reduced neurosteroids in order to limit these well-known side effects. This pharmacological approach has the advantage of targeting specific structures, fully equipped with the necessary biosynthetic enzymatic machinery, where neurosteroids already act as endogenous pain modulators. The various pharmacological trials which attempted to treat pain symptoms by stimulating the production of 3-alpha reduced neurosteroids are reviewed here, as well as novel neurotransmitter systems possibly regulating their endogenous production.Frontiers in Cellular Neuroscience 06/2014; 8(8):174. DOI:10.3389/fncel.2014.00174 · 4.18 Impact Factor
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ABSTRACT: Recently, the translocator protein (18 kDa) (TSPO), previously called peripheral benzodiazepine receptor (PBR) and both the starting point and an important rate-limiting step in neurosteroidogenesis, has received increased attention in the pathophysiology of post-traumatic stress disorder (PTSD) because it affects the production of neurosteroids, reinforcing the hypothesis that selective TSPO ligands could potentially be used as anti-PTSD drugs. As expected, we showed that chronic treatment with YL-IPA08 [N-ethyl-N-(2-pyridinylmethyl)-2-(3,4-ichlorophenyl)-7-methylimidazo [1,2-a] pyridine-3-acetamide hydrochloride], a potent and selective TSPO ligand synthesized by our institute, caused significant suppression of enhanced anxiety and contextual fear induced in the inescapable electric foot-shock-induced mouse model of PTSD and the time-dependent sensitization (TDS) procedure. These effects were completely blocked by the TSPO antagonist PK11195. Furthermore, YL-IPA08 could increase the level of allopregnanolone in the prefrontal cortex and serum of post-TDS rats, and these effects were antagonized by PK11195. In summary, the findings from the current study showed that YL-IPA08, a potent and selective TSPO ligand, had a clear anti-PTSD-like effect, which might be partially mediated by binding to TSPO and the subsequent synthesis of allopregnanolone.The International Journal of Neuropsychopharmacology 04/2014; 17(10):1-11. DOI:10.1017/S1461145714000479 · 5.26 Impact Factor