No abstract

Anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis is an immune-mediated disease characterized by a complex neuropsychiatric syndrome in association with an antibody-mediated decrease of NMDAR. About 85% of patients respond to immunotherapy (and removal of an associated tumour if it applies), but it often takes several months or more than 1 year for patients to recover. There are no complementary treatments, beyond immunotherapy, to accelerate this recovery. Previous studies showed that SGE-301, a synthetic analogue of 24(S)-hydroxycholesterol, which is a potent and selective positive allosteric modulator of NMDAR, reverted the memory deficit caused by phencyclidine (a non-competitive antagonist of NMDAR), and prevented the NMDAR dysfunction caused by patients’ NMDAR antibodies in cultured neurons. An advantage of SGE-301 is that it is optimized for systemic delivery such that plasma and brain exposures are sufficient to modulate NMDAR activity. Here, we used SGE-301 to confirm that in cultured neurons it prevented the antibody-mediated reduction of receptors, and then we applied it to a previously reported mouse model of passive cerebroventricular transfer of patient’s CSF antibodies. Four groups were established: mice receiving continuous (14-day) infusion of patients’ or controls’ CSF, treated with daily subcutaneous administration of SGE-301 or vehicle (no drug). The effects on memory were examined with the novel object location test at different time points, and the effects on synaptic levels of NMDAR (assessed with confocal microscopy) and plasticity (long-term potentiation) were examined in the hippocampus on Day 18, which in this model corresponds to the last day of maximal clinical and synaptic alterations. As expected, mice infused with patient’s CSF antibodies, but not those infused with controls’ CSF, and treated with vehicle developed severe memory deficit without locomotor alteration, accompanied by a decrease of NMDAR clusters and impairment of long-term potentiation. All antibody-mediated pathogenic effects (memory, synaptic NMDAR, long-term potentiation) were prevented in the animals treated with SGE-301, despite this compound not antagonizing antibody binding. Additional investigations on the potential mechanisms related to these SGE-301 effects showed that (i) in cultured neurons SGE-301 prolonged the decay time of NMDAR-dependent spontaneous excitatory postsynaptic currents suggesting a prolonged open time of the channel; and (ii) it significantly decreased, without fully preventing, the internalization of antibody-bound receptors suggesting that additional, yet unclear mechanisms, contribute in keeping unchanged the surface NMDAR density. Overall, these findings suggest that SGE-301, or similar NMDAR modulators, could potentially serve as complementary treatment for anti-NMDAR encephalitis and deserve future investigations.

Brexanolone (allopregnanolone), was recently approved by the FDA for the treatment of post-partum depression, demonstrating long-lasting antidepressant effects. Despite our understanding of the mechanism of action of neurosteroids as positive allosteric modulators (PAMs) of GABAA receptors, we still do not fully understand how allopregnanolone exerts these persistent antidepressant effects. We demonstrate that allopregnanolone and similar synthetic neuroactive steroid analogs, SGE-516 (tool-compound) and zuranolone (SAGE-217, investigational-compound), modulate oscillations across species. We further demonstrate a critical role for interneurons in generating oscillations in the basolateral amygdala (BLA) and a role for delta-containing GABAARs in mediating the ability of neurosteroids to modulate network and behavioral states. Actions of allopregnanolone in the BLA confer anxiolytic/antidepressant behavior and enhance BLA high-theta oscillations (6-12Hz) through delta-containing GABAA receptors, a mechanism distinct from other GABAA PAMs, such as benzodiazepines. Moreover, treatment with the allopregnanolone analog SGE-516 protects mice from chronic stress-induced disruption of network and behavioral states. Our findings demonstrate a novel molecular and cellular mechanism mediating the well-established anxiolytic and antidepressant effects of neuroactive steroids.

Preclinical testing of treatments for postpartum depression (PPD) has been limited due to the lack of available animal models of such a complex disorder. To address this limitation, our laboratory has generated unique preclinical mouse models that exhibit abnormal postpartum behaviors. Mice with a loss or reduction in the expression of the GABAA receptor (GABAAR) δ subunit (Gabrd−/− or Gabrd+/−, respectively) and mice that lack the K+/Cl− co-transporter, KCC2, specifically in corticotropin-releasing hormone (CRH) neurons (KCC2/Crh mice) exhibit depression-like behaviors restricted to the postpartum period and deficits in maternal care, which serve as useful tools for testing novel therapeutic compounds. Utilizing these preclinical models, we tested the ability of a novel, synthetic, neuroactive steroid developed by SAGE Therapeutics, SGE-516, to improve abnormal postpartum behaviors. Gabrd−/−, Gabrd+/−, and KCC2/Crh dams treated with SGE-516 (450 mg/kg chow) during late pregnancy exhibit a decrease in depression-like behaviors and improvements in maternal care at 48 h postpartum. Interestingly, acute treatment with SGE-516 also exhibits robust therapeutic effects in these preclinical PPD models. We previously discovered abnormal stress reactivity associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation associated with depression-like behaviors in the preclinical PPD models, evident from an increase in stress-induced corticosterone levels and dephosphorylation and downregulation of KCC2 in the paraventricular nucleus of the hypothalamus (PVN) during the peripartum period. Here we demonstrated that SGE-516 treatment is sufficient to prevent the stress-induced increase in corticosterone and dephosphorylation and downregulation of KCC2 in the PVN. In contrast, and consistent with the distinct pharmacology of SGE-516 compared to benzodiazepines, treatment with clobazam (250 mg/kg chow) did not alter the depression-like phenotype or deficits in maternal care observed in these preclinical models of PPD. These findings are consistent with the positive double-blind, randomized, placebo-controlled trial findings of a similar compound, brexanolone, in the treatment of patients with postpartum depression. Further, these findings validate the use of these preclinical models of PPD for screening novel compounds for the treatment of postpartum depression.

Background and ObjectivesTo demonstrate that an analog (SGE-301) of a brain-derived cholesterol metabolite, 24(S)-hydroxycholesterol, which is a selective positive allosteric modulator (PAM) of NMDA receptors (NMDARs), is able to reverse the memory and synaptic alterations caused by CSF from patients with anti-NMDAR encephalitis in an animal model of passive transfer of antibodies.MethodsFour groups of mice received (days 1–14) patients' or controls' CSF via osmotic pumps connected to the cerebroventricular system and from day 11 were treated with daily subcutaneous injections of SGE-301 or vehicle (no drug). Visuospatial memory, locomotor activity (LA), synaptic NMDAR cluster density, hippocampal long-term potentiation (LTP), and paired-pulse facilitation (PPF) were assessed on days 10, 13, 18, and 26 using reported techniques.ResultsOn day 10, mice infused with patients' CSF, but not controls' CSF, presented a significant visuospatial memory deficit, reduction of NMDAR clusters, and impairment of LTP, whereas LA and PPF were unaffected. These alterations persisted until day 18, the time of maximal deficits in this model. In contrast, mice that received patients' CSF but from day 11 were treated with SGE-301 showed memory recovery (day 13), and on day 18, all paradigms (memory, NMDAR clusters, and LTP) had reversed to values similar to those of controls. On day 26, no differences were observed among experimental groups.DiscussionAn oxysterol biology-based PAM of NMDARs is able to reverse the synaptic and memory deficits caused by CSF from patients with anti-NMDAR encephalitis. These findings suggest a novel adjuvant treatment approach that deserves future clinical evaluation.