Endogenous and synthetic neurosteroids in treatment of Niemann–Pick Type C disease

Abstract

The functions for neurosteroids during development and in response to nervous system injury are beginning to be identified. We focused on a mouse model in which we believed neurosteroid production would be altered, and which had a neurodegenerative phenotype. Niemann Pick Type-C (NP-C) is an autosomal recessive neurodegenerative disease caused by mutations in NPC1 (95%) or NPC2 (5%), resulting in lysosomal accumulation of unesterified cholesterol and glycolipids. The NIH mouse model of NP-C has a mutation in the NPC1 gene, and exhibits several pathological features of the most severe NP-C patients. How lysosomal storage and trafficking defects lead to neurodegeneration is unknown. We found that these mice had normal neurosteroidogenic enzyme activity during development, but lost this activity in the early neonatal period, prior to onset of neurological symptoms. Neurons that expressed P450scc, 3ß HSD, as well as those that expressed 3α HSD and 5α reductase were lost in adult NP-C brains, resulting in diminished concentrations of allopregnanolone. We treated NP-C mice with allopregnanolone and found that a single dose in the neonatal period resulted in a doubling of lifespan, substantial delay in onset of neurological symptoms, survival of cerebellar Purkinje and granule cell neurons, and reduction in cholesterol and ganglioside accumulation. The mechanism by which allopregnanolone elicited these effects is unknown. Our in vitro studies showed that Purkinje cell survival promoted by allopregnanolone was lost by treatment with bicuculline, suggesting GABA A receptors may play a role. We treated NP-C mice with a synthetic GABA A neurosteroid, ganaxolone (3α-hydroxy-3β-methyl-5α -pregnan-20-one). Ganaxolone treatment of NP-C mice produced beneficial neurological effects, but these effects were not as robust as those obtained using allopregnanolone. Thus, allopregnanolone may elicit its effects through GABA A receptors and through other mechanisms. Additional studies also suggest that allopregnanolone may elicit its effects through pregnane-X receptors (PXR). Our data suggest that mouse models of neurodegeneration may be beneficial in establishing both physiologic and pharmacologic actions of neurosteroids. These animal models further establish the wide range of functions of these compounds, which may ultimately be useful for treatment of human diseases.

Requirement of Npc1 and availability of cholesterol for early embryonic cell movements in zebrafish

“…Steroid hormone replacement therapy may be an option for alleviating NP-C patient symptoms as this method of treatment has proven to be successful in studies involving Npc1-defi cient mice. Injection of allopregnanolone perenterally to Npc1-defi cient mouse embryos results in delayed onset of symptoms, prolonged life span, and improved neurological function ( 21,27 ), possibly by quenching elevated levels of reactive oxygen species in the brain ( 28 ). Moreover, chronic treatment with the sex steroid estradiol in Npc1-defi cient mice improves defective pituitary development and is capable of reversing ovarian defects and infertility in Npc1-defi cient females ( 29,30 ).…”

Genetic identification of HSD-1, a conserved steroidogenic enzyme that directs larval development inCaenorhabditis elegans

“…In mice, it has been demonstrated that a combination of the neurosteroid allopregnanolone and a synthetic oxysterol can promote neuronal survival and mildly suppress the lethality of NPC1-deficient mice (Griffin et al, 2004;Langmade et al, 2006). Neurosteroids have thus become a possible direction for development of drugs to treat NPC disease (Mellon et al, 2008).…”

“…As defects in the NPC1 protein impact the production of multiple known neurosteroids (Mellon et al, 2008) and potentially others awaiting identification, an effective treatment may rely on the use of steroid intermediates that are trafficked independently of NPC1 and can still be processed into a diverse range of hormones. Our results showing effective bypassing of the NCR transporters in the worm suggests that a similar steroid intermediate approach may also work in mammals.…”

Involvement of pregnane xenobiotic receptor in mating-induced allopregnanolone formation in the midbrain and hippocampus and brain-derived neurotrophic factor in the hippocampus among female rats

“…PXR has been identified in the brain across many species (e.g. humans, pigs, rabbits, and rodents; Bauer et al, 2004; Frye, 2011; Lamba et al, 2004; Marini et al, 2007; Mellon et. al.…”