Background and purpose:Neuroactive steroids are potent modulators of GABA A receptors and are thus of interest for their sedative, anxiolytic, anticonvulsant and anaesthetic properties. Cyclodextrins may be useful tools to manipulate neuroactive effects of steroids on GABA A receptors because cyclodextrins form inclusion complexes with at least some steroids that are active at the GABA A receptor, such as (3α,5α)-3-hydroxypregnan-20-one (3α5αP, allopregnanolone).Experimental approach:To assess the versatility of cyclodextrins as steroid modulators, we investigated interactions between γ-cyclodextrin and neuroactive steroids of different structural classes.Key results:Both a bioassay based on electrophysiological assessment of GABA A receptor function and optical measurements of cellular accumulation of a fluorescent steroid analogue suggest that γ-cyclodextrin sequesters steroids rather than directly influencing GABA A receptor function. Neither a 5β-reduced A/B ring fusion nor a sulphate group at carbon 3 affected the presumed inclusion complex formation between steroid and γ-cyclodextrin. Apparent dissociation constants for interactions between natural steroids and γ-cyclodexrin ranged from 10-60 μM. Although γ-cyclodextrin accommodates a range of natural and synthetic steroids, C 11 substitutions reduced inclusion complex formation. Using γ-cyclodextrin to remove steroid not directly bound to GABA A receptors, we found that cellular retention of receptor-unbound steroid rate limits potentiation by 3α- hydroxysteroids but not inhibition by sulphated steroids.Conclusions and implications:We conclude that γ-cyclodextrins can be useful, albeit non-specific, tools for terminating the actions of multiple classes of naturally occurring neuroactive steroids.
- GABA receptors
- Inhibitory postsynaptic currents
- γ-aminobutyric acid