A comparison of the pharmacological properties of recombinant human and rat alpha(1)beta(2)gamma(2L) GABA(A) receptors in Xenopus oocytes

Allopregnanolone and its antagonist modulate neuroinflammation and neurological impairment

Neuroinflammation accompanies several brain disorders, either as a secondary consequence or as a primary cause and may contribute importantly to disease pathogenesis. Neurosteroids which act as Positive Steroid Allosteric GABA-A receptor Modulators (Steroid-PAM) appear to modulate neuroinflammation and their levels in the brain may vary because of increased or decreased local production or import from the systemic circulation. The increased synthesis of steroid-PAMs is possibly due to increased expression of the mitochondrial cholesterol transporting protein (TSPO) in neuroinflammatory tissue, and reduced production may be due to changes in the enzymatic activity. Microglia and astrocytes play an important role in neuroinflammation, and their production of inflammatory mediators can be both activated and inhibited by steroid-PAMs and GABA. What is surprising is the finding that both allopregnanolone, a steroid-PAM, and golexanolone, a novel GABA-A receptor modulating steroid antagonist (GAMSA), can inhibit microglia and astrocyte activation and normalize their function. This review focuses on the role of steroid-PAMs in neuroinflammation and their importance in new therapeutic approaches to CNS and liver disease.

Extra-Synaptic GABAA Receptor Potentiation and Neurosteroid-Induced Learning Deficits Are Inhibited by GR3027, a GABAA Modulating Steroid Antagonist

Objectives In Vitro: To study the effects of GR3027 (golexanolone) on neurosteroid-induced GABA-mediated current responses under physiological GABAergic conditions with recombinant human α5β3γ2L and α1β2γ2L GABAA receptors expressed in human embryonic kidney cells, using the response patch clamp technique combined with the Dynaflow™ application system. With α5β3γ2L receptors, 0.01-3 μM GR3027, in a concentration-dependent manner, reduced the current response induced by 200 nM THDOC + 0.3 µM GABA, as well as the THDOC-induced direct gated effect. GR3027 (1 μM) alone had no effect on the GABA-mediated current response or current in the absence of GABA. With α1β2γ2L receptors, GR3027 alone had no effect on the GABA-mediated current response or did not affect the receptor by itself. Meanwhile, 1-3 µM GR3027 reduced the current response induced by 200 nM THDOC + 30 µM GABA and 3 µM GR3027 that induced by 200 nM THDOC when GABA was not present. Objectives In Vivo: GR3027 reduces allopregnanolone (AP)-induced decreased learning and anesthesia in male Wistar rats. Rats treated i.v. with AP (2.2 mg/kg) or vehicle were given GR3027 in ratios of 1:0.5 to 1:5 dissolved in 10% 2-hydroxypropyl-beta-cyclodextrin. A dose ratio of AP:GR3027 of at least 1:2.5 antagonized the AP-induced decreased learning in the Morris Water Mase (MWM) and 1:7.5 antagonized the loss of righting reflex (LoR). GR3027 treatment did not change other functions in the rat compared to the vehicle group. Conclusions: GR3027 functions in vitro as an inhibitor of GABAA receptors holding α5β3γ2L and α1β2γ2L, in vivo, in the rat, as a dose-dependent inhibitor toward AP's negative effects on LoR and learning in the MWM.

Isoallopregnanolone Inhibits Estrus Cycle-Dependent Aggressive Behavior

Among female rats, some individuals show estrus cycle-dependent irritability/aggressive behaviors, and these individual rats may be used as a model for premenstrual dysphoric disorder (PMDD). We wanted to investigate if these behaviors are related to the estrus cycle phase containing moderately increased levels of positive GABA-A receptor-modulating steroids (steroid-PAM), especially allopregnanolone (ALLO), and if the adverse behavior can be antagonized. The electrophysiology studies in this paper show that isoallopregnanolone (ISO) is a GABA-A-modulating steroid antagonist (GAMSA), meaning that ISO can antagonize the agonistic effects of positive GABA-A receptor-modulating steroids in both α1β2γ2L and α4β3δ GABA-A receptor subtypes. In this study, we also investigated whether ISO could antagonize the estrus cycle-dependent aggressive behaviors in female Wistar rats using a resident-intruder test. Our results confirmed previous reports of estrus cycle-dependent behaviors in that 42% of the tested rats showed higher levels of irritability/aggression at diestrus compared to those at estrus. Furthermore, we found that, during the treatment with ISO, the aggressive behavior at diestrus was alleviated to a level comparable to that of estrus. We noticed an 89% reduction in the increase in aggressive behavior at diestrus compared to that at estrus. Vehicle treatment in the same animals showed a minimal effect on the diestrus-related aggressive behavior. In conclusion, we showed that ISO can antagonize Steroid-PAM both in α1β2γ2L and α4β3δ GABA-A receptor subtypes and inhibit estrus cycle-dependent aggressive behavior.

Treatment of premenstrual dysphoric disorder with the GABAA receptor modulating steroid antagonist Sepranolone (UC1010)-A randomized controlled trial

CONTEXT

Allopregnanolone is a metabolite from progesterone and a positive modulator of the GABA_A receptor. This endogenous steroid may induce negative mood in sensitive women when present in serum levels comparable to the premenstrual phase. Its endogenous isomer, isoallopregnanolone, has been shown to antagonize allopregnanolone effects in experimental animal and human models.

OBJECTIVE

The objective was to test whether inhibition of allopregnanolone by treatment with the GABA_A modulating steroid antagonist (GAMSA) Sepranolone (UC1010) during the premenstrual phase could reduce symptoms of the premenstrual dysphoric disorder (PMDD). The pharmacokinetic parameters of UC1010 when given as a subcutaneous injection were measured in healthy women prior to the study in women with PMDD.

DESIGN

This was an explorative randomized, double-blind, placebo-controlled study.

SETTING

Swedish multicentre study with 10 centers.

PARTICIPANTS

Participants were 26 healthy women in a pharmacokinetic phase I study part, and 126 women with PMDD in a phase II study part. Diagnosis followed the criteria for PMDD in DSM-5 using Daily Record of Severity of Problems (DRSP) and Endicott's algorithm.

INTERVENTION

Subjects were randomized to treatment with UC1010 (10 or 16mg) subcutaneously every second day during the luteal phase or placebo during one menstrual cycle.

OUTCOME MEASURES

The primary outcome measure was the sum of all 21 items in DRSP (Total DRSP score). Secondary outcomes were Negative mood score i.e. the ratings of the 4 key symptoms in PMDD (anger/irritability, depression, anxiety and lability) and impairment (impact on daily life).

RESULTS

26 healthy women completed the pharmacokinetic phase I study and the dosing in the following trial was adjusted according to the results. 106 of the 126 women completed the phase II study. Within this group, a significant treatment effect with UC1010 compared to placebo was obtained for the Total DRSP score (p=0.041) and borderline significance (p=0.051) for the sum of Negative mood score. Nineteen participants however showed symptoms during the follicular phase that might be signs of an underlying other conditions, and 27 participants had not received the medication as intended during the symptomatic phase. Hence, to secure that the significant result described above was not due to chance, a post hoc sub-group analysis was performed, including only women with pure PMDD who completed the trial as intended (n=60). In this group UC1010 reduced Total DRSP scores by 75% compared with 47% following placebo; the effect size 0.7 (p=0.006), and for sum of Negative mood score (p=0.003) and impairment (p=0.010) with the effect size 0.6. No severe adverse events were reported during the treatment and safety parameters (vital signs and blood chemistry) remained normal during the study.

CONCLUSIONS

This explorative study indicates promising results for UC1010 as a potential treatment for PMDD. The effect size was comparable to that of SSRIs and drospirenone containing oral contraceptives. UC1010 was well tolerated and deemed safe.

Allopregnanolone and pregnanolone analogues modified in the C ring: synthesis and activity

(25R)-3β-Hydroxy-5α-spirostan-12-one (hecogenin) and 11α-hydroxypregn-4-ene-3,20-dione (11α-hydroxyprogesterone) were used as starting materials for the synthesis of a series of 11- and 12-substituted derivatives of 5ξ-pregnanolone (3α-hydroxy-5α-pregnan-20-one and 3α-hydroxy-5β-pregnan-20-one), the principal neurosteroid acting via γ-aminobutyric acid (GABA). These analogues were designed to study the structural requirements of the corresponding GABAA receptor. Their biological activity was measured by in vitro test with [(3)H]flunitrazepam as radioligand in which allopregnanolone and its active analogues stimulated the binding to the GABAA receptor. Analysis of the SAR data suggests dependence of the flunitrazepam binding activity on the hydrophobic-hydrophilic balance of the groups at the C-ring edge rather than on specific interactions between them and the receptor.

Age- and gender-related differences in GABAA receptor-mediated postsynaptic currents in GABAergic neurons of the substantia nigra reticulata in the rat

The responsiveness of the rat anterior substantia nigra pars reticulata (SNR) GABAergic neurons to GABA(A)ergic drugs changes with age and gender, altering its role in seizure control. To determine whether maturational and gender-specific differences in the properties of spontaneous GABA(A)Rs-mediated inhibitory postsynaptic currents (sIPSCs) underlie these events, we studied sIPSCs at baseline and after application of the alpha1 GABA(A)Rs subunit selective agonist zolpidem, at postnatal days (PN) 5-9, PN12-15, and PN28-32. Results were correlated with the alpha1 and alpha 3 GABA(A)Rs subunit immunoreactivity (-ir) at PN5, PN15, and PN30, using immunochemistry. The mean frequency, amplitude and charge transfer increased whereas the 10-90% rise time and decay time accelerated with age in both genders. The faster sIPSC kinetics in older rats were paralleled by increased alpha1-ir and decreased alpha 3-ir. At PN5-9, males had more robust sIPSCs (frequency, amplitude, charge carried per event and charge transfer) than females. At PN28-32, males exhibited higher amplitudes and faster kinetics than females. The zolpidem-induced increase of decay times, amplitude and charge transfer and alpha1-ir expression were the lowest in PN5-9 males but increased with age, in both genders. Our findings demonstrate that alterations in GABA(A)Rs subunit expression partially underlie age- and gender-specific sIPSC changes in SNR neurons. However, the observation of gender differences in sIPSC kinetics that cannot be attributed to changes in perisomatic alpha1 expression suggests the existence of additional gender-specific factors that control the sIPSC kinetics in rat SNR.