A pilot study of golexanolone, a new GABA-A receptor-modulating steroid antagonist, in patients with covert hepatic encephalopathy.

BACKGROUND & AIMS: Golexanolone is a novel small molecule GABA-A receptor-modulating steroid antagonist under development for the treatment of cognitive and vigilance disorders caused by allosteric over-activation of GABA-A receptors by neurosteroids. It restored spatial learning and motor coordination in animal models of hepatic encephalopathy (HE) and mitigated the effects of intravenous allopregnanolone in healthy adults in a dose-dependent fashion. Herein, we report data on the safety, pharmacokinetics (PK) and efficacy of golexanolone in adult patients with cirrhosis. METHODS: Following single/multiple ascending dose studies, adults with Child-Pugh A/B cirrhosis and abnormal continuous reaction time (CRT) on screening were randomized to 3 weeks' dosing with golexanolone (10, 40 or 80 mg BID) or placebo. CRT, psychometric hepatic encephalopathy score (PHES), animal naming test (ANT), Epworth sleepiness scale (ESS) and electroencephalogram (mean dominant frequency [MDF]; delta+theta/alpha+beta ratio [DT/AB]) were obtained at baseline, 10, and 21 days. RESULTS: Golexanolone exhibited satisfactory safety and PK. Baseline characteristics were similar between the 12 and 33 patients randomized to placebo or golexanolone, respectively. By prespecified analyses, golexanolone was associated with directionally favourable changes vs. placebo in ESS (p = 0.047), MDF (p = 0.142) and DT/AB (p = 0.021). All patients also showed directionally favourable changes in CRT, PHES and ANT, but with no statistical difference between golexanolone and placebo. Post hoc analyses taking into account the variability and improvement in CRT, PHES and ANT observed between screening and baseline suggested an efficacy signal by cognitive measures as well. CONCLUSION: Golexanolone was well tolerated and associated with improvement in cognitive performance. These results implicate GABA-A receptor-modulating neurosteroids in the pathogenesis of HE and support the therapeutic potential of golexanolone. LAY SUMMARY: Many patients with cirrhosis experience subtle but disabling cognitive problems, including sleepiness and poor attention span, that impair their ability to be gainfully employed or carry out activities of daily living. This pilot study tested the hypothesis that these problems with cognition, for which there is no approved treatment, might be improved by an experimental drug, golexanolone, designed to normalize the function of receptors which inhibit brain function. The results of this study suggest that golexanolone is well tolerated and may improve cognition, as reflected by measures of sleepiness, attention span and brain wave activity, paving the way for future larger studies of this promising experimental drug. CLINICAL TRIAL REGISTRATION NUMBER: EudraCT 2016-003651-30.

Effects of (+)-bicuculline, a GABAa receptor antagonist, on auditory steady state response in free-moving rats.

Auditory steady-state responses (ASSRs) are states in which the electrical activity of the brain reacts steadily to repeated auditory stimuli. They are known to be useful for testing the functional integrity of neural circuits in the cortex, as well as for their capacity to generate synchronous activity in both human and animal models. Furthermore, abnormal gamma oscillations on ASSR are typically observed in patients with schizophrenia (SZ). Changes in neural synchrony may reflect aberrations in cortical gamma-aminobutyric acid (GABA) neurotransmission. However, GABA's impact and effects related to ASSR are still unclear. Here, we examined the effect of a GABAa receptor antagonist, (+)-bicuculline, on ASSR in free-moving rats. (+)-Bicuculline (1, 2 and 4 mg/kg, sc) markedly and dose-dependently reduced ASSR signals, consistent with current hypotheses. In particular, (+)-bicuculline significantly reduced event-related spectral perturbations (ERSPs) at 2 and 4 mg/kg between 10 and 30 minutes post-dose. Further, bicuculline (2 and 4 mg/kg) significantly and dose-dependently increased baseline gamma power. Furthermore, the occurrence of convulsions was consistent with the drug's pharmacokinetics. For example, high doses of (+)-bicuculline such as those greater than 880 ng/g in the brain induced convulsion. Additionally, time-dependent changes in ERSP with (+)-bicuculline were observed in accordance with drug concentration. This study partially unraveled the contribution of GABAa receptor signals to the generation of ASSR.

PKPD and cardiac single cell modeling of a DDI study with a CYP3A4 substrate and itraconazole to quantify the effects on QT interval duration.

Plasma drug concentration and electrocardiogram (ECG) data from a drug-drug interaction (DDI) study employing the metabolic inhibitor itraconazole have been used as part of a prospectively defined pharmacokinetic/pharmacodynamic modelling strategy to quantify the potential for QT interval prolongation from basmisanil, an investigational compound. ECG data were collected on multiple days during repeat dosing treatment regimens, thereby allowing the capture of QT data across a wide range of drug concentrations in each study participant and encompassing both "therapeutic" and "supra-therapeutic" exposures. The data were used to develop a non-linear mixed effect concentration-QT (C-QT) model that differentiated drug-induced QT prolongation from other factors altering QT interval duration. Food effects were accounted by quantitating their influences on the parameters describing the diurnal variation of QT. The final model demonstrated that itraconazole does not cause QT prolongation, while for basmisanil, the 1-sided upper 95% CI of the QT interval at 240 mg (the highest dose tested in ongoing phase 2 studies) with DDI, was below the 10 ms threshold considered to be of clinical significance by regulatory authorities. The empirical modelling was complemented with a human mechanistic cardiac single cell model that was used to simulate the change in action potential duration as a function of drug concentration. The results of the two approaches were in agreement, suggesting that the effect of basmisanil on QT interval duration can be attributed to the effect on hERG alone. The C-QT model for basmisanil can be used to derive the QT interval corrected changes in heart rate (QTc) and thus inform cardiac safety strategy in later development without the need for a separate, dedicated study.

Brain pharmacology of intrathecal antisense oligonucleotides revealed through multimodal imaging.

Intrathecal (IT) delivery and pharmacology of antisense oligonucleotides (ASOs) for the CNS have been successfully developed to treat spinal muscular atrophy. However, ASO pharmacokinetic (PK) and pharmacodynamic (PD) properties remain poorly understood in the IT compartment. We applied multimodal imaging techniques to elucidate the IT PK and PD of unlabeled, radioactively labeled, or fluorescently labeled ASOs targeting ubiquitously expressed or neuron-specific RNAs. Following lumbar IT bolus injection in rats, all ASOs spread rostrally along the neuraxis, adhered to meninges, and were partially cleared to peripheral lymph nodes and kidneys. Rapid association with the pia and arterial walls preceded passage of ASOs across the glia limitans, along arterial intramural basement membranes, and along white-matter axonal bundles. Several neuronal and glial cell types accumulated ASOs over time, with evidence of probable glial accumulation preceding neuronal uptake. IT doses of anti-GluR1 and anti-Gabra1 ASOs markedly reduced the mRNA and protein levels of their respective neurotransmitter receptor protein targets by 2 weeks and anti-Gabra1 ASOs also reduced binding of the GABAA receptor PET ligand 18F-flumazenil in the brain over 4 weeks. Our multimodal imaging approaches elucidate multiple transport routes underlying the CNS distribution, clearance, and efficacy of IT-dosed ASOs.

Thujone and thujone-containing herbal medicinal and botanical products: toxicological assessment.

Thujone, a major component of the notoriously famous absinthe drink, is neurotoxic, although the current view rather downgrades its risk to humans. In animal studies, thujone inhibits the gamma-aminobutyric acid A (GABA(A)) receptor causing excitation and convulsions in a dose-dependent manner, although there are uncertainties about the doses required in humans. Toxicity of thujone has been extensively studied. Neurotoxicity is the principal toxic outcome in acute and chronic studies. There is some equivocal evidence of carcinogenicity in rats. Metabolism of thujone has been elucidated both in vitro and in vivo in several species and in vitro in human liver preparations. CYP2A6 is the principal metabolic enzyme, followed by CYP3A4 and, to a lesser extent, CYP2B6. CYP-associated metabolism may give rise to some potential pharmacogenetic and metabolic interaction consequences. Although the data base for determining exposure limits is of variable usefulness, the best estimates for allowable daily intakes via herbal preparations and diet are of the order of 3-7 mg/day. There are still important gaps in the knowledge required to assess thujone toxicity, the most important ones being human dose-concentration-effect relationships including the elucidation of bioavailability, and the actual toxicological consequences of potential pharmacogenetic variations and environmental factors.

Tranexamic acid concentrations associated with human seizures inhibit glycine receptors.

Antifibrinolytic drugs are widely used to reduce blood loss during surgery. One serious adverse effect of these drugs is convulsive seizures; however, the mechanisms underlying such seizures remain poorly understood. The antifibrinolytic drugs tranexamic acid (TXA) and ε-aminocaproic acid (EACA) are structurally similar to the inhibitory neurotransmitter glycine. Since reduced function of glycine receptors causes seizures, we hypothesized that TXA and EACA inhibit the activity of glycine receptors. Here we demonstrate that TXA and EACA are competitive antagonists of glycine receptors in mice. We also showed that the general anesthetic isoflurane, and to a lesser extent propofol, reverses TXA inhibition of glycine receptor-mediated current, suggesting that these drugs could potentially be used to treat TXA-induced seizures. Finally, we measured the concentration of TXA in the cerebrospinal fluid (CSF) of patients undergoing major cardiovascular surgery. Surprisingly, peak TXA concentration in the CSF occurred after termination of drug infusion and in one patient coincided with the onset of seizures. Collectively, these results show that concentrations of TXA equivalent to those measured in the CSF of patients inhibited glycine receptors. Furthermore, isoflurane or propofol may prevent or reverse TXA-induced seizures.

Axonal failure during high frequency stimulation of rat subthalamic nucleus.

Deep brain stimulation (DBS) has been established as an effective surgical therapy for advanced Parkinson's disease (PD) and gains increasing acceptance for otherwise intractable neuropsychiatric diseases such as major depression or obsessive­compulsive disorders. In PD, DBS targets predominantly the subthalamic nucleus (STN) and relieves motor deficits only at high frequency (>100 Hz). In contrast to the well-documented clinical efficacy of DBS, its underlying principle remains enigmatic spawning a broad and, in part, contradictory spectrum of suggested synaptic and non-synaptic mechanisms within and outside STN. Here we focused on a crucial, but largely neglected issue in this controversy, namely the axonal propagation of DBS within and away from STN. In rat brain slices preserving STN projections to substantia nigra (SN) and entopeduncular nucleus (EP, the rodent equivalent of internal globus pallidus), STN-DBS disrupted synaptic excitation onto target neurons through an unexpected failure of axonal signalling. The rapid onset and, upon termination of DBS, recovery of this effect was highly reminiscent of the time course of DBS in the clinical setting. We propose that DBS-induced suppression of axonal projections from and to STN serves to shield basal ganglia circuitry from pathological activity arising in or amplified by this nucleus.

Effects of GABA(A) receptor blockade on regional cerebral blood flow and blood-brain barrier disruption in focal cerebral ischemia.

In cerebral ischemia, transmission by the inhibitory neurotransmitter, γ-aminobutyric acid (GABA) is altered. This study was performed to determine whether blockade of GABA(A) receptor would affect regional cerebral blood flow (rCBF) and blood-brain barrier (BBB) permeability in a focal ischemic area of the brain. Rats were anesthetized with isoflurane and mechanically ventilated. Fifteen minutes after a permanent middle cerebral artery (MCA) occlusion, one half of the rats were infused with bicuculline 1mg/kg/min iv for 2 min followed by 0.1mg/kg/min iv to the end of the experiment. The other half were infused with normal saline. At one hour after MCA occlusion, rCBF was determined using ¹4C-iodoantipyrine and BBB permeability was determined by measuring the transfer coefficient (Ki) of ¹4C-α-aminoisobutyric acid. With MCA occlusion, rCBF was decreased in the ischemic cortex (IC) (-70%) in the control rats. In the bicuculline treated rats, the rCBF of the IC was lower (-48%) than the contralateral cortex but higher than the rCBF of the IC of the control rats (+55%). MCA occlusion increased Ki in the IC of the control rats (+72%) and bicuculline administration increased Ki further (+53%) in the IC. Blockade of GABA(A) receptors did not significantly affect rCBF or BBB permeability in the non-ischemic brain regions under isoflurane anesthesia. Our data demonstrated that blockade of GABA(A) receptors increased rCBF and enhanced the BBB disruption in focal cerebral ischemia. Our data suggest that GABA(A) receptors are involved, at least in part, in modulating rCBF and BBB disruption in focal cerebral ischemia.

Encoding of the cough reflex in anesthetized guinea pigs.

We have previously described the physiological and morphological properties of the cough receptors and their sites of termination in the airways and centrally in the nucleus tractus solitarius (nTS). In the present study, we have addressed the hypothesis that the primary central synapses of the cough receptors subserve an essential role in the encoding of cough. We found that cough requires sustained, high-frequency (≥8-Hz) afferent nerve activation. We also found evidence for processes that both facilitate (summation, sensitization) and inhibit the initiation of cough. Sensitization of cough occurs with repetitive subthreshold activation of the cough receptors or by coincident activation of C-fibers and/or nTS neurokinin receptor activation. Desensitization of cough evoked by repetitive and/or continuous afferent nerve activation has a rapid onset (<60 s) and does not differentiate between tussive stimuli, suggesting a central nervous system-dependent process. The cough reflex can also be actively inhibited upon activation of other airway afferent nerve subtypes, including slowly adapting receptors and pulmonary C-fibers. The sensitization and desensitization of cough are likely attributable to the prominent, primary, and unique role of N-methyl-d-aspartate receptor-dependent signaling at the central synapses of the cough receptors. These attributes may have direct relevance to the presentation of cough in disease and for the effectiveness of antitussive therapies.