Insights into functional pharmacology of α₁ GABA(A) receptors: how much does partial activation at the benzodiazepine site matter?

Effect of Intravenous Lipid Emulsion on Clozapine Acute Toxicity in Rats

Objectives

Many studies have been reported the efficacy of intravenous lipid emulsion (ILE) as an antidote on acute lipophilic drug toxicity. Clozapine, highly lipophilic dibenzodiazepine neuroleptics, is an important medication in the schizophrenia therapy regimen. Acute intoxication with antipsychotics is one of the main reasons for the referral of poisoned patients to the hospital. We expected that ILE could be used for the therapy of acute clozapine intoxicated patients.

Methods

We used two groups of consisting of six male rats. Both groups received a toxic dose of clozapine (40 mg/kg) intravenously, via the tail vein. After 15 minutes, they were treated with intravenous infusion of 18.6 mg/kg normal saline (NS group), or 18.6 mg/kg ILE 20% (ILE group). We evaluated blood pressure (BP) and heart rate by power lab apparatus through the tail artery, ataxia by a rat rotary circle, seizure scores and death in multiple times after starting clozapine administration. For biochemical and pathological evaluations the samples of tissue and blood were taken.

Results

Our results demonstrated that ILE 20% could return hypotension-induced clozapine better than normal saline. Furthermore, ataxia and seizure have rectified more rapidly and deaths reduced. Clozapine administration causes pancreatitis and lung injury but fat emulsion did not show an optimal effect on tissue damages caused by clozapine toxicity.

Conclusion

In conclusion, ILE can remove toxic signs of clozapine same as other lipophilic medicines, however, clinical uses of ILE for this intention requires more appraisement to determine the precise implication and safety.

Anticonvulsant and sedative-hypnotic activity screening of pearl and nacre (mother of pearl)

ETHNOPHARMACOLOGICAL RELEVANCE

Pearl and nacre are valuable traditional medicines to treat palpitations, convulsions or epilepsy in China for thousands of years. However, the active ingredients are not clear till now.

AIM OF THE STUDY

The main purpose of the current investigation was to assess the anticonvulsant and sedative-hypnotic activity of pearl powder and nacre powder, including their corresponding 6 protein extracts.

MATERIAL AND METHODS

Determination of the amino acid composition of the obtained protein was carried out by ultra-performance liquid chromatography (UPLC) combined with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) pre-column derivatisation. The influence of the tested drugs on locomotor activity and convulsions latency was recorded. The contents of 5-Hydroxytryptamine (5-HT) and γ-aminobutyric acid (GABA) in brain were detected by enzyme-linked immunesorbent assay (ELISA) kits. In addition, immunohistochemistry was carried out to evaluate the changes of 5-HT3 and GABAB. In parallel, the expressions of them were demonstrated by western blot.

RESULTS

The obtained data suggested that pearl original powder (1.1g/kg), pearl water-soluble protein (0.2g/kg), pearl acid-soluble protein (0.275g/kg), pearl conchiolin protein (1.1g/kg), nacre original powder (1.1g/kg), nacre water-soluble protein (0.2g/kg), nacre acid-soluble protein (0.7g/kg) and nacre conchiolin protein (1.1g/kg) could down-regulate the expression of 5-HT3 and up-regulate the level of GABAB to varying degrees compared with the control group. Besides, drug administration also reduced the locomotor activity and increased convulsions latency with a certain mortality.

CONCLUSIONS

These findings correlated with the traditional use of pearl and nacre as sedation and tranquilization agents, thus making them interesting sources for further drug development and also providing critical important evidence for the selection of quality control markers.

The Direct Actions of GABA, 2'-Methoxy-6-Methylflavone and General Anaesthetics at β3γ2L GABAA Receptors: Evidence for Receptors with Different Subunit Stoichiometries

2'-Methoxy-6-methylflavone (2'MeO6MF) is an anxiolytic flavonoid which has been shown to display GABAA receptor (GABAAR) β2/3-subunit selectivity, a pharmacological profile similar to that of the general anaesthetic etomidate. Electrophysiological studies suggest that the full agonist action of 2'MeO6MF at α2β3γ2L GABAARs may mediate the flavonoid's in vivo effects. However, we found variations in the relative efficacy of 2'MeO6MF (2'MeO6MF-elicited current responses normalised to the maximal GABA response) at α2β3γ2L GABAARs due to the presence of mixed receptor populations. To understand which receptor subpopulation(s) underlie the variations observed, we conducted a systematic investigation of 2'MeO6MF activity at all receptor combinations that could theoretically form (α2, β3, γ2L, α2β3, α2γ2L, β3γ2L and α2β3γ2L) in Xenopus oocytes using the two-electrode voltage clamp technique. We found that 2'MeO6MF activated non-α-containing β3γ2L receptors. In an attempt to establish the optimal conditions to express a uniform population of these receptors, we found that varying the relative amounts of β3:γ2L subunit mRNAs resulted in differences in the level of constitutive activity, the GABA concentration-response relationships, and the relative efficacy of 2'MeO6MF activation. Like 2'MeO6MF, general anaesthetics such as etomidate and propofol also showed distinct levels of relative efficacy across different injection ratios. Based on these results, we infer that β3γ2L receptors may form with different subunit stoichiometries, resulting in the complex pharmacology observed across different injection ratios. Moreover, the discovery that GABA and etomidate have direct actions at the α-lacking β3γ2L receptors raises questions about the structural requirements for their respective binding sites at GABAARs.