Alphaxalone Reformulated

Repurposing General Anesthetic Drugs to Treat Depression: A New Frontier for Anesthesiologists in Neuropsychiatric Care

During the last 100 years, the role of anesthesiologists in psychiatry has focused primarily on facilitating electroconvulsive therapy and mitigating postoperative delirium and other perioperative neurocognitive disorders. The discovery of the rapid and sustained antidepressant properties of ketamine, and early results suggesting that other general anesthetic drugs (including nitrous oxide, propofol, and isoflurane) have antidepressant properties, has positioned anesthesiologists at a new frontier in the treatment of neuropsychiatric disorders. Moreover, shared interest in understanding the biologic underpinnings of anesthetic drugs as psychotropic agents is eroding traditional academic boundaries between anesthesiology and psychiatry. This article presents a brief overview of anesthetic drugs as novel antidepressants and identifies promising future candidates for the treatment of depression. The authors issue a call to action and outline strategies to foster collaborations between anesthesiologists and psychiatrists as they work toward the common goals of repurposing anesthetic drugs as antidepressants and addressing mood disorders in surgical patients.

A review of equine anesthetic induction: Are all equine anesthetic inductions "crash" inductions?

Horses are the most challenging of the common companion animals to anesthetize. Induction of anesthesia in the horse is complicated by the fact that it is accompanied by a transition from a conscious standing position to uncconconscious recumbency. The purpose of this article is to review the literature on induction of anesthesia with a focus on the behavioral and physiologic/pharmacodynamic responses and the actions and interactions of the drugs administered to induce anesthesia in the healthy adult horse with the goal of increasing consistency and predictability.

Pharmacologic blockade of nicotinic receptors in the suprachiasmatic nucleus increases ovarian atresia and inhibits follicular growth

Reproduction in all mammalian species depends on the growth and maturation of ovarian follicles, that is, folliculogenesis. Follicular development can culminate with the rupture of mature follicles and the consequent expulsion of their oocytes (ovulation) or in atresia, characterized by the arrest of development and eventual degeneration. These processes are regulated by different neuroendocrine signals arising at different hypothalamic nuclei, including the suprachiasmatic nucleus (SCN). In the later, the activation of muscarinic receptors (mAChRs) and nicotinic receptors (nAChRs) by acetylcholine is essential for the regulation of the pre-ovulatory signals that stimulate the rupture of mature follicles. To evaluate the participation of the nAChRs in the SCN throughout the oestrous cycle in the regulation of the hypothalamic-pituitary-ovarian axis. For this purpose, 90-day-old adult female rats in metoestrus, dioestrus, proestrus or oestrus were microinjected into the left- or right-SCN with 0.3 μL of saline solution as vehicle or with 0.225 μg of mecamylamine (Mec), a non-selective antagonist of the nicotinic receptors, diluted in 0.3 μL of vehicle. The animals were sacrificed when they presented vaginal cornification, indicative of oestrus stage, and the effects of the unilateral pharmacological blockade of the nAChRs in the SCN on follicular development, ovulation and secretion of oestradiol and follicle-stimulating hormone (FSH) were evaluated. The microinjection of Mec decreased the serum levels of FSH, which resulted in a lower number of growing and healthy follicles and an increase in atresia. The higher percentage of atresia in pre-ovulatory follicles was related to a decrease in the number of ova shed and abnormalities in oestradiol secretion. We also detected asymmetric responses between the left and right treatments that depended on the stage of the oestrous cycle. The present results allow us to suggest that during all the stages of the oestrous cycle, cholinergic signals that act on the nAChRs in the SCN are pivotal to modulate the secretion of gonadotropins and hence the physiology of the ovaries. Further research is needed to determine if such signals are generated by the cholinergic neurons in the SCN or by cholinergic afferents to the SCN.

Neurosteroids and their potential as a safer class of general anesthetics

Neurosteroids (NS) are a class of steroids that are synthesized within the central nervous system (CNS). Various NS can either enhance or inhibit CNS excitability and they play important biological roles in brain development, brain function and as mediators of mood. One class of NS, 3α-hydroxy-pregnane steroids such as allopregnanolone (AlloP) or pregnanolone (Preg), inhibits neuronal excitability; these endogenous NS and their analogues have been therapeutically applied as anti-depressants, anti-epileptics and general anesthetics. While NS have many favorable properties as anesthetics (e.g. rapid onset, rapid recovery, minimal cardiorespiratory depression, neuroprotection), they are not currently in clinical use, largely due to problems with formulation. Recent advances in understanding NS mechanisms of action and improved formulations have rekindled interest in development of NS as sedatives and anesthetics. In this review, the synthesis of NS, and their mechanism of action will be reviewed with specific emphasis on their binding sites and actions on γ-aminobutyric acid type A (GABAA) receptors. The potential advantages of NS analogues as sedative and anesthetic agents will be discussed.

The differential sensitivity of the hypothalamic-hypophysial-ovarian axis to 5-hydroxytryptophan alters the secretion of estradiol

Serotonin [5-hydroxytryptamine (5-HT)] modulates ovarian function. The precursor of 5-HT, 5-hydroxytryptophan (5-HTP), has been used to treat depression. However, the effects of 5-HTP on ovarian and reproductive physiology remain unknown. In this research, we analysed the impact of 5-HTP on the monoaminergic system and its interactions with the reproductive axis and ovarian estradiol secretion when administered by distinct routes. Female rats 30 days of age were injected with 5-HTP i.p. (100 mg/kg), into the ovarian bursa (1.5 µg/40 µL) or into the median raphe nucleus (20 µg/2.5 µL) and were killed 60 or 120 min after injection. As controls, we used rats of the same age injected with vehicle (0.9% NaCl). Monoamine, gonadotrophin and steroid ovarian hormone concentrations were measured. The injection of 5-HTP either i.p. or directly into the ovarian bursa increased the concentrations of 5-HT and the metabolite 5-hydroxyindole-3-acetic acid in the ovary. For both routes of administration, the serum concentration of estradiol increased. After i.p. injection of 5-HTP, the concentrations of luteinizing hormone were decreased and follicle-stimulating hormone increased after 120 min. Micro-injection of 5-HTP into the median raphe nucleus increased the concentrations of 5-HT in the anterior hypothalamus and dopamine in the medial hypothalamus after 120 min. Our results suggest that the administration of 5-HTP either i.p. or directly into the ovarian bursa enhances ovarian estradiol secretion.

Recent trends in anesthetic agents and techniques for ophthalmic anesthesia

Effective and safe ophthalmic anesthesia is essential for the delivery of ophthalmic perioperative care both for children and adults. Recent years have seen a major change in form of smaller incisions for most ophthalmic surgical techniques, thus making them less invasive. Additionally, most ophthalmic surgeries are now day-care surgeries at ambulatory surgical centers. The parallel advancements in the field of anesthesiology have boosted the standard of perioperative care. The purpose of this narrative review was to evaluate current trends in anesthetic agents and techniques for ophthalmic anesthesia primarily centered around deep sedation and general anesthesia as per the concerns of practicing anesthesiologists while briefly acquainting with local anesthesia advances.

Alfaxalone Alleviates Neurotoxicity and Cognitive Impairment Induced by Isoflurane Anesthesia in Offspring Rats

BACKGROUND

The anesthetic isoflurane can cause neurotoxicity in fetuses and offspring of rats, affecting their neurodevelopment. However, the underlying mechanisms and therapeutic targets of isoflurane-induced neurotoxicity remain to be identified. Alfaxalone (ALF) is a steroid anesthetic. Steroids have been reported to have neuroprotective effects. This study aimed to investigate whether ALF could alleviate the isoflurane-induced neurotoxicity in fetuses and offspring of rats.

METHODS

On gestation day 15 (G15), the pregnant SD rats were randomly assigned to 4 groups: control 1 (CTL1) + control 2 (CTL2), isoflurane (ISO) + CTL2, CTL1 + ALF, and ISO + ALF. To analyze the changes in the expression levels of inflammatory cytokines, apoptotic factors, and synaptophysin, the brain tissues from the G15 fetuses and offspring at postnatal day 7 (P7), postnatal day 14 (P14), and postnatal day 31 (P31) were collected. The newborn neurons in the rats' offspring at P7, P14, and P31 were counted using immunofluorescence techniques. The Morris water maze (MWM) test was performed to assess the learning and memory abilities of P31 offspring rats.

RESULTS

ALF significantly alleviated the isoflurane-induced increase in the expression levels of inflammatory cytokines and apoptotic factors, such as interleukin (IL)-6 (ISO + CTL2 versus ISO + ALF: 5.133 ± 0.739 versus 1.093 ± 0.213, P < .001) and Caspase-3 (6.457 ± 0.6 versus 1.062 ± 0.1, P < .001) in the G15 fetuses. In P31 offspring rats, the expression levels of synaptophysin (0.719 ± 0.04 versus 1.068 ± 0.072, P < .001) and the number of newborn neurons in the dentate gyrus of the hippocampus were significantly lower in the ISO + CTL2 group as compared to those in the ISO + ALF group (118 ± 6 versus 140 ± 7, P < .001). These changes also occurred in the rat offspring at P7 and P14. In the MWM test, the escape latency of CTL1 + ALF group rats was significantly lower than that of ISO + ALF group rats (41 ± 6 versus 31 ± 7, P < .001) at P31.

CONCLUSIONS

Based on these findings, this study suggested that isoflurane exposure during pregnancy in rats could cause neuroinflammation and death of embryos as well as impairment of cognitive function in the offspring rats. ALF can be used to counteract the negative effects of isoflurane.

Suprachiasmatic nucleus and vagus nerve trigger preovulatory LH and ovulation

In brief

In the proestrus day, the neural and endocrine signals modulate ovarian function. This study shows vagus nerve plays a role in the multisynaptic pathways of communication between the suprachiasmatic nucleus and the ovaries where such neural information determines ovulation.

Abstract

The suprachiasmatic nucleus (SCN) regulates the activity of several peripheral organs through a parasympathetic-sympathetic pathway. Previously, we demonstrated that atropine (ATR) microinjection in the right SCN of rats during proestrus blocks ovulation. In the present study, we analysed whether the vagus nerve is one of the neural pathways by which the SCN regulates ovulation. For this, CIIZ-V strain cyclic rats on the day of proestrus were microinjected with a saline solution (vehicle) or ATR in the right or left SCN, which was followed by ventral laparotomy or ipsilateral vagotomy to the microinjection side. Some animal groups were sacrificed (i) on the same day of the surgery to measure oestradiol, progesterone and luteinizing hormone (LH) levels or (ii) at 24 h after surgery to evaluate ovulation. The left vagotomy in rats microinjected with ATR in the left SCN did not modify ovulation. In rats with ATR microinjection in the right SCN, the right vagotomy increased the levels of steroids and LH on the proestrus and ovulatory response. The present results suggest that the right vagus nerve plays a role in the multisynaptic pathways of communication between the SCN and the ovaries and indicate that such neural information participates in the regulation of the oestradiol and progesterone surge, which triggers the preovulatory peak of LH and determines ovulation.

Alfaxalone population pharmacokinetics in the rat: Model application for pharmacokinetic and pharmacodynamic design in inbred and outbred strains and sexes

The translation of new injectable anesthetic drugs from rodent to humans remains slow, despite the realization that reliance on the volatile agents is unsustainable from an environmental perspective. The aim of this study was to investigate the influence of rat sex and strain on the PK and PD of the anesthetic neurosteroid alfaxalone. Forty rats had cannulas inserted under isoflurane anesthesia for drug administration and sampling. Carotid artery blood samples were collected for blood gas analysis, hematology, biochemistry, and plasma concentrations of alfaxalone. Plasma samples were assayed using liquid chromatography-mass spectrometry. Compartmental non-linear mixed effects methods (NLME) models were applied to two rat populations to determine whether body weight, sex, and strain influenced PK parameters. There were significant differences between the sexes for plasma clearance, half-life and mean residence time in Lewis rats, and mean arterial blood pressure was significantly lower in the female rats at 120 min. An initial NLME PK population model was used to design an adjusted alfaxalone infusion for SD females matching plasma concentrations in males and minimizing cardiopulmonary depression but maintaining an appropriate hypnotic effect. A final NLME population model showed that alfaxalone clearance was dependent on both bodyweight and sex, whereas volume of distribution was influenced by strain. NLME PK models offer the advantage of having a single model that describes a population and therefore shares data interpretation between animals unlike the standard deterministic PK approach. This approach can be used to propose bespoke dosing regimens for optimal use of alfaxalone.

Novel anesthetics in pediatric practice: is it time?

PURPOSE OF REVIEW

Steadily mounting evidence of anesthesia-induced developmental neurotoxicity has been a challenge in pediatric anesthesiology. Considering that presently used anesthetics have, in different animal models, been shown to cause lasting behavioral impairments when administered at the peak of brain development, the nagging question, 'Is it time for the development of a new anesthetic' must be pondered.

RECENT FINDINGS

The emerging 'soft analogs' of intravenous anesthetics aim to overcome the shortcomings of currently available clinical drugs. Remimazolam, a novel ester-analog of midazolam, is a well tolerated intravenous drug with beneficial pharmacological properties. Two novel etomidate analogs currently in development are causing less adrenocortical suppression while maintaining equally favorable hemodynamic stability and rapid metabolism. Quaternary lidocaine derivatives are explored as more potent and longer lasting alternatives to currently available local anesthetics. Xenon, a noble gas with anesthetic properties, is being considered as an anesthetic-sparing adjuvant in pediatric population. Finally, alphaxalone is being reevaluated in a new drug formulation because of its favorable pharmacological properties.

SUMMARY

Although a number of exciting anesthetic drugs are under development, there is currently no clear evidence to suggest their lack of neurotoxic properties in young brain. Well designed preclinical studies are needed to evaluate their neurotoxic potential.

Cyclodextrin-based delivery systems in parenteral formulations: a critical update review

Parenteral formulations are indispensable in clinical practice and often are the only option to administer drugs that cannot be administrated through other routes, such as proteins and certain anticancer drugs - which are indispensable to treat some of the most prevailing chronic diseases worldwide (like diabetes and cancer). Additionally, parenteral formulations play a relevant role in emergency care since they are the only ones that provide an immediate action of the drug after its administration. However, the development of parenteral formulations is a complex task owing to the specific quality and safety requirements set for these preparations and the intrinsic properties of the drugs. Amongst all the strategies that can be useful in the development of parenteral formulations, the formation of water-soluble host-guest inclusion complexes with cyclodextrins (CDs) has proven to be one of the most advantageous. CDs are multifunctional pharmaceutical excipients able to form water-soluble host-guest inclusion complexes with a wide variety of molecules, particularly drugs, and thus improve their apparent water-solubility, chemical stability, and bioavailability, to make them suitable for parenteral administration. Besides, CDs can be employed as building blocks of more complex injectable drug delivery systems with enhanced characteristics, such as nanoparticles and supramolecular hydrogels, that has been found particularly beneficial for the delivery of anticancer drugs. However, only a few CDs are considered safe when parenterally administered, and some of these types are already approved to be used in parenteral dosage forms. Therefore, the application of CDs in the development of parenteral formulations has been a more common practice in the last few years, due to their significant worldwide acceptance by the health authorities, promoting the development of safer and more efficient injectable drug delivery systems.

What's New in Intravenous Anaesthesia? New Hypnotics, New Models and New Applications

New anaesthetic drugs and new methods to administer anaesthetic drugs are continually becoming available, and the development of new PK-PD models furthers the possibilities of using arget controlled infusion (TCI) for anaesthesia. Additionally, new applications of existing anaesthetic drugs are being investigated. This review describes the current situation of anaesthetic drug development and methods of administration, and what can be expected in the near future.

Current status of perioperative hypnotics, role of benzodiazepines, and the case for remimazolam: a narrative review

Anaesthesiologists and non-anaesthesiologist sedationists have a limited set of available i.v. hypnotics, further reduced by the withdrawal of thiopental in the USA and its near disappearance in Europe. Meanwhile, demand for sedation increases and new clinical groups are using what traditionally are anaesthesiologists' drugs. Improved understanding of the determinants of perioperative morbidity and mortality has spotlighted hypotension as a potent cause of patient harm, and practice must be adjusted to respect this. High-dose propofol sedation may be harmful, and a critical reappraisal of drug choices and doses is needed. The development of remimazolam, initially for procedural sedation, allows reconsideration of benzodiazepines as the hypnotic component of a general anaesthetic even if their characterisation as i.v. anaesthetics is questionable. Early data suggest that a combination of remimazolam and remifentanil can induce and maintain anaesthesia. Further work is needed to define use cases for this technique and to determine the impact on patient outcomes.

Discovery of the EL-0052 as a potential anesthetic drug

As a γ-aminobutyric acid A receptor (GABA_AR) inhibitor, etomidate fulfills several characteristics of an ideal anesthetic agent, such as rapid onset with rapid clearance and high potency, along with cardiovascular stability. Unfortunately, etomidate has been reported to inhibit CYP11B1 at hypnotic doses, which is associated with a marked increase in patient deaths due to this unexpected off-target effect. In this study, molecular docking was used to simulate the binding mode of etomidate with GABA_AR and CYP11B1. Based on the in-depth analysis of the binding mode, strong electron-withdrawing group on the C4 position of the imidazole ring was introduced to reduce the charge density of the nitrogen, which is beneficial in reducing the coordination bond between the imidazole nitrogen and heme iron in CYP11B1, as well as in reducing the adrenocortical suppression. Based on the results of ADMET property prediction, MEP analysis, and molecular docking simulation, 4-fluoroetomidate (EL-0052) was designed and synthesized. In vivo studies in rats and mice confirmed that EL-0052 had the efficacy similar to etomidate, but without adrenocortical suppression. These findings suggested that EL-0052 was superior to etomidate and support the continued development of EL-0052 as a preclinical candidate as an anesthetic.

Cyclodextrins in Parenteral Formulations

Most drugs have very limited solubility in water and some can be extremely difficult to formulate as parenteral solutions where the dose should preferably be dissolved in couple of ml of aqueous media without use of organic solvents and surface active agents, or application of somewhat extreme techniques such as prodrug formation. Thus, pharmaceutical formulators are constantly looking for new, biologically acceptable, and low-cost armamentarium for parenteral formulation development. Cyclodextrins (CDs) are enabling pharmaceutical excipients that can temporarily camouflage undesirable physiochemical drug properties such as low aqueous solubility through formation of drug/CD inclusion complexes. CDs are cyclic oligosaccharides that have similar physiological and biological properties like linear saccharides of comparable molecular weight. Due to their very favorable toxicological and pharmacokinetic profiles their usage in parenteral drug formulations is frequently preferred over other solubilizing techniques. Here the physiochemical and biological properties of CDs are reviewed as well as their pharmacokinetics after intravenous administration. Their regulatory status is briefly reviewed and their tendency to self-assemble to form clusters or aggregates discussed. Finally, some examples are given of how CDs are applied in aqueous parenteral formulations, how their solubilizing effect has been enhanced and how their target concentration is determined.

Allopregnanolone Enhances GABAergic Inhibition in Spinal Motor Networks

The neurosteroid allopregnanolone (ALLO) causes unconsciousness by allosteric modulation of γ-aminobutyric acid type A (GABA_A) receptors, but its actions on the spinal motor networks are unknown. We are therefore testing the hypothesis that ALLO attenuates the action potential firing of spinal interneurons and motoneurons predominantly via enhancing tonic, but not synaptic GABAergic inhibition. We used video microscopy to assess motoneuron-evoked muscle activity in organotypic slice cultures prepared from the spinal cord and muscle tissue. Furthermore, we monitored GABA_A receptor-mediated currents by performing whole-cell voltage-clamp recordings. We found that ALLO (100 nM) reduced the action potential firing of spinal interneurons by 27% and that of α-motoneurons by 33%. The inhibitory effects of the combination of propofol (1 µM) and ALLO on motoneuron-induced muscle contractions were additive. Moreover, ALLO evoked a tonic, GABA_A receptor-mediated current (amplitude: 41 pA), without increasing phasic GABAergic transmission. Since we previously showed that at a clinically relevant concentration of 1 µM propofol enhanced phasic, but not tonic GABAergic inhibition, we conclude that ALLO and propofol target distinct subpopulations of GABA_A receptors. These findings provide first evidence that the combined application of ALLO and propofol may help to reduce intraoperative movements and undesired side effects that are frequently observed under total intravenous anesthesia.

Remimazolam for anaesthesia or sedation

PURPOSE OF REVIEW

Anaesthesia and sedation are ubiquitous in contemporary medical practice. Developments in anaesthetic pharmacology are targeted on reducing physiological disturbance whilst maintaining or improving titrateability, recovery profile and patient experience. Remimazolam is a new short-acting benzodiazepine in the final stages of clinical development.

RECENT FINDINGS

Clinical experience with remimazolam comprises volunteer studies and a limited number of clinical investigations. In addition, laboratory investigations explore the implications of its 'soft drug' pharmacology.

SUMMARY

Remimazolam provides effective procedural sedation with superior success rates and recovery profile when compared to midazolam. Comparisons with propofol are required. Preliminary studies suggest potential for using remimazolam as the hypnotic component of general anaesthesia. Definitive studies are awaited. As a benzodiazepine, remimazolam could be evaluated as an anticonvulsant and for intensive care sedation.

Recent advances in intravenous anesthesia and anesthetics

Anesthesiology, as a field, has made promising advances in the discovery of novel, safe, effective, and efficient methods to deliver care. This review explores refinement in the technology of soft drug development, unique anesthetic delivery systems, and recent drug and device failures.

New insights in the systemic and molecular underpinnings of general anesthetic actions mediated by γ-aminobutyric acid A receptors

PURPOSE OF REVIEW

The review highlights novel insights into the role of γ-aminobutyric acid A (GABAA) receptors in mediating clinically relevant actions of anesthetic agents.

RECENT FINDINGS

GABAA receptors in the hippocampus are located on glutamatergic pyramidal cells and GABAergic interneurons. Etomidate-induced inhibition of a synaptic correlate of learning and memory is caused by receptors on nonpyramidal neurons, likely on interneurons that incorporate α5 subunits. Selective enhancement of α2 subunit containing GABAA receptors in the spinal cord provides antihyperalgesia against inflammatory and neuropathic pain without causing sedation, motor impairment, and tolerance development. Inflammation, traumatic brain injury, and exposure to anesthetic agents modify the expression patterns of GABAA receptors in a subtype-specific manner. These modifications may persist for weeks. The neuroactive steroid alphaxalone causes fast-onset and short-duration anesthesia in humans. Cardiovascular and respiratory side-effects are less severe than with propofol.

SUMMARY

Identification of the molecular and cellular substrates involved in anesthesia and insights into disease and drug-induced alterations in the expression patterns of GABAA receptors in the central nervous system are emphasizing the need for individualized anesthesia care. Introducing neuroactive steroids into clinical anesthesia is expected to reduce cardiovascular and respiratory side-effects.

The Role of GABA Receptor Agonists in Anesthesia and Sedation

GABA (γ-aminobutyric acid) receptors, of which there are two types, are involved in inhibitory synapses within the central nervous system. The GABA_A receptor (GABAAR) has a central role in modern anesthesia and sedation practice, which is evident from the high proportion of agents that target the GABAAR. Many GABAAR agonists are used in anesthesia practice and sedation, including propofol, etomidate, methohexital, thiopental, isoflurane, sevoflurane, and desflurane. There are advantages and disadvantages to each GABAAR agonist currently in clinical use. With increasing knowledge regarding the pharmacology of GABAAR agonists, however, newer sedative agents have been developed which employ 'soft pharmacology', a term used to describe the pharmacology of agents whereby their chemical configuration allows rapid metabolism into inactive metabolites after the desired therapeutic effect(s) has occurred. These newer 'soft' GABAAR agonists may well approach ideal sedative agents, as they can offer well-controlled, titratable activity and ultrashort action. This review provides an overview of the role that GABAAR agonists currently play in sedation and anesthesia, in addition to discussing the future role of novel GABAAR agonists in anesthesia and sedation.

Novel propofol derivatives and implications for anesthesia practice

Propofol (2,6-diisopropylphenol) is the most commonly used intravenous agent for induction of anesthesia. It is also used for maintenance of anesthesia and sedation in both Intensive Care Units and outpatient procedural settings. Its success in the clinical setting has been a result of its rapid onset, short duration of action, and minimal side effects despite disadvantages associated with its oil emulsion formulation. Early attempts to alter the standard emulsion or to develop new formulations with cyclodextrins and micelles to resolve issues with pain upon injection, the need for antimicrobial agents, and possible hyperlipidemia have mostly failed. With these challenges in the foreground, attention has now shifted to the use of more prodrugs and exogenous alternatives, the success of which is yet to be determined. These new agents must offer significant clinical advantages over the well-entrenched, generic propofol oil emulsion to justify higher costs and to be well received in the increasingly cost-conscious healthcare marketplace.

Characterization, in Vivo Evaluation, and Molecular Modeling of Different Propofol-Cyclodextrin Complexes To Assess Their Drug Delivery Potential at the Blood-Brain Barrier Level

In this study, we investigated the ability of the general anesthetic propofol (PR) to form inclusion complexes with modified β-cyclodextrins, including sulfobutylether-β-cyclodextrin (SBEβCD) and hydroxypropyl-β-cyclodextrin (HPβCD). The PR/SBEβCD and PR/HPβCD complexes were prepared and characterized, and the blood-brain barrier (BBB) permeation potential of the formulated PR was examined in vivo for the purpose of controlled drug delivery. The PR/SBEβCD complex was found to be more stable in solution with a minimal degradation constant of 0.25 h^-1, a t_1/2 of 2.82 h, and a K_c of 5.19 × 10³ M^-1 and revealed higher BBB permeability rates compared with the reference substance (PR-LIPURO) considering the calculated brain-to-blood concentration ratio (logBB) values. Additionally, the diminished PR binding affinity to SBEβCD was confirmed in molecular dynamics simulations by a maximal Gibbs free energy of binding (ΔG_bind = -18.44 kcal·mol^-1), indicating the more rapid PR/SBEβCD dissociation. Overall, the results demonstrated that SBEβCD has the potential to be used as a prospective candidate for drug delivery vector development to improve the pharmacokinetic and pharmacodynamic properties of general anesthetic agents at the BBB level.

Unilaterally blocking the muscarinic receptors in the suprachiasmatic nucleus in proestrus rats prevents pre-ovulatory LH secretion and ovulation

BACKGROUND

The suprachiasmatic nucleus (SCN) and the cholinergic system of various regions of the hypothalamus participate in the regulation of gonadotropin-releasing hormone (GnRH) and gonadotropin secretion, which are necessary for the occurrence of ovulation. In the present study, our goal was to analyse the effects of unilaterally blocking the muscarinic receptors in the SCN on ovulation and steroid secretion.

METHODS

Cyclic rats were randomly allotted to one of the experimental groups. Groups of 8-14 rats were anaesthetized and microinjected with 0.3 μl of saline or a solution of atropine (62.5 ng in 0.3 μl of saline) into the left or right SCN at 09.00 or 19.00 h during diestrus-1 or on the proestrus day. The rats were euthanized on the predicted day of oestrus, and evaluated ovulation and levels of progesterone and oestradiol. Other groups of 10 rats were microinjected with atropine into the left or right SCNs at 09.00 h on the proestrus day, were euthanized eight h later, and luteinizing hormone (LH) was measured.

RESULTS

At 09.00 or 19.00 h during diestrus-1, atropine microinjections into the SCNs on either side did not modify ovulation. The atropine microinjections performed at 09.00 h of proestrus into either side of the SCN blocked ovulation (right SCN: 1/9 ovulated vs. 9/10 in the saline group; left SCN: 8/14 ovulated vs. 10/10 in the saline group). The LH levels at 17.00 h in the rats that were microinjected with atropine at 09.00 h of proestrus were lower than those of the controls. In the non-ovulating atropine-treated rats, the injection of synthetic LH-releasing hormone (LHRH) restored ovulation. Atropine treatment at 19.00 h of proestrus on either side of the SCN did not modify ovulation, while the progesterone and oestradiol levels were lower.

CONCLUSION

Based on the present results, we suggest that the cholinergic neural information arriving on either side of the SCN is necessary for the pre-ovulatory secretion of LH to induce ovulation. Additionally, the regulation of progesterone and oestradiol secretion by the cholinergic innervation of the SCN varies with the time of day, the day of the cycle, and the affected SCN.

A Phase 1c Trial Comparing the Efficacy and Safety of a New Aqueous Formulation of Alphaxalone with Propofol

BACKGROUND:

Phaxan™ (PHAX, Chemic Labs, Canton, MA) is an aqueous solution of 10 mg/mL alphaxalone and 13% 7-sulfobutylether β-cyclodextrin (betadex). In preclinical studies, PHAX is a fast onset–offset IV anesthetic like propofol, but causes less cardiovascular depression. This first-in-man study was designed to find the anesthetic dose of PHAX and to compare it with an equivalent dose of propofol for safety, efficacy, and quality of recovery from anesthesia and sedation.

METHODS:

The study adhered to compliance with Good Clinical Practices regulations (clinical trials registry number, ACTRN12611000343909). This randomized, double-blind study compared PHAX and propofol using a Bayesian algorithm to determine dose equivalence for effects on the bispectral index (BIS). Male volunteers, ASA physical status I, gave written informed consent (n = 12 per group; PHAX or propofol). Parameters assessed for 80 minutes after drug injection (single bolus dose) were pain on injection, involuntary movement, BIS, blood pressure, need for airway support, and, as measures of recovery from sedation, the Richmond Agitation and Sedation Scale and the Digit Symbol Substitution Test. Arterial blood was withdrawn for biochemistry, hematology, and complement levels.

RESULTS:

No subject complained of pain on injection with PHAX, whereas 8 of the 12 subjects given propofol did. Nine PHAX and 8 propofol subjects reached BIS values of ≤50: median (interquartile range [IQR]) mg/kg dose = 0.5 (0.5–0.6) for PHAX and 2.9 (2.4–3.0) for propofol. The lowest median BIS reached was 27 to 28 for both agents with no significant differences between them for timing of onset and recovery of BIS. The concomitant median changes in systolic and diastolic blood pressures were −11% vs −19% for systolic and −25% vs −37% for diastolic in PHAX- and propofol-treated subjects, respectively. Nine of the 12 propofol-treated subjects and none of 12 PHAX-treated subjects required airway support. For subjects reaching an equivalent BIS of ≤50: a Richmond Agitation and Sedation Scale score of 0 was reached at a median of 5 (IQR, 5–10) and 15 (IQR, 10–20) minutes after PHAX and propofol, respectively; BIS returned to 90 at a mean of 21 (SD, 10.1) and 21 (SD, 9.2) minutes after PHAX and propofol, respectively; and Digit Symbol Substitution Test scores returned to predrug injection values at median of 50 (IQR, 35–72.5) and 42.5 (IQR, 35–76.3) minutes after PHAX and propofol, respectively. There was no increase in C3 and C4 complement fractions after either drug.

CONCLUSIONS:

PHAX causes fast-onset, short-duration anesthesia with fast cognitive recovery similar to propofol, but with less cardiovascular depression, or airway obstruction and no pain on injection.

Published ahead of print July 29, 2015

Sevoflurane-Sulfobutylether-β-Cyclodextrin Complex: Preparation, Characterization, Cellular Toxicity, Molecular Modeling and Blood-Brain Barrier Transport Studies

The objective of the present investigation was to study the ability of sulfobutylether-β-cyclodextrin (SBEβCD) to form an inclusion complex with sevoflurane (SEV), a volatile anesthetic with poor water solubility. The inclusion complex was prepared, characterized and its cellular toxicity and blood-brain barrier (BBB) permeation potential of the formulated SEV have also been examined for the purpose of controlled drug delivery. The SEV-SBEβCD complex was nontoxic to the primary brain microvascular endothelial (pEND) cells at a clinically relevant concentration of sevoflurane. The inclusion complex exhibited significantly higher BBB permeation profiles as compared with the reference substance (propranolol) concerning calculated apparent permeability values (P_app). In addition, SEV binding affinity to SBEβCD was confirmed by a minimal Gibbs free energy of binding (ΔG_bind) value of −1.727 ± 0.042 kcal·mol⁻¹ and an average binding constant (K_b) of 53.66 ± 9.24 mM indicating rapid drug liberation from the cyclodextrin amphiphilic cavity.