Neuroactive steroids alphaxalone and CDNC24 are effective hypnotics and potentiators of GABAA currents, but are not neurotoxic to the developing rat brain.

BACKGROUND: The most currently used general anaesthetics are potent potentiators of γ-aminobutyric acid A (GABAA) receptors and are invariably neurotoxic during the early stages of brain development in preclinical animal models. As causality between GABAA potentiation and anaesthetic-induced developmental neurotoxicity has not been established, the question remains whether GABAergic activity is crucial for promoting/enhancing neurotoxicity. Using the neurosteroid analogue, (3α,5α)-3-hydroxy-13,24-cyclo-18,21-dinorchol-22-en-24-ol (CDNC24), which potentiates recombinant GABAA receptors, we examined whether this potentiation is the driving force in inducing neurotoxicity during development. METHODS: The neurotoxic potential of CDNC24 was examined vis-à-vis propofol (2,6-diisopropylphenol) and alphaxalone (5α-pregnan-3α-ol-11,20-dione) at the peak of rat synaptogenesis. In addition to the morphological neurotoxicity studies of the subiculum and medial prefrontal cortex (mPFC), we assessed the extra-, pre-, and postsynaptic effects of these agents on GABAergic neurotransmission in acute subicular slices from rat pups. RESULTS: CDNC24, like alphaxalone and propofol, caused dose-dependent hypnosis in vivo, with a higher therapeutic index. CDNC24 and alphaxalone, unlike propofol, did not cause developmental neuroapoptosis in the subiculum and mPFC. Propofol potentiated post- and extrasynaptic GABAA currents as evidenced by increased spontaneous inhibitory postsynaptic current (sIPSC) decay time and prominent tonic currents, respectively. CDNC24 and alphaxalone had a similar postsynaptic effect, but also displayed a strong presynaptic effect as evidenced by decreased frequency of sIPSCs and induced moderate tonic currents. CONCLUSIONS: The lack of neurotoxicity of CDNC24 and alphaxalone may be at least partly related to suppression of presynaptic GABA release in the developing brain.

Effects of a single intravenous bolus injection of alfaxalone on canine splenic volume as determined by computed tomography.

The purpose of this study was to evaluate the effects of a single intravenous dose of alfaxalone on canine splenic volume. In 6 adult beagle dogs the splenic volume [mean ± standard error (SE)] was determined by computed tomography to be 0.17 ± 0.02 L before alfaxalone administration and 0.24 ± 0.02 L (P = 0.0091) and 0.23 ± 0.02 L (P = 0.0268) 15 and 30 min, respectively, after alfaxalone administration. Hematocrits (mean ± SE) obtained at the same times were, respectively, 46.3% ± 1.3%, 40.6% ± 1.3% (P = 0.0015), and 41.7% ± 1.3% (P = 0.0057). In conclusion, alfaxalone caused relaxation of the canine splenic capsule and an increase in the splenic volume, along with a decrease in the hematocrit in these dogs.

Le but de cette étude était d'évaluer les effets d'administration intraveineuse d'alfaxalone intraveineuse sur le volume splénique canin déterminé par la tomodensitométrie. Le volume de rate de 6 chiens beagle adultes a été déterminé par tomodensitométrie avant et après l'administration d'alfaxalone. Le volume splénique moyen (± erreur type) était 0,17 ± 0,02 L avant l'administration d'alfaxalone et 0,24 ± 0,02 L (P = 0,0091) et 0,23 ± 0,02 L (P = 0,0268) à 15 min et à 30 min après l'administration d'alfaxalone, respectivement. L'hématocrite moyen (± erreur type) était 46,3 % ± 1,3 % (SEM) avant l'administration d'alfaxalone et 40,6 % ± 1,3 % (P = 0,0015) et 41,7 % ± 1,3 % (P = 0,0057) à 15 min et à 30 min après l'injection. En conclusion, dans cette étude, l'alfaxalone a provoqué une relaxation de la capsule splénique canine et une augmentation de son volume avec une diminution de l'hématocrite.(Traduit par les auteurs).

Alphaxalone Reformulated: A Water-Soluble Intravenous Anesthetic Preparation in Sulfobutyl-Ether-ß-Cyclodextrin.

BACKGROUND: Alphaxalone is a neuroactive steroid anesthetic that is poorly water soluble. It was formulated in 1972 as Althesin® using Cremophor® EL, a nonionic surfactant additive. The product was a versatile short-acting IV anesthetic used in clinical practice in many countries from 1972 to 1984. It was withdrawn from clinical practice because of hypersensitivity to Cremophor EL. In the investigations reported here, we compared the properties of 3 anesthetics: a new aqueous solution of alphaxalone dissolved in 7-sulfobutyl-ether-ß-cyclodextrin (SBECD, a water-soluble molecule with a lipophilic cavity that enables drug solubilization in water); a Cremophor EL preparation of alphaxalone; and propofol. METHODS: Two solutions of alphaxalone (10 mg/mL) were prepared: one using 13% w/v solution of SBECD in 0.9% saline (PHAX) and the other a solution of alphaxalone prepared as described in the literature using 20% Cremophor EL (ALTH). A solution of propofol (10 mg/mL; PROP) in 10% v/v soya bean oil emulsion was used as a comparator anesthetic. Jugular IV catheters were implanted in male Wistar rats (180-220 g) under halothane anesthesia. Separate groups of 10 implanted rats each were given IV injections of PHAX, ALTH, or PROP from 1.2 mg/kg to lethal doses. Doses of each drug that caused anesthesia (loss of righting reflex and response to tail pinch) and lethality in 50% of rats were calculated by probit analysis. The drugs were also compared for effects on arterial blood pressure and heart rate. RESULTS: IV PHAX, ALTH, and PROP caused dose-related sedation and anesthesia, with 50% effective dose (ED50) values for loss of righting reflex being 2.8, 3.0, and 4.6 mg/kg, respectively. PROP led to death in 10 of 10 rats at doses >30 mg/kg (50% lethal dose (LD50) = 27.7 mg/kg). A dose of alphaxalone 53 mg/kg as ALTH caused 10 of 10 rats to die (LD50 = 43.6 mg/kg), whereas none died when given the same doses of alphaxalone formulated in SBECD. PHAX caused 20% lethality at the maximal dose tested of 84 mg/kg. PHAX caused less cardiovascular depression than PROP. Control experiments with the 3 drug-free vehicles showed no effects. CONCLUSIONS: Alphaxalone caused fast-onset anesthesia at the same dose for both formulations (PHAX and ALTH). The use of SBECD as a drug-solubilizing excipient did not alter the anesthetic effect of alphaxalone, but it did increase the therapeutic index of alphaxalone in PHAX compared with ALTH. PHAX has a higher safety margin than the propofol lipid formulation and also the alphaxalone formulation in Cremophor EL (ALTH).

Myoclonic seizures in the mouse induced by alphaxalone and related steroid anaesthetics.

The anaesthetic steroids alphaxalone. 5 beta-alphaxalone and pregnanolone each caused myoclonic jerks in mice in a dose-related manner between 4 and 16 mg kg-1 i.v. There was no loss of righting reflex at these doses. The veterinary product Saffan, which contains alphaxalone and alphadalone, also caused myoclonic jerks at 2 mg kg-1 i.v., and a loss of righting reflex at doses of 4 mg kg-1 and above. These effects appear to be unrelated to the wide spectrum of potencies at the GABAA receptor complex of the three individual steroids as potentiators of muscimol, or as attenuators of picrotoxin.

[Influence of age and sex on the acute toxicity of two steroid anesthetics in rats]. / Influence de l'âge at du sexe sur la toxicité aiguë de deux anesthésiques stéroïdiens chez le rat.

During the newborn period, there is a hight increase of the acute toxicity of two steroid anaesthetics (Hydroxydione, Althesin) given by intraperitoneal route on the rat as also an influence of hormonal conditions.

Production of male pseudohermaphroditism in rats by two new inhibitors of steroid 17alpha-hydroxylase and C 17-20 lyase.

Two new synthetic steroid analogues, (I) 16beta-bromo-3beta,17alpha-dihydroxy-5alpha-pregnane-11,20-dione and (II) 17beta-ureido-1,4-androstadien-3-one have been shown to give kinetic patterns consistent with active-site-directed irreversible inhibition of adult rat testicular microsomal steroid 17alpha-hydroxylase and C17-20 lyase in vitro. Administration of both analogues to adult male rats for 24 h produced potent inhibition of these testicular enzymes in vivo. Given to pregnant rats during the critical period of male organogenesis they produced hypospadias: a characteristic of the syndrome in man in which these enzymes are defective genetically. Given to male rat pups during the first 9 days of life, inhibitor II produced significantly smaller prostates and seminal vesicles in adulthood, indicating the usefulness of this inhibitor in studies on the role of testosterone in neonatal programming of target organ size in adulthood. Thus, two new enzyme inhibitors have been shown to block testosterone production in the foetal and neonatal rat selectively at the site of the hydroxylase without other apparent hormonal effects or influence on adrenal size.

[On the toxicity of CT-1341 evoked by long-term administration. III. Subacute toxicity of alphadolone acetate and solvent contained in CT-1341 (author's transl)].

Subacute toxicity of solvent adjuvant, alphadolone acetate and solvent, 20 per cent Cremophor solution contained in CT-1341 was studied by using rats of both sexes. Alphadolone acetate and Cremophor solution were intraperitoneally injected every day for a period of one month. Total rats tolerated to daily administration of 60 mg/kg of alphadolone acetate or of 20 ml/kg of 20 per cent Cremophor solution, without showing significant changes in body weight curves and food intake. No change was observed in blood cells and in biochemical data of blood and urine as compared with control. Rats subjected to daily administration of 60 mg/kg of alphadolone acetate presented slight patho-histological changes such as swelling of cells of the liver and kidneys, and also cell infiltration of pericapillary tissues of the lung.

[On the toxicity of CT-1341 evoked by long-term administration. I. Subacute toxicity of the intravenous anesthetic, CT-1341 in rats (author's transl)].

CT-1341, an intravenous anesthetic was given in various daily doses in rats for a period of one month to test the subacute toxicity. The drug was administered intraperitoneally in rats. Rats tolerated to daily administration of CT-1341 at doses of less than 1.8 ml/kg without showing other particular toxic signs than anesthesia. Main pathological findings were swelling of cells in the liver and renal tubules, and perivascular cuffing in lungs. No severe patho-histological changes were observed in any organs. Mortal cases were seen in the group of rats, in which CT-1341 was given in a daily dose of 5.4 ml/kg. A paralysis of respiratory center was suggested to be cause of death, because no severe patho-histological changes were observed in any organs of mortal rats. Survivals of this group showed no particular symptom except anesthesia, but an inhibition of the growth curve was seen in male rats only.

[On the toxicity of CT-1341 evoked by long-term administration. II. Subacute and chronic toxicities of alphaxalone in rats (author's transl)].

Alphaxalone, an anesthetic steroid dissolved in 20% Cremophor solution was administered intraperitoneally to test the subacute toxicity (administration for one month) and chronic toxicity (administration for 3 months). In daily doses less than 8 mg/kg, alphaxalone did not show any particular toxic sign after administered for three months. Rats tolerated to daily administration of 20 mg/kg for three months, without showing severe toxic signs in body weight curve, blood cells and biochemical data obtained in blood and urine. However, some female rats receiving 50 mg/kg/day of alphaxalone, died by paralysis of respiratory center at the second day. Main histo-pathological changes induced by subacute and chronic administrations of the larger doses than 20 mg/kg, were swelling of cells in the liver and kidneys, but severe pathological changes were not seen in any organs.