γ-Hydroxybutyric Acid-Ethanol Drug-Drug Interaction: Reversal of Toxicity with Monocarboxylate Transporter 1 Inhibitors

Abstract

The drug of abuse, γ-hydroxybutyric acid (GHB), is commonly co-ingested with ethanol, resulting in a high incidence of toxicity and death. Our laboratory has previously reported that GHB is a substrate for the monocarboxylate transporters (MCTs), necessary for its absorption, renal clearance, and tissue distribution, including across the blood-brain barrier. Our goal was to investigate the drug-drug interaction (DDI) between GHB and ethanol and to evaluate MCT1 inhibition as a strategy to reverse toxicity. The toxicokinetics of this DDI were investigated, including brain-to-plasma concentration ratios, in the presence and absence of ethanol. The toxicodynamic parameters examined were respiratory depression (breathing frequency, tidal volume) and sedation (time of return-of-righting reflex). Ethanol was administered (2 g/kg i.v.) 5 minutes before the intravenous or oral administration of GHB, and MCT1 inhibitors AZD-3965 and AR-C155858 (5 mg/kg i.v.) were administered 60 minutes after GHB administration. Ethanol administration did not alter the toxicokinetics or respiratory depression caused by GHB after intravenous or oral administration; however, it significantly increased the sedation effect, measured by return-to-righting time. AZD-3965 or AR-C155858 significantly decreased the effects of the co-administration of GHB and ethanol on respiratory depression and sedation of this DDI and decreased brain concentrations and the brain-to-plasma concentration ratio of GHB. The results indicate that ethanol co-administered with GHB increases toxicity and that MCT1 inhibition is effective in reversing toxicity by inhibiting GHB brain uptake when given after GHB-ethanol administration. SIGNIFICANCE STATEMENT: These studies investigated the enhanced toxicity observed clinically when γ-hydroxybutyric acid (GHB) is co-ingested with alcohol and evaluated strategies to reverse this toxicity. The effects of the novel monocarboxylate transporter 1 (MCT1) inhibitors AR-C155858 and AZD-3965 on this drug-drug interaction have not been studied before, and these preclinical studies indicate that MCT1 inhibitors can decrease brain concentrations of GHB by inhibiting brain uptake, even when administered at times after GHB-ethanol. AZD-3965 represents a potential treatment strategy for GHB-ethanol overdoses.

Graphical abstract

Fig. 1.

Molecular structures of AR-C155858 (A) and AZD-3965 (B).

Fig. 2.

GHB plasma concentrations (A) and amount of GHB excreted unchanged (B) after administration of 600 mg/kg GHB i.v., alone, with ethanol (EtOH), and with MCT1-specific inhibitors (administered 60 minutes after GHB administration). Dashed line represents the time of administration of the treatments. GHB-alone data were obtained from previous publications by our laboratory. Data are presented as means (n = 4–5).

Fig. 3.

Effect of ethanol and treatment with specific MCT1 inhibitors on GHB-induced respiratory depression after intravenous administration of GHB. (A) Ethanol (EtOH) was administered as 2 g/kg i.v. bolus. The administration of 600 mg/kg GHB i.v. was 5 minutes after the ethanol bolus administration. (B) AZD-3965 and AR-155858 were administered 60 minutes after GHB administration at a dose of 5 mg/kg i.v. The dashed line represents the time of administration of each treatment at 60 minutes after GHB administration. Data are presented as means ± S.D. (n = 4–6).

Fig. 4.

Effect of ethanol and treatment with specific MCT1 inhibitors on GHB toxicokinetics after administration oral administration. (A) GHB plasma concentrations over time. (B) The amount of GHB excreted unchanged in the urine. Ethanol (EtOH) was administered as 2 g/kg i.v. bolus. The administration of 1500 mg/kg GHB p.o. was 5 minutes after the ethanol administration. Administration of AZD-3965 was 60 minutes after GHB administration at a dose of 5 mg/kg i.v. The dashed line represents the time of administration of treatment. Data are presented as means ± S.D. (n = 4–5). Data from 1500 mg/kg GHB alone were from a previous study (Morse and Morris, 2013b).

Fig. 5.

Effect of ethanol and treatment with the specific MCT1 inhibitor AZD-3965 on GHB-induced respiratory frequency (A, B) and tidal volume (C, D) after oral administration of GHB. Ethanol (EtOH) was administered as 2 g/kg i.v. bolus. The administration of 1500 mg/kg GHB p.o. was 5 minutes after the ethanol administration (A, C). Administration of AZD-3965 (AZD) was 60 minutes after GHB administration at a dose of 5 mg/kg i.v. (B, D). The dashed line represents the time of administration of AZD-3965 at 60 minutes after GHB administration. Data are presented as means ± S.D. (n = 4). Data from 1500 mg/kg GHB alone were from a previous study (Morse and Morris, 2013b).

Fig. 6.

Effect of ethanol co-administration and treatment with AZD-3965 on the toxicodynamic sedative effect of GHB. Ethanol (EtOH; 2 g/kg i.v.) was administered 5 minutes before GHB administration. GHB was administered at a dose of 1500 mg/kg by oral gavage, and AZD-3965 (AZD) treatment was administered 60 minutes after GHB administration at a 5 mg/kg i.v. dose. Ethanol infusion was given to see the sedative effects of ethanol alone. Animals were euthanized at RRR. One-way ANOVA followed by Dunnett’s post hoc test was used to determine statistically significant differences between groups. Data are presented as means ± S.D. (n = 3–7). *Significantly different from GHB + ethanol. ^#Significantly different from GHB alone.

Fig. 7.

Effect of ethanol and AZD-3965 treatment on GHB plasma (A), brain (B), and brain-to-plasma ratio (C) concentrations at 90 minutes after oral GHB dose. Ethanol (EtOH; 2.0 g/kg i.v.) was administered 5 minutes before GHB. GHB (1500 mg/kg p.o.) was administered at time zero, and AZD-3965 (AZD; 5 mg/kg) was given intravenously 60 minutes after GHB. Animals were euthanized at 90 minutes after GHB dose. One-way analysis of variance followed by Dunnett’s post hoc test was used to determine statistically significant differences compared with GHB plus ethanol. Data are presented as means ± S.D. (n = 4–6). Significantly different *P < 0.05, **P < 0.01.