GHB toxicokinetics and renal monocarboxylate transporter expression are influenced by the estrus cycle in rats

Abstract

Background The illicit use and abuse of gamma-hydroxybutyric acid (GHB) occurs due to its sedative/hypnotic and euphoric effects. Currently, there are no clinically available therapies to treat GHB overdose, and care focuses on symptom treatment until the drug is eliminated from the body. Proton- and sodium-dependent monocarboxylate transporters (MCTs (SLC16A) and SMCTs (SLC5A)) transport and mediate the renal clearance and distribution of GHB. Previously, it has been shown that MCT expression is regulated by sex hormones in the liver, skeletal muscle and Sertoli cells. The focus of the current study is to evaluate GHB toxicokinetics and renal monocarboxylate transporter expression over the estrus cycle in females, and in the absence of male and female sex hormones. Methods GHB toxicokinetics and renal transporter expression of MCT1, SMCT1 and CD147 were evaluated in females over the estrus cycle, and in ovariectomized (OVX) female, male and castrated (CST) male rats. GHB was administered iv bolus (600 and 1000 mg/kg) and plasma and urine samples were collected for six hours post-dose. GHB concentrations were quantified using a validated LC/MS/MS assay. Transporter mRNA and protein expression was quantified by qPCR and Western Blot. Results GHB renal clearance and AUC varied between sexes and over the estrus cycle in females with higher renal clearance and a lower AUC in proestrus females as compared to males (intact and CST), and OVX females. We demonstrated that renal MCT1 membrane expression varies over the estrus cycle, with the lowest expression observed in proestrus females, which is consistent with the observed changes in GHB renal clearance. Conclusions Our results suggest that females may be less susceptible to GHB-induced toxicity due to decreased exposure resulting from increased renal clearance, as a result of decreased renal MCT1 expression.

Sex and Cross-Sex Testosterone Treatment Alters Gamma-Hydroxybutyrate Acid Toxicokinetics and Toxicodynamics in Rats

“…Female rats in the estrus stage were selected for the study. Estrus cycle stages of female rats were monitored daily by vaginal lavage smear, as described in previously published literature [ 20 , 21 , 30 , 31 ]. The Institutional Animal Care and Use Committee (IACUC) at the University of the Pacific approved all experiments.…”

“…GHB in plasma and urine were quantified using a validated liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay that was described previously [ 21 ]. Briefly, for the preparation of plasma standards and quality controls (QCs), 5 μL of GHB-d6 and 5 μL of standard stock solution or QC stock solution were added to 45 μL of blank plasma.…”

“…LC/MS/MS equipment consisted of an Agilent 1200 series UPLC consisting of an online degasser, binary pump, and autosampler (Agilent Technologies, Santa Clara, CA, USA) connected to a Agilent 6460 Triple Quad Mass Spectrometer. HPLC conditions, mass spectrometer parameters ( Table S1 ), and linear calibration ranges were described in a previous publication [ 21 ].…”

“…In a study with valproic acid, one of the substrates of MCTs, women showed higher peak plasma concentrations in comparison to men unless they were on hormonal birth control [ 19 ], which may be attributed to the sex differences in MCT expression. Previously, our laboratory demonstrated that hepatic MCT and renal MCT/SMCT expression levels are different between sexes and vary over the estrus cycle in female rats in a tissue-specific manner [ 20 , 21 ]. The sex-dependent variations in renal MCTs/SMCTs lead to alterations in GHB toxicokinetics and renal clearance [ 21 ].…”

“…Previously, our laboratory demonstrated that hepatic MCT and renal MCT/SMCT expression levels are different between sexes and vary over the estrus cycle in female rats in a tissue-specific manner [ 20 , 21 ]. The sex-dependent variations in renal MCTs/SMCTs lead to alterations in GHB toxicokinetics and renal clearance [ 21 ]. Moreover, there were significant alterations in renal MCT expression following exogenous sex and cross-sex hormone treatment in ovariectomized (OVX) and castrated (CST) rats [ 22 ].…”