In vivo blood and ex vivo brain solid-phase microextraction coupled with LC-MS/MS for mapping unbound cannabidiol, phase I metabolites, and endocannabinoid tone

Introduction Evaluating the central nervous system distribution of cannabidiol (CBD) and its dynamic interplay with the endocannabinoid system (ECS) is fundamentally constrained by conventional tissue homogenization, which fails to distinguish pharmacologically active fractions from total pool of analyte. To resolve active biophase kinetics, this study established a minimally invasive solid-phase microextraction (SPME) coupled with LC-MS/MS platform to monitor CBD, its phase I metabolites, and key endocannabinoids directly within circulating blood in vivo and intact anatomical brain regions ex vivo . Methods Male rats received a single oral dose of medicinal cannabis (100 mg/kg CBD). Systemic fractions of analytes were captured via in vivo SPME (10-min sampling window) in the circulating blood of living animals. Following sacrifice, ex vivo SPME (30-min sampling window) was deployed across four anatomical brain regions (hippocampus, amygdala, cerebellum, and brainstem). SPME-based microextraction was performed across a 1–6 h temporal baseline, and was then cross-validated against traditional solid-liquid extraction (SLE). Analytes were quantified using validated, high-sensitivity liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Results and Discussion In vivo blood sampling captured rapid oral absorption of parent CBD, reaching a maximum free systemic concentration (Cmax ≈160 μg/mL) at 2 h post-dose followed by rapid systemic clearance. Among the phase I metabolites, only 6-hydroxy-CBD (6-OH-CBD) was recovered from circulating blood at the 2-h interval at trace levels. Mean systemic 2-arachidonoylglycerol (2-AG) concentrations were higher than baseline at all post-dose time points, with the highest mean value observed at 6 h. Ex vivo brain microextraction uncovered marked neuropharmacokinetic heterogeneity. Furthermore, while total tissue SLE detected abundant phase I metabolites with total 7-OH-CBD higher than parent CBD, SPME may reflect limited freely available concentrations and/or strong tissue association of those analytes in brain structures. This exploratory study confirms the technical feasibility of coupling living intravascular extractions with localized regional brain sampling of CBD and endocannabinoids. By demonstrating that CBD concentrations clear dynamically and account for only a minute fraction of total tissue homogenate mass, this methodology-driven proof of concept establishes a more accurate bioanalytical framework for evaluating novel ECS modulators and lipophilic neuropharmacological candidates.