Fast and Sensitive Quantification of Δ(9)-Tetrahydrocannabinol and Its Main Oxidative Metabolites by Liquid Chromatography/Tandem Mass Spectrometry

Introduction: Few animal studies have evaluated the pharmacological effects of Δ(9)-tetrahydrocannabinol (THC) in relation to its pharmacokinetic properties. Understanding this relationship is essential, however, if comparisons are to be drawn across conditions—such as sex, age, and route of administration—which are associated with variations in the absorption, metabolism, and distribution of THC. As a first step toward addressing this gap, in this report, we describe a rapid, sensitive, and accurate method for the quantification of THC and its main oxidative metabolites, and apply it to representative rodent tissues. Materials and Methods: The sample workup procedure consisted of two steps: bulk protein precipitation with cold acetonitrile (ACN) followed by phospholipid removal by elution through Captiva-Enhanced Matrix Removal cartridges. The liquid chromatography/tandem mass spectrometry (LC/MS-MS) protocol utilized a commercially available C18 reversed-phase column and a simple methanol/water gradient system. The new method was validated following Food and Drug Administration (FDA) guidelines, and was applied to the quantification of THC and its main oxidative metabolites—11-hydroxy-Δ(9)-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Δ(9)-tetrahydrocannabinol (11-COOH-THC)—in plasma and brain of mice treated with a single intraperitoneal dose of THC (10 mg/kg). Results: ACN precipitation and column elution effectively depleted matrix constituents—most notably choline-containing phospholipids—which are known to interfere with THC analysis, with average recovery values of >85% for plasma and >80% for brain. The LC conditions yielded baseline separation of all analytes in a total run time of 7 min (including re-equilibration). The 10–point calibration curves showed excellent linearity (R(2)>0.99) over a wide range of concentrations (1–1000 pmol/100 μL). Lowest limit of quantification was 2 pmol/100 μL for all analytes, and lowest limits of detection were 0.5 pmol/100 μL for THC and 11-OH-THC, and 1 pmol/100 μL for 11-COOH-THC. Intraday and interday accuracy and precision values were within the FDA-recommended range (±15% of nominal concentration). An application of the method to adult male mice is presented. Conclusions: We present a fast and sensitive method for the analysis of THC, which should facilitate studies aimed at linking the pharmacokinetics and pharmacodynamics of this compound in animal models.