A sensitive HILIC-MS/MS method for quantification of theanine in rat plasma and tissues: Application to preclinical pharmacokinetic study

Adolescent depression is a significant public health problem, with the major depressive disorder having been the leading risk factor for suicide and death amongst children and adolescents. For treating depression, antidepressants are used with minimal clinical evidence data and uncertain efficacy in children. L-theanine has anti-depression and other physiological functions. However, few reports are available on the pharmacokinetics of L-theanine, especially in children and adolescents. In this study, a rapid and sensitive hydrophilic interaction liquid chromatography-tandem mass spectrometry method was established and validated for the quantification of L-theanine in juvenile rat plasma and tissues. Chromatographic separation was conducted via an Agilent ZORBAX HILIC plus column in gradient elution mode. L-theanine and [2H5]-L-glutamic acid (internal standard) were determined under the multi-reaction monitoring mode transitions of m/z 175.0 → 157.9 and m/z 153.0 → 88.2 in positive ionisation mode, respectively, and completed methodology verification. In addition, 10 and 35 mg kg-1 of L-theanine were given by intragastric administration to determine the brain and plasma pharmacokinetic characteristics in healthy and chronic unpredictable mild stress rats, respectively. The distribution of tissues and the limbic system were measured at the same time. The results showed that juvenile and diseased rats have higher absorption than adult rats, and age, dosage and health status could affect the process of L-theanine in vivo. L-theanine also has a high degree of tissue distribution. This study lays a foundation for the clinical treatment of depression in children and adolescents.