Pharmacokinetics of theanine enantiomers in rats
Author: Desai MJ, and Gill MS, and Hsu WH, and Armstrong DW
Theanine, first discovered in tea, is a chiral nonproteinic amino acid that has been reported to have cardiovascular, neurological, and oncological effects. It is being considered as a therapeutic/medicinal agent and additive in consumer products. The present study evaluated the pharmacokinetics of d-theanine, l-theanine, and d,l-theanine in plasma and urine using LC-ESI/MS in rats after oral (p.o.) and intraperitoneal (i.p.) administration. Oral administration data indicated that gut absorption of d-theanine was far less than that of l-theanine. However, after i.p. administration, plasma theanine concentrations of l- and d-theanine were similar. This indicated that d- and l-theanine may exhibit a competitive effect with respect to intestinal absorption. Regardless of the route of administration, p.o. or i.p., the presence of the other enantiomer always decreased theanine plasma concentrations, indicating d,l-theanine competition with respect to urinary reabsorption. Data on urinary concentrations of d-theanine suggested that the d-isomer may be eliminated with minimal metabolism. l-Theanine appeared to be preferentially reabsorbed and metabolized by the kidney while d-theanine was preferentially excreted. Clearly, the bioequivalencies of d,l-theanine and its enantiomers were found to be quite different from one another. Consequently, the efficacy of commercial theanine products containing d-theanine, l-theanine, or d,l-theanine may be quite different.