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Serotonin (5-hydroxytryptamine) glucuronidation in vitro: assay development, human liver microsome activities and
S Krishnaswamy1, S X Duan, L L Von Moltke
1Comparative and Molecular Pharmacogenetics Laboratory, Tufts University School of Medicine, Boston, MA 02111, USA.
Summary
A new high-performance liquid chromatography (HPLC) method accurately measures serotonin glucuronidation activity. This assay reveals significant interspecies differences in UDP-glucuronosyltransferase (UGT) enzyme kinetics, crucial for drug metabolism studies.
Area of Science:
- Pharmacology
- Biochemistry
- Analytical Chemistry
Background:
- Serotonin glucuronidation is a key metabolic pathway.
- Understanding UDP-glucuronosyltransferase (UGT) enzyme activity is vital for drug development and personalized medicine.
Purpose of the Study:
- To develop and validate a high-performance liquid chromatography (HPLC)-based assay for quantifying serotonin glucuronidation activity.
- To determine the enzyme kinetics of serotonin UDP-glucuronosyltransferase (UGT) in human liver microsomes and with recombinant UGT1A6.
- To investigate interspecies variations in serotonin glucuronidation activity.
Main Methods:
- Liver microsomes were incubated with serotonin, UDP-glucuronic acid, and magnesium.
- Product formation was detected and confirmed using HPLC with fluorescence and UV absorbance detection, beta-glucuronidase sensitivity, and mass spectrometry.
- Metabolite structure was elucidated using preparative HPLC and 1H-NMR spectroscopy.
- Enzyme kinetics were determined via Michaelis-Menten analysis.
Main Results:
- A sensitive and specific HPLC method was established for serotonin glucuronidation.
- Serotonin-5-O-glucuronide was identified as the primary metabolite.
- Kinetic parameters (Km, Vmax) were determined for human liver microsomes and recombinant UGT1A6.
- Significant interspecies differences in serotonin-UGT activity were observed, with notable variations in Gunn rats.
Conclusions:
- The developed HPLC assay is a novel, sensitive, and specific tool for measuring in vitro serotonin-UGT activity.
- The study highlights substantial species-specific differences in serotonin metabolism, impacting drug efficacy and safety.
- UGT1A isoforms play a significant role in serotonin glucuronidation across different species.