Assessing Amino Acid Concentration Changes as a Result of Drug Dosing and Cytochrome P450 and Non-cytochrome P450-Mediated Metabolism

When a drug is dosed into a hepatic cell culture, an animal, or a human, dozens of intracellular metabolites are produced and transported into the systemic blood flow along with the drug molecule. The metabolites arise from a number of cellular metabolism enzymes, including cytochrome P450 (CYP) and non-CYP enzymes. Adverse effects on the structure and/or functional properties of one or more cell components may occur due to the presence of the dosed drug or its metabolites. Nuclear magnetic resonance (NMR) enables the characterization and accurate quantitation of small metabolites in biological fluids, and thus can be utilized for metabolomics studies. An NMR assay, utilizing a one-dimensional proton (H-1) Car-Purcell-Meiboom-Gill (CPMG) NMR pulse sequence, was utilized to quantitate 18 amino acids in human plasma and serum. Asparagine and cysteine could not be quantified by this approach due to the low concentration of these amino acids in the blood. The average percent coefficient of variation (%CV) of the detected amino acids was 3.5% in human plasma and 3.4% in human serum. Amino acid profiles of biological systems can be used in conjunction with typical absorption, distribution, metabolism, excretion (ADME), and pharmacokinetics (PK) assays to detect off-target and toxicity issues that might arise due to drug/metabolites exposure.