title: Simultaneous determination of N(1)-methylnicotinamide, L-carnitine, and creatinine in human plasma and urine by liquid chromatography with mass spectrometry for assessing the activities of multiple renal cationic transporters.
abstract: Organic cation transporters are responsible for the disposition of various endogenous and therapeutic agents in humans; thus, there is a great need for the development of a simple assay for simultaneous assessment of the activities of multiple transporters. Using liquid chromatography-mass spectrometry (LC/MS), we developed an assay that allows for simultaneous quantitation of plasma and urinary levels of N(1)-methylnicotinamide (a substrate of hOCT2/hMATEs), L-carnitine (a substrate of hOCTN2), and creatinine (an indicator of glomerular filtration). Samples were diluted with ultrapure water, deproteinized with trichloroacetic acid, filtered, and then injected on a cation exchange column. The analytes were separated with a gradient LC technique and detected by MS. The total assay time was less than 8 min. The lower detection limits for N(1)-methylnicotinamide, L-carnitine, and creatinine were 2, 10, and 24 ng/mL, respectively. Recovery of the analytes was almost complete. A preliminary clinical study conducted in 25 healthy subjects revealed that the mean±SD for the renal clearance (CLR) of N(1)-methylnicotinamide (272.7±81.0 mL/min) far exceeded the glomerular filtration rate (116.3±19.6 mL/min), indicating the involvement of active tubular secretion, while the mean CLR of clearance of L-carnitine was close to nil (1.5±1.4 mL/min), indicating almost complete tubular reabsorption. The present method is potentially useful for clinical studies on the genetic control of cationic transporter activities and the transporter-mediated drug interactions.
authors.affiliation: Department of Pharmacotherapy, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose-shi, Tokyo 204-0004, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nobuoka
authors.affiliation: Department of Pharmacotherapy, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose-shi, Tokyo 204-0004, Japan. Electronic address: smridron@my-pharm.ac.jp.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Ogawa
authors.affiliation: Department of Pharmacotherapy, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose-shi, Tokyo 204-0004, Japan.
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Echizen
mesh_terms: D002331:Carnitine / Q000097:blood* / Q000737:chemistry / Q000652:urine*; D002853:Chromatography, Liquid / Q000379:methods; D003404:Creatinine / Q000097:blood* / Q000737:chemistry / Q000652:urine*; D004355:Drug Stability; D005260:Female; D006801:Humans; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000097:blood / Q000737:chemistry / Q000652:urine; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D009536:Niacinamide; D003404:Creatinine; D002331:Carnitine; C024058:N(1)-methylnicotinamide
keywords: Creatinine; Humans; LC/MS; N(1)-Methylnicotinamide; Plasma; Urine; l-carnitine