LC-MS/MS and GC-MS/MS measurement of plasma and urine di-paracetamol and 3-nitro-paracetamol: proof-of-concept studies on a novel human model of oxidative stress based on oral paracetamol administration.
Paracetamol (acetaminophen) is a widely used safe analgesic drug when administered at therapeutic doses. Given the chemical reactivity of its phenolic group towards electrophilic species, we assumed that detection of paracetamol metabolites distinctly different from its known phase I metabolite N-acetyl-p-benzoquinone imine (NAPQI) and the phase II glucuronic, sulfuric and mercapturic acids in biological samples upon oral administration of paracetamol (e.g., a 500-mg tablet) may represent a novel model of oxidative stress in humans. Such potential paracetamol metabolites are di-paracetamol and 3-nitro-paracetamol, in analogy to the well-investigated endogenous biomarkers di-tyrosine and 3-nitro-tyrosine. Di-paracetamol and 3-nitro-paracetamol are known to be formed both by enzymatic and non-enzymatic routes. In the present work we report on mouse and human pilot studies on the formation and appearance of di-paracetamol and 3-nitro-paracetamol in blood of mice intraperitoneally administered paracetamol, as well as in plasma and urine samples of healthy subjects who received a 500-mg paracetamol tablet or placebo. For the analysis of di-paracetamol and 3-nitro-paracetamol in plasma and urine samples, analytes were extracted by solvent extraction with ethyl acetate and subsequently analyzed by LC-MS/MS without and with derivatization with pentafluorobenzyl bromide. GC-MS/MS was used to detect 3-nitro-paracetamol and quantify paracetamol as pentafluorobenzyl derivatives. Our studies indicate that di-paracetamol and 3-nitro-paracetamol appear in plasma and urine when paracetamol is given orally to healthy humans at the therapeutic dosage of 5-7 mg/kg. The molar ratio of di-paracetamol to paracetamol in urine was determined to be 1:535 in the paracetamol group and 1:6844 in the placebo group; the molar ratio of 3-nitro-paracetamol to paracetamol in urine was determined to be 1:199 in the paracetamol group and 1:8657 in the placebo group. Our studies suggest that a fraction of circulating and excretory di-paracetamol and 3-nitro-paracetamol may be formed artefactually during sample workup including derivatization. Further studies based on the quantitative determination of di-paracetamol and 3-nitro-paracetamol in biological samples by LC-MS/MS and/or GC-MS/MS using stable-isotope labeled analogues as internal standards are warranted to test the utility of paracetamol as a probe of oxidative stress in animals and in humans in health and disease.
Institute of Clinical Pharmacology, Hannover Medical School, 30625 Hannover, Germany.
Arne
A
Trettin
Department of Pharmacology, School of Medicine, University of Split, 21000 Split, Croatia.
Darko
D
Modun
Department of Internal Medicine, University Hospital Split, 21000 Split, Croatia.
Sanja
S
Madunic
Department of Internal Medicine, University Hospital Split, 21000 Split, Croatia.
Jonatan
J
Vukovic
Department of Internal Medicine, University Hospital Split, 21000 Split, Croatia.
Maja
M
Radman
Institute of Molecular and Translational Therapeutic Strategies, IFB-TX, Hannover Medical School, 30625 Hannover, Germany.
Sandor
S
Batkai
Institute of Molecular and Translational Therapeutic Strategies, IFB-TX, Hannover Medical School, 30625 Hannover, Germany; Excellence Cluster REBIRTH, Hannover Medical School, 30625 Hannover, Germany.
Thomas
T
Thum
Institute of Clinical Pharmacology, Hannover Medical School, 30625 Hannover, Germany.
Jens
J
Jordan
Institute of Clinical Pharmacology, Hannover Medical School, 30625 Hannover, Germany. Electronic address: tsikas.dimitros@mh-hannover.de.
Dimitrios
D
Tsikas
D000082:Acetaminophen / Q000009:adverse effects / Q000097:blood* / Q000737:chemistry / Q000652:urine*; D000284:Administration, Oral; D000328:Adult; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000097:blood* / Q000737:chemistry / Q000652:urine*; D000818:Animals; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D015394:Molecular Structure; D018384:Oxidative Stress / Q000187:drug effects*; D053719:Tandem Mass Spectrometry; D055815:Young Adult
D018712:Analgesics, Non-Narcotic; D000082:Acetaminophen
Clinical trial; Dimerization; Human model; Nitration; Oxidative stress; Tandem mass spectrometry