title: Quantification of fumarate and investigation of endogenous and exogenous fumarate stability in rat plasma by LC-MS/MS.
abstract: BACKGROUND
  Fumaric acid is a commonly used excipient in pharmaceutical products. It is not known if its presence may lead to fluctuation of endogenous fumarate levels. An LC-MS/MS method was developed and validated to quantify fumarate in support of a toxicokinetics study.
  
  
  RESULTS
  Stability evaluation showed that endogenous fumarate was stable for 6 h at room temperature, while exogenously added fumaric acid was converted to malate within 1 h due to the presence of fumarase. Citric acid, a fumarase inhibitor, prevented the conversion of added fumaric acid in rat plasma.
  
  
  CONCLUSIONS
  The method was validated in citric acid stabilized rat plasma using a surrogate matrix approach. A discrepancy in stability was observed between endogenous fumarate and exogenously added fumaric acid.
authors.affiliation: Covance Laboratories Inc., 3301 Kinsman Blvd, Madison, WI 53704, USA.
authors.forename: Yao
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Pfizer Inc., Eastern Point Road, Groton, CT 06340, USA.
authors.forename: Susanna
authors.initials: S
authors.lastname: Tse
authors.affiliation: Pfizer Inc., Eastern Point Road, Groton, CT 06340, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Rago
authors.affiliation: Pfizer Inc., Eastern Point Road, Groton, CT 06340, USA.
authors.forename: Udeni
authors.initials: U
authors.lastname: Yapa
authors.affiliation: Covance Laboratories Inc., 3301 Kinsman Blvd, Madison, WI 53704, USA.
authors.forename: Fumin
authors.initials: F
authors.lastname: Li
authors.affiliation: Covance Laboratories Inc., 3301 Kinsman Blvd, Madison, WI 53704, USA.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Fast
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid / Q000592:standards; D019343:Citric Acid / Q000737:chemistry / Q000378:metabolism; D004355:Drug Stability; D005649:Fumarate Hydratase / Q000037:antagonists & inhibitors / Q000378:metabolism; D005650:Fumarates / Q000097:blood* / Q000592:standards; D007553:Isotope Labeling; D008293:Malates / Q000032:analysis / Q000378:metabolism; D011786:Quality Control; D051381:Rats; D053719:Tandem Mass Spectrometry / Q000592:standards; D013696:Temperature
chemical_list: D002250:Carbon Radioisotopes; D005650:Fumarates; D008293:Malates; D019343:Citric Acid; C030298:malic acid; C032005:fumaric acid; D005649:Fumarate Hydratase
keywords: TCA cycle; biomarker stability; endogenous; exogenous; fumarase; fumarate; fumaric acid; isotope effects; small-molecule biomarker; surrogate matrix