title: Identification of 2,3-epoxymethacrylic acid as an intermediate in the metabolism of dental materials in human liver microsomes.
abstract: OBJECTIVE
  In previous studies it could be demonstrated that methacrylic acid (MA) is an intermediate in the metabolism of unpolymerized dental comonomers, released from dental restorative materials. This study was performed to identify the possible dental material intermediate 2,3-epoxymethacrylic acid (2,3-EMA) from MA in human liver microsomes. Most epoxy compounds are regarded as highly toxic substances.
  
  
  METHODS
  The formation and hydrolysis were studied in defined systems containing only MA and human liver microsomes at 37 degrees C. Hydrolysis was inhibited by cyclohexene oxide, a competitive inhibitor of epoxide hydrolase. The reaction product 2,3-EMA was analyzed by the headspace gas chromatography-mass spectrometry. After 5, 30, and 60 min samples were taken and analyzed.
  
  
  RESULTS
  For the reaction of MA to 2,3-EMA the average conversion rate was about 5% within 1h. It was found that without cyclohexene oxide the rate constant of enzymatic hydrolysis at pH 7.4 was about 10 times higher than the rate constant of the formation from MA in combination with cyclohexene oxide (k=8.3 versus 0.83 micromol/l min), indicating an instability and thus a high reactivity of 2,3-EMA. The formation of the MA intermediate 2,3-EMA was not observed when heat-inactivated liver microsomes were used (controls).
  
  
  CONCLUSIONS
  It could be clearly demonstrated that 2,3-EMA is a product of dental material metabolisms in biological systems. Therefore, increased toxicity might occur on dental restorative materials which are able to release (co)monomers which can be metabolized to MA.
authors.affiliation: Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-University of Munich, 80336 Munich, Germany. mario.seiss@gmx.de
authors.forename: Mario
authors.initials: M
authors.lastname: Seiss
authors.forename: Siegfried
authors.initials: S
authors.lastname: Nitz
authors.forename: Norbert
authors.initials: N
authors.lastname: Kleinsasser
authors.forename: Jeroen T M
authors.initials: JT
authors.lastname: Buters
authors.forename: Heidrun
authors.initials: H
authors.lastname: Behrendt
authors.forename: Reinhard
authors.initials: R
authors.lastname: Hickel
authors.forename: Franz X
authors.initials: FX
authors.lastname: Reichl
mesh_terms: D046508:Culture Techniques; D053138:Cyclohexenes / Q000494:pharmacology; D003764:Dental Materials / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004851:Epoxide Hydrolases / Q000037:antagonists & inhibitors; D004852:Epoxy Compounds / Q000302:isolation & purification / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008689:Methacrylates / Q000302:isolation & purification / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
chemical_list: C519317:2,3-epoxymethacrylic acid; D053138:Cyclohexenes; D003764:Dental Materials; D004791:Enzyme Inhibitors; D004852:Epoxy Compounds; D008689:Methacrylates; C008384:methacrylic acid; C007193:cyclohexene oxide; D009249:NADP; D004851:Epoxide Hydrolases