Identification of 2,3-epoxymethacrylic acid as an intermediate in the metabolism of dental materials in human liver microsomes

Seiss, Mario; Nitz, Siegfried; Kleinsasser, Norbert; Buters, Jeroen T.M.; Behrendt, Heidrun; Hickel, Reinhard; Reichl, Franz X.

doi:10.1016/j.dental.2005.11.038

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Volume 23, Issue 1 , Pages 9-16, January 2007

Identification of 2,3-epoxymethacrylic acid as an intermediate in the metabolism of dental materials in human liver microsomes

Mario Seiss
- Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-University of Munich, 80336 Munich, Germany
- Corresponding author at: Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-University, Goethestr. 31, D-80336 Munich, Germany. Tel.: +49 89 2180 75754; fax: +49 89 2180 75701.
Siegfried Nitz
- Chair of Chemical–Technical Analysis and Chemical Food Technology, Technical University of Munich, 85350 Freising, Germany
Norbert Kleinsasser
- Department of Otolaryngology — Head and Neck Surgery, University of Regensburg, 93053 Regensburg, Germany
Jeroen T.M. Buters
- Center for Allergy and Environment, Technical University of Munich, 80802 Munich, Germany
Heidrun Behrendt
- Center for Allergy and Environment, Technical University of Munich, 80802 Munich, Germany
Reinhard Hickel
- Department of Operative Dentistry and Periodontology, Ludwig-Maximilians-University, 80336 Munich, Germany
Franz X. Reichl
- Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-University of Munich, 80336 Munich, Germany

Received 12 May 2005; received in revised form 15 November 2005; accepted 28 November 2005.

Abstract

Objectives

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°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 60min 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 0.83μmol/lmin), 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).

Significance

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.

Keywords: Methacrylic acid, 2,3-Epoxymethacrylic acid, Human liver microsomes, Metabolism