Use of Methyl Malondialdehyde as an Internal Standard for Malondialdehyde Detection: Validation by Isotope-Dilution Gas Chromatography–Mass Spectrometry

Abstract

Malondialdehyde (MDA), a compound derived from lipid peroxidation and from eicosanoid biosynthesis, exists in biological matrices both in the free form and bound to SH and/or NH2 groups of various biomolecules (1). Although other compounds (isoprostanes) have been proposed as more reliable indicators of oxidative damage (2), MDA is still widely used in clinical chemistry laboratories to monitor oxidative stress (3). Several methods have been developed to evaluate MDA in biological samples (1)(4), but the different analytical conditions used and the lack of a suitable internal standard have led to large discrepancies in measurements even at physiologic MDA concentrations in human plasma (5). We (6) recently reported a “reference method” for free and total plasma MDA quantification, as the phenylpyrazole derivative, by isotope-dilution gas chromatography–mass spectrometry (ID-GC-MS) with dideuterated MDA (d2-MDA) as internal standard. This method, used for clinical MDA detection (7)(8)(9), offers the possibility of validating other proposed internal standards that differ from MDA in structure, stability, and reactivity. Unfortunately, the major limitations of d2-MDA include its difficult synthesis (10) and that it is detectable only by GC-MS, a method not always available in clinical laboratories. A compound that appears to be more suitable as an internal standard is methyl malondialdehyde (MMDA) because it is structurally close to MDA, is absent from biological matrices, is easily obtainable from a commercial compound, and is detectable by common methods such as HPLC, GC, and capillary electrophoresis. MMDA was first evaluated as an internal standard for MDA determinations by Bull and Marnett (11), who unfortunately experienced difficulties in resolving the underivatized MDA and MMDA by HPLC. Recently, Claeson et al. (12) reported the use of MMDA as an internal standard for measurement of MDA in rat brain by capillary electrophoresis, …