EthicsThe animal studies described here were all approved by the Animal Ethics Board of the University of Maastricht, The Netherlands. At the end of the experiment all adult animals were killed by carbon dioxide inhalation (unless stated otherwise). They were initially exposed to a mixture of O 2 and CO 2 for 3-4 min (in a sealed container) after which the O 2 was discontinued for 1-2 min. Animals were left in pure CO 2 for ~1 h to ensure they were dead.

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Background. Plasma and urinary levels of D-lactate have been linked to the presence of diabetes. Previously developed techniques have shown several limitations to further evaluate D-lactate as a biomarker for this condition.Methods. D- and L-lactate were quantified using ultraperformance liquid chromatography tandem mass spectrometry with labelled internal standard. Samples were derivatized with diacetyl-L-tartaric anhydride and separated on a C18-reversed phase column. D- and L-lactate were analysed in plasma and urine of controls, patients with inflammatory bowel disease (IBD), and patients with type 2 diabetes (T2DM).Results. Quantitative analysis of D- and L-lactate was achieved successfully. Calibration curves were linear (r2>0.99) over the physiological and pathophysiological ranges. Recoveries for urine and plasma were between 96% and 113%. Inter- and intra-assay variations were between 2% and 9%. The limits of detection of D-lactate and L-lactate in plasma were 0.7 μmol/L and 0.2 μmol/L, respectively. The limits of detection of D-lactate and L-lactate in urine were 8.1 nmol/mmol creatinine and 4.4 nmol/mmol creatinine, respectively. Plasma and urinary levels of D- and L-lactate were increased in patients with IBD and T2DM as compared with controls.Conclusion. The presented method proved to be suitable for the quantification of D- and L-lactate and opens the possibility to explore the use of D-lactate as a biomarker.

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