An enzymatic cycling method for the measurement of myo-inositol in biological samples

Abstract

Introduction: A sensitive and simple enzymatic cycling method is described for the quantitation of myo-inositol in biological samples. Methods: The method involves the use of a sensitive and simple enzymatic cycling method is described for the quantitation of myo-inositol in biological samples. The method involves use of thio-NAD +, NADH and thermostable myo-inositol dehydrogenase (IDH; EC. 1.1.1.18) and measurement of the increase in absorbance at 405 nm of thio-NADH at 37 °C. Results: The calibration curve for myo-inositol was linear ( r=1.00) between 10 and 400 μmol/l. Analytical recoveries of exogenous myo-inositol added to serum and urine were 100–105% and 98–103%, respectively. Within-run and between-run coefficient of variation (CV) were 0.6–2.1% and 1.1–3.0%, respectively. This method was free from interference by hemoglobin, bilirubin, ascorbate, chyle, various sugars, sugar alcohol and myo-inositol phosphates. With the use of myo-inositol as a standard solution, the serum myo-inositol concentration (mean±SD) was significantly greater in patients with diabetes mellitus (DM) without nephropathy (73.0±13.8 μmol/l, n=7) than in healthy individuals without DM (61.0±12.4 μmol/l, n=20). The urinary myo-inositol concentration was also significantly greater in patients with DM without nephropathy (793.3±870.3 μmol/l, n=7) than in healthy individuals without DM (76.0±63.0 μmol/l, n=13). Conclusions: This new method is simple, sensitive and enables quantitative analysis of myo-inositol.