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

Introduction: A sensitive and simple enzymatic cycling method is described for the quantitation of myo-inositol in biological samples. Methods: The me thod 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 dehy drogenase (IDH; EC. 1.1.1.18) and measurement of the increase in absorbance at 405 nm of thio-NADH at 37 degreesC. Results: The calibration curve for myo-inositol was linear (r=1.00) between 10 and 400 mu mol/l. Analytical re coveries of exogenous myo-inositol added to serum and urine were 100-105% a nd 98-103%, respectively. Within-run and between-run coefficient of variati on (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, s ugar alcohol and myo-inositol phosphates. With the use of myo-inositol as a standard solution, the serum myo-inositol concentration (mean SD) was sign ificantly greater in patients with diabetes mellitus (DM) without nephropat hy (73.0 +/- 13.8 mu inol/l, n=7) than in healthy individuals without DM (6 1.0 +/- 12.4 mu nol/l, n=20). The urinary myo-inositol concentration was al so significantly greater in patients with DM without nephropathy (793.3 +/- 870.3 mu mol/l, n=7) than in healthy individuals without DM (76.0 +/- 63.0 mu mol/l, n=13). Conclusions: This new method is simple, sensitive and ena bles quantitative analysis of myo-inositol. (C) 2001 Elsevier Science B.V. All rights reserved.