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 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 degrees C. RESULTS The calibration curve for myo-inositol was linear (r=1.00) between 10 and 400 micromol/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 micromol/l, n=7) than in healthy individuals without DM (61.0+/-12.4 micromol/l, n=20). The urinary myo-inositol concentration was also significantly greater in patients with DM without nephropathy (793.3+/-870.3 micromol/l, n=7) than in healthy individuals without DM (76.0+/-63.0 micromol/l, n=13). CONCLUSIONS This new method is simple, sensitive and enables quantitative analysis of myo-inositol.