Determination of urinary myo-inositol concentration by an improved enzymatic cycling method using myo-inositol dehydrogenase from Flavobacterium sp.

Abstract

Background: To determine myo-inositol more accurately, we improved the enzymatic cycling method. Methods: We screened myo-inositol dehydrogenase (MIDH; EC.1.1.1.18) from Flavobacterium sp., which was highly specific to myo-inositol. We measured urinary myo-inositol/creatinine ratio 2 h after 75-g oral glucose tolerance test (2 h MI) of 71 volunteers, and investigated the relationship between diabetes and urinary myo-inositol concentration. Results: The calibration curve was linear ( r=1.00) up to 2000 μmol/l, and the detection limit was 10 μmol/l. Within-run and between-run CVs were 0.5–1.1% and 0.4–1.3%, respectively. The 2 h MI of impaired fasting glycemia (IFG; 65.1±46.6 mg/g Cr, P<0.005), impaired glucose tolerance (IGT; 85.0±73.7 mg/g Cr, P<0.001) and diabetes (163.4±73.7 mg/g Cr, P<0.0001) increased significantly compared with that of normal glucose tolerance (NGT; 24.0±14.4 mg/g Cr). From receiver operating characteristic analyses on 2 h MI, with 50 mg/g Cr as a tentative cutoff value to detect diabetes, the sensitivity and specificity were 100% and 77%, respectively. With 40 mg/g Cr as a tentative cutoff value to detect NGT, the sensitivity and specificity were 74% and 85%, respectively. Conclusions: The myo-inositol measurement method demonstrated high specificity and yielded accurate results. The results of clinical trials suggested that 2 h MI could not only determine diabetes but also distinguish IFG and IGT from NGT.