Determination of urinary myo-inositol concentration by an improved enzymatic cycling method using myo-inositol dehydrogenase from Flavobacterium sp.
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 micromol/l, and the detection limit was 10 micromol/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.
Yamakoshi
Masaru
M
Diagnostics R&D Department, Fine Chemicals and Diagnostics Division, Health Care Company, Asahi Kasei Corporation, 632-1, Mifuku, Ohito-cho, Tagata-gun, Shizuoka 410-2321, Japan. yamakoshi.mb@om.asahi-kasei.co.jp
Takahashi
Mamoru
M
Kouzuma
Takuji
T
Imamura
Shigeyuki
S
Tsuboi
Isami
I
Kawazu
Shoji
S
Yamagata
Fumio
F
Tominaga
Makoto
M
Noritake
Masayuki
M
D000328:Adult; D005260:Female; D005417:Flavobacterium / Q000201:enzymology*; D006801:Humans; D007294:Inositol / Q000652:urine*; D008297:Male; D008875:Middle Aged; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D012680:Sensitivity and Specificity
D007294:Inositol; D010744:Phosphoric Monoester Hydrolases; C053087:inositol-1,4-bisphosphate 1-phosphatase