High performance liquid chromatographic determination of 1,5-anhydroglucitol in human plasma for diagnosis of diabetes mellitus

Reference intervals for serum 1,5-anhydroglucitol of a population with normal glucose tolerance in Jiangsu Province

BACKGROUND

Serum 1,5-anhydroglucitol (1,5-AG) is a new glycemic marker which can reflect glucose fluctuation over 3 to 7 days and is now increasingly used to monitor glucose control and to screen for diabetes. However, 1,5-AG has not been widely used in China due to lack of epidemiological support. Our study aims to establish the reference intervals for a population with normal glucose tolerance in Jiangsu Province and to explore the determinants of these intervals.

METHOD

The study enrolled 646 healthy adults aged 20 to 70 years in Jiangsu Province in 2018 after oral glucose tolerance test. 1,5-AG, fasting and 2-hour glucose, UA, liver enzyme, serum lipid, creatinine, and glycosylated hemoglobin were measured. We calculated reference intervals using the parametric method and examined the relationship between 1,5-AG and influence factors.

RESULTS

The average age of the participants was 50.5 ± 9.0 years, and 69.5% of them were females. The reference intervals were 15.8 to 52.6 μg/mL for males and 14.3 to 48.0 μg/mL for females. Among females, the reference intervals were 13.9 to 45.3 and 14.6 to 49.6 μg/mL for menopausal and postmenopausal females, respectively. Males showed higher 1,5-AG concentrations than females, and postmenopausal females had higher 1,5-AG than menopausal females. There was a positive correlation between uric acid and 1,5-AG in both genders. Positive correlation between 1,5-AG and age was only observed in females.

CONCLUSION

We established reference intervals for 1,5-AG in Jiangsu Province, and the level of 1,5-AG is affected by sex, uric acid, and age.

Evaluation of 1,5-anhydro-d-glucitol in clinical and forensic urine samples

Because of the lack of characteristic morphological findings post mortem diagnosis of diabetes mellitus and identification of diabetic coma can be complicated. 1,5-Anhydroglucitol (1,5-AG), the 1-deoxy form of glucose, competes with glucose for renal reabsorption. Therefore low serum concentrations of 1,5-AG, reflect hyperglycemic excursions over the prior 1-2 weeks in diabetic patients. Next to clinical applications determination of 1,5-AG can also be used in forensic analysis. To investigate the elimination of 1,5-AG, a liquid chromatographic-mass spectrometric method for the determination of 1,5-AG and creatinine in urine was developed and validated according to international guidelines. To evaluate ante mortem concentrations of 1,5-AG spot urine samples of 30 healthy subjects, 46 type 1 and 46 type 2 diabetic patients were analyzed. 1,5-AG urine concentrations of diabetic patients were significantly (p<0.001) lower (mean: 1.54μg/ml, n=92) compared to concentrations of healthy subjects (mean: 4.76μg/ml, n=30) which led to the idea that 1,5-AG urine concentrations post mortem might help in the interpretation of a diabetic coma post mortem. Urine of 47 deceased non-diabetics, 37 deceased diabetic and 9 cases of diabetic coma were measured. Comparison of blood and urine 1,5-AG concentrations in clinic samples (linear, R²=0.13) and forensic samples (linear, R²=0.02) showed no correlation. Urinary levels of 1,5-AG in deceased diabetic (mean 6.9μg/ml) and in non-diabetic patients (mean 6.3μg/ml) did not show a significant difference (p=0.752). However, urinary 1,5-AG concentrations in deceased due to diabetic coma (mean: 1.7μg/ml) were significantly lower than in non-diabetic (mean: 6.3μg/ml, p=0.039) and lower than in diabetic cases (mean: 4.7μg/ml, p=0.058). The determination of a reliable cut-off for the differentiation of diabetic to diabetic coma cases was not possible. Normalization of urinary 1,5-AG concentrations with the respective creatinine concentrations did not show any gain of information. In clinical (serum) and forensic blood samples a significant difference between all groups could be detected (p<0.05). Comparison of blood and urine 1,5-AG concentrations in clinical samples (linear, R²=0.13) and forensic samples (linear, R²=0.02) showed no correlation.

A novel method for the determination of 1,5-anhydroglucitol, a glycemic marker, in human urine utilizing hydrophilic interaction liquid chromatography/MS(3)

Plasma levels of 1,5-anhydroglucitol (1-deoxyglucose), a short-term marker of glycemic control, have been measured and used clinically in Japan since the early 1990s. Plasma levels of 1,5-anhydroglucitol are typically measured using either a commercially available enzymatic kit or GC/MS. A more sensitive method is needed for the analysis of 1,5-anhydroglucitol in urine, where levels are significantly lower than in plasma. We have developed a sensitive and selective LC/MS(3) assay utilizing hydrophilic interaction liquid chromatography and ion trap mass spectrometry for the quantitative determination of 1,5-anhydroglucitol in human urine. Diluted human urine samples were analyzed by LC/MS(3) using an APCI source operated in the negative ionization mode. Use of an ion trap allowed monitoring of MS(3) transitions for both 1,5-anhydroglucitol and the internal standard which provided sufficient selectivity and sensitivity for analysis from 50 microL of human urine. Quantitation of 1,5-anhydroglucitol levels in urine was accomplished using a calibration curve generated in water (calibration range 50 ng/mL to 10 microg/mL). Method ruggedness and reproducibility were evaluated by determining the intra- and inter-day accuracies and precision of the assay, as well as the bench-top and freeze-thaw stability. For both inter- and intra-assay evaluations, the accuracy of the assay was found to be acceptable, with the concentrations of all QCs tested not deviating more than 8% from theoretical. Four-hour bench-top and freeze-thaw stabilities were also evaluated; 1,5-anhydroglucitol was found to be stable at room temperature (<18% deviation from theoretical) and during 3 freeze-thaw cycles (<1% deviation from theoretical, except at the lowest QC level). The LC/MS(3) assay was then used to successfully determine the concentration of 1,5-AG in more than 200 urine samples from diabetic patients enrolled in a clinical study.

A novel NAD-dependent dehydrogenase, highly specific for 1,5-anhydro-D-glucitol, from Trichoderma longibrachiatum strain 11-3

A novel NAD-dependent dehydrogenase highly specific for 1,5-anhydro-D-glucitol (1,5-AG) was found in the cell extract of an imperfect fungus, Trichoderma longibrachiatum strain 11-3. This fungus used 1,5-AG as a sole carbon source for growth and transformed 1,5-AG into glucose. 1,5-AG dehydrogenase (AGH) was purified to homogeneity, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular mass of the purified enzyme was estimated to be 36 and 141 kDa by SDS-PAGE and by gel filtration, respectively, suggesting that the enzyme was homotetrameric. The enzyme was highly specific for 1,5-AG and did not exhibit activity with any sugar or sugar alcohol tested in this study other than 1,5-AG. A linear relationship between the initial rate of the enzyme reaction and the concentration of 1,5-AG at the physiological level was observed. The presence of glucose in abundance did not interfere with the relationship. The optimum temperature for the enzyme reaction was 50 degrees C, and the enzyme was stable at temperatures up to 70 degrees C. These results suggested that AGH is a novel enzyme and is useful for specifically diagnosing diabetes mellitus.

Comparison of micro-enzymatic and high-performance liquid chromatographic methods for the assay of serum 1,5-anhydroglucitol

Serum 1,5-anhydro-D-glucitol (AG) has been proposed as a marker of glycaemic control in diabetic patients. Two methods have been developed which could be applied to routine clinical monitoring of serum AG. We have compared the assay characteristics of an adapted enzyme assay, based on the enzyme pyranose oxidase, with a high-performance anion-exchange chromatographic method using pulsed amperometric detection (HPAEC-PAD). Linearity and minimum detectable concentrations were practically identical (to at least 400 mumol/l and 4 mumol/l AG, respectively), though intra- and inter-assay precision was better with the HPAEC PAD system at a clinically relevant concentration of 40 mumol/l AG (9.8% vs. 11.8% and 9.2% vs. 13.0%, respectively). The recovery of added AG to serum samples was lower with the micro-enzyme assay than the HPAEC-PAD assay (74 +/- 15% vs. 102 +/- 8%). Despite good agreement by linear regression (r = 0.974, P < 0.005), the assay methods did not demonstrate satisfactory agreement when using a difference plot (limits of agreement -16.1 to 18.7 mumol/l). We conclude that although both assay methods are applicable to routine analyses, the HPAEC-PAD is more precise and is more specific for AG than the enzyme based assay.

Determination of 1,5-anhydroglucitol in urine by high performance liquid chromatography and an enzyme sensor

A simple high performance liquid chromatographic method combined with an enzyme sensor has been developed to measure 1,5-anhydroglucitol in urine. The enzyme sensor consists of a hydrogen peroxide electrode and a chitosan membrane of an immobilized pyranose oxidase. As the system does not resist interfering substances, urine samples are first purified by passing them through a two-layer column packed with (1) strongly basic anion (OH- form, the upper layer) and (2) strongly acidic cation (H+ form, the lower layer) exchange resins. 1,5-Anhydroglucitol is efficiently recovered in the flow-through fraction of the column. In this system, the minimum detectable concentration of 1,5-anhydroglucitol is 0.1 mg/L, and the measurable range extends from 0.1 to 60 mg/L. The coefficient of variation values of the within-day and day-to-day precisions are 3.0-6.5% and and 4.4-6.7% respectively, and there is good agreement between the results measured by our method and those obtained by the gas-liquid chromatographic/mass spectrometric method (r = 0.994). The method we have described here has been successfully used to elucidate a mechanism for the reducing 1,5-anhydroglucitol level in the serum and plasma of patients.