In Vivo Metabolism of 1,5-Anhydro-d-fructose to 1,5-Anhydro-d-glucitol.

BACKGROUND/AIM: 1,5-Anhydro-d-fructose (1,5-AF, saccharide) and 1,5-anhydro-d-glucitol (1,5-AG) converted from 1,5-AF via the glycemic pathway have health benefits. However, this metabolism has not been sufficiently elucidated. To clarify the in vivo metabolism of 1,5-AF to 1,5-AG, porcine (blood kinetics) and human (urinary excretion) studies were conducted. MATERIALS AND METHODS: Microminipigs were administrated 1,5-AF orally or intravenously. Blood samples were obtained to analyse the kinetics of 1,5-AF and 1,5-AG. Urine samples were collected from human subjects who had orally ingested 1,5-AF, and the amounts of 1,5-AF and 1,5-AG excreted in the urine were analysed. RESULTS: In blood kinetics analysis, the time to the maximum concentration of 1,5-AF after intravenous administration was 0.5 h, whereas 1,5-AF was not observed after oral administration. The times to the maximum concentration of 1,5-AG after intravenous and oral administration were 1.5 h and 2 h, respectively. In urinary excretion, the concentration of 1,5-AG in urine rapidly increased after the administration of 1,5-AF, peaked at 2 h, whereas 1,5-AF was not detected. CONCLUSION: 1,5-AF was rapidly metabolized to 1.5-AG in vivo in swine and human.

Time-based investigation of urinary metabolic markers for Type 2 diabetes: Metabolomics approach for diabetes management.

Diabetes is considered one of the most important health emergencies worldwide and Egypt has 8.2 million diabetic patients according to the International Diabetes Federation report in 2017. The objective of this study was to monitor the time-course variation in the metabolic profile of diabetic rats to detect urinary metabolic biomarkers using the metabolomics approach. Type 2 diabetes was induced in male Wistar albino rats using a single intraperitoneal injection of 40 mg/kg of streptozotocin following oral administration of 10% fructose in drinking water for 3 weeks. Then, urine was collected for 24 h from rats at three time points (0, 2, and 4 weeks after confirmation of diabetes), and were analyzed by nuclear magnetic resonance (H1 -NMR), followed by multivariate data analysis. The results from H1 -NMR pointed out that d-glucose, taurine, l-carnitine, l-fucose, 1,5-anhydrosorbitol, and d-galactose levels showed consistent significant variation (p < 0.05) between the positive (diabetic) and negative (normal) controls during the whole experimental period. Also, with the disease progression, myoinositol, and l-phenylalanine levels were significantly altered (p < 0.05) after 2 weeks and this alteration was maintained till the end of the 4-week experimental period in the positive control group. From the results of the present study, it could be concluded that we cannot depend only on glucose levels for prognostic purposes since there are other metabolic disturbances in diabetes which need to be tracked for better disease prognosis.

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.

Dietary influence on urinary excretion of 3-deoxyglucosone and its metabolite 3-deoxyfructose.

3-Deoxyglucosone (3-DG), a reactive 1,2-dicarbonyl compound derived from d-glucose in food and in vivo, is an important precursor for advanced glycation endproducts (AGEs). At present, virtually no information about the metabolic transit of dietary 3-DG is available. One possible metabolic pathway of 3-DG during digestion is enzymatic transformation to less reactive compounds such as 3-deoxyfructose (3-DF). To study the handling of dietary 1,2-dicarbonyl compounds by the human body, 24 h urinary excretion of 3-DG and its metabolite, 3-deoxyfructose, was investigated. Urinary 3-DG and 3-DF excretion was monitored for nine healthy volunteers following either a diet with no dietary restrictions or a diet avoiding the ingestion of 3-DG and other Maillard reaction products ("raw food" diet). During the "raw food" diet, the urinary 3-DG and 3-DF excretion decreased approximately to 50% compared to the excretions during the diet with no restrictions. When subjects received a single dose of wild honey (50 g) naturally containing a defined amount of 3-DG (505 µmol), median excretion of 3-DG and 3-DF increased significantly from 4.6 and 77 to 7.5 and 147 µmol/day, respectively. The obtained experimental data for the first time demonstrate a dietary influence on urinary 3-DG and 3-DF levels in healthy human subjects.

Analysis of metabolism of 6FDG: a PET glucose transport tracer.

INTRODUCTION: We are developing (18)F-labeled 6-fluoro-6-deoxy-D-glucose ([(18)F]6FDG) as a tracer of glucose transport. As part of this process it is important to characterize and quantify putative metabolites. In contrast to the ubiquitous positron emission tomography (PET) tracer (18)F-labeled 2-fluoro-2-deoxy-D-glucose ([(18)F]2FDG) which is phosphorylated and trapped intracellularly, the substitution of fluorine for a hydroxyl group at carbon-6 in [(18)F]6FDG should prevent its phosphorylation. Consequently, [(18)F]6FDG has the potential to trace the transport step of glucose metabolism without the confounding effects of phosphorylation and subsequent steps of metabolism. Herein the focus is to determine whether, and the degree to which, [(18)F]6FDG remains unchanged following intravenous injection. METHODS: Biodistribution studies were performed using 6FDG labeled with (18)F or with the longer-lived radionuclides (3)H and (14)C. Tissues were harvested at 1, 6, and 24 h following intravenous administration and radioactivity was extracted from the tissues and analyzed using a combination of ion exchange columns, high-performance liquid chromatography, and chemical reactivity. RESULTS: At the 1 h time-point, the vast majority of radioactivity in the liver, brain, heart, skeletal muscle, and blood was identified as 6FDG. At the 6-h and 24-h time points, there was evidence of a minor amount of radioactive material that appeared to be 6-fluoro-6-deoxy-D-sorbitol and possibly 6-fluoro-6-deoxy-D-gluconic acid. CONCLUSION: On the time scale typical of PET imaging studies radioactive metabolites of [(18)F]6FDG are negligible.

Evaluation of serum and urine 1,5-anhydro-D-glucitol and myo-inositol concentrations in healthy dogs.

1,5-anhydro-D-glucitol (1,5AG) is a pyranoid polyol compound found in human circulating blood. Myo-inositol (MI) is a stereoisomer of inositol and serves as a precursor of inositol phospholipids. 1,5AG and MI are filtered by the glomerulus and almost completely reabsorbed through the renal tubules. However, under hyperglycemic conditions, reabsorption through the renal tubules is competitively inhibited because the structures of 1,5AG and MI resemble that of glucose. In this study, we investigated the kinetics of serum and urine 1,5AG and MI levels in healthy dogs. We demonstrated that 1,5AG and MI exist in canine serum and urine by gas chromatography-mass spectrometry. Under continuous hyperglycemic conditions, the serum 1,5AG concentration in healthy dogs decreased while the serum MI concentration remained unchanged. Urinary excretion of 1,5AG and MI increased significantly after blood glucose concentrations reached 200 to 220 mg/dl. A significant negative correlation was observed between serum 1,5AG and glucose concentrations during hyperglycemia. However, no significant correlation was observed between serum MI and glucose concentrations. In this study, we demonstrated that serum and urine 1,5AG and MI levels were changed by blood glucose concentrations. The serum 1,5AG concentration was decreased by continuous hyperglycemia. However, the serum MI concentration does not reflect hyperglycemia.

Plasma and urinary HPLC-ED determination of the ratio of 8-OHdG/2-dG in Parkinson's disease.

BACKGROUND: Oxidative stress may be directly or indirectly involved in the pathogenesis of Parkinson's disease (PD). 8-hydroxy-2'deoxyguanosine (8-OHdG) is the major product of DNA oxidative damage but its determination in plasma or urine may have controversial significance. The concentration of 8-OHdG not only depends on its oxidation rate but also on the efficacy of the DNA repairing systems. METHODS: We studied the ratio between 8-OHdG and 2-dG (the corresponding not hydroxylated base 2'-deoxyguanosine) in plasma and urine as a marker of oxydative stress in PD. This enabled the determination of the real DNA damage in terms of oxidation rate regardless of the efficacy of the DNA repairing mechanisms. RESULTS: We optimized two different analytical methods: one for 8-OHdG and the other for 2-dG, both based on a common preliminary solid-phase extraction step (SPE) followed by two different HPLC analytical separations with electrochemical detection (HPLC-ED). The reliability of these methods was confirmed by analysing plasma and urine samples collected in parkinsonian patients and in age-matched healthy control subjects. CONCLUSIONS: In urine samples, the measurement of 8-OHdG alone as well as the ratio 8-OHdG/2-dG were significantly different in healthy controls and PD patients. In plasma samples, only the ratio 8-OHdG/2-dG was significantly higher in PD compared to healthy controls showing that the ratio 8-OHdG/2-dG is a reliable diagnostic tool in studies on DNA oxydative damage.

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.

Different effects of two alpha-glucosidase inhibitors, acarbose and voglibose, on serum 1,5-anhydroglucitol (1,5AG) level.

Serum 1,5-anhydroglucitol (1,5AG) is a useful glycemic marker in the control of diabetes; however, treated with alpha-glucosidase inhibitors (alpha-GIs), acarbose (Aca) and voglibose (Vog), it tends to show the discrepancy between serum 1,5AG and related glucose levels. Twenty patients were randomly assigned to adding Aca or Vog to the current treatment. We measured serum 1,5AG levels and other parameters of diabetic control before, 2 and 4 weeks after the alpha-GI treatment. We also measured urinary 1,5AG levels using gas chromatography/mass spectrometry (GC/MS). Glycated albumin, Hb(A1c), and fasting plasma glucose (FPG) levels were significantly decreased after 2 and 4 weeks of treatment, and the changes were similar in the two groups. Despite the similar urinary excretion of 1,5AG and other glycemic parameters, serum 1,5AG level was significantly lower in the Aca group than in the Vog group (3.4+/-0.5 vs. 7.9+/-1.2 microg/ml, P<.005; mean+/-S.E.) at the period of 4 weeks. Even in the same glycemic level, the less increase of serum 1,5AG after treatment with Aca might be due to a reduction of intestinal 1,5AG absorption via inhibition of alpha-amylase that features Aca.

Serum concentration and renal handling of 1,5-anhydro-D-glucitol in patients with chronic renal failure.

We measured serum and urinary 1,5-anhydro-D-glucitol (1,5-AG) during a glucose tolerance test (GTT) in patients with chronic renal failure (CRF) and compared the fractional excretion of 1,5-AG (FEAG) with that of diabetes mellitus (DM) patients and healthy controls. The mean serum 1,5-AG in CRF patients [60 +/- 23(SE) mumol/L] was significantly lower than in controls (155 +/- 7 mumol/L) in spite of a normal glycaemia. The levels in the CRF group were similar to those in the DM group. During GTT, the blood glucose profile in the CRF group was not significantly different from that of the control group, and urinary glucose excretion was negligible. However, FEAG was significantly higher in CRF patients than in controls. These data suggest that serum 1,5-AG in patients with CRF decreases due to a decrease in 1,5-AG reabsorption, independently of glucose excretion, and that serum and/or urinary 1,5-AG can be a useful marker for renal tubular dysfunction because the 1,5-AG reabsorption system is more vulnerable than the glucose reabsorption system.

Preliminary assessment of fluorine-18 fluorodeoxyglucose positron emission tomography in patients with bladder cancer.

The purpose of this study was to assess the feasibility of imaging of bladder cancer with fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) scanning. We studied 12 patients with histologically proven bladder cancer who had undergone surgical procedures and/or radiotherapy. Retrograde irrigation of the urinary bladder with 1000-3710 ml saline was performed during nine of the studies. Dynamic and static PET images were obtained, and standardized uptake value images were reconstructed. FDG-PET scanning was true-positive in eight patients (66.7%), but false-negative in four (33.3%). Of 20 organs with tumor mass lesions confirmed pathologically or clinically, 16 (80%) were detected by FDG-PET scanning. FDG-PET scanning detected all of 17 distant metastatic lesions and two of three proven regional lymph node metastases. FDG-PET was also capable of differentiating viable recurrent bladder cancer from radiation-induced alterations in two patients. In conclusion, these preliminary data indicate the feasibility of FDG-PET imaging in patients with bladder cancer, although a major remaining pitfall is intense FDG accumulation in the urine.

Quantification of 1,5-anhydro-D-glucitol in urine by automated borate complex anion-exchange chromatography with an immobilized enzyme reactor.

HPLC using a borate form of a strongly anion-exchange resin column and an immobilized enzyme reactor for colorimetric detection was used to quantify urinary 1,5-anhydro-D-glucitol. Urine samples were introduced into the system every 7 min without any pretreatment, and after separation of interfering substances in the column, 1,5-anhydro-D-glucitol was successively detected. Quantitative determination of urinary 1,5-anhydro-D-glucitol was possible within the 1.2-300 micromol/l range. The coefficient of variance was less than 3% and the correlation between results obtained with our system (y) and those obtained by gas chromatography-mass spectrometry (x) was y=0.983x-1.287 micromol/l (n=42, r=0.998).

Common reabsorption system of 1,5-anhydro-D-glucitol, fructose, and mannose in rat renal tubule.

1,5-Anhydro-D-glucitol (AG) is a major polyol, 99.9% of which is reabsorbed by the kidney. However, such reabsorption is inhibited by competition with glucose excreted in excess, i.e., glucosuria. Under such conditions, AG is excreted into the urine. We administered various types of sugars to rats by continuous intravenous infusion for two hours to evaluate the competition between AG and these sugars for renal reabsorption in vivo. The reabsorption of AG was significantly inhibited by competition with fructose and mannose. The excretion of AG in the 120 min after a load of 3.64 mmol of fructose was 1.99 +/- 0.33 mumol, that after 3.64 mmol of mannose loading was 2.34 +/- 0.43 mumol. These levels were comparable to the AG excretion observed after the administration of the same amount of glucose (3.87 +/- 0.61 mumol). No competition was observed with sucrose, xylose, myoinositol or galactose. The reabsorption of fructose and mannose was significantly inhibited by the presence of AG (P < 0.001) after a mixed load. Results suggest that AG is reabsorbed in the renal tubule by an AG/fructose/mannose-common transport system that is distinct from the major glucose reabsorption system. These findings may help to clarify the specific transport systems for various sugars in the renal tubule, as well as their physiological importance.

Prolonged hyperalimentation as a possible cause of renal tubular dysfunction: evaluation of 1,5-anhydro-D-glucitol resorption and N-acetylglucosaminidase excretion in humans.

1. A major polyol found in the sera and other tissues of humans, 1,5-anhydro-D-glucitol, is mainly ingested in the diet and is excreted in urine. We compared the influence of the long-term administration of total parenteral nutrition free of 1,5-anhydro-D-glucitol with that of total enteral nutrition on the serum level of 1,5-anhydro-D-glucitol in 46 patients who could not take food by mouth. 2. The serum concentration of 1,5-anhydro-D-glucitol and its kinetics remained unchanged in the group receiving total enteral nutrition (n = 21) over a period of 12 months. However, after 1 month on total parenteral nutrition (n = 25), the serum level of 1,5-anhydro-D-glucitol decreased, falling to about one-sixth the pretreatment level in the 12th month. Because the serum level of 1,5-anhydro-D-glucitol continued to decline, falling below the limit at which its renal reabsorption is normally activated, this decrease did not seem to be caused directly by a nutritional deficiency of this substance. 3. The urinary excretion of 1,5-anhydro-D-glucitol was closely correlated (r = 0.792) with that of N-acetyl-beta-glucosaminidase; but not with the serum creatinine level or of the urinary excretion of microalbumin or of urinary beta 2-microglobulin. We observed no glucosuria, hyperuricuria or changes in serum electrolytes during total parenteral nutrition. 4. The reduction in the serum level of 1,5-anhydro-D-glucitol and the urinary excretion of N-acetyl-beta-glucosaminidase were correlated with the duration of total parenteral nutrition administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum 1,5-anhydroglucitol (1,5 AG): new clinical marker for glycemic control.

We review the use of 1,5-anhydroglucitol (1,5 AG) in diagnosing and monitoring patients with diabetes. This six-carbon chain monosaccharide is one of the major polyols present in humans. Its concentration in serum is normally about 12 to 40 micrograms/ml. This substance is derived mainly from food, is well absorbed in the intestine, and is distributed to all organs and tissues. It is metabolically stable, being excreted in the urine when its level exceeds the renal threshold. It is reabsorbed in the renal tubules, and is competitively inhibited by glucosuria, which leads to a reduction in its level in serum. The correlation between this reduction and the amount of glucose present in urine is so close that 1,5 AG can be used as a sensitive, day-to-day, real-time marker of glycemic control. It provides useful information on current glycemic control and is superior to both HbA1c and fructosamine in detecting near-normoglycemia.

A new method of quantitating serum and urinary levels of 1,5-anhydroglucitol in insulin-dependent diabetes mellitus.

A new method was developed for quantitating the serum and urinary levels of 1,5-anhydroglucitol (AG), a sensitive and informative marker of glycemic control. This method utilized a combination of ODS and pyranose oxidase-immobilized columns for HPLC, and monitored hydrogen peroxide production with an electrochemical detector. We applied this method to determine the serum and urinary AG levels in 15 patients with insulin-dependent diabetes mellitus (IDDM) as well as in control subjects. Baseline separation of AG from other sugars such as glucose and myoinositol was achieved. Quantitation of AG was achieved over the range from 0.2 ng to 0.3 micrograms based upon peak heights. The serum and urinary AG levels in the IDDM patients were 4.4 +/- 8.3 mg/l and 5.1 +/- 4.3 mg/day, respectively. We found that the urinary AG to serum AG ratio showed a linear correlation with the urinary glucose level in the IDDM patients (urinary glucose (y) vs. urinary AG to serum AG ratio (x): y = 9.071x-0.991; r = 0.968, P < 0.001). This method proved efficient and reliable for quantitating urinary AG. Since determination of both the AG and glucose levels in urine gives equivalent clinical information to the serum AG level, urinary monitoring could provide a valuable addition to the available methods for assessing the glycemic status of IDDM patients.

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.

Origin and disposal of 1,5-anhydroglucitol, a major polyol in the human body.

The origin and disposal of 1,5-anhydro-D-glucitol (AG), one of the main polyols found in the human body, was studied in normal subjects and diabetic patients. AG was detected in various kinds of foods. The mean AG supplement through foods was estimated to be approximately 4.38 mg/day, which was compatible with that calculated in a food analysis (average 0.22 mg AG/100 kcal in Japanese foods) on eight healthy subjects. The mean AG excretion in urine was approximately 4.76 mg/day in these subjects. Excretion into stools was negligible. From observations on the patients without oral supplement of AG, 0.4 mg of daily de novo synthesis of AG was strongly suggested. It was also implied that urinary AG excretion occurred soon after food ingestion and that its amount was closely correlated with daily supplement through foods. Thus the fundamental kinetics of AG were recognized as follows: 1) AG in the body originates mainly from foods and is well absorbed in the intestine, 2) AG is little degraded and metabolized in the body, and 3) an equilibrium exists between oral supplement plus a small but steady amount of de novo synthesis and excretion in urine.

Detection of 3-deoxyfructose and 3-deoxyglucosone in human urine and plasma: evidence for intermediate stages of the Maillard reaction in vivo.

3-Deoxyglucose (3-deoxy-D-erythro-hexos-2-ulose) (3-DG) is a reactive dicarbonyl intermediate involved in the polymerization and browning of proteins by glucose in vitro. Damage to protein by formation of 3-DG in vivo is thought to be limited by enzymes which convert 3-DG to less reactive species, such as 3-deoxyfructose (3-DF). We have developed a sensitive and specific assay for measuring 3-DG and 3-DF in human urine and plasma. In this assay, 3-DG and 3-DF are reduced to 3-deoxy-hexitols (3-DH), using either NaBH4 or NaBD4, and then analyzed by selected ion monitoring gas chromatography-mass spectrometry. Based on comparative analysis of samples reduced with NaBD4 versus NaBD4, 3-DH in urine was derived exclusively (greater than 99%) from 3-DF, while 3-DG accounted for approximately 15% of 3-DH in plasma. The concentrations of 3-DH in fasting human urine and plasma were 5.3 +/- 1.5 micrograms/mg creatinine (n = 18) and 7.2 +/- 1.7 micrograms/dl (n = 18), respectively. The concentrations of 3-DG and 3-DF in plasma (n = 7) were 1.0 +/- 0.2 and 6.7 +/- 1.6 micrograms/dl, respectively. These results suggest that several milligrams of 3-DG are formed in the body per day and detoxified by reduction to 3-DF and support the role of 3-DG as an intermediate in the browning of protein via the Maillard reaction in vivo.