Variation in polyol levels in cerebrospinal fluid and serum in diabetic patients

Serum Levels of Myo-inositol Predicts Clinical Outcome 1 Year After Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Early prognostication of long-term outcome in patients suffering from spontaneous subarachnoid hemorrhage (SAH) remains a challenge. No biomarkers are routinely used for prognostication. A previous study has indicated that the metabolite myo-inositol (MI) may be used to predict long-term outcome.

OBJECTIVE

To investigate if MI measured in serum correlates with long-term clinical outcome in patients suffering from SAH.

METHODS

We conducted an observational cohort study including 88 patients treated for SAH at Umeå University Hospital. Serum samples were collected in the hospital, and a gas chromatography/mass spectroscopy method was used to quantitatively measure MI. Patients were assessed after 1 year using the Glasgow Outcome Scale Extended and dichotomized to favorable or unfavorable outcome. Differences in MI levels between the 2 groups were analyzed.

RESULTS

There was no difference in MI levels between the groups upon admission. Myo-inositol levels decreased over time in the entire study population. The decrease was significantly larger in the unfavorable outcome group. A receiver operating characteristics analysis yielded an area under the curve of 0.903 (CI 0.8-1.0, P < .001) for the MI value on day 7 to predict favorable outcome after 1 year.

CONCLUSION

Myo-inositol measured in serum may aid prognostication of outcome in patients with SAH. The mechanism behind this remains unclear, although it can be theorized to reflect processes leading to delayed cerebral ischemia, which affects long-term outcome. This is the first study to quantitively measure MI in serum for prognostication of outcome in patients with SAH.

Solute Carrier Transporters as Potential Targets for the Treatment of Metabolic Disease

The solute carrier (SLC) superfamily comprises more than 400 transport proteins mediating the influx and efflux of substances such as ions, nucleotides, and sugars across biological membranes. Over 80 SLC transporters have been linked to human diseases, including obesity and type 2 diabetes (T2D). This observation highlights the importance of SLCs for human (patho)physiology. Yet, only a small number of SLC proteins are validated drug targets. The most recent drug class approved for the treatment of T2D targets sodium-glucose cotransporter 2, product of the SLC5A2 gene. There is great interest in identifying other SLC transporters as potential targets for the treatment of metabolic diseases. Finding better treatments will prove essential in future years, given the enormous personal and socioeconomic burden posed by more than 500 million patients with T2D by 2040 worldwide. In this review, we summarize the evidence for SLC transporters as target structures in metabolic disease. To this end, we identified SLC13A5/sodium-coupled citrate transporter, and recent proof-of-concept studies confirm its therapeutic potential in T2D and nonalcoholic fatty liver disease. Further SLC transporters were linked in multiple genome-wide association studies to T2D or related metabolic disorders. In addition to presenting better-characterized potential therapeutic targets, we discuss the likely unnoticed link between other SLC transporters and metabolic disease. Recognition of their potential may promote research on these proteins for future medical management of human metabolic diseases such as obesity, fatty liver disease, and T2D. SIGNIFICANCE STATEMENT: Given the fact that the prevalence of human metabolic diseases such as obesity and type 2 diabetes has dramatically risen, pharmacological intervention will be a key future approach to managing their burden and reducing mortality. In this review, we present the evidence for solute carrier (SLC) genes associated with human metabolic diseases and discuss the potential of SLC transporters as therapeutic target structures.

Hypothesis: A Novel Neuroprotective Role for Glucose-6-phosphatase (G6PC3) in Brain-To Maintain Energy-Dependent Functions Including Cognitive Processes

The isoform of glucose-6-phosphatase in liver, G6PC1, has a major role in whole-body glucose homeostasis, whereas G6PC3 is widely distributed among organs but has poorly-understood functions. A recent, elegant analysis of neutrophil dysfunction in G6PC3-deficient patients revealed G6PC3 is a neutrophil metabolite repair enzyme that hydrolyzes 1,5-anhydroglucitol-6-phosphate, a toxic metabolite derived from a glucose analog present in food. These patients exhibit a spectrum of phenotypic characteristics and some have learning disabilities, revealing a potential linkage between cognitive processes and G6PC3 activity. Previously-debated and discounted functions for brain G6PC3 include causing an ATP-consuming futile cycle that interferes with metabolic brain imaging assays and a nutritional role involving astrocyte-neuron glucose-lactate trafficking. Detailed analysis of the anhydroglucitol literature reveals that it competes with glucose for transport into brain, is present in human cerebrospinal fluid, and is phosphorylated by hexokinase. Anhydroglucitol-6-phosphate is present in rodent brain and other organs where its accumulation can inhibit hexokinase by competition with ATP. Calculated hexokinase inhibition indicates that energetics of brain and erythrocytes would be more adversely affected by anhydroglucitol-6-phosphate accumulation than heart. These findings strongly support the paradigm-shifting hypothesis that brain G6PC3 removes a toxic metabolite, thereby maintaining brain glucose metabolism- and ATP-dependent functions, including cognitive processes.

Development of an organ bath technique for isolated rat pancreas preparations to assess the effect of 1,5-AG on insulin secretion

To investigate substances related to insulin secretion, we reported a convenient experimental method to reproduce insulin secretion from isolated rat pancreas preparations using an organ bath. While the method has experimental utility for investigating insulin secretion, optimization of the experimental design is still needed. The level of insulin outflow in the control decreased over time in our previous study. Decreasing serum 1,5-anhydroglucitol (1,5-AG) levels is also known to be shown in patients with worsening glycemic control. There is one in vitro report demonstrated that 1,5-AG induced insulin release. It appears that discussion needs to be deepened further on it. In this study, we investigated the effect of 1,5-AG on insulin secretion through to optimize the condition of endocrine function using the ex vivo organ bath technique. The level of insulin outflow in the control and 1,5-AG groups decreased over time in the organ bath experiment. To analyze the effect of trypsin on reduced insulin secretion, pancreas preparation was treated with soybean trypsin inhibitor (TI). Insulin outflow levels of the TI group were significantly higher than the control group. An enzyme indicator of tissue damage tended to be lower in the TI group. There was no significant enhancement of insulin secretion by 1,5-AG. The present study demonstrated the utility of TI application for the organ bath technique. This finding supported the development of an organ bath technique for the assessment of the effects of novel therapeutics on insulin secretion.

Vitreous humor endogenous compounds analysis for post-mortem forensic investigation

The chemical and biochemical analysis of bodily fluids after death is an important thanatochemical approach to assess the cause and time since death. Vitreous humor (VH) has been used as a biofluid for forensic purposes since the 1960s. Due to its established relevance in toxicology, a literature review highlighting the use of VH with an emphasis on endogenous compounds has not yet been undertaken. VH is a chemically complex aqueous solution of carbohydrates, proteins, electrolytes and other small molecules present in living organisms; this biofluid is useful tool for its isolated environment, preserved from bacterial contamination, decomposition, autolysis, and metabolic reactions. The post-mortem analysis of VH provides an important tool for the estimation of the post-mortem interval (PMI), which can be helpful in determining the cause of death. Consequently, the present review evaluates the recent chemical and biochemical advances with particular importance on the endogenous compounds present at the time of death and their modification over time, which are valuable for the PMI prediction and to identify the cause of death.

Reference intervals for serum 1,5-anhydroglucitol in children, adolescents, adults, and pregnant women

BACKGROUND

1,5-anhydroglucitol (1,5-AG) is a validated marker of short-term glycemic control. We determined the reference intervals of 1,5-AG in different age groups and during pregnancy.

METHODS

Blood samples were collected from 2303 Euro-Brazilian healthy subjects: 580 children, 496 adolescents, 922 adults matched by age and sex, and 305 pregnant women in four gestational periods. Serum 1,5-AG was measured using an enzymatic reagent in an automated system.

RESULTS

The calculated reference intervals (nonparametric, 2.5th-97.5th) for males and females were, respectively: children, 96-302 and 89-277 μmol/l; adolescents, 84-311 and 79-277 μmol/l; and adults, 80-260 and 62-241 μmol/l. Males consistently showed significantly higher concentrations than females. 1,5-AG reference intervals in pregnant women were 56-298 μmol/l at <23 weeks gestation (n = 110), 37-166 μmol/l at 24-28 weeks gestation (n = 106), 34-155 μmol/l at 29-32 weeks gestation (n = 52), and 33-246 μmol/l at >32 weeks gestation (n = 37). No significant differences in 1,5-AG concentration were observed between non-pregnant and pregnant women at <23 weeks of gestation. A negative correlation (r = -0.287; p < .001) between 1,5-AG concentration and age was observed.

CONCLUSIONS

The reference intervals for 1,5-AG were affected by sex and age.

Pharmacodynamics and pharmacokinetics of inositol(s) in health and disease

INTRODUCTION

Inositol and its derivatives comprise a huge field of biology. Myo-inositol is not only a prominent component of membrane-incorporated phosphatidylinositol, but participates in its free form, with its isomers or its phosphate derivatives, to a multitude of cellular processes, including ion channel permeability, metabolic homeostasis, mRNA export and translation, cytoskeleton remodeling, stress response.

AREAS COVERED

Bioavailability, safety, uptake and metabolism of inositol is discussed emphasizing the complexity of interconnected pathways leading to phosphoinositides, inositol phosphates and more complex molecules, like glycosyl-phosphatidylinositols.

EXPERT OPINION

Besides being a structural element, myo-inositol exerts unexpected functions, mostly unknown. However, several reports indicate that inositol plays a key role during phenotypic transitions and developmental phases. Furthermore, dysfunctions in the regulation of inositol metabolism have been implicated in several chronic diseases. Clinical trials using inositol in pharmacological doses provide amazing results in the management of gynecological diseases, respiratory stress syndrome, Alzheimer's disease, metabolic syndrome, and cancer, for which conventional treatments are disappointing. However, despite the widespread studies carried out to identify inositol-based effects, no comprehensive understanding of inositol-based mechanisms has been achieved. An integrated metabolomics-genomic study to identify the cellular fate of therapeutically administered myo-inositol and its genomic/enzymatic targets is urgently warranted.

The role of inositol and the principles of labelling, extraction, and analysis of inositides in mammalian cells

Inositides have an important impact on diverse areas of cellular regulation. However, since this area has grown exponentially from the mid 1980s onwards, many workers find themselves relatively new to the field. In this chapter, we establish a broad foundation for the rest of the book by covering some important principles of inositide methodologies. The focus is especially directed to those methods or aspects of methodology not covered in detail in other chapters. This includes the often neglected influence of the inositide precursor, inositol, and important background information relating to the labelling and extraction of inositides from cells and tissues. This introductory section also gives a "birds eye" view of important methods and protocols found within this volume and hopefully acts as a touchstone to assess which of the methodologies described within this book is most appropriate for your particular study(ies) of inositides.

Cerebrospinal fluid sorbitol and myoinositol in diabetic polyneuropathy

Changes in cerebrospinal fluid (CSF) concentrations of sorbitol and myoinositol in 21 patients with diabetic polyneuropathy were studied with gas-liquid chromatography. The sorbitol concentration was significantly increased in diabetic patients with elevated plasma glucose. Myoinositol concentration was significantly decreased in patients with polyneuropathy compared with the controls. Both alterations in polyol concentrations of the CSF were present already two months from onset of symptoms of diabetes. Patients with peripheral polyneuropathy receiving oral hypoglycemic drugs did not have elevated plasma glucose and CSF sorbitol levels, but showed significantly decreased CSF myoinositol concentrations compared with the controls. These observations suggest that myoinositol concentration may be decreased in the central nervous system in adult onset mild diabetes with normal plasma glucose and that the decrease in the myoinositol in CSF possibly is connected with the development of neuropathy.

Relationship of cerebrospinal fluid glucose metabolites to MRI deep white matter hyperintensities and treatment resistance in bipolar disorder patients

OBJECTIVES

Both diabetes mellitus and magnetic resonance image (MRI) deep white matter hyperintensities (WMHs) are more common in bipolar disorder (BD) patients than in matched controls. Deep-as opposed to periventricular--WMHs and diabetes are associated with treatment resistance and poorer outcome. This study investigated whether brain glucose metabolism by the polyol pathway--a pathway linked to nervous tissue disease in diabetes--is related to deep WMH volume and treatment resistance in BD patients.

METHODS

Volumes of fluid-attenuated inversion recovery WMHs were quantified and correlated with cerebrospinal fluid (CSF) concentrations of glucose metabolites in 20 nondiabetic patients with BD and nondiabetic comparison subjects with schizophrenia (n = 15) or transient neurologic symptoms (neurologic controls, n = 15).

RESULTS

BD patients, but not schizophrenic patients, had significantly greater volumes of deep but not periventricular WMHs compared to neurologic controls. BD subjects also had significantly greater CSF concentrations of sorbitol and fructose (the polyol pathway metabolites of glucose) compared to controls. Significant positive correlations between CSF metabolites and WMH volumes were found only in the BD group and were between deep WMH volumes and CSF sorbitol (rho = 0.487, p = 0.029) and fructose (rho = 0.474, p = 0.035). An index of treatment resistance correlated significantly with deep WMH volume (rho = 0.578, p = 0.008), sorbitol (rho = 0.542, p = 0.013), and fructose (rho = 0.692, p = 0.001) in BD subjects but not in other subjects.

CONCLUSIONS

This is the first reported evidence of relationships between abnormal brain glucose metabolism and both deep WMHs and treatment resistance in a group of BD patients. Further studies are necessary to determine the significance of these findings to BD pathophysiology.

1,5-anhydroglucitol monitoring in diabetes: a mass balance perspective

1,5-anhydroglucitol (AG) is a nonmetabolizable glucose analogue found in plasma due to ingestion. The normal steady-state concentration can be dramatically decreased by inhibition of tubular reabsorption during periods of hyperglycemia. For this reason, monitoring of AG has been plausibly advocated for detection of periodic glucosuric hyperglycemia. In this review, we examine the influence of variation in factors affecting both steady-state and transient changes in plasma AG. Among normals, the lower and upper limits of the plasma AG reference range vary by a factor of 5. Using a simplified mass balance model (a single compartment model with 3-6x larger-than-plasma volume of distribution), reasonable inter-individual variations of ingestion rate, glomerular filtration rate and fractional post-filtration reabsorption are each able to account for the wide range of normal, steady-state AG concentrations. In monitoring of changes in AG, inter-individual variations in the threshold for glucose excretion, volume of distribution and glomerular filtration rate are all likely to significantly affect correspondence of integral changes in AG to integral glucosuria/hyperglycemia. This combination of variables, affecting both steady-state and transient changes, is significantly confounding with respect to interpretation of serial plasma AG concentrations. Resolution of information content of AG monitoring is thus largely that of crossing simple characterization of deltas [+,0,-] for changes in AG concentration against the information content of hemoglobin A1c monitoring. Despite this limitation, AG monitoring can in principle provide information about glycemic control in the short term that is not apparent through monitoring of hemoglobin A1c alone. However, whether AG monitoring can lead to improved outcomes in diabetes management remains to be established.

A novel fully enzymatic method for determining glucose and 1,5-anhydro-D-glucitol in serum of one cuvette

The aim of the study was to set up a novel fully enzymatic method for screening glucose and 1,5-anhydro-D-glucitol (1,5-AG) in one cuvette. We have determined glucose and 1,5-AG, based on glucokinase (GK) converting glucose to G6P, a compound that can be catalyzed ultimately into 6-PGA by G-6PD and its coenzyme NADP(+), and then calculated glucose concentration according to absorbance variety. Furthermore, pyranose oxidase was used to oxidize 1,5-AG with the formation of 1, 5-anhydro-fructose and H(2)O(2). Measurement was done according to Trinder's reaction principle. The mean within-run and day-to-day precision (CV) of this method for glucose was 0.88% and 1.4%, and also that for 1,5-AG was 1.05% and 1.94%, respectively. The mean recovery rate of two targets was 100.2% and 101.6%, respectively. The correlation (R(2)) between the results of 1,5-AG obtained with our proposed method (y) and those obtained with LanaAG method (x) was 0.999 (y=1.002x-0.675 micromol/l; n=86), and the correlation (R(2)) of glucose between the results obtained with our GK method (y) and those obtained with recommendatory hexokinase method (x) was 0.9999 (y=1.0043x+0.1229 mmol/l; n=86). The reference range (95%) of serological glucose and 1,5-AG was 3.7 to 5.7 mmol/l (4.70+/-0.51 mmol/l) and 83.1 to 240.7 micromol/l (161.9+/-40.2 micromol/l), respectively; and there was no difference with age and sex (P>0.05). This newly developed method was dependable and steady-going, with analysis automatization, and allows quicker and easier measurement of serum glucose and 1,5-AG in one identical reaction cuvette in-phase than previously described methods.

Novel sites of aldose reductase immunolocalization in normal and streptozotocin-diabetic rats

Glucose metabolism by aldose reductase (AR) is implicated in the pathogenesis of many diabetic complications, including neuropathy. We have re-evaluated the distribution of AR in the sciatic nerve and dorsal root ganglion (DRG) of normal rats, expanded these observations to describe the location of AR in the spinal cord and footpad skin, and investigated whether diabetes alters the distribution of AR. In sciatic nerve, AR was restricted to cytoplasm of myelinated Schwann cells and endothelial cells of epineurial, but not endoneurial, blood vessels. AR immunoreactivity (IR) was present in satellite cells in the DRG. In skin, AR-IR was detected in vascular endothelial cells, Schwann cells of myelinated fibers, and axons of perivascular sympathetic nerves. AR was localized selectively to oligodendrocytes of the white matter of spinal cord. The distribution of AR-IR in sciatic nerve, DRG, skin, and spinal cord was not altered by up to 12 weeks of streptozotocin-induced diabetes. Identification of perineuronal satellite cells, oligodendrocytes, and perivascular sympathetic nerves as AR-expressing cells reveals them as cellular sites with the potential to contribute to diabetic neuropathy.

Relationship of white matter hyperintensities to cerebrospinal fluid glucose polyol pathway metabolites-a pilot study in treatment-resistant affective disorder patients

BACKGROUND

Magnetic resonance imaging (MRI) white matter hyperintensities (WMHs) are found at higher rates in patients with affective disorders, particularly late-life or treatment-resistant disorders. Studies support a vascular pathogenesis for WMHs in late-life onset disorders; however, pathogenesis in typical early-life onset disorders is less clear. Based on associations between diabetes mellitus and both WMHs and affective disorders, this study investigated the relationship between WMHs and brain glucose metabolism by the polyol pathway-a pathway linked to nervous tissue disease in diabetes.

METHODS

Burdens of fluid-attenuated inversion recovery (FLAIR) WMHs were quantified and correlated with cerebrospinal fluid (CSF) concentrations of glucose metabolites in 10 nondiabetic inpatients with treatment-resistant bipolar, unipolar, and schizoaffective disorders and 10 nondiabetic control patients who had been investigated clinically for transient neurological symptoms.

RESULTS

Deep but not periventricular WMH burden correlated positively and significantly with elevated CSF concentrations of sorbitol, the specific polyol pathway metabolite of glucose (rho=0.86, p=0.002), in the affective disorders but not the control group.

LIMITATIONS

This was a pilot study with a relatively small number of subjects; therefore, conclusions are tentative. Controls were not healthy subjects; they were patients with transient neurological symptoms.

CONCLUSIONS

This is the first reported evidence of a relationship between WMHs and increased brain glucose metabolism by the polyol pathway in patients with affective disorders. More extensive studies are necessary to determine whether this preliminary finding represents a pathogenetic relationship.

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.

Clinical application of the serum 1,5-anhydroglucitol assay method using glucose 3-dehydrogenase

We attempted to develop a novel serum 1,5-anhydroglucitol (1,5-AG) assay kit using glucose 3-dehydrogenase (G3DH) from Halomonas sp. alpha-15 strain. The major advantages of this method are that the 1,5-AG detection requires a very small amount of G3DH, and the enzyme catalyzes a simple reaction. The analytical performances were acceptable for clinical use operated with a clinical automatic analyzer. The correlation with a commercial assay kit against sera of healthy volunteers was y=0.975x+0.008, r=0.993, Sylx=1.32 microg/mL. However, sham-negative specimens were observed in the validation of this method using specimens from hospital patients.

The predictive value of serum 1,5-anhydro-D-glucitol in pregnancies at increased risk of gestational diabetes mellitus and gestational impaired glucose tolerance

The objective of the study was to determine the efficacy of 1,5-anhydro-D-glucitol (1,5 AG) for the prediction of gestational diabetes and gestational impaired glucose tolerance (GIGT). One hundred and eighty-five pregnant women with epidemiological risk factors of gestational diabetes or GIGT underwent 75 g oral glucose tolerance test and plasma 1,5 AG assay at 26 to 28 weeks of gestation. There was no significant difference in plasma 1,5 AG either before or after an oral glucose load. The area under the receiver operator characteristic curve for 1,5 AG was only 0.485 which implies that 1,5 AG is a poor predictor of GIGT or gestational diabetes.

Increases in 1,5-anhydroglucitol levels in germinating amaranth seeds and in ripening banana

To examine whether 1,5-anhydroglucitol (AG) is derived from starch degradation in plant tissues, we colorimetrically measured AG contents of germinating amaranth seeds and ripening banana pulp. In both cases, as starch degradation proceeded, AG levels were significantly increased, but were 1,700-5,000 times lower than those of total soluble carbohydrates. alpha-1,4-Glucan lyase activity, which is measured by the 1,5-anhydrofructose (AF) liberated from non-reducing glucose residues of starch or glycogen, was too low to be detected in amaranth or banana by the 3,5-dinitrosalicylic acid method. On the other hand, AF reductase, which reduces AF to AG, was detected in germinating amaranth seeds and banana pulp. Thus, the increases in AG levels are conceived to be derived from starch breakdown, although further investigation is needed to answer whether the starch degradation pathway via alpha-1,4-glucan lyase/AF reductase exists in plant tissues.

Plasma 1,5-anhydroglucitol concentrations are influenced by variations in the renal threshold for glucose

AIMS

Measurement of serum 1,5-anhydroglucitol (1,5AG) concentrations has been proposed as an alternative to HbA1c as both a marker of diabetic glycaemic control and as a screening test for diabetes. The sugar competes with glucose for renal tubular reabsorption, so hyperglycaemia leads to reduced serum 1,5AG concentrations through increased urinary loss. This study has sought to establish whether plasma 1,5AG can be influenced by not only hyperglycaemia, but by variations in renal threshold for glucose.

METHODS

Thirty-eight pregnant women (median age 30 years, range 20-43) found to be normoglycaemic after a 75-g carbohydrate load had plasma 1,5AG and urine glucose measured.

RESULTS

Using multivariate analysis, the presence and degree of detectable glycosuria at 2 h post glucose load was strongly predictive of a low plasma 1,5AG concentration (P=0.0012) independently of fasting plasma glucose (P=0.96), 2 h glucose (P=0.029), subject age (P=0.97) and gestation (P=0.36). Thus, when matched for plasma glucose areas under the glucose load curve, 16 glycosuric subjects had significantly lower 1,5AG concentrations compared to 16 nonglycosuric ones (median 1,5AG 46 micromol/l (IQR 30-56) vs. 72 micromol/l (IQR 55-79, P=0.017).

CONCLUSIONS

People with the same glucose tolerance may demonstrate variable plasma 1,5AG concentrations depending on their renal threshold for glucose. This inherent characteristic is likely to limit the usefulness of the test when monitoring or screening for diabetes.

A kinetic mass balance model for 1,5-anhydroglucitol: applications to monitoring of glycemic control

The polyol 1,5-anhydroglucitol (AG) present in human plasma is derived largely from ingestion and is excreted unmetabolized. Reduction of plasma [AG] has been noted in diabetics and is due to accelerated excretion of AG during hyperglycemia. Plasma [AG] has therefore been proposed as a marker for glycemic control. A precise understanding of its utility relies on a quantitative understanding of the mass balance for AG. In this study, non-steady-state data from the literature were analyzed to develop a dynamic mass balance model for AG that is based on the two-compartment model proposed by Yamanouchi et al. [T. Yamanouchi, Y. Tachibana, H. Akanuma, S. Minoda, T. Shinohara, H. Moromizato, H. Miyashita, and I. Akaoka. Am. J. Physiol. 263 (Endocrinol. Metab. 26): E268-E273, 1992]. The data are consistent with a model in which exchange between tissue and plasma pools is rapid and in which the tissue compartment mass is two to three times the mass of the plasma compartment. According to model estimates, accelerated excretion of AG due to hyperglycemia can cause marked net depletion of total AG over a time scale of days. Recovery from a depleted state is slow because the total body capacity represents >5 wk of normal intake. Accordingly, AG monitoring should be able to indicate the presence of past glucosuric hyperglycemic episodes during a period of days to weeks, as well as provide information on the extent to which high deviations from the average plasma glucose concentration are operative.

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.

Purification of a marine bacterial glucose dehydrogenase from Cytophaga marinoflava and its application for measurement of 1,5-anhydro-D-glucitol

A novel glucose dehydrogenase (GDH) from a marine bacterium Cytophaga marinoflava IFO 14170 was isolated from its membrane fraction. This GDH catalyzes the oxidation of a hydroxy group of glucose, but does not react in its C-1 position. This enzyme is composed of a single peptide with a mol wt of 67,000. The GDH can react under high salinity. The optimum pH is around 8.0, showing typical property of marine bacterial enzymes. Using this novel enzyme, and enzymatic determination of 1,5-anhydro-D-glucitol (1,5AG) utilizing 2,6-dichrolophenolindophenol (DCIP) and phenazine methosulfate (PMS) as electron mediators was carried out. A good linear correlation was observed from 0.5 mM to 4 mM of 1,5AG.

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.

Conditional synthesis and utilization of 1,5-anhydroglucitol in Escherichia coli

A cyclic polyol, 1,5-anhydro-D-glucitol (AG), is widely detected in most organisms, although little is known about its metabolism and physiological roles. The present study demonstrates the synthesis of AG in Escherichia coli C600. The major portion of the synthesized AG was indicated to be derived from glucose retaining all the six carbon atoms, and only 5% was attributed to AG synthesized from C3 compounds. AG synthesis is apparent in an early stage of the stationary phase, and accumulation is transient both in cells and in medium. Evidence is also presented for AG uptake and metabolism and for effects of cyclic AMP.

Renal tubular reabsorption of 1,5-anhydro-D-glucitol and D-mannose in vivo in the rat

1,5-Anhydro-D-glucitol (AG) is efficiently reabsorbed in renal tubuli by a mechanism that is saturated at high AG concentrations. To gain insight into the stereospecific requirements of the mechanism, we employed an in vivo loading test technique in which rats were injected with anhydrosugars and aldohexoses in doses that led to excretion of the sugar injected, thus saturating tubular reabsorption. Administration of AG elicited an increase in the excretion of D-mannose (P less than 0.0005), while D-mannose caused AG to appear in urine. Administration of 1,5-anhydro-D-mannitol led to increased excretion of D-mannose (P less than 0.0005) and the appearance of AG in urine. The effects of 1,5-anhydro-D-mannitol on the excretion of D-mannose and AG, and the effect of D-mannose on AG were dependent on the dose. Myoinositiol, mannitol and C-3-C-6 epimers of AG did not interfere with the reabsorption. The mechanism was highly phlorizin-sensitive. Repeated administration of 1,5-anhydro-D-mannitol rapidly depleted the rat organism from mobilizable AG. The AG space calculated (53% of body weight) suggested the presence of considerable cellular stores of AG. D-Mannose and AG are regular components of the plasma monosaccharide profile. The data suggest that the two sugars are reabsorbed in renal tubuli by a common mechanism, which is distinct from the main D-glucose reabsorption system. The presence of a glucose-type C-3-C-6 and pyranose structure is required for a sugar to be transported by the system.(ABSTRACT TRUNCATED AT 250 WORDS)

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

This paper describes a high performance liquid chromatographic (HPLC) method for determining 1,5-anhydroglucitol in plasma, in which anion exchange chromatography and pulsed amperometric detection are used. Plasma samples deproteinized with trichloroacetic acid are passed through a three-layer column packed with (1) strongly basic anion (BO3(3-) form, the upper layer), (2) strongly basic anion (OH- form, the middle layer) and (3) strongly acidic cation (H+ form, the lower layer) exchange resins. 1,5-Anhydroglucitol is efficiently recovered in the flow-through fraction and interfering substances are completely removed by the column treatment. The analytical response of the method is linear with concentration to 40 mg/L, and it is possible to detect as little as 0.1 mg 1,5-anhydroglucitol per litre of plasma. Analytical recovery is between 96 and 103%, and there is good agreement between the results measured by our method and by a gas/liquid chromatographic method (r = 0.998). The method has been successfully used for the determination of very low 1,5-anhydroglucitol concentrations (less than 1 mg/L) in the plasma of diabetic patients.

Plasma 1,5-anhydroglucitol in experimental galactosemia in the rat

Feeding with a galactose-rich diet induced a substantial drop in blood plasma 1,5-anhydroglucitol concentration. The decline was proportional to the dose of galactose. The decline was less marked in xylose-fed rats.

Urinary excretion of 1,5-anhydro-D-glucitol accompanying glucose excretion in diabetic patients

The urinary excretion of 1,5-anhydro-D-glucitol, a pyranoid polyol, in humans was studied. The plasma of nondiabetic human subjects contained high concentrations of this polyol (greater than 110 mumol/l), and there was a tendency for the 24-h excretion of it to become more variable in direct proportion to its plasma concentration. In contrast, diabetic patients showed lower plasma concentrations of this polyol, and the variation in the 24-h excretion of 1,5-anhydro-D-glucitol was especially notable among the patients with an extremely low plasma concentration of the polyol. This diabetic group showed a statistically significant correlation (p less than 0.01), between the urinary 1,5-anhydro-D-glucitol and urinary glucose. This correlation was more markedly demonstrated during a 100-g oral glucose tolerance test: parallel changes were observed in the concentrations of 1,5-anhydro-D-glucitol and glucose in the urine collected every hour after the glucose load. These observations led to the proposal that low plasma concentration of this polyol, which is observed in diabetes mellitus, may be the result of a frequent and/or prolonged high blood glucose concentration beyond the renal threshold for glucose excretion.

Reduction of plasma 1,5-anhydroglucitol (1-deoxyglucose) concentration in diabetic patients

The plasma concentration of 1,5-anhydro-D-glucitol(AG)(1-deoxyglucose) is known to decrease in diabetic patients. In order to evaluate the usefulness of this polyol as a diabetic marker, we examined the specificity of the plasma AG reduction in various diseases: the plasma AG level was determined in 108 newly diagnosed diabetic patients, 229 normal subjects and 200 patients with various other disorders. The mean plasma AG concentration in diabetes mellitus was 1.9 +/- 1.8 micrograms/ml (mean +/- SD), which was definitely lower than that in healthy subjects and patients with other diseases including some metabolic and hormonal diseases (mean value range: 13.4-28.3 micrograms/ml). Only the "malignancies" group showed statistically different mean values from that in normal subjects; however, these values were much higher than those of diabetic patients. The AG concentration seemed to be relatively low in some severe by uraemic patients, but is likely to be little influenced by the glomerular filtration rate. Upon adjustment for sex and age, AG concentration was not found to be correlated with the degree of obesity in both healthy subjects and diabetic patients. The plasma AG concentration showed a tendency to be higher in healthy males than in healthy females in all age-matched groups; however, statistically significant differences were not seen. Also, no significant influence of age was observed.

Myo-inositol enhances the proliferation of human endothelial cells in culture but fails to prevent the delay induced by high glucose

Evidence is accumulating, indicating that the abnormal metabolic milieu of diabetes might interfere with orderly replication of some cellular systems and in vitro studies point to a causal contribution of elevated glucose. We had previously shown that human umbilical vein endothelial cells cultured in 20 mmol/L glucose are delayed in achieving saturation density primarily as a consequence of decreased cellular proliferation. We have now addressed whether depletion of myo-inositol--a prevailing consequence of hyperglycemia in other tissues and overcome by provision of supplemental inositol--might play a role in the observed replicative abnormality. Control cultures (5 mmol/L glucose) displayed a dose-dependent response to myo-inositol supplementation that was maximal at concentrations (40 mumol/L) matching physiologic serum levels. The increment in cell number was (mean +/- SD) 141 +/- 20% of control (P less than 0.001), and saturation density was achieved at a cell number 160% higher than in nonsupplemented cultures. Thymidine incorporation and cell cycle studies documented that myo-inositol increased the number of cells cycle studies documented that myo-inositol increased the number of cells engaged in DNA synthesis. These effects of myo-inositol, as well as the dose-response relationship between ambient inositol levels and increments in cell number, were not significantly modified by 20 mmol/L glucose with the exceptions of a transient lesser effect of the physiologic doses during rapid proliferation (day 6) and a larger effect of all doses of myo-inositol in later stages of growth curve (day 12).(ABSTRACT TRUNCATED AT 250 WORDS)

An enzymatic fluorimetric assay for myo-inositol

An enzymatic assay for myo-inositol (MI) is described. The method is based on the oxidation of MI by NAD+-dependent myo-inositol dehydrogenase, coupled to reoxidation of NADH with oxalacetate and malate dehydrogenase. The resultant malate is measured fluorimetrically. Several variations of the assay are described for measuring MI in serum and in tissues in amounts ranging from 0.2 pmol to 8 nmol. Highest sensitivity is achieved by applying an oil-well technique for handling small droplets, and by using the principle of enzymatic cycling. The potential of the technique is illustrated by MI measurements in several tissues of normal and diabetic rats and Chinese hamsters.

The elimination of 1,5-anhydroglucitol administered to rats

Rat serum contains natural 1,5-anhydroglucitol. Injected or orally administered 1,5-anhydroglucitol was efficiently reabsorbed by the renal tubuli via a mechanism which had a saturation point at high serum 1,5- anhydroglucitol levels. The compound had a slow turnover rate in the body; its half-life is approximately 3 days. The compound was readily absorbed in the gut when administered orally.

Oral supplementation of myoinositol: effects on peripheral nerve function in human diabetics and on the concentration in plasma, erythrocytes, urine and muscle tissue in human diabetics and normals

28 young diabetics with short disease duration participated in a double-blind study by taking 6 g of myoinositol or placebo daily for 2 months. The aim was to demonstrate a possible beneficial effect of this compound on subclinical diabetic neuropathy. Measurement of vibratory perception threshold, motor and sensory conduction velocity and amplitude of nerve potential did not disclose any effect of the myoinositol given. In accordance with this, no indication for a lack of myoinositol in human diabetic blood or tissue could be found. The concentration of myoinositol in the plasma and erythrocyte of 4 human diabetics was normal or high, even though the loss of urinary myoinositol was greater than in the case of 4 normals. Further, an analysis of the content of free and lipid-bound myoinositol in muscle biopsies taken from the 4 diabetics did not give any indication of deficiency. The content of myoinositol in their muscle tissue remained uninfluenced by oral supplementation of myoinositol.

Enzyme relationships in a sorbitol pathway that bypasses glycolysis and pentose phosphates in glucose metabolism

A pathway from glucose via sorbitol bypasses the control points of hexokinase and phosphofructokinase in glucose metabolism. It also may produce glycerol, linking the bypass to lipid synthesis. Utilization of this bypass is favored by a plentiful supply of glucose--hence, conditions under which glycolysis also is active. The bypass further involves oxidation of NADPH, so the pentose phosphate pathway and the bypass are mutually facilitative. Possible consequences in different organs under normal and pathological, especially diabetic, conditions are detailed. Enzymes with related structures (for example, sorbitol dehydrogenase and alcohol dehydrogenase, and possibly, aldehyde reductase and aldose reductase, respectively) are linked functionally by this scheme. Some enzymes of the bypass also feature in glycolysis (aldolase and alcohol dehydrogenase), and these enzymes, with the reductases involved, are proteins known to occur in different classes or multiple isozyme forms. Two of the enzymes (aldolase and alcohol dehydrogenase) both involve classes with and without a catalytic metal (zinc). The existence of parallel pathways and the occurrence of similar enzymic steps in one pathway may help to explain the abundance and multiplicity of enzymes such as reductases, aldolases, and alcohol dehydrogenases.

Serum 1,5-anhydroglucitol in normal subjects and in patients with insulin-dependent diabetes mellitus

The serum levels of 1,5-anhydroglucitol were measured by gas chromatography in normal subjects and in patients with type 1 (insulin-dependent) diabetes mellitus and compared with those found in some other common diseases. The identity of the compound was checked by thin-layer chromatography and by means of mass fragmentography. The mean level was 81 mumol/l (range 10-146 mumol/l, n = 139) in normal subjects and comparable levels were found in patients with rheumatic disease (n = 20) and in several patients with circulatory diseases. The level was less than 10 mumol/l in 44 patients with insulin-dependent diabetes mellitus, both in newly diagnosed cases and in patients with a long history of the disease with or without nephropathy. The compound did not appear in serum during near normoglycaemic periods elicited by continuous subcutaneous insulin infusion therapy, nor after successful kidney transplantation.

Gas chromatographic mass spectrometric determination of myo-inositol in humans utilizing a deuterated internal standard

The isotopic dilution technique was used for determining the content of myo-inositol in human urine, plasma and haemolysed erythrocyte samples. A deuterated myo-inositol, synthesized from inosose-2 by base-catalysed exchange of hydrogens by deuterium, followed by reduction of the inosose with 2H2, was added as internal standard to the samples at an early stage in the analytical procedure. After separation and derivatization to the hexa-acetate, the gas chromatographic mass spectrometric analysis was carried out. A 25 m fused silica capillary column coated with methyl silicone was used, and the ions selected for monitoring were m/z 210 and m/z 214, which are characteristic and abundant fragment ions from unlabelled and hexadeuterated myo-inositolhexa-acetate, respectively. Calibration curves from water, urine, plasma and haemolysed erythrocytes show parallel, linear responses in the ratio between analyte and internal standard in the area of interest (0.2-2.0).

Localization of aldose reductase and sorbitol dehydrogenase in the nervous system of normal and diabetic rats

Intraneuronal accumulations of sorbitol and fructose have been postulated to predispose the nervous system to the cerebral edema associated with the treatment of diabetic ketoacidosis. In the present study, the enzymes of the pathway for the production of sorbitol and fructose, aldose reductase and sorbitol dehydrogenase, were localized histochemically in brain, spinal cord and sciatic nerve. Enzyme activity was limited to the choroidal epithelium, ependymal cells, and pia mater in normal, 2- and 10-week streptozotocin diabetic and vehicle-treated rats. Sorbitol dehydrogenase activity was located in blood vessels and perineurium of the sciatic nerve in these groups of rats. Comparison of diabetic and vehicle groups did not demonstrate any alteration in the activity of either enzyme in the central nervous system. However, there was a decrease in sorbitol dehydrogenase activity in the blood vessels in the sciatic nerve in 50% of the 10-week diabetic rats.

Identification of 1,5-anhydroglucitol in thin-layer chromatograms

The chromatographical characteristics of 1,5-anhydroglucitol in thin-layer chromatograms can be studied using the customary carbohydrate solvents. Both hydrogen peroxide and sodium metaperiodate oxidation reactions were tested in order to find a specific colour reaction for the detection of the compound. 1,5-anhydroglucitol was readily converted by periodate into an intermediate product which produced an intense orange-red colour with diphenylamine aniline reagent. According to data obtained from periodate oxidation, IR spectroscopy and mass fragmentography, the intermediate product was a dialdehyde compound with a C6 structure, possibly formed through cleavage at C2-C3. The formation of a compound of this kind without chain cleavage in the periodate oxidation of C6 carbohydrates is uncommon. Periodate oxidation followed by diphenylamine-aniline reaction affords a sensitive and specific method for the detection of 1,5-anhydroglucitol.

Polyols in the cerebrospinal fluid and plasma of neurological, diabetic and uraemic patients

Five polyols, arabinitol, anhydroglucitol, mannitol, sorbitol and myoinositol, normally present in the cerebrospinal fluid (CSF), were studied. Quantitative gas-liquid chromatographic analysis of 211 CSF and 112 plasma samples indicated significantly altered concentrations in several clinical conditions. All five polyols were decreased in the CSF of patients suffering from meningitis, cerebral atrophy, sepsis, and in patients receiving intrathecal cytostate therapy. Equilibration between plasma and CSF may explain the changes in sepsis and meningitis, while decreased total number of functioning cells may cause the decrease in cerebral atrophy. Intrathecal cytostates seem to have a destroying effect on the cell metabolism of the central nervous system. Renal failure causes accumulation of polyols in the plasma. Alterations in the metabolism of sorbitol, myoinositol and anhydroglucitol seem to be present in diabetes. The plasma concentration of anhydroglucitol is decreased in renal failure.

Gas chromatographic separation and mass spectrometric identification of polyols in human cerebrospinal fluid and plasma

Seven polyols, erythritol, arabinitol, anhydroflucitol, mannitol, sorbitol, myoinositol and possibly ribitol were identified in human cerebrospinal fluid by means of gas-liquid chromatography and mass spectrometry. Quantitative data were obtained for five polyols, arabinitol, anhydroglucitol, mannitol, sorbitol and myoinositol, by screening of 205 CSF samples. These five polyols represented 90-95 per cent of the polyol-concentration which was 340 +/- 105 mumol/1 in the total series. The concentration of polyols in the CSF was two times higher than that in the plasma (148 +/- 30 mumol/1), where only anhydroglucitol and myoinositol could be quantitated. The variations noted were not associated with age, sex or the plasma concentrations of polyols. The polyols of the CSF most likely originate from brain tissue and/or spinal cord since penetration from the plasma against a gradient seems unlikely.

Accumulation of myoinositol in plasma and red cells of diabetic patients

The concentration of myoinositol in plasma, cerebrospinal fluid and red cells and its elimination by the kidneys have been studied in 51 diabetic patients with normal or impaired kidney function, 16 non-diabetic patients with renal failure and 37 healthy controls. All diabetic patients who had a glomerular filtration rate considerably below normal, was the plasma concentration of myoinositol higher than in controls. The findings show that the rise in plasma concentration of myoinositol most probably results from a decreased glomerular filtration rate. In diabetic patients, urinary excretion of myoinositol correlated with an exponential increase in glucose excretion. That myoinositol accumulates in red cells of diabetic patients may be the result of its retention within these cells caused primarily by a transient, abnormal increase in the plasma concentration of myoinositol after an average meal.