A review of glycated albumin as an intermediate glycation index for controlling diabetes

Studies of drug interactions with glycated human serum albumin by high-performance affinity chromatography

Diabetes is a health condition associated with elevated levels of glucose in the bloodstream and affects 366 million people worldwide. Type II diabetes is often treated with sulfonylurea drugs, which are known to bind tightly in blood to the transport protein human serum albumin (HSA). One consequence of the elevated levels of glucose in diabetes is the non-enzymatic glycation of proteins such as HSA. Several areas of HSA are now known to be affected by glycation-related modifications, which may in turn affect the binding of sulfonylurea drugs and other solutes to this protein. This review discusses some recent studies that have examined these changes in drug-protein binding by employing high-performance affinity chromatography (HPAC). A description of the theoretical and experimental techniques that were used in these studies is given. The information on drug interactions with glycated HSA, as obtained through this method, is also summarized. In addition, the potential advantages of this approach in the areas of biointeraction analysis and personalized medicine are considered.

Tandem mass spectral libraries of peptides in digests of individual proteins: Human Serum Albumin (HSA)

This work presents a method for creating a mass spectral library containing tandem spectra of identifiable peptide ions in the tryptic digestion of a single protein. Human serum albumin (HSA(1)) was selected for this purpose owing to its ubiquity, high level of characterization and availability of digest data. The underlying experimental data consisted of ∼3000 one-dimensional LC-ESI-MS/MS runs with ion-trap fragmentation. In order to generate a wide range of peptides, studies covered a broad set of instrument and digestion conditions using multiple sources of HSA and trypsin. Computer methods were developed to enable the reliable identification and reference spectrum extraction of all peptide ions identifiable by current sequence search methods. This process made use of both MS2 (tandem) spectra and MS1 (electrospray) data. Identified spectra were generated for 2918 different peptide ions, using a variety of manually-validated filters to ensure spectrum quality and identification reliability. The resulting library was composed of 10% conventional tryptic and 29% semitryptic peptide ions, along with 42% tryptic peptide ions with known or unknown modifications, which included both analytical artifacts and post-translational modifications (PTMs) present in the original HSA. The remaining 19% contained unexpected missed-cleavages or were under/over alkylated. The methods described can be extended to create equivalent spectral libraries for any target protein. Such libraries have a number of applications in addition to their known advantages of speed and sensitivity, including the ready re-identification of known PTMs, rejection of artifact spectra and a means of assessing sample and digestion quality.

Introduction of glycated albumin measurement for all blood donors and the prevalence of a high glycated albumin level in Japan

(J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00224.x, 2012) Aims/Introduction:  The Japanese Red Cross Society introduced measurement of glycated albumin (GA) for all blood donors as a glycemic control marker. The GA levels were examined by sex and age.

MATERIALS AND METHODS

  GA was measured in 3.14 million blood donors who donated between April 2009 and March 2010. For the reference range for GA, values that were three times the reference range for glycated hemoglobin (Japan Diabetes Society value) were used. All donors were notified of their GA levels. For repeat donors, a comparison was made between the GA levels at the first and second donations to verify the GA change after notification.

RESULTS

  The mean GA was significantly lower in males than in females in donors aged <60 years. The mean GAs of both sexes increased with age and reached the same level of 14.8% in their 60s. The percentage of donors with prediabetes/diabetes (GA ≥16.5%) was 2.8% in males and 2.3% in females. In the normal high group (15.6% ≤ GA < 16.5%), the mean GA at the second donation was lower by 0.20% than at the first donation. In 42.4% of these donors, GA decreased to the normal range at the second donation.

CONCLUSIONS

  Overall, 2.7% of otherwise healthy Japanese blood donors had a high GA (GA ≥16.5%). Donor blood screening for GA represents an effective measure to identify people at risk of diabetes. The decrease in the GA level after GA notification might indicate the potential usefulness of this strategy to improve glycemic control among people with high GA.

Prediction of near-future glycated hemoglobin levels using glycated albumin levels before and after treatment for diabetes

Aims/Introduction:  In the present study, whether near‐future glycated hemoglobin (A1C) levels could be predicted by changes in glycated albumin (GA) levels before and after treatment for diabetes was investigated.

Materials and Methods:  After starting diabetes treatment, GA and A1C levels are assumed to change exponentially. From this assumption, the equation for predicting near‐future GA and A1C levels was derived. A total of 54 patients with type 2 diabetes mellitus in whom diabetes treatment was initiated or altered were enrolled. By incorporating GA and A1C values before and 2–4 weeks after starting treatment (second visit) into the equation, the predicted GA and A1C levels at the third visit (5–7 weeks after treatment) were obtained.

Results:  A strong and positive correlation was observed between predicted GA and measured GA at the third visit (R = 0.669, P < 0.0001). Similarly, a strong and positive correlation was observed between the predicted A1C and the measured A1C at the third visit (R = 0.795, P < 0.0001).

Conclusions:  GA and A1C levels 1–3 months after starting diabetes treatment could be predicted using the equation developed. The prediction of near‐future A1C levels using GA levels at two points would be useful for judging the effectiveness of ongoing diabetes treatment at an earlier stage. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00107.x, 2011)

Glycated albumin: an overview of the In Vitro models of an In Vivo potential disease marker

Glycation is a general spontaneous process in proteins which has significant impact on their physical and functional properties. These changes in protein properties could be related to several pathological consequences such as cataract, arteriosclerosis and Alzheimer's disease. Among the proteins, glycation of Human serum albumin (HSA) is of special interest. Human serum albumin is the most abundant protein in the plasma and because of its high sensitivity for glycation, undergoes structural and functional changes due to binding of reducing sugars in vitro. The glycation process occurs by plasma glucose in vivo which has great impacts on the three dimensional structure of protein. These changes are efficient and stable enough which makes the protein to be considered as a new special disease marker instead of HbA1C for diabetes. In some cases, glycated albumin was used as an alternative marker for glycemic control. Glycated albumin reacts with glucose ten times more rapidly than HbA1C and has shorter half-life which makes it more reliable for indicating glycemic states. In this review, glycation of Human Serum Albumin has been overviewed, starting from overall concepts of glycation, followed by some Examples of pathological consequences of protein glycation. The BSA aggregation was reviewed in terms of structural and biological impacts of glycation on the protein followed by reporting documents which indicate possibility of glycated albumin to be used as specific marker for diabetes. Finally, some of the studies related to the models of glycated albumin have been briefly described, with an emphasis on In vitro studies. It is interesting to note the relationship found between in vitro glycation experiments and the propensity of proteins to form amyloid structures, a point that could be further explored as to its significance in hyperglycemic states.

Inhibition of nonenzymatic protein glycation by pomegranate and other fruit juices

The nonenzymatic glycation of proteins and the formation of advanced glycation endproducts in diabetes leads to the crosslinking of proteins and disease complications. Our study sought to demonstrate the effect of commonly consumed juices (pomegranate, cranberry, black cherry, pineapple, apple, and Concord grape) on the fructose-mediated glycation of albumin. Albumin glycation decreased by 98% in the presence of 10 μL of pomegranate juice/mL; other juices inhibited glycation by only 20%. Pomegranate juice produced the greatest inhibition on protein glycation when incubated at both the same phenolic concentration and the same antioxidant potential. Both punicalagin and ellagic acid significantly inhibited the glycation of albumin by ~90% at 5 μg/mL. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that pomegranate, but not apple juice, protected albumin from modification. These results demonstrate that pomegranate juice and two of its major constituents are potent inhibitors of fructose-mediated protein glycation.

Effects of Fatty Acids and Glycation on Drug Interactions with Human Serum Albumin

The presence of elevated glucose concentrations in diabetes is a metabolic change that leads to an increase in the amount of non-enzymatic glycation that occurs for serum proteins. One protein that is affected by this process is the main serum protein, human serum albumin (HSA), which is also an important carrier agent for many drugs and fatty acids in the circulatory system. Sulfonylureas drugs, used to treat type 2 diabetes, are known to have significant binding to HSA. This study employed ultrafiltration and high-performance affinity chromatography to examine the effects of HSA glycation on the interactions of several sulfonylurea drugs (i.e., acetohexamide, tolbutamide and gliclazide) with fatty acids, whose concentrations in serum are also affected by diabetes. Similar overall changes in binding were noted for these drugs with normal HSA or glycated HSA and in the presence of the fatty acids. For most of the tested drugs, the addition of physiological levels of the fatty acids to normal HSA and glycated HSA produced weaker binding. At low fatty acid concentrations, many of these systems followed a direct competition model while others involved a mixed-mode interaction. In some cases, there was a change in the interaction mechanism between normal HSA and glycated HSA, as seen with linoleic acid. Systems with only direct competition also gave notable changes in the affinities of fatty acids at their sites of drug competition when comparing normal HSA and glycated HSA. This research demonstrated the importance of considering how changes in the concentrations and types of metabolites (e.g., in this case, glucose and fatty acids) can alter the function of a protein such as HSA and its ability to interact with drugs or other agents.

Review: Glycation of human serum albumin

Glycation involves the non-enzymatic addition of reducing sugars and/or their reactive degradation products to amine groups on proteins. This process is promoted by the presence of elevated blood glucose concentrations in diabetes and occurs with various proteins that include human serum albumin (HSA). This review examines work that has been conducted in the study and analysis of glycated HSA. The general structure and properties of HSA are discussed, along with the reactions that can lead to modification of this protein during glycation. The use of glycated HSA as a short-to-intermediate term marker for glycemic control in diabetes is examined, and approaches that have been utilized for measuring glycated HSA are summarized. Structural studies of glycated HSA are reviewed, as acquired for both in vivo and in vitro glycated HSA, along with data that have been obtained on the rate and thermodynamics of HSA glycation. In addition, this review considers various studies that have investigated the effects of glycation on the binding of HSA with drugs, fatty acids and other solutes and the potential clinical significance of these effects.

Role of oxidative stress in physiological albumin glycation: a neglected interaction

Protein glycation is a key mechanism involved in chronic disease development in both diabetic and nondiabetic individuals. About 12-18% of circulating proteins are glycated in vivo in normoglycemic blood, but in vitro studies have hitherto failed to demonstrate glucose-driven glycation below a concentration of 30mM. Bovine serum albumin (BSA), reduced BSA (mercaptalbumin) (both 40g/L), and human plasma were incubated with glucose concentrations of 0-30mM for 4 weeks at 37°C. All were tested preoxidized for 8h before glycation with 10nM H2O2 or continuously exposed to 10nM H2O2 throughout the incubation period. Fructosamine was measured (nitroblue tetrazolium method) at 2 and 4 weeks. Oxidized BSA (both preoxidized and continuously exposed to H2O2) was more readily glycated than native BSA at all glucose concentrations (p = 0.03). Moreover, only oxidized BSA was glycated at physiological glucose concentration (5mM) compared to glucose-free control (glycation increased by 35% compared to native albumin, p < 0.05). Both 5 and 10mM glucose led to higher glycation when mercaptalbumin was oxidized than when unoxidized (p < 0.05). Fructosamine concentration in human plasma was also significantly higher when oxidized and exposed to 5mM glucose, compared to unoxidized plasma (p = 0.03). The interaction between glucose concentration and oxidation was significant in all protein models (p < 0.05). This study has for the first time demonstrated albumin glycation in vitro, using physiological concentrations of albumin, glucose, and hydrogen peroxide, identifying low-grade oxidative stress as a key element early in the glycation process.

Clinical, pathophysiological and structure/function consequences of modification of albumin by Amadori-glucose adducts

BACKGROUND

The nonenzymatic condensation of glucose with albumin results in the formation of albumin modified by Amadori glucose adducts, the principal form in which glycated albumin exists in vivo.

SCOPE OF REVIEW

This review focuses on (a) the utility of measurement of Amadori-modified glycated albumin (AGA) as a biomarker in diabetes, where elevated levels attend the hyperglycemic state; (b) the role of AGA as a causal factor in the pathogenesis of complications of diabetes; (c) effects on transport properties; and (d) structural and functional consequences of the modification of albumin by Amadori glucose adducts. It does not discuss counterparts with respect to Advanced Glycation Endproducts (AGE), which may be found in other publications.

MAJOR CONCLUSIONS

Nonenzymatic glycation of albumin, which is increased in diabetes, has clinical relevance and pathophysiologic importance, with ramifications for the management of this disease, the development of its complications, and the transport of endogenous and exogenous ligands.

GENERAL SIGNIFICANCE

Appreciation of the manifold consequences of AGA has afforded new avenues for assessing clinical management of diabetes, awareness of the impact of nonenzymatic glycation on albumin biology, insights into the pathogenesis of vascular complications of diabetes, and avenues of investigation of and intervention strategies for these complications. This article is part of a Special Issue on albumin. This article is part of a Special Issue entitled Serum Albumin.

Evaluation of biological variation of glycated albumin (GA) and fructosamine in healthy subjects

BACKGROUND

Glycated albumin (GA) and fructosamine are nonenzymatically glycated proteins still frequently utilized for monitoring glycemic control in diabetics. To investigate the analytical variation and the degree of individuality of these glycemic markers, we have performed an experimental study under a well designed and standardized protocol.

METHODS

We collected five specimens from each of 18 apparently healthy subjects (9 men and 9 women, ages 26-52 years), on the same day, every two weeks for two months. Samples were stored at -80°C until analysis and assayed in duplicate in a single analytical run. GA and fructosamine were measured using enzymatic (Lucica®GA-L, Asahi Kasei Pharma, AKP, Tokyo, Japan) and colorimetric assays, respectively, on a Modular P Roche system (Roche Diagnostics GmbH, Mannheim, Germany). Data were analyzed by ANOVA.

RESULTS

Analytical coefficient of variation (CVA) was 1.7%, 2.3% and 2.8% for GA, albumin and fructosamine, respectively. Within-subject (CVW) and between-subject (CVG) coefficients of variation were 2.1% and 10.6% for GA, 2.3% and 2.9% for albumin, and 2.3% and 6.3% for fructosamine. The estimated critical difference (CD) was 7.5% for GA, 9% for albumin and 10% for fructosamine.

CONCLUSIONS

The good quality achieved by the analytical method for GA assessment and the reduced within-subject biological variation would allow to recommend this test in clinical practice for evaluation of glycemic control along with measurement of glycated hemoglobin.

Investigation of non-enzymatic glycosylation of human serum albumin using ion trap-time of flight mass spectrometry

Non-enzymatic glycosylation or glycation involves covalent attachment of reducing sugar residues to proteins without enzyme participation. Glycation of glucose to human serum albumin in vivo is related to diabetes and many other diseases. We present an approach using liquid chromatography coupled to an electrospray ionization source of a hybrid ion trap-time of flight (IT-TOF-MS/MS) tandem mass spectrometer to identify the glycation sites on serum albumin from both a healthy person and a diabetic patient. The MetID software, which is commonly used for screening metabolites, is adapted for peptide fingerprinting based on both m/z values and isotopic distribution profiles. A total of 21 glycation sites from the healthy person and 16 glycation sites from the diabetic patient were identified successfully. We also demonstrate the use of matrix assisted laser desorption ionization-time of flight mass spectrometry to estimate the incorporation ratio of glucose to albumin during glycation. Results from this study show that the glycation in healthy person is more complicated than previously thought. Further analysis of incorporation ratio distribution may be necessary to accurately reflect the change of serum albumin glycation in diabetic patients.

Impaired drug-binding capacities of in vitro and in vivo glycated albumin

Albumin, the major circulating protein in blood, can undergo increased glycation in diabetes. One of the main properties of this plasma protein is its strong affinity to bind many therapeutic drugs, including warfarin and ketoprofen. In this study, we investigated whether or not there were any significant changes related to in vitro or in vivo glycation in the structural properties and the binding of human albumin to both therapeutic drugs. Structural parameters, including redox state and ketoamine contents of in vitro and in vivo glycated purified albumins, were investigated in parallel with their affinity for warfarin and ketoprofen. High-performance liquid chromatography was used to determine the free drug concentrations and dissociation constants according to the Scatchard method. An alternative method based on fluorescence spectroscopy was also used to assess drug-binding properties. Oxidation and glycation levels were found to be enhanced in albumin purified from diabetic patients or glycated with glucose or methylglyoxal, after determination of their ketoamine, free thiol, amino group and carbonyl contents. In parallel, significant impairments in the binding affinity of in vitro and in vivo glycated albumin, as indicated by the higher dissociation constant values and confirmed by higher free drug fractions, were observed. To a lesser extent, this alteration also significantly affected diabetic albumin affinity, indicated by a lower static quenching in fluorescence spectroscopy. This work provides useful information supporting in vivo diabetic albumin could be the best model of glycation for monitoring diabetic physiopathology and should be valuable to know if glycation of albumin could contribute to variability in drugs response during diabetes.

Estimating average glucose levels from glycated albumin in patients with end-stage renal disease

PURPOSE

In patients with diabetic end stage renal disease (ESRD), glycated albumin (GA) reflects recent glycemic control more accurately than glycated hemoglobin (HbA1c). We evaluated the relationship between GA and average blood glucose (AG) level and developed an estimating equation for translating GA values into easier-to-understand AG levels.

MATERIALS AND METHODS

A total of 185 ESRD patients, including 154 diabetic and 31 non-diabetic participants, were enrolled (108 hemodialysis, 77 peritoneal dialysis). Patients were asked to perform four-point daily self-monitoring of capillary blood glucose (SMBG) at least three consecutive days each week for four weeks. Serum levels of GA, HbA1c and other biochemical parameters were checked at baseline, as well as at 4 and 8 weeks.

RESULTS

Approximately 74.3±7.0 SMBG readings were obtained from each participant and mean AG was 169.1±48.2 mg/dL. The correlation coefficient between serum GA and AG levels (r=0.70, p<0.001) was higher than that of HbA1c and AG (r=0.54, p<0.001). Linear regression analysis yielded the following equation: estimated AG (eAG) (mg/dL)=4.71×GA%+73.35, and with this formula, serum GA levels could be easily translated to eAG levels. Multivariate analysis revealed significant contributions of postprandial hyperglycemia (β=0.25, p=0.03) and serum albumin (β=0.17, p=0.04) in determining serum GA level, independent to other clinical parameters.

CONCLUSION

Compared to HbA1c, serum GA levels were better correlated with AG levels. Using the estimating equation, an average blood glucose level of 155-160 mg/dL could be matched to a GA value of 18-19% in patients with ESRD.

The roles of glycated albumin as intermediate glycation index and pathogenic protein

The conventional glycemic indices used in management of diabetic patients includes A1c, fructosamine, 1,5-anhydroglucitol, and glycated albumin (GA). Among these indices, A1c is currently used as the gold standard. However, A1c cannot reflect the glycemic change over a relatively short period of time, and its accuracy is known to decrease when abnormalities in hemoglobin metabolism, such as anemia, coexist. When considering these weaknesses, there have been needs for finding a novel glycemic index for diagnosing and managing diabetes, as well as for predicting diabetic complications properly. Recently, several studies have suggested the potential of GA as an intermediate-term glycation index in covering the short-term effect of treatment. Furthermore, its role as a pathogenic protein affecting the worsening of diabetes and occurrence of diabetic complications is receiving attention as well. Therefore, in this article, we wanted to review the recent status of GA as a glycemic index and as a pathogenic protein.

Structural modifications of human albumin in diabetes

AIM

Albumin, a major protein in the blood circulation, can undergo increased glycation in diabetes. From recent studies, it has become evident that glycation has important implications for albumin actions and impact on cell functioning. This study compares the structural and functional properties of albumin glycated by glucose and methylglyoxal (MGO) with those of albumin purified from diabetic patients.

METHODS

Human serum albumin (HSA) was purified from diabetic patients and control subjects using affinity chromatography, and oxidation parameters in various albumin preparations were determined. Tryptophan and 1-anilino-8-naphthalene sulphonic acid (ANSA) probe fluorescence, redox state, antioxidant and copper-binding capacities of the different preparations of albumin were also determined and compared.

RESULTS

Occurrence of oxidative modifications was enhanced in albumin whether purified from diabetic patients, or glycated by glucose or MGO, after determination of their fructosamine and free thiol and amino group contents, carbonyl content and antioxidant activities. Whereas more quantitative changes in oxidative and structural parameters were observed in the glucose- and MGO-modified albumins, significant impairment of albumin function (free-radical-scavenging and copper-binding capacities) were demonstrated in the HSA purified from diabetics. These findings reveal different structural and functional features of diabetic HSA compared with in vitro models.

CONCLUSION

This study provides new information supporting albumin as an important biomarker for monitoring diabetic pathophysiology. In addition, it reconfirms the influence of experimental conditions in which advanced glycation end-products (AGEs) are generated in tests designed to mimic the pathological conditions of diabetes.

Spontaneous platelet aggregation evaluated by laser light scatter in patients with type 2 diabetes: effects of short-term improved glycemic control and adiponectin

Spontaneous platelet aggregation (SPA) is enhanced in patients with type 2 diabetes. Adiponectin may inhibit platelet aggregation. The aims of the current study were to identify factors associated with in vitro SPA measured by a laser light scattering method and to investigate the effects of short-term glycemic control and adiponectin on SPA. In study 1, we investigated platelet aggregation in 20 healthy control subjects and 82 patients with type 2 diabetes. In study 2, we evaluated the changes of SPA and serum high-molecular-weight (HMW) adiponectin after 2 weeks of improved glycemic control in 20 hospitalized diabetic patients. In study 3, using washed platelets from 10 healthy subjects, in vitro SPA was measured over 15 min in the absence or presence of recombinant adiponectin (20 μg/mL). Platelet aggregation was assessed with a laser light scatter aggregometer that measured the size of platelet aggregates. SPA was defined as formation of small aggregates under constant stirring in the absence of any agonists. The area under the curve was calculated for SPA and also for agonist-induced small, medium, and large aggregates. SPA was increased in diabetic patients compared with control subjects. In diabetic patients, SPA was correlated positively with plasma fibrinogen, fasting plasma glucose, glycated albumin, and high-sensitivity C-reactive protein. A stepwise multivariate analysis showed that plasma fibrinogen was the strongest independent determinant of SPA in diabetic patients. In 20 diabetic patients, SPA decreased significantly after 2 weeks of glycemic control. A significant negative correlation was found between changes of SPA and those of HMW adiponectin during treatment. The in vitro study showed that adiponectin inhibited the spontaneous aggregation of washed platelets. In conclusion, hyperfibrinogenemia and hyperglycemia are associated independently with SPA in patients with type 2 diabetes. SPA is reduced after even short-term improvement of glycemic control and adiponectin also inhibits SPA directly.

Evaluation of Aromatic Boronic Acids as Ligands for Measuring Diabetes Markers on Carbon Nanotube Field-Effect Transistors

Biomolecular detections performed on carbon nanotube field-effect transistors (CNT-FETs) frequently use reactive pyrenes as an anchor to tether bioactive ligands to the hydrophobic nanotubes. In this paper, we explore the possibility of directly using bioactive aromatic compounds themselves as CNT-FET ligands. This would be an efficient way to functionalize CNT-FETs since many aromatic compounds bind avidly to nanotubes, and it would also ensure that ligand-binding molecules would be brought in close proximity to the nanotubes. Using a model system consisting of pyrene, phenanthrene, naphthalene, or phenyl boronic acids immobilized on CNT-FET wafers, we show that all are able to bind glycated human serum albumin (gHSA), which is an important diabetes marker. Pyrene boronic acid proved to bind CNTs with the greatest apparent affinity as measured by gHSA impedance. Interestingly, gHSA CNT-FET signal intensity, which is proportional to amount of protein bound, remained essentially unchanged for all the boronic acids tested.

Reduction in glycated albumin can predict change in HbA1c: comparison of oral hypoglycaemic agent and insulin treatments

AIM

To investigate whether the change in glycated albumin 3 weeks after initiating anti-diabetes treatment (oral hypoglycaemic agent or insulin) could predict the corresponding change in HbA(1c) 3 months later in Korean patients with Type 2 diabetes.

METHODS

A total of 140 patients were enrolled into two groups: group I (insulin-based; n = 100) and group II (oral hypoglycaemic agent-based; n = 40). Both glycated albumin and HbA(1c) levels were measured as 'glucose control markers' during hospitalization. Glycated albumin was measured again at 3 weeks (first visit) after the initial measurement, and HbA(1c) was measured at 3 months (second visit) after the initial measurement.. The change in glucose control marker was defined as 100 × (follow-up glucose control marker--hospital glucose control marker)/hospital glucose control marker.

RESULTS

In both groups, the change in glycated albumin at the first visit and in HbA(1c) at the second visit showed a moderate linear relationship (r = 0.735; P < 0.01). In group II (r = 0.778; P < 0.01), a slightly stronger linear relationship was demonstrated than in group I (r = 0.738; P < 0.001); however, there was no statistically significant difference between the two groups. A correlation coefficient between the change in glycated albumin and HbA(1c) was not affected by sex, age, BMI, haemoglobin, serum creatinine or albumin.

CONCLUSION

The reduction in glycated albumin 3 weeks after the initiation of treatment corresponded with the reduction in HbA(1c) 3 months after starting treatment in both the group treated with a oral hypoglycaemic agent and the insulin-treated group of Korean patients with Type 2 diabetes.

Basic performance of an enzymatic method for glycated albumin and reference range determination

BACKGROUND

Glycated albumin (GA) is a medium-term glycemic control marker of diabetes and may be more sensitive to changes in plasma glucose than hemoglobin A1c. We studied where and how many fructosyl groups bind to albumin, and which glycation sites are measured by the enzymatic method for GA. We also studied the basic performance of the enzymatic method for GA.

METHODS

Glycated albumin was measured using an enzymatic method (Lucica®GA-L, Asahi Kasei Pharma) on a biochemical autoanalyzer. Molecular weights of purified GA and nonglycated albumin were measured by a mass spectrometry system. Two hundred one healthy volunteers with normal results of oral glucose tolerance testing were recruited to determine the reference range in Americans.

RESULTS

The present method measured only glycated amino acids from albumin in serum protein. We estimate that the number of glycated amino acids measured by this method was approximately two per molecule of albumin. The general performance (sensitivity, specificity, reproducibility, linearity, interference) of the method was good. The reference range of GA% in Americans with normal glucose tolerance was determined to be 11.9-15.8% (mean ± 2 standard deviations). Significant differences were not observed between the sexes; however, race differences were observed (higher levels in blacks relative to whites).

CONCLUSIONS

The method was specific for measuring glycated amino acids in albumin and had good basic performance characteristics. The reference range in Americans was 11.9-15.8%. This method may be a useful indicator for diabetes control.

Enhanced iron availability by protein glycation may explain higher infection rates in diabetics

Serum proteins exist in a state of higher glycation among individuals with poor glycemic control, notably diabetics. These non-enzymatic modifications via the Maillard reaction have far reaching effects on metabolism and regulation, and may be responsible for increased infection rates within this population. Here we explore the effects of glycation on iron metabolism and innate immunity by investigating the interaction between siderophores and bovine serum albumin (BSA). Using a quartz crystal microbalance with dissipation monitoring to quantify association rates, glycated BSA exhibited a significantly reduced affinity for apo and holo enterobactin compared to a non-glycated BSA standard. Bacterial growth assays in the presence of BSA and under iron-limited conditions indicated the growth rate of enterobactin-producing E. coli increased significantly when the BSA was in a glycated form. The results, in addition to data in the literature, support the hypothesis that glycation of serum proteins may effectively increase the available free iron pool for bacteria in blood serum and weaken our innate immunity. This phenomenon may be partially responsible for higher infection rates in some diabetics, especially those with poor glycemic control.

Glycated albumin is a useful glycation index for monitoring fluctuating and poorly controlled type 2 diabetic patients

Glycated albumin (GA) is recognized as a reliable marker for short-term glycemic monitoring in diabetic patients. We investigated the clinical relevance of GA and the ratio of GA to glycated hemoglobin (A1c) in Korean type 2 diabetic patients. In this retrospective study, we compared A1c, GA, and the GA/A1c ratio and analyzed the relationship between glycemic indices and various parameters in 1,038 Korean type 2 diabetic patients. The patients were divided into two groups: a stably maintained A1c group whose A1c levels did not fluctuate by more than 0.5% for at least 6 months and an unstably maintained A1c group whose A1c levels fluctuated by more than 0.5%. Serum GA was strongly correlated with A1c in both groups. Fasting plasma glucose and postprandial glucose were correlated with GA in unstably maintained A1c group, whereas they were correlated with A1c in stably maintained A1c group. The GA/A1c ratio tended to increase as A1c increased. Postprandial glucose and body mass index affected the GA/A1c ratio. Our data show that serum GA may be a more useful glycation index than A1c for monitoring glycemic control in type 2 diabetic patients with fluctuating and poorly controlled glycemic excursions.

The glycation of albumin: structural and functional impacts

Oxidative stress and protein modifications are frequently observed in numerous disease states. Glucose constitutes a vital nutrient necessary to cellular oxygen metabolism. However, hyperglycemia-associated damage is an important factor in diabetes disorders. Albumin, the major circulating protein in blood, can undergo increased glycation in diabetes. From recent studies, it has become evident that protein glycation has important implications for protein activity, unfolding, and degradation, as well as for cell functioning. After giving a brief overview of the key role of albumin in overall antioxidant defense, this review examines its role as a target of glycation reactions. A synthesis of state of the art methods for measuring and characterizing albumin glycation is detailed. In light of recent data, we then report the impact of glycation on the structure of albumin and its various activities, especially its antioxidant and binding capacities. The biological impact of glycated albumin on cell physiology is also discussed, specifically the role of the protein as a biological marker of diabetes.

Chromosome 7p linkage and association study for diabetes related traits and type 2 diabetes in an African-American population enriched for nephropathy

BACKGROUND

Previously we performed a linkage scan of 638 African American affected sibling pairs (ASP) with type 2 diabetes (T2D) enriched for end-stage renal disease (ESRD). Ordered subset linkage analysis (OSA) revealed a linkage peak on chromosome 7p in the subset of families with earlier age of T2D diagnosis.

METHODS

We fine mapped this region by genotyping 11 additional polymorphic markers in the same ASP and investigated a total of 68 single nucleotide polymorphisms (SNPs) in functional candidate genes (GCK1, IL6, IGFBP1 and IGFBP3) for association with age of T2D diagnosis, age of ESRD diagnosis, duration of T2D to onset of ESRD, body mass index (BMI) in African American cases and T2D-ESRD in an African American case-control cohort. OSA of fine mapping markers supported linkage at 28 cM on 7p (near D7S3051) in early-onset T2D families (max. LOD = 3.61, P = 0.002). SNPs in candidate genes and 70 ancestry-informative markers (AIMs) were evaluated in 577 African American T2D-ESRD cases and 596 African American controls.

RESULTS

The most significant association was observed between ESRD age of diagnosis and SNP rs730497, located in intron 1 of the GCK1 gene (recessive T2D age-adjusted P = 0.0006). Nominal associations were observed with GCK1 SNPs and T2D age of diagnosis (BMI-adjusted P = 0.014 to 0.032). Also, one IGFBP1 and four IGFBP3 SNPs showed nominal genotypic association with T2D-ESRD (P = 0.002-0.049). After correcting for multiple tests, only rs730497 remanined significant.

CONCLUSION

Variant rs730947 in the GCK1 gene appears to play a role in early ESRD onset in African Americans.