The colorimetric determination of HbA1c in normal and diabetic subjects

Selective detection of HbA1c using surface enhanced resonance Raman spectroscopy

In the current work, we report on selective detection of HbA1c, a marker for glycemic control in diabetic patients, using surface enhanced resonance raman spectroscopy (SERRS). We found a characteristic band around 770-830 cm(-1) in the SERRS spectrum of HbA1c which was not present in the SERRS spectrum of HbA. To examine the contribution of glucosyl moiety to the characteristic SERRS band of HbA1c, we investigated SERRS spectra for nonenzymatically glycosylated HbA. We found that the SERRS spectral features are essentially identical for both HbA1c and nonenzymatically glycosylated HbA. Furthermore, addition of HbA into colloidal solution of silver nanoparticles (Ag NPs) resulted in the formation of large aggregates of Ag NPs and subsequent sedimentation. On the other hand, aggregation of Ag NPs was considerably low in the case of HbA1c. The differential effect of HbA and HbA1c on colloidal solution of Ag NPs, probably due to their difference in hydrophilicity, enabled us to separate them in a mixture. The separation was characterized by electrophoresis and SERRS analysis. Thus, colloidal solution of Ag NPs and SERRS would be a promising tool for the selective detection of HbA1c.

Evaluation of autofluorescent property of hemoglobin-advanced glycation end product as a long-term glycemic index of diabetes

Current methods for measuring long-term glycemia in patients with diabetes are HbA(1c) and advanced glycation end products (AGEs), which are estimated by phenyl boronate affinity chromatography and competitive enzyme-linked immunosorbent assay, respectively. In this study, we hypothesize that the intrinsic fluorescence property of hemoglobin-AGE (Hb-AGE) may be a simple, accurate, and therefore better index for long-term glycemic status due to its highly specific nature and longer half-life. To establish this contention, in vitro and in vivo experiments were carried out. The former was performed by incubating commercially available hemoglobin with 5 and 20 mmol/l glucose and the latter through experimentally induced (streptozotocin) diabetes in an animal model (male Wistar rats) to identify the new fluorophore formed due to the nonenzymatic glycosylation of hemoglobin. An adduct exhibiting fluorescence at 308/345 nm of excitation/emission wavelengths has been identified and its time-dependent formation established. Under in vitro conditions, the first appearance of the new fluorophore was noticed only after a period of 2 months, whereas under in vivo conditions, it increased significantly after 2 months of hyperglycemia. Consistent with the observations, studies on patients with type 2 diabetes demonstrated an elevated level of this new fluorescent adduct in patients with persisting high levels of plasma glucose for >2 months. Based on the results obtained, Hb-AGE appears to be an efficient fluorescence-based biosensing molecule for the long-term monitoring of glycemic control in diabetes.

Nonenzymatic glycation alters properties of collagen as a substratum for cells

Acid-soluble collagen from rat skin was glycated in vitro by incubating with 0.2 M D-ribose at 37 degrees C for several days, and properties of the glycated collagen as a substratum for fibroblasts 3 Y 1 were studied. The cells attached but spread poorly on the glycated collagen as compared with on the untreated collagen. Thymidine incorporation by the cells on the glycated collagen was higher than that by the cells on untreated collagen. These results indicate that the glycation significantly alters properties of collagen as a substratum for cells.

In vivo glycosylation of dermal and tendon type I collagen

Recent studies show that native collagen fibers in the extracellular space can be subject to nonenzymatic glycosylation and that the extent of such glycosylation increases in clinical hyperglycemia and aging. In the present study, a comparison was made on the extent of glycosylation in rat tail tendon and in the soluble and insoluble fractions of collagen separated from rat skin after in vivo labeling with [14C]glucose. It was observed that nonenzymatic glycosylation occurred maximally in the salt-soluble fraction as measured by the level of ketoamine linked hexose. 14C radioactivity incorporation as well as the number of free amino groups was also increased in this fraction. However, the amounts of O-glycosidically linked sugars did not show much variation between the soluble and insoluble fractions. These findings could be correlated to the enhanced metabolic turnover of newly synthesized collagen in diabetics.

Evaluation of a structured treatment and teaching programme on non-insulin-dependent diabetes

A structured treatment and teaching programme for non-insulin-treated non-insulin-dependent (type 2) diabetes was evaluated prospectively in general practice. The four group sessions were mainly conducted by paramedical personnel. 65 patients from five general practices were assessed at the start of the programme and 50 (mean age 65 years, diabetes duration 7 years) completed the 1 year follow-up (intervention group). The control group consisted of 49 patients (mean age 63 years, diabetes duration 7 years) from three other general practices without the programme. In the intervention group the percentage of patients receiving sulfonylureas fell from 68% at the start of the study to 38% after 1 year (mean difference 30%, 95% confidence interval [CI] 16-44%); the mean weight loss was 2.7 kg (95% CI 1.6-3.8 kg), and non-fasting triglycerides were reduced by 0.77 mmol/1 (95% CI 0.35-1.19 mmol/l); and glycosylated haemoglobin remained unchanged (7.1% of total haemoglobin). In the control group none of these indices was changed during the study year, and 10% of patients started insulin treatment. The structured treatment and teaching programme improved the overall quality of patient care in elderly non-insulin-dependent diabetic patients treated by general practitioners.

Determination of glycosylated haemoglobin in normal, newborn and diabetic Saudi Arabs

Colorimetric determinations of glycosylated haemoglobin by the thiobarbituric acid method were carried out in normal adults (n = 142), newly born infants of healthy mothers (n = 81), and in a group of patients with diabetes mellitus (n = 124). The glycosylated haemoglobin level in normal adult males was 4.9%, which is close to that reported for other populations. No correlation was found between age and the levels of glycosylated haemoglobin in males over 10 years old. However, the mean value for glycosylated haemoglobin in cord blood was 4.1%, significantly different from that of adults. The range values for glycosylated haemoglobin in diabetic patients was 7-19%. The mean value for glycosylated haemoglobin was 10.9%, similar to that established in other diabetic populations. Results of colorimetric determinations of glycosylated haemoglobin in the Saudi population compare well with other ethnic groups and, therefore, suggest no ethnic differences in glycosylated haemoglobin levels.

Nonenzymatically glycosylated proteins

Nonenzymatic glycosylation takes place in all proteins with a free-reacting lysine or valine in the presence of glucose. The formation of glycosylated plasma albumin, hemoglobin (Hb A1c), and skin collagen provides a diagnostic index of short- to long-term time-concentration of glucose in vivo. A wide range of assay methods are available, with affinity chromatographic, isoelectric focusing, and spectrophotometric methods providing the best accuracy and versatility. Glycosylated hemoglobin assays indicate glucose pressure over the previous 2 to 3 months and are of diagnostic value in general diabetic control, while glycosylated plasma albumin determinations are preferable in acute episodes in the life of a diabetic (e.g., pregnancy, infection, stress, trauma, surgery), since they provide an overview of changing blood glucose values of the previous 2 to 4 weeks. Glycosylated collagen estimations reflect tissue aging and are relevant in healing processes. Glycosylation alters the biologic activity of proteins, and these may relate to the manifold complications concomitant on the lifelong elevation of blood and tissue glucose in the diabetic (C6a). Assays for glycosylated hemoglobin have been routinely performed in clinical chemistry laboratories for a decade, and convenient determination for other nonenzymatically glycosylated proteins is proceeding apace.

Levels of glycosylated haemoglobin in the Arabian camel (Camelus dromedarius)

Proportions of glycosylated haemoglobin (Hb) were determined in 10 Arabian camels (Camelus dromedarius) and were compared with normal controls (n = 59) and diabetic patients (n = 47) using the thiobarbituric acid (TBA) method. The level of glycosylated haemoglobin (5.5%) in camels is significantly different from that of normal healthy humans (4.9%) (P less than 0.001). Whereas the glucose levels were comparable, this difference in percentages of glycosylated haemoglobin may be explained by the difference in survival time between human and camel red blood cells.

Glycosylated plasma protein measurement by a semi-automated method

A semi-automated method for determination of glycosylation of plasma proteins using the thiobarbituric acid method is described. Plasma samples (100 microL) and a plasma pool used as a secondary standard were incubated in 0.3 M oxalic acid at 100 degrees C for exactly 2 h. The hydroxymethyl furfural released and the total protein were measured concurrently on a Technicon AAII Autoanalyzer. Addition of 10 or 20 mmol glucose to plasma samples caused a minimal increase in the measured glycosylated protein. Within-batch and between-batch coefficients of variation were 3.1% and 4.9% respectively. The mean glycosylated protein levels for 52 normals and 48 maturity-onset diabetics were (+/- 1SD) 0.96 +/- 0.13 and 1.75 +/- 0.32 nmol HMF/mg protein/2 h incubation.

[Comparison of various methods for determining glycosylated hemoglobins]

Determination of glycosilated haemoglobin (HbA1) has become an important parameter for the control of diabetes mellitus. Although several methods are available today, some are time consuming and complicated and may lead to differing results. Two methods, the thiobarbituric-acid (TBA) method and microcolumn chromatography, were compared with the reference method, high performance liquid chromatography (HPLC), with respect to precision, accuracy and practicability. Seventy different blood samples from diabetics were analysed. Using the TBA method, good results were achieved which were generally consistent with those of the reference method (r = 0.90); there were no significant differences in values determined with the two methods. However, the TBA method requires an inordinate amount of work. Microcolumn chromatography is better suited to the needs of physicians in private practice. Results with this method also correlate well with those of the reference method (r = 0.92) when the labile aldimine fraction has been removed by dialysis of the sample. Quality control can be performed using either lyophilized or deep-frozen control samples.

Nonenzymatic glycosylation of basement membrane collagen in diabetes mellitus

For a better understanding of the processes leading to diabetic microangiopathy, type IV collagen from kidneys of patients with long-term diabetes was compared with the collagen from kidneys of sex- and age-matched controls. Type IV collagen from diabetic kidneys revealed no abnormalities in amino acid composition, hydroxylation of proline and lysine, enzymatic glycosylation of hydroxylysine, and immunological reactivity with several monoclonal and polyclonal, anti-type IV collagen antibodies. However, ketoamine-linked hexose, resulting from the nonenzymatic condensation of glucose with lysyl or hydroxylysyl residues, was 1.7-fold higher in diabetic type IV collagen. The stoichiometry of this modification was estimated to be 1-2 residues of hexose per triple helical molecule (Mr 380,000). This small amount of ketoamine-linked hexose might hardly have an effect on the function and turnover of type IV collagen, unless it is bound to a crucial site along the collagen molecule. The nonenzymatic glycosylation of collagen might therefore be a mere consequence of the metabolic disturbances, rather than the primary cause for the late complications of diabetes mellitus.

Glycosylated haemoglobin: measurement and clinical use

The discovery, biochemistry, laboratory determination, and clinical application of glycosylated haemoglobins are reviewed. Sources of error are discussed in detail. No single assay method is suitable for all purposes, and in the foreseeable future generally acceptable standards and reference ranges are unlikely to be agreed. Each laboratory must establish its own. Nevertheless, the development of glycosylated haemoglobin assays is an important advance. They offer the best available means of assessing diabetic control.

Nonenzymatic glucosylation of proteins: a new and rapid solution for in vitro investigation

The rates of nonenzymatic glucosylation of albumin, high density lipoprotein (HDL) and low density lipoprotein (LDL) were determined in vitro using [14C]glucose repurified by a new and rapid HPLC method. All commercial preparations were found to contain contaminants reacting 15-20-times faster with protein than the repurified [14C]glucose. Removal of contaminants was critical to the rate determinations and constitutes a substantial improvement over the widely used existing method. The initial rates of nonenzymatic glucosylation determined in vitro for albumin, HDL and LDL were used to predict normal in vivo levels of 0.40, 0.65 and 0.08 mol glucose per mol protein, respectively. This is within the range of values found in vivo for albumin and LDL, but low for HDL. These values would be expected to increase 2-4-fold in diabetes.

Glycosylated haemoglobins: biochemical evaluation and clinical utility

A review is given of the biochemical background of the glycosylated haemoglobins, their methods of determination, and their clinical significance. Special attention is paid to the sample preparation. For all methods except the colorimetric TBA-method, the removal of the labile pre-HbA1c fraction is essential. Under proper conditions, high-performance liquid chromatography, agar-gel electrophoresis and affinity chromatography are suitable methods for use in the clinical laboratory for the estimation of HbA1c and HbA1. However, the colorimetric TBA-method must be considered to be the method of choice. The clinical utility of the test is stressed with special respect to the management of diabetic pregnancies, the control of home-monitoring of blood glucose, and the objective measurement of the effect of changing diabetic therapy.

Recent advances in glycosylated hemoglobin measurements

Glycosylated hemoglobins have gained wide acceptance as an accurate index of long-term blood glucose control in diabetes mellitus. A variety of glycosylated hemoglobin assays is available. There is a high degree of correlation between results determined by these assays. The ideal laboratory method for measuring glycosylated hemoglobin in the diabetic should be accurate, precise, easily standardized, inexpensive, and rapidly performed. Unfortunately, none of the currently used methods meet all of the criteria necessary to be considered the ideal laboratory method. The most widely used methods for quantitating glycosylated hemoglobins--including ion exchange chromatography, electrophoresis, isoelectric focusing, thiobarbituric acid colorimetry, and affinity chromatography--are reviewed with respect to the important advantages and disadvantages of each method for the clinical laboratory. Techniques for quantitating glycosylated proteins other than hemoglobins, such as albumin, are also discussed.

A simplified colorimetric method for the measurement of glycosylated hemoglobin

A colorimetric method for the measurement of glycosylated hemoglobin is described. The method is based on the detection of hydroxymethylfurfural liberated from the ketoamine-linked hexose of glycosylated hemoglobin. Rapid hydrolysis is achieved by heating at 120-124 degrees C under pressure, and simplification of the procedure enables the test to be performed in one disposable test tube. Standardization is by means of easily prepared lyophilized human hemoglobin preparations. The test has proven to be reliable and economical in routine use.