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.

Determination of glycosylated hemoglobin by affinity electrophoresis on agarose gel

We describe a method for electrophoretic determination of glycosylated hemoglobin (GHb) on agarose gel membrane. Clear separation of GHb from non-GHb is achieved after 30 min electrophoresis at 60 V using a sodium citrate buffer solution (34 mmol/l, pH 6.5) containing 0.6 g/l dextran sulfate. The results obtained by this method correlate well with those by agar gel electrophoresis (r = 0.98) and column chromatography (r = 0.96). However, unlike column chromatographic methods, GHb values obtained on agarose gel are not affected by fluctuations in ambient temperature (18-28 degrees C), changes in pH (6.2-6.6) and ionic strength of buffer solution (26-40 mmol/l), or variant hemoglobin S and C. Also, electrophoresis on agarose gel membrane eliminates the lengthy preparative steps required for cellulose acetate electrophoresis. We conclude that agarose gel electrophoresis is a simple method for quantitative determination of GHb.

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.

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.

An automatic method for determination of glycosylated hemoglobins using low-pressure liquid chromatography

Several studies have revealed a correlation between blood levels of glucose and hemoglobin A1c (HbA1c), a minor form of hemoglobin (Hb) present at elevated concentrations in patients with diabetes mellitus. To facilitate a clinical study of the level of circulating HbA1c we have developed an automatic chromatographic system. An efficient separation of HbA1c from HbA0 and other rapid hemoglobins (HbA1a, HbA1b) was achieved on Bio-Rex-70 columns using three buffers. This system allows the daily analysis of 40 samples. The mean level of HbA1c in normal subjects was 5.4 +/- 0.4%. The method also detects the presence of elevated levels of HbF and the most frequent forms of abnormal hemoglobin (HbS, HbC).

A chromatographic method for measuring haemoglobin A1: comparison with two commercial kits

A modified chromatographic method for the separation of haemoglobin A1 is described. Its use for the estimation of the concentrations of the fractions is compared with those of two commercial kits.

Temperature dependence of the chromatographic assay of hemoglobin A1 and application of a temperature controlled assay to clinical evaluation of diabetic control

We investigated the temperature dependence of the cation-exchange chromatographic properties of hemoglobin A1 using the "Fast Hemoglobins Test System" obtained from Isolab, Inc., Akron, OH, U.S.A. and a temperature control chamber constructed in our laboratory. Six patient samples, two each from the "normal" range (5--8.5%, "transitional" range (8.5--12.0%) and "uncontrolled diabetic" range (12--20%) described by Isolab (as measured at 24 degrees C) were collected, hemolyzed and assayed according to product insert instructions. Each sample was assayed in triplicate in three separate runs at 20 degrees C, 22 degrees C, 24 degrees C, 26 degrees C and 28 degrees C in the temperature controlled (+/- 0.25 degrees C) chamber. Resultant mean increases in assay results of 0.8, 1.1 and 1.6% hemoglobin A1 per 2 degrees C increase in temperature for the three ranges respectively, indicate that the temperature dependence of the microcolumn assay for hemoglobin A1 is at least partially a function of the relative percentage of glycosylated hemoglobin in the sample. By controlling assay temperature we have reduced interassay variation throughout all concentration ranges by more than one-half to less than 5%. We applied this temperature controlled assay to measurement of hemoglobin A1 levels in 33 non-diabetic subjects and to the screening of hemoglobin A1 levels in 77 diabetic patients regularly attending the diabetic-endocrine outpatient clinic of this hospital. No non-diabetic subject had a HbA1 level above 8.5% and of the diabetic patients, 26% fell within the "normal" range, 43% within the "transitional" range and 31% within the "uncontrolled diabetic" range.

A temperature conversion nomogram for glycosylated hemoglobin analysis

Analysis of glycosylated hemoglobins by commercial mini-column methods was shown to vary linearly with the ambient temperature. However, the slopes of the temperature dependence lines for diabetic and healthy individuals was different. A method for temperature correction and a nomogram is proposed.