High pressure liquid chromatographic separation of the labile aldimine (pre-hemoglobin AIc) and the stable Hb AIc

Evaluation of the Menarini–Arkray HA 8140 hemoglobin A1c analyzer

We describe a multinational evaluation of the Menarini– Arkray HA 8140 hemoglobin (Hb) A1canalyzer, which utilizes a high degree of automation, including bar code reading, cap piercing, and whole-blood sampling. Within- and between-batch CVs were <2%. Linearity was confirmed throughout the working range of the analyzer. Common Hb variants, including Hb S, Hb C, and Hb F, did not interfere with the Hb A1c separation, and the potentially interfering labile Schiff base was effectively removed during the chromatographic procedure. The HA 8140 analyzer displayed good correlation to the Bio-Rad Variant analyzer, Tinaquant immunoassay, affinity chromatography, and an optimized “in-house” HPLC Hb A1c method. The methods when compared by Altman and Bland plots showed bias (upper, lower 95% confidence limits) of: Variant minus HA 8140 = 0.99 (0.23, 1.74), Tinaquant minus HA 8140 = 0.14 (−0.71, 0.98); affinity minus HA 8140 (after log transformation) = 1.13 (0.90, 1.41), and “in house” HPLC minus HA 8140 (after log transformation) = 0.91 (0.82, 1.01).

Glycated haemoglobins

The association between elevated levels of glycated haemoglobins and diabetes mellitus has been known for twenty years [92]. Since then the determination of glycated haemoglobins has become a valuable tool for the objective assessment of long-term glycaemia in diabetic patients. The marked clinical interest in reliable measurements of glycated haemoglobins has stimulated the development and perfection of the necessary methodology. Limitations of the techniques have led to investigation of the underlying causes. Some of them led to the recognition of processes that were not known to occur in vivo before, such as glycation at sites other than the amino terminus of the beta-chains, modification of haemoglobin by reactants other than glucose or the existence of labile haemoglobin adducts. With ideal methodology these features would have gone unnoticed. Furthermore, the determination of glycated haemoglobin in large populations of diabetic patients has lead to the discovery of new, clinically silent mutant haemoglobins. Today, the routine determination of glycated haemoglobins in diabetic patients probably represents the broadest screening for mutant haemoglobins. The experience with glycated haemoglobins shows that overcoming difficulties in their determination, and progress in biomedical research, are closely intertwined.

High-performance liquid chromatographic separation and quantitation of glycosylated hemoglobin A2 as an alternate index of glycemic control

By a combination of DEAE-cellulose chromatography and cation-exchange high-performance liquid chromatography glycosylated components of hemoglobin (Hb) A2 were separated and quantitated from persons with diabetes and some common hemoglobinopathies. Hb A2Ic values correlated well with total glycosylated Hb levels assayed by affinity chromatography, and Hb AIc, Hb SIc and Hb CIc levels, determined by high-performance liquid chromatography. The results indicate that Hb A2Ic may serve as an alternate index of glycemic control.

Non-enzymatic glycosylation influences Hb S polymerization

In vivo glycosylated components of Hb S were isolated from red cell hemolysates of sickle cell anemia patients by application of affinity chromatographic and cation exchange chromatographic techniques. The total glycosylated fraction (GHb) of the whole hemolysate, Hb SIc, Hb So-glycosylated (formed mostly by glycosylation epsilon-NH2 groups of lysyl residues), and Hb So-nonglycosylated fractions were isolated in this manner. GHb contained about 33% Hb SIc and 42% Hb So (Hb So-glycosylated) and the rest was glycosylated Hb F and Hb A2. As expected, the binding of 2,3-DPG was affected only in Hb SIc and not in Hb So-glycosylated. Hb SIc and Hb So-glycosylated had higher solubility in concentrated phosphate solutions and had higher minimum gelling concentrations than the non-glycosylated form of Hb So. These effects are interpreted to be due to modification by glycosylation of specific sites that are directly or indirectly involved in the intermolecular contacts.

New less temperature-sensitive microchromatographic method for the separation and quantitation of glycosylated hemoglobins using a non-cyanide buffer system

This paper describes a new microchromatographic method on Bio-Rex 70 ion-exchanger, which enables the isolation and quantitation of the minor components hemoglobin AIa+b and hemoglobin AIc. The method relies on the equilibration of the resin in a polyphosphate buffer with a pH closer to the pKa of the carboxylic group of the resin, and on the adjustment of the sample pH at 5. This induces linear pH and ionic strength gradient during the elution of the hemoglobin components. The method is little affected by temperature between 20 and 30 degrees C, by the presence of the aldimine Schiff base, and is not expected to be greatly influenced by moderate fluctuations in pH and ionic strength of the buffers used. There was good correlation between the values obtained by the new micromethod and four procedures currently used, namely high-performance liquid chromatography (r = 0.96), and Trivelli Bio-Rex 70 macromethod (r = 0.99), bioaffinity chromatography (r = 0.98), and Isolab hemoglobin AI kit (r = 0.91). The method is reproducible, the interassay and the intra-assay correlation coefficients did not exceed 4.2%. The mean value for hemoglobin AIc was 4.6 +/- 0.35% for eleven non-diabetics and 8.9 +/- 2.6% for twenty-one diabetics.