Modification of glycosylated haemoglobin concentration during artificial endocrine pancreas treatment of diabetics. Evidence for a short-term effect on HbA 1 (a+b+c) levels

The value of glycosylated haemoglobin as a substitute for the oral glucose tolerance test in the detection of impaired glucose tolerance (IGT)

In a prospective study of South African Indian subjects with IGT, glycosylated hemoglobin [specifically HbA1 (HbA1(a+b+c)] and its relationship to the oral glucose tolerance test (OGTT) was studied in 128 study subjects who were classified IGT a year previously (Year 0 of study) and in 64 control subjects. At Year 1 of the study, the standard 75-g OGTT was performed on all subjects; study subjects were further divided into three groups based on World Health Organisation criteria [Normal (N), impaired glucose tolerance (IGT), diabetes mellitus (D)]. HbA1, a glycosylated hemoglobin (GHb), was measured by a cation-exchange microchromatographic method. Based on OGTT results, 47 of the 128 study subjects were classified IGT, 41 diabetes (newly-diagnosed diabetes) and 40 subjects had normal glucose tolerance. Mean GHb was significantly higher in the D group (7.61 +/- 1.76%) compared to the control group (6.99 +/- 1.22%) and the N group (6.9 +/- 1.12%), respectively (P less than 0.05); there was no significant difference between the IGT group (7.48 +/- 1.44%) and each of the other three groups. Compared to the OGTT, GHb was relatively insensitive in the diagnosis of IGT or diabetes mellitus: only 17% of the IGT group and 26.8% of the D group has elevated GHb values; the specificity of GHb as a measure of normal glucose tolerance was 85.9%. The majority of subjects, irrespective of the category of glucose tolerance, had GHb levels within the normal range and there was marked overlap between the four groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of three methods for the elimination of the labile fraction of HbA1

Three different procedures were used to remove the "labile" fraction in the chromatographic quantitation of hemoglobin A1 (HbA1) by a minicolumn assay: (a) preincubation of the erythrocytes at 37 degrees C in isotonic saline for 4 h, (b) preincubation in the presence of semicarbazide-aniline at pH 5.0 for 30 min, and (c) preincubation in acetate buffer at pH 5.5 for 30 min. The results show that the two latter methods are not only more rapid but are also slightly more effective. The use of the acetate buffer is preferred because this reagent is more easily prepared and also because the presence of semicarbazide and aniline did not markedly accelerate the dissociation of Hb pre-A1c at pH 5.5. The procedure relies simply on the greater instability of Schiff base in acidic solution. There is a significant correlation between the "labile" fraction and the plasma glucose concentration at sampling time. The results support the view that the elimination of the "labile" precursor is essential to preserve the utility of the assay.

The oxygen-release capacity of red blood cells in insulin-dependent diabetics after artificial pancreas

Oxygen-release capacity of the red blood cells was investigated in non-acidotic insulin-dependent diabetics before and after the achievement of strict metabolic control with the aid of the artificial pancreas. P50std (oxygen tension at 50% oxygen saturation) values were low in basal condition and returned to normal after the 24-h treatment period. No significant changes were observed in the content of red cell 2,3-diphosphoglycerate nor in the acid-base balance. Only the labile form of glycosylated hemoglobin showed significant decreases after treatment. These results suggest that insulin-dependent diabetics may have a state of relative tissue hypoxia which can be easily overcome by the achievement of strict metabolic control.

Use of the artificial beta cell (ABC) in the assessment of peripheral insulin sensitivity: effect of chromium supplementation in diabetic patients

The artificial beta cell (ABC), a closed-loop insulin delivery system, was used to determine insulin sensitivity. Progressively increasing glucose loads were administered after initial stabilization of the blood glucose at euglycemic levels such that the serum C-peptide was suppressed. The amount of insulin required to maintain euglycemia was considered a measure of sensitivity to insulin. Six stable maturity onset diabetics were studied before and after supplementation with chromium-rich brewer's yeast. All patients demonstrated an increase in sensitivity to insulin as indicated by a decrease in the fasting blood glucose concentration and a decrease in insulin requirement during the glucose challenge (P less than 0.02). The data obtained support the hypothesis that chromium or some other factor(s) present in brewer's yeast potentiates the peripheral effects of insulin. It remains to be established whether this effect occurs at the receptor or post-receptor level.

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.

Glycosylated hemoglobin (Hb AI) as an indicator of therapy effects in different clinical types of diabetes

The levels of glycosylated hemoglobin (Hb AI), intermittent glycemia and glycosuria over 24 hr, Mw index, fasting serum cholesterol and triglycerides, and 24-hr proteinuria were determined in 20 healthy subjects and 88 diabetics representing different clinical types of diabetes mellitus. In each of the subjects all the tests were carried out on a single day. The other investigations included endogenous creatinine clearance, ECG and ophthalmoscopic examination of the eye-fundus. The mean Hb AI levels in the "A" control group (up to 40 yr of age) and in the "B" control group (41-60 yr) were mean +/- SD = 6.8 +/- 0.65% and mean +/- SD = 6.49 +/- 0.99% of the total hemoglobin concentration, respectively. A significant increase in Hb AI concentration was found in all the diabetic patients. The increase, independent of the subject's age, clinical type of diabetes and the therapy employed, was related to the degree of hyperglycemia. In Type I diabetes there was no positive correlation between Hb AI concentration on the one hand and fasting glycemia, the 24-hr profile of glycemia, glycosuria and Mw index on the other. The latter indices of diabetes mellitus control seem thus to differ in value and significance. In Type II diabetes, both newly-diagnosed and of long duration, treated with the sulfonylurea derivatives, a marked correlation was found between Hb AI level and fasting glycemia, the mean value of 8 glycemia determinations over 24-hr, Mw index and 24-hr glycosuria. In Type II diabetes treated with insulin a correlation was established between Hb AI and other findings, except fasting glycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophoretically determined haemoglobin A1 concentrations during short-term changes in glucose concentration

In our experience, electrophoresis on agar gel is a very satisfactory alternative to the more widely used chromatographic methods for the determination of haemoglobin A1 (HbA1). Like the chromatographic method, the electrophoretic method is unable to detect any difference between the labile intermediate form of HbA1, which changes rapidly with acute changes in blood glucose level, and the more stable end-product, which reflects long-term glucose levels. In vitro at 37 degrees C the electrophoretically determined HbA1 concentration increases with increasing glucose concentration and with time in both normal and diabetic erythrocytes, but decreases to the preincubation concentration during further incubation of the erythrocytes in a glucose-free medium at 37 degrees C. Similarly, if normal or diabetic erythrocytes are incubated with isotonic saline before the HbA1 assay, the labile fraction is eliminated. In diabetics, the decrease in HbA1 concentration correlates with both the blood glucose level and the preincubation HbA1 concentration. Thus for HbA1 to be an accurate indicator of long-term glucose control in diabetic patients saline incubation of the erythrocytes may be necessary before HbA1 assay by the electrophoretic method, otherwise the assay results will also reflect recent changes in the blood glucose level.

Rapid and slow rate of decrease in HbA1a + b and HbA1c during improved glycaemic control

The change in glycosylated haemoglobins was studied with a column chromatographic method when glycaemic control was rapidly improved in nine diabetic patients. The patients were followed for 3 weeks or more. There was a decrease in HbA1a+b and HbA1c within the first few days of improved control and this decrease was faster than later on. The initial decrease of HbA1a+b was faster than that of HbA1c. In individual patients the initial decrease in glycosylated haemoglobins correlated with the initial rate of decrease in blood glucose. It is concluded that HbA1a+b and HbA1c decrease biphasically during improved glycaemic control. The rapid initial decrease may be due to labile HbA1 and it is large enough to influence the value of HbA1 as an indicator of long-term glycaemic control in some patients.

Glycosylated hemoglobin and its temporal relationship to plasma glucose in non-insulin dependent (type 2) diabetes mellitus

Total glycosylated hemoglobin (HbAI) and random plasma glucose were measured at monthly intervals for 6 mo in 33 non-insulin dependent (type 2) diabetics. The mean HbAI and mean plasma glucose in individual patients over the 6 mo showed a close correlation (p less than 0.001). A significantly higher HbAI (p less than 0.001) for a given plasma glucose was seen in those patients receiving combined chlorpropamide and metformin therapy (n = 14) than in those receiving chlorpropamide alone (n = 19). For each patient correlation coefficients were calculated between plasma glucose and HbAI with time lags of 0.1 and 2 mo. The coefficients with no time lag showed a significant tendency to be positive (p less than 0.01) whereas those with time lags of 1 or 2 mo were not significant. A constant proportional variability of both HbAI and plasma glucose over time was demonstrated, the mean coefficient of variation for HbAI being 8.4 +/- 2.7% and for plasma glucose 22.3 +/- 9.7%. We conclude that HbAI provides an index of plasma glucose control, not during the preceding few months as was previously thought but, during the previous few weeks. In terms of variability from month to month a single HbAI determination was equivalent to approximately the mean of 3 single plasma glucose values.

Changes in glycosylated haemoglobin after oral glucose load

To study the relation between hyperglycaemia and a change in the concentration of glycosylated haemoglobin (HbA1) blood glucose and HbA1 concentrations were measured during an oral glucose tolerance test and for 120 days afterwards in 20 normal subjects. These measurements showed that a minor degree of hyperglycaemia led to a significant increase in lycosylated haemoglobin concentrations. The increase appeared 10 days after the test, and values remained raised until 30 days and returned to normal 60 days after the test. If such a minor fluctuation of blood glucose can lead to a significant increase in HbA1 concentrations the test may be too sensitive as an index of long-term blood glucose control in diabetics.

Analysis of short-term changes in reversibly and irreversibly glycosylated haemoglobin AI: relevance to diabetes mellitus

We have determined the stable (irreversibly glycosylated) fraction of haemoglobin AI (HbAI) on Bio-Rex 70 after incubation of red blood cells in 0.9 % saline solution for 6 h at 37 degrees C. The total (reversibly + irreversibly glycosylated fractions) HbAI was determined before each incubation. Labile (reversibly glycosylated) HbAI represented the difference between total and stable HbAI fractions. Total and stable HbAI fractions were determined during insulin- or meal-induced blood glucose fluctuations in 24 insulin-dependent diabetics and in seven subjects with impaired glucose tolerance. In the diabetics, the maximal fluctuation of total HbAI was 1.47% over 2-12 h, while the simultaneous plasma glucose variation was 21.5 mmol/l. The stable HbAI fraction did not change significantly. In diabetics the differences between the maximal and minimal values of plasma glucose and total HbAI were significantly correlated. Plasma glucose correlated with simultaneously determined total and labile HbAI fractions, but not with stable HbAI. In subjects with impaired glucose tolerance, similar changes in total but not in stable HbAI were observed during an oral glucose tolerance test. We conclude that, although rapid changes in chromatographically determined HbAI are relatively small, the determination of stable HbAI should be performed to circumvent this problem and to ensure a more accurate index of blood glucose control.

Labile and stable glycosylated hemoglobin during OGTT in healthy subjects and maturity-onset diabetics

HbA1 levels were determined by a rapid chromatographic column test in 15 healthy subjects (HS) and in 15 maturity-onset diabetics (MOD), fasting and 2 h after glucose ingestion (100 g for HS, 50 g for MOD). Chromatography was carried out both before and after 6 h of red cell incubation in saline at 37 degrees C. HbA1 in HS at 0 and 120 min of OGTT was not significantly different, either before (6.24 +/- 0.61% and 6.22 +/- 0.62%) or after red cell incubation in saline (5.85 +/- 0.61% and 5.87 +/- 0.55%). Red cell incubation in saline significantly reduced HbA1 levels both at 0 and 120 min (2p less than 0.001). HbA1 in MOD before red cell incubation in saline, was slightly but significantly higher at 120 min (8.61 +/- 1.03%) than at 0 min (8.39 +/- 1.01%): 2p less than 0.001. After incubation in saline, this difference was cancelled (7.86 +/- 0.85% at 0 min and 7.97 +/- 0.83% at 120 min: n.s.). Post-incubation levels were lower than pre-incubation ones both at 0 and 120 min (2p less than 0.001). The HbA1 increment observed in MOD is significantly correlated (p less than 0.01; r=0.64) to the blood glucose increment observed at the glycemic peak. We conclude that hemoglobin glycosylation may show rapid changes also in MOD, reflecting blood glucose changes, whereas in HS the physiological glycemic excursions are not wide enough to produce rapid HbA1 changes. Since labile and stable HbA1 co-elute in the rapid chromatographic methods, red cell incubation in saline for 6 h at 37 degrees C is recommended as a simple procedure which allows the measurement of the stable fraction alone, i.e. the real index of long-term glycemic control, independent of rapid glycemic fluctuations.

Nonenzymatic glycosylation of protein: relevance to diabetes

Glucose can react nonenzymatically with proteins to form stable covalent linkages. The most abundant minor hemoglobin component in human red cells is hemoglobin AIc: glucose is attached to the N-terminal amino group of the beta chain by a ketoamine linkage. Hemoglobin AIc is increased two to three-fold in the red cells of diabetic patients. It is formed slowly and continuously throughout the 120-day lifespan of the red cell. Measurement of hemoglobin AIc provides an index of average blood glucose levels over the preceding two or three months. Thus, hemoglobin AIc has proved to be useful in assessing diabetic control and, perhaps, in screening people for diabetes. Many other proteins, such as lens crystallins, collagen and proteins in serum and in red cell membrane, are modified by nonenzymatic glycosylation. This structural alteration may lead to impaired protein function and, perhaps, contribute to the long-term complications of diabetes.

Glycosylated hemoglobin in patients with newly discovered juvenile-onset diabetes mellitus in the days immediately following the beginning of insulin treatment

We studied the behavior of fast hemoglobin fractions in newly discovered diabetic patients, before and in the 10 days immediately following the beginning of insulin therapy, in order to verify whether or not the rapid improvement of glycemic control involved a rapid reduction of total HbA1 and of its fractions. We observed a rapid and highly significant fall of HbA1(a+b+c) and HbA1c levels after only 1 or 2 days of insulin therapy, followed by a slower decrement in the other 3-10 days. HbA1(a+b) showed a slower decrement trend, reaching levels significantly below baseline values only after 7-10 days. These results suggest that rapid changes occurring in glycosylated hemoglobin levels after the beginning of insulin treatment in newly discovered diabetic patients involve mainly HbA1c. The kinetics of glycosylated hemoglobin reduction, with a first rapid decrement followed by a slower one, may suggest the hypothesis that rapid changes are due to reversible Schiff base de-glycosylation, the ketoamine linkage being the true index of long term glycemic control.

Treatment of diabetes mellitus by devices

A very important aspect of diabetes mellitus is whether or not normalization or near-normalization of blood glucose and/or other metabolites and hormones may reduce or eliminate the chronic complications of this disease. To answer this question and to provide a more "physiologic" approach to insulin administration, a constellation of devices have reached the stage of clinical investigation. These include small portable pump systems that can provide variable rates of insulin infusion via the subcutaneous intravenous or intraperitoneal routes. In addition, bedside artificial "beta cells" having the capability of providing insulin infusions, with the rate varying as a function of continuous glucose measurements, are available for short-term studies. Under development are implantable continuous infusion devices and implantable glucose sensors that could in the future lead to a miniaturized implantable glucose-controlled insulin administration system.

Rapid changes of glycosylated hemoglobin in diabetics submitted to artificial pancreas control

This study was performed in order to investigate the possibility of rapid changes in glycosylated hemoglobin levels. Hb A1(a + b + c) values were evaluated by a chromatographic Column Test (Bio-Rad) in 20 insulin-dependent diabetic patients before and after 48 h of glycemic control obtained by an artificial pancreas (Biostator Miles). A significant decrease of glycosylated hemoglobin levels was observed: from 11.21 +/- 2.8% to 9.89 +/- 2.15% of total hemoglobin content (p less than 0.005). Our data bring to the conclusion that rapid changes of glycosylated hemoglobin partially reduce, but do not abolish the clinical significance of Hb A1 determination as a reliable index of long-term glycemic control in diabetic patients.

Glycosylated haemoglobin in children with insulin-dependent diabetes mellitus

Glycosylated haemoglobin (HbA1) was measured serially by microcolumn chromatography in 38 children with newly diagnosed insulin-dependent diabetes. Initial HbA1 levels of 13.6 +/- 0.5% fell signficiantly from day 0 (prior to therapy) both to day 1 (1.6 +/- 0.2% decrease) and to day 3-5 (2.6 +/- 0.4% decrease) (P < 0.001). This drop correlated closely with changes in blood glucose (P < 0.001), less closely and inversely with plasma bicarbonate levels (P < 0.01), but not with prior duration of symptoms or changes in serum cholesterol and triglyceride concentrations. HbA1 levels reached a nadir of 8.2 +/- 0.3% 3 weeks to 6 months after diagnosis, and correlated with decreasing insulin dosage (P < 0.001). HbA1 levels rose again to 11.4 +/- 0.5% in 21 patients followed for more than 3-6 months. Our results indicate that (1) HbA1 level change rapidly during initial stabilization of insulin-dependent diabetes suggesting that glycosylation may not be entirely irreversible, and (2) HbA1 levels are consistent with clinical assessment of control during remission and postremission phases.

Rapid changes in chromatographically determined haemoglobin A1c induced by short-term changes in glucose concentration

Chromatographically determined haemoglobin A1c concentration was measured during short-term (1-24h) changes in glucose concentration in vitro and in vivo. In vitro at 37 degrees C the HbA1c concentration increased with glucose concentration and time both in normal and diabetic erythrocytes. In normal erythrocytes incubated in 20--100 mmol/l glucose, the increases in the HbA1c concentration were maximal after 4--6 h and then stable for the next 18--20 h. During the first hour, increases in the HbA1c concentration were linear with time and on average 0.034% HbA1c x h-1 x mmol/l glucose-1. In erythrocytes, after a rapidly produced increase (2 h), HbA1c decreased to preincubation concentrations during a further incubation of the erythrocytes in a glucose-free medium at 37 degrees C for 4--6 h. The mean rate of linear decrease was 0.017% x h-1 x mmol/l glucose-1. After incubation of erythrocytes in 100 mmol/l glucose for 24 h, 1.3% HbA1c remained stable for 6 h in saline. The rapid increase in HbA1c concentration, as determined by chromatography, was not due to stable HbA1c (ketoamine linked glucose) as no increase was found in the HbA1c concentrations determined by the thiobarbiturate method. In juvenile diabetics controlled by an artificial beta-cell, rapid changes of blood glucose concentration (up to 20 mmol/l) resulted in increases in HbA1c concentration of as much as 1.9% within 12 h (mean 1.1%). Rapid in vivo increases in HbA1c concentration were reversible by normalization of the blood glucose concentration. That rapid changes in HbA1c may occur in daily diabetic life was evidenced by differences in HbA1c concentration between blood samples from out-patient diabetics incubated in saline for 16 hours at 4 degrees C and 37 degrees C (range of differences 0.2--1.4% HbA1c). The differences correlated to the blood glucose concentration at the time of sampling blood for HbA1c determination. Thus, incubation of blood at a low glucose concentration prior to determination of the glycosylated haemoglobin concentration may overcome interference from rapidly produced HbA1c.