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  • 1
    ISSN: 1432-0428
    Keywords: Haemoglobin A1c ; rapid glycosylation ; chromatography ; glucose ; 2-ketohexose derivatives ; artificial pancreas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Chromatographically determined haemoglobin A1c concentration was measured during short-term (1–24 h) changes in glucose concentration in vitro and in vivo. In vitro at 37 °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 × h−1 × mmol/l glucose−1. In erythrocytes, after a rapidly produced increase (2h), HbA1c decreased to preincubation concentrations during a further incubation of the erythrocytes in a glucose-free medium at 37 °C for 4–6 h. The mean rate of linear decrease was 0.017% × h−1 × 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 °C and 37 °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.
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  • 2
    ISSN: 1432-0428
    Keywords: Haemoglobin A1c ; synthesis ; glucose ; hyperglycaemia ; artificial pancreas ; density separated erythrocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The synthesis of glycosylated haemoglobins in vivo was measured during 24 h of controlled hyperglycaemia in seven insulin dependent diabetics. The mean blood glucose concentration was 22 mmol/l, while electrolytes and other metabolites were kept normal by infusion of 4–23 IU of insulin during hyperglycaemia. The study confirmed the velocity and magnitude of unstable HbA1c formation previously found in vitro. The stable HbA1c formed in 24 h was on average 0.006% of total haemoglobin/ mmol glucose. This compares well with the rate of HbA1c synthesis reported in normal subjects using 59Fe-kinetic measurements, and is in accordance with the concept of slow changes in stable HbA1c with time and glucose concentration. To investigate the possibility that the rate of HbA1c synthesis varies with erythrocyte age, glycosylated haemoglobins were measured in erythrocyte fractions after density separation on Percoll-Albumin gradients. We found both in normal subjects and in insulin treated diabetics that the 5% least dense cells contained 70%–80% of whole blood HbA1c. Assuming the least dense cells to be the youngest erythrocytes, this observation is inconsistent with a slow linear increase in HbA1c. Similar results were obtained in six newly diagnosed insulin dependent diabetic patients both before and after the first 30 days of insulin treatment, even though a marked decrease in young cell HbA1c would be expected with the improved glucose control observed. We therefore conclude that density separation of erythrocytes is an inadequate technique to study age related HbA1c synthesis.
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  • 3
    ISSN: 1432-0428
    Keywords: Long-term mean blood glucose concentration ; glycaemic control ; haemoglobin A1c ; Type 1 diabetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Since glucose control and glycosylated haemoglobin varies asyncroneously, we have studied the steady-state relationship between these two factors. In Type 1 (insulin-dependent) diabetic patients with a constant haemoglobin A1c during the preceding 2 years, 15 ambulatory blood glucose profiles during a 5-week period showed a constant glucose level and provided a precise estimate of the mean blood glucose concentration. In addition, we studied 15 non-diabetic subjects who provided three glucose profiles and had one haemoglobin A1c determination performed. A good correlation was found for a curvilinear relationship (haemoglobin A1c=2.07 x mean blood glucose0.596, r=0.98). This close relationship indicates that glycosylated haemoglobin is a valuable, but not very sensitive, index of glucose control.
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  • 4
    ISSN: 1432-0428
    Keywords: Type 1 diabetes ; selectivity index ; glycated albumin ; renal albumin clearance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Altered filtration of macromolecules due to decreased electrical charge of the glomerular basement membrane might be the initial step in the development of albuminuria in patients with Type 1 (insulin-dependent) diabetes mellitus. We therefore investigated the selectivity index, i. e. renal clearance of non-glycated plasma albumin/clearance of glycated plasma albumin in 38 patients with Type 1 diabetes mellitus. The two albumin molecules differed slightly in charge, non-enzymatic glycated albumin being more anionic at physiological pH compared with unmodified plasma albumin. Glycated albumin in plasma and urine was determined by a specific, sensitive and highly reproducible chromatographic procedure. In diabetic patients with normal urinary albumin excretion, the selectivity index was increased threefold compared with that of non-diabetic subjects (2p〈 0.01). A significant correlation (r=0.53, 2p 〈 0.01) between haemoglobin A1c and selectivity index was demonstrated in these patients, indicating a change in charge-dependent renal filtration could possibly be attributed to non-enzymatic glycation of components in the glomerular basement membrane and tubuli. Diabetic patients with increased albumin excretion rate had a significantly lower selectivity index compared with patients with normal albumin excretion (2p 〈 0.01). A significant negative correlation (r=0.85, 2p 〈0.001, exponential curve fit) was seen between urinary albumin excretion and selectivity index in the diabetic patients, indicating that the capability of differentiating between macromolecules of different charges is again lost with increasing urinary albumin excretion. In conclusion, the selectivity index is significantly increased in Type 1 diabetic patients with normal urinary albumin excretion, possibly due to non-enzymatic glycation of structural glomerular proteins. The selectivity index is again reduced with increasing urinary albumin excretion, possibly due to structural changes different from non-enzymatic glycation. This observation is in accordance with the hypothesis that loss of anionic charges due to reduced heparan sulphate content in glomerular basement membranes plays an important role in the early stages of diabetic renal disease.
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