Glycosylated hemoglobins: increased glycosylation of hemoglobin A in diabetic patients

Changes in biomarkers of endothelial function in the blood after intracerebral hemorrhage in rats with type 2 diabetes mellitus

Clinical evidence suggests that type 2 diabetes mellitus can increase the risk of intracerebral hemorrhage and provocation of neurodegeneration. This study was aimed at evaluating biomarkers of glycemic control, lipid profile, oxidative modification of proteins, as well as the functional state of endothelium in Wistar rats with type 2 diabetes mellitus complicated by intracerebral hemorrhage. Experimental type 2 diabetes mellitus was induced by intraperitoneal injection of streptozotocin (65 mg/kg) and nicotinamide (230 mg/kg). The intracerebral hemorrhage was induced by microinjection of sterile saline containing 0.2 IU bacterial collagenase into the striatum. Assessed biomarkers included the area under glycemic curve, glycated hemoglobin, total cholesterol, triglyceride, high-density lipoprotein, advanced glycation end products, markers of oxidative modification of proteins – aldehyde- and ketonephenylhydrazones, and markers of endothelial dysfunction – homocysteine, endothelin-1, von Willebrand factor and asymmetric dimethylarginine in blood serum. Both rats with type 2 diabetes mellitus and rats with intracerebral hemorrhage and diabetes had a significant elevated glycemic control as compared to intact animals. But combined pathology was additionally characterized by an impairment of lipid profile (increased triglyceride level and decreased as total cholesterol and high-density lipoprotein) resulting in a rise in the atherogenic index of plasma. A significant increase in the content of the markers of oxidative modification of proteins was observed in both experimental groups. But the rats with intracerebral hemorrhage and diabetes only had higher levels of advanced glycation end products in comparison with intact animals. The highest levels of endothelin-1, as a biomarker of endothelial dysfunction, were observed in animals with intracerebral hemorrhage and diabetes. Homocysteine and von Willebrand factor were elevated in rats with type 2 diabetes mellitus, while acute intracerebral hemorrhage did not potentiate the further growth in its levels. Such effect was not accompanied by a marked increase of asymmetric dimethylarginine level in blood serum, although there was a clear trend. In conclusion, the development of intracerebral hemorrhage in rats with type 2 diabetes mellitus can intensify the manifestations of oxidative stress, worsen lipid profile, and aggravate endothelial dysfunction. In this case, the pathological process may have the character of a “vicious circle”.

Marked increase in rat red blood cell membrane protein glycosylation by one-month treatment with a cafeteria diet

Background and Objectives. Glucose, an aldose, spontaneously reacts with protein amino acids yielding glycosylated proteins. The compounds may reorganize to produce advanced glycosylation products, which regulatory importance is increasingly being recognized. Protein glycosylation is produced without the direct intervention of enzymes and results in the loss of function. Glycosylated plasma albumin, and glycosylated haemoglobin are currently used as index of mean plasma glucose levels, since higher glucose availability results in higher glycosylation rates. In this study we intended to detect the early changes in blood protein glycosylation elicited by an obesogenic diet. Experimental Design. Since albumin is in constant direct contact with plasma glucose, as are the red blood cell (RBC) membranes, we analyzed their degree or glycosylation in female and male rats, either fed a standard diet or subjected to a hyper-energetic self-selected cafeteria diet for 30 days. This model produces a small increase in basal glycaemia and a significant increase in body fat, leaving the animals in the initial stages of development of metabolic syndrome. We also measured the degree of glycosylation of hemoglobin, and the concentration of glucose in contact with this protein, that within the RBC. Glycosylation was measured by colorimetric estimation of the hydroxymethylfurfural liberated from glycosyl residues by incubation with oxalate. Results. Plasma glucose was higher in cafeteria diet and in male rats, both independent effects. However, there were no significant differences induced by sex or diet in either hemoglobin or plasma proteins. Purified RBC membranes showed a marked effect of diet: higher glycosylation in cafeteria rats, which was more marked in females (not in controls). In any case, the number of glycosyl residues per molecule were higher in hemoglobin than in plasma proteins (after correction for molecular weight). The detected levels of glucose in RBC were lower than those of plasma, even when expressed in molal units, and were practically nil in cafeteria-diet fed rats compared with controls; there was no effect of sex. Conclusions. RBC membrane glycosylation is a sensitive indicator of developing metabolic syndrome-related hyperglycemia, more sensitive than the general measurement of plasma or RBC protein glycosylation. The extensive glycosylation of blood proteins does not seem to be markedly affected by sex; and could be hardly justified from an assumedly sustained plasma hyperglycemia. The low levels of glucose found within RBC, especially in rats under the cafeteria diet, could hardly justify the extensive glycosylation of hemoglobin and the lack of differences with controls, which contained sizeable levels of intracellular glucose. Additional studies are needed to study the dynamics of glucose in vivo in the RBC to understand how such extensive protein glycosylation could take place.

Effects of opium addiction on some serum factors in addicts with non-insulin-dependent diabetes mellitus

The aim of this study was to determine the effect of opium on biochemical parameters in addicts with non-insulin-dependent diabetes mellitus (NIDDM). Twenty-three males and 26 females between 35 and 65 years of age, with NIDDM, addicted to opium, were selected as the case group. Twenty-three males and 26 females with NIDDM and no opium addiction served as controls. Fasting glucose, glycated haemoglobin (HbA1c), total cholesterol, high density lipoproteins-cholesterol (HDL-c), triglycerides (TGs), sodium (Na(+)), potassium (K(+)), calcium (Ca(2+)), iron (Fe(2+)), total iron binding capacity (TIBC), serum total protein, albumin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), uric acid and urea were measured in the serum of the two groups. Serum protein electrophoresis was also carried out. Compared to the control group, in addicted males with NIDDM, HbA1c, K(+) and Fe(2+) were higher, and serum total protein, ALT and HDL-c were lower. No significant difference was observed between other factors. Albumin was lower in addicts, but no significant difference was observed between the albumin/globulin ratios. In addicted females with NIDDM, serum total protein, TIBC, ALT and AST were lower compared to non-addicts. Cholesterol tends to be lower in diabetic addicted males, HbA1c in addicted females and uric acid in addicted males was higher compared to non-addicted diabetics. Their differences, however, were not significant. According to our results, smoking opium increases serum glucose and decreases HDL-c, and thus adds to metabolic disorders in NIDDM patients. It also increases potassium and Fe(2) in males and decreases TIBC in females, and could therefore potentially interfere with water and iron metabolism.

Assessing glycemic control in patients with diabetes and end-stage renal failure

Blood glucose monitoring is important in optimizing long-term outcomes in diabetic patients. Reliance on near-patient testing and the use of longer term measures of glycation are the current cornerstones. However, as this review details, there are significant problems using blood tests as measures of metabolic control in uremic diabetic patients.

Hemoglobin Görwihl [alpha2beta(2)5(A2)Pro-->Ala], an electrophoretically silent variant with impaired glycation

BACKGROUND

Some of the genetic variants of hemoglobin (Hb) and their chemically modified species are known to affect the measurement of Hb A(1c). The purpose of this study was to characterize Hb species in the blood sample of a 74-year-old German male with an exceptionally low Hb A(1c) value.

METHODS

Hemolysates from the propositus and a healthy individual were analyzed by electrophoresis, cation-exchange HPLC, boronate affinity chromatography, and electrospray ionization-mass spectrometry (ESMS). Genomic DNA was amplified by PCR, and the sequencing was performed on an ABI 310 sequencer. Functional properties of Hb were determined by oxygen equilibrium studies and CO recombination kinetics after flash photodissociation. Glycohemoglobin species were synthesized by incubating hemolysates with glucose.

RESULTS

A novel, electrophoretically silent beta chain, beta5(A2)Pro-->Ala or Hb Görwihl, was detected by cation-exchange HPLC. It accounted for approximately 44% of the total Hb and had functional properties similar to those of normal Hb A and a mild degree of heat instability. During incubation with glucose, glycation of the beta chains (assessed by ESMS) in the hemolysate of a healthy volunteer was twice as fast as in hemolysate from the propositus.

CONCLUSIONS

The substitution beta5(A2)Pro-->Ala seems to affect neither the functional properties nor the heterotropic interactions of Hb, but slows glycation of the N-terminal valine by an unknown mechanism.

Potential of electrospray mass spectrometry for quantifying glycohemoglobin

An electrospray ionization–mass spectrometric procedure has been developed for determining glycohemoglobin. Whole-blood samples from 78 diabetic and 50 nondiabetic subjects (glycation range 3–15%, as determined by electrospray mass spectrometry) were diluted 500-fold in an acidic denaturing solvent and introduced directly into a mass spectrometer. The resulting mass spectra were then processed to estimate the percentage of glycohemoglobin present in the sample. Total analysis time, including plotting the spectra and computing the percentage of glycation, was ∼3 min. The imprecision (CV) of the method was <5.1% for inter- and intrabatch analyses for total glycohemoglobin in the range 3.6–14%. Comparison of the mass spectrometric results with those from established affinity chromatographic procedures showed good overall agreement. The relative glycation of the α- and β-chains was determined directly and was shown to be constant (0.64:1) over the glycation range measured. Only single glucose attachment to both the α- and β-chains was observed.

Non-enzymatic glycation of epidermal proteins of the stratum corneum in diabetic patients

A selected group of diabetic patients showed a statistically significant increase in levels of glycated proteins in the stratum corneum compared with a control group. The values of glycated proteins correlated with those of glycohaemoglobin (GHb), and in diabetic patients also with serum glucose concentrations. The values of glycated proteins (and GHb) exhibited a positive correlation with age both in a control group and in diabetic patients. The average values of glycated proteins (and GHb) were slightly higher in women than in men. Determination of glycated proteins levels of the stratum corneum can serve as a stable parameter for long-term monitoring of the course of non-enzymatic glycation in structural and connective tissues and thus also for the prognosis of the development of dermatological complications related to diabetes mellitus. In vitro incubation of stratum corneum proteins and keratin with glucose resulted in an increase of their glycation. The values of glycated proteins and glycated keratin increased proportionally to the glucose concentration and duration of incubation. Glucose binding to keratin and proteins of the insoluble stratum corneum fraction appeared to occur at practically the same rate, and it is a first-order reaction with regard to the glucose concentration. Water-soluble proteins of the stratum corneum undergo non-enzymatic glycation preferentially (on average, 83.4% of the total amount of glycated proteins is present in the soluble fraction), regardless of the initial content of glycated proteins in the sample. The content of glycated soluble proteins of a higher molecular weight significantly increased after 4 weeks of incubation with glucose.

Glycated haemoglobin predicts progression to diabetes mellitus in Pima Indians with impaired glucose tolerance

Glycated haemoglobin could offer several practical advantages over the OGTT for assessing glucose metabolism. Initial cross-sectional studies (1983-1985) on 381 subjects (mostly Pima Indians) described the relationship between HbA1c (a specific glycated Hb) and the OGTT. We performed follow-up OGTTs and HbA1c measurements on 257 of these same subjects 1.6-6.1 years later. Subjects were again grouped according to both the result of the OGTT (normal, IGT or diabetes, by WHO criteria) and HbA1c result (normal or elevated based on mean +/- 1.96 SD of normal). Of 66 subjects with IGT at baseline, 47 (71%) had normal HbA1c and 19 (29%) had elevated HbA1c. Twenty-six (39%) of these subjects had diabetes at follow-up. Of these subjects with IGT, a significantly greater percentage of subjects with elevated HbA1c at baseline (68%) showed worsening to diabetes than those with a normal HbA1c (28%); (chi-square = 7.8, df = 1, p < 0.01). Thus, in subjects with IGT, glycated Hb may be a useful predictor of progression to diabetes.

Glycated haemoglobin centiles: a basis for audit in children's clinics?

Services for children with diabetes are a good model for audit because of relatively well-defined and available measures of outcome. Estimation of glycated haemoglobin (HbA1) is accepted as one index of control, although the assay and normal ranges vary in different centres. Sheffield has a stable clinic population and we have taken blood for HbA1 on each patient two to four times per year since 1983. HbA1 values have been aligned in 3-monthly increments from time of diagnosis to construct a graph showing the mean plus or minus two standard deviation values for the clinic population and also a rough 'centile chart' that describes the unfortunate but expected pattern of deteriorating control with duration of diabetes. There are undoubtedly methodological flaws in this novel approach; however, such charts constructed for each clinic may be a suitable basis for comparative assessment of the control of an individual and also for auditing the effects of changes in practice that strive for optimum glucose levels in the clinic population.

Aldimine to ketoamine isomerization (Amadori rearrangement) potential at the individual nonenzymic glycation sites of hemoglobin A: preferential inhibition of glycation by nucleophiles at sites of low isomerization potential

The relative roles of the two structural aspects of nonenzymic glycation sites of hemoglobin A, namely the ease with which the amino groups could form the aldimine adducts and the propensity of the microenvironments of the respective aldimines to facilitate the Amadori rearrangement, in dictating the site selectivity of nonenzymic glycation with aldotriose has been investigated. The chemical reactivity of the amino groups of hemoglobin A for in vitro reductive glycation with aldotriose is distinct from that in the nonreductive mode. The reactivity of amino groups of hemoglobin A toward reductive glycation (i.e., propensity for aldimine formation) decreases in the order Val-1(beta), Val-1(alpha), Lys-66(beta), Lys-61(alpha), and Lys-16(alpha). The overall reactivity of hemoglobin A toward nonreductive glycation decreased in the order Lys-16(alpha), Val-1(beta), Lys-66(beta), Lys-82(beta), Lys-61(alpha), and Val-1(alpha). Since the aldimine is the common intermediate for both the reductive and nonreductive modification, the differential selectivity of protein for the two modes of glycation is clearly a reflection of the propensity of the microenvironments of nonenzymic glycation sites to facilitate the isomerization reaction (i.e., Amadori rearrangement). A semiquantitative estimate of this propensity of the microenvironment of the nonenzymic glycation sites has been obtained by comparing the nonreductive (nonenzymic) and reductive modification at individual glycation sites. The microenvironment of Lys-16(alpha) is very efficient in facilitating the rearrangement and the relative efficiency decreases in the order Lys-16(alpha), Lys-82(beta), Lys-66(beta), Lys-61(alpha), Val-1(beta), and Val-1(alpha). The propensity of the microenvironment of Lys-16(alpha) to facilitate the Amadori rearrangement of the aldimine is about three orders of magnitude higher than that of Val-1(alpha) and is about 50 times higher than that of Val-1(beta). The extent of nonenzymic glycation at the individual sites is modulated by various factors, such as the pH, concentration of aldotriose, and the concentration of the protein. The nucleophiles--such as tris, glycine ethyl ester, and amino guanidine--inhibit the glycation by trapping the aldotriose. The nonenzymic glycation inhibitory power of nucleophile is directly related to its propensity to form aldimine. Thus, the extent of inhibition of nonenzymic glycation at a given site by a nucleophile directly reflects the relative role of pKa of the site in dictating the glycation at that site.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of glycation in aging and diabetes mellitus

One of the hypotheses trying to explain the process of aging is the idea of glycation of proteins. This reaction, also called the Maillard or browning reaction, may explain age-related symptoms such as cataract, atherosclerosis and modification of collagen-containing tissues. Diabetics, which possess elevated blood sugar levels, show signs of accelerated aging exposing similar complications. The Maillard reaction, which occurs on a large scale in vivo, may play a key role in the initiation of these symptoms.

Purification of glycated hemoglobin free of hemoglobin A1c and its use to produce monoclonal antibodies specific for deoxyfructosyllysine [correction of deoxyfructosyllsine] residues in glycohemoglobin

Hemoglobin nonenzymatically glycated at E-amino groups of lysine residues was purified from human erythrocyte lysates and used for immunization of BALB/c mice. Hybridomas secreting monoclonal antibodies for glycated hemoglobin were produced by fusion of mouse spleen cells with SP 2/0 myeloma cells. Immunoblotting with purified monoclonal antibody demonstrated specificity for glycated hemoglobin, with no reaction with HbAO. Glycated hemoglobin was effectively separated from other hemoglobins upon application of erythrocyte lysates to an affinity column of monoclonal antibody immobilized onto Sepharose 4B. A small fraction of purified HbA1c adsorbed to the monoclonal antibody affinity column, indicating that glycation can occur at both E-amino lysine and N-terminal valine positions in the same molecule. HbA1c did not react with the antibody after removal by immunoadsorption of molecules containing glycated lysine, confirming specificity of the antibody for deoxyfructosyl-lysine residues. The findings indicate that these monoclonal antibodies are site specific for glycated lysine amino groups in hemoglobin, and can provide rapid and efficient separation and identification of glycated hemoglobin in human erythrocyte lysates.

Comparison of glycosylated fibrinogen, albumin, and haemoglobin as indices of blood glucose control in diabetic patients

The value of glycosylated fibrinogen as an index of short-term diabetic control was compared with indices of long-term (glycosylated haemoglobin) and intermediate-term (glycosylated albumin) diabetic control, respectively. In this study, percentages of these glycosylated proteins and fasting plasma glucose concentration were determined in 95 healthy non-diabetic subjects and 48 diabetic patients (22 well-controlled and 26 poorly-controlled) after an overnight fast. The differences in the percentages of glycosylated fibrinogen, haemoglobin, and albumin between non-diabetic subjects (4.7, 6.4, and 2.0), well-controlled diabetic patients (6.9, 9.5 and 2.9), and poorly-controlled diabetic patients (11.3, 15.8, and 5.1) were statistically significant (p less than 0.05). The percent glycosylated fibrinogen exhibited significant association with severity of hyperglycaemia when diabetic patients were divided by 2, 4, and 6 standard deviations above the mean of fasting plasma glucose of non-diabetic subjects. There were significant correlations between glycosylated fibrinogen and fasting plasma glucose (r = 0.83, p less than 0.001), glycosylated haemoglobin (r = 0.94, p less than 0.001) and glycosylated albumin (r = 0.92, p less than 0.001) for all subjects studied. In ten newly diagnosed diabetic patients after 6 days of treatment, only the decrease in glycosylated fibrinogen (33.4%) was significant (p less than 0.05), but not that of glycosylated haemoglobin (4.8%) or albumin (8.0%). It is suggested that glycosylated fibrinogen provides the clinician with earlier objective evidence of the metabolic response to therapeutic intervention, and might be regarded as a short-term (2-3 days) index of blood glucose control.

Antibodies to human albumin epitopes in type 1 (insulin-dependent) diabetes mellitus

The presence of antibodies to glycosylated albumin was studied by means of a newly developed sandwich enzyme-linked immunosorbent assay in 29 long-standing Type 1 (insulin-dependent) diabetic patients with microvascular complications and in 20 normal subjects. Two types of antibody reactivity were detected. One directed against glucitol-albumin expressing G and M isotypes. The second, predominantly belonging to the IgG class, reacted with an epitope shared by non-glycosylated albumin and the ketoamine adduct of albumin glycosylation. Both types of antibodies, with affinity constant ranging from 10(4) to 10(7) (mol/l)-1 were found in normal and diabetic subjects, but higher titres were significantly more prevalent in the diabetic patients. These antibodies may represent the result of immune tolerance breakdown or, alternatively, be natural antibodies. Although their function remains to be established, their raised prevalence in Type 1 diabetes may be relevant to diabetic microvascular disease.

Intestinal adaptation to diabetes. Altered Na-dependent nutrient absorption in streptozocin-treated chronically diabetic rats

To examine the pattern and mechanisms of enhanced intestinal nutrient absorption in diabetes, we measured intestinal transport of 3-O-methylglucose (3OMG), l-alanine (ALA), and SO4 in male Lewis rats made diabetic with streptozocin. Diabetes enhanced 3OMG absorption fivefold in ileum and threefold in jejunum; ALA absorption increased twofold in ileum but not at all in jejunum; ileal SO4 transport was unaffected. Increases in 3OMG and ALA transport were due solely to increases in maximum velocity. The enhancement of ileal glucose absorption was half-maximal in 40-45 d, could be reversed by 10 d of treatment with insulin and did not result from adrenergic denervation. The density of glucose carriers per milligram brush border protein (measured as [3H]phlorizin binding sites) was not altered but there was a sixfold increase in the number of glucose-inhibitable [3H]phlorizin-binding sites in the intact epithelium. Generalized mucosal hypertrophy accounted for less than 30% of this increase. We conclude that the intestine adapts to streptozocin-induced diabetes through recruitment of additional brush border carriers for sugar, probably in the midvillus-to-crypt region.

Retrospective glycemic status of diabetic patients: glycosylation of blood proteins in diabetes and chronic renal failure

In vivo and in vitro studies were carried out to evaluate the clinical application of glycosylated hemoglobin and plasma proteins in the diagnosis and management of diabetes mellitus. Glycosylated hemoglobin registered an almost 80% fall in diabetic patients following controlled glycemia for two months while glycosylated plasma protein level registered an 80% fall in the patients after fifteen days of blood glucose homeostasis. Human serum proteins were glycosylated in vitro and glycosylation was linearly proportional to the glucose concentration and incubation time. Polyacrylamide gel electrophoresis of glycosylated serum proteins revealed that albumin and transferrin are the major proteins that are significantly glycosylated. Glycosylated hemoglobin and plasma protein levels were also increased in chronic renal failure patients without any history of diabetes.

Effects of sorbinil therapy in diabetic patients with painful peripheral neuropathy and autonomic neuropathy

Clinical investigations with the aldose reductase inhibitor sorbinil in patients with peripheral neuropathy due to diabetes are described. After an improvement in motor and sensory nerve conduction velocities was demonstrated in asymptomatic diabetic patients taking sorbinil (compared with velocities during a placebo period), 11 patients with painful diabetic neuropathy were treated with sorbinil for three weeks without alterations in diabetic management or control. Therapy was placebo-controlled in a single-blind fashion in eight patients. Pain (assessed by or on a zero to 20 rating scale), which had been constant for many months before entry into the study and unresponsive to numerous medications, improved from a mean score of 16 to 8 and returned when the drug was discontinued. Objective improvement in sensation and strength were observed in some cases. Improvements in nerve conduction velocity and cardiac autonomic function were also documented. Cardiac autonomic neuropathy was studied in 36 patients in a double-blind, placebo-controlled, randomized, noncrossover trial. Patients received one 250-mg sorbinil tablet or one placebo tablet daily for six weeks, after a one-week baseline period. Glycemic control did not change during the study period, as indicated by unaltered glycohemoglobin levels. Response was assessed by expiration-inspiration ratios, obtained on electrocardiography during six cycles per minute respiration, and by resting minimal heart rate, both measures of vagal function. In the sorbinil-treated group, expiration-inspiration ratios improved from 1.074 +/- 0.012 to 1.096 +/- 0.020 (p less than 0.03). There was a slight decrease in the ratios in the placebo-treated group, from 1.112 +/- 0.023 to 1.105 +/- 0.023 (not significant). The difference between the Week 0 to Week 6 changes in each group was significant (p less than 0.01). Resting minimal heart rate decreased in the sorbinil-treated group from 76.4 +/- 2.3 to 66.8 +/- 2.8 +/- 2.4 beats per minute (p less than 0.001), with a mean change of 10 +/- 2. In the placebo-treated group, heart rate was unchanged (77.9 +/- 3.9 to 77.5 +/- 3.3 beats per minute). The two-sample t test of the within-group differences was also significant (p less than 0.001). The changes in both expiration-inspiration ratios and resting minimal heart rate are consistent with a sorbinil-related improvement in cardiac parasympathetic nerve function. Several isolated cases of apparent sorbinil-related improvements in autonomic symptoms have been observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Diarrhea in streptozocin-treated rats. Loss of adrenergic regulation of intestinal fluid and electrolyte transport

Diarrhea was noted in rats with streptozocin-induced chronic diabetes. We have investigated the possibility that this diarrhea is a consequence of altered neuronal control of water and electrolyte absorption in the intestinal epithelium. In particular, we examined noradrenergic control because alpha-2-adrenergic agonists are known to stimulate intestinal fluid absorption. When compared with nondiabetic littermates, chronically diabetic rats exhibited significant impairment of fluid absorption by the ileum and colon, but not the jejunum. This impairment of intestinal fluid absorption was not found in either insulin-treated or untreated acutely diabetic (7 d) animals. Mucosal histology appeared normal in all of the above groups. Mucosal norepinephrine stores in the jejunum and ileum of chronically diabetic rats were estimated in vitro by the short-circuit current (Isc) response to tyramine, an agent that effectively releases stored norepinephrine. Pargyline was added to inhibit enzymatic destruction of the added tyramine. In chronically diabetic rats, the Isc response to tyramine was significantly decreased in ileum, but not in jejunum. However, when these responses were expressed as a fraction of the maximal Isc tissue response to exogenously added epinephrine, significant decreases were noted in both ileum and jejunum. In tissues from acutely diabetic rats, Isc responses to tyramine and epinephrine were no different from controls. When sympathetic denervation was produced in nondiabetic rats by treatment with 6-OH-dopamine, the pattern of impaired fluid absorption that developed was the same as that observed in chronically diabetic rats. We conclude that impaired intestinal mucosal absorption of fluid and electrolytes slowly develops in rats made diabetic with streptozocin and that this absorptive impairment is due to a loss of normally present noradrenergic innervation of enterocytes.

Glycosylated haemoglobin in normal pregnancy: a longitudinal study with two independent methods

Twenty-one women completed a longitudinal study of glycosylated haemoglobin in normal pregnancy. Glycosylated haemoglobin levels were measured using two independent techniques (ion-exchange column and colorimetric). Concurrent serial oral glucose tolerance tests (75-g glucose load) and erythrocyte indices were obtained. Changes in mean glycosylated haemoglobin were similar with both techniques with a nadir at 17 weeks, a peak at delivery (p less than 0.002 versus 17 weeks) and a fall post-partum. Glycosylated haemoglobin levels in abnormal pregnancies, e.g. diabetic, should be interpreted in the knowledge of these physiological changes.

Colorimetric measurement of glycosylated protein in whole blood, red blood cells, plasma and dried blood

A colorimetric method for the measurement of whole-blood glycosylation (WBG), glycosylated haemoglobin in red blood cells (GHb), glycosylated plasma protein (GPP) and dried-blood glycosylation (DBG) is described which is rapid, inexpensive and precise. GHb correlated well with HbA1 measured by cation-exchange chromatography and was also correlated with WBG, DBG and GPP. DBG, which showed good correlation with GHb, could be measured on several drops of blood dried on filter paper treated with glucose oxidase. Filter papers are posted to the laboratory prior to clinic visits, and by having the DBG result available more rational diabetic management is possible. For DBG, the intra- and inter-assay coefficient of variation at three levels is less than 6%. Reference values in non-diabetic children have been calculated and are compared with values obtained in 'good' clinical diabetic control and in 'fair' control. The filter-paper assay DBG method has a high degree of patient acceptance.

Alterations in lymphocyte subpopulations in type 1 (insulin-dependent) diabetes mellitus: exploration of possible mechanisms and relationships to autoimmune phenomena

Previous studies have shown a variety of immunological abnormalities in Type 1 (insulin-dependent) diabetes, including disturbances in peripheral lymphocytes and anti-lymphocyte antibodies. We measured subsets of T and natural killer cells with monoclonal antibodies in patients with diabetes, and also assayed for anti-lymphocyte antibodies using dual colour immunofluorescence and flow cytometry. We found a significant decrease in numbers of Leu 3a (helper/inducer) cells in Type 1 diabetic patients of recent onset and intermediate levels in patients with longer duration of the disease. Leu 4 (pan T cell) levels were reduced in Type 1 diabetic patients of more than 4 months duration. Leu 7 (natural killer cells) were increased in Type 2 (non-insulin-dependent) diabetic patients. Individual Type 1 diabetic patients of recent onset showed low levels of Leu 7 and 11 a (natural killer cell) levels with normal 3a levels. Autoantibodies against Leu 3a + cells were present in higher titres in the Type 1 diabetic patients of recent onset than in control subjects. We conclude: (1) Leu 3a cells may be decreased in Type 1 diabetic patients of recent onset and return to normal with time; (2) low numbers of Leu 7 and 11a cells with normal numbers of Leu 3a may be seen in some Type 1 diabetic patients of recent onset, which may help explain previous reports of decreased suppressor cells; (3) Leu 7 levels may be increased in Type 2 diabetes; (4) autoantibodies against Leu 3a + peripheral lymphocytes may be seen in Type 1 diabetic patients of recent onset. These appear to be a marker of autoimmune phenomena rather than immunological mediators.

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.

Glycosylated haemoglobin in cord blood following normal and diabetic pregnancies

Cord and maternal blood samples were obtained at delivery in 25 normal and 14 diabetic pregnancies (13 insulin-dependent, one gestational). Total glycosylated haemoglobin, measured by the colorimetric thiobarbiturate method (mmol hydroxymethylfurfural/mol haemoglobin), was lower in cord than maternal blood (mean 18.7 +/- 1.7 versus 26.5 +/- 2.1, mean +/- SD, p less than 0.001). Glycosylated haemoglobin was higher following diabetic pregnancies, both in cord (diabetic 19.9 +/- 1.6 versus normal 17.9 +/- 1.4, p less than 0.001) and maternal samples (diabetic 27.7 +/- 1.5 versus normal 25.6 +/- 2.1, p less than 0.005). Cord and maternal glycosylated haemoglobin correlated in the normal (r = 0.60, p less than 0.01) but not in the diabetic group (r = 0.02, NS). Birth weight ratio was higher in infants of diabetic than of normal mothers (1.10 +/- 0.16 versus 0.99 +/- 0.13, p less than 0.05) but failed to correlate with cord or maternal glycosylated haemoglobin or, in the diabetic group, with mean blood glucose.

Characterization of glycosylated hemoglobins. Relevance to monitoring of diabetic control and analysis of other proteins

Boronate affinity chromatography and ion exchange chromatography were used to measure the levels of glycosylated hemoglobins in normal and diabetic hemolysates, as well as the distribution of glucose adducts on alpha-NH2-valine and epsilon-NH2-lysine residues. When analyzed by ion exchange chromatography on BioRex 70 resin, the Hb Alc peak comprised 4.4 +/- 0.6% of 15 normal hemolysates and 9.1 +/- 2.1% of 15 diabetic hemolysates. The "Hb Alc" was rechromatographed on GlycoGel B boronate affinity resin that binds vicinal hydroxyl groups of covalently linked sugars. Only 70 +/- 5% of the hemoglobin adhered to the resin. Analysis by the thiobarbituric acid colorimetric test confirmed that the affinity resin effectively separated glycosylated from nonglycosylated hemoglobin. When corrected for nonglycosylated contaminants, the mean level of Hb Alc in normal hemolysates was 2.9 +/- 0.4%, a value considerably lower than those previously reported. In addition to Hb Alc, 5.2 +/- 0.5% of the remaining hemoglobin (Hb Ao) was glycosylated. In diabetics, glycosylated Ao was increased in parallel with Hb Alc. After reduction with [3H]borohydride and acid hydrolysis, glycosylated amino acids were first purified on Affi-Gel boronate affinity resin and then analyzed by ion exchange chromatography. The glucose adducts on Hb Ao were distributed as follows: alpha-chain N-terminal valine, 14%; alpha-chain lysines, 40%; beta-chain lysines, 46%. This study has revealed several pitfalls in the analysis of nonenzymatically glycosylated proteins. Peaks isolated by ion exchange chromatography or electrophoresis are likely to be contaminated by nonglycosylated proteins. Furthermore, both the thiobarbituric acid test and [3H]borohydride reduction show variable reactivity depending upon the site of the ketoamine-linked glucose.

Separation of glycosylated haemoglobins using immobilized phenylboronic acid. Effect of ligand concentration, column operating conditions, and comparison with ion-exchange and isoelectric-focusing

Haemoglobins from diabetic and non-diabetic individuals have been separated by affinity chromatography using immobilized phenylboronate, which interacts specifically with diol-containing compounds such as glycosylated haemoglobin. The effects of ligand concentration, flow rate, column geometry, preincubation of sample, buffer composition and temperature have been investigated. Significant correlation was found between results from affinity-chromatography and ion-exchange and isoelectric-focusing methods. Isoelectric-focusing of the haemoglobin fractions obtained from affinity chromatography indicate that, in addition to haemoglobin A1c, some haemoglobin A is also bound to immobilized phenylboronic acid. Assays of haemolysates obtained from red blood cells incubated in glucose solutions suggest that unstable pre-(haemoglobin A1c) does not interfere. The assay is not affected by the presence of haemoglobin F.

Low serum 3, 5, 3'-triiodothyronine (T3) and raised 3, 3', 5'-triidothyronine (reverse T3 or RT3) in diabetes mellitus: normalization on improvement in hyperglycemia

In several pathophysiologic states, i.e., cirrhosis of liver, protein calorie malnutrition, starvation, carbohydrate deprivation, etc., thyroid hormone metabolism is reported to be altered with a decrease in serum T3 and a reciprocal increase in TR3. Uncontrolled diabetes mellitus is a similar state in which glucose does not enter the cells causing cellular starvation and hyperglycemia ensues. Therefore, serum T4, T3, RT3, T3-resin uptake, TSH, and glucose were determined after an overnight fast in 94 male diabetics (aged 28 to 85 years) during a routine follow-up visit to the outpatient clinic and 24 healthy male adults (aged 24 to 81 years). Glycosylated hemoglobin concentrations were measured as well in normal subjects and 16 newly discovered diabetics. In normal subjects, no significant relationships between fasting plasma glucose and T3 and RRT3 levels were observed. In diabetics there was a significant positive (r = 0.611; p less than 0.001) correlation between glucose and RT3. Similarly, a significant negative relationship was observed between glucose and T3 (r = 0.491; p less than 0.001). T4, free T4, T3-resin uptake, and TSH were normal in diabetics. In 16 newly discovered diabetics, with fasting plasma glucose greater than 200 mg/dl, serum T3 rose (96 +/- 5 to 128 +/- 5 ng/dl) and RT3 declined (26.3 +/- 10.4 +/- 1.4 ng/dl) on improvement of hyperglycemia (fasting plasma glucose less than 140 mg/dl) after intensive therapy for 6 to 8 weeks. Glycosylated hemoglobin levels declined as well (14.6 +/- 0.9% to 9.3 +/- 0.7%). These data indicate: (1) thyroid hormone metabolism may be altered in diabetes mellitus with a fall in serum T3 and a reciprocal rise in RT3; and (2) T3 and RT3 concentrations may serve as indicators of metabolic control in diabetes mellitus.

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.

HbA1 determination by agar gel electrophoresis after elimination of labile HbA1: a comparison with ion-exchange chromatography

A rapid and simple method, Agar gel electrophoresis (GlytracTM, Corning Medical), for HbA1 analysis was evaluated and compared with an ion-exchange chromatography method capable of estimating HbA1 (a+b) and HbA1c separately. Preincubated samples from diabetics and normals were analysed by both methods and showed good correlation (r=0.97, n=89). The following data were obtained with agar gel electrophoresis. Incubation of erythrocytes at a glucose concentration of 30 mmol/l for 6 h at 37 degrees C gave an increase of 1.39% HbA1. This increase was almost reversed by reincubation in low glucose medium. By preincubation of erythrocytes in saline HbA1 decreased 0.90 +/- 0.39% HbA1 (mean +/- SD) in diabetics and 0.38 +/- 0.26% HbA1 in normal controls. This preincubation step is necessary to eliminate the labile HbA1 fraction when HbA1 is to be used as an index of long term glucose control in diabetes. The HbA1 ranged from 5.1 to 7.4% (n=68), mean 5.8% (SD 0.5). HbA1 in patients with juvenile diabetes ranged from 6.1 to 19.3%. Within-run precision (CV) was 2.3 and 2.5% in normal and diabetic samples, respectively. Between-run precision was 5.7%. Variation in temperature between 18.5 and 31.5 degrees C did not affect the HbA1 values significantly. Within-run and between-run precision for chromatography was 3.4 and 4.7% respectively. Agar gel electrophoresis is a simple and rapid method for HbA1 determination, with acceptable precision and accuracy.

Non-enzymatically glycosylated serum protein in diabetes mellitus: an index of short-term glycaemia

We measured non-enzymatically-glycosylated serum protein by a colorimetric assay in 107 diabetic and 82 control subjects. The mean level in diabetics was more than twice that in controls. Cross sectional and longitudinal studies in diabetic patients showed that glycosylated serum protein levels correlated with both fasting serum glucose and glycosylated haemoglobin levels. The correlation between glycosylated serum protein and fasting serum glucose was closer in Type 2 than in Type 1 diabetes. Treatment aimed at improving control in eight poorly controlled diabetic patients resulted in a 37% mean fall in glycosylated serum protein within one week, whereas glycosylated haemoglobin decreased only 8%. These studies confirm that non-enzymatic glycosylation of serum proteins is enhanced in diabetes. Measurement of glycosylated serum protein appears to provide an index of glycaemia over the preceding several days. It has the advantage of detecting improvements in glycaemic control much sooner than does glycosylated haemoglobin measurement.

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.

The clinical utility of glycosylated hemoglobin

Measurement of glycosylated hemoglobins in diabetic patients has been available to clinicians for about five years. Such measurements correlate with mean serum glucose determinations over time; therefore, they have stimulated a number of studies to determine (1) if these assays are useful in diagnosing diabetes, (2) the clinical utility of determinations of minor hemoglobins in monitoring diabetic control, and (3) the relationship of glucose "control" (as indicated by concentrations of glycosylated hemoglobins) to abnormalities or "sequelae" of the diabetic state. High concentrations of glycosylated hemoglobins are highly specific for diabetes, and positive findings provide a useful diagnostic test. However, this measurement is less sensitive than a glucose tolerance test. As a clinical tool, these hemoglobins are most useful in labile diabetes, i.e., juvenile-onset diabetes and diabetes in pregnancy. In adult-onset diabetes, the fasting serum glucose concentration is apt to correlate well with the concentration of hemoglobins A1a-c. A correlation between several abnormalities associated with diabetes mellitus and concentrations of hemoglobins A1a-c have been reported. These abnormalities include abnormalities of the erythrocyte, leukocyte, platelet, and coagulation cascade and hormonal profiles in juvenile-onset diabetes and diabetes in pregnancy. In addition, correlation have been reported between certain risk factors or abnormalities, associated with vascular disease and concentrations of minor hemoglobins, including lipid profiles microvascular disease as reflected by retinal changes and quadriceps capillary basement membrane thickening, and macrovascular disease as reflected by pulse volume recordings. These studies have led to a reevaluation of the role of glucose "control" in contributing to diabetic sequelae, and, thus, have stimulated new approaches to the management 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.

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.

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.