Kenji Shima

Kinetics of HbA1c, Glycated Albumin, and Fructosamine and Analysis of Their Weight Functions Against Preceding Plasma Glucose Level

OBJECTIVE To examine the kinetics of HbA1c, glycated albumin (GA), and fructosamine (FA) levels in response to plasma glucose change and their relationship with the preceding plasma glucose level. RESEARCH DESIGN AND METHODS The time courses of HbA1c, GA, and FA after acute glycemic normalization were observed in nine patients with newly diagnosed non-insulin-dependent diabetes mellitus and compared with theoretical ones. Their weight functions against preceding plasma glucose level were analyzed assuming a stepwise plasma glucose change and compared with the theoretical prediction. RESULTS The fasting plasma glucose level was acutely normalized after admission with a half-time of 6.3 ± 2.4 days (mean ± SD). The HbA1c level decreased linearly during the initial 2 months with a half-time of 34.6 ± 10.1 days, followed by a gradual decrease thereafter. GA and FA levels decreased very rapidly during the initial 2–3 weeks with half-times of 17.1 ± 2.8 and 12.2 ± 4.8 days, respectively, followed by a gradual decrease thereafter. The time courses of HbA1c, GA, and FA agreed well with theoretically estimated decay curves. Experimental values of weight functions against the preceding plasma glucose level agreed well with the theoretical prediction. The weight functions for glycated proteins had maximum values on the days just before the measurement of glycated proteins and gradually decreased with an increasing time interval. The lengths of the periods over which the weight functions for HbA1c, GA, and FA extend back were estimated to be roughly 100, 40, and 30 days, respectively. CONCLUSIONS The levels of HbA1c, GA, and FA do not reflect the simple mean but reflect the weighted mean of the preceding plasma glucose level over a considerably longer period than was previously speculated.

Leptin Receptor of Zucker Fatty Rat Performs Reduced Signal Transduction

Zucker fatty (fa/fa) rats exhibit overt obesity, hypercholesterolemia, hyperlipidemia, and hyperglycemia as recessive traits. The fa mutation has been determined to be a missense mutation in the extracellular domain of the leptin receptor. We report herein the construction of CHO cells that stably express the fa-type leptin receptor and the characterization of this receptor using mRNA expression levels of the immediate early genes, c-fos, c-jun, and jun-B, which are induced by leptin as a criterion of signal transduction. The fa-type receptor not only exhibits a slightly reduced leptinbinding affinity, but also performs reduced signal transduction.

Correlation Between Minimal Secretory Capacity of Pancreatic β-Cells and Stability of Diabetic Control

The significance of the minimal secretory capacity of pancreatic β-cells for the stability of the plasma glucose level was studied in 20 patients with insulin-dependent diabetes mellitus. Changes in plasma concentrations of major counterregulatory hormones in response to hypoglycemia were also investigated in these patients to clarify their contribution to diabetic brittleness. β-Cell function was evaluated on the basis of elevation of plasma C-peptide immunoreactivity (CPR) during the intravenous glucagon test with a highly sensitive assay for plasma CPR that could detect as little as 0.03 ng/ml. After stimulation with glucagon, a significant increase in plasma CPR was observed in 10 of the patients whose β-cell function had been evaluated as completely depleted by a conventional assay for plasma CPR. A clear inverse correlation was found between the secretory capacity of pancreatic β-cells measured in this way and the degree of glycemic instability (r = −.74, P < .01). Infusion of insulin at a rate of 0.15 U.kg−1.h−1 for 60 min caused a continuous decrease in the plasma glucose level, resulting in neuroglycopenia in 7 of the 10 CPR nonresponders but only 2 of the CPR responders. During insulin-induced hypoglycemia, plasma glucagon immunoreactivity did not increase in the CPR nonresponders but increased significantly in the CPR responders. A positive correlation was found between the minimal residual β-cell capacity and the responsiveness of α-cells to hypoglycemia (r = .65, P < .01).In contrast to the difference in the responses of their pancreatic α-cells to hypoglycemia, the two groups showed more or less the same responses of plasma epinephrine, norepinephrine, growth hormone, and cortisol to hypoglycemia. Total lack of insulinogenic reserve inevitably results in loss of automatic regulation of the circulating insulin level and seems to be a major factor in causing hyperlability of diabetic control. The lack of β-cell function may be related causally to pancreatic α-cell dysfunction, which also contributes in part to metabolic variability in brittle diabetes.

Effect of Exercise Training and Food Restriction on Endothelium-Dependent Relaxation in the Otsuka Long-Evans Tokushima Fatty Rat, a Model of Spontaneous NIDDM

We investigated whether endothelial function may be impaired in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model of spontaneous NIDDM. The effect of exercise training and food restriction on endothelial function was also studied. OLETF rats were divided into three groups at age 16 weeks: sedentary, exercise trained, and food restricted (70% of the food intake of sedentary rats). Otsuka Long-Evans Tokushima rats were used as the age-matched nondiabetic controls. Endothelium-dependent relaxation of the thoracic aorta induced by histamine was significantly attenuated in the sedentary or food-restricted rats, and exercise training improved endothelial function. Relaxation induced by sodium nitroprusside, a donor of nitric oxide, did not differ significantly among groups. Both exercise training and food restriction significantly suppressed plasma levels of glucose and insulin and serum levels of triacylglycerol and cholesterol and reduced the accumulation of abdominal fat. Insulin sensitivity, as measured by the hyperinsulinemic- euglycemic clamp technique, was significantly decreased in sedentary rats but was enhanced in exercise- trained and food-restricted rats. The urinary excretion of nitrite was significantly decreased in sedentary and food-restricted rats compared with nondiabetic rats and was significantly increased in exercise-trained rats. These results indicate that exercise training, but not food restriction, prevents endothelial dysfunction in NIDDM rats, presumably due to the exercise-induced increase in the production of nitric oxide.

Is caloric restriction effective in preventing diabetes mellitus in the Otsuka Long Evans Tokushima fatty rat, a model of spontaneous non-insulin-dependent diabetes mellitus?

Studies were made on the effectiveness of caloric restriction in preventing the development of diabetes mellitus in a model rat (Otsuka-Long-Evans-Tokushima Fatty; OLETF) with non-insulin-dependent diabetes mellitus (NIDDM). Groups of 8 male OLETF rats aged 5 weeks were supplied with rat chow ad libitum (100% group) and 85% and 70% of the amount of food consumed by the 100% group (85% and 70% groups, respectively). The average weights of the 100%, 85% and 70% groups were 617, 536 and 450 g at 19 weeks of age and their abdominal fat deposits were 50, 38 and 21 g, respectively, at 22 weeks of age when they were killed. At 20 weeks of age, the cumulative incidences of diabetes mellitus in the 100%, 85% and 70% groups were 67%, 13% and zero, respectively. The plasma immunoreactive insulin (IRI) levels 60 and 120 min after oral glucose administration were significantly lower in the 70% group than in the other groups. In vivo insulin-stimulated glucose uptake measured by a euglycemic clamp technique, was significantly higher in the 70% group than in the 100% group. There was no significant difference in the glucose transporter 4 protein levels of skeletal muscles in the three groups, but the highest ratio of glucose transporter 4 in the plasma membrane to that in intracellular membranes was observed in the 70% group. Morphological studies on the pancreas of rats in the 100% group showed enlarged multilobulated fibrotic islets, whereas sections of islets of rats in the other groups appeared normal, though slightly enlarged. These results demonstrate that caloric restriction is effective in preventing NIDDM in diabetes-prone rats, probably due to increased insulin sensitivity.

The Response of GHb to Stepwise Plasma Glucose Change Over Time in Diabetic Patients

G lycation of red cell hemoglobin and serum proteins is increased in diabetic patients by chronic hyperglycemia. Because glycation takes place throughout the life span of these proteins, the levels of glycated proteins provide information about the degree of hyperglycemia, during their life span. GHb is generally considered to reflect the mean plasma glucose level in the preceding 2 3 mo, whereas glycated albumin is considered to reflect the mean plasma glucose level in the preceding 2 -3 wk. However, this idea is not clearly verified because few reports answered the question of exactly how the plasma glucose level, in the preceding period, contributes to the level of glycated proteins. In a recent paper (1), we analyzed the relationship between the level of glycated protein and the preceding plasma glucose level using a linear kinetic model. We derived a simple, generalized formula, which describes how the plasma glucose level in the preceding period contributes to the level of glycated protein. The results indicate that the level of glycated protein reflects the weighted mean plasma glucose level found in the past. To examine whether or not this result is applicable to GHb levels in humans, we analyzed responses of HbAlc levels to stepwise plasma glucose decrements in 10 NIDDM patients. Glycemic control of these patients was very poor on admission: FPG > 11 mM and HbAlc > 10%. Their plasma glucose level was rapidly normalized after admission, and FPG was kept <8 mM over 4 mo. Four patients were treated with insulin, 5 with oral hypoglycemic agent, and 1 with diet alone. Plasma glucose was measured by the glucose oxidase method. HbAlc was measured by the HPLC method using HLC-723GHb (Tosoh, Tokyo, Japan). The mean ± SD FPG level on admission was 15.5 ± 2.6 mM and was rapidly reduced to 10.2 ± 2.6, 8.1 ± 2.0, 7.0 ± 1.2, 6.6 ± 0.7, 7.0 ± 1.0, 6.6 ± 0.8, and 6.4 ± 0.7 mM after 1, 2, 3, 4, 8, 12, and 16 wk, respectively. The half-time of FPG change was 6.9 ± 2.6 days. The HbAlc level was 12.7 ± 2.5% on admission and was gradually reduced to 9.9 ± 1.7, 8.3 ± 1 . 1 , 7.3 ± 0.8, and 6.6 ± 0.6% after 4, 8, 12, and 16 wk, respectively. The proportion of the total change in HbAlc during 4, 8, 12, and 16 wk was 45 ± 7, 71 ± 7, 87 ± 6, and 98 ± 4% (theoretically 41, 72, 91, and 99.6%, respectively). The times for 50 and 75% HbAlc change were 32 ± 6 and 63 ± 11 days (theoretically, 35 and 60 days). The time course of HbAlc change closely agreed with the theoretical prediction (Fig. 1).

High-performance liquid chromatographic assay of serum glycated albumin

SummaryA method for determination of serum glycated albumin by high-performance liquid chromatography is presented. The system involves anion exchange chromatography to separate albumin and consecutive boronate affinity chromatography to separate glycated and nonglycated albumin. The method is rapid (20 min), precise (coefficient of variation, 0.7–4.9%), requires only a small sample (5 μl), and can be automated. Assay of glycated albumin by this method is not influenced by the protein concentration of the sample or the presence of glucose. The variation in glycated albumin values in consecutive samples obtained within a day from diabetic patients (coefficient of variation, 2.02±0.65%) was significantly smaller (p<0.001) than that of values for fructosamine (coefficient of variation, 4.33±2.0%). The values of glycated albumin in normal subjects (20.2±1.6%) were clearly less than those in diabetic patients [39,6±5.4% in 40 Type 1 (insulin-dependent) and 39.4±5.9% in 25 Type 2 (non-insulin-dependent) patients]. The serum glycated albumin level was well correlated with HbA1c in 65 diabetic patients (r=0.60). Because the life span of albumin in the circulation is short, measurement of glycated albumin should be useful as a short-term index of glycaemic control.

Which is the primary etiologic event in Otsuka Long-Evans Tokushima Fatty rats, a model of spontaneous non—insulin-dependent diabetes mellitus, insulin resistance, or impaired insulin secretion?

To identify the primary disorder causing diabetes mellitus in a model rat (Otsuka Long-Evans Tokushima Fatty [OLETF]) with non-insulin-dependent diabetes mellitus (NIDDM), we studied the temporal relationship between insulin resistance and impairment of pancreatic beta-cell function. Groups of 28 male OLETF rats and male nondiabetic control Long-Evans Tokushima Otsuka (LETO) rats were given an intravenous (i.v.) glucose and glucagon tolerance test (IVGTT) and hyperinsulinemic euglycemic clamp tests at 10, 16, 24, and 40 weeks of age. After the euglycemic clamp test, abdominal fat was measured and the pancreas was examined histologically. At 16 weeks of age, insulin-mediated whole-body glucose uptake as measured by the hyperinsulinemic euglycemic clamp technique was significantly reduced in OLETF rats (glucose infusion rat [GIR], 40.9 +/- 4.2 mumol/kg.min) as compared with LETO rats (78.4 +/- 6.9). On the other hand, plasma insulin responses to glucose and glucagon in OLETF rats were higher than those in LETO rats at 16 and 24 weeks of age, but clearly decreased at 40 weeks of age (sigma immunoreactive insulin [IRI] to glucagon, 8.81 +/- 1.81 v 27.32 +/- 4.59 nmol.min in OLETF and LETO rats, respectively, P < .01). Abdominal fat deposition was significantly greater in OLETF rats than in LETO rats at all ages tested except 10 weeks. Pancreatic islets of OLETF rats became enlarged and fibrotic. These results demonstrated that insulin resistance preceded impairment of pancreatic beta-cell function in OLETF rats, and that insulin resistance seemed closely related to fat deposition in the abdominal cavity.

Dynamic Changes in Serum Leptin Concentrations during the Fetal and Neonatal Periods

We investigated the dynamics of the leptin concentration throughout the perinatal period. Serum leptin concentrations in venous cord blood at different gestational ages were measured in 20 preterm and 139 term newborns, as well as in 143 pregnant women and 24 term newborns at approximately 6 d of life. Leptin concentrations in preterm newborns (mean 4.6 ± 6.9 ng/mL) were lower than those in term newborns (mean 19.6 ± 14.3 ng/mL) and tended to increase according to gestational age and birth weight, especially from the late stage of gestation. Leptin concentrations in pregnant women increased from the first trimester and then remained higher than those in non-pregnant women throughout the remainder of pregnancy even after controlling for body mass index. The leptin concentrations of newborns declined rapidly and were extremely low by approximately 6 d of life (mean 1.9 ± 1.1 ng/mL). These results suggest that fetuses might produce a part of circulating leptin in their own adipocytes and that the relatively high leptin concentrations at birth and their rapid decline in the early neonatal period might reflect the dramatic changes of the hormonal and nutritional state during the perinatal period.

Is exercise training effective in preventing diabetes mellitus in the Otsuka-Long-Evans-Tokushima Fatty rat, a model of spontaneous non-insulin-dependent diabetes mellitus?

We determined whether exercise training is effective in preventing the development of diabetes mellitus in a model rat (Otsuka-Long-Evans-Tokushima Fatty [OLETF]) with non-insulin-dependent diabetes mellitus (NIDDM). Thirty male OLETF rats aged 5 weeks were assigned to one of the following three groups: trained rats placed individually in an exercise wheel (EW) cage, EW-control rats housed in the same cages equipped with a fixed rotatory wheel, and sedentary rats maintained two or three to a conventional cage. Eight male diabetes-resistant Long-Evans rats were used as nondiabetic controls. At 24 weeks of age, the trained, EW-control, sedentary, and nondiabetic control rats weighed an average of 445, 559, 621 and 513 g and had abdominal fat deposits of 16, 55, 67, and 23 g, respectively. The mean amount of exercise of trained rats was 5,243 m/d. At 24 weeks of age, the cumulative incidences of diabetes mellitus in sedentary and EW-control rats were 78% and 50%, respectively, while neither trained nor nondiabetic control rats became diabetic. Fasting and 120-minute plasma immunoreactive insulin (IRI) levels after oral glucose administration were significantly lower in the trained group than in the other groups. In vivo insulin-stimulated glucose uptake as measured with a euglycemic clamp was reduced 37% in sedentary rats and increased 35% in trained rats compared with that in nondiabetic control rats. Morphological studies on the pancreas of sedentary and EW-control rats showed enlarged multilobulated fibrotic islets, whereas sections of islets from trained rats appeared normal but slightly enlarged.(ABSTRACT TRUNCATED AT 250 WORDS)