Pathophysiological study of the non-insulin-dependent phase of type I diabetes mellitus

Summary The usual practice of considering type I diabetes synonymous with insulin-dependent diabetes has been criticized. Since type I diabetes can have a non-insulin-dependent phase (pre-type I diabetes and/or honeymoon) the differentiation of two main types of diabetes according to insulin-dependency is not absolute. We studied the insulin, C-peptide and glucagon responses to various tests (OGTT, IVGTT, glibenclamide test, mixed meal tolerance test and ITT) performed during the non-insulin-dependent phase of 3 young patients (range 8–18 years) who developed ketosis 12–24 months after the discovery of fasting hyperglycemia, and in 6 patients (age 15–23 years) who presented a remission phase 4–6 months after the sudden clinical onset of type I diabetes. An insignificant insulin and C-peptide increase following i.v. glucose was observed in all patients, wheras the B-cell response to both oral glucose and other secretagogues was preserved, although at a subnormal level. In the three hyperglycemic and preketoacidotic patients the basal levels of glucagon were low and no significant increase after secretagogues was seen. Sensitivity to exogenous insulin in all patients was good. Thus, B-cell response in our patients was reminiscent of the differential responsiveness to various stimulants in the early stage of type II (non-insulin-dependent) diabetes. These results suggest that type I and type II diabetes can be characterized by the same functional B-cell defect during a period of their natural history.     

2型糖尿病第1时相胰岛素分泌受损治疗策略

2型糖尿病(T2DM)两大发病机制是胰岛素抵抗和胰岛细胞分泌受损。研究表明，有T2DM相似遗传背景的人群中，如同卵双生子或T2DM的一级亲属，第1时相胰岛素分泌减低。B细胞第1时相胰岛素分泌受损与糖尿病个体从糖耐量正常(NGT)向糖耐量受损(IGT)，并向糖尿病的转归有关，并且可预测糖尿病进程，是糖尿病发病的独立危险因素。     

Importance of early phase insulin secretion to intravenous glucose tolerance in subjects with type 2 diabetes mellitus.

Insulin secretion is impaired in type 2 diabetes with the early response being essentially absent. The loss of this early insulin secretion is hypothesized to be important in the deterioration of glucose tolerance. To determine whether enhancement of the early-phase insulin response can enhance glucose tolerance, we administered 1) 120 mg nateglinide, an insulinotropic agent that enhances early insulin secretion; 2) 10 mg glyburide, which enhances the later phases of insulin secretion; or 3) placebo in random order to 21 subjects with type 2 diabetes (14 males and 7 females; aged 59.2 +/- 2.1 yr, x +/- SEM; body mass index 29.7 +/- 1.0 kg/m(2); fasting plasma glucose 8.1 +/- 0.1 mM). beta-Cell function was quantified as the incremental area under the curve for different time periods for the 5 h following iv glucose administration and glucose tolerance as the glucose disappearance constant (Kg) from 10 to 60 min. Insulin release commenced immediately after nateglinide administration, even before glucose injection, but this was not observed with glyburide. Both nateglinide and glyburide enhanced glucose-induced insulin release, compared with placebo (area under the curve -15-300 min: nateglinide 23,595 +/- 11,212 pM/min, glyburide 54,556 +/- 15,253 pM/min, placebo 10,242 +/- 2,414 pM/min). The profiles of insulin release demonstrated significant enhancement of release between -15 and 30 min for nateglinide, compared with glyburide and between 60 and 300 min for glyburide over nateglinide. Kg increased by 15% with nateglinide (0.87 +/- 0.04%/min), but it did not increase significantly with glyburide (0.79 +/- 0.04%/min), compared with placebo (0.76 +/- 0.04%/min). The enhancement of insulin release by glyburide resulted in a lower minimal glucose concentration with glyburide (3.8 +/- 0.2 mM), compared with nateglinide (5.0 +/- 0.2 mM) and placebo (5.9 +/- 0.2 mM). Thus, enhancement of the early phase of insulin secretion improves iv glucose tolerance, whereas delaying it by 30 min results in a slower rate of glucose disappearance for the first 2 h after iv glucose administration. Further, the differences in the kinetics of nateglinide and glyburide action results in continued insulin release with glyburide despite the fact that glucose levels have returned to basal, thus resulting in a further reduction in glucose levels and a lower nadir.     

The first and second phase of insulin secretion in naive Chinese type 2 diabetes mellitus

Impaired insulin secretion (ISEC) has been recognized as one of the most important pathophysiologies of type 2 diabetes mellitus. There are 2 phases of ISEC: the first phase (first ISEC) and second phase (second ISEC). This study aimed to evaluate the 2 phases of ISEC in newly diagnosed type 2 diabetes mellitus patients. Fifty-two drug-naive type 2 diabetes mellitus patients were given 2 tests: a modified low-dose graded glucose infusion (M-LDGGI) and frequent sample intravenous glucose tolerance test. The M-LDGGI is a simplified version of the Polonsky method. Two stages of intravenous infusion of glucose with different rates were given, starting from 2 mg/(kg min) and then followed by 6 mg/(kg min). Each stage was maintained for 80 minutes. The results were interpreted as the slope of the changes of plasma insulin against the glucose levels. The slope of these curves was regarded as the second ISEC and used as the criterion for grouping-the responders and nonresponders. The responders are older and had higher body mass index and log (homeostasis model assessment of β-cell function) (log HOMA-β) but lower fasting plasma glucose and hemoglobin A_1c (HbA_1c) than the nonresponders. Significant correlations were only noted between the second ISEC and first ISEC (r = 0.278, P = .046) and between the second ISEC and log HOMA-β (r = 0.533, P = .000). Correlation between different parameters and HbA_1c was also evaluated. Only second ISEC and log HOMA-β were correlated significantly with HbA_1c (r = −0.388, P = .015 and r = −0.357, P = .026, respectively). In type 2 diabetes mellitus, subjects with higher second ISEC are older and have higher body mass index. At the same time, second ISEC is the most important factor for determining glucose levels in naive Chinese type 2 diabetes mellitus patients. The first and second ISECs were only modestly correlated, which indicated that the deterioration of these 2 phases was not synchronized. Finally, we also recommend using the M-LDGGI for quantifying second ISEC. This practical method could be done in many centers without difficulty.     

Coeliac autoimmunity in type I diabetes mellitus

Background and study aimsCoeliac autoimmunity (CA) has a known association with type 1 diabetes mellitus (T1DM) for which screening is routinely recommended but less frequently followed. The impact of CA in T1DM has been variably reported. The aims of this study are as follows: (1) to study the prevalence of CA in patients with T1DM and (2) to study the impact of CA not only on nutritional parameters but also on glycaemic control, endocrine axes and bone health.Patients and methodsEighty-six consecutive patients with T1DM were screened for CA using immunoglobulin A (IgA) tissue transglutaminase as a marker (TTG; IgG anti-gliadin in IgA-deficient case). CA positive (CA+) cases were compared with age-matched and sex-matched CA negative (CA−) T1DM cases for anthropometry, glycaemic control (assessed by glycated haemoglobin (HbA1c) and hypoglycaemic/hyperglycaemic episodes), endocrine (thyroid function, cortisol, growth hormone (GH) axis, gonadal axes), haematological (haemoglobin, iron profile and vitamin B₁₂ status) and calcium metabolism parameters and bone densitometry (by dual-energy X-ray absorptiometry (DXA)). Consenting patients with CA also underwent upper gastrointestinal (GI) endoscopy with duodenal biopsy.ResultsOut of 86 patients, 11 (12.75%) screened positive for CA (seven patients underwent duodenal biopsies which were suggestive of Marsh grade III(2), II(3) and I(2) disease). The CA+ T1DM patients were comparable with CA− T1DM in terms of anthropometry. CA+ patients had higher HbA1c (10.7 ± 1.8 vs. 8.4 ± 1.0 (93 ± 19 vs. 68 ± 11 mmol/mol); p < 0.01), more hypoglycaemic episodes (five vs. two; p < 0.05), higher prevalence of iron and vitamin B₁₂ deficiency, lower insulin-like growth factor-1 (IGF-1) levels and lower bone mineral density (BMD) z-score at total body (−1.91 ± 1.05 vs. −0.63 ± 0.73; p < 0.05) and lumbar spine (−1.69 ± 0.92 vs. −0.36 ± 0.93; p < 0.05). The incidence of fractures in the past 3 years was also more in CA+ patients than in CA− patients (four vs. one; p < 0.05).ConclusionCA has an important autoimmune association with T1DM. The concomitant presence of CA adversely affects stature, bone health, glycaemic control and iron and B₁₂ levels in T1DM. IgA sufficiency should be ensured before using an IgA-based screening test for CA.     

Abnormalities in insulin secretion in type 2 diabetes mellitus

Type 2 diabetes mellitus is a multifactorial disease, due to decreased glucose peripheral uptake, and increased hepatic glucose production, due to reduced both insulin secretion and insulin sensitivity. Multiple insulin secretory defects are present, including absence of pulsatility, loss of early phase of insulin secretion after glucose, decreased basal and stimulated plasma insulin concentrations, excess in prohormone secretion, and progressive decrease in insulin secretory capacity with time. beta-cell dysfunction is genetically determined and appears early in the course of the disease. The interplay between insulin secretory defect and insulin resistance is now better understood. In subjects with normal beta-cell function, increase in insulin is compensated by an increase in insulin secretion and plasma glucose levels remain normal. In subjects genetically predisposed to type 2 diabetes, failure of beta-cell to compensate leads to a progressive elevation in plasma glucose levels, then to overt diabetes. When permanent hyperglycaemia is present, progressive severe insulin secretory failure with time ensues, due to glucotoxicity and lipotoxicity, and oxidative stress. A marked reduction in beta-cell mass at post-mortem examination of pancreas of patients with type 2 diabetes has been reported, with an increase in beta-cell apoptosis non-compensated by neogenesis.     

Blood hyperviscosity syndrome in type I diabetes mellitus

Blood rheological properties and oxygen metabolism were investigated in 50 patients with type I insulin dependent diabetes mellitus. Metabolic and morphological phases of the blood hyperviscosity syndrome were defined in relation to the nature of hemorheological disturbances. Oxygen metabolic disturbances were of unidirectional type manifesting themselves in a decrease in tissue oxygenation and the development of tissue hypoxia. Such disturbances of rheological properties and oxygen metabolism caused the development and progression of diabetic microangiopathies. Therefore pharmacological correction of hemorheological disturbances is a reserve method of therapy of patients with diabetes mellitus.     

Effects of low intensity exercise therapy on early phase insulin secretion in overweight subjects with impaired glucose tolerance and type 2 diabetes mellitus

This study was designed to evaluate effects of exercise therapy on early phase insulin secretion in overweight subjects with impaired glucose tolerance (IGT) and type 2 diabetes mellitus (DM). The subjects consisted of overweight subjects with normal glucose tolerance (NGT, n=10), IGT (n=10) and DM (n=10) (age: 51.1+/-8.2, 56.3+/-8.8 and 58.5+/-6.2 years, respectively). All of these patients performed exercise therapy at lactate threshold intensity for 12 weeks. Before intervention, area under the glucose curve (AUC(PG)) was higher in DM, IGT and NGT groups, and area under the insulin curve (AUC(IRI)) and the early phase insulin secretion as calculated by insulinogenic index was higher in the NGT group than in either the IGT or DM groups (p<0.05). After exercise therapy, the insulin sensitivity, AUC(PG) and AUC(IRI) improved in three groups (p<0.05, respectively). The insulinogenic index increased in IGT and DM groups (p<0.05, respectively), but the changes in the insulinogenic index showed no significant differences between IGT and DM groups. These results suggest that the ss-cell function in subjects with IGT and DM could therefore improve after exercise therapy. Moreover, AUC(PG), AUC(IRI) and insulin sensitivity were also improved no relation to NGT, IGT and DM.     

Progression from IGT to type 2 diabetes mellitus: the central role of impaired early insulin secretion

Impaired glucose tolerance (IGT) is characterized by plasma glucose responses to an oral glucose challenge that are above normal but not at the level defining diabetes. IGT is a common condition that greatly increases risk for the subsequent development of type 2 diabetes. Individuals with IGT manifest abnormalities in both insulin action and early insulin secretion similar to those seen in patients with type 2 diabetes. These abnormalities not only precede diabetes, they predict it as well. Furthermore, the progression from IGT to diabetes is characterized by a dramatic decline in early insulin secretion. It is now evident that early insulin secretion plays an important role in the rapid and efficient suppression of endogenous glucose production following a meal. Loss of early insulin secretion initially leads to post-prandial hyperglycemia which, as the disease progresses, worsens to clinical hyperglycemia. Obesity and a high fat diet may contribute to the development of both insulin resistance and insulin secretory dysfunction in susceptible individuals. Strategies that improve insulin resistance and enhance early insulin secretion may prevent the progression from IGT to diabetes. Already, there is substantial evidence the weight loss and exercise may reduce the risk of developing diabetes by up to 58%. Other trials using pharmacologic agents to decrease insulin resistance and increase early insulin secretion are underway. Prevention remains the best hope for a long-term solution to the worldwide epidemic of diabetes.     

Early disturbances in insulin secretion in the development of type 2 diabetes mellitus

In-vitro studies of mouse oocytes have provided evidence that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on resumption of meiosis. These sterols are synthesized by cytochrome P450 (CYP) lanosterol 14alpha-demethylase (LDM), a key enzyme in cholesterol biosynthesis. Our studies in the rat with specific inhibitors and molecular approaches did not support the hypothesis that MAS is an obligatory step in the stimulation of the resumption of meiosis. (i) Specific inhibitors of MAS synthesizing enzymes did not prevent spontaneous or LH-stimulated meiosis at doses that have previously been shown to effectively suppress LDM activity. At higher doses, they caused degeneration of oocytes. (ii) The timing of LDM expression in the ovary was incompatible with a role for MAS in meiosis. (iii) The preferential localization of LDM protein in the oocytes suggests MAS production in oocytes, rather than its transport from the somatic compartment as expected by the suggested role of MAS in the regulation of meiosis as a putative cumulus-oocyte signal molecule. (iv) AY-9944, which supposedly increases MAS levels by inhibiting its metabolism, induced the maturation of follicle-enclosed oocytes that was much delayed as compared with gonadotropic stimulation. Thus, the resumption of meiosis induced by added MAS [Biol. Reprod. 61 (1999) 1362, Biol. Reprod. 64 (2001) 418] or presumed endogenous MAS accumulation by AY-9944, resulted in oocyte maturation with remarkably slower kinetics than observed with LH stimulation. This delay in meiosis after MAS stimulation, the studies with LDM inhibitors and its spatial and temporal expression, cast serious doubts whether MAS is indeed mediating the meiosis inducing action of the gonadotropins, as suggested.     

Low fecal elastase-1 in type I diabetes mellitus

BACKGROUND: Previous studies suggested impaired pancreatic exocrine function in type I diabetes patients, but have been limited by small or highly selected samples. Fecal elastase-1 has facilitated evaluation of pancreatic dysfunction in population-based studies. METHODS: 112 type I diabetic patients (age +/- SD: 37 +/- 11 years; 47 % males; diabetes duration: 12.5 +/- 10.5 years) were consecutively selected from main regional diabetes centers in Essen, West-Germany. 116 non-diabetic control subjects, similar with respect to age and sex, were recruited from the same geographical region. Elastase-1 measurement was performed centrally by ELISA (ScheboTech, Germany). RESULTS: Elastase-1 concentrations in type I diabetic patients were significantly lower than in control subjects (median; inter-quartile range: diabetic patients: 227, 98-386 microgram/g stool; non-diabetic subjects: 544, 377-702 microgram/g stool) (p < 0.01). Elastase-1 < 100 microgram/g stool (E1 < 100) was found in 25.9 % of diabetic and 5.2 % of non-diabetic subjects, yielding an age-sex-adjusted prevalence Odds ratio (POR; 95 % CI) for diabetes and E1 < 100 of 6.9 (2.8-19.6). After adjusting for potential confounders (history of gastrointestinal diseases, smoking, alcohol consumption) the strong association remained (POR: 6.7; 2.7-19.2). Among patients with diabetes, E1 < 100 was associated with quality of glycemic control (HbA1c, change per 1 %: POR 1.5; 1.1-2.0), diabetes duration (per year: POR 1.1; 1.03-1.2), and age at diabetes onset (per age year: POR 1.1; 1.02-1.1). No association was found with history of gastrointestinal diseases, smoking, or alcohol consumption (current, life-time). CONCLUSIONS: Fecal elastase-1 concentrations were lower in type I diabetes patients compared to control subjects, indicating impaired pancreatic exocrine function. Low elastase-1 was associated with poor metabolic control and longer diabetes duration.     

Insulin secretion in diabetes mellitus

A brief review of the normal physiology of insulin secretion is given. The dual role of glucose to directly stimulate insulin release and to potentiate insulin secretion to other islet regulators is emphasized. The B cell of the pancreatic islet is discussed as a metabolic integrator for nutrients, modulated by neural and hormonal input. A feedback model for the normal regulation of glucose concentrations is also described. This model is based on a closed loop between the islet, the liver and peripheral tissues for the production and utilization of glucose. Diabetes mellitus with overt hyperglycemia is characterized by impaired pancreatic B-cell function; however, in noninsulin-dependent diabetic subjects, many aspects of insulin secretion are maintained by a compensatory increase in plasma glucose concentration. The model shows why this increase in plasma glucose occurs and the importance of this hyperglycemia to the restoration of insulin responses to nonglucose secretagogues, second-phase insulin secretion to glucose and basal insulin. The model can account for the usual stability of plasma glucose in noninsulin-dependent diabetes mellitus and the very high glucose levels and lack of glucose stability in insulin-dependent diabetes mellitus. Sulfonylurea drugs increase insulin secretion, but this increase is dependent on the glucose level. Thus, the augmented B-cell function can be masked by a decrease in plasma glucose concentrations. During long-term therapy, the insulin level and responses are unchanged despite lower concentrations of glucose. Therefore, it is hypothesized that sulfonylureas still act by enhancement of B-cell function.