Islet amyloid polypeptide response to maximal hyperglycemia and arginine is altered in impaired glucose tolerance and type 2 diabetes mellitus

Impaired Suppression of Glucagon in Obese Subjects Parallels Decline in Insulin Sensitivity and Beta-Cell Function

AIM

To examine the relationship between plasma glucagon levels and insulin sensitivity and insulin secretion in obese subjects.

METHODS

Suppression of plasma glucagon was examined in 275 obese Hispanic Americans with varying glucose tolerance. All subjects received a 2-hour oral glucose tolerance test (OGTT) and a subset (n = 90) had euglycemic hyperinsulinemic clamp. During OGTT, we quantitated suppression of plasma glucagon concentration, Matsuda index of insulin sensitivity, and insulin secretion/insulin resistance (disposition) index. Plasma glucagon suppression was compared between quartiles of insulin sensitivity and beta-cell function.

RESULTS

Fasting plasma glucagon levels were similar in obese subjects with normal glucose tolerance (NGT), prediabetes, and type 2 diabetes (T2D), but the fasting glucagon/insulin ratio decreased progressively from NGT to prediabetes to T2D (9.28 ± 0.66 vs 6.84 ± 0.44 vs 5.84 ± 0.43; P < 0.001). Fasting and 2-hour plasma glucagon levels during OGTT progressively increased and correlated positively with severity of insulin resistance (both Matsuda index and euglycemic hyperinsulinemic clamp). The fasting glucagon/insulin ratio declined with worsening insulin sensitivity and beta-cell function, and correlated with whole-body insulin sensitivity (Matsuda index, r = 0.81; P < 0.001) and beta-cell function (r = 0.35; P < 0.001). The glucagon/insulin ratio also correlated and with beta-cell function during OGTT at 60 and 120 minutes (r = -0.47; P < 0.001 and r = -0.32; P < 0.001).

CONCLUSION

Insulin-mediated suppression of glucagon secretion in obese subjects is impaired with increasing severity of glucose intolerance and parallels the severity of insulin resistance and beta-cell dysfunction.

Effect of linagliptin on glucose metabolism and pancreatic beta cell function in patients with persistent prediabetes after metformin and lifestyle

The goal of the study was to evaluate the effect of adding linagliptin to metformin and lifestyle on glucose levels and pancreatic β-cell function in patients with persistent impaired glucose tolerance (IGT) after 12 months of metformin and lifestyle. A single center parallel double-blind randomized clinical trial with 6 months of follow-up was performed in patients with persistent IGT after 12 months of treatment with metformin and lifestyle; patients were randomized to continue with metformin 850 mg twice daily (M group, n = 12) or linagliptin/metformin 2.5/850 mg twice daily (LM group, n = 19). Anthropometric measurements were obtained by standard methods and by bioelectrical impedance; glucose was measured by dry chemistry, insulin by chemiluminescence, and pancreatic β-cell function was calculated with the disposition index using glucose and insulin values during oral glucose tolerance test (OGTT) and adjusting by insulin sensitivity. The main outcomes were glucose levels during OGTT and pancreatic β-cell function. Patients in the LM group had a reduction in weight (-1.7 ± 0.6, p < 0.05) and body mass index (BMI, -0.67 ± 0.2, p < 0.05). Glucose levels significantly improved in LM group with a greater reduction in the area under the glucose curve during OGTT (AUCGluc_{0_120min}) as compared to the M group (-4425 ± 871 vs -1116 ± 1104 mg/dl/120 min, p < 0.001). Pancreatic β-cell function measured with the disposition index, improved only in LM group (2.3 ± 0.23 vs 1.7 ± 0.27, p 0.001); these improvements persisted after controlling for OGTT glucose levels. The differences in pancreatic β-cell function persisted also after pairing groups for basal AUCGluc_{0_120min}. The addition of linagliptin to patients with persistent IGT after 12 months of treatment with metformin and lifestyle, improved glucose levels during OGTT and pancreatic β-cell function after 6 months of treatment.Trial registration: Clinicaltrials.gov with the ID number NCT04088461.

The combination of linagliptin, metformin and lifestyle modification to prevent type 2 diabetes (PRELLIM). A randomized clinical trial

BACKGROUND

Prediabetes is a highly prevalent health problem with a high risk of complications and progression to type 2 diabetes (T2D). The goals of this study were to evaluate the effect of the combination of lingaliptin + metformin + lifestyle on glucose tolerance, pancreatic β-cell function and T2D incidence in patients with prediabetes.

METHODS

A single center parallel double-blind randomized clinical trial with 24 months of follow-up in patients with impaired glucose tolerance plus two T2D risk factors which were randomized to linagliptin 5 mg + metformin 1700 mg daily + lifestyle (LM group) or metformin 1700 mg daily + lifestyle (M group). Primary outcomes were regression to normoglycemia and T2D incidence; glucose levels and pancreatic β-cell function were secondary outcomes.

RESULTS

Subjects were screened for eligibility by OGTT and 144 patients with prediabetes were randomized to LM group (n = 74) or M group (n = 70); 52 and 36 participants in the LM group and 52 and 27 participants in the M group, completed the 12 and 24 months of treatment, respectively; average follow-up was 17 ± 6 and 18 ± 7 months in M and LM group, respectively. Glucose levels during OGTT improved more in LM group. OGTT disposition index (DI) improved significantly better during the first months in LM group, increasing from 1·31 (95% CI: 1·14-1·49) to 2·41 (95% CI: 2.10-2.72) and to 2.07 (95% CI: 1.82-2.31) at 6 and 24 months in LM group vs from 1.21 (95% CI: 0.98-1.34) to 1.56 (95% CI: 1.17-1.95) and to 1.72 (95% CI: 1.45-1.98) at 6 and 24 months in M group (p < .05). T2D incidence was higher in M group in comparison to LM group (HR 4.0, 95% CI: 1.24-13.04, p = .020). The probability of achieving normoglycemia was higher in LM group (OR 3.26 CI 95% 1.55-6.84). No major side effects were observed during the study.

CONCLUSIONS

The combination of linagliptin, metformin and lifestyle improved significantly glucose metabolism and pancreatic β-cell function, and reduced T2D incidence in subjects with prediabetes as compared to metformin and lifestyle.

Pancreatic β-cell dysfunction in normoglycemic patients and risk factors

AIMS

To evaluate pancreatic β-cell function (βf) in patients with normoglycemia (NG) and normal glucose tolerance (NGT) and related risk factors.

METHODS

An observational and comparative study in 527 patients with NG and NGT that were divided by quartiles of βf according to the disposition index derived from OGTT. Anthropometrical, clinical, nutritional, and biochemical variables were measured and associated with βf.

RESULTS

Quartiles of βf were Q1 = DI < 1.93 n = 131, Q2 = DI 1.93-2.45 n = 134, Q3 = DI 2.46-3.1 n = 133, and Q4 = DI > 3.1 n = 129. There was a progressive reduction in pancreatic β-cell function and it is negatively correlated with age, weight, BMI, total body fat and visceral fat, waist circumference, total cholesterol, LDL, and triglycerides (p < 0.01). Glucose levels during OGTT had a negative correlation with βf; the product of fasting glucose by 1-h glucose had the best correlation with βf (r = 0.611, p < 0.001) and was the best predictor of βdf (AUC 0.816, CI 95% 0.774-0.857), even better than 1-h glucose (r = 0.581, p < 0.001). Energy, fat, and carbohydrate intake were negatively correlated with βf (p < 0.05). Glucose levels at 1-h OGTT > 110 mg/dl were positively associated with pancreatic βdf (OR 6.85, CI 95% 3.86-12.4). In the multivariate analysis, glucose levels during OGTT, fasting insulin, and BMI were the main factors associated with βf.

CONCLUSIONS

A subgroup of patients with NG and NGT may have a loss of 40% of their βf. Factors related to this βdf were age, adiposity, glucose during OGTT, and the product of fasting and 1-h glucose, as well as food intake.

High-Fat Diet Increases Amylin Accumulation in the Hippocampus and Accelerates Brain Aging in hIAPP Transgenic Mice

The accumulation of human islet amyloid polypeptide (hIAPP) in pancreatic islets under induction by a high-fat diet plays a critical role in the development of type-2 diabetes mellitus (T2DM). T2DM is a risk factor of late-onset Alzheimer’s disease (AD). Nevertheless, whether hIAPP in combination with hyperlipidemia may lead to AD-like pathological changes in the brain remains unclear. hIAPP transgenic mice were fed with a high-fat diet for 6 or 12 months to establish the T2DM model. The accumulation of amylin, the numbers of Fluoro-Jade C (FJC)-positive and β-gal positive cells, and the deposition level of Aβ42 in the hippocampi of the transgenic mice were detected by using brain sections. Cytoplasmic and membrane proteins were extracted from the hippocampi of the transgenic mice, and the ratio of membrane GLUT4 expression to cytoplasmic GLUT4 expression was measured through Western blot analysis. Changes in the cognitive functions of hIAPP transgenic mice after 12 months of feeding with a high-fat diet were evaluated. hIAPP transgenic mice fed with a high-fat diet for 6 or 12 months showed elevated blood glucose levels and insulin resistance; increased amylin accumulation, number of FJC-positive and β-gal positive cells, and Aβ42 deposition in the hippocampi; and reduced membrane GLUT4 expression levels. hIAPP transgenic mice fed with a high-fat diet for 12 months showed reductions in social cognitive ability and passive learning ability. A high-fat diet increased amylin accumulation in the hippocampi of hIAPP transgenic mice, which presented AD-like pathology and behavior characterized by neural degeneration, brain aging, Aβ42 deposition, and impaired glucose utilization and cognition.

Pancreatic islet of Langerhans' cytoarchitecture and ultrastructure in normal glucose tolerance and in type 2 diabetes mellitus

While a number of structural and cellular abnormalities occur in the islet of Langerhans in diabetes, and in particular in type 2 diabetes, the focus has been mostly on the insulin producing β-cells and only more recently on glucagon producing α- and δ-cells. There is ample evidence that in type 2 diabetes mellitus (T2DM), in addition to a progressive decline in β-cell function and associated insulin resistance in a number of insulin-sensitive tissues, alterations in glucagon secretion are also present and may play an important role in the pathogenesis of hyperglycemia both in the fasting and in the postprandial state. Recently, a number of studies have showed that there are also functional and structural alterations in glucagon-producing α-cells and somatostatin-producing δ-cells. Thus, it is becoming increasingly clear that multiple cellular alterations of multiple cell types occur, which adds even more complexity to our understanding of the pathophysiology of this common and severe disease. We believe that persistent efforts to increase the understanding of the pathophysiology of hormone secretion in the islets of Langerhans will also improve our capability to better prevent and treat diabetes mellitus.