Aleksey V. Matveyenko

Pancreatitis, Pancreatic, and Thyroid Cancer With Glucagon-Like Peptide-1–Based Therapies

BACKGROUND & AIMS Glucagon-like peptide-1-based therapy is gaining widespread use for type 2 diabetes, although there are concerns about risks for pancreatitis and pancreatic and thyroid cancers. There are also concerns that dipeptidyl peptidase-4 inhibitors could cause cancer, given their effects on immune function. METHODS We examined the US Food and Drug Administrations database of reported adverse events for those associated with the dipeptidyl peptidase-4 inhibitor sitagliptin and the glucagon-like peptide-1 mimetic exenatide, from 2004-2009; data on adverse events associated with 4 other medications were compared as controls. The primary outcomes measures were rates of reported pancreatitis, pancreatic and thyroid cancer, and all cancers associated with sitagliptin or exenatide, compared with other therapies. RESULTS Use of sitagliptin or exenatide increased the odds ratio for reported pancreatitis 6-fold as compared with other therapies (P<2×10(-16)). Pancreatic cancer was more commonly reported among patients who took sitagliptin or exenatide as compared with other therapies (P<.008, P<9×10(-5)). All other cancers occurred similarly among patients who took sitagliptin compared with other therapies (P=.20). CONCLUSIONS These data are consistent with case reports and animal studies indicating an increased risk for pancreatitis with glucagon-like peptide-1-based therapy. The findings also raise caution about the potential long-term actions of these drugs to promote pancreatic cancer.

Transcription Factor 7-Like 2 Regulates β-Cell Survival and Function in Human Pancreatic Islets

OBJECTIVE—Type 2 diabetes is characterized by impaired insulin secretion in response to increased metabolic demand. This defect in β-cell compensation seems to result from the interplay between environmental factors and genetic predisposition. Genome-wide association studies reveal that common variants in transcription factor 7-like 2 (TCF7L2) are associated with increased risk of type 2 diabetes. The aim of the present study was to establish whether TCF7L2 plays a role in β-cell function and/or survival. RESEARCH DESIGN AND METHODS—To investigate the effects of TCFL7L2 depletion, isolated islets were exposed to TCF7L2 small interfering RNA (siRNA) versus scrambled siRNA, and β-cell survival and function were examined. For TCF7L2 overexpression, islets were cultured in glucose concentrations of 5.5–33.3 mmol/l and the cytokine mix interleukin-1β/γ-interferon with or without overexpression of TCF7L2. Subsequently, glucose-stimulated insulin secretion (GSIS), β-cell apoptosis [by transferase-mediated dUTP nick-end labeling assay and Western blotting for poly(ADP-ribose) polymerase and Caspase-3 cleavage], and β-cell proliferation (by Ki67 immunostaining) were analyzed. RESULTS—Depleting TCF7L2 by siRNA resulted in a 5.1-fold increase in β-cell apoptosis, 2.2-fold decrease in β-cell proliferation (P < 0.001), and 2.6-fold decrease in GSIS (P < 0.01) in human islets. Similarly, loss of TCF7L2 resulted in impaired β-cell function in mouse islets. In contrast, overexpression of TCF7L2 protected islets from glucose and cytokine-induced apoptosis and impaired function. CONCLUSIONS—TCF7L2 is required for maintaining GSIS and β-cell survival. Changes in the level of active TCF7L2 in β-cells from carriers of at-risk allele may be the reason for defective insulin secretion and progression of type 2 diabetes.

Beneficial Endocrine but Adverse Exocrine Effects of Sitagliptin in the Human Islet Amyloid Polypeptide Transgenic Rat Model of Type 2 Diabetes: Interactions With Metformin

OBJECTIVE We sought to establish the extent and mechanisms by which sitagliptin and metformin singly and in combination modify islet disease progression in human islet amyloid polypeptide transgenic (HIP) rats, a model for type 2 diabetes. RESEARCH DESIGN AND METHODS HIP rats were treated with sitagliptin, metformin, sitagliptin plus metformin, or no drug as controls for 12 weeks. Fasting blood glucose, insulin sensitivity, and β-cell mass, function, and turnover were measured in each group. RESULTS Sitagliptin plus metformin had synergistic effects to preserve β-cell mass in HIP rats. Metformin more than sitagliptin inhibited β-cell apoptosis. Metformin enhanced hepatic insulin sensitivity; sitagliptin enhanced extrahepatic insulin sensitivity with a synergistic effect in combination. β-Cell function was partially preserved by sitagliptin plus metformin. However, sitagliptin treatment was associated with increased pancreatic ductal turnover, ductal metaplasia, and, in one rat, pancreatitis. CONCLUSIONS The combination of metformin and sitagliptin had synergistic actions to preserve β-cell mass and function and enhance insulin sensitivity in the HIP rat model of type 2 diabetes. However, adverse actions of sitagliptin treatment on exocrine pancreas raise concerns that require further evaluation.

Decreased TCF7L2 protein levels in type 2 diabetes mellitus correlate with downregulation of GIP- and GLP-1 receptors and impaired beta-cell function

Recent human genetics studies have revealed that common variants of the TCF7L2 (T-cell factor 7-like 2, formerly known as TCF4) gene are strongly associated with type 2 diabetes mellitus (T2DM). We have shown that TCF7L2 expression in the beta-cells is correlated with function and survival of the insulin-producing pancreatic beta-cell. In order to understand how variations in TCF7L2 influence diabetes progression, we investigated its mechanism of action in the beta-cell. We show robust differences in TCF7L2 expression between healthy controls and models of T2DM. While mRNA levels were approximately 2-fold increased in isolated islets from the diabetic db/db mouse, the Vancouver Diabetic Fatty (VDF) Zucker rat and the high fat/high sucrose diet-treated mouse compared with the non-diabetic controls, protein levels were decreased. A similar decrease was observed in pancreatic sections from patients with T2DM. In parallel, expression of the receptors for glucagon-like peptide 1 (GLP-1R) and glucose-dependent insulinotropic polypeptide (GIP-R) was decreased in islets from humans with T2DM as well as in isolated human islets treated with siRNA to TCF7L2 (siTCF7L2). Also, insulin secretion stimulated by glucose, GLP-1 and GIP, but not KCl or cyclic adenosine monophosphate (cAMP) was impaired in siTCF7L2-treated isolated human islets. Loss of TCF7L2 resulted in decreased GLP-1 and GIP-stimulated AKT phosphorylation, and AKT-mediated Foxo-1 phosphorylation and nuclear exclusion. Our findings suggest that beta-cell function and survival are regulated through an interplay between TCF7L2 and GLP-1R/GIP-R expression and signaling in T2DM.

Chronic GLP-1 Receptor Activation by Exendin-4 Induces Expansion of Pancreatic Duct Glands in Rats and Accelerates Formation of Dysplastic Lesions and Chronic Pancreatitis in the KrasG12D Mouse Model

Pancreatic duct glands (PDGs) have been hypothesized to give rise to pancreatic intraepithelial neoplasia (PanIN). Treatment with the glucagon-like peptide (GLP)-1 analog, exendin-4, for 12 weeks induced the expansion of PDGs with mucinous metaplasia and columnar cell atypia resembling low-grade PanIN in rats. In the pancreata of Pdx1-Cre; LSL-KrasG12D mice, exendin-4 led to acceleration of the disruption of exocrine architecture and chronic pancreatitis with mucinous metaplasia and increased formation of murine PanIN lesions. PDGs and PanIN lesions in rodent and human pancreata express the GLP-1 receptor. Exendin-4 induced proproliferative signaling pathways in human pancreatic duct cells, cAMP–protein kinase A and mitogen-activated protein kinase phosphorylation of cAMP-responsive element-binding protein, and increased cyclin D1 expression. These GLP-1 effects were more pronounced in the presence of an activating mutation of Kras and were inhibited by metformin. These data reveal that GLP-1 mimetic therapy may induce focal proliferation in the exocrine pancreas and, in the context of exocrine dysplasia, may accelerate formation of neoplastic PanIN lesions and exacerbate chronic pancreatitis.

Relationship between β-cell mass and diabetes onset

Regulation of blood glucose concentrations requires an adequate number of β‐cells that respond appropriately to blood glucose levels. β‐Cell mass cannot yet be measured in humans in vivo, necessitating autopsy studies, although both pre‐ and postmorbid changes may confound this approach. Autopsy studies report deficits in β‐cell mass ranging from 0 to 65% in type 2 diabetes (T2DM), and ∼70–100% in type 1 diabetes (T1DM), and, when evaluated, increased β‐cell apoptosis in both T1DM and T2DM. A deficit of β‐cell mass of ∼50% in animal studies leads to impaired insulin secretion (when evaluated directly in the portal vein) and induction of insulin resistance. We postulate three phases for diabetes progression. Phase 1: selective β‐cell cytotoxicity (autoimmune in T1DM, unknown in T2DM) leading to impaired β‐cell function and gradual loss of β‐cell mass through apoptosis. Phase 2: decompensation of glucose control when the pattern of portal vein insulin secretion is sufficiently impaired to cause hepatic insulin resistance. Phase 3: adverse consequences of glucose toxicity accelerate β‐cell dysfunction and insulin resistance. The relative contribution of β‐cell loss versus β‐cell dysfunction to diabetes onset remains an area of controversy. However, because cytotoxicity sufficient to induce β‐cell apoptosis predictably disturbs β‐cell function, it is naïve to attempt to distinguish the relative contributions of these linked processes to diabetes onset.

Disruption of Circadian Rhythms Accelerates Development of Diabetes through Pancreatic Beta-Cell Loss and Dysfunction

Type 2 diabetes mellitus (T2DM) is complex metabolic disease that arises as a consequence of interactions between genetic predisposition and environmental triggers. One recently described environmental trigger associated with development of T2DM is disturbance of circadian rhythms due to shift work, sleep loss, or nocturnal lifestyle. However, the underlying mechanisms behind this association are largely unknown. To address this, the authors examined the metabolic and physiological consequences of experimentally controlled circadian rhythm disruption in wild-type (WT) Sprague Dawley and diabetes-prone human islet amyloid polypeptide transgenic (HIP) rats: a validated model of T2DM. WT and HIP rats at 3 months of age were exposed to 10 weeks of either a normal light regimen (LD: 12:12-h light/dark) or experimental disruption in the light-dark cycle produced by either (1) 6-h advance of the light cycle every 3 days or (2) constant light protocol. Subsequently, blood glucose control, beta-cell function, beta-cell mass, turnover, and insulin sensitivity were examined. In WT rats, 10 weeks of experimental disruption of circadian rhythms failed to significantly alter fasting blood glucose levels, glucose-stimulated insulin secretion, beta-cell mass/turnover, or insulin sensitivity. In contrast, experimental disruption of circadian rhythms in diabetes-prone HIP rats led to accelerated development of diabetes. The mechanism subserving early-onset diabetes was due to accelerated loss of beta-cell function and loss of beta-cell mass attributed to increases in beta-cell apoptosis. Disruption of circadian rhythms may increase the risk of T2DM by accelerating the loss of beta-cell function and mass characteristic in T2DM.

β-Cell Deficit Due to Increased Apoptosis in the Human Islet Amyloid Polypeptide Transgenic (HIP) Rat Recapitulates the Metabolic Defects Present in Type 2 Diabetes

Type 2 diabetes is characterized by defects in insulin secretion and action and is preceded by impaired fasting glucose (IFG). The islet anatomy in IFG and type 2 diabetes reveals an ∼50 and 65% deficit in β-cell mass, with increased β-cell apoptosis and islet amyloid derived from islet amyloid polypeptide (IAPP). Defects in insulin action include both hepatic and extrahepatic insulin resistance. The relationship between changes in β-cell mass, β-cell function, and insulin action leading to type 2 diabetes are unresolved, in part because it is not possible to measure β-cell mass in vivo, and most available animal models do not recapitulate the islet pathology in type 2 diabetes. We evaluated the HIP rat, a human IAPP transgenic rat model that develops islet pathology comparable to humans with type 2 diabetes, at age 2 months (nondiabetic), 5 months (with IFG), and 10 months (with diabetes) to prospectively examine the relationship between changes in islet morphology versus insulin secretion and action. We report that increased β-cell apoptosis and impaired first-phase insulin secretion precede the development of IFG, which coincides with an ∼50% defect in β-cell mass and onset of hepatic insulin resistance. Diabetes was characterized by ∼70% deficit in β-cell mass, progressive hepatic and extrahepatic insulin resistance, and hyperglucagonemia. We conclude that IAPP-induced β-cell apoptosis causes defects in insulin secretion and β-cell mass that lead first to hepatic insulin resistance and IFG and then to extrahepatic insulin resistance, hyperglucagonemia, and diabetes. We conclude that a specific β-cell defect can recapitulate the metabolic phenotype of type 2 diabetes and note that insulin resistance in type 2 diabetes may at least in part be secondary to β-cell failure.

Activation of Vascular Bone Morphogenetic Protein Signaling in Diabetes Mellitus

Rationale: Diabetes mellitus is frequently complicated by cardiovascular disease, such as vascular calcification and endothelial dysfunction, which have been associated with bone morphogenetic proteins (BMPs). Objective: To determine whether hyperglycemia in vitro and diabetes in vivo promote vascular BMP activity and correlate with vascular calcification. Methods and Results: Increased glucose augmented expression of BMP-2 and BMP-4; the BMP inhibitors matrix Gla protein (MGP) and Noggin; activin-like kinase receptor (ALK)1, -2, -3 and -6; the BMP type 2 receptor; and the vascular endothelial growth factor in human aortic endothelial cells (HAECs). Diabetes induced expression of the same factors in the aortic wall of 3 animal models of diabetes, Ins2Akita/+ mice, db/db mice, and HIP rats (rats transgenic for human islet amyloid polypeptide), representative of types 1 and 2 diabetes. Conditioned media from glucose-treated HAECs increased angiogenesis in bovine aortic endothelial cells, as mediated by BMP-4, and osteogenesis in calcifying vascular cells, as mediated by BMP-2. BMP-4, MGP, ALK1, and ALK2 were predominantly expressed on the endothelial side of the aorta, and small interfering RNA experiments showed that these genes were regulated as a group. Diabetic mice and rats showed a dramatic increase in aortic BMP activity, as demonstrated by SMAD1/5/8 phosphorylation. This was associated with increased osteogenesis and calcium accumulation. These changes were prevented in the Ins2Akita/+ mice by breeding them with MGP transgenic mice, which increased aortic BMP inhibition. Conclusions: Hyperglycemia and diabetes activate vascular BMP activity, which is instrumental in promoting vascular calcification and may be limited by increasing BMP inhibition.

Human-IAPP disrupts the autophagy/lysosomal pathway in pancreatic β-cells: protective role of p62-positive cytoplasmic inclusions

In type II diabetes (T2DM), there is a deficit in β-cells, increased β-cell apoptosis and formation of intracellular membrane-permeant oligomers of islet amyloid polypeptide (IAPP). Human-IAPP (h-IAPP) is an amyloidogenic protein co-expressed with insulin by β-cells. IAPP expression is increased with obesity, the major risk factor for T2DM. In this study we report that increased expression of human-IAPP led to impaired autophagy, due at least in part to the disruption of lysosome-dependant degradation. This action of IAPP to alter lysosomal clearance in vivo depends on its propensity to form toxic oligomers and is independent of the confounding effect of hyperglycemia. We report that the scaffold protein p62 that delivers polyubiquitinated proteins to autophagy may have a protective role against human-IAPP-induced apoptosis, apparently by sequestrating protein targets for degradation. Finally, we found that inhibition of lysosomal degradation increases vulnerability of β-cells to h-IAPP-induced toxicity and, conversely, stimulation of autophagy protects β-cells from h-IAPP-induced apoptosis. Collectively, these data imply an important role for the p62/autophagy/lysosomal degradation system in protection against toxic oligomer-induced apoptosis.