Aims/hypothesis Beta cell loss contributes to type 2 diabetes, with increased apoptosis representing an underlying mechanism. Autophagy, i.e. the physiological degradation of damaged organelles and ...proteins, may, if altered, be associated with a distinct form of cell death. We studied several features of autophagy in beta cells from type 2 diabetic patients and assessed the role of metabolic perturbation and pharmacological intervention. Methods Pancreatic samples were obtained from organ donors and isolated islets prepared both by collagenase digestion and density gradient centrifugation. Beta cell morphology and morphometry were studied by electron microscopy. Gene expression studies were performed by quantitative RT-PCR. Results Using electron microscopy, we observed more dead beta cells in diabetic (2.24 ± 0.53%) than control (0.66 ± 0.52%) samples (p < 0.01). Massive vacuole overload (suggesting altered autophagy) was associated with 1.18 ± 0.54% dead beta cells in type 2 diabetic samples and with 0.36 ± 0.26% in control samples (p < 0.05). Density volume of autophagic vacuoles and autophagosomes was significantly higher in diabetic beta cells. Unchanged gene expression of beclin-1 and ATG1 (also known as ULK1), and reduced transcription of LAMP2 and cathepsin B and D was observed in type 2 diabetic islets. Exposure of non-diabetic islets to increased NEFA concentration led to a marked increase of vacuole accumulation, together with enhanced beta cell death, which was associated with decreased LAMP2 expression. Metformin ameliorated autophagy alterations in diabetic beta cells and beta cells exposed to NEFA, a process associated with normalisation of LAMP2 expression. Conclusions/interpretation Beta cells in human type 2 diabetes have signs of altered autophagy, which may contribute to loss of beta cell mass. To preserve beta cell mass in diabetic patients, it may be necessary to target multiple cell-death pathways.
Aims/hypothesis Insulin secretion in pancreatic islets is dependent upon mitochondrial function and production of ATP. The transcriptional coactivator peroxisome proliferator activated receptor gamma ...coactivator-1 alpha (protein PGC-1α; gene PPARGC1A) is a master regulator of mitochondrial genes and its expression is decreased and related to impaired oxidative phosphorylation in muscle from patients with type 2 diabetes. Whether it plays a similar role in human pancreatic islets is not known. We therefore investigated if PPARGC1A expression is altered in islets from patients with type 2 diabetes and whether this expression is influenced by genetic (PPARGC1A Gly482Ser polymorphism) and epigenetic (DNA methylation) factors. We also tested if experimental downregulation of PPARGC1A expression in human islets influenced insulin secretion. Methods The PPARGC1A Gly482Ser polymorphism was genotyped in human pancreatic islets from 48 non-diabetic and 12 type 2 diabetic multi-organ donors and related to PPARGC1A mRNA expression. DNA methylation of the PPARGC1A promoter was analysed in pancreatic islets from ten type 2 diabetic and nine control donors. Isolated human islets were transfected with PPARGC1A silencing RNA (siRNA). Results PPARGC1A mRNA expression was reduced by 90% (p < 0.005) and correlated with the reduction in insulin secretion in islets from patients with type 2 diabetes. After downregulation of PPARGC1A expression in human islets by siRNA, insulin secretion was reduced by 41% (p <= 0. 01). We were able to ascribe reduced PPARGC1A expression in islets to both genetic and epigenetic factors, i.e. a common PPARGC1A Gly482Ser polymorphism was associated with reduced PPARGC1A mRNA expression (p < 0.00005) and reduced insulin secretion (p < 0.05). In support of an epigenetic influence, the PPARGC1A gene promoter showed a twofold increase in DNA methylation in diabetic islets compared with non-diabetic islets (p < 0.04). Conclusions/interpretation We have shown for the first time that PPARGC1A might be important in human islet insulin secretion and that expression of PPARGC1A in human islets can be regulated by both genetic and epigenetic factors.
•We investigated the mechanisms of dioxin acute toxicity in pancreatic beta cells.•We tested the protective effect of the AhR inhibitor epigallocatechine-3-gallate.•Dioxin is highly toxic for ...pancreatic beta cells.•EGCG is able to protect beta cells against dioxin acute toxicity.•The most likely target for this protective effect seems to be the mitochondrion.
The aim of this research was to investigate the mechanism(s) underlying the acute toxicity of dioxin in pancreatic beta cells and to evaluate the protective effects of epigallocatechin-3-gallate (EGCG), the most abundant of the green tea’s catechins and a powerful inhibitor of the aryl hydrocarbon receptor (AhR). Using the insulin-secreting INS-1E cell line we have explored the effect of 1h exposure to different concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), alone or in the presence of EGCG, on: (a) cell survival; (b) cellular ultrastructure; (c) intracellular calcium levels; (d) mitochondrial membrane potential; (e) glucose-stimulated insulin secretion and (f) activation of MAP kinases. Our results demonstrate that TCDD is highly toxic for INS-1E cells, suggesting that pancreatic beta cells should be considered a relevant and sensitive target for dioxin acute toxicity. EGCG significantly protects INS-1E cells against TCDD-induced toxicity in terms of both cell survival and preservation of cellular ultrastructure. The mechanism of this protective effect seems to be related to: (a) the ability of EGCG to preserve the mitochondrial function and thus to prevent the TCDD-induced inhibition of glucose-stimulated insulin secretion and (b) the ability of EGCG to inhibit the TCDD-induced activation of selected kinases, such as e.g. ERK 1/2 and JNK. Our results clearly show that EGCG is able to protect pancreatic beta cells against dioxin acute toxicity and indicate the mitochondrion as the most likely target for this beneficial effect.
Type 2 diabetes is increasingly viewed as a disease of insulin deficiency due not only to intrinsic pancreatic β-cell dysfunction but also to reduction of β-cell mass. It is likely that, in ...diabetes-prone subjects, the regulated β-cell turnover that adapts cell mass to body's insulin requirements is impaired, presumably on a genetic basis. We still have a limited knowledge of how and when this derangement occurs and what might be the most effective therapeutic strategy to preserve β-cell mass. The animal models of type 2 diabetes with reduced β-cell mass described in this review can be extremely helpful (a) to have insight into the mechanisms underlying the defective growth or accelerated loss of β-cells leading to the β-cell mass reduction; (b) to investigate in prospective studies the mechanisms of compensatory adaptation and subsequent failure of a reduced β-cell mass. Furthermore, these models are of invaluable importance to test the effectiveness of potential therapeutic agents that either stimulate β-cell growth or inhibit β-cell death.
The aim of this study was to determine the role of fatty acid signalling in islet beta cell compensation for insulin resistance in the Zucker fatty fa/fa (ZF) rat, a genetic model of severe obesity, ...hyperlipidaemia and insulin resistance that does not develop diabetes.
NEFA augmentation of insulin secretion and fatty acid metabolism were studied in isolated islets from ZF and Zucker lean (ZL) control rats.
Exogenous palmitate markedly potentiated glucose-stimulated insulin secretion (GSIS) in ZF islets, allowing robust secretion at physiological glucose levels (5-8 mmol/l). Exogenous palmitate also synergised with glucagon-like peptide-1 and the cyclic AMP-raising agent forskolin to enhance GSIS in ZF islets only. In assessing islet fatty acid metabolism, we found increased glucose-responsive palmitate esterification and lipolysis processes in ZF islets, suggestive of enhanced triglyceride-fatty acid cycling. Interruption of glucose-stimulated lipolysis by the lipase inhibitor Orlistat (tetrahydrolipstatin) blunted palmitate-augmented GSIS in ZF islets. Fatty acid oxidation was also higher at intermediate glucose levels in ZF islets and steatotic triglyceride accumulation was absent.
The results highlight the potential importance of NEFA and glucoincretin enhancement of insulin secretion in beta cell compensation for insulin resistance. We propose that coordinated glucose-responsive fatty acid esterification and lipolysis processes, suggestive of triglyceride-fatty acid cycling, play a role in the coupling mechanisms of glucose-induced insulin secretion as well as in beta cell compensation and the hypersecretion of insulin in obesity.
We previously reported that in a diabetes mouse model, characterised by moderate hyperglycaemia and reduced β-cell mass, the radical scavenger ...bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decandioate di-hydrochloride (IAC), a non-conventional cyclic hydroxylamine derivative, improves metabolic alterations by counteracting β-cell dysfunction associated with oxidative stress. The aims of this study were to ascertain whether the beneficial effects of IAC treatment could be maintained after its discontinuation and further elucidate the underlying mechanisms. Diabetes was induced in C57Bl/6J mice by streptozotocin (STZ) and nicotinamide (NA) administration. Diabetic mice were treated for 7 weeks with various doses of IAC (7.5, 15, or 30 mg/kg b.w./die i.p.) and monitored for additional 8 weeks after suspension of IAC. Then, pancreatic tissue was used for determination of β-cell mass by immunohistochemistry and β-cell ultrastructural analysis. STZ-NA mice showed moderate hyperglycaemia, glucose intolerance and reduced β-cell mass (25% of controls). IAC-treated STZ-NA mice (at both doses of 15 and 30 mg/kg b.w.) showed long-term reduction of hyperglycaemia even after discontinuation of treatment, attenuation of glucose intolerance and partial preservation of β-cell mass. The lowest IAC dose was much less effective. Plasma nitrotyrosine levels (an oxidative stress index) significantly increased in untreated diabetic mice and were lowered upon IAC treatment. At ultrastructural level, β cells of IAC-treated diabetic mice were protected against degranulation and mitochondrial alterations. In the STZ-NA diabetic mouse model, the radical scavenger IAC induces a prolonged reduction of hyperglycaemia associated with partial restoration of β-cell mass and function, likely dependent on blockade of oxidative stress-induced damaging mechanisms.
Abstract Oxidative stress is a putative mechanism leading to beta-cell damage in type 2 diabetes. We studied isolated human pancreatic islets from type 2 diabetic and non-diabetic subjects, matched ...for age and body mass index. Evidence of increased oxidative stress in diabetic islets was demonstrated by measuring nitrotyrosine concentration and by electron paramagnetic resonance. This was accompanied by reduced glucose-stimulated insulin secretion, as compared to non-diabetic islets (Stimulation Index, SI: 0.9 ± 0.2 vs. 2.0±0.4, P < 0.01), and by altered expression of insulin (approximately –60%), catalase (approximately +90%) and glutathione peroxidase (approximately +140%). When type 2 diabetic islets were pre-exposed for 24 h to the new antioxidant bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decandioate di-hydrochloride, nitrotyrosine levels, glucose-stimulated insulin secretion (SI: 1.6 ± 0.5) and gene expressions improved/normalized. These results support the concept that oxidative stress may play a role in type 2 diabetes beta-cell dysfunction; furthermore, it is proposed that therapy with antioxidants could be an interesting adjunctive pharmacological approach to the treatment of type 2 diabetes.
Abstract
Introduction
The traditional surgical management for acute Type A aortic dissection focuses on handling emergencies in the aortic root and ascending aorta. The remaining untreated distal ...portion of the aorta has a potential risk of rupture or causing malperfusion syndrome. Therefore, an aggressive repair approach using total aortic arch replacement combined with the frozen elephant trunk (FET) implantation has been advocated. We describe the early and midterm clinical outcomes of the Thoraflex Hybrid graft for the treatment of emergency type A aortic dissection.
Methods
Between December 2017 and January 2022, 69 consecutive patients were admitted with acute type A aortic dissection; of those, 66 patients (62.9 ± 10.2 years of age, 81.8% men) underwent emergency hybrid aortic arch and frozen elephant trunk repair with the multibranched Thoraflex hybrid graft and were enrolled in the study. Primary end point were 30 days– and in–hospital mortality. To better clarify the impact of age on surgical outcomes, we have divided the study population into two groups: group A for patients < 70 years of age (47 patients), group B for patients ≥ 70 years (19 patients).
Results
All 66 device implants were technically successful. Mean follow–up was 19.7 ±17.4 months. 30–days– and in–hospital mortality were 10.6 and 13.6%, respectively. Stroke occurred in 3 (4.5%) patients. Two (3.0%) patients experienced spinal cord ischemia. Renal failure requiring CVVH and respiratory failure requiring tracheostomy were 30.3% and 28.8%, respectively. Overall survival for the entire cohort at 3 months, 6 months, 12 months and 24 months was 85%, 80.3%, 76.5%, 74.4% respectively. We did not find any statistically significant difference among the two groups in terms of main post–operative outcomes. The multivariable Cox proportional hazard model showed left ventricular ejection fraction (HR: 0.83, 95% CI: 0.79–0.92, p <0.01), peripheral vascular disease (HR: 15.8, 95% CI: 3.9–62.9, p < 0.01), coronary malperfusion (HR: 0.10, 95% CI: 0.01–0.77, p =0.03), lower limbs malperfusion (HR: 5.1, 95% CI: 1.10–23.4, p = 0.04) and cardiopulmonary bypass time (HR: 1.02, 95% CI: 1 – 1.04, p = 0.01) as independent predictors of long term mortality.
Conclusions
Hybrid aortic arch and frozen elephant trunk repair with the Thoraflex Hybrid graft to treat emergency type A aortic dissection appears to be associated with good early and mid–term clinical outcomes even in the elderly.
Abstract
Introduction
Post–infarct ventricular septal defect (VSD) is a life tethering complication of acute myocardial infarction which is associated to high in–hospital mortality (90–95%). The ...optimal peri–operative management including timing of surgical correction is still debated. There is a large body of evidence demonstrating that surgical repair is also associated to poor post–operative outcomes due to cardiogenic shock and multiorgan failure (MOF). The use of extracorporeal membrane oxygenation (ECMO) system in adult cardiac surgery is not routine, occurring in a minority of critically ill patients, typically postoperatively. Here we present our single centre experience of patients with post–infarct VSD managed preoperatively with ECMO support as a bridge to definitive surgical closure. Materials and methods Between February 2020 to July 2021, 5 patients presented to our unit with diagnosis of post–infarct VSD and were managed with preoperative veno–arterial (V–A) ECMO implantation and enrolled in our study. Clinical parameters (such as mean arterial pressure, central venous pressure, ECG, pulmonary artery pressure), blood tests, trans–thoracic and trans–esophageal echocardiography, chest X–rays have been evaluated both before and after surgery. Primary end–point was all causes in–hospital mortality.
Results
Three (60%) patients were male and mean age was 70,4 (60–78) years. All patients underwent surgical repair. ECMO was positioned between 1 and 9 days prior to surgical correction, giving the chance to reduce the pharmacological inotropic support while still reverting the MOF as demonstrated by the reduction of AST, ALT, bilirubin level, decreased CVP and systemic lactate levels. Two (40%) patients were successfully weaned off from the mechanical support and discharged home in good clinical conditions. Two (40%) patients developed MOF after surgery leading to the exitus.
Conclusions
We postulate that the use of V–A use preoperatively in patients with cardiogenic shock secondary to post–infarct VSD is appropriate and where feasible should be considered. It allows restoration of haemodynamic stability and resolution of MOF. This provides for a delayed surgical repair with a likely higher chance of operative success and reduced mortality.
PDF
