Glucagon-like peptide-1 counteracts the detrimental effects of Advanced Glycation End-Products in the pancreatic beta cell line HIT-T 15

Metabolic Adaptions/Reprogramming in Islet Beta-Cells in Response to Physiological Stimulators—What Are the Consequences

Irreversible pancreatic β-cell damage may be a result of chronic exposure to supraphysiological glucose or lipid concentrations or chronic exposure to therapeutic anti-diabetic drugs. The β-cells are able to respond to blood glucose in a narrow concentration range and release insulin in response, following activation of metabolic pathways such as glycolysis and the TCA cycle. The β-cell cannot protect itself from glucose toxicity by blocking glucose uptake, but indeed relies on alternative metabolic protection mechanisms to avoid dysfunction and death. Alteration of normal metabolic pathway function occurs as a counter regulatory response to high nutrient, inflammatory factor, hormone or therapeutic drug concentrations. Metabolic reprogramming is a term widely used to describe a change in regulation of various metabolic enzymes and transporters, usually associated with cell growth and proliferation and may involve reshaping epigenetic responses, in particular the acetylation and methylation of histone proteins and DNA. Other metabolic modifications such as Malonylation, Succinylation, Hydroxybutyrylation, ADP-ribosylation, and Lactylation, may impact regulatory processes, many of which need to be investigated in detail to contribute to current advances in metabolism. By describing multiple mechanisms of metabolic adaption that are available to the β-cell across its lifespan, we hope to identify sites for metabolic reprogramming mechanisms, most of which are incompletely described or understood. Many of these mechanisms are related to prominent antioxidant responses. Here, we have attempted to describe the key β-cell metabolic adaptions and changes which are required for survival and function in various physiological, pathological and pharmacological conditions.

Glucagon-like peptide receptor agonists attenuate advanced glycation end products-induced inflammation in rat mesangial cells

BACKGROUND

Hyperglycemia-induced advanced glycation end products (AGEs) and receptor for AGEs (RAGE) production play major roles in progression of diabetic nephropathy. Anti-RAGE effect of peroxisome proliferator-activated receptor-delta (PPARδ) agonists was shown in previous studies. PPARδ agonists also stimulate glucagon-like peptide-1 (GLP-1) secretion from human intestinal cells.

METHODS

In this study, the individual and synergic anti-inflammatory effects of GLP-1 receptor (exendin-4) and PPARδ (L-165,041) agonists in AGE-treated rat mesangial cells (RMC) were investigated.

RESULTS

The results showed both exendin-4 and L-165,041 significantly attenuated AGE-induced IL-6 and TNF-α production, RAGE expression, and cell death in RMC. Similar anti-inflammatory potency was seen between 0.3 nM exendin-4 and 1 μM L-165,041. Synergic effect of exendin-4 and L-165,041 was shown in inhibiting cytokines production, but not in inhibiting RAGE expression or cell death.

CONCLUSIONS

These results suggest that both GLP-1 receptor and PPARδ agonists have anti-inflammatory effect on AGE-treated rat mesangial cells.

TRB3 mediates advanced glycation end product-induced apoptosis of pancreatic β-cells through the protein kinase C β pathway

Advanced glycation end products (AGEs), which accumulate in the body during the development of diabetes, may be one of the factors leading to pancreatic β-cell failure and reduced β-cell mass. However, the mechanisms responsible for AGE‑induced apoptosis remain unclear. This study identified the role and mechanisms of action of tribbles homolog 3 (TRB3) in AGE-induced β-cell oxidative damage and apoptosis. Rat insulinoma cells (INS-1) were treated with 200 µg/ml AGEs for 48 h, and cell apoptosis was then detected by TUNEL staining and flow cytometry. The level of intracellular reactive oxygen species (ROS) was measured by a fluorescence assay. The expression levels of receptor of AGEs (RAGE), TRB3, protein kinase C β2 (PKCβ2) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4) were evaluated by RT-qPCR and western blot analysis. siRNA was used to knockdown TRB3 expression through lipofection, followed by an analysis of the effects of TRB3 on PKCβ2 and NOX4. Furthermore, the PKCβ2-specific inhibitor, LY333531, was used to analyze the effects of PKCβ2 on ROS levels and apoptosis. We found that AGEs induced the apoptosis of INS-1 cells and upregulated RAGE and TRB3 expression. AGEs also increased ROS levels in β-cells. Following the knockdown of TRB3, the AGE-induced apoptosis and intracellular ROS levels were significantly decreased, suggesting that TRB3 mediated AGE-induced apoptosis. Further experiments demonstrated that the knockdown of TRB3 decreased the PKCβ2 and NOX4 expression levels. When TRB3 was knocked down, the cells expressed decreased levels of PKCβ2 and NOX4. The PKCβ2‑specific inhibitor, LY333531, also reduced AGE-induced apoptosis and intracellular ROS levels. Taken together, our data suggest that TRB3 mediates AGE-induced oxidative injury in β-cells through the PKCβ2 pathway.

Glucagon-like peptide-1 inhibits the receptor for advanced glycation endproducts to prevent podocyte apoptosis induced by advanced oxidative protein products

OBJECTIVE

To investigate whether and how glucagon-like peptide-1 (GLP-1) can protect podocytes from apoptosis induced by advanced oxidative protein products (AOPPs).

METHODS

Murine podocytes were stimulated with 200 μg/ml AOPP for 48 h in the presence or absence of GLP-1. Cell viability was assessed using the cell counting kit-8 assay. Podocyte apoptosis was detected by flow cytometry and Hoechst 33258 staining. Superoxide radical production was assayed using lucigenin-enhanced chemiluminescence, and Western blotting was used to measure expression of RAGE, NADPH oxidase subunits p47^phox and gp91^phox, as well as apoptosis-associated proteins p53, Bax, Bcl-2 and caspase-3.

RESULTS

Incubating podocytes with AOPPs reduced cell viability, triggered changes in cell morphology and promoted apoptosis. GLP-1 partially inhibited AOPP-induced apoptosis, O₂^- overproduction, and AOPP-induced expression of RAGE. GLP-1 inhibited expression of p47^phox and gp91^phox in AOPP-treated podocytes, and it attenuated AOPP-induced expression of p53, Bax and cleaved caspase-3, whereas it restored expression of Bcl-2.

CONCLUSION

GLP-1 partially inhibits AOPP-induced apoptosis in podocytes, perhaps by interfering with the AOPP-RAGE axis, decreasing oxidative stress and inhibiting the downstream p53/Bax/caspase-3 apoptotic pathway. GLP-1 may be a useful anti-apoptotic agent for early intervention in diabetic nephropathy.

Glucagon-like peptide-1 attenuates advanced oxidation protein product-mediated damage in islet microvascular endothelial cells partly through the RAGE pathway

Advanced oxidation protein products (AOPPs) are knownt to play a role in the pathogenesis of diseases and related complications. However, whether AOPPs affect the survival of islet microvascular endothelial cells (IMECs) has not been reported to date, at least to the best of our knowledge. In this study, we aimed to investigate the mechanisms underlying AOPP-mediated damage in IMECs and the protective role of glucagon-like peptide-1 (GLP-1), which has been suggested to exert beneficial effects on the cardiovascular system. IMECs were treated with AOPPs (0-200 µg/ml) for 0-72 h in the presence or absence of GLP-1 (100 nmol/l). Apoptosis, cell viability and reactive oxygen species (ROS) production were examined, the expression levels of p53, Bax, receptor for advanced glycation end-products (RAGE) and NAD(P)H oxidase subunit were determined, and the activity of NAD(P)H oxidase, caspase-9 and caspase-3 was also determined. The results revealed that AOPPs increased the expression of RAGE, p47phox and p22phox; induced NAD(P)H oxidase-dependent ROS generation, increased p53 and Bax expression, enhanced the activity of caspase-9 and caspase-3, and induced cell apoptosis. Treatment with GLP-1 decreased the expression of RAGE, inhibited NAD(P)H oxidase activity, decreased cell apoptosis and increased cell viability. On the whole, our findings indicate that AOPPs induce the apoptosis of IMECs via the RAGE-NAD(P)H oxidase-dependent pathway and that treatment with GLP-1 effectively reverses these detrimental effects by decreasing AOPP-induced RAGE expression and restoring the redox balance. Our data may indicate that GLP-1 may prove to be beneficial in attenuating the progression of diabetes mellitus.

Dietary Advanced Glycation End Products and Their Potential Role in Cardiometabolic Disease in Children

The rising incidence of obesity and metabolic diseases such as diabetes mellitus and cardiovascular disease in adolescents and young adults is of grave concern. Recent studies favor a role of lifestyle factors over genetics in the perpetuation of inflammation, insulin resistance and oxidative stress, which are pathophysiologic processes common to the above diseases; furthermore, the importance of dietary factors in addition to calories and physical activity in these processes is being increasingly recognized. Advanced glycation end products (AGEs) belong to a category of dietary oxidants which have been implicated in the pathogenesis of inflammation, oxidative stress, insulin resistance, β-cell failure and endothelial dysfunction. This paper reviews the studies of AGEs with a focus on their role in cardiometabolic disease in children. A Medline search was performed using the key words 'childhood obesity', 'metabolic syndrome' and 'advanced glycation end products'. Articles published in English between 1975 and 2015 and their references were reviewed. While most studies were performed in adults, a few studies also demonstrated a role of AGEs in obesity and associated cardiometabolic comorbidities in the younger population. Available evidence suggests an involvement of AGEs in the pathogenesis of adiposity and β-cell failure in children. Potential areas for further research to investigate underlying mechanisms are proposed.

Does Glucagon-like Peptide-1 Ameliorate Oxidative Stress in Diabetes? Evidence Based on Experimental and Clinical Studies

Glucagon-like peptide-1 (GLP-1) has shown to influence the oxidative stress status in a number of in vitro, in vivo and clinical studies. Well-known effects of GLP-1 including better glycemic control, decreased food intake, increased insulin release and increased insulin sensitivity may indirectly contribute to this phenomenon, but glucose-independent effects on ROS level, production and antioxidant capacity have been suggested to also play a role. The potential 'antioxidant' activity of GLP-1 along with other proposed glucose-independent modes of action related to ameliorating redox imbalance remains a controversial topic but could hold a therapeutic potential against micro- and macrovascular diabetic complications. This review discusses the presently available knowledge from experimental and clinical studies on the effects of GLP-1 on oxidative stress in diabetes and diabetes-related complications.

Glucagon-like peptide-1 protects cardiomyocytes from advanced oxidation protein product-induced apoptosis via the PI3K/Akt/Bad signaling pathway

Cardiomyocyte apoptosis is a major event in the pathogenesis of diabetic cardiomyopathy. Currently, no single effective treatment for diabetic cardiomyopathy exists. The present study investigated whether advanced oxidative protein products (AOPPs) have a detrimental role in the survival of cardiomyocytes and if glucagon-like peptide-1 (GLP-1) exerts a cardioprotective effect under these circumstances. The present study also aimed to determine the underlying mechanisms. H9c2 cells were exposed to increasing concentrations of AOPPs in the presence or absence of GLP-1, and the viability and apoptotic rate were detected using a cell counting kit-8 assay and flow cytometry, respectively. In addition, a phosphatidylino-sitol-4,5-bisphosphate 3-kinase (PI3K) inhibitor, LY294002, was employed to illustrate the mechanism of the antiapoptotic effect of GLP-1. The expression levels of the apoptotic-associated proteins, Akt, B-cell lymphoma (Bcl)-2, Bcl-2-associated death promoter (Bad), Bcl-2-associated X protein (Bax) and caspase-3 were measured by western blotting. It was revealed that GLP-1 significantly attenuated AOPP-induced cell toxicity and apoptosis. AOPPs inactivated the phosphorylation of Akt, reduced the phosphorylation of Bad, decreased the expression of Bcl-2, increased the expression of Bax and the activation of caspase-3 in H9c2 cells. GLP-1 reversed the above changes induced by AOPPs and the protective effects of GLP-1 were abolished by the PI3K inhibitor, LY294002. In conclusion, the present data suggested that GLP-1 protected cardiomyocytes against AOPP-induced apoptosis, predominantly via the PI3K/Akt/Bad pathway. These results provided a conceivable mechanism for the development of diabetic cardiomyopathy and rendered a novel application of GLP-1 exerting favorable cardiac effects for the treatment of diabetic cardiomyopathy.

A novel animal model of impaired glucose tolerance induced by the interaction of vitamin E deficiency and (60)Co radiation

Impaired glucose tolerance (IGT), known as the prediabetes stage, is usually induced by habits of life or environmental factors. Established IGT animal models are mostly conducted with chemical compounds such as streptozocin or genetic modification. However, the occasion of exposure to these factors in daily life is seldom. The objective of this study was to establish a new animal model of IGT induced by VE deficiency in diet and exposure to radiation. SD rats were treated individually or in combination of these two factors. In the combination group, the calculated insulin sensitivity index decreased; then HOMA-β value increased. Oxidative damage and IGT were observed. Insulin secretion level in perfusate from pancreas response to glucose was characterized by a rapid but reduced first phase and an obviously defective second phase upon pancreas perfusion. Histopathological images demonstrated the pathological changes. Western blotting analysis showed that the insulin signaling pathway was downregulated. The interaction of VE deficiency in diet and exposure to radiation could break the equilibrium of oxidation and antioxidation and result in IGT. More importantly, a new IGT model was successfully established which may be conducive to further research into development of drugs against human IGT.

Crosstalk between advanced glycation end products (AGEs)-receptor RAGE axis and dipeptidyl peptidase-4-incretin system in diabetic vascular complications

Advanced glycation end products (AGEs) consist of heterogenous group of macroprotein derivatives, which are formed by non-enzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids, and whose process has progressed at an accelerated rate under diabetes. Non-enzymatic glycation and cross-linking of protein alter its structural integrity and function, contributing to the aging of macromolecules. Furthermore, engagement of receptor for AGEs (RAGE) with AGEs elicits oxidative stress generation and subsequently evokes proliferative, inflammatory, and fibrotic reactions in a variety of cells. Indeed, accumulating evidence has suggested the active involvement of accumulation of AGEs in diabetes-associated disorders such as diabetic microangiopathy, atherosclerotic cardiovascular diseases, Alzheimer's disease and osteoporosis. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins, gut hormones secreted from the intestine in response to food intake, both of which augment glucose-induced insulin release, suppress glucagon secretion, and slow gastric emptying. Since GLP-1 and GIP are rapidly degraded and inactivated by dipeptidyl peptidase-4 (DPP-4), inhibition of DPP-4 and/or DPP-4-resistant GLP-1 analogues have been proposed as a potential target for the treatment of diabetes. Recently, DPP-4 has been shown to cleave multiple peptides, and blockade of DPP-4 could exert diverse biological actions in GLP-1- or GIP-independent manner. This article summarizes the crosstalk between AGEs-RAGE axis and DPP-4-incretin system in the development and progression of diabetes-associated disorders and its therapeutic intervention, especially focusing on diabetic vascular complications.

Effects of High Glucose Levels and Glycated Serum on GIP Responsiveness in the Pancreatic Beta Cell Line HIT-T15

Glucose-dependent insulinotropic peptide (GIP) is an incretin hormone produced in the gastrointestinal tract that stimulates glucose dependent insulin secretion. Impaired incretin response has been documented in diabetic patients and was mainly related to the inability of the pancreatic beta cells to secrete insulin in response to GIP. Advanced Glycation End Products (AGEs) have been shown to play an important role in pancreatic beta cell dysfunction. The aim of this study is to investigate whether the exposure to AGEs can induce GIP resistance in the pancreatic beta cell line HIT-T15. Cells were cultured for 5 days in low (CTR) or high glucose (HG) concentration in the presence of AGEs (GS) to evaluate the expression of GIP receptor (GIPR), the intracellular signaling activated by GIP, and secretion of insulin in response to GIP. The results showed that incubation with GS alone altered intracellular GIP signaling and decreased insulin secretion as compared to CTR. GS in combination with HG reduced the expression of GIPR and PI3K and abrogated GIP-induced AKT phosphorylation and GIP-stimulated insulin secretion. In conclusion, we showed that treatment with GS is associated with the loss of the insulinotropic effect of GIP in hyperglycemic conditions.

The gut-renal axis: do incretin-based agents confer renoprotection in diabetes?

Diabetic nephropathy is the leading cause of end-stage renal disease worldwide, and is associated with a high risk of cardiovascular morbidity and mortality. Intensive control of glucose levels and blood pressure is currently the mainstay of both prevention and treatment of diabetic nephropathy. However, this strategy cannot fully prevent the development and progression of diabetic nephropathy, and an unmet need remains for additional novel therapies. The incretin-based agents--agonists of glucagon-like peptide 1 receptor (GLP-1R) and inhibitors of dipeptidyl peptidase 4 (DPP-4), an enzyme that degrades glucagon-like peptide 1--are novel blood-glucose-lowering drugs used in the treatment of type 2 diabetes mellitus (T2DM). Therapeutic agents from these two drug classes improve pancreatic islet function and induce extrapancreatic effects that ameliorate various phenotypic defects of T2DM that are beyond glucose control. Agonists of GLP-1R and inhibitors of DPP-4 reduce blood pressure, dyslipidaemia and inflammation, although only GLP-1R agonists decrease body weight. Both types of incretin-based agents inhibit renal tubular sodium reabsorption and decrease glomerular pressure as well as albuminuria in rodents and humans. In rodents, incretin-based therapies also prevent onset of the morphological abnormalities of diabetic nephropathy.

Retinal pigment epithelial cells express a functional receptor for glucagon-like peptide-1 (GLP-1)

Glucagon-like peptide-1 (GLP-1) is a gut-derived incretin hormone that has been shown to improve glucose homeostasis in type 2 diabetes. The biological effects of GLP-1 are mediated by its specific receptor GLP-1R that is expressed in a wide range of tissues, where it is responsible of the extra-pancreatic effects of GLP-1. Since the retinal pigment epithelium (RPE), that forms the outer retinal barrier, has a key role in protecting from diabetic retinopathy (DR), we investigated the potential expression and function of GLP-1R in a RPE cell line. ARPE-19 cells were cultured in DMEM/F12 supplemented with 10% FBS. The expression of GLP-1R was evaluated at both mRNA and protein levels. Then, the activation postreceptor intracellular signal transduction pathways (extracellular signal-regulated kinases 1 and 2 [ERK1/2] and protein kinase B [PKB]) were assessed by western blot in normal cells or silenced for GLP-1R in the presence or absence of 10 nmol/L GLP-1. The potential connections between intracellular signalling pathways triggered by GLP-1 stimulation were performed before incubating cells with kinase pharmacological inhibitors of mitogen-activated protein kinase (MEK)1/2, phosphatydilinositol-3kinase (PI3K), or epidermal growth factor receptor (EGFR). The results showed that GLP1R is expressed at both mRNA and protein level in ARPE-19 cells. Stimulation with GLP-1 strongly activated PKB and ERK1/2 phosphorylation till 40 min of exposure. GLP-1-mediated activation of both kinases was dependent on the upstream activation of PI3K and EGFR. Finally, treatment with GLP-1 did not affect the spontaneous release of VEGF-A from ARPE-19 cells. In conclusion, this paper showed that the presence of functional GLP-1R is expressed in RPE cells. These data might represent the rationale to further investigate the potential direct beneficial effects of GLP-1 treatment against DR.

Glycated albumin causes pancreatic β-cells dysfunction through autophagy dysfunction

Growing evidence suggests that advanced glycation end-products (AGEs) are cytotoxic to pancreatic β-cells. The aims of this study were to investigate whether glycated albumin (GA), an early precursor of AGEs, would induce dysfunction in pancreatic β-cells and to determine which kinds of cellular mechanisms are activated in GA-induced β-cell apoptosis. Decreased viability and increased apoptosis were induced in INS-1 cells treated with 2.5 mg/mL GA under 16.7mM high-glucose conditions. Insulin content and glucose-stimulated secretion from isolated rat islets were reduced in 2.5 mg/mL GA-treated cells. In response to 2.5 mg/mL GA in INS-1 cells, autophagy induction and flux decreased as assessed by green fluorescent protein-microtubule-associated protein 1 light chain 3 dots, microtubule-associated protein 1 light chain 3-II conversion, and SQSTM1/p62 in the presence and absence of bafilomycin A1. Accumulated SQSTM1/p62 through deficient autophagy activated the nuclear factor-κB (p65)-inducible nitric oxide synthase-caspase-3 cascade, which was restored by treatment with small interfering RNA against p62. Small interfering RNA treatment against autophagy-related protein 5 significantly inhibited the autophagy machinery resulting in a significant increase in iNOS-cleaved caspase-3 expression. Treatment with 500μM 4-phenyl butyric acid significantly alleviated the expression of endoplasmic reticulum stress markers and iNOS in parallel with upregulated autophagy induction. However, in the presence of bafilomycin A1, the decreased viability of INS-1 cells was not recovered. Glycated albumin, an early precursor of AGE, caused pancreatic β-cell death by inhibiting autophagy induction and flux, resulting in nuclear factor-κB (p65)-iNOS-caspase-3 cascade activation as well as by increasing susceptibility to endoplasmic reticulum stress and oxidative stress.

Advanced glycation end products impair glucose-induced insulin secretion from rat pancreatic β-cells

BACKGROUND

Advanced glycation end products (AGEs) are derivative compounds generated from non-enzymatic glycosylation and oxidation. In comparison with glucose-derived AGEs (Glu-AGEs), glyceraldehyde-derived AGEs (Glycer-AGEs) have stronger toxicity to living systems. In this study, we compared the effects of Glu-AGE and Glycer-AGE on insulin secretion.

METHOD

Rat pancreatic islets were isolated by collagenase digestion and primary-cultured in the presence of 0.1 mg/ml bovine serum albumin (BSA) or 0.1 mg/ml Glu-AGE or Glycer-AGE-albumin. After 48 h of culture, we performed an insulin secretion test and identified the defects by a battery of rescue experiments [corrected]. Also, mRNA expression of genes associated with insulin secretion was measured.

RESULTS

Insulin secretion induced by a high glucose concentration was 164.1 ± 6.0, 124.4 ± 4.4 (P < 0.05) and 119.8 ± 7.1 (P < 0.05) μU/3 islets/h in the presence of BSA, Glu-AGE, and Glycer-AGE, respectively. Inhibition of insulin secretion by Glu-AGE or Glycer-AGE was rescued by a high extracellular potassium concentration, tolbutamide and α-ketoisocaproic acid, but not by glyceraldehyde, dihydroxacetone, methylpyruvate, glucagon-like peptide-1 and acetylcholine. Glu-AGE or Glycer-AGE reduced the expression of the malate dehydrogenase (Mdh1/2) gene, which plays a critical role in the nicotinamide adenine dinucleotide (NADH) shuttle.

CONCLUSION

Despite its reported cytotoxicity, the effects of Glycer-AGE on insulin secretion are similar to those of Glu-AGE.

Update on the protective molecular pathways improving pancreatic beta-cell dysfunction

The primary function of pancreatic beta-cells is to produce and release insulin in response to increment in extracellular glucose concentrations, thus maintaining glucose homeostasis. Deficient beta-cell function can have profound metabolic consequences, leading to the development of hyperglycemia and, ultimately, diabetes mellitus. Therefore, strategies targeting the maintenance of the normal function and protecting pancreatic beta-cells from injury or death might be crucial in the treatment of diabetes. This narrative review will update evidence from the recently identified molecular regulators preserving beta-cell mass and function recovery in order to suggest potential therapeutic targets against diabetes. This review will also highlight the relevance for novel molecular pathways potentially improving beta-cell dysfunction.

Glucagon-like peptide-1 triggers protective pathways in pancreatic beta-cells exposed to glycated serum

Advanced glycation end products (AGEs) might play a pathophysiological role in the development of diabetes and its complications. AGEs negatively affect pancreatic beta-cell function and the expression of transcriptional factors regulating insulin gene. Glucagon-like peptide-1 (GLP-1), an incretin hormone that regulates glucose homeostasis, might counteract the harmful effects of AGEs on the beta cells in culture. The aim of this study was to identify the intracellular mechanisms underlying GLP-1-mediated protection from AGE-induced detrimental activities in pancreatic beta cells. HIT-T15 cells were cultured for 5 days with glycated serum (GS, consisting in a pool of AGEs), in the presence or absence of 10 nmol/L GLP-1. After evaluation of oxidative stress, we determined the expression and subcellular localization of proteins involved in maintaining redox balance and insulin gene expression, such as nuclear factor erythroid-derived 2 (Nrf2), glutathione reductase, PDX-1, and MafA. Then, we investigated proinsulin production. The results showed that GS increased oxidative stress, reduced protein expression of all investigated factors through proteasome activation, and decreased proinsulin content. Furthermore, GS reduced ability of PDX-1 and MafA to bind DNA. Coincubation with GLP-1 reversed these GS-mediated detrimental effects. In conclusion, GLP-1, protecting cells against oxidants, triggers protective intercellular pathways in HIT-T15 cells exposed to GS.

An emerging role of glucagon-like peptide-1 in preventing advanced-glycation-end-product-mediated damages in diabetes

Glucagon-like peptide-1 (GLP-1) is a gut hormone produced in the intestinal epithelial endocrine L cells by differential processing of the proglucagon gene. Released in response to the nutrient ingestion, GLP-1 plays an important role in maintaining glucose homeostasis. GLP-1 has been shown to regulate blood glucose levels by stimulating glucose-dependent insulin secretion and inhibiting glucagon secretion, gastric emptying, and food intake. These antidiabetic activities highlight GLP-1 as a potential therapeutic molecule in the clinical management of type 2 diabetes, (a disease characterized by progressive decline of beta-cell function and mass, increased insulin resistance, and final hyperglycemia). Since chronic hyperglycemia contributed to the acceleration of the formation of Advanced Glycation End-Products (AGEs, a heterogeneous group of compounds derived from the nonenzymatic reaction of reducing sugars with free amino groups of proteins implicated in vascular diabetic complications), the administration of GLP-1 might directly counteract diabetes pathophysiological processes (such as pancreatic β-cell dysfunction). This paper outlines evidence on the protective role of GLP-1 in preventing the deleterious effects mediated by AGEs in type 2 diabetes.

Glucagon-like peptide-1 preserves coronary microvascular endothelial function after cardiac arrest and resuscitation: potential antioxidant effects

Glucagon-like peptide-1 (GLP-1) has protective effects in the heart. We hypothesized that GLP-1 would mitigate coronary microvascular and left ventricular (LV) dysfunction if administered after cardiac arrest and resuscitation (CAR). Eighteen swine were subjected to ventricular fibrillation followed by resuscitation. Swine surviving to return of spontaneous circulation (ROSC) were randomized to receive an intravenous infusion of either human rGLP-1 (10 pmol·kg(-1)·min(-1); n = 8) or 0.9% saline (n = 8) for 4 h, beginning 1 min after ROSC. CAR caused a decline in coronary flow reserve (CFR) in control animals (pre-arrest, 1.86 ± 0.20; 1 h post-ROSC, 1.3 ± 0.05; 4 h post-ROSC, 1.25 ± 0.06; P < 0.05). GLP-1 preserved CFR for up to 4 h after ROSC (pre-arrest, 1.31 ± 0.17; 1 h post-ROSC, 1.5 ± 0.01; 4 h post-ROSC, 1.55 ± 0.22). Although there was a trend toward improvement in LV relaxation in the GLP-1-treated animals, overall LV function was not consistently different between groups. 8-iso-PGF(2α), a measure of reactive oxygen species load, was decreased in post-ROSC GLP-1-treated animals [placebo, control (NS): 38.1 ± 1.54 pg/ml; GLP-1: 26.59 ± 1.56 pg/ml; P < 0.05]. Infusion of GLP-1 after CAR preserved coronary microvascular and LV diastolic function. These effects may be mediated through a reduction in oxidative stress.

Glucagon-like peptide-1 (GLP-1) protects vascular endothelial cells against advanced glycation end products (AGEs)-induced apoptosis

Background

The peptide glucagon-like peptide-1 (GLP-1) is a hormone secreted by intestinal L cells in response to food intake. GLP-1 has been proposed as the basis of emerging therapy for patients with type 2 diabetes. However, the effects of GLP-1 on vascular injury in diabetes have not been identified. Advanced glycation end products (AGEs) induce endothelial cell apoptosis and have been implicated in the process of vascular complications from diabetes.

Material/Methods

The aim of this work was to investigate whether and how GLP-1 protects endothelial cells from apoptosis induced by AGEs. Human umbilical vein endothelial cells (HUVECs) were treated with AGEs (200 μg/mL) for 48 h in the presence or absence of GLP-1. Cell morphology, viability, apoptosis, ratio of Bcl-2 protein to Bax protein, cytochrome c release, and activity of caspase-9 and −3 were determined.

Results

Treatment of cells with AGEs led to cell morphology changes and decreased cell viability, resulting in apoptosis. GLP-1 alone increased cell viability in a concentration-dependent manner. GLP-1 partially inhibited AGEs-induced apoptosis in HUVECs. GLP-1 increased Bcl-2/Bax ratio, reduced cytochrome c levels in the cytoplasm, and reduced the activity of caspase-9 and −3 in AGEs-treated HUVECs.

Conclusions

AGEs induces apoptosis via the mitochondrion-cytochrome c-caspase protease pathway, and GLP-1 protects endothelial cells by interfering with this mechanism. GLP-1 may represent an anti-apoptotic agent in the treatment of vascular complications arising from diabetes.

Pioglitazone attenuates the detrimental effects of advanced glycation end-products in the pancreatic beta cell line HIT-T15

Pioglitazone is an anti-diabetic agent that preserves pancreatic beta cell mass and improves their function. Advanced Glycation End-Products (AGEs) are implicated in diabetic complications. We previously demonstrated that exposure of the pancreatic islet cell line HIT-T15 to high concentrations of AGEs significantly decreases cell proliferation and insulin secretion, and affects transcription factors regulating insulin gene transcription. The aim of this work was to investigate the effects of Pioglitazone on the function and viability of HIT-T15 cells cultured with AGEs. HIT-T15 cells were cultured for 5 days in the presence of AGEs alone, or supplemented with 1 μmol/l Pioglitazone. Cell viability, insulin secretion and insulin content, redox balance, expression of the AGE receptor (RAGE), and NF-kB activation were then determined. The results showed that Pioglitazone protected beta cells against AGEs-induced apoptosis and necrosis. Moreover, Pioglitazone restored the redox balance and improved the responsiveness to low glucose concentration. Adding Pioglitazone to the AGEs culture attenuated NF-kB phosphorylation, and prevented AGEs to down-regulate IkBα expression. These findings suggest that Pioglitazone protects beta cells from the dangerous effects of AGEs.

Biogerontology in Italy

In this paper experimental gerontology in Italy is reviewed on the basis of research developed in Academic and non Academic Centres. There are several groups across Italy working actively on basic science of aging producing high impact papers with a significant contribution to biogerontology. Some distinguished Italian scientist working abroad is also mentioned. Interesting issues on longevity and interventions on aging (including caloric restriction) and on aging brain are quoted. Relevant studies encompass the (glyco-)oxidative stress as direct damage mechanism and main process of theory of aging, other research lines include IGF-1, mitochondria DNA, obesity/sarcopenia and exercise and also an animal model for aging studies is reported. Notwithstanding financial restrictions and structure deficit the biogerontology research in Italy could be judged as good, but additional resources are necessary to keep this good rank.