Beta-cell Apoptosis Research Articles

Liquiritigenin prevents palmitate-induced beta-cell apoptosis via estrogen receptor-mediated AKT activation

Liquiritigenin (LQ) is a major active component of licorice root, which is a flavone used for treating many diseases, including diabetes. LQ has been shown to exhibit a glucose-lowering effect in diabetic mice. Therefore, we investigated the potential of LQ to protect against lipotoxicity-induced beta-cell apoptosis and the underlying molecular mechanisms. Exposure of INS-1 rat insulinoma cells to LQ significantly increased cell viability and blocked palmitate (PA)-induced apoptosis, as evidenced by the reduction of Annexin-V-stained cells, cleaved caspase-3 levels, and poly (ADP-ribose) polymerase (PARP) activity, as well as upregulation of Bcl-2 expression. Moreover, LQ treatment significantly reduced the endoplasmic reticulum (ER) stress response by reducing phosphorylated protein kinase RNA-like endoplasmic reticulum kinase (PERK), phosphorylated eIF-2a, and CHOP expression in PA-treated INS-1 cells. The anti-apoptotic effect of LQ treatment was reversed through co-treatment with fulvestrant, a specific inhibitor of the estrogen receptor. LQ also increased AKT phosphorylation, and inactivation of this molecular event failed to decrease PERK phosphorylation with LQ treatment in PA-treated INS-1 cells. This effect was further accompanied by an inability to recover cell viability. These results suggest that LQ protects INS-1 cells from lipotoxicity-induced apoptosis by suppressing ER stress. We conclude that estrogen receptor-mediated AKT phosphorylation is one of the mechanisms contributing to the anti-apoptotic effect of LQ.

Beta cell extracellular vesicle miR-21-5p cargo is increased in response to inflammatory cytokines and serves as a biomarker of type 1 diabetes.

Improved biomarkers are acutely needed for the detection of developing type 1 diabetes, prior to critical loss of beta cell mass. We previously demonstrated that elevated beta cell microRNA 21-5p (miR-21-5p) in rodent and human models of type 1 diabetes increased beta cell apoptosis. We hypothesised that the inflammatory milieu of developing diabetes may also increase miR-21-5p in beta cell extracellular vesicle (EV) cargo and that circulating EV miR-21-5p would be increased during type 1 diabetes development. MIN6 and EndoC-βH1 beta cell lines and human islets were treated with IL-1β, IFN-γ and TNF-α to mimic the inflammatory milieu of early type 1 diabetes. Serum was collected weekly from 8-week-old female NOD mice until diabetes onset. Sera from a cross-section of 19 children at the time of type 1 diabetes diagnosis and 16 healthy children were also analysed. EVs were isolated from cell culture media or serum using sequential ultracentrifugation or ExoQuick precipitation and EV miRNAs were assayed. Cytokine treatment in beta cell lines and human islets resulted in a 1.5- to threefold increase in miR-21-5p. However, corresponding EVs were further enriched for this miRNA, with a three- to sixfold EV miR-21-5p increase in response to cytokine treatment. This difference was only partially reduced by pre-treatment of beta cells with Z-VAD-FMK to inhibit cytokine-induced caspase activity. Nanoparticle tracking analysis showed cytokines to have no effect on the number of EVs, implicating specific changes within EV cargo as being responsible for the increase in beta cell EV miR-21-5p. Sequential ultracentrifugation to separate EVs by size suggested that this effect was mostly due to cytokine-induced increases in exosome miR-21-5p. Longitudinal serum collections from NOD mice showed that EVs displayed progressive increases in miR-21-5p beginning 3weeks prior to diabetes onset. To validate the relevance to human diabetes, we assayed serum from children with new-onset type 1 diabetes compared with healthy children. While total serum miR-21-5p and total serum EVs were reduced in diabetic participants, serum EV miR-21-5p was increased threefold compared with non-diabetic individuals. By contrast, both serum and EV miR-375-5p were increased in parallel among diabetic participants. We propose that circulating EV miR-21-5p may be a promising marker of developing type 1 diabetes. Additionally, our findings highlight that, for certain miRNAs, total circulating miRNA levels are distinct from circulating EV miRNA content.

Progress of prolactin in regulating the function of pancreatic β cells

Prolactin is a polypeptide hormone that regulates cell growth and development. Recent studies have shown that prolactin is involved in the regulation of glucose metabolism and is closely related to blood glucose homeostasis. This paper is to review the research progress of prolactin in islet β cells, including the understanding of prolactin and its receptor, the associations of prolactin with glucose metabolism, and the proliferation, apoptosis and secretion of pancreatic beta cells. (Chin J Endocrinol Metab, 2018, 34: 79-82) Key words: Prolactin; Prolactin receptor; Glucose metabolism; Pancreatic β cells

FAM3B/PANDER inhibits cell death and increases prostate tumor growth by modulating the expression of Bcl-2 and Bcl-XL cell survival genes

BackgroundFAM3B/PANDER is a novel cytokine-like protein that induces apoptosis in insulin-secreting beta-cells. Since in silico data revealed that FAM3B can be expressed in prostate tumors, we evaluated the putative role of this cytokine in prostate tumor progression.MethodsFAM3B expression was analyzed by quantitative PCR in tumor tissue clinical samples and prostate tumor cell lines. Culture growth and viability of DU145 cell line were evaluated after treatment with either exogenous FAM3B protein obtained from conditioned media (CM) of 293 T cells overexpressing FAM3B or a recombinant FAM3B protein produced in a bacterial host. DU145 cells overexpressing FAM3B protein were produced by lentiviral-mediated transduction of full-length FAM3B cDNA. Cell viability and apoptosis were analyzed in DU145/FAM3B cells after treatment with several cell death inducers, such as TNF-alpha, staurosporine, etoposide, camptothecin, and serum starvation conditions. Anchorage-independent growth in soft agarose assay was used to evaluate in vitro tumorigenicity. In vivo tumorigenicity and invasiveness were evaluated by tumor xenograft growth in nude mice.ResultsWe observed an increase in FAM3B expression in prostate tumor samples when compared to normal tissues. DU145 cell viability and survival increased after exogenous treatment with recombinant FAM3B protein or FAM3B-secreted protein. Overexpression of FAM3B in DU145 cells promoted inhibition of DNA fragmentation and phosphatidylserine externalization in a time and dose-dependent fashion, upon apoptosis triggered by TNF-alpha. These events were accompanied by increased gene expression of anti-apoptotic Bcl-2 and Bcl-XL, decreased expression of pro-apoptotic Bax and diminished caspase-3, −8 and −9 proteolytic activities. Furthermore, inhibition of Bcl-2 anti-apoptotic family proteins with small molecules antagonists decreases protective effects of FAM3B in DU145 cells. When compared to the respective controls, cells overexpressing FAM3B displayed a decreased anchorage- independent growth in vitro and increased tumor growth in xenografted nude mice. The immunohistochemistry analysis of tumor xenografts revealed a similar anti-apoptotic phenotype displayed by FAM3B-overexpressing tumor cells.ConclusionsTaken together, by activating pro-survival mechanisms FAM3B overexpression contributes to increased resistance to cell death and tumor growth in nude mice, highlighting a putative role for this cytokine in prostate cancer progression.

Dioscin Promotes Proliferation of Pancreatic Beta Cells via Wnt/β-Catenin Signaling Pathways.

Dysfunction of pancreatic beta cells is related with type 2 diabetes mellitus. Dioscin, a natural steroid saponin, has many pharmacological effects. The aim of this study was to investigate the effects of dioscin on apoptosis of pancreatic beta cells induced by high glucose. Pancreatic cell line RNAKT-15 was treated with 20 mM glucose with or without different concentrations of dioscin and viability and apoptosis of cells were measured. Western blot assay was used to measure the expression levels of some proteins such as phosphorylated glycogen synthase kinase 3β (GSK-3β) and β-catenin. Enzymelinked immunosorbent assay (ELISA) was used to detect the pro-inflammatory cytokines. High-glucose could significantly increase cell RNAKT-15 apoptosis and reduce cell viability (p < 0.01). Dioscin could improve the cell degeneration (p < 0.05). The results demonstrated that high-glucose could increase the proinflammatory cytokines, such as tumor necrosis factor α (TNF-α), interferon-γ (INF-γ), and transforming growth factor-β (TGF-β), while these effects were reduced when treated with dioscin (p < 0.05). Western blot results demonstrated that high-glucose affects p-GSK 3β and β-catenin expression levels (p < 0.01) and dioscin could significantly reduce these two protein levels (p < 0.05). The effects of dioscin against high-glucose induced apoptosis of pancreatic cells may occur through the Wnt signaling pathway. High-glucose led to increased pancreatic cell apoptosis and dioscin could attenuate these impairments. These findings highlight an important role of dioscin in the treatment potential of type 2 diabetes mellitus (T2DM).

Antidiabetic and Antiobesity Effects of Artemether in db/db Mice.

This study is designed to investigate the effect of artemether on type 2 diabetic db/db mice. The experiments consisted of three groups: normal control (NC, db/+, 1% methylcellulose, intragastric administration), diabetic control (DM, db/db, 1% methylcellulose, intragastric administration), and artemether treated (artemether, db/db, 200 mg/kg of artemether, intragastric administration). The treatment lasted for two weeks. The food intake, body weight, and fasting blood glucose of mice were measured every three days. At the start and end of the experiment, the intraperitoneal glucose tolerance test (IPGTT) and insulin tolerance test (IPITT) were performed. We determined the serum insulin and glucagon levels by ELISA kits and calculated insulin resistance index (HOME-IR). HE staining was used to observe the morphologies of pancreas and liver in mice. The damage of pancreatic beta cells was evaluated by TUNEL staining and immunofluorescence. We found the following: (1) compared with the DM group, the food intake and weight increase rate of artemether group significantly reduced (P < 0.05); (2) compared with pretreatment, artemether significantly reduced the fasting blood glucose levels, and the areas under the curves (AUCs) of IPGTT were decreased significantly, increasing the tolerance to glucose of db/db mice. (P < 0.05); (3) artemether improved hyperinsulinemia and decreased the AUCs of IPITT and HOME-IR, increasing the insulin sensitivity of db/db mice. (4) Artemether significantly ameliorated islet vacuolar degeneration and hepatic steatosis in db/db mice. (5) Artemether reduced the apoptosis of pancreatic beta cells and increased insulin secretion in db/db mice compared with DM group (P < 0.05). Our results indicated that artemether significantly improved glucose homeostasis and insulin resistance and had the potential activity to prevent obesity, reduced the severity of fatty liver, and protected pancreatic beta cells, promising to treat type 2 diabetes.

Low-dose tributyltin exposure induces an oxidative stress-triggered JNK-related pancreatic beta-cell apoptosis and a reversible hypoinsulinemic hyperglycemia in mice

Low-dose tributyltin exposure induces an oxidative stress-triggered JNK-related pancreatic beta-cell apoptosis and a reversible hypoinsulinemic hyperglycemia in mice

Association between Field Liming and the Epidemic of Type 1 Diabetes

Zinc is an essential nutrient for mammals. Zinc has only one oxidation state Zn2+ but it has many coordination states, which can alter without demanding energy. Coordination states depend on prevailing pH. In soils the coordination state changes from octahedral (nonphysiologic) form to tetrahedral (physiologic) form when pH rises to about 6.5. Weathering processes of common soil mineral mica are also pH dependent. Large scale argricultural field liming began from 1950's onward in the Western Countries and since that time the incidence of T1D began to increase in the Western Countries. Liming elevates soil pH often near 6.5 and favours mosaic mica-vermiculite nanoparticle formation in which vermiculite corner binds zinc in tetrahedral (physiological) coordination state. In this pH mica corner remains in native form and offers the plane for soluble pMHC molecule (binded with antigenic beta-cell specific self peptide) to adhere on mica and as a consequence to trigger the activation of autoreactive CD4 and/or CD8 T cells. Beta-cell specific autoantigens are released because abundant zinc derived from endocytosed zinc-mica-vermiculite particles in lysosomes leads to incresed beta-cell apoptosis, also the physiological neonatal beta-cell mass remodeling enhance beta-cell specific auto-antigen release. Furthermore enterovirusinfections during first years of life are common and can release beta-cell specific auto-antigens. The probable disease mechanism is dealt with this review article.

ERK5 plays an essential role in gestational beta-cell proliferation.

Restoring a functional beta-cell mass is a fundamental goal in treating diabetes. A complex signalling pathway network coordinates the regulation of beta-cell proliferation, although a role for ERK5 in this network has not been reported. This question was addressed in this study. We studied the activation of extracellular-signal-regulated kinase 5 (ERK5) in pregnant mice, a well-known mouse model of increased beta-cell proliferation. A specific inhibitor of ERK5 activation, BIX02189, was intraperitoneally injected into the pregnant mice to suppress ERK5 signalling. Beta-cell proliferation was determined by quantification of Ki-67+ beta cells. Beta-cell apoptosis was determined by TUNEL assay. The extent of beta-cell proliferation was determined by beta-cell mass. The alteration of ERK5 activation and CyclinD1 levels in purified mouse islets was examined by Western blotting. Extracellular-signal-regulated kinase 5 phosphorylation, which represents ERK5 activation, was significantly upregulated in islets from pregnant mice. Suppression of ERK5 activation by BIX02189 in pregnant mice significantly reduced beta-cell proliferation, without affecting beta-cell apoptosis, resulting in increases in random blood glucose levels and impairment of glucose response of the mice. ERK5 seemed to activate CyclinD1 to promote gestational beta-cell proliferation. Extracellular-signal-regulated kinase 5 plays an essential role in the gestational augmentation of beta-cell proliferation. ERK5 may be a promising target for increasing beta-cell mass in diabetes patients.

Islet neuropeptide Y receptors are functionally conserved and novel targets for the preservation of beta-cell mass.

Two unmet therapeutic strategies for diabetes treatment are prevention of beta-cell death and stimulation of beta-cell replication. Our aim was to characterize the role of neuropeptide Y receptors in the control of beta-cell mass. We used endogenous and selective agonists of the NPY receptor system to explore its role in the prevention of beta-cell apoptosis and proliferation in islets isolated from both mouse and human donors. We further explored the intra-cellular signalling cascades involved, using chemical inhibitors of key signalling pathways. As proof of principle we designed a long-acting analogue of [Leu31 Pro34 ]-NPY, an agonist of the islet-expressed Y receptors, to determine if targeting this system could preserve beta-cell mass in vivo. Our data reveal that NPY Y1, 4 and 5 receptor activation engages a generalized and powerful anti-apoptotic pathway that protects mouse and human islets from damage. These anti-apoptotic effects were dependent on stimulating a Gαi-PLC-PKC signalling cascade, which prevented cytokine-induced NFkB signalling. NPY receptor activation functionally protected islets by restoring glucose responsiveness following chemically induced injury in both species. NPY receptor activation attenuated beta-cell apoptosis, preserved functional beta-cell mass and attenuated the hyperglycaemic phenotype in a low-dose streptozotocin model of diabetes. Taken together, our observations identify the islet Y receptors as promising targets for the preservation of beta-cell mass. As such, targeting these receptors could help to maintain beta-cell mass in both type 1 and type 2 diabetes, and may also be useful for improving islet transplantation outcomes.

The rs2292239 polymorphism in ERBB3 gene is associated with risk for type 1 diabetes mellitus in a Brazilian population

The Erb-b2 receptor tyrosine kinase 3 (ERBB3) belongs to a family of epidermal growth factor receptors of protein tyrosine kinases, and regulates cell survival, differentiation and proliferation in several cell types. Previous studies have suggested that ERBB3 contributes to T1DM pathogenesis by modulating antigen presenting cell function, autoimmunity and cytokine-induced beta-cell apoptosis. Accordingly, some genome-wide association studies identified ERBB3 gene as a susceptibility locus for T1DM, with the strongest association signal being observed for the rs2292239 single nucleotide polymorphism (SNP) in intron 7 of the gene. Therefore, the aim of the present study was to replicate the association of the ERBB3 rs2292239 SNP with T1DM in a Brazilian population. We analyzed 421 T1DM patients (cases) and 510 nondiabetic subjects (controls). All subjects were self-declared as white. The ERBB3 rs2292239 (A/C) SNP was genotyped by real-time PCR using TaqMan MGB probes. Genotype (P=0.001) and allele (P=0.002) frequencies of the ERBB3 rs2292239 SNP were differently distributed between T1DM patients and nondiabetic controls. Moreover, the A allele was significantly associated with risk for T1DM when considering recessive (OR=1.58, 95% CI 1.11–2.27; P=0.015), additive (OR=1.78, 95% CI 1.21–2.62; P=0.004), and dominant (OR=1.39, 95% CI 1.07–1.81; P=0.016) models of inheritance. However, after adjustment for presence of high-risk HLA DR/DQ genotypes, the rs2292239 SNP remained independently associated with T1DM only for the additive model (OR=1.62, 95% CI 1.02–2.59; P=0.043). Our results suggest that the A/A genotype of the ERBB3 rs2292239 SNP is associated with risk for T1DM in a white Brazilian population.

Glucocorticoids and beta-cell function.

Glucocorticoids (GCs) play a pivotal role in carbohydrate metabolism. They counteract insulin by decreasing peripheral glucose uptake and stimulating hepatic gluconeogenesis, although they are best known for inducing insulin resistance (IR). Moreover, GCs may attenuate the incretin effect. Nevertheless, their direct impact on beta cells is not fully defined. This review aims to present the current understanding of this subject. Humans exposed to GC excess display IR, impaired glucose tolerance, and eventually develop diabetes. Although their insulin levels are elevated, they present lower insulin output in response to glucose than obese individuals. Rodent models demonstrate that GC-induced IR is accompanied by compensatory beta-cell hyperplasia. GC excess with high-fat diet leads to fasting hyperglycaemia and suppressed glucose-stimulated insulin secretion (GSIS) despite increased beta cell mass. The majority of in vitro studies confirm an inhibitory GC effect on insulin secretion. The mechanism remains ambiguous but might involve its direct influence upon expression of molecules essential for glucose sensing and metabolism, enhanced glucose cycling, down-regulated insulin gene transcription, hampered insulin exocytosis, amplified alpha-adrenergic signalling, and/or increased beta-cell apoptosis. There are also reports that suggest increased GSIS after beta cell exposure to GCs in vitro. Transgenic mice with enhanced corticosterone regeneration within their beta cells present augmented secretory capacity of their islets. To summarise, GCs exert a significant role in carbohydrate balance through various mechanisms, including direct impact on beta cell function. Observed discrepancies may arise from differences in study design. A thorough understanding of GC action will provide important clinical clues for disorders of glucose homeostasis.

Circulating microRNA-375 as biomarker of pancreatic beta cell death and protection of beta cell mass by cytoprotective compounds

ObjectivePrevious studies demonstrated that circulating microRNA-375 (miR-375) is a suitable plasma biomarker for real-time detection of beta cell death. The present study evaluated the use of this biomarker to assess the beta cytoprotective effect of phenylpropenoic acid glucoside (PPAG), which was previously demonstrated to protect beta cells against various types of injury, and of exendin-4, which is an established antidiabetic drug.MethodsPPAG or exendin-4 were administered in mice treated with streptozotocin (STZ) to acutely induce beta cell death. Beta cell mass and apoptotic death were measured in pancreatic tissue sections. Circulating miR-375 was measured in blood plasma by RT-qPCR. The release of miR-375 was also measured in vitro by MIN-6 beta cells.ResultsAdministration of STZ resulted in measurable circulating levels of miR-375, a decrease in beta cell mass and increase in frequency of apoptotic beta cells. In vitro, there was a good correlation between miR-375 release and the extent of beta cell death. Treatment of mice with PPAG or exendin-4 significantly attenuated STZ-induced loss of beta cell mass and beta cell apoptosis, and normalized the blood level of miR-375.ConclusionsThese findings show the potential use of serological miR-375 measurements to evaluate the beta cytoprotective effect of (potential) antidiabetic drugs in vivo.

The anti-aging protein Klotho is induced by GABA therapy and exerts protective and stimulatory effects on pancreatic beta cells

Systemic gamma-aminobutyric acid (GABA) therapy prevents or ameliorates type 1 diabetes (T1D), by suppressing autoimmune responses and stimulating pancreatic beta cells. In beta cells, it increases insulin secretion, prevents apoptosis, and induces regeneration. It is unclear how GABA mediates these effects. We hypothesized that Klotho is involved. It is a multi-functional protein expressed in the kidneys, brain, pancreatic beta cells, other tissues, and is cell-bound or soluble. Klotho knockout mice display accelerated aging, and in humans Klotho circulating levels decline with age, renal disease and diabetes. Here, we report that GABA markedly increased circulating levels of Klotho in streptozotocin (STZ)-induced diabetes. GABA also increased Klotho in the islet of Langerhans of normal mice, as well as the islets and kidneys of STZ-treated mice. In vitro, GABA stimulated production and secretion of Klotho by human islet cells. Knockdown (KD) of Klotho with siRNA in INS-1E insulinoma cells abrogated the protective effects of GABA against STZ toxicity. Following KD, soluble Klotho reversed the effects of Klotho deficiency. In human islet cells soluble Klotho protected against cell death, and stimulated proliferation and insulin secretion. NF-κB activation triggers beta-cell apoptosis, and both GABA and Klotho suppress this pathway. We found Klotho KD augmented NF-κB p65 expression, and abrogated the ability of GABA to block NF-κB activation. This is the first report that GABAergic stimulation increases Klotho expression. Klotho protected and stimulated beta cells and lack of Klotho (KD) was reversed by soluble Klotho. These findings have important implications for the treatment of T1D.

Effect of Crocin and Voluntary Exercise on P53 Protein in Pancreas of Type2 Diabetic Rats

Background: Excessive apoptosis of the pancreatic beta-cell has been associated with type 2 diabetes. Hyperglycemia significantly stimulates pancreatic islet cell apoptosis. We evaluated the role of crocin and voluntary exercise on apoptosis of pancreas tissue in type2 diabetic rats. Methods: Animals divided into 5 groups as: control (Con), diabetes (Dia), diabetic-crocin (Dia-Cro), diabetic-voluntary exercise (Dia-Exe), diabetic-crocin-voluntary exercise (Dia-Cro-Exe). Type 2 diabetes was induced by high-fat diet (4 weeks) and injection of streptozotocin (STZ) (i.p, 35 mg/kg). Animals received crocin orally (50 mg/kg), voluntary exercise performed alone or together for 8 weeks. At the final of study, blood glucose levels and HbA1c were detected. Also p53 protein levels of pancreas tissue were measured by ELISA. Results: P53 levels in pancreas tissue of diabetic group were significantly higher than control group. Crocin and exercise significantly decreased the blood glucose, HbA1c levels and p53 expression in treated diabetic groups compared to diabetic group. The glucose, HbA1c and p53 levels were also significantly lower in crocin-voluntary exercise group in comparison to the other experimental groups. Conclusion: Our results reveal that both crocin and voluntary exercise reduce apoptosis of pancreas through reduction of p53 levels. Moreover, treatments with crocin and voluntary exercise have synergistic anti-apoptotic effects on pancreas tissue of type 2 diabetic rats. Protective effects of these interventions probably perform through the decreasing of glucose and HbA1c levels in blood of rats suffering from diabetes.

Levothyroxine enhances glucose clearance and blunts the onset of experimental type 1 diabetes mellitus in mice.

Thyroid hormones induce several changes in whole body metabolism that are known to improve metabolic homeostasis. However, adverse side effects have prevented its use in the clinic. In view of the promising effects of thyroid hormones, we investigated the effects of levothyroxine supplementation on glucose homeostasis. C57BL/6 mice were treated with levothyroxine from birth to 24weeks of age, when mice were killed. The effects of levothyroxine supplementation on metabolic health were determined. C57BL/6 mice treated with levothyroxine for 2weeks and then challenged with streptozotocin to monitor survival. Mechanistic experiments were conducted in the pancreas, liver and skeletal muscle. RIP-B7.1 mice were treated with levothyroxine for 2weeks and were subsequently immunized to trigger experimental autoimmune diabetes (EAD). Metabolic tests were performed. Mice were killed and metabolic tissues were extracted for immunohistological analyses. Long-term levothyroxine supplementation enhanced glucose clearance and reduced circulating glucose in C57BL/6 mice. Levothyroxine increased simultaneously the proliferation and apoptosis of pancreatic beta cells, promoting the maintenance of a highly insulin-expressing beta cell population. Levothyroxine increased circulating insulin levels, inducing sustained activation of IRS1-AKT signalling in insulin-target tissues. Levothyroxine-treated C57BL/6 mice challenged with streptozotocin exhibited extended survival. Levothyroxine blunted the onset of EAD in RIP-B7.1 mice by inducing beta cell proliferation and preservation of insulin-expressing cells. Interventions based on the use of thyroid hormones or thyromimetics could be explored to provide therapeutic benefit in patients with type 1 diabetes mellitus.

Improving glycemic control in model mice with type 2 diabetes by increasing superoxide dismutase (SOD) activity using silk fibroin hydrolysate (SFH)

Islet cell dysfunction in type 2 diabetes is primarily attributed to the increased apoptosis of pancreatic beta cells. Silk fibroin hydrolysate (SFH) has an effect on blood in type 2 diabetes model mice (C57BL/KsJ-db/db). However, its exact mechanism is unknown. The type 2 diabetes model mice were randomly divided into non-diabetic mice (ND), diabetic mice (DB), and diabetic mice treated with silk fibroin hydrolysate (DB-SFH). The results showed that SFH significantly decreased fasting blood glucose and hemoglobin A1c (HbA1c). The oral glucose tolerance and insulin tolerance were significantly improved in the DB-SFH group. The DB-SFH group exhibited increased superoxide dismutase (SOD) activity in the plasma, as well as increased Mn-SOD and CuZn-SOD activities in the pancreatic islets. Furthermore, the pancreatic islet cells' death was decreased in the DB-SFH group. In the DB-SFH group, the protein expression of caspase-3 was significantly decreased compared with the DB group. The expression of the Nkx6.1 and Pdx1 proteins were increased in the DB-SFH group. The results suggest that SFH prevents the degeneration of pancreatic islets via increasing SOD while hyperglycemia is alleviated by maintaining beta cell mass in type 2 diabetes model mice.

Anti-diabetic actions of esculentin-2CHa(1-30) and its stable analogues in a diet-induced model of obesity-diabetes.

Actions of esculentin-2CHa(1-30) (GFSSIFRGVAKFASKGLGKDLAKLGVDLVA) and its analogues, ([D-Arg7, D-Lys15, D-Lys23]-esculentin-2CHa(1-30) and [Lys15-octanoate]-esculentin-2CHa(1-30), were evaluated in high-fat fed NIH Swiss mice with impaired glucose tolerance and insulin resistance. Twice-daily i.p. administration of the esculentin-2CHa(1-30) peptides (75nmol/kg body weight) or exendin-4 (25nmol/kg) for 28days reduced body weight, without altering cumulative energy intake. All peptides reduced blood glucose levels by 6-12mmol/l concomitant with lower plasma insulin levels, with significance evident from day 6. All peptides improved glucose tolerance, insulin sensitivity, blood glucose profile over 24h and decreased HbA1c to a similar extent as exendin-4. The peptides also reduced high fat diet-induced increases in plasma GLP-1 and glucagon. None of the peptides altered bone mineral density/content or lean mass but decreased fat mass. Islets isolated from peptide-treated mice exhibited improved glucose-, alanine- and GLP-1-stimulated insulin secretion. Islet morphometric analyses revealed that exendin-4 and the esculentin-2CHa(1-30) peptides significantly reduced islet, beta and alpha cell areas compared to high-fat controls. Esculentin-2CHa(1-30) peptides markedly reduced high fat diet-induced increase in beta cell proliferation and apoptosis. Peptide treatments had beneficial effects on expression of islet genes (Ins1, Slc2a2, Pdx1) and skeletal muscle genes involved in insulin action (Slc2a4, Pdk1, Irs1, Akt1). High-fat diet significantly increased LDL cholesterol which was reduced by the acylated esculentin-2CHa(1-30) analogue. Peptide treatments did not alter circulating concentrations of amylase and marker enzymes of liver function, indicating a lack of toxicity. These data indicate that esculentin-2CHa(1-30) and its analogues may be useful for improvement of blood glucose control and weight loss in type 2 diabetes.

The role of tumour suppressor PDCD4 in beta cell death in hypoxia.

ObjectiveHypoxia is known to induce pancreatic beta cell dysfunction and apoptosis. Changes in Programmed Cell Death Gene 4 (PDCD4) expression have previously been linked with beta cell neogenesis and function. Our aim was to investigate the effects of hypoxia on cell viability, PDCD4 expression and subcellular localisation.MethodsMIN6 beta cells and ARIP ductal cells were exposed to 1% (hypoxia) or 21% O2 (normoxia) for 12 or 24 hours. MTT assay, HPI staining, scanning electron microscopy, western blotting and immunocytochemistry analyses were performed to determine the effect of hypoxia on cell viability, morphology and PDCD4 expression.Results24 hour exposure to hypoxia resulted in ~70% loss of beta cell viability (P<0.001) compared to normoxia. Both HPI staining and SEM analysis demonstrated beta cell apoptosis and necrosis after 12 hours exposure to hypoxia. ARIP cells also displayed hypoxia-induced apoptosis and altered surface morphology after 24 hours, but no significant growth difference (p>0.05) was observed between hypoxic and normoxic conditions. Significantly higher expression of PDCD4 was observed in both beta cells (P<0.001) and ductal (P<0.01) cells under hypoxic conditions compared to controls. PDCD4 expression was localised to the cytoplasm of both beta cells and ductal cells, with no observed effects of hypoxia, normoxia or serum free conditions on intracellular shuttling of PDCD4.ConclusionThese findings indicate that hypoxia-induced expression of PDCD4 is associated with increased beta cell death and suggests that PDCD4 may be an important factor in regulating beta cell survival during hypoxic stress.

Differential expression of glucagon-like peptide-2 (GLP-2) is involved in pancreatic islet cell adaptations to stress and beta-cell survival

Recent studies have confirmed that locally released proglucagon derived gene products, other than glucagon, have a major influence on pancreatic endocrine function. We assessed the impact of glucagon-like peptide-2 (GLP-2) on beta-cell secretory function, proliferation and apoptosis, as well as glucose tolerance, feeding behaviour and islet adaptions to chemically-induced insulin deficiency and resistance. The GLP-2 receptor was evidenced on cultured rodent and human beta-cells, rodent alpha-cells and isolated mouse islets. GLP-2 had no effect on insulin secretion from beta-cells, or isolated mouse islets. In vivo, GLP-2 administration significantly (P<0.05 to P<0.01) decreased food intake in mice. Conversely, GLP-2 had no discernible effects on glucose disposal or insulin secretion. As expected, streptozotocin treatment decreased and hydrocortisone increased beta-cell mass in mice. GLP-2 was visualised in mouse islets and intestinal L-cells. Islet GLP-2 co-localisation with glucagon was significantly decreased (P<0.01) by both streptozotocin and hydrocortisone. In contrast, both interventions increased (P<0.05) co-localisation of GLP-2 with somatostatin. Interestingly, GLP-2 positive cells were reduced (P<0.05) in the intestines of streptozotocin, but not hydrocortisone, treated mice. Further in vitro investigations revealed that GLP-2 protected rodent and human 1.1B4 beta-cells against streptozotocin induced DNA damage. Furthermore, GLP-2 augmented (P<0.05) BRIN BD11 beta-cell proliferation, but was less efficacious in 1.1B4 cells. These data highlight the involvement of GLP-2 receptor signalling in the adaptations to pancreatic islet cell stress.