Cadmium-induced pancreatic toxicity in rats: comparing vitamin C and Nigella sativa as protective agents: a histomorphometric and ultrastructural study.

The study aimed to assess the toxic effect of cadmium (Cd) on the exocrine and endocrine functions of pancreas, the changes in pancreatic tissue after Cd withdrawal, and the protective effects of vitamin C (VC) and Nigella sativa (NS) against Cd-induced damage. Rats were assigned to: control, Cd-treated (0.5 mg/kg/d intraperitoneal [IP] injection), VC and Cd-treated (receiving 100 mg/kg/d VC orally and Cd concomitantly), NS and Cd-treated (receiving 20 mg/kg/d NS and Cd, simultaneously), and Cd withdrawal (receiving Cd for 30 d then living free for recovery for other 30 d). Blood samples were collected and post-sacrifice pancreatic specimens were processed for light and electron microscope study. Quantitative analyses of pancreatic collagen area%, pancreatic islet parameters, ß cell density, and insulin immunoexpression were done. Fasting blood glucose was significantly increased in Cd-treated and Cd-withdrawal groups, while co-treatment with VC and NS caused significant reductions (p < 0.05). Cd-induced extensive degenerative changes in pancreatic acini and islets at light and ultrastructure levels. Obvious fibrosis and congestion of blood vessels were noticed. Significant reductions in pancreatic islet number, volume, and surface area and diminished beta cell count and insulin immunoexpression were observed. After withdrawal of Cd, the whole pancreatic tissue still showed a serious impact. Concomitant treatment with VC or NS obviously reduced these degenerative changes and significantly improved pancreatic islet parameters and insulin immunoexpression. VC showed a better amendment than NS, but this difference was statistically insignificant. Therefore, VC and NS could be used as prophylactic agents that lessen Cd consequences on the pancreas.

Therapeutic Potential of Blocking Nephrin Phosphorylation to Improve Pancreatic ß-cell Function.

The phosphorylation of the transmembrane protein nephrin has been shown to play an important role in signaling in kidney podocytes, and it has now been shown to also play a key role in regulating pancreatic ß-cell function. Williamson et al have recently shown that the loss of nephrin tyrosine phosphorylation on its 3 cytoplasmic YDxV motifs can enhance insulin release in aged female mice. These studies suggest that blocking nephrin phosphorylation may be an effective treatment option for improving ß-cell function.

Islet transplantation in Korea.

Type 1 diabetes mellitus is characterized by absolute insulin deficiency, which requires life-long insulin replacement. Exogenous multiple-daily insulin injections are most commonly prescribed for patients with type 1 diabetes mellitus. However, exogenous insulin supply often fails to cope with real-time changing life-log variables, such as activity, diet and stress, which results in recurrent hypo- and hyperglycemia in patients with type 1 diabetes mellitus. Islet transplantation is an ideal method to treat patients with type 1 diabetes mellitus, as it can restore the endogenous capacity of glucose-stimulated insulin secretion. However, due to donor scarcity and technical barriers, only a limited number of islet transplantations have been carried out in Asia, including South Korea. Since 2013, our center has carried out two allogenic islet transplantations, with one case leading to near total insulin independence after one-to-one islet transplantation. Although the other patient failed to restore endogenous insulin production, there was a remarkable improvement in hypoglycemia. We speculate that islet transplantation remains an important and ideal treatment option for patients with type 1 diabetes mellitus who suffer from recurrent severe hypoglycemia.

The interplay of extracellular vesicles in the pathogenesis of metabolic impairment and type 2 diabetes.

The pathogenesis of type 2 diabetes (T2D) involves dysfunction in multiple organs, including the liver, muscle, adipose tissue, and pancreas, leading to insulin resistance and ß cell failure. Recent studies highlight the significant role of extracellular vesicles (EVs) in mediating inter-organ communication in T2D. This review investigates the role of EVs, focusing on their presence and biological significance in human plasma and tissues affected by T2D. We explore specific EV cargo, such as miRNAs and proteins, which affect insulin signaling and glucose metabolism, emphasizing their potential as biomarkers. By highlighting the diagnostic and therapeutic potential of EVs, we aim to provide new insights into their role in early detection, disease monitoring, and innovative treatment strategies for T2D.

The Proton Leak of the Inner Mitochondrial Membrane Is Enlarged in Freshly Isolated Pancreatic Islets.

In a number of investigations on the mechanism of the metabolic amplification of insulin secretion, differences between the response of freshly isolated islets and of islets cultured for one day have been observed. Since no trivial explanation like insufficient numbers of viable cells after cell culture could be found, a more thorough investigation into the mechanisms responsible for the difference was made, concentrating on the function of the mitochondria as the site where the metabolism of nutrient stimulators of secretion forms the signals impacting on the transport and fusion of insulin granules. Using combinations of inhibitors of oxidative phosphorylation, we come to the conclusion that the mitochondrial membrane potential is lower and the exchange of mitochondrial reducing equivalents is faster in freshly isolated islets than in cultured islets. The significantly higher rate of oxygen consumption in fresh islets than in cultured islets (13 vs. 8 pmol/min/islet) was not caused by a different activity of the F1F0-ATPase, but by a larger proton leak. These observations raise the questions as to whether the proton leak is a physiologically regulated pathway and whether its larger size in fresh islets reflects the working condition of the islets within the pancreas.

Adipose tissue-derived mesenchymal stem cells promote the vascularization of pancreatic islets transplanted into decellularized pancreatic skeletons.

We have recently developed a model of pancreatic islet transplantation into a decellularized pancreatic tail in rats. As the pancreatic skeletons completely lack endothelial cells, we investigated the effect of co-transplantation of mesenchymal stem cells and endothelial cells to promote revascularization. Decellularized matrix of the pancreatic tail was prepared by perfusion with Triton X-100, sodium dodecyl sulfate and DNase solution. Isolated pancreatic islets were infused into the skeletons via the splenic vein either alone, together with adipose tissue-derived mesenchymal stem cells (adMSCs), or with a combination of adMSCs and rat endothelial cells (rat ECs). Repopulated skeletons were transplanted into the subcutaneous tissue and explanted 9 days later for histological examination. Possible immunomodulatory effects of rat adMSCs on the survival of highly immunogenic green protein-expressing human ECs were also tested after their transplantation beneath the renal capsule. The immunomodulatory effects of adMSCs were also tested in vitro using the Invitrogen Click-iT EdU system. In the presence of adMSCs, the proliferation of splenocytes as a response to phytohaemagglutinin A was reduced by 47% (the stimulation index decreased from 1.7 to 0.9, P = 0.008) and the reaction to human ECs was reduced by 58% (the stimulation index decreased from 1.6 to 0.7, P = 0.03). Histological examination of the explanted skeletons seeded only with the islets showed their partial disintegration and only a rare presence of CD31-positive cells. However, skeletons seeded with a combination of islets and adMSCs showed preserved islet morphology and rich vascularity. In contrast, the addition of syngeneic rat ECs resulted in islet-cell necrosis with only few endothelial cells present. Live green fluorescence-positive endothelial cells transplanted either alone or with adMSCs were not detected beneath the renal capsule. Though the adMSCs significantly reduced in vitro proliferation stimulated by either phytohaemagglutinin A or by xenogeneic human ECs, in vivo co-transplanted adMSCs did not suppress the post-transplant immune response to xenogeneic ECs. Even in the syngeneic model, ECs co-transplantation did not lead to sufficient vascularization in the transplant area. In contrast, islet co-transplantation together with adMSCs successfully promoted the revascularization of extracellular matrix in the subcutaneous tissue.

V1bR enhances glucose-stimulated insulin secretion by paracrine production of glucagon which activates GLP-1 receptor.

BACKGROUND: Arginine vasopressin (AVP) has been reported to regulate insulin secretion and glucose homeostasis in the body. Previous study has shown that AVP and its receptor V1bR modulate insulin secretion via the hypothalamic-pituitary-adrenal axis. AVP has also been shown to enhance insulin secretion in islets, but the exact mechanism remains unclear. RESULTS: In our study, we unexpectedly discovered that AVP could only stimulates insulin secretion from islets, but not ß cells, and AVP-induced insulin secretion could be blocked by V1bR selective antagonist. Single-cell transcriptome analysis identified that V1bR is only expressed by the α cells. Further studies indicated that activation of the V1bR stimulates the α cells to secrete glucagon, which then promotes glucose-dependent insulin secretion from ß cells in a paracrine way by activating GLP-1R but not GCGR on these cells. CONCLUSIONS: Our study revealed a crosstalk between α and ß cells initiated by AVP/V1bR and mediated by glucagon/GLP-1R, providing a mechanism to develop new glucose-controlling therapies targeting V1bR.

PAX4 gene delivery improves ß-cell function in human islets of Type II diabetes.

Aim: Type II diabetes (T2D) stems from insulin resistance, with ß-cell dysfunction as a hallmark in its progression. Studies reveal that ß cells undergo apoptosis or dedifferentiation during T2D development. The transcription factor PAX4 is vital for ß differentiation and survival, thus may be a potential enhancer of ß-cell function in T2D islets. Materials & methods: Human PAX4 cDNA was delivered into T2D human islets with an adenoviral vector, and its effects on ß cells were examined. Results: PAX4 gene delivery significantly improved ß-cell survival, and increased ß-cell composition in the T2D human islets. Basal insulin and glucose-stimulated insulin secretion in PAX4-expressing islets were substantially higher than untreated or control-treated T2D human islets. Conclusion: Introduced PAX4 expression in T2D human islets improves ß-cell function, thus could provide therapeutic benefits for T2D treatment.

Type II diabetes (T2D) results from insulin resistance, with ß-cell dysfunction playing a pivotal role in its progression. Deficits in ß-cell mass and function have been attributed primarily to ß-cell death through apoptosis; however, recent studies suggest ß-cell failure can also arise from ß-cell dedifferentiation ­ that is, ß cells undergo a loss of mature identity, adopting either progenitor-like or glucagon-producing α cell states during T2D development. Therefore, a strategy preventing ß-cell dedifferentiation while promoting its survival is beneficial for T2D treatment. In this study, we explored whether PAX4, a critical transcription factor for ß differentiation and survival, could alleviate ß-cell dysfunction in human islets derived from T2D patients. To accomplish that, human PAX4 cDNA was delivered into human islets isolated from T2D donors by an adenoviral vector-based vector, Ad5.Pax4 and its effects on ß-cell function were evaluated. The results showed PAX4 expression significantly improved ß-cell survival and increased ß-cell composition in the T2D islets. Notably, PAX4-treated T2D islets exhibited significantly higher basal insulin secretion and glucose-stimulated insulin secretion than control-treated islets. The data demonstrate that PAX4 gene delivery into T2D human islets enhances ß-cell mass and function, and thus may offer therapeutic benefits in the treatment of T2D.

Single Cell RNAseq Analysis of Cytokine-Treated Human Islets: Association of Cellular Stress with Impaired Cytokine Responsiveness.

Pancreatic ß-cells are essential for survival, being the only cell type capable of insulin secretion. While they are believed to be vulnerable to damage by inflammatory cytokines such as interleukin-1 beta (IL-1ß) and interferon-gamma, we have recently identified physiological roles for cytokine signaling in rodent ß-cells that include the stimulation of antiviral and antimicrobial gene expression and the inhibition of viral replication. In this study, we examine cytokine-stimulated changes in gene expression in human islets using single-cell RNA sequencing. Surprisingly, the global responses of human islets to cytokine exposure were remarkably blunted compared to our previous observations in the mouse. The small population of human islet cells that were cytokine responsive exhibited increased expression of IL-1ß-stimulated antiviral guanylate-binding proteins, just like in the mouse. Most human islet cells were not responsive to cytokines, and this lack of responsiveness was associated with high expression of genes encoding ribosomal proteins. We further correlated the expression levels of RPL5 with stress response genes, and when expressed at high levels, RPL5 is predictive of failure to respond to cytokines in all endocrine cells. We postulate that donor causes of death and isolation methodologies may contribute to stress of the islet preparation. Our findings indicate that activation of stress responses in human islets limits cytokine-stimulated gene expression, and we urge caution in the evaluation of studies that have examined cytokine-stimulated gene expression in human islets without evaluation of stress-related gene expression.

Simultaneous Pancreatic and Kidney Transplant in Adult with Autosomal Dominant Polycystic Kidney Disease and Type I Diabetes Mellitus: Post Surgical Events and Genetic Review.

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited condition characterized by the growth of multiple bilateral cysts in the kidneys. We describe the case of a 35-year-old male with combined ADPKD and type 1 diabetes mellitus with a strong family history of both. At the age of 32, he developed end-stage kidney disease for which he underwent preemptive simultaneous pancreatic and kidney transplant, which in turn led to multiple perioperative complications. Evaluation of familial clustering of genetic disease is critical in genetic epidemiology and precision medicine as it enables estimation of lifetime disease risk and early assessment as well as detection of the disease among one's siblings.

Diabetes current and future translatable therapies.

Diabetes is one of the major diseases and concerns of public health systems that affects over 200 million patients worldwide. It is estimated that 90% of these patients suffer from diabetes type 2, while 10% present diabetes type 1. This type of diabetes and certain types of diabetes type 2, are characterized by dysregulation of blood glycemic levels due to the total or partial depletion of insulin-secreting pancreatic ß-cells. Different approaches have been proposed for long-term treatment of insulin-dependent patients; amongst them, cell-based approaches have been the subject of basic and clinical research since they allow blood glucose level sensing and in situ insulin secretion. The current gold standard for insulin-dependent patients is on-demand exogenous insulin application; cell-based therapies aim to remove this burden from the patient and caregivers. In recent years, protocols to isolate and implant pancreatic islets from diseased donors have been developed and tested in clinical trials. Nevertheless, the shortage of donors, along with the need of immunosuppressive companion therapies, have pushed researchers to focus their attention and efforts to overcome these disadvantages and develop alternative strategies. This review discusses current tested clinical approaches and future potential alternatives for diabetes type 1, and some diabetes type 2, insulin-dependent patients. Additionally, advantages and disadvantages of these discussed methods.

Single-cell transcriptomic profiling of human pancreatic islets reveals genes responsive to glucose exposure over 24 h.

AIMS/HYPOTHESIS: Disruption of pancreatic islet function and glucose homeostasis can lead to the development of sustained hyperglycaemia, beta cell glucotoxicity and subsequently type 2 diabetes. In this study, we explored the effects of in vitro hyperglycaemic conditions on human pancreatic islet gene expression across 24 h in six pancreatic cell types: alpha; beta; gamma; delta; ductal; and acinar. We hypothesised that genes associated with hyperglycaemic conditions may be relevant to the onset and progression of diabetes. METHODS: We exposed human pancreatic islets from two donors to low (2.8 mmol/l) and high (15.0 mmol/l) glucose concentrations over 24 h in vitro. To assess the transcriptome, we performed single-cell RNA-seq (scRNA-seq) at seven time points. We modelled time as both a discrete and continuous variable to determine momentary and longitudinal changes in transcription associated with islet time in culture or glucose exposure. Additionally, we integrated genomic features and genetic summary statistics to nominate candidate effector genes. For three of these genes, we functionally characterised the effect on insulin production and secretion using CRISPR interference to knock down gene expression in EndoC-ßH1 cells, followed by a glucose-stimulated insulin secretion assay. RESULTS: In the discrete time models, we identified 1344 genes associated with time and 668 genes associated with glucose exposure across all cell types and time points. In the continuous time models, we identified 1311 genes associated with time, 345 genes associated with glucose exposure and 418 genes associated with interaction effects between time and glucose across all cell types. By integrating these expression profiles with summary statistics from genetic association studies, we identified 2449 candidate effector genes for type 2 diabetes, HbA1c, random blood glucose and fasting blood glucose. Of these candidate effector genes, we showed that three (ERO1B, HNRNPA2B1 and RHOBTB3) exhibited an effect on glucose-stimulated insulin production and secretion in EndoC-ßH1 cells. CONCLUSIONS/INTERPRETATION: The findings of our study provide an in-depth characterisation of the 24 h transcriptomic response of human pancreatic islets to glucose exposure at a single-cell resolution. By integrating differentially expressed genes with genetic signals for type 2 diabetes and glucose-related traits, we provide insights into the molecular mechanisms underlying glucose homeostasis. Finally, we provide functional evidence to support the role of three candidate effector genes in insulin secretion and production. DATA AVAILABILITY: The scRNA-seq data from the 24 h glucose exposure experiment performed in this study are available in the database of Genotypes and Phenotypes (dbGap; https://www.ncbi.nlm.nih.gov/gap/ ) with accession no. phs001188.v3.p1. Study metadata and summary statistics for the differential expression, gene set enrichment and candidate effector gene prediction analyses are available in the Zenodo data repository ( https://zenodo.org/ ) under accession number 11123248. The code used in this study is publicly available at https://github.com/CollinsLabBioComp/publication-islet_glucose_timecourse .

Beta-Hydroxybutyrate Promotes Basal Insulin Secretion While Decreasing Glucagon Secretion in Mouse and Human Islets.

Dietary carbohydrates raise blood glucose levels, and limiting carbohydrate intake improves glycemia in patients with type 2 diabetes. Low carbohydrate intake (< 25 g) allows the body to utilize fat as its primary fuel. As a consequence of increased fatty acid oxidation, the liver produces ketones to serve as an alternative energy source. ß-Hydroxybutyrate (ßHB) is the most abundant ketone. While ßHB has a wide range of functions outside of the pancreas, its direct effects on islet cell function remain understudied. We examined human islet secretory response to acute racemic ßHB treatment and observed increased insulin secretion at a low glucose concentration of 3 mM. Because ßHB is a chiral molecule, existing as both R and S forms, we further studied insulin and glucagon secretion following acute treatment with individual ßHB enantiomers in human and C57BL/6J mouse islets. We found that acute treatment with R-ßHB increased insulin secretion and decreased glucagon secretion at physiological glucose concentrations in both human and mouse islets. Proteomic analysis of human islets treated with R-ßHB over 72 hours showed altered abundance of proteins that may promote islet cell health and survival. Collectively, our data show that physiological concentrations of ßHB influence hormone secretion and signaling within pancreatic islets.

Mesenchymal stromal cells and their secretory products reduce the inflammatory crosstalk between islets and endothelial cells.

PURPOSE: Preculturing isolated islets with Mesenchymal Stromal Cells (MSCs) improves their functional survival in vitro and subsequent transplantation outcomes in vivo. The MSC secretory product Annexin A1 (ANXA1) is a key modulator of MSC-mediated improvements in islet function. The current study aims to determine the influence of MSCs and defined MSC secretory products, including ANXA1, on the inflammatory crosstalk between isolated islets and Endothelial Cells (ECs), using in vitro models of the clinically-preferred intraportal islet transplantation niche. METHODS: Islets were cultured alone, with MSCs, or with MSC secretory products and exposed to pro-inflammatory cytokines. Islet gene expression of C-C Motif Chemokine Ligand 2 (CCL2), C-X-C Motif Chemokine Ligand (CXCL)-10 (CXCL10) and CXCL1 were assessed by RT-qPCR. EC activation was induced with 100 U/ml TNF for 24 h. Islet-EC co-cultures were used to determine the influence of MSCs, or MSC secretory products on the inflammatory crosstalk between isolated islets and ECs. VCAM-1 and ICAM-1 expression were assessed at the mRNA and protein level in ECs, using RT-qPCR and immunofluorescence. RESULTS: MSCs reduce pro-inflammatory cytokine-induced islet CCL2, CXCL10, and CXCL1 gene expression, which is partially mimicked by ANXA1. MSCs and ANXA1 have a similar capacity to reduce TNF-induced EC activation. Isolated islets exacerbate TNF-induced EC activation. Preculturing islets with MSCs reduces islet-exacerbated EC activation. ANXA1 reduces islet-exacerbated EC activation, when present during the islet preculture and islet-EC co-culture period. CONCLUSION: MSC-derived secretory factors, including ANXA1, may be used in islet transplantation protocols to target donor islet and host EC inflammation at the intraportal niche.

Proteomic predictors of individualized nutrient-specific insulin secretion in health and disease.

Population-level variation and mechanisms behind insulin secretion in response to carbohydrate, protein, and fat remain uncharacterized. We defined prototypical insulin secretion responses to three macronutrients in islets from 140 cadaveric donors, including those with type 2 diabetes. The majority of donors' islets exhibited the highest insulin response to glucose, moderate response to amino acid, and minimal response to fatty acid. However, 9% of donors' islets had amino acid responses, and 8% had fatty acid responses that were larger than their glucose-stimulated insulin responses. We leveraged this heterogeneity and used multi-omics to identify molecular correlates of nutrient responsiveness, as well as proteins and mRNAs altered in type 2 diabetes. We also examined nutrient-stimulated insulin release from stem cell-derived islets and observed responsiveness to fat but not carbohydrate or protein-potentially a hallmark of immaturity. Understanding the diversity of insulin responses to carbohydrate, protein, and fat lays the groundwork for personalized nutrition.

Extracellular electrophysiology on clonal human ß-cell spheroids.

Background: Pancreatic islets are important in nutrient homeostasis and improved cellular models of clonal origin may very useful especially in view of relatively scarce primary material. Close 3D contact and coupling between ß-cells are a hallmark of physiological function improving signal/noise ratios. Extracellular electrophysiology using micro-electrode arrays (MEA) is technically far more accessible than single cell patch clamp, enables dynamic monitoring of electrical activity in 3D organoids and recorded multicellular slow potentials (SP) provide unbiased insight in cell-cell coupling. Objective: We have therefore asked whether 3D spheroids enhance clonal ß-cell function such as electrical activity and hormone secretion using human EndoC-ßH1, EndoC-ßH5 and rodent INS-1 832/13 cells. Methods: Spheroids were formed either by hanging drop or proprietary devices. Extracellular electrophysiology was conducted using multi-electrode arrays with appropriate signal extraction and hormone secretion measured by ELISA. Results: EndoC-ßH1 spheroids exhibited increased signals in terms of SP frequency and especially amplitude as compared to monolayers and even single cell action potentials (AP) were quantifiable. Enhanced electrical signature in spheroids was accompanied by an increase in the glucose stimulated insulin secretion index. EndoC-ßH5 monolayers and spheroids gave electrophysiological profiles similar to EndoC-ßH1, except for a higher electrical activity at 3 mM glucose, and exhibited moreover a biphasic profile. Again, physiological concentrations of GLP-1 increased AP frequency. Spheroids also exhibited a higher secretion index. INS-1 cells did not form stable spheroids, but overexpression of connexin 36, required for cell-cell coupling, increased glucose responsiveness, dampened basal activity and consequently augmented the stimulation index. Conclusion: In conclusion, spheroid formation enhances physiological function of the human clonal ß-cell lines and these models may provide surrogates for primary islets in extracellular electrophysiology.

The potential Association of Bisphenol A exposure and type 1 diabetes mellitus among Dakahlia Governorate's children sample, Egypt.

Background: Bisphenol A (BPA) is an endocrine disrupter affecting glucose homeostasis. Objectives: This study aimed to investigate BPA's relationship with Type 1 Diabetes Mellitus (T1DM) in Dakahlia Governorate's children, in Egypt. Subjects materials and methods: The study had two parts: clinical and experimental. Clinical Study was conducted on 200 children, equally divided into control and T1DM groups. They underwent: demographic data, height, weight, body mass index, glycosylated HbA1C, random blood glucose, and urinary BPA measurements. Experimental Study was conducted on 60 adult albino rats. Rats were randomly divided into three equal groups: control group: received 0.5 mL of pure olive oil, group 1: received 20 mg/kg/day BPA, and group 2: received 100 mg/kg/day BPA orally for 6 weeks. Fasting and two hours postprandial glucose levels were measured at the beginning and end of the study. Histopathological examination and imaging study of the pancreas were done. Results: In clinical study: HbA1C and random blood glucose levels in diabetic children showed a significant increase compared to control. Children in control group showed controlled HbA1C, while the T1DM group showed 86% with poor diabetic control. There was a significant increase in BPA level in the T1DM group compared to the control. Rats that received BPA showed a marked increase in fasting and two hours postprandial glucose levels, histopathological changes in the pancreas with more changes determined in the high dose group, and a significant decrease in the islets of Langerhans diameters with group 2 more affected. Conclusion: So, BPA exposure could be considered a risk factor for T1DM in children.

[Mechanism of electroacupuncture regulating nuclear factor-κB pathway to improve the dedifferentiation of pancreatic ß-cells in rats with T2DM].

OBJECTIVE: To observe the effects of electroacupuncture (EA) on the expression of serum interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), and the pancreatic nuclear factor-κB (NF-κB) pathway in type 2 diabetes mellitus (T2DM) rats, and to explore the possible mechanism by which EA improving the dedifferentiation of pancreatic ß-cells in the treatment of T2DM. METHODS: Among 18 SPF-grade male Wistar rats, 6 rats were randomly selected as the control group, and the remaining 12 rats were fed with high-sugar and high-fat diet combined with intraperitoneal injection of 2% streptozotocin solution (35 mg/kg) to establish T2DM model. After successful modeling, the 12 rats were randomly divided into a model group and an EA group, with 6 rats in each group. The EA group received EA at bilateral "Zusanli" (ST 36), "Sanyinjiao" (SP 6), "Weiwanxiashu" (EX-B 3), and "Pishu" (BL 20), with continuous wave, frequency of 15 Hz, current intensity of 2 mA, for 20 min each time, once a day, 6 times a week, for a total of 6 weeks. Fasting blood glucose (FBG) levels were measured before modeling and before and after intervention. After intervention, ELISA was used to detect the serum fasting insulin (FINS), IL-1ß and TNF-α levels, and the ß-cell function index (HOMA-ß) and insulin resistance index (HOMA-IR) were calculated; HE staining was used to observe the morphology of the pancreatic islets; Western blot was used to detect the protein expression of pancreatic forkhead box protein O1 (FoxO1), pancreatic and duodenal homeobox 1 (PDX-1), neurogenin 3 (NGN3), and NF-κB p65. RESULTS: After intervention, the FBG in the model group was higher than that in the control group (P<0.01), and the FBG in the EA group was lower than that in the model group (P<0.01). Compared with the control group, the model group had increased levels of serum FINS, IL-1ß, TNF-α, and HOMA-IR (P<0.01), and decreased HOMA-ß (P<0.01), reduced protein expression of pancreatic FoxO1 and PDX-1 (P<0.01), and increased protein expression of pancreatic NGN3 and NF-κB p65 (P<0.01, P<0.05). Compared with the model group, the EA group had lower serum FINS, IL-1ß, TNF-α levels, and HOMA-IR (P<0.01), higher HOMA-ß (P<0.05), increased protein expression of pancreatic FoxO1 and PDX-1 (P<0.01, P<0.05), and decreased protein expression of pancreatic NGN3 and NF-κB p65 (P<0.01, P<0.05). The control group's pancreatic islets showed no obvious abnormalities; the model group's pancreatic islets were irregular in shape and had unclear boundaries with the surrounding area, with immune cell infiltration, reduced ß-cell nuclei, disordered arrangement of islet cells, and increased intercellular spaces; the EA group showed improvements in islet morphology, immune cell infiltration, ß-cell nuclei count, and the arrangement and spacing of islet cells approaching normal. CONCLUSION: EA could lower the blood glucose levels in T2DM rats, alleviate chronic inflammatory responses in the islets, and improve the dedifferentiation of pancreatic ß-cells, which may be related to the inhibition of pancreatic NF-κB pathway expression.

Regulatory Role of Fatty Acid Metabolism on Glucose-Induced Changes in Insulin and Glucagon Secretion by Pancreatic Islet Cells.

A detailed study of palmitate metabolism in pancreatic islets subject to different experimental conditions, like varying concentrations of glucose, as well as fed or starved conditions, has allowed us to explore the interaction between the two main plasma nutrients and its consequences on hormone secretion. Palmitate potentiates glucose-induced insulin secretion in a concentration-dependent manner, in a physiological range of both palmitate (0-2 mM) and glucose (6-20 mM) concentrations; at glucose concentrations lower than 6 mM, no metabolic interaction with palmitate was apparent. Starvation (48 h) increased islet palmitate oxidation two-fold, and the effect was resistant to its inhibition by glucose (6-20 mM). Consequently, labelled palmitate and glucose incorporation into complex lipids were strongly suppressed, as well as glucose-induced insulin secretion and its potentiation by palmitate. 2-bromostearate, a palmitate oxidation inhibitor, fully recovered the synthesis of complex lipids and insulin secretion. We concluded that palmitate potentiation of the insulin response to glucose is not attributable to its catabolic mitochondrial oxidation but to its anabolism to complex lipids: islet lipid biosynthesis is dependent on the uptake of plasma fatty acids and the supply of α-glycerol phosphate from glycolysis. Islet secretion of glucagon and somatostatin showed a similar dependence on palmitate anabolism as insulin. The possible mechanisms implicated in the metabolic coupling between glucose and palmitate were commented on. Moreover, possible mechanisms responsible for islet gluco- or lipotoxicity after a long-term stimulation of insulin secretion were also discussed. Our own data on the simultaneous stimulation of insulin, glucagon, and somatostatin by glucose, as well as their modification by 2-bromostearate in perifused rat islets, give support to the conclusion that increased FFA anabolism, rather than its mitochondrial oxidation, results in a potentiation of their stimulated release. Starvation, besides suppressing glucose stimulation of insulin secretion, also blocks the inhibitory effect of glucose on glucagon secretion: this suggests that glucagon inhibition might be an indirect or direct effect of insulin, but not of glucose. In summary, there seems to exist three mechanisms of glucagon secretion stimulation: 1. glucagon stimulation through the same secretion coupling mechanism as insulin, but in a different range of glucose concentrations (0 to 5 mM). 2. Direct or indirect inhibition by secreted insulin in response to glucose (5-20 mM). 3. Stimulation by increased FFA anabolism in glucose intolerance or diabetes in the context of hyperlipidemia, hyperglycemia, and hypo-insulinemia. These conclusions were discussed and compared with previous published data in the literature. Specially, we discussed the mechanism for inhibition of glucagon release by glucose, which was apparently contradictory with the secretion coupling mechanism of its stimulation.

Marginal Zinc Deficiency Promotes Pancreatic Islet Enlargement While Zinc Supplementation Improves the Pancreatic Insulin Response in Zucker Diabetic Fatty Rats.

Zinc deficiency has been associated with the worsening of diabetes while zinc supplementation has been proposed to ameliorate diabetes. This study examined the effects of marginal zinc deficiency (MZD) and zinc supplementation (ZS) on obesity, glycemic control, pancreatic islets, hepatic steatosis and renal function of Zucker diabetic fatty (ZDF) rats. Male ZDF rats were fed an MZD, zinc control (ZC) or ZS diet (4, 30 and 300 mg Zn/kg diet, respectively), and lean Zucker rats were fed a ZC diet for 8 weeks. MZD and ZS did not alter body weight or whole-body composition in ZDF rats. MZD ZDF rats had reduced zinc concentrations in the femur and pancreas, a greater number of enlarged pancreatic islets and a diminished response to an oral glucose load based on a 1.8-fold greater incremental area-under-the-curve (AUC) for glucose compared to ZC ZDF. ZS ZDF rats had elevated serum, femur and pancreatic zinc concentrations, unchanged pancreatic parameters and a 50% reduction in the AUC for insulin compared to ZC ZDF rats, suggesting greater insulin sensitivity. Dietary zinc intake did not alter hepatic steatosis, creatinine clearance, or levels of proteins that contribute to insulin signaling, inflammation or zinc transport in epididymal fat. Potential adverse effects of ZS were suggested by reduced hepatic copper concentrations and elevated serum urea compared to ZC ZDF rats. In summary, ZS improved the pancreatic insulin response but not the glucose handling. In contrast, reduced zinc status in ZDF rats led to impaired glucose tolerance and a compensatory increase in the number and size of pancreatic islets which could lead to ß-cell exhaustion.