Nrf2: The Master and Captain of Beta Cell Fate

Mitigating Hyperglycaemic Oxidative Stress in HepG2 Cells: The Role of Carica papaya Leaf and Root Extracts in Promoting Glucose Uptake and Antioxidant Defence

Background/Objectives: Diabetes often goes undiagnosed, with 60% of people in Africa unaware of their condition. Type 2 diabetes mellitus (T2DM) is associated with insulin resistance and is treated with metformin, despite the undesirable side effects. Medicinal plants with therapeutic potential, such as Carica papaya, have shown promising anti-diabetic properties. This study explored the role of C. papaya leaf and root extracts compared to metformin in reducing hyperglycaemia-induced oxidative stress and their impact on liver function using HepG2 as a reference. Methods: The cytotoxicity was assessed through the MTT assay. At the same time, glucose uptake and metabolism (ATP and ∆Ψm) in HepG2 cells treated with C. papaya aqueous leaf and root extract were evaluated using a luminometry assay. Additionally, antioxidant properties (SOD2, GPx1, GSH, and Nrf2) were measured using qPCR and Western blot following the detection of MDA, NO, and iNOS, indicators of free radicals. Results: The MTT assay showed that C. papaya extracts did not exhibit toxicity in HepG2 cells and enhanced glucose uptake compared to the hyperglycaemic control (HGC) and metformin. The glucose levels in C. papaya-treated cells increased ATP production (p < 0.05), while the ∆Ψm was significantly increased in HGR1000-treated cells (p < 0.05). Furthermore, C. papaya leaf extract upregulated GPx1 (p < 0.05), GSH, and Nrf2 gene (p < 0.05), while SOD2 and Nrf2 proteins were reduced (p > 0.05), ultimately lowering ROS (p > 0.05). Contrarily, the root extract stimulated SOD2 (p > 0.05), GPx1 (p < 0.05), and GSH levels (p < 0.05), reducing Nrf2 gene and protein expression (p < 0.05) and resulting in high MDA levels (p < 0.05). Additionally, the extracts elevated NO levels and iNOS expression (p < 0.05), suggesting potential RNS activation. Conclusion: Taken together, the leaf extract stimulated glucose metabolism and triggered ROS production, producing a strong antioxidant response that was more effective than the root extract and metformin. However, the root extract, particularly at high concentrations, was less effective at neutralising free radicals as it did not stimulate Nrf2 production, but it did maintain elevated levels of SOD2, GSH, and GPx1 antioxidants.

Genetics of type-1 diabetes

Type-1 diabetes is a multifactorial disease characterized by genetic and environmental factors that contribute to its development and progression. Despite progress in the management of type-1 diabetes, the final goal of curing the disease is yet to be achieved. To establish effective methods for the prevention, intervention, and cure of the disease, the molecular mechanisms and pathways involved in its development and progression should be clarified. One effective approach is to identify genes responsible for disease susceptibility and apply information obtained from the function of genes in disease etiology for the protection, intervention, and cure of type-1 diabetes. In this review, we discuss the genetic basis of type-1 diabetes, along with prospects for its prevention, intervention, and cure for type-1 diabetes.

1,8-Cineole alleviates Nrf2-mediated redox imbalance and mitochondrial dysfunction in diabetes mellitus by targeting Sirt1

BACKGROUND

Type 2 diabetes mellitus (T2DM) is primarily attributed to impaired insulin secretion caused by β cell dysfunction. 1,8-Cineole is a key bioactive compound in the essential oil extracted from Fructus Alpiniae Zerumbet, which possesses anti-inflammatory and antioxidant properties. Nevertheless, it remains elusive about the protective effect and precise mechanisms of 1,8-Cineole against the β cell deterioration in T2DM.

PURPOSE

To investigate the effect of 1,8-Cineole on β cell dysfunction in T2DM and the potential mechanism of its action.

METHODS

A mouse model of T2DM and a β cell model of high glucose induction were generated to analyze the pharmacological properties of 1,8-Cineole. Proteomic and network pharmacological analyses were conducted to identify the crucial pathways involved in T2DM. Resveratrol [a Sirtuin1 (Sirt1) agonist] and Sirt1 knockdown were used to ascertain the mechanism of 1,8-Cineole in T2DM. The binding affinity of 1,8-Cineole to Sirt1 was assessed with molecular docking, surface plasmon resonance, immunoprecipitation assay, and cellular thermal shift assay.

RESULTS

Firstly, dysregulated crucial pathways in T2DM were screened out, including redox imbalance and mitochondrial dysfunction. Subsequently, 1,8-Cineole was found to activate Sirt1 and nuclear factor E2-related factor 2 (Nrf2) to repress oxidative stress in both T2DM mice and high glucose-induced β cells, thereby relieving mitochondrial dysfunction and apoptosis. Furthermore, 1,8-Cineole specifically targeted Sirt1 and favored the direct interaction between Sirt1 and Nrf2, ultimately restoring β cell function.

CONCLUSIONS

Our findings provide the first evidence that 1,8-Cineole directly binds to Sirt1 and enhances its stability, therefore rectifying impaired oxidative homeostasis, and then suppressing mitochondrial dysfunction and apoptosis in T2DM, indicating that 1,8-Cineole may be a potential candidate drug for T2DM treatment.

PEGylated β-Cell-Targeting Exosomes from Mesenchymal Stem Cells Improve β Cell Function and Quantity by Suppressing NRF2-Mediated Ferroptosis

Background

The depletion of β cell mass is widely recognized as a significant contributor to the progression of type 2 diabetes mellitus (T2DM). Exosomes derived from mesenchymal stem cells (MSC-EXOs) hold promise as cell-free therapies for treating T2DM. However, the precise effects and mechanisms through which MSC-EXO affects β cell function remain incompletely understood, and the limited ability of MSC-EXO to target β cells and the short blood circulation time hampers its therapeutic effectiveness.

Methods

The effects of MSC-EXO were investigated in T2DM mice induced by a high-fat diet combined with STZ. Additionally, the high glucose-stimulated INS-1 cell line was used to investigate the potential mechanism of MSC-EXO. Michael addition reaction-mediated chemical coupling was used to modify the surface of the exosome membrane with a β-cell-targeting aptamer and polyethylene glycol (PEG). The β-cell targeting and blood circulation time were evaluated, and whether this modification enhanced the islet-protective effect of MSC-EXO was further analyzed.

Results

We observed that the therapeutic effects of MSC-EXO on T2DM manifested through the reduction of random blood glucose levels, enhancement of glucose and insulin tolerance, and increased insulin secretion. These effects were achieved by augmenting β cell mass via inhibiting nuclear factor erythroid 2-related factor 2 (NRF2)-mediated ferroptosis. Mechanistically, MSC-EXOs play a role in the NRF2-mediated anti-ferroptosis mechanism by transporting active proteins that are abundant in the AKT and ERK pathways. Moreover, compared to MSC-EXOs, aptamer- and PEG-modified exosomes (Apt-EXOs) were more effective in islet protection through PEG-mediated cycle prolongation and aptamer-mediated β-cell targeting.

Conclusion

MSC-EXO suppresses NRF2-mediated ferroptosis by delivering bioactive proteins to regulate the AKT/ERK signaling pathway, thereby improving the function and quantity of β cells. Additionally, Apt-EXO may serve as a novel drug carrier for islet-targeted therapy.

β-cell dedifferentiation in HOMA-βlow and HOMA-βhigh subjects

CONTEXT

β-cell dedifferentiation ratio is increased in type 2 diabetes; but its direct link to in vivo β-cell function in human remains unclear.

OBJECTIVE

The present study was designed to investigate whether β-cell dedifferentiation in situ was closely associated with β-cell function in vivo and to identify targets crucial for β-cell dedifferentiation/function in human.

METHODS

We acquired HOMA-β values, calculated the number of hormone-negative endocrine cells and evaluated important markers and novel candidates for β-cell dedifferentiation/function on paraneoplastic pancreatic tissues from 13 patients with benign pancreatic cystic neoplasm (PCN) or intrapancreatic accessory spleen.

RESULTS

Both β-cell dedifferentiation ratio and dedifferentiation marker (Aldh1a3) were inversely related with in vivo β-cell function (HOMA-β) and in situ β-cell functional markers Glut2 and Ucn3 in human. Moreover, the islets from HOMA-βlow subjects were manifested as 1) increased β-cell dedifferentiation ratio, 2) enriched dedifferentiation maker Aldh1a3, and 3) lower expression of Glut2 and Ucn3, compared to those from HOMA-βhigh subjects. We found that basic leucine zipper transcription factor 2 (Bach2) expression was significantly induced in islets from HOMA-βlow patients and was positively correlated with the ratio of β-cell dedifferentiation in human.

CONCLUSIONS

Our findings emphasize the contribution of β-cell dedifferentiation to β-cell dysfunction in human. The Bach2 induction in β-cells with higher frequency of dedifferentiation observed in HOMA-βlow subjects reinforce its distinctive role as a pharmaceutical target of β-cell dedifferentiation for the treatment of human diabetes.

The cellular and molecular targets of natural products against metabolic disorders: a translational approach to reach the bedside

Metabolic disorders, including obesity, dyslipidemia, diabetes, nonalcoholic fatty liver disease, and metabolic syndrome, are characterized by insulin resistance, abnormalities in circulating cholesterol and lipid profiles, and hypertension. The most common pathophysiologies of metabolic disorders are glucose/lipid metabolism dysregulation, insulin resistance, inflammatory response, and oxidative stress. Although several agents have been approved for the treatment of metabolic disorders, there is still a strong demand for more efficacious drugs with less side effects. Natural products have been critical sources of drug research and discovery for decades. However, the usefulness of bioactive natural products is often limited by incomplete understanding of their direct cellular targets. In this review, we highlight the current understanding of the established and emerging molecular mechanisms of metabolic disorders. We further summarize the therapeutic effects and underlying mechanisms of natural products on metabolic disorders, with highlights on their direct cellular targets, which are mainly implicated in the regulation of glucose/lipid metabolism, insulin resistance, metabolic inflammation, and oxidative stress. Finally, this review also covers the clinical studies of natural products in metabolic disorders. These progresses are expected to facilitate the application of these natural products and their derivatives in the development of novel drugs against metabolic disorders.

Hyperglycemia impairs EAAT2 glutamate transporter trafficking and glutamate clearance in islets of Langerhans: implications for type 2 diabetes pathogenesis and treatment

Pancreatic endocrine cells employ a sophisticated system of paracrine and autocrine signals to synchronize their activities, including glutamate, which controls hormone release and β-cell viability by acting on glutamate receptors expressed by endocrine cells. We here investigate whether alteration of the excitatory amino acid transporter 2 (EAAT2), the major glutamate clearance system in the islet, may occur in type 2 diabetes mellitus and contribute to β-cell dysfunction. Increased EAAT2 intracellular localization was evident in islets of Langerhans from T2DM subjects as compared with healthy control subjects, despite similar expression levels. Chronic treatment of islets from healthy donors with high-glucose concentrations led to the transporter internalization in vesicular compartments and reduced [H3]-d-glutamate uptake (65 ± 5% inhibition), phenocopying the findings in T2DM pancreatic sections. The transporter relocalization was associated with decreased Akt phosphorylation protein levels, suggesting an involvement of the phosphoinositide 3-kinase (PI3K)/Akt pathway in the process. In line with this, PI3K inhibition by a 100-µM LY294002 treatment in human and clonal β-cells caused the transporter relocalization in intracellular compartments and significantly reduced the glutamate uptake compared to control conditions, suggesting that hyperglycemia changes the trafficking of the transporter to the plasma membrane. Upregulation of the glutamate transporter upon treatment with the antibiotic ceftriaxone rescued hyperglycemia-induced β-cells dysfunction and death. Our data underscore the significance of EAAT2 in regulating islet physiology and provide a rationale for potential therapeutic targeting of this transporter to preserve β-cell survival and function in diabetes.NEW & NOTEWORTHY The glutamate transporter SLC1A2/excitatory amino acid transporter 2 (EAAT2) is expressed on the plasma membrane of pancreatic β-cells and controls islet glutamate clearance and β-cells survival. We found that the EAAT2 membrane expression is lost in the islets of Langerhans from type 2 diabetes mellitus (T2DM) patients due to hyperglycemia-induced downregulation of the phosphoinositide 3-kinase/Akt pathway and modification of its intracellular trafficking. Pharmacological rescue of EAAT2 expression prevents β-cell dysfunction and death, suggesting EAAT2 as a new potential target of intervention in T2DM.

Endoplasmic reticulum stress in pancreatic β-cell dysfunction: The potential therapeutic role of dietary flavonoids

Diabetes mellitus (DM) is a global health burden that is characterized by the loss or dysfunction of pancreatic β-cells. In pancreatic β-cells, endoplasmic reticulum (ER) stress is a fact of life that contributes to β-cell loss or dysfunction. Despite recent advances in research, the existing treatment approaches such as lifestyle modification and use of conventional therapeutics could not prevent the loss or dysfunction of pancreatic β-cells to abrogate the disease progression. Therefore, targeting ER stress and the consequent unfolded protein response (UPR) in pancreatic β-cells may be a potential therapeutic strategy for diabetes treatment. Dietary phytochemicals have therapeutic applications in human health owing to their broad spectrum of biochemical and pharmacological activities. Flavonoids, which are commonly obtained from fruits and vegetables worldwide, have shown promising prospects in alleviating ER stress. Dietary flavonoids including quercetin, kaempferol, myricetin, isorhamnetin, fisetin, icariin, apigenin, apigetrin, vitexin, baicalein, baicalin, nobiletin hesperidin, naringenin, epigallocatechin 3-O-gallate hesperidin (EGCG), tectorigenin, liquiritigenin, and acacetin have shown inhibitory effects on ER stress in pancreatic β-cells. Dietary flavonoids modulate ER stress signaling components, chaperone proteins, transcription factors, oxidative stress, autophagy, apoptosis, and inflammatory responses to exert their pharmacological effects on pancreatic β-cells ER stress. This review focuses on the role of dietary flavonoids as potential therapeutic adjuvants in preserving pancreatic β-cells from ER stress. Highlights of the underlying mechanisms of action are also presented as well as possible strategies for clinical translation in the management of DM.

Inhibition of glycogen synthase kinase-3 enhances NRF2 protein stability, nuclear localisation and target gene transcription in pancreatic beta cells

Accumulation of reactive oxygen species (i.e., oxidative stress) is a leading cause of beta cell dysfunction and apoptosis in diabetes. NRF2 (NF-E2 p45-related factor-2) regulates the adaptation to oxidative stress, and its activity is negatively regulated by the redox-sensitive CUL3 (cullin-3) ubiquitin ligase substrate adaptor KEAP1 (Kelch-like ECH-associated protein-1). Additionally, NRF2 is repressed by the insulin-regulated Glycogen Synthase Kinase-3 (GSK3). We have demonstrated that phosphorylation of NRF2 by GSK3 enhances β-TrCP (beta-transducin repeat-containing protein) binding and ubiquitylation by CUL1 (cullin-1), resulting in increased proteasomal degradation of NRF2. Thus, we hypothesise that inhibition of GSK3 activity or β-TrCP binding upregulates NRF2 and so protects beta cells against oxidative stress. We have found that treating the pancreatic beta cell line INS-1 832/13 with the KEAP1 inhibitor TBE31 significantly enhanced NRF2 protein levels. The presence of the GSK3 inhibitor CT99021 or the β-TrCP-NRF2 protein-protein interaction inhibitor PHAR, along with TBE31, resulted in prolonged NRF2 stability and enhanced nuclear localisation (P < 0.05). TBE31-mediated induction of NRF2-target genes encoding NAD(P)H quinone oxidoreductase 1 (Nqo1), glutamate-cysteine ligase modifier (Gclm) subunit and heme oxygenase (Hmox1) was significantly enhanced by the presence of CT99021 or PHAR (P < 0.05) in both INS-1 832/13 and in isolated mouse islets. Identical results were obtained using structurally distinct GSK3 inhibitors and inhibition of KEAP1 with sulforaphane. In summary, we demonstrate that GSK3 and β-TrCP/CUL1 regulate the proteasomal degradation of NRF2, enhancing the impact of KEAP1 regulation, and so contributes to the redox status of pancreatic beta cells. Inhibition of GSK3, or β-TrCP/CUL1 binding to NRF2 may represent a strategy to protect beta cells from oxidative stress.

Hypoglycemic effects and associated mechanisms of resveratrol and related stilbenes in diet

Hyperglycemia has become a global health problem due to changes in diet and lifestyle. Most importantly, persistent hyperglycemia can eventually develop into type II diabetes. While the usage of current drugs is limited by their side effects, stilbenes derived from fruits and herbal/dietary plants are considered as important phytochemicals with potential hypoglycemic properties. Herein, the most common stilbenoids in consumed foods, i.e. resveratrol, pterostilbene, piceatannol, oxyresveratrol, and 2,3,5,4'-tetrahydroxystilbene-2-O-β-glucopyranoside (THSG), are reviewed in this paper. These stilbenes are found to regulate glucose homeostasis via (a) modulation of feeding behaviour and nutrition absorption; (b) restoration of insulin signalling by enhancing insulin production/insulin sensitivity; (c) improvement of gut permeability, gut microbial profile and resulting metabolomes; and (d) amelioration of circadian rhythm disruption. In this review, we have summarized the underlying mechanisms for the hypoglycemic effects of the five most common dietary stilbenoids listed above, providing a comprehensive framework for future study and applications.

NRF2 is required for neonatal mouse beta cell growth by maintaining redox balance and promoting mitochondrial biogenesis and function

AIMS/HYPOTHESIS

All forms of diabetes result from insufficient functional beta cell mass. Due to the relatively limited expression of several antioxidant enzymes, beta cells are highly vulnerable to pathological levels of reactive oxygen species (ROS), which can lead to the reduction of functional beta cell mass. During early postnatal ages, both human and rodent beta cells go through a burst of proliferation that quickly declines with age. The exact mechanisms that account for neonatal beta cell proliferation are understudied but mitochondrial release of moderated ROS levels has been suggested as one of the main drivers. We previously showed that, apart from its conventional role in protecting beta cells from oxidative stress, the nuclear factor erythroid 2-related factor 2 (NRF2) is also essential for beta cell proliferation. We therefore hypothesised that NRF2, which is activated by ROS, plays an essential role in beta cell proliferation at early postnatal ages.

METHODS

Beta cell NRF2 levels and beta cell proliferation were measured in pancreatic sections from non-diabetic human cadaveric donors at different postnatal ages, childhood and adulthood. Pancreatic sections from 1-, 7-, 14- and 28-day-old beta cell-specific Nrf2 (also known as Nfe2l2)-knockout mice (βNrf2KO) or control (Nrf2lox/lox) mice were assessed for beta cell NRF2 levels, beta cell proliferation, beta cell oxidative stress, beta cell death, nuclear beta cell pancreatic duodenal homeobox protein 1 (PDX1) levels and beta cell mass. Seven-day-old βNrf2KO and Nrf2lox/lox mice were injected daily with N-acetylcysteine (NAC) or saline (154 mmol/l NaCl) to explore the potential contribution of oxidative stress to the phenotypes seen in βNrf2KO mice at early postnatal ages. RNA-seq was performed on 7-day-old βNrf2KO and Nrf2lox/lox mice to investigate the mechanisms by which NRF2 stimulates beta cell proliferation at early postnatal ages. Mitochondrial biogenesis and function were determined using dispersed islets from 7-day-old βNrf2KO and Nrf2lox/lox mice by measuring MitoTracker intensity, mtDNA/gDNA ratio and ATP/ADP ratio. To study the effect of neonatal beta cell-specific Nrf2 deletion on glucose homeostasis in adulthood, blood glucose, plasma insulin and insulin secretion were determined and a GTT was performed on 3-month-old βNrf2KO and Nrf2lox/lox mice fed on regular diet (RD) or high-fat diet (HFD).

RESULTS

The expression of the master antioxidant regulator NRF2 was increased at early postnatal ages in both human (1 day to 19 months old, 31%) and mouse (7 days old, 57%) beta cells, and gradually declined with age (8% in adult humans, 3.77% in adult mice). A significant correlation (R2=0.568; p=0.001) was found between beta cell proliferation and NRF2 levels in human beta cells. Seven-day-old βNrf2KO mice showed reduced beta cell proliferation (by 65%), beta cell nuclear PDX1 levels (by 23%) and beta cell mass (by 67%), and increased beta cell oxidative stress (threefold) and beta cell death compared with Nrf2lox/lox control mice. NAC injections increased beta cell proliferation in 7-day-old βNrf2KO mice (3.4-fold) compared with saline-injected βNrf2KO mice. Interestingly, RNA-seq of islets isolated from 7-day-old βNrf2KO mice revealed reduced expression of mitochondrial RNA genes and genes involved in the electron transport chain. Islets isolated from 7-day old βNrf2KO mice presented reduced MitoTracker intensity (by 47%), mtDNA/gDNA ratio (by 75%) and ATP/ADP ratio (by 68%) compared with islets from Nrf2lox/lox littermates. Lastly, HFD-fed 3-month-old βNrf2KO male mice displayed a significant reduction in beta cell mass (by 35%), a mild increase in non-fasting blood glucose (1.2-fold), decreased plasma insulin (by 14%), and reduced glucose tolerance (1.3-fold) compared with HFD-fed Nrf2lox/lox mice.

CONCLUSIONS/INTERPRETATION

Our study highlights NRF2 as an essential transcription factor for maintaining neonatal redox balance, mitochondrial biogenesis and function and beta cell growth, and for preserving functional beta cell mass in adulthood under metabolic stress.

DATA AVAILABILITY

Sequencing data are available in the NCBI Gene Expression Omnibus, accession number GSE242718 ( https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE242718 ).

Transcriptional activation of the Myc gene by glucose in β-cells requires a ChREBP-dependent 3-D chromatin interaction between the Myc and Pvt1 genes

OBJECTIVE

All forms of diabetes result from insufficient functional β-cell mass. Thus, achieving the therapeutic goal of expanding β-cell mass requires a better mechanistic understanding of how β-cells proliferate. Glucose is a natural β-cell mitogen that mediates its effects in part through the glucose-responsive transcription factor, carbohydrate response element binding protein (ChREBP) and the anabolic transcription factor, MYC. However, mechanistic details by which glucose activates Myc at the transcriptional level are poorly understood.

METHODS

Here, siRNA was used to test the role of ChREBP in the glucose response of MYC, ChIP and ChIPseq to identify potential regulatory binding sites, chromatin conformation capture to identify DNA/DNA interactions, and an adenovirus was constructed to expresses x-dCas9 and an sgRNA that specifically disrupts the recruitment of ChREBP to a specific targeted ChoRE.

RESULTS

We found that ChREBP is essential for glucose-mediated transcriptional induction of Myc, and for increases in Myc mRNA and protein abundance. Further, ChIPseq revealed that the carbohydrate response element (ChoRE) nearest to the Myc transcriptional start site (TSS) is immediately upstream of the gene encoding the lncRNA, Pvt1, 60,000 bp downstream of the Myc gene. Chromatin Conformation Capture (3C) confirmed a glucose-dependent interaction between these two sites. Transduction with an adenovirus expressing x-dCas9 and an sgRNA specifically targeting the highly conserved Pvt1 ChoRE, attenuates ChREBP recruitment, decreases Myc-Pvt1 DNA/DNA interaction, and decreases expression of the Pvt1 and Myc genes in response to glucose. Importantly, isolated and dispersed rat islet cells transduced with the ChoRE-disrupting adenovirus also display specific decreases in ChREBP-dependent, glucose-mediated expression of Pvt1 and Myc, as well as decreased glucose-stimulated β-cell proliferation.

CONCLUSIONS

The mitogenic glucose response of Myc is mediated via glucose-dependent recruitment of ChREBP to the promoter of the Pvt1 gene and subsequent DNA looping with the Myc promoter.

Beta-cell compensation and gestational diabetes

Gestational diabetes mellitus (GDM) is characterized by glucose intolerance in pregnant women without a previous diagnosis of diabetes. While the etiology of GDM remains elusive, the close association of GDM with increased maternal adiposity and advanced gestational age implicates insulin resistance as a culpable factor for the pathogenesis of GDM. Pregnancy is accompanied by the physiological induction of insulin resistance in the mother secondary to maternal weight gain. This effect serves to spare blood glucose for the fetus. To overcome insulin resistance, maternal β-cells are conditioned to release more insulin into the blood. Such an adaptive response, termed β-cell compensation, is essential for maintaining normal maternal metabolism. β-cell compensation culminates in the expansion of β-cell mass and augmentation of β-cell function, accounting for increased insulin synthesis and secretion. As a result, a vast majority of mothers are protected from developing GDM during pregnancy. In at-risk pregnant women, β-cells fail to compensate for maternal insulin resistance, contributing to insulin insufficiency and GDM. However, gestational β-cell compensation ensues in early pregnancy, prior to the establishment of insulin resistance in late pregnancy. How β-cells compensate for pregnancy and what causes β-cell failure in GDM are subjects of investigation. In this mini-review, we will provide clinical and preclinical evidence that β-cell compensation is pivotal for overriding maternal insulin resistance to protect against GDM. We will highlight key molecules whose functions are critical for integrating gestational hormones to β-cell compensation for pregnancy. We will provide mechanistic insights into β-cell decompensation in the etiology of GDM.

Activation of the Nrf-2/HO-1 signalling axis can alleviate metabolic syndrome in cardiovascular disease

Background: Cardiovascular disease (CVD) is widely observed in modern society. CVDs are responsible for the majority of fatalities, with heart attacks and strokes accounting for approximately 80% of these cases. Furthermore, a significant proportion of these deaths, precisely one-third, occurs in individuals under 70. Metabolic syndrome encompasses a range of diseases characterized by various physiological dysfunctions. These include increased inflammation in adipose tissue, enhanced cholesterol synthesis in the liver, impaired insulin secretion, insulin resistance, compromised vascular tone and integrity, endothelial dysfunction, and atheroma formation. These factors contribute to the development of metabolic disorders and significantly increase the likelihood of experiencing cardiovascular complications.Method: We selected studies that proposed hypotheses regarding metabolic disease syndrome and cardiovascular disease (CVD) and the role of Nrf2/HO-1 and factor regulation in CVD research investigations based on our searches of Medline and PubMed.Results: A total of 118 articles were included in the review, 16 of which exclusively addressed hypotheses about the role of Nrf2 on Glucose regulation, while 16 involved Cholesterol regulation. Likewise, 14 references were used to prove the importance of mitochondria on Nrf2. Multiple studies have provided evidence suggesting the involvement of Nrf2/HO-1 in various physiological processes, including metabolism and immune response. A total of 48 research articles and reviews have been used to highlight the role of metabolic syndrome and CVD.Conclusion: This review provides an overview of the literature on Nrf2/HO-1 and its role in metabolic disease syndrome and CVD.

Nrf2 modulates the benefits of evening exercise in type 2 diabetes

Exercise has well-characterized therapeutic benefits in the management of type 2 diabetes mellitus (T2DM). Most of the beneficial effects of exercise arise from the impact of nuclear factor erythroid 2 related factor-2 (Nrf2) activation of glucose metabolism. Nrf2 is an essential controller of cellular anti-oxidative capacity and circadian rhythms. The circadian rhythm of Nrf2 is influenced by circadian genes on its expression, where the timing of exercise effects the activation of Nrf2 and the rhythmicity of Nrf2 and signaling, such that the timing of exercise has differential physiological effects. Exercise in the evening has beneficial effects on diabetes management, such as lowering of blood glucose and weight. The mechanisms responsible for these effects have not yet been associated with the influence of exercise on the circadian rhythm of Nrf2 activity. A better understanding of exercise-induced Nrf2 activation on Nrf2 rhythm and signaling can improve our appreciation of the distinct effects of morning and evening exercise. This review hypothesizes that activation of Nrf2 by exercise in the morning, when Nrf2 level is already at high levels, leads to hyperactivation and decrease in Nrf2 signaling, while activation of Nrf2 in the evening, when Nrf2 levels are at nadir levels, improves Nrf2 signaling and lowers blood glucose levels and increases fatty acid oxidation. Exploring the effects of Nrf2 activators on rhythmic signaling could also provide valuable insights into the optimal timing of their application, while also holding promise for timed treatment of type 2 diabetes.

Urolithin C alleviates pancreatic β-cell dysfunction in type 1 diabetes by activating Nrf2 signaling

AIMS

Type 1 diabetes (T1D) is an autoimmune disorder that destroys insulin-generating pancreatic β-cells. Preserving pancreatic β-cell function is important for treating T1D. Our study aims to explore the mechanism underlying urolithin C (UC)-mediated regulation of β-cell function.

METHODS

Non-obese diabetic (NOD) mice were administrated with UC to evaluate UC-mediated protection of T1D. The inflammation of the pancreas islets was examined by hematoxylin and eosin staining. Glucose-stimulated insulin secretion (GSIS) assay and oral glucose tolerance test were applied to evaluate the progression of T1D. MIN6 cells were treated with TNF-α, IL-1β and IFN-γ in the presence of UC. Cell viability was analyzed by CCK-8. Cell apoptosis, proliferation and DNA fragmentation were examined by Annexin V-FITC and PI staining, EdU incorporation and comet assays. Keap1, Nrf2, HO-1 and NQO1 were examined by western blot. Immunofluorescence staining was applied to detect Nrf2 and insulin.

RESULTS

UC administration significantly reduced diabetes incidence, attenuated insulitis, elevated insulin levels and GSIS and reduced blood glucose and AUC in NOD mice. Cytokine treatment suppressed MIN6 cell viability and proliferation but enhanced apoptosis and DNA damage, and these detrimental effects were relieved by UC treatment. Furthermore, UC administration inhibited Keap1 expression and promoted the expression of Nrf2, HO-1 and NQO1 in NOD mice. Nrf2 signaling has been reported to be implicated in preventing the onset of diabetes, and HO-1 and NQO1 are phase II antioxidant enzymes that are regulated by Nrf2 signaling. Cytokine treatment upregulated Keap1 and downregulated Nrf2, HO-1 and NQO1 in MIN6 cells, but it was reversed by UC. The nuclear translocation of Nrf2 was prevented by cytokine treatment, but UC promoted its nuclear translocation. UC-mediated upregulation of Nrf2, HO-1 and NQO1, decreased cell apoptosis and increased proliferation and insulin secretion were abolished by silencing of Nrf2.

CONCLUSION

UC improves pancreatic β-cell function by activating Nrf2 signaling, thereby alleviating T1D progression.

Nrf2: Therapeutic target of islet function protection in diabetes and islet transplantation

Nuclear factor-erythroid 2-related factor 2 (Nrf2) has been reported as a major intracellular regulator of antioxidant stress, notably in islet β cells with low antioxidant enzyme content. Nrf2 is capable of regulating antioxidant function, while it can also regulate insulin secretion, proliferation, and differentiation of β cells, ER stress, as well as mitochondrial function. Thus, Nrf2 pharmacological activators have been employed in the laboratory for the treatment of diabetic mice. Islet cells are exposed to oxidative environment when islet is being transplanted. Accordingly, less than 50% of islet cells are well transplanted, and their normal function is maintained. The pharmacological activation of Nrf2 has been confirmed to protect islet cells at different stages of transplantation stages during experiments for islet transplantation.

Mitochondrial Reactive Oxygen Species, Insulin Resistance, and Nrf2-Mediated Oxidative Stress Response-Toward an Actionable Strategy for Anti-Aging

Reactive oxygen species (ROS) are produced mainly by mitochondrial respiration and function as signaling molecules in the physiological range. However, ROS production is also associated with the pathogenesis of various diseases, including insulin resistance (IR) and type 2 diabetes (T2D). This review focuses on the etiology of IR and early events, especially mitochondrial ROS (mtROS) production in insulin-sensitive tissues. Importantly, IR and/or defective adipogenesis in the white adipose tissues (WAT) is thought to increase free fatty acid and ectopic lipid deposition to develop into systemic IR. Fatty acid and ceramide accumulation mediate coenzyme Q reduction and mtROS production in IR in the skeletal muscle, while coenzyme Q synthesis downregulation is also involved in mtROS production in the WAT. Obesity-related IR is associated with the downregulation of mitochondrial catabolism of branched-chain amino acids (BCAAs) in the WAT, and the accumulation of BCAA and its metabolites as biomarkers in the blood could reliably indicate future T2D. Transcription factor NF-E2-related factor 2 (Nrf2), which regulates antioxidant enzyme expression in response to oxidative stress, is downregulated in insulin-resistant tissues. However, Nrf2 inducers, such as sulforaphane, could restore Nrf2 and target gene expression and attenuate IR in multiple tissues, including the WAT.

NRF2 Dysregulation in Mice Leads to Inadequate Beta-Cell Mass Expansion during Pregnancy and Gestational Diabetes

The late stages of the mammalian pregnancy are accompanied with increased insulin resistance due to the increased glucose demand of the growing fetus. Therefore, as a compensatory response to maintain the maternal normal blood glucose levels, maternal beta-cell mass expands leading to increased insulin release. Defects in beta-cell adaptive expansion during pregnancy can lead to gestational diabetes mellitus (GDM). Although the exact mechanisms that promote GDM are poorly understood, GDM strongly associates with impaired beta-cell proliferation and with increased levels of reactive oxygen species (ROS). Here, we show that NRF2 levels are upregulated in mouse beta-cells at gestation day 15 (GD15) concomitant with increased beta-cell proliferation. Importantly, mice with tamoxifen-induced beta-cell-specific NRF2 deletion display inhibition of beta-cell proliferation, increased beta-cell oxidative stress and elevated levels of beta-cell death at GD15. This results in attenuated beta-cell mass expansion and disturbed glucose homeostasis towards the end of pregnancy. Collectively, these results highlight the importance of NRF2-oxidative stress regulation in beta-cell mass adaptation to pregnancy and suggest NRF2 as a potential therapeutic target for treating GDM.

IMT504 protects beta cells against apoptosis and maintains beta cell identity, without modifying proliferation

We have demonstrated that oligodeoxynucleotide IMT504 promotes significant improvement in the diabetic condition in diverse animal models. Based on these results, here we evaluated whether these effects observed in vivo could be due to direct effects on β-cells. We demonstrate by immunofluorescence that IMT504 enters the cell and locates in cytoplasm where it induces GSK-3β phosphorylation that inactivates this kinase. As GSK-3β tags Pdx1 for proteasomal degradation, by inactivating GSK-3β, IMT504 induces an increase in Pdx1 protein levels, demonstrated by Western blotting. Concomitantly, an increase in Ins2 and Pdx1 gene transcription was observed, with no significant increase in insulin content or secretion. Enhanced Pdx1 is promising since it is a key transcription factor for insulin synthesis and is also described as an essential factor for the maintenance β-cell phenotype and function. Dose-dependent inhibition of H2 O2 -induced apoptosis determined by ELISA as well as decreased expression of Bax was also observed. These results were confirmed in another β-cell line, beta-TC-6 cells, in which a cytokine mix induced apoptosis that was reversed by IMT504. In addition, an inhibitor of IMT504 entrance into cells abrogated the effect IMT504. Based on these results we conclude that the β-cell recovery observed in vivo may include direct effects of IMT504 on β-cells, by maintaining their identity/phenotype and protecting them from oxidative stress and cytokine-induced apoptosis. Thus, this work positions IMT504 as a promising option in the framework of the search of new therapies for type I diabetes treatment.

Lambda-cyhalothrin-induced pancreatic toxicity in adult albino rats

Lambda-cyhalothrin (LCT) is one of the most frequently utilized pyrethroids. This study aimed to explore the toxic effects of subacute exposure to LCT on the pancreas and the hepatic glucose metabolism in adult male albino rats. 20 rats were equally grouped into; Control group and LCT group. The latter received LCT (61.2 mg/kg b.wt.), orally on a daily basis for 28 days. At the end of experiment, blood samples were collected for the determination of serum glucose and insulin levels. Pancreases were harvested and levels of malondialdehyde (MDA); catalase (CAT); superoxide dismutase (SOD); reduced glutathione (GSH); tumor necrosis factor-α (TNF-α); interleukin-6 (IL-6); nuclear factor erythroid 2-related factor 2 (Nrf2); heme oxygenase 1 (HO-1); and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) were assessed. Also, liver samples were analyzed for the activity of glucose metabolism enzymes, glycogen content, and pyruvate and lactate concentrations. Histopathological and immunohistochemical examinations of pancreatic tissues were undertaken as well. Results revealed hyperglycemia, hypoinsulinemia, increased MDA, TNF-α, IL-6, and NF-κB levels, in association with reduced CAT, SOD, GSH, Nrf2, and HO-1 levels in LCT group. Liver analyses demonstrated a clear disturbance in the hepatic enzymes of glucose metabolism, diminished glycogen content, decreased pyruvate, and increased lactate concentrations. Besides, pancreatic islets displayed degenerative changes and β-cells loss. Immunohistochemistry revealed diminished area percentage (%) of insulin and Nrf2 and increased TNF-α immunoreaction. In conclusion, subacute exposure to LCT induces pancreatic toxicity, mostly via oxidative and inflammatory mechanisms, and dysregulates hepatic glucose metabolism in albino rats.

Selenium Nanodots (SENDs) as Antioxidants and Antioxidant-Prodrugs to Rescue Islet β Cells in Type 2 Diabetes Mellitus by Restoring Mitophagy and Alleviating Endoplasmic Reticulum Stress

Preventing islet β-cells death is crucial for treating type 2 diabetes mellitus (T2DM). Currently, clinical drugs are being developed to improve the quality of T2DM care and self-care, but drugs focused on reducing islets β-cell death are lacking. Given that β-cell death in T2DM is dominated ultimately by excessive reactive oxygen species (ROS), eliminating excessive ROS in β-cells is a highly promising therapeutic strategy. Nevertheless, no antioxidants have been approved for T2DM therapy because most of them cannot meet the long-term and stable elimination of ROS in β-cells without eliciting toxic side-effects. Here, it is proposed to restore the endogenous antioxidant capacity of β-cells to efficiently prevent β-cell death using selenium nanodots (SENDs), a prodrug of the antioxidant enzyme glutathione peroxidase 1 (GPX1). SENDs not only scavenge ROS effectively, but also "send" selenium precisely to β-cells with ROS response to greatly enhance the antioxidant capacity of β-cells by increasing GPX1 expression. Therefore, SENDs greatly rescue β-cells by restoring mitophagy and alleviating endoplasmic reticulum stress (ERS), and demonstrate much stronger efficacy than the first-line drug metformin for T2DM treatment. Overall, this strategy highlights the great clinical application prospects of SENDs, offering a paradigm for an antioxidant enzyme prodrug for T2DM treatment.

GHRH agonist MR-409 protects β-cells from streptozotocin-induced diabetes

Patients with type 1 diabetes (T1D) suffer from insufficient functional β-cell mass, which results from infiltration of inflammatory cells and cytokine-mediated β-cell death. Previous studies demonstrated the beneficial effects of agonists of growth hormone-releasing hormone receptor (GHRH-R), such as MR-409 on preconditioning of islets in a transplantation model. However, the therapeutic potential and protective mechanisms of GHRH-R agonists on models of T1D diabetes have not been explored. Using in vitro and in vivo models of T1D, we assessed the protective propertie of the GHRH agonist, MR409 on β-cells. The treatment of insulinoma cell lines and rodent and human islets with MR-409 induces Akt signaling by induction of insulin receptor substrate 2 (IRS2), a master regulator of survival and growth in β-cells, in a PKA-dependent manner. The increase in cAMP/PKA/CREB/IRS2 axis by MR409 was associated with decrease in β-cell death and improved insulin secretory function in mouse and human islets exposed to proinflammatory cytokines. The assessment of the effects of GHRH agonist MR-409 in a model of T1D induced by low-dose streptozotocin showed that mice treated with MR-409 exhibited better glucose homeostasis, higher insulin levels, and preservation of β-cell mass. Increased IRS2 expression in β-cells in the group treated with MR-409 corroborated the in vitro data and provided evidence for the underlying mechanism responsible for beneficial effects of MR-409 in vivo. Collectively, our data show that MR-409 is a novel therapeutic agent for the prevention and treatment of β-cells death in T1D.

Activation of the Cap'n'collar C pathway (Nrf2 pathway in vertebrates) signaling in insulin pathway compromised Drosophila melanogaster flies ameliorates the diabetic state upon pro-oxidant conditions

The insulin pathway is a crucial central system for metabolism and growth. The Nrf2 signaling pathway functions to counteract oxidative stress. Here we sought to study the consequences of an oxidative stress challenge to insulin compromised and control adult flies of different ages, varying the activation state of the Nrf2 pathway in flies, the Cap'n'collar C pathway. For this, we employed two different pro-oxidative conditions: 3 % hydrogen peroxide or 20 mM paraquat laced in the food. In both cases, wild type (control) flies die within a few days, yet there are significant differences between males and females, and also within flies of different ages (seven versus thirty days old flies). We repeated the same conditions with young (seven days old) flies that were heterozygous for a loss-of-function mutation in Keap1. There were no significant differences. We then tested two hypomorphic viable conditions of the insulin pathway (heteroallelic combination for the insulin receptor and the S6 Kinase), challenged in the same way: Whereas they also die in the pro-oxidant conditions, they fare significantly better when heterozygous for Keap1, in contrast to controls. We also monitored locomotion in all of these conditions, and, in general, found significant differences between flies without and with a mutant allele (heterozygous) for Keap1. Our results point to altered oxidative stress conditions in diabetic flies. These findings suggest that modest activation of the Cap'n'collar C pathway may be a treatment for diabetic symptoms.

A beta cell subset with enhanced insulin secretion and glucose metabolism is reduced in type 2 diabetes

The pancreatic islets are composed of discrete hormone-producing cells that orchestrate systemic glucose homeostasis. Here we identify subsets of beta cells using a single-cell transcriptomic approach. One subset of beta cells marked by high CD63 expression is enriched for the expression of mitochondrial metabolism genes and exhibits higher mitochondrial respiration compared with CD63lo beta cells. Human and murine pseudo-islets derived from CD63hi beta cells demonstrate enhanced glucose-stimulated insulin secretion compared with pseudo-islets from CD63lo beta cells. We show that CD63hi beta cells are diminished in mouse models of and in humans with type 2 diabetes. Finally, transplantation of pseudo-islets generated from CD63hi but not CD63lo beta cells into diabetic mice restores glucose homeostasis. These findings suggest that loss of a specific subset of beta cells may lead to diabetes. Strategies to reconstitute or maintain CD63hi beta cells may represent a potential anti-diabetic therapy.

Anti-oxidant effect of nitrite in the pancreatic islets of type 2 diabetic male rats

Objectives

Nitrite, a nitric oxide (NO) donor, increases insulin secretion from pancreatic islets and has positive metabolic effects in type 2 diabetes (T2D). Here, we test the hypothesis of whether nitrite-induced insulin secretion is due to blunting of diabetes-induced oxidative stress in the islets.

Materials and Methods

T2D was created in male rats using a combination of streptozotocin at 25 mg/kg and a high-fat diet. Wistar rats were assigned to 3 groups (n=6 in each group), including control, T2D, and T2D+nitrite; the latter group consumed drinking water containing sodium nitrite (50 mg/l) for eight weeks. At the end of the study, mRNA levels of NADPH oxidase (Nox1, 2, 3, and 4), superoxide dismutase (SOD1, 2, and 3), glutathione peroxides (GPX1 and 7), glutathione reductase (GR), catalase, thioredoxin (TXN1 and 2), and thioredoxin reductase (TXNRD1) were measured in the isolated pancreatic islets.

Results

In the islets of diabetic rats, mRNA expressions of Nox1, 2, and 4 were higher, whereas expressions of SOD1, 2, catalase, GPX1, 7, GR, and TXN1 were lower than controls. Nitrite significantly (all P-values<0.05) decreased gene expression of Nox1 (0.39-fold) and Nox4 (0.23-fold) and increased gene expression of SOD1 (2.2-fold), SOD2 (2.8-fold), catalase (2.7-fold), GPX1 (2.2-fold), GPX7 (6.0-fold), GR (3.0-fold), TXN1 (2.1-fold), and TXNRD1 (2.3-fold) in diabetic rats.

Conclusion

Nitrite decreased oxidative stress in isolated pancreatic islets of rats with T2D by suppressing oxidants and augmenting anti-oxidants. These findings favor the notion that nitrite-induced insulin secretion is partially due to decreased oxidative stress.

Pancreatic β-cell dysfunction in type 2 diabetes: Implications of inflammation and oxidative stress

Insulin resistance and pancreatic β-cell dysfunction are major pathological mechanisms implicated in the development and progression of type 2 diabetes (T2D). Beyond the detrimental effects of insulin resistance, inflammation and oxidative stress have emerged as critical features of T2D that define β-cell dysfunction. Predominant markers of inflammation such as C-reactive protein, tumor necrosis factor alpha, and interleukin-1β are consistently associated with β-cell failure in preclinical models and in people with T2D. Similarly, important markers of oxidative stress, such as increased reactive oxygen species and depleted intracellular antioxidants, are consistent with pancreatic β-cell damage in conditions of T2D. Such effects illustrate a pathological relationship between an abnormal inflammatory response and generation of oxidative stress during the progression of T2D. The current review explores preclinical and clinical research on the patho-logical implications of inflammation and oxidative stress during the development of β-cell dysfunction in T2D. Moreover, important molecular mechanisms and relevant biomarkers involved in this process are discussed to divulge a pathological link between inflammation and oxidative stress during β-cell failure in T2D. Underpinning the clinical relevance of the review, a systematic analysis of evidence from randomized controlled trials is covered, on the potential therapeutic effects of some commonly used antidiabetic agents in modulating inflammatory makers to improve β-cell function.

Modulation of transcription factors by small molecules in β-cell development and differentiation

Transcription factors regulate gene expression and play crucial roles in development and differentiation of pancreatic β-cell. The expression and/or activities of these transcription factors are reduced when β-cells are chronically exposed to hyperglycemia, which results in loss of β-cell function. Optimal expression of such transcription factors is required to maintain normal pancreatic development and β-cell function. Over many other methods of regenerating β-cells, using small molecules to activate transcription factors has gained insights, resulting in β-cells regeneration and survival. In this review, we discuss the broad spectrum of transcription factors regulating pancreatic β-cell development, differentiation and regulation of these factors in normal and pathological states. Also, we have presented set of potential pharmacological effects of natural and synthetic compounds on activities of transcription factor involved in pancreatic β-cell regeneration and survival. Exploring these compounds and their action on transcription factors responsible for pancreatic β-cell function and survival could be useful in providing new insights for development of small molecule modulators.

Characterization of Polysaccharides from the Pericarp of Zanthoxylum bungeanum Maxim by Saccharide Mapping and Their Neuroprotective Effects

The pericarp of Zanthoxylum bungeanum maxim (PZM) is a commonly used spice and herbal medicine in China. In the present study, the structural characteristics of PPZM were investigated by saccharide mapping after enzymatic digestion by using high-performance thin layer chromatography (HPTLC) and polysaccharide analysis by using carbohydrate gel electrophoresis (PACE). The mechanisms of protective effects of PPZM on Aβ_25-35-induced oxidative damage were explored in PC12 cells. The results showed that PPZM contained 1,4-α-D-galactosidic, 1,4-α-D-galactosiduronic, and (1→4)-β-D-glucosidic linkages. Pretreatment with PPZM significantly increased the cell viability of Aβ_25-35-injured PC12 cells. Flow cytometry and Hoechst/PI staining indicated that PPZM gradually relieved the apoptosis of the Aβ_25-25-treated cells. PPZM markedly decreased the ROS level of PC12 cells and suppressed Aβ_25-35-induced oxidative stress by increasing the SOD level, and decreasing the level of MDA and LDH. The mRNA expressions of caspase-3 and Bax were significantly downregulated, and Bcl-2 expression was upregulated by treatment with PPZM. PPZM significantly increased the mRNA expression of Nrf2 and HO-1 in Aβ_25-35 treated cells. The results indicated that PPZM alleviated apoptosis and oxidative stress induced by Aβ_25-25 through the inhibition of mitochondrial dependent apoptosis and activation of Nrf2/HO-1 pathway. PPZM can be used as a potential protective agent against Aβ_25-25-induced neurotoxicity.

An investigation into the potential action of polyphenols against human Islet Amyloid Polypeptide aggregation in type 2 diabetes

Type 2 diabetes (T2D), a chronic metabolic disease characterized by hyperglycemia, results in significant disease burden and financial costs globally. Whilst the majority of T2D cases seem to have a genetic basis, non-genetic modifiable and non-modifiable risk factors for T2D include obesity, diet, physical activity and lifestyle, smoking, age, ethnicity, and mental stress. In healthy individuals, insulin secretion from pancreatic islet β-cells is responsible for keeping blood glucose levels within normal ranges. T2D patients suffer from multifactorial onset of β-cell dysfunction and/or loss of β-cell mass owing to reactive oxygen species (ROS) production, mitochondrial dysfunction, autophagy, and endoplasmic reticulum (ER) stress. Most predominantly however, and the focus of this review, it is the aggregation and misfolding of human Islet Amyloid Polypeptide (hIAPP, also known as amylin), which is detrimental to β-cell function and health. Whilst hIAPP is found in healthy individuals, its misfolded version is cytotoxic and able to induce β-cell dysfunction and/or death through various mechanisms including membrane changes in β-cell causing influx of calcium ions, arresting complete granule membrane recovery and ER stress. There are several existing therapeutics for T2D. However, there is a need for alternative or adjunct therapies for T2D with milder adverse effects and greater availability. Foremost among the potential natural therapeutics are polyphenols. Extensive data from studies evaluating the potential of polyphenols to inhibit hIAPP aggregation and disassemble aggregated hIAPP are promising. Moreover, in-vivo, and in-silico studies also highlight the potential effects of polyphenols against hIAPP aggregation and mitigation of larger pathological effects of T2D. Whilst there have been some promising clinical studies on the therapeutic potential of polyphenols, extensive further clinical studies and in-vitro studies evaluating the mechanisms of action and ideal doses for many of these compounds are required. The need for these studies is made more important by the postulated link between Alzheimer's disease (AD) and T2D pathophysiology given the similar aggregation process of their respective amyloid proteins, which evokes thoughts of cross-reactive polyphenols which can be effective for both AD and T2D patients.

Transcription factor Nrf2 as a potential therapeutic target for COVID-19

The coronavirus disease 2019 (COVID-19) is caused by a novel severe acute respiratory syndrome (SARS)-like coronavirus (SARS-CoV-2). Critically ill patients with SARS-COV-2 infection frequently exhibit signs of high oxidative stress and systemic inflammation, which accounts for most of the mortality. Antiviral strategies to inhibit the pathogenic consequences of COVID-19 are urgently required. The nuclear factor erythroid 2-related transcription factor (Nrf2) is a transcription factor that is involved in antioxidant and anti-inflammatory defense in several tissues and cells. This review tries to present an overview of the role of Nrf2 in the treatment of COVID-19.

Single-Cell RNA Sequencing Reveals a Role for Reactive Oxygen Species and Peroxiredoxins in Fatty Acid-Induced Rat β-Cell Proliferation

The functional mass of insulin-secreting pancreatic β-cells expands to maintain glucose homeostasis in the face of nutrient excess, in part via replication of existing β-cells. Type 2 diabetes appears when these compensatory mechanisms fail. Nutrients including glucose and fatty acids are important contributors to the β-cell compensatory response, but their underlying mechanisms of action remain poorly understood. We investigated the transcriptional mechanisms of β-cell proliferation in response to fatty acids. Isolated rat islets were exposed to 16.7 mmol/L glucose with or without 0.5 mmol/L oleate (C18:1) or palmitate (C16:0) for 48 h. The islet transcriptome was assessed by single-cell RNA sequencing. β-Cell proliferation was measured by flow cytometry. Unsupervised clustering of pooled β-cells identified different subclusters, including proliferating β-cells. β-Cell proliferation increased in response to oleate but not palmitate. Both fatty acids enhanced the expression of genes involved in energy metabolism and mitochondrial activity. Comparison of proliferating versus nonproliferating β-cells and pseudotime ordering suggested the involvement of reactive oxygen species (ROS) and peroxiredoxin signaling. Accordingly, N-acetyl cysteine and the peroxiredoxin inhibitor conoidin A both blocked oleate-induced β-cell proliferation. Our study reveals a key role for ROS signaling through peroxiredoxin activation in oleate-induced β-cell proliferation.

The Nrf2 in Obesity: A Friend or Foe?

Obesity and its complications have become serious global health concerns recently and increasing work has been carried out to explicate the underlying mechanism of the disease development. The recognized correlations suggest oxidative stress and inflammation in expanding adipose tissue with excessive fat accumulation play important roles in the pathogenesis of obesity, as well as its associated metabolic syndromes. In adipose tissue, obesity-mediated insulin resistance strongly correlates with increased oxidative stress and inflammation. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been described as a key modulator of antioxidant signaling, which regulates the transcription of various genes coding antioxidant enzymes and cytoprotective proteins. Furthermore, an increasing number of studies have demonstrated that Nrf2 is a pivotal target of obesity and its related metabolic disorders. However, its effects are controversial and even contradictory. This review aims to clarify the complicated interplay among Nrf2, oxidative stress, lipid metabolism, insulin signaling and chronic inflammation in obesity. Elucidating the implications of Nrf2 modulation on obesity would provide novel insights for potential therapeutic approaches in obesity and its comorbidities.

4-OI Protects MIN6 Cells from Oxidative Stress Injury by Reducing LDHA-Mediated ROS Generation

Pancreatic beta cells are highly susceptible to oxidative stress, which plays a crucial role in diabetes outcomes. Progress has been slow to identify molecules that could be utilized to enhance cell survival and function under oxidative stress. Itaconate, a byproduct of the tricarboxylic acid cycle, has both anti-inflammatory and antioxidant properties. The effects of itaconate on beta cells under oxidative stress are relatively unknown. We explored the effects of 4-octyl itaconate—a cell-permeable derivative of itaconate—on MIN6 (a beta cell model) under oxidative stress conditions caused by hypoxia, along with its mechanism of action. Treatment with 4-OI reversed hypoxia-induced cell death, reduced ROS production, and inhibited cell death pathway activation and inflammatory cytokine secretion in MIN6 cells. The 4-OI treatment also suppressed lactate dehydrogenase A (LDHA)activity, which increases under hypoxia. Treatment of cells with the ROS scavenger NAC and LDHA-specific inhibitor FX-11 reproduced the beneficial effects of 4-OI on MIN6 cell viability under oxidative stress conditions, confirming its role in regulating ROS production. Conversely, overexpression of LDHA reduced the beneficial effects exerted by 4-OI on cells. Our findings provide a strong rationale for using 4-OI to prevent the death of MIN6 cells under oxidative stress.

Epigallocatechin-3-gallate suppresses hemin-aggravated colon carcinogenesis through Nrf2-inhibited mitochondrial reactive oxygen species accumulation

BACKGROUND

Previous studies have presented evidence to support the significant association between red meat intake and colon cancer, suggesting that heme iron plays a key role in colon carcinogenesis. Epigallocatechin-3-gallate (EGCG), the major constituent of green tea, exhibits anti-oxidative and anti-cancer effects. However, the effect of EGCG on red meat-associated colon carcinogenesis is not well understood.

OBJECTIVES

We aimed to investigate the regulatory effects of hemin and EGCG on colon carcinogenesis and the underlying mechanism of action.

METHODS

Hemin and EGCG were treated in Caco2 cells to perform the water-soluble tetrazolium salt-1 assay, lactate dehydrogenase release assay, reactive oxygen species (ROS) detection assay, real-time quantitative polymerase chain reaction and western blot. We investigated the regulatory effects of hemin and EGCG on an azoxymethane (AOM) and dextran sodium sulfate (DSS)-induced colon carcinogenesis mouse model.

RESULTS

In Caco2 cells, hemin increased cell proliferation and the expression of cell cycle regulatory proteins, and ROS levels. EGCG suppressed hemin-induced cell proliferation and cell cycle regulatory protein expression as well as mitochondrial ROS accumulation. Hemin increased nuclear factor erythroid-2-related factor 2 (Nrf2) expression, but decreased Keap1 expression. EGCG enhanced hemin-induced Nrf2 and antioxidant gene expression. Nrf2 inhibitor reversed EGCG reduced cell proliferation and cell cycle regulatory protein expression. In AOM/DSS mice, hemin treatment induced hyperplastic changes in colon tissues, inhibited by EGCG supplementation. EGCG reduced the hemin-induced numbers of total aberrant crypts and malondialdehyde concentration in the AOM/DSS model.

CONCLUSIONS

We demonstrated that EGCG reduced hemin-induced proliferation and colon carcinogenesis through Nrf2-inhibited mitochondrial ROS accumulation.

Nrf2 dictates the neuronal survival and differentiation of embryonic zebrafish harboring compromised alanyl-tRNA synthetase

tRNA synthetase deficiency leads to unfolded protein responses in neuronal disorders; however, its function in embryonic neurogenesis remains unclear. This study identified an aars1cq71/cq71 mutant zebrafish allele that showed increased neuronal apoptosis and compromised neurogenesis. aars1 transcripts were highly expressed in primary neural progenitor cells, and their aberration resulted in protein overloading and activated Perk. nfe2l2b, a paralog of mammalian Nfe2l2, which encodes Nrf2, is a pivotal executor of Perk signaling that regulates neuronal phenotypes in aars1cq71/cq71 mutants. Interference of nfe2l2b in nfe2l2bΔ1/Δ1 mutants did not affect global larval development. However, aars1cq71/cq71;nfe2l2bΔ1/Δ1 mutant embryos exhibited increased neuronal cell survival and neurogenesis compared with their aars1cq71/cq71 siblings. nfe2l2b was harnessed by Perk at two levels. Its transcript was regulated by Chop, an implementer of Perk. It was also phosphorylated by Perk. Both pathways synergistically assured the nuclear functions of nfe2l2b to control cell survival by targeting p53. Our study extends the understanding of tRNA synthetase in neurogenesis and implies that Nrf2 is a cue to mitigate neurodegenerative pathogenesis.

Potential role of oxidative stress in the pathogenesis of diabetic bladder dysfunction

Diabetes mellitus is a chronic metabolic disease, posing a considerable threat to global public health. Treating systemic comorbidities has been one of the greatest clinical challenges in the management of diabetes. Diabetic bladder dysfunction, characterized by detrusor overactivity during the early stage of the disease and detrusor underactivity during the late stage, is a common urological complication of diabetes. Oxidative stress is thought to trigger hyperglycaemia-dependent tissue damage in multiple organs; thus, a growing body of literature has suggested a possible link between functional changes in urothelium, muscle and the corresponding innervations. Improved understanding of the mechanisms of oxidative stress could lead to the development of novel therapeutics to restore the redox equilibrium and scavenge excessive free radicals to normalize bladder function in patients with diabetes.

Role of Nuclear Factor Erythroid 2 (Nrf2) in the Recovery of Long COVID-19 Using Natural Antioxidants: A Systematic Review

Coronavirus disease 2019 (COVID-19) is an infectious disease with approximately 517 million confirmed cases, with the average number of cases revealing that patients recover immediately without hospitalization. However, several other cases found that patients still experience various symptoms after 3–12 weeks, which is known as a long COVID syndrome. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can activate nuclear factor kappa beta (NF-κβ) and unbind the nuclear factor erythroid 2-related factor 2 (Nrf2) with Kelch-like ECH-associated protein 1 (Keap1), causing inhibition of Nrf2, which has an important role in antioxidant response and redox homeostasis. Disrupting the Keap1–Nrf2 pathway enhances Nrf2 activity, and has been identified as a vital approach for the prevention of oxidative stress and inflammation. Hence, natural antioxidants from various sources have been identified as a promising strategy to prevent oxidative stress, which plays a role in reducing the long COVID-19 symptoms. Oxygen-rich natural antioxidant compounds provide an effective Nrf2 activation effect that interact with the conserved amino acid residues in the Keap1-binding pocket, such as Ser602, Ser363, Ser508, and Ser555. In this review, the benefits of various natural antioxidant compounds that can modulate the Nrf2 signaling pathway, which is critical in reducing and curing long COVID-19, are highlighted and discussed.

Inside the diabetic brain: Insulin resistance and molecular mechanism associated with cognitive impairment and its possible therapeutic strategies

Type 2 diabetes mellitus (T2DM) the most prevalent metabolic disease that has evolved into a major public health issue. Concerning about its secondary complications, a growing body of evidence links T2DM to cognitive impairment and neurodegenerative disorders. The underlying pathology behind this secondary complication disease is yet to be fully known. Nonetheless, they are likely to be associated with poor insulin signaling as a result of insulin resistance. We have combed through a rising body of literature on insulin signaling in the normal and diabetic brains along with various factors like insulin resistance, hyperglycemia, obesity, oxidative stress, neuroinflammation and Aβ plaques which can act independently or synergistically to link T2DM with cognitive impairments. Finally, we explored several pharmacological and non-pharmacological methods in the hopes of accelerating the rational development of medications for cognitive impairment in T2DM by better understanding these shared pathways.

Maladaptive positive feedback production of ChREBPβ underlies glucotoxic β-cell failure

Preservation and expansion of β-cell mass is a therapeutic goal for diabetes. Here we show that the hyperactive isoform of carbohydrate response-element binding protein (ChREBPβ) is a nuclear effector of hyperglycemic stress occurring in β-cells in response to prolonged glucose exposure, high-fat diet, and diabetes. We show that transient positive feedback induction of ChREBPβ is necessary for adaptive β-cell expansion in response to metabolic challenges. Conversely, chronic excessive β-cell-specific overexpression of ChREBPβ results in loss of β-cell identity, apoptosis, loss of β-cell mass, and diabetes. Furthermore, β-cell "glucolipotoxicity" can be prevented by deletion of ChREBPβ. Moreover, ChREBPβ-mediated cell death is mitigated by overexpression of the alternate CHREBP gene product, ChREBPα, or by activation of the antioxidant Nrf2 pathway in rodent and human β-cells. We conclude that ChREBPβ, whether adaptive or maladaptive, is an important determinant of β-cell fate and a potential target for the preservation of β-cell mass in diabetes.

Asafoetida exerts neuroprotective effect on oxidative stress induced apoptosis through PI3K/Akt/GSK3β/Nrf2/HO-1 pathway

Background

Alzheimer's Disease (AD) is a serious neurodegenerative disease and there is currently no effective treatment for AD progression. The use of TCM as a potential treatment strategy for AD is an evolving field of investigation. Asafoetida (ASF), an oleo-gum-resin isolated from Ferula assa-foetida root, has been proven to possess antioxidative potential and neuroprotective effects, which is closely associated with the neurological disorders. However, the efficacy and further mechanisms of ASF in AD experimental models are still unclear.

Methods

A cognitive impairment of mouse model induced by scopolamine was established to determine the neuroprotective effects of ASF in vivo, as shown by behavioral tests, biochemical assays, Nissl staining, TUNEL staining, Immunohistochemistry, western blot and qPCR. Furthermore, the PC12 cells stimulated by H₂O₂ were applied to explore the underlying mechanisms of ASF-mediated efficacy. Then, the UPLCM analysis and integrated network pharmacology approach was utilized to identified the main constitutes of ASF and the potential target of ASF against AD, respectively. And the main identified targets were validated in vitro by western blot, qPCR and immunofluorescence staining.

Results

In vivo, ASF treatment significantly ameliorated cognitive impairment induced by scopolamine, as evidenced by improving learning and memory abilities, and reducing neuronal injury, cholinergic system impairment, oxidative stress and apoptosis in the hippocampus of mice. In vitro, our results validated that ASF can dose-dependently attenuated H₂O₂-induced pathological oxidative stress in PC12 cells by inhibiting ROS and MDA production, as well as promoting the activities of SOD, CAT, GSH. We also found that ASF can significantly suppressed the apoptosis rate of PC12 cells increased by H₂O₂ exposure, which was confirmed by flow cytometry analysis. Moreover, treatment with ASF obviously attenuated H₂O₂-induced increase in caspase-3 and Bax expression levels, as well as decrease in Bcl-2 protein expression. KEGG enrichment analysis indicated that the PI3K/Akt/GSK3β/Nrf2 /HO-1pathway may be involved in the regulation of cognitive impairment by ASF. The results of western blot, qPCR and immunofluorescence staining of vitro assay proved it.

Conclusions

Collectively, our work first uncovered the significant neuroprotective effect of ASF in treating AD in vivo. Then, we processed a series of vitro experiments to clarify the biological mechanism action. These data demonstrate that ASF can inhibit oxidative stress induced neuronal apoptosis to foster the prevention of AD both in vivo and in vitro, and it may exert the function of inhibiting AD through PI3K/Akt/GSK3β/Nrf2/HO-1pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-022-00630-7.

The Therapeutic Potential of Kaemferol and Other Naturally Occurring Polyphenols Might Be Modulated by Nrf2-ARE Signaling Pathway: Current Status and Future Direction

Kaempferol is a natural flavonoid, which has been widely investigated in the treatment of cancer, cardiovascular diseases, metabolic complications, and neurological disorders. Nrf2 (nuclear factor erythroid 2-related factor 2) is a transcription factor involved in mediating carcinogenesis and other ailments, playing an important role in regulating oxidative stress. The activation of Nrf2 results in the expression of proteins and cytoprotective enzymes, which provide cellular protection against reactive oxygen species. Phytochemicals, either alone or in combination, have been used to modulate Nrf2 in cancer and other ailments. Among them, kaempferol has been recently explored for its anti-cancer and other anti-disease therapeutic efficacy, targeting Nrf2 modulation. In combating cancer, diabetic complications, metabolic disorders, and neurological disorders, kaempferol has been shown to regulate Nrf2 and reduce redox homeostasis. In this context, this review article highlights the current status of the therapeutic potential of kaempferol by targeting Nrf2 modulation in cancer, diabetic complications, neurological disorders, and cardiovascular disorders. In addition, we provide future perspectives on kaempferol targeting Nrf2 modulation as a potential therapeutic approach.

In vitro comparison of various antioxidants and flavonoids from Rooibos as beta cell protectants against lipotoxicity and oxidative stress-induced cell death

Oxidative stress and lipotoxicity effects on pancreatic β cells play a major role in the pathogenesis of type 2 diabetes (T2D). Flavonoids and antioxidants are under study for their cytoprotective effects and antidiabetic potential. In this study, we aimed to compare the protective effect of the Rooibos components aspalathin, isoorientin, 3-hydroxyphloretin (3-OH) and green Rooibos extract (GRT) itself, and exendin-4 and N-acetylcysteine (NAC) as reference molecules, against lipotoxicity and oxidative stress. The insulin-producing β cell line INS1E was exposed to hydrogen peroxide or streptozotocin (STZ) to induce oxidative stress, and palmitate to induce lipotoxicity. Cell viability was assessed by a MTS cell viability assay. Antioxidant response and antiapoptotic gene expression was performed by qRT-PCR. Glucose transporter 2 (GLUT 2) transporter inhibition was assessed through 2-NBDG uptake. GRT and the flavonoids aspalathin and 3-hydroxyphloretin offered significant protection against oxidative stress and lipotoxicity. GRT downregulated expression of pro-apoptotic genes Txnip and Ddit3. The flavonoids aspalathin and 3-hydroxyphloretin also downregulated these genes and in addition upregulated expression of antioxidant response genes Hmox1, Nqo1 and Sod1. Isoorientin gave no cytoprotection. Cytoprotection by Rooibos components was significantly higher than by NAC or exendin-4. Rooibos components strongly protect INS1E β cells against diabetogenic stress. Cytoprotection was associated with the upregulation of antioxidant response genes of the NRF2/KEAP1 pathway or suppression of the TXN system. The Rooibos molecules offered better protection against these insults than exendin-4 and NAC, making them interesting candidates as β cell cytoprotectants for therapeutic or nutraceutical applications.

Nrf2 Regulates β-Cell Mass by Suppressing β-Cell Death and Promoting β-Cell Proliferation

Finding therapies that can protect and expand functional β-cell mass is a major goal of diabetes research. Here, we generated β-cell-specific conditional knockout and gain-of-function mouse models and used human islet transplant experiments to examine how manipulating Nrf2 levels affects β-cell survival, proliferation, and mass. Depletion of Nrf2 in β-cells results in decreased glucose-stimulated β-cell proliferation ex vivo and decreased adaptive β-cell proliferation and β-cell mass expansion after a high-fat diet in vivo. Nrf2 protects β-cells from apoptosis after a high-fat diet. Nrf2 loss of function decreases Pdx1 abundance and insulin content. Activating Nrf2 in a β-cell-specific manner increases β-cell proliferation and mass and improves glucose tolerance. Human islets transplanted under the kidney capsule of immunocompromised mice and treated systemically with bardoxolone methyl, an Nrf2 activator, display increased β-cell proliferation. Thus, by managing reactive oxygen species levels, Nrf2 regulates β-cell mass and is an exciting therapeutic target for expanding and protecting β-cell mass in diabetes.

Molecular Mechanism of Pancreatic β-Cell Failure in Type 2 Diabetes Mellitus

Various important transcription factors in the pancreas are involved in the process of pancreas development, the differentiation of endocrine progenitor cells into mature insulin-producing pancreatic β-cells and the preservation of mature β-cell function. However, when β-cells are continuously exposed to a high glucose concentration for a long period of time, the expression levels of several insulin gene transcription factors are substantially suppressed, which finally leads to pancreatic β-cell failure found in type 2 diabetes mellitus. Here we show the possible underlying pathway for β-cell failure. It is likely that reduced expression levels of MafA and PDX-1 and/or incretin receptor in β-cells are closely associated with β-cell failure in type 2 diabetes mellitus. Additionally, since incretin receptor expression is reduced in the advanced stage of diabetes mellitus, incretin-based medicines show more favorable effects against β-cell failure, especially in the early stage of diabetes mellitus compared to the advanced stage. On the other hand, many subjects have recently suffered from life-threatening coronavirus infection, and coronavirus infection has brought about a new and persistent pandemic. Additionally, the spread of coronavirus infection has led to various limitations on the activities of daily life and has restricted economic development worldwide. It has been reported recently that SARS-CoV-2 directly infects β-cells through neuropilin-1, leading to apoptotic β-cell death and a reduction in insulin secretion. In this review article, we feature a possible molecular mechanism for pancreatic β-cell failure, which is often observed in type 2 diabetes mellitus. Finally, we are hopeful that coronavirus infection will decline and normal daily life will soon resume all over the world.

Ferroptosis as a Novel Determinant of β-Cell Death in Diabetic Conditions

The main pathological hallmark of diabetes is the loss of functional β-cells. Among several types of β-cell death in diabetes, the involvement of ferroptosis remains elusive. Therefore, we investigated the potential of diabetes-mimicking factors: high glucose (HG), proinflammatory cytokines, hydrogen peroxide (H₂O₂), or diabetogenic agent streptozotocin (STZ) to induce ferroptosis of β-cells in vitro. Furthermore, we tested the contribution of ferroptosis to injury of pancreatic islets in an STZ-induced in vivo diabetic model. All in vitro treatments increased loss of Rin-5F cells along with the accumulation of reactive oxygen species, lipid peroxides and iron, inactivation of NF-E2-related factor 2 (Nrf2), and decrease in glutathione peroxidase 4 expression and mitochondrial membrane potential (MMP). Ferrostatin 1 (Fer-1), ferroptosis inhibitor, diminished the above-stated effects and rescued cells from death in case of HG, STZ, and H₂O₂ treatments, while failed to increase MMP and to attenuate cell death after the cytokines' treatment. Moreover, Fer-1 protected pancreatic islets from STZ-induced injury in diabetic in vivo model, since it decreased infiltration of macrophages and accumulation of lipid peroxides and increased the population of insulin-positive cells. Such results revealed differences between diabetogenic stimuli in determining the destiny of β-cells, emerging HG, H₂O₂, and STZ, but not cytokines, as contributing factors to ferroptosis and shed new light on an antidiabetic strategy based on Nrf2 activation. Thus, targeting ferroptosis in diabetes might be a promising new approach for preservation of the β-cell population. Our results obtained from in vivo study strongly justify this approach.

Recent Advances in Understanding Nrf2 Agonism and Its Potential Clinical Application to Metabolic and Inflammatory Diseases

Oxidative stress is a major component of cell damage and cell fat, and as such, it occupies a central position in the pathogenesis of metabolic disease. Nuclear factor-erythroid-derived 2-related factor 2 (Nrf2), a key transcription factor that coordinates expression of genes encoding antioxidant and detoxifying enzymes, is regulated primarily by Kelch-like ECH-associated protein 1 (Keap1). However, involvement of the Keap1–Nrf2 pathway in tissue and organism homeostasis goes far beyond protection from cellular stress. In this review, we focus on evidence for Nrf2 pathway dysfunction during development of several metabolic/inflammatory disorders, including diabetes and diabetic complications, obesity, inflammatory bowel disease, and autoimmune diseases. We also review the beneficial role of current molecular Nrf2 agonists and summarize their use in ongoing clinical trials. We conclude that Nrf2 is a promising target for regulation of numerous diseases associated with oxidative stress and inflammation. However, more studies are needed to explore the role of Nrf2 in the pathogenesis of metabolic/inflammatory diseases and to review safety implications before therapeutic use in clinical practice.

Dysregulation of β-Cell Proliferation in Diabetes: Possibilities of Combination Therapy in the Development of a Comprehensive Treatment

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia as a result of insufficient insulin levels and/or impaired function as a result of autoimmune destruction or insulin resistance. While Type 1 DM (T1DM) and Type 2 DM (T2DM) occur through different pathological processes, both result in β-cell destruction and/or dysfunction, which ultimately lead to insufficient β-cell mass to maintain normoglycemia. Therefore, therapeutic agents capable of inducing β-cell proliferation is crucial in treating and reversing diabetes; unfortunately, adult human β-cell proliferation has been shown to be very limited (~0.2% of β-cells/24 h) and poorly responsive to many mitogens. Furthermore, diabetogenic insults result in damage to β cells, making it ever more difficult to induce proliferation. In this review, we discuss β-cell mass/proliferation pathways dysregulated in diabetes and current therapeutic agents studied to induce β-cell proliferation. Furthermore, we discuss possible combination therapies of proliferation agents with immunosuppressants and antioxidative therapy to improve overall long-term outcomes of diabetes.

The Role of NRF2 in Obesity-Associated Cardiovascular Risk Factors

The raising prevalence of obesity is associated with an increased risk for cardiovascular diseases (CVDs), particularly coronary artery disease (CAD), and heart failure, including atrial fibrillation, ventricular arrhythmias and sudden death. Obesity contributes directly to incident cardiovascular risk factors, including hyperglycemia or diabetes, dyslipidemia, and hypertension, which are involved in atherosclerosis, including structural and functional cardiac alterations, which lead to cardiac dysfunction. CVDs are the main cause of morbidity and mortality worldwide. In obesity, visceral and epicardial adipose tissue generate inflammatory cytokines and reactive oxygen species (ROS), which induce oxidative stress and contribute to the pathogenesis of CVDs. Nuclear factor erythroid 2-related factor 2 (NRF2; encoded by Nfe2l2 gene) protects against oxidative stress and electrophilic stress. NRF2 participates in the regulation of cell inflammatory responses and lipid metabolism, including the expression of over 1000 genes in the cell under normal and stressed environments. NRF2 is downregulated in diabetes, hypertension, and inflammation. Nfe2l2 knockout mice develop structural and functional cardiac alterations, and NRF2 deficiency in macrophages increases atherosclerosis. Given the endothelial and cardiac protective effects of NRF2 in experimental models, its activation using pharmacological or natural products is a promising therapeutic approach for obesity and CVDs. This review provides a comprehensive summary of the current knowledge on the role of NRF2 in obesity-associated cardiovascular risk factors.

Regulation of Pdx1 by oxidative stress and Nrf2 in pancreatic beta-cells

The beta-cell identity gene, pancreatic duodenal homeobox 1 (Pdx1), plays critical roles in many aspects of the life of beta-cells including differentiation, maturation, function, survival and proliferation. High levels of reactive oxygen species (ROS) are extremely toxic to cells and especially to beta-cells due to their relatively low expression of antioxidant enzymes. One of the major mechanisms for beta-cell dysfunction in type-2 diabetes results from oxidative stress-dependent inhibition of PDX1 levels and function. ROS inhibits Pdx1 by reducing Pdx1 mRNA and protein levels, inhibiting PDX1 nuclear localization, and suppressing PDX1 coactivator complexes. The nuclear factor erythroid 2-related factor (Nrf2) antioxidant pathway controls the redox balance and allows the maintenance of high Pdx1 levels. Therefore, pharmacological activation of the Nrf2 pathway may alleviate diabetes by preserving Pdx1 levels.