Myricetin Protects Against High Glucose-Induced β-Cell Apoptosis by Attenuating Endoplasmic Reticulum Stress via Inactivation of Cyclin-Dependent Kinase 5

Network-based identification and mechanism exploration of active ingredients against Alzheimer's disease via targeting endoplasmic reticulum stress from traditional chinese medicine

Alzheimer's disease is a neurodegenerative disease that leads to dementia and poses a serious threat to the health of the elderly. Traditional Chinese medicine (TCM) presents as a promising novel therapeutic therapy for preventing and treating dementia. Studies have shown that natural products derived from kidney-tonifying herbs can effectively inhibit AD. Furthermore, endoplasmic reticulum (ER) stress is a critical factor in the pathology of AD. Regulation of ER stress is a crucial approach to prevent and treat AD. Thus, in this study, we first collected kidney-tonifying herbs, integrated chemical ingredients from multiple TCM databases, and constructed a comprehensive drug-target network. Subsequently, we employed the endophenotype network (network proximity) method to identify potential active ingredients in kidney-tonifying herbs that prevented AD via regulating ER stress. By combining the predicted outcomes, we discovered that 32 natural products could ameliorate AD pathology via regulating ER stress. After a comprehensive evaluation of the multi-network model and systematic pharmacological analyses, we further selected several promising compounds for in vitro testing in the APP-SH-SY5Y cell model. Experimental results showed that echinacoside and danthron were able to effectively reduce ER stress-mediated neuronal apoptosis by inhibiting the expression levels of BIP, p-PERK, ATF6, and CHOP in APP-SH-SY5Y cells. Overall, this study utilized the endophenotype network to preliminarily decipher the effective material basis and potential molecular mechanism of kidney-tonifying Chinese medicine for prevention and treatment of AD.

Detection of polyphenols in carob pods (Ceratonia siliqua) from Southern Italy by a LC-HRMS method

The presence of polyphenols was examined in carob pods (Ceratonia siliqua) from Southern Italy 90 days after harvest by the validation of a reliable LC-HRMS method. A greater abundance of Apigenin (51490.22 ± 34399.16 μg/Kg) and Myricetin (24897.92 ± 108332.05 μg/Kg) compared to previous research works conducted in Mediterranean countries. Significant differences in the polyphenol content between sampling areas (p < 0.05) were observed, particularly differences in hesperidin and myricetin. These differences confirmed the role of geochemical and climatic conditions in the variation of polyphenol content. This study is a first regarding the phenolic content of carob pods from Southern Italy, confirming the presence of these substances even long after harvest and that carob pods are valuable sources of phenolic substances that may be useful in the prevention of diseases related to oxidative stress.

Efficacy of Myricetin Supplementation on Glucose and Lipid Metabolism: A Systematic Review and Meta-Analysis of In Vivo Mice Studies

BACKGROUND/OBJECTIVES

Type 2 diabetes mellitus (T2DM) is a disorder characterized by insulin resistance, hyperglycemia, and dyslipidemia. Myricetin, a flavonoid found in various plants, has shown potential anti-diabetic effects in murine studies. This meta-analysis aimed to evaluate the impact of myricetin supplementation on glucose metabolism and lipid profiles in mouse models of metabolic diseases.

METHODS

A systematic review and meta-analysis were conducted in accordance with PRISMA guidelines (PROSPERO: CRD42024591569). Studies involving mice with metabolic disease models and exclusively using myricetin supplementation were checked across four databases (Embase, Scopus, PubMed, and WoS) until 23rd September 2024. The primary outcomes assessed were blood glucose (BG), insulin levels, triacylglycerol (TAG), total cholesterol (TC), HDL, and LDL. A random-effects model was applied to estimate standardized mean differences (SMD), and SYRCLE's risk-of-bias tool for animal studies was used.

RESULTS

Twenty-one studies with 514 mice met the inclusion criteria. Myricetin supplementation significantly reduced BG (SMD = -1.45, CI: -1.91 to -0.99, p < 0.00001, I2 = 74%), insulin (SMD = -1.78, CI: -2.89 to -0.68, p = 0.002, I2 = 86%), TAG (SMD = -2.60, CI: -3.24 to -1.96, p < 0.00001, I2 = 81%), TC (SMD = -1.86, CI: -2.29 to -1.44, p < 0.00001, I2 = 62%), and LDL (SMD = -2.95, CI: -3.75 to -2.14, p < 0.00001, I2 = 74%). However, the effect on HDL was not statistically significant (SMD = 0.71, CI: -0.01 to 1.43, p = 0.05, I2 = 83%).

CONCLUSIONS

Myricetin supplementation improved glucose metabolism and lipid profiles in mouse models, suggesting its potential as a therapeutic agent for managing T2DM. However, further research is needed to confirm these findings in human studies.

HDAC1 Promotes Mitochondrial Pathway Apoptosis and Inhibits the Endoplasmic Reticulum Stress Response in High Glucose-Treated Schwann Cells via Decreased U4 Spliceosomal RNA

Dysfunction of Schwann cells, including cell apoptosis, autophagy inhibition, dedifferentiation, and pyroptosis, is a pivotal pathogenic factor in induced diabetic peripheral neuropathy (DPN). Histone deacetylases (HDACs) are an important family of proteins that epigenetically regulate gene transcription by affecting chromatin dynamics. Here, we explored the effect of HDAC1 on high glucose-cultured Schwann cells. HDAC1 expression was increased in diabetic mice and high glucose-cultured RSC96 cells, accompanied by cell apoptosis. High glucose also increased the mitochondrial pathway apoptosis-related Bax/Bcl-2 and cleaved caspase-9/caspase-9 ratios and decreased endoplasmic reticulum response-related GRP78, CHOP, and ATF4 expression in RSC96 cells (P < 0.05). Furthermore, overexpression of HDAC1 increased the ratios of Bax/Bcl-2, cleaved caspase-9/caspase-9, and cleaved caspase-3 and reduced the levels of GRP78, CHOP, and ATF4 in RSC96 cells (P < 0.05). In contrast, knockdown of HDAC1 inhibited high glucose-promoted mitochondrial pathway apoptosis and suppressed the endoplasmic reticulum response. Moreover, RNA sequencing revealed that U4 spliceosomal RNA was significantly reduced in HDAC1-overexpressing RSC96 cells. Silencing of U4 spliceosomal RNA led to an increase in Bax/Bcl-2 and cleaved caspase-9 and a decrease in CHOP and ATF4. Conversely, overexpression of U4 spliceosomal RNA blocked HDAC1-promoted mitochondrial pathway apoptosis and inhibited the endoplasmic reticulum response. In addition, alternative splicing analysis of HDAC1-overexpressing RSC96 cells showed that significantly differential intron retention (IR) of Rpl21, Cdc34, and Mtmr11 might be dominant downstream targets that mediate U4 deficiency-induced Schwann cell dysfunction. Taken together, these findings indicate that HDAC1 promotes mitochondrial pathway-mediated apoptosis and inhibits the endoplasmic reticulum stress response in high glucose-cultured Schwann cells by decreasing the U4 spliceosomal RNA/IR of Rpl21, Cdc34, and Mtmr11.

Myricetin Restores Autophagy to Attenuate Lumbar Intervertebral Disk Degeneration Via Negative Regulation of the JAK2/STAT3 Pathway

Autophagy is a critical player in lumbar intervertebral disk degeneration (IDD), and autophagy activation has been suggested to prevent the apoptosis of nucleus pulposus cells (NPCs). Myricetin has anti-cancer, anti-inflammatory, and antioxidant potentials and can activate autophagy. Thus, this study focused on the roles and mechanisms of myricetin in IDD. A puncture-induced rat IDD model was established and intraperitoneally injected with 20-mg/kg/day myricetin. Histopathological changes of intervertebral disks (IVDs) were assessed by hematoxylin and eosin staining and Safranin O/Fast Green staining. The isolated NPCs from IVDs of healthy rats were stimulated with IL-1β to mimic IDD-like conditions. The roles of myricetin in cell apoptosis, extracellular matrix (ECM) degradation, autophagy repression, and the JAK2/STAT3 pathway activation were examined by cell counting kit-8, flow cytometry, western blotting, real-time quantitative polymerase chain reaction, and immunofluorescence staining. Myricetin treatment attenuated the apoptosis and ECM degradation, and enhanced autophagy in the IL-1β-treated NPCs, whereas the myricetin-mediated protection was limited by autophagy inhibition. Mechanistically, myricetin activated autophagy through blocking the JAK2/STAT3 signaling. In vivo experiments revealed that intraperitoneal injection of myricetin activated NPC autophagy to relieve puncture injury in rats. Myricetin prevents IDD by attenuating NPC apoptosis and ECM degradation through blocking the JAK2/STAT3 pathway to enhance autophagy.

Immunopeptidome mining reveals a novel ERS-induced target in T1D

Autoreactive CD8+ T cells play a key role in type 1 diabetes (T1D), but the antigen spectrum that activates autoreactive CD8+ T cells remains unclear. Endoplasmic reticulum stress (ERS) has been implicated in β-cell autoantigen generation. Here, we analyzed the major histocompatibility complex class I (MHC-I)-associated immunopeptidome (MIP) of islet β-cells under steady and ERS conditions and found that ERS reshaped the MIP of β-cells and promoted the MHC-I presentation of a panel of conventional self-peptides. Among them, OTUB258-66 showed immunodominance, and the corresponding autoreactive CD8+ T cells were diabetogenic in nonobese diabetic (NOD) mice. High glucose intake upregulated pancreatic OTUB2 expression and amplified the OTUB258-66-specific CD8+ T-cell response in NOD mice. Repeated OTUB258-66 administration significantly reduced the incidence of T1D in NOD mice. Interestingly, peripheral blood mononuclear cells (PBMCs) from patients with T1D, but not from healthy controls, showed a positive IFN-γ response to human OTUB2 peptides. This study provides not only a new explanation for the role of ERS in promoting β-cell-targeted autoimmunity but also a potential target for the prevention and treatment of T1D. The data are available via ProteomeXchange with the identifier PXD041227.

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.

Naturally occurring small molecules with dual effect upon inflammatory signaling pathways and endoplasmic reticulum stress response

The endoplasmic reticulum (ER) is determinant to maintain cellular proteostasis. Upon unresolved ER stress, this organelle activates the unfolded protein response (UPR). Sustained UPR activates is known to occur in inflammatory processes, deeming the ER a potential molecular target for the treatment of inflammation. This work characterizes the inflammatory/UPR-related molecular machinery modulated by an in-house library of natural products, aiming to pave the way for the development of new selective drugs that act upon the ER to counter inflammation-related chronic diseases. Starting from a library of 134 compounds of natural occurrence, mostly occurring in medicinal plants, nontoxic molecules were screened for their inhibitory capacity against LPS-induced nuclear factor kappa B (NF-κB) activation in a luciferase-based reporter gene assay. Since several natural products inhibited NF-κB expression in THP-1 macrophages, their effect on reactive oxygen species (ROS) production and inflammasome activation was assessed, as well as their transcriptional outcome regarding ER stress. The bioactivities of several natural products are described herein for the first time. We report the anti-inflammatory potential of guaiazulene and describe 5-deoxykaempferol as a novel inhibitor of inflammasome activation. Furthermore, we describe the dual potential of 5-deoxykaempferol, berberine, guaiazulene, luteolin-4'-O-glucoside, myricetin, quercetagetin and sennoside B to modulate inflammatory signaling ER stress. Our results show that natural products are promising molecules for the discovery and pharmaceutical development of chemical entities able to modulate the inflammatory response, as well as proteostasis and the UPR.

Mitochondrial aldehyde dehydrogenase-2 coordinates the hydrogen sulfide - AMPK axis to attenuate high glucose-induced pancreatic β-cell dysfunction by glutathione antioxidant system

Progression of β-cell loss in diabetes mellitus is significantly influenced by persistent hyperglycemia. At the cellular level, a number of signaling cascades affect the expression of apoptotic genes, ultimately resulting in β-cell failure; these cascades have not been elucidated. Mitochondrial aldehyde dehydrogenase-2 (ALDH2) plays a central role in the detoxification of reactive aldehydes generated from endogenous and exogenous sources and protects against mitochondrial deterioration in cells. Here we report that under diabetogenic conditions, ALDH2 is strongly inactivated in β-cells through CDK5-dependent glutathione antioxidant imbalance by glucose-6-phosphate dehydrogenase (G6PD) degradation. Intriguingly, CDK5 inhibition strengthens mitochondrial antioxidant defense through ALDH2 activation. Mitochondrial ALDH2 activation selectively preserves β-cells against high-glucose-induced dysfunction by activating AMPK and Hydrogen Sulfide (H2S) signaling. This is associated with the stabilization and enhancement of the activity of G6PD by SIRT2, a cytoplasmic NAD+-dependent deacetylase, and is thereby linked to an elevation in the GSH/GSSG ratio, which leads to the inhibition of mitochondrial dysfunction under high-glucose conditions. Furthermore, treatment with NaHS, an H2S donor, selectively preserves β-cell function by promoting ALDH2 activity, leading to the inhibition of lipid peroxidation by high-glucose concentrations. Collectively, our results provide the first direct evidence that ALDH2 activation enhances H2S-AMPK-G6PD signaling, leading to improved β-cell function and survival under high-glucose conditions via the glutathione redox balance.

The pharmacological mechanism of Abelmoschus manihot in the treatment of chronic kidney disease

Abelmoschus manihot (A.manihot) is a herbaceous flowering medicinal plant and flavonoids are its main pharmacological active ingredients. A.manihot is listed in the 2020 edition of the Chinese Pharmacopoeia for the treatment of chronic kidney disease (CKD). A.manihot significantly reduces proteinuria in CKD, and the effectiveness and safety of A.manihot in the treatment including primary glomerulonephropathy and diabetic kidney disease (DKD) have been proved by several randomized controlled trials (RCT). Emerging pharmacological studies have explored the potential active small molecules and the underlying mechanisms in A.manihot. The active constituents of A.manihot are mainly seven flavonoids, including hibifolin, hyperoside, isoquercetin, rutin, quercetin, myricetin, and quercetin-3-O-robinobioside. The mechanisms of action mainly include alleviating renal fibrosis, reducing the inflammatory response and decreasing the apoptosis of podocytes. In this review, we summarize the updated information of active components and molecular mechanisms of A.manihot on chronic kidney disease.

TFP5 attenuates cyclin-dependent kinase 5-mediated islet β-cell damage in diabetes

Islet β-cell damage and dysfunction represent the pathophysiological basis of diabetes. Excessive activation of cyclin-dependent kinase 5 (CDK5) is involved in the pathogenesis of type 2 diabetes mellitus (T2DM), although the exact mechanism remains unclear. Therefore, this study investigated the role of a CDK5 inhibitor (TFP5) in islet β-cell damage under diabetic conditions by regulating the expression of CDK5 in vitro and in vivo. CDK5 was upregulated under high glucose conditions in vivo and in vitro, which resulted in inflammation, oxidative stress, and apoptosis of islet β-cells, thereby decreasing insulin secretion. However, TFP5 treatment inhibited the overexpression of CDK5; reduced the inflammatory response, oxidative stress, and apoptosis of islet β cells; and restored insulin secretion. In conclusion, CDK5 is involved in islet β-cell damage under high glucose conditions, and TFP5 may represent a promising candidate for the development of treatments for T2DM.

Bioactive compounds from Polygonatum genus as anti-diabetic agents with future perspectives

Diabetes mellitus (DM) is one of the most serious health problems worldwide. Species in the genus Polygonatum are traditional food and medicinal plants, which play an important role in controlling blood glucose. In this reveiw, we systematically summarized the traditional and modern applications of the genus Polygonatum in DM, focused on the material bases of polysaccharides, flavonoids and saponins. We highlighted their mechanisms of action in preventing obese diabetes, improving insulin resistance, promoting insulin secretion, regulating intestinal microecology, inhibiting advanced glycation end products (AGEs) accumulation, suppressing carbohydrate digestion and obsorption and modulating gluconeogenesis. Based on the safety and efficacy of this 'medicinal food' and its utility in the prevention and treatment of diabetes, we proposed a research and development program that includs diet design (supplementary food), medical nutrition therapy and new drugs, which could provide new pathways for the use of natural plants in prevention and treatment of DM.

In Vitro and In Silico Protocols for the Assessment of Anti-Tick Compounds from Pinus roxburghii against Rhipicephalus (Boophilus) microplus Ticks

Pinus roxburghii, also known by the name "Himalayan chir pine," belongs to the Pinaceae family. Rhipicephalus (Boophilus) microplus tick is one of the most significant bovine ectoparasites, making it a major vector of economically important tick-borne diseases. The researchers conducted adult immersion tests (AIT) and larval packet tests (LPT) to investigate the acaricidal effect of P. roxburghii plant extract on R. (B.) microplus and its potential modulatory function when used with cypermethrin. Eggs were also assessed for their weight, egg-laying index (IE), hatchability rate, and control rate. After exposure to essential extract concentrations ranging from 2.5 to 40 mg/mL for 48 h, adult female ticks' oviposition inhibition and unfed R. (B.) microplus larvae's mortality rates were analyzed. Engorged females exposed to P. roxburghii at 40 mg/mL had reduced biological activity (oviposition, IE) compared to positive and negative controls. A concentration of 40 mg/mL of P. roxburghii caused 90% mortality in R. (B.) microplus larvae, whereas cypermethrin (the positive control) caused 98.3% mortality in LPT. In AIT, cypermethrin inhibited 81% of oviposition, compared to the 40 mg/mL concentration of P. roxburghii, which inhibited 40% of the ticks' oviposition. Moreover, this study assessed the binding capacity of selected phytocompounds with the targeted protein. Three servers (SWISS-MODEL, RoseTTAFold, and TrRosetta) recreated the target protein RmGABACl's 3D structure. The modeled 3D structure was validated using the online servers PROCHECK, ERRAT, and Prosa. Molecular docking using Auto Dock VINA predicted the binding mechanisms of 20 drug-like compounds against the target protein. Catechin and myricetin showed significant interactions with active site residues of the target protein, with docking scores of -7.7 kcal/mol and -7.6 kcal/mol, respectively. In conclusion, this study demonstrated the acaricidal activity of P. roxburghii extract, suggesting its potential as an alternative natural acaricide for controlling R. (B.) microplus.

Venom Peptides, Polyphenols and Alkaloids: Are They the Next Antidiabetics That Will Preserve β-Cell Mass and Function in Type 2 Diabetes?

Improvement of insulin secretion by pancreatic β-cells and preservation of their mass are the current challenges that future antidiabetic drugs should meet for achieving efficient and long-term glycemic control in patients with type 2 diabetes (T2D). The successful development of glucagon-like peptide 1 (GLP-1) analogues, derived from the saliva of a lizard from the Helodermatidae family, has provided the proof of concept that antidiabetic drugs directly targeting pancreatic β-cells can emerge from venomous animals. The literature reporting on the antidiabetic effects of medicinal plants suggests that they contain some promising active substances such as polyphenols and alkaloids, which could be active as insulin secretagogues and β-cell protectors. In this review, we discuss the potential of several polyphenols, alkaloids and venom peptides from snake, frogs, scorpions and cone snails. These molecules could contribute to the development of new efficient antidiabetic medicines targeting β-cells, which would tackle the progression of the disease.

Myricetin inhibits pseudorabies virus infection through direct inactivation and activating host antiviral defense

Myricetin, a polyhydroxyflavone compound, is one of the main ingredients of various human foods and therefore also known as dietary flavonoids. Due to the continuous emergence of resistant strains of herpesviruses, novel control measures are required. In the present study, myricetin exhibited potent antiviral activity against pseudorabies virus (PRV), a model organism of herpesvirus. The suppression rate could reach up to 96.4% at a concentration of 500 μM in cells, and the 50% inhibitory concentration (IC50) was 42.69 μM. Moreover, the inhibitory activity was not attenuated by the increased amount of infective dose, and a significant reduction of intracellular PRV virions was observed by indirect immunofluorescence. A mode of action study indicated that myricetin could directly inactivate the virus in vitro, leading to inhibition of viral adsorption, penetration and replication in cells. In addition to direct killing effect, myricetin could also activate host antiviral defense through regulation of apoptosis-related gene expressions (Bcl-2, Bcl-xl, Bax), NF-κB and MAPK signaling pathways and cytokine gene expressions (IL-1α, IL-1β, IL-6, c-Jun, STAT1, c-Fos, and c-Myc). In PRV-infected mouse model, myricetin could enhance the survival rate by 40% at 5 days post infection, and viral loads in kidney, liver, lung, spleen, and brain were significantly decreased. The pathological changes caused by PRV infection were improved by myricetin treatment. The gene expressions of inflammatory factors (MCP-1, G-CSF, IL-1α, IL-1β, and IL-6) and apoptotic factors (Bcl-xl, Bcl-2, and Bax) were regulated by myricetin in PRV-infected mice. The present findings suggest that myricetin can effectively inhibit PRV infection and become a candidate for development of new anti-herpesvirus drugs.

Natural Polyphenols as SERCA Activators: Role in the Endoplasmic Reticulum Stress-Related Diseases

Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) is a key protein responsible for transporting Ca²⁺ ions from the cytosol into the lumen of the sarco/endoplasmic reticulum (SR/ER), thus maintaining Ca²⁺ homeostasis within cells. Accumulating evidence suggests that impaired SERCA function is associated with disruption of intracellular Ca²⁺ homeostasis and induction of ER stress, leading to different chronic pathological conditions. Therefore, appropriate strategies to control Ca²⁺ homeostasis via modulation of either SERCA pump activity/expression or relevant signaling pathways may represent a useful approach to combat pathological states associated with ER stress. Natural dietary polyphenolic compounds, such as resveratrol, gingerol, ellagic acid, luteolin, or green tea polyphenols, with a number of health-promoting properties, have been described either to increase SERCA activity/expression directly or to affect Ca²⁺ signaling pathways. In this review, potential Ca²⁺-mediated effects of the most studied polyphenols on SERCA pumps or related Ca²⁺ signaling pathways are summarized, and relevant mechanisms of their action on Ca²⁺ regulation with respect to various ER stress-related states are depicted. All data were collected using scientific search tools (i.e., Science Direct, PubMed, Scopus, and Google Scholar).

Regulation of reactive oxygen species by phytochemicals for the management of cancer and diabetes

Cancer and diabetes mellitus are served as typical life-threatening diseases with common risk factors. Developing therapeutic measures in cancers and diabetes have aroused attention for a long time. However, the problems with conventional treatments are in challenge, including side effects, economic burdens, and patient compliance. It is essential to secure safe and efficient therapeutic methods to overcome these issues. As an alternative method, antioxidant and pro-oxidant properties of phytochemicals from edible plants have come to the fore. Phytochemicals are naturally occurring compounds, considered promising agent applicable in treatment of various diseases with beneficial effects. Either antioxidative or pro-oxidative activity of various phytochemicals were found to contribute to regulation of cell proliferation, differentiation, cell cycle arrest, and apoptosis, which can exert preventive and therapeutic effects against cancer and diabetes. In this article, the antioxidant or pro-oxidant effects and underlying mechanisms of flavonoids, alkaloids, and saponins in cancer or diabetic models demonstrated by the recent studies are summarized.

Research progress on the mechanism of beta-cell apoptosis in type 2 diabetes mellitus

Type 2 diabetes mellitus(T2DM) is regarded as one of the most severe chronic metabolic diseases worldwide, which poses a great threat to human safety and health. The main feature of T2DM is the deterioration of pancreatic beta-cell function. More and more studies have shown that the decline of pancreatic beta-cell function in T2DM can be attributable to beta-cell apoptosis, but the exact mechanisms of beta-cell apoptosis in T2DM are not yet fully clarified. Therefore, in this review, we will focus on the current status and progress of research on the mechanism of pancreatic beta-cell apoptosis in T2DM, to provide new ideas for T2DM treatment strategies.

Omnifarious fruit polyphenols: an omnipotent strategy to prevent and intervene diabetes and related complication?

Diabetes mellitus is a metabolic syndrome which cannot be cured. Recently, considerable interest has been focused on food ingredients to prevent and intervene in complications of diabetes. Polyphenolic compounds are one of the bioactive phytochemical constituents with various biological activities, which have drawn increasing interest in human health. Fruits are part of the polyphenol sources in daily food consumption. Fruit-derived polyphenols possess the anti-diabetic activity that has already been proved either from in vitro studies or in vivo studies. The mechanisms of fruit polyphenols in treating diabetes and related complications are under discussion. This is a comprehensive review on polyphenols from the edible parts of fruits, including those from citrus, berries, apples, cherries, mangoes, mangosteens, pomegranates, and other fruits regarding their potential benefits in preventing and treating diabetes mellitus. The signal pathways of characteristic polyphenols derived from fruits in reducing high blood glucose and intervening hyperglycemia-induced diabetic complications were summarized.

Chlorogenic acid and β-glucan from highland barley grain ameliorate β-cell dysfunction via inhibiting apoptosis and improving cell proliferation

Recent studies have reported that highland barley as a whole grain diet has anti-hyperglycemic effects, however little information is available about the active compounds that ameliorate pancreatic β-cell dysfunction and the related mechanisms. In this study, chlorogenic acid (CA) and β-glucan (BG) were identified as the active compounds that ameliorated β-cell dysfunction. CA ameliorated β-cell dysfunction by inhibiting cell apoptosis and improving glucose-stimulated insulin secretion via targeting G protein-coupled receptor 40 (GPR40) and regulating the phospholipase C β (PLCβ) pathway. BG ameliorated β-cell dysfunction by improving cell proliferation via targeting mammalian target of rapamycin (mTOR) and regulating the protein kinase B (Akt)/glycogen synthase kinase-3β (GSK-3β) pathway. Furthermore, CA and BG improved β-cell sensitivity and pancreatic insulin secretion, and inhibited β-cell apoptosis in impaired glucose tolerance (IGT) mice. Notably, CA restored homeostasis model assessment (HOMA)-β values and Ca²⁺-ATP and K⁺-ATP levels back to normal levels, and BG at 300 mg per kg BW restored β-cell insulin contents back to normal levels in IGT mice. Additionally, the combination of CA and BG had an additive effect on ameliorating β-cell dysfunction. These results help develop whole highland barley grain as a functional food for preventing type 2 diabetes by ameliorating pancreatic β-cell damage.

Silencing cyclophilin A improves insulin secretion, reduces cell apoptosis, and alleviates inflammation as well as oxidant stress in high glucose-induced pancreatic β-cells via MAPK/NF-kb signaling pathway

Cyclophilin A is increased in the plasm of diabetic patients, while its effects on high glucose (HG)-stimulated pancreatic β-cells are still pending. The aim of this research is to investigate the effects of cyclophilin A inhibition on HG-challenged pancreatic β-cells. For investigating the effects of cyclophilin A decrease on HG-induced pancreatic β-cells, the cells were separated into normal glucose (NG), Mannitol, HG, HG + shRNA-NC, and HG + shRNA-Cyclophilin A-1 groups. The protein and mRNA expression were detected via Western blot and qRT-PCR. CCK-8 assay and flow cytometry were employed for assessing cell viability and apoptosis. The levels of oxidative stress, inflammation, and insulin secretion were detected by corresponding kits. The cyclophilin A was higher in HG group. Knockdown of cyclophilin A was able to increase insulin secretion, decrease cell apoptosis, and alleviate inflammation as well as oxidant stress in HG-treated pancreatic β-cells via MAPK/NF-kb pathway. Taken together, Cyclophilin A, highly expressed in pancreatic β-cells induced by HG, is a promising therapeutic target for diabetes. Knockdown of cyclophilin A has protective effects against HG-challenged pancreatic β-cells via regulation of MAPK/NF-kb pathway. The findings in this study provided a new strategy for diabetic treatment and paved the way for future researches on diabetes treatment.

The cyclin dependent kinase inhibitor Roscovitine prevents diet-induced metabolic disruption in obese mice

Most strategies to treat obesity-related disorders have involved prevention of diet-induced weight gain in lean mice. Treatment of obese individuals will require therapies that reverse the detrimental effects of excess body weight. Cyclin-dependent kinases have been shown to contribute to obesity and its adverse complications. Here, we show that roscovitine; a an orally available cyclin-dependent kinase inhibitor; given to male mice during the last six weeks of a 19-week high fat diet, reduced weight gain and prevented accompanying insulin resistance, hepatic steatosis, visceral adipose tissue (eWAT) inflammation/fibrosis as well as restored insulin secretion and enhanced whole body energy expenditure. Proteomics and phosphoproteomics analysis of eWAT demonstrated that roscovitine suppressed expression of peptides and phosphopeptides linked to inflammation and extracellular matrix proteins. It also identified 17 putative protein kinases perturbed by roscovitine, including CMGC kinases, AGC kinases and CAMK kinases. Pathway enrichment analysis showed that lipid metabolism, TCA cycle, fatty acid beta oxidation and creatine biosynthesis are enriched following roscovitine treatment. For brown adipose tissue (BAT), analysis of upstream kinases controlling the phosphoproteome revealed two major kinase groups, AGC and CMGC kinases. Among the top enriched pathways were insulin signaling, regulation of lipolysis in adipocytes, thyroid hormone signaling, thermogenesis and cAMP-PKG signaling. We conclude that roscovitine is effective at preventing prolonged diet-induced metabolic disruption and restoring mitochondrial activity in BAT and eWAT.

Pioglitazone-induced AMPK-Glutaminase-1 prevents high glucose-induced pancreatic β-cell dysfunction by glutathione antioxidant system

Prolonged hyperglycemia plays a major role in the progression of β-cell loss in diabetes mellitus. Here we report an insulin sensitizer thiazolidinedione Pioglitazone selectively preserves the beta cells against high glucose-induced dysfunction by activation of AMPK and Glutaminase 1 (GLS1) axis. AMPK activation increases the stability of Glutaminase 1 by HSP90 family mitochondrial heat shock protein 75 (HSP75/TRAP1). This is associated with an elevation of GSH/GSSG ratio which leads to inhibition of mitochondrial dysfunction by induction of BCL2/BCL-XL in high glucose conditions. Pioglitazone was able to also protect against high glucose-induced elevations in maladaptive ER stress markers and increase the adaptive unfolded protein response (UPR) by inhibiting mTORC1-eEF2 protein translation machinery. Moreover, the pioglitazone effect on AMPK activation was not dependent on the PPARγ pathway. Strikingly, chemical inhibition of AMPK signaling or glutaminase-1 inhibition abrogates the pioglitazone effect on the TRAP1-GLS1 axis and GSH/GSSG ratio linked to mitochondrial dysfunction. Finally, inhibition of AMPK signaling enhanced maladaptive ER stress markers by mTORC1-eEF2 activation. Altogether, these results support the proposal that pioglitazone induced AMPK activation stabilizes a novel interaction of TRAP1/HSP75-GLS1 and its downstream signaling leads to improved β-cell function and survival under high glucose conditions.

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Pioglitazone activates AMPK independent of PPARγ.

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AMPK activation induces Glutaminase-1 (GLS1) stability by TRAP1/HSP75.

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GLS1 activation enhances GSH antioxidant system.

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AMPK inhibit mTORC1-eEF2 axis and reduce ER stress.

Effects of myricetin against cadmium-induced neurotoxicity in PC12 cells

Cadmium (Cd) is one of the most prevalent toxic metals widely found in the environment. Cd induces toxicity and apoptosis in various organs and cells. The nervous system is one of the primary organs targeted by Cd. Cd toxicity is correlated with induction of severe oxidative stress. Myricetin, a natural product, has been found to exert protective effects against various disease conditions. The present study aimed to evaluate the potential protective effects of myricetin on Cd-induced neurotoxicity in PC12 cells. The cells were pretreated with myricetin in the absence and presence of Cd. The viability of cells was assessed using the MTT assay. Markers of oxidative stress were investigated by the lipid peroxidation (LPO), glutathione (GSH) content, and total antioxidant capacity (TAC). Moreover, activation of caspase 3 was examined by Western blot analysis. Myricetin could significantly enhance the viability of PC12 cells. Pretreatment of the cells with myricetin, prior to Cd exposure, showed a significant decrease in the levels of LPO whereas GSH and TAC levels were increased. In addition, the activity of caspase-3 was notably prevented by myricetin. These findings revealed that myricetin has protective effects on Cd-induced neurotoxicity in PC12 cells, which can be linked to its antioxidant potential, inhibition of LPO, and prevention of caspase-3 activation.

Current Pharmacological Trends on Myricetin

Myricetin is a member of the group of flavonoids called flavonols. Myricetin is obtained from various fruit, vegetables, tea, berries and red wine. Myricetin is characterized by the pysrogallol B-ring, and the more hydroxylated structure is known to be capable for its increased biological properties compared with other flavonols. Myricetin is produced by the Myricaceae, Anacardiaceae, Polygonaceae, Pinaceae and Primulacea families. It is soluble in organic solvent such as ethanol, DMSO (dimethyl sulfoxide), and dimethyl formamide (DMF). It is sparingly soluble in aqueous buffers. Myricetin shows its various pharmacological activities including antioxidant, anti-amyloidogenic, antibacterial, antiviral, antidiabetic, anticancer, anti-inflammatory, anti-epileptic and anti-ulcer. This review article focuses on pharmacological effects of Myricetin on different diseases such as osteoporotic disorder, anti-inflammatory disorder, alzheimer’s disease, anti-epileptic, cancer, cardiac disorder, diabetic metabolic disorder, hepatoprotective disorder and gastro protective disorder.

Mitochondrial dysfunction in the fetoplacental unit in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is a disease of pregnancy that is associated with d-glucose intolerance and foeto-placental vascular dysfunction. GMD causes mitochondrial dysfunction in the placental endothelium and trophoblast. Additionally, GDM is associated with reduced placental oxidative phosphorylation due to diminished activity of the mitochondrial F₀F₁-ATP synthase (complex V). This phenomenon may result from a higher generation of reactive superoxide anion and nitric oxide. Placental mitochondrial biogenesis and mitophagy work in concert to maintain cell homeostasis and are vital mechanisms securing the efficient generation of ATP, whose demand is higher in pregnancy, ensuring foetal growth and development. Additional factors disturbing placental ATP synthase activity in GDM include pre-gestational maternal obesity or overweight, intracellular pH, miRNAs, fatty acid oxidation, and foetal (and 'placental') sex. GDM is also associated with maternal and foetal hyperinsulinaemia, altered circulating levels of adiponectin and leptin, and the accumulation of extracellular adenosine. Here, we reviewed the potential interplay between these molecules or metabolic conditions on the mechanisms of mitochondrial dysfunction in the foeto-placental unit in GDM pregnancies.

Myricetin bioactive effects: moving from preclinical evidence to potential clinical applications

Several flavonoids have been recognized as nutraceuticals, and myricetin is a good example. Myricetin is commonly found in plants and their antimicrobial and antioxidant activities is well demonstrated. One of its beneficial biological effects is the neuroprotective activity, showing preclinical activities on Alzheimer, Parkinson, and Huntington diseases, and even in amyotrophic lateral sclerosis. Also, myricetin has revealed other biological activities, among them as antidiabetic, anticancer, immunomodulatory, cardiovascular, analgesic and antihypertensive. However, few clinical trials have been performed using myricetin as nutraceutical. Thus, this review provides new insights on myricetin preclinical pharmacological activities, and role in selected clinical trials.

A kinase of many talents: non-neuronal functions of CDK5 in development and disease

The cyclin-dependent kinase 5 (CDK5) represents an unusual member of the family of cyclin-dependent kinases, which is activated upon binding to non-cyclin p35 and p39 proteins. The role of CDK5 in the nervous system has been very well established. In addition, there is growing evidence that CDK5 is also active in non-neuronal tissues, where it has been postulated to affect a variety of functions such as the immune response, angiogenesis, myogenesis, melanogenesis and regulation of insulin levels. Moreover, high levels of CDK5 have been observed in different tumour types, and CDK5 was proposed to play various roles in the tumorigenic process. In this review, we discuss these various CDK5 functions in normal physiology and disease, and highlight the therapeutic potential of targeting CDK5.

AdipoRon promotes diabetic fracture repair through endochondral ossification-based bone repair by enhancing survival and differentiation of chondrocytes

Diabetic bone defects may exhibit impaired endochondral ossification (ECO) leading to delayed bone repair. AdipoRon, a receptor agonist of adiponectin polymers, can ameliorate diabetes and related complications, as well as overcome the disadvantages of the unstable structure of artificial adiponectin polymers. Here, the effects of AdipoRon on the survival and differentiation of chondrocytes in a diabetic environment were explored focusing on related mechanisms in gene and protein levels. In vivo, AdipoRon was applied to diet-induced-obesity (DIO) mice, a model of obesity and type 2 diabetes, with femoral fracture. Sequential histological evaluations and micro-CT were examined for further verification. We found that AdipoRon could ameliorate cell viability, apoptosis, and reactive oxygen species (ROS) production and promote mRNA expression of chondrogenic markers and cartilaginous matrix production of ATDC5 cells in high glucose medium via activating ERK1/2 pathway. Additionally, DIO mice with intragastric AdipoRon administration had more neocartilage and accelerated new bone formation. These data suggest that AdipoRon could stimulate bone regeneration via ECO in diabetes.

CDK5: Key Regulator of Apoptosis and Cell Survival

The atypical cyclin-dependent kinase 5 (CDK5) is considered as a neuron-specific kinase that plays important roles in many cellular functions including cell motility and survival. The activation of CDK5 is dependent on interaction with its activator p35, p39, or p25. These activators share a CDK5-binding domain and form a tertiary structure similar to that of cyclins. Upon activation, CDK5/p35 complexes localize primarily in the plasma membrane, cytosol, and perinuclear region. Although other CDKs are activated by cyclins, binding of cyclin D and E showed no effect on CDK5 activation. However, it has been shown that CDK5 can be activated by cyclin I, which results in anti-apoptotic functions due to the increased expression of Bcl-2 family proteins. Treatment with the CDK5 inhibitor roscovitine sensitizes cells to heat-induced apoptosis and its phosphorylation, which results in prevention of the apoptotic protein functions. Here, we highlight the regulatory mechanisms of CDK5 and its roles in cellular processes such as gene regulation, cell survival, and apoptosis.

Myricetin prevents thapsigargin-induced CDK5-P66Shc signalosome mediated pancreatic β-cell dysfunction

Chronic endoplasmic reticulum (ER) stress has deleterious effects on pancreatic β-cell function and survival in type 2 diabetes (T2D). Cyclin-dependent kinase 5 (CDK5) plays a critical role in β-cell failure under diabetic milieu conditions. However, little information is available on CDK5's ability to impair the function of β-cells via a chemical ER stress inducer thapsigargin. Myricetin, a natural flavonoid, has therapeutic potential for the treatment of type 2 diabetes mellitus. Therefore, we examined the effect of CDK5 on thapsigargin-induced β-cell apoptosis, and explored the relationship between myricetin and CDK5. Exposure of beta cells with thapsigargin, induced a Src-mediated redox signaling (VAV2-Rac1-NOX) formation and CDK5 activation. Activated CDK5 induced antiapoptotic protein myeloid cell leukemia sequence 1 (Mcl-1) degradation which was associated with p66Shc serine 36 phosphorylation, causing beta cell apoptosis via mitochondrial dysfunction. Exposure of beta cells to myricetin resulted in an acute inhibition of Src-mediated redox signaling (VAV2-Rac1-NOX) formation and CDK5 activation. Myricetin inhibited CDK5 activation by directly binding to its ATP-binding pocket. Treatment with myricetin also enhanced the stability of Mcl-1 after thapsigargin treatment. Inhibition of CDK5 with myricetin or roscovitine, a CDK5 inhibitor attenuates thapsigargin induced p66Shc serine 36 phosphorylation and also reduced mitochondrial dysfunction by decreasing mitochondrial ROS and caspase-3 activation. In addition, myricetin was observed to enhance PDX-1 and insulin mRNA expression and potentiate glucose stimulated insulin secretion (GSIS). Taken together, these findings indicate that thapsigargin-induced early molecular events lead to CDK5-p66Shc signalosome contributes to thapsigargin-induced pancreatic β-cell dysfunction. Myricetin blocked thapsigargin induced CDK5-p66Shc signalosome formation and prevented pancreatic beta cell dysfunction. In this study, we demonstrated for the first time that thapsigargin initiated CDK5-p66Shc signalosome mediates the pancreatic beta cell dysfunction and myricetin protects the pancreatic beta cells through the inhibition of CDK5-p66Shc signalosome.

Dapagliflozin rescues endoplasmic reticulum stress-mediated cell death

The new type 2 diabetes drug, dapagliflozin, reduces blood glucose levels and body weight by inhibiting sodium glucose transporter 2 (SGLT2) in proximal tubular cells. SGLT2 inhibitors might modulate glucose influx into renal tubular cells, thereby regulating the metabolic conditions that cause endoplasmic reticulum (ER) stress in the cells. In this study, we examined the effect of dapagliflozin on ER stress in the HK-2 proximal tubular cell line and in the kidney of db/db mice to characterise its function in diabetic nephropathy (DN). We found that dapagliflozin regulated ER stress-mediated apoptosis in vitro and in vivo. Only the elf2α-ATF4-CHOP pathway was regulated under these conditions. Notably, the drug rescued C2 ceramide-induced ER stress-mediated apoptosis and ER stress-mediated apoptosis, which might occur in DN, in db/db mice. Our study shows a novel role for dapagliflozin as an inhibitor of ER stress and suggests that dapagliflozin might be useful for the prevention of DN.

Endoplasmic reticulum stress contributes to NMDA-induced pancreatic β-cell dysfunction in a CHOP-dependent manner

AIMS

Accumulating evidence suggest that endoplasmic reticulum (ER) stress is an important mechanism underlying the development of diabetes. We have reported that sustained treatment with N-methyl-d-aspartate (NMDA) results in apoptotic β-cell death and impairs insulin secretion. However, the molecular mechanism responsible for NMDA-induced β-cell dysfunction remains largely obscure. Thus, this study aimed to determine whether sustained activation of NMDA receptors (NMDARs) causes β-cell dysfunction through ER stress.

MAIN METHODS

Primary mouse islets and MIN6 mouse pancreatic β-cells were treated with NMDA for 24 h or high-glucose for 72 h. After the treatment, glucose-stimulated insulin secretion (GSIS) and the expression of ER stress markers were measured, respectively. In vivo, the expression of ER stress markers was measured in the pancreas of diabetic mice treated with or without NMDARs inhibitor Memantine.

KEY FINDINGS

NMDA treatment caused an increase in the expression of ER stress markers (ATF4, CHOP, GRP78, and Xbp1s) in primary islets. While, tauroursodeoxycholic acid (TUDCA), an inhibitor of ER stress, significantly attenuated NMDA-induced β-cell dysfunction, including the loss of glucose-stimulated insulin secretion and reduction of pancreas duodenum homeobox factor-1 (Pdx-1) mRNA expression, a transcription factor regulating insulin synthesis. Besides, NMDA-induced ER stress strongly promoted pro-inflammatory cytokines synthesis (IL-1β and TNF-α) in β cells. Interestingly, knockdown of CHOP attenuated β-cell dysfunction evoked by NMDA. Furthermore, we demonstrated that blockade of NMDARs ameliorated high-glucose-induced ER stress in vitro and in vivo.

SIGNIFICANCE

This study confirms that ER stress is actively involved in the activation of NMDARs-related β-cell dysfunction.

Oral DhHP-6 for the Treatment of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is associated with pancreatic β-cell dysfunction which can be induced by oxidative stress. Deuterohemin-βAla-His-Thr-Val-Glu-Lys (DhHP-6) is a microperoxidase mimetic that can scavenge reactive oxygen species (ROS) in vivo. In our previous studies, we demonstrated an increased stability of linear peptides upon their covalent attachment to porphyrins. In this study, we assessed the utility of DhHP-6 as an oral anti-diabetic drug in vitro and in vivo. DhHP-6 showed high resistance to proteolytic degradation in vitro and in vivo. The degraded DhHP-6 product in gastrointestinal (GI) fluid retained the enzymatic activity of DhHP-6, but displayed a higher permeability coefficient. DhHP-6 protected against the cell damage induced by H₂O₂ and promoted insulin secretion in INS-1 cells. In the T2DM model, DhHP-6 reduced blood glucose levels and facilitated the recovery of blood lipid disorders. DhHP-6 also mitigated both insulin resistance and glucose tolerance. Most importantly, DhHP-6 promoted the recovery of damaged pancreas islets. These findings suggest that DhHP-6 in physiological environments has high stability against enzymatic degradation and maintains enzymatic activity. As DhHP-6 lowered the fasting blood glucose levels of T2DM mice, it thus represents a promising candidate for oral administration and clinical therapy.