High glucose inhibits glucose-6-phosphate dehydrogenase, leading to increased oxidative stress and beta-cell apoptosis

Resilience to diabetic retinopathy

Chronic elevation of blood glucose at first causes relatively minor changes to the neural and vascular components of the retina. As the duration of hyperglycemia persists, the nature and extent of damage increases and becomes readily detectable. While this second, overt manifestation of diabetic retinopathy (DR) has been studied extensively, what prevents maximal damage from the very start of hyperglycemia remains largely unexplored. Recent studies indicate that diabetes (DM) engages mitochondria-based defense during the retinopathy-resistant phase, and thereby enables the retina to remain healthy in the face of hyperglycemia. Such resilience is transient, and its deterioration results in progressive accumulation of retinal damage. The concepts that co-emerge with these discoveries set the stage for novel intellectual and therapeutic opportunities within the DR field. Identification of biomarkers and mediators of protection from DM-mediated damage will enable development of resilience-based therapies that will indefinitely delay the onset of DR.

Checkpoint kinase 2 controls insulin secretion and glucose homeostasis

After the discovery of insulin, a century ago, extensive work has been done to unravel the molecular network regulating insulin secretion. Here we performed a chemical screen and identified AZD7762, a compound that potentiates glucose-stimulated insulin secretion (GSIS) of a human β cell line, healthy and type 2 diabetic (T2D) human islets and primary cynomolgus macaque islets. In vivo studies in diabetic mouse models and cynomolgus macaques demonstrated that AZD7762 enhances GSIS and improves glucose tolerance. Furthermore, genetic manipulation confirmed that ablation of CHEK2 in human β cells results in increased insulin secretion. Consistently, high-fat-diet-fed Chk2-/- mice show elevated insulin secretion and improved glucose clearance. Finally, untargeted metabolic profiling demonstrated the key role of the CHEK2-PP2A-PLK1-G6PD-PPP pathway in insulin secretion. This study successfully identifies a previously unknown insulin secretion regulating pathway that is conserved across rodents, cynomolgus macaques and human β cells in both healthy and T2D conditions.

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.

Glucose-6-phosphate dehydrogenase deficiency accelerates arterial aging in diabetes

AIMS

High glucose levels and Glucose-6-Phosphate Dehydrogenase deficiency (G6PDd) have both tissue inflammatory effects. Here we determined whether G6PDd accelerates arterial aging (information linked stiffening) in diabetes.

METHODS

Plasma glucose, interleukin 6 (IL6), and arterial stiffness (indexed as carotid-femoral Pulse Wave Velocity, PWV) and red blood cell G6PD activity were assessed in a large (4448) Sardinian population.

RESULTS

Although high plasma glucose in diabetics, did not differ by G6DP status (178.2 ± 55.1 vs 169.0 ± 50.1 mg/dl) in G6DPd versus non-G6PDd subjects, respectively, IL6, and PWV (adjusted for age and glucose) were significantly increased in G6PDd vs non-G6PDd subjects (PWV, 8.0 ± 0.4 vs 7.2 ± 0.2 m/sec) and (IL6, 6.9 ± 5.0 vs 4.2 ± 3.0 pg/ml). In non-diabetics, neither fasting plasma glucose, nor IL6, nor PWV were impacted by G6PDd.

CONCLUSION

G6PDd in diabetics is associated with increased inflammatory markers and accelerated arterial aging.

NADPH Dynamics: Linking Insulin Resistance and β-Cells Ferroptosis in Diabetes Mellitus

This review offers an in-depth exploration of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) in metabolic health. It delves into how NADPH affects insulin secretion, influences insulin resistance, and plays a role in ferroptosis. NADPH, a critical cofactor in cellular antioxidant systems and lipid synthesis, plays a central role in maintaining metabolic homeostasis. In adipocytes and skeletal muscle, NADPH influences the pathophysiology of insulin resistance, a hallmark of metabolic disorders such as type 2 diabetes and obesity. The review explores the mechanisms by which NADPH contributes to or mitigates insulin resistance, including its role in lipid and reactive oxygen species (ROS) metabolism. Parallelly, the paper investigates the dual nature of NADPH in the context of pancreatic β-cell health, particularly in its relation to ferroptosis, an iron-dependent form of programmed cell death. While NADPH's antioxidative properties are crucial for preventing oxidative damage in β-cells, its involvement in lipid metabolism can potentiate ferroptotic pathways under certain pathological conditions. This complex relationship underscores the delicate balance of NADPH homeostasis in pancreatic health and diabetes pathogenesis. By integrating findings from recent studies, this review aims to illuminate the nuanced roles of NADPH in different tissues and its potential as a therapeutic target. Understanding these dynamics offers vital insights into the development of more effective strategies for managing insulin resistance and preserving pancreatic β-cell function, thereby advancing the treatment of metabolic diseases.

The Emerging Roles of the Metabolic Regulator G6PD in Human Cancers

Metabolic reprogramming, especially reprogrammed glucose metabolism, is a well-known cancer hallmark related to various characteristics of tumor cells, including proliferation, survival, metastasis, and drug resistance. Glucose-6-phosphate dehydrogenase (G6PD) is the first and rate-limiting enzyme of the pentose phosphate pathway (PPP), a branch of glycolysis, that converts glucose-6-phosphate (G6P) into 6-phosphogluconolactone (6PGL). Furthermore, PPP produces ribose-5-phosphate (R5P), which provides sugar-phosphate backbones for nucleotide synthesis as well as nicotinamide adenine dinucleotide phosphate (NADPH), an important cellular reductant. Several studies have shown enhanced G6PD expression and PPP flux in various tumor cells, as well as their correlation with tumor progression through cancer hallmark regulation, especially reprogramming cellular metabolism, sustaining proliferative signaling, resisting cell death, and activating invasion and metastasis. Inhibiting G6PD could suppress tumor cell proliferation, promote cell death, reverse chemoresistance, and inhibit metastasis, suggesting the potential of G6PD as a target for anti-tumor therapeutic strategies. Indeed, while challenges-including side effects-still remain, small-molecule G6PD inhibitors showing potential anti-tumor effect either when used alone or in combination with other anti-tumor drugs have been developed. This review provides an overview of the structural significance of G6PD, its role in and regulation of tumor development and progression, and the strategies explored in relation to G6PD-targeted therapy.

Sustained hyperglycemia specifically targets translation of mRNAs for insulin secretion

Pancreatic β cells are specialized for coupling glucose metabolism to insulin peptide production and secretion. Acute glucose exposure robustly and coordinately increases translation of proinsulin and proteins required for secretion of mature insulin peptide. By contrast, chronically elevated glucose levels that occur during diabetes impair β cell insulin secretion and have been shown experimentally to suppress insulin translation. Whether translation of other genes critical for insulin secretion is similarly downregulated by chronic high glucose is unknown. Here, we used high-throughput ribosome profiling and nascent proteomics in MIN6 insulinoma cells to elucidate the genome-wide impact of sustained high glucose on β cell mRNA translation. Before induction of ER stress or suppression of global translation, sustained high glucose suppressed glucose-stimulated insulin secretion and downregulated translation of not only insulin, but also mRNAs related to insulin secretory granule formation, exocytosis, and metabolism-coupled insulin secretion. Translation of these mRNAs was also downregulated in primary rat and human islets following ex vivo incubation with sustained high glucose and in an in vivo model of chronic mild hyperglycemia. Furthermore, translational downregulation decreased cellular abundance of these proteins. Our study uncovered a translational regulatory circuit during β cell glucose toxicity that impairs expression of proteins with critical roles in β cell function.

Hemolytic Anemia due to Glucose 6 Phosphate Dehydrogenase Deficiency Triggered by Type 1 Diabetes Mellitus

Glucose 6 phosphate dehydrogenase (G6PD) is expressed in all tissues and is necessary to maintain oxidant stress capacity of cells. G6PD deficiency is the most common enzymopathy in humans and is among the important causes of hemolytic anemia. It has been reported that severe hemolytic anemia due to G6PD deficiency may develop in newly diagnosed diabetes, especially during the correction of hyperglycemia. To date, nine cases have been published. Genetic analysis was not performed for G6PD deficiency in these published patients. We present a case of hemolytic anemia due to G6PD deficiency secondary to newly diagnosed type 1 diabetes mellitus. Genetic testing was performed for the index patient and revealed a previously reported missense pathogenic variant (c.653C>T; p.Ser218Phe) in the G6PD gene.

Alleviative effect of microRNA-497 on diabetic neuropathic pain in rats in relation to decreased USP15

The current study tries to discuss the functional role of microRNA-497 (miR-497) in diabetic neuropathic pain (DNP) and the related downstream mechanism. Bioinformatics analysis was implemented for the identification of differentially expressed miRNAs and genes. DNP was simulated in rats through intraperitoneal injection of streptozotocin. The expression patterns of miR-497, USP15, NRF2, and G6PD were then determined. The binding of miR-497 and USP15 was confirmed. Using gain- and loss-of-function assays, we analyzed the critical role of miR-497-mediated USP15 in DNP through the NRF2/G6PD axis. Downregulated miR-497 and elevated USP15 were observed in the dorsal root ganglion neurons isolated from spinal cord tissues of STZ-induced DNP rats. miR-497 could alleviate DNP, which was associated with suppression of USP15, a confirmed target of miR-497. USP15 enhanced the degradation and ubiquitination of NRF2 and induced G6PD expression, leading to the progression of DNP. We highlighted the crucial role of miR-497-mediated USP15 in DNP through the NRF2/G6PD axis. 1. miR-497 is downregulated in DRG neurons from spinal cord tissues of STZ-induced DNP rats. 2. miR-497 inhibits the expression of USP15, thereby alleviating STZ-induced DNP in rats. 3. USP15 promotes ubiquitination and degradation of NRF2, reducing the expression of G6PD. 4. miR-497 alleviates STZ-induced DNP in rats by regulating the USP15/NRF2/G6PD axis.

Sustained hyperglycemia specifically targets translation of mRNAs for insulin secretion

Pancreatic β-cells are specialized for coupling glucose metabolism to insulin peptide production and secretion. Acute glucose exposure robustly and coordinately increases translation of proinsulin and proteins required for secretion of mature insulin peptide. By contrast, chronically elevated glucose levels that occur during diabetes impair β-cell insulin secretion and have been shown experimentally to suppress insulin translation. Whether translation of other genes critical for insulin secretion are similarly downregulated by chronic high glucose is unknown. Here, we used high-throughput ribosome profiling and nascent proteomics in MIN6 insulinoma cells to elucidate the genome-wide impact of sustained high glucose on β-cell mRNA translation. Prior to induction of ER stress or suppression of global translation, sustained high glucose suppressed glucose-stimulated insulin secretion and downregulated translation of not only insulin, but also of mRNAs related to insulin secretory granule formation, exocytosis, and metabolism-coupled insulin secretion. Translation of these mRNAs was also downregulated in primary rat and human islets following ex-vivo incubation with sustained high glucose and in an in vivo model of chronic mild hyperglycemia. Furthermore, translational downregulation decreased cellular abundance of these proteins. Our findings uncover a translational regulatory circuit during β-cell glucose toxicity that impairs expression of proteins with critical roles in β-cell function.

Cognitive dysfunction in diabetes: abnormal glucose metabolic regulation in the brain

Cognitive dysfunction is increasingly recognized as a complication and comorbidity of diabetes, supported by evidence of abnormal brain structure and function. Although few mechanistic metabolic studies have shown clear pathophysiological links between diabetes and cognitive dysfunction, there are several plausible ways in which this connection may occur. Since, brain functions require a constant supply of glucose as an energy source, the brain may be more susceptible to abnormalities in glucose metabolism. Glucose metabolic abnormalities under diabetic conditions may play an important role in cognitive dysfunction by affecting glucose transport and reducing glucose metabolism. These changes, along with oxidative stress, inflammation, mitochondrial dysfunction, and other factors, can affect synaptic transmission, neural plasticity, and ultimately lead to impaired neuronal and cognitive function. Insulin signal triggers intracellular signal transduction that regulates glucose transport and metabolism. Insulin resistance, one hallmark of diabetes, has also been linked with impaired cerebral glucose metabolism in the brain. In this review, we conclude that glucose metabolic abnormalities play a critical role in the pathophysiological alterations underlying diabetic cognitive dysfunction (DCD), which is associated with multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, inflammation, and others. Brain insulin resistance is highly emphasized and characterized as an important pathogenic mechanism in the DCD.

EPISODE OF ACUTE HEMOLYSIS DUE TO UNDIAGNOSED GLUCOSE-6-PHOSPHATE DEHIDROGENASE DEFICIENCY IN AN ADOLESCENT WITH NEWLY DIAGNOSED TYPE 1 DIABETES MELLITUS: CASE REPORT AND REVIEW OF LITERATURE

Glucose-6-phosphate dehydrogenase (G6PD) enzyme deficiency is common in the community. The most important clinical manifestation of G6PD deficiency is acute hemolytic anemia due to oxidative stressors. Diabetes Mellitus (DM) can precipitate hemolysis in patients with G6PD deficiency. Here, we described a 15-year-old male with newly diagnosed type 1 DM (T1DM) and unknown G6PD deficiency who suffered from hemolytic anemia during normalization of blood glucose. On admission, the patient did not have ketoacidosis. After the patient's blood sugars were regulated with insulin therapy, he presented five days later with hemolytic anemia. The cause of hemolytic anemia was G6PD deficiency. The patient had no previous episodes of hemolysis and had no relevant family history. Hypoglycemia did not occur during blood glucose regulation. The return of blood sugar to normal after a long period of hyperglycemia was thought to be the possible cause of hemolysis. In conclusion, G6PD deficiency should be considered when there is an episode of hemolysis in newly diagnosed children and adolescents with T1DM, especially in the absence of ketoacidosis and hypoglycemia.

Targeting glucose-6-phosphate dehydrogenase by 6-AN induces ROS-mediated autophagic cell death in breast cancer

Dysregulation of G6PD involved in the pentose phosphate pathway (PPP) is known to promote tumorigenesis. The PPP plays a pivotal role in meeting the anabolic demands of cancer cells. However, the detailed underlying molecular mechanisms of targeting the G6PD-regulated PPP in breast cancer remain unclear. In this study, we aimed to elucidate the molecular pathways mediating the effects of G6PD on cancer progression. Clinical sample analysis found that the expression of G6PD in breast cancer patients was higher than that in normal controls, and patients with higher G6PD expression had poor survival. Gene knockdown or inhibition of G6PD by 6-AN in MCF-7 and MDA-MB-231 cells significantly decreased cell viability, migration, and colony formation ability. G6PD enzyme activity was inhibited by 6-AN treatment, which caused a transient upregulation of ROS. The elevated ROS was independent of cell apoptosis and thus associated with abnormal activated autophagy. Accumulated ROS levels induced autophagic cell death in breast cancer. Inhibition of G6PD suppresses tumour growth in preclinical models of breast cancer. Our results indicate that targeting the G6PD-regulated PPP could restrain tumours in vitro and in vivo, inhibiting G6PD caused cell death by over-activating autophagy, therefore leading to inhibited proliferation and tumour formation.

Recurrent chronic suppurative osteomyelitis in the maxilla of a patient with diabetes mellitus and glucose-6-phosphate dehydrogenase deficiency

AIMS

To report the case of chronic osteomyelitis of a maxilla in a woman with uncontrolled diabetes mellitus (DM), glucose-6-phosphate dehydrogenase (G6PD) deficiency and mental illness, in an attempt to clarify its pathogenesis and treatment.

METHODS AND RESULTS

A case of a woman with moderate G6PD deficiency (Class III) who developed bilateral and asynchronous chronic suppurative osteomyelitis (CSO) of her maxilla with extensive bone sequestra, fistulae and whose management was performed by local surgery for bony sequestra and fistulae removal; closure communication under 4 weeks antibiotic cover.

CONCLUSIONS

CSO of the jaw may be a complication of the G6PD deficiency and DM and its severity depends on patient's medical status.

Hydrogen peroxide detoxification through the peroxiredoxin/thioredoxin antioxidant system: A look at the pancreatic β-cell oxidant defense

Reactive oxygen species (ROS), such as hydrogen peroxide, are formed when molecular oxygen obtains additional electrons, increasing its reactivity. While low concentrations of hydrogen peroxide are necessary for regulation of normal cellular signaling events, high concentrations can be toxic. To maintain this balance between beneficial and deleterious concentrations of hydrogen peroxide, cells utilize antioxidants. Our recent work supports a primary role for peroxiredoxin, thioredoxin, and thioredoxin reductase as the oxidant defense pathway used by insulin-producing pancreatic β-cells. These three players work in an antioxidant cycle based on disulfide exchange, with oxidized targets ultimately being reduced using electrons provided by NADPH. Peroxiredoxins also participate in hydrogen peroxide-based signaling through disulfide exchange with redox-regulated target proteins. This chapter will describe the catalytic mechanisms of thioredoxin, thioredoxin reductase, and peroxiredoxin and provide an in-depth look at the roles these enzymes play in antioxidant defense pathways of insulin-secreting β-cells. Finally, we will evaluate the physiological relevance of peroxiredoxin-mediated hydrogen peroxide signaling as a regulator of β-cell function.

Ferroptosis Signaling in Pancreatic β-Cells: Novel Insights & Therapeutic Targeting

Metabolic stress impairs pancreatic β-cell survival and function in diabetes. Although the pathophysiology of metabolic stress is complex, aberrant tissue damage and β-cell death are brought on by an imbalance in redox equilibrium due to insufficient levels of endogenous antioxidant expression in β-cells. The vulnerability of β-cells to oxidative damage caused by iron accumulation has been linked to contributory β-cell ferroptotic-like malfunction under diabetogenic settings. Here, we take into account recent findings on how iron metabolism contributes to the deregulation of the redox response in diabetic conditions as well as the ferroptotic-like malfunction in the pancreatic β-cells, which may offer insights for deciphering the pathomechanisms and formulating plans for the treatment or prevention of metabolic stress brought on by β-cell failure.

Kinetic and data-driven modeling of pancreatic β-cell central carbon metabolism and insulin secretion

Pancreatic β-cells respond to increased extracellular glucose levels by initiating a metabolic shift. That change in metabolism is part of the process of glucose-stimulated insulin secretion and is of particular interest in the context of diabetes. However, we do not fully understand how the coordinated changes in metabolic pathways and metabolite products influence insulin secretion. In this work, we apply systems biology approaches to develop a detailed kinetic model of the intracellular central carbon metabolic pathways in pancreatic β-cells upon stimulation with high levels of glucose. The model is calibrated to published metabolomics datasets for the INS1 823/13 cell line, accurately capturing the measured metabolite fold-changes. We first employed the calibrated mechanistic model to estimate the stimulated cell's fluxome. We then used the predicted network fluxes in a data-driven approach to build a partial least squares regression model. By developing the combined kinetic and data-driven modeling framework, we gain insights into the link between β-cell metabolism and glucose-stimulated insulin secretion. The combined modeling framework was used to predict the effects of common anti-diabetic pharmacological interventions on metabolite levels, flux through the metabolic network, and insulin secretion. Our simulations reveal targets that can be modulated to enhance insulin secretion. The model is a promising tool to contextualize and extend the usefulness of metabolomics data and to predict dynamics and metabolite levels that are difficult to measure in vitro. In addition, the modeling framework can be applied to identify, explain, and assess novel and clinically-relevant interventions that may be particularly valuable in diabetes treatment.

Glucose 6-P Dehydrogenase—An Antioxidant Enzyme with Regulatory Functions in Skeletal Muscle during Exercise

Hypomorphic Glucose 6-P dehydrogenase (G6PD) alleles, which cause G6PD deficiency, affect around one in twenty people worldwide. The high incidence of G6PD deficiency may reflect an evolutionary adaptation to the widespread prevalence of malaria, as G6PD-deficient red blood cells (RBCs) are hostile to the malaria parasites that infect humans. Although medical interest in this enzyme deficiency has been mainly focused on RBCs, more recent evidence suggests that there are broader implications for G6PD deficiency in health, including in skeletal muscle diseases. G6PD catalyzes the rate-limiting step in the pentose phosphate pathway (PPP), which provides the precursors of nucleotide synthesis for DNA replication as well as reduced nicotinamide adenine dinucleotide phosphate (NADPH). NADPH is involved in the detoxification of cellular reactive oxygen species (ROS) and de novo lipid synthesis. An association between increased PPP activity and the stimulation of cell growth has been reported in different tissues including the skeletal muscle, liver, and kidney. PPP activity is increased in skeletal muscle during embryogenesis, denervation, ischemia, mechanical overload, the injection of myonecrotic agents, and physical exercise. In fact, the highest relative increase in the activity of skeletal muscle enzymes after one bout of exhaustive exercise is that of G6PD, suggesting that the activation of the PPP occurs in skeletal muscle to provide substrates for muscle repair. The age-associated loss in muscle mass and strength leads to a decrease in G6PD activity and protein content in skeletal muscle. G6PD overexpression in Drosophila Melanogaster and mice protects against metabolic stress, oxidative damage, and age-associated functional decline, and results in an extended median lifespan. This review discusses whether the well-known positive effects of exercise training in skeletal muscle are mediated through an increase in G6PD.

Nicotinamide mononucleotide improves spermatogenic function in streptozotocin-induced diabetic mice via modulating the glycolysis pathway

Spermatogenic dysfunction is one of the major secondary complications of diabetes; however, the underlying mechanisms remain ill-defined, and there is no available drug or strategy for the radical treatment of diabetic spermatogenic dysfunction. Therefore, the objective of this study is to investigate the protective effects of nicotinamide mononucleotide (NMN) on testicular spermatogenic function in streptozotocin (STZ)-induced diabetic mice. The results show that oral administration of NMN significantly increases the body and testis weight and the number of sperms. Moreover, the abnormal sperm count and the rate of sperm malformation are significantly decreased compared with the saline-treated diabetic mice. Histological analysis reveals that NMN treatment significantly increases the area and diameter of seminiferous tubules, accompanied by an increased number of spermatogenic cells and sperms. Immunohistochemistry and qRT-PCR results show that NMN increases Bcl-2 expression and decreases Bax expression in the testis. NMN also increases the protein expression of Vimentin and the mRNA expressions of WT1 and GATA4. In addition, qRT-PCR, western blot analysis and immunohistochemistry results also show that NMN increases the expressions of glycolysis-related rate-limiting enzymes including HK2, PKM2, and LDHA. In summary, this study demonstrates the protective effects of NMN on the testis in an STZ-induced diabetic mice model. NMN exerts its protective effects via reducing spermatogenic cell apoptosis by regulating glycolysis of Sertoli cells in diabetic mice. This study provides an experimental basis for the future clinical application of NMN in diabetes-induced spermatogenic dysfunction.

Reduced nicotinamide adenine dinucleotide phosphate in redox balance and diseases: a friend or foe?

The nicotinamide adenine dinucleotide (NAD⁺/NADH) and nicotinamide adenine dinucleotide phosphate (NADP⁺/NADPH) redox couples function as cofactors or/and substrates for numerous enzymes to retain cellular redox balance and energy metabolism. Thus, maintaining cellular NADH and NADPH balance is critical for sustaining cellular homeostasis. The sources of NADPH generation might determine its biological effects. Newly-recognized biosynthetic enzymes and genetically encoded biosensors help us better understand how cells maintain biosynthesis and distribution of compartmentalized NAD(H) and NADP(H) pools. It is essential but challenging to distinguish how cells sustain redox couple pools to perform their integral functions and escape redox stress. However, it is still obscure whether NADPH is detrimental or beneficial as either deficiency or excess in cellular NADPH levels disturbs cellular redox state and metabolic homeostasis leading to redox stress, energy stress, and eventually, to the disease state. Additional study of the pathways and regulatory mechanisms of NADPH generation in different compartments, and the means by which NADPH plays a role in various diseases, will provide innovative insights into its roles in human health and may find a value of NADPH for the treatment of certain diseases including aging, Alzheimer's disease, Parkinson's disease, cardiovascular diseases, ischemic stroke, diabetes, obesity, cancer, etc.

Energy Metabolism on Mitochondrial Maturation and Its Effects on Cardiomyocyte Cell Fate

Alterations in energy metabolism play a major role in the lineage of cardiomyocytes, such as the dramatic changes that occur in the transition from neonate to newborn. As cardiomyocytes mature, they shift from a primarily glycolytic state to a mitochondrial oxidative metabolic state. Metabolic intermediates and metabolites may have epigenetic and transcriptional roles in controlling cell fate by increasing mitochondrial biogenesis. In the maturing cardiomyocyte, such as in the postnatal heart, fatty acid oxidation increases in conjunction with increased mitochondrial biogenesis driven by the transcriptional coregulator PGC1-α. PGC1-α is necessary for mitochondrial biogenesis in the heart at birth, with deficiencies leading to postnatal cardiomyopathy. While stem cell therapy as a treatment for heart failure requires further investigation, studies suggest that adult stem cells may secrete cardioprotective factors which may regulate cardiomyocyte differentiation and survival. This review will discuss how metabolism influences mitochondrial biogenesis and how mitochondrial biogenesis influences cell fate, particularly in the context of the developing cardiomyocyte. The implications of energy metabolism on stem cell differentiation into cardiomyocytes and how this may be utilized as a therapy against heart failure and cardiovascular disease will also be discussed.

Hypoglycemic Effect of Nobiletin via Regulation of Islet β-Cell Mitophagy and Gut Microbiota Homeostasis in Streptozocin-Challenged Mice

Nobiletin is a natural nutrient (or polymethoxyflavonoid) in orange peels exerting a preventive effect against metabolic diseases. However, there are very few reports on the hypoglycemic effect of nobiletin. In the present study, the hypoglycemic effect of nobiletin was investigated using NIT-1 cells and streptozocin (STZ)-challenged mouse models. Our results indicated that nobiletin could significantly suppress the high blood glucose in STZ-challenged mice. In addition, nobiletin could effectively activate the mitophagy and inhibit the inflammatory pathways in NIT-1 cells. The mitochondria membrane potential dysbiosis induced by glucotoxicity in NIT-1 cells was restored after treatment by nobiletin. Further investigation revealed that the hypoglycemic effect of nobiletin was mainly through regulation of gut microbiota dysbiosis, activation of mitophagy flux, inhibition of inflammasome expression, and restoration of islet morphological destruction in the pancreas of STZ-challenged mice. Our study revealed that nobiletin could be used as a functional food or drug candidate for the treatment of diabetes.

Contribution of Mitochondria to Insulin Secretion by Various Secretagogues

Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca²⁺ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca²⁺ influx was found to enhance GSIS, reflecting cytosolic Ca²⁺ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca²⁺ and K⁺ channels) or the superimposed Ca²⁺ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca²⁺ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub β-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.

The ginger extract could improve diabetic retinopathy by inhibiting the expression of e/iNOS and G6PDH, apoptosis, inflammation, and angiogenesis

Diabetic retinopathy is a complication of diabetes, caused by high blood sugar levels damaging the retina. It is the result of damage to the small blood vessels and neurons of the retina. Ginger and its phytochemical compounds can improve oxidative damage and inflammation. However, the effects of this plant on ocular expression G6PDH and e/iNOS, eye cell apoptosis, and angiogenesis are not well known in this tissue. Therefore, the aim of this study was to evaluate the therapeutic potential of ginger extract on rats with type 2 diabetic retinopathy. Thirty-two Wistar rats were randomly divided into four controlled and treated groups. The serum level of metabolic factors such as lipid profiles, insulin and glucose, and the level of oxidative biomarkers along with the TNF-α level in eye tissue were measured. The expression of NF-κB, VEGF, BAX, Bcl-2, caspase-3, e/iNOS, and G6PDH in eye tissue was measured. Serum levels of lipid profiles, glucose, and insulin, oxidative and inflammatory markers were significantly increased in the diabetic group compared to control. While, treatment with ginger extract could significantly improve these factors in diabetic rats. Moreover, the ocular expression of e/iNOS, G6PDH, VEGF, NF-κB, and genes involved in apoptosis was changed in diabetic rats. However, treatment with ginger extract could ameliorate these changes in the diabetic-treated group. It can be concluded that ginger extract could improve diabetic retinopathy by inhibiting oxidative damage, inflammation, iNOS, VEGF, apoptosis, and improving eNOS and G6PDH. PRACTICAL APPLICATIONS: Microvascular complications of diabetes such as retinopathy can be one of the main causes of disability in people with diabetes. Chronic hyperglycemia, oxidative stress, inflammation, and apoptosis cause diabetic retinopathy through retinal damage. Ginger, on the other hand, is an available, inexpensive, and uncomplicated medicinal plant that contains more than 20 different phytochemicals, such as gingerol and shogaol, which have anti-inflammatory, antioxidant, antihypertensive, hypoglycemic, and hypolipidemic properties. The results of our study showed well that the ginger extract could improve diabetic retinopathy by inhibiting the expression of e/iNOS and G6PDH and oxidative damage, apoptosis, inflammation, and angiogenesis. Therefore, ginger and its compounds can be a good option to improve the complications of diabetes.

Chlorogenic acid alleviates thioacetamide-induced toxicity and promotes liver development in zebrafish (Danio rerio) through the Wnt signaling pathway

Chlorogenic acid (CGA) is a phenylpropanoid compound that is well known to improve the antioxidant capacity and other biological activities. However, the roles of CGA in the liver development of organisms are unclear. In the present study, we aimed to investigate the function of CGA in the hepatic development in thioacetamide (TAA)-induced zebrafish embryos. We found that CGA exerted certain beneficial effects on zebrafish larvae from TAA-exposed zebrafish embryos, such as increasing the liver size, body length, heart rate, acetylcholinesterase activity, and motor ability. In addition, CGA displayed an antioxidant effect on TAA-induced zebrafish embryos by enhancing the activities of superoxide dismutase (SOD), catalase (CAT), and glucose-6-phosphate dehydrogenase (G6PDH), and decreasing of the contents of malondialdehyde (MDA), reactive oxygen species (ROS), and nitric oxide (NO). The results of western blotting analysis showed that CGA inhibited cell apoptosis by increasing the levels of Bcl2 apoptosis regulator and decreasing the levels of Bcl2 associated X (Bax), apoptosis regulator and tumor protein P53. Moreover, CGA promoted cell proliferation in TAA-induced zebrafish larvae, as detected using proliferating cell nuclear antigen fluorescence immunostaining. In addition, CGA inhibited the expression of Wnt signaling pathway genes Dkk1 (encoding Dickkopf Wnt signaling pathway inhibitors), and promoted the expression of Lef1 (encoding lymphoid enhancer binding factor 1) and Wnt2bb (encoding wingless-type MMTV integration site family, member 2Bb). When the Wnt signal inhibitor IWR-1 was added, there was no significant change in liver development in the IWR-1 + TAA group compared with the IWR-1 + TAA + CGA group (p <0.05), which suggested that CGA regulates liver development via Wnt signaling pathway. Overall, our results suggested that CGA might alleviate TAA-induced toxicity in zebrafish and promote liver development through the Wnt signaling pathway, which provides a basis for the therapeutic effect of CGA on liver dysplasia.

Rhubarb granule promotes diethylnitrosamine-induced liver tumorigenesis by activating the oxidative branch of pentose phosphate pathway via G6PD in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Rhubarb is a natural herbal medicine widely used clinically with numerous pharmacological activities including anti-cancer. Specifically, several studies reported that free anthraquinones from Rhubarb suppressed the proliferation of hepatoma cells. Nonetheless, recent studies revealed that Rhubarb caused hepatotoxicity in vivo, confirming its "two-way" effect on the liver. Therefore, the efficacy and safety of Rhubarb in the in vivo treatment of liver cancer should be further elucidated.

AIM OF THE STUDY

This study investigated the presence of hepatoprotection or hepatotoxicity of Rhubarb in diethylnitrosamine (DEN)-induced hepatocarcinogenesis.

MATERIAL AND METHODS

A total of 112 male Sprague-Dawley rats weighing 190-250 g were enrolled. The rats were induced hepatocarcinogenesis using diethylnitrosamine (0.002 g/rat) until 17 weeks. Starting at week 11, Rhubarb granules (4 g/kg and 8 g/kg) were intragastrically administered daily for 7 weeks. All rats were euthanized at week 20 and the livers were analyzed via non-targeted metabolomics analysis. We established hepatic glucose 6 phosphate (6PG) levels and glucose 6 phosphate dehydrogenase (G6PD) activities to assess the pentose phosphate pathway (PPP). And the liver injuries of rats were analyzed via histological changes, hepatic function, as well as hepatic protein levels of alpha-fetoprotein (AFP), pyruvate kinase isozyme type M2 (PKM2), and proliferating cell nuclear antigen (PCNA). Furthermore, polydatin (0.1 g/kg/d) as a specific inhibitor of G6PD was used to treat rats. Notably, their histological changes, hepatic function, hepatic 6PG levels, hepatic G6PD activities, PCNA levels, and PKM2 levels were recorded.

RESULTS

Non-targeted metabolomics revealed that Rhubarb regulated the PPP in the liver of Rhubarb-DEN-treated rats. Besides, Rhubarb activated the oxidative branch of the PPP by activating G6PD (a rate-limiting enzyme in the oxidative PPP) in the liver of Rhubarb-DEN-treated rats. Meanwhile, Rhubarb promoted DEN-induced hepatocarcinogenesis. Moreover, polydatin attenuated the promoting effect of Rhubarb on DEN-induced hepatocarcinogenesis.

CONCLUSIONS

Rhubarb promoted DEN-induced hepatocarcinogenesis by activating the PPP, indicating that the efficacy and safety of Rhubarb in the treatment of liver cancer deserve to be deliberated.

Evaluation of the Antidiabetic Potential of Extracts of Urtica dioica, Apium graveolens, and Zingiber officinale in Mice, Zebrafish, and Pancreatic β-Cell

Medicinal plants are commonly used in the treatment of diabetes, particularly as they contain flavonoids and phenolic compounds. The present study aims to investigate the activities of a polyherbal formulation made from Urtica dioica, Apium graveolens, and Zingiber officinale (UAZ) against streptozotocin–nicotinamide ((STZ-NA)-induced type 2 diabetes in CD1 mice, glucose-induced type 2 diabetes (T2DM) in zebrafish, and high glucose-induced damage in RINm5F pancreatic β-cells. In fasting mice, plasma glucose, glycosylated hemoglobin (HbA1C), lipid hydroperoxides (LOOH), thiobarbituric acid reactive substances (TBARS), and lipid profiles were significantly increased, whereas insulin, enzymatic antioxidants, and carbohydrate metabolic enzymes were altered significantly in diabetic mice. Zebrafish had similar glucose levels, liver enzymes, and lipid profiles compared to mice. The study investigated the effects of the extract in enhancing cell viability, insulin secretion, and reducing lipid peroxidation and intracellular reactive oxygen species (ROS) levels in RINm5F cells damaged by high glucose. All the above biochemical parameters were enhanced in both mice and zebrafish treated; the combined extract UAZ normalized all the biochemical parameters. The medicinal plant extracts, used either separately or in combination, ameliorated the adverse effect of glucose on cell viability and functionality of beta-RINm5F cells.

PHLPP1/Nrf2-Mdm2 axis induces renal apoptosis via influencing nucleo-cytoplasmic shuttling of FoxO1 during diabetic nephropathy

Impaired PI3K/Akt signaling (insulin resistance) and poor glycemic control (hyperglycemia) are the major risk factors involved in the progression of diabetic nephropathy (DN). This study was designed to identify factors influencing cell survival during DN. We found that high glucose exposure in renal proximal tubular cells (NRK52E) upregulated PHLPP1, an Akt phosphatase (Ser473), causing suppression in Akt and IGF1β phosphorylation leading to inhibition in insulin signaling pathway. Results demonstrate that sustained activation of PHLPP1 promoted nuclear retention of FoxO1 by preventing its ubiquitination via Mdm2, an Akt/ Nrf2-dependent E3 ligase. Thus, enhanced FoxO1 nuclear stability caused aberration in renal gluconeogenesis and activated apoptotic cascade. Conversely, gene silencing of PHLPP1-enhanced Nrf2 expression and attenuated FoxO1 regulated apoptosis compared to hyperglycemic cells. Mechanistic aspects of PHLPP1-Nrf2/FoxO1 signaling were further validated in STZ-nicotinamide-induced type 2 diabetic Wistar rats. Importantly, we observed via immunoblotting and dual immunocytochemical studies that treatment of Morin (2',3,4',5,7-Pentahydroxyflavone) during diabetes significantly augmented FoxO1 nuclear exclusion, resulting in its ubiquitination via Akt-Nrf2/Mdm2 pathway. Furthermore, lowering of PHLPP1 expression by Morin also prevented FoxO1/Mst1-mediated apoptotic signaling in vitro and in vivo. Morin treatment under the experimental conditions, effectively decreased blood glucose levels, ameliorated insulin resistance, alleviated oxidative stress and attenuated renal apoptosis in diabetic rats comparable to metformin thereby exhibiting tremendous potential against renal complications of diabetes. These novel results further acclaim that inhibition of PHLPP1/FoxO1-Mdm2 axis is critical in the pathogenesis of diabetic nephropathy.

The Controversial Role of Glucose-6-Phosphate Dehydrogenase Deficiency on Cardiovascular Disease: A Narrative Review

Cardiovascular disorders (CVD) are highly prevalent and the leading cause of death worldwide. Atherosclerosis is responsible for most cases of CVD. The plaque formation and subsequent thrombosis in atherosclerosis constitute an ongoing process that is influenced by numerous risk factors such as hypertension, diabetes, dyslipidemia, obesity, smoking, inflammation, and sedentary lifestyle. Among the various risk and protective factors, the role of glucose-6-phosphate dehydrogenase (G6PD) deficiency, the most common inborn enzyme disorder across populations, is still debated. For decades, it has been considered a protective factor against the development of CVD. However, in the recent years, growing scientific evidence has suggested that this inherited condition may act as a CVD risk factor. The role of G6PD deficiency in the atherogenic process has been investigated using in vitro or ex vivo cellular models, animal models, and epidemiological studies in human cohorts of variable size and across different ethnic groups, with conflicting results. In this review, the impact of G6PD deficiency on CVD was critically reconsidered, taking into account the most recent acquisitions on molecular and biochemical mechanisms, namely, antioxidative mechanisms, glutathione recycling, and nitric oxide production, as well as their mutual interactions, which may be impaired by the enzyme defect in the context of the pentose phosphate pathway. Overall, current evidence supports the notion that G6PD downregulation may favor the onset and evolution of atheroma in subjects at risk of CVD. Given the relatively high frequency of this enzyme deficiency in several regions of the world, this finding might be of practical importance to tailor surveillance guidelines and facilitate risk stratification.

The impact of polyphenols extracted from Tricholoma matsutake on UVB-induced photoaging in mouse skin

BACKGROUND

Despite Tricholoma matsutake has been used as natural health products with multiple medicinal properties, detailed information about its polyphenolic composition as sources of anti-photoaging agents remains to be determined.

OBJECTIVE

To investigate the impact of polyphenols extracted from Tricholoma matsutake (TME) on Ultraviolet B (UVB)-induced skin photoaging.

MATERIALS AND METHODS

Various factors of oxidative stress and inflammation as well as histological and immunohistochemical analysis in the mouse dorsal skin were determined after UVB radiation.

RESULTS

Topical administration with TME suppressed the UVB-induced skin thickness, wrinkles and erythema, and increased skin collagen content. Furthermore, TME decreased reactive oxygen species (ROS) level, upregulated glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT) and glucose-6-phosphate dehydrogenase (G6PDH) activities and inhibited the expression of IL-1, IL-6, IL-8 and TNF-α in mice irradiated with UVB. TME could reduce UVB-induced p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation and effectively inhibited the activity of the transcriptional factor nuclear factor-kappa B (NF-κB), thereby reducing the cyclooxygenase-2 (COX-2) expression, which is an important mediator of inflammatory cascade leading to the inflammatory response.

CONCLUSION

Our data demonstrated that TME had various beneficial effects on UVB-induced skin photoaging due to its antioxidant and anti-inflammatory activities, and it might be exploited as a promising natural product in skin care, anti-photoaging and the therapeutic intervention of skin disorders related to both oxidative stress and inflammation.

Possible mechanisms of the hypoglycaemic effect of artesunate: Gender implication

Background

We investigated the mechanism of artesunate’s glucose-modulating effect especially with gender implication.

Methods

Twenty-five (25) male and 25 female rats were separately and blindly allocated into five identical groups (n = 5/group). Group I (control) received 0.2 ml/kg distilled water. Groups II and III both received 2.90 mg/kg artesunate on day one, but 1.45 mg/kg from day two till day five and day fifteen respectively. Groups IV and V both received 8.70 mg/kg artesunate on day one, but 4.35 mg/kg artesunate from day two till day five and day fifteen respectively.

Results

In male rats, glucose was reduced by both doses of artesunate at 5 days but increased by high dose at 15 days. Artesunate increased glycogen concentration at short duration which normalised at long duration in both genders. Artesunate increased G6P concentration only in male rats at 15 days but reduced G6Pase activity in male and female rats (except in those that received low and high doses of artesunate for 15 days). Artesunate increased insulin only in male rats treated with low dose artesunate for 5 days. Artesunate increased cortisol concentration in male but reduced it in female rats. Artesunate decreased glucagon concentration except in female rats treated with high dose for 5 days. Artesunate increased oestrogen concentration in male rats that received low dose artesunate for 5 days but reduced it in female rats that received high dose for 15 days.

Conclusions

Artesunate reduces plasma glucose by reducing plasma glucagon concentrations and inhibiting liver glycogenolysis via inhibition of G6Pase activity in both sexes. Increase in insulin concentration contributed to the reduction in blood glucose caused by artesunate in male but not female rats; and artesunate-induced increase in G6P, a substrate for G6PD, could enhance NADPH generation and antioxidant enzyme activation in male rats.

•

Reducing glucagon concentration and inhibiting G6Pase activity in both genders. .

•

Increasing plasma insulin in male but not in female.

•

Increasing G6P, a substrate for G6PD, in male rats.

Overexpression of glucose 6 phosphate dehydrogenase preserves mouse pancreatic beta cells function until late in life

NAD(P)H donates electrons for reductive biosynthesis and antioxidant defense across all forms of life. Glucose-6-phosphate dehydrogenase (G6PD) is a critical enzyme to provide NADPH. G6PD deficiency is present in more than 400 million people worldwide. This enzymopathy provides protection against malaria but sensitizes cells to oxidative stressors. Oxidative stress has been involved in the pathogenesis of the diabetic complications and several studies have provided evidences of a link between G6PD deficiency and type 2 diabetes (T2D). We hypothesized that a moderate overexpression of G6PD (G6PD-Tg) could protect β-cells from age-associated oxidative stress thus reducing the risk of developing T2D. Here we report, that G6PD-Tg mice show an improved glucose tolerance and insulin sensitivity when compared to old age-matched Wild Type (WT) ones. This is accompanied by a decrease in oxidative damage and stress markers in the pancreas of the old Tg animals (20-24month-old). Pancreatic β-cells progress physiologically towards a state of reduced responsiveness to glucose. In pancreatic islets isolated from G6PD-Tg and WT animals at different ages, and using electrophysiological techniques, we demonstrate a wider range of response to glucose in the G6PD-Tg cells that may explain the improvements in glucose tolerance and insulin sensitivity. Together, our results show that overexpression of G6PD maintains pancreatic β-cells from old mice in a "juvenile-like" state and points to the G6PD dependent generation of NADPH as an important factor to improve the natural history of diabetes.

Blunted Reducing Power Generation in Erythrocytes Contributes to Oxidative Stress in Prepubertal Obese Children with Insulin Resistance

Childhood obesity, and specifically its metabolic complications, are related to deficient antioxidant capacity and oxidative stress. Erythrocytes are constantly exposed to multiple sources of oxidative stress; hence, they are equipped with powerful antioxidant mechanisms requiring permanent reducing power generation and turnover. Glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) are two key enzymes on the pentose phosphate pathway. Both enzymes supply reducing power by generating NADPH, which is essential for maintaining the redox balance within the cell and the activity of other antioxidant enzymes. We hypothesized that obese children with insulin resistance would exhibit blunted G6PDH and 6PGDH activities, contributing to their erythrocytes’ redox status imbalances. We studied 15 control and 24 obese prepubertal children, 12 of whom were insulin-resistant according to an oral glucose tolerance test (OGTT). We analyzed erythroid malondialdehyde (MDA) and carbonyl group levels as oxidative stress markers. NADP+/NADPH and GSH/GSSG were measured to determine redox status, and NADPH production by both G6PDH and 6PGDH was assayed spectrophotometrically to characterize pentose phosphate pathway activity. Finally, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR) activities were also assessed. As expected, MDA and carbonyl groups levels were higher at baseline and along the OGTT in insulin-resistant children. Both redox indicators showed an imbalance in favor of the oxidized forms along the OGTT in the insulin-resistant obese group. Additionally, the NADPH synthesis, as well as GR activity, were decreased. H₂O₂ removing enzyme activities were depleted at baseline in both obese groups, although after sugar intake only metabolically healthy obese participants were able to maintain their catalase activity. No change was detected in SOD activity between groups. Our results show that obese children with insulin resistance present higher levels of oxidative damage, blunted capacity to generate reducing power, and hampered function of key NADPH-dependent antioxidant enzymes.

The Pancreatic β-Cell: The Perfect Redox System

Pancreatic β-cell insulin secretion, which responds to various secretagogues and hormonal regulations, is reviewed here, emphasizing the fundamental redox signaling by NADPH oxidase 4- (NOX4-) mediated H₂O₂ production for glucose-stimulated insulin secretion (GSIS). There is a logical summation that integrates both metabolic plus redox homeostasis because the ATP-sensitive K⁺ channel (K_ATP) can only be closed when both ATP and H₂O₂ are elevated. Otherwise ATP would block K_ATP, while H₂O₂ would activate any of the redox-sensitive nonspecific calcium channels (NSCCs), such as TRPM2. Notably, a 100%-closed K_ATP ensemble is insufficient to reach the -50 mV threshold plasma membrane depolarization required for the activation of voltage-dependent Ca²⁺ channels. Open synergic NSCCs or Cl^- channels have to act simultaneously to reach this threshold. The resulting intermittent cytosolic Ca²⁺-increases lead to the pulsatile exocytosis of insulin granule vesicles (IGVs). The incretin (e.g., GLP-1) amplification of GSIS stems from receptor signaling leading to activating the phosphorylation of TRPM channels and effects on other channels to intensify integral Ca²⁺-influx (fortified by endoplasmic reticulum Ca²⁺). ATP plus H₂O₂ are also required for branched-chain ketoacids (BCKAs); and partly for fatty acids (FAs) to secrete insulin, while BCKA or FA β-oxidation provide redox signaling from mitochondria, which proceeds by H₂O₂ diffusion or hypothetical SH relay via peroxiredoxin "redox kiss" to target proteins.

Role of Glucose Metabolism and Mitochondrial Function in Diabetic Kidney Disease

PURPOSE OF REVIEW

Diabetic kidney disease (DKD) continues to be the primary cause of chronic kidney disease in the USA and around the world. The numbers of people with DKD also continue to rise despite current treatments. Certain newer hypoglycemic drugs offer a promise of slowing progression, but it remains to be seen how effective these will be over time. Thus, continued exploration of the mechanisms underlying the development and progression of DKD is essential in order to discover new treatments. Hyperglycemia is the main cause of the cellular damage seen in DKD. But, exactly how hyperglycemia leads to the activation of processes that are ultimately deleterious is incompletely understood.

RECENT FINDINGS

Studies primarily over the past 10 years have provided novel insights into the interplay of hyperglycemia, glucose metabolic pathways, mitochondrial function, and the potential importance of what has been called the Warburg effect on the development and progression of DKD. This review will provide a brief overview of glucose metabolism and the hypotheses concerning the pathogenesis of DKD and then discuss in more detail the supporting data that indicate a role for the interplay of glucose metabolic pathways and mitochondrial function.

The Role of Thioredoxin/Peroxiredoxin in the β-Cell Defense Against Oxidative Damage

Oxidative stress is hypothesized to play a role in pancreatic β-cell damage, potentially contributing to β-cell dysfunction and death in both type 1 and type 2 diabetes. Oxidative stress arises when naturally occurring reactive oxygen species (ROS) are produced at levels that overwhelm the antioxidant capacity of the cell. ROS, including superoxide and hydrogen peroxide, are primarily produced by electron leak during mitochondrial oxidative metabolism. Additionally, peroxynitrite, an oxidant generated by the reaction of superoxide and nitric oxide, may also cause β-cell damage during autoimmune destruction of these cells. β-cells are thought to be susceptible to oxidative damage based on reports that they express low levels of antioxidant enzymes compared to other tissues. Furthermore, markers of oxidative damage are observed in islets from diabetic rodent models and human patients. However, recent studies have demonstrated high expression of various isoforms of peroxiredoxins, thioredoxin, and thioredoxin reductase in β-cells and have provided experimental evidence supporting a role for these enzymes in promoting β-cell function and survival in response to a variety of oxidative stressors. This mini-review will focus on the mechanism by which thioredoxins and peroxiredoxins detoxify ROS and on the protective roles of these enzymes in β-cells. Additionally, we speculate about the role of this antioxidant system in promoting insulin secretion.

Flavonoids in the Treatment of Diabetes: Clinical Outcomes and Mechanism to Ameliorate Blood Glucose Levels

BACKGROUND

For thousands of years, natural food products have been used as a medicine for treating diseases that affect the human body, including diabetes mellitus (DM). Lately, several investigations have been performed on the flavonoid derivatives of plant origin, and their biological activity has been extensively studied.

METHODS

Given our need to know more mechanisms for treating DM, we performed a thorough research review on treating diabetes mellitus based on flavonoids, their therapeutic potential, and biological action.

RESULTS

Flavonoids reduce complications in addition to their vital role as effective supplements for preventing diabetes mellitus by regulating glucose metabolism, lipid profile, liver enzyme activity, a protein kinase inhibitor, PPAR, and AMPK with NF-κB.

CONCLUSION

The articles that we reviewed showed the positive role of flavonoids, which in a certain way reduce diabetes, but their side effects still need to be studied further.This review is focused on describing the different types of dietary flavonoids along with their mechanisms of reducing blood glucose and enhancing insulin sensitivity, as well as their side effects.

The Impact of Diabetes Mellitus in COVID-19: A Mechanistic Review of Molecular Interactions

The ongoing pandemic of COVID-19 is now the major issue in global health. Evidence implies that patients with diabetes are at a higher risk of severe disease or death due to COVID-19 than individuals without diabetes. However, the underlying mechanism for this differential effect in individuals with and without diabetes is not clearly understood. We have reviewed the pathophysiological pathways which may facilitate the entry of virus or an increase in its infectivity in host cells in the diabetic milieu. We suggest that the preexisting pathological pathways in patients with poorly controlled diabetes increase the risk of infectivity and are responsible for the higher levels of tissue injury and death in patients with diabetes.

Identification and characterization of anti-diabetic principle in Senna alata (Linn.) flower using alloxan-induced diabetic male Wistar rats

ETHNO-PHARMACOLOGICAL RELEVANCE

The age-long folkloric use of Senna alata flower (SAF) was recently substantiated with scientific evidence. However, the study did not account for the anti-diabetic principle(s) in SAF.

AIM OF THE STUDY

The study aimed to identify and characterize the bioactive principle(s) responsible for the anti-diabetic activity in SAF.

MATERIALS AND METHODS

Ninety-one male Wistar rats were used for the two phases of this study. In phase 1, forty-two of these were allotted into six groups (A-F) of seven rats each. Animals in group A received distilled water while those in groups B-F were made diabetic by treatment with 150 mg/kg body weight (b.w.) of alloxan. Group B received 0.5 mL of distilled water; C, D and E were treated each with 75 mg/kg b.w. of ethyl acetate, n-butanol and aqueous residual fractions of SAF, while F received 2.5 mg/kg b.w. of glibenclamide. In the second phase, forty-nine rats were assigned into seven groups (A-G) of seven rats each. Group A received distilled water. Animals in Groups B-G were also made diabetic by alloxan treatment. B received 0.5 mL of distilled water; C, D, E and F were treated with 5.77, 25.96, 15.40, 27.87 mg/kg b.w (equivalent dose of 75 mg/kg b.w.) of sub-fractions obtained from the ethyl acetate fraction of SAF respectively whereas G received 2.5 mg/kg b.w. of glibenclamide. Fasting blood glucose (FBG), serum lipids, albumin, globulin, liver glycogen, urine ketone, hexokinase and glucose-6-phosphate dehydrogenase activities, α-glucosidase and α-amylase inhibitory activities and cardiac function indices were evaluated using standard methods. Compounds D, E and F isolated from ethyl acetate sub-fraction B were evaluated for in vitro anti-diabetic activity. The structure of the anti-diabetic compound was identified using FTIR, ¹H-NMR, ¹³C-NMR, HCOSY, HSQC and HMBC. Data were subjected to Analysis of Variance and Duncan Multiple Range Test at p < 0.05.

RESULTS

Alloxan treatment increased the levels of FBG, total cholesterol, LDL-cholesterol, VLDL-cholesterol, urine ketone and cardiac function indices and reduced the levels of globulin, albumin, HDL-cholesterol, globulin, liver glycogen, hexokinase and glucose-6-phosphate dehydrogenase activities. Ethyl acetate fraction and sub-fraction B reversed the level and/or activities of these biochemical indices to levels and/or activities that compared favourably with the distilled water treated non-diabetic animals. Of the three compounds (D, E and F) that were obtained from the sub-fraction B, compound E which was Emodin (1, 3, 8-trihydroxy-6-methylanthraquinone) produced the highest α-glucosidase and α-amylase inhibitory activities.

CONCLUSION

Emodin is one of the bioactive constituents present in Senna alata flower.

Centrality of G6PD in COVID-19: The Biochemical Rationale and Clinical Implications

Introduction: COVID-19 is a novel and devastating disease. Its manifestations vary from asymptomatic to lethal. Moreover, mortality rates differ based on underlying health conditions and ethnicity. We investigated the biochemical rationale behind these observations using machine reasoning by the sci.AI system (https://sci.ai/). Facts were extracted and linked from publications available in nlm.nih.gov and Europe PMC to form the dataset which was validated by medical experts. Results: Based on the analysis of experimental and clinical data, we synthesized detailed biochemical pathways of COVID-19 pathogenesis which were used to explain epidemiological and clinical observations. Clinical manifestations and biomarkers are highlighted to monitor the course of COVID-19 and navigate treatment. As depicted in the Graphical Abstract, SARS-CoV-2 triggers a pro-oxidant (PO) response leading to the production of reactive oxygen species (ROS) as a normal innate defense. However, SARS-CoV-2's unique interference with the antioxidant (AO) system, through suppression of nitric oxide (NO) production in the renin- angiotensin-aldosterone system (RAAS), leads to an excessive inflammatory PO response. The excessive PO response becomes critical in cohorts with a compromised AO system such as patients with glucose-6-phosphate dehydrogenase deficiency (G6PDd) where NO and glutathione (GSH) mechanisms are impaired. G6PDd develops in patients with metabolic syndrome. It is mediated by aldosterone (Ald) which also increases specifically in COVID-19. Conclusion: G6PD is essential for an adequate immune response. Both G6PDd and SARS-CoV-2 compromise the AO system through the same pathways rendering G6PDd the Achilles' heel for COVID-19. Thus, the evolutionary antimalarial advantage of the G6PDd cohort can be a disadvantage against SARS-CoV-2.

A proteoglycan extract from Ganoderma Lucidum protects pancreatic beta-cells against STZ-induced apoptosis

The pancreatic β-cell death or dysfunction induced by oxidative stress plays an important effect on the development and progression of diabetes mellitus. Based on our previous findings, a natural proteoglycan extracted from Ganoderma Lucidum, named FYGL, could treat T2DM in vivo. In this study, we investigated the effects of FYGL on STZ-induced apoptosis of INS-1 cells and its underlying mechanisms. The results showed that FYGL significantly improved the cell viability and alleviated the apoptosis in STZ-treated INS-1 cells. Moreover, FYGL markedly decreased the intracellular ROS accumulation and NO release, and deactivated NF-κB, JNK, and p38 MAPK signaling pathways in STZ-induced INS-1 cells. Furthermore, FYGL improved the insulin secretion through inhibiting the activation of JNK and improving the expression of Pdx-1 in INS-1 cells damaged by STZ. These results indicated that FYGL could protect pancreatic β-cells against apoptosis and dysfunction, and be used as a promising pharmacological medicine for diabetes management. Abbreviations: T2DM: type 2 diabetes mellitus; FYGL: Fudan-Yueyang G. lucidum; ROS: reactive oxygen species; NO: reactive oxygen species; NF-κB: nuclear factor kappa beta; JNK: c-jun N-terminal kinase; MAPK: mitogen-activated protein kinase; Pdx-1: Pancreatic duodenal homeobox 1.

A Comparative Transcriptomics Approach to Analyzing the Differences in Cold Resistance in Pomacea canaliculata between Guangdong and Hunan

Pomacea canaliculata, known as an invasive freshwater snail, is also called a golden apple snail; its survival and expansion are greatly affected by temperature. In this study, high-throughput sequencing (RNA-seq) was used to perform comparative transcriptome analysis on the muscular tissue (G_M) of snails in Guangdong and Hunan. Differential gene screening was performed with FDR <0.05 and |log2FoldChange| >1 as the threshold, and a total of 1,368 differential genes were obtained (671 genes showed upregulation in snails from Guangdong, and 697 genes displayed upregulation in snails from Hunan). Fifteen genes were identified as candidate genes for the cold hardiness of Pomacea canaliculata. Among them, three genes were involved in energy metabolism (glycogen synthase, 1; DGK, 1; G6PD, 1); seven genes were involved in homeostasis regulation (HSP70, 2; BIP, 1; GPX, 1; GSTO 1, G6PD, 1; caspase-9, 1); two genes were involved in amino acid metabolism (glutamine synthetase, 1; PDK, 1); and four genes were involved in membrane metabolism (inositol-3-phosphate synthase, 1; Na⁺/K⁺-ATPase, 1; calcium-binding protein, 2). This study presents the molecular mechanisms for the cold hardiness of Pomacea canaliculata, which could provide a scientific basis for the forecast and prevention of harm from Pomacea canaliculata.

Harmful effects of high amounts of glucose on the immune system: An updated review

Release and storage of energy can be regulated by the metabolic parameter dependent on the central nervous system. Macrophages are one of the most professional antigen-presenting cells that are formed by the accumulation of dead or damaged cells or in response to the infection, which has the main function of phagocytosis, secretion of cytokines, and presenting antigen to T cells. A proper immune response is needed for the production of effector cytokines along with comprehensive and rapid cell proliferation and growth. Activation of the immune system and immune cells is needed to increase glucose metabolism. When the immune system responds to pathogens, chemokines inform immune cells such as macrophages and T cells to travel to the infected area. Although glucose is vital for the proper function of immune cells and their proliferation, a high amount of glucose may lead to impaired function of the immune system and pathological conditions. However, a suitable amount of glucose is indispensable for the immune system, but its elevated amount leads to excessive proinflammatory cytokines production. In this study, we focused on the master regulatory role of glucose on the immune system.

Reactive Oxygen Species, Metabolic Plasticity, and Drug Resistance in Cancer

The metabolic abnormality observed in tumors is characterized by the dependence of cancer cells on glycolysis for their energy requirements. Cancer cells also exhibit a high level of reactive oxygen species (ROS), largely due to the alteration of cellular bioenergetics. A highly coordinated interplay between tumor energetics and ROS generates a powerful phenotype that provides the tumor cells with proliferative, antiapoptotic, and overall aggressive characteristics. In this review article, we summarize the literature on how ROS impacts energy metabolism by regulating key metabolic enzymes and how metabolic pathways e.g., glycolysis, PPP, and the TCA cycle reciprocally affect the generation and maintenance of ROS homeostasis. Lastly, we discuss how metabolic adaptation in cancer influences the tumor’s response to chemotherapeutic drugs. Though attempts of targeting tumor energetics have shown promising preclinical outcomes, the clinical benefits are yet to be fully achieved. A better understanding of the interaction between metabolic abnormalities and involvement of ROS under the chemo-induced stress will help develop new strategies and personalized approaches to improve the therapeutic efficiency in cancer patients.

Mitigation of Glucolipotoxicity-Induced Apoptosis, Mitochondrial Dysfunction, and Metabolic Stress by N-Acetyl Cysteine in Pancreatic β-Cells

Glucolipotoxicity caused by hyperglycemia and hyperlipidemia are the common features of diabetes-induced complications. Metabolic adaptation, particularly in energy metabolism; mitochondrial dysfunction; and increased inflammatory and oxidative stress responses are considered to be the main characteristics of diabetes and metabolic syndrome. However, due to various fluctuating endogenous and exogenous stimuli, the precise role of these factors under in vivo conditions is not clearly understood. In the present study, we used pancreatic β-cells, Rin-5F, to elucidate the molecular and metabolic changes in glucolipotoxicity. Cells treated with high glucose (25 mM) and high palmitic acid (up to 0.3 mM) for 24 h exhibited increased caspase/poly-ADP ribose polymerase (PARP)-dependent apoptosis followed by DNA fragmentation, alterations in mitochondrial membrane permeability, and bioenergetics, accompanied by alterations in glycolytic and mitochondrial energy metabolism. Our results also demonstrated alterations in the expression of mammalian target of rapamycin (mTOR)/5′ adenosine monophosphate-activated protein kinase (AMPK)-dependent apoptotic and autophagy markers. Furthermore, pre-treatment of cells with 10 mM N-acetyl cysteine attenuated the deleterious effects of high glucose and high palmitic acid with improved cellular functions and survival. These results suggest that the presence of high energy metabolites enhance mitochondrial dysfunction and apoptosis by suppressing autophagy and adapting energy metabolism, mediated, at least in part, via enhanced oxidative DNA damage and mTOR/AMPK-dependent cell signaling.

The Role of the Pentose Phosphate Pathway in Diabetes and Cancer

The pentose phosphate pathway (PPP) branches from glucose 6-phosphate (G6P), produces NADPH and ribose 5-phosphate (R5P), and shunts carbons back to the glycolytic or gluconeogenic pathway. The PPP has been demonstrated to be a major regulator for cellular reduction-oxidation (redox) homeostasis and biosynthesis. Enzymes in the PPP are reported to play important roles in many human diseases. In this review, we will discuss the role of the PPP in type 2 diabetes and cancer.

Erythrocyte glucose-6-phosphate dehydrogenase activity and risk of gestational diabetes

Purpose

Glucose-6-phosphate dehydrogenase (G6PD) is the regulating enzyme in the pentose phosphate pathway. A link between the activity of G6PD and diabetes mellitus has previously been reported. The association of G6PD activity with the pathogenesis of gestational diabetes mellitus (GDM) has not yet been investigated. The aim of the present study was to investigate the association of erythrocyte G6PD activity with major characteristics of GDM.

Methods

This case-control study was conducted at Hafez Hospital, Shiraz University of Medical Sciences, Shiraz, Iran from March to November 2017. Eighty-four age-matched pregnant women including GDM (n = 33), impaired glucose tolerance (IGT; n = 7), and normal glucose tolerance (NGT; n = 44) subjects were enrolled in this study. The levels of erythrocyte G6PD activity, fasting plasma glucose (FPG), insulin, malondialdehyde (MDA), and ferric reducing power (FRAP) of serum were measured. The level of homeostasis model for the assessment of insulin resistance (HOMA-IR) was calculated. The data were analyzed using SPSS software. P < 0.05 was considered statistically significant.

Results

The values of FPG, insulin, HOMA-IR, G6PD activity, and FRAP were significantly higher in GDM patients compared to NGT subjects. G6PD activity was correlated with FPG ((r = 0.224; P = 0.041). Binary logistic regression analysis revealed independent association of body mass index >25.88 [OR = 3.23, 95% CI 1.071-9.75, P = 0.037], HOMA- IR >2.33 [OR = 7.15, 95% CI 2.26-22.56, P < 0.001], and G6PD activity>21.17 U/g Hb [OR = 4.63, 95% CI 1.49-14.38, P = 0.008] with an increased risk of GDM. No significant change was observed among serum MDA levels in the three groups.

Conclusion

The findings demonstrate that increased G6PD activity is positively associated with the risk of GDM.

Where Metabolism Meets Senescence: Focus on Endothelial Cells

Despite the decline in their proliferative potential, senescent cells display a high metabolic activity. Senescent cells have been shown to acquire a more glycolytic state even in presence of high oxygen levels, in a way similar to cancer cells. The diversion of pyruvate, the final product of glycolysis, away from oxidative phosphorylation results in an altered bioenergetic state and may occur as a response to the enhanced oxidative stress caused by the accumulation of dysfunctional mitochondria. This metabolic shift leads to increased AMP/ATP and ADP/ATP ratios, to the subsequent AMPK activation, and ultimately to p53-mediated growth arrest. Mounting evidences suggest that metabolic reprogramming is critical to direct considerable amounts of energy toward specific activities related to the senescent state, including the senescence-associated secretory phenotype (SASP) and the modulation of immune responses within senescent cell tissue microenvironment. Interestingly, despite the relative abundance of oxygen in the vascular compartment, healthy endothelial cells (ECs) produce most of their ATP content from the anaerobic conversion of glucose to lactate. Their high glycolytic rate further increases during senescence. Alterations in EC metabolism have been identified in age-related diseases (ARDs) associated with a dysfunctional vasculature, including atherosclerosis, type 2 diabetes and cardiovascular diseases. In particular, higher production of reactive oxygen species deriving from a variety of enzymatic sources, including uncoupled endothelial nitric oxide synthase and the electron transport chain, causes DNA damage and activates the NAD+-consuming enzymes polyADP-ribose polymerase 1 (PARP1). These non-physiological mechanisms drive the impairment of the glycolytic flux and the diversion of glycolytic intermediates into many pathological pathways. Of note, accumulation of senescent ECs has been reported in the context of ARDs. Through their pro-oxidant, pro-inflammatory, vasoconstrictor, and prothrombotic activities, they negatively impact on vascular physiology, promoting both the onset and development of ARDs. Here, we review the current knowledge on the cellular senescence-related metabolic changes and their contribution to the mechanisms underlying the pathogenesis of ARDs, with a particular focus on ECs. Moreover, current and potential interventions aimed at modulating EC metabolism, in order to prevent or delay ARD onset, will be discussed.