Glucose 6-phosphate dehydrogenase and the kidney

Cell type-specific regulation of the pentose phosphate pathway during development and metabolic stress-driven autoimmune diseases: Relevance for inflammatory liver, renal, endocrine, cardiovascular and neurobehavioral comorbidities, carcinogenesis, and aging

The pathogenesis of autoimmunity is incompletely understood which limits the development of effective therapies. New compelling evidence indicates that the pentose phosphate pathway (PPP) profoundly regulate lineage development in the immune system that are influenced by genetic and environmental factors during metabolic stress underlying the development of autoimmunity. The PPP provides two unique metabolites, ribose 5-phosphate for nucleotide biosynthesis in support of cell proliferation and NADPH for protection against oxidative stress. The PPP operates two separate branches, oxidative (OxPPP) and non-oxidative (NOxPPP). While the OxPPP functions in all organisms, the NOxPPP reflects adaptation to niche-specific metabolic requirements. The OxPPP primarily depends on glucose 6-phosphate dehydrogenase (G6PD), whereas transaldolase (TAL) controls the rate and directionality of metabolic flux though the NOxPPP. G6PD is essential for normal development but its partial deficiency protects from malaria. Although men and mice lacking TAL develop normally, they exhibit liver cirrhosis progressing to hepatocellular carcinoma. Mechanistic target of rapamycin-dependent loss of paraoxonase 1 drives autoimmunity and cirrhosis in TAL deficiency, while hepatocarcinogenesis hinges on polyol pathway activation via aldose reductase (AR). Accumulated polyols, such as erythritol, xylitol, and sorbitol, which are commonly used as non-caloric sweeteners, may act as pro-inflammatory oncometabolites under metabolic stress, such as TAL deficiency. The TAL/AR axis is identified as a checkpoint of pathogenesis and target for treatment of metabolic stress-driven systemic autoimmunity with relevance for inflammatory liver, renal and cardiovascular disorders, diabetes, carcinogenesis, and aging.

In defence of ferroptosis

Rampant phospholipid peroxidation initiated by iron causes ferroptosis unless this is restrained by cellular defences. Ferroptosis is increasingly implicated in a host of diseases, and unlike other cell death programs the physiological initiation of ferroptosis is conceived to occur not by an endogenous executioner, but by the withdrawal of cellular guardians that otherwise constantly oppose ferroptosis induction. Here, we profile key ferroptotic defence strategies including iron regulation, phospholipid modulation and enzymes and metabolite systems: glutathione reductase (GR), Ferroptosis suppressor protein 1 (FSP1), NAD(P)H Quinone Dehydrogenase 1 (NQO1), Dihydrofolate reductase (DHFR), retinal reductases and retinal dehydrogenases (RDH) and thioredoxin reductases (TR). A common thread uniting all key enzymes and metabolites that combat lipid peroxidation during ferroptosis is a dependence on a key cellular reductant, nicotinamide adenine dinucleotide phosphate (NADPH). We will outline how cells control central carbon metabolism to produce NADPH and necessary precursors to defend against ferroptosis. Subsequently we will discuss evidence for ferroptosis and NADPH dysregulation in different disease contexts including glucose-6-phosphate dehydrogenase deficiency, cancer and neurodegeneration. Finally, we discuss several anti-ferroptosis therapeutic strategies spanning the use of radical trapping agents, iron modulation and glutathione dependent redox support and highlight the current landscape of clinical trials focusing on ferroptosis.

Alterations of urine microRNA-7977/G6PD level in patients with diabetic kidney disease and its association with dysfunction of albumin-induced autophagy in proximal epithelial tubular cells

Diabetic kidney disease (DKD) remains as one of the leading long-term complications of type 2 diabetic mellitus (T2DM). Studies have shown that decreased expression of glucose-6-phosphate dehydrogenase (G6PD) plays an important role in DKD. However, the upstream and downstream pathways of G6PD downregulation leading to DKD have not been elucidated. We conducted a series of studies including clinical study, animal studies, and in vitro studies to explore this. First, a total of 90 subjects were evaluated including 30 healthy subjects, 30 patients with T2DM, and 30 patients with DKD. The urinary G6PD activity and its association with the clinical markers were analyzed. Multivariate linear regression analysis was used to analyze the risk factors of urinary G6PD in these patients. Then, microRNAs that were differentially expressed in urine and could bind and degrade G6PD were screened and verified in patients with DKD. After that, high glucose (HG)-cultured human kidney cells (HK-2) and Zucker diabetic fatty (ZDF) rats were used to test the roles of miR-7977/G6PD/albumin-induced autophagy in DKD. Beclin and P62 were used as markers of kidney autophagy indicators. A dual-luciferase reporter assay system was used to test the binding of G6PD by mir-7977. The plasma and urinary G6PD activity were decreased significantly in patients with DKD, accompanied by increased urinary mir-7977 level. The fasting plasma glucose (FPG), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and urinary albumin excretion were independent predictors of urinary G6PD activity, according to multiple linear regression analysis. The increased expression of miR-7977 and decreased expression of G6PD were also found in the kidney of ZDF rats with early renal tubular damage. The correlation analysis showed that beclin protein expression levels were positively correlated with kidney G6PD activity, whereas P62 protein expression was negatively correlated with kidney G6PD activity in rats. In HK-2 cells cultured with normal situation, a low level of albumin could induce autophagy along with the stimulation of G6PD, although this was impaired under high glucose. Overexpression of G6PD reversed albumin-induced autophagy in HK-2 cells under high glucose. Further study revealed that G6PD was a downstream target of miR-7977. Inhibition of miR-7977 expression led to significantly increased expression of G6PD and reversed the effects of high glucose on albumin-induced autophagy. In conclusion, our study supports a new mechanism of G6PD downregulation in DKD. Therapeutic measures targeting the miR-7977/G6PD/autophagy signaling pathway may help in the prevention and treatment of DKD.NEW & NOTEWORTHY This study provides new evidence that reduced glucose-6-phosphate dehydrogenase (G6PD) may damage the endocytosis of renal tubular epithelial cells by reducing albumin-induced autophagy. More importantly, for the first time, our study has provided evidence from humans that the decrease in urinary G6PD activity is positively associated with renal injury, and abnormal glucose and lipid metabolism may be important reasons for reduced G6PD levels. Increased miR-7977 may at least in part explain the downregulation of G6PD.

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.

Identification of a venetoclax-resistance prognostic signature base on 6-senescence genes and its clinical significance for acute myeloid leukemia

Background

Satisfactory responses can be obtained for acute myeloid leukemia (AML) treated by Venetoclax (VEN)-based therapy. However, there are still quite a few AML patients (AMLs) resistant to VEN, and it is critical to understand whether VEN-resistance is regulated by senescence.

Methods

Here, we established and validated a signature for predicting AML prognosis based on VEN resistance-related senescence genes (VRSGs). In this study, 51 senescence genes were identified with VEN-resistance in AML. Using LASSO algorithms and multiple AML cohorts, a VEN-resistance senescence prognostic model (VRSP-M) was developed and validated based on 6-senescence genes.

Results

According to the median score of the signature, AMLs were classified into two subtypes. A worse prognosis and more adverse features occurred in the high-risk subtype, including older patients, non-de novo AML, poor cytogenetics, adverse risk of European LeukemiaNet (ELN) 2017 recommendation, and TP53 mutation. Patients in the high-risk subtype were mainly involved in monocyte differentiation, senescence, NADPH oxidases, and PD1 signaling pathway. The model's risk score was significantly associated with VEN-resistance, immune features, and immunotherapy response in AML. In vitro, the IC50 values of ABT-199 (VEN) rose progressively with increasing expression of G6PD and BAG3 in AML cell lines.

Conclusions

The 6-senescence genes prognostic model has significant meaning for the prediction of VEN-resistance, guiding personalized molecularly targeted therapies, and improving AML prognosis.

Clinical challenges in the treatment of a patient with decompensated heart failure and glucose-6-phosphate dehydrogenase deficiency (G6PDd)

We present a case of a man in his 60s, known with glucose-6-phosphate dehydrogenase deficiency (G6PDd) and cor pulmonale, admitted to the department of cardiology due to cardiac decompensation and anaemia. The main complaint was dyspnoea. Echocardiography confirmed severe cor pulmonale with compression of the left ventricle. G6PDd has been linked with pulmonary hypertension which could contribute to aforementioned echocardiographic findings. Diuretics are the first line of treatment when it comes to cardiac decompensation, but sulfonamide diuretics can induce or exacerbate haemolysis in patients with G6PDd. Due to the respiratory distress of the patient, a treatment plan including sulfonamide diuretics was initiated in collaboration with the haematologists. Unfortunately, the patient died 2 days after admission. This case emphasises that not all cardiac patients can tolerate standard treatment with sulfonamide diuretics; despite this, they remain essential in the acute setting, and they are associated with foreseeable but only partly manageable complications in susceptible patients.

The pentose phosphate pathway in health and disease

The pentose phosphate pathway (PPP) is a glucose-oxidizing pathway that runs in parallel to upper glycolysis to produce ribose 5-phosphate and nicotinamide adenine dinucleotide phosphate (NADPH). Ribose 5-phosphate is used for nucleotide synthesis, while NADPH is involved in redox homoeostasis as well as in promoting biosynthetic processes, such as the synthesis of tetrahydrofolate, deoxyribonucleotides, proline, fatty acids and cholesterol. Through NADPH, the PPP plays a critical role in suppressing oxidative stress, including in certain cancers, in which PPP inhibition may be therapeutically useful. Conversely, PPP-derived NADPH also supports purposeful cellular generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) for signalling and pathogen killing. Genetic deficiencies in the PPP occur relatively commonly in the committed pathway enzyme glucose-6-phosphate dehydrogenase (G6PD). G6PD deficiency typically manifests as haemolytic anaemia due to red cell oxidative damage but, in severe cases, also results in infections due to lack of leucocyte oxidative burst, highlighting the dual redox roles of the pathway in free radical production and detoxification. This Review discusses the PPP in mammals, covering its roles in biochemistry, physiology and disease.

Metabolic Responses of Normal Rat Kidneys to a High Salt Intake

In this study, novel methods were developed, which allowed continuous (24/7) measurement of arterial blood pressure and renal blood flow in freely moving rats and the intermittent collection of arterial and renal venous blood to estimate kidney metabolic fluxes of O2 and metabolites. Specifically, the study determined the effects of a high salt (HS; 4.0% NaCl) diet upon whole kidney O2 consumption and arterial and renal venous plasma metabolomic profiles of normal Sprague-Dawley rats. A separate group of rats was studied to determine changes in the cortex and outer medulla tissue metabolomic and mRNAseq profiles before and following the switch from a 0.4% to 4.0% NaCl diet. In addition, targeted mRNA expression analysis of cortical segments was performed. Significant changes in the metabolomic and transcriptomic profiles occurred with feeding of the HS diet. A progressive increase of kidney O2 consumption was found despite a reduction in expression of most of the mRNA encoding enzymes of TCA cycle. A novel finding was the increased expression of glycolysis-related genes in Cx and isolated proximal tubular segments in response to an HS diet, consistent with increased release of pyruvate and lactate from the kidney to the renal venous blood. Data suggests that aerobic glycolysis (eg, Warburg effect) may contribute to energy production under these circumstances. The study provides evidence that kidney metabolism responds to an HS diet enabling enhanced energy production while protecting from oxidative stress and injury. Metabolomic and transcriptomic analysis of kidneys of Sprague-Dawley rats fed a high salt diet.

Anti-Alzheimer, antioxidants, glucose-6-phosphate dehydrogenase effects of Taverniera glabra mediated ZnO and Fe2O3 nanoparticles in alloxan-induced diabetic rats

The current study aimed to assess the neuroprotective effect of Zn and Fe oxide nanoparticles biofabricated by Taverniera glabra in alloxan-induced diabetic rats. The experimental animals (160–200 g) were divided into nine groups (n = 9). The blood glucose, body weight, glucose-6-phosphate dehydrogenase (G6PD), superoxide dismutase (SOD), catalase test (CAT), lipid peroxidation (TBARS), glutathione (GSH), and acetylcholinesterase (AChE) activities were determined. Oral administration of nanoparticles and T. glabra methanol extract (TGME; 10 and 15 mg/kg b.w) significantly decreased the glucose level, increased the body weight, controlled the quantitative level of G6PD, and significantly decreased the levels of ALT, ALP, cholesterol, and creatinine. Moreover, TGME and their Zn and Fe oxide nanoparticles significantly restored the antioxidant enzymes (SOD, CAT, GPx, and GSH) that decreased during induced diabetes. In the diabetic group, a significant increase in TBARS was noted and recovered in diabetic animals (p < 0.05) as compared to glibenclamide. The AChE activity was significantly recovered by nanoparticles and TGME both in the blood and brain of the diabetic group (p < 0.05). Taken together, it can be suggested that TGME and Zn and Fe oxide nanoparticles significantly improved memory and could be considered as an effective biogenic nanomaterial for diabetes, Alzheimer’s disease, and oxidative stress.

Metabolic responses of normal rat kidneys to a high salt intake

In the present study, novel methods were developed which allowed continuous (24/7) measurement of blood pressure (BP) and renal blood flow (RBF) in freely moving rats and the intermittent collection of arterial and renal venous blood to estimate kidney metabolic fluxes of O 2 and metabolites. The study determined the effects of a high salt (HS) diet upon whole kidney O 2 consumption and the metabolomic profiles of normal Sprague Dawley (SD) rats. A separate group of rats was studied to determine changes in the cortex (Cx) and outer medulla (OM) tissue metabolomic and mRNAseq profiles before and following the switch from a 0.4% to a 4.0% NaCl diet. Significant changes in the metabolomic and transcriptomic profiles occurred with feeding of the HS diet. A progressive increase of kidney O 2 consumption was found despite a reduction in expression of most of the mRNA encoding enzymes of TCA cycle. Increased glycolysis was evident with the elevation of mRNA expression encoding key glycolytic enzymes and release of pyruvate and lactate from the kidney in the renal venous blood. Glycolytic production of NADH is used in either the production of lactate or oxidized via the malate aspartate shuttle. Aerobic glycolysis (e.g., Warburg-effect) may account for the needed increase in cellular energy. The study provides evidence that kidney metabolism responds to a HS diet enabling enhanced energy production while protecting from oxidate stress and injury.

Clinical outcomes and performance indicators of patients with kidney failure and acute kidney injuries in ASEAN countries

INTRODUCTION

This review article reports clinical outcomes and performance indicators of patients with kidney failure (KF) and acute kidney injuries (AKI) in Association of South East Asian Nations (ASEAN) countries.

METHODOLOGY

Association of South East Asian Nations data, segregated by income status, from national registries and literature were collated, compared and benchmarked against international references.

RESULTS

The national incidence and prevalence of treated KF ranged from 172 to 479 per million population (pmp) and 36-2255 pmp, respectively. Brunei (79%), Malaysia (66%) and Singapore (66%) had world-leading proportions of diabetes-related KF. Hemodialysis (HD), Peritoneal Dialysis (PD) and transplant accounted for 68-100%, 0-27% and 0-18% of all KF replacement therapy, respectively. Transplant patient survival was superior with 90%-93% at 5 years and 71%-90% at 10 years, compared to PD (44%-54%) and HD (53-64%) at 5 years. Higher-income countries were able to achieve good anemia control, HD and PD adequacy targets, while usage of arteriovenous fistula in HD varied from 70% to 85%. Acute Kidney Injury rates ranged from 24.2% to 49.2% of high-dependency admissions. Lower incidences of PD peritonitis and HD catheter-related Bloodstream Infections; and PD-favouring quality-of-life were evident in higher-income countries.

CONCLUSION

Association of South East Asian Nations has a challenging burden of kidney disease, with extremely high incidence, prevalence, DM-related KF and AKI rates. The magnitude of the prevailing problem calls for the creation of a regional society under the auspices of ASEAN with a shared perspective of universal, equitable and charitable access to quality renal care; consistent with the founding premises and healthcare initiatives of ASEAN.

mTORC1 activation induced proximal tubular damage via the pentose phosphate pathway in lupus nephritis

More recent studies suggested that metabolic disorders could contribute to the pathogenesis of systemic lupus erythematosus (SLE) and lupus nephritis (LN). The present work aimed at identifying metabolic reprogramming in the kidney of lupus nephritis via proteomics and investigating the potential regulatory mechanism. The proteomic studies on the renal biopsies revealed that the pentose phosphate pathway (PPP) was significantly enriched in the kidneys of LN patients compared with normal controls (NCs). Immunohistochemical stanning of glucose-6-phosphate dehydrogenase (G6PD), the key rate-limiting enzyme of PPP, verify the results of proteomics. We found that G6PD was highly expressed in the kidneys of LN patients and correlated with several clinicopathological indices. The univariate Cox regression analysis (HR, 95%CI, 1.877 (1.059-3.328), P = 0.031) and Kaplan-Meier (KM) analysis (P = 0.028) suggested that high G6PD expression in the tubulointerstitial area was a risk factor for worse prognosis. Moreover, the Gene set enrichment analysis (GSEA) demonstrated that the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway ranked first in the kidneys of LN patients with high G6PD expression and G6PD was co-localized with mTORC1 activation in the tubule. Immunoglobulin G (IgG) isolated from LN patients significantly activated the mTORC1 pathway and increased G6PD expression, G6PD activity, NADPH production, NADPH oxidase 2 (NOX2) expression, reactive oxygen species (ROS) production, and cell apoptosis in tubule cells in vitro. The above phenotypes were partially rescued after the addition of rapamycin or knock-down of G6PD. Overall, our study suggested that renal G6PD expression was associated with the overall enhanced disease activity and worse renal prognosis. mTORC1 activation might be involved in IgG-LN-induced tubular damage via PPP.

The Multiple Roles of Glucose-6-Phosphate Dehydrogenase in Tumorigenesis and Cancer Chemoresistance

The pentose phosphate pathway (PPP) is a branch from glycolysis that begins from glucose-6-phosphate (G6P) and ends up with fructose-6-phosphate (F6P) and glyceraldehyde-3-phosphate (GADP). Its primary physiological significance is to provide nicotinamide adenine dinucleotide phosphate (NADPH) and nucleotides for vital activities such as reactive oxygen species (ROS) defense and DNA synthesis. Glucose-6-phosphate dehydrogenase (G6PD) is a housekeeping protein with 514 amino acids that is also the rate-limiting enzyme of PPP, catalyzing G6P into 6-phosphogluconolactone (6PGL) and producing the first NADPH of this pathway. Increasing evidence indicates that G6PD is upregulated in diverse cancers, and this dysfunction influences DNA synthesis, DNA repair, cell cycle regulation and redox homeostasis, which provides advantageous conditions for cancer cell growth, epithelial-mesenchymal transition (EMT), invasion, metastasis and chemoresistance. Thus, targeting G6PD by inhibitors has been shown as a promising strategy in treating cancer and reversing chemotherapeutic resistance. In this review, we will summarize the existing knowledge concerning G6PD and discuss its role, regulation and inhibitors in cancer development and chemotherapy resistance.

Biomarkers of Glyco-Metabolic Control in Hemodialysis Patients: Glycated Hemoglobin vs. Glycated Albumin

Background and Objectives: Glycated hemoglobin (HbA1c) dosage is considered the gold standard in glycol-metabolic monitoring, but it presents limits, which can underestimate the glycemia trend. In this regard, it was introduced the glycated albumin (GA). The aim of the study is to verify the predictivity of the GA compared to HbA1c in identifying glyco-metabolic alterations in non-diabetic and diabetic hemodialysis (HD) patients. Materials and Methods: For this purpose, we conducted a multicenter study involving one analysis laboratory and six dialysis centers in the Lazio region (Rome, Italy). Both diabetic and non-diabetic HD patients represent the study population, and the protocol included five time points. Results: The analyzed data highlighted the ability of GA to predict changes in glycemic metabolism in HD patients, and GA values are not significantly influenced, like HbA1c, by dialysis therapy itself and by comorbidities of the uremic state, such as normochromic and normocytic anemia. Thus, GA seems to reflect early glyco-metabolic alterations, both in patients with a previous diagnosis of diabetes and in subjects without diabetes mellitus. As part of this study, we analyzed two HD patients (one diabetic and one non-diabetic) in which GA was more predictive of glycol-metabolic alterations compared to HbA1c. Our study confirms the need to compare classical biomarkers used for the monitoring of glyco-metabolic alterations with new ones, likely more reliable and effective in specific subgroups of patients in which the classic biomarkers can be influenced by the preexisting pathological conditions. Conclusions: In conclusion, our evidence highlights that in uremic patients, GA shows a better ability to predict glyco-metabolic alterations allowing both an earlier diagnosis of DM and a prompt modulation of the hypoglycemic therapy, thus improving the clinical management of these patients.

Suppression of Adenosine Deaminase and Xanthine Oxidase Activities by Mineralocorticoid and Glucocorticoid Receptor Blockades Restores Renal Antioxidative Barrier in Oral Contraceptive-Treated Dam

OBJECTIVE

We tested the hypothesis that postpartum combined oral contraceptive (COC) treatment would induce oxidative stress via the adenosine deaminase-xanthine oxidase pathway in the kidney. We also sought to determine whether mineralocorticoid receptor (MR) or glucocorticoid receptor (GR ) blockade would suppress the activities of ADA and xanthine oxidase caused by postpartum COC treatment in the kidney.

METHODS

Twenty-four Wistar dams were randomly assigned to 4 groups (n = 6/group). Dams received vehicle (po), COC (1.0 μg ethinylestradiol and 5.0 μg levonorgestrel; po), COC with GR blockade (mifepristone; 80.0 mg/kg; po), and COC with MR blockade (spironolactone; 0.25 mg/kg; po) daily between 3rd and 11th week postpartum.

RESULTS

Data showed that postpartum COC caused increased plasma creatinine and urea, increased renal triglyceride/high-density lipoprotein ratio, free fatty acid accumulation, alanine aminotransferase, gamma-glutamyltransferase, uric acid, and activities of renal XO and ADA. On the other hand, postpartum COC resulted in decreased plasma albumin, renal glutathione, and Na+-K+-ATPase activity with no effect on lactate production. However, MR or GR blockade ameliorated the alterations induced by postpartum COC treatment. The present results demonstrate that MR or GR blockade ameliorates postpartum COC-induced increased activities of ADA and xanthine oxidase and restores glutathione-dependent antioxidative defense.

CONCLUSION

These findings implicate the involvements of GR and MR in renal dysfunctions caused by COC in dams via disrupted glutathione antioxidative barrier.

NADH/NAD+ Redox Imbalance and Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common and severe complication of diabetes mellitus. If left untreated, DKD can advance to end stage renal disease that requires either dialysis or kidney replacement. While numerous mechanisms underlie the pathogenesis of DKD, oxidative stress driven by NADH/NAD⁺ redox imbalance and mitochondrial dysfunction have been thought to be the major pathophysiological mechanism of DKD. In this review, the pathways that increase NADH generation and those that decrease NAD⁺ levels are overviewed. This is followed by discussion of the consequences of NADH/NAD⁺ redox imbalance including disruption of mitochondrial homeostasis and function. Approaches that can be applied to counteract DKD are then discussed, which include mitochondria-targeted antioxidants and mimetics of superoxide dismutase, caloric restriction, plant/herbal extracts or their isolated compounds. Finally, the review ends by pointing out that future studies are needed to dissect the role of each pathway involved in NADH-NAD⁺ metabolism so that novel strategies to restore NADH/NAD⁺ redox balance in the diabetic kidney could be designed to combat DKD.

Diabetic Complications and Oxidative Stress: A 20-Year Voyage Back in Time and Back to the Future

Twenty years have passed since Brownlee and colleagues proposed a single unifying mechanism for diabetic complications, introducing a turning point in this field of research. For the first time, reactive oxygen species (ROS) were identified as the causal link between hyperglycemia and four seemingly independent pathways that are involved in the pathogenesis of diabetes-associated vascular disease. Before and after this milestone in diabetes research, hundreds of articles describe a role for ROS, but the failure of clinical trials to demonstrate antioxidant benefits and some recent experimental studies showing that ROS are dispensable for the pathogenesis of diabetic complications call for time to reflect. This twenty-year journey focuses on the most relevant literature regarding the main sources of ROS generation in diabetes and their role in the pathogenesis of cell dysfunction and diabetic complications. To identify future research directions, this review discusses the evidence in favor and against oxidative stress as an initial event in the cellular biochemical abnormalities induced by hyperglycemia. It also explores possible alternative mechanisms, including carbonyl stress and the Warburg effect, linking glucose and lipid excess, mitochondrial dysfunction, and the activation of alternative pathways of glucose metabolism leading to vascular cell injury and inflammation.

DHEA-pretreatment attenuates oxidative stress in kidney-cortex and liver of diabetic rabbits and delays development of the disease

In view of reported discrepancies concerning antioxidant activity of dehydroepiandrosterone (DHEA), a widely used dietary supplement, the current investigation was undertaken to evaluate the antioxidant properties of DHEA in both kidney-cortex and liver of alloxan (ALX)-induced diabetic rabbits, as this diabetogenic compound exhibits the ROS-dependent action. ALX was injected to animals following 7 days of DHEA administration. Four groups of rabbits were used in the experiments: control, DHEA-treated control, diabetic and DHEA-treated diabetic. Our results show for the first time, that in kidney-cortex DHEA resulted in normalization of hydroxyl free radicals (HFR) levels and restoration of catalase (CAT) and glutathione peroxidase (GPx) activities to near the control values, while in liver DHEA prevented the malondialdehyde (MDA) accumulation and normalized glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G6PDH) activities. Moreover, in both kidney-cortex and liver DHEA supplementation prevented GSSG elevation accompanied by a decrease in GSH/GSSG ratio. Although DHEA attenuated oxidative stress in both kidney-cortex and liver of ALX-induced diabetic rabbits and significantly delayed the onset of diabetes in time, it did not protect against the final development of diabetes. In conclusion, the current investigation underscores the complexity of the antioxidant action of DHEA. The data are of clinical interest since DHEA supplementation could prevent the deleterious effects of ROS and delay, or even prevent the onset of many diseases. However, in view of the reported pro-oxidant effects of high DHEA doses, the potential use of this agent as a supplement needs a careful evaluation.

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.

Caffeine Targets G6PDH to Disrupt Redox Homeostasis and Inhibit Renal Cell Carcinoma Proliferation

Glucose-6-phosphate dehydrogenase (G6PDH) is the rate-limiting enzyme in the pentose phosphate pathway (PPP) and plays a crucial role in the maintenance of redox homeostasis by producing nicotinamide adenine dinucleotide phosphate (NADPH), the major intracellular reductant. G6PDH has been shown to be a biomarker and potential therapeutic target for renal cell carcinoma (RCC). Here, we report a previously unknown biochemical mechanism through which caffeine, a well-known natural small molecule, regulates G6PDH activity to disrupt cellular redox homeostasis and suppress RCC development and progression. We found that caffeine can inhibit G6PDH enzymatic activity. Mechanistically, caffeine directly binds to G6PDH with high affinity (K _D = 0.1923 μM) and competes with the coenzyme NADP⁺ for G6PDH binding, as demonstrated by the decreased binding affinities of G6PDH for its coenzyme and substrate. Molecular docking studies revealed that caffeine binds to G6PDH at the structural NADP⁺ binding site, and chemical cross-linking analysis demonstrated that caffeine inhibits the formation of dimeric G6PDH. G6PDH inhibition abrogated the inhibitory effects of caffeine on RCC cell growth. Moreover, inhibition of G6PDH activity by caffeine led to a reduction in the intracellular levels of NADPH and reactive oxygen species (ROS), and altered the expression of redox-related proteins in RCC cells. Accordingly, caffeine could inhibit tumor growth through inhibition of G6PDH activity in vivo. Taken together, these results demonstrated that caffeine can target G6PDH to disrupt redox homeostasis and inhibit RCC tumor growth, and has potential as a therapeutic agent for the treatment of RCC.

The Warburg Effect, Lactate, and Nearly a Century of Trying to Cure Cancer

Nearly 100 years ago, Otto Warburg undertook a study of tumor metabolism, and discovered increased lactate caused by increased glycolysis in cancer cells. His experiments were conducted in the presence of excess oxygen, but today tumor tissue is known to be a hypoxic environment. However, an increase of glycolysis and lactate production is still a valid observation. Numerous abnormalities and mutations of metabolic enzymes have been found in many cancers. For example, pyruvate kinase M2 has been associated with many cancers and is a major contributor to directing glycolysis into fermentation, forming lactate. Increases in several enzymes, including glucose 6-phosphate dehydrogenase, pyruvate kinase M2, Rad6, or deficiency of other enzymes such as succinate dehydrogenase, all may contribute directly or indirectly to increases in lactate associated with the Warburg effect. In addition, the increased lactate and acid-base changes are modified further by monocarboxylate transporters and carbonic anhydrase, which contribute to alkalinizing tumor cells while acidifying the tumor extracellular environment. This acidification leads to cancer spread. Fully understanding the mechanisms underlying the Warburg effect should provide new approaches to cancer treatment.

Metabolic requirements of the nephron

The mammalian kidney is a complex organ that has several metabolically active cell types to aid in waste filtration, salt-water balance, and electrolyte homeostasis in the body. These functions are done primarily through the nephron, which relies on strict regulation of various metabolic pathways. Any deviations in the metabolic profile of nephrons or their precursor cells called nephron progenitors can lead to renal pathologies and abnormal development. Metabolism encompasses the mechanisms by which cells generate intermediate molecules and energy in the form of adenosine triphosphate (ATP). ATP is required by all cells and is mainly generated through glycolysis, fatty acid oxidation, and oxidative phosphorylation. During kidney development, self-renewing or proliferating cells rely on glycolysis to a greater extent than the other metabolic pathways to supply energy, replenish reducing equivalents, and generate nucleotides. However, terminally differentiated cell types rely more heavily on fatty acid oxidation and oxidative phosphorylation performed in the mitochondria to fulfill energy requirements. Further, the mature nephron is comprised of distinct segments and each segment utilizes metabolic pathways to varying degrees depending on the specific function. This review will focus on major metabolic processes performed by the nephron during health and disease.

Incidence of Glucose-6-Phosphate Dehydrogenase Deficiency among Swedish Newborn Infants

Sweden has 10.2 million inhabitants and more than 2.4 million have a foreign background. A substantial number of immigrants come from countries where glucose-6-phosphate dehydrogenase deficiency (G6PDD) is frequent. The total birth rate annually in Sweden is approximately 117,000 and newborn screening is centralized to one laboratory. We determined glucose-6-phosphate dehydrogenase (G6PD) activity in 10,098 dried blood spot samples (DBS) from the whole country with a fluorometric assay (LabSystems Diagnostics Oy, Finland). The first 5451 samples were anonymised and run as singletons, whilst the following 4647 samples were coded. Enzyme activity ≤40% of the mean of the day was found in 58 samples (1/170) and among these, 29 had activities ≤10% (1/350). Twenty-nine samples with residual activities between 2-39% in the coded cohort were subjected to Sanger sequencing. Disease-causing variants were identified in 26 out of 29 infants, of which six were girls. In three patients, we did not find any disease-causing variants, although two patients were hemizygous for the known polymorphisms c.1311T>C and c.1365-13C>T. The most common disease-causing variant found in 15 of the 29 samples (12 hemizygotes, two heterozygotes, one homozygote) was the Mediterranean mutation, c.563C>T (p.(Ser188Phe)) in exon 6. G6PDD is thus a surprisingly prevalent disorder in Sweden.

Impaired inflammasome activation and bacterial clearance in G6PD deficiency due to defective NOX/p38 MAPK/AP-1 redox signaling

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the pentose phosphate pathway that modulates cellular redox homeostasis via the regeneration of NADPH. G6PD-deficient cells have a reduced ability to induce the innate immune response, thus increasing host susceptibility to pathogen infections. An important part of the immune response is the activation of the inflammasome. G6PD-deficient peripheral blood mononuclear cells (PBMCs) from patients and human monocytic (THP-1) cells were used as models to investigate whether G6PD modulates inflammasome activation. A decreased expression of IL-1β was observed in both G6PD-deficient PBMCs and PMA-primed G6PD-knockdown (G6PD-kd) THP-1 cells upon lipopolysaccharide (LPS)/adenosine triphosphate (ATP) or LPS/nigericin stimulation. The pro-IL-1β expression of THP-1 cells was decreased by G6PD knockdown at the transcriptional and translational levels in an investigation of the expression of the inflammasome subunits. The phosphorylation of p38 MAPK and downstream c-Fos expression were decreased upon G6PD knockdown, accompanied by decreased AP-1 translocation into the nucleus. Impaired inflammasome activation in G6PD-kd THP-1 cells was mediated by a decrease in the production of reactive oxygen species (ROS) by NOX signaling, while treatment with hydrogen peroxide (H₂O₂) enhanced inflammasome activation in G6PD-kd THP-1 cells. G6PD knockdown decreased Staphylococcus aureus and Escherichia coli clearance in G6PD-kd THP-1 cells and G6PD-deficient PBMCs following inflammasome activation. These findings support the notion that enhanced pathogen susceptibility in G6PD deficiency is, in part, due to an altered redox signaling, which adversely affects inflammasome activation and the bactericidal response.

The Redox Role of G6PD in Cell Growth, Cell Death, and Cancer

The generation of reducing equivalent NADPH via glucose-6-phosphate dehydrogenase (G6PD) is critical for the maintenance of redox homeostasis and reductive biosynthesis in cells. NADPH also plays key roles in cellular processes mediated by redox signaling. Insufficient G6PD activity predisposes cells to growth retardation and demise. Severely lacking G6PD impairs embryonic development and delays organismal growth. Altered G6PD activity is associated with pathophysiology, such as autophagy, insulin resistance, infection, inflammation, as well as diabetes and hypertension. Aberrant activation of G6PD leads to enhanced cell proliferation and adaptation in many types of cancers. The present review aims to update the existing knowledge concerning G6PD and emphasizes how G6PD modulates redox signaling and affects cell survival and demise, particularly in diseases such as cancer. Exploiting G6PD as a potential drug target against cancer is also discussed.

Hexose monophosphate shunt, the role of its metabolites and associated disorders: A review

The hexose monophosphate (HMP) shunt acts as an essential component of cellular metabolism in maintaining carbon homeostasis. The HMP shunt comprises two phases viz. oxidative and nonoxidative, which provide different intermediates for the synthesis of biomolecules like nucleotides, DNA, RNA, amino acids, and so forth; reducing molecules for anabolism and detoxifying the reactive oxygen species during oxidative stress. The HMP shunt is significantly important in the liver, adipose tissue, erythrocytes, adrenal glands, lactating mammary glands and testes. We have researched the articles related to the HMP pathway, its metabolites and disorders related to its metabolic abnormalities. The literature for this paper was taken typically from a personal database, the Cochrane database of systemic reviews, PubMed publications, biochemistry textbooks, and electronic journals uptil date on the hexose monophosphate shunt. The HMP shunt is a tightly controlled metabolic pathway, which is also interconnected with other metabolic pathways in the body like glycolysis, gluconeogenesis, and glucuronic acid depending upon the metabolic needs of the body and depending upon the biochemical demand. The HMP shunt plays a significant role in NADPH₂ formation and in pentose sugars that are biosynthetic precursors of nucleic acids and amino acids. Cells can be protected from highly reactive oxygen species by NADPH ₂ . Deficiency in the hexose monophosphate pathway is linked to numerous disorders. Furthermore, it was also reported that this metabolic pathway could act as a therapeutic target to treat different types of cancers, so treatments at the molecular level could be planned by limiting the synthesis of biomolecules required for proliferating cells provided by the HMP shunt, hence, more experiments still could be carried out to find additional discoveries.

Effects of Timolol Treatment on Pancreatic Antioxidant Enzymes in Streptozotocin-induced Diabetic Rats: An Experimental and Computational Study

BACKGROUND

The study aimed to investigate whether timolol-treatment has a beneficial effect on pentose phosphate pathway enzyme activities such as glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGDH) enzyme activities and cAMP level in streptozotocin-induced diabetic rats in pancreatic tissues.

METHODS

Diabetes was induced by streptozotocin (STZ) in 3-month old male Wistar rats. The diabetic rats were treated with timolol (5 mg/kg body weight, for 12 weeks) while the control group received saline. Enzyme activities were determined in pancreas tissue. To support our results, we performed in silico calculations, using Protein Data Bank structures.

RESULTS

Timolol treatment of STZ-induced diabetic rats had no noteworthy effect on high blood-glucose levels. However, this treatment induced activities of G6PD and 6PGDH in diabetic rats. Timolol treatment significantly increased cAMP level in diabetic pancreatic tissue. We found that timolol cannot bind strongly to either G6PD or 6PGD, but there is a relatively higher binding affinity to adenylyl cyclase, responsible for cAMP production, serving as a regulatory signal via specific cAMP-binding proteins.

CONCLUSIONS

Our data point out that timolol treatment has beneficial effects on the antioxidant defence mechanism enzymes in the pancreas of STZ-induced diabetic rats.

Coupling between Protein Stability and Catalytic Activity Determines Pathogenicity of G6PD Variants

G6PD deficiency, an enzymopathy affecting 7% of the world population, is caused by over 160 identified amino acid variants in glucose-6-phosphate dehydrogenase (G6PD). The clinical presentation of G6PD deficiency is diverse, likely due to the broad distribution of variants across the protein and the potential for multidimensional biochemical effects. In this study, we use bioinformatic and biochemical analyses to interpret the relationship between G6PD variants and their clinical phenotype. Using structural information and statistical analyses of known G6PD variants, we predict the molecular phenotype of five uncharacterized variants from a reference population database. Through multidimensional analysis of biochemical data, we demonstrate that the clinical phenotypes of G6PD variants are largely determined by a trade-off between protein stability and catalytic activity. This work expands the current understanding of the biochemical underpinnings of G6PD variant pathogenicity and suggests a promising avenue for correcting G6PD deficiency by targeting essential structural features of G6PD.