Aldose Reductase Inhibitor Protects against Hyperglycemic Stress by Activating Nrf2-Dependent Antioxidant Proteins

SIRT1-NRF2-TFEB axis-mediated hepatic lipophagy alleviates the lipid deposition induced by high glucose in yellow catfish Pelteobagrus fulvidraco

Metabolic stress induces lipophagy, a crucial process in lipid catabolism, which is under the regulation of autophagy involving transcription factor EB (TFEB). However, the precise mechanisms underlying TFEB's control remain enigmatic. In this study, we focused on yellow catfish (Pelteobagrus fulvidraco) as the model to investigate lipophagy activation under high glucose-induced lipid deposition. We hypothesized that lipophagy mediates high glucose-induced lipid deposition and proposed the involvement of the SIRT1-NRF2-TFEB pathway in the activation of lipophagy. We found that there was a functional antioxidative responsive element (ARE) on the tfeb gene promoter; high glucose (HG) increased the nuclear translocation of nuclear factor E2-related factor 2 (NRF2) recruitment to the tfeb promoter; TFEB, whose expression is regulated by NRF2, mediated the HG-induced activation of lipophagy and lipolysis. Moreover, we found that HG increased the silencing information regulator 2 related enzymes 1 (SIRT1) expression, and that the SIRT1 mediates NRF2 translocation to the nucleus, increased TFEB expression and activated autophagy. In the glucose tolerance test, blood glucose increased rapidly and plateaued at 4-h glucose after injection and then declined until 48-h post-injection. Generally speaking, the transcript level and protein expression of SIRT1, NRF2, TFEB, microtubule-associated proteins 1A/1B light chain 3B (LC3B), and autophagy-related 6 (Beclin1) showed similar trend after glucose injection, and trends to increase and plateau at 4-h injection, then decline until 16-h post-injection, and finally increased until 48-h post-injection. These results indicated that the SIRT1-NRF2-TFEB axis-mediated lipophagy may be an adaptive response to glucose injection. Collectively, for the first time, we found that NRF2 was associated directly with TFEB-mediated transcriptional control of hepatic lipophagy, and that lipophagy helps to alleviate the HG-induced lipid deposition via SIRT1-NRF2-TFEB activation in yellow catfish.

Multiple biomarker responses in female Clarias gariepinus exposed to acetaminophen

Several authors have documented the presences of acetaminophen (APAP) in both surface and groundwater and have received attention from government agencies and basic authorities across the globe. The impacts of such pharmaceutical products on non-target organism like fish are underestimated as a result of selected investigation using few biomarkers. We evaluated the sub-chronic impacts of APAP in female catfish (Clarias gariepinus) using multiple biomarkers. The exposure of female catfish to APAP induced oxidative stress. Markers such as superoxide dismutase (SOD), glutathione peroxidase (GPx), and total antioxidant capacity (TAC) were significantly higher in all exposed groups. Exposure of Clarias gariepinus to APAPA caused histological alterations in the gills (fusion and shortening of some filaments, hyperplasia of the epithelial gill cells, aneurism, congestion, and epithelial rupture of the gills), liver (apoptotic hyperplasia, sinusoidal congestion, and necrosis of the hepatocytes), and gonad (degenerated follicles and ovarian apoptosis). Furthermore, multivariate results indicated that there was a distinct response from the acetaminophen-exposed female catfish, with over 95% of the biomarkers significantly contributing to the discrimination between the acetaminophen-exposed female catfish and the control groups. Our research provides evidence supporting the use of a multiple biomarker approach to evaluate the impacts of drugs on the health status of exposed fish.

Metabolomics of oxidative stress: Nrf2 independent depletion of NAD or increases of sugar alcohols

Nrf2 encodes a transcription factor best known for regulating the expression of antioxidant and detoxification genes. Recent evidence suggested that Nrf2 mediates metabolic reprogramming in cancer cells. However, the role of Nrf2 in the biochemical metabolism of cardiac cells has not been studied. Using LC-MS/MS-based metabolomics, we addressed whether knocking out the Nrf2 gene in AC16 human cardiomyocytes affects metabolic reprogramming by oxidative stress. Profiling the basal level metabolites showed an elevated pentose phosphate pathway and increased levels of sugar alcohols, sorbitol, L-arabitol, xylitol and xylonic acid, in Nrf2 KO cells. With sublethal levels of oxidative stress, depletion of NAD, an increase of GDP and elevation of sugar alcohols, sorbitol and dulcitol, were detected in parent wild type (WT) cells. Knocking out Nrf2 did not affect these changes. Biochemical assays confirmed depletion of NAD in WT and Nrf2 KO cells due to H₂O₂ treatment. These data support that although Nrf2 deficiency caused baseline activation of the pentose phosphate pathway and sugar alcohol synthesis, a brief exposure to none-lethal doses of H₂O₂ caused NAD depletion in an Nrf2 independent manner. Loss of NAD may contribute to oxidative stress associated cell degeneration as observed with aging, diabetes and heart failure.

The Role of NRF2 in Obesity-Associated Cardiovascular Risk Factors

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

Tea polyphenols alleviate hydrogen peroxide-induced oxidative stress damage through the Mst/Nrf2 axis and the Keap1/Nrf2/HO-1 pathway in murine RAW264.7 cells

Tea polyphenols (TPs) are the major bioactive extract from green tea that have been extensively reported to prevent and treat oxidative stress damage. In previous studies, TPs have been demonstrated to protect cells against oxidative injury induced by hydrogen peroxide (H₂O₂). However, the underlying mechanism remains unclear. The aim of the current study was to investigate whether the protective and regulatory effects of TPs on oxidative stress damage were dependent on the mammalian STE20-like protein kinase (Mst)/nuclear factor (erythroid-derived 2)-like 2 (Nrf2) axis and the Kelch-like ECH-associated protein 1 (Keap1)/Nrf2/heme oxygenase 1 (HO-1) pathway in RAW264.7 cells, a murine macrophage cell line. Maintaining a certain range of intracellular reactive oxygen species (ROS) levels is critical to basic cellular activities, while excessive ROS generation can override the antioxidant capacity of the cell and result in oxidative stress damage. The inhibition of ROS generation offers an effective target for preventing oxidative damage. The results of the present study revealed that pretreatment with TPs inhibited the production of intracellular ROS and protected RAW264.7 cells from H₂O₂-induced oxidative damage. TPs was also demonstrated to attenuate the production of nitric oxide and malondialdehyde and increase the levels of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase). In addition, following TPs treatment, alterations in Mst1/2 at the mRNA and protein level inhibited the production of ROS and promoted the self-regulation of antioxidation. TPs-induced Keap1 gene downregulation also increased the expression of Nrf2 and HO-1. Collectively, the results of the present study demonstrated that TPs provided protection against H₂O₂-induced oxidative injury in RAW264.7 cells.

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.

Targeting Multiple Signal Transduction Pathways of SARS-CoV-2: Approaches to COVID-19 Therapeutic Candidates

Due to the complicated pathogenic pathways of coronavirus disease 2019 (COVID-19), related medicinal therapies have remained a clinical challenge. COVID-19 highlights the urgent need to develop mechanistic pathogenic pathways and effective agents for preventing/treating future epidemics. As a result, the destructive pathways of COVID-19 are in the line with clinical symptoms induced by severe acute coronary syndrome (SARS), including lung failure and pneumonia. Accordingly, revealing the exact signaling pathways, including inflammation, oxidative stress, apoptosis, and autophagy, as well as relative representative mediators such as tumor necrosis factor-α (TNF-α), nuclear factor erythroid 2-related factor 2 (Nrf2), Bax/caspases, and Beclin/LC3, respectively, will pave the road for combating COVID-19. Prevailing host factors and multiple steps of SARS-CoV-2 attachment/entry, replication, and assembly/release would be hopeful strategies against COVID-19. This is a comprehensive review of the destructive signaling pathways and host-pathogen interaction of SARS-CoV-2, as well as related therapeutic targets and treatment strategies, including potential natural products-based candidates.

Protective Effects of Novel Substituted Triazinoindole Inhibitors of Aldose Reductase and Epalrestat in Neuron-like PC12 Cells and BV2 Rodent Microglial Cells Exposed to Toxic Models of Oxidative Stress: Comparison with the Pyridoindole Antioxidant Stobadine

Aldose reductase (AR) catalyzes the conversion of glucose to sorbitol in a NADPH-dependent reaction, thereby increasing the production of reactive oxygen species (ROS). Since AR activation is linked to redox dysregulation and cell damage in neurodegenerative diseases, AR inhibitors (ARIs) constitute promising therapeutic tools for the treatment of these disorders. Among these compounds, the novel substituted triazinoindole derivatives cemtirestat (CMTI) and COTI, as well as the clinically employed epalrestat (EPA) and the pyridoindole-antioxidant stobadine (STB), were tested in both PC12 cells and BV2 microglia exposed to four different neurotoxic models. These include (1) oxidative stress with hydrogen peroxide (H₂O₂), (2) mitochondrial complex IV inhibition with NaN₃, (3) endoplasmic reticulum-stress and lipotoxicity induced by palmitic acid/bovine serum albumin (PAM/BSA), and (4) advanced carbonyl compound lipotoxicity by 4-hydroxynonenal (4-HNE). All toxic compounds decreased cell viability and increased ROS formation in both PC12 and BV2 cells in a concentration-dependent manner (1-1000 μM; NaN₃ < H₂O₂≈PAM/BSA < 4-HNE). In PC12 cells, EPA increased cell viability in all toxic models only at 1 μM, whereas CMTI restored baseline viability in all toxic models. COTI afforded protection against lipotoxicity, while STB only prevented H₂O₂-induced toxicity. Except for the 4-HNE model, EPA prevented ROS generation in all other toxic models, whereas CMTI, COTI, and STB prevented ROS production in all toxic models. In BV2 cells, EPA and CMTI restored baseline cell viability in all toxic models tested, while COTI and STB did not prevent the loss of viability in the NaN₃ model. All ARIs and STB efficiently prevented ROS formation in all toxic models in a concentration-independent manner. The differential protective effects evoked by the novel ARIs and STB on the toxic models tested herein provide novel and relevant comparative evidence for the design of specific therapeutic strategies against neurodegenerative events associated with neurological disorders.

Structural characterization and antioxidant activity of an acetylated Cyclocarya paliurus polysaccharide (Ac-CPP0.1)

The aim of this study was to investigate the primary structure of an acetylated Cyclocarya paliurus polysaccharide (Ac-CPP_0.1) and its protective effect on H₂O₂-treated dendritic cells. The backbone of Ac-CPP_0.1 was →3)-β-D-Galp-(1→, with some branches α-L-Araf-(1→ residues at O-6 and O-5, β-D-Galp-(1→ and 3,5,6)-β-D-Galf-(1 residues at O-4 and acetyl groups were substituted at the O-2 and O-6 positions of 3)-β-D-Galp-(1 residues. The CPP_0.1 and Ac-CPP_0.1 significantly increased the levels of superoxide dismutase, glutathione peroxidase and catalase on H₂O₂-treated dendritic cells. Meanwhile, both CPP_0.1 and Ac-CPP_0.1 up-regulated the expression of Nrf2 (NF-E2-related factor 2) and down-regulated the Keap1 (Kelch-like ECH-associated protein-1), but Ac-CPP_0.1 had a better effect on antioxidant capacity. These results indicated that potential application of Ac-CPP_0.1 as an antioxidant agent.

Combatting Nitrosative Stress and Inflammation with Novel Substituted Triazinoindole Inhibitors of Aldose Reductase in PC12 Cells Exposed to 6-Hydroxydopamine Plus High Glucose

Cellular redox dysregulation produced by aldose reductase (AR) in the presence of high blood sugar is a mechanism involved in neurodegeneration commonly observed in diabetes mellitus (DM) and Parkinson's disease (PD); therefore, AR is a key target for treatment of both diseases. The substituted triazinoindole derivatives 2-(3-thioxo-2H-[1,2,4]triazino[5,6-b]indol-5(3H)-yl) acetic acid (cemtirestat or CMTI) and 2-(3-oxo-2H-[1,2,4]triazino[5,6-b]indol-5(3H)-yl) acetic acid (COTI) are well-known AR inhibitors (ARIs). The neuroprotective properties of CMTI, COTI, the clinically used epalrestat (EPA), and the pyridoindole antioxidants stobadine and SMe1EC2 were all tested in the neurotoxic models produced by hyperglycemic glucotoxicity (HG, 75 mM D-glucose, 72 h), 6-hydroxydopamine (6-OHDA), and HG+6-OHDA models in PC12 cells. Cell viability decreased in all toxic models, increased by 1-5 μM EPA, and decreased by COTI at ≥ 2.5 μM. In the HG model alone, where compounds were present in the medium for 24 h after a continuous 24-h exposure to HG, cell viability was improved by 100 nM-5 μM EPA, 1-10 μM ARIs, and the antioxidants studied, but decreased by EPA at ≥ 10 μM. In the 6-OHDA model alone, where cells were treated with compounds for 24 h and further exposed to 100 μM 6-OHDA (8 h), only the antioxidants protected cell viability. In the HG+6-OHDA model, where cells were treated with all compounds (1 nM to 50 μM) for 48 h and exposed to 75 mM glucose for 24 h followed by incubation with 6-OHDA for 8 h, cell viability was protected by 100 nM-10 μM ARIs and 100-500 nM EPA, but not by antioxidants. All ARIs inhibited the HG+6-OHDA-induced increase in iNOS, IL-1β, TNF-α, 3-NT, and total oxidant status at 1-50 μM, while increased SOD, CAT, GPx, and total antioxidant status at 1-10 μM. EPA and CMTI also reduced the HG+6-OHDA-induced increase in the cellular levels of nuclear factor kB (NF-KB). The neuroprotective potential of the novel ARIs and the pyridoindole antioxidants studied constitutes a promising tool for the development of therapeutic strategies against DM-induced and PD-related neurodegeneration.

Aldose Reductase Differential Inhibitors in Green Tea

Aldose reductase (AKR1B1), the first enzyme in the polyol pathway, is likely involved in the onset of diabetic complications. Differential inhibition of AKR1B1 has been proposed to counteract the damaging effects linked to the activity of the enzyme while preserving its detoxifying ability. Here, we show that epigallocatechin gallate (EGCG), one of the most representative catechins present in green tea, acts as a differential inhibitor of human recombinant AKR1B1. A kinetic analysis of EGCG, and of its components, gallic acid (GA) and epigallocatechin (EGC) as inhibitors of the reduction of L-idose, 4-hydroxy2,3-nonenal (HNE), and 3-glutathionyl l-4-dihydroxynonanal (GSHNE) revealed for the compounds a different model of inhibition toward the different substrates. While EGCG preferentially inhibited L-idose and GSHNE reduction with respect to HNE, gallic acid, which was still active in inhibiting the reduction of the sugar, was less active in inhibiting HNE and GSHNE reduction. EGC was found to be less efficient as an inhibitor of AKR1B1 and devoid of any differential inhibitory action. A computational study defined different interactive modes for the three substrates on the AKR1B1 active site and suggested a rationale for the observed differential inhibition. A chromatographic fractionation of an alcoholic green tea extract revealed that, besides EGCG and GA, other components may exhibit the differential inhibition of AKR1B1.

Pharmacological management of vascular endothelial dysfunction in diabetes: TCM and western medicine compared based on biomarkers and biochemical parameters

Diabetes, a worldwide health concern while burdening significant populace of countries with time due to a hefty increase in both incidence and prevalence rates. Hyperglycemia has been buttressed both in clinical and experimental studies to modulate widespread molecular actions that effect macro and microvascular dysfunctions. Endothelial dysfunction, activation, inflammation, and endothelial barrier leakage are key factors contributing to vascular complications in diabetes, plus the development of diabetes-induced cardiovascular diseases. The recent increase in molecular, transcriptional, and clinical studies has brought a new scope to the understanding of molecular mechanisms and the therapeutic targets for endothelial dysfunction in diabetes. In this review, an attempt made to discuss up to date critical and emerging molecular signaling pathways involved in the pathophysiology of endothelial dysfunction and viable pharmacological management targets. Importantly, we exploit some Traditional Chinese Medicines (TCM)/TCM isolated bioactive compounds modulating effects on endothelial dysfunction in diabetes. Finally, clinical studies data on biomarkers and biochemical parameters involved in the assessment of the efficacy of treatment in vascular endothelial dysfunction in diabetes was compared between clinically used western hypoglycemic drugs and TCM formulas.

Protective effect of polysaccharides of sea cucumber Acaudina leucoprocta on hydrogen peroxide-induced oxidative injury in RAW264.7 cells

The aim of this experiment was to investigate the protective effects of polysaccharides of sea cucumber Acaudina leucoprocta (ALP) against hydrogen peroxide (H₂O₂) induced oxidative injury in RAW264.7 cells. Analysis of monosaccharide composition and structure of one fraction from ALP (ALP_N) were analyzed by High Performance Liquid Chromatography (HPLC) and Fourier Transform Infrared Spectoscopy (FT-IR). The results showed that ALP_N contain sulfate groups, which is sulfated polysaccharides. The results from MTT assay indicated that ALP_N could markedly increase viability of cells compared with RAW264.7 cells exposed to H₂O₂. Moreover, ALP_N significantly increased the levels of catalase (CAT), glutathione peroxidase (GSH-P_X) and superoxide dismutase (SOD), decreased the production of malondialdehyde (MDA) and lactate dehydrogenase (LDH) in RAW264.7 cells. The data from RT-PCR showed that ALP_N (300 μg/mL) could increase the gene expression levels of SOD1 and GPX1. ALP_N could also observably increase the protein expression level of Nrf2 and decrease the protein expression level of Keap1 with western blot. Collectively, this study suggested that polysaccharides of sea cucumber Acaudina leucoprocta (ALP) could effectively protect RAW264.7 cells against H₂O₂-induced oxidative injury. This protection mechanism may be related to activation of the Nrf2/Keap1 signaling pathway.

Aldose reductase regulates hyperglycemia-induced HUVEC death via SIRT1/AMPK-α1/mTOR pathway

Although hyperglycemia-mediated death and dysfunction of endothelial cells have been reported to be a major cause of diabetes associated vascular complications, the mechanisms through which hyperglycemia cause endothelial dysfunction is not well understood. We have recently demonstrated that aldose reductase (AR, AKR1B1) is an obligatory mediator of oxidative and inflammatory signals induced by growth factors, cytokines and hyperglycemia. However, the molecular mechanisms by which AR regulates hyperglycemia-induced endothelial dysfunction is not well known. In this study, we have investigated the mechanism(s) by which AR regulates hyperglycemia-induced endothelial dysfunction. Incubation of human umbilical vein endothelial cells (HUVECs) with high glucose (HG) decreased the cell viability and inhibition of AR prevented it. Further, AR inhibition prevented the HG-induced ROS generation and expression of BCL-2, BAX and activation of Caspase-3 in HUVECs. AR inhibition also prevented the adhesion of THP-1 monocytes on HUVECs, expression of iNOS and eNOS and adhesion molecules ICAM-1 and VCAM-1 in HG-treated HUVECs. Further, AR inhibition restored the HG-induced depletion of SIRT1 in HUVECs and increased the phosphorylation of AMPKα1 along-with a decrease in phosphorylation of mTOR in HG-treated HUVECs. Fidarestat decreased SIRT1 expression in HUVECs pre-treated with specific SIRT1 inhibitor but not with the AMPKα1 inhibitor. Similarly, knockdown of AR in HUVECs by siRNA prevented the HG-induced HUVECs cell death, THP-1 monocyte adhesion and SIRT1 depletion. Furthermore, fidarestat regulated the phosphorylation of AMPKα1 and mTOR, and expression of SIRT1 in STZ-induced diabetic mice heart and aorta tissues. Collectively, our data suggest that AR regulates hyperglycemia-induced endothelial death and dysfunction by altering the ROS/SIRT1/AMPKα1/mTOR pathway.