Mechanisms of Flavonoids and Their Derivatives in Endothelial Dysfunction Induced by Oxidative Stress in Diabetes

Diabetic complications pose a significant threat to life and have a negative impact on quality of life in individuals with diabetes. Among the various factors contributing to the development of these complications, endothelial dysfunction plays a key role. The main mechanism underlying endothelial dysfunction in diabetes is oxidative stress, which adversely affects the production and availability of nitric oxide (NO). Flavonoids, a group of phenolic compounds found in vegetables, fruits, and fungi, exhibit strong antioxidant and anti-inflammatory properties. Several studies have provided evidence to suggest that flavonoids have a protective effect on diabetic complications. This review focuses on the imbalance between reactive oxygen species and the antioxidant system, as well as the changes in endothelial factors in diabetes. Furthermore, we summarize the protective mechanisms of flavonoids and their derivatives on endothelial dysfunction in diabetes by alleviating oxidative stress and modulating other signaling pathways. Although several studies underline the positive influence of flavonoids and their derivatives on endothelial dysfunction induced by oxidative stress in diabetes, numerous aspects still require clarification, such as optimal consumption levels, bioavailability, and side effects. Consequently, further investigations are necessary to enhance our understanding of the therapeutic potential of flavonoids and their derivatives in the treatment of diabetic complications.

GKT137831 in combination with adipose-derived stem cells alleviates high glucose-induced inflammaging and improves diabetic wound healing

Adipose-derived stem cells (ADSCs) have been proven to promote healing in diabetic wounds, which are one of the most serious chronic refractory wounds. However, reactive oxygen species (ROS) induced by high glucose (HG) lead to oxidative stress and aging in ADSCs, which limits the therapeutic effect of ADSCs. In this study, we investigated the role of GKT137831, a NOX1/4 inhibitor that can reduce ROS production, in protecting ADSCs from hyperglycemia and in diabetic wound healing. In vitro, ROS levels and NOX4 expression were increased after HG treatment of ADSCs, while the oxidative stress marker malondialdehyde was increased; mitochondrial membrane potential was decreased; inflammatory aging-related indicators such as p16, p21, matrix metalloproteinase-1 (MMP1), MMP3, interleukin-6, and β-galactosidase were increased; and migration was weakened. In vivo, we constructed a diabetic mouse wound model and found that the combination of ADSCs and GKT137831 synergistically promoted the 21-day wound healing rate, increased the expression of collagen and hydroxyproline, increased the number of blood vessels and the expression of CD31, and reduced the expression of interleukin-6, MMP1, MMP3, and p21. These results suggest that GKT137831 could protect ADSCs from oxidative stress and aging induced by HG and enhance the therapeutic effect of ADSCs on diabetic wounds.

A proteoglycan isolated from Ganoderma lucidum attenuates diabetic kidney disease by inhibiting oxidative stress-induced renal fibrosis both in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Ganoderma lucidum (G. lucidum) was regarded as "miraculous herb" by the Chinese and recorded detailly in the "Shen Nong Ben Cao Jing" as a tonic to improve health and prolong life. A proteoglycan (namely, FYGL) was extracted from Ganoderma lucidum, which was a water-soluble hyperbranched proteoglycan, and was found to be able to protect pancreatic tissue against oxidative stress damage.

AIM OF THE STUDY

Diabetic kidney disease (DKD) is a complication of diabetes, but the effective treatment is still lack. Chronic hyperglycemia in diabetic patients induce the accumulation of ROS, which injure the renal tissue and lead to the renal dysfunction. In this work, the efficacy and target mechanics of FYGL on diabetic renal function were investigated.

MATERIALS AND METHODS

In the present study, the mechanism of the reno-protection of FYGL was analyzed on diabetic db/db mice and rat glomerular mesangial cells (HBZY-1) induced by high glucose (HG) with palmitate (PA) (HG/PA). In vitro, the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) were evaluated by commercial kits. the expressions of NOX1 and NOX4, phosphorylation of MAPK and NF-κB, and pro-fibrotic proteins were measured by Western blot. In vivo, diabetic db/db mice were gavaged with FYGL for 8 weeks, body weight and fasting blood glucose (FBG) were tested weekly. On 8th week, the serum, urine and renal tissue were collected for glucose tolerance test (OGTT), redox indicator (SOD, CAT, GSH and MDA), lipid metabolism (TC, TG, LDL and HDL), blood urea nitrogen (BUN), serum creatinine (Scr), uric acid (UA), 8-oxo-deoxyguanosine (8-OHdG), and the changes of histopathology and expression of collagen IV and AGEs.

RESULTS

The results in vitro showed that FYGL significantly inhibited the HG/PA-induced HBZY-1 cells proliferation, ROS generation, MDA production, promoted SOD activity, and suppressed NOX1, NOX4, MAPK, NF-κB, and pro-fibrotic proteins expression. In addition, FYGL markedly alleviated blood glucose, antioxidant activity and lipid metabolism, improved renal functions, and relieved renal histopathological abnormalities, especially renal fibrosis.

CONCLUSIONS

The antioxidant activity of FYGL can reduce ROS caused by diabetes and protect renal from oxidative stress-induced dysfunction, thereby improving renal function. This study shows that FYGL has the potential to treat diabetic kidney disease.

NQO1 alleviates renal fibrosis by inhibiting the TLR4/NF-κB and TGF-β/Smad signaling pathways in diabetic nephropathy

OBJECTIVE

Diabetic nephropathy (DN) is one of the main complications of diabetes, and inflammation and fibrosis play an important role in its progression. NAD(P)H: quinone oxidoreductase 1 (NQO1) protects cells from oxidative stress and damage caused by toxic quinones. In the present study, we aimed to investigate the protective effects of NQO1 against diabetes-induced renal inflammation and fibrosis and the underlying mechanisms.

METHODS

In vivo, the kidneys of type 2 diabetes model db/db mice were infected with adeno-associated virus vectors to induce NQO1 overexpression. In vitro, human renal tubular epithelial (HK-2) cells transfected with NQO1 pcDNA3.1(+) were cultured under high-glucose (HG) conditions. Gene and protein expression was assessed by quantitative real-time PCR, Western blotting, immunofluorescence, and immunohistochemical staining. Mitochondrial reactive oxygen species (ROS) were detected with MitoSOX Red.

RESULT

Our study revealed that the expression of NQO1 was markedly downregulated and that Toll-like receptor (TLR)4 and TGF-β1 expression was upregulated in vivo and in vitro under diabetic conditions. Overexpression of NQO1 suppressed proinflammatory cytokine (IL-6, TNF-α, MCP-1) secretion, extracellular matrix (ECM) (collagen IV, fibronectin) accumulation and epithelial-mesenchymal transition (EMT) (α-SMA, E-cadherin) in the db/db mouse kidneys and HG-cultured HK-2 cells. Furthermore, NQO1 overexpression ameliorated HG-induced TLR4/NF-κB and TGF-β/Smad pathways activation. Mechanistic studies demonstrated that a TLR4 inhibitor (TAK-242) suppressed the TLR4/NF-κB signaling pathway, proinflammatory cytokine secretion, EMT and ECM-related protein expression in HG-exposed HK-2 cells. In addition, we found that the antioxidants N-acetylcysteine (NAC) and tempol increased the expression of NQO1 and decreased the expression of TLR4, TGF-β1, Nox1, and Nox4 and ROS production in HK-2 cells cultured under HG conditions.

CONCLUSIONS

These data suggest that NQO1 alleviates diabetes-induced renal inflammation and fibrosis by regulating the TLR4/NF-κB and TGF-β/Smad signaling pathways.

SH3YL1 Protein Predicts Renal Outcomes in Patients with Type 2 Diabetes

NADPH oxidase (NOX)-derived oxidative stress is an important factor in renal progression, with NOX4 being the predominant NOX in the kidney. Recently, Src homology 3 (SH3) domain-containing YSC84-like 1 (SH3YL1) was reported to be a regulator of NOX4. In this study, we tested whether the SH3YL1 protein could predict 3-year renal outcomes in patients with type 2 diabetes. A total of 131 patients with type 2 diabetes were enrolled in this study. Renal events were defined as a 15% decline in the estimated glomerular filtration rate (eGFR) from the baseline, the initiation of renal replacement therapy, or death during the 3 years. The levels of the urinary SH3YL1-to-creatinine ratio (USCR) were significantly different among the five stages of chronic kidney disease (CKD) and the three groups, based on albuminuria levels. The USCR levels showed a significant negative correlation with eGFR and a positive correlation with the urinary albumin-to-creatinine ratio (UACR). Plasma SH3YL1 levels were significantly correlated with UACR. The highest tertile group of USCR and plasma SH3YL1 had a significantly lower probability of renal event-free survival. Furthermore, the highest tertile group of USCR showed a significant association with the incidence of renal events after full adjustment: adjusted hazard ratio (4.636: 95% confidence interval, 1.416-15.181, p = 0.011). This study suggests that SH3YL1 is a new diagnostic biomarker for renal outcomes in patients with type 2 diabetes.

An update on the role of thioredoxin-interacting protein in diabetic kidney disease: A mini review

Thioredoxin-interacting protein (TXNIP) was first isolated from Vitamin D3-exposed HL60 cells. TXNIP is the main redox-regulating factor in various organs and tissues. We begin with an overview of the TXNIP gene and protein information, followed by a summary of studies that have shown its expression in human kidneys. Then, we highlight our current understanding of the effect of TXNIP on diabetic kidney disease (DKD) to improve our understanding of the biological roles and signal transduction of TXNIP in DKD. Based on the recent review, the modulation of TXNIP may be considered as a new target in the management of DKD.

Nutraceutical Prevention of Diabetic Complications—Focus on Dicarbonyl and Oxidative Stress

Oxidative and dicarbonyl stress, driven by excess accumulation of glycolytic intermediates in cells that are highly permeable to glucose in the absence of effective insulin activity, appear to be the chief mediators of the complications of diabetes. The most pathogenically significant dicarbonyl stress reflects spontaneous dephosphorylation of glycolytic triose phosphates, giving rise to highly reactive methylglyoxal. This compound can be converted to harmless lactate by the sequential activity of glyoxalase I and II, employing glutathione as a catalyst. The transcription of glyoxalase I, rate-limiting for this process, is promoted by Nrf2, which can be activated by nutraceutical phase 2 inducers such as lipoic acid and sulforaphane. In cells exposed to hyperglycemia, glycine somehow up-regulates Nrf2 activity. Zinc can likewise promote glyoxalase I transcription, via activation of the metal-responsive transcription factor (MTF) that binds to the glyoxalase promoter. Induction of glyoxalase I and metallothionein may explain the protective impact of zinc in rodent models of diabetic complications. With respect to the contribution of oxidative stress to diabetic complications, promoters of mitophagy and mitochondrial biogenesis, UCP2 inducers, inhibitors of NAPDH oxidase, recouplers of eNOS, glutathione precursors, membrane oxidant scavengers, Nrf2 activators, and correction of diabetic thiamine deficiency should help to quell this.

Inhibition of ChREBP ubiquitination via the ROS/Akt-dependent downregulation of Smurf2 contributes to lysophosphatidic acid-induced fibrosis in renal mesangial cells

Background

Mesangial cell fibrosis, a typical symptom of diabetic nephropathy (DN), is a major contributor to glomerulosclerosis. We previously reported that the pharmacological blockade of lysophosphatidic acid (LPA) signaling improves DN. Although LPA signaling is implicated in diabetic renal fibrosis, the underlying molecular mechanisms remain unclear. Here, the role of carbohydrate-responsive element-binding protein (ChREBP) in LPA-induced renal fibrosis and the underlying mechanisms were investigated.

Methods

Eight-week-old wild-type and db/db mice were intraperitoneally injected with the vehicle or an LPAR1/3 antagonist, ki16425 (10 mg/kg), for 8 weeks on a daily basis, following which the mice were sacrificed and renal protein expression was analyzed. SV40 MES13 cells were treated with LPA in the presence or absence of ki16425, and the expression of ChREBP and fibrotic factors, including fibronectin, TGF-β, and IL-1β, was examined. The role of ChREBP in the LPA-induced fibrotic response was investigated by ChREBP overexpression or knockdown. The involvement of Smad ubiquitination regulatory factor-2 (Smurf2), an E3 ligase, in LPA-induced expression of ChREBP and fibrotic factors was investigated by Smurf2 overexpression or knockdown. To identify signaling molecules regulating Smurf2 expression by LPA, pharmacological inhibitors such as A6370 (Akt1/2 kinase inhibitor) and Ly 294002 (PI3K inhibitor) were used.

Results

The renal expression of ChREBP increased in diabetic db/db mice, and was reduced following treatment with the ki16425. Treatment with LPA induced the expression of ChREBP and fibrotic factors, including fibronectin, TGF-β, and IL-1β, in SV40 MES13 cells, which were positively correlated. The LPA-induced expression of fibrotic factors increased or decreased following ChREBP overexpression and knockdown, respectively. The production of reactive oxygen species (ROS) mediated the LPA-induced expression of ChREBP and fibrotic factors, and LPA decreased Smurf2 expression via Traf4-mediated ubiquitination. The LPA-induced expression of ubiquitinated-ChREBP increased or decreased following Smurf2 overexpression and knockdown, respectively. Additionally, Smurf2 knockdown significantly increased the expression of ChREBP and fibrotic factors. The pharmacological inhibition of Akt signaling suppressed the LPA-induced alterations in the expression of ChREBP and Smurf2.

Conclusion

Collectively, the results demonstrated that the ROS/Akt-dependent downregulation of Smurf2 and the subsequent increase in ChREBP expression might be one of the mechanisms by which LPA induces mesangial cell fibrosis in DN.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00814-1.

Clinical Phenotypes of Heart Failure With Preserved Ejection Fraction to Select Preclinical Animal Models

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To better define HFpEF clinically, patients are nowadays often clustered into phenogroups, based on their comorbidities and symptoms

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Many animal models claim to mimic HFpEF, but phenogroups are not yet regularly used to cluster them

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HFpEF animals models often lack reports of clinical symptoms of HF, therefore mainly presenting as extended models of LVDD, clinically seen as a prestate of HFpEF

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We investigated if clinically relevant phenogroups can guide selection of animal models aiming at better defined animal research

At least one-half of the growing heart failure population consists of heart failure with preserved ejection fraction (HFpEF). The limited therapeutic options, the complexity of the syndrome, and many related comorbidities emphasize the need for adequate experimental animal models to study the etiology of HFpEF, as well as its comorbidities and pathophysiological changes. The strengths and weaknesses of available animal models have been reviewed extensively with the general consensus that a “1-size-fits-all” model does not exist, because no uniform HFpEF patient exists. In fact, HFpEF patients have been categorized into HFpEF phenogroups based on comorbidities and symptoms. In this review, we therefore study which animal model is best suited to study the different phenogroups—to improve model selection and refinement of animal research. Based on the published data, we extrapolated human HFpEF phenogroups into 3 animal phenogroups (containing small and large animals) based on reports and definitions of the authors: animal models with high (cardiac) age (phenogroup aging); animal models focusing on hypertension and kidney dysfunction (phenogroup hypertension/kidney failure); and models with hypertension, obesity, and type 2 diabetes mellitus (phenogroup cardiometabolic syndrome). We subsequently evaluated characteristics of HFpEF, such as left ventricular diastolic dysfunction parameters, systemic inflammation, cardiac fibrosis, and sex-specificity in the different models. Finally, we scored these parameters concluded how to best apply these models. Based on our findings, we propose an easy-to-use classification for future animal research based on clinical phenogroups of interest.

Crosstalk Between SMPDL3b and NADPH Oxidases Mediates Radiation-Induced Damage of Renal Podocytes

Patients undergoing radiotherapy (RT) for various tumors localized in the abdomen or pelvis often suffer from radiation nephrotoxicity as collateral damage. Renal podocytes are vulnerable targets for ionizing radiation and contribute to radiation-induced nephropathies. Our prior work previously highlighted the importance of the lipid-modifying enzyme sphingomyelinase acid phosphodiesterase like 3b (SMPDL3b) in modulating the radiation response in podocytes and glomerular endothelial cells. Hereby, we investigated the interplay between SMPDL3b and oxidative stress in mediating radiation injury in podocytes. We demonstrated that the overexpression of SMPDL3b in cultured podocytes (OE) reduced superoxide anion generation and NADPH oxidase activity compared to wild-type cells (WT) post-irradiation. Furthermore, OE podocytes showed downregulated levels of NOX1 and NOX4 after RT. On the other hand, treatment with the NOX inhibitor GKT improved WTs' survival post-RT and restored SMPDL3b to basal levels. in vivo, the administration of GKT restored glomerular morphology and decreased proteinuria in 26-weeks irradiated mice. Taken together, these results suggest a novel role for NOX-derived reactive oxygen species (ROS) upstream of SMPDL3b in modulating the response of renal podocytes to radiation.

The Effect of Chalcones on the Main Sources of Reactive Species Production: Possible Therapeutic Implications in Diabetes Mellitus

Diabetes mellitus (DM) is characterized by hyperglycaemia, resulting from defects in insulin secretion, insulin action or both. There are several factors such as hyperlipidemia and oxidative stress (OS), namely the production of reactive oxygen/nitrogen species (ROS/RNS), that actively contribute to the development and worsening of DM. Chalcones, also termed as benzalacetophenone or benzylidene acetophenone, present a 1,3-diaryl-2-propen-1-one scaffold that has been shown to be highly promising in the development of new antioxidant compounds. Considering the potential interest of antioxidant therapy, the present review scrutinizes the role of the main sources of ROS/RNS production during DM. The modulatory effect of chalcones against nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, xanthine oxidase, mitochondrial respiratory chain and nitric oxide synthase, is also thoroughly discussed, establishing, whenever possible, a structure-activity relationship (SAR). From the SAR analysis, it can be stated that the presence of catechol groups, hydroxyl and methoxyl substituents in the chalcones scaffold improves their modulatory activity against the main sources of ROS/RNS production in DM.

The Mystery of Red Blood Cells Extracellular Vesicles in Sleep Apnea with Metabolic Dysfunction

Sleep is very important for overall health and quality of life, while sleep disorder has been associated with several human diseases, namely cardiovascular, metabolic, cognitive, and cancer-related alterations. Obstructive sleep apnea (OSA) is the most common respiratory sleep-disordered breathing, which is caused by the recurrent collapse of the upper airway during sleep. OSA has emerged as a major public health problem and increasing evidence suggests that untreated OSA can lead to the development of various diseases including neurodegenerative diseases. In addition, OSA may lead to decreased blood oxygenation and fragmentation of the sleep cycle. The formation of free radicals or reactive oxygen species (ROS) can emerge and react with nitric oxide (NO) to produce peroxynitrite, thereby diminishing the bioavailability of NO. Hypoxia, the hallmark of OSA, refers to a decline of tissue oxygen saturation and affects several types of cells, playing cell-to-cell communication a vital role in the outcome of this interplay. Red blood cells (RBCs) are considered transporters of oxygen and nutrients to the tissues, and these RBCs are important interorgan communication systems with additional functions, including participation in the control of systemic NO metabolism, redox regulation, blood rheology, and viscosity. RBCs have been shown to induce endothelial dysfunction and increase cardiac injury. The mechanistic links between changes of RBC functional properties and cardiovascular are largely unknown. Extracellular vesicles (EVs) are secreted by most cell types and released in biological fluids both under physiological and pathological conditions. EVs are involved in intercellular communication by transferring complex cargoes including proteins, lipids, and nucleic acids from donor cells to recipient cells. Advancing our knowledge about mechanisms of RBC-EVs formation and their pathophysiological relevance may help to shed light on circulating EVs and to translate their application to clinical practice. We will focus on the potential use of RBC-EVs as valuable diagnostic and prognostic biomarkers and state-specific cargoes, and possibilities as therapeutic vehicles for drug and gene delivery. The use of RBC-EVs as a precision medicine for the diagnosis and treatment of the patient with sleep disorder will improve the prognosis and the quality of life in patients with cardiovascular disease (CVD).

Resveratrol-Elicited PKC Inhibition Counteracts NOX-Mediated Endothelial to Mesenchymal Transition in Human Retinal Endothelial Cells Exposed to High Glucose

Diabetes-associated long-term hyperglycaemia leads to oxidative stress-mediated fibrosis in different tissues and organs. Endothelial-to-mesenchymal-transition (EndMT) appears to play a role in diabetes-associated fibrotic conditions. Here, we investigate whether EndMT is implicated in the diabetic retinopathy fibrotic process and evaluate the possibility that resveratrol could counteract EndMT by inhibiting high glucose (HG)-induced increases in ROS. Primary Human Retinal Endothelial Cells (HRECs) were either pre-treated for 24 h with 1 µM resveratrol or left untreated, then glucose (30 mM) was applied at 3-day intervals for 10 days. qRT-PCR and ELISA were used to detect mRNA or protein expression of endothelial markers (CD31, CDH5, vWF) or mesenchymal markers (VIM, αSMA and collagen I), respectively. Intracellular ROS levels were measured with carboxy-DCFDA, while NOX-associated ROS levels were evaluated using the NADPH-specific redox biosensor p47-roGFP. Treatment of HRECs with HG increased intracellular ROS levels and promoted phenotype shifting towards EndMT, evidenced by decreased expression of endothelial markers concomitant with increased expression of mesenchymal ones. HG-induced EndMT appears to be mediated by NADPH-associated ROS generation as pre-treatment of HRECs with resveratrol or the NADPH inhibitor, diphenyleneiodonium chloride (DPI), attenuated ROS production and EndMT transition, suggesting that the effect of resveratrol on HG-induced ROS occurs via down-regulation of NADPH oxidase. It is worth noting that resveratrol or Chelerythrine, a Protein kinase C (PKC) inhibitor, reduce ROS and EndMT in HG-exposed cells, suggesting that NADPH activation occurs via a PKC-dependent mechanism. Taken together, our results provide the basis for a resveratrol-based potential protective therapy to prevent diabetic-associated complications.

Impairment of type H vessels by NOX2-mediated endothelial oxidative stress: critical mechanisms and therapeutic targets for bone fragility in streptozotocin-induced type 1 diabetic mice

Rationale: Mechanisms underlying the compromised bone formation in type 1 diabetes mellitus (T1DM), which causes bone fragility and frequent fractures, remain poorly understood. Recent advances in organ-specific vascular endothelial cells (ECs) identify type H blood vessel injury in the bone, which actively direct osteogenesis, as a possible player.

Methods: T1DM was induced in mice by streptozotocin (STZ) injection in two severity degrees. Bony endothelium, the coupling of angiogenesis and osteogenesis, and bone mass quality were evaluated. Insulin, antioxidants, and NADPH oxidase (NOX) inhibitors were administered to diabetic animals to investigate possible mechanisms and design therapeutic strategies.

Results: T1DM in mice led to the holistic abnormality of the vascular system in the bone, especially type H vessels, resulting in the uncoupling of angiogenesis and osteogenesis and inhibition of bone formation. The severity of osteopathy was positively related to glycemic levels. These pathological changes were attenuated by early-started, but not late-started, insulin therapy. ECs in diabetic bones showed significantly higher levels of reactive oxygen species (ROS) and NOX 1 and 2. Impairments of bone vessels and bone mass were effectively ameliorated by treatment with anti-oxidants or NOX2 inhibitors, but not by a NOX1/4 inhibitor. GSK2795039 (GSK), a NOX2 inhibitor, significantly supplemented the insulin effect on the diabetic bone.

Conclusions: Diabetic osteopathy could be a chronic microvascular complication of T1DM. The impairment of type H vessels by NOX2-mediated endothelial oxidative stress might be an important contributor that can serve as a therapeutic target for T1DM-induced osteopathy.

Apocynin ameliorates NADPH oxidase 4 (NOX4) induced oxidative damage in the hypoxic human retinal Müller cells and diabetic rat retina

NADPH oxidase (NOX) is a main producers of reactive oxygen species (ROS) that may contribute to the early pathogenesis of diabetic retinopathy (DR). ROS has harmful effects on endogenous neuro-survival factors brain-derived neurotrophic factor (BDNF) and sirtuin 1 (SIRT1) are necessary for the growth and survival of the retina. The role of NOX isoforms NOX4 in triggering ROS in DR is not clear. Here we determine the protective effects of a plant-derived NOX inhibitor apocynin (APO) on NOX4-induced ROS production which may contribute to the depletion of survival factors BDNF/SIRT1 or cell death in the diabetic retinas. Human retinal Müller glial cells (MGCs) were treated with hypoxia mimetic agent cobalt chloride (CoCl₂) in the absence or presence of APO. Molecular analysis demonstrates that NOX4 is upregulated in CoCl₂-treated MGCs and in the diabetic retinas. Increased NOX4 was accompanied by the downregulation of BDNF/SIRT1 expression or in the activation of apoptotic marker caspase-3. Whereas, APO treatment downregulates NOX4 and subsequently upregulates BDNF/SIRT1 or alleviate caspase-3 expression. Accordingly, in the diabetic retina we found a positive correlation in NOX4 vs ROS (p = 0.025; R² = 0.488) and caspase-3 vs ROS (p = 0.04; R² = 0.428); whereas a negative correlation in BDNF vs ROS (p = 0.009; R² = 0.596) and SIRT1 vs ROS (p = 0.0003; R² = 0.817) respectively. Taken together, NOX4-derived ROS could be a main contributor in downregulating BDNF/SIRT1 expression or in the activation of caspase-3. Whereas, APO treatment may minimize the deleterious effects occurring due to hyperglycemia and/or diabetic mimic hypoxic condition in early pathogenesis of DR.

Hyperhomocysteinemia-Induced Oxidative Stress Aggravates Renal Damage in Hypertensive Rats

BACKGROUND

Hyperhomocysteinemia (HHcy) plays a synergistic role with hypertension in vascular injury; however, the relationship between HHcy and hypertension in renal injury remains unclear. Here, we sought to evaluate the relationship between HHcy and hypertension in the context of renal injury and to elucidate the mechanism of action underlying this relationship.

METHODS

Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were randomized into WKY, WKY + HHcy, SHR, and SHR + HHcy groups. Blood pressure, plasma homocysteine, serum malondialdehyde (MDA), serum superoxide dismutase (SOD), urinary albumin creatinine ratio (UACR), and glomerular filtration rate (GFR) were measured. Renal histopathology and expression levels of NOX2, NOX4, and nephrin in the kidneys were examined.

RESULTS

The WKY + HHcy and SHR groups exhibited lower serum SOD and GFR levels, relative to the WKY group, along with higher levels of both serum MDA and UACR. Higher mRNA and protein expression levels of NOX2 and NOX4, along with lower expression levels of nephrin, were observed in the kidneys of WKY + HHcy and SHR rats, relative to WKY controls, respectively. Similar effects were observed in the SHR + HHcy group, relative to the SHR group and WKY + HHcy group, respectively. Periodic acid-Schiff staining showed an increase in the glomerular extracellular matrix in the WKY + HHcy and SHR + HHcy groups compared with their respective controls.

CONCLUSIONS

HHcy appears to synergistically increase hypertensive renal damage by enhancing oxidative stress.

APX-115, a pan-NADPH oxidase inhibitor, protects development of diabetic nephropathy in podocyte specific NOX5 transgenic mice

NADPH oxidases (NOXs) are comprised of different isoforms, NOX1 to 5 and Duox1 and 2, and they trigger diabetic nephropathy (DN) in the patients with diabetes mellitus. Recently, it was shown that, compared to the other isoforms, the expression of NOX5 was increased in the patients with DN and, NOX5 has been suggested to be important in the development of therapeutic agents. The effect of pan-NOX inhibition by APX-115 has also been investigated in type 2 diabetic mice. However, since NOX5 is absent in mice, we evaluated the effect of pan-NOX inhibition by APX-115 in Nox5 transgenic mouse. Wild type and renal podocyte specific NOX5 transgenic mice (NOX5 pod+) were fed with high-fat diet (60% kcal fat) and treated with APX-115 (60 mg/kg) by oral gavage for 14 weeks. APX-115 significantly improved pancreatic beta cell function by decreased fasting blood glucose levels and increased insulin levels. Further, the total serum cholesterol, triglycerides, and urinary albumin/creatinine levels were also significantly decreased by APX-115 treatment. Increased NOX5 mRNA expressions, increased desmin levels, and reduced podocin protein expressions in the kidney of NOX5 pod + mice were also significantly restored to normal levels by APX-115 treatment. Moreover, APX-115 inhibited the expression of inflammation-related proteins such as TRAF6. Collectively, these data suggest that APX-115 might be a promising therapeutic agent for the treatment of DN because of its pan-NOX inhibitory activity, including its NOX5 inhibitory activity, and also owing to its anti-inflammatory effect.

Interrelation between ROS and Ca2+ in aging and age-related diseases

Calcium (Ca2+) and reactive oxygen species (ROS) are versatile signaling molecules coordinating physiological and pathophysiological processes. While channels and pumps shuttle Ca2+ ions between extracellular space, cytosol and cellular compartments, short-lived and highly reactive ROS are constantly generated by various production sites within the cell. Ca2+ controls membrane potential, modulates mitochondrial adenosine triphosphate (ATP) production and affects proteins like calcineurin (CaN) or calmodulin (CaM), which, in turn, have a wide area of action. Overwhelming Ca2+ levels within mitochondria efficiently induce and trigger cell death. In contrast, ROS comprise a diverse group of relatively unstable molecules with an odd number of electrons that abstract electrons from other molecules to gain stability. Depending on the type and produced amount, ROS act either as signaling molecules by affecting target proteins or as harmful oxidative stressors by damaging cellular components. Due to their wide range of actions, it is little wonder that Ca2+ and ROS signaling pathways overlap and impact one another. Growing evidence suggests a crucial implication of this mutual interplay on the development and enhancement of age-related disorders, including cardiovascular and neurodegenerative diseases as well as cancer.

Sweet dreams: therapeutic insights, targeting imaging and physiologic evidence linking sleep, melatonin and diabetic nephropathy

Melatonin is the main biochronologic molecular mediator of circadian rhythm and sleep. It is also a powerful antioxidant and has roles in other physiologic pathways. Melatonin deficiency is associated with metabolic derangements including glucose and cholesterol dysregulation, hypertension, disordered sleep and even cancer, likely due to altered immunity. Diabetic nephropathy (DN) is a key microvascular complication of both type 1 and 2 diabetes. DN is the end result of a complex combination of metabolic, haemodynamic, oxidative and inflammatory factors. Interestingly, these same factors have been linked to melatonin deficiency. This report will collate in a clinician-oriented fashion the mechanistic link between melatonin deficiency and factors contributing to DN.

Flavonoids Activation of the Transcription Factor Nrf2 as a Hypothesis Approach for the Prevention and Modulation of SARS-CoV-2 Infection Severity

The Nrf2-Keap1-ARE pathway is the principal regulator of antioxidant and phase II detoxification genes. Its activation increases the expression of antioxidant and cytoprotective proteins, protecting cells against infections. Nrf2 modulates virus-induced oxidative stress, ROS generation, and disease pathogenesis, which are vital in the viral life cycle. During respiratory viral infections, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), an inflammatory process, and oxidative stress of the epithelium lining cells activate the transcription factor Nrf2, which protects cells from oxidative stress and inflammation. Nrf2 reduces angiotensin-converting enzyme 2 (ACE2) receptors expression in respiratory epithelial cells. SARS-CoV2 has a high affinity for ACE2 that works as receptors for coronavirus surface spike glycoprotein, facilitating viral entry. Disease severity may also be modulated by pre-existing conditions, such as impaired immune response, obesity, and age, where decreased level of Nrf2 is a common feature. Consequently, Nrf2 activators may increase Nrf2 levels and enhance antiviral mediators' expression, which could initiate an "antiviral state", priming cells against viral infection. Therefore, this hypothesis paper describes the use of flavonoid supplements combined with vitamin D3 to activate Nrf2, which may be a potential target to prevent and/or decrease SARS-CoV-2 infection severity, reducing oxidative stress and inflammation, enhancing innate immunity, and downregulating ACE2 receptors.

A Protein/Lipid Preload Attenuates Glucose-Induced Endothelial Dysfunction in Individuals with Abnormal Glucose Tolerance

Postprandial hyperglycemia interferes with vascular reactivity and is a strong predictor of cardiovascular disease. Macronutrient preloads reduce postprandial hyperglycemia in subjects with impaired glucose tolerance (IGT) or type 2 diabetes (T2D), but the effect on endothelial function is unknown. Therefore, we examined whether a protein/lipid preload can attenuate postprandial endothelial dysfunction by lowering plasma glucose responses in subjects with IGT/T2D. Endothelial function was assessed by the reactive hyperemia index (RHI) at fasting, 60 min and 120 min during two 75 g oral glucose tolerance tests (OGTTs) preceded by either water or a macronutrient preload (i.e., egg and parmesan cheese) in 22 volunteers with IGT/T2D. Plasma glucose, insulin, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), glucagon, free fatty acids, and amino acids were measured through each test. RHI negatively correlated with fasting plasma glucose. During the control OGTT, RHI decreased by 9% and its deterioration was associated with the rise in plasma glucose. The macronutrient preload attenuated the decline in RHI and markedly reduced postprandial glycemia. The beneficial effect of the macronutrient preload on RHI was proportional to the improvement in glucose tolerance and was associated with the increase in plasma GLP-1 and arginine levels. In conclusion, a protein/lipid macronutrient preload attenuates glucose-induced endothelial dysfunction in individuals with IGT/T2D by lowering plasma glucose excursions and by increasing GLP-1 and arginine levels, which are known regulators of the nitric oxide vasodilator system.

Protective action of melatonin on diabetic rat testis at cellular, hormonal and immunohistochemical levels

The aim of the present study was to analyze the effects of melatonin treatment on diabetic rat testes. Fifty albino rats were divided into the following groups: CG: control group; GD: placebo-induced and placebo-treated mice; GDI: insulin-induced and post-confirmation diabetes-induced rats; GDM: diabetes-induced and melatonin-treated post-confirmation mice and GDMS: diabetes-induced and melatonin-treated mice simultaneously. Melatonin was administered at a dose of 10 mg/kg in drinking water every day for 20 days at night. Diabetes was induced by streptozotocin (60 mg/kg) and confirmed after the fifth day of induction. Insulin was administered at 5 IU (international units)/day at different times of the day for 20 days. The testes were submitted to histopathological, morphometric, immunohistochemical and oxidative stress analysis. Melatonin moderately decreased glycemic levels, protected weight loss and morphometric changes in the testicles, increased antioxidant enzyme levels and stabilized plasma testosterone and androgen receptor levels and decreased inflammatory markers in the testicles. Showing its potential to mitigate diabetes effects.

Effects of a Red Orange and Lemon Extract in Obese Diabetic Zucker Rats: Role of Nicotinamide Adenine Dinucleotide Phosphate Oxidase

Diabetic nephropathy (DN) is the primary cause of end-stage renal disease, worldwide, and oxidative stress has been recognized as a key factor in the pathogenesis and progression of DN. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has the most important contribution to reactive oxygen species generation during the development of DN. Bioactive compound use has emerged as a potential approach to reduce chronic renal failure. Therefore, a red orange and lemon extract (RLE) rich in anthocyanins was chosen in our study, to reduce the toxic renal effects during the development of DN in Zucker diabetic fatty rat (ZDF). RLE effects were examined daily for 24 weeks, through gavage, in ZDF rats treated with RLE (90 mg/kg). At the end of the experiment, ZDF rats treated with RLE showed a reduction of the diabetes-associated up-regulation of both NOX4 and the p47-phox and p22-phox subunits, and restored the BAX/BCL-2 ratio respect to ZDF rats. Furthermore, RLE was able to reduce the oxidative DNA damage measured in urine samples in ZDF rats. This study showed that RLE could prevent the renal damage induced by DN through its capacity to inhibit NOX4 and apoptosis mechanisms.

Inhibitor of myogenic differentiation family isoform a, a new positive regulator of fibronectin production by glomerular mesangial cells

Overproduction of extracellular matrix proteins, including fibronectin by mesangial cells (MCs), contributes to diabetic nephropathy. Inhibitor of myogenic differentiation family isoform a (I-mfa) is a multifunctional cytosolic protein functioning as a transcriptional modulator or plasma channel protein regulator. However, its renal effects are unknown. The present study was conducted to determine whether I-mfa regulated fibronectin production by glomerular MCs. In human MCs, overexpression of I-mfa significantly increased fibronectin abundance. Silencing I-mfa significantly reduced the level of fibronectin mRNA and blunted transforming growth factor-β1-stimulated production of fibronectin. We further found that high glucose increased I-mfa protein content in a time course (≥48 h) and concentration (≥25 mM)-dependent manner. Although high glucose exposure increased I-mfa at the protein level, it did not significantly alter transcripts of I-mfa in MCs. Furthermore, the abundance of I-mfa protein was significantly increased in the renal cortex of rats with diabetic nephropathy. The I-mfa protein level was also elevated in the glomerulus of mice with diabetic kidney disease. However, there was no significant difference in glomerular I-mfa mRNA levels between mice with and without diabetic nephropathy. Moreover, H2O2 significantly increased I-mfa protein abundance in a dose-dependent manner in cultured human MCs. The antioxidants polyethylene glycol-catalase, ammonium pyrrolidithiocarbamate, and N-acetylcysteine significantly blocked the high glucose-induced increase of I-mfa protein. Taken together, our results suggest that I-mfa, increased by high glucose/diabetes through the production of reactive oxygen species, stimulates fibronectin production by MCs.

Id1 expression in kidney endothelial cells protects against diabetes-induced microvascular injury

The inhibitor of differentiation (Id) transcription regulators, which are induced in response to oxidative stress, promote cell proliferation and inhibit senescence. Inhibitor of differentiation 1 (Id1) expression is limited to endothelial cells (EC) in the normal mouse kidney and is required for a normal response to injury. Endothelial dysfunction leads to the development of diabetic nephropathy, and so, we hypothesized that endothelial Id1 may help protect against hyperglycemia-induced microvascular injury and nephropathy. Here, we tested this hypothesis by using streptozotocin to induce diabetes in Id1 knockout (KO) mice and WT B6;129 littermates and examining the mice at 3 months. Expression of Id1 was observed to be increased 15-fold in WT kidney EC, and Id1 KO mice exhibited increased mesangial and myofibroblast proliferation, matrix deposition, and albuminuria compared with WT mice. Electron microscopy demonstrated peritubular capillary EC injury and lumen narrowing, and fluorescence microangiography showed a 45% reduction in capillary perfusion area with no reduction in CD31-stained areas in Id1 KO mice. Microarray analysis of EC isolated from WT and KO control and diabetic mice demonstrated activation of senescence pathways in KO cells. Kidneys from KO diabetic mice showed increased histological expression of senescence markers. In addition, premature senescence in cultured KO EC was also seen in response to oxidative stress. In conclusion, endothelial Id1 upregulation with hyperglycemia protects against microvascular injury and senescence and subsequent nephropathy.

Inhalation exposure to cigarette smoke induces endothelial nitric oxide synthase uncoupling and enhances vascular collagen deposition in streptozotocin-induced diabetic rats

Smoking is an acknowledged risk factor for vascular disorders, and vascular complication is a main outcome of diabetes. Hence, we investigated the impact of cigarette smoke on blood vessels in diabetes, postulating that smoking might aggravate diabetic vascular impairment. Sprague-Dawley rats were divided into four groups: control, cigarette smoke-exposed, diabetic, and cigarette smoke-exposed diabetic groups. Streptozotocin-induced diabetic rats were exposed to cigarette smoke by inhalation at total particulate matter concentration of 200 μg/L for 4 h/day, 5 day/week for a total of 4 weeks. Diabetes caused structural change of aorta, but additional cigarette smoke exposure did not induce further alteration. Collagen, a marker for fibrosis, was increased in media of diabetic aorta, and this increase was augmented by cigarette smoke. Cigarette smoke induced endothelial nitric oxide synthase (eNOS) uncoupling in the diabetic group. Malondialdehyde was increased and glutathione was decreased in blood from diabetes, but these effects were not exaggerated by cigarette smoke. Cigarette smoke caused NADPH oxidase (NOX) 2 expression in diabetic aorta and enhanced diabetes-induced NOX4 expression in aorta. Taken together, cigarette smoke exposure can aggravate vascular fibrosis and induce eNOS uncoupling in diabetes under experimental condition, suggesting that smoking might exacerbate diabetic vascular impairments.

Diabetes inhibits corneal epithelial cell migration and tight junction formation in mice and human via increasing ROS and impairing Akt signaling

Corneal wounds usually heal quickly; but diabetic patients have more fragile corneas and experience delayed and painful healing. In the present study, we compared the healing capacity of corneal epithelial cells (CECs) between normal and diabetic conditions and the potential mechanisms. Primary murine CEC derived from wild-type and diabetic (db/db) mice, as well as primary human CEC were prepared. Human CEC were exposed to high glucose (30 mM) to mimic diabetic conditions. Cell migration and proliferation were assessed using Scratch test and MTT assays, respectively. Reactive oxygen species (ROS) production in the cells was measured using dichlorofluorescein reagent. Western blot was used to evaluate the expression levels of Akt. Transepithelial electrical resistance (TEER) and zonula occludens-1 (ZO-1) expression were used to determine tight junction integrity. We found that the diabetic CEC displayed significantly slower cell proliferation and migration compared with the normal CEC from both mice and humans. Furthermore, ROS production was markedly increased in CEC grown under diabetic conditions. Treatment with an antioxidant N-acetyl cysteine (NAC, 100 μM) significantly decreased ROS production and increased wound healing in diabetic CEC. Barrier function was significantly reduced in both diabetic mouse and human CEC, while NAC treatment mitigated these effects. We further showed that Akt signaling was impaired in diabetic CEC, which was partially improved by NAC treatment. These results show that diabetic conditions lead to delayed wound-healing capacity of CEC and impaired tight junction formation in both mice and human. Increased ROS production and inhibited Akt signaling may contribute to this outcome, implicating these as potential targets for treating corneal wounds in diabetic patients.

Endothelial Dysfunction: Is There a Hyperglycemia-Induced Imbalance of NOX and NOS?

NADPH oxidases (NOX) are enzyme complexes that have received much attention as key molecules in the development of vascular dysfunction. NOX have the primary function of generating reactive oxygen species (ROS), and are considered the main source of ROS production in endothelial cells. The endothelium is a thin monolayer that lines the inner surface of blood vessels, acting as a secretory organ to maintain homeostasis of blood flow. The enzymatic production of nitric oxide (NO) by endothelial NO synthase (eNOS) is critical in mediating endothelial function, and oxidative stress can cause dysregulation of eNOS and endothelial dysfunction. Insulin is a stimulus for increases in blood flow and endothelium-dependent vasodilation. However, cardiovascular disease and type 2 diabetes are characterized by poor control of the endothelial cell redox environment, with a shift toward overproduction of ROS by NOX. Studies in models of type 2 diabetes demonstrate that aberrant NOX activation contributes to uncoupling of eNOS and endothelial dysfunction. It is well-established that endothelial dysfunction precedes the onset of cardiovascular disease, therefore NOX are important molecular links between type 2 diabetes and vascular complications. The aim of the current review is to describe the normal, healthy physiological mechanisms involved in endothelial function, and highlight the central role of NOX in mediating endothelial dysfunction when glucose homeostasis is impaired.

Toxicological Risk Assessments of Iron Oxide Nanocluster- and Gadolinium-Based T1MRI Contrast Agents in Renal Failure Rats

Gadolinium-based contrast agents (GBCAs) are widely used for T1-weighted magnetic resonance imaging (MRI) in clinic diagnosis. However, a major drawback of GBCAs is that they can increase the toxicological risk of nephrogenic systemic fibrosis (NSF) in patients with advanced renal dysfunction. Hence, safer alternatives to GBCAs are currently in demand, especially for patients with renal diseases. Here we investigated the potential of polyethylene glycol (PEG)-stabilized iron oxide nanoclusters (IONCs) as biocompatible T1MRI contrast agents and systematically evaluated their NSF-related risk in rats with renal failure. We profiled the distribution, excretion, histopathological alterations, and fibrotic gene expressions after administration of IONCs and GBCAs. Our results showed that, compared with GBCAs, IONCs exhibited dramatically improved biosafety and a much lower risk of causing NSF, suggesting the feasibility of substituting GBCAs with IONCs in clinical MRI diagnosis of patients with renal diseases.

The Effect of 8-Week Aerobic Exercise on the Expression of Regulatory Subunits of NADPH Oxidase 2 (p47phox and p67phox) in the Cardiac Tissue of Diabetic Rats

Introduction: Oxidative stress seems to play a major role in diabetes-induced cardiac dysfunction, known as diabetic cardiomyopathy (DCM). Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 is considered as one of the main enzymatic systems which primarily contributes to the production of reactive oxygen species in various organs including the heart. The present study aimed to investigate the effects of 8 weeks of aerobic exercise (AE) on the expression of p47phox and p67phox, which are regarded as the regulatory subunits of NADPH oxidase 2 in the cardiac tissue in diabetic rats. Methods: A total of 36 male Wistar rats with a mean weight of 231±25 g were randomly divided into non-diabetic, control diabetic, and trained diabetic groups (each containing 12 rats). Nicotinamide and streptozotocin were used to induce diabetes in the rats. The cardiac muscle was removed under sterile conditions 48 hours following the last training session. Finally, the mRNA levels of p47phox and p67phox were evaluated using the real-time polymerase chain reaction. Results: The results showed that diabetes induction significantly increased the gene expressions of p47phox and p67phox in the cardiac tissue of diabetic rats. The expression of these genes was significantly attenuated after 8 weeks of AE. Conclusion: In general, AE was found to prevent the negative effects of diabetes by suppressing p47phox and p67phox in the cardiac tissue of diabetic rats. Therefore, this can improve cardiac function and may be a potential preventive or therapeutic modality for DCM.

Astragaloside IV inhibits palmitate-mediated oxidative stress and fibrosis in human glomerular mesangial cells via downregulation of CD36 expression

BACKGROUND

The increased influx of free fatty acids (FFAs) into the kidney is a risk factor for diabetes nephropathy (DN). In the present study we investigated the effects of astragaloside IV (AS-IV) on FFA-induced lipid accumulation, oxidative stress, and activation of TGF-β1 signaling in human glomerular mesangial cells (HMCs).

METHODS

A DN model was induced in Sprague Dawley rats by the administration of a high-fat diet and streptozocin, and HMCs were stimulated with palmitate. Lipid accumulation and FFA uptake were detected using Oil Red O and BODIPY™ FL C₁₆ staining, respectively. The expression levels of TGF-β1, p-Smad2/3, FN, Col4 A1, NOX4, p22phox, and CD36 were evaluated by western blotting or immunofluorescence/immunohistochemistry. The level of reactive oxygen species (ROS) was detected using 2',7'-dichlorofluorescein diacetate and dihydroethidium.

RESULTS

Exposure to palmitate induced marked lipid accumulation in HMCs, whereas co-treatment with AS-IV significantly attenuated this phenomenon. Moreover, AS-IV suppressed palmitate-induced expression of TGF-β1, p-Smad2/3, FN, Col4 A1, NOX4, and p22phox, in addition to ROS production. Notably, AS-IV reduced the palmitate-induced expression of CD36 in HMCs and DN rats. Treatment of HMCs with the CD36 inhibitor, sulfo-N-succinimidyl oleate (SSO), significantly attenuated FFA uptake, oxidative stress, and fibrosis. Nevertheless, the combined use of SSO and AS-IV did not enhance the efficacy.

CONCLUSION

AS-IV inhibited palmitate-induced HMCs oxidative stress and fibrosis via the downregulation of CD36 expression, mediating FFA uptake and lipid accumulation.

Activation of Nrf2 signaling by natural products-can it alleviate diabetes?

Type 2 diabetes mellitus (DM) has reached pandemic proportions and effective prevention strategies are wanted. Its onset is accompanied by cellular distress, the nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor boosting cytoprotective responses, and many phytochemicals activate Nrf2 signaling. Thus, Nrf2 activation by natural products could presumably alleviate DM. We summarize function, regulation and exogenous activation of Nrf2, as well as diabetes-linked and Nrf2-susceptible forms of cellular stress. The reported amelioration of insulin resistance, β-cell dysfunction and diabetic complications by activated Nrf2 as well as the status quo of Nrf2 in precision medicine for DM are reviewed.

SOCS1-targeted therapy ameliorates renal and vascular oxidative stress in diabetes via STAT1 and PI3K inhibition

Oxidative stress resulting from excessive production of reactive oxygen species (ROS) or impaired antioxidant defenses is closely related to the development of diabetic vascular complications, including nephropathy and atherosclerosis. Chronic activation of Janus kinase/Signal transducer and activator of transcription (JAK/STAT) signaling pathway contributes to diabetic complications by inducing expression of genes involved in cell proliferation, fibrosis, inflammation, and oxidative stress. Suppressors of cytokine signaling (SOCS) family of endogenous JAK/STAT regulators is an attractive target for therapeutic intervention. We investigated the beneficial effect of two different SOCS1-targeted therapies (adenovirus-mediated gene transfer and kinase-inhibitory region peptidomimetic) to combat oxidative stress injury in an experimental diabetes model of concomitant renal and macrovascular disease (streptozotocin-induced diabetic apolipoprotein E-deficient mouse). Diabetes resulted in progressive alteration of redox balance in mice, as demonstrated by increased ROS levels and decreased antioxidant activity, which ultimately led to renal dysfunction and vascular injury. The molecular and pathological alterations in early diabetes were partially reversed by preventive intervention with SOCS1-targeted therapies. Importantly, SOCS1 peptidomimetic provided reno- and atheroprotection in diabetic mice even in a setting of established disease. Compared with untreated controls, kidney and aorta from SOCS1-treated mice exhibited significantly lower levels of superoxide anion, DNA oxidation marker and NADPH oxidase (Nox) subunits, along with higher expression of antioxidant enzymes. These trends correlated with a reduction in parameters of renal damage (albuminuria, creatinine and tubular injury), atherosclerosis (lesion size) and inflammation (leukocytes and chemokines). Mechanistic studies in renal, vascular and phagocytic cells exposed to cytokines and high-glucose showed that SOCS1 blocked ROS generation by inhibiting both Nox complex assembly and Nox subunit expression, an effect mediated by inactivation of JAK2, STAT1, and PI3K signaling pathways. This study provides evidence for SOCS1-targeted therapies, especially SOCS1 peptidomimetic, as an alternative antioxidant strategy to limit the progression of diabetic micro- and macrovascular complications.

Red Meat Consumption (Heme Iron Intake) and Risk for Diabetes and Comorbidities?

PURPOSE OF REVIEW

To examine the role of red meat consumption, especially heme iron intake, and risk for diabetes and its comorbidities.

RECENT FINDINGS

Studies consistently show that consumption of red meat has been contributory to a multitude of chronic conditions such as diabetes, CVD, and malignancies. There are various emerging reasons that strengthen this link-from the basic constituents of red meat like the heme iron component, the metabolic reactions that take place after consumption, and finally to the methods used to cook it. The causative links show that even occasional use raises the risk of T2DM. Prior studies show how nitrites and nitrates in red meat can lead to increased insulin resistance, dysregulated blood glucose levels, and elevated oxidative stress all leading to chronic diseases. With the rise in these preventable chronic diseases, we examine how disease-causing links can be eliminated with appropriate lifestyle choices.

Angiogenesis impairment by the NADPH oxidase-triggered oxidative stress at the bone-implant interface: Critical mechanisms and therapeutic targets for implant failure under hyperglycemic conditions in diabetes

Mechanism underlying the diabetes-induced poor osteointegration of implants remains elusive, making it a challenge to develop corresponding solutions. Here, we studied the role of angiogenesis in the diabetes-induced poor bone repair at the bone-implant interface (BII) and the related mechanisms. In vivo, titanium screws were implanted in the femurs of mice, and, in vitro, vascular endothelial cell (VEC) was cultured on titanium surface. Results showed that, compared with normal milieu (NM), diabetic milieu (DM) led to angiogenesis inhibition around implants which resulted in reduced osteoprogenitors and poor bone formation on BII in vivo. In vitro, DM caused significant increase of NADPH oxidases (NOX), dysfunction of mitochondria and overproduction of reactive oxygen species (ROS) in VEC on titanium surface, inducing obvious cell dysfunction. Both Mito-TEMPO (Mito, a mitochondria-targeted ROS antagonist) and apocynin (APO, a NOX inhibitor) effectively attenuated the oxidative stress and dysfunction of VEC, with the beneficial effects of APO significantly better than those of Mito. Further study showed that the diabetes-induced metabolic disturbance of VEC was significantly related to the increase of advanced glycation end products (AGEs) at the BII. Our results suggested that the AGEs-related and NOX-triggered cellular oxidative stress leads to VEC dysfunction and angiogenesis impairment at the BII, which plays a critical role in the compromised implant osteointegration under diabetic conditions. These demonstrated new insights into the BII in pathological states and also provided NOX and AGEs as promising therapeutic targets for developing novel implant materials to accelerate the angiogenesis and osteointegration of implants in diabetic patients with hyperglycemia.

STATEMENT OF SIGNIFICANCE

The high failure rate of bone implants in diabetic patients causes patients terrible pain and limits the clinical application of implant materials. The mechanism underlying this phenomenon needs elucidation so that it would be possible to develop corresponding solutions. Our study demonstrated that the AGEs-related and NOX-triggered oxidative stress of VEC leads to angiogenesis impairment at the bone-implant interface (BII) in diabetes. These are critical mechanisms underlying the compromised implant osteointegration in diabetic hyperglycemia. These provide new insights into the BII in diseased states and also suggest NOX and AGEs as crucial therapeutic targets for developing novel implant materials which could modulate the oxidative stress on BII to get improved osteointegration and reduced implant failure, especially in diabetic patients.

Short-term high-glucose treatment decreased abundance of Orai1 protein through posttranslational mechanisms in rat mesangial cells

The short-term effect of high-glucose (HG) treatment on store-operated Ca²⁺ entry in mesangial cells (MCs) is not well-known. The aim of the present study was to determine whether and how HG treatment for a short period altered protein abundance of Orai1, the channel mediating store-operated Ca²⁺ entry in MCs. Rat and human MCs were exposed to HG (25 mM) for 2, 4, 8, and 24 h, and the abundance of Orai1 protein was significantly decreased at the time points of 8 and 16 h. Consistently, HG treatment for 8 h significantly reduced store-operated Ca²⁺ entry in rat MCs. However, HG treatment for the same time periods did not alter the levels of Orai1 transcript. Cycloheximide, a protein synthesis inhibitor, did not affect the HG-induced decrease of Orai1 protein, suggesting a posttranslational mechanism was involved. However, the HG effect on Orai1 protein was significantly attenuated by MG132 (a ubiquitin-proteasome inhibitor) and NH₄Cl (a lysosomal pathway inhibitor). Furthermore, HG treatment for 8 h stimulated ubiquitination of Orai1 protein. We further found that polyethylene glycol-catalase, an antioxidant, significantly blunted the HG-induced reduction of Orai1 protein. In support of involvement of reactive oxygen species in the HG effects, hydrogen peroxide (H₂O₂) itself significantly decreased abundance of Orai1 protein and increased the level of ubiquitinated Orai1. Taken together, these results suggest that a short-term HG treatment decreased abundance of Orai1 protein in MCs by promoting the protein degradation through the ubiquitination-proteasome and -lysosome mechanisms. This HG-stimulated posttranslational mechanism was mediated by H₂O₂.

Recent novel approaches to limit oxidative stress and inflammation in diabetic complications

Diabetes is considered a major burden on the healthcare system of Western and non‐Western societies with the disease reaching epidemic proportions globally. Diabetic patients are highly susceptible to developing micro‐ and macrovascular complications, which contribute significantly to morbidity and mortality rates. Over the past decade, a plethora of research has demonstrated that oxidative stress and inflammation are intricately linked and significant drivers of these diabetic complications. Thus, the focus now has been towards specific mechanism‐based strategies that can target both oxidative stress and inflammatory pathways to improve the outcome of disease burden. This review will focus on the mechanisms that drive these diabetic complications and the feasibility of emerging new therapies to combat oxidative stress and inflammation in the diabetic milieu.

Nox4 is a Target for Tuberin Deficiency Syndrome

The mechanism by which TSC2 inactivation or deficiency contributes to the pathology of tuberous sclerosis complex (TSC) is not fully clear. We show that renal angiomyolipomas from TSC patients and kidney cortex from Tsc2+/− mice exhibit elevated levels of reactive oxygen species (ROS). Downregulation of tuberin (protein encoded by TSC2 gene) in renal proximal tubular epithelial cells significantly increased ROS concomitant with enhanced Nox4. Similarly, we found elevated levels of Nox4 in the renal cortex of Tsc2+/− mice and in the renal angiomyolipomas from TSC patients. Tuberin deficiency is associated with activation of mTORC1. Rapamycin, shRNAs targeting raptor, or inhibition of S6 kinase significantly inhibited the expression of Nox4, resulting in attenuation of production of ROS in tuberin-downregulated proximal tubular epithelial cells. In contrast, activation of mTORC1 increased Nox4 and ROS. These results indicate that Nox4 may be a potential target for tuberin-deficiency-derived diseases. Using a xenograft model from tuberin-null tubular cells in nude mice, both anti-sense Nox4 and GKT137831, a specific inhibitor of Nox1/4, significantly inhibited the tumor growth. Thus, our results demonstrate the presence of an antagonistic relationship between tuberin and Nox4 to drive oncogenesis in the tuberin deficiency syndrome and identify Nox4 as a target to develop a therapy for TSC.

Diabetic nephropathy: Is there a role for oxidative stress?

Oxidative stress has been implicated in the pathophysiology of diabetic nephropathy. Studies in experimental animal models of diabetes strongly implicate oxidant species as a major determinant in the pathophysiology of diabetic kidney disease. The translation, in the clinical setting, of these concepts have been quite disappointing, and new theories have challenged the concepts that oxidative stress per se plays a role in the pathophysiology of diabetic kidney disease. The concept of mitochondrial hormesis has been introduced to explain this apparent disconnect. Hormesis is intended as any cellular process that exhibits a biphasic response to exposure to increasing amounts of a substance or condition: specifically, in diabetic kidney disease, oxidant species may represent, at determined concentration, an essential and potentially protective factor. It could be postulated that excessive production or inhibition of oxidant species formation might result in an adverse phenotype. This review discusses the evidence underlying these two apparent contradicting concepts, with the aim to propose and speculate on potential mechanisms underlying the role of oxidant species in the pathophysiology of diabetic nephropathy and possibly open future more efficient therapies to be tested in the clinical settings.

Modulation of glutathione peroxidase activity by age-dependent carbonylation in glomeruli of diabetic mice

AIMS

Low levels of reactive oxygen species and resulting oxidative protein modifications may play a beneficial role in cellular function under stress conditions. Here we studied the influence of age-dependent protein carbonylation on expression and activity of the anti-oxidative selenoenzyme glutathione peroxidase (GPx) in insulin-deficient Ins2^Akita mice and type 2 diabetic obese db/db mice in context of diabetic nephropathy.

METHODS

Protein carbonylation, GPx expression and activity were examined in kidney tissue and lysates by common histological and protein biochemical methods.

RESULTS

In kidneys of Ins2^Akita mice, carbonylated proteins, GPx-1 and GPx-4 expression were mainly detected in podocytes and mesangial cells. GPx activity was increased in kidney cortex homogenates of these mice. Remarkably, young animals did not show a concomitant increase in GPx expression but enhanced GPx carbonylation. No carbonylation-dependent modification of GPx activity was detected in db/db mice. In cultured podocytes hyperglycemia induced an increase in GPx expression but had no effect on activity or carbonylation. In kidney tissue sections of type 1 or type 2 diabetes patients, GPx-1 and GPx-4 expression but not overall protein carbonylation was significantly decreased.

CONCLUSIONS

These results indicate the existence of a threshold for beneficial carbonylation-dependent redox signaling during the progression of diabetic nephropathy.

Redox Regulation of Inflammatory Processes Is Enzymatically Controlled

Redox regulation depends on the enzymatically controlled production and decay of redox active molecules. NADPH oxidases, superoxide dismutases, nitric oxide synthases, and others produce the redox active molecules superoxide, hydrogen peroxide, nitric oxide, and hydrogen sulfide. These react with target proteins inducing spatiotemporal modifications of cysteine residues within different signaling cascades. Thioredoxin family proteins are key regulators of the redox state of proteins. They regulate the formation and removal of oxidative modifications by specific thiol reduction and oxidation. All of these redox enzymes affect inflammatory processes and the innate and adaptive immune response. Interestingly, this regulation involves different mechanisms in different biological compartments and specialized cell types. The localization and activity of distinct proteins including, for instance, the transcription factor NFκB and the immune mediator HMGB1 are redox-regulated. The transmembrane protein ADAM17 releases proinflammatory mediators, such as TNFα, and is itself regulated by a thiol switch. Moreover, extracellular redox enzymes were shown to modulate the activity and migration behavior of various types of immune cells by acting as cytokines and/or chemokines. Within this review article, we will address the concept of redox signaling and the functions of both redox enzymes and redox active molecules in innate and adaptive immune responses.

Polymorphisms of Antioxidant Genes as a Target for Diabetes Management

Diabetes mellitus (DM) is one of the most important health problems with increasing prevalence worldwide. Oxidative stress, a result of imbalance between reactive oxygen species (ROS) generation and antioxidant defense mechanisms has been demonstrated as the main pathology in DM. Hyperglycemia-induced ROS productions can induce oxidative stress through four major molecular mechanisms including the polyol pathway, advanced glycation end- products formation, activation of protein kinase C isoforms, and the hexosamine pathways. In the development of type 2 DM (T2DM) and its complications, genetic and environmental factors play important roles. Therefore, the aim of this review was to focus on the assessment of single-nucleotide polymorphisms within antioxidant enzymes including superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, nitric oxide synthase, and NAD(P)H oxidase and their association with T2DM. The results would be helpful in understanding the mechanisms involved in pathogenesis of disease besides discovering new treatment approaches in management of DM.

SPARC paucity alleviates superoxide-mediated oxidative stress, apoptosis, and autophagy in diabetogenic hepatocytes

Secreted protein acidic and rich in cysteine (SPARC) is known to play a previously unappreciated role in diabetes, but its precise mechanism in liver/hepatocyte pathology remains unknown. Inhibition of SPARC is critical in resolving candidate pathogenic events such as production of reactive oxygen species (ROS), which are broadly considered for their roles in diabetes, and is capable of protecting functional hepatocytes. Here, we provide in vitro and in vivo evidence demonstrating pathological correlations between SPARC and streptozotocin (STZ)-induced diabetic rat livers as well as cultured hepatocytes induced by diabetogenic stimuli. Under these conditions, transient SPARC silencing was carried out to investigate the role of SPARC in the pathogenesis of pro-diabetic hepatocyte damage and dysfunction. The constitutive expression of SPARC in hepatocytes was up-regulated under a diabetic environment. In addition, Nox4-dependent superoxide generation contributed to increased expression of SPARC, and this was inhibited by tiron and pharmacological or genetic inactivation of Nox4-containing NADPH oxidase. Remarkably, SPARC deficiency inhibited diabetic stimuli-induced elevation of superoxide production and resolved salient features of hepatocyte damage such as impaired cytoprotection, inflammation, apoptosis, and autophagy. At the same time, links between SPARC, integrin-β1, Nox4-derived superoxide, and JNK signaling provide a basis for these phenotypes. Taken together with the observations that SPARC deficiency had protective effects on hepatocytes via a favorable inhibition profile, functional knowledge of SPARC may offer a unique therapeutic approach to preserve hepatocellular fate decisions in diabetes.

ROS signalling in the biology of cancer

Increased reactive oxygen species (ROS) production has been detected in various cancers and has been shown to have several roles, for example, they can activate pro-tumourigenic signalling, enhance cell survival and proliferation, and drive DNA damage and genetic instability. Counterintuitively ROS can also promote anti-tumourigenic signalling, initiating oxidative stress-induced tumour cell death. Tumour cells express elevated levels of antioxidant proteins to detoxify elevated ROS levels, establish a redox balance, while maintaining pro-tumourigenic signalling and resistance to apoptosis. Tumour cells have an altered redox balance to that of their normal counterparts and this identifies ROS manipulation as a potential target for cancer therapies. This review discusses the generation and sources of ROS within tumour cells, the regulation of ROS by antioxidant defence systems, as well as the effect of elevated ROS production on their signalling targets in cancer. It also provides an insight into how pro- and anti-tumourigenic ROS signalling pathways could be manipulated in the treatment of cancer.

APX-115, a first-in-class pan-NADPH oxidase (Nox) inhibitor, protects db/db mice from renal injury

Recent studies have suggested that renal Nox is important in the progression of diabetic nephropathy. Therefore, we investigated the effect of a novel pan-NOX-inhibitor, APX-115, on diabetic nephropathy in type 2 diabetic mice. Eight- week-old db/m and db/db mice were treated with APX-115 for 12 weeks. APX-115 was administered by oral gavage at a dose of 60 mg/kg per day. To compare the effects of APX-115 with a dual Nox1/Nox4 inhibitor, db/db mice were treated with GKT137831 according to the same protocol. APX-115 significantly improved insulin resistance in diabetic mice, similar to GKT137831. Oxidative stress as measured by plasma 8-isoprostane level was decreased in the APX-115 group compared with diabetic controls. All lipid profiles, both in plasma and tissues improved with Nox inhibition. APX-115 treatment decreased Nox1, Nox2, and Nox4 protein expression in the kidney. APX-115 decreased urinary albumin excretion and preserved creatinine level. In diabetic kidneys, APX-115 significantly improved mesangial expansion, but GKT137831 did not. In addition, F4/80 infiltration in the adipose tissue and kidney decreased with APX-115 treatment. We also found that TGF-β stimulated ROS generation in primary mouse mesangial cells (pMMCs) from wild-type, Nox1 KO, and Duox1 KO mice, but did not induce Nox activity in pMMCs from Nox2 knockout (KO), Nox4 KO, or Duox2 KO mice. These results indicate that activating Nox2, Nox4, or Duox2 in pMMCs is essential for TGF-β-mediated ROS generation. Our findings suggest that APX-115 may be as effective or may provide better protection than the dual Nox1/Nox4 inhibitor, and pan-Nox inhibition with APX-115 might be a promising therapy for diabetic nephropathy.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to "pinch hit" for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin-that boost cellular expression of antioxidant enzymes and glutathione-as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

Caveolin-1 in the Pathogenesis of Diabetic Nephropathy: Potential Therapeutic Target?

PURPOSE OF REVIEW

Diabetic nephropathy, a major microvascular complication of diabetes and the most common cause of end-stage renal disease, is characterized by prominent accumulation of extracellular matrix. The membrane microdomains caveolae, and their integral protein caveolin-1, play critical roles in the regulation of signal transduction. In this review we discuss current knowledge of the contribution of caveolin-1/caveolae to profibrotic signaling and the pathogenesis of diabetic kidney disease, and assess its potential as a therapeutic target.

RECENT FINDINGS

Caveolin (cav)-1 is key to facilitating profibrotic signal transduction induced by several stimuli known to be pathogenic in diabetic nephropathy, including the most prominent factors hyperglycemia and angiotensin II. Phosphorylation of cav-1 on Y14 is an important regulator of these responses. In vivo studies support a pathogenic role for caveolae in the progression of diabetic nephropathy. Targeting caveolin-1/caveolae would enable inhibition of multiple profibrotic pathways, representing a novel and potentially potent therapeutic option for diabetic nephropathy.