The role of cPLA2 in Methylglyoxal-induced cell apoptosis of HUVECs

Inhibitory effects and mechanisms of phenolic compounds in rapeseed oil on advanced glycation end product formation in chemical and cellular models in vitro

Sinapic acid (SA), canolol (CAO) and canolol dimer (CAO dimer) are the main phenolic compounds in rapeseed oil. However, their possible efficacy against glycation remains unclear. This study aims to explore the impacts of these substances on the formation of advanced glycation end products (AGEs) based on chemical and cellular models in vitro. Based on fluorescence spectroscopy results, three chemical models of BSA-fructose, BSA-methylglyoxal (MGO), and arginine (Arg)-MGO showed that SA/CAO/CAO dimer could effectively reduce AGE formation but with different abilities. After SA/CAO/CAO dimer incubation, effective protection against BSA protein glycation was observed and three different MGO adducts were formed. In MGO-induced HUVEC cell models, only CAO and CAO dimer significantly inhibited oxidative stress and cell apoptosis, accompanied by the regulation of the Nrf2-HO-1 pathway. During the inhibition, 20 and 12 lipid mediators were reversed in the CAO and CAO dimer groups compared to the MGO group.

Methylglyoxal induces endothelial cell apoptosis and coronary microvascular dysfunction through regulating AR-cPLA2 signaling

OBJECTIVE

Since diabetic patients with coronary microvascular dysfunction (CMD) exhibit high cardiac mortality and women have higher prevalence of non-obstructive coronary artery disease than men, we tried to expand the limited understanding about the etiology and the sex difference of diabetic CMD.

APPROACH AND RESULTS

Accumulated methylglyoxal (MGO) due to diabetes promotes vascular damage and it was used for mimicking diabetic status. Flow cytometry analysis and isometric tension measurement were performed to evaluate coronary artery endothelial injury. MGO induced apoptosis of coronary endothelial cells, accompanied by downregulation of androgen receptor (AR). Lentivirus-mediated stable expression of AR in coronary endothelial cells increased anti-apoptotic Bcl-2 expression and attenuated MGO-induced cell apoptosis. cPLA2 activation was the downstream of AR downregulation by MGO treatment. Moreover, MGO also activated cPLA2 rapidly to impair endothelium-dependent vasodilation of coronary arteries from mice. Reactive oxygen species (ROS) overproduction was demonstrated to account for MGO-mediated cPLA2 activation and endothelial dysfunction. Importantly, AR blockade increased endothelial ROS production whereas AR activation protected coronary artery endothelial vasodilatory function from the MGO-induced injury. Although galectin-3 upregulation was confirmed by siRNA knockdown in endothelial cells not to participate in MGO-induced endothelial apoptosis, pharmacological inhibitor of galectin-3 further enhanced MGO-triggered ROS generation and coronary artery endothelial impairment.

CONCLUSIONS

Our data proposed the AR downregulation-ROS overproduction-cPLA2 activation pathway as one of the mechanisms underlying diabetic CMD and postulated a possible reason for the sex difference of CMD-related angina. Meanwhile, MGO-induced galectin-3 activation played a compensatory role against coronary endothelial dysfunction.

In Vitro Methodologies to Study the Role of Advanced Glycation End Products (AGEs) in Neurodegeneration

Advanced glycation end products (AGEs) can be present in food or be endogenously produced in biological systems. Their formation has been associated with chronic neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis. The implication of AGEs in neurodegeneration is related to their ability to bind to AGE-specific receptors and the ability of their precursors to induce the so-called “dicarbonyl stress”, resulting in cross-linking and protein damage. However, the mode of action underlying their role in neurodegeneration remains unclear. While some research has been carried out in observational clinical studies, further in vitro studies may help elucidate these underlying modes of action. This review presents and discusses in vitro methodologies used in research on the potential role of AGEs in neuroinflammation and neurodegeneration. The overview reveals the main concepts linking AGEs to neurodegeneration, the current findings, and the available and advisable in vitro models to study their role. Moreover, the major questions regarding the role of AGEs in neurodegenerative diseases and the challenges and discrepancies in the research field are discussed.

Metformin prevents methylglyoxal-induced apoptosis by suppressing oxidative stress in vitro and in vivo

Methylglyoxal (MGO) is an active metabolite of glucose and plays a prominent role in the pathogenesis of diabetic vascular complications, including endothelial cell apoptosis induced by oxidative stress. Metformin (MET), a widely prescribed antidiabetic agent, appears to reduce excessive reactive oxygen species (ROS) generation and limit cell apoptosis. However, the molecular mechanisms underlying this process are still not fully elucidated. We reported here that MET prevents MGO-induced apoptosis by suppressing oxidative stress in vitro and in vivo. Protein expression and protein phosphorylation were investigated using western blotting, ELISA, and immunohistochemical staining, respectively. Cell viability and apoptosis were assessed by the MTT assay, TUNEL staining, and Annexin V-FITC and propidium iodide double staining. ROS generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Our results revealed that MET prevented MGO-induced HUVEC apoptosis, inhibited apoptosis-associated biochemical changes such as loss of MMP, the elevation of the Bax/Bcl-2 ratio, and activation of cleaved caspase-3, and attenuated MGO-induced mitochondrial morphological alterations in a dose-dependent manner. MET pretreatment also significantly suppressed MGO-stimulated ROS production, increased signaling through the ROS-mediated PI3K/Akt and Nrf2/HO-1 pathways, and markedly elevated the levels of its downstream antioxidants. Finally, similar results were obtained in vivo, and we demonstrated that MET prevented MGO-induced oxidative damage, apoptosis, and inflammation. As expected, MET reversed MGO-induced downregulation of Nrf2 and p-Akt. In addition, a PI3K inhibitor (LY-294002) and a Nrf2 inhibitor (ML385) observably attenuated the protective effects of MET on MGO-induced apoptosis and ROS generation by inhibiting the Nrf2/HO-1 pathways, while a ROS scavenger (NAC) and a permeability transition pores inhibitor (CsA) completely reversed these effects. Collectively, these findings broaden our understanding of the mechanism by which MET regulates apoptosis induced by MGO under oxidative stress conditions, with important implications regarding the potential application of MET for the treatment of diabetic vascular complications.

New terpenic and phenolic compounds from Suaeda monoica reverse oxidative and apoptotic damages in human endothelial cells

Elevation in hyperglycemia-associated methylglyoxal level can trigger vascular endothelial cells oxidative stress and apoptosis. The present work assesses the cell proliferative, anti-oxidative and anti-apoptotic potential of Suaeda monoica derived four new terpenes: a norsesquaterpenol (normonisesquaterpenol), a monocyclic triterpenoid (suaedanortriterpene dione), an aromatic monoterpenic ester and a labdane-type norditerpenic xyloside as well as two new phenols: an alkylated β-naphthol and a β-methoxy naphthalene in cultured human umbilical vein endothelial cells (HUVEC). Of these, suaedanortriterpenedione (53.7%), normonisesquaterpenol (51.4%) and norditerpenic xyloside (48%) showed the most promising cell proliferative activities compared to others. Moreover, normonisesquaterpenol, norditerpenic xyloside and suaedanortriterpenedione efficiently reversed the oxidative and apoptotic cell damage via downregulation of capase-3/7 by 44.3%, 42.2% and 39.4%, respectively against dichlorofluorescin, whereas by 46.2%, 43.5% and 42.5%, respectively against methylglyoxal. Aminoguanidine, the reference drug inhibited caspase-3/7 activity by 56.2% and 54.7% through attenuation of dichlorofluorescin and methylglyoxal, respectively. Further in silico molecular docking analysis revealed formation of stable complexes between the tested compounds and caspase-3/7. Conclusively, we for the first time demonstrate the growth stimulatory, anti-oxidative and anti-apoptotic salutations of S. monoica derived novel compounds in human endothelial cells. This warrants their further assessment as vascular cell protective and rejuvenating therapeutics, especially in hyperglycemic conditions.

Endothelial Dysfunction in Atherosclerotic Cardiovascular Diseases and Beyond: From Mechanism to Pharmacotherapies

The endothelium, a cellular monolayer lining the blood vessel wall, plays a critical role in maintaining multiorgan health and homeostasis. Endothelial functions in health include dynamic maintenance of vascular tone, angiogenesis, hemostasis, and the provision of an antioxidant, anti-inflammatory, and antithrombotic interface. Dysfunction of the vascular endothelium presents with impaired endothelium-dependent vasodilation, heightened oxidative stress, chronic inflammation, leukocyte adhesion and hyperpermeability, and endothelial cell senescence. Recent studies have implicated altered endothelial cell metabolism and endothelial-to-mesenchymal transition as new features of endothelial dysfunction. Endothelial dysfunction is regarded as a hallmark of many diverse human panvascular diseases, including atherosclerosis, hypertension, and diabetes. Endothelial dysfunction has also been implicated in severe coronavirus disease 2019. Many clinically used pharmacotherapies, ranging from traditional lipid-lowering drugs, antihypertensive drugs, and antidiabetic drugs to proprotein convertase subtilisin/kexin type 9 inhibitors and interleukin 1β monoclonal antibodies, counter endothelial dysfunction as part of their clinical benefits. The regulation of endothelial dysfunction by noncoding RNAs has provided novel insights into these newly described regulators of endothelial dysfunction, thus yielding potential new therapeutic approaches. Altogether, a better understanding of the versatile (dys)functions of endothelial cells will not only deepen our comprehension of human diseases but also accelerate effective therapeutic drug discovery. In this review, we provide a timely overview of the multiple layers of endothelial function, describe the consequences and mechanisms of endothelial dysfunction, and identify pathways to effective targeted therapies. SIGNIFICANCE STATEMENT: The endothelium was initially considered to be a semipermeable biomechanical barrier and gatekeeper of vascular health. In recent decades, a deepened understanding of the biological functions of the endothelium has led to its recognition as a ubiquitous tissue regulating vascular tone, cell behavior, innate immunity, cell-cell interactions, and cell metabolism in the vessel wall. Endothelial dysfunction is the hallmark of cardiovascular, metabolic, and emerging infectious diseases. Pharmacotherapies targeting endothelial dysfunction have potential for treatment of cardiovascular and many other diseases.

Renal tubular injury induced by glyphosate combined with hard water: the role of cytosolic phospholipase A2

Background

The combined effects of glyphosate and hard water on chronic kidney disease of unknown etiology (CDKu) have attracted much interest, but the mechanisms remain unknown. Cytoplasmic phospholipase A₂ (cPLA₂) plays a key role in the acute and chronic inflammatory reactions. This study explored the effect of glyphosate combined with hard water on renal tubules and the possible targets and mechanisms involved.

Methods

In vivo experiments were conducted to investigate the synergistic effects and potential mechanisms of glyphosate and hard water on renal tubular injury in mice.

Results

Administration of glyphosate in mice resulted in elevated levels of β2-microglobulin (β₂-MG), albumin (ALB), and serum creatinine (SCr) compared to control mice. This increase was more pronounce when glyphosate was combined with hard water. In the glyphosate-treated mice, small areas of the kidney revealed fibroblast proliferation and vacuolar degeneration, particularly at the higher dose of 400 mg/kg glyphosate. However, the combination of glyphosate and hard water induced an even greater degree of pathological changes in the kidney. Immunofluorescence and western blot analyses showed that glyphosate and hard water had a coordinated effect on calcium ions (Ca²⁺)-activated phospholipase A₂ and the activation may play a key role in inflammation and renal tubular injury. Exposure to glyphosate alone or glyphosate plus hard water increased the levels of oxidative stress markers and inflammatory biomarkers, namely, thromboxane A₂ (TX-A₂), leukotriene B₄ (LTB₄), prostaglandin E₂ (PGE₂), nitric oxide synthase (NOS), and nitric oxide (NO). Parameters of oxidative stress, including the levels of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were decreased. Further analysis showed that the levels of these biomarkers were significantly different between the mice treated with glyphosate plus hard water and the mice treated with glyphosate alone.

Conclusions

These findings suggested that hard water combined with glyphosate can induce renal tubular injury in mice, and this may involve mitogen-activated protein kinases (MAPK)/cytosolic phospholipase A₂ (cPLA₂)/arachidonic acid (AA) and its downstream factors.

Urocortin participates in LPS-induced apoptosis of THP-1 macrophages via S1P-cPLA2 signaling pathway

There is little literature showing the effect of urocortin (UCN) on macrophage apoptosis. The underlying mechanism is also unclear. This work was to investigate the involvement of UCN in the regulation of LPS-induced macrophage apoptosis and hence in the prevention from the atherosclerotic lesion development through targeting PLA2. Flow cytometry analysis showed that cell apoptosis was increased by more than 50% after LPS treatment in human THP-1 macrophage. Lp-PLA2 and cPLA2 were found to mediate LPS-induced macrophage apoptosis and NF-κB differentially influenced the expression of Lp-PLA2 and cPLA2. However, the reverse regulation of the expression of Lp-PLA2 and cPLA2 by NF-κB suggested that NF-κB may not be a key target for regulating macrophage apoptosis. Interestingly, we found that the approximate three folds upregulation of cPLA2 was in line with the induction of S1P formation and cell apoptosis by LPS. Inversely, LPS obviously decreased UCN expression by about 50% and secretion by about 25%. Both the enzyme inhibitor and knockdown expression of cPLA2 could completely abolish LPS-induced cell apoptosis. In addition, suppression of S1P synthesis by Sphk1 inhibitor PF-543 reduced the expression of cPLA2 and cell apoptosis but at the same time restored the normal level of UCN in cell culture supernatant. Furthermore, addition of exogenous UCN also reversed LPS-induced expression of cPLA2 and apoptosis. Taken together, UCN may be the reverse regulator of LPS-S1P-cPLA2-apoptosis pathway, thereby contributing to the prevention from the formation of unstable plaques.

Methylglyoxal-Induced Dysfunction in Brain Endothelial Cells via the Suppression of Akt/HIF-1α Pathway and Activation of Mitophagy Associated with Increased Reactive Oxygen Species

Methylglyoxal (MG) is a dicarbonyl compound, the level of which is increased in the blood of diabetes patients. MG is reported to be involved in the development of cerebrovascular complications in diabetes, but the exact mechanisms need to be elucidated. Here, we investigated the possible roles of oxidative stress and mitophagy in MG-induced functional damage in brain endothelial cells (ECs). Treatment of MG significantly altered metabolic stress as observed by the oxygen-consumption rate and barrier-integrity as found in impaired trans-endothelial electrical resistance in brain ECs. The accumulation of MG adducts and the disturbance of the glyoxalase system, which are major detoxification enzymes of MG, occurred concurrently. Reactive oxygen species (ROS)-triggered oxidative damage was observed with increased mitochondrial ROS production and the suppressed Akt/hypoxia-inducible factor 1 alpha (HIF-1α) pathway. Along with the disturbance of mitochondrial bioenergetic function, parkin-1-mediated mitophagy was increased by MG. Treatment of N-acetyl cysteine significantly reversed mitochondrial damage and mitophagy. Notably, MG induced dysregulation of tight junction proteins including occludin, claudin-5, and zonula occluden-1 in brain ECs. Here, we propose that diabetic metabolite MG-associated oxidative stress may contribute to mitochondrial damage and autophagy in brain ECs, resulting in the dysregulation of tight junction proteins and the impairment of permeability.

Osteomeles schwerinae Extract and Its Major Compounds Inhibit Methylglyoxal-Induced Apoptosis in Human Retinal Pigment Epithelial Cells

The accumulation and formation of advanced glycation end products (AGEs) are related to diabetes and age-related disease. Osteomeles schwerinae C. K. Schneid. (Rosaceae, OSSC) is used traditionally for the treatment of various diseases in Asia. Previous studies have shown that OSSC elicits preventive effects in an in vivo model of diabetes. This study was to evaluate the antiapoptotic effects of dried leaves and twigs of OSSC extract and its major compounds in ARPE-19 cells-spontaneously arising human retinal pigment epithelial cells-under diabetic conditions. To examine the effects of an OSSC extract and its active compounds (acetylvitexin, hyperoside and quercitrin) on apoptosis in methylglyoxal (MG, the active precursor in the formation of AGEs)-treated ARPE-19 cells and the mechanism by which these effects occur, apoptosis was measured using flow cytometry analysis. Protein expression levels of phospho-p53 (p-p53), Bax and Bcl-2 were determined by western blot analyses. The OSSC extract inhibited apoptosis in MG-treated ARPE-19 cells in a dose-dependent manner. The major compounds also reduced the rate of apoptosis. Both the extract and major compounds also inhibited the expression of p-p53 and Bax and increased the levels of Bcl-2 that had been previously reduced by MG treatment. The OSSC extract (0.1 μg/mL) and its major compounds (0.01 μM) attenuated apoptosis in ARPE-19 cells under toxic diabetic conditions by downregulating of expression of p-p53 and Bax. OSSC may serve as an alternative therapy to retard the development of diabetic retinopathy.

Proanthocyanidins from the stem bark of Rhus tripartita ameliorate methylgloxal-induced endothelial cell apoptosis

In traditional Arabian medicine, the Rhus tripartita plant (family Anacardiaceae) has been used to treat inflammatory conditions. Although Rhus extracts have been reported for their cardioprotective effects, information regarding their active principle compounds remains insufficient. The present investigation was aimed at determining the antioxidant chemical constituents of the methanolic extract of R. tripartita stem bark and evaluating their ability to ameliorate methylglyoxal-induced endothelial cell apoptosis. Ten flavonoid compounds (1–10) were isolated and identified using DPPH radical scavenging bioassay-guided chromatographic separation. A new proanthocyanidin (rhuspartin) (1) was isolated and identified as 3,5,13,14-flavantetrol-(4β→8)-catechin, using extensive spectroscopic data and high resolution-mass spectrometry. Among the compounds (1, 5, 7–10) tested for toxicity toward cultured endothelial cells (HUVECs), the non-cytotoxic compounds 1 and 7 evinced cytoprotective potential that reversed the methylglyoxal-induced apoptosis (by 62% and 64%, respectively) through downregulation of caspase 3/7.

Methylglyoxal down-regulates the expression of cell cycle associated genes and activates the p53 pathway in human umbilical vein endothelial cells

Although methylglyoxal (MGO) has emerged as key mediator of diabetic microvascular complications, the influence of MGO on the vascular transcriptome has not thoroughly been assessed. Since diabetes is associated with low grade inflammation causing sustained nuclear factor-kappa B (NF-κB) activation, the current study addressed 1) to what extent MGO changes the transcriptome of human umbilical vein endothelial cells (HUVECs) exposed to an inflammatory milieu, 2) what are the dominant pathways by which these changes occur and 3) to what extent is this affected by carnosine, a putative scavenger of MGO. Microarray analysis revealed that exposure of HUVECs to high MGO concentrations significantly changes gene expression, characterized by prominent down-regulation of cell cycle associated genes and up-regulation of heme oxygenase-1 (HO-1). KEGG-based pathway analysis identified six significantly enriched pathways of which the p53 pathway was the most affected. No significant enrichment of inflammatory pathways was found, yet, MGO did inhibit VCAM-1 expression in Western blot analysis. Carnosine significantly counteracted MGO-mediated changes in a subset of differentially expressed genes. Collectively, our results suggest that MGO initiates distinct transcriptional changes in cell cycle/apoptosis genes, which may explain MGO toxicity at high concentrations. MGO did not augment TNF-α induced inflammation.

Hormetic potential of methylglyoxal, a side-product of glycolysis, in switching tumours from growth to death

Metabolic reprogramming toward aerobic glycolysis unavoidably favours methylglyoxal (MG) and advanced glycation end products (AGEs) formation in cancer cells. MG was initially considered a highly cytotoxic molecule with potential anti-cancer value. However, we have recently demonstrated that MG enhanced tumour growth and metastasis. In an attempt to understand this dual role, we explored MG-mediated dicarbonyl stress status in four breast and glioblastoma cancer cell lines in relation with their glycolytic phenotype and MG detoxifying capacity. In glycolytic cancer cells cultured in high glucose, we observed a significant increase of the conversion of MG to D-lactate through the glyoxalase system. Moreover, upon exogenous MG challenge, glycolytic cells showed elevated amounts of intracellular MG and induced de novo GLO1 detoxifying enzyme and Nrf2 expression. Thus, supporting the adaptive nature of glycolytic cancer cells to MG dicarbonyl stress when compared to non-glycolytic ones. Finally and consistent with the pro-tumoural role of MG, we showed that low doses of MG induced AGEs formation and tumour growth in vivo, both of which can be reversed using a MG scavenger. Our study represents the first demonstration of a hormetic effect of MG defined by a low-dose stimulation and a high-dose inhibition of tumour growth.