Neetu Sud
New Delhi, India.
DOI: 10.4236/jdm.2026.162007   PDF    HTML   XML   61 Downloads   248 Views   Citations

Abstract

Diabetes is a highly prevalent disease worldwide. It is associated with perturbation in glucose metabolism. Diabetic environment has immense impact on endothelial cells (ECs) which line the endothelium and regulate many vascular functions. Hyperglycemia (HG) is a hallmark of diabetes and it promotes formation of Advanced Glycation End Products (AGEs), oxidative stress, mitochondrial abnormalities, inflammation, polyol pathway, hexosamine pathway, etc. These cellular processes hamper EC function resulting in endothelial cell dysfunction (ED). Several diabetic vascular complications are initiated by ED. The persistence of diabetes related endothelial cell damage even after normalization of glucose levels is known as metabolic memory, which further accelerates diabetic complications. Therefore, diabetes makes patients more susceptible to vascular complications. Herein, some important diabetes related cellular phenomena that perturb EC function are described briefly. Understanding these deleterious phenomena is essential for developing treatment strategies to ameliorate diabetic ED.

Keywords

Diabetes, Endothelial Dysfunction, Hyperglycemia, Oxidative Stress, Inflammation

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1. Introduction

Diabetes is a serious global disease [1]. Diabetes immensely increases risk of developing diabetic complications including macrovascular complications such as cardiovascular diseases, atherosclerosis, coronary artery disease, stroke, etc., and microvascular complications such as diabetic retinopathy, diabetic nephropathy, and diabetic neuropathy [2]-[4]. ECs produce vasodilator nitric oxide (NO) and regulate many functions including vascular tone, inflammation, etc. [5] [6]. Many studies have shown that expression of various genes related to EC pathways including vasoconstriction, vasodilation, inflammation, apoptosis, cell adhesion, extracellular matrix (ECM), etc., is altered under diabetic conditions suggesting prevalence of ED, which is known to act as a stimulus for diabetic vascular disease [7]-[9]. Several studies have analyzed the impact of antidiabetic therapy on endothelial function; no therapy has yet proved to be fully successful in ameliorating ED related to diabetes [10] [11]. Hence, it is imperative to find more potent therapies targeting diabetic ED to ameliorate complications. In this context, it is important to understand the mechanisms of diabetic ED, which is promoted by diverse molecular mediators. Herein, such critical mediators are briefly described. The literature described here provides brief overview of the effect of diabetic conditions mostly on EC function in different types of ECs and is selected from some articles available mainly in PubMed.

2. Advanced Glycation End Products (AGEs)

Nonenzymatic glycation and oxidation of proteins or lipids produce AGEs under normal physiological environment but their production increases in many diseases including diabetes, cardiovascular disease, cancer, etc. [12]. The harmful effects of AGEs in many diseases including diabetic cardiovascular complications arise due to either crosslinking of proteins or by interaction with AGE receptors such as Receptor for AGE (RAGE) [13] [14]. RAGE-expressing cells are usually present in vicinity of sites of high AGE accumulation in regions such as diabetic vasculature. High concentrations of AGEs in serum of type 2 diabetes patients are related to ED [15]. AGE levels are known to be significantly higher in diabetics having vascular complications as compared to those without complications [16].

AGEs act as driver of diabetic ED. HG-induced AGE production involves reactive oxygen species (ROS) and can be prevented by antioxidants in ECs [17]. Albumin-derived AGEs decrease expression of NO-producing enzyme eNOS by decreasing half-life of its mRNA [18]. AGE-modified albumin decreases eNOS activity quickly by causing decrease in its serine phosphorylation and slowly by decreasing its expression [19]. AGE-RAGE binding induces oxidant stress and activation of inflammation related transcription factor NF-ĸB in ECs, which induces expression of atherosclerosis related adhesion molecule VCAM-1 (Vascular Cell Adhesion Molecule 1), that potentiates their ability to bind with circulating monocytes and contributes to diabetic vascular disease [20]. The oxidant stress is harmful as it can potentially favor formation of vascular lesions [21]. AGE-BSA induces aberration in coagulant and barrier functions of ECs [22]. AGE product of low density lipoprotein induces inflammation related cytokine production [23].

Because of low mitochondrial content, ECs mainly depend on glycolysis for ATP production, rather than on mitochondrial oxidative phosphorylation [24]. HG increases glycolytic flux, resulting in increased concentration of glycolysis byproduct methylglyoxal (MGO), which is a dicarbonyl metabolite and AGE precursor and augments ED by multiple mechanisms including apoptosis, oxidative stress, inflammation, etc. [25]. It alters brain EC permeability by decreasing gene expression, promoting mislocalization, or glycation of tight junction proteins [26]. High plasma MGO levels are linked with cardiovascular disease in diabetes patients [27] [28]. Methylglyoxal-derived hemoglobin-AGEs are involved in inducing ROS formation, apoptosis and cause ED [29]. ED induced by HG is suggested to be mediated by MGO [30]. HG-induced MGO formation also disrupts attachment of EC to ECM by glycation of human type IV collagen, which hinders EC survival and angiogenesis, and is considered to be linked with diabetic vascular dysfunction [31]. MGO is detoxified by glyoxalase system which has two cooperating enzymes Glyoxalase 1 (Glo1) and Glyoxalase 2 (Glo2) [32]. HG mediated AGE formation is abrogated by overexpression of glyoxalase-I in ECs [33]. GLO1-knockdown in Human Aortic Endothelial Cells (HAECs) exposed to HG causes MGO accumulation and resultant inflammation, apoptosis and ED [34]. Overall, AGEs are critically involved in promoting conditions that favour diabetic complications.

3. Mitochondrial Abnormalities

Altered mitochondrial dynamics is observed in diabetic conditions. HG induces EC mitochondrial abnormalities such as mitochondria fragmentation, increased mitochondrial (mt) ROS production, alterations in mitochondrial morphology, membrane potential, fission, fusion, etc., and mitochondrial alterations are associated with many harmful effects such as apoptosis, reduced nitric oxide bioavailability, etc. [35]-[37]. HG induced mtROS production triggers leakage of mtDNA into the cytosol, which is sensed by DNA sensing cyclic GMP-AMP synthase (cGAS). This activates STING (stimulator of interferon genes) signaling, which stimulates inflammation and apoptosis, thus augmenting diabetes related aortic endothelial cell injury [38].

Hyperglycemia causes endothelial damage by activation of Protein Kinase C (PKC), AGE production, sorbitol accumulation, and the hexosamine pathway via increase in mitochondrial ROS production in ECs [39] [40]. Several studies show that HG induces alterations in levels of proteins related to mitochondrial dynamics. HG induces increase in EC mitochondrial fission and increases protein levels of fission proteins Fis-1 (Fission protein 1), Drp1 (dynamin-related protein 1) whereas that of fusion proteins OPA1 (optic atrophy 1) or Mfn2 (Mitofusin 2) is not significantly altered and ECs from diabetes mellitus (DM) patients with ED have higher Fis1 protein levels, modified mitochondria morphology and network compared to healthy volunteers [36]. Drp1 expression is increased while Fis1, MFN2, and OPA1 expression is unaltered by HG treatment of cultured human umbilical vein endothelial cells (HUVEC) in a different study [41]. Another study shows that HG induces decrease in fusion proteins Mfn1, Mfn2, and Opa1 while fission protein Fis1 first increases and then decreases in ECs and suggests that HG mediated mitochondrial fragmentation is regulated mainly by fusion inhibition rather than by fission activation [42]. HG has also been shown to induce altered mitochondria morphology and enhance Drp1 and reduce OPA1 in ECs [43]. The differences in results of different studies arise because mitochondrial fission and fusion continuously go through dynamic changes and the studies have not fully examined the dynamic changes [42]. Increased mitochondria fragmentation, reduced OPA1 protein levels, higher DRP1, and higher superoxide levels are seen in coronary ECs isolated from diabetic mice compared to ECs from control mice [35]. Overall imbalance of mitochondrial fission and fusion is induced by HG. ED in diabetic conditions is related to mitochondrial abnormalities.

4. PKC Activation

PKC is a family of serine/threonine kinases involved in diverse cell signaling pathways and several studies suggest key role of PKC in impairing endothelial function in diabetes [44]. HG induces EC PKC activation, which triggers ED by several mechanisms such as decrease in NO production or bioavailability, reduction in endothelium-dependent relaxation, increase in EC permeability, oxidative stress, apoptosis, etc. [45]-[48]. Intermittent high glucose is more potent than stable high glucose in stimulating PKC activation related expression of adhesion molecules in ECs via overproduction of mitochondrial free radicals [49]. Overall, PKC plays key role in HG induced ED.

5. Inflammation

Inflammation and ED are induced by postprandial HG, which may augment atherosclerosis and cardiovascular complications [50]. Fluctuating glucose is a critical inducer of inflammation [51]. Fluctuating glucose exposure of ECs triggers increase in several proinflammatory molecules [51]. Monocytes treated with HG show increased adhesion to ECs and increased expression of inflammatory molecules that are important in the pathogenesis of diabetes complications [52]. Monocytes from hyperglycemic diabetes patients without hyperlipidemia also show higher EC binding compared to controls [53]. ICAM-1 (Intercellular Adhesion Molecule-1) and VCAM-1 protein expression in HUVECs isolated from pregnant women with Gestational Diabetes Mellitus (GDM) is elevated compared to HUVECs without GDM. Monocyte adhesion is higher in GDM-HUVECs than in normal HUVECs [54].

PKC dependent endothelial-neutrophil cell adhesion and expression of endothelial adhesion molecules such as (ICAM-1), P-selectin, and E-selectin are induced by HG treatment of HUVECs and EC-neutrophil adhesion is known to augment vascular inflammation leading to vascular diseases [55]. Periodic high glucose is more potent than constant high glucose treatment in inducing secretion and expression of inflammation causing molecules such as IL-6, TNF-α (tumour necrosis factor-alpha) and ICAM-1 in human coronary artery endothelial cells (HCAECs) [56].

HG induced elevation of Microtubule affinity regulating kinase 4 (MARK4) expression mediates activation of NOD-like receptor pyrin domain 3 (NLRP3) inflammasome and production of cytokines interleukin (IL)-1β and IL-18 in ECs [57]. Increase in inflammation related transcription factor ELF3 (E74-like ETS transcription factor 3) and decrease in SET8 protein (SET domain-containing protein 8) by HG upregulate MARK4 expression. Diabetic patients and rats show SET8 downregulation and ELF3 upregulation. Inhibition of NLRP3 inflammasome attenuates HG induced ED [58]. Hence, a diabetic environment activates EC inflammation.

6. Polyol Pathway

Under physiological conditions, the glucose metabolism pathway called polyol pathway is insignificant as its first enzyme Aldose Reductase (AR), has low affinity for glucose. However, in diabetic conditions, about 30% of blood glucose is fluxed via polyol pathway and generates oxidative stress in many cell types of the body including lens and nerve [59] [60]. This pathway involves reduction of glucose to sorbitol by AR, which consumes reduced nicotinamide adenine dinucleotide phosphate (NADPH). This creates deficiency of reduced NADPH for enzymes such as antioxidant reduced Glutathione (GSH) regenerating antioxidant enzyme glutathione reductase. This leads to reduction in cellular antioxidant capacity. The second enzyme of this pathway sorbitol dehydrogenase utilizes NAD+ as cofactor and oxidizes sorbitol to fructose, which reduces NAD+ to NADH ratio, and the increase in NADH levels promotes ROS generation by NADH oxidase. The increase in polyol pathway by HG contributes to cellular stress [61]. Accumulation of triose phosphates due to increase in cytosolic NADH/NAD+ ratio provokes AGE precursor (MGO) formation and PKC activation via diacylglycerol formation [62]. Sorbitol is hydrophyllic and cannot easily cross cell membrane; its intracellular accumulation disturbs osmotic balance [63]. HG treatment of HUVECs increases sorbitol levels, fragmented DNA, caspase-3 activity, and oxidative stress, all of which are reduced by aldose reductase inhibitor SNK-860, suggesting involvement of polyol pathway in HG mediated EC damage [64]. Hence polyol pathway is harmful in a diabetic environment.

7. Hexosamine Biosynthesis Pathway (HBP)

In diabetes, increased glucose flux via hexosamine biosynthesis results in increased levels of its end product, uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), which is a substrate of the enzyme O-GlcNAc transferase (OGT), that catalyzes protein O-GlcNAcylation (which is defined as addition of N-acetylglucosamine to serine or threonine amino acids of proteins) [65] [66]. HG induces excessive mitochondria derived superoxide production which triggers activation of hexosamine pathway in ECs [40]. HG induces eNOS O-GlcNAcylation, which is reversed by inhibiting the first and rate-limiting enzyme of the hexosamine biosynthesis using glutamine: fructose-6-phosphate amidotransferase (GFAT) inhibitor azaserine in HCAECs [67]. The presence of eNOS O-GlcNAcylation sites around the Ser1177 residue disables Akt binding to phosphorylate and activate eNOS. HG induced eNOS O-GlcNAcylation and decrease in serine1177 phosphorylation is reversed by GFAT antisense oligonucleotides or by inhibitors of mitochondrial superoxide production in cultured bovine aortic endothelial cells (BAECs) [68]. O-GlcNAcylation promotes atherosclerosis-related complications in diabetes. Higher EC O-GlcNAcylation was observed in carotid plaques from diabetic patients compared to nondiabetics [67]. Aorta of diabetic rats also exhibits increased GlcNAc modification of eNOS and reduced eNOS activity compared to age-matched nondiabetic rats [68]. Coronary ECs isolated from diabetic mice have reduced levels of O-GlcNAc modification removing enzyme called O-GlcNAcase (OGA), and also have elevated OGT protein levels and higher protein O-GlcNAc modification compared to ECs from control mice. Protein O-GlcNAcylation levels decrease and coronary EC function becomes better in diabetic mice by overexpressing OGA in ECs [69]. HG induces O-GlcNAc modification of transcription factor Specificity protein 1 (Sp1), which upregulates EC expression of inflammatory molecule ICAM-1, which is known to cause damage to the retina in diabetic retinopathy [70]. Enhancement of O-GlcNAcylation using OGA inhibitor PUGNAc decreases glyoxal (AGE precursor) induced ROS generation and apoptosis in Human Retinal Microvascular Endothelial Cells (HRECs) suggesting that it plays protective role in diabetic retinopathy [71]. These studies indicate that O-GlcNAcylation has damaging effect or protective effect on ECs depending on the target protein or the stress type.

8. Metabolic Memory

Several studies show persistence of harmful effects of diabetic conditions even after glucose levels normalization, which is known as metabolic memory. Under diabetic conditions, epigenetic alterations involving DNA methylation, histone modifications, and non-coding RNAs contribute to diabetic complications [72]. Transient HG is shown to trigger persistent NFκB-p65 gene transcription by different mechanisms such as recruitment of SET7 (SET domain containing lysine methyltransferase 7), H3K4 mono-methylation, decrease in H3K9 methylation and enhanced recruitment of Lysine-Specific Demethylase 1 (LSD1) on the NFκB-p65 promoter [73]. Metabolic memory of HG causes persistent increase in pro-inflammatory molecules and elevated atherosclerosis [73].

The mitochondrial adaptor p66Shc acts as a key mediator of vascular hyperglycemic memory in diabetes [74]. HG induces PKC mediated activation of p66Shc via Ser-36 phosphorylation, which persists even after achievement of normoglycemia in ECs. This causes persistent p66Shc dependent effects such as oxidative stress, mitochondrial damage, apoptosis, increase of MGO, ROS mediated persistent PKC activation and PKC-mediated eNOS inhibitory Thr-495 phosphorylation. HG induces p66Shc upregulation via epigenetic modifications such as promoter hypomethylation and increased histone 3 acetylation, which maintain p66Shc upregulation despite glucose normalization. Overexpression of SIRT1 (Sirtuin 1), a class III histone deacetylase, represses HG induced p66Shc expression, and it has been shown that SIRT1 binds to p66Shc promoter and when overexpressed, it results in reduced acetylated histone H3 binding to p66Shc promoter [75]. HG induced epigenetic modifications of Sod2 gene, which encodes mitochondrial superoxide scavenging enzyme Manganese Superoxide Dismutase (MnSOD), decrease its expression and are suggested to be involved in metabolic memory [76] [77]. It is important to understand that results of different studies vary depending on several factors such as species of ECs, in vitro or in vivo conditions, cell type, etc.

HG reduces expression of SET8 and its expression remains low even after glucose normalization in HUVECs suggesting that reduced SET8 is related to cellular hyperglycemic metabolic memory [78] [79]. SET8 overexpression protects EC from the damaging consequences of HG and hyperglycemic memory such as oxidative stress, inflammation, etc., by reducing these damaging conditions. Oscillating glucose is more potent in damaging ECs and in inducing higher metabolic memory effect compared to constant high glucose [80]. Therefore, metabolic memory is dangerous phenomenon as it causes persistent damaging conditions.

9. Conclusions

In summary, diabetic conditions such as HG augment ED by stimulating diverse harmful processes such as excessive AGE formation, PKC activation, polyol pathway, etc. in ECs. Most of these deleterious events converge on molecular mechanisms such as oxidative stress, inflammation, apoptosis, reduction in NO bioavailability, etc. The persistence of glucose induced damaging effects even after glucose normalization is referred to as hyperglycemic memory, which increases risk of diabetes related vascular complications.

The limitation herein is that most of findings described are mainly from EC models used in some studies relevant to diabetic ED. Describing all the findings and mechanisms from all types of diabetic ED models, patients is beyond the scope here.

The conclusion is that diabetes promotes EC damage, which acts as trigger for diabetic vascular complications. Effectively controlling the diabetes induced molecular mediators of EC damage is critical for alleviating diabetic vascular complications.

Conflicts of Interest

The author declares no conflicts of interest regarding the publication of this paper.

References

[1]	Hossain, M.J., Al-Mamun, M. and Islam, M.R. (2024) Diabetes Mellitus, the Fastest Growing Global Public Health Concern: Early Detection Should Be Focused. Health Science Reports, 7, e2004.[CrossRef] [PubMed]
[2]	Kannel, W.B. and McGee, D.L. (1979) Diabetes and Cardiovascular Disease: The Framingham Study. JAMA, 241, 2035-2038.[CrossRef] [PubMed]
[3]	Dal Canto, E., Ceriello, A., Rydén, L., Ferrini, M., Hansen, T.B., Schnell, O., et al. (2019) Diabetes as a Cardiovascular Risk Factor: An Overview of Global Trends of Macro and Micro Vascular Complications. European Journal of Preventive Cardiology, 26, 25-32.[CrossRef] [PubMed]
[4]	Fowler, M.J. (2008) Microvascular and Macrovascular Complications of Diabetes. Clinical Diabetes, 26, 77-82.[CrossRef]
[5]	Palmer, R.M.J., Ferrige, A.G. and Moncada, S. (1987) Nitric Oxide Release Accounts for the Biological Activity of Endothelium-Derived Relaxing Factor. Nature, 327, 524-526.[CrossRef] [PubMed]
[6]	De Caterina, R., Libby, P., Peng, H.B., Thannickal, V.J., Rajavashisth, T.B., Gimbrone, M.A., et al. (1995) Nitric Oxide Decreases Cytokine-Induced Endothelial Activation. Nitric Oxide Selectively Reduces Endothelial Expression of Adhesion Molecules and Proinflammatory Cytokines. Journal of Clinical Investigation, 96, 60-68.[CrossRef] [PubMed]
[7]	Stenina, O. (2005) Regulation of Vascular Genes by Glucose. Current Pharmaceutical Design, 11, 2367-2381.[CrossRef] [PubMed]
[8]	Ambra, R., Manca, S., Palumbo, M.C., Leoni, G., Natarelli, L., De Marco, A., et al. (2014) Transcriptome Analysis of Human Primary Endothelial Cells (HUVEC) from Umbilical Cords of Gestational Diabetic Mothers Reveals Candidate Sites for an Epigenetic Modulation of Specific Gene Expression. Genomics, 103, 337-348.[CrossRef] [PubMed]
[9]	Moradipoor, S., Ismail, P., Etemad, A., Wan Sulaiman, W.A. and Ahmadloo, S. (2016) Expression Profiling of Genes Related to Endothelial Cells Biology in Patients with Type 2 Diabetes and Patients with Prediabetes. BioMed Research International, 2016, Article ID: 1845638.[CrossRef] [PubMed]
[10]	Wang, Y., Yao, M., Wang, J., Liu, H., Zhang, X., Zhao, L., et al. (2022) Effects of Antidiabetic Drugs on Endothelial Function in Patients with Type 2 Diabetes Mellitus: A Bayesian Network Meta-Analysis. Frontiers in Endocrinology, 13, Article ID: 818537.[CrossRef] [PubMed]
[11]	Pereira, C.A., Carneiro, F.S., Matsumoto, T. and Tostes, R.C. (2018) Bonus Effects of Antidiabetic Drugs: Possible Beneficial Effects on Endothelial Dysfunction, Vascular Inflammation and Atherosclerosis. Basic & Clinical Pharmacology & Toxicology, 123, 523-538.[CrossRef] [PubMed]
[12]	Twarda-Clapa, A., Olczak, A., Białkowska, A.M. and Koziołkiewicz, M. (2022) Advanced Glycation End-Products (AGEs): Formation, Chemistry, Classification, Receptors, and Diseases Related to AGEs. Cells, 11, Article No. 1312.[CrossRef] [PubMed]
[13]	Zieman, S.J. and Kass, D.A. (2004) Advanced Glycation End Product Cross-Linking: Pathophysiologic Role and Therapeutic Target in Cardiovascular Disease. Congestive Heart Failure, 10, 144-151.[CrossRef] [PubMed]
[14]	Schmidt, A.M., Yan, S.D., Wautier, J. and Stern, D. (1999) Activation of Receptor for Advanced Glycation End Products: A Mechanism for Chronic Vascular Dysfunction in Diabetic Vasculopathy and Atherosclerosis. Circulation Research, 84, 489-497.[CrossRef] [PubMed]
[15]	Tan, K.C.B., Chow, W., Ai, V.H.G., Metz, C., Bucala, R. and Lam, K.S.L. (2002) Advanced Glycation End Products and Endothelial Dysfunction in Type 2 Diabetes. Diabetes Care, 25, 1055-1059.[CrossRef] [PubMed]
[16]	Hegab, Z. (2012) Role of Advanced Glycation End Products in Cardiovascular Disease. World Journal of Cardiology, 4, 90-102.[CrossRef] [PubMed]
[17]	Giardino, I., Edelstein, D. and Brownlee, M. (1996) BCL-2 Expression or Antioxidants Prevent Hyperglycemia-Induced Formation of Intracellular Advanced Glycation Endproducts in Bovine Endothelial Cells. Journal of Clinical Investigation, 97, 1422-1428.[CrossRef] [PubMed]
[18]	Rojas, A., Romay, S., González, D., Herrera, B., Delgado, R. and Otero, K. (2000) Regulation of Endothelial Nitric Oxide Synthase Expression by Albumin-Derived Advanced Glycosylation End Products. Circulation Research, 86, e50-e54.[CrossRef] [PubMed]
[19]	Xu, B., Ji, Y., Yao, K., Cao, Y. and Ferro, A. (2005) Inhibition of Human Endothelial Cell Nitric Oxide Synthesis by Advanced Glycation End-Products but Not Glucose: Relevance to Diabetes. Clinical Science, 109, 439-446.[CrossRef] [PubMed]
[20]	Schmidt, A.M., Hori, O., Chen, J.X., Li, J.F., Crandall, J., Zhang, J., et al. (1995) Advanced Glycation Endproducts Interacting with Their Endothelial Receptor Induce Expression of Vascular Cell Adhesion Molecule-1 (VCAM-1) in Cultured Human Endothelial Cells and in Mice. a Potential Mechanism for the Accelerated Vasculopathy of Diabetes. Journal of Clinical Investigation, 96, 1395-1403.[CrossRef] [PubMed]
[21]	Yan, S.D., Schmidt, A.M., Anderson, G.M., Zhang, J., Brett, J., Zou, Y.S., et al. (1994) Enhanced Cellular Oxidant Stress by the Interaction of Advanced Glycation End Products with Their Receptors/binding Proteins. Journal of Biological Chemistry, 269, 9889-9897.[CrossRef] [PubMed]
[22]	Esposito, C., Gerlach, H., Brett, J., Stern, D. and Vlassara, H. (1989) Endothelial Receptor-Mediated Binding of Glucose-Modified Albumin Is Associated with Increased Monolayer Permeability and Modulation of Cell Surface Coagulant Properties. The Journal of Experimental Medicine, 170, 1387-1407.[CrossRef] [PubMed]
[23]	Hodgkinson, C.P., Laxton, R.C., Patel, K. and Ye, S. (2008) Advanced Glycation End-Product of Low Density Lipoprotein Activates the Toll-Like 4 Receptor Pathway Implications for Diabetic Atherosclerosis. Arteriosclerosis, Thrombosis, and Vascular Biology, 28, 2275-2281.[CrossRef] [PubMed]
[24]	Quintero, M., Colombo, S.L., Godfrey, A. and Moncada, S. (2006) Mitochondria as Signaling Organelles in the Vascular Endothelium. Proceedings of the National Academy of Sciences, 103, 5379-5384.[CrossRef] [PubMed]
[25]	Schalkwijk, C.G., Micali, L.R. and Wouters, K. (2023) Advanced Glycation Endproducts in Diabetes-Related Macrovascular Complications: Focus on Methylglyoxal. Trends in Endocrinology & Metabolism, 34, 49-60.[CrossRef] [PubMed]
[26]	Berends, E., van Oostenbrugge, R.J., Foulquier, S. and Schalkwijk, C.G. (2023) Methylglyoxal, a Highly Reactive Dicarbonyl Compound, as a Threat for Blood Brain Barrier Integrity. Fluids and Barriers of the CNS, 20, Article No. 75.[CrossRef] [PubMed]
[27]	Hanssen, N.M.J., Scheijen, J.L.J.M., Jorsal, A., Parving, H., Tarnow, L., Rossing, P., et al. (2017) Higher Plasma Methylglyoxal Levels Are Associated with Incident Cardiovascular Disease in Individuals with Type 1 Diabetes: A 12-Year Follow-Up Study. Diabetes, 66, 2278-2283.[CrossRef] [PubMed]
[28]	Hanssen, N.M.J., Westerink, J., Scheijen, J.L.J.M., van der Graaf, Y., Stehouwer, C.D.A., Schalkwijk, C.G., et al. (2018) Higher Plasma Methylglyoxal Levels Are Associated with Incident Cardiovascular Disease and Mortality in Individuals with Type 2 Diabetes. Diabetes Care, 41, 1689-1695.[CrossRef] [PubMed]
[29]	Lee, J.H., Samsuzzaman, M., Park, M.G., Park, S.J. and Kim, S.Y. (2021) Methylglyoxal-Derived Hemoglobin Advanced Glycation End Products Induce Apoptosis and Oxidative Stress in Human Umbilical Vein Endothelial Cells. International Journal of Biological Macromolecules, 187, 409-421.[CrossRef] [PubMed]
[30]	Dhar, A., Dhar, I., Desai, K.M. and Wu, L. (2010) Methylglyoxal Scavengers Attenuate Endothelial Dysfunction Induced by Methylglyoxal and High Concentrations of Glucose. British Journal of Pharmacology, 161, 1843-1856.[CrossRef] [PubMed]
[31]	Dobler, D., Ahmed, N., Song, L., Eboigbodin, K.E. and Thornalley, P.J. (2006) Increased Dicarbonyl Metabolism in Endothelial Cells in Hyperglycemia Induces Anoikis and Impairs Angiogenesis by RGD and GFOGER Motif Modification. Diabetes, 55, 1961-1969.[CrossRef] [PubMed]
[32]	Thornalley, P.J. (1993) The Glyoxalase System in Health and Disease. Molecular Aspects of Medicine, 14, 287-371.[CrossRef] [PubMed]
[33]	Shinohara, M., Thornalley, P.J., Giardino, I., Beisswenger, P., Thorpe, S.R., Onorato, J., et al. (1998) Overexpression of Glyoxalase-I in Bovine Endothelial Cells Inhibits Intracellular Advanced Glycation Endproduct Formation and Prevents Hyperglycemia-Induced Increases in Macromolecular Endocytosis. Journal of Clinical Investigation, 101, 1142-1147.[CrossRef] [PubMed]
[34]	Stratmann, B., Engelbrecht, B., Espelage, B.C., Klusmeier, N., Tiemann, J., Gawlowski, T., et al. (2016) Glyoxalase 1-Knockdown in Human Aortic Endothelial Cells—Effect on the Proteome and Endothelial Function Estimates. Scientific Reports, 6, Article No. 37737.[CrossRef] [PubMed]
[35]	Makino, A., Scott, B.T. and Dillmann, W.H. (2010) Mitochondrial Fragmentation and Superoxide Anion Production in Coronary Endothelial Cells from a Mouse Model of Type 1 Diabetes. Diabetologia, 53, 1783-1794.[CrossRef] [PubMed]
[36]	Shenouda, S.M., Widlansky, M.E., Chen, K., Xu, G., Holbrook, M., Tabit, C.E., et al. (2011) Altered Mitochondrial Dynamics Contributes to Endothelial Dysfunction in Diabetes Mellitus. Circulation, 124, 444-453.[CrossRef] [PubMed]
[37]	Trudeau, K., Molina, A.J.A., Guo, W. and Roy, S. (2010) High Glucose Disrupts Mitochondrial Morphology in Retinal Endothelial Cells: Implications for Diabetic Retinopathy. The American Journal of Pathology, 177, 447-455.[CrossRef] [PubMed]
[38]	An, Y., Geng, K., Wang, H., Wan, S., Ma, X., Long, Y., et al. (2023) Hyperglycemia-induced STING Signaling Activation Leads to Aortic Endothelial Injury in Diabetes. Cell Communication and Signaling, 21, Article No. 365.[CrossRef] [PubMed]
[39]	Nishikawa, T., Edelstein, D., Du, X.L., Yamagishi, S., Matsumura, T., Kaneda, Y., et al. (2000) Normalizing Mitochondrial Superoxide Production Blocks Three Pathways of Hyperglycaemic Damage. Nature, 404, 787-790.[CrossRef] [PubMed]
[40]	Du, X., Edelstein, D., Rossetti, L., Fantus, I.G., Goldberg, H., Ziyadeh, F., et al. (2000) Hyperglycemia-Induced Mitochondrial Superoxide Overproduction Activates the Hexosamine Pathway and Induces Plasminogen Activator Inhibitor-1 Expression by Increasing Sp1 Glycosylation. Proceedings of the National Academy of Sciences, 97, 12222-12226.[CrossRef] [PubMed]
[41]	Wang, Q., Zhang, M., Torres, G., Wu, S., Ouyang, C., Xie, Z., et al. (2016) Metformin Suppresses Diabetes-Accelerated Atherosclerosis via the Inhibition of Drp1-Mediated Mitochondrial Fission. Diabetes, 66, 193-205.[CrossRef] [PubMed]
[42]	Zheng, Y., Luo, A. and Liu, X. (2021) The Imbalance of Mitochondrial Fusion/Fission Drives High-Glucose-Induced Vascular Injury. Biomolecules, 11, Article No. 1779.[CrossRef] [PubMed]
[43]	Scrimieri, R., Locatelli, L., Cazzaniga, A., Cazzola, R., Malucelli, E., Sorrentino, A., et al. (2023) Ultrastructural Features Mirror Metabolic Derangement in Human Endothelial Cells Exposed to High Glucose. Scientific Reports, 13, Article No. 15133.[CrossRef] [PubMed]
[44]	Xiao, Q., Wang, D., Li, D., Huang, J., Ma, F., Zhang, H., et al. (2023) Protein Kinase C: A Potential Therapeutic Target for Endothelial Dysfunction in Diabetes. Journal of Diabetes and Its Complications, 37, Article ID: 108565.[CrossRef] [PubMed]
[45]	Geraldes, P. and King, G.L. (2010) Activation of Protein Kinase C Isoforms and Its Impact on Diabetic Complications. Circulation Research, 106, 1319-1331.[CrossRef] [PubMed]
[46]	Lynch, J.J., Ferro, T.J., Blumenstock, F.A., Brockenauer, A.M. and Malik, A.B. (1990) Increased Endothelial Albumin Permeability Mediated by Protein Kinase C Activation. Journal of Clinical Investigation, 85, 1991-1998.[CrossRef] [PubMed]
[47]	Huang, Y., Menne, J., Melk, A., Shushakova, N., Güler, F., Kirsch, T., et al. (2011) High Glucose Impairs Endothelium-Dependent Vasodilation Through PKC-Mediated NADPH-Oxidase Activation. Journal of Hypertension, 29, e64.[CrossRef]
[48]	Shao, B. and Bayraktutan, U. (2014) Hyperglycaemia Promotes Human Brain Microvascular Endothelial Cell Apoptosis via Induction of Protein Kinase C-βI and Prooxidant Enzyme NADPH Oxidase. Redox Biology, 2, 694-701.[CrossRef] [PubMed]
[49]	Quagliaro, L., Piconi, L., Assaloni, R., Daros, R., Maier, A., Zuodar, G., et al. (2005) Intermittent High Glucose Enhances ICAM-1, VCAM-1 and E-Selectin Expression in Human Umbilical Vein Endothelial Cells in Culture: The Distinct Role of Protein Kinase C and Mitochondrial Superoxide Production. Atherosclerosis, 183, 259-267.[CrossRef] [PubMed]
[50]	Node, K. and Inoue, T. (2009) Postprandial Hyperglycemia as an Etiological Factor in Vascular Failure. Cardiovascular Diabetology, 8, Article No. 23.[CrossRef] [PubMed]
[51]	Mudaliar, H., Pollock, C., Ma, J., Wu, H., Chadban, S. and Panchapakesan, U. (2014) The Role of TLR2 and 4-Mediated Inflammatory Pathways in Endothelial Cells Exposed to High Glucose. PLOS ONE, 9, e108844.[CrossRef] [PubMed]
[52]	Shanmugam, N., Reddy, M.A., Guha, M. and Natarajan, R. (2003) High Glucose-Induced Expression of Proinflammatory Cytokine and Chemokine Genes in Monocytic Cells. Diabetes, 52, 1256-1264.[CrossRef] [PubMed]
[53]	Kunt, T., Forst, T., Früh, B., Flohr, T., Schneider, S., Harzer, O., et al. (2009) Binding of Monocytes from Normolipidemic Hyperglycemic Patients with Type 1 Diabetes to Endothelial Cells Is Increased in Vitro. Experimental and Clinical Endocrinology & Diabetes, 107, 252-256.[CrossRef] [PubMed]
[54]	Zhang, Q., Wu, S., Sun, G., Zhang, R., Li, X., Zhang, Y., et al. (2021) Hyperglycemia Aggravates Monocyte-Endothelial Adhesion in Human Umbilical Vein Endothelial Cells from Women with Gestational Diabetes Mellitus by Inducing Cx43 Overexpression. Annals of Translational Medicine, 9, 234-234.[CrossRef] [PubMed]
[55]	Omi, H., Okayama, N., Shimizu, M., Okouchi, M., Ito, S., Fukutomi, T., et al. (2002) Participation of High Glucose Concentrations in Neutrophil Adhesion and Surface Expression of Adhesion Molecules on Cultured Human Endothelial Cells: Effect of Anti-Diabetic Medicines. Journal of Diabetes and Its Complications, 16, 201-208.[CrossRef] [PubMed]
[56]	Liu, T., Gong, J., Chen, Y. and Jiang, S. (2013) Periodic vs Constant High Glucose in Inducing Pro-Inflammatory Cytokine Expression in Human Coronary Artery Endothelial Cells. Inflammation Research, 62, 697-701.[CrossRef] [PubMed]
[57]	Wang, J., Shen, X., Liu, J., Chen, W., Wu, F., Wu, W., et al. (2020) High Glucose Mediates NLRP3 Inflammasome Activation via Upregulation of ELF3 Expression. Cell Death & Disease, 11, Article No. 383.[CrossRef] [PubMed]
[58]	Jiang, T., Jiang, D., Zhang, L., Ding, M. and Zhou, H. (2019) Anagliptin Ameliorates High Glucose-Induced Endothelial Dysfunction via Suppression of NLRP3 Inflammasome Activation Mediated by SIRT1. Molecular Immunology, 107, 54-60.[CrossRef] [PubMed]
[59]	Gonzalez, R.G., Barnett, P., Aguayo, J., Cheng, H.M. and Chylack, L.T. (1984) Direct Measurement of Polyol Pathway Activity in the Ocular Lens. Diabetes, 33, 196-199.[CrossRef]
[60]	Chung, S.S.M., Ho, E.C.M., Lam, K.S.L. and Chung, S.K. (2003) Contribution of Polyol Pathway to Diabetes-Induced Oxidative Stress. Journal of the American Society of Nephrology, 14, S233-S236.[CrossRef] [PubMed]
[61]	Lorenzi, M. (2007) The Polyol Pathway as a Mechanism for Diabetic Retinopathy: Attractive, Elusive, and Resilient. Journal of Diabetes Research, 2007, Article ID: 061038.[CrossRef] [PubMed]
[62]	Brownlee, M. (2005) The Pathobiology of Diabetic Complications: A Unifying Mechanism. Diabetes, 54, 1615-1625.[CrossRef] [PubMed]
[63]	Burg, M.B. and Kador, P.F. (1988) Sorbitol, Osmoregulation, and the Complications of Diabetes. Journal of Clinical Investigation, 81, 635-640.[CrossRef] [PubMed]
[64]	Oyama, T., Miyasita, Y., Watanabe, H. and Shirai, K. (2006) The Role of Polyol Pathway in High Glucose-Induced Endothelial Cell Damages. Diabetes Research and Clinical Practice, 73, 227-234.[CrossRef] [PubMed]
[65]	Buse, M.G. (2006) Hexosamines, Insulin Resistance, and the Complications of Diabetes: Current Status. American Journal of Physiology-Endocrinology and Metabolism, 290, E1-E8.[CrossRef] [PubMed]
[66]	Hart, G.W., Housley, M.P. and Slawson, C. (2007) Cycling of O-Linked Β-N-Acetylglucosamine on Nucleocytoplasmic Proteins. Nature, 446, 1017-1022.[CrossRef] [PubMed]
[67]	Federici, M., Menghini, R., Mauriello, A., Hribal, M.L., Ferrelli, F., Lauro, D., et al. (2002) Insulin-Dependent Activation of Endothelial Nitric Oxide Synthase Is Impaired by O-Linked Glycosylation Modification of Signaling Proteins in Human Coronary Endothelial Cells. Circulation, 106, 466-472.[CrossRef] [PubMed]
[68]	Du, X.L., Edelstein, D., Dimmeler, S., Ju, Q., Sui, C. and Brownlee, M. (2001) Hyperglycemia Inhibits Endothelial Nitric Oxide Synthase Activity by Posttranslational Modification at the Akt Site. Journal of Clinical Investigation, 108, 1341-1348.[CrossRef] [PubMed]
[69]	Makino, A., Dai, A., Han, Y., Youssef, K.D., Wang, W., Donthamsetty, R., et al. (2015) o-Glcnacase Overexpression Reverses Coronary Endothelial Cell Dysfunction in Type 1 Diabetic Mice. American Journal of Physiology-Cell Physiology, 309, C593-C599.[CrossRef] [PubMed]
[70]	Zhang, Y., Qu, Y., Niu, T., Wang, H. and Liu, K. (2017) O-GlcNAc Modification of Sp1 Mediates Hyperglycaemia-Induced ICAM-1 Up-Regulation in Endothelial Cells. Biochemical and Biophysical Research Communications, 484, 79-84.[CrossRef] [PubMed]
[71]	Liu, G.D., Xu, C., Feng, L. and Wang, F. (2015) The Augmentation of O-GlcNAcylation Reduces Glyoxal-Induced Cell Injury by Attenuating Oxidative Stress in Human Retinal Microvascular Endothelial Cells. International Journal of Molecular Medicine, 36, 1019-1027.[CrossRef] [PubMed]
[72]	Reddy, M.A., Zhang, E. and Natarajan, R. (2015) Epigenetic Mechanisms in Diabetic Complications and Metabolic Memory. Diabetologia, 58, 443-455.[CrossRef] [PubMed]
[73]	Brasacchio, D., Okabe, J., Tikellis, C., Balcerczyk, A., George, P., Baker, E.K., et al. (2009) Hyperglycemia Induces a Dynamic Cooperativity of Histone Methylase and Demethylase Enzymes Associated with Gene-Activating Epigenetic Marks That Coexist on the Lysine Tail. Diabetes, 58, 1229-1236.[CrossRef] [PubMed]
[74]	Paneni, F., Mocharla, P., Akhmedov, A., Costantino, S., Osto, E., Volpe, M., et al. (2012) Gene Silencing of the Mitochondrial Adaptor P66shc Suppresses Vascular Hyperglycemic Memory in Diabetes. Circulation Research, 111, 278-289.[CrossRef] [PubMed]
[75]	Zhou, S., Chen, H., Wan, Y., Zhang, Q., Wei, Y., Huang, S., et al. (2011) Repression of P66shc Expression by SIRT1 Contributes to the Prevention of Hyperglycemia-Induced Endothelial Dysfunction. Circulation Research, 109, 639-648.[CrossRef] [PubMed]
[76]	Zhong, Q. and Kowluru, R.A. (2011) Epigenetic Changes in Mitochondrial Superoxide Dismutase in the Retina and the Development of Diabetic Retinopathy. Diabetes, 60, 1304-1313.[CrossRef] [PubMed]
[77]	Zhong, Q. and Kowluru, R.A. (2013) Epigenetic Modification of sod2 in the Development of Diabetic Retinopathy and in the Metabolic Memory: Role of Histone Methylation. Investigative Opthalmology & Visual Science, 54, 244-250.[CrossRef] [PubMed]
[78]	Fang, J., Feng, Q., Ketel, C.S., Wang, H., Cao, R., Xia, L., et al. (2002) Purification and Functional Characterization of SET8, a Nucleosomal Histone H4-Lysine 20-Specific Methyltransferase. Current Biology, 12, 1086-1099.[CrossRef] [PubMed]
[79]	Chen, X., Wu, Q., Jiang, H., Wang, J., Zhao, Y., Xu, Y., et al. (2018) SET8 Is Involved in the Regulation of Hyperglycemic Memory in Human Umbilical Endothelial Cells. Acta Biochimica et Biophysica Sinica, 50, 635-642.[CrossRef] [PubMed]
[80]	Schisano, B., Tripathi, G., McGee, K., McTernan, P.G. and Ceriello, A. (2011) Glucose Oscillations, More than Constant High Glucose, Induce p53 Activation and a Metabolic Memory in Human Endothelial Cells. Diabetologia, 54, 1219-1226.[CrossRef] [PubMed]