Methylglyoxal-induced imbalance in the ratio of vascular endothelial growth factor to angiopoietin 2 secreted by retinal pigment epithelial cells leads to endothelial dysfunction

Immune Fingerprint in Diabetes: Ocular Surface and Retinal Inflammation

Diabetes is a prevalent global health issue associated with significant morbidity and mortality. Diabetic retinopathy (DR) is a well-known inflammatory, neurovascular complication of diabetes and a leading cause of preventable blindness in developed countries among working-age adults. However, the ocular surface components of diabetic eyes are also at risk of damage due to uncontrolled diabetes, which is often overlooked. Inflammatory changes in the corneas of diabetic patients indicate that inflammation plays a significant role in diabetic complications, much like in DR. The eye's immune privilege restricts immune and inflammatory responses, and the cornea and retina have a complex network of innate immune cells that maintain immune homeostasis. Nevertheless, low-grade inflammation in diabetes contributes to immune dysregulation. This article aims to provide an overview and discussion of how diabetes affects the ocular immune system's main components, immune-competent cells, and inflammatory mediators. By understanding these effects, potential interventions and treatments may be developed to improve the ocular health of diabetic patients.

Impairment of the angiogenic process may contribute to lower success rate of root canal treatments in diabetes mellitus

AIM

To investigate the association between root canal treatment outcome, diabetes mellitus, and alterations of the angiogenic process.

METHODOLOGY

A retrospective observational study was conducted in healthy (control group, CG) and diabetic (type II diabetes mellitus group, DG) patients after root canal treatment. The follow-up appointments were performed to clinically and radiographically observe symptoms, the healing of periapical lesions and the quality of root fillings. In the animal model study, diabetic Goto-Kakizaki (GK) rats and control Wistar rats were used. After 21 days of pulp exposure and the development of apical periodontitis (AP), the mandibles were removed for scintigraphic, radiographic, histopathological and molecular analyses. Chi-square tests were performed to examine the variables related to endodontic outcome and differences between animal groups were assessed using the Student's t-test.

RESULTS

The group of patients with diabetes had a significantly lower rate of success following root canal treatment than the CG (p < .001). Logistic regression suggested that diabetes is a risk factor for success of root canal treatment. In the animal study, GK rats had significantly higher fasting glycaemia at t0 and t21 (p < .001) and triglycerides levels (p < .05) and area under the curve (AUC) during the insulin tolerance test at t21 (p < .001). AP area was significantly greater in GK rats (p < .05). Histologically, diabetic rats had increased signs of periodontal ligament inflammation 21 days after the induction of apical periodontitis, with fibro-hyaline matrix filling and vessel with undefined walls. Wistar rats had significantly increased vascular endothelial growth factor (VEGF) levels and VEGF/Ang-2 ratio 21 days after AP induction (p < .08; p < .07). GK rats had intrinsically lower levels of VEGF than control rats (p < .05), which did not change after AP.

CONCLUSION

Diabetes mellitus should be considered as an important factor in the prognosis of root canal treatment and its outcomes over time. Future strategies to improve angiogenesis and tissue repair should be pursued to achieve better root canal treatment outcomes in diabetic patients.

Early AGEing and metabolic diseases: is perinatal exposure to glycotoxins programming for adult-life metabolic syndrome?

Perinatal early nutritional disorders are critical for the developmental origins of health and disease. Glycotoxins, or advanced glycation end-products, and their precursors such as the methylglyoxal, which are formed endogenously and commonly found in processed foods and infant formulas, may be associated with acute and long-term metabolic disorders. Besides general aspects of glycotoxins, such as their endogenous production, exogenous sources, and their role in the development of metabolic syndrome, we discuss in this review the sources of perinatal exposure to glycotoxins and their involvement in metabolic programming mechanisms. The role of perinatal glycotoxin exposure in the onset of insulin resistance, central nervous system development, cardiovascular diseases, and early aging also are discussed, as are possible interventions that may prevent or reduce such effects.

Endostatin as a Mediator Between Endothelial Function and Cognitive Performance in Those at Risk for Vascular Cognitive Impairment

Background:

Patients with coronary artery disease have an increased risk for developing vascular cognitive impairment. Endothelial function is often diminished and has been associated with lower cognitive performance in these patients. The link between endothelial function and cognition in coronary artery disease is not fully understood. Angiogenesis may play a role in mediating the association between endothelial function and cognition since angiogenic processes rely heavily on the endothelium.

Objective:

The aim of this study was to determine if markers of angiogenesis mediate the relationship between endothelial function and cognition in coronary artery disease patients.

Methods:

In 50 participants with coronary artery disease, endothelial function was assessed using peripheral arterial tonometry. Vascular endothelial growth factor (pro-angiogenic) and endostatin (anti-angiogenic) were measured in peripheral serum samples. Cognition was assessed using the Montreal Cognitive Assessment. A mediation analysis, using a bias corrected inferential bootstrapping method with 10,000 permutations, was used to determine if vascular endothelial growth factor or endostatin mediated an association between peripheral arterial tonometry measures and cognitive performance on the Montreal Cognitive Assessment.

Results:

Endostatin, but not vascular endothelial growth factor, mediated a relationship between endothelial function and cognitive performance when controlling for total years of education, body mass index, coronary artery bypass graft, stent, diabetes, and diuretic use. This analysis was also significant when delayed recall was substituted for the overall score on the Montreal Cognitive Assessment.

Conclusion:

These results suggest that endostatin mediates an association between endothelial function and cognitive performance in coronary artery disease.

The glucose degradation product methylglyoxal induces immature angiogenesis in patients undergoing peritoneal dialysis

The accumulation of glucose degradation products (GDPs) can lead to tissue damage in patients with diabetes and those undergoing long-term peritoneal dialysis (PD). Angiogenesis is occasionally observed in the peritoneal membrane of patients undergoing PD, where it is associated with failure of ultrafiltration. To investigate the mechanism underlying the influence of angiogenesis on fluid absorption, we evaluated the effects of accumulation of the glucose degradation product methylglyoxal (MGO) on angiogenesis in vitro, and analyzed the association with angiogenesis in the peritoneal membrane. To this end, we measured the levels of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF)-BB in cultured endothelial and smooth muscle cells after administration of MGO. The expression of PDGF-BB mRNA and protein decreased significantly after exposure to MGO, while the expression of VEGF mRNA increased (both P < 0.01). The expression of PDGF-Rβ mRNA in cultured smooth muscle cells did not change after administration of MGO, although the expression of VEGF mRNA increased (P < 0.01). We also evaluated the associations between the number of capillary vessels, peritoneal function, and the degree of MGO deposition using peritoneum samples collected from patients undergoing PD. The number of immature capillary vessels was significantly associated with peritoneal dysfunction and the degree of MGO accumulation (both P < 0.01). In conclusion, MGO enhances the production of VEGF and suppresses the production of PDGF-BB, potentially leading to disturbance of angiogenesis in the peritoneal membrane. Accumulation of MGO in the peritoneum may cause immature angiogenesis and peritoneal dysfunction.

Dicarbonyl Stress and S-Glutathionylation in Cerebrovascular Diseases: A Focus on Cerebral Cavernous Malformations

Dicarbonyl stress is a dysfunctional state consisting in the abnormal accumulation of reactive α-oxaldehydes leading to increased protein modification. In cells, post-translational changes can also occur through S-glutathionylation, a highly conserved oxidative post-translational modification consisting of the formation of a mixed disulfide between glutathione and a protein cysteine residue. This review recapitulates the main findings supporting a role for dicarbonyl stress and S-glutathionylation in the pathogenesis of cerebrovascular diseases, with specific emphasis on cerebral cavernous malformations (CCM), a vascular disease of proven genetic origin that may give rise to various clinical signs and symptoms at any age, including recurrent headaches, seizures, focal neurological deficits, and intracerebral hemorrhage. A possible interplay between dicarbonyl stress and S-glutathionylation in CCM is also discussed.

LncRNA TDRG1-Mediated Overexpression of VEGF Aggravated Retinal Microvascular Endothelial Cell Dysfunction in Diabetic Retinopathy

Purpose

Diabetic retinopathy (DR), a neurovascular disease, is one of the leading causes of blindness in working-age adults. Long noncoding RNAs (lncRNAs) have attracted attention as indicators for DR. This study aimed to characterize the role of lncRNA human testis development-related gene 1 (TDRG1) and its modulation of vascular endothelial growth factor (VEGF) in deteriorating DR.

Methods

Tissue samples were obtained from patients with epiretinal membranes (EMs) or proliferative DR, and human retinal microvascular endothelial cells (HRECs) were cultured with high-glucose medium to mimic DR as the in vitro model. The expression of lncRNA TDRG1 and VEGF was determined by immunofluorescence staining, Western blotting, and RT-qPCR. Transfection of small-interfering RNA was conducted to knock down target gene expression. HREC functions were evaluated by cell viability, fluorescein isothiocyanate (FITC)-dextran extravasation, migration, and tube formation assays under different conditions.

Results

LncRNA TDRG1 and VEGF were found to be co-expressed and significantly upregulated in fibrovascular membranes (FVMs) from DR patients compared to those from EM patients. In the in vitro model, hyperglycemic treatment markedly increased the expression of lncRNA TDRG1 and VEGF at the mRNA and protein levels, which promoted cell proliferation and migration, enhanced permeability, and disrupted tube formation of HRECs. However, knockdown of lncRNA TDRG1 or VEGF notably decreased the expression of VEGF and reversed the impaired functions of high-glucose-treated HRECs.

Conclusions

LncRNA TDRG1 promoted microvascular cell dysfunction via upregulating VEGF in the progression of DR and may serve as a potential therapeutic target in DR treatment.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

Dicarbonyl Stress at the Crossroads of Healthy and Unhealthy Aging

Dicarbonyl stress occurs when dicarbonyl metabolites (i.e., methylglyoxal, glyoxal and 3-deoxyglucosone) accumulate as a consequence of their increased production and/or decreased detoxification. This toxic condition has been associated with metabolic and age-related diseases, both of which are characterized by a pro-inflammatory and pro-oxidant state. Methylglyoxal (MGO) is the most reactive dicarbonyl and the one with the highest endogenous flux. It is the precursor of the major quantitative advanced glycated products (AGEs) in physiological systems, arginine-derived hydroimidazolones, which accumulate in aging and dysfunctional tissues. The aging process is characterized by a decline in the functional properties of cells, tissues and whole organs, starting from the perturbation of crucial cellular processes, including mitochondrial function, proteostasis and stress-scavenging systems. Increasing studies are corroborating the causal relationship between MGO-derived AGEs and age-related tissue dysfunction, unveiling a previously underestimated role of dicarbonyl stress in determining healthy or unhealthy aging. This review summarizes the latest evidence supporting a causal role of dicarbonyl stress in age-related diseases, including diabetes mellitus, cardiovascular disease and neurodegeneration.

Methylglyoxal as a prognostic factor in patients with chronic kidney disease

AIM

Advanced glycation end products and their precursors cause vascular damage through oxidative stress. We investigated the hypothesis that methylglyoxal (MG), 3-deoxyglucosone (3-DG) and pentosidine influence outcomes of chronic kidney disease (CKD) patients.

METHODS

We conducted a 3 years prospective observational study involving 150 outpatients at CKD stages 3-5. At enrolment, MG, 3-DG and pentosidine plasma concentrations were measured; patients were divided into tertiles according to the concentration of each substance. The primary endpoint was death, a cardiovascular event or end-stage renal disease. Survival analysis was performed using the Cox regression model.

RESULTS

The patients' mean age was 62 ± 12 years, 97 were men, and 20 had diabetic nephropathy. The mean estimated glomerular filtration rate was 25.0 ± 12.1 mL/min per 1.73 m² , which negatively correlated with MG but not with 3-DG and pentosidine. Forty-eight patients reached the primary endpoint. Compared with the lowest MG tertile, the hazard ratio for the primary endpoint was 7.57 (95% confidence interval (CI): 1.71-33.54) in the middle tertile and 27.00 (CI: 6.46-112.82) in the highest tertile. When adjusted for characteristics at baseline, the corresponding hazard ratio decreased to 2.09 (CI: 0.37-11.96) and 6.13 (CI: 0.97-38.82), but MG tertile remained an independent risk factor for the primary endpoint. However, 3-DG and pentosidine were not related to the primary outcome.

CONCLUSION

Methylglyoxal has a close clinical association with CKD. Higher MG concentrations may contribute renal function deterioration in CKD. In CKD patients, MG concentration might be useful when determining the prognosis.

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.

Angiopoietins in Diabetic Retinopathy: Current Understanding and Therapeutic Potential

Diabetic retinopathy (DR) is the commonest cause of blindness in the working-age population of the developed world. The molecular pathophysiology of DR is complex, and a complete spatiotemporal model of the disease is still being elucidated. Recently, a role for angiopoietin (Ang) proteins in the pathophysiology of DR has been proposed by several research groups, and several aspects of Ang signalling are being explored as novel therapeutic strategies. Here, we review the role of the Ang proteins in two important forms of DR, diabetic macular oedema and proliferative diabetic retinopathy. The function of the Ang proteins in regulating blood vessel permeability and neovascularisation is discussed, and we also evaluate recent preclinical and clinical studies highlighting the potential benefits of modulating Ang signalling as a treatment for DR.

Streptozotocin‑induced diabetic mice exhibit reduced experimental choroidal neovascularization but not corneal neovascularization

The present study aimed to investigate the effects of diabetes mellitus (DM) on the generation of experimental corneal neovascularization (CrNV) and choroidal neovascularization (ChNV). Diabetes was induced in mice by intraperitoneal injection of streptozotocin (STZ). Experimental CrNV and ChNV were induced by alkali injury and laser photocoagulation, respectively. CrNV and ChNV were compared between the STZ‑induced diabetic mice and control mice two weeks after injury. Relative expression of angiogenic factors was quantified by reverse transcription‑quantitative polymerase chain reaction, and progenitor cell or macrophage accumulation in the early phase following injury was examined by flow cytometric analysis. Compared with the alkali‑injured normal mice, the alkali‑injured diabetic mice (STZ‑induced) exhibited no significant difference in CrNV occurrence, whereas the laser‑injured diabetic mice exhibited significantly reduced levels of ChNV compared with those of the laser‑injured control animals. The laser‑induced intrachoroidal mRNA expression levels of angiogenic factors, including vascular endothelial growth factor, hypoxia‑induced factor‑1α, chemokine (C‑C motif) ligand 3, and stromal cell‑derived factor‑1α, were reduced in the laser‑injured diabetic mice when compared with laser‑injured control mice. Furthermore, the laser‑induced intrachoroidal infiltration of c‑Kit+ progenitor cells was impaired in the laser‑injured diabetic mice compared with the laser‑injured control mice. Overall, diabetes did not exert a significant effect on the generation of experimental CrNV. However, diabetes reduced laser‑induced ChNV through downregulation of intrachoroidal progenitor cell infiltration and angiogenic factor expression.

Sweet Stress: Coping With Vascular Dysfunction in Diabetic Retinopathy

Oxidative stress plays key roles in the pathogenesis of retinal diseases, such as diabetic retinopathy. Reactive oxygen species (ROS) are increased in the retina in diabetes and the antioxidant defense system is also compromised. Increased ROS stimulate the release of pro-inflammatory cytokines, promoting a chronic low-grade inflammation involving various signaling pathways. An excessive production of ROS can lead to retinal endothelial cell injury, increased microvascular permeability, and recruitment of inflammatory cells at the site of inflammation. Recent studies have started unraveling the complex crosstalk between retinal endothelial cells and neuroglial cells or leukocytes, via both cell-to-cell contact and secretion of cytokines. This crosstalk is essential for the maintenance of the integrity of retinal vascular structure. Under diabetic conditions, an aberrant interaction between endothelial cells and other resident cells of the retina or invading inflammatory cells takes place in the retina. Impairment in the secretion and flow of molecular signals between different cells can compromise the retinal vascular architecture and trigger angiogenesis. In this review, the synergistic contributions of redox-inflammatory processes for endothelial dysfunction in diabetic retinopathy will be examined, with particular attention paid to endothelial cell communication with other retinal cells.

Roles of miRNAs and long noncoding RNAs in the progression of diabetic retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults across the world. The pathogenesis of DR is multifactorial and the molecular mechanisms are still not fully understood. Accumulating evidence has demonstrated that noncoding RNAs (ncRNAs) may be aberrantly expressed and may play vital roles in the development of DR. Amongst ncRNAs, miRNAs and long ncRNAs (lncRNAs) are known for their regulatory functions. Here, we summarize the functions and mechanisms of known aberrantly expressed miRNAs and lncRNAs in DR. Additionally, a novel lncRNA–mRNA–miRNA network is included in this review. We highlight original studies that provide detailed data about the mechanisms of miRNAs and lncRNAs, their applications as diagnostic or prognostic biomarkers, and their potential therapeutic targets. In conclusion, this review will help us gain a better understanding of the molecular mechanisms by which miRNAs and lncRNAs perform their functions in DR, and provide general strategies and directions for future research.

Elevated serum fetuin-A levels are associated with grades of retinopathy in type 2 diabetic patients

PURPOSE

Fetuin-A is a physiological inhibitor of insulin receptor tyrosine kinase and thus associated with insulin resistance, metabolic syndrome, and an increased risk for type 2 diabetes mellitus (T2DM). This study aims to investigate the possible relation between the serum fetuin-A levels and the stages of diabetic retinopathy (DR) in patients with T2DM.

METHODS

This prospective study included 82 patients with T2DM and 19 age- and gender-matched healthy controls (HCs) (group 1). Diabetic patients were subclassified into three groups according to ocular findings: without DR (group 2; n = 26); non-proliferative DR (group 3; n = 29), and proliferative DR (group 4; n = 27). Serum fetuin-A levels were determined by a spectrophotometric technique using an immulite chemiluminescent immunometric assay. The data were analyzed using a Mann-Whitney U test, and the results were expressed as mean ± standard deviation.

RESULTS

Mean fetuin-A values were 256.4 ± 21.3 μg/ml in group 1, 263.5 ± 24.2 μg/ml in group 2, 282.2 ± 31.1 μg/ml in group 3, and 296.3 ± 26.2 μg/ml in group 4. Group 2 had higher mean fetuin-A level compared with group 1, but the difference was not statistically significant (p > 0.05). Serum fetuin-A levels were significantly higher in groups 3 and 4 compared with HCs (both p < 0.05). Compared with group 2, both DR groups had higher fetuin-A levels with a significant difference (both p < 0.05); and patients with proliferative DR had significantly higher serum fetuin-A levels compared with non-proliferative DR (p < 0.05). The mean serum fetuin-A levels increased with the stage of DR, and the highest levels were found in patients with proliferative DR.

CONCLUSION

Our findings suggest an association between fetuin-A levels and DR stage. In diabetic patients, the risk of retinopathy development increases with higher fetuin-A values. Fetuin-A may play an important role in the pathophysiology and progression of DR.

Viewing the choroid: where we stand, challenges and contradictions in diabetic retinopathy and diabetic macular oedema

Diabetic macular oedema (DMO) is the leading cause of vision loss in the working-age population. Blood-retinal barrier (BRB) dysfunction in diabetic retinopathy (DR), mainly at the level of the retinal vessels, has long been related with leakage and fluid accumulation, leading to macular oedema. However, the nourishment of the macula is provided by the choroid and a diabetic choroidopathy has been described. Therefore, there has been a growing interest in studying the role of the choroid in the pathophysiology of DR and DMO, mainly by optical coherence tomography (OCT). Nevertheless, there are conflicting results in the different studies. We summarize the results from the available studies, describe the limitations and confounding factors and discuss future procedures to avoid bias.

Transcription factor SP1 mediates hyperglycemia-induced upregulation of roundabout4 in retinal microvascular endothelial cells

Roundabout4 (Robo4) is a gene that is expressed specifically in vasculature and is involved in the angiogenesis and integrity of blood vessels. The expression level of Robo4 increases gradually along with the development of diabetic retinopathy (DR). In this study, we explored the mechanism of transcriptional regulation of Robo4 in retinal endothelial cells, and investigated the effects of this regulation on cellular functions under hyperglycemic conditions. Human retinal endothelial cells (HREC) exposed to hyperglycemia were used to detect the expression levels of specificity protein 1 (SP1) and Robo4 by RT-qPCR and western blotting. Small interfering RNA (SiRNA) transfection technology was used to analyze the regulatory relationship between SP1 and Robo4. The effect of transcription factor SP1 on Robo4 promoter activity and the location of SP1 binding sites were investigated using chromatin immunoprecipitation (ChIP) and luciferase assay. Cell migration, monolayer permeability and tube formation assays were performed to demonstrate the role of SP1/Robo4 in regulating HREC functions in hyperglycemic conditions. The results showed that hyperglycemia upregulated the mRNA and protein levels of SP1 and Robo4 in HREC. Depletion of SP1 by siRNA transfection inhibited the hyperglycemia induced overexpression of Robo4. ChIP combined with luciferase assay showed that under hyperglycemic conditions, SP1 significantly increased the transcriptional level of Robo4 via an additional SP1 binding site at -1912/-1908 in the Robo4 promoter. Repressing the SP1/Robo4 pathway effectively mitigated the abnormity in HREC migration, permeability and angiogenesis induced by hyperglycemia. All these findings indicate that hyperglycemia-induced upregulation of Robo4 is mediated by enhanced transcription of SP1. The SP1/Robo4 signaling pathway can regulate the migratory ability, monolayer permeability and angiogenesis of HREC under hyperglycemic conditions, suggesting that it may play an important role in microvascular dysfunction during DR.

Methylglyoxal-induced glycation changes adipose tissue vascular architecture, flow and expansion, leading to insulin resistance

Microvascular dysfunction has been suggested to trigger adipose tissue dysfunction in obesity. This study investigates the hypothesis that glycation impairs microvascular architecture and expandability with an impact on insulin signalling. Animal models supplemented with methylglyoxal (MG), maintained with a high-fat diet (HFD) or both (HFDMG) were studied for periepididymal adipose (pEAT) tissue hypoxia and local and systemic insulin resistance. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to quantify blood flow in vivo, showing MG-induced reduction of pEAT blood flow. Increased adipocyte size and leptin secretion were observed only in rats feeding the high-fat diet, without the development of hypoxia. In turn, hypoxia was only observed when MG was combined (HFDMG group), being associated with impaired activation of the insulin receptor (Tyr1163), glucose intolerance and systemic and muscle insulin resistance. Accordingly, the adipose tissue angiogenic assay has shown decreased capillarization after dose-dependent MG exposure and glyoxalase-1 inhibition. Thus, glycation impairs adipose tissue capillarization and blood flow, hampering its expandability during a high-fat diet challenge and leading to hypoxia and insulin resistance. Such events have systemic repercussions in glucose metabolism and may lead to the onset of unhealthy obesity and progression to type 2 diabetes.

Hyperglycemia-induced degradation of HIF-1α contributes to impaired response of cardiomyocytes to hypoxia

INTRODUCTION AND OBJECTIVES

Cardiovascular disease is the leading cause of mortality and morbidity associated with diabetes. Although impairment of the cell response to hypoxia due to destabilization of the transcription factor hypoxia-inducible factor-1α (HIF-1α), which regulates the expression of genes that help cells to cope with low oxygen tension, has been implicated in diabetes-associated disease, the molecular mechanisms involved remain elusive. It is known that hyperglycemia leads to the enhanced production of methylglyoxal (MGO). Therefore, the main objective of this study was to establish whether MGO leads to the degradation of HIF-1α in cardiomyocytes subjected to hypoxia.

METHODS

The mouse atrial cardiomyocyte cell line, HL-1, was exposed to chemical hypoxia with CoCl₂ in the absence or presence of MGO. Cell viability was assessed by MTT assay, and levels of HIF-1α and endogenous ubiquitin conjugates were determined by western blotting. Proteasome activity was analyzed using a specific chymotrypsin-like fluorogenic substrate.

RESULTS

The results obtained indicate that MGO induces time- and dose-dependent degradation of HIF-1α accumulated under hypoxia. Additionally, we show that accumulation of endogenous ubiquitin conjugates in the presence of MGO is associated with decreased proteasome activity.

CONCLUSION

Taken together, the results obtained in this study suggest that MGO compromises the ability of cells to adapt to low oxygen tensions, by stimulating the degradation of HIF-1α, likely contributing to the development of diabetes-associated cardiac dysfunction.

Methylglyoxal in Metabolic Disorders: Facts, Myths, and Promises

Glucose and fructose metabolism originates the highly reactive byproduct methylglyoxal (MG), which is a strong precursor of advanced glycation end products (AGE). The MG has been implicated in classical diabetic complications such as retinopathy, nephropathy, and neuropathy, but has also been recently associated with cardiovascular diseases and central nervous system disorders such as cerebrovascular diseases and dementia. Recent studies even suggested its involvement in insulin resistance and beta-cell dysfunction, contributing to the early development of type 2 diabetes and creating a vicious circle between glycation and hyperglycemia. Despite several drugs and natural compounds have been identified in the last years in order to scavenge MG and inhibit AGE formation, we are still far from having an effective strategy to prevent MG-induced mechanisms. This review summarizes the endogenous and exogenous sources of MG, also addressing the current controversy about the importance of exogenous MG sources. The mechanisms by which MG changes cell behavior and its involvement in type 2 diabetes development and complications and the pathophysiological implication are also summarized. Particular emphasis will be given to pathophysiological relevance of studies using higher MG doses, which may have produced biased results. Finally, we also overview the current knowledge about detoxification strategies, including modulation of endogenous enzymatic systems and exogenous compounds able to inhibit MG effects on biological systems.

Function and Dysfunction of Adipose Tissue

Adipose tissue is an endocrine organ which is responsible for postprandial uptake of glucose and fatty acids, consequently producing a broad range of adipokines controlling several physiological functions like appetite, insulin sensitivity and secretion, immunity, coagulation, and vascular tone, among others. Many aspects of adipose tissue pathophysiology in metabolic diseases have been described in the last years. Recent data suggest two main factors for adipose tissue dysfunction: accumulation of nonesterified fatty acids and their secondary products and hypoxia. Both of these factors are thought to be on the basis of low-grade inflammatory activation, further increasing metabolic dysregulation in adipose tissue. In turn, inflammation is involved in the inhibition of substrate uptake, alteration of the secretory profile, stimulation of angiogenesis, and recruitment of further inflammatory cells, which creates an inflammatory feedback in the tissue and is responsible for long-term establishment of insulin resistance.

Dynamic Expression Patterns of Progenitor and Neuron Layer Markers in the Developing Human Dentate Gyrus and Fimbria

The molecular mechanisms that orchestrate the development of the human dentate gyrus are not known. In this study, we characterized the formation of human dentate and fimbrial progenitors and postmitotic neurons from 9 gestational weeks (GW9) to GW25. PAX6+ progenitor cells remained proliferative until GW16 in the dentate ventricular zone. By GW11, the secondary dentate matrix had developed in the intermediate zone, surrounding the dentate anlage and streaming toward the subpial layer. This secondary matrix contained proliferating PAX6+ and/or TBR2+ progenitors. In parallel, SOX2+ and PAX6+ fimbrial cells were detected approaching the dentate anlage, representing a possible source of extra-dentate progenitors. By GW16, when the granule cell layer could be delineated, a hilar matrix containing PAX6+ and some TBR2+ progenitors had become identifiable. By GW25, when the 2 limbs of the granule cell layer had formed, the secondary dentate matrix was reduced to a pool of progenitors at the fimbrio-dentate junction. Although human dentate development recapitulates key steps previously described in rodents, differences seemed to emerge in neuron layer markers expression. Further studies are necessary to better elucidate their role in dentate formation and connectivity.

Madecassic Acid protects against hypoxia-induced oxidative stress in retinal microvascular endothelial cells via ROS-mediated endoplasmic reticulum stress

Madecassic acid (MA) is an abundant triterpenoid in Centella asiatica (L.) Urban. (Apiaceae) that has been used as a wound-healing, anti-inflammatory and anti-cancer agent. Up to now, the effects of MA against oxidative stress remain unclear. In this study, we investigated the effect of MA and its mechanisms on hypoxia-induced human Retinal Microvascular Endothelial Cells (hRMECs). hRMECs were pre-treated with different concentrations of MA (0-50μM) for 30min before being incubated under hypoxia condition (37°C, 5% CO₂ and 95% N₂). Cell apoptosis was evaluated with MTT assay and TUNEL staining, and the expression of apoptosis- and endoplasmic reticulum (ER) stress-related molecules was assessed with western blotting and RT-PCR analysis. Intracellular ROS level was evaluated using DCFH-DA. Intracellular malondialdehyde (MDA), dehydrogenase (LDH), glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD) were evaluated using related Kits. Activating transcription factor 4 (ATF4) nuclear translocation was assessed with western blotting analysis and immunofluorescence staining. MA significantly reduced oxidative stress in hypoxia-induced hRMECs, as shown by increased cell viability, SOD and GSH-PX leakage, decreased TUNEL- and ROS-positive cell ratio, LDH and MDA leakage, caspase-3 and -9 activity, and Bax/Bcl-2 ratio. In addition, MA also attenuated hypoxia-induced ER stress in hRMECs, as shown by reduced mRNA levels of glucose-regulated protein 78 (GRP78), C/EBP homologous transcription factor (CHOP), protein levels of cleaved activating transcription factor 6 (ATF6) and inositol-requiring kinase/endonuclease 1 alpha (IRE1α), phosphorylation of pancreatic ER stress kinase (PERK) and eukaryotic initiation factor 2 alpha (eIF2α), cleaved caspase-12 and ATF4 translocation to nucleus. The current study indicated that the regulation of oxidative stress and ER stress by MA would be a promising therapy to reverse the process and development of hypoxia-induced hRMECs dysfunction.

Hypoxia-induced vascular endothelial growth factor secretion by retinal pigment epithelial cells is inhibited by melatonin via decreased accumulation of hypoxia-inducible factors-1α protein

BACKGROUND

Hypoxia is the most important stimulus leading to up-regulation of vascular endothelial growth factor (VEGF) in the retina via elevation of hypoxia-inducible factors-1α (HIF-1α) protein. The purpose of this study was to test the effects of melatonin on the expression of VEGF and HIF-1α in the cultured human retinal pigment epithelial (RPE) cells under normoxia and hypoxia.

METHOD

An in vitro RPE cell hypoxia model was established by placing cells under 1% oxygen pressure or by adding cobalt chloride (CoCl₂ ) to the culture medium. RPE cells and conditioned media were collected from cultures treated with and without melatonin under normoxia and hypoxia. The protein and RNA levels of VEGF and HIF-1α were measured by ELISA kits and RT-PCR, respectively.

RESULT

Hypoxia induced a significant increase of expression and secretion of VEGF and accumulation of HIF-1α protein in RPE cells (P < 0.05). Melatonin at 10^-5 to 10^-8 M significantly inhibited hypoxia-induced expression, the secretion of VEGF and the accumulation of HIF-1α protein (P < 0.05), but not affected expression of VEGF and HIF-1α under normoxia (P > 0.05).

CONCLUSION

This study suggests that melatonin may have potential value in the prevention and treatment of various retinal diseases associated with increase of VEGF, vascular leakage and angiogenesis.

Methylglyoxal-Induced Endothelial Cell Loss and Inflammation Contribute to the Development of Diabetic Cardiomyopathy

The mechanisms for the development of diabetic cardiomyopathy remain largely unknown. Methylglyoxal (MG) can accumulate and promote inflammation and vascular damage in diabetes. We examined if overexpression of the MG-metabolizing enzyme glyoxalase 1 (GLO1) in macrophages and the vasculature could reduce MG-induced inflammation and prevent ventricular dysfunction in diabetes. Hyperglycemia increased circulating inflammatory markers in wild-type (WT) but not in GLO1-overexpressing mice. Endothelial cell number was reduced in WT-diabetic hearts compared with nondiabetic controls, whereas GLO1 overexpression preserved capillary density. Neuregulin production, endothelial nitric oxide synthase dimerization, and Bcl-2 expression in endothelial cells was maintained in the hearts of GLO1-diabetic mice and corresponded to less myocardial cell death compared with the WT-diabetic group. Lower receptor for advanced glycation end products and tumor necrosis factor-α (TNF-α) levels were also observed in GLO1-diabetic versus WT-diabetic mice. Over a period of 8 weeks of hyperglycemia, GLO1 overexpression delayed and limited the loss of cardiac function. In vitro, MG and TNF-α were shown to synergize in promoting endothelial cell death, which was associated with increased angiopoietin 2 expression and reduced Bcl-2 expression. These results suggest that MG in diabetes increases inflammation, leading to endothelial cell loss. This contributes to the development of diabetic cardiomyopathy and identifies MG-induced endothelial inflammation as a target for therapy.

Alagebrium attenuates methylglyoxal induced oxidative stress and AGE formation in H9C2 cardiac myocytes

AIM

Diabetes mellitus associated cardiovascular complications are a leading cause of morbidity and mortality worldwide. Methylglyoxal (MG) is a reactive ketoaldehyde and a byproduct of glucose metabolism and an inducer of advanced glycation endproducts (AGEs). Alagebrium (ALA) is an AGEs crosslink breaker, however, the effects of ALA on MG levels and its consequences in cultured rat cardiomyocytes are not known. The aim of the present study was to examine the effect of high glucose and MG on cultured rat cardiomyocytes and to investigate whether ALA could prevent any deleterious effects of high glucose and MG in these cells.

MAIN METHODS

MG levels were determined by HPLC. The expression of different genes was measured by RT-PCR. Oxidative stress and AGEs formation was determined by DCF probe and immunocytochemistry respectively.

KEY FINDINGS

High glucose- and MG treated- cardiomyocytes developed a significant increase in MG, and the expression for caspase-3, Bax, RAGE and NF-KB, which were all attenuated after pretreatment with ALA. A significant increase in reactive oxygen species generation and AGEs formation in high glucose- and MG treated- cultured cardiomyocytes was also observed, which was attenuated after pretreatment with ALA.

SIGNIFICANCE

ALA may have a preventive role against the deleterious effects of high glucose and MG in the heart. Prevention of dicarbonyl-induced AGEs, by safer and specific scavengers of MG is an attractive therapeutic option.

Methylglyoxal, a reactive glucose metabolite, enhances autophagy flux and suppresses proliferation of human retinal pigment epithelial ARPE-19 cells

Methylglyoxal (MGO), a glycolytic metabolite, induces oxidative injury and apoptotic cell death that play a pathogenetic role in age-related macular degeneration (AMD). This study examined the impact of MGO on cell proliferation and autophagy flux in retinal pigment epithelium (RPE) ARPE-19 cells and elucidated the underlying mechanism. Short-term MGO exposure suppressed cell proliferation without induction of apoptotic cell death, increased production of reactive oxygen species, and potentiated H2O2-exhibited cytotoxicity in ARPE-19 cells. Conversely, pretreatment with N-acetylcysteine, a ROS scavenger, and aminoguanidine, an MGO blocker, prevented MGO-induced growth retardation. MGO significantly enhanced autophagy flux and increased intracellular accumulation of autophagosomes, which was functionally confirmed by addition of autophagy enhancer or inhibitors. Signaling kinetic observation indicated that MGO remarkably triggered phosphorylation of Akt, ERK1/2, p38 MAPK, and JNK1/2. Blockade of kinase activity demonstrated that the hyperphosphorylation of Akt, ERK1/2, JNK, and p38 MAPK were all involved in the MGO-enhanced autophagy and growth-arresting effect in ARPE-19 cells. Moreover, pretreatment with autophagic flux inhibitors including 3-methyladenine, bafilomycin A, and chloroquine effectively ameliorated MGO- but not H2O2-mediated ARPE-19 cytotoxicity. In conclusion, modulation of autophagy flux activity by using autophagic or kinase inhibitors may be an applicable modality to treat AMD.

The role of methylglyoxal and the glyoxalase system in diabetes and other age-related diseases

The formation and accumulation of advanced glycation endproducts (AGEs) are related to diabetes and other age-related diseases. Methylglyoxal (MGO), a highly reactive dicarbonyl compound, is the major precursor in the formation of AGEs. MGO is mainly formed as a byproduct of glycolysis. Under physiological circumstances, MGO is detoxified by the glyoxalase system into D-lactate, with glyoxalase I (GLO1) as the key enzyme in the anti-glycation defence. New insights indicate that increased levels of MGO and the major MGO-derived AGE, methylglyoxal-derived hydroimidazolone 1 (MG-H1), and dysfunctioning of the glyoxalase system are linked to several age-related health problems, such as diabetes, cardiovascular disease, cancer and disorders of the central nervous system. The present review summarizes the mechanisms through which MGO is formed, its detoxification by the glyoxalase system and its effect on biochemical pathways in relation to the development of age-related diseases. Although several scavengers of MGO have been developed over the years, therapies to treat MGO-associated complications are not yet available for application in clinical practice. Small bioactive inducers of GLO1 can potentially form the basis for new treatment strategies for age-related disorders in which MGO plays a pivotal role.

Actin cytoskeletal rearrangement and dysfunction due to activation of the receptor for advanced glycation end products is inhibited by thymosin beta 4

KEY POINTS

Thymosin beta 4 (Tβ4 ) attenuates the vascular cellular toxicity induced by advanced glycation end products (AGEs) in human umbilical vein endothelial cells (HUVECs). Tβ4 reduces expression of both the receptor of AGEs (RAGE) and the filamentous actin (F-actin) to globular actin (G-actin) ratio. RAGE expression was regulated by actin cytoskeleton involved in Tβ4 . Tβ4 attenuates the vascular cellular toxicity induced by AGEs via remodelling of the actin cytoskeleton. AGEs attenuate vascular-like tube formation of HUVECs, which is reversed by Tβ4 via remodelling of the actin cytoskeleton.

ABSTRACT

The receptor of advanced glycation end products (RAGE) is a cell-surface receptor that is a key factor in the pathogenesis of diabetic complications, including vascular disorders. Dysfunction of the actin cytoskeleton contributes to disruption of cell membrane repair in response to various type of endothelial cell damage. However, mechanism underlying RAGE remodelling of the actin cytoskeleton, by which globular actin (G-actin) forms to filamentous actin (F-actin), remains unclear. In this study we examined the role of thymosin beta 4 (Tβ4 ) - which binds to actin, blocks actin polymerization, and maintains the dynamic equilibrium between G-actin and F-actin in human umbilical vein endothelial cells (HUVECs) - in the response to RAGE. Tβ4 increased cell viability and decreased levels of reactive oxygen species in HUVECs incubated with AGEs. Tβ4 reduced the expression of RAGE, consistent with a down-regulation of the F-actin to G-actin ratio. The effect of remodelling of the actin cytoskeleton on RAGE expression was clarified by adding Phalloidin, which stabilizes F-actin. Moreover, small interfering RNA was used to determine whether intrinsic Tβ4 regulates RAGE expression in the actin cytoskeleton. The absence of intrinsic Tβ4 in HUVECs evoked actin cytoskeleton disorder and increased RAGE expression. These findings suggest that regulation of the actin cytoskeleton by Tβ4 plays a pivotal role in the RAGE response to AGEs.

Zeaxanthin inhibits hypoxia-induced VEGF secretion by RPE cells through decreased protein levels of hypoxia-inducible factors-1α

Hypoxia is the most important stimulus leading to upregulation of VEGF in the retina and this is caused by accumulation of hypoxia-inducible factors-1α (HIF-1α) protein. The effects of zeaxanthin, a natural phytochemical, on the VEGF and HIF-1α expression in the primary culture of human retinal pigment epithelial (RPE) cells were studied. An in vitro RPE cell hypoxia model was established by placing cells under 1% oxygen pressure or by adding cobalt chloride (CoCl2) to the culture medium. RPE cells and conditioned media were collected from cultures treated with and without zeaxanthin under normoxic and hypoxic conditions. VEGF and HIF-1α protein and RNA levels were measured by ELISA kits and RT-PCR, respectively. Hypoxia caused a significant increase of VEGF expression and accumulation of HIF-1α in RPE cells. Zeaxanthin at 50-150 μM significantly inhibited the expression of VEGF and accumulation of HIF-1α protein caused by hypoxia but did not affect expression of VEGF and HIF-1α under normoxic conditions. This is the first report on the effect of zeaxanthin on VEGF and HIF-1α levels in cultured RPE cells and suggests that zeaxanthin may have potential value in the prevention and treatment of various retinal diseases associated with vascular leakage and neovascularization.

Serum fetuin-A concentrations are positively associated with serum VEGF levels in patients with newly diagnosed type 2 diabetes

Fetuin-A was considered to be involved in pathogenesis of type 2 diabetes. On the other hand, higher vascular endothelial growth factor (VEGF) expression is associated with diabetes and its vascular complications, but the mechanisms leading to higher VEGF levels are still not clear. To the best of our knowledge, there are no data to show the associations between fetuin-A and VEGF in patients with type 2 diabetes. Therefore, the aim of this study is to investigate the relationship between serum fetuin-A concentrations and serum VEGF levels in patients with type 2 diabetes. We recruited 345 patients with newly diagnosed type 2 diabetes. Serum fetuin-A concentrations and serum VEGF levels were measured using enzyme-linked immunosorbent assay (ELISA) method. In this study, there was a significant positive correlation between serum fetuin-A concentrations and serum VEGF levels (r=0.223, P<0.001), and the correlation remained significant even after adjustment for other confounding factors in the multivariate regression model (β=0.151, P=0.006). Mantel-Haenszel (M-H) stratified analysis showed that the degree of association of high concentrations of fetuin-A with high levels of VEGF is higher than that with low levels of VEGF (odds ratio of M-H [ORM-H], 2.938; 95% confidence interval [CI], 1.896-4.553). In addition, this study showed that both fetuin-A and VEGF were positively associated with fasting plasma glucose (FPG), glycated hemoglobin A1c (HbA1c) and C-reactive protein (CRP). These data suggested that serum fetuin-A concentrations were positively associated with serum VEGF levels in patients with newly diagnosed type 2 diabetes.

Hypoxia in vascular networks: a complex system approach to unravel the diabetic paradox

In this work we model the extent of hypoxia in the diabetic retina as a function of the area affected by vessel disruption. We find two regimes that differ on the ratio between the area of disrupted vasculature and the area of tissue in hypoxia. In the first regime the hypoxia is localized in the vicinity of the vascular disruption, while in the second regime there is a generalized hypoxia in the affected tissue. The transition between these two regimes occurs when the tissue area affected by individual sites of vessel damage is on the order of the square of the characteristic irrigation length in the tissue (the maximum distance that an irrigated point in the tissue is from an existing vessel). We observe that very high levels of hypoxia are correlated with the rupture of larger vessels in the retina, and with smaller radii of individual sites of vessel damage. Based on this property of vascular networks, we propose a novel mechanism for the transition between the nonproliferative and the proliferative stages in diabetic retinopathy.

The Role of MicroRNAs in Diabetic Complications-Special Emphasis on Wound Healing

Overweight and obesity are major problems in today’s society, driving the prevalence of diabetes and its related complications. It is important to understand the molecular mechanisms underlying the chronic complications in diabetes in order to develop better therapeutic approaches for these conditions. Some of the most important complications include macrovascular abnormalities, e.g., heart disease and atherosclerosis, and microvascular abnormalities, e.g., retinopathy, nephropathy and neuropathy, in particular diabetic foot ulceration. The highly conserved endogenous small non-coding RNA molecules, the micro RNAs (miRNAs) have in recent years been found to be involved in a number of biological processes, including the pathogenesis of disease. Their main function is to regulate post-transcriptional gene expression by binding to their target messenger RNAs (mRNAs), leading to mRNA degradation, suppression of translation or even gene activation. These molecules are promising therapeutic targets and demonstrate great potential as diagnostic biomarkers for disease. This review aims to describe the most recent findings regarding the important roles of miRNAs in diabetes and its complications, with special attention given to the different phases of diabetic wound healing.

Impaired hypoxia-inducible factor (HIF) regulation by hyperglycemia

The mechanisms that contribute to the development of diabetes complications remain unclear. A defective reaction of tissues to hypoxia has recently emerged as a new pathogenic mechanism and consists of a complex repression of hypoxia-inducible factor (HIF), which is the main regulator of the adaptive response to hypoxia. This paper discusses the mechanisms by which hyperglycaemia contributes to HIF repression in diabetes. Furthermore, a comprehensive analysis of the functional relevance of these new findings to the development of chronic diabetes complications is provided, along with examples from animal models and clinics.

Oxygen delivery, consumption, and conversion to reactive oxygen species in experimental models of diabetic retinopathy

Retinal tissue receives its supply of oxygen from two sources – the retinal and choroidal circulations. Decreases in retinal blood flow occur in the early stages of diabetes, with the eventual development of hypoxia thought to contribute to pathological neovascularization. Oxygen consumption in the retina has been found to decrease in diabetes, possibly due to either a reduction in neuronal metabolism or to cell death. Diabetes also enhances the rate of conversion of oxygen to superoxide in the retina, with experimental evidence suggesting that mitochondrial superoxide not only drives the overall production of reactive oxygen species, but also initiates several pathways leading to retinopathy, including the increased activity of the polyol and hexosamine pathways, increased production of advanced glycation end products and expression of their receptors, and activation of protein kinase C.

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Diabetes alters oxygen delivery and consumption in the retina.

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Conversion of oxygen to superoxide increases in the diabetic retina.

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An initial production of mitochondrial superoxide generates further ROS.

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ROS have been found to mediate deleterious pathways in the diabetic retina.

A vascular piece in the puzzle of adipose tissue dysfunction: mechanisms and consequences

In the last years, several studies unravelled many aspects of adipose tissue pathophysiology in metabolic diseases. Some studies suggested hypoxia as one of such aspects, despite the exact mechanisms and pathophysiological significance is still partially unknown. Adipose tissue was shown to be hypoxic in obesity, mainly resulting from adipocyte hypertrophy, leading to increased activation of inflammatory pathways. In animal and cell models, hypoxia-induced inflammation was shown to lead to endocrine alterations and dysmetabolism. However, recent evidences suggest that instead of a simple low oxygenation theory, adipose tissue microvasculature may be regulated by a series of factors, including vasoactive factors like angiotensin II, angiogenesis and glycation, among others. This review summarizes the current knowledge about the role of these factors in the regulation of adipose tissue irrigation and the functional consequences of adipose tissue microvascular dysfunction.

Methylglyoxal further impairs adipose tissue metabolism after partial decrease of blood supply

We previously showed that methylglyoxal-induced glycation induces adipose tissue lesions, including decreased irrigation and macrophage recruitment, independently of obesity. Here, we developed a model of partially decreased adipose tissue irrigation, a common condition in obese individuals. We aimed to study the role of methylglyoxal in the metabolic adaptations to such conditions 1 and 48 hours after decreased blood supply, avoiding other confoundable variables. Irrigation decrease during 1 hour leaded to increased activation of ERK1/2 and degradation of Ikappa-Balpha and Perilipin A in methylglyoxal-treated normal Wistar rats. After 48 hours, all rats showed increased fasting glycaemia and insulinemia. However, methylglyoxal-treated rats had higher free fatty acids and triglycerides levels and decreased adiponectinemia, consequent to decreased PPARgamma levels in partially irrigated adipose tissue. Our data show that besides causing vascular dysfunction, glycation further contributes to impaired adipocyte metabolism after a decrease of tissue irrigation, what may hamper metabolic adaptation during tissue expansion.

Glyoxalase-1 overexpression in bone marrow cells reverses defective neovascularization in STZ-induced diabetic mice

AIMS

Methylglyoxal (MG) accumulates in diabetes and impairs neovascularization. This study assessed whether overexpressing the MG-metabolizing enzyme glyoxalase-1 (GLO1) in only bone marrow cells (BMCs) could restore neovascularization in ischaemic tissue of streptozotocin-induced diabetic mice.

METHODS AND RESULTS

After 24 h of hyperglycaemic and hypoxic culture, BMCs from GLO1 overexpressing and wild-type (WT) diabetic mice were compared for migratory potential, viability, and mRNA expression of anti-apoptotic genes (Bcl-2 and Bcl-XL). In vivo, BMCs from enhanced green fluorescent protein (eGFP) mice that overexpress GLO1 were used to reconstitute the BM of diabetic mice (GLO1-diabetics). Diabetic and non-diabetic recipients of WT GFP(+) BM served as controls (WT-diabetics and non-diabetics, respectively). Following hindlimb ischaemia, the mobilization of BMCs was measured by flow cytometry. In hindlimbs, the presence of BM-derived angiogenic (GFP(+)CXCR4(+)) and endothelial (GFP(+)vWF(+)) cells and also arteriole density were determined by immunohistochemistry. Hindlimb perfusion was measured using laser Doppler. GLO1-BMCs had superior migratory potential, increased viability, and greater Bcl-2 and Bcl-XL expression, compared with WT BMCs. In vivo, the mobilization of pro-angiogenic BMCs (CXCR4(+), c-kit(+), and Flk(+)) was enhanced post-ischaemia in GLO1-diabetics compared to WT-diabetics. A greater number of GFP(+)CXCR4(+) and GFP(+)vWF(+) BMCs incorporated into the hindlimb tissue of GLO1-diabetics and non-diabetics than in WT-diabetics. Arteriole and capillary density and perfusion were also greater in GLO1-diabetics and non-diabetics.

CONCLUSION

This study demonstrates that protection from MG uniquely in BM is sufficient to restore BMC function and neovascularization of ischaemic tissue in diabetes and identifies GLO1 as a potential therapeutic target.

Methylglyoxal, obesity, and diabetes

Methylglyoxal (MG) is a highly reactive compound derived mainly from glucose and fructose metabolism. This metabolite has been implicated in diabetic complications as it is a strong AGE precursor. Furthermore, recent studies suggested a role for MG in insulin resistance and beta-cell dysfunction. Although several drugs have been developed in the recent years to scavenge MG and inhibit AGE formation, we are still far from having an effective strategy to prevent MG-induced mechanisms. This review summarizes the mechanisms of MG formation, detoxification, and action. Furthermore, we review the current knowledge about its implication on the pathophysiology and complications of obesity and diabetes.

Common mechanisms of dysfunctional adipose tissue and obesity-related cancers

The relation between cancer and metabolic disorders was recognized several decades ago, but the underlying mechanisms involved in cancer development and progression remain obscure. In the last years, many groups have been studying systemic adipose tissue markers in cancer patients. However, few consistent results were obtained. On the other hand, several studies revealed many aspects of adipose tissue physiology in obesity. Nowadays, it is recognized that excessive lipid uptake in adipocytes leads to hypertrophy and consequently to metabolic dysregulation, hypoxia, inflammation, impaired adipocytokine expression and angiogenesis, insulin resistance and macrophage recruitment. In obese patients, tumours commonly colocalize with excessive adipose tissue accumulation, and most of the features of hypertrophic adipose tissue are observed in cancer patients, namely breast and colon. This review aimed to summarize pathological adipose tissue alterations that may contribute to cancer aetiology and development.

Reduction of methylglyoxal-induced glycation by pyridoxamine improves adipose tissue microvascular lesions

Background and Aims. Adipose tissue dysfunction results from many factors, including glycation-induced microvascular damages. We tested the usefulness of inhibiting methylglyoxal-induced glycation to adipose tissue microvasculature in this work, using the antioxidant and dicarbonyl scavenger drug pyridoxamine. Methods. A group of Wistar rats was treated daily with methylglyoxal (MG, 75 mg/Kg/day, 8 weeks). Half of this group was treated with pyridoxamine in the following 4 weeks (Pyr) (100 mg/Kg/day) and the other half did not have any further treatment (MG). A group of Wistar rats without MG treatment was used as control (C). Results. MG group showed decreased HDL cholesterol and increased plasma free fatty acids levels, what was reverted by pyridoxamine. MG also caused an increase of tissue CEL levels (glycation marker), as well as increased staining of PAS and Masson Trichrome-positive components. Pyridoxamine led to CEL and TGF- β levels similar to those observed in control rats and inhibited the accumulation of PAS and Masson Trichrome-positive components. MG caused a decrease of Bcl-2/Bax ratio (marker of apoptosis) and vWF staining (microvascular marker), what was partially reverted by the treatment with pyridoxamine. Conclusions. Preventing methylglyoxal-induced accumulation of glycated and fibrotic materials using pyridoxamine improves the microvascular lesions of the adipose tissue.

The possible mechanisms underlying the impairment of HIF-1α pathway signaling in hyperglycemia and the beneficial effects of certain therapies

Hypoxia-inducible factor 1 alpha (HIF-1α), an essential transcription factor which mediates the adaptation of cells to low oxygen tensions, is regulated precisely by hypoxia and hyperglycemia, which are major determinants of the chronic complications associated with diabetes. The process of HIF-1α stabilization by hypoxia is clear; however, the mechanisms underlying the potential deleterious effect of hyperglycemia on HIF-1α are still controversial, despite reports of a variety of studies demonstrating the existence of this phenomenon. In fact, HIF-1α and glucose can sometimes influence each other: HIF-1α induces the expression of glycolytic enzymes and glucose metabolism affects HIF-1α accumulation in some cells. Although hyperglycemia upregulates HIF-1α signaling in some specific cell types, we emphasize the inhibition of HIF-1α by high glucose in this review. With regard to the mechanisms of HIF-1α impairment, the role of methylglyoxal in impairment of HIF-1α stabilization and transactivation ability and the negative effect of reactive oxygen species (ROS) on HIF-1α are discussed. Other explanations for the inhibition of HIF-1α by high glucose exist: the increased sensitivity of HIF-1α to Von Hippel-Lindau (VHL) machinery, the role of osmolarity and proteasome activity, and the participation of several molecules. This review aims to summarize several important developments regarding these mechanisms and to discuss potentially effective therapeutic techniques (antioxidants eicosapentaenoic acid (EPA) and metallothioneins (MTs), pharmaceuticals cobalt chloride (CoCl2), dimethyloxalylglycine (DMOG), desferrioxamine (DFO) and gene transfer of constitutively active forms of HIF-1α) and their mechanisms of action for intervention in the chronic complications in diabetes.

Protective effects of the dipeptidyl peptidase IV inhibitor sitagliptin in the blood-retinal barrier in a type 2 diabetes animal model

AIM

The aim of this study was to evaluate the efficacy of sitagliptin, a dipeptidyl peptidase IV inhibitor (DPP-IV), in preventing the deleterious effects of diabetes on the blood-retinal barrier in male Zucker Diabetic Fatty (ZDF) rats.

METHODS

ZDF rats at 20 weeks of age were treated with sitagliptin (10 mg/kg/day) during 6 weeks. The effect of the drug on glycaemia was assessed by evaluating glycated haemoglobin (HbA1c). The content and/or distribution of tight junction (TJ) proteins occludin and claudin-5, as well as nitrotyrosine residues, interleukin (IL)-1β, BAX and Bcl-2 was evaluated in the retinas by western blotting and/or immunohistochemistry. Retinal cell apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay. The number of CD34+ cells present in peripheral circulation was assessed by flow cytometry, and endothelial progenitor cells (EPC) adhesion ability to the retinal vessels was evaluated by immunohistochemistry.

RESULTS

Sitagliptin improved glycaemic control as reflected by a significant decrease in HbA1c levels by about 1.2%. Treatment with sitagliptin prevented the changes in the endothelial subcellular distribution of the TJ proteins induced by diabetes. Sitagliptin also decreased the nitrosative stress, the inflammatory state and cell death by apoptosis in diabetic retinas. Diabetic animals presented decreased levels of CD34+ cells in the peripheral circulation and decreased adhesion ability of EPC to the retinal vessels. Sitagliptin allowed a recovery of the number of CD34+ cells present in the bloodstream to levels similar to their number in controls and increased the adhesion ability of EPC to the retinal vessels.

CONCLUSIONS

Sitagliptin prevented nitrosative stress, inflammation and apoptosis in retinal cells and exerted beneficial effects on the blood-retinal barrier integrity in ZDF rat retinas.