Methylglyoxal, a reactive glucose metabolite, increases renin angiotensin aldosterone and blood pressure in male Sprague-Dawley rats

Modelling the effects of elevated methylglyoxal levels on vascular and metabolic complications

Methylglyoxal (MGO), a glycolysis by-product and precursor to advanced glycation endproducts (AGEs), is associated with glucose intolerance, type 2 diabetes, and vascular dysfunction. This study examined the long-term effects of elevated MGO on blood pressure, insulin sensitivity, and vascular function in healthy mice. Male C57Bl/6J mice were assigned to control (n = 16) or MGO-treated groups (50 mM in drinking water for 13 weeks, n = 16). Measurements included body weight, fasting plasma glucose, water consumption, blood pressure, and analysis of plasma/tissue for MGO, AGEs, glyoxalase activity, and inflammation markers. Endothelial function was assessed using wire myography, and the response of human placental arteries to MGO-modified insulin was evaluated. MGO treatment significantly increased plasma MGO (123.3%, p < 0.001), AGEs MG-H1 (208.6%, p < 0.001) and CEL (64.3%, p < 0.001), and AGEs in the heart, kidney, and liver, along with body weight (+ 6.4%, p = 0.032) and blood pressure (systolic + 5.0%, p = 0.046; diastolic + 6.5%, p = 0.043). Glucose sensitivity and endothelial function remained unaffected. CRP levels rose, and MGO-modified insulin enhanced vascular contraction. In conclusion, chronic MGO exposure increased plasma MGO to diabetic-like levels, raised body weight and blood pressure, and did not alter glucose sensitivity or endothelial function. Modification of insulin by MGO may contribute to MGO-related changes in blood pressure.

Decoding the role of aldosterone in glycation-induced diabetic complications

Diabetes-mediated development of micro and macro-vascular complications is a global concern. One of the factors is hyperglycemia induced the non-enzymatic formation of advanced glycation end products (AGEs). Accumulated AGEs bind with receptor of AGEs (RAGE) causing inflammation, oxidative stress and extracellular matrix proteins (ECM) modifications responsible for fibrosis, cell damage and tissue remodeling. Moreover, during hyperglycemia, aldosterone (Aldo) secretion increases, and its interaction with mineralocorticoid receptor (MR) through genomic and non-genomic pathways leads to inflammation and fibrosis. Extensive research on individual involvement of AGEs-RAGE and Aldo-MR pathways in the development of diabetic nephropathy (DN), cardiovascular diseases (CVDs), and impaired immune system has led to the discovery of therapeutic drugs. Despite mutual repercussions, the cross-talk between AGEs-RAGE and Aldo-MR pathways remains unresolved. Hence, this review focuses on the possible interaction of Aldo and glycation in DN and CVDs, considering the clinical significance of mutual molecular targets.

Placental Methylglyoxal in Preeclampsia: Vascular and Biomarker Implications

BACKGROUND

Preeclampsia is a multifaceted syndrome that includes maternal vascular dysfunction. We hypothesize that increased placental glycolysis and hypoxia in preeclampsia lead to increased levels of methylglyoxal (MGO), consequently causing vascular dysfunction.

METHODS

Plasma samples and placentas were collected from uncomplicated and preeclampsia pregnancies. Uncomplicated placentas and trophoblast cells (BeWo) were exposed to hypoxia. The reactive dicarbonyl MGO and advanced glycation end products (Nε-(carboxymethyl)lysine [CML], Nε-(carboxyethyl)lysine [CEL], and MGO-derived hydroimidazolone [MG-H]) were quantified using liquid chromatography-tandem mass spectrometry. The activity of GLO1 (glyoxalase-1), that is, the enzyme detoxifying MGO, was measured. The impact of MGO on vascular function was evaluated using wire/pressure myography. The therapeutic potential of the MGO-quencher quercetin and mitochondrial-specific antioxidant mitoquinone mesylate (MitoQ) was explored.

RESULTS

MGO, CML, CEL, and MG-H2 levels were elevated in preeclampsia-placentas (+36%, +36%, +25%, and +22%, respectively). Reduced GLO1 activity was observed in preeclampsia-placentas (-12%) and hypoxia-exposed placentas (-16%). Hypoxia-induced MGO accumulation in placentas was mitigated by the MGO-quencher quercetin. Trophoblast cells were identified as the primary source of MGO. Reduced GLO1 activity was also observed in hypoxia-exposed BeWo cells (-26%). Maternal plasma concentrations of CML and the MGO-derived MG-H1 increased as early as 12 weeks of gestation (+16% and +17%, respectively). MGO impaired endothelial barrier function, an effect mitigated by MitoQ, and heightened vascular responsiveness to thromboxane A2.

CONCLUSIONS

This study reveals the accumulation of placental MGO in preeclampsia and upon exposure to hypoxia, demonstrates how MGO can contribute to vascular impairment, and highlights plasma CML and MG-H1 levels as promising early biomarkers for preeclampsia.

Molecular Assessment of Methylglyoxal-Induced Toxicity and Therapeutic Approaches in Various Diseases: Exploring the Interplay with the Glyoxalase System

This comprehensive exploration delves into the intricate interplay of methylglyoxal (MG) and glyoxalase 1 (GLO I) in various physiological and pathological contexts. The linchpin of the narrative revolves around the role of these small molecules in age-related issues, diabetes, obesity, cardiovascular diseases, and neurodegenerative disorders. Methylglyoxal, a reactive dicarbonyl metabolite, takes center stage, becoming a principal player in the development of AGEs and contributing to cell and tissue dysfunction. The dual facets of GLO I-activation and inhibition-unfold as potential therapeutic avenues. Activators, spanning synthetic drugs like candesartan to natural compounds like polyphenols and isothiocyanates, aim to restore GLO I function. These molecular enhancers showcase promising outcomes in conditions such as diabetic retinopathy, kidney disease, and beyond. On the contrary, GLO I inhibitors emerge as crucial players in cancer treatment, offering new possibilities in diseases associated with inflammation and multidrug resistance. The symphony of small molecules, from GLO I activators to inhibitors, presents a nuanced understanding of MG regulation. From natural compounds to synthetic drugs, each element contributes to a molecular orchestra, promising novel interventions and personalized approaches in the pursuit of health and wellbeing. The abstract concludes with an emphasis on the necessity of rigorous clinical trials to validate these findings and acknowledges the importance of individual variability in the complex landscape of health.

Angiotensin II reduces glyoxalase 1 activity and expression in vascular smooth muscle cells: Implications for diabetic vascular complications

Angiotensin II (Ang II), a key mediator of vascular diseases, is linked to methylglyoxal (MGO) formation, a by-product of glucose metabolism implicated in vascular complications. The glyoxalase system, consisting of glyoxalase 1 (Glo1) and reduced glutathione (GSH), is responsible for detoxifying MGO. This study investigated the effect of Ang II on Glo1 activity and expression in vascular smooth muscle cells (VSMCs). Primary VSMCs were isolated from rat aortas and exposed to Ang II under standard or high glucose conditions. We examined Glo1 activity, expression, intracellular GSH, and methylglyoxal-derived hydroimidazolone 1 (MG-H1) levels. We also analyzed the expressions of nuclear factor-κB (NF-κB) p65 and nuclear factor erythroid 2-related factor 2 (Nrf2) as potential regulators of Glo1 expression. The results demonstrated that Ang II reduced Glo1 activity, expression, and GSH levels while increasing MG-H1 levels in VSMCs. Telmisartan and irbesartan, AT1R blockers, restored Glo1 activity, expression, and GSH levels and alleviated MG-H1 levels. Treatment with AT1R blockers or inhibitors targeting signaling pathways involved in Ang II-induced responses mitigated these effects. High glucose exacerbated the reduction in Glo1 activity and expression. In conclusion, this study provides evidence that Ang II reduces Glo1 activity and expression in VSMCs, which may contribute to developing vascular complications in diabetes. AT1R blockers and inhibitors targeting specific signaling pathways show potential in restoring Glo1 function and mitigating MGO-associated damage. These findings highlight the complex interactions between RAS, MGO, and vascular diseases, highlighting potential therapeutic targets for diabetic vascular complications.

Methylglyoxal in Cardiometabolic Disorders: Routes Leading to Pathology Counterbalanced by Treatment Strategies

Methylglyoxal (MGO) is the major compound belonging to reactive carbonyl species (RCS) responsible for the generation of advanced glycation end products (AGEs). Its upregulation, followed by deleterious effects at the cellular and systemic levels, is associated with metabolic disturbances (hyperglycemia/hyperinsulinemia/insulin resistance/hyperlipidemia/inflammatory processes/carbonyl stress/oxidative stress/hypoxia). Therefore, it is implicated in a variety of disorders, including metabolic syndrome, diabetes mellitus, and cardiovascular diseases. In this review, an interplay between pathways leading to MGO generation and scavenging is addressed in regard to this system's impairment in pathology. The issues associated with mechanistic MGO involvement in pathological processes, as well as the discussion on its possible causative role in cardiometabolic diseases, are enclosed. Finally, the main strategies aimed at MGO and its AGEs downregulation with respect to cardiometabolic disorders treatment are addressed. Potential glycation inhibitors and MGO scavengers are discussed, as well as the mechanisms of their action.

Methylglyoxal enhances the proliferation of vascular smooth muscle cells via Akt phosphorylation

Methylglyoxal (MGO) is predominantly produced as a by-product of the glycolysis pathway. The glyoxalase system effectively removes it in a healthy organism. However, this process is impaired, and MGO level is elevated in people with diabetes. MGO's effects on proliferation were mostly studied in cancer cells, and the data in other cell types are limited. This study inspected the proliferative capacity of MGO in vascular smooth muscle cells (VSMCs), which have a crucial role in atherosclerosis and restenosis. The roles of ERK1/2 MAPK and Akt phosphorylations in proliferation were determined. Telmisartan, irbesartan, and NF-κB inhibitor JSH-23's roles in protecting the cells from MGO-induced proliferation were also investigated. Primary VSMCs were isolated from the rat aorta. The proliferation was spectrophotometrically measured by using a tetrazolium salt (Wst-1). The cells were cultured in standard media (SM, glucose conc. 5.5 mM) or high glucose media (HGM, glucose conc. 25 mM; an in vitro model of hyperglycemia). ERK1/2 MAPK and Akt phosphorylations were determined by the western blot method. MGO triggered the proliferation at 24, 48, and 72 hrs in SM and 48 and 72 hrs in HGM. Low doses of MGO such as 1-10 µM can induce proliferation. The phosphorylated ERK1/2 MAPK and Akt participated in MGO-induced proliferation. Telmisartan, irbesartan, and JSH-23 effectively alleviated the proliferation and Akt phosphorylation. MGO could proliferate VSMCs even at low doses. Moreover, hypertensive diabetic patients might benefit from a sartan family drug to protect VSMCs from MGO-induced proliferation.

Mineralocorticoid receptor antagonism improves transient receptor potential vanilloid 4-dependent dilation of cerebral parenchymal arterioles and cognition in a genetic model of hypertension

OBJECTIVE

In a model of secondary hypertension, mineralocorticoid receptor (MR) antagonism during the development of hypertension prevents the impairment of transient receptor potential vanilloid 4 (TRPV4) activation in parenchymal arterioles (PAs) and cognitive impairment. However, it is unknown whether MR antagonism can improve these impairments when treatment begins after the onset of essential hypertension. We tested the hypothesis that MR activation in stroke-prone spontaneously hypertensive rats (SHRSP) leads to impaired TRPV4-mediated dilation in PAs that is associated with cognitive dysfunction and neuroinflammation.

METHODS

20-22-week-old male SHRSP ± eplerenone (EPL; 100 mg/kg daily for 4 weeks) were compared to normotensive Sprague-Dawley (SD) rats. Pressure myography was used to assess PA function. Cognition was tested using Y-maze. Neuroinflammation was assessed using immunofluorescence and qRT-PCR.

RESULTS

Carbachol-mediated endothelium-dependent dilation was impaired in SHRSP, and MR antagonism improved this without affecting myogenic tone. Dilation to TRPV4 agonist GSK1016790A was impaired in SHRSP, and ELP treatment restored this. Intermediate conductance potassium channel (IKCa)/small conductance potassium channel (SKCa)-mediated dilation was impaired by hypertension and unaffected by EPL treatment. TRPV4 and IKCa/SKCa channel mRNA expression were reduced in PAs from hypertensive rats, and EPL did not improve this. Impairments in PA dilation in SHRSP were associated with cognitive decline, microglial activation, reactive astrogliosis, and neuroinflammation; cognitive and inflammatory changes were improved with MR blockade.

CONCLUSIONS

These data advance our understanding of the effects of hypertension on cerebral arterioles using a clinically relevant model and treatment paradigm. Our studies suggest TRPV4 and the MR are potential therapeutic targets to improve cerebrovascular function and cognition during hypertension.

Irbesartan treatment does not influence plasma levels of the dicarbonyls methylglyoxal, glyoxal and 3-deoxyglucosone in participants with type 2 diabetes and microalbuminuria: An IRMA2 sub-study

AIM

Angiotensin receptor blockers (ARBs) reduce vascular complications in diabetes independently of blood pressure. Experimental studies suggested that ARBs may restore the detoxifying enzyme glyoxalase 1, thereby lowering dicarbonyls such as methylglyoxal. Human data on the effects of ARBs on plasma dicarbonyl levels are lacking. We investigated, in individuals with type 2 diabetes, whether irbesartan lowered plasma levels of the dicarbonyls methylglyoxal, glyoxal, 3-deoxyglucosone and their derived advanced glycation end products (AGEs), and increased d-lactate, reflecting greater methylglyoxal flux.

METHODS

We analysed a subset of the Irbesartan in Patients with T2D and Microalbuminuria (IRMA2) study. We measured plasma dicarbonyls methylglyoxal, glyoxal and 3-deoxyglucosone, free AGEs and d-lactate using ultra-performance liquid chromatography tandem mass-spectrometry (UPLC-MS/MS) in the treatment arm receiving 300 mg irbesartan (n = 121) and a placebo group (n = 101) at baseline and after 1 and 2 years. Effect of treatment was analysed with repeated measurements ANOVA.

RESULTS

There was a slight, but significant difference in baseline median methylglyoxal levels [placebo 1119 (907-1509) nmol/l vs. irbesartan 300 mg 1053 (820-1427) nmol/l], but no significant changes were observed in any of the plasma dicarbonyls over time in either group and there was no effect of irbesartan treatment on plasma free AGEs or d-lactate levels at either 1 or 2 years.

CONCLUSION

Irbesartan treatment does not change plasma levels of the dicarbonyls methylglyoxal, glyoxal and 3-deoxyglucosone, free AGEs or d-lactate in type 2 diabetes. This indicates that increased dicarbonyls in type 2 diabetes are not targetable by ARBs, and other approaches to lower systemic dicarbonyls are needed in type 2 diabetes. (Clinical Trial Registry No: #NCT00317915).

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.

Collagen IV, a promising serum biomarker for evaluating the prognosis of revascularization in a 2-kidney, 1-clip hypertensive rat model

OBJECTIVES

The goal of this study was to investigate the expression of serum collagen IV and its value for evaluating the prognosis of revascularization in a 2-kidney, 1-clip hypertensive rat model.

METHODS

A total of 40 Sprague-Dawley rats were randomly and evenly divided into a control group and 3-, 10- and 20-day (D) groups (namely, the ischaemic time for 3, 10 and 20 days, respectively). The systolic blood pressure and laboratory values such as serum creatinine and collagen IV levels were measured before and after clipping the renal artery. Histological Masson staining and immunohistochemical staining of collagen IV were conducted in a kidney specimen from each group to assess the severity of renal fibrosis and the level of collagen IV expression.

RESULTS

After clipping, systolic blood pressure in the 3D, 10D and 20D groups increased significantly from 108 ± 8 to 126 ± 7 and from 153 ± 8 to 157 ± 6 mmHg, respectively (10D vs 20D group, P = 0.224; between other groups, P < 0.001). The expression of serum creatinine in the 3D, 10D and 20D groups increased significantly from 35.39 ± 5.64 to 57.53 ± 7.05, 101.86 ± 8.94 and 119.76 ± 9.37 mmol/l, respectively (between each group: P < 0.001). Serum collagen IV levels in the 10D and 20D groups increased significantly from 38.5 ± 10.4 to 60.8 ± 15.0 and 87.3 ± 11.5 ng/ml, respectively (control vs 3D group, P = 0.718; between other groups, P < 0.001). The Masson staining indicated that sclerotic changes in the glomeruli of the 10D and 20D groups significantly increased from 2.20 ± 1.03 to 15.20 ± 5.03 and 28.20 ± 7.07%, respectively (control vs 3D group, P = 0.175; between other groups, P < 0.001). The grade of tubulointerstitial damage in the 3D, 10D and 20D groups increased significantly from 0.30 ± 0.48 to 1.90 ± 0.74, 1.80 ± 0.79 and 3.20 ± 0.79, respectively (3D vs 10D group, P = 0.755; between other groups, P < 0.001). The semi-quantification from immunohistochemical staining indicated that the percentage of collagen IV positive areas in the 3D, 10D and 20D groups increased significantly from 3.50 ± 1.58 to 8.60 ± 2.11, 16.60 ± 8.55 and 23.10 ± 6.15, respectively (control vs 3D group, P = 0.043; 3D vs 10D group, P = 0.002; 10D vs 20D group, P = 0.011; between other groups, P < 0.001). The area under the curve of the receiver operating characteristic curve was 0.783 (P = 0.008; 95% confidence interval 0.634-0.932). There were positive associations of serum collagen IV levels with systolic blood pressure, serum creatinine and collagen IV quantification in kidney with correlation coefficients of 0.665, 0.775 and 0.628, respectively (P < 0.001).

CONCLUSIONS

As the clear ischaemia time-response relationship identified in our study indicates, the increase in serum collagen IV levels may be a satisfactory biomarker to indicate a poor prognosis of renal artery revascularization in a 2-kidney, 1-clip hypertensive rat model. However, it is perhaps not a good early biomarker for the early detection of renovascular hypertension.

Long-term intake of the reactive metabolite methylglyoxal is not toxic in mice

Reactive carbonyls, including methylglyoxal (MG), are considered toxic compounds in foodstuffs because they irreversibly modify proteins and produce advanced glycation end products (AGEs). Therefore, we studied the long-term effect of increased MG intake in mature adult mice. Six-month-old C57BL/6N mice received MG by drinking water (2.5 mg/ml; i.e., 200-300 mg/kg BW/d) until death. This treatment caused an immediate strong increase in urine MG and a delayed moderate increase in plasma MG. At 24 months of age, mice administered MG showed no changes in the blood and tissue activity of glyoxalase-1 (Glo1), an intracellular MG-detoxifying enzyme; no signs of renal insufficiency and diabetes, including unchanged AGE modifications of plasma and vessel proteins; reduced tumour incidence; and slightly increased survival. Mice simultaneously deficient in the receptor for AGEs (RAGE) and overexpressing Glo1 exhibited higher basal plasma MG levels and did generally not respond to long-term MG intake. In vitro experiments supported the minor relevance of Glo1 in the detoxification of circulating MG but the important role of plasma albumin as an MG scavenger. In conclusion, the detoxification of dietary MG through renal excretion and further mechanisms largely prevents the toxicity of MG and possibly other food-derived reactive carbonyls in mature adults.

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.

Alagebrium and Complications of Diabetes Mellitus

Glycation is the process of linking a sugar and free amino groups of proteins. Cross-linking of glycation products to proteins results in the formation of cross-linked proteins that inhibit the normal functioning of the cell. Advanced glycation end products (AGEs) are risk molecules for the cell aging process. These ends products are increasingly synthesized in diabetes and are essentially responsible for diabetic complications. They accumulate in the extracellular matrix and bind to receptors (receptor of AGE [RAGE]) to generate oxidative stress and inflammation. particularly in the cardiovascular system. Treatment methods targeting the AGE system may be of clinical importance in reducing and preventing the complications induced by AGEs in diabetes and old age. The AGE cross-link breaker alagebrium (a thiazolium derivative) is the most studied anti-AGE compound in the clinical field. Phase III clinical studies with alagebrium have been successfully conducted, and this molecule has positive effects on cardiovascular hypertrophy, diabetes, hypertension, vascular sclerotic pathologies, and similar processes. However, the mechanism is still not fully understood. The primary mechanism is that alagebrium removes newly formed AGEs by chemically separating α-dicarbonyl carbon-carbon bonds formed in cross-linked structures. However, it is also reported that alagebrium is a methylglyoxal effective inhibitor. It is not yet clear whether alagebrium inhibits copper-catalyzed ascorbic acid oxidation through metal chelation or destruction of the AGEs. It is not known whether alagebrium has a direct association with RAGEs. The safety profile is favorably in humans, and studies have been terminated due to financial insufficiency and inability to license as a drug.

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.

Evidence of changes in alpha-1/AT1 receptor function generated by diet-induced obesity

To study whether hypercaloric diet-induced obesity deteriorates vascular contractility of rat aorta through functional changes in α₁ adrenergic and/or AT1 Angiotensin II receptors. Angiotensin II- or phenylephrine-induced contraction was tested on isolated aorta rings with and without endothelium from female Wistar rats fed for 7 weeks with hypercaloric diet or standard diet. Vascular expression of Angiotensin II Receptor type 1 (AT1R), Angiotensin II Receptor type 2 (AT2R), Cyclooxygenase-1 (COX-1), Cyclooxygenase-2 (COX-2), inducible Nitric Oxide Synthase (iNOS) and endothelial Nitric Oxide Synthase (eNOS), as well as blood pressure, glucose, insulin and angiotensin II blood levels were measured. Diet-induced obesity did not significantly change agonist-induced contractions (Emax and pD₂ hypercaloric diet vs standard diet n.s.d.) of both intact (e+) or endothelium free (e-) vessels but significantly decrease both phenylephrine and angiotensin II contraction (Emax p < 0.01 hypercaloric diet vs standard diet) in the presence of both prazosin and losartan but only in endothelium-intact vessels. Diet-induced obesity did not change angiotensin II AT1, AT2 receptor proteins expression but reduced COX-1 and NOS2 ( p < 0.05 vs standard diet). Seven-week hypercaloric diet-induced obesity produces alterations in vascular adrenergic and angiotensin II receptor dynamics that suggest an endothelium-dependent adrenergic/angiotensin II crosstalk. These changes reflect early-stage vascular responses to obesity.

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.

Methylglyoxal-Glyoxalase 1 Balance: The Root of Vascular Damage

The highly reactive dicarbonyl methylglyoxal (MGO) is mainly formed as byproduct of glycolysis. Therefore, high blood glucose levels determine increased MGO accumulation. Nonetheless, MGO levels are also increased as consequence of the ineffective action of its main detoxification pathway, the glyoxalase system, of which glyoxalase 1 (Glo1) is the rate-limiting enzyme. Indeed, a physiological decrease of Glo1 transcription and activity occurs not only in chronic hyperglycaemia but also with ageing, during which MGO accumulation occurs. MGO and its advanced glycated end products (AGEs) are associated with age-related diseases including diabetes, vascular dysfunction and neurodegeneration. Endothelial dysfunction is the first step in the initiation, progression and clinical outcome of vascular complications, such as retinopathy, nephropathy, impaired wound healing and macroangiopathy. Because of these considerations, studies have been centered on understanding the molecular basis of endothelial dysfunction in diabetes, unveiling a central role of MGO-Glo1 imbalance in the onset of vascular complications. This review focuses on the current understanding of MGO accumulation and Glo1 activity in diabetes, and their contribution on the impairment of endothelial function leading to diabetes-associated vascular damage.

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.

CHOP deficiency prevents methylglyoxal-induced myocyte apoptosis and cardiac dysfunction

Epidemiological studies indicate that methylglyoxal (MGO) plasma levels are closely linked to diabetes and the exacerbation of diabetic cardiovascular complications. Recently, it was established that endoplasmic reticulum (ER) stress importantly contributes to the pathogenesis of diabetes and its cardiovascular complications. The objective of this study was to explore the mechanism by which diabetes instigates cardiomyocyte apoptosis and cardiac dysfunction via MGO-mediated myocyte apoptosis. Intriguingly, the MGO activated unfolded protein response pathway accompanying apoptotic events, such as cleavages of PARP-1 and caspase-3. In addition, Western blot analysis revealed that MGO-induced myocyte apoptosis was inhibited by depletion of CHOP with siRNA against Ddit3, the gene name for rat CHOP. To investigate the physiologic roles of CHOP in vivo, glucose tolerance and cardiac dysfunction were assessed in CHOP-deficient mice. No significant difference was observed between CHOP KO and littermate naïve controls in terms of the MGO-induced impairment of glucose tolerance. In contrast, myocyte apoptosis, inflammation, and cardiac dysfunction were significantly diminished in CHOP KO compared with littermate naïve controls. These results showed that CHOP is the key signal for myocyte apoptosis and cardiac dysfunction induced by MGO. These findings suggest a therapeutic potential of CHOP inhibition in the management of diabetic cardiovascular complications including diabetic cardiomyopathy.

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.

Lower urinary pH is useful for predicting renovascular disorder onset in patients with diabetes

BACKGROUND AND OBJECTIVES

A lower urinary pH (UpH) is closely linked to diabetes. However, its relation to diabetic renovascular damage is unclear. This study aimed to identify the relationship between UpH and the exacerbation of diabetic renovascular disorders.

METHODS

This is a 10-year observational study targeting 400 outpatients with diabetes who registered in 2003. We investigated the relationship between UpH in 2003 and renovascular damage from 2003 to 2013.

RESULTS

A total of 350 participants were eligible for the analysis. During their 10-year outpatient treatment, a decrease was seen in glycated hemoglobin levels, blood pressure, and estimated glomerular filtration rates (eGFRs), and an increase was seen in their urinary albumin-creatinine ratios (ACRs), uric acid (UA) levels, and intima-media thickness (IMT). UpH negatively correlated with urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), body mass index, UA, and ACR, and positively correlated with eGFR. The results of a multiple regression analysis showed that the independent risk factors for UpH were 8-OHdG, UA, eGFR, and ACR. UpH also negatively correlated with the percent change in IMT (%IMT), the percent change in pulse wave velocity (%PWV), and the change in log ACR (Δlog ACR), and positively correlated with the percent change in eGFR. A multiple regression analysis revealed that UpH was an independent risk factor for the %IMT, %PWV and Δlog ACR. Obese patients with low UpH values frequently suffered from sleep apnea syndrome.

CONCLUSIONS

These results suggest that UpH is a useful marker for predicting the onset of renovascular disorder in patients with diabetes.

Proinflammation of aging central arteries: a mini-review

Arterial aging is a cornerstone of organismal aging. The central arterial wall structurally and functionally remodels under chronic proinflammatory stress over a lifetime. The low-grade proinflammation that accompanies advancing age causes arterial wall thickening and stiffening. These structural and functional alterations are consequences of adverse molecular and cellular events, e.g. an increase in local angiotensin II signaling that induces an inflammatory phenotypic shift of endothelial and smooth muscle cells. Thus, interventions to restrict proinflammatory signaling are a rational approach to delay or prevent age-associated adverse arterial remodeling.