Glycated and oxidized protein degradation products are indicators of fasting and postprandial hyperglycemia in diabetes

Sex differences in the development of experimental diabetic retinopathy

This study aimed to characterize the role of female sex in the pathogenesis of diabetic retinopathy. In the retinae of female Ins2Akita-diabetic mice (F-IA), ovariectomized female Ins2Akita-diabetic mice (F-IA/OVX), male Ins2Akita-diabetic mice (M-IA), and female STZ-diabetic mice (F-STZ), the formation of reactive metabolites and post-translational modifications, damage to the neurovascular unit, and expression of cellular stress response genes were analyzed. Compared to the male diabetic retina, the concentrations of the glycation adduct fructosyl-lysine, the Maillard product 3-deoxyglucosone, and the reactive metabolite methylglyoxal were significantly reduced in females. In females, there was also less evidence of diabetic damage to the neurovascular unit, as shown by decreased pericyte loss and reduced microglial activation. In the male diabetic retina, the expression of several members of the crystallin gene family (Cryab, Cryaa, Crybb2, Crybb1, and Cryba4) was increased. Clinical data from type 1 diabetic females showed that premenopausal women had a significantly lower prevalence of diabetic retinopathy compared to postmenopausal women stratified for disease duration and glycemic control. These data emphasize the importance of estradiol in protecting the diabetic retina and highlight the pathogenic relevance of sex in diabetic retinopathy.

Protein glycation products associate with progression of kidney disease and incident cardiovascular events in individuals with type 1 diabetes

BACKGROUND

Despite improved glycemic treatment, the impact of glycation on pathological consequences may persist and contribute to adverse clinical outcomes in diabetes. In the present study we investigated the association between serum protein glycation products and progression of kidney disease as well as incident major adverse cardiovascular events (MACE) in type 1 diabetes.

METHODS

Fructosamine, advanced glycation end products (AGEs), and methylglyoxal-modified hydro-imidazolone (MG-H1) were measured from baseline serum samples in the FinnDiane study (n = 575). Kidney disease progression was defined as steep eGFR decline (> 3 mL/min/1.73 m2/year) or progression of albuminuria (from lower to higher stage of albuminuria). MACE was defined as acute myocardial infarction, coronary revascularization, cerebrovascular event (stroke), and cardiovascular death.

RESULTS

Fructosamine was independently associated with steep eGFR decline (OR 2.15 [95% CI 1.16-4.01], p = 0.016) in the fully adjusted model (age, sex, baseline eGFR). AGEs were associated with steep eGFR decline (OR 1.58 per 1 unit of SD [95% CI 1.07-2.32], p = 0.02), progression to end-stage kidney disease (ESKD) (HR 2.09 per 1 unit of SD [95% CI 1.43-3.05], p < 0.001), and pooled progression (to any stage of albuminuria) (HR 2.72 per 1 unit of SD [95% CI 2.04-3.62], p < 0.001). AGEs (HR 1.57 per 1 unit of SD [95% CI 1.23-2.00], p < 0.001) and MG-H1 (HR 4.99 [95% CI 0.98-25.55], p = 0.054) were associated with incident MACE. MG-H1 was also associated with pooled progression (HR 4.19 [95% CI 1.11-15.89], p = 0.035). Most AGEs and MG-H1 associations were no more significant after adjusting for baseline eGFR.

CONCLUSIONS

Overall, these findings suggest that protein glycation products are an important risk factor for target organ damage in type 1 diabetes. The data provide further support to investigate a potential causal role of serum protein glycation in the progression of diabetes complications.

Soluble RAGE and skeletal muscle tissue RAGE expression profiles in lean and obese young adults across differential aerobic exercise intensities

Nearly 40% of Americans have obesity and are at increased risk for developing type 2 diabetes. Skeletal muscle is responsible for >80% of insulin-stimulated glucose uptake that is attenuated by the inflammatory milieu of obesity and augmented by aerobic exercise. The receptor for advanced glycation endproducts (RAGE) is an inflammatory receptor directly linking metabolic dysfunction with inflammation. Circulating soluble isoforms of RAGE (sRAGE) formed either by proteolytic cleavage (cRAGE) or alternative splicing (esRAGE) act as decoys for RAGE ligands, thereby counteracting RAGE-mediated inflammation. We aimed to determine if RAGE expression or alternative splicing of RAGE is altered by obesity in muscle, and whether acute aerobic exercise (AE) modifies RAGE and sRAGE. Young (20-34 yr) participants without [n = 17; body mass index (BMI): 22.6 ± 2.6 kg/m2] and with obesity (n = 7; BMI: 32.8 ± 2.9 kg/m2) performed acute aerobic exercise (AE) at 40%, 65%, or 80% of maximal aerobic capacity (V̇o2max; mL/kg/min) on separate visits. Blood was taken before and 30 min after each AE bout. Muscle biopsy samples were taken before, 30 min, and 3 h after the 80% V̇o2max AE bout. Individuals with obesity had higher total RAGE and esRAGE mRNA and RAGE protein (P < 0.0001). In addition, RAGE and esRAGE transcripts correlated to transcripts of the NF-κB subunit P65 (P < 0.05). There was no effect of AE on total RAGE or esRAGE transcripts, or RAGE protein (P > 0.05), and AE tended to decrease circulating sRAGE in particular at lower intensities of exercise. RAGE expression is exacerbated in skeletal muscle with obesity, which may contribute to muscle inflammation via NF-κB. Future work should investigate the consequences of increased skeletal muscle RAGE on the development of obesity-related metabolic dysfunction and potential mitigating strategies.NEW & NOTEWORTHY This study is the first to investigate the effects of aerobic exercise intensity on circulating sRAGE isoforms, muscle RAGE protein, and muscle RAGE splicing. sRAGE isoforms tended to diminish with exercise, although this effect was attenuated with increasing exercise intensity. Muscle RAGE protein and gene expression were unaffected by exercise. However, individuals with obesity displayed nearly twofold higher muscle RAGE protein and gene expression, which positively correlated with expression of the P65 subunit of NF-κB.

Glyoxalase I is a novel target for the prevention of metabolic derangement

Obesity prevalence in the US has nearly tripled since 1975 and a parallel increase in prevalence of type 2 diabetes (T2D). Obesity promotes a myriad of metabolic derangements with insulin resistance (IR) being perhaps the most responsible for the development of T2D and other related diseases such as cardiovascular disease. The precarious nature of IR development is such that it provides a valuable target for the prevention of further disease development. However, the mechanisms driving IR are numerous and complex making the development of viable interventions difficult. The development of metabolic derangement in the context of obesity promotes accumulation of reactive metabolites such as the reactive alpha-dicarbonyl methylglyoxal (MG). MG accumulation has long been appreciated as a marker of disease progression in patients with T2D as well as the development of diabetic complications. However, recent evidence suggests that the accumulation of MG occurs with obesity prior to T2D onset and may be a primary driving factor for the development of IR and T2D. Further, emerging evidence also suggests that this accumulation of MG with obesity may be a result in a loss of MG detoxifying capacity of glyoxalase I. In this review, we will discuss the evidence that posits MG accumulation because of GLO1 attenuation is a novel target mechanism of the development of metabolic derangement. In addition, we will also explore the regulation of GLO1 and the strategies that have been investigated so far to target GLO1 regulation for the prevention and treatment of metabolic derangement.

Green Synthesis of Copper Oxide Nanoparticles Using Sesbania grandiflora Leaf Extract and Their Evaluation of Anti-Diabetic, Cytotoxic, Anti-Microbial, and Anti-Inflammatory Properties in an In-Vitro Approach

Green methods of synthesizing nanoparticles are safer than chemical and physical methods, as well as being eco-friendly and cost-efficient. In this study, we use copper oxide nanoparticles (CuO NPs) fabricated with Sesbania grandiflora (Sg) (Hummingbird tree) leaves to test the effectiveness of green synthesizing methods. The attained Sg-CuO NPs physical and optical nature is characterized by UV-Vis spectroscopy Differential Reflectance Spectroscopy (UV-Vis DRS), Fourier Transform Infra-Red spectroscopy (FTIR), X-ray Diffraction spectroscopy (XRD), Scanning Electron Microscope (SEM), and Energy Dispersive X-ray Analysis (EDAX). UV-Vis spectrum for Sg-CuO NPs revealed a peak at 410 nm. SEM images showed the aggregation of needle-shaped particles, at a size of 33 nm. The amylase and glucosidase enzymes were inhibited by the Sg-CuO NPs up to 76.7% and 72.1%, respectively, indicating a possible antihyperglycemic effect. Fabricated Sg-CuO NPs disclosed the excellent inhibition of DPPH-free radicle formation (89.7%) and repressed protein degradation (81.3%). The results showed that Sg-CuO NPs display good anti-bacterial activity against the gram-negative (Escherichia coli and Pseudomonas aeruginosa) and gram-positive (Staphylococcus aureus). Cytotoxicity of the Sg-CuO NPs was determined using anIC50 of 37 μg/mL. Sg-CuO NPs have shown promising anti-diabetic, anti-oxidant, protein degradation-inhibiting, and anti-microbial properties. Our findings have shown that synthesized Sg-CuO NPs have biological activities that may be utilized to treat bacterial infections linked to hyperglycemia.

Inhibition of dipeptidyl peptidase-4 (DPP4), antioxidant, antiglycation and anti-inflammatory effect of Ferulic acid against streptozotocin toxicity mediate nephropathy in diabetic rats

The protein glycation due to high blood glucose mediate release of inflammatory intermediate contributes in the development of diabetic nephropathy. Ferulic acid (FA) is a phenolic compound distributed in different foods as whole grains. Inhibitors of DPP4 improve GLP-1-mediated insulin secretion and inhibit liver gluconeogenesis. This study investigated the impact of FA as anti-inflammatory, antioxidant and antiglycation against streptozotocin-induced diabetic nephropathy in rats. This study was carried out on total ninety male rats allocated into six (each 15 rats); group I (control). All other animals (groups II-VI) were receiving 65 mg/kg STZ for induction of diabetes. Rats in group II (untreated diabetic). Rats in groups III-V were treated with FA (10, 20, 30 mg/kg bw) respectively, i.p. for 8 weeks. Group VI received 10 units insulin daily, sc. Fasting blood samples were subjected for assay of glycated hemoglobin (HA1c), serum MDA, aldose reductase, total antioxidant, DPP4 while kidney tissue subjected for assay of malondialdehyde (MDA), reduced glutathione (GSH), catalase (CAT), superoxide dismutase (SOD), tumor necrosis factor-α (TNF-α), IL-1β and AGEs. Data obtained showed that, FA showed antioxidant activity by reducing MDA and enhancement antioxidant activity compared with untreated rats (p < 0.001) with dose dependence. In addition, FA reduced the activities of aldose reductase, DPP4 (p < 0.001), decreased IL-6, TNF-α and AGEs versus untreated rats (p < 0.001). Histological investigation revealed an improvement in the nephron structure in diabetic rat treated with FA versus untreated group. It was concluded that, FA possesses a potent antioxidant and anti-inflammatory and DPP4 inhibitor. For that, it was considered as a protective agent against the risk of diabetic nephropathy and can be used as alternative or complementary supplement.

AGEomics Biomarkers and Machine Learning-Realizing the Potential of Protein Glycation in Clinical Diagnostics

Protein damage by glycation, oxidation and nitration is a continuous process in the physiological system caused by reactive metabolites associated with dicarbonyl stress, oxidative stress and nitrative stress, respectively. The term AGEomics is defined as multiplexed quantitation of spontaneous modification of proteins damage and other usually low-level modifications associated with a change of structure and function—for example, citrullination and transglutamination. The method of quantitation is stable isotopic dilution analysis liquid chromatography—tandem mass spectrometry (LC-MS/MS). This provides robust quantitation of normal and damaged or modified amino acids concurrently. AGEomics biomarkers have been used in diagnostic algorithms using machine learning methods. In this review, I describe the utility of AGEomics biomarkers and provide evidence why these are close to the phenotype of a condition or disease compared to other metabolites and metabolomic approaches and how to train and test algorithms for clinical diagnostic and screening applications with high accuracy, sensitivity and specificity using machine learning approaches.

The Role of Advanced Glycation End Products and Its Soluble Receptor in Kidney Diseases

Patients with chronic kidney disease (CKD) are more prone to oxidative stress and chronic inflammation, which may lead to an increase in the synthesis of advanced glycation end products (AGEs). Because AGEs are mostly removed by healthy kidneys, AGE accumulation is a result of both increased production and decreased kidney clearance. On the other hand, AGEs may potentially hasten decreasing kidney function in CKD patients, and are independently related to all-cause mortality. They are one of the non-traditional risk factors that play a significant role in the underlying processes that lead to excessive cardiovascular disease in CKD patients. When AGEs interact with their cell-bound receptor (RAGE), cell dysfunction is initiated by activating nuclear factor kappa-B (NF-κB), increasing the production and release of inflammatory cytokines. Alterations in the AGE-RAGE system have been related to the development of several chronic kidney diseases. Soluble RAGE (sRAGE) is a decoy receptor that suppresses membrane-bound RAGE activation and AGE-RAGE-related toxicity. sRAGE, and more specifically, the AGE/sRAGE ratio, may be promising tools for predicting the prognosis of kidney diseases. In the present review, we discuss the potential role of AGEs and sRAGE as biomarkers in different kidney pathologies.

Glucose Uptake by Skeletal Muscle within the Contexts of Type 2 Diabetes and Exercise: An Integrated Approach

Type 2 diabetes continues to negatively impact the health of millions. The inability to respond to insulin to clear blood glucose (insulin resistance) is a key pathogenic driver of the disease. Skeletal muscle is the primary tissue for maintaining glucose homeostasis through glucose uptake via insulin-dependent and -independent mechanisms. Skeletal muscle is also responsive to exercise-meditated glucose transport, and as such, exercise is a cornerstone for glucose management in people with type 2 diabetes. Skeletal muscle glucose uptake requires a concert of events. First, the glucose-rich blood must be transported to the skeletal muscle. Next, the glucose must traverse the endothelium, extracellular matrix, and skeletal muscle membrane. Lastly, intracellular metabolic processes must be activated to maintain the diffusion gradient to facilitate glucose transport into the cell. This review aims to examine the physiology at each of these steps in healthy individuals, analyze the dysregulation affecting these pathways associated with type 2 diabetes, and describe the mechanisms by which exercise acts to increase glucose uptake.

Potential of karamunting (Rhodomyrtus tomentosa) fraction against kidney damage in diabetic rats

Introduction: Karamunting (Rhodomyrtus tomentosa) is Indonesian native plant that contains high anti-oxidant compounds with the potential to suppress oxidative stress activity in cells. This study is the first research to specifically explore the role of the karamunting fraction in protecting kidney damage due to the formation of AGEs in the renal glomerulus in diabetes mellitus.

Objective: This study aims to assess the impact of karamunting on blood glucose profile, HbA1c, insulin profile and kidney condition (AGEs expression, TNF-α and kidney histology) in diabetic rats.

Methods: The karamunting extraction process was carried out by maceration with ethanol. Induction of diabetes mellitus was carried out using streptozotocin. Thirty male rats (Rattus norvegicus), Wistar strain weighing between 200–250 grams were the subject in this study. HbA1c, insulin, TNF-α, AGEs levels were evaluated in the kidney tissue. Histological assessment of the kidney was carried out.

Results: Karamunting can improve blood glucose levels in diabetic rats. This improvement in blood glucose levels causes an improvement in the level of HbA1c. Administration of karamunting fraction can prevent AGEs deposition in renal tissue, which in turn will inhibits the inflammation and prevents further damage of kidneys.

Conclusion: Karamunting fraction can improve blood glucose regulation so that it can prevent further damage and complications of kidney organs in diabetic rats.

Protein glycation - biomarkers of metabolic dysfunction and early-stage decline in health in the era of precision medicine

Protein glycation provides a biomarker in widespread clinical use, glycated hemoglobin HbA1c (A1C). It is a biomarker for diagnosis of diabetes and prediabetes and of medium-term glycemic control in patients with established diabetes. A1C is an early-stage glycation adduct of hemoglobin with glucose; a fructosamine derivative. Glucose is an amino group-directed glycating agent, modifying N-terminal and lysine sidechain amino groups. A similar fructosamine derivative of serum albumin, glycated albumin (GA), finds use as a biomarker of glycemic control, particularly where there is interference in use of A1C. Later stage adducts, advanced glycation endproducts (AGEs), are formed by the degradation of fructosamines and by the reaction of reactive dicarbonyl metabolites, such as methylglyoxal. Dicarbonyls are arginine-directed glycating agents forming mainly hydroimidazolone AGEs. Glucosepane and pentosidine, an intense fluorophore, are AGE covalent crosslinks. Cellular proteolysis of glycated proteins forms glycated amino acids, which are released into plasma and excreted in urine. Development of diagnostic algorithms by artificial intelligence machine learning is enhancing the applications of glycation biomarkers. Investigational glycation biomarkers are in development for: (i) healthy aging; (ii) risk prediction of vascular complications of diabetes; (iii) diagnosis of autism; and (iv) diagnosis and classification of early-stage arthritis. Protein glycation biomarkers are influenced by heritability, aging, decline in metabolic, vascular, renal and skeletal health, and other factors. They are applicable to populations of differing ethnicities, bridging the gap between genotype and phenotype. They are thereby likely to find continued and expanding clinical use, including in the current era of developing precision medicine, reporting on multiple pathogenic processes and supporting a precision medicine approach.

Biochemical Regulation of the Glyoxalase System in Response to Insulin Signaling

Methylglyoxal (MG) is a reactive glycation metabolite and potentially induces dicarbonyl stress. The production of MG in cells is increased along with an increase in carbohydrate metabolism. The efficiency of the glyoxalase system, consisting of glyoxalase 1 (GlxI) and glyoxalase 2 (GlxII), is crucial for turning the accumulated MG into nontoxic metabolites. Converting MG-glutathione hemithioacetal to S-d-lactoylglutathione by GlxI is the rate-determining step of the enzyme system. In this study, we found lactic acid accumulated during insulin stimulation in cells, however, cellular MG and S-d-lactoylglutathione also increased due to the massive flux of glycolytic intermediates. The insulin-induced accumulation of MG and S-d-lactoylglutathione were efficiently removed by the treatment of metformin, possibly via affecting the glyoxalase system. With the application of isotopic ¹³C₃-MG, the flux of MG from extracellular and intracellular origins was dissected. While insulin induced an influx of extracellular MG, metformin inhibited the trafficking of MG across the plasma membrane. Therefore, metformin could maintain the extracellular MG by means of reducing the secretion of MG rather than facilitating the scavenging. In addition, metformin may affect the glyoxalase system by controlling the cellular redox state through replenishing reduced glutathione. Overall, alternative biochemical regulation of the glyoxalase system mediated by insulin signaling or molecules like biguanides may control cellular MG homeostasis.

Uremic Toxins, Oxidative Stress, Atherosclerosis in Chronic Kidney Disease, and Kidney Transplantation

Patients with chronic kidney disease (CKD) are at a high risk for cardiovascular disease (CVD), and approximately half of all deaths among patients with CKD are a direct result of CVD. The premature cardiovascular disease extends from mild to moderate CKD stages, and the severity of CVD and the risk of death increase with a decline in kidney function. Successful kidney transplantation significantly decreases the risk of death relative to long-term dialysis treatment; nevertheless, the prevalence of CVD remains high and is responsible for approximately 20-35% of mortality in renal transplant recipients. The prevalence of traditional and nontraditional risk factors for CVD is higher in patients with CKD and transplant recipients compared with the general population; however, it can only partly explain the highly increased cardiovascular burden in CKD patients. Nontraditional risk factors, unique to CKD patients, include proteinuria, disturbed calcium, and phosphate metabolism, anemia, fluid overload, and accumulation of uremic toxins. This accumulation of uremic toxins is associated with systemic alterations including inflammation and oxidative stress which are considered crucial in CKD progression and CKD-related CVD. Kidney transplantation can mitigate the impact of some of these nontraditional factors, but they typically persist to some degree following transplantation. Taking into consideration the scarcity of data on uremic waste products, oxidative stress, and their relation to atherosclerosis in renal transplantation, in the review, we discussed the impact of uremic toxins on vascular dysfunction in CKD patients and kidney transplant recipients. Special attention was paid to the role of native and transplanted kidney function.

Reading patterns of proteome damage by glycation, oxidation and nitration: quantitation by stable isotopic dilution analysis LC-MS/MS

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) provides a high sensitivity, high specificity multiplexed method for concurrent detection of adducts formed by protein glycation, oxidation and nitration, also called AGEomics. Combined with stable isotopic dilution analysis, it provides for robust quantitation of protein glycation, oxidation and nitration adduct analytes. It is the reference method for such measurements. LC-MS/MS has been used to measure glycated, oxidized and nitrated amino acids - also called glycation, oxidation and nitration free adducts, with a concurrent quantitation of the amino acid metabolome in physiological fluids. Similar adduct residues in proteins may be quantitated with prior exhaustive enzymatic hydrolysis. It has also been applied to quantitation of other post-translation modifications, such as citrullination and formation of Nε-(γ-glutamyl)lysine crosslink by transglutaminases. Application to cellular and extracellular proteins gives estimates of the steady-state levels of protein modification by glycation, oxidation and nitration, and measurement of the accumulation of glycation, oxidation and nitration adducts in cell culture medium and urinary excretion gives an indication of flux of adduct formation. Measurement of glycation, oxidation and nitration free adducts in plasma and urine provides for estimates of renal clearance of free adducts. Diagnostic potential in clinical studies has been enhanced by the combination of estimates of multiple adducts in optimized diagnostic algorithms by machine learning. Recent applications have been in early-stage detection of metabolic, vascular and renal disease, and arthritis, metabolic control and risk of developing vascular complication in diabetes, and a blood test for autism.

Primary Dysmenorrhea in Relation to Oxidative Stress and Antioxidant Status: A Systematic Review of Case-Control Studies

Primary dysmenorrhea is defined as painful menstrual cramps of uterine origin in the absence of pelvic pathology and is the most common gynecological disorder among women of reproductive age. The aim of this study was to systematically review case-control studies that have investigated the oxidative stress, antioxidant status, and inflammation markers among women with primary dysmenorrhea and controls. The study protocol was registered with PROSPERO (no. CRD42020183104). By searching PubMed and Scopus databases as well as reference lists, six case-control studies with fifteen eligible markers (seven oxidative stress, seven antioxidant status, one inflammation) were included in this review. The quality of the included studies was assessed as medium or high. The systematic review included 175 women with primary dysmenorrhea and 161 controls. The results indicate an elevated level of oxidative stress, especially of lipid peroxidation among dysmenorrheal women. For the antioxidant status, limited evidence was found for a lower status among primary dysmenorrhea women, and only one study examined one inflammation marker (hs-CRP), which makes it impossible for such a conclusion. To establish whether oxidative stress, antioxidant status or inflammation participate in the pathophysiology of primary dysmenorrhea, high-quality studies with larger study groups and clear case definitions are needed.

Antiglycation Activities and Common Mechanisms Mediating Vasculoprotective Effect of Quercetin and Chrysin in Metabolic Syndrome

Multiple risk factors combine to increase the risk of vascular dysfunction in patients suffering from metabolic syndrome (MetS). The current study investigates the extent to which quercetin (Q) and chrysin (CH) protect against vascular dysfunction in MetS rats. MetS was induced by feeding rats a high-salt diet (3%) and fructose-enriched water (10%) for 12 weeks. Thoracic aorta was isolated from MetS rats and from control rats, with the latter being injured by methylglyoxal (MG). Aortae were incubated with CH and Q, and vascular reactivity was evaluated through the analysis of aortic contraction and relaxation in response to PE and ACh, respectively. The formation of advanced glycation end products (AGEs) and the free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH) were also evaluated following the introduction of CH and Q. The increased vasoconstriction and impaired vasodilation in MetS aortae were significantly ameliorated by Q and CH. Similarly, they ameliorated glycation-associated exaggerated vasoconstriction and impaired vasodilation produced by MG in control aortae. In addition, both Q and CH were effective in reducing the formation of AGEs and inhibition of glycosylation in response to MG or fructose treatment. Finally, Q successfully scavenged DPPH free radicals while CH showed significant vasodilation of precontracted aorta that was inhibited by L-NAME. In conclusion, Q and CH provide protection against vascular dysfunction in MetS by interfering with AGEs formations and AGEs-associated vascular deterioration, with CH being largely dependent on NO-mediated mechanisms of vasodilation.

Interference with AGEs formation and AGEs-induced vascular injury mediates curcumin vascular protection in metabolic syndrome

Vascular dysfunction predisposes to cardiovascular complications of metabolic syndrome (MetS). The current study investigated the mechanism(s) of curcumin's (CUR) protective effect against vascular reactivity irregularities in MetS. MetS was induced by feeding rats on high fructose high salt diet. Tension studies were undertaken in aortic rings to assess the influence of CUR on vasoconstrictor or vasorelaxant responses. The effect on advanced glycation endproducts (AGEs) was studied by incubating aortic tissues with methylglyoxal, the AGEs precursor, in the absence and presence of CUR. In addition, CUR effects on in-vitro generation of AGEs and diphenyl-2-picrylhydrazyl (DPPH) free radicals were studied. The incubation with CUR for 1 hr produced significant and concentration-dependent alleviation of the exaggerated vasoconstriction observed in aortas isolated from MetS, however failed to improve the concomitant attenuation of vasodilatory responses to ACh in PE-precontracted aortas. By contrast, CUR caused direct concentration-dependent vasodilations of precontracted aortas, effects that were blunted after nitric oxide synthase inhibition by L-NAME. Similar to its effects in MetS aortas, CUR alleviated exaggerated PE vasoconstriction but did not affect impaired ACh vasodilations in AGEs-exposed aortas. In addition, CUR showed significant dose-dependent DPPH free radicals scavenging activity and inhibited both MG and fructose induced AGEs formation at the level of protein oxidation step as evident from the effect on dityrosine and N-formylkyramine. CUR alleviates exaggerated vasoconstriction in MetS through interfering with AGEs formation and AGEs-induced vascular injury. Free radical scavenging and direct vasodilatory activities could also participate in the advantageous vascular actions of CUR.

Attenuation of diabetic kidney injury in DPP4-deficient rats; role of GLP-1 on the suppression of AGE formation by inducing glyoxalase 1

Dipeptidyl peptidase 4 (DPP4) inactivates incretin hormone glucagon-like peptide-1. DPP4 inhibitors may exert beneficial effects on diabetic nephropathy (DN) independently of glycemic control; however, the mechanisms underlying are not fully understood. Here, we investigated the mechanisms of the beneficial effects of DPP4 inhibition on DN using DPP4-deficient (DPP4-def) rats and rat mesangial cells.

Blood glucose and HbA1c significantly increased by streptozotocin (STZ) and no differences were between WT-STZ and DPP4-def-STZ. The albumin level in urine decreased significantly and the albumin/creatinine ratio decreased slightly in DPP4-def-STZ. The glomerular volume in DPP4-def-STZ significantly decreased compared with that of WT-STZ. Advanced glycation end products formation, receptor for AGE (RAGE) protein expression, and its downstream inflammatory cytokines and fibrotic factors in kidney tissue, were significantly suppressed in the DPP4-def-STZ compared to the WT-STZ with increasing glyoxalase-1 (GLO-1) expression responsible for the detoxification of methylglyoxal (MGO). In vitro, exendin-4 suppressed MGO-induced AGEs production by enhancing the expression of GLO-1 and nuclear factor-erythroid 2 p45 subunit-related factor 2, resulting in decreasing pro-inflammatory cytokine levels. This effect was abolished by GLO-1 siRNA.

Our data suggest that endogenously increased GLP-1 in DPP4-deficient rats contributes to the attenuation of DN partially by regulating AGEs formation via upregulation of GLO-1 expression.

Urinary Metabolomic Markers of Protein Glycation, Oxidation, and Nitration in Early-Stage Decline in Metabolic, Vascular, and Renal Health

Glycation, oxidation, nitration, and crosslinking of proteins are implicated in the pathogenic mechanisms of type 2 diabetes, cardiovascular disease, and chronic kidney disease. Related modified amino acids formed by proteolysis are excreted in urine. We quantified urinary levels of these metabolites and branched-chain amino acids (BCAAs) in healthy subjects and assessed changes in early-stage decline in metabolic, vascular, and renal health and explored their diagnostic utility for a noninvasive health screen. We recruited 200 human subjects with early-stage health decline and healthy controls. Urinary amino acid metabolites were determined by stable isotopic dilution analysis liquid chromatography-tandem mass spectrometry. Machine learning was applied to optimise and validate algorithms to discriminate between study groups for potential diagnostic utility. Urinary analyte changes were as follows: impaired metabolic health-increased N ε -carboxymethyl-lysine, glucosepane, glutamic semialdehyde, and pyrraline; impaired vascular health-increased glucosepane; and impaired renal health-increased BCAAs and decreased N ε -(γ-glutamyl)lysine. Algorithms combining subject age, BMI, and BCAAs discriminated between healthy controls and impaired metabolic, vascular, and renal health study groups with accuracy of 84%, 72%, and 90%, respectively. In 2-step analysis, algorithms combining subject age, BMI, and urinary N ε -fructosyl-lysine and valine discriminated between healthy controls and impaired health (any type), accuracy of 78%, and then between types of health impairment with accuracy of 69%-78% (cf. random selection 33%). From likelihood ratios, this provided small, moderate, and conclusive evidence of early-stage cardiovascular, metabolic, and renal disease with diagnostic odds ratios of 6 - 7, 26 - 28, and 34 - 79, respectively. We conclude that measurement of urinary glycated, oxidized, crosslinked, and branched-chain amino acids provides the basis for a noninvasive health screen for early-stage health decline in metabolic, vascular, and renal health.

An amperometric biosensor for specific detection of glycated hemoglobin based on recombinant engineered fructosyl peptide oxidase

Here, we present a specific biosensor based on the detection of glycated hemoglobin (HbA1c) proteolytic digestion product, fructosyl valyl histidine (Fru-ValHis). A recombinant engineered fructosyl peptide oxidase (FPOX) enzyme with improved specificity was immobilized on the electrode surface modified by chitosan (CHIT), graphene oxide (GO) and gold nanoparticles (AuNPs). The biosensor exhibited a linear response toward different concentrations of Fru-ValHis ranging from 0.1 to 2 mM with a sensitivity of 8.45 µA mM^-1 cm^-2. Detection limit of the current biosensor for Fru-ValHis was 0.3 µM as the lowest quantity required giving a signal to a background. Analytical recovery of added Fru-ValHis in whole blood was 95.1-98.35% for FPOX/AuNPs/GO/CHIT/FTO electrode. For Fru-ValHis determination by FPOX-AuNPs-GO-CHIT/FTO electrode, within-run coefficient of variation (CV) was between 1.3% and 2.4% and between run CV was between 2.1% and 3.5%. A significant change in electron transfer resistance after the incubation of FPOX-modified electrode with Fru-ValHis was observed, while no response was achieved with control, indicating specific measurement of Fru-ValHis. Moreover, designed biosensor measured HbA1c in human blood samples and the results were well agreed with that obtained with NORUDIA™ N HbA1c diagnostic kit. Overall, suitable specificity of the engineered FPOX made the bioelectrode responded well to the Fru-ValHis level, which demonstrates a promising application for specific detection of HbA1c biomarker.

Advanced glycation end products (AGEs) and their soluble receptors (sRAGE) as early predictors of reno-vascular complications in patients with uncontrolled type 2 diabetes mellitus

AIM

To evaluate the role of advanced glycation end-products (AGEs) and their soluble receptors (sRAGE) expression levels as predictors of vascular complications in uncontrolled type 2 diabetes mellitus (T2DM).

METHODS

Cross-sectional study was conducted on T2DM adults of both sexes who attended the outpatient service of Al-Karak Teaching Hospital, Jordan during the period from June 2017 to August 2018. Participants were categorized in two groups according to their glycemic control and the presence of reno-vascular complications. Twenty healthy subjects were recruited as control group. Blood sample was obtained from all participants and used for the assessment of FBG, HbA1c, serum AGEs and sRAGE, serum urea and creatinine; 24 h urine was also collected for the determination of urinary albumin.

RESULTS

Diabetic subjects with vascular complication had a significantly higher serum AGEs 50.3 ± 13 vs. 28.9 ± 8 pg/ml) and AGEs/sRAGE ratio (0.058 ± 0.02 vs. 0.037 ± 0.02) associated with significantly lower serum sRAGE (868.7 ± 50.8 vs. 912.8 ± 294.3) compared to those with no complications. Serum AGEs and sRAGE showed weak negative and non-significant association in both groups of patients. However, the AGEs/sRAGE ration was inversely and significantly associated with the urinary albumin/creatinine ratio (r = - 0.51, P = 0.009) only in DM patients with reno-vascular complications.

CONCLUSION

We found an association between AGEs/sRAGE ratio and urinary albumin/serum creatinine ratio in T2DM patients with reno-vascular complications; providing evidence that serum AGEs and sRAGE can be considered as predictors of vascular complications in uncontrolled T2DM patients.

Serum Levels of Protein-Bound Methylglyoxal-Derived Hydroimidazolone-1 are Independently Correlated with Asymmetric Dimethylarginine

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase, being involved in endothelial dysfunction. Furthermore, ADMA levels have been shown to predict future cardiovascular events in patients with coronary risk factors, such as diabetes and hypertension. We have previously found that glyceraldehyde-derived advanced glycation end products (glycer-AGEs) stimulate ADMA generation in vitro and the levels are associated with ADMA, endothelial dysfunction, and vascular inflammation in humans. However, it remains unclear what structurally distinct glycer-AGEs are independent correlates of ADMA. In this study, we addressed the issue. We measured serum levels of protein-bound and free methylglyoxal-derived hydroimidazolone-1 (MG-H1) and argpyrimidine, two major structurally identified glycer-AGEs by liquid chromatography-tandem mass spectrometry in 128 outpatients, and examined the correlations of these AGEs, vascular stiffness, and inflammation with ADMA. Moreover, we examined whether the changes in serum MG-H1 and argpyrimidine levels after 4-month treatment with oral hypoglycemic agents (OHAs) were associated with those of ADMA in other 44 patients with impaired glucose tolerance or type 2 diabetes. Multiple stepwise regression analysis revealed that protein-bound MG-H1, high-density lipoprotein cholesterol (inversely), high-sensitivity C-reactive protein, and cardio-ankle vascular index were independently correlated with ADMA (R² = 0.259). Treatment with OHAs significantly decreased ADMA levels in 44 glucose-intolerant or type 2 diabetic patients, and the changes in protein-bound MG-H1 levels were positively associated with those in ADMA values (p < 0.05). This study demonstrates that serum levels of protein-bound MG-H1 are independently correlated with ADMA and may be a therapeutic target for cardiovascular disease.

Experimental Hyperglycemia Alters Circulating Concentrations and Renal Clearance of Oxidative and Advanced Glycation End Products in Healthy Obese Humans

The purpose of this investigation was to evaluate the effects of experimental hyperglycemia on oxidative damage (OX), advanced glycation end products (AGEs), and the receptor for AGEs (RAGE) through an in vivo approach. Obese subjects (n = 10; 31.2 ± 1.2 kg·m⁻²; 56 ± 3 years) underwent 24 h of hyperglycemic clamp (+5.4 mM above basal), where plasma at basal and after 2 h and 24 h of hyperglycemic challenge were assayed for OX (methionine sulfoxide, MetSO, and aminoadipic acid, AAA) and AGE-free adducts (N^e-carboxymethyllysine, CML; N^e-carboxyethyllysine, CEL; glyoxal hydroimidazolone-1, GH-1; methylglyoxal hydroimidazolone-1, MG-H1; and 3-deoxyglucosone hydroimidazolone, 3DG-H) via liquid chromatography–tandem mass spectrometry (LC–MS/MS). Urine was also analyzed at basal and after 24 h for OX and AGE-free adducts and plasma soluble RAGE (sRAGE) isoforms (endogenous secretory RAGE, esRAGE, and cleaved RAGE, cRAGE), and inflammatory markers were determined via enzyme-linked immunosorbent assay (ELISA). Skeletal muscle tissue collected via biopsy was probed at basal, 2 h, and 24 h for RAGE and OST48 protein expression. Plasma MetSO, AAA, CEL, MG-H1, and G-H1 decreased (−18% to −47%; p < 0.05), while CML increased (72% at 24 h; p < 0.05) and 3DG-H remained unchanged (p > 0.05) with the hyperglycemic challenge. Renal clearance of MetSO, AAA, and G-H1 increased (599% to 1077%; p < 0.05), CML decreased (−30%; p < 0.05), and 3DG-H, CEL, and MG-H1 remained unchanged (p > 0.05). Fractional excretion of MetSO, AAA, CEL, G-H1, and MG-H1 increased (5.8% to 532%; p < 0.05) and CML and 3DG-H remained unchanged (p > 0.05). Muscle RAGE and OST48 expression, plasma sRAGE, IL-1β, IL-1Ra, and TNFα remained unchanged (p > 0.05), while IL-6 increased (159% vs. basal; p > 0.05). These findings suggest that individuals who are obese but otherwise healthy have the capacity to prevent accumulation of OX and AGEs during metabolic stress by increasing fractional excretion and renal clearance.

Divergent Changes in Plasma AGEs and sRAGE Isoforms Following an Overnight Fast in T1DM

Advanced glycation end products (AGEs) promote the development of diabetic complications through activation of their receptor (RAGE). Isoforms of soluble RAGE (sRAGE) sequester AGEs and protect against RAGE-mediated diabetic complications. We investigated the effect of an overnight fast on circulating metabolic substrates, hormones, AGEs, and sRAGE isoforms in 26 individuals with type 1 diabetes (T1DM). Blood was collected from 26 young (18–30 years) T1DM patients on insulin pumps before and after an overnight fast. Circulating AGEs were measured via LC-MS/MS and sRAGE isoforms were analyzed via ELISA. Glucose, insulin, glucagon, and eGFR_cystatin-c decreased while cortisol increased following the overnight fast (p < 0.05). AGEs (CML, CEL, 3DG-H, MG-H1, and G-H1) decreased (21–58%, p < 0.0001) while total sRAGE, cleaved RAGE (cRAGE), and endogenous secretory RAGE (esRAGE) increased (22–24%, p < 0.0001) following the overnight fast. The changes in sRAGE isoforms were inversely related to MG-H1 (rho = −0.493 to −0.589, p < 0.05) and the change in esRAGE was inversely related to the change in G-H1 (rho = −0.474, p < 0.05). Multiple regression analyses revealed a 1 pg/mL increase in total sRAGE, cRAGE, or esRAGE independently predicted a 0.42–0.52 nmol/L decrease in MG-H1. Short-term energy restriction via an overnight fast resulted in increased sRAGE isoforms and may be protective against AGE accumulation.

Influence of Piracetam on Gliclazide-Glycated Human Serum Albumin Interaction. A Spectrofluorometric Study

Advanced Glycation End-Products (AGEs) are created in the last step of protein glycation and can be a factor in aging and in the development or worsening of many degenerative diseases (diabetes, chronic kidney disease, atherosclerosis, Alzheimer’s disease, etc.). Albumin is the most susceptible to glycation plasma protein. Modified albumin by AGEs may be more resistant to enzymatic degradation, which further increases the local accumulation of AGEs in tissues. The aim of the present study was to analyze in vitro glycation of serum albumin in the presence of piracetam (PIR) and the gliclazide (GLZ)-glycated albumin interaction. The analysis of PIR as an inhibitor and GLZ interaction with nonglycated human albumin (HSA) and glycated by fructose human albumin (gHSA_FRC), in the absence and presence of piracetam (gHSA_FRC-PIR), was performed by fluorescence quenching of macromolecules. On the basis of obtained data we concluded that under the influence of glycation, association constant (Ka) of gliclazide to human serum albumin decreases and GLZ binds to HSA with less strength than under physiological conditions. PIR strongly inhibited the formation of AGEs in the system where the efficiency of HSA glycation was the largest. The analysis of piracetam influence on the GLZ-glycated albumin interaction has shown that piracetam increases the binding strength of GLZ to glycated albumin and weakens its therapeutic effect. Based on the obtained data we concluded that monitoring therapy and precautions are required in the treatment when the combinations of gliclazide and piracetam are used at the same time.

Methylglyoxal and insulin resistance in berberine-treated type 2 diabetic patients

Background:

Diabetes mellitus is a chronic metabolic disorder of hyperglycemia. Chronic hyperglycemia produces advanced glycation end products such as the methylglyoxal (MGO) which interferes with cell functions, insulin signaling, and β-cell functions. The present study was conducted to determine the effects of berberine (BBR) therapy on serum MGO and insulin resistance in newly diagnosed type 2 diabetic patients.

Materials and Methods:

The present case–control study was conducted at the Department of Medicine, Liaquat University of Medical and Health Sciences, Jamshoro/Hyderabad, from March 2016 to January 2017. A sample of 200 newly diagnosed type 2 diabetic patients was divided into two groups. Group 1 received metformin 500 mg (×3 daily) and Group 2 received BBR 500 mg (×3 daily) for 3 months. Blood samples were collected at baseline and after 3 months to analyze biochemical parameters on Roche biochemical analyzer. MGO was assayed by ELISA kit and homeostasis model assessment of insulin resistance (HOMA-IR) model. SPSS version 23.0 (IBM, Incorporation, USA) analyzed the data at 95% confidence interval (P ≤ 0.05).

Results:

Baseline HOMA-IR (% IR) and MGO were found elevated in metformin and BBR groups. After 3 months of metformin and BBR therapy, the HOMA-IR (% IR) and MGO were decreased to 3.69 ± 1.13 and 2.64 ± 0.76 and 35.84 ± 12.56 and 26.64 ± 10.73 ng/dl, respectively (P = 0.0001). HOMA-IR (% IR) was improved by 40% and 73% (P = 0.0001) and MGO by 43% and 56% in metformin and BBR groups, respectively (P = 0.0001).

Conclusion:

BBR is more effective in decreasing the serum MGO levels and insulin resistance through improved glycemic control in newly diagnosed type 2 diabetic patients.

Gold Nanoparticle-Based Detection of Low Molecular Weight AGEs from In Vitro Glycated Haemoglobin A0 Samples

Protein glycation is a major biochemical event that takes place in the plasma of diabetic patients due to increased sugar levels. Extensive glycation leads to the formation of advanced glycation end products (AGEs) that is well known for having detrimental effects on diabetic patients. In the current work, we have glycated the physiologically important protein Haemoglobin A0 in vitro to study AGE formation and activity by using them as a template for gold nanoparticle (GNPs) synthesis. It was found that the surface plasmon resonance of synthesised GNPs showed high correlation with the extent of glycation. On fractionation, the glycated Haemoglobin A0 segregated into two distinct population of products, one consisting of proteinaceous, cross-linked larger fragments of Haemoglobin A0 and a second population of non-proteinaceous low molecular weight AGEs. Only low molecular weight AGEs contributed to synthesis of GNPs upon using the fractions as a template, substantiating the principle of proposed GNP-based assay. Owing to its physiological importance, AGEs can be used as a diagnostic means for diabetes and its associated complications. In this study, we have employed the high reactivity of AGEs for the development of a GNP-based novel colorimetric sensor to enable their detection. Our proposed GNP-based sensing could have high clinical significance in detecting diabetes and its associated complexities.

Dicarbonyl Stress and Glyoxalase-1 in Skeletal Muscle: Implications for Insulin Resistance and Type 2 Diabetes

Glyoxalase-1 (GLO1) is a ubiquitously expressed cytosolic protein which plays a role in the natural maintenance of cellular health and is abundantly expressed in human skeletal muscle. A consequence of reduced GLO1 protein expression is cellular dicarbonyl stress, which is elevated in obesity, insulin resistance and type 2 diabetes (T2DM). Both in vitro and pre-clinical models suggest dicarbonyl stress per se induces insulin resistance and is prevented by GLO1 overexpression, implicating a potential role for GLO1 therapy in insulin resistance and type 2 diabetes (T2DM). Recent work has identified the therapeutic potential of novel natural agents as a GLO1 inducer, which resulted in improved whole-body metabolism in obese adults. Given skeletal muscle is a major contributor to whole-body glucose, lipid, and protein metabolism, such GLO1 inducers may act, in part, through mechanisms in skeletal muscle. Currently, investigations examining the specificity of dicarbonyl stress and GLO1 biology in human skeletal muscle are lacking. Recent work from our lab indicates that dysregulation of GLO1 in skeletal muscle may underlie human insulin resistance and that exercise training may impart therapeutic benefits. This minireview will summarize the existing human literature examining skeletal muscle GLO1 and highlight the emerging therapeutic concepts for GLO1 gain-of-function in conditions such as insulin resistance and cardiometabolic disease.

Elevated Levels of the Reactive Metabolite Methylglyoxal Recapitulate Progression of Type 2 Diabetes

The molecular causes of type 2 diabetes (T2D) are not well understood. Both type 1 diabetes (T1D) and T2D are characterized by impaired insulin signaling and hyperglycemia. From analogy to T1D, insulin resistance and hyperglycemia are thought to also play causal roles in T2D. Recent clinical studies, however, found that T2D patients treated to maintain glycemia below the diabetes definition threshold (HbA_1c < 6.5%) still develop diabetic complications. This suggests additional insulin- and glucose-independent mechanisms could be involved in T2D progression and/or initiation. T2D patients have elevated levels of the metabolite methylglyoxal (MG). We show here, using Drosophila glyoxalase 1 knockouts, that animals with elevated methylglyoxal recapitulate several core aspects of T2D: insulin resistance, obesity, and hyperglycemia. Thus elevated MG could constitute one root cause of T2D, suggesting that the molecular causes of elevated MG warrant further study.

Advanced Glycation End Products, Oxidation Products, and Incident Cardiovascular Events in Patients With Type 2 Diabetes

OBJECTIVE

The goal of this study was to determine whether plasma levels of advanced glycation end products (AGE) and oxidation products (OP) predict the incidence of cardiovascular disease (CVD) in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Five specific AGE (methylglyoxal hydroimidazolone, carboxymethyl lysine, carboxyethyl lysine, 3-deoxyglucosone hydroimidazolone, and glyoxal hydroimidazolone) and two OP (2-aminoadipic acid and methionine sulfoxide [MetSO]) were measured at baseline in two intensive glucose-lowering studies: 1) a subcohort of the Veterans Affairs Diabetes Trial (VADT) (n = 445) and 2) a nested case-control subgroup from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) study (n = 271).

RESULTS

Increased levels of several AGE and OP were associated with older age, decreased kidney function, previous CVD, and longer diabetes duration, but not with hemoglobin A_1c. In the VADT, increased risk of incident CVD events (n = 107) was associated with lower MetSO after adjusting for age, race/ethnicity, sex, prior CVD event, kidney function, treatment assignment, and diabetes duration (hazard ratio [HR] 0.53; 95% CI 0.28-0.99; P = 0.047). Individuals with both low MetSO and high 3-deoxyglucosone hydroimidazolone concentrations were at highest risk for CVD (HR 1.70; P = 0.01). In the ACCORD study, those with incident CVD events (n = 136) had lower MetSO (by 14%; P = 0.007) and higher glyoxal hydroimidazolone and carboxymethyl lysine (by 18% and 15%, respectively; P = 0.04 for both); however, only the difference in MetSO remained significant after adjustment for prior CVD event (P = 0.002).

CONCLUSIONS

Lower levels of MetSO and higher levels of select AGE are associated with increased incident CVD and may help account for the limited benefit of intensive glucose lowering in type 2 diabetes.

The "Metabolic Memory" Theory and the Early Treatment of Hyperglycemia in Prevention of Diabetic Complications

Several epidemiological and prospective studies suggest that an early intensive control of hyperglycaemia is able to decrease the risk of diabetic micro- and macro-vascular complications. A growing body of experimental evidence supports the concept that the risk for diabetes complications may be linked to oxidative stress, non-enzymatic glycation of proteins, epigenetic changes, and chronic inflammation, laying the foundation for the “metabolic memory” theory. From a clinical point of view, this theory supports the need for a very early aggressive treatment, with the goal of normalizing metabolic control as soon as possible. It may also prove beneficial to introduce therapeutic agents that are able to reduce reactive species and glycation, in addition to presenting better control of glucose levels in patients with diabetes, in order to minimize long-term diabetes complications. In this review, we evaluate the effect of glucose intake and metabolism in the light of this theory.

Prevention of advanced glycation end-products formation in diabetic rats through beta-cell modulation by Aegle marmelos

Background

Although the anti-diabetic activity of Aegle marmelos (AM) is known, however, its anti-glycation activity is not reported yet. In this study, we have investigated its anti-glycation activity under in vitro and in vivo conditions and determined possible mechanism(s) in streptozotocin-induced diabetic rats.

Methods

Effective dose of AM (400 mg/kg) was administrated orally to diabetic rats for 42 days. Thereafter, blood glucose, serum insulin, HbA1c, antioxidant status, and advanced glycation end-products (AGEs) were measured. AGEs and its receptor (RAGE) in kidney were analyzed by immunohistochemistry and immunoblotting. Additionally, pancreatic sections were co-stained for insulin and glucagon and images were acquired using NIKON TE2000E fluorescence microscopy.

Results

Oral administration of AM extract resulted in a significant increase in serum insulin by better functioning of β-cell and preserving pancreatic β-cell integrity in diabetic rats. Treatment of AM extract significantly (p = 0.000) prevented the formation of HbA1c in the diabetic rats (8.20 ± 0.18% vs. 11.92 ± 0.59%). The circulatory AGEs level found in diabetic rat was significantly (p = 0.002) attenuated by AM treatment (0.66 ± 0.05 mg/ml vs. 1.18 ± 0.19 mg/ml). AM treatment also reduced AGEs accumulation around Bowman’s capsule and in tubular basement membrane around arteries in diabetic rat kidney. The accumulation of RAGE was very similar to that of AGEs in diabetic rats and RAGE accumulation was also prevented by AM treatment. The extract showed potent antioxidant activity both under in vitro and in vivo systems. Eugenol, one of the active constituent of AM fruit extract, showed acute blood glucose-lowering activity in diabetic rats and enhanced glucose-stimulated insulin secretion from mice islets.

Conclusion

AM extract prevents AGEs formation by modulating β-cell function, and eugenol may play important role in preventing complications of diabetes in this rat model.

Osmotic stress is accompanied by protein glycation in Arabidopsis thaliana

Among the environmental alterations accompanying oncoming climate changes, drought is the most important factor influencing crop plant productivity. In plants, water deficit ultimately results in the development of oxidative stress and accumulation of osmolytes (e.g. amino acids and carbohydrates) in all tissues. Up-regulation of sugar biosynthesis in parallel to the increasing overproduction of reactive oxygen species (ROS) might enhance protein glycation, i.e. interaction of carbonyl compounds, reducing sugars and α-dicarbonyls with lysyl and arginyl side-chains yielding early (Amadori and Heyns compounds) and advanced glycation end-products (AGEs). Although the constitutive plant protein glycation patterns were characterized recently, the effects of environmental stress on AGE formation are unknown so far. To fill this gap, we present here a comprehensive in-depth study of the changes in Arabidopsis thaliana advanced glycated proteome related to osmotic stress. A 3 d application of osmotic stress revealed 31 stress-specifically and 12 differentially AGE-modified proteins, representing altogether 56 advanced glycation sites. Based on proteomic and metabolomic results, in combination with biochemical, enzymatic and gene expression analysis, we propose monosaccharide autoxidation as the main stress-related glycation mechanism, and glyoxal as the major glycation agent in plants subjected to drought.

Advanced Glycation End Products Predict Loss of Renal Function and Correlate With Lesions of Diabetic Kidney Disease in American Indians With Type 2 Diabetes

We examined associations of advanced glycation end products (AGEs) with renal function loss (RFL) and its structural determinants in American Indians with type 2 diabetes. Data were from a 6-year clinical trial that assessed renoprotective efficacy of losartan. Participants remained under observation after the trial concluded. Glomerular filtration rate (GFR) was measured annually. Kidney biopsies were performed at the end of the trial. Five AGEs were measured in serum collected at enrollment and at kidney biopsy. RFL was defined as ≥40% decline of measured GFR from baseline. Of 168 participants (mean baseline age 41 years, HbA_1c 9.2%, GFR 164 mL/min, and albumin-to-creatinine ratio 31 mg/g), 104 reached the RFL end point during median follow-up of 8.0 years. After multivariable adjustment, each doubling of carboxyethyl lysine (hazard ratio [HR] 1.60 [95% CI 1.08-2.37]) or methylglyoxal hydroimidazolone (HR 1.30 [95% CI 1.02-1.65]) concentration was associated with RFL. Carboxyethyl lysine, carboxymethyl lysine, and methylglyoxal hydroimidazolone correlated positively with cortical interstitial fractional volume (partial r = 0.23, P = 0.03; partial r = 0.25, P = 0.02; and partial r = 0.31, P = 0.003, respectively). Glyoxyl hydroimidazolone and methylglyoxal hydroimidazolone correlated negatively with total filtration surface per glomerulus (partial r = -0.26, P = 0.01; and partial r = -0.21, P = 0.046, respectively). AGEs improve prediction of RFL and its major structural correlates.

A Snapshot of the Plant Glycated Proteome: STRUCTURAL, FUNCTIONAL, AND MECHANISTIC ASPECTS

Glycation is the reaction of carbonyl compounds (reducing sugars and α-dicarbonyls) with amino acids, lipids, and proteins, yielding early and advanced glycation end products (AGEs). The AGEs can be formed via degradation of early glycation intermediates (glycoxidation) and by interaction with the products of monosaccharide autoxidation (autoxidative glycosylation). Although formation of these potentially deleterious compounds is well characterized in animal systems and thermally treated foods, only a little information about advanced glycation in plants is available. Thus, the knowledge of the plant AGE patterns and the underlying pathways of their formation are completely missing. To fill this gap, we describe the AGE-modified proteome ofBrassica napusand characterize individual sites of advanced glycation by the methods of liquid chromatography-based bottom-up proteomics. The modification patterns were complex but reproducible: 789 AGE-modified peptides in 772 proteins were detected in two independent experiments. In contrast, only 168 polypeptides contained early glycated lysines, which did not resemble the sites of advanced glycation. Similar observations were made withArabidopsis thaliana The absence of the early glycated precursors of the AGE-modified protein residues indicated autoxidative glycosylation, but not glycoxidation, as the major pathway of AGE formation. To prove this assumption and to identify the potential modifying agents, we estimated the reactivity and glycative potential of plant-derived sugars using a model peptide approach and liquid chromatography-mass spectrometry-based techniques. Evaluation of these data sets together with the assessed tissue carbohydrate contents revealed dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, ribulose, erythrose, and sucrose as potential precursors of plant AGEs.

Esculin improves dyslipidemia, inflammation and renal damage in streptozotocin-induced diabetic rats

Background

Increasing studies have shown that dyslipidemia and inflammatory responses play important roles in the progression of microvascular diabetic complications. Esculin (ES), a coumarin derivative, was extracted from Fraxinus rhynchophylla. The present study was to evaluate the potential effects of ES on lipid metabolism, inflammation responses and renal damage in streptozotocin (STZ)-induced experimental diabetic rats and explore the possible mechanism.

Methods

Diabetic rat model was established by administration high-glucose-fat diet and intraperitoneal injection of STZ 45 mg/kg. ES was administrated to diabetic rats intragastrically at 10, 30 and 90 mg/kg for 10 weeks respectively. The levels of triglycerides (TG), total cholesterol (T-CHO), low density lipoproteins (LDL), and high-density-cholesterol (HDL-C) in serum were measured. IL-1, IL-6, ICAM-1, NO, NAGL, and AGEs level in serum were detected by ELISA assay. The accumulation of AGEs in kidney tissue was examined by immunohistochemistry assay.

Results

The results showed that ES could decrease TG, T-CHO, LDL levels in serum of diabetic rats in a dose dependent manner. ES also decreased IL-1, IL-6, ICAM-1, NO and NGAL levels in serum of diabetic rats in a dose dependent manner. Furthermore, ES at 30 and 90 mg/kg significantly decreased AGEs level in serum and alleviated AGEs accumulation in renal in diabetic rats.

Conclusions

Our findings indicate that ES could improve dyslipidemia, inflammation responses, renal damage in STZ-induced diabetic rats and the possible mechanism might be associated with the inhibition of AGEs formation.

Methylglyoxal-derived hydroimidazolone residue of plasma protein can behave as a predictor of prediabetes in Spontaneously Diabetic Torii rats

Prediabetes, typically defined as impaired glucose tolerance and/or impaired fasting blood glucose, is a high-risk state of developing diabetes. The association of diabetes-related metabolites with prediabetes has not been investigated intensively. This study aimed to get insights into the metabolic behaviors of some typical diabetes-related metabolites in plasma of male Spontaneously Diabetic Torii (SDT) rats during pathogenic progress of diabetes and to assess in vivo if the variation in these metabolites related to the progression of prediabetic stage. To address this question, SDT rats and Sprague Dawley (SD) rats as control were maintained from the age of 7 to 25 weeks. Five typical advanced glycation end products (AGEs) residue of plasma protein and their free adducts were determined by liquid chromatography with tandem mass detection over the duration of the investigation. The SDT rats exhibited impaired glucose tolerance since the age of 12 weeks and developed diabetes with significantly elevated fasting glucose levels after 22 weeks. At the prediabetic stage (12–21 weeks), no significant differences were observed on AGE-free adducts levels of SDT rats compared with SD rats. However, methylglyoxal-derived hydroimidazolone (MG-H1) residue contents of plasma protein were significantly elevated in SDT rats at the age of 16 weeks, whereas other AGE residues of plasma protein did not show marked difference. The present study has revealed significant increase in MG-H1 residue content of plasma protein at the prediabetic stage of a spontaneously diabetic rat model, irrespective of unaltered fasting blood glucose and constant plasma levels of other AGEs.

Methylglyoxal in diabetes: link to treatment, glycaemic control and biomarkers of complications

Diabetic complications are major health problems worldwide, with the cost of caring for diabetes rising to US$245 billion in 2012 in the U.S.A. alone. It is widely recognized that non-enzymatic glycation in diabetes is a major cause of damage and dysfunction of key vascular cells. MG (methylglyoxal) is directly toxic to tissues, and is a major precursor of AGEs (advanced glycation end-products). Various propensities to diabetic complications are seen among individuals with diabetes, with accelerated rates occurring in some individuals with modest hyperglycaemia, while others never progress in spite of poor glycaemic control over many years. Since production and detoxification of MG is ultimately controlled by enzymatic mechanisms, both genetic and environmental factors could regulate tissue glycation and potentially account for these variable complication rates. Activation of pathways that determine MG levels occurs in susceptible patients, indicting an important role in pathogenesis. MG leads to formation of specific AGEs, which are likely to predict propensity to diabetic complications. We have shown recently that three specific plasma AGE biomarkers [MG-H1 (MG-derived hydroimidazolones), CEL (Nε-carboxyethyl-lysine) and CML (Nε-carboxymethyl-lysine)] predict biopsy-documented fast DN (diabetic nephropathy) progression. Since two of the predictive biomarkers are MG end-products, these outcomes support a role for MG in the development of DN. Our studies on MG and its end-products have also shown anti-complication effects of the drug metformin, which binds and inactivates MG, thus reducing MG-related AGEs. We have also shown that reducing post-meal glucose decreases MG levels, as well as levels of MG-related AGEs. Our clinical outcome studies have been based on the novel concept that the unique glycation products that we can measure reflect the activity of specific chemical pathways that are selectively activated by hyperglycaemia in patients that are inherently more susceptible to diabetic complications, and can be used to solve other diabetes-related medical questions.

Association between Advanced Glycation End Products and Impaired Fasting Glucose: Results from the SALIA Study

Advanced glycation end products (AGEs) may contribute to the development of type 2 diabetes and related complications, whereas their role in the early deterioration of glycaemia is unknown. While previous studies used antibody-based methods to quantify AGEs, data from tandem mass spectrometry coupled liquid chromatography (LC-MS/MS)-based measurements are limited to patients with known diabetes. Here, we used the LC-MS/MS method to test the hypothesis that plasma AGE levels are higher in individuals with impaired fasting glucose (IFG) than in those with normal fasting glucose (NFG). Secondary aims were to assess correlations of plasma AGEs with quantitative markers of glucose metabolism and biomarkers of subclinical inflammation. This study included on 60 women with NFG or IFG (n = 30 each, mean age 74 years) from the German SALIA cohort. Plasma levels of free metabolites (3-deoxyfructose, 3-deoxypentosone, 3-deoxypentulose), two hydroimidazolones, oxidised adducts (carboxymethyllysine, carboxyethyllysine, methionine sulfoxide) and Nε-fructosyllysine were measured using LC-MS/MS. Plasma concentrations of all tested AGEs did not differ between the NFG and IFG groups (all p>0.05). Associations between plasma levels of AGEs and fasting glucose, insulin and HOMA-IR as a measure of insulin resistance were weak (r between -0.2 and 0.2, all p>0.05). The association between 3-deoxyglucosone-derived hydroimidazolone with several proinflammatory biomarkers disappeared upon adjustment for multiple testing. In conclusion, plasma AGEs assessed by LC-MS/MS were neither increased in IFG nor associated with parameters of glucose metabolism and subclinical inflammation in our study. Thus, these data argue against strong effects of AGEs in the early stages of deterioration of glucose metabolism.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

Chronic kidney disease influences multiple systems: describing the relationship between oxidative stress, inflammation, kidney damage, and concomitant disease

Chronic kidney disease (CKD) is characterized by increased levels of oxidative stress and inflammation. Oxidative stress and inflammation promote renal injury via damage to molecular components of the kidney. Unfortunately, relationships between inflammation and oxidative stress are cyclical in that the inflammatory processes that exist to repair radical-mediated damage may be a source of additional free radicals, resulting in further damage to renal tissue. Oxidative stress and inflammation also have the ability to become systemic, serving to injure tissues distal to the site of original insult. This review describes select mediators in the exacerbatory relationship between oxidative stress, inflammation, and CKD. This review also discusses oxidative stress, inflammation, and CKD as they pertain to the development and progression of common CKD-associated comorbidities. Lastly, the utility of several widely accessible and cost-effective lifestyle interventions and their ability to reduce oxidative stress and inflammation are discussed and recommendations for future research are provided.

Systemic uptake, albumin and hemoglobin binding of [(14)C]2,3-butanedione administered by intratracheal instillation in male Harlan Sprague Dawley rats and oropharyngeal aspiration in male B6C3F1/N mice

2,3-Butanedione (BD) is a reactive diketone in artificial butter flavors that is thought to cause bronchiolitis obliterans in workers in microwave popcorn manufacturing. Bronchiolitis obliterans is generally not diagnosed until irreversible damage has occurred; therefore a biomarker of early exposure is needed. The potential systemic uptake of BD from inhalation exposure has not been evaluated. The objective here was to evaluate the systemic exposure of BD and binding to hemoglobin and albumin. [(14)C]BD was administered to male Harlan Sprague Dawley rats (100 mg/kg, intratracheal instillation) and B6C3F1/N mice (157 mg/kg, oropharyngeal aspiration). Blood and plasma was collected 24 h after administration and analyzed for (14)C content. At 24h, 0.88±0.07% of the administered dose was in rat blood, 0.66±0.06% in rat plasma, 0.38±0.13% in mouse blood and 0.17±0.05% in mouse plasma. Albumin binding in rats was 269±24.2 ng equiv./mg, which accounts for 38% of the radioactivity in plasma. In mice, binding was 85.0±22.3 ng equiv./mg albumin, which accounts for 51% of the radioactivity in plasma. The binding to hemoglobin in rats was 38.2±17.6 ng equiv./mg, and to globin was 29.1±3.96 ng equiv./mg. In mice, the binding to hemoglobin was 16.2±9.0 ng equiv./mg. The site(s) of adduction on hemoglobin and albumin was investigated by mass spectrometry. In rat globin, arginine adducts were detected at R-30 and R-104 of the beta chain in vitro and in vivo. In rat albumin, adducts were detected in vitro on R-219/221, R-360, and R-368, and in vivo on a variety of arginine residues. This study demonstrated that BD enters the systemic circulation and reacts with arginine on hemoglobin and albumin. These results indicate that hemoglobin and albumin adducts may be useful as biomarkers of BD exposure in humans.

Consumption of Mesona chinensis attenuates postprandial glucose and improves antioxidant status induced by a high carbohydrate meal in overweight subjects

Edible plants constitute a potential source for controlling postprandial hyperglycemia and oxidative stress. The objective of this study was to investigate in vitro antioxidant and intestinal α-glucosidase inhibitory activities of Mesona chinensis (MC). In addition, the acute effect of MC on postprandial glucose and plasma antioxidant status after the consumption of a high carbohydrate (HC) meal by overweight subjects was also determined. The results showed that total phenolic and flavonoid contents in the extract were 212.37 ± 5.64 mg gallic acid equivalents/g dried extract and 23.44 ± 2.50 mg catechin equivalents/g dried extract, respectively. MC extract markedly inhibited the intestinal maltase and sucrose with the IC50 values of 4.66 ± 0.22 mg/mL and 1.30 ± 0.43 mg/mL, respectively. However, MC extract had no inhibitory activity against pancreatic α-amylase. In addition, MC extract had antioxidant properties including DPPH radical scavenging activity, superoxide radical scavenging activity (SRSA), hydroxyl radical scavenging activity (HRSA), trolox equivalent antioxidant capacity (TEAC), ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), and ferrous ion cheating activity (FICP). The significant decrease in postprandial plasma glucose, triglyceride and malondialdehyde levels, and the increase in plasma antioxidant capacity (FRAP and ORAC) were observed in overweight subjects receiving a HC meal together with MC extract (1 g). The finding supports that MC helps normalize and enhance antioxidant defense induced by a HC meal, suggesting that MC may have the potential for the prevention of chronic conditions and diseases associated with overweight and obesity.