Formation Of Advanced Glycosylation End Products Research Articles

Exploring the Associated Genetic Causes of Diabetic Retinopathy as a Model of Inflammation in Retinal Diseases.

To investigate potential biomarkers and biological processes associated with diabetic retinopathy (DR) using transcriptomic and proteomic data. The OmicsPred PheWAS application was interrogated to identify genes and proteins associated with DR and diabetes mellitus (DM) at a false discovery rate (FDR)-adjusted p-value of <0.05 and also <0.005. Gene Ontology PANTHER analysis and STRING database analysis were conducted to explore the biological processes and protein interactions related to the identified biomarkers. The interrogation identified 49 genes and 22 proteins associated with DR and/or DM; these were divided into those uniquely associated with diabetic retinopathy, uniquely associated with diabetes mellitus, and the ones seen in both conditions. The Gene Ontology PANTHER and STRING database analyses highlighted associations of several genes and proteins associated with diabetic retinopathy with adaptive immune response, valyl-TRNA aminoacylation, complement activation, and immune system processes. Our analyses highlight potential transcriptomic and proteomic biomarkers for DR and emphasize the association of known aspects of immune response, the complement system, advanced glycosylation end-product formation, and specific receptor and mitochondrial function with DR pathophysiology. These findings may suggest pathways for future research into novel diagnostic and therapeutic strategies for DR.

Evaluation of human skin response to solar-simulated radiation in an ex vivo model: Effects and photoprotection of L-Carnosine.

Sunlight, and more specifically the UV component, induces several skin damages, including sunburns, erythema and photoaging. The purpose of this work is to set up an ex vivo human skin model to assess the capacity of active principles in protecting skin from the deleterious effects of solar radiation. Ex vivo human skin biopsies were cultured in an air-liquid interface and exposed to solar-simulated radiation (SSR, 300-750 nm). L-Carnosine (0.2% and 2%) was applied topically to be tested as photoprotective compound. The effect on oxidative stress induction, photoaging and skin transcriptional profile was assessed by evaluating reactive oxygen species, advanced glycosylation end products formation and gene expression changes. In our model, SSR increases ROS production and AGE accumulation and affects the expression of genes related to oxidative stress, pigmentation, immunity, inflammation and photoaging. Among these pathways, 11 genes were selected as biomarkers to evaluate the skin solar radiation response. Results showed that L-Carnosine provides effective prevention against solar radiation damages reducing ROS, AGEs and mitigating the modulation of the selected biomarker genes. In conclusion, we report that our ex vivo skin model is a valuable system to assess the consequences of solar light exposure and the capacity of topically applied L-Carnosine to counteract them.

Diabetic neuropathy: Past, present, and future.

A sedentary lifestyle and an unhealthy diet have considerably increased the incidence of diabetes mellitus worldwide in recent decades, which has generated a high rate of associated chronic complications. A narrative review was performed in MEDLINE, EMBASES and SciELO databases, including 162 articles. Diabetic neuropathy (DN) is the most common of these complications, mainly producing two types of involvement: sensorimotor neuropathy, whose most common form is symmetric distal polyneuropathy, and autonomic neuropathies, affecting the cardiovascular, gastrointestinal, and urogenital system. Although hyperglycemia is the main metabolic alteration involved in its genesis, the presents of obesity, dyslipidemia, arterial hypertension, and smoking, play an additional role in its appearance. In the pathophysiology, three main phenomena stand out: oxidative stress, the formation of advanced glycosylation end-products, and microvasculature damage. Diagnosis is clinical, and it is recommended to use a 10 g monofilament and a 128 Hz tuning fork as screening tools. Glycemic control and non-pharmacological interventions constitute the mainstay of DN treatment, although there are currently investigations in antioxidant therapies, in addition to pain management. Diabetes mellitus causes damage to peripheral nerves, being the most common form of this, distal symmetric polyneuropathy. Control of glycemia and comorbidities contribute to prevent, postpone, and reduce its severity. Pharmacological interventions are intended to relieve pain.

Novel cross-link breaker based on zwitterion structure: Synthesis, structure and druggability studies

It has been universally acknowledged that the increase in cardiac and vascular stiffness is due to the formation of advanced glycosylation end-products (AGEs). Research on the stable form of 3-(carboxymethyl)-4-methylthiazol bromide sodium salt (C6H7BrNNaO2S) showed that it had a notable effect on breaking the AGEs. Two compounds with novel structures, zwitterionic 3-(carboxymethyl)-4-methylthiazol (C6H7O2NS) and a dipolymer (C12H15O4N2S2Br) complex, were obtained. When compared with the forms of sodium salt and dipolymer, zwitterion had an obvious advantage in stability, solubility, synthesis and pH, which made the zwitterion a promising drug. The structure of sodium salt, dipolymer and zwitterion was comparatively analyzed by such methods as single crystal X-ray diffraction, ESI-MS, 1H NMR, FT-IR and in situ IR.

Contemporary Insights into Painful Diabetic Neuropathy and Treatment with Spinal Cord Stimulation

A substantial body of literature is available on the natural history of diabetes, but much less is understood of the natural history of painful diabetic peripheral neuropathy (PDPN), a pervasive and costly complication of diabetes mellitus. Multiple mechanisms have been proposed, including polyol pathway activation, advanced glycosylation end-product formation, and vasculopathic changes. Nevertheless, specific treatment modalities addressing these basic issues are still lacking. The mainstay of treatment includes pharmacological management with antidepressants, anticonvulsants, and opioids, but these drugs are often limited by unfavorable side-effect profiles. For over 30years, spinal cord stimulation (SCS) has been used extensively for the management of various chronic neuropathic pain states. In the past decade, interest in the use of SCS for treatment of PDPN has increased. This article reviews pathophysiological mechanisms of PDPN, proposed mechanisms of SCS, and the role of SCS for the treatment of PDPN.

Karl D. Nolph State of the Art Lecture: Feasible and Future Options for Salvation of the Peritoneal Membrane

A review is given of the various available strategies that can be used to protect the peritoneal membrane. A discussion of experimental studies on approaches that are still experimental, but that might be applied in patients in the future, follows. The currently available approaches include dietary sodium restriction, use of high-dose loop diuretics and of inhibitors of the renin-angiotensin system. All should preferably be combined with a dialysis prescription aimed at reducing the patient's exposure to glucose and its degradation products. The experimental studies indicate favorable effects of combining osmotic agents, together with drugs that interfere with the polyol pathway and the formation of advanced glycosylation end-products.

Poly(ADP-ribose) polymerase inhibition as a novel therapeutic approach against intraepidermal nerve fiber loss and neuropathic pain associated with advanced diabetic neuropathy: A commentary on “PARP Inhibition or gene deficiency counteracts intraepidermal nerve fiber loss and neuropathic pain in advanced diabetic neuropathy”

Poly(ADP-ribose) polymerase inhibition as a novel therapeutic approach against intraepidermal nerve fiber loss and neuropathic pain associated with advanced diabetic neuropathy: A commentary on “PARP Inhibition or gene deficiency counteracts intraepidermal nerve fiber loss and neuropathic pain in advanced diabetic neuropathy”

Non-enzymatic glycosylation reaction contributes to a rise of blood glucose in alloxan-induced diabetic rats

Non-enzymatic glycosylation reaction, which proceeded at an accelerated rate in diabetes, directly caused sharp diminution oftotal haemoglobin due to glycosylated proteins including haemoglobin digested by macrophages. The diminution contributedto hypoxia of tissue that repressed the enzymatic activities in the respiratory chain as well as in the tri-carboxylic acid cycle(TCA) and Embden-Meyerhof-Parnas (EMP) pathways. It was postulated that non-enzymatic glycosylation reactionaccelerated the rise of blood glucose. The theory was further proven by the hypoglycaemic activities of the extract fromTremella aurantialba broth (TBE). TBE inhibited the formation of advanced glycosylation end-products (AGEs) in vitro (IC50=1.7 mg/ml) and in vivo. TBE, when given in vitro, increased the concentration of total haemoglobin and supply of oxygen,enhanced respiration of tissue, decreased the levels of NADH, speeded up catabolism of glucose and finally generatedsignificant anti-hyperglycaemic and hypoglycaemic effect on alloxan-induced diabetic rats. In addition it elevated plasmainsulin level. Oral administration of TBE (100 mg/Kg bw) once a day for 4 weeks resulted in significant reduction in theplasma levels of glucose, fructosamine and the ratio of glycosylated haemoglobin to total haemoglobin. Moreover, oraladministration of TBE increased the total haemoglobin and plasma insulin levels and enhanced some key enzymatic activitiesof EMP, TCA pathways and respiratory chain in the blood of diabetic rats compared with control. (Int J Diabetes Metab 15:52-59, 2007)

Cardiovascular and renal effects of a collagen cross-link breaker (ALT 711) in adult and aged spontaneously hypertensive rats

Background Increased formation of advanced glycosylation end-products on body proteins is a consequence of aging and leads to exaggerated collagen cross-linking eventually increasing cardiovascular stiffness. This study reports our initial inquires into the cardiovascular and renal effects of a cross-link breaker (ALT-711) in aged spontaneously hypertensive rats (SHR). Methods and results The first experiment, in 45-week-old SHR, showed that (among four doses) the dose of 1 mg/kg/d of ALT-711 given for 4 months was most effective in reducing left ventricular and aortic mass indexes. ALT-711 also reduced left ventricular hydroxyproline concentration (5.8 ± 0.2 v 5.1 ± 0.3 mg/g in controls, P < .05); however, it did not affect systemic or regional hemodynamics. In older SHR, ALT-711 (1 mg/kg/d) reduced ( P < .05) systolic pressure (tail-cuff) (from 203 ± 3 mm Hg at outset to 187 ± 3 mm Hg at 8 weeks). Systolic pressure remained unchanged in placebo-treated rats. In addition, left ventricular index (3.09 ± 0.10 v 3.44 ± 0.05 mg/g) and aortic mass index (1.54 ± 0.04 v 1.74 ± 0.05 mg/mm) were reduced by ALT-711. In the third experiment, 1-year-old SHR were given vehicle or ALT-711 (1 mg/kg/d) or placebo until natural death. After 3 months, ALT-711 markedly reduced urinary protein excretion (74.5 ± 8.6 v 135.4 ± 11.8 mg/24 h). Echocardiographic studies, performed at the outset and after 3 and 6 months, revealed two changed indexes. Left ventricular end-diastolic diameter increased more in control than in ALT rats, whereas E-wave deceleration time decreased more in control than in ALT rats. Conclusions Therapy with ALT-711 exerted beneficial cardiovascular and renal effects in aged SHR, improving systolic pressure, left ventricular mass, geometry, and hydroxyproline content while reducing urinary protein excretion.

Collagen cross-link breakers: a beginning of a new era in the treatment of cardiovascular changes associated with aging, diabetes, and hypertension.

Aging, diabetes, and hypertension are conditions in which arterial and myocardial stiffness is increased. Increased arterial stiffness is manifested by an increased systolic arterial pressure, pulse pressure and pulse wave velocity, whereas increased myocardial stiffness is manifested by impaired left ventricular diastolic filling. Moreover, increased arterial stiffness increases cardiac workload, further aggravating already existing adverse changes in left ventricular structure and function. Indeed, studies in human beings have clearly shown that increased cardiovascular stiffness is a reliable predictor of cardiovascular morbidity and mortality. Increased cardiovascular stiffness is usually attributed to the development of fibrosis (i.e., accumulation of collagen). It has also been recognized that the increased cardiac and vascular stiffness may be due to increased collagen cross-linking due to the formation of advanced glycosylation end-products (AGEs). In agreement with this notion is the finding that an inhibitor of AGEs formation improves vascular stiffness in diabetic rats. More recently, cross-link breakers have been developed, and the beneficial effects of one such agent (ALT-711) have been shown in experimental and clinical settings. This report briefly summarizes age related changes in cardiovascular structure and function and describes results of experimental and clinical studies involving collagen cross-link breakers.

What Can We Do to Preserve the Peritoneum?

Long-term peritoneal dialysis may lead to peritoneal membrane failure. Loss of ultrafiltration is the most important clinical abnormality. Loss of ultrafiltration is associated with an increased number of peritoneal blood vessels, with fibrotic alterations, and with loss of mesothelium. Continuous exposure to bioincompatible dialysis solutions is likely to be important in the pathogenesis of these alterations. This article reviews the toxicity of various constituents of dialysate, current assessments of interventions, and the results of interventions aimed at preserving the peritoneum. Glucose, possibly in combination with lactate, and glucose degradation products (GDPs) are likely to be the most toxic constituents of dialysate. Diabetiform peritoneal neoangiogenesis is likely to be mediated by vascular endothelial growth factor (VEGF). Release of VEGF might be influenced by glucose-induced cellular pseudohypoxia, which is likely to be increased by exposure to lactate. Glucose and GDPs are both toxic to peritoneal cells. Glucose degradation products induce the formation of advanced glycosylation end-products at a much faster rate than does glucose itself, but the relative importance of GDPs and glucose in clinical PD has not been clarified. The effects of interventions should first be assessed in long-term animal models, followed by clinical studies on peritoneal transport and on effluent markers that may reflect the status of the peritoneum. Possible interventions aim at reducing peritoneal exposure to glucose, GDPs, and lactate. Techniques include peritoneal resting, replacing some glucose-based exchanges with amino acid-based and icodextrin-based dialysate, using bicarbonate as a buffer, and administering solutions that have a low GDP content. Exposure to various dialysis solutions with a reduced GDP content has resulted in an increase in the effluent concentration of the mesothelial cell marker CA125, irrespective of the buffer used. Experimental studies in a long-term peritoneal exposure model in rats showed that the combination of a reduction in the concentration of lactate and replacement of lactate with pyruvate resulted in a reduction of the number of peritoneal blood vessels. Results of drug therapy have been studied in various animal models. Their use in patients is still experimental. Strategies to preserve the peritoneum aim at reducing membrane exposure to bioincompatible solutions. Currently available dialysis fluids that are more biocompatible are likely to have some beneficial effects. Further research on the development of dialysis solutions that use combinations of osmotic agents and alternative buffers is necessary.

New insights on oxidative stress and diabetic complications may lead to a "causal" antioxidant therapy.

Evidence implicates hyperglycemia-derived oxygen free radicals as mediators of diabetic complications. However, intervention studies with classic antioxidants, such as vitamin E, failed to demonstrate any beneficial effect. Recent studies demonstrate that a single hyperglycemia-induced process of overproduction of superoxide by the mitochondrial electron-transport chain seems to be the first and key event in the activation of all other pathways involved in the pathogenesis of diabetic complications. These include increased polyol pathway flux, increased advanced glycosylation end product formation, activation of protein kinase C, and increased hexosamine pathway flux. Superoxide overproduction is accompanied by increased nitric oxide generation, due to an endothelial NOS and inducible NOS uncoupled state, a phenomenon favoring the formation of the strong oxidant peroxynitrite, which in turn damages DNA. DNA damage is an obligatory stimulus for the activation of the nuclear enzyme poly(ADP-ribose) polymerase. Poly(ADP-ribose) polymerase activation in turn depletes the intracellular concentration of its substrate NAD(+), slowing the rate of glycolysis, electron transport, and ATP formation, and produces an ADP-ribosylation of the GAPDH. These processes result in acute endothelial dysfunction in diabetic blood vessels that, convincingly, also contributes to the development of diabetic complications. These new findings may explain why classic antioxidants, such as vitamin E, which work by scavenging already-formed toxic oxidation products, have failed to show beneficial effects on diabetic complications and may suggest new and attractive "causal" antioxidant therapy. New low-molecular mass compounds that act as SOD or catalase mimetics or L-propionyl-carnitine and lipoic acid, which work as intracellular superoxide scavengers, improving mitochondrial function and reducing DNA damage, may be good candidates for such a strategy, and preliminary studies support this hypothesis. This "causal" therapy would also be associated with other promising tools such as LY 333531, PJ34, and FP15, which block the protein kinase beta isoform, poly(ADP-ribose) polymerase, and peroxynitrite, respectively. While waiting for these focused tools, we may have other options: thiazolinediones, statins, ACE inhibitors, and angiotensin 1 inhibitors can reduce intracellular oxidative stress generation, and it has been suggested that many of their beneficial effects, even in diabetic patients, are due to this property.

Macrophage function in alloxan diabetic mice: expression of adhesion molecules, generation of monokines and oxygen and NO radicals.

The increased incidence of bacterial and mycotic infections in poorly controlled diabetic patients or animals is frequently attributed to impaired activities of professional phagocytes (granulocytes, macrophages) in hypoinsulinaemic milieu. We measured production of monokines (IL-6 and tumour necrosis factor-alpha (TNF-alpha)), active NO and reactive oxygen intermediates (ROIs), as well as expression of several cell surface adhesion molecules (Mac-1, -2 and -3, intercellular adhesion molecule-1 (ICAM-1) and Fc gammaRII), by thioglycollate medium-induced peritoneal macrophages of normoglycaemic and alloxan diabetic CBA/J mice (blood glucose level in the range 300 or 500 mg/dl). Macrophages of animals with moderate diabetes (300 mg/dl) produced significantly more IL-6 and TNF-alpha and ROIs than cells of control mice and showed an increased expression of all cell surface molecules, except Mac-3. NO/NO2 production was not affected. Administration of insulin restored enhanced values to normal levels, except for the production of ROIs which remained unusually high. We conclude that two separate mechanisms influence macrophage physiology in diabetes--lack of saturation of insulin receptors on macrophages and an indirect effect due to formation of advanced glycosylation endproducts (AGE) on their surfaces. The latter is possibly responsible for increased generation of ROIs, since it cannot be down-regulated by prolonged insulin treatment. How the increased activity of macrophages of moderately diabetic mice (enhanced production of proinflammatory monokines and oxygen radicals as well as expression of molecules) is related to their ability to kill bacteria is now under investigation.

Biologic Significance of Reduced Levels of Glucose Degradation Products

Conventional fluids for peritoneal dialysis (PD) are potentially bioincompatible, as demonstrated in numerous in vitro and in vivo reports (1). These bioincompatible characteristics are related to acidity, hyperosmolality, and high lactate and glucose concentrations. Furthermore, during heat sterilization and during storage, some of the glucose is affected by the added heat and degraded to biologically reactive substances called glucose degradation products (GDPs) (2,3). The most common GDPs found in conventional, heat-sterilized PD fluids are methylglyoxal, glyoxal, formaldehyde, 3-deoxyglucosone (3-DG), acetaldehyde, 2-furaldehyde, and 5-hydroxymethylfuraldehyde (4,5). Indications are that GDPs, by causing protein denaturation or cross-linking, are basically cytotoxic (6). Indeed, they have been demonstrated to inhibit cell proliferation and to cause necrosis of fibroblasts, macrophages, and human mesothelial cells in vitro, and to cause impairment of cytokine release and superoxide radical generation by peritoneal macrophages and by blood polymorphonuclear cells (7,8). Glucose degradation products also take part in the nonenzymatic crosslinking of proteins, leading to the formation of advanced glycosylation end-products (AGEs) (9). The role of GDPs in AGE formation is of great relevance, because AGEs are considered to participate in the remodeling and fibrosis of the peritoneal membrane that may occur in long-term continuous ambulatory peritoneal dialysis (CAPD) and that may linked to an increased risk of ultrafiltration failure (UFF) (1,10). While GDPs are highly toxic in vitro, the in vivo

Peritoneal Accumulation of Advanced Glycosylation End-Products in Diabetic Rats on Dialysis with Icodextrin

To evaluate and compare the effects of glucose-based solutions to those of icodextrin with respect to peritoneal transport characteristics and formation of advanced glycosylation end-products (AGEs) in the peritoneal membrane in the diabetic rat model of peritoneal dialysis (PD). Thirty-three male Sprague-Dawley rats weighing between 275 - 300 g were divided into 5 groups: group C (n = 6), control rats with catheter but not dialyzed; group D (n = 5), diabetic rats with catheter but not dialyzed; group G (n = 7), diabetic rats dialyzed with standard 2.5% glucose solution for daytime exchanges and 4.25% glucose solution for the overnight exchange; group H (n = 8), diabetic rats dialyzed with standard 2.5% glucose solution for daytime exchanges and 7.5% icodextrin solution for overnight exchanges; group I (n = 7), diabetic rats dialyzed with 7.5% icodextrin solution for all exchanges. Dialysis exchanges were performed three times daily with an instillation volume of 25 mL per exchange for a period of 12 weeks. Tissue sections were stained using a monoclonal anti-AGE antibody. One-hour peritoneal equilibration tests (PET) were performed every 4 weeks for comparison of transport characteristics. The level of immunostaining was lowest in group C and highest in group G. Significant differences were seen between group C and groups G, H, and I (p < 0.001, p = 0.001, and p< 0.05 respectively). Significant differences were also found between group G and groups D and I (p < 0.05 and p < 0.05 respectively). Over time, glucose concentration at the end of an exchange versus concentration at instillation (D/D0 glucose) decreased and dialysate-to-plasma ratio (D/P) of urea increased. Significant differences were found between groups C and H for D/D0 glucose (0.40+/-0.01 vs 0.35+/-0.01, p < 0.05); and between groups C and H for D/P urea (0.87+/-0.03 vs 0.97+/-0.02, p < 0.05). These results suggest that AGE formation is lower with the use of peritoneal dialysis solution containing icodextrin than with glucose-based solutions. We conclude that the use of icodextrin may be helpful in slowing the deterioration of the peritoneal membrane, prolonging its use for dialysis.

Analysis of Non Enzymatic Glycosylation In Vivo: Impact of Different Dialysis Solutions

Glucose-containing dialysis solutions in peritoneal dialysis (PD) patients induce non enzymatic glycosylation (NEG) within the peritoneal cavity. The subsequent formation of advanced glycosylation end-products (AGEs) may be implicated in the functional deterioration of the peritoneal membrane in long-term PD patients. AIM OF THE STUDY AND PARAMETERS: Measurement of NEG by the determination of percent glycation of albumin and IgG (GP), and of AGEs by measuring pentosidine content of protein in 4-hour effluents (Peff) and serum. In 5 patients each, a comparison was made between 3.86% glucose and 1.36% glucose (GP and Peff), and between 3.86% glucose and 7.5% icodextrin (Peff). Nine patients with clinically severe ultrafiltration failure (UFF) were compared to nine patients treated with PD for 1 month. Six of the patients with UFF were treated with non glucose dialysis solutions and Peff was studied again after 6 weeks. No difference was found between Peff comparing 3.86% glucose to either 1.36% glucose or icodextrin. GP were higher in 3.86% glucose than in 1.36%. Glycated/non glycated (G/NG) protein clearance ratios were 1.29 for albumin and 1.12 for IgG (p = 0.003). In contrast to GP, both Peff and serum pentosidine were higher in the UFF patients than in the recently started patients. Peff, but not GP, correlated with duration of PD (r = 0.67, p = 0.04). In 5 of 6 patients treated with non glucose dialysate, Peff decreased while serum pentosidine was stable. These data show that 4-hour Peff contents are not influenced by glucose concentration or osmolality, in contrast to GP. The relation between Peff and duration of PD, and the effect of non glucose dialysate on Peff, suggest that long-term glucose exposure is an important determinant of membrane glycosylation. Thus Peff probably reflects the long-term effects of intraperitoneal glycosylation of peritoneal membrane proteins. Treatment with non glucose dialysis solutions may result in "washout" of glycosylated proteins from the peritoneal membrane.

Age Accumulation in Peritoneal Membrane and Cavity during Peritoneal Dialysis and Its Effect on Peritoneal Structure and Function

T he conventional dialysis solutions contain a high concentration of glucose to induce sufficient ultra filtration and to maintain fluid balance in uremic patients. During continuous ambulatory peritoneal dialysis (CAPD), the peritoneal cavity is therefore continuously exposed to high glucose for a long time. Histological examination of the peritoneum from peritoneal dialysis patients revealed duplication of submesothelial basement membrane in both diabetic and non diabetic patients and acceleration of preexisting duplication of capillary basement membrane in diabetic patients (1-4). These histologic changes, similar to diabetic complications, are believed to be due to continuous exposure of the peritoneum to an unphysiologic ally high concentration of glucose. Hyperglycemia is associated with the presence or progression of complications in non insulin-dependent diabetes mellitus (NIDDM) (1,5) and insulindependent diabetes mellitus (IDDM) (2). One of the major consequences of prolonged hyperglycemia is accelerated formation of advanced glycosylation endproducts (AGEs) on long-lived structural proteins (3). AGEs are excreted mainly by the kidneys and, therefore, serum level increases as renal function decreases (4). AGE peptide levels in spent dialysate in PD patients is higher than plasma levels (6,7). Peritoneal accumulation of AGEs was reported in PD patients (8,9). Exogenous administration of AGEs induced an increase in vascular permeability in normal animals (10) and the accumulation of AGE induced structural and functional alterations of tis sue proteins (11). Peritoneal accumulation of AGEs, structural and functional alterations of tissue proteins, and increased permeability of the peritoneal vasculature may re

Carnosine Protects Proteins against Methylglyoxal-Mediated Modifications

Methylglyoxal (MG) (pyruvaldehyde) is an endogenous metabolite which is present in increased concentrations in diabetics and implicated in formation of advanced glycosylation end-products (AGEs) and secondary diabetic complications. Carnosine (β-alanyl-L-histidine) is normally present in long-lived tissues at concentrations up to 20mM in humans. Previous studies showed that carnosine can protect proteins against aldehyde-containing cross-linking agents such as aldose and ketose hexose and triose sugars, and malondialdehyde, the lipid peroxidation product. Here we examine whether carnosine can protect protein exposed to MG. Our results show that carnosine readily reacts with MG thereby inhibiting MG-mediated protein modification as revealed electrophoretically. We also investigated whether carnosine could intervene when proteins were exposed to an MG-induced AGE (i.e. lysine incubated with MG). Our results show that carnosine can inhibit protein modification induced by a lysine-MG-AGE; this suggests a second intervention site for carnosine and emphasizes its potential as a possible non-toxic modulator of diabetic complications.

The Hydrazine Derivative Aminoguanidine Inhibits the Reaction of Tetrahydrofolic Acid with Hydroxymethylarginine Biomolecule

Aminoguanidine (AG), a hydrazine derivative is known to inhibit the formation of Advanced Glycosylation Endproducts (AGE) and AG has been proposed as an agent in prophylaxis of diabetic complications. However, treatment with hydrazine produced liver and lung tumors by formation of N7- and O6-methylguanine in the DNA of rodents. The hydrazine derivative, isonicotinic acid hydrazide induced pulmonary tumors in mice. N(G)-hydroxymethyl-arginine (HMA) was synthesized by our research group and it showed anticancer effect against experimental tumors. HMA was found earlier in human blood and urine, and recently in many plants (in fruits and vegetables). We could demonstrate a reaction (pH = 7.5, 37 degrees C, 1h) between HMA and tetrahydrofolate (THF) producing N5,N10-methylene-tetrahydrofolate (CH2-THF), the coenzyme of thymidylate synthase (TS). In model experiments AG proved to react with formaldehyde (HCHO) and to eliminate the C1-fragment of HMA, but not that of CH2-THF. In the presence of AG burst chemiluminescence and a higher speed of the formylation and methylation reactions were found in the AG, HCHO, hydrogen peroxide (H2O2) and L-lysine system than without AG. HMA as a biomolecule is one of the compounds which are responsible for the endogenous HCHO level. The biochemical function of HMA may be the direct supply of C1-fragment for the folate cycle. AG can disturb the above function of HMA. The reaction between AG and HCHO seems to be dangerous for biological systems because of the possible presence of L-lysine and H2O2. The burst chemiluminescence indicates excited molecules with extreme high energy producing uncontrolled formylation and methylation reactions. Considering the results of the experiments with AG its use as a medicament seems to be questionable.

Distinct Associations of HbA1c and the Urinary Excretion of Pentosidine, an Advanced Glycosylation End-product, with Markers of Endothelial Function in Insulin-dependent Diabetes mellitus

Dysfunction of the vascular endothelium is considered an early step in the development of diabetic angiopathy. Hyperglycaemia results in endothelial dysfunction, both through direct effects of glucose and through formation of advanced glycosylation end-products (AGEs). We hypothesized that the effects of glucose and AGEs on endothelial function in insulin-dependent diabetes mellitus (IDDM) are distinct and are reflected by distinct plasma markers of endothelial function. We therefore measured plasma levels of von Willebrand factor (vWF), soluble (s) E-selectin and vascular cell adhesion molecule-1 (sVCAM-1), and evaluated the relationship with HbA1c and urinary excretion of pentosidine, an AGE product, in 56 patients with IDDM. Urinary pentosidine excretion was higher in the diabetic than in a control group (n = 60) of similar age (P < 0.0001) and showed a steeper increase with age (P < 0.02 vs controls). In the diabetic group, sE-selectin was correlated to HbA1c (r = 0.52, P < 0.0001), whereas sVCAM-1 was not (r = 0.11, P = 0.47). In contrast, sVCAM-1 showed a trend towards a correlation with log (pentosidine excretion) (r = 0.27, P = 0.06), whereas sE-selectin did not (r = -0.16, P = 0.27). Log(vWF) was correlated to HbA1c (r = 0.50, P < 0.0001) and tended to correlate with log (pentosidine excretion) (r = 0.25, P = 0.07). Multivariate analyses with both pentosidine and HbA1c as independent variables showed significant associations of sE-selectin with HbA1c, of sVCAM-1 with pentosidine, and of log(vWF) with both HbA1c and pentosidine (all P-values < 0.02). Our results imply that the effects of glucose and AGEs on the endothelium can be reflected by distinct endothelial markers. Plasma sE-selectin may reflect short-term effects of glucose on the endothelium, sVCAM-1 the effects of AGEs, and vWF the combined effect of glucose and AGEs.