Dietary antioxidant interventions in type 2 diabetes patients:a meta-analysis

An imbalance between reactive oxygen species (ROS) production and antioxidant scavenging has been implicated in type 2 diabetes. ROS are a byproduct in type 2 diabetes, generated during protein glycation and as a consequence of advanced glycation end-products-receptor binding; they impair insulin signalling pathways and induce cytotoxicity in pancreatic beta cells. Neutralisation of oxidants by increased antioxidant availability may mitigate these effects. Several human intervention studies have been undertaken to determine whether dietary antioxidants exert beneficial effects for type 2 diabetes patients. This paper describes a systematic review and meta-analysis of the effects of dietary supplementation with antioxidant vitamins C or E on (1) plasma glucose and insulin concentrations, as an indicator of the capacity for antioxidant to interfere with disease process and (2) on glycated haemoglobin A as a measure of antioxidant effects on posttranslational protein modification implicated in disease complications. Combined analysis of 14 studies that met inclusion criteria revealed that dietary antioxidant supplementation did not affect plasma glucose or insulin levels, suggesting that they could not interfere with the pathogenesis of insulin resistance. However, HbA levels were significantly reduced by antioxidant supplementation, suggesting that antioxidants may have some benefit in protecting against the complications of type 2 diabetes. © 2011 The Author(s).

Impairment of calcium ATPases by high glucose and potential pharmacological protection

The review deals with impairment of Ca2+-ATPases by high glucose or its derivatives in vitro, as well as in human diabetes and experimental animal models. Acute increases in glucose level strongly correlate with oxidative stress. Dysfunction of Ca2+-ATPases in diabetic and in some cases even in nondiabetic conditions may result in nitration of and in irreversible modification of cysteine-674. Nonenyzmatic protein glycation might lead to alteration of Ca2+-ATPase structure and function contributing to Ca2+ imbalance and thus may be involved in development of chronic complications of diabetes. The susceptibility to glycation is probably due to the relatively high percentage of lysine and arginine residues at the ATP binding and phosphorylation domains. Reversible glycation may develop into irreversible modifications (advanced glycation end products, AGEs). Sites of SERCA AGEs are depicted in this review. Finally, several mechanisms of prevention of Ca2+-pump glycation, and their advantages and disadvantages are discussed. © 2013 Informa UK, Ltd.

Perioperative cerebrospinal fluid and plasma inflammatory markers after orthopedic surgery.

BACKGROUND: Postoperative delirium is prevalent in older patients and associated with worse outcomes. Recent data in animal studies demonstrate increases in inflammatory markers in plasma and cerebrospinal fluid (CSF) even after aseptic surgery, suggesting that inflammation of the central nervous system may be part of the pathogenesis of postoperative cognitive changes. We investigated the hypothesis that neuroinflammation was an important cause for postoperative delirium and cognitive dysfunction after major non-cardiac surgery. METHODS: After Institutional Review Board approval and informed consent, we recruited patients undergoing major knee surgery who received spinal anesthesia and femoral nerve block with intravenous sedation. All patients had an indwelling spinal catheter placed at the time of spinal anesthesia that was left in place for up to 24 h. Plasma and CSF samples were collected preoperatively and at 3, 6, and 18 h postoperatively. Cytokine levels were measured using ELISA and Luminex. Postoperative delirium was determined using the confusion assessment method, and cognitive dysfunction was measured using validated cognitive tests (word list, verbal fluency test, digit symbol test). RESULTS: Ten patients with complete datasets were included. One patient developed postoperative delirium, and six patients developed postoperative cognitive dysfunction. Postoperatively, at different time points, statistically significant changes compared to baseline were present in IL-5, IL-6, I-8, IL-10, monocyte chemotactic protein (MCP)-1, macrophage inflammatory protein (MIP)-1α, IL-6/IL-10, and receptor for advanced glycation end products in plasma and in IFN-γ, IL-6, IL-8, IL-10, MCP-1, MIP-1α, MIP-1β, IL-8/IL-10, and TNF-α in CSF. CONCLUSIONS: Substantial pro- and anti-inflammatory activity in the central neural system after surgery was found. If confirmed by larger studies, persistent changes in cytokine levels may serve as biomarkers for novel clinical trials.

Antioxidant status in J774A.1 macrophage cell line during chronic exposure to glycated serum

Advanced glycation end-products (AGEs) are linked to aging and correlated diseases. The aim of present study was to evaluate oxidative stress related parameters in J774A.1 murine macrophage cells during chronic exposure to a subtoxic concentration of AGE (5% ribose-glycated serum (GS)) and subsequently for 48 h to a higher dose (10% GS). No effects on cell viability were evident in either experimental condition. During chronic treatment, glycative markers (free and bound pentosidine) increased significantly in intra- and extracellular environments, but the production and release of thiobarbituric acid reactive substances (TBARs), as an index of lipid peroxidation, underwent a time-dependent decrease. Exposure to 10% GS evidenced that glycative markers rose further, while TBARs elicited a cellular defence against oxidative stress. Nonadapted cultures showed an accumulation of AGEs, a marked oxidative stress, and a loss of viability. During 10% GS exposure, reduced glutathione levels in adapted cultures remained constant, as did the oxidized glutathione to reduced glutathione ratio, while nonadapted cells showed a markedly increased redox ratio. A constant increase of heat shock protein 70 (HSP70) mRNA was observed in all experimental conditions. On the contrary, HSP70 expression became undetectable for a longer exposure time; this could be due to the direct involvement of HSP70 in the refolding of damaged proteins. Our findings suggest an adaptive response of macrophages to subtoxic doses of AGE, which could constitute an important factor in the spread of damage to other cellular types during aging.Key words: in vitro cytotoxicity, AGE, pentosidine, glycoxidation, oxidative stress, TBARs.

Glycation, carbonyl stress, EAGLEs, and the vascular complications of diabetes

The association between poor metabolic control and the microvascular complications of diabetes is now well established, but the relationship between long-term metabolic control and the accelerated atherosclerosis of diabetes is as yet poorly defined. Hyperglycemia is the standard benchmark by which metabolic control is assessed. One mechanism by which elevated glucose levels may mediate vascular injury is through early and advanced glycation reactions affecting a wide variety of target molecules. The "glycation hypothesis'' has developed over the past 30 years, evolving gradually into a "carbonyl stress hypothesis'' and taking into account not only the modification of proteins by glucose, but also the roles of oxidative stress, a wide range of reactive carbonyl-containing intermediates (derived not only from glucose but also from lipids), and a variety of extra- and intracellular target molecules. The final products of these reactions may now be termed "Either Advanced Glycation or Lipoxidation End-Products'' or "EAGLEs.'' The ubiquity of carbonyl stress within the body, the complexity of the reactions involved, the variety of potential carbonyl intermediates and target molecules and their differing half-lives, and the slow development of the complications of diabetes all pose major challenges in dissecting the significance of these processes. The extent of the reactions tends to correlate with overall metabolic control, creating pitfalls in the interpretation of associative data. Many animal and cell culture studies, while supporting the hypothesis, must be viewed with caution in terms of relevance to human diabetes. In this article, the development of the carbonyl stress hypothesis is reviewed, and implications for present and future treatments to prevent complications are discussed.

Lipoxidation products as biomarkers of oxidative damage to proteins during lipid peroxidation reactions

Oxidative stress is implicated in the pathogenesis of numerous disease processes including diabetes mellitus, atherosclerosis, ischaemia reperfusion injury and rheumatoid arthritis. Chemical modification of amino acids in protein during lipid peroxidation results in the formation of lipoxidation products which may serve as indicators of oxidative stress in vivo. The focus of the studies described here was initially to identify chemical modifications of protein derived exclusively from lipids in order to assess the role of lipid peroxidative damage in the pathogenesis of disease. Malondialdehye (MDA) and 4-hydroxynonenal (HNE) are well characterized oxidation products of polyunsaturated fatty acids on low-density lipoprotein (LDL) and adducts of these compounds have been detected by immunological means in atherosclerotic plaque. Thus, we first developed gas chromatography-mass spectrometry assays for the Schiff base adduct of MDA to lysine, the lysine-MDA-lysine diimine cross-link and the Michael addition product of HNE to lysine. Using these assays, we showed that the concentrations of all three compounds increased significantly in LDL during metal-catalysed oxidation in vitro. The concentration of the advanced glycation end-product N epsilon-(carboxymethyl)lysine (CML) also increased during LDL oxidation, while that of its putative carbohydrate precursor the Amadori compound N epsilon-(1-deoxyfructose-1-yl)lysine did not change, demonstrating that CML is a marker of both glycoxidation and lipoxidation reactions. These results suggest that MDA and HNE adducts to lysine residues should serve as biomarkers of lipid modification resulting from lipid peroxidation reactions, while CML may serve as a biomarker of general oxidative stress resulting from both carbohydrate and lipid oxidation reactions.

Glycation, oxidation, and lipoxidation in the development of the complications of diabetes: a carbonyl stress hypothesis

Modifications of extant plasma proteins, structural proteins,and other macromolecules are enhanced in diabetes because of increased glycation (secondary to increased glucose concentrations) and perhaps because of increased oxidative stress, Increased glycation is present from the time of onset of diabetes, but the relation between diabetes and oxidative stress is less clear: increased oxidative stress may occur later in the course of disease, as vascular damage becomes established, or it may be a feature of uncomplicated diabetes, The combined effects of protein modification by glycation and oxidation may contribute to the development of accelerated atherosclerosis in diabetes and to the development of microvascular complications, Thus, even if not increased by diabetes, variations in oxidative stress may modulate the consequences of hyperglycemia in individual diabetic patients, In this review, the close interaction between glycation and oxidative processes is discussed, and the theme is developed that the most significant modifications of proteins are the result of interactions with reactive carbonyl groups, While glucose itself contains a carbonyl group that is involved in the initial glycation reaction, the most important and reactive carbonyls are formed by free radical-oxidation reactions damaging either carbohydrates (including glucose itself) or lipids, The resulting carbonyl-containing intermediate products then modify proteins, yielding "glycoxidation" and "lipoxidation" products, respectively, This common pathway for glucose and lipid-mediated stress, which may contribute to diabetic complications, is the basis for the carbonyl stress hypothesis for the development of diabetic complications.

Advanced glycation endproduct modified basement membrane attenuates endothelin-1 induced [Ca2+]i signalling and contraction in retinal microvascular pericytes

PURPOSE: To assess the effects of advanced glycation endproduct (AGE) modification of vascular basement membrane (BM) on endothelin-1 (Et-1) induced intracellular [Ca2+] ([Ca2+]i) homeostasis and contraction in retinal microvascular pericytes (RMP). METHODS: RMPs were isolated from bovine retinal capillaries and propagated on AGE modified BM extract (AGE-BM) or non-modified native BM. Cytosolic Ca2+ was estimated using fura-2 microfluorimetry and cellular contraction determined by measurement of planimetric cell surface area. ETA receptor mRNA and protein expression was assessed by real time RT-PCR and western blotting, respectively. RESULTS: Exogenous endothelin-1 (Et-1) evoked rises in [Ca2+]i and contraction in RMPs were found to be mediated entirely through ETA receptor (ETAR) activation. Both peak and plateau phases of the Et-1 induced [Ca2+]i response and contraction were impaired in RMPs propagated on AGE modified BM. ETAR mRNA expression remained unchanged in RMPs exposed to native or AGE-BM, but protein expression for ETAR (66 kDa) was lower in the AGE exposed cells. CONCLUSIONS: These results suggest that substrate derived AGE crosslinks can influence RMP physiology by mechanisms which include disruption of ETA receptor signalling. AGE modification of vascular BMs may contribute to the retinal hemodynamic abnormalities observed during diabetes.

Fate of products of degradation processes: consequences for climatic change.

The end products of atmospheric degradation are not only CO2 and H2O but also sulfate and nitrate depending on the chemical composition of the substances which are subject to degradation processes. Atmospheric degradation has thus a direct influence on the radiative balance of the earth not only due to formation of greenhouse gases but also of aerosols. Aerosols of a diameter of 0.1 to 2 micrometer, reflect short wave sunlight very efficiently leading to a radiative forcing which is estimated to be about -0.8 watt per m2 by IPCC. Aerosols also influence the radiative balance by way of cloud formation. If more aerosols are present, clouds are formed with more and smaller droplets and these clouds have a higher albedo and are more stable compared to clouds with larger droplets. Not only sulfate, but also nitrate and polar organic compounds, formed as intermediates in degradation processes, contribute to this direct and indirect aerosol effect. Estimates for the Netherlands indicate a direct effect of -4 watt m-2 and an indirect effect of as large as -5 watt m-2. About one third is caused by sulfates, one third by nitrates and last third by polar organic compounds. This large radiative forcing is obviously non-uniform and depends on local conditions.

Metabolism of Maillard reaction products by the human gut microbiota - implications for health

The human colonic microbiota imparts metabolic versatility on the colon, interacts at many levels in healthy intestinal and systemic metabolism, and plays protective roles in chronic disease and acute infection. Colonic bacterial metabolism is largely dependant on dietary residues from the upper gut. Carbohydrates, resistant to digestion, drive colonic bacterial fermentation and the resulting end products are considered beneficial. Many colonic species ferment proteins but the end products are not always beneficial and include toxic compounds, such as amines and phenols. Most components of a typical Western diet are heat processed. The Maillard reaction, involving food protein and sugar, is a complex network of reactions occurring during thermal processing. The resultant modified protein resists digestion in the small intestine but is available for colonic bacterial fermentation. Little is known about the fate of the modified protein but some Maillard reaction products (MRP) are biologically active by, e.g. altering bacterial population levels within the colon or, upon absorption, interacting with human disease mechanisms by induction of inflammatory responses. This review presents current understanding of the interactions between MRP and intestinal bacteria. Recent scientific advances offering the possibility of elucidating the consequences of microbe-MRP interactions within the gut are discussed.

High concentrations of AGE-LDL and oxidized LDL in circulating immune complexes are associated with progression of retinopathy in type 1 diabetes

To determine whether immunocomplexes (ICs) containing advanced glycation end product (AGE)-LDL (AGE-LDL) and oxidized LDL (oxLDL) contribute to the development of retinopathy over a 16-year period in subjects with type 1 diabetes.

S-(2-Succinyl)cysteine:a novel chemical modification of tissue proteins by a Krebs cycle intermediate

S-(2-Succinyl)cysteine (2SC) has been identified as a chemical modification in plasma proteins, in the non-mercaptalbumin fraction of human plasma albumin, in human skin collagen, and in rat skeletal muscle proteins and urine. 2SC increases in human skin collagen with age and is increased in muscle protein of diabetic vs. control rats. The concentration of 2SC in skin collagen and muscle protein correlated strongly with that of the advanced glycation/lipoxidation end-product (AGE/ALE), N(epsilon)-(carboxymethyl)lysine (CML). 2SC is formed by a Michael addition reaction of cysteine sulfhydryl groups with fumarate at physiological pH. Fumarate, but not succinate, inactivates the sulfhydryl enzyme, glyceraldehyde-3-phosphate dehydrogenase in vitro, in concert with formation of 2SC. 2SC is the first example of spontaneous chemical modification of protein by a metabolic intermediate in the Krebs cycle. These observations identify fumarate as an endogenous electrophile and suggest a role for fumarate in regulation of metabolism.

'Lipoproteins, glycoxidation and diabetic angiopathy'

The chronic vascular complications of diabetes (nephropathy, retinopathy and accelerated atherosclerosis) are a major cause of morbidity and premature mortality. In spite of the more widespread availability of intensive diabetes management, approximately one in three people with diabetes develop aggressive complications and over 70% die of atherosclerosis-related diseases. Genetic and acquired factors are likely to be contributory. Potential mediators of vascular damage may include the interrelated processes of lipoprotein abnormalities, glycation, oxidation and endothelial dysfunction. Lipoprotein abnormalities encompass alterations in lipid concentrations, lipoprotein composition and subclass distribution and lipoprotein-related enzymes. Nonenzymatic glycation and oxidative damage to lipoproteins, other proteins and to vascular structures may also be deleterious. As atherosclerosis is a chronic condition commencing in youth, and because clinical events may be silent in diabetes, surrogate measures of vascular disease are important for early identification of diabetic patients with or at high risk of vascular damage, and for monitoring efficacy of interventions. The increasing array of biochemical assays for markers and mediators of vascular damage, noninvasive measures of vascular health, and therapeutic options should enable a reduction in the excessive personal and economic burden of vascular disease in type 1 and type 2 diabetes.

Quantification of N-(glucitol)ethanolamine and N-(carboxymethyl)serine:two products of nonenzymatic modification of aminophospholipids formed in vivo

Chemical, nonenzymatic modification of protein and lipids by reducing sugars, such as glucose, is thought to contribute to age-related deterioration in tissue protein and cellular membranes and to the pathogenesis of diabetic complications. This report describes the synthesis and quantification of N-(glucitol)ethanolamine (GE) and N-(carboxymethyl)serine (CMS), two products of nonenzymatic modification of aminophospholipids. GE is the product of reduction and hydrolysis of glycated phosphatidylethanolamine (PE), while CMS is formed through reaction of phosphatidylserine (PS) with products of oxidation of either carbohydrate (glycoxidation) or lipids (lipoxidation). Gas chromatography/mass spectrometry procedures for quantification of the N,O-acetyl methyl ester derivatives of the modified head groups were developed. GE and CMS were quantified in samples of PE and PS, respectively, following incubation with glucose in vitro; CMS formation was dependent on the presence of oxygen during the incubation. Both GE and CMS were detected and quantified in lipid extracts of human red blood cell membranes. The content of GE, but not CMS, was increased in the lipids from diabetic compared to nondiabetic subjects. Measurement of these modified lipids should prove useful for assessing the role of carbonyl-amine reactions of aminophospholipids in aging and age-related diseases.

Carboxymethylethanolamine, a biomarker of phospholipid modification during the maillard reaction in vivo

Nepsilon-(Carboxymethyl)lysine (CML) is a stable chemical modification of proteins formed from both carbohydrates and lipids during autoxidation reactions. We hypothesized that carboxymethyl lipids such as (carboxymethyl)phosphatidylethanolamine (carboxymethyl-PE) would also be formed in these reactions, and we therefore developed a gas chromatography-mass spectrometry assay for quantification of carboxymethylethanolamine (CME) following hydrolysis of phospholipids. In vitro, CME was formed during glycation of dioleoyl-PE under air and from linoleoylpalmitoyl-PE, but not from dioleoyl-PE, in the absence of glucose. In vivo, CME was detected in lipid extracts of red blood cell membranes, approximately 0.14 mmol of CME/mol of ethanolamine, from control and diabetic subjects, (n = 22, p > 0.5). Levels of CML in erythrocyte membrane proteins were approximately 0.2 mmol/mol of lysine for both control and diabetic subjects (p > 0.5). For this group of diabetic subjects there was no indication of increased oxidative modification of either lipid or protein components of red cell membranes. CME was also detected in fasting urine at 2-3 nmol/mg of creatinine in control and diabetic subjects (p = 0.085). CME inhibited detection of advanced glycation end product (AGE)-modified protein in a competitive enzyme-linked immunosorbent assay using an anti-AGE antibody previously shown to recognize CML, suggesting that carboxymethyl-PE may be a component of AGE lipids detected in AGE low density lipoprotein. Measurement of levels of CME in blood, tissues, and urine should be useful for assessing oxidative damage to membrane lipids during aging and in disease.