Inhibition of advanced glycation endproduct formation by acetaldehyde: role in the cardioprotective effect of ethanol

Chemical synthesis of polysaccharide-protein and polysaccharide-peptide conjugates: A review

Polysaccharides are abundant natural polymers, which in nature are at times covalently modified with peptides and proteins. Polysaccharide-protein or polysaccharide-peptide conjugates, natural or otherwise, may have increased solubility, improved emulsion properties, prolonged circulation time, reduced immunogenicity, and enhanced selectivity for targeting specific tissues compared to native peptides and proteins. In this paper, we will review recent advances in synthetic methods for producing polysaccharide-protein conjugates and discuss their advantages with a focus on drug targeting.

Strategies to Reduce Glucose Exposure in Peritoneal Dialysis Patients

Glucose has been used successfully for more than two decades in peritoneal dialysis, and in this regard, must be considered a safe and effective osmotic agent. Recently, however, insight has been growing about the potential for metabolic and peritoneal effects arising from long-term exposure to high glucose concentrations—for example, hyperlipidemia and loss of peritoneal ultrafiltration. Clinical concerns over exposure to excessive glucose and glucose degradation products (GDPs) during peritoneal dialysis can be significantly ameliorated by the use of non-glucose-based peritoneal dialysis (PD) solutions, in combination with more biocompatible glucose-based formulations. Peritoneal exposure to GDPs can be reduced by using low-GDP-containing glucose formulations and non glucose solutions such as amino acids and icodextrin. Peritoneal glucose exposure, hyperosmolar stress, and carbohydrate absorption can be reduced by using a combination of icodextrin and amino acids.

Maillard Proteomics: Opening New Pages

Protein glycation is a ubiquitous non-enzymatic post-translational modification, formed by reaction of protein amino and guanidino groups with carbonyl compounds, presumably reducing sugars and α-dicarbonyls. Resulting advanced glycation end products (AGEs) represent a highly heterogeneous group of compounds, deleterious in mammals due to their pro-inflammatory effect, and impact in pathogenesis of diabetes mellitus, Alzheimer's disease and ageing. The body of information on the mechanisms and pathways of AGE formation, acquired during the last decades, clearly indicates a certain site-specificity of glycation. It makes characterization of individual glycation sites a critical pre-requisite for understanding in vivo mechanisms of AGE formation and developing adequate nutritional and therapeutic approaches to reduce it in humans. In this context, proteomics is the methodology of choice to address site-specific molecular changes related to protein glycation. Therefore, here we summarize the methods of Maillard proteomics, specifically focusing on the techniques providing comprehensive structural and quantitative characterization of glycated proteome. Further, we address the novel break-through areas, recently established in the field of Maillard research, i.e., in vitro models based on synthetic peptides, site-based diagnostics of metabolism-related diseases (e.g., diabetes mellitus), proteomics of anti-glycative defense, and dynamics of plant glycated proteome during ageing and response to environmental stress.

Advanced glycation end-products (AGEs) and associations with cardio-metabolic, lifestyle, and dietary factors in a general population: the NQplus study

BACKGROUND

Advanced glycation end-products are a heterogeneous group of molecules that are formed during reactions between reducing sugars and proteins. Advanced glycation end-products are thought to play a role in several diseases, including diabetes mellitus and can be measured non-invasively using skin autofluorescence (AF). The aim of this cross-sectional study was to investigate associations between skin AF and cardio-metabolic, lifestyle, and dietary factors within a general population.

METHODS

The NQplus study is an ongoing longitudinal study in the surroundings of Wageningen, the Netherlands. In this cross-sectional study, skin AF was measured in 957 participants, aged 20 to 77 years, with the AGE Reader. Logistic regression was used to assess associations between skin AF and the following factors: demographics, adiposity, blood lipids, fasting glucose, HbA_1c , blood pressure, dietary intake, and disease history. Stepwise linear regression was used to identify factors correlating with skin AF.

RESULTS

In males, skin AF was significantly associated with age, coffee intake, systolic and diastolic blood pressure, body fat, full fat dairy, and educational level. In females, significant associations were found with age, coffee intake, HbA_1c , diabetes, and eGFR. In the total population, current smoking was positively associated with skin AF.

CONCLUSIONS

This cross-sectional study in a general population showed that age and coffee intake were associated with skin AF in both males and females. We observed a gender disparity for some of the associations with skin AF, which need to be confirmed by further research. More detailed research is needed to assess the association between skin AF and diet.

Prevention of non-enzymatic glycosylation (glycation): Implication in the treatment of diabetic complication

Non-enzymatic glycosylation (glycation) plays an important role in the development of physiological and pathophysiological processes such as aging, diabetes, atherosclerosis, neurodegenerative diseases and chronic renal failure. Preventing glycation can minimize diabetic complications. Glycation can be prevented by the natural defence system in the body, synthetic inhibitors and natural inhibitors. Synthetic inhibitors may prevent glycation through several possible mechanisms. They might inhibit the glycation by interfering with the attachment of sugars with proteins, by inhibiting the late stage of glycation or by preventing Amadori product formation. Furthermore, their ability to scavenge free radicals and to break cross-links might be other mechanisms responsible for their potential to inhibit glycation. Naturally occurring phytochemicals/products have been found to be relatively non-toxic as compared to synthetic compounds, and are inexpensive and available in an ingestible form. A large number of plants and natural biomolecules have been shown to have antidiabetic effects. Several hypoglycaemic compounds have anti-oxidant properties. The present review describes the various ways in which glycation can be prevented.

Determinants of concentrations of N(ε)-carboxymethyl-lysine and soluble receptor for advanced glycation end products and their associations with risk of pancreatic cancer

The soluble receptor for advanced glycation end-products (sRAGE) is shown to mitigate pro-inflammatory effects triggered by ligation of RAGE with N(ε)-carboxymethyl-lysine (CML)-AGE or other ligands. We examined the associations among host, lifestyle, and genetic determinants of CML-AGE or sRAGE and risk of pancreatic cancer in the prospective ATBC Study. We obtained baseline exposure information, data on serological and genetic biomarkers from 141 patients with pancreatic cancer and 141 subcohort controls. Stepwise linear and logistic regression models were used for data analysis. Multiple linear regression analyses showed that CML-AGE concentrations were independently inversely correlated with the minor allele of rs640742 of DDOST, physical activity, alcohol consumption, diastolic blood pressure (BP), and positively correlated with heart rate, serum sRAGE and HDL concentrations (P < 0.05). sRAGE concentrations were independently inversely correlated with the 82Ser allele of rs2070600 of RAGE, age, body mass index, heart rate, and serum HDL; and positively correlated with serum CML-AGE, sucrose consumption, and diastolic BP (P < 0.05). The minor allele of rs1035786 of RAGE was associated with reduced risk of pancreatic cancer (any T compared with CC: multivariate OR = 0.61, 95% CI: 0.38-0.98). We identified host metabolic profile, lifestyle and genetic factors that explained approximately 50% of variability of CML-AGE or sRAGE in Finnish men smokers. The association between RAGE SNPs and pancreatic cancer risk warrants further investigation.

Flushing response modifies the association of alcohol consumption with markers of glucose metabolism in Japanese men and women

BACKGROUND

Influences of alcohol use on glucose metabolism may depend on alcohol flushing response. We investigated the effect of alcohol flushing response on the associations between alcohol consumption and markers of glucose metabolism in Japanese men and women.

METHODS

The subjects were 979 employees (885 men and 94 women), aged 18 to 69 years, of a manufacturing company in Japan. Flushing response and alcohol consumption were determined using a self-administered questionnaire. Homeostasis model assessment-insulin resistance (HOMA-IR) and homeostasis model assessment for β-cell function (HOMA-β) were computed using fasting plasma glucose and insulin. For each group of flushers and nonflushers, multiple regression analysis was used to estimate means of fasting plasma glucose, hemoglobin A1c (HbA1c), and HOMAs for each category of alcohol consumption, with adjustments for potential confounders.

RESULTS

In flushers, alcohol consumption was associated with HbA1c levels in a U-shaped manner, with the lowest HbA1c levels being observed at an alcohol consumption level of 23.0 to <34.5 g ethanol/d (p for quadratic trend = 0.002). In nonflushers, alcohol consumption was linearly and inversely associated with HbA1c levels (p for linear trend = 0.001). Decreases in HbA1c were more evident among flushers compared with nonflushers at moderate alcohol consumption levels (p for interaction = 0.049). An increase of fasting glucose associated with highest alcohol consumption was observed in both flushers and nonflushers. A statistically significant decrease in HOMA-IR with increasing alcohol consumption was observed in flushers (p for trend = 0.007), whereas HOMA-IR levels slightly decreased at higher alcohol consumption in nonflushers. HOMA-β similarly decreased with increasing alcohol consumption in both flushers and nonflushers (both p for trend < 0.001).

CONCLUSIONS

The results suggest that the alcohol flushing response may improve glucose metabolism and insulin resistance at moderate alcohol use levels in apparently healthy Japanese adults.

The effects of oxidative stress on female reproduction: a review

Oxidative stress (OS), a state characterized by an imbalance between pro-oxidant molecules including reactive oxygen and nitrogen species, and antioxidant defenses, has been identified to play a key role in the pathogenesis of subfertility in both males and females. The adverse effects of OS on sperm quality and functions have been well documented. In females, on the other hand, the impact of OS on oocytes and reproductive functions remains unclear. This imbalance between pro-oxidants and antioxidants can lead to a number of reproductive diseases such as endometriosis, polycystic ovary syndrome (PCOS), and unexplained infertility. Pregnancy complications such as spontaneous abortion, recurrent pregnancy loss, and preeclampsia, can also develop in response to OS. Studies have shown that extremes of body weight and lifestyle factors such as cigarette smoking, alcohol use, and recreational drug use can promote excess free radical production, which could affect fertility. Exposures to environmental pollutants are of increasing concern, as they too have been found to trigger oxidative states, possibly contributing to female infertility. This article will review the currently available literature on the roles of reactive species and OS in both normal and abnormal reproductive physiological processes. Antioxidant supplementation may be effective in controlling the production of ROS and continues to be explored as a potential strategy to overcome reproductive disorders associated with infertility. However, investigations conducted to date have been through animal or in vitro studies, which have produced largely conflicting results. The impact of OS on assisted reproductive techniques (ART) will be addressed, in addition to the possible benefits of antioxidant supplementation of ART culture media to increase the likelihood for ART success. Future randomized controlled clinical trials on humans are necessary to elucidate the precise mechanisms through which OS affects female reproductive abilities, and will facilitate further explorations of the possible benefits of antioxidants to treat infertility.

Naturally occurring inhibitors against the formation of advanced glycation end-products

Advanced glycation end-products (AGEs) are the final products of the non-enzymatic reaction between reducing sugars and amino groups in proteins, lipids and nucleic acids. Recently, the accumulation of AGEs in vivo has been implicated as a major pathogenic process in diabetic complications, atherosclerosis, Alzheimer's disease and normal aging. The early recognition of AGEs can ascend to the late 1960s when a non-enzymatic glycation process was found in human body which is similar to the Maillard reaction. To some extent, AGEs can be regarded as products of the Maillard reaction. This review firstly introduces the Maillard reaction, the formation process of AGEs and harmful effects of AGEs to human health. As AGEs can cause undesirable diseases or disorders, it is necessary to investigate AGE inhibitors to offer a potential therapeutic approach for the prevention of diabetic or other pathogenic complications induced by AGEs. Typical effective AGE inhibitors with different inhibition mechanisms are also reviewed in this paper. Both synthetic compounds and natural products have been evaluated as inhibitors against the formation of AGEs. However, considering toxic or side effects of synthetic molecules present in clinical trials, natural products are more promising to be developed as potent AGE inhibitors.

Alcohol and acetaldehyde in public health: from marvel to menace

Alcohol abuse is a serious medical and social problem. Although light to moderate alcohol consumption is beneficial to cardiovascular health, heavy drinking often results in organ damage and social problems. In addition, genetic susceptibility to the effect of alcohol on cancer and coronary heart disease differs across the population. A number of mechanisms including direct the toxicity of ethanol, its metabolites [e.g., acetaldehyde and fatty acid ethyl esters (FAEEs)] and oxidative stress may mediate alcoholic complications. Acetaldehyde, the primary metabolic product of ethanol, is an important candidate toxin in developing alcoholic diseases. Meanwhile, free radicals produced during ethanol metabolism and FAEEs are also important triggers for alcoholic damages.

Alcohol consumption and the risk of coronary heart disease in postmenopausal women with diabetes: Women's Health Initiative Observational Study

BACKGROUND

Although several observational studies have consistently reported an inverse association between moderate alcohol consumption and risk of coronary heart disease (CHD), it is yet not well established if this association also exists among people with type 2 diabetes. The aim of this study is to evaluate the association between the frequency and quantity of alcohol intake and the risk of developing CHD among postmenopausal women with diabetes.

METHODS

We conducted a prospective cohort study, which included 3,198 women with self-reported diabetes and without any history of cardiovascular disease at baseline, in the Women's Health Initiative Observational Study. Alcohol intake was assessed by a semiquantitative food frequency questionnaire. The primary outcome of this study was CHD, which was validated by medical record review. Cox proportional hazards regression was used to estimate the hazard ratio (HR) for the association of alcohol intake and risk of incident CHD while adjusting for several potential confounders.

RESULTS

During the 22,546 person-years of follow-up, there were 336 incident cases of CHD. Both frequency and quantity of alcohol intake were inversely associated with the risk of developing CHD. Compared to nondrinkers, the multivariable HRs across categories of frequency of alcohol consumption (<or=0.5, 0.5-2 and >or=2 drinks/week) were 0.89 (95% confidence intervals [CI]: 0.63, 1.26), 0.84 (95% CI: 0.56, 1.25) and 0.65 (95% CI: 0.43, 0.99), respectively (p for trend: 0.04). This association did not appear to differ based on the type of the alcoholic beverage consumed.

CONCLUSIONS

Moderate alcohol consumption of postmenopausal women with type 2 diabetes may have a benefit on CHD similar to that seen in postmenopausal nondiabetic women. The potential risks of alcohol on noncardiac outcomes may need consideration when recommending alcohol to women with diabetes.

Toward an "omic" physiopathology of reactive chemicals: thirty years of mass spectrometric study of the protein adducts with endogenous and xenobiotic compounds

Cancer and degenerative diseases are major causes of morbidity and death, derived from the permanent modification of key biopolymers such as DNA and regulatory proteins by usually smaller, reactive molecules, present in the environment or generated from endogenous and xenobiotic components by the body's own biochemical mechanisms (molecular adducts). In particular, protein adducts with organic electrophiles have been studied for more than 30 [see, e.g., Calleman et al., 1978] years essentially for three purposes: (a) as passive monitors of the mean level of individual exposure to specific chemicals, either endogenously present in the human body or to which the subject is exposed through food or environmental contamination; (b) as quantitative indicators of the mean extent of the individual metabolic processing which converts a non-reactive chemical substance into its toxic products able to damage DNA (en route to cancer induction through genotoxic mechanisms) or key proteins (as in the case of several drugs, pesticides or otherwise biologically active substances); (c) to relate the extent of protein modification to that of biological function impairment (such as enzyme inhibition) finally causing the specific health damage. This review describes the role that contemporary mass spectrometry-based approaches employed in the qualitative and quantitative study of protein-electrophile adducts play in the discovery of the (bio)chemical mechanisms of toxic substances and highlights the future directions of research in this field. A particular emphasis is given to the measurement of often high levels of the protein adducts of several industrial and environmental pollutants in unexposed human populations, a phenomenon which highlights the possibility that a number of small organic molecules are generated in the human organism through minor metabolic processes, the imbalance of which may be the cause of "spontaneous" cases of cancer and of other degenerative diseases of still uncharacterized etiology. With all this in mind, it is foreseen that a holistic description of cellular functions will take advantage of new analytical methods based on time-integrated metabolomic measurements of a new biological compartment, the "adductome," aimed at better understanding integrated organism response to environmental and endogenous stressors.

Alcohol in moderation, cardioprotection, and neuroprotection: epidemiological considerations and mechanistic studies

In contrast to many years of important research and clinical attention to the pathological effects of alcohol (ethanol) abuse, the past several decades have seen the publication of a number of peer-reviewed studies indicating the beneficial effects of light-moderate, nonbinge consumption of varied alcoholic beverages, as well as experimental demonstrations that moderate alcohol exposure can initiate typically cytoprotective mechanisms. A considerable body of epidemiology associates moderate alcohol consumption with significantly reduced risks of coronary heart disease and, albeit currently a less robust relationship, cerebrovascular (ischemic) stroke. Experimental studies with experimental rodent models and cultures (cardiac myocytes, endothelial cells) indicate that moderate alcohol exposure can promote anti-inflammatory processes involving adenosine receptors, protein kinase C (PKC), nitric oxide synthase, heat shock proteins, and others which could underlie cardioprotection. Also, brain functional comparisons between older moderate alcohol consumers and nondrinkers have received more recent epidemiological study. In over half of nearly 45 reports since the early 1990s, significantly reduced risks of cognitive loss or dementia in moderate, nonbinge consumers of alcohol (wine, beer, liquor) have been observed, whereas increased risk has been seen only in a few studies. Physiological explanations for the apparent CNS benefits of moderate consumption have invoked alcohol's cardiovascular and/or hematological effects, but there is also experimental evidence that moderate alcohol levels can exert direct "neuroprotective" actions-pertinent are several studies in vivo and rat brain organotypic cultures, in which antecedent or preconditioning exposure to moderate alcohol neuroprotects against ischemia, endotoxin, beta-amyloid, a toxic protein intimately associated with Alzheimer's, or gp120, the neuroinflammatory HIV-1 envelope protein. The alcohol-dependent neuroprotected state appears linked to activation of signal transduction processes potentially involving reactive oxygen species, several key protein kinases, and increased heat shock proteins. Thus to a certain extent, moderate alcohol exposure appears to trigger analogous mild stress-associated, anti-inflammatory mechanisms in the heart, vasculature, and brain that tend to promote cellular survival pathways.

Alcohol in moderation, cardioprotection, and neuroprotection: epidemiological considerations and mechanistic studies

In contrast to many years of important research and clinical attention to the pathological effects of alcohol (ethanol) abuse, the past several decades have seen the publication of a number of peer-reviewed studies indicating the beneficial effects of light-moderate, nonbinge consumption of varied alcoholic beverages, as well as experimental demonstrations that moderate alcohol exposure can initiate typically cytoprotective mechanisms. A considerable body of epidemiology associates moderate alcohol consumption with significantly reduced risks of coronary heart disease and, albeit currently a less robust relationship, cerebrovascular (ischemic) stroke. Experimental studies with experimental rodent models and cultures (cardiac myocytes, endothelial cells) indicate that moderate alcohol exposure can promote anti-inflammatory processes involving adenosine receptors, protein kinase C (PKC), nitric oxide synthase, heat shock proteins, and others which could underlie cardioprotection. Also, brain functional comparisons between older moderate alcohol consumers and nondrinkers have received more recent epidemiological study. In over half of nearly 45 reports since the early 1990s, significantly reduced risks of cognitive loss or dementia in moderate, nonbinge consumers of alcohol (wine, beer, liquor) have been observed, whereas increased risk has been seen only in a few studies. Physiological explanations for the apparent CNS benefits of moderate consumption have invoked alcohol's cardiovascular and/or hematological effects, but there is also experimental evidence that moderate alcohol levels can exert direct "neuroprotective" actions-pertinent are several studies in vivo and rat brain organotypic cultures, in which antecedent or preconditioning exposure to moderate alcohol neuroprotects against ischemia, endotoxin, beta-amyloid, a toxic protein intimately associated with Alzheimer's, or gp120, the neuroinflammatory HIV-1 envelope protein. The alcohol-dependent neuroprotected state appears linked to activation of signal transduction processes potentially involving reactive oxygen species, several key protein kinases, and increased heat shock proteins. Thus to a certain extent, moderate alcohol exposure appears to trigger analogous mild stress-associated, anti-inflammatory mechanisms in the heart, vasculature, and brain that tend to promote cellular survival pathways.

Review of methods for the reduction of dietary content and toxicity of acrylamide

Potentially toxic acrylamide is largely derived from heat-induced reactions between the amino group of the free amino acid asparagine and carbonyl groups of glucose and fructose in cereals, potatoes, and other plant-derived foods. This overview surveys and consolidates the following dietary aspects of acrylamide: distribution in food originating from different sources; consumption by diverse populations; reduction of the acrylamide content in the diet; and suppression of adverse effects in vivo. Methods to reduce adverse effects of dietary acrylamide include (a) selecting potato, cereal, and other plant varieties for dietary use that contain low levels of the acrylamide precursors, namely, asparagine and glucose; (b) removing precursors before processing; (c) using the enzyme asparaginase to hydrolyze asparagine to aspartic acid; (d) selecting processing conditions (pH, temperature, time, processing and storage atmosphere) that minimize acrylamide formation; (e) adding food ingredients (acidulants, amino acids, antioxidants, nonreducing carbohydrates, chitosan, garlic compounds, protein hydrolysates, proteins, metal salts) that have been reported to prevent acrylamide formation; (f) removing/trapping acrylamide after it is formed with the aid of chromatography, evaporation, polymerization, or reaction with other food ingredients; and (g) reducing in vivo toxicity. Research needs are suggested that may further facilitate reducing the acrylamide burden of the diet. Researchers are challenged to (a) apply the available methods and to minimize the acrylamide content of the diet without adversely affecting the nutritional quality, safety, and sensory attributes, including color and flavor, while maintaining consumer acceptance; and (b) educate commercial and home food processors and the public about available approaches to mitigating undesirable effects of dietary acrylamide.

Involvement of advanced glycation end products in the pathogenesis of diabetic complications: the protective role of regular physical activity

Advanced glycation end products (AGEs) may play an important role in the pathogenesis of chronic diabetic complications and in the natural process of biological aging. In fact, maintained hyperglycaemia favours the formation of AGEs at the tissue level in diabetic patients, which may influence the triggering of different chronic pathologies of diabetes such as retinopathy, nephropathy, neuropathy and macro- and micro-vascular diseases. Moreover, the literature has also demonstrated the involvement of AGEs in biological aging, which may explain the accelerated process of aging in diabetic patients. The practice of regular physical activity appears to positively influence glycaemic control, particularly in type 2 diabetes mellitus patients. This occurs through the diminution of fasting glycaemia, with a consequent reduction of glycation of plasmatic components suggested by the normalisation of HbA1c plasmatic levels. This exercise-induced positive effect is evident in the blood of diabetic patients and may also reach the endothelium and connective tissues of different organs, such as the kidneys and eyes, and systems, such as the cardiovascular and nervous systems, with a local reduction of AGEs production and further deceleration of organ dysfunction. The aim of this paper was to review the literature concerning this topic to coherently describe the harmful effects of AGEs in organ dysfunction induced by diabetes in advanced age as well as the mechanisms behind the apparent protection given by the practice of regular physical activity.

ε-Glycation, APP and Aβ in ageing and Alzheimer disease: A hypothesis

The post-translational modifications of protein molecules include glycation, which may not only occur enzymatically controlled in N and O position, but also wherever proteins meet reducing sugars non-enzymatically in epsilon position at lysines (non-enzymatic (epsilon) glycation (NEG)). The formation of keto-amines from the amine-sugar compounds (Amadori re-arrangement) and further processing of the largely undigestible Amadori compounds eventually results in insoluble advanced glycation end products (AGEs). The latter can induce or favour disease including mental disorders. Preferential targets of NEG include large cell surface proteins. Ample evidence has been provided that NEG also occurs in the brain where cross-linking of epsilon-glycated proteins, induction of oxidative stress and signalling of AGEs through their specific receptor (RAGE) likely play a role in (brain) ageing and Alzheimer disease (AD). This is underscored by the demonstration of particular interactions between AGE/RAGE and amyloid-beta (Abeta) that favour the aggregation and deposition of Abeta and, perhaps, the formation of Abeta itself. The close relationship between NEG and Abeta, as well as other facts foster the hypothesis that NEG of the large trans-membrane amyloid precursor protein (APP) might be a significant factor in the induction of aberrant APP cleavage with production of Abeta, not only in normal ageing, but also in AD. Blockade of lysine cleavage sites on APP by sugar chains or marker effects induced by NEG akin to ubiquitination of proteins for degradation at lysines could be expected to contribute to altered processing of APP. The hypothesis of epsilon-glycation in APP proposed here and the review of evidences for the significance of NEG in brain ageing and AD are aimed at the stimulation of investigations into the still open question which role NEG plays with respect to APP and its abnormal processing in AD. It can be rendered likely that such research might open new avenues towards decreasing the risk of AD and/or slowing its progression through the prevention of NEG in APP with aberrant APP processing, increased generation of Abeta and the formation of AGEs from epsilon-glycated APP.

3,4-di-deoxyglucosone-3-ene promotes leukocyte apoptosis

BACKGROUND

Heat-sterilized, single-chambered, glucose-containing peritoneal dialysis solutions promote neutrophil apoptosis and impair the peritoneal antibacterial response. It has been proposed that glucose degradation products may be responsible for this effect. However, the precise contribution of individual glucose degradation products had not been addressed.

METHODS

The effect of individual glucose degradation products on apoptosis in cultured human neutrophils and peripheral blood mononuclear cells was studied.

RESULTS

Peritoneal dialysis solutions with a high content of both glucose and glucose degradation products accelerated neutrophil and mononuclear cell apoptosis. Among the different glucose degradation products, 3,4-di-deoxyglucosone-3-ene (3,4-DGE) accelerated apoptosis in neutrophils and peripheral blood mononuclear cells at concentrations (25 micromol/L) in the range found in heat-sterilized, single-chambered, 4.25% glucose peritoneal dialysis fluids. Apoptosis induced by 3,4-DGE was caspase-dependent and could be prevented by the broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-DL-Asp-fluoromethylketone (zVAD-fmk). By contrast, no cytotoxicity was observed following the addition of methylglyoxal, acetaldehyde, formaldehyde, or 3-deoxyglucosone at concentrations found in peritoneal dialysis solutions.

CONCLUSION

3,4-DGE appears to be the main proapoptotic factor in high glucose peritoneal dialysis solutions. 3,4-DGE may impair peritoneal defenses by accelerating leukocyte apoptosis.

TAGE (toxic AGEs) hypothesis in various chronic diseases

The advanced stage of the glycation process (one of the post-translational modifications of proteins) leads to the formation of advanced glycation end-products (AGEs) and plays an important role in the pathogenesis of angiopathy in diabetic patients, in aging, and in neurodegenerative diseases. However, it is still not clear which AGEs subtypes play a pathogenetic role and which of several AGEs receptor mediate AGEs effects on cells. We have provided direct immunochemical evidence for the existence of six distinct AGEs structures (AGEs-1 to -6) within the AGEs-modified proteins and peptides that circulate in the serum of diabetic patients. Recently we demonstrated for the first time that glyceraldehyde-derived AGEs (AGEs-2) and glycolaldehyde-derived AGEs (AGE-3) have diverse biological activities on vascular wall cells, mesangial cells, Schwann cells, malignant melanoma cells and cortical neurons. We also demonstrated for the first time that acetaldehyde (AA)-derived AGEs (AA-AGE) have cytotoxic activity on cortical neurons and the AA-AGE epitope was detected in human brain of alcoholics. These results indicate that of the various types of AGEs structures that can form in vivo, the toxic AGEs (TAGE) structures (AGEs 2, 3, and AA-AGE), but not non-toxic AGEs (N-carboxymethyllysine, pentosidine, pyrraline etc.) are likely to play an important role in the pathophysiological processes associated with AGEs formation.

Oxidative stress and uremia

Oxidative stress is a pathogenic element of great importance in uremic patients, with a great impact on their survival. The cause of oxidative stress in patients on hemodialysis is traditionally attributed to the recurrent activation of polymorphonucleate neutrophils and monocytes. The effects of oxidative stress are evident on all biochemical components of biological tissues: lipids, proteins, carbohydrates, and nucleic acids. This study briefly reviews the effects of different dialytic techniques and of kidney transplant on several parameters of oxidative stress. Many different modalities of pharmaceutical intervention are then analyzed, and the clinical evidences reported.

The Role of Antioxidant Micronutrients in the Prevention of Diabetic Complications

Diabetes mellitus is associated with an increased production of reactive oxygen species and a reduction in antioxidant defenses. This leads to oxidative stress, which is partly responsible for diabetic complications. Tight glycemic control is the most effective way of preventing or decreasing these complications. Nevertheless, antioxidant micronutrients can be proposed as adjunctive therapy in patients with diabetes. Indeed, some minerals and vitamins are able to indirectly participate in the reduction of oxidative stress in diabetic patients by improving glycemic control and/or are able to exert antioxidant activity. This article reviews the use of minerals (vanadium, chromium, magnesium, zinc, selenium, copper) and vitamins or cofactors (tocopherol [vitamin E], ascorbic acid [vitamin C], ubidecarenone [ubiquinone; coenzyme Q], nicotinamide, riboflavin, thioctic acid [lipoic acid], flavonoids) in diabetes, with a particular focus on the prevention of diabetic complications. Results show that dietary supplementation with micronutrients may be a complement to classical therapies for preventing and treating diabetic complications. Supplementation is expected to be more effective when a deficiency in these micronutrients exists. Nevertheless, many clinical studies have reported beneficial effects in individuals without deficiencies, although several of these studies were short term and had small sample sizes. However, a randomized, double-blind, placebo-controlled, multicenter trial showed that thioctic acid at an oral dosage of 800 mg/day for 4 months significantly improved cardiac autonomic neuropathy in type 2 diabetic patients. Above all, individuals with diabetes should be educated about the importance of consuming adequate amounts of vitamins and minerals from natural food sources, within the constraints of recommended sugar and carbohydrate intake.

Identification of a New Cross-link and Unique Histidine Adduct from Bovine Serum Albumin Incubated with Malondialdehyde

Malondialdehyde, acetaldehyde, acrolein, and 4-hydroxynonenal are all products of fatty acid oxidation found in the fatty streaks of atherosclerotic arteries due to a lack of antioxidants and an increase in glycation products. Previously identified cross-links derived from these molecules have nearly always required more than one molecule of each type, although this is physiologically less likely than a reaction involving a single molecule. Here we provide indirect but strong evidence for a malondialdehyde-derived cross-link requiring just one malondialdehyde molecule to link arginine and lysine, giving 2-ornithinyl-4-methyl(1epsilon-lysyl)1,3-imidazole following a 4-day incubation of albumin with 8 mm malondialdehyde. This cross-link was identified as its partial degradation product Nepsilon-(2-carboxyl,2-aminoethane)-Nepsilon-methanoyl-lysine by NMR and mass spectrometry. Analysis of plasma from treated diabetic patients revealed that one patient levels had as high as 0.46%, 0.67% of their lysine/arginine residues modified by this cross-link, although others had lower levels. Alkaline hydrolysis of serum albumin also revealed two acid-labile malondialdehyde adducts of histidine in significant quantities, the isomers 4- and 2-ethylidene-histidine. These constituted up to 0.93% of the histidines in treated diabetic patients. Although collagen is readily cross-linked by malondialdehyde, none of these particular products could be found in incubations of collagen with malondialdehyde.

Effects of anabolic steroids and antioxidant vitamins on ethanol-induced tissue injury

Various mechanisms are involved in the process of ethanol-induced tissue impairment. Oxidative stress and its effects are among the most important. We compared the effects of antioxidant vitamins (vitamin C and E in combination) and steroids (testosterone and nandrolone separately) on the toxicity of ethanol in rats. Animals (male Wistar rats, n = 48) were randomised into following groups-Control, Ethanol, Testosterone, Ethanol + Testosterone, Ethanol + Nandrolone, Ethanol + Vitamins. Alcohol was given daily by gavage in a dose of 5 g/kg of body weight. On the 27th day of the study the animals were sacrificed by decapitation and tissue samples were taken. Metabolic status, parameters of the hepatic metabolism, hormone levels (testosterone, ACTH, corticosterone), lipoperoxidation markers (malondialdehyde and conjugated diens in forebrain cortex and in cerebellum) and advanced glycation end-products were analysed. Tissue samples underwent histological examination. Histological outcomes showed a protective effect of antioxidants on hepatic and cerebellar injury caused by chronic ethanol intake. Anabolic steroids protected especially the central nervous tissue against the toxicity of alcohol. Both, antioxidant vitamins and anabolic steroids protect against the ethanol-induced toxicity, however, this effect is tissue specific.

Neurotoxicity of acetaldehyde-derived advanced glycation end products for cultured cortical neurons

The Maillard reaction that leads to the formation of advanced glycation end products (AGEs) plays an important role in the pathogenesis of angiopathy in diabetic patients, in aging, and in neurodegenerative processes. We hypothesize that acetaldehyde (AA), one of the main metabolites of alcohol, may be involved in alcohol-induced neurotoxicity in vivo by formation of AA-derived AGEs (AA-AGEs) with brain proteins. Incubation of cortical neurons with AA-AGE produced a dose-dependent increase in neuronal cell-death, and the neurotoxicity of AA-AGE was neutralized by the addition of an anti-AA-AGE-specific antibody, but not by anti-N-ethyllysine (NEL) antibody. The AA-AGE epitope was detected in human brain of alcoholism. We propose that the structural epitope AA-AGE is an important toxic moiety for neuronal cells in alcoholism.

Preconditioning with ethanol prevents postischemic leukocyte-endothelial cell adhesive interactions

Long-term ethanol consumption at low to moderate levels exerts cardioprotective effects in the setting of ischemia and reperfusion (I/R). The aims of this study were to determine whether 1) a single orally administered dose of ethanol [ethanol preconditioning (EtOH-PC)] would induce a biphasic temporal pattern of protection (early and late phases) against the inflammatory responses to I/R and 2) adenosine and nitric oxide (NO) act as initiators of the late phase of protection. Ethanol was administered as a bolus to C57BL/6 mice at a dose that achieved a peak plasma concentration of ~45 mg/dl 30 min after gavage and returned to control levels within 60 min of alcohol ingestion. The superior mesenteric artery was occluded for 45 min followed by 60 min of reperfusion beginning 10 min or 1, 2, 3, 4, or 24 h after ethanol ingestion, and the numbers of fluorescently labeled rolling and firmly adherent (stationary) leukocytes in single postcapillary venules of the small intestine were quantified using intravital microscopic approaches. I/R induced marked increases in leukocyte rolling and adhesion, effects that were attenuated by EtOH-PC 2-3 h before I/R (early phase), absent when assessed after 10 min, 1 h, and 4 h of ethanol ingestion, with an even more powerful late phase of protection reemerging when I/R was induced 24 h later. The anti-inflammatory effects of late EtOH-PC were abolished by treatment with adenosine deaminase, an adenosine A(2) (but not A(1)) receptor antagonist, or a NO synthase (NOS) inhibitor during the period of EtOH-PC. Preconditioning with an adenosine A(2) (but not an A(1)) receptor agonist in lieu of ethanol 24 h before I/R mimicked the protective actions of late phase EtOH-PC. Like EtOH-PC, the effect of preconditioning with an adenosine A(2) receptor agonist was abrogated by coincident NOS inhibition. These findings suggest that EtOH-PC induces a biphasic temporal pattern of protection against the proinflammatory effects of I/R. In addition, our observations are consistent with the hypothesis that the late phase of EtOH-PC is triggered by NO formed secondary to adenosine A(2) receptor-dependent activation of NOS during the period of ethanol exposure.

Neurovascular disease, antioxidants and glycation in diabetes

People with diabetes are ten to fifteen times more likely to have a lower limb amputation (LLA) than non-diabetic individuals. Fifteen percent of people with diabetes will develop a foot ulcer during their lifetime, the rate of major amputation amongst diabetic individuals continues to rise, foot problems remain the commonest reason for diabetes-related hospitalisation and recurrence rates in patients with previous foot ulcers are 50% or more. Hyperglycaemia-induced oxidative stress has been shown to result in decreased nerve conduction velocity, and decreased endoneural blood flow-both precursors for neuropathy. Vitamin antioxidants have been shown to be effective therapy in experimental models in reducing free radical species and inhibiting the oxidative process in diabetes subjects. Little work has been published, however, regarding the dietary use of antioxidants from foods, and their specific effects on neurovascular disease and glycation within the diabetes population. Aetiological and prevention studies with dietary antioxidants from foods aimed at the complex nature of foot problems in diabetes are needed.

Effect of alcohol on lipids and lipoproteins in relation to atherosclerosis

Several studies indicate that light-to-moderate alcohol consumption is associated with a low prevalence of coronary heart disease. An increase in high-density lipoprotein (HDL) cholesterol is associated with alcohol intake and appears to account for approximately half of alcohol's cardioprotective effect. In addition to changes in the concentration and composition of lipoproteins, alcohol consumption may alter the activities of plasma proteins and enzymes involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, paraoxonase-1 and phospholipases. Alcohol intake also results in modifications of lipoprotein particles: low sialic acid content in apolipoprotein components of lipoprotein particles (e.g., HDL apo E and apo J) and acetaldehyde modification of apolipoproteins. In addition, "abnormal" lipids, phosphatidylethanol, and fatty acid ethyl esters formed in the presence of ethanol are associated with lipoproteins in plasma. The effects of lipoproteins on the vascular wall cells (endothelial cells, smooth muscle cells, and monocyte/macrophages) may be modulated by ethanol and the alterations further enhanced by modified lipids. The present review discusses the effects of alcohol on lipoproteins in cholesterol transport, as well as the novel effects of lipoproteins on vascular wall cells.

Alcohol consumption and risk of coronary heart disease among men with type 2 diabetes mellitus

OBJECTIVES

The goal of this study was to examine the relationship between alcohol intake and risk of coronary heart disease (CHD) among men with type 2 diabetes.

BACKGROUND

Type 2 diabetes is associated with an increased risk of CHD. Emerging evidence suggests that moderate alcohol intake is associated with an important reduction in risk of CHD in individuals with type 2 diabetes.

METHODS

We studied 2,419 men who reported a diagnosis of diabetes at age 30 or older in the Health Professionals' Follow-up study (HPFS). During 11,411 person-years of follow-up after diagnosis, we documented 150 new cases of CHD (81 nonfatal myocardial infarction [MI] and 69 fatal CHD). Relative risks (RR) were estimated from pooled logistic regression adjusting for potential confounders.

RESULTS

Alcohol use was inversely associated with risk of CHD in men with type 2 diabetes. The age-adjusted RRs corresponding to intakes of < or =0.5 drinks/day, 0.5 to 2 drinks/day and >2 drinks/day were 0.76 (95% confidence interval: [CI]: 0.52 to 1.12), 0.64 (95% CI: 0.40 to 1.02) and 0.59 (95% CI: 0.32 to 1.09), respectively, as compared with nondrinkers (p for trend = 0.06). When we controlled for body mass index, smoking, family history of MI, hypertension, hypercholesterolemia, duration of diabetes, physical activity level, vitamin E supplements and intake of trans fat, polyunsaturated fat, fiber and folate, RRs were 0.78 (95% CI: 0.52 to 1.15), 0.62 (95% CI: 0.40 to 1.00) and 0.48 (95% CI: 0.25 to 0.94) (p for trend = 0.03). The benefits of moderate consumption did not statistically differ by beverage type.

CONCLUSIONS

Moderate alcohol consumption is associated with lower risk of CHD in men with type 2 diabetes.

Alcohol consumption and risk of coronary heart disease among individuals with type 2 diabetes

The epidemiologic evidence on the association between moderate alcohol intake and risk of coronary heart disease (CHD), biological mechanisms for this association, and potential hazards of alcohol intake in individuals with type 2 diabetes is reviewed here. Three prospective cohort studies have examined the association between alcohol consumption and risk of CHD among diabetics. The results indicated significant risk reductions, ranging from 34% to 79%, associated with light to moderate alcohol intake. Potential mechanisms include increased high-density lipoprotein cholesterol, decreased coagulation, and enhanced insulin sensitivity. Alcohol intake is also associated with certain risks among diabetics. However, for moderate alcohol consumption, the benefits would likely outweigh the risks.

Malondialdehyde modification of proteins in vitro is enhanced in the presence of acetaldehyde

To test the hypothesis that the cardioprotective effect of alcohol is related to the inhibition of malondialdehyde (MDA) modification of proteins by acetaldehyde (AA), we studied the effect of AA on MDA modification of bovine serum albumin (BSA) in vitro. BSA was incubated simultaneously with a fixed concentration of MDA (70 mM) and different concentrations of AA (120, 60, 30, 10, or 0 mM) for 24 h at 37 degrees C. The MDA-modified or AA-modified BSA was quantitated with immunoblotting by using specific anti-MDA and specific anti-AA protein antisera, respectively. In another set of experiments, BSA was incubated sequentially, first with different concentrations of AA and then with 70 mM of MDA. In both incubation protocols, the presence of AA and AA modification of BSA enhanced MDA binding. These in vitro observations suggest that the putative cardioprotective effects of alcohol or wine cannot be ascribed to AA-mediated reduction in MDA protein formation, a possible biochemical pathway of accelerated atherosclerosis.

Monitoring glycation of lysozyme by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to study the glycation of lysozyme by D-glucose (LZM-G) and by D-fructose (LZM-F) under dry heating conditions in the presence and in the absence of oxygen. ESI-MS proved to be a precise method for monitoring protein glycation with respect to following the extent of glycation and changes in the glycoconjugate profile with time. The ESI-MS spectrum of glycated LZM revealed a heterogeneous distribution of glycoforms of LZM at different reaction stages. D-Glucose showed a higher level of reactivity with the amino groups of LZM than D-fructose, both in the presence and in the absence of oxygen. The presence of oxygen in the reaction system induced oxidative side reactions, which competed with and slowed the initial rate of formation of Amadori or Heyns products. The more reactive glycoxidation products formed during the initial stages of incubation in the presence of oxygen accelerated the rate of glycation during the later stages of incubation and increased the involvement of arginine residues of LZM in the glycation reaction. The interaction between the initial glycoxidation product(s) of the reducing sugars and intact lysozyme during the later stages of incubation was observed by the appearance of a different cluster of glycoconjugates in the mass spectrum during the latter stages of incubation. The molecular weight differences between the molecular ions of the new cluster of glycoconjugates are consistent with the formation of D-glucosone from the autoxidation of D-glucose or from the oxidative cleavage of the glucose-lysozyme imine adduct in the lysozyme-glucose system. The effect of oxygen-induced glycoxidation on the glycation reaction was also more pronounced in the LZM-G system compared with that in the LZM-F system.

Is ethanol an important antioxidant in alcoholic beverages associated with risk reduction of cataract and atherosclerosis?

It has been reported in the epidemiological literature that cataract, stroke, and atherosclerosis risk is reduced by 50% in people consuming one alcoholic drink per day. Peroxide has been implicated as a causative agent in cataractogenesis, and LDL oxidation appears to play a role in atherosclerosis. The antioxidant activity of alcohol was measured by: (i) use of a luminescent assay developed in our laboratory, confirmed as appropriate; (ii) electron spin resonance (ESR) spin-trapping; and (iii) copper-catalysed oxidation of LDL and VLDL from hamsters fed 6% ethanol in their drinking water. Ethanol reduced the luminescent counts/min from peroxide and superoxide. It significantly reduced the spin-trapped signal of hydroxyl radical, but not the superoxide signal. Other alcohols also showed large reductions in counts from hydrogen peroxide. Plasma from hamsters fed 6% ethanol had lower lipid peroxides and the oxidizability of LDL and VLDL was significantly reduced compared to controls. These data provide a possible explanation for the effect of beverages containing ethanol in the reduction of cataract and atherosclerosis risk observed in human population studies.