Suppression of native defense mechanisms, SIRT1 and PPARγ, by dietary glycoxidants precedes disease in adult humans; relevance to lifestyle-engendered chronic diseases

Nutrigenómica humana: efectos de los alimentos o sus componentes sobre la expresión RNA

<p>Los resultados del proyecto del genoma humano fueron el punto de partida de grandes avances técnicos, metodológicos y conceptuales en la ciencia de la genética. Hoy en día es claro que el DNA es una molécula compleja que presenta diversas interacciones dinámicas consigo misma y con otros componentes del entorno celular. Asimismo, se sabe que el RNA es una molécula fundamental para el entendimiento de las características del organismo y de la respuesta de este a los estímulos del medioambiente. Además, los mecanismos epigenéticos conjugan todos los eventos moleculares que determinan cuáles serán los rasgos —anatómicos, fisiológicos, metabólicos, etc.— particulares de una entidad biológica definida. Todos los aspectos mencionados antes ofrecen la oportunidad de estudiar el conjunto de interacciones existentes entre el genoma y la dieta, lo cual es muy relevante dado que la ingesta de alimentos —o de los componentes contenidos o derivados de los mismos— es uno de los factores del entorno más importantes a los que está expuesto un individuo a lo largo de su vida, puesto que es capaz de condicionar positiva o negativamente el estado de salud. El presente artículo tiene el propósito de dar un panorama general de los aspectos básicos que integran el concepto nutrigénomica y proporcionar un estado del arte actualizado de algunos de los estudios realizados en este campo in vivo en humanos.</p>

Dietary Advanced Glycation End Products and Risk Factors for Chronic Disease: A Systematic Review of Randomised Controlled Trials

Dietary advanced glycation end-products (AGEs) form during heating and processing of food products and are widely prevalent in the modern Western diet. Recent systematic reviews indicate that consumption of dietary AGEs may promote inflammation, oxidative stress and insulin resistance. Experimental evidence indicates that dietary AGEs may also induce renal damage, however, this outcome has not been considered in previous systematic reviews. The purpose of this review was to examine the effect of consumption of a high AGE diet on biomarkers of chronic disease, including chronic kidney disease (CKD), in human randomized controlled trials (RCTs). Six databases (SCOPUS, CINHAL, EMBASE, Medline, Biological abstracts and Web of Science) were searched for randomised controlled dietary trials that compared high AGE intake to low AGE intake in adults with and without obesity, diabetes or CKD. Twelve dietary AGE interventions were identified with a total of 293 participants. A high AGE diet increased circulating tumour necrosis factor-alpha and AGEs in all populations. A high AGE diet increased 8-isoprostanes in healthy adults, and vascular cell adhesion molecule-1 (VCAM-1) in patients with diabetes. Markers of CKD were not widely assessed. The evidence presented indicates that a high AGE diet may contribute to risk factors associated with chronic disease, such as inflammation and oxidative stress, however, due to a lack of high quality randomised trials, more research is required.

The Possible Mechanism of Advanced Glycation End Products (AGEs) for Alzheimer's Disease

Amyloid precursor protein (APP) has been modified by β and γ-secretase that cause amyloid deposits (plaques) in neuronal cells. Glyceraldhyde-derived AGEs has been identified as a major source of neurotoxicity in Alzheimer’s disease (AD). In a previous study, we demonstrated that glyceraldehyde-derived AGEs increase APP and Aβ via ROS. Furthermore, the combination of AGEs and Aβ has been shown to enhance neurotoxicity. In mice, APP expression is increased by tail vein injection of AGEs. This evidence suggests a correlation between AGEs and the development of AD. However, the role played by AGEs in the pathogenesis of AD remains unclear. In this report, we demonstrate that AGEs up-regulate APP processing protein (BACE and PS1) and Sirt1 expression via ROS, but do not affect the expression of downstream antioxidant genes HO-1 and NQO-1. Moreover, we found that AGEs increase GRP78 expression and enhance the cell death-related pathway p53, bcl-2/bax ratio, caspase 3. These results indicate that AGEs impair the neuroprotective effects of Sirt1 and lead to neuronal cell death via ER stress. Our findings suggest that AGEs increase ROS production, which stimulates downstream pathways related to APP processing, Aβ production, Sirt1, and GRP78, resulting in the up-regulation of cell death related pathway. This in-turn enhances neuronal cell death, which leads to the development of AD.

Effect of diet-derived advanced glycation end products on inflammation

Advanced glycation end products (AGEs) formed via the Maillard reaction during the thermal processing of food contributes to the flavor, color, and aroma of food. A proportion of food-derived AGEs and their precursors is intestinally absorbed and accumulates within cells and tissues. AGEs have been implicated in the pathogenesis of diabetes-related complications and several chronic diseases via interaction with the receptor for AGEs, which promotes the transcription of genes that control inflammation. The dicarbonyls, highly reactive intermediates of AGE formation, are also generated during food processing and may incite inflammatory responses through 1) the suppression of protective pathways, 2) the incretin axis, 3) the modulation of immune-mediated signaling, and 4) changes in gut microbiota profile and metabolite sensors. In animal models, restriction of dietary AGEs attenuates chronic low-grade inflammation, but current evidence from human studies is less clear. Here, the emerging relationship between excess dietary AGE consumption and inflammation is explored, the utility of dietary AGE restriction as a therapeutic strategy for the attenuation of chronic diseases is discussed, and possible avenues for future investigation are suggested.

Slowing the progression of Alzheimer's disease; what works?

Alzheimer's disease (AD) is an age-related progressive dementia, which is increasing in prevalence world-wide. Typically affecting short-term memory at onset, this devastating illness advances to impair all aspects of cognition, as well as non-cognitive domains. Although much effort has been made in recent years to develop disease-modifying treatments, medications which provided promising results in pre-clinical research have so far faltered in human clinical trials. Attention has recently shifted into trying to identify preventative measures that may delay the onset of the illness. Preventative factors include physical activity, proper diet, cognitive stimulation and the management of conditions such as hypertension, diabetes and obesity. However, it remains imperative to identify approaches that may help patients already diagnosed with the illness. Alongside pharmacological research, much work has been done on uncovering strategies which may slow down the progression of AD. This review aims to summarize evidence supporting or refuting methods impacting on the progression of the disease. AD remains a chronic and serious condition, therefore any intervention delaying the onset of moderate/severe symptoms will have a significant impact on patients and their families.

Advanced glycation end-products: modifiable environmental factors profoundly mediate insulin resistance

Advanced glycation end-products are toxic by-products of metabolism and are also acquired from high-temperature processed foods. They promote oxidative damage to proteins, lipids and nucleotides. Aging and chronic diseases are strongly associated with markers for oxidative stress, especially advanced glycation end-products, and resistance to peripheral insulin-mediated glucose uptake. Modifiable environmental factors including high levels of refined and simple carbohydrate diets, hypercaloric diets and sedentary lifestyles drive endogenous formation of advanced glycation end-products via accumulation of highly reactive glycolysis intermediates and activation of the polyol/aldose reductase pathway producing high intracellular fructose. High advanced glycation end-products overwhelm innate defenses of enzymes and receptor-mediated endocytosis and promote cell damage via the pro-inflammatory and pro-oxidant receptor for advanced glycation end-products. Oxidative stress disturbs cell signal transduction, especially insulin-mediated metabolic responses. Here we review emerging evidence that restriction of dietary advanced glycation end-products significantly reduces total systemic load and insulin resistance in animals and humans in diabetes, polycystic ovary syndrome, healthy populations and dementia. Of clinical importance, this insulin sensitizing effect is independent of physical activity, caloric intake and adiposity level.

Elevated serum advanced glycation endproducts in obese indicate risk for the metabolic syndrome: a link between healthy and unhealthy obesity?

CONTEXT

Although obesity can predispose to the metabolic syndrome (MS), diabetes, and cardiovascular disease, not all obese subjects develop MS, hence the need for new indicators of risk for this syndrome. Advanced glycation end products (AGEs) correlate with factors involved in the MS, including inflammation and insulin resistance (IR). Because AGEs can be derived from food and are modifiable, it is important to determine whether they are a risk factor for MS.

OBJECTIVE

The objective of this study was to assess the association of endogenous and exogenous AGEs with MS criteria.

DESIGN

The following data were collected in a cross-sectional study of subjects with and without the MS: serum AGEs (sAGEs) and mononuclear cell AGEs, metabolites, pro- and antiinflammatory markers, body fat mass measures, including abdominal magnetic resonance imaging, and caloric and dietary AGE (dAGE) consumption.

SETTING

The study was conducted in the general community.

PARTICIPANTS

Participants included 130 MS and 139 non-MS subjects of both sexes, older than 50 years.

RESULTS

sAGEs ((ϵ)N-carboxymethyllysine, methylglyoxal) were markedly elevated in obese persons with more than one other MS criteria but not in obese without MS criteria. sAGEs directly correlated with markers of IR (HOMA) and inflammation (leptin, TNFα, RAGE) and inversely with innate defenses (SIRT1, AGE receptor 1 [AGER1], glyoxalase-I, adiponectin). sAGEs correlated with dAGEs but not with calories, nutrient consumption, or fat mass measures. Consumption of dAGE, but not of calories, was markedly higher in MS than in non-MS.

CONCLUSION

High sAGEs, a modifiable risk factor for IR, may indicate risk for the MS, type 2 diabetes, and cardiovascular disease. High dietary AGE consumption and serum AGE levels may link healthy obesity to at-risk obesity.

The low AGE diet: a neglected aspect of clinical nephrology practice?

Increasing evidence in the literature suggests an important role for advanced glycation end products (AGEs) in the generation of a state of increased oxidative stress and chronic subclinical inflammation, which underlies most modern chronic diseases, including diabetes, cardiovascular disease and chronic kidney disease (CKD). Although AGEs were originally thought to form only endogenously, primarily as the result of the hyperglycemia of diabetes, it is now clear that exogenous AGEs, specially incorporated in foods, are an important contributor to the body pool of AGEs. Over the past decade, several clinical trials have been performed in a variety of conditions demonstrating that the application of an AGE-restricted diet reduces not only the systemic levels of AGEs but also the levels of markers of oxidative stress and inflammation. This has been shown in CKD patients before and after the initiation of dialysis and either in the presence or absence of coexistent diabetes. Reduction of the AGE content in food is obtained by simple changes in culinary techniques and appears to be a feasible, easily applicable and safe intervention, even in advanced CKD patients.

Sirt1 deletion leads to enhanced inflammation and aggravates endotoxin-induced acute kidney injury

Bacterial endotoxin has been known to induce excessive inflammatory responses and acute kidney injury. In the present study, we used a mouse model of endotoxemia to investigate the role of Sirt1 in inflammatory kidney injury. We examined molecular and cellular responses in inducible Sirt1 knockout (Sirt1-/-) mice and wild type littermates (Sirt1+/+) in lipopolysaccharide (LPS)-induced kidney injury. Our studies demonstrated that Sirt1 deletion caused aggravated kidney injury, which was associated with increased inflammatory responses including elevated pro-inflammatory cytokine production, and increased ICAM-1 and VCAM-1 expression. Inflammatory signaling such as STAT3/ERK phosphorylation and NF-κB activation was markedly elevated in kidney tissues of Sirt1 knockout mice after LPS challenge. The results indicate that Sirt1 is protective against LPS-induced acute kidney injury by suppressing kidney inflammation and down-regulating inflammatory signaling.

Oral glycotoxins are a modifiable cause of dementia and the metabolic syndrome in mice and humans

Age-associated dementia and Alzheimer's disease (AD) are currently epidemic. Neither their cause nor connection to the metabolic syndrome (MS) is clear. Suppression of deacetylase survival factor sirtuin 1 (SIRT1), a key host defense, is a central feature of AD. Age-related MS and diabetes are also causally associated with suppressed SIRT1 partly due to oxidant glycotoxins [advanced glycation end products (AGEs)]. Changes in the modern diet include excessive nutrient-bound AGEs, such as neurotoxic methyl-glyoxal derivatives (MG). To determine whether dietary AGEs promote AD, we evaluated WT mice pair-fed three diets throughout life: low-AGE (MG(-)), MG-supplemented low-AGE (MG(+)), and regular (Reg) chow. Older MG(+)-fed mice, similar to old Reg controls, developed MS, increased brain amyloid-β42, deposits of AGEs, gliosis, and cognitive deficits, accompanied by suppressed SIRT1, nicotinamide phosphoribosyltransferase, AGE receptor 1, and PPARγ. These changes were not due to aging or caloric intake, as neither these changes nor the MS were present in age-matched, pair-fed MG(-) mice. The mouse data were enhanced by significant temporal correlations between high circulating AGEs and impaired cognition, as well as insulin sensitivity in older humans, in whom dietary and serum MG levels strongly and inversely associated with SIRT1 gene expression. The data identify a specific AGE (MG) as a modifiable risk factor for AD and MS, possibly acting via suppressed SIRT1 and other host defenses, to promote chronic oxidant stress and inflammation. Because SIRT1 deficiency in humans is both preventable and reversible by AGE reduction, a therapeutic strategy that includes AGE reduction may offer a new strategy to combat the epidemics of AD and MS.