Intracellular Toxic AGEs (TAGE) Triggers Numerous Types of Cell Damage

The habitual intake of large amounts of sugar, which has been implicated in the onset/progression of lifestyle-related diseases (LSRD), induces the excessive production of glyceraldehyde (GA), an intermediate of sugar metabolism, in neuronal cells, hepatocytes, and cardiomyocytes. Reactions between GA and intracellular proteins produce toxic advanced glycation end-products (toxic AGEs, TAGE), the accumulation of which contributes to various diseases, such as Alzheimer’s disease, non-alcoholic steatohepatitis, and cardiovascular disease. The cellular leakage of TAGE affects the surrounding cells via the receptor for AGEs (RAGE), thereby promoting the onset/progression of LSRD. We demonstrated that the intracellular accumulation of TAGE triggered numerous cellular disorders, and also that TAGE leaked into the extracellular space, thereby increasing extracellular TAGE levels in circulating fluids. Intracellular signaling and the production of reactive oxygen species are affected by extracellular TAGE and RAGE interactions, which, in turn, facilitate the intracellular generation of TAGE, all of which may contribute to the pathological changes observed in LSRD. In this review, we discuss the relationships between intracellular TAGE levels and numerous types of cell damage. The novel concept of the “TAGE theory” is expected to open new perspectives for research into LSRD.

Potential of an Interorgan Network Mediated by Toxic Advanced Glycation End-Products in a Rat Model

Excessive intake of glucose and fructose in beverages and foods containing high-fructose corn syrup (HFCS) plays a significant role in the progression of lifestyle-related diseases (LSRD). Glyceraldehyde-derived advanced glycation end-products (AGEs), which have been designated as toxic AGEs (TAGE), are involved in LSRD progression. Understanding of the mechanisms underlying the effects of TAGE on gene expression in the kidneys remains limited. In this study, DNA microarray analysis and quantitative real-time polymerase chain reaction (PCR) were used to investigate whether HFCS-consuming Wister rats generated increased intracellular serum TAGE levels, as well as the potential role of TAGE in liver and kidney dysfunction. HFCS consumption resulted in significant accumulation of TAGE in the serum and liver of rats, and induced changes in gene expression in the kidneys without TAGE accumulation or upregulation of receptor for AGEs (RAGE) upregulation. Changes in specific gene expression profiles in the kidney were more correlated with TAGE levels in the liver tissue than in the serum. These findings suggest a direct or indirect interaction may be present between the liver and kidneys that does not involve serum TAGE or RAGE. The involvement of internal signal transduction factors such as exosomes or cytokines without IL-1β and TNF-α is suggested to contribute to the observed changes in kidney gene expression.

Evidence for Toxic Advanced Glycation End-Products Generated in the Normal Rat Liver

Glucose/fructose in beverages/foods containing high-fructose corn syrup (HFCS) are metabolized to glyceraldehyde (GA) in the liver. We previously reported that GA-derived advanced glycation end-products (toxic AGEs, TAGE) are generated and may induce the onset/progression of non-alcoholic fatty liver disease (NAFLD). We revealed that the generation of TAGE in the liver and serum TAGE levels were higher in NAFLD patients than in healthy humans. Although we propose the intracellular generation of TAGE in the normal liver, there is currently no evidence to support this, and the levels of TAGE produced have not yet been measured. In the present study, male Wister/ST rats that drank normal water or 10% HFCS 55 (HFCS beverage) were maintained for 13 weeks, and serum TAGE levels and intracellular TAGE levels in the liver were analyzed. Rats in the HFCS group drank 127.4 mL of the HFCS beverage each day. Serum TAGE levels and intracellular TAGE levels in the liver both increased in the HFCS group. A positive correlation was observed between intracellular TAGE levels in the liver and serum TAGE levels. On the other hand, in male Wister/ST rats that drank Lactobacillus beverage for 12 weeks-a commercial drink that contains glucose, fructose, and sucrose- no increases were observed in intracellular TAGE or serum TAGE levels. Intracellular TAGE were generated in the normal rat liver, and their production was promoted by HFCS, which may increase the risk of NAFLD.

Serum Levels of Toxic AGEs (TAGE) May Be a Promising Novel Biomarker for the Onset/Progression of Lifestyle-Related Diseases

Advanced glycation end-products (AGEs) generated with aging or in the presence of diabetes mellitus, particularly AGEs derived from the glucose/fructose metabolism intermediate glyceraldehyde (Glycer-AGEs; termed toxic AGEs (TAGE)), were recently shown to be closely involved in the onset/progression of diabetic vascular complications via the receptor for AGEs (RAGE). TAGE also contribute to various diseases, such as cardiovascular disease; nonalcoholic steatohepatitis; cancer; Alzheimer's disease, and; infertility. This suggests the necessity of minimizing the influence of the TAGE-RAGE axis in order to prevent the onset/progression of lifestyle-related diseases (LSRD) and establish therapeutic strategies. Changes in serum TAGE levels are closely associated with LSRD related to overeating, a lack of exercise, or excessive ingestion of sugars/dietary AGEs. We also showed that serum TAGE levels, but not those of hemoglobin A1c, glucose-derived AGEs, or Nε-(carboxymethyl)lysine, have potential as a biomarker for predicting the progression of atherosclerosis and future cardiovascular events. We herein introduce the usefulness of serum TAGE levels as a biomarker for the prevention/early diagnosis of LSRD and the evaluation of the efficacy of treatments; we discuss whether dietary AGE/sugar intake restrictions reduce the generation/accumulation of TAGE, thereby preventing the onset/progression of LSRD.