Correlation between serum advanced glycation end-products and vascular complications in patient with type 2 diabetes.

Advanced glycation end-products (AGEs) formation increases with metabolic disorders, leading to higher serum AGE levels in patients with progressive vascular complications. Measuring AGE levels in biological samples requires multiple pre-analytical processing steps, rendering analysis of multiple samples challenging. This study evaluated the progression of diabetic complications by analyzing AGE levels using a pre-analytical processing strategy based on a fully automated solid phase-extraction system. Serum samples from patients with diabetes, with or without macrovascular complications (Mac or non-Mac) or microvascular complications (Mic or non-Mic), were processed with the established methods. Free and total AGE levels in sera were measured using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). In patients with diabetes, both free and total AGE levels were elevated in those with complications compared to those without complications. In Mac and Mic groups, free and total AGE levels and z-scores (the sum of normalized AGE levels) also increased. AGE z-scores were markedly higher than those of single AGE levels in distinguishing each complication. Our study demonstrated that the free AGE z-score, measured using a new analytical method without hydrolysis, correlated with the presence of vascular complications and may serve as a marker of disease complications.

Soymilk yogurt fermented using Pediococcus pentosaceus TOKAI 759 m improves mice gut microbiota and reduces pro-inflammatory cytokine production.

This study aimed to determine the anti-inflammatory activities and bioactive compounds of soymilk yogurt prepared using Lactiplantibacillus plantarum TOKAI 17 or Pediococcus pentosaceus TOKAI 759 m. Mice were divided into five groups: normal diet (ND), soymilk (SM), soymilk yogurt using L. plantarum TOKAI 17 (SY 17) or P. pentosaceus TOKAI 759 m (SY 759 m), and 0.5 × 109 cells of each starter strain (BC 17 or BC759m). In the SY 759 m group, the serum pro-inflammatory cytokine levels and the cytotoxicity of natural killer cells were attenuated compared to the ND group. In the cecum microbiota, the abundances of butyrate-producing bacteria increased in the SY 759 m and BC 17 groups. Furthermore, SY 759 m metabolites contained high levels of aglycone isoflavone, adenine and showed a significant decrease in CCL-2 and IL-6 production in LPS-induced macrophage. In conclusion, soymilk yogurt produced using P. pentosaceus TOKAI 759 m modulates the gut microbiota and can potentially prevent pro-inflammatory cytokine production.

Glucoselysine, a unique advanced glycation end-product of the polyol pathway and its association with vascular complications in type 2 diabetes.

Glucoselysine (GL) is an unique advanced glycation end-product derived from fructose. The main source of fructose in vivo is the polyol pathway, and an increase in its activity leads to diabetic complications. Here, we aimed to demonstrate that GL can serve as an indicator of the polyol pathway activity. Additionally, we propose a novel approach for detecting GL in peripheral blood samples using liquid chromatography-tandem mass spectrometry and evaluate its clinical usefulness. We successfully circumvent interference from fructoselysine, which shares the same molecular weight as GL, by performing ultrafiltration and hydrolysis without reduction, successfully generating adequate peaks for quantification in serum. Furthermore, using immortalized aldose reductase KO mouse Schwann cells, we demonstrate that GL reflects the downstream activity of the polyol pathway and that GL produced intracellularly is released into the extracellular space. Clinical studies reveal that GL levels in patients with type 2 diabetes are significantly higher than those in healthy participants, while Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine (MG-H1) levels are significantly lower. Both GL and MG-H1 show higher values among patients with vascular complications; however, GL varies more markedly than MG-H1 as well as hemoglobin A1c, fasting plasma glucose, and estimated glomerular filtration rate. Furthermore, GL remains consistently stable under various existing drug treatments for type 2 diabetes, whereas MG-H1 is impacted. To the best of our knowledge, we provide important insights in predicting diabetic complications caused by enhanced polyol pathway activity via assessment of GL levels in peripheral blood samples from patients.

Glucuronic acid is a novel source of pentosidine, associated with schizophrenia.

Pentosidine (PEN) is an advanced glycation end-product (AGEs), where a fluorescent cross-link is formed between lysine and arginine residues in proteins. Accumulation of PEN is associated with aging and various diseases. We previously reported that a subpopulation of patients with schizophrenia showed PEN accumulation in the blood, having severe clinical features. PEN is thought to be produced from glucose, fructose, pentoses, or ascorbate. However, patients with schizophrenia with high PEN levels present no elevation of these precursors of PEN in their blood. Therefore, the molecular mechanisms underlying PEN accumulation and the molecular pathogenesis of schizophrenia associated with PEN accumulation remain unclear. Here, we identified glucuronic acid (GlcA) as a novel precursor of PEN from the plasma of subjects with high PEN levels. We demonstrated that PEN can be generated from GlcA, both in vitro and in vivo. Furthermore, we found that GlcA was associated with the diagnosis of schizophrenia. Among patients with high PEN, the proportion of those who also have high GlcA is 25.6%. We also showed that Aldo-keto reductase (AKR) activity to degrade GlcA was decreased in patients with schizophrenia, and its activity was negatively correlated with GlcA levels in the plasma. This is the first report to show that PEN is generated from GlcA. In the future, this finding will contribute to understanding the molecular pathogenesis of not only schizophrenia but also other diseases with PEN accumulation.

RAGE activation in macrophages and development of experimental diabetic polyneuropathy.

It is suggested that activation of receptor for advanced glycation end products (RAGE) induces proinflammatory response in diabetic nerve tissues. Macrophage infiltration is invoked in the pathogenesis of diabetic polyneuropathy (DPN), while the association between macrophage and RAGE activation and the downstream effects of macrophages remain to be fully clarified in DPN. This study explored the role of RAGE in the pathogenesis of DPN through the modified macrophages. Infiltrating proinflammatory macrophages impaired insulin sensitivity, atrophied the neurons in dorsal root ganglion, and slowed retrograde axonal transport (RAT) in the sciatic nerve of type 1 diabetic mice. RAGE-null mice showed an increase in the population of antiinflammatory macrophages, accompanied by intact insulin sensitivity, normalized ganglion cells, and RAT. BM transplantation from RAGE-null mice to diabetic mice protected the peripheral nerve deficits, suggesting that RAGE is a major determinant for the polarity of macrophages in DPN. In vitro coculture analyses revealed proinflammatory macrophage-elicited insulin resistance in the primary neuronal cells isolated from dorsal root ganglia. Applying time-lapse recording disclosed a direct impact of proinflammatory macrophage and insulin resistance on the RAT deficits in primary neuronal cultures. These results provide a potentially novel insight into the development of RAGE-related DPN.

Rapid pretreatment for multi-sample analysis of advanced glycation end products and their role in nephropathy.

Advanced glycation end products (AGEs), produced by the Maillard reaction between carbohydrates and proteins, may be involved in diabetes and its complications. Accurate quantification of AGEs in vivo can demonstrate the relation between AGEs and pathological conditions, but it is not widely used in clinical practice because of the multiple pretreatment steps before analyses. We developed a fully automated solid-phase extraction system (FSPES) to simplify rate-limiting pretreatment using a cation exchange column. We applied this device to evaluate AGEs in nephropathy. Among the standard samples, we used arginine, lysine, N|ε-(carboxymethyl)lysine (CML), N|ω-(carboxymethyl)arginine (CMA), N|ε-(carboxyethyl)lysine (CEL), and N|δ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine (MG-H1) for FSPES. We analyzed the coefficient of variation (CV) by mass spectrometry. FSPES performed column operations rapidly at a pressure three times higher compared with the conventional method. FSPES stably performed pretreatment. CV results for CML, CMA, CEL, and MG-H1 measurements in bovine and human serum were the same as those in the conventional pretreatment. Among the AGE structures we measured, CML and CEL increased with the decline in kidney function. The CML and CEL levels of patients with nephropathy were significantly higher than those in normal subjects. Thus, FSPES is useful for clarifying the relation between AGEs and various pathological conditions.

Histone functions as a cell-surface receptor for AGEs.

Reducing sugars can covalently react with proteins to generate a heterogeneous and complex group of compounds called advanced glycation end products (AGEs). AGEs are generally considered as pathogenic molecules, mediating a pro-inflammatory response and contributing to the development of a number of human diseases. However, the intrinsic function of AGEs remains to be elucidated. We now provide multiple lines of evidence showing that AGEs can specifically bind histone localized on the cell surface as an AGE-binding protein, regulate the function of histone as a plasminogen receptor, and result in the regulation of monocytes/macrophage recruitment to the site of inflammation. Our finding of histone as a cell-surface receptor for AGEs suggests that, beside our common concept of AGEs as danger-associated molecular patterns mediating a pro-inflammatory response, they may also be involved in the homeostatic response via binding to histone.

Changes in S-(2-succinyl)cysteine and advanced glycation end-products levels in mouse tissues associated with aging.

Cysteine is non-enzymatically modified by fumarate, which is an intermediate of the tricarboxylic acid cycle, leading to the formation of S-(2-succinyl)cysteine (2SC). Post-translational modification of physiological proteins by fumarate causes enzyme dysfunction. The aim of the study was to evaluate the changes in 2SC accumulation in physiological tissues associated with aging. Brain, liver, kidney, and serum samples were collected from 4-, 12-, and 96-week-old male C57BL/6J mice, and the level of 2SC was determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) after pretreatment, including delipidation, protein precipitation, and hydrolysis using hydrochloric acid. The 2SC level in the brain was higher than that in other tissues, and its accumulation significantly increased with age. Similarly, Nε-(carboxymethyl)lysine levels, an advanced glycation end-products (AGEs) that accumulates in tissues in an age-dependent manner, was found to be increased in the brain and kidneys of elderly mice. Accumulation of Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine increased significantly with age, but only in the kidneys. The fumarate content in the brain was similar to that in the liver and kidney at 4 and 12 weeks of age. Furthermore, fumarate contents increased in the liver and kidney at 96 weeks of age, whereas its level did not change in the brain. Our results demonstrated that the changes in 2SC and AGEs levels in tissues reflected differing metabolism and enhanced oxidative stress in each organ; in particular, the metabolism in the brain and kidneys is highly affected by aging.

Protein Modification with Ribose Generates Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine.

Advanced glycation end products (AGEs) are associated with diabetes and its complications. AGEs are formed by the non-enzymatic reactions of proteins and reducing sugars, such as glucose and ribose. Ribose is widely used in glycation research as it generates AGEs more rapidly than glucose. This study analyzed the AGE structures generated from ribose-modified protein by liquid chromatography-quadrupole time-of-flight mass spectrometry. Among these AGEs, Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine (MG-H1) was the most abundant in ribose-glycated bovine serum albumin (ribated-BSA) among others, such as Nε-(carboxymethyl) lysine, Nε-(carboxyethyl) lysine, and Nω-(carboxymethyl) arginine. Surprisingly, MG-H1 was produced by ribated-BSA in a time-dependent manner, whereas methylglyoxal levels (MG) were under the detectable level. In addition, Trapa bispinosa Roxb. hot water extract (TBE) possesses several anti-oxidative compounds, such as ellagic acid, and has been reported to inhibit the formation of MG-H1 in vivo. Thus, we evaluated the inhibitory effects of TBE on MG-H1 formation using ribose- or MG-modified proteins. TBE inhibited MG-H1 formation in gelatin incubated with ribose and ribated-BSA, but not in MG-modified gelatin. Furthermore, MG-H1 formation was inhibited by diethylenetriaminepentaacetic acid. These results demonstrated that ribose reacts with proteins to generate Amadori compounds and form MG-H1 via oxidation.

Trapa bispinosa Roxb. extract lowers advanced glycation end-products and increases live births in older patients with assisted reproductive technology: a randomized controlled trial.

BACKGROUND: Advanced glycation end-products (AGE), which accumulate with insulin resistance and aging, impair folliculogenesis and may decrease endometrial receptivity. Hishi (Trapa bispinosa Roxb.) extract, a safe herbal medicine, strongly inhibits AGE formation in vitro. We determined whether Hishi lowers AGE and increases live births in older assisted reproductive technology (ART) patients. METHODS: This prospective randomized open-label controlled trial included 64 patients 38 to 42 years old undergoing ART with or without Hishi extract between June 11, 2015 and July 12, 2019. None had over 2 ART failures, diabetes, uterine anomalies, or exhausted ovarian reserve. After allocation, the Hishi group received Hishi extract (100 mg/day) until late pregnancy or failure. The control group received no extract. Both groups underwent 1 cycle of conventional infertility treatment; 1 long-protocol cycle of ovarian stimulation, oocyte retrieval, in vitro fertilization/intracytoplasmic sperm injection, and fresh embryo transfer (ET); and, if needed, cryopreserved ET until live birth or embryo depletion. Serum AGE were measured before and during ART, as were AGE in follicular fluid (FF). RESULTS: Cumulative live birth rate among 32 Hishi patients was 47%, significantly higher than 16% among 31 controls (p<0.01; RR, 4.6; 95% CI, 1.4 - 15.0; 1 control dropped out). Live birth rate per ET, including fresh and cryopreserved, was significantly higher with Hishi (28% in 47 ET vs. 10% in 49 ET; p<0.05; RR, 3.4; 95% CI, 1.1-10.4). Among variables including age, day-3 FSH, anti-Müllerian hormone, and Hishi, logistic regression identified only Hishi as significantly associated with increased cumulative live birth (p<0.05; OR, 5.1; 95% CI, 1.4 - 18.3). Hishi significantly enhanced oocyte developmental potential, improved endometrial receptivity in natural cycles, and decreased AGE in serum and FF. Larger serum AGE decreases with Hishi were associated with more oocytes becoming day-2 embryos. CONCLUSIONS: Hishi decreased AGE in serum and FF and improved oocyte developmental potential and endometrial receptivity, increasing live births in older patients. Treatment of infertility by AGE reduction represents a new addition to infertility treatment. Therapeutic trials of Hishi for other AGE-associated diseases might be considered. TRIAL REGISTRATION: UMIN registration in Japan ( UMIN000017758 ) on June 1, 2015. https://www.umin.ac.jp/ctr/index.htm.

Accumulation of Nε-(carboxyethyl) lysine in Caenorhabditis elegans is correlated with the formation of ketone body.

Advanced glycation end-products (AGEs) are formed when proteins react with carbonyl compounds, and they gradually accumulate with age. However, AGE accumulation with ageing is not fully understood because longevity studies in mammals are time-consuming. Therefore, we used Caenorhabditis elegans to evaluate the correlation between ageing and AGE accumulation. Age-synchronized C.elegans nematodes were cultured for 3 and 12 days. The levels of Nε-(carboxymethyl) lysine, Nω-(carboxymethyl) arginine, Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl) ornithine and Nε-(carboxyethyl) lysine (CEL) were compared. Glucose, methylglyoxal and acetol were incubated with human serum albumin, and CEL formation was evaluated. The levels of methylglyoxal and ketone bodies in C.elegans were quantified. CEL accumulation increased significantly with culture duration. Methylglyoxal and ketone bodies-possible forerunners of AGE accumulation-were also quantified with respect to culture duration. The levels of ketone bodies increased significantly during culture, and correlated closely with CEL accumulation (R2 = 0.72, P = 0.0008), whereas the levels of methylglyoxal did not increase over time. CEL was formed in vitro in a time-dependent manner from methylglyoxal and acetol when incubated with human serum albumin (HSA) at the same temperature as C.elegans culture, suggesting that increased levels of CEL in C.elegans are attributable to ketone bodies.

Development of a conventional immunochemical detection system for determination of Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine in methylglyoxal-modified proteins.

Methylglyoxal (MGO) produced during glycolysis is known to react with arginine residues on proteins to generate advanced glycation end products, such as Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine (MG-H1). Since the production of MGO is increased during hyperglycemia or metabolic disorders in vivo, it is considered that the measurement of MG-H1 is useful for evaluating abnormalities in carbohydrate metabolism. Thus, we prepared a monoclonal antibody against MG-H1 to develop a conventional measurement system for MG-H1. Reactivity and specificity of the antibody to MGO-modified protein were confirmed by enzyme-linked immunosorbent assay and western blotting, respectively. The measurement of MG-H1 content by the antibody was positively correlated with that by electrospray ionization-liquid chromatography-tandem mass spectrometry and the ratio of modified arginine residues by amino acid analysis. Our results demonstrated that immunochemical methods could be useful for the estimation of MG-H1 content in modified proteins.

Drosera tokaiensis extract containing multiple phenolic compounds inhibits the formation of advanced glycation end-products.

The accumulation of advanced glycation end-products (AGEs) correlates with aging and accompanies the onset of age-related diseases, such as diabetes and arteriosclerosis. Therefore, a daily intake of natural compounds that inhibit the production of AGEs may be beneficial in preventing these diseases. In this study, we evaluated the inhibitory effects of 14 natural crude extracts, including those of Drosera species, which possess anti-inflammatory activity, on the formation of AGEs, such as Nω-(carboxymethyl)arginine (CMA) and Nε-(carboxymethyl)lysine (CML). Crude extracts of Drosera inhibited the formation of CMA and CML by incubation on gelatin with ribose more effectively than with other extracts, so active compounds that prevent AGE formation were purified from Drosera tokaiensis, which is endemic to Japan. Several compounds were purified from D. tokaiensis extracts using HPLC and identified by NMR analysis. These compounds included ellagic acid, 3,3'-di-O-methylellagic acid 4'-glucoside, myricitrine, and quercimelin. Furthermore, all compounds showed a significantly higher inhibitory effect on CMA and CML formations than aminoguanidine. Specifically, ellagic acid and myricitrine had the highest inhibitory effects of the compounds tested. However, not all compounds showed inhibition of CMA formation in a mixture of gelatin and glyoxal (GO). These results suggest that the compounds in D. tokaiensis inhibit CMA and CML formations via the antioxidative activity of phenolic compounds, rather than GO trapping action. This study provides the first evidence that D. tokaiensis inhibits CMA and CML formations and that phenolic compounds such as ellagic acid and myricitrine play an important role as active components of D. tokaiensis extracts.

Trapa bispinosa Roxb. and lutein ameliorate cataract in type 1 diabetic rats.

Trapa bispinosa Roxb. is an annual aquatic grass of the citrus family. Although its hot water extract displays antioxidative activity in vitro, little is known about its biological effectiveness. In the present study, we evaluated the extract's inhibitory effect on diabetic cataractogenesis and formation of advanced glycation end-product. Lutein, which is beneficial for eye diseases, was administered concurrently. For short-term administration, Trapa bispinosa Roxb. hot water extract and/or lutein were administered to type 1 diabetic rats. N ɛ-(carboxymethyl)lysine and N ɛ-(carboxyethyl)lysine were quantified in serum using mass spectrometry. The long-term administration study was similar to the short-term, except that the dosages were lower. In the short-term study, co-administration of the extract and lutein inhibited N ɛ-(carboxymethyl)lysine and N ɛ-(carboxyethyl)lysine in serum. However, in the long-term study, only lutein inhibited N ɛ-(carboxymethyl)lysine and N ɛ-(carboxyethyl)lysine in serum. These results suggest that lutein exerts its long-term effect regardless of the concentration administered, while the extract exerts its effect when its concentration is increased. Relative to the consumption of the control diet, oral intake of the combination of the extract and lutein significantly inhibited the progression of cataractogenesis in the lens of diabetic rats, even at low doses, and the combination was more effective than individual treatments.

Glucoselysine is derived from fructose and accumulates in the eye lens of diabetic rats.

Prolonged hyperglycemia generates advanced glycation end-products (AGEs), which are believed to be involved in the pathogenesis of diabetic complications. In the present study, we developed a polyclonal antibody against fructose-modified proteins (Fru-P antibody) and identified its epitope as glucoselysine (GL) by NMR and LC-electrospray ionization (ESI)- quadrupole TOF (QTOF) analyses and evaluated its potential role in diabetes sequelae. Although the molecular weight of GL was identical to that of fructoselysine (FL), GL was distinguishable from FL because GL was resistant to acid hydrolysis, which converted all of the FLs to furosine. We also detected GL in vitro when reduced BSA was incubated with fructose for 1 day. However, when we incubated reduced BSA with glucose, galactose, or mannose for 14 days, we did not detect GL, suggesting that GL is dominantly generated from fructose. LC-ESI-MS/MS experiments with synthesized [13C6]GL indicated that the GL levels in the rat eye lens time-dependently increase after streptozotocin-induced diabetes. We observed a 31.3-fold increase in GL 8 weeks after the induction compared with nondiabetic rats, and Nϵ-(carboxymethyl)lysine and furosine increased by 1.7- and 21.5-fold, respectively, under the same condition. In contrast, sorbitol in the lens levelled off at 2 weeks after diabetes induction. We conclude that GL may be a useful biological marker to monitor and elucidate the mechanism of protein degeneration during progression of diabetes.

[Preventive Effects of Aphanothece sacrum on Diabetic Cataracts].

Approximately 20% of diabetic patients develop diabetic cataracts. As lens proteins are known to be only slightly metabolized during the lifetime, cataracts are difficult to recover from once they have progressed. Therefore, the daily intake of natural compounds would be an important strategy for the prevention of diabetic cataracts. Aphanothece sacrum Okada (Asa) is a freshwater blue-green algae endemic to Japan. It has been eaten since the Edo period in Kyushu. In this study, the inhibitory effects of Asa on the pathogenesis of diabetic cataracts were evaluated. Furthermore, the inhibitory effects of Asa on the formation of Nε-(carboxymethyl) lysine (CML), an oxidation-dependent advanced glycation end-product, were also measured. After 3-month administration, the CML contents in the lens were measured by liquid chromatography tandem mass spectrometry using an internal standard of CML or lysine. Asa significantly inhibited the progression of cataractogenesis and accumulation of CML in diabetic lens compared with the normal diet group. These results suggested that daily intake of Asa reduces oxidative stress and prevents the pathogenesis of cataracts.

Aphanothece sacrum (Sur.) Okada Prevents Cataractogenesis in Type 1 Diabetic Mice.

Aphanothece sacrum (Sur.) Okada is a species of cyanobacteria found in Japan. Although it has been used in local cuisine in Kyushu, Japan, for 250 y, little is known about its beneficial effect as food. The daily intake of health beneficial phytochemicals is believed to be useful for preventing lifestyle-related diseases, such as diabetic cataracts. In this study, the inhibitory effect of freeze-dried A. sacrum (Asa) on the formation of diabetic cataracts (DCs) was evaluated. Type 1 diabetes was induced in mice using streptozotocin (STZ). The mice were divided into two groups: one was fed a normal diet (DM-control group) and the other was fed a diet containing 1% Asa (DM-Asa group). During the study, changes in blood glucose levels and the amount of food and water consumed were measured. After 3 mo, the amount of Nε-(carboxymethyl)lysine (CML), an oxidative stress marker, in the lens was measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Although the blood glucose levels (p=0.91) and food consumption did not significantly change in any group, the oral administration of Asa tended to suppress CML accumulation (p=0.15) and significantly inhibited the progression of cataractogenesis in the diabetic lens compared with that reported for the normal diet (p=0.009). These results suggested that the daily intake of A. sacrum prevents the pathogenesis of cataracts, and indicated that may reduce the number of DC patients.

Antibody-based detection of advanced glycation end-products: promises vs. limitations.

Advanced glycation end-products (AGEs) of the Maillard reaction were originally measured according to their fluorescent and browning properties. A subsequent study with instrumental analyses such as high-performance liquid chromatography and gas chromatography mass spectrometry more clearly demonstrated the involvement of each AGE structure in pathological conditions. Furthermore, immunochemical methods have also been developed to clarify the localization of AGEs in tissues and measurement of AGEs in multiple clinical samples. Although the involvement of AGEs in age-related diseases has progressed due to immunochemical techniques, the relationship between AGE structure and diseases has not been clear because little was known about the epitope structure of each anti-AGE antibody. However, the development of epitope-identified antibodies against AGEs has made it possible to clarify AGE structures involved in diseases. This review discusses not only the usability of anti-AGE antibodies to evaluate AGEs and disease pathology and screen AGE inhibitors, but also describes their usage.

Eucommia ulmoides extracts prevent the formation of advanced glycation end products.

Proteins non-enzymatically react with reducing sugars to form advanced glycation end-products (AGEs), resulting in the induction of protein denaturation. Because the levels of AGE increase with age and are elevated in age-related diseases, such as diabetes and atherosclerosis, the intake of compound(s) that inhibit the formation of AGEs by daily meal may represent a potential strategy for preventing age-related diseases. In this study, we measured the inhibitory effects of several Eucommia ulmoides extracts on the formation of AGEs, N(ε)-(carboxymethyl)lysine (CML) and N(ω)-(carboxymethyl)arginine (CMA). Although a crude extract obtained from E. ulmoides bark is widely used as herbal medicine, E. ulmoides leaf extract (ELE) inhibited CML and CMA formation more effectively during the incubation of gelatin with ribose. Therefore, the inhibitory effects of compounds present in ELE on CML and CMA formation were studied. As a result, isoquercetin showed the strongest inhibitory effect of all the tested ELE components. These results indicate that the oral intake of ELE may inhibit the formation of AGEs, thereby ameliorating age-related diseases.

Salacia chinensis L. extract ameliorates abnormal glucose metabolism and improves the bone strength and accumulation of AGEs in type 1 diabetic rats.

Although extracts of the roots and stems of Salacia chinensis have been used in folk medicines for chronic diseases such as rheumatism, irregular menstruation, asthma and diabetes mellitus, little is known about the mechanism by which Salacia chinensis extract (SCE) ameliorates these diseases. To clarify whether SCE ameliorates the progression of lifestyle-related diseases, the inhibitory effect of SCE on the formation of advanced glycation end products (AGEs) was analyzed in a rat model of streptozotocin-induced diabetes. Although the oral administration of SCE did not ameliorate the diabetes-induced decrease in body weight, it ameliorated the increase in glycoalbumin levels in diabetic rats. An analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS) demonstrated that the levels of N(ε)-(carboxymethyl)lysine (CML) were highest in the femurs and that they increased by the induction of diabetes. The administration of SCE also ameliorated the decreased femur strength and the accumulation of CML. Furthermore, when all of the carbohydrates in the chow of diabetic rats were replaced with free glucose, the administration of SCE significantly ameliorated a diabetes-induced increase in glycoalbumin and decrease in serum creatinine level and body weight. This study provides evidence to support that SCE ameliorates diabetes-induced abnormalities by improving the uptake of glucose by various organs.