Glycated bovine serum albumin for use in feeding trials with animal models - In vitro methodology and characterization of a glycated substrate for modifying feed pellets

This study investigated different methods to produce N^ε-carboxymethyl-lysine (CML)-enriched bovine serum albumin (BSA) as alternatives to the classical approach using glyoxylic acid (GA) and sodium cyanoborohydride (NaBH₃CN) which results in toxic hydrogen cyanide (HCN). The reaction of GA (6 mmol/L) and NaBH₃CN (21 mmol/L) to produce CML remained the most effective with CML yields of 24-35%, followed by 13-24% using 300 mmol/L glyoxal (GO). GA promoted specific modification of lysine to CML, and fewer structural modifications of the BSA molecule compared with GO, as evidenced by fluorescence and proteomic analyses. GO promoted greater arginine modification compared with GA (76 vs 23%). Despite structural changes to BSA with GO, murine fecal clearance of CML was similar to literature values. Hence, BSA glycation with 300 mmol/L glyoxal is a suitable alternative to GA and NaBH₃CN for generating CML-enriched protein free of HCN, but a CML-only fortification model remains to be described.

Formation of advanced glycation end-products in minced pork during frozen-then-chilled storage and subsequent heating

The influences of frozen-then-chilled storage of minced pork on the formation of advanced glycation end-products (AGEs) including N^ε-carboxymethyllysine and N^ε-carboxyethyllysine, and their corresponding α-dicarbonyl precursors (α-DPs; glyoxal and methylglyoxal) during storage and subsequent heating were investigated in comparison with chilled storage. During cold storage, the levels of AGEs, trichloroacetic acid-soluble peptides, and Schiff bases in minced pork continuously increased while α-DPs decreased. The 30 min heating (100 °C) resulted in 64-560% increase of AGEs in pork, corresponding with an increase of Schiff bases and decreases of α-DPs. Compared to the chilled storage, the frozen-then-chilled storage led to no significant difference (P > 0.05) on the levels of AGEs and α-DPs in raw or heat-treated pork, implying that the formation and thawing of ice crystals in pork during the frozen-then-chilled storage had minor to no effects on the formation of AGEs and their α-DPs.

Dietary advanced glycation end-products (dAGEs) intake and its relation to sarcopenia and frailty - The Rotterdam Study

Studies on mice have shown a relationship between dietary intake of advanced glycation end-products (dAGEs) and deterioration of musculoskeletal health, but human studies are absent. We investigated the relationship between dietary intake of carboxymethyllysine (dCML) - an AGE prototype - and risk of sarcopenia at baseline and after 5 years of follow-up and a single evaluation of physical frailty in participants from the population-based Rotterdam Study. Appendicular lean mass (ALM) was obtained using insight dual-energy X-ray absorptiometry and hand grip strength (HGS) using a hydraulic hand dynamometer. Subjects with both low ALM and weak HGS were classified as having sarcopenia. Frailty (yes/no) was defined by presence of ≥3 and pre-frailty by presence of 1 or 2 components namely, exhaustion, weakness, slowness, weight loss or low physical activity. dCML was calculated using a food frequency questionnaire and dAGE databases. Logistic regression analysis was used to evaluate the odds of physical frailty and prevalent sarcopenia at baseline and follow-up and incident sarcopenia. 2782 participants with an age 66.4 ± 9.9 years and dCML intake 3.3 ± 1.3 mg/day, had data on sarcopenia at both time points. Of whom 84 had sarcopenia at baseline and 73 developed sarcopenia at follow-up. We observed an association of one SD increase in dCML intake with prevalent sarcopenia at baseline [odds ratio, OR = 1.27 (1.01-1.59)] and no association of dCML with incident sarcopenia at 5-year follow-up [OR = 1.12 (0.86-1.44)]. For frailty we analyzed 3577 participants, of whom 1972 were pre-frail and 158 were frail. We observed no association of dCML with either pre-frailty [OR = 0.99 (0.91-1.07)] or frailty [OR = 1.01 (0.83-1.22)] when non-frail subjects were used as reference. Our results show an association of dAGEs with sarcopenia cross-sectionally but not longitudinally where inconclusive findings are observed possibly due to a very low incidence of sarcopenia. There was no association with frailty cross-sectionally.

Heat-induced formation of advanced glycation end-products in ground pork as affected by the addition of acetic acid or citric acid and the storage duration prior to the heat treatments

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Organic acids affected advanced glycation end-product (AGE) levels in heated pork.

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Heat-induced AGEs in pork with citric acid (ca 0.5–1%) were reduced by 30–54%.

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Adding acetic acid at the same level led to 14–48% reduction of AGEs.

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The reduction of AGEs corresponded to decreased levels of TBARS and Schiff bases.

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Marinating time (pork & acid) did not affect the acid’s inhibiting effect for AGEs.

The heat-induced (121 °C, 10 or 30 min) formation of two potentially hazardous advanced glycation end-products (AGEs), protein-bound N^ɛ-carboxymethyllysine (CML) and N^ɛ-carboxyethyllysine (CEL), in pork as affected by citric or acetic acid (0.5, 1 g/100 pork) and the storage duration (0 °C, 0 – 8 d) prior to the heating was investigated. A longer storage time of raw pork resulted in higher levels of AGEs produced during the later heating, likely due to the accumulation of some AGE precursors during the storage. Depending on the acid level and heating time, adding acid in pork led to 30 – 54% (citric acid) or 14 – 48% (acetic acid) average reduction of heat-induced production of CML/CEL, which corresponded to the reduction of thiobarbituric acid reactive substances and Schiff bases. The marinating time of raw pork with an acid did not significantly affect (P = 0.959 – 0.998) the acid’s inhibition effect on heat-induced formation of CML/CEL.

Association Between the Tissue and Circulating Advanced Glycation End-Products and the Micro- and Macrovascular Complications in Type 1 Diabetes: The DIABAGE Study

INTRODUCTION

Type 1 diabetes is associated with an increased risk of vascular complications. We aimed to investigate the association between serum and tissue advanced glycation end-products (AGEs) and micro- and macrovascular complications in type 1 diabetes (T1D).

METHODS

We conducted a cross-sectional study on 196 adults with T1D (mean age 44.53 ± 16, mean duration of diabetes 22 ± 12 years, mean HbA1c 8 ± 1.2%). AGEs were measured in blood serum (i.e., carboxymethyllysine (CML), methylglyoxal-hydroimidazolone-1 (MGH1), and pentosidine) and by measurement of skin autofluorescence (SAF). Associations between AGEs levels and vascular complications were analyzed using binary logistic regression. Correlations between AGEs and pulse wave velocity (PWV) were also assessed by linear regressions. Significant differences were set for p values less than 0.05.

RESULTS

We found positive associations between different AGEs and vascular complications. SAF was associated with both microangiopathy (retinopathy: OR = 1.92, p = 0.011; neuropathy: OR = 2.02, p = 0.04; any microangiopathy: OR = 2.83, p < 0.0001) and macroangiopathy (coronaropathy: OR = 3.11, p = 0.009; any macroangiopathy: OR = 2.78, p = 0.003). For circulating AGEs, pentosidine was significantly associated with coronaropathy (OR = 1.61, p = 0.01) and any macroangiopathy (OR = 1.52, p = 0.005) while MGH1 was associated with nephropathy (OR 1.72, p = 0.03). Furthermore, a significant linear correlation was found between PWV and SAF (r = 0.43, p < 0.001), pentosidine (r = 0.28, p < 0.001), and MGH1 (r = 0.16, p = 0.031), but not for CML (r = 0.03, p = 0.598).

CONCLUSIONS

Skin autofluorescence appears to be a useful marker for investigating both micro- and macrovascular complications in T1D. In this study, pentosidine was associated with macroangiopathy and MGH1 with nephropathy among the circulating AGEs. Furthermore, the correlations between PWV and AGEs may suggest their value in early prediction of vascular complications in T1D.

Biophysical and mass spectrometry based characterization of methylglyoxal-modified myoglobin: Role of advanced glycation end products in inducing protein structural alterations

Methylglyoxal (MG) is a highly reactive α-dicarbonyl compound which reacts with proteins to form advanced glycation end products (AGEs). MG-induced AGE (MAGE) formation is particularly significant in diabetic condition. In the current study, we have undertaken a time-dependant characterization of MG-modified myoglobin following incubation of the heme protein with the α-dicarbonyl compound for different time periods. Interestingly, mass spectrometric studies indicated modifications at two specific lysine residues, Lys-87 and Lys-133. The AGE adducts identified at Lys-87 were carboxymethyllysine and carboxyethyllysine, while those detected at Lys-133 included pyrraline-carboxymethyllysine and carboxyethyllysine, respectively. Far-UV CD studies revealed a decrease in the native α-helical content of the heme protein gradually with increasing time of MG incubation. In addition, MG modification was found to induce changes in tertiary structure as well as surface hydrophobicity of the heme protein. MG-derived AGE adducts thus appear to alter the structure of Mb considerably. Considering the increased level of MG in diabetic condition, the current study appears physiologically relevant in terms of understanding AGE-mediated protein modification and subsequent structural changes.

Altered hepatic sphingolipid metabolism in insulin resistant mice: Role of advanced glycation endproducts

High plasma levels of the sphingolipid intermediates ceramide (Cer) and sphingosine-1-phosphate (S1P) are suggested to be involved in the development of insulin resistance (IR). Recent evidence indicates that advanced glycation endproducts (AGEs) can alter the sphingolipids metabolism equilibrium. Since enzymes responsible for sphingolipid rheostat maintenance are highly expressed in liver, we thus investigated whether AGEs accumulation can affect hepatic sphingolipids metabolism in insulin resistant mice. Two different models of IR were examined: genetically diabetic LeptrDb-/- (DbDb) and diet-induced insulin resistant C57Bl/6J mice fed a 60% trans-fat diet (HFD). In addition, a group of HFD mice was supplemented with the anti-AGEs compound pyridoxamine. AGEs were evaluated in the liver by western blotting. Cer and S1P were measured by UHPLC-MS/MS. The expression of RAGE and of enzymes involved in sphingolipid metabolism were assessed by RT-PCR and western blotting. HepG2 cells were used to study the effect of the major AGE Nε-(carboxymethyl)lysine (CML)-albumin on sphingolipid metabolism and the role of the receptor of AGEs (RAGE). High levels of AGEs and RAGE were detected in the liver of both DbDb and HFD mice in comparison to controls. The expression of enzymes of sphingolipid metabolism was altered in both models, accompanied by increased levels of Cer and S1P. Specifically, ceramide synthase 5 and sphingosine kinase 1 were increased, while neutral ceramidase was reduced. Pyridoxamine supplementation to HFD mice diminished hepatic AGEs and prevented alterations of sphingolipid metabolism and the development of IR. CML administration to HepG2 cells evoked alterations similar to those observed in vivo, that were in part mediated by the binding to RAGE. The present study shows a direct involvement of AGEs in alterations of sphingolipid metabolism associated to the development of IR. The modulation of sphingolipids metabolism through the prevention of AGEs accumulation by pyridoxamine may reduce the development of IR.

Association of dietary intake, medication and anthropometric indices with serum levels of advanced glycation end products, caspase-3, and matrix metalloproteinase-9 in diabetic patients

Background and objective

Increased serum levels of advanced glycation end products (AGEs), caspase-3 (Cas-3) and matrix metalloproteinase-9 (MMP-9) have been reported in diabetic patients. This study aimed to evaluate association of anthropometric, dietary, and therapeutic factors with serum levels of methylglyoxal (MGO), carboxymethyl lysine (CML), pentosidine (Pen), Cas-3, and MMP-9 in diabetic patients.

Methods

The current study included 36 diabetic subjects. Dietary intake of the participants was assessed using three-day 24-h recall survey and anthropometric indices were measured. Demographic factors and medication intake of every subject were obtained. Serum levels of CML, MGO, Pen, MMP-9, and Cas-3 were measured using ELISA method.

Results

Gliclazide consumption was positively correlated with MMP-9 and Cas-3, but not AGEs levels. Females had higher MGO level compared with males. Further, CML levels were negatively correlated with BMI and WHR. Dietary protein intake was positively correlated with MMP-9, Cas-3, and MGO levels. As well as dietary energy and fat intake had significant positive relationship with serum Cas-3 concentration.

Conclusion

It is concluded that anthropometric characteristics, dietary intake, and therapeutic medications are possible factors that may determine the circulating levels of AGEs, MMP-9, and Cas-3 in patients with diabetes.

Metabolic transit of dietary advanced glycation end-products - the case of NƐ-carboxymethyllysine

The Maillard reaction, also called glycation, is one of the major chemical reactions responsible for most yellow-to-brown colors and aromas in cooked foods. This reaction between reducing sugars and amino functions on proteins affects not only the flavor of food, but also leads to the formation of an heterogenous group of structurally-modified amino acids. Some of these, known as "advanced glycation end products" (AGEs), have been found in both foods and human biological fluids, tissues and organs. Except for those that are formed over long periods in vivo at 37 °C, AGEs in the body originate from the digestion and absorption of dietary sources. A high or chronic exposure to dietary AGEs (dAGEs) is suspected as potentially detrimental to human health and studies in the field of food safety have begun to focus their attention on the metabolic transit of dAGEs. This review presents some important findings in this field, with a focus on N^Ɛ-carboxymethyllysine, and presents the evidence for and against an association between intake of dAGEs and their presence in the body. New and promising avenues of research are described, and some future directions outlined.

Advanced glycation end products and protein carbonyl levels in plasma reveal sex-specific differences in Parkinson's and Alzheimer's disease

Neurodegenerative diseases (NDD) such as Alzheimer's (AD) and Parkinson's disease (PD) are distinct clinical entities, however, the aggregation of key neuronal proteins, presumably leading to neuronal demise appears to represent a common mechanism. It has become evident, that advanced glycation end products (AGEs) trigger the accumulation of such modified proteins, which eventually contributes to pathological aspect of NDDs. Increased levels of AGEs are found in amyloid plaques in AD brains and in both advanced and early PD (incidental Lewy body disease). The molecular mechanisms by which AGE dependent modifications may modulate the susceptibility towards NDDs, however, remain enigmatic and it is unclear, whether AGEs may serve as biomarker of NDD. In the present study, we examined AGEs (CML: Carboxymethyllysine and CEL: Carboxyethyllysine), markers of oxidative stress and micronutrients in the plasma of PD and AD patients and controls. As compared to healthy controls, AD females displayed lower levels of CEL while higher levels of CML were found in AD and PD patients. A somewhat similar pattern was observed for protein carbonyls (PC), revealing lower values exclusively in AD females, whereas AD males displayed significantly higher values compared to healthy controls and PD. Sex-specific differences were also observed for other relevant markers such as malondialdehyde, 3-nitrotyrosine, γ -tocopherols, retinol, plasma proteins and α-carotene, while α-tocopherols, β-carotene, lutein/zeaxanthin, β-cryptoxanthin and lycopene showed no relevant association. Taken together, our study suggests yet unappreciated differences of the distribution of AGEs among the sexes in NDD. We therefore suggest to make a clear distinction between sexes when analyzing oxidative (AGEs)-related stress and carbonyl-related stress and vitamins.

Vitamin D and advanced glycation end products and their receptors

Advanced glycation end products (AGEs) are destructive molecules in the body that, at high levels, contribute to the progression of various chronic diseases. Numerous studies have suggested a modifying effect of vitamin D on AGEs and their receptors. This study sought to summarize the effects of vitamin D on AGEs and their receptors, including receptor for AGEs (RAGE) and soluble receptor for AGEs (sRAGE). The search method initially identified 484 articles; 331 remained after duplicate removal. Thirty-five articles were screened and identified as relevant to the study topic. After critical analysis, 27 articles were included in the final analysis. Vitamin D treatment may possibly be beneficial to reduce AGE levels and to augment sRAGE levels, particularly in vitamin D-deficient situations. Treatment with this vitamin may be effective in reducing RAGE expression in some disease conditions, but might be even harmful under normal conditions. The inhibitory or stimulatory effects of vitamin D on AGE receptors are mediated by various signaling pathways, MAPK/NF-κB, ADAM10/MMP9 and AT1R. In populations with chronic diseases and concomitant hypovitaminosis D, vitamin D supplementation can be used as a strategy to ameliorate AGE-mediated complications by modifying the AGE-RAGE and sRAGE systems.

Formation of Pentosidine Cross-Linking in Myoglobin by Glyoxal: Detection of Fluorescent Advanced Glycation End Product

Glyoxal, a reactive α-oxoaldehyde, increases in diabetic condition and reacts with proteins to form advanced glycation end products (AGEs) following Maillard-like reaction. Considering the significance of protein modification by glyoxal-derived AGEs, we investigated the in vitro effect of glyoxal (200 μM) on the monomeric heme protein myoglobin (Mb) (100 μM) after incubation for one week at 25 °C. Glyoxal-treated Mb exhibited increased absorbance around the Soret region, decreased α-helicity and thermal stability compared to control Mb. Intrinsic fluorescence spectrum of the treated Mb showed an additional signal in the 400-500 nm region on excitation at 280 nm that was absent in control Mb. When excited at 335 nm, the glyoxal-treated sample gave a strong fluorescence indicating AGE formation. Mass spectrometric studies revealed formation of glyoxal-derived fluorescent AGE adduct pentosidine between Lys-145 and Arg-139 residues of Mb. Other than pentosidine, additional AGE adducts, namely, carboxymethyllysine at Lys-133, hydroimidazolone at Arg-31 and pyrrolidone-carboxymethyllysine at Lys-145 were also detected. Lys-145 was thus found to contain two different types of AGE adducts, indicating the heterogeneous nature of in vitro glycation reaction. AGE-induced protein modifications might be associated with complications in disease conditions.

Quantitative assessment of organ distribution of dietary protein-bound 13 C-labeled Nɛ -carboxymethyllysine after a chronic oral exposure in mice

SCOPE

N^ɛ -Carboxymethyl-lysine (CML) is a prominent advanced glycation end-product which is not only found in vivo but also in food. It is known that a percentage of the dietary CML (dCML) is absorbed into the circulation and only partly excreted in the urine. Several studies have tried to measure how much dCML remains in tissues. However obstacles to interpreting the data have been found.

METHODS AND RESULTS

A new protocol which discriminates dCML from native CML (nCML) has been developed. Three CML isotopes with different mass-to-charge ratios were used: nCML N^ε -carboxymethyl-L-lysine, dCML N^ε -[¹³ C]carboxy[¹³ C]methyl-L-lysine and internal standard N^ε -carboxymethyl-L-[4,4,5,5-² H₄ ]lysine. Wild-type (n = 7) and RAGE^-/- (n = 8) mice were fed for 30 days with either a control, or a BSA-bound dCML-enriched diet. Organs were analyzed for nCML and dCML using liquid chromatography-tandem mass spectrometry. Mice exposed to dCML showed an accumulation in all tissues tested except fat. The rate of deposition was high (81-320 μg_dCML /g dry matter) in kidneys, intestine, and lungs and low (<5 μg/g) in heart, muscle, and liver. This accumulation was not RAGE dependent.

CONCLUSION

The kidney is not the only organ affected by the accumulation of dCML. Its high accumulation in other tissues and organs may also, however, have important physiological consequences.

Advanced glycation end products induce differential structural modifications and fibrillation of albumin

Glycation induced amyloid fibrillation is fundamental to the development of many neurodegenerative and cardiovascular complications. Excessive non-enzymatic glycation in conditions such as hyperglycaemia results in the increased accumulation of advanced glycation end products (AGEs). AGEs are highly reactive pro-oxidants, which can lead to the activation of inflammatory pathways and development of oxidative stress. Recently, the effect of non-enzymatic glycation on protein structure has been the major research area, but the role of specific AGEs in such structural alteration and induction of fibrillation remains undefined. In this study, we determined the specific AGEs mediated structural modifications in albumin mainly considering carboxymethyllysine (CML), carboxyethyllysine (CEL), and argpyrimidine (Arg-P) which are the major AGEs formed in the body. We studied the secondary structural changes based on circular dichroism (CD) and spectroscopic analysis. The AGEs induced fibrillation was determined by Congo red binding and examination of scanning and transmission electron micrographs. The amyloidogenic regions in the sequence of BSA were determined using FoldAmyloid. It was observed that CEL modification of BSA leads to the development of fibrillar structures, which was evident from both secondary structure changes and TEM analysis.

RAGE-mediated inflammation in patients with septic shock

BACKGROUND

The receptor for advanced glycation end-products (RAGE)-pathway is described to be a crucial component of the innate immune response in sepsis. The aims of the present study were, therefore, to delineate the kinetics of membrane-bound RAGE expression, to quantify its soluble isoforms, and to determine the extent of metabolic (e.g., AGE-CML) as well as immunologic (e.g., S100A8/A9) ligands in different inflammatory settings in humans.

MATERIALS AND METHODS

The presented data result from secondary analyses of an observational clinical pilot study, including patients with septic shock (n = 60), postoperative controls (n = 30), and healthy volunteers (n = 30). Surface-bound expression of RAGE by peripheral blood leukocytes was determined by flow cytometry. In addition, plasma levels of sRAGE, esRAGE, AGE-CML, S100A8/A9, S100A8/A9-CML, RBP, RBP-CML, HSA-CML, HMBG-1, and ß-Amyloid were measured using ELISA.

RESULTS

In patients with septic shock, RAGE expression was significantly increased in comparison to both control groups, which was paralleled by a significant increase in sRAGE plasma levels. Formation of AGE-CML was shown to be dependent on the availability of the unmodified protein. However, the total amount of AGE-CML did not differ significantly between septic patients and healthy volunteers at early stages or was even lower in patients with sepsis at later stages. In contrast, immunologic ligands (e.g., S100A8/A9) were shown to be significantly elevated in septic patients within the entire study period.

CONCLUSIONS

Activation of the RAGE-pathway was shown to be of relevance in patients with septic shock, mainly driven by an increase in immunologic (e.g., S100A8/A9) rather than metabolic ligands (e.g., CML-derived AGE-formation).

Advanced Glycation-Modified Human Serum Albumin Evokes Alterations in Membrane and Eryptosis in Erythrocytes

Increased burden of advanced glycation end-products (AGEs) in case of hyperglycemic conditions leads to the development of retinopathy, nephropathy, and cardiovascular and neurological disorders such as Alzheimer's disease. AGEs are considered as pro-oxidants, and their accumulation increases the oxidative stress. The prolonged exposure to these AGEs is the fundamental cause of chronic oxidative stress. Abnormal morphology of red blood cells (RBCs) and excessive eryptosis has been observed in diabetes, glomerulonephritis, dyslipidemia, and obesity, but yet the contribution of extracellular AGEs remains undefined. In this study, we investigated the effect of AGEs on erythrocytes to determine their impact on the occurrence of different pathological forms of these blood cells. Specifically, carboxymethyllysine (CML), carboxyethyllysine (CEL), and Arg-pyrimidine (Arg-P) which have been reported to be the most pre-dominant AGEs formed under in vivo conditions were used in this study. Results suggested the eryptotic properties of CML, CEL, and Arg-P for RBCs, which were evident from the highly damaged cell membrane and occurrence of abnormal morphologies. Methylglyoxal-modified albumin showed more severe effects, which can be attributed to the high reactivity and pro-oxidant nature of glycation end products. These findings suggest the possible role of AGE-modified albumin towards the morphological changes in erythrocyte's membrane associated with diabetic conditions.

Impact of Oxidative Stress Biomarkers and Carboxymethyllysine (an Advanced Glycation End Product) on Prostate Cancer: A Prospective Study

OBJECTIVE

Biomarkers of oxidative stress and advanced glycation end products (AGE) have been linked to the development of prostate cancer, but evidence from human studies is scarce or controversial.

METHODS

We conducted a prospective nested case-control study among 48 men (24 prostate cancer cases and 24 controls) aged 48 to 76 years at baseline. The participants of our study were a part of the Fernald Community Cohort. Prostate cancer cases and controls were matched individually on age (± 3 years) with a 1:1 ratio. Biomarkers included urine F2-isoprostanes (markers of lipid oxidation), plasma fluorescent oxidation products (markers of global oxidation), and carboxymethyllysine (CML) (a major end-stage AGE).

RESULTS

At baseline, cases had similar age, body mass index, proportion of family history of prostate cancer, history of benign prostatic hyperplasia, history of hypertension, history of diabetes, number of smokers, and plasma glucose levels compared with controls. Levels of plasma CML were significantly higher in cases than in controls (182 vs. 152 μg/mL, P < .05). In the conditional logistic regression model, an increase in CML equivalent to 1 standard deviation was associated with an increased risk of incident prostate cancer (relative risk, 1.79; 95% confidence interval, 1.00-3.21) and accounted for approximately 8% variance of prostate cancer liability. Urine F2-isoprostanes and plasma fluorescent oxidation products were not associated with prostate cancer incidence.

CONCLUSIONS

Higher levels of plasma CML were associated with increased risk of prostate cancer. This suggests a potential new pathway for prostate cancer prediction and treatment.

Hydroxyl radical induced by lipid in Maillard reaction model system promotes diet-derived N(ε)-carboxymethyllysine formation

N(ε)-carboxymethyllysine (CML) is commonly found in food, and is considered as a potential hazard to human health. However, the effect of lipids on CML formation in Maillard reaction is still not clarified. In this study, the content of diet-derived CML and its key intermediates, epsilon-fructoselysine (FL) and glyoxal (GO), is determined with high performance liquid chromatography mass spectrum (HPLC-MS) in model system containing lipid compounds. According to the results, hydroxyl radical (OH) induced by Fenton reagent can promote the three pathways of CML formation. Moreover, in the Maillard reaction system, linoleic acid (Lin), oleic acid (Ole) and glycerol trioleate (Tri) can induce more OH·, which promotes CML formation. Their level of promoting CML formation is in the order of Ole>Lin>Tri. On the contrary, glycerol (Gly) can scavenge OH·, which inhibit the CML formation. Finally, it is proved that FL content and GO content decreases with heating time in model system, while CML content increases with heating time. Thus, it is concluded that in the Maillard reaction system lipids can induce more OH·, which promotes the conversion from FL and GO to CML. Our research may contribute to the development of inhibitory methods for diet-derived CML by scavenging OH·.