OBJECTIVE: Advanced glycation end products (AGEs) play a role in kidney disease in type 2 diabetes mellitus (T2DM). However, there have been no prior controlled clinical trials examining the effects of specific diets on AGE metabolism and their impact on kidney function. Our aim was to assess whether modulating AGE metabolism resulting in reduced AGEs levels, after consumption of two healthy diets, could delay kidney function decline in patients with T2DM and coronary heart disease (CHD).
METHODS: T2DM patients (540 out of 1002 patients from the CORDIOPREV study), with estimated glomerular filtration rate (eGFR) ≥ 30 ml/min/1.73 m2, were classified based on their baseline kidney function: normal eGFR (≥ 90 ml/min/1.73 m2), mildly decreased eGFR (60- < 90 ml/min/1.73 m2) and moderately decreased eGFR (<60 ml/min/1.73 m2). Serum AGE levels, methylglyoxal (MG) and N-carboximethyllysine (CML), and gene expression related to AGE metabolism (AGER1, RAGE, and GloxI mRNA) were measured before and after 5-years of dietary intervention (a Mediterranean diet or a low-fat diet).
RESULTS: Mediterranean diet produced a lower declined of eGFR compared to the low-fat diet only in patients with mildly decreased eGFR (P = 0.035). Moreover, Mediterranean diet was able to decrease MG levels and increase GloxI expression in normal and mildly decreased eGFR patients (all P < 0.05). One standard deviation increment of MG levels after dietary intervention resulted in a 6.8-fold (95 % CI 0.039;0.554) higher probability of eGFR decline.
CONCLUSIONS: Our study showed that lowering circulating AGE levels, specifically MG, after following a Mediterranean diet, might be linked to the preservation of kidney function, evidenced by a decreased decline of eGFR in T2DM patients with CHD. Patients with mildly decreased eGFR could potentially benefit more from AGE reduction in maintaining kidney function.

Reactive α-dicarbonyls (α-DCs), such as methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG), are potent precursors in the formation of advanced glycation end products (AGEs). In particular, MGO and MGO-derived AGEs are thought to be involved in the development of vascular complications in diabetes. Experimental studies showed that citrus and pomegranate polyphenols can scavenge α-DCs. Therefore, the aim of this study was to evaluate the effect of a citrus and pomegranate complex (CPC) on the α-DCs plasma levels in a double-blind, placebo-controlled cross-over trial, where thirty-six elderly subjects were enrolled. They received either 500 mg of Citrus sinensis peel extract and 200 mg of Punica granatum concentrate in CPC capsules or placebo capsules for 4 weeks, with a 4-week washout period in between. For the determination of α-DCs concentrations, liquid chromatography tandem mass spectrometry was used. Following four weeks of CPC supplementation, plasma levels of MGO decreased by 9.8% (-18.7 nmol/L; 95% CI: -36.7, -0.7 nmol/L; p = 0.042). Our findings suggest that CPC supplementation may represent a promising strategy for mitigating the conditions associated with MGO involvement. This study was registered on clinicaltrials.gov as NCT03781999.

Dicarbonyls are reactive precursors of advanced glycation end-products (AGEs). Dicarbonyls are formed endogenously, but also during food processing. Circulating dicarbonyls are positively associated with insulin resistance and type 2 diabetes, but the consequences of dietary dicarbonyls are unknown.
We aimed to examine the associations of dietary intake of dicarbonyls with insulin sensitivity, β-cell function, and the prevalence of prediabetes or type 2 diabetes.
In 6282 participants (aged 60 ± 9 y; 50% men, 23% type 2 diabetes [oversampled]) of the population-based cohort the Maastricht Study, we estimated the habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) using food frequency questionnaires. Insulin sensitivity (n = 2390), β-cell function (n = 2336), and glucose metabolism status (n = 6282) were measured by a 7-point oral glucose tolerance test. Insulin sensitivity was assessed as the Matsuda index. Additionally, insulin sensitivity was measured as HOMA2-IR (n = 2611). β-cell function was assessed as the C-peptidogenic index, overall insulin secretion, glucose sensitivity, potentiation factor, and rate sensitivity. Cross-sectional associations of dietary dicarbonyls with these outcomes were investigated using linear or logistic regression adjusting for age, sex, cardiometabolic risk factors, lifestyle, and dietary factors.
Higher dietary MGO and 3-DG intakes were associated with greater insulin sensitivity after full adjustment, indicated by both a higher Matsuda index (MGO: Std. β [95% CI] = 0.08 [0.04, 0.12]; 3-DG: 0.09 [0.05, 0.13]) and a lower HOMA2-IR (MGO: Std. β = -0.05 [-0.09, -0.01]; 3-DG: -0.04 [-0.08, -0.01]). Moreover, higher MGO and 3-DG intakes were associated with a lower prevalence of newly diagnosed type 2 diabetes (OR [95% CI] = 0.78 [0.65, 0.93] and 0.81 [0.66, 0.99]). There were no consistent associations of MGO, GO, and 3-DG intakes with β-cell function.
Higher habitual consumption of the dicarbonyls MGO and 3-DG was associated with better insulin sensitivity and lower prevalence of type 2 diabetes, after excluding individuals with known diabetes. These novel observations warrant further exploration in prospective cohorts and intervention studies.

Dicarbonyls are major reactive precursors of advanced glycation endproducts (AGEs). Dicarbonyls are formed endogenously and also during food processing. Circulating dicarbonyls and AGEs are associated with inflammation and microvascular complications of diabetes, but for dicarbonyls from the diet these associations are currently unknown.
We sought to examine the associations of dietary dicarbonyl intake with low-grade inflammation and microvascular function.
In 2792 participants (mean ± SD age: 60 ± 8 y; 50% men; 26% type 2 diabetes) of the population-based cohort the Maastricht Study, we estimated the habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) by linking FFQ outcome data to our food composition database of the MGO, GO, and 3-DG content of >200 foods. Low-grade inflammation was assessed as six plasma biomarkers, which were compiled in a z score. Microvascular function was assessed as four plasma biomarkers, compiled in a zscore; as diameters and flicker light-induced dilation in retinal microvessels; as heat-induced skin hyperemic response; and as urinary albumin excretion. Cross-sectional associations of dietary dicarbonyls with low-grade inflammation and microvascular function were investigated using linear regression with adjustments for age, sex, potential confounders related to cardiometabolic risk factors, and lifestyle and dietary factors.
Fully adjusted analyses revealed that higher intake of MGO was associated with a lower z score for inflammation [standardized β coefficient (STD β): -0.05; 95% CI: -0.09 to -0.01, with strongest inverse associations for hsCRP and TNF-α: both -0.05; -0.10 to -0.01]. In contrast, higher dietary MGO intake was associated with impaired retinal venular dilation after full adjustment (STD β: -0.07; 95% CI: -0.12 to -0.01), but not with the other features of microvascular function. GO and 3-DG intakes were not consistently associated with any of the outcomes.
Higher habitual intake of MGO was associated with less low-grade inflammation. This novel, presumably beneficial, association is the first observation of an association between MGO intake and health outcomes in humans and warrants further investigation.

BACKGROUND: 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.

Dicarbonyls are highly reactive compounds and major precursors of advanced glycation end products (AGEs). Both dicarbonyls and AGEs are associated with development of age-related diseases. Dicarbonyls are formed endogenously but also during food processing. To what extent dicarbonyls from the diet contribute to circulating dicarbonyls and AGEs in tissues is unknown.
To examine cross-sectional associations of dietary dicarbonyl intake with plasma dicarbonyl concentrations and skin AGEs.
In 2566 individuals of the population-based Maastricht Study (age: 60 ± 8 y, 50% males, 26% with type 2 diabetes), we estimated habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) by combining FFQs with our dietary dicarbonyl database of MGO, GO, and 3-DG concentrations in > 200 commonly consumed food products. Fasting plasma concentrations of MGO, GO, and 3-DG were measured by ultra-performance liquid chromatography-tandem mass spectrometry. Skin AGEs were measured as skin autofluorescence (SAF), using the AGE Reader. Associations of dietary dicarbonyl intake with their respective plasma concentrations and SAF (all standardized) were examined using linear regression models, adjusted for age, sex, potential confounders related to cardiometabolic risk factors, and lifestyle.
Median intake of MGO, GO, and 3-DG was 3.6, 3.5, and 17 mg/d, respectively. Coffee was the main dietary source of MGO, whereas this was bread for GO and 3-DG. In the fully adjusted models, dietary MGO was associated with plasma MGO (β: 0.08; 95% CI: 0.02, 0.13) and SAF (β: 0.12; 95% CI: 0.07, 0.17). Dietary GO was associated with plasma GO (β: 0.10; 95% CI: 0.04, 0.16) but not with SAF. 3-DG was not significantly associated with either plasma 3-DG or SAF.
Higher habitual intake of dietary MGO and GO, but not 3-DG, was associated with higher corresponding plasma concentrations. Higher intake of MGO was also associated with higher SAF. These results suggest dietary absorption of MGO and GO. Biological implications of dietary absorption of MGO and GO need to be determined. The study has been approved by the institutional medical ethical committee (NL31329.068.10) and the Minister of Health, Welfare and Sports of the Netherlands (Permit 131088-105234-PG).

Despite more than 100 years of research, formation of food melanoidins from carbohydrates and amino acids in the course of the Maillard reaction is still not fully understood. Experiments with relevant precursors are commonly used to limit the pathways of the complex reaction and to elucidate the formation mechanisms of the colored end-products. Here as a simple model, methylglyoxal was incubated with l-alanine or l-lysine in aqueous solutions at 100 °C and pH 5. The reaction mixtures were analyzed for color formation, molecular weight distribution, and conversion of methylglyoxal. High-resolution mass spectrometry was used to characterize the variety of products formed. With the help of Kendrick and van Krevelen analyses, the complex data sets were investigated for common substructures and reaction patterns. This study revealed that methylglyoxal forms oligomers via aldol reaction under involvement of its prevalent reaction products such as formaldehyde, acetaldehyde, acetol, and aminoacetone with amino acids.

BACKGROUND: Increased oxidative/dicarbonyl stress and chronic inflammation are considered key pathophysiological mediators in the progression of complications in obesity and type 2 diabetes (T2D). Lifestyle and diet composition have a major impact. In this study, we tested the effects of a vegan (V) and a conventional meat containg (M) meal, matched for energy and macronutrients, on postprandial oxidative and dicarbonyl stress, inflammatory markers and appetite hormones.
METHODS: A randomised crossover design was used to evaluate T2D, obese with normal glucose tolerance and control participants (n = 20 in each group), with serum concentrations of analytes determined at 0, 120 and 180 min. Repeated-measures ANOVA was used for statistical analysis.
RESULTS: In T2D subjects, we observed decreased postprandial concentrations of oxidised glutathione (p ˂ 0.001) and increased glutathione peroxidase activity (p = 0.045) after the V-meal consumption, compared with the M-meal. In obese participants, V-meal consumption increased postprandial concentrations of reduced glutathione (p = 0.041) and decreased methylglyoxal concentrations (p = 0.023). There were no differences in postprandial secretion of TNFα, MCP-1 or ghrelin in T2D or obese men, but we did observe higher postprandial secretion of leptin after the V-meal in T2D men (p = 0.002) compared with the M-meal.
CONCLUSIONS: The results show that a plant-based meal is efficient in ameliorating the postprandial oxidative and dicarbonyl stress compared to a conventional energy- and macronutrient-matched meal, indicating the therapeutic potential of plant-based nutrition in improving the progression of complications in T2D and obese patients. Registered under ClinicalTrials.gov Identifier No. NCT02474147.

Hypoxia and inflammation are hallmarks of critical illness, related to multiple organ failure. A possible mechanism leading to multiple organ failure is hypoxia- or inflammation-induced down-regulation of the detoxifying glyoxalase system that clears dicarbonyl stress. The dicarbonyl methylglyoxal (MGO) is a highly reactive agent produced by metabolic pathways such as anaerobic glycolysis and gluconeogenesis. MGO leads to protein damage and ultimately multi-organ failure. Whether detoxification of MGO into D-lactate by glyoxalase functions appropriately under conditions of hypoxia and inflammation is largely unknown. We investigated the effect of inflammation and hypoxia on the MGO pathway in humans in vivo.
After prehydration with glucose 2.5% solution, ten healthy males were exposed to hypoxia (arterial saturation 80-85%) for 3.5 h using an air-tight respiratory helmet, ten males to experimental endotoxemia (LPS 2 ng/kg i.v.), ten males to LPS+hypoxia and ten males to none of these interventions (control group). Serial blood samples were drawn, and glyoxalase-1 mRNA expression, MGO, methylglyoxal-derived hydroimidazolone-1 (MG-H1), D-lactate and L-lactate levels, were measured serially.
Glyoxalase-1 mRNA expression decreased in the LPS (β (95%CI); -0.87 (-1.24; -0.50) and the LPS+hypoxia groups; -0.78 (-1.07; -0.48) (P<0.001). MGO was equal between groups, whereas MG-H1 increased over time in the control group only (P=0.003). D-Lactate was increased in all four groups. L-Lactate was increased in all groups, except in the control group.
Systemic inflammation downregulates glyoxalase-1 mRNA expression in humans. This is a possible mechanism leading to cell damage and multi-organ failure in critical illness with potential for intervention.

Glyoxalase 1 (Glo1) is the rate-limiting enzyme in the detoxification of methylglyoxal (MGO) into D-lactate. MGO is a major precursor of advanced glycation endproducts (AGEs), and both are associated with development of age-related diseases. Since genetic variation in GLO1 may alter the expression and/or the activity of Glo1, we examined the association of nine SNPs in GLO1 with Glo1 expression and markers of MGO stress (MGO in fasting plasma and after an oral glucose tolerance test, D-lactate in fasting plasma and urine, and MGO-derived AGEs CEL and MG-H1 in fasting plasma and urine). We used data of the Cohort on Diabetes and Atherosclerosis Maastricht (CODAM, n = 546, 60 ± 7 y, 25% type 2 diabetes). Outcomes were compared across genotypes using linear regression, adjusted for age, sex, and glucose metabolism status. We found that SNP4 (rs13199033) was associated with Glo1 expression (AA as reference, standardized beta AT = -0.29, p = 0.02 and TT = -0.39, p = 0.3). Similarly, SNP13 (rs3799703) was associated with Glo1 expression (GG as reference, standardized beta AG = 0.17, p = 0.14 and AA = 0.36, p = 0.005). After correction for multiple testing these associations were not significant. For the other SNPs, we observed no consistent associations over the different genotypes. Thus, polymorphisms of GLO1 were not associated with Glo1 expression or markers of MGO stress, suggesting that these SNPs are not functional, although activity/expression might be altered in other tissues.