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Aims: Dicarbonyl compounds contribute to the formation of advanced glycation endproducts (AGEs) and the development of insulin resistance and vascular complications. Dicarbonyl stress may already be detrimental in obesity. We evaluated whether diet-induced weight loss can effectively reverse dicarbonyl stress in abdominally obese men. Materials and methods: Plasma samples were collected from lean (n = 25) and abdominally obese men (n = 52) in the fasting state, and during a mixed meal test (MMT). Abdominally obese men were randomized to 8 weeks of dietary weight loss or habitual diet, followed by a second MMT. The α-dicarbonyls methylglyoxal (MGO), glyoxal (GO) and 3-deoxyglucosone (3-DG) and AGEs were measured by UPLC-MS/MS. Skin autofluorescence (SAF) was measured using the AGE reader. T-tests were used for the cross-sectional analysis and ANCOVA to assess the treatment effect. Results: Postprandial glucose, MGO and 3-DG concentrations were higher in obese men as compared to lean men (p < 0.05 for all). Fasting dicarbonyls, AGEs, and SAF were not different between lean and obese men. After the weight loss intervention, fasting MGO levels tended to decrease by 25 nmol/L (95%-CI: -51-0.5; p = 0.054). Postprandial dicarbonyls were decreased after weight loss as compared to the control group: iAUC of MGO decreased by 57% (5280 nmol/L∙min; 95%-CI: 33–10526; p = 0.049), of GO by 66% (11,329 nmol/L∙min; 95%-CI: 495–22162; p = 0.041), and of 3-DG by 45% (20,175 nmol/L∙min; 95%-CI: 5351–35000; p = 0.009). AGEs and SAF did not change significantly after weight loss. Conclusion: Abdominal obesity is characterized by increased postprandial dicarbonyl stress, which can be reduced by a weight loss intervention. Registered under ClinicalTrials.gov Identifier no. NCT01675401.

Carbonyl stress and accumulation of advanced glycation end-products (AGEs) in human tissues are involved in diabetic complications, atherosclerosis, Alzheimer's disease and aging. The objective of this study was to evaluate the in vitro protective effect of aqueous extracts of coffee silverskin (CS) in the formation of AGEs and trapping of carbonyl reactive species such as methylglyoxal (MGO). Aqueous extracts of CS from Arabica and Robusta coffee varieties were obtained under environment friendly extraction conditions. CS extracts were characterized by the analysis of dietary fiber, caffeine, chlorogenic acids (CGAs), total phenolic compounds, browning, melanoidins, and antioxidant capacity. CS extracts and CGA exhibited a dose-dependent anti-AGE capacity in the protein–glucose model system (37 °C/21 days) with an IC50 of 0.6 mg/mL and 0.4 mg/mL, respectively. Caffeine did not prevent AGE formation under the studied conditions. Regardless to protein–MGO assay (37 °C/14 days), the anti-AGE capacity of CS extracts and CGA was also dose-dependent with an IC50 of 1.3 mg/mL and 0.1 mg/mL, respectively. Caffeine weakly inhibited the reaction of protein and MGO. The MGO trapping capacity was established as a model for protection against carbonyl stress. Robusta CS was very effective for the direct trapping of MGO with an IC50 of 0.055 mg/mL as compared with Arabica CS (IC50 of 0.6 mg/mL). CGA and caffeine showed an IC50 for MGO trapping capacity of 0.14 mg/mL and > 10 mg/mL, respectively. The highest CGA content in the Robusta CS extract could explain its higher MGO trapping activity as compared with the Arabica CS extract. The anti-AGE and MGO trapping capacities of CS may be associated to other chemical components besides CGA. In conclusion, aqueous CS extract may be considered as a natural source of inhibitors of in vitro formation of AGEs and carbonyl stress. The inhibitory effect of the coffee extracts may be associated to their carbonyl trapping capacity.