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Comment on Linkens, et al.

Submitter: Jaime Uribarri | Jaime.uribarri@mountsinai.org

Authors: Manuel Portero-Otin, M. Pia de la Maza, Michal S. Beeri, Jaime Uribarri

Published December 16, 2022

We have several concerns about the authors’ conclusion that a high dietary AGE intervention may not negatively affect humans (1), contradicting several previous studies (2-5), and we respectfully wish to raise several issues that might help interpretation of these results.  

First, as remarked by the authors, their low AGE diets were “obtained without drastically altering food preparation methods …”, while changes in cooking of food has been the essential intervention of most prior published clinical trials (2-6).  AGE databases employed in the present study differ in the content of several AGE products that, due to the use of MS-based methods, are not comparable to many cellular, animal and human studies based on ELISA (3-5). For instance, cereals and meats contributed 37% and 27% of CML intake in the current study (1), while the respective percentages were 1% and 65% in previous interventions (3-5). Thus, one may legitimately doubt whether these “low AGE” or “high AGE” diets here were assessing different chemical entities unrelated to those based on peptide- and lipid-bound AGEs by ELISA, which have previously been shown to produce clinically demonstrable effects including insulin resistance (4-5).

Second, serum protein-bound AGEs did not change across the two dietary regimes. It is possible that previously reported effects of low-AGE diets in other studies are mainly due to the modification of circulating proteome by AGE products, which in this case was not measured. Indeed, previous data from randomized-controlled trials where the low AGE regimes showed beneficial effects induced a significant decrease in the protein-bound bioaccessible AGE content detected by antibodies (2-5). The lack of effect in serum protein-bound AGEs in the current report reinforces that these different studies are measuring different parameters and strongly suggest that in tandem comparions of MS-based and ELISA methods might be important to clarify these issues in future studies.

Third, the “low AGE” diet group already had a higher intake of AGEs at baseline in the diet, so epigenetic changes induced by these AGEs cannot be discarded. In a way, this intervention was ineffective since it did not significantly affect plasma and urinary AGE levels, while the high AGE diet did only for the free AGEs (Ref 1; Supplemental Table 4).

Fourth, the length of the current study, only 4 weeks, is an important limitation since one would not have expected effects on vascular tissues and even on insulin resistance during that short period of time.

References

1. Linkens AMA et al. A 4-week high-AGE diet does not impair glucose metabolism and vascular function in obese individuals. JCI insight 2022; 7(6)e156950
2. Uribarri J, Peppa M, Godlberg T, Cai W, Lu M, He C, Vlassara H: Restriction of dietary glycotoxins markedly reduces elevated advanced glycation end products in renal failure patients. J Am Soc Nephrol 14:728-731,2003
3. Vlassara H, Cai W, Goodman S, Pyzik R, Yong A, Chen X, Zhu L, Neade T, Beeri M, Silverman JM, Ferrucci L, Tansman L, Striker GE, Uribarri J Protection Against Loss Of Innate Defenses In Adulthood By Low AGE Intake; Role Of An Anti-Inflammatory Age-Receptor-1. J Clin Endo Met 2009; 94:4483-91.
4. Uribarri J, Cai W, Ramdas M, Goodman S, Pyzick R, Chen X, Zhu L, Striker GE, Vlassara H. Restriction of advanced glycation end products improves insulin resistance in human type 2 diabetes: potential role of AGER1 and SIRT1. Diabetes Care 2011; 34:1610-16
5. Vlassara H, Cai W, Tripp E, Pyzik R, Yee K, Goldberg L, Tansman L, Chen X, Mani V, Fayad ZA, Nadkarni GN, Striker GE, He JC, Uribarri J. Oral AGE restriction ameliorates insulin resistance in obese individuals with the metabolic syndrome: a randomized controlled trial. Diabetologia 2016: 59:2181
6. Lotan R et al. Long-term dietary restriction of advanced glycation end-products (AGEs) in older adults with type 2 Diabetes is feasibe and efficacious-results from a pilot RCT. Nutrients 2010; 12:3143

Signed,

Manuel Portero-Otin, University of Lleida, Spain

M. Pia de la Maza, University of Chile, Chile

Michal S. Beeri, Icahn School of Medicine at Mount Sinai, US

Jaime Uribarri, Icahn School of Medicine at Mount Sinai, US

 

None of the four authors above have any conflicts of interest to declare.

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Reply to Potero-Otin, et al

Submitter: Casper Schalkwijk | C.Schalkwijk@maastrichtuniversity.nl

Authors: Armand M.A. Linkens, Jean L.J.M. Scheijen, Simone J.M.P. Eussen, Casper G. Schalkwijk

Published December 16, 2022

We thank Potero-Otin and colleagues for their interest in our study¹. We reported that a high-AGE diet does not impair glucose metabolism and vascular function in obese individuals.  Below, we would like to respond to the points made.    

First, most studies so far have investigated effects of dietary AGEs in humans based on ELISA techniques and found harmful effects.  Potero-Otin and colleagues highlight the point that dietary AGEs as measured by UPLC-MS/MS, as we have used in our study, are unrelated to those measured by ELISA. Indeed, we did not find a significant correlation between concentration of AGEs measured by UPLC-MS/MS and ELISA. However, it should be emphasized that using ELISA for the detection of AGEs is an important limitation because of difficulties with standardization, antibody immunoreactivity, and high risk of matrix interference, resulting in lesser sensitivity and specificity. Therefore, data obtained with ELISA warrants cautious interpretation. In our view, UPLC-MS/MS is the current gold standard method to determine AGEs in both food and plasma.  As such, it is our legitimate doubt whether the negative health effects observed in studies using ELISA techniques are due to dietary AGEs.    

Second, the lack of change in serum protein-bound AGEs in our trial between the intervention and control group was expected. While dietary AGEs are consumed mainly as protein-bound AGEs, their uptake into the circulation takes place after digestion into free AGEs. Indeed, we found increased levels of plasma free AGEs in the high-AGE group.  

Third, our low-AGE group indeed had a somewhat higher habitual AGE intake at baseline. If anything, we would expect that effects of a low-AGE diet on glucose metabolism and vascular function would then be more profound.

Fourth, we agree with Dr Potero-Otin and colleagues that a 4-week intervention is too short to provide conclusions on long-term effects of dietary AGEs. Nonetheless, vascular function and insulin sensitivity are dynamic and can surely respond to a short-term dietary intervention². Most importantly, we have additionally studied associations of habitual AGE intake in a large population-based cohort. Results from these observational studies were in line with the null findings of our randomized controlled trial, indicating that habitual AGE intake is not associated with arterial stiffness⁴ and generalized microvascular function⁵, nor with insulin sensitivity, beta-cell function, and presence of type 2 diabetes (submitted).  

References

1.         Linkens AM, Houben AJ, Niessen PM, Wijckmans NE, de Goei EE, Van den Eynde MD, Scheijen JL, van den Waarenburg MP, Mari A, Berendschot TT, Streese L, Hanssen H, van Dongen MC, van Gool CC, Stehouwer CD, Eussen SJ and Schalkwijk CG. A 4-week high-AGE diet does not impair glucose metabolism and vascular function in obese individuals. JCI insight. 2022;7.

2.         Joris PJ, Plat J, Kusters YH, Houben AJ, Stehouwer CD, Schalkwijk CG and Mensink RP. Diet-induced weight loss improves not only cardiometabolic risk markers but also markers of vascular function: a randomized controlled trial in abdominally obese men. Am J Clin Nutr. 2017;105:23-31.

3.         Scheijen J, Clevers E, Engelen L, Dagnelie PC, Brouns F, Stehouwer CDA and Schalkwijk CG. Analysis of advanced glycation endproducts in selected food items by ultra-performance liquid chromatography tandem mass spectrometry: Presentation of a dietary AGE database. Food chemistry. 2016;190:1145-1150.

4.         Linkens AM, Eussen SJ, Houben AJ, Kroon AA, Schram MT, Reesink KD, Dagnelie PC, Henry RM, van Greevenbroek M, Wesselius A, Stehouwer CD and Schalkwijk CG. Habitual Intake of Dietary Advanced Glycation End Products Is Not Associated with Arterial Stiffness of the Aorta and Carotid Artery in Adults: The Maastricht Study. The Journal of nutrition. 2021;151:1886-1893.

5.         Linkens AMA, Houben A, Kroon AA, Schram MT, Berendschot T, Webers CAB, van Greevenbroek M, Henry RMA, de Galan B, Stehouwer CDA, Eussen S and Schalkwijk CG. Habitual intake of dietary advanced glycation end products is not associated with generalized microvascular function-the Maastricht Study. Am J Clin Nutr. 2022;115:444-455.

 

Armand M.A. Linkens

Jean L.J.M. Scheijen

Simone J.M.P. Eussen

Casper G. Schalkwijk

Department of Internal Medicine, 

Maastricht University Medical Centre

E-mail: C.Schalkwijk@maastrichtuniversity.nl

 

None of the four authors above has any conflicts of interest to declare.