Recent studies have debunked the myth about bacterial immortality. Two independent publications, by Stewart et al. (PLoS Biol. 2005;3(2):e45) and Wang et al. (Curr Biol. 2010;20(12):p.1099–1103), provided strong evidence that the two fission products of Escherichia coli K-12, albeit morphologically equivalent, are functionally asymmetric. The growth and the survival rate of one of the cells, the mother cell, are lower than those of the other, the daughter cell. In view of this intriguing finding, bacteria, and in particular E. coli, emerged as a promising model for exploration of the basic principles of aging. It is not yet clear to what extent human and bacterial cells age similarly but at least some signatures of aging, especially at the molecular level, appear to be common. Spontaneous chemical reactions including hydrolysis, oxidation, and glycation (the Maillard reaction) are well known to cause structural and functional deterioration of biomacromolecules. The Maillard reaction, yielding early (Schiff’s bases and Amadori products) and Advanced Glycation End Products (AGEs) on proteins, DNA and amino-lipids, has been long associated with diseases (diabetes, Alzheimer’s, and Parkinson’s diseases) and aging in humans. In previous studies, we have demonstrated that despite the short life span of E. coli, its proteins and chromosomal DNA accumulate both Amadori products and AGEs under normal physiological conditions (Mironova et al. Mol Microbiol. 2005;55(6):p.1801–1811). This article reviews data on the Maillard reaction as a cause of stochastic damage to proteins and DNA implicated in E. coli and human aging.

Maillard reaction and immunogenicity of protein therapeutics

Glycation is a spontaneous chemical reaction, which affects the structure and function of proteins under normal physiological conditions. Therefore, organisms have evolved diverse mechanisms to combat glycation. In this study, we show that the Escherichia coli glycolytic enzyme phosphoglucose isomerase (Pgi) exhibits deglycation activity. We found that E. coli Pgi catalyzes the breakdown of glucose 6-phosphate (G6P)-derived Amadori products (APs) in chicken lysozyme. The affinity of Pgi to the glycated lysozyme (K_m, 1.1 mM) was ten times lower than the affinity to its native substrate, fructose 6-phosphate (K_m, 0.1 mM). However, the high kinetic constants of the enzyme with the glycated lysozyme (k_cat, 396 s^-1 and k_cat/K_m, 3.6 × 10⁵ M^-1 s^-1) indicated that the Pgi amadoriase activity may have physiological implications. Indeed, when using total E. coli protein (20 mg/mL) as a substrate in the deglycation reaction, we observed a release of G6P from the bacterial protein at a Pgi specific activity of 33 μmol/min/mg. Further, we detected 11.4 % lower APs concentration in protein extracts from Pgi-proficient vs. deficient cells (p = 0.0006) under conditions where the G6P concentration in Pgi-proficient cells was four times higher than in Pgi-deficient cells (p = 0.0001). Altogether, these data point to physiological relevance of the Pgi deglycation activity.

Background: N^ε-(carboxymethyl)-lysine (CML) is formed in the human body by non-enzymatically driven reactions including glycation, oxidation, and lipoxidation. CML is a ubiquitous product of normal physiology, but its levels are increased under disease conditions like chronic kidney disease (CKD) and diabetes mellitus (DM). Free CML is eliminated from the human body mainly through kidney excretion, and its accumulation in the kidney tissue is linked to CKD pathogenesis. Aim: The main goal of this study was to evaluate the relative contribution of CKD and Type 2 DM (T2DM) to the accumulation of CML in patients’ sera. Methods: The study included 22 patients with CKD without DM, 55 with CKD and comorbid T2DM, and 21 with T2DM without CKD. Serum CML levels were measured by ELISA. The Kruskal-Wallis test was used to detect differences among groups. Spearman correlation analysis was performed, and the one-tailed Dunn test was considered to indicate statistical significance at p < 0.05. Results: The median serum CML levels (CKD, 658.4 ± 434.3 ng/mL; CKD + T2DM, 431.3 ± 327.9 ng/mL; T2DM, 273.9 ± 134.2 ng/mL) differed significantly (p < 0.05) among the three patient groups. A positive correlation was observed between serum CML and microalbuminuria (p = 0.004; r = 0.58), proteinuria (p = 0.002; r = 0.6), and age (p = 0.007; r = 0.52) only in the CKD patients. In all T2DM patients, independent of CKD status, serum CML correlated negatively (p < 0.05) with postprandial glucose and duration of diabetes, while its correlation with fasting glucose and HbA1c was negative only in the T2DM cohort without CKD. Conclusions: In patients with CKD, higher levels of CML were observed compared to those with T2DM. Serum CML correlated positively with proteinuria, albuminuria, and patient age in non-diabetic CKD patients, and negatively with blood glucose, HbA1c, and DM duration of T2DM in patients without CKD.