Controversial behavior of aminoguanidine in the presence of either reducing sugars or soluble glycated bovine serum albumin
ABSTRACT The elucidation of the controversial inhibitory effect of aminoguanidine (AG) on the cross-linking and fluorescent advanced glycation end products (AGEs) formation during long-term in vitro glycation of type I collagen with 250 mM reducing sugars or 0.5mg/ml soluble glycated bovine serum albumin (AGE-BSA) was researched. Chromatographic and SDS-PAGE analyses revealed the formation of aggregates during collagen glycation. AG at all concentrations (5-80 mM) prevented the cross-linking of collagen peptides with monosaccharides but an increase in fluorescence with a maximum value at 10 mM AG was noticed. In the presence of AGE-BSA, AG prevented the cross-linking process and decreased the fluorescence levels in a concentration-dependent manner. Our results suggest that AG is an efficient inhibitor of collagen cross-linking and the highest increase in fluorescence due to reducing sugars and AG can be explained by the competition between guanidine group of AG and arginine residues of some protein-bound dideoxyosones, which could form fluorescent compounds.
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ABSTRACT: Interstitial fibrosis is induced by imbalances in extracellular matrix homeostasis. Advanced glycation end products (AGEs) can bind and activate the receptor for AGEs (RAGE), which is involved in diabetic nephropathy. We set out to identify the role of AGEs in producing alterations leading to matrix hypertrophy and the pathway through which aminoguanidine, as well as anti-RAGE and anti-TGF-β1 antibody treatments could prevent these modifications. Human embryonic kidney (HEK-293) cells were exposed to glycated bovine serum albumin (AGE-BSA) and co-treated with neutralizing antibodies or aminoguanidine. The effects on the transcriptional and translational levels of RAGE, TGF-β1 and collagen IV were evaluated, while metalloproteinase activity was assessed by gelatin zymography. AGE-BSA (200 μg/ml) upregulated RAGE's expression, while TGF-β1 synthesis and the formation of its bioactive form were increased in a dose-dependent manner by AGEs. AGE-BSA exposure increased both MMP activity and collagen IV synthesis, boosted by TGF-β1 up-regulation. Aminoguanidine's effects revealed that small concentrations (10 μmol/l) enhance AGE-BSA effects, by increasing the expression of RAGE and TGF-β1, while higher concentrations (100 μmol/l) contribute to their down-regulation. Although AGEs regulate RAGE and TGF-β1 by distinct pathways, RAGE activation leads to a further increase of TGF-β1 levels. MMP-2 activity seems to rely on TGF-β1, while MMP-9 was dependent on RAGE. These factors converge to control collagen IV turnover. Furthermore, although the antibody treatments might appear more efficient than AG in decreasing collagen IV levels, the cells compensate the RAGE and TGF-β1 blockade by increasing the mRNA expression of these proteins.Journal of Diabetes 03/2014; DOI:10.1111/1753-0407.12154 · 2.35 Impact Factor