Controversial behavior of aminoguanidine in the presence of either reducing sugars or soluble glycated bovine serum albumin
University of Agricultural Science and Veterinary Medicine, Faculty of Veterinary Medicine, 105 Splaiul Independentei 050097, Bucharest 5, Romania.Carbohydrate research (Impact Factor: 1.93). 10/2011; 346(18):2872-80. DOI: 10.1016/j.carres.2011.10.017
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.
- [Show abstract] [Hide abstract]
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.
- [Show abstract] [Hide abstract]
ABSTRACT: Advanced glycation end products (AGEs) can activate the inflammatory pathways involved in diabetic nephropathy. Understanding these molecular pathways could contribute to therapeutic strategies for diabetes complications. We evaluated the modulation of inflammatory and oxidative markers, as well as the protective mechanisms employed by human embryonic kidney cells (HEK 293) upon exposure to 200 μg/mL bovine serum albumine (BSA) or AGEs–BSA for 12, 24 and 48 h. The mRNA and protein expression levels of AGEs receptor (RAGE) and heat shock proteins (HSPs) 27, 60 and 70, the activity of antioxidant enzymes and the expression levels of eight cytokines were analysed. Cell damage via oxidative mechanisms was evaluated by glutathione and malondialdehyde levels. The data revealed two different time scale responses. First, the up-regulation of interleukin-6 (IL-6), HSP 27 and high catalase activity were detected as early as 12 h after exposure to AGEs–BSA, while the second response, after 24 h, consisted of NF-κB p65, RAGE, HSP 70 and inflammatory cytokine up-regulation, glutathione depletion, malondialdehyde increase and the activation of antioxidant enzymes. IL-6 might be important in the early ignition of inflammatory responses, while the cellular redox imbalance, RAGE activation and NF-κB p65 increased expression further enhance inflammatory signals in HEK 293 cells.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.