Abstract
Background
Advanced glycation end products (AGPs) promote human aortic smooth muscle cell calcification in vitro. Moreover, reduction of AGPs levels and inhibition of RAGE signaling decrease vascular calcification in vivo in animal studies. The role of AGPs in aortic valve calcification has not been investigated.
Purpose
We sought to investigate the role of AGPs in aortic valve calcification, in the absence of diabetes mellitus (DM).
Methods
We used human and animal cohorts. Firstly, we obtained aortic valves from patients without DM that underwent aortic valve replacement due to aortic valve stenosis. We studied the valves with Fourier-Transformed Infrared spectroscopy (FT-IR, Nicolet 6700 spectrometer, with Attenuated Total Reflection-ATR accessory, each spectrum consisted of 120 co-added spectra) in order to evaluate chemical changes. In the animal cohort, New Zealand male rabbits where randomized in calcification diet (normal chow+cholesterol 0,5%+3500 IU ergocalciferol/kg daily) and control group and sacrificed at 2, 4, 6, 8 10 and 12 weeks. The valves were longitudinally assessed with FT-IR.
Results
A total of 200 human aortic valves were studied (age 64–78). All patients demonstrated characteristic vibrations at the area about 1165 cm-1, where the C-O-C bonds absorb, attributed to AGPs. Thirty six rabbit valves were used, 3 per group. Glucose levels were within normal range and did not differ between groups. The FT-IR spectra of the rabbit aortic valves showed increasing intensity of the C-O-C band at 1165 cm-1 in experimental group in comparison to control group. The band at 1744 cm-1 is attributed to aldehyde formation due to oxidative stress and inflammation. Shifts and shape changes were detected at the bands of amide I and II at 1650 cm-1 and 1550 cm-1, respectively, concerning protein misfolding, fiber formation and sclerosis. The bands in the region 1299–900 cm-1 correspond to phosphate groups of phospholipidsand the formed calcium phosphate salts and non-biological hydroxyapatite Ca3(PO4)2 formation. All vibrations increased significantly longitudinally during experimental diet period.
Representative FT-IR spectra of valves
Conclusions
Advanced glycation end products are detected in human calcified aortic valves irrespectively of DM. Moreover, AGPs correlate with presence and gradual development of aortic valve calcification in experimental rabbit model, along with acidosis, oxidation and protein secondary misfolding. Accumulation of AGPs in valve tissue is implicated in mechanisms of disease development.
Decreased levels of soluble receptor for advanced glycation end-products in aortic valve calcification patients
