Novel analytical approach to monitoring advanced glycosylation end products in human serum with on-line spectrophotometric and spectrofluorometric detection in a flow system

We proposed a simple analytical procedure for measurement of serum advanced glycosylation end products (AGEs) based on simultaneous detection of low-molecular-mass peptides and AGEs with a flow system and two detectors connected on-line: spectrophotometric for peptides (lambda = 280 nm) and spectrofluorometric for AGEs (lambda ex = 247 nm, lambda em = 440 nm). Sample pretreatment was carried out in microcentrifuge tubes: Serum (20 microL) was deproteinized with trichloroacetic acid (480 microL, 0.15 mol/L) and lipids were extracted with chloroform (100 microL). Twenty microliters of the filtered aqueous layer was injected to the flow system and the relation between fluorescence and absorption signals was measured. A peptide-derived AGE calibrator was used for calibration. Within-day and between-day CVs were 6.7% and 9.1%, respectively, at an AGE concentration corresponding approximately to that in healthy individuals. Mean results (+/-SD) in 10 healthy individuals were 10.1% +/- 1.0%, in 21 patients with diabetes without complications 18.0% +/- 6.2%, in 25 patients with complications 24.1% +/- 15.4%, and in 12 diabetic patients in end-stage renal disease 92% +/- 30%. Comparison with an ELISA procedure (x, in arbitrary units/L) yields a regression equation y = 0.713x + 1.24 (Sy symbol: see text] x = 6777, r = 0.8477, n = 41).