Determination of pentosidine in fingernails by liquid chromatography with fluorescence detection (LC-FL) - Methodology and association with glycated hemoglobin (HbA1c), skin autofluorescence (SAF) and other ungual glycation biomarkers among people with diabetes.

Pentosidine, a pentose-derived, cross-link advanced glycation end-product (AGE), exhibits fluorescence properties which favor its analysis by liquid chromatography with fluorescence detection (LC-FL), and has been reported to be a biomarker for diabetes- and age-related disorders. Fingernails have recently garnered interest as a non-invasive matrix for the assessment of several diseases. Here, we developed and validated a LC-FL method to quantify ungual pentosidine as a companion to our tandem mass spectrometry (LC-MS/MS) method for the analysis of glycation biomarkers in nails. Method development and validation, including linearity, sensitivity, trueness, precision, and stability, proved the LC-FL method to be robust and sensitive, despite very low concentrations of pentosidine in nail keratin. Pentosidine was stable for 6 months in nails stored at 25 °C, and in nail hydrolysates stored at 4 °C. Ungual pentosidine was analyzed in fingernails from 171 type 1 and type 2 diabetic patients using this new LC-FL method, while two other AGEs and furosine were analyzed with our recently developed LC-MS/MS method. In this population with diabetes, pentosidine correlated moderately with the surrogate early-stage glycation biomarker furosine (Spearman rs = 0.461, [95% CI = 0.329-0.574]), and was respectively moderately and weakly correlated with the AGEs carboxymethyllysine (CML; rs = 0.538 [0.418-0.639]) and carboxyethyllysine (CEL; rs = 0.263 [0.117-0.402]), but showed no significant association with either HbA1c or skin autofluorescence. Ungual furosine may reflect glycemia over the previous 4-6 months in a way analogous to HbA1c, while ungual concentrations of the AGEs pentosidine, CML and CEL potentially reflect the glycation status of long-lived, extracellular matrices implicated in diabetic complications.