Glycation in human fingernail clippings using ATR-FTIR spectrometry, a new marker for the diagnosis and monitoring of diabetes mellitus.
OBJECTIVE
Although HbA1c is a good diagnostic tool for diabetes, the precarity of the health system and the costs limit the use of this biomarker in developing countries. Fingernail clippings contain ±85% of keratins, which are prone to glycation. Nail keratin glycation may reflect the average glycemia over the last months. We explored if attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) can be used as a non-invasive tool for assessing glycation in diabetes.


METHODS
Using ATR-FTIR spectroscopy, glycation and deglycation experiments with fructosamine 3-kinase allowed to identify the spectrum that corresponds with keratin glycation in fingernail clippings. Clippings of 105 healthy subjects and 127 diabetics were subjected to the standardized ATR-FTIR spectroscopy method.


RESULTS
In vitro glycation resulted in an increased absorption at 1047cm-1. Following enzymatic deglycation, this peak diminished significantly, proving that the AUC between 970 and 1140cm-1corresponded with glycated proteins. Within-run CV of the assay was 3%. Storage of nail clippings at 37°C for 2weeks did not significantly change results. In diabetics, glycated nail protein concentrations (median: 1.51μmol/g protein, IQR: 1.37-1.85μmol/g protein) were significantly higher than in the controls (median: 1.19μmol/g protein, IQR: 1.09-1.26μmol/g protein) (p<0.0001). ROC analysis yielded an AUC of 0.92 at a cut-off point of 1.28μmol/g nail (specificity: 82%; sensitivity: 90%). No correlation was observed between the glycated nail protein concentrations and HbA1c.


CONCLUSIONS
Protein glycation analysis in fingernails with ATR-FTIR spectroscopy could be an alternative affordable technique for diagnosing and monitoring diabetes. As the test does not consume reagents, and the preanalytical phase is extremely robust, the test could be particularly useful in developing countries.
Department of Clinical Chemistry, Ghent University Hospital, Gent, Belgium.
Renaat
R
Coopman
Department of Clinical Chemistry, Ghent University Hospital, Gent, Belgium.
Thijs
T
Van de Vyver
Department of Laboratory Medicine, Catholic University of Bukavu, Bukavu, Democratic Republic of the Congo.
Antoine Sadiki
AS
Kishabongo
Department of Internal Medicine, Catholic University of Bukavu, Bukavu, Democratic Republic of the Congo.
Philippe
P
Katchunga
Department of Ophthalmology, Sint-Elisabeth Ziekenhuis, Zottegem, Belgium.
Elisabeth H
EH
Van Aken
Department of Internal Medicine, Catholic University of Bukavu, Bukavu, Democratic Republic of the Congo.
Justin
J
Cikomola
Department of Clinical Chemistry, Ghent University Hospital, Gent, Belgium.
Tinne
T
Monteyne
Department of Nephrology, Ghent University Hospital, Gent, Belgium.
Marijn M
MM
Speeckaert
Department of Clinical Chemistry, Ghent University Hospital, Gent, Belgium. Electronic address: joris.delanghe@ugent.be.
Joris R
JR
Delanghe
D003920:Diabetes Mellitus / Q000175:diagnosis* / Q000378:metabolism*; D005260:Female; D005947:Glucose / Q000737:chemistry*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D009262:Nails / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
D005947:Glucose
Fingernails; Fructosamine; Glycation; Infrared spectroscopy; Keratin