Serum transferrin (Tf) comprises several isoforms with up to two complex oligosaccharide
chains containing zero to eight sialic acid residues and neutral sugars. The major
glycoform, known as tetrasialo-Tf, contains four sialic acid residues and accounts
for about 80% of whole Tf in human serum. Carbohydrate-deficient transferrin (CDT)
encompasses isoforms that are deficient in carbohydrate chains and consequently in
sialic acid residues (including asialo-, monosialo- and disialo-Tf) and is a well
known marker for chronic alcohol abuse. Recently capillary zone electrophoresis (CZE)
has been reported as a tool extremely effective for the simultaneous, individual,
quantitative determination of CDT isoforms. Three CZE methods that feature different
dynamic capillary coatings were evaluated and optimized for CDT determination in human
serum of alcohol abusers and control subjects. CZE separation was performed in alkaline
borate buffers after serum sample saturation with iron, electropherograms were detected
at 200 nm, data were evaluated as % area of disialo-Tf in relation to tetrasialo-Tf
and peak identification was accomplished via relative migration times to tetrasialo-Tf,
immunosubtraction and enzymatic sequential cleavage of sialic acid residues. Dynamic
capillary coatings with diaminobutane, spermine and a double coating produced by commercially
available proprietary agents were investigated and found to be suitable for determination
of CDT in human serum. For all three approaches, best results were obtained in 50
microm I.D. fused-silica capillaries of 50 cm effective length and a capillary cartridge
temperature of 20-25 degrees C. Using 3 mM 1,4-diaminobutane or 0.02 mM spermine in
a borate-based running buffer of pH 8.3 provided data of remarkable similarity with
resolution of di-, tri-, tetra- and pentasialo-Tf within 15-18 min. With the double
coating, asialo-Tf and Tf isoforms with two to six sialic acid residues were baseline
separated. Compared to the two amine-based procedures, the run times were found to
be somewhat shorter, the detector signals higher, the applied power level significantly
lower and the reproducibility better.