Use of Sialic Acid as a Complementary Method in the Cytological Diagnosis: Preliminary Study

Cellular morphology does not allow, in many cases, to safely establish a diagnosis of malignancy or benignity. Sialic acid is found in the membranes of well-differentiated mature cells, normally located in the alpha-2,3 position. During tumor progression, changes occur in glycosylation of proteins and lipids, including alterations in the sialylation patterns of tumor cells.

To confirm the overexpression of alpha-2,6 sialinization in exfoliated cells of body fluids and bronchoalveolar lavage (BAL) as a malignant indicator mechanism, using glycan-binding lectins.

Thirty samples (20 effusion liquids and 10 BAL) diagnosed by Giemsa and Papanicolaou staining as negative and positive for malignancy, were studied. They were then stained with fluorescein-labeled Sambucus nigra lectin (Sigma Chemicals, USA), which specifically recognizes sialic acid in alpha-2,6 position. The fluorescence obtained at 515 nm evidenced the presence of sialic acid in the 2,6 position.

Negative body fluids for malignancy showed a fine and homogeneous fluorescence pattern for reactive mesothelial cells. Neoplastic cells revealed a thick, heterogeneous pattern. In BAL, benign hyperplastic cells showed a homogeneous fine pattern while neoplastic cells showed a thick and heterogeneous fluorescence pattern. The pattern described was observed in all cases in the cell membrane.

It was observed that the change in sialic acid conformation detected through Sambucus nigra Lectin could be used as a complementary method for the diagnosis of malignancy in different cytological samples.