Isoenzymes of N-acetyl-β-hexosaminidase in human pleomorphic adenoma and healthy salivary glands: a preliminary study

Abstract

Pleomorphic adenoma (PA) is a benign tumour of the salivary gland with a tendency to malignancy which creates many diagnostic problems. N-acetyl-beta-hexosaminidase (HEX) is a lysosomal exoglycosidase involved in degradation of oligosaccharide chains of glycoproteins, glycolipids and glycosaminoglycans, known as a potential tumour marker. In the majority of tissues and body fluids, HEX exists as two major isoenzymes: HEX A and HEX B. The aim of our study was to evaluate HEX A and HEX B activity in healthy and PA human salivary glands using colorimetric and isoelectrofocusing methods. PA (n=8) and macroscopically unchanged salivary glands (n=8), served as controls, were used for the study. After preliminary preparation, isoenzymes of HEX were determined by colorimetric and isoelectrofocusing methods. Total activity of HEX, as well as HEX A and HEX B, in PA specimens determined by a colorimetric method was significantly higher compared with normal human salivary gland specimens. After isoelectrofocusing, in normal human salivary and PA glands, two sets of HEX isoforms were found corresponding to HEX A and HEX B. There was no significant difference in the amount of HEX A and HEX B isoforms. In PA tissue, activities of HEX isoforms in the pI ranges 1, 3b, 6 and 8 were significantly lower, and in ranges 5 and 8 significantly higher than in normal tissue. The observed significant shifts were localised mostly in HEX B activity area. The present data indicate that HEX activity and activity of its isoenzymes in tumour specimens is significantly and consistently elevated, and thus suggest the need for further studies on the degradation of glycoconjugates, both in healthy salivary glands and PA. It appears that HEX may be considered as a new tumour marker in these salivary gland diseases.