High beta-galactosidase and ganglioside G(M1) levels in the human parotid gland

Background: Ganglioside G(M1) is a membrane glycolipid typical of nerve cel l membranes, where it partakes in neurotransmitter release and is cataboliz ed by the lysosomal alpha -galactosidase (GM1ase) (EC 3.2.1.23). After demo nstrating a novel degenerative disease of the parotid gland in mice deficie nt in GM1ase, mimicking the human storage disease GM(1) gangliosidosis, we studied GM1ase and ganglioside G-(M1) content in the human parotid glands. Study Design: Levels of GM1ase and ganglioside GM(1) were determined in sam ples of parotid tissues and neighboring muscle (as a negative control) for 3 subjects. Tissues were also processed for histochemical demonstration of GM1ase. Results: The mean specific activity of GM1ase was more than 6-fold higher i n the healthy human parotid tissues (1.4 +/-0.5 nmol of 4-methylumbellifero ne per minute per milligram of protein) relative to the neighboring muscle tissue (0.23 +/- 0.07 nmol of 4-methylumbelliferone per minute permilligram of protein). Activity, of GM1ase was histochemically localized mainly to s triated duct and acinar cells of the parotid gland. Ganglioside G(M1) conte nt in the parotid gland was on average 30-fold higher relative to muscle. Conclusions: Our results are consistent with previous findings reported in the mouse and the rabbit, and probably reflect a general property of the ma mmalian parotid glands. The novel mechanism we previously proposed for the mouse parotid saliva secretion, mimicking neurotransmitter release in gangl ioside G(M1)-containing nerve cells, is probably applicable also to the hum an parotid gland. Similarly, the human parotid gland is probably also sever ely affected in GM(1) gangliosidosis.