GLYCOSAMINOGLYCAN METABOLISM IN OTOSCLEROTIC BONE-CELLS

Normal and otosclerotic bone cells were cultured in vitro in serum-fre e medium to evaluate single glycosaminoglycan (GAG) class synthesis an d secretion. Moreover, the degradative process was studied by inhibiti ng the lysosomal functions through the addition of ammonium chloride t o the cultures, an ammine known to inhibit lysosomal degradation by ne utralizing organelle activity. Otosclerotic bone cells accumulated a l ower amount of GAG both in the cellular and extracellular pool compare d to normal ones. The decrease was markedly higher for secreted GAG. M oreover a different pattern of single GAG class distribution was obser ved in the two cell types considered. In the medium of otosclerotic ce lls a percentage increase of hyaluronic acid (HA) and dermatan sulphat e (DS) and a percentage decrease of heparan sulfate (HS) and chondroit in sulfate (CS) were observed compared to normal bone cells. Ammonium chloride had a lower effect on pathologic than on normal cells, indica ting a decrease in the degradative process in otosclerotic bone cells. These results were also confirmed by the experiments on GAG uptake an d degradation and by the dosage of enzymatic activity of two exoglycos idases. Since extracellular GAG composition influences bone deposition and mineralization, these data support the hypothesis that otoscleros is is the result of an error in the connective tissue matrix structure .