The Effect of Glucosamine Sulfate on the Proliferative Potential and Glycosaminoglycan Synthesis of Nucleus Pulposus Intervertebral Disc Cells

Abstract

On the basis of the similarities in the structure of cartilage and intervertebral disc and on the property of glucosamine of being the building block for the construction of proteoglycan aggregates, we investigated the compound's role in the proliferation of nucleus pulposus cells under iso- and hyperosmotic conditions, the putative activation of signaling cascades, and the induction of glycosaminoglycan production. We examined the mode of action of glucosamine in nucleus pulposus cells. Glucosamine that naturally occurs in cartilage tissues has been widely used for treating osteoarthritis, but its role in nucleus pulposus cells is largely unknown. The effect of glucosamine sulfate on the viability and proliferation of nucleus pulposus cells was assessed by the microculture tetrazolium test (MTT) assay, direct cell counting, and tritiated thymidine incorporation. Changes in the expression and phosphorylation profile of selected proteins were estimated by Western analysis. Glycosaminoglycan production was measured using the Blyscan assay. We showed that glucosamine sulfate up to 1 mM did not influence the viability, proliferation rate, or novel DNA synthesis of nucleus pulposus cells in the presence or absence of elevated osmolality but induced the transient phosphorylation of p38 mitogen-activated protein kinase. The highest concentration used (10 mM) negatively affected cellular proliferation and resulted in deactivation of extracellular signal-regulated kinases and c-Jun N-terminal kinases. Interestingly, these effects resulted from an additional hyperosmotic stress provoked by glucosamine alone. Finally, we found that a long-term incubation with glucosamine leads to an increase in the glycosaminoglycan content of nucleus pulposus cells. Glucosamine sulfate was not found to reverse the high osmolality-mediated delay of proliferation in nucleus pulposus cells needed for the maintenance of the tissue's homeostasis. In addition, glycosaminoglycan synthesis stimulated by glucosamine provides a possible promising clinical role for treating disc degenerative disorders.