Chondroitin Bioactivity

Chondroitin sulfates are known to play a role in cell division, neuronal development, and spinal cord injury. The nature and mechanism of these effects have been controversial and difficult to study, however, because the structures of these carbohydrates vary widely and they have generally been available only as complex mixtures.

Now, the first study of the bioactivity of pure, synthetic chondroitin sulfates has helped to elucidate their neuronal effects and could point the way toward potential clinical applications of the agents.

Chondroitin sulfates are structurally diverse polysaccharides having a range of lengths and sulfation patterns. The complex mixtures of the compounds that are found in nature have deterred efforts to better understand their biological roles.

Assistant professor of chemistry Linda C. Hsieh-Wilson and coworkers at California Institute of Technology have synthesized two chondroitin sulfate oligomers and have found that a chondroitin sulfate tetrasaccharide stimulates neuronal growth and differentiation, whereas a disaccharide does not [J. Am. Chem. Soc., 126, 7736 (2004)]. This result suggests that a four-unit structure may be the smallest chondroitin sulfate capable of neuronal bioactivity.

“Although much evidence has accumulated at the polysaccharide level for the neurogenic [nerve-growth-inducing] activity of chondroitin sulfates, no evidence has been reported before about the minimum chain size and the minimum functional domain structure,” says professor Kazuyuki Sugahara of the biochemistry department at Kobe Pharmaceutical University, in Japan. “Biochemists like me have been trying to enzymatically dissect active polysaccharides to isolate fragments, without success. Hsieh-Wilson and coworkers now appear to have demonstrated neurogenic activity for small, chemically synthesized chondroitin sulfate oligosaccharides for the first time.”

Sugahara was a member of a team that first reported, in 1999, neurogenic activity by chondroitin sulfate bearing the “CS-E” sulfation motif. The chondroitin sulfates synthesized by Hsieh-Wilson and coworkers bear that motif. The finding that the tetrasaccharide is bioactive helps confirm that CS-E sulfation “is an important structural determinant for chondroitin sulfate activity in vivo, endowing chondroitin sulfate polysaccharides with the ability to induce neuronal growth,” the researchers write.

In the syntheses, two chondroitin sulfate monosaccharides were generated from simple sugars and coupled together to form a disaccharide building block. In one case, the building block was sulfated to form a chondroitin sulfate disaccharide. In a separate process, the building block was either derivatized or activated, forming two other disaccharides, which were joined to form a tetrasaccharide. The latter was then deprotected and sulfated to form the chondroitin sulfate tetrasaccharide.

A neuronal assay revealed the difference in bioactivity between the tetrasaccharide and the disaccharide. Sugahara notes that another group had synthesized a similar chondroitin sulfate tetrasaccharide earlier, but its bioactivity “was not reported or tested, as far as I know,” he says.

“An exciting implication of our work,” Hsieh-Wilson says, is that such small-molecule oligosaccharides “should provide new approaches to understand and manipulate neuronal growth and regeneration.” In addition, Sugahara points out that the Caltech study could help lead to the use of such compounds “to control heparin-binding growth factors, which may be required to treat certain cancers,” and to their use as antiviral, antibacterial, or anti-inflammatory agents.