Background: Low molecular mass hyaluronan (LMHA) is proinflammatory, but the role of the N-acetyl moieties is unknown. Results: Chemical reacetylation of LMHA results in maximal proinflammatory cytokine production by human macrophages, compared with other N-acylations. Partial N-butyrylation blocks cytokine stimulation. Conclusion:The N-acetyl moieties of glucosamine are critical for LMHA proinflammatory properties. Significance: N-Acetylation and butyrylation of LMHA modulate proinflammatory cytokine production.

Aldehyde reductase is an enzyme capable of metabolizing a wide variety of aldehydes to their corresponding alcohols. The tertiary structures of aldehyde reductase and aldose reductase are similar and consist of an alpha/beta-barrel with the active site located at the carboxy terminus of the strands of the barrel. We have determined the X-ray crystal structure of porcine aldehyde reductase holoenzyme in complex with an aldose reductase inhibitor, tolrestat, at 2.4 A resolution to obtain a picture of the binding conformation of inhibitors to aldehyde reductase. Tolrestat binds in the active site pocket of aldehyde reductase and interacts through van der Waals contacts with Arg 312 and Asp 313. The carboxylate group of tolrestat is within hydrogen bonding distance with His 113 and Trp 114. Mutation of Arg 312 to alanine in porcine aldehyde reductase alters the potency of inhibition of the enzyme by aldose reductase inhibitors. Our results indicate that the structure of the inhibitor-binding site of aldehyde reductase differs from that of aldose reductase due to the participation of nonconserved residues in its formation. A major difference is the participation of Arg 312 and Asp 313 in lining the inhibitor-binding site in aldehyde reductase but not in aldose reductase.

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The free amino group of GlcN seems responsible for inhibition of chondrocyte proliferation and PG synthesis. These effects were greater under higher concentrations of GlcN in AD vs AI conditions. GlcN.HCl behaves similarly to GlcN.S, but differential effects with GlcN-X,Y,Z(SO(4))(n) isomers were observed. Acetylation or sulfation of the GlcN amino group reverses or partially reverses, respectively, anti-proliferative effects of GlcN. Sulfation of GlcN, at positions 3 and 6 results in complex effects on AC proliferation and PG synthesis.