Lectin affinity chromatography of articular cartilage fibromodulin: Some molecules have keratan sulphate chains exclusively capped by α(2-3)-linked sialic acid.

Fibromodulin from bovine articular cartilage has been subjected to lectin affinity chromatography by Sambucus nigra lectin which binds α(2-6)- linked N-acetylneuraminic acid, and the structure of the keratan sulphate in the binding and non-binding fractions examined by keratanase II digestion and subsequent high pH anion exchange chromatography. It has been confirmed that the keratan sulphate chains attached to fibromodulin isolated from bovine articular cartilage may have the chain terminating N-acetylneuraminic acid residue α(2-3)- or α(2-6)-linked to the adjacent galactose residue. Although the abundance of α(2-6)-linked N-acetylneuraminic acid (ca. 22%) is such that this could cap one of the four chains in almost all fibromodulin molecules, it was found that ca. 34% of the fibromodulin proteoglycan molecules from bovine articular cartilage were capped exclusively with α(2-3)-linked N-acetylneuraminic acid. The remainder of the fibromodulin proteoglycans, which bound to the lectin had a mixture of α(2-3)- and α(2-6)-linked N-acetylneuraminic acid capping structures. The keratan sulphates attached to fibromodulin molecules capped exclusively with α(2-3)- linked N-acetylneuraminic acid were found to have a higher level of galactose sulphation than those from fibromodulin with both α(2-3)- and α(2-6)-linked N-acetylneuraminic acid caps, which bound to the Sambucus nigra lectin. In addition, both pools contained chains of similar length (ca. 8-9 disaccharides). Both also contained α(1-3)-linked fucose, showing that this feature does not co-distribute with α(2-6)-linked N-acetylneuraminic acid, although these two features are present only in mature articular cartilage. These data show that there are discrete populations of fibromodulin within articular cartilage, which may have differing impacts upon tissue processes.

Characterization of oligosaccharides from the chondroitin/dermatan sulfates. 1H-NMR and 13C-NMR studies of reduced trisaccharides and hexasaccharides.

Chondroitin and dermatan sulfate (CS and DS) chains were isolated from bovine tracheal cartilage and pig intestinal mucosal preparations and fragmented by enzymatic methods. The oligosaccharides studied include a disaccharide and hexasaccharides from chondroitin ABC lyase digestion as well as trisaccharides already present in some commercial preparations. In addition, other trisaccharides were generated from tetrasaccharides by chemical removal of nonreducing terminal residues. Their structures were examined by high-field 1H and 13C NMR spectroscopy, after reduction using sodium borohydride. The main hexasaccharide isolated from pig intestinal mucosal DS was found to be fully 4-O-sulfated and have the structure: DeltaUA(beta1-3)GalNAc4S(beta1-4)L-IdoA(alpha1-3)GalNAc4S(beta1-4)L-IdoA(alpha1-3)GalNAc4S-ol, whereas one from bovine tracheal cartilage CS comprised only 6-O-sulfated residues and had the structure: DeltaUA(beta1-3)GalNAc6S(beta1-4)GlcA(beta1-3)GalNAc6S(beta1-4)GlcA(beta1-3)GalNAc6S-ol. No oligosaccharide showed any uronic acid 2-sulfation. One novel disaccharide was examined and found to have the structure: GalNAc6S(beta1-4)GlcA-ol. The trisaccharides isolated from the CS/DS chains were found to have the structures: DeltaUA(beta1-3)GalNAc4S(beta1-4)GlcA-ol and DeltaUA(beta1-3)GalNAc6S(beta1-4)GlcA-ol. Such oligosaccharides were found in commercial CS/DS preparations and may derive from endogenous glucuronidase and other enzymatic activity. Chemically generated trisaccharides were confirmed as models of the CS/DS chain caps and included: GalNAc6S(beta1-4)GlcA(beta1-3)GalNAc4S-ol and GalNAc6S(beta1-4)GlcA(beta1-3)GalNAc6S-ol. The full assignment of all signals in the NMR spectra are given, and these data permit the further characterization of CS/DS chains and their nonreducing capping structures.

Characterisation of oligosaccharides from the chondroitin/dermatan sulphates: (1)H and (13)C NMR studies of oligosaccharides generated by nitrous acid depolymerisation.

The polymers chondroitin sulphate and dermatan sulphate have been fragmented by an anhydrous hydrazine/nitrous acid procedure. The resulting disaccharides from the polymer repeat sequences were reduced with NaBH(4) and purified by ion exchange chromatography. Whereas enzymatic depolymerisation leads to the loss of the distinction between glucuronic and iduronic acids of CS and DS in the resultant disaccharides, nitrous acid depolymerisation retains these structures. Complete (1)H and (13)C NMR data have been derived for the major components which were shown to have the structures: GlcA-(ß1→3)-anTal6S-ol (I) and L-IdoA-(α1→3)-anTal4S-ol (II), where anTal-ol represents (2,5)anhydro-D-talitol and 6S/4S represent O-ester sulphate groups at C-6/C-4 sites.

Galantamine inhibits beta-amyloid aggregation and cytotoxicity.

The ability of galantamine (Reminyl) to inhibit the aggregation and toxicity of the beta-amyloid peptide (Abeta) was investigated. Galantamine showed concentration-dependent inhibition of aggregation of both Abeta 1-40 and Abeta 1-42, as determined by an ELISA method. Electron microscope studies of Abeta 1-40 incubated in the presence of galantamine revealed fibrils that were disordered and clumped in appearance. MTT and lactate dehydrogenase assays, employing SH-SY5Y human neuroblastoma cells, showed that galantamine reduced the cytotoxicity induced by Abeta 1-40. Galantamine also dramatically reduced Abeta 1-40-induced cellular apoptosis in these cells. There is some evidence that galantamine may not be acting purely as a symptomatic treatment. Disease-modifying effects of the drug could be due to an additional effect on Abeta aggregation and/or toxicity.

Both the D-(+) and L-(-) enantiomers of nicotine inhibit Abeta aggregation and cytotoxicity.

The underlying cause of Alzheimer's disease is thought to be the aggregation of monomeric beta-amyloid (Abeta), through a series of toxic oligomers, which forms the mature amyloid fibrils that accumulate at the center of senile plaques. It has been reported that L-(-)-nicotine prevents Abeta aggregation and toxicity, and inhibits senile plaque formation. Previous NMR studies have suggested that this could be due to the specific binding of L-(-)-nicotine to histidine residues (His6, His13, and His14) in the peptide. Here, we have looked at the effects of both of the L-(-) and D-(+) optical enantiomers of nicotine on the aggregation and cytotoxicity of Abeta(1-40). Surprisingly, both enantiomers inhibited aggregation of the peptide and reduced the toxic effects of the peptide on cells. In NMR studies with Abeta(1-40), both enantiomers of nicotine were seen to interact with the three histidine residues. Overall, our data indicate that nicotine can delay Abeta fibril formation and maintain a population of less toxic Abeta species. This effect cannot be due to a highly specific binding interaction between nicotine and Abeta, as previously thought, but could be due instead to weaker, relatively nonspecific binding, or to the antioxidant or metal chelating properties of nicotine. D-(+)-nicotine, being biologically much less active than L-(-)-nicotine, might be a useful therapeutic agent.