Spectroscopic properties of complexes of acridine orange with glycosaminoglycans II. Aggregated complexes-evidence for long-range order

Small-molecule-induced clustering of heparan sulfate promotes cell adhesion

Adhesamine is an organic small molecule that promotes adhesion and growth of cultured human cells by binding selectively to heparan sulfate on the cell surface. The present study combined chemical, physicochemical, and cell biological experiments, using adhesamine and its analogues, to examine the mechanism by which this dumbbell-shaped, non-peptidic molecule induces physiologically relevant cell adhesion. The results suggest that multiple adhesamine molecules cooperatively bind to heparan sulfate and induce its assembly, promoting clustering of heparan sulfate-bound syndecan-4 on the cell surface. A pilot study showed that adhesamine improved the viability and attachment of transplanted cells in mice. Further studies of adhesamine and other small molecules could lead to the design of assembly-inducing molecules for use in cell biology and cell therapy.

Tilorone-induced lysosomal lesions: the bisbasic character of the drug is essential for its high potency to cause storage of sulphated glycosaminoglycans

The immunomodulatory agent tilorone -2,7-bis-[2-(diethyl-amino)ethoxy]fluoren-9-one- and congeners are potent inducers of lysosomal storage of sulphated glycosaminoglycans (GAGs) in animals and cultured fibroblasts of animals and man. All potent inducers of GAG storage hitherto described are bisbasic polycyclic aromatic compounds. They are accumulated in lysosomes and disturb the degradation of GAGs, mainly dermatan sulphate. It has been proposed that the drugs cross-link the polyanionic GAG chains giving rise to undergradable drug-GAG complexes. This hypothesis implies that the bisbasic character of the drug molecules is essential for the side effect in question. In the present study, this was tested by comparing tilorone and its monobasic derivative (MT) with respect to (i) induction of GAG storage in cultured bovine corneal fibroblasts and (ii) physicochemical interactions with GAGs in vitro. The intralysosomal concentration of MT achieved after 1-3 days was of the same order of magnitude as previously shown for tilorone. Nevertheless, under conditions that did not enhance the secretion of a lysosomal enzyme (beta-hexosaminidase, EC 3.2.1.52), the ability of MT to cause storage of [35S]GAGs was significantly lower than that of tilorone. Morphological observations showed that MT was much more potent in causing lysosomal storage of polar lipids than of GAGs. CD spectroscopy with tilorone revealed that the presence of GAGs caused the primarily achiral drug molecules to display CD. This suggested a helical orientation of the tilorone molecules within GAG-drug complexes, and short intermolecular distances which allowed electronic coupling of the aromatic ring systems of adjacent drug molecules. In contrast, MT failed to display any induced optical activity, indicating the absence of highly ordered GAG-drug complexes. In conclusion, the present results show that the substitution of the planar aromatic ring system with two basic side chains is essential for the high potency of tilorone in inducing lysosomal GAG storage. This is paralleled by, and presumably causally related to, strong physicochemical interactions with GAGs.

Acridine Orange, a precipitant for sulfated glycosaminoglycans, causes mucopolysaccharidosis in cultured fibroblasts

The purpose of the present investigation was to examine whether or not a di-cationic amphiphilic compound that is known (1) to be accumulated in lysosomes and (2) to form insoluble complexes with sulfated glycosaminoglycans (sGAG) in vitro, is able to interfere with the lysosomal degradation of sGAG, thus causing mucopolysaccharidosis (MPS) in cultured cells. Acridine Orange (AO) was chosen for this study since it is known to meet the above requirements. Cultured fibroblasts from rat cornea were exposed to AO (0.7 microM to 30 microM) for 72 h; tilorone served as reference compound. AO (1.75 microM to 10 microM) caused MPS in a concentration-dependent manner, higher concentrations were cytotoxic. MPS was demonstrated by cytochemical staining with cuprolinic blue and by measuring the intracellular accumulation of [35S]-GAG. The sGAG-complexing properties of AO were demonstrated by using it as a fixative for the intralysosomal sGAG accumulated in tilorone-treated cells. The present findings give support to the working hypothesis that the MPS induced by di-cationic amphiphilic drugs is due to the formation of insoluble sGAG-drug complexes, with the result that the sGAG become resistant to lysosomal degradation.

Cationic dye binding by hyaluronate fragments: dependence on hyaluronate chain length

Sodium hyaluronate, digested with bovine testicular hyaluronidase, yielded a mixture of oligosaccharides with identical repeating disaccharide structures and differing molecular weights. The oligosaccharides were separated into a ladder-like series of bands by electrophoresis on a 10% polyacrylamide gel matrix. Coelectrophoresis of purified oligosaccharides has established that adjacent bands differ in chain length by one disaccharide unit. This procedure formed the basis for a rapid screening method in which the binding of cationic dyes by hyaluronate oligosaccharides may be assayed. As a function of chain length, the oligosaccharides showed a marked change in dye binding. Species containing less than seven repeating disaccharide units are not detected by any dye tested, even at very high sample loads. Larger oligosaccharides show an increase in dye binding. The chain length at which constant maximal dye binding is reached depends on the dye structure and solvent conditions, varying from approximately 12 to 30 disaccharide units. The hyaluronate fragments of sufficient chain length to duplicate polymer behavior should be useful models for the study of hyaluronate structure and interactions in solution.

Glycosaminoglycans: structure and interaction

In the last few years, there has been considerable progress in the studies on glycosaminoglycans, a group of acidic polysaccharides present in the intercellular matrix of connective tissue. X-ray diffraction studies have indicated that these polymers can exist in the condensed phase in some helical form. Chiroptical and hydrodynamic measurements have provided significant information regarding the molecular conformation in solution and other physicochemical properties of the polymers. Studies related to the interaction properties of glycosaminoglycans with polypeptides, metal ions, and other molecules are numerous. This review covers mainly the results and their interpretations of both published and as yet unpublished material of the 1970s, but certain previous data are also included. A present-day concept regarding the structure and interaction properties of these molecules on the basis of various physicochemical measurements is presented. The biosynthesis and metabolism of glycosaminoglycans, and the structure of proteoglycans and glycoproteins, are not discussed.