Binding of metal ions to polysaccharides. V. Potentiometric, spectroscopic, and viscosimetric studies of the binding of cations to chondroitin sulfate and chondroitin in neutral and acidic aqueous media

A Review of Chondroitin Sulfate's Preparation, Properties, Functions, and Applications

Chondroitin sulfate (CS) is a natural macromolecule polysaccharide that is extensively distributed in a wide variety of organisms. CS is of great interest to researchers due to its many in vitro and in vivo functions. CS production derives from a diverse number of sources, including but not limited to extraction from various animals or fish, bio-synthesis, and fermentation, and its purity and homogeneity can vary greatly. The structural diversity of CS with respect to sulfation and saccharide content endows this molecule with distinct complexity, allowing for functional modification. These multiple functions contribute to the application of CS in medicines, biomaterials, and functional foods. In this article, we discuss the preparation of CS from different sources, the structure of various forms of CS, and its binding to other relevant molecules. Moreover, for the creation of this article, the functions and applications of CS were reviewed, with an emphasis on drug discovery, hydrogel formation, delivery systems, and food supplements. We conclude that analyzing some perspectives on structural modifications and preparation methods could potentially influence future applications of CS in medical and biomaterial research.

Comparative Analysis of Antioxidant, Anticholinesterase, and Antibacterial Activity of Microbial Chondroitin Sulfate and Commercial Chondroitin Sulfate

Chondroitin synthesis was performed using the recombinant Escherichia coli(C2987) strain created by transforming the plasmid pETM6-PACF-vgb, which carries the genes responsible for chondroitin synthesis, kfoA, kfoC, kfoF, and the Vitreoscilla hemoglobin gene (vgb). Then, Microbial chondroitin sulfate (MCS)'s antioxidant, anticholinesterase, and antibacterial activity were compared with commercial chondroitin sulfate (CCS). The antioxidant studies revealed that the MCS and CCS samples could be potential targets for scavenging radicals and cupric ion reduction. MCS demonstrated better antioxidant properties in the ABTS assay with the IC50 value of 0.66 mg than CCS. MCS showed 2.5-fold for DPPH and almost 5-fold for ABTS⋅+ (with a value of 3.85 mg/mL) better activity than the CCS. However, the compounds were not active for cholinesterase enzyme inhibitions. In the antibacterial assay, the Minimum inhibitory concentration (MIC) values of MCS against S. aureus, E. aerogenes, E. coli, P. aeruginosa, and K. pneumoniae (0.12, 0.18, 0.12, 0.18, and 0.18 g/mL, respectively) were found to be greater than that of CCS (0.42, 0.48, 0.36, 0.36, and 0.36 g/mL, respectively). This study demonstrates that MCS is a potent pharmacological agent due to its physicochemical properties, and its usability as a therapeutic-preventive agent will shed light on future studies.

The molecular basis of memory. Part 2: chemistry of the tripartite mechanism

We propose a tripartite mechanism to describe the processing of cognitive information (cog-info), comprising the (1) neuron, (2) surrounding neural extracellular matrix (nECM), and (3) numerous "trace" metals distributed therein. The neuron is encased in a polyanionic nECM lattice doped with metals (>10), wherein it processes (computes) and stores cog-info. Each [nECM:metal] complex is the molecular correlate of a cognitive unit of information (cuinfo), similar to a computer "bit". These are induced/sensed by the neuron via surface iontophoretic and electroelastic (piezoelectric) sensors. The generic cuinfo are used by neurons to biochemically encode and store cog-info in a rapid, energy efficient, but computationally expansive manner. Here, we describe chemical reactions involved in various processes that underline the tripartite mechanism. In addition, we present novel iconographic representations of various types of cuinfo resulting from"tagging" and cross-linking reactions, essential for the indexing cuinfo for organized retrieval and storage of memory.

The molecular basis of memory

We propose a tripartite biochemical mechanism for memory. Three physiologic components are involved, namely, the neuron (individual and circuit), the surrounding neural extracellular matrix, and the various trace metals distributed within the matrix. The binding of a metal cation affects a corresponding nanostructure (shrinking, twisting, expansion) and dielectric sensibility of the chelating node (address) within the matrix lattice, sensed by the neuron. The neural extracellular matrix serves as an electro-elastic lattice, wherein neurons manipulate multiple trace metals (n > 10) to encode, store, and decode coginive information. The proposed mechanism explains brains low energy requirements and high rates of storage capacity described in multiples of Avogadro number (N(A) = 6 × 10(23)). Supportive evidence correlates memory loss to trace metal toxicity or deficiency, or breakdown in the delivery/transport of metals to the matrix, or its degradation. Inherited diseases revolving around dysfunctional trace metal metabolism and memory dysfunction, include Alzheimer's disease (Al, Zn, Fe), Wilson's disease (Cu), thalassemia (Fe), and autism (metallothionein). The tripartite mechanism points to the electro-elastic interactions of neurons with trace metals distributed within the neural extracellular matrix, as the molecular underpinning of "synaptic plasticity" affecting short-term memory, long-term memory, and forgetting.

Chondroitin-4-sulfate protects high-density lipoprotein against copper-dependent oxidation

We investigated the effect of chondroitinsulphate (CS), the major glycosaminoglycan of the arterial wall, on the oxidation of human high-density lipoprotein (HDL) by kinetic analysis. Chondroitin-4-sulfate (C4S) increased the lag time and reduced the maximum rate of HDL oxidation induced by Cu2+, as assessed by monitoring both conjugated diene formation and low-level chemiluminescence. On the contrary, chondroitin-6-sulfate (C6S) was ineffective. Dermatansulfate exhibited an inhibitory effect comparable to that of C4S. C4S protected also the protein moiety of HDL, as it reduced tryptophan destruction by lipid-oxidizing species and delayed the formation of fluorescent adducts between end products of lipid peroxidation and amino acid residues. Again, C6S was ineffective. C4S was able to bind Cu2+; this resulted in less Cu2+ available for HDL oxidation and likely represented the mechanism of the protective effect. Neither C4S nor C6S affected HDL oxidation by peroxyl radicals, indicating that free radical scavenging activity was not involved in the protective effect. These results suggest that C4S might prevent the oxidative modification of HDL in arterial wall, thus preserving its antiatherogenic potential for reverse cholesterol transport and, possibly, for clearance of oxidized lipids.

The interaction of the vanadyl (IV) cation with chondroitin sulfate A

The interaction of VO2+ with the muchopolysaccharide chondroitin sulfate A (CSA) has been investigated by electron absorption spectroscopy and infrared measurements in aqueous solutions at different pH-values and ligand to metal ratios up to 6:1. The generation of a VO(CSA)2 species could be demonstrated. Coordination of the oxocation through the carboxylate group and the glycosidic oxygen of the D-glucuronate moieties is suggested. Infrared spectra of some poorly characterized solid VO/CSA complexes point to the same bonding characteristics. Preliminary results obtained at higher ligand to metal ratios suggest a different coordination behavior.

Binding of calcium to glycosaminoglycans: an equilibrium dialysis study

Binding of calcium to the glycosaminoglycans (GAGs) heparin, chondroitin sulfate (CS), keratan sulfate (KS), and hyaluronic acid (HA) has been studied by equilibrium dialysis using exclusion of sulfate to correct for Gibbs-Donnan effects. Calcium binding occurs to all of these GAG species, suggesting that both sulfate and carboxylate groups are involved in cation binding. For all GAGs, the binding stoichiometry is consistent with a calcium-binding "site" consisting of two anionic groups. The order of calcium binding affinities is heparin greater than CS greater than KS greater than HA, and is critically dependent upon charge density; heparin binds calcium with 10-fold higher affinity than CS. The mode of calcium binding to GAGs is consistent with a recently proposed mechanism of growth plate calcification which states that cartilage proteoglycan functions as a reservoir of calcium for calcification of epiphyseal cartilage.

The basis and applicability of the dimethylmethylene blue binding assay for sulfated glycosaminoglycans

A rapid spectrophotometric assay for sulfated glycosaminoglycans, based on reaction of these compounds with the dye 1,9-dimethylmethylene blue (DMMB), is gaining widespread acceptance. The limitations of the assay have not been explored, and we have investigated the absorption spectra of the dye in the presence of a variety of compounds in order to understand the mechanism of colour formation. The dye exhibits classical metachromasia in the presence of sulfated glycosaminoglycans, but appears to do so by a much simpler mechanism than other thiazine dyes such as Azure A. Evidence is offered to support the conclusion that dye dimer reacts with the polyanion to produce a single metachromatic species by ionic perturbation of the chromophore. As predicted, factors which disrupt dimerization, such as pyridine and pyridine nucleotides, preclude use of the assay in their presence, and high salt concentrations can give false positive readings by inducing metachromasia in the absence of polyanion. When these factors are understood, the assay can be used with convenience. In particular, it allows direct measurement of the glycosaminoglycan content of a few mg of alkaline-solubilized basement membrane.

Chondroitin sulfate-derivatized agarose beads: a new system for studying cation binding to glycosaminoglycans

Chondroitin sulfate (CS) has been covalently attached to aminoethyl-agarose beads in a carbodiimide-catalyzed reaction. In this process, an amide bond is formed between carboxylate groups on the glycosaminoglycan (GAG) and the primary amine groups of the beads. Under optimal conditions, up to 160 micrograms of CS is attached per milligram of beads. CS-agarose beads have been used to study Ca binding to GAGs. The beads are mixed with a solution containing CaCl2 and 45Ca and allowed to sediment under unit gravity. An aliquot of supernatant is then removed and 45Ca activity is determined to quantitate remaining (free) Ca. Using this system, it was shown that CS binds approximately 0.7 Ca/disaccharide unit at saturation. Under the conditions used, the apparent association constant (KA) is approximately 14 mM. In principle, this derivatization protocol may be used to attach any proteoglycan or GAG (except keratan sulfate) to an insoluble support. CS-agarose beads provide a rapid, simple, and relatively artifact-free system for studying cation-GAG interactions.

An ion-exchange mechanism of cartilage calcification

The provisional calcification of epiphyseal cartilage involves deposition of hydroxyapatite (calcium phosphate) crystals in an extracellular matrix consisting principally of Type II collagen and cartilage proteoglycan. A mechanism is now proposed to explain how epiphyseal cartilage calcification is initiated. Calcium exists at high concentration in cartilage, but is mainly bound to the anionic groups of proteoglycans, and thus is unavailable for precipitation. A local increase in phosphate concentration displaces calcium ions from proteoglycan by an ion-exchange effect, raising the Ca X PO4 product above the threshold for precipitation of hydroxyapatite. Evidence for this hypothesis has been derived from studies of the effect of phosphate on the binding of calcium to cartilage proteoglycan, and on hydroxyapatite formation in the presence of chondroitin sulfate.