Gallic Acid-Chitosan Conjugate Inhibits the Formation of Calcium Oxalate Crystals

Abstract

It has recently been shown that chitosan (Chit) induces the formation of calcium oxalate (CaOx) crystals, which are mainly responsible for the appearance of kidney stones, and this might limit the use of Chit in vivo. Here, Chit was conjugated with gallic acid (Chit-Gal) to decrease the formation of CaOx crystal. This conjugation was confirmed by FTIR and NMR analyses. Chit-Gal contains 10.2 ± 1.5 mg GA per g of Chit. Compared to the control group, Chit increased the number of crystals by six-fold, mainly in the number of monohydrated CaOx crystals, which are the most harmful CaOx crystals. In addition, Chit increased the zeta potential (ζ) of CaOx crystals by three-fold, indicating that Chit was associated with the crystals. These alterations were abolished when Chit-gal was used in these tests. As oxidative stress is related to renal calculus formation, Chit and Chit-Gal were also evaluated as antioxidants using total antioxidant Capacity (TAC), reducing power, ferrous chelation, and copper chelation tests. Chit-gal was more efficient antioxidant agent in TAC (2 times), in ferrous chelation (90 times), and in reducing Power (5 times) than Chit. Overall, Chit-gal has higher antioxidant activity than Chit, does not induce the formation of CaOx crystals. Thus, Chit-Gal has potential to be used as a chit substitute.

Gallic Acid-Dextran Conjugate: Green Synthesis of a Novel Antioxidant Molecule

“…Therefore, the lower the polysaccharide amount, the better is this effect. The comparison of the data demonstrated in Table 1 with those reported by Vittorio et al [14] highlights the proposal of Queiroz et al [26]. The data of Vittorio et al [14] showed the possibility of conjugating 0.068 mmol of catechin per gram of 4 kDa dextran.…”

“…Cúrcio [23] first reported the addition of GA to the polysaccharide, chitosan using a green method and demonstrated the subsequent increase in the antioxidant activity of chitosan; this was consistent with the reports from other groups [24,25,26]. Although this method is a cost-effective, easy-to-perform green method, it has already been used for the conjugation of catechin to dextran [14], but it has never been tested with the combination of GA and dextran.…”

“…The process of the conjugation of phenolic compounds using a free radical system has been frequently employed in the last few years; this includes systems that use hydrogen peroxide and ascorbic acid [14,23,26,29]. In this case, the interaction between the redox pairs of the two reactants at room temperature (22 °C) results in the formation of ascorbate and hydroxyl radicals, which initiate the conjugation reaction with GA [23].…”

“…To the best of our knowledge, this is the first study to demonstrate the conjugation of GA to dextran; therefore, it was not possible to compare the results of Table 1 with those of other studies. However, the application of the same GA conjugation method with chitosan resulted in the reduction in the molecular weight of chitosan between 10% [26] and 25% [29]. The interaction of the peroxide with the polysaccharide was probably responsible for generating this break in the molecule.…”

“…An important factor in GA conjugation to polysaccharides is the size of the polysaccharide molecule. Queiroz et al [26] found that the higher the molecular weight of chitosan, the greater was the amount of AG entering the molecule. These authors suggest that this observation may be attributed to the steric interference that the entrance of each GA molecule poses to the conjugating compound.…”