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

Moacir Fernandes Queiroz,Hugo Alexandre Oliveira Rocha,Karoline Rachel Teodosio Melo,Guilherme Lanzi Sassaki,Diego Araujo Sabry,Leandro Silva Costa

doi:10.3390/molecules24112074

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.

Highlights

Calcium oxalate (CaOx) crystals are involved in the formation of kidney stones, and previous reports show that they account for 70% of the cases of kidney stones [1,2]
This paper showed that Chit can induce the formation of calcium oxalate (CaOx) monohydrate (COM) crystals in vitro, which are the major kidney stone-forming crystals [8]
We evaluated whether the conjugation of Chit with gallic acid (GA) using a green method would yield a molecule that would interfere less in the formation of CaOx with better antioxidant activity

Summary

Introduction

Calcium oxalate (CaOx) crystals are involved in the formation of kidney stones, and previous reports show that they account for 70% of the cases of kidney stones [1,2]. Oxalate crystals form naturally during the water reabsorption process in the kidneys as well as during the formation of urine. This reabsorption raises the concentration of the salts, leaving the urine supersaturated with these ions, thereby inducing interaction between the molecules, leading to the formation of crystals [3]. The renal pathways have mechanisms that stabilize the CaOx crystals so they can be excreted thereby preventing their accumulation [4]. Several factors can lead to a failure of this protection system and induce the formation of oxalate crystals that are difficult to excrete and remain for a longer time in the renal system, allowing them to grow and interact with the renal epithelium [5]. When crystals interact with a renal epithelium cells, they can cause oxidative damage, which can lead to cell death, thereby damaging nearby cells; this initiates a destructive cycle: in the damaged area the crystal adhesion is easier, inducing more oxidative damage, leading to more cell death, and so on [6,7]

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