Repair of Tea Polysaccharide Promotes the Endocytosis of Nanocalcium Oxalate Monohydrate by Damaged HK-2 Cells

Different Degrees of Sulfated Laminaria Polysaccharides Recovered Damaged HK-2 Cells and Inhibited Adhesion of Nano-COM and Nano-COD Crystals

Purpose

The crystal adhesion caused by the damage of renal tubular epithelial cells (HK-2) is the key to the formation of kidney stones. However, no effective preventive drug has been found. This study aims to explore the recovery effects of four Laminaria polysaccharides (SLPs) with different sulfate (-OSO3-) contents on damaged HK-2 cells and the difference in the adhesion of damaged cells to nanometer calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) before and after recovery.

Methods

Sodium oxalate (2.6 mmol/L) was used to damage HK-2 cells to establish a damaged model. SLPs (LP0, SLP1, SLP2, and SLP3) with -OSO3- contents of 0.73%, 15.1%, 22.8%, and 31.3%, respectively, were used to restore the damaged cells, and the effects of SLPs on the adhesion of COM and COD, with a size of about 100 nm before and after recovery, were measured.

Results

The following results were observed after SLPs recovered the damaged HK-2 cells: increased cell viability, restored cell morphology, decreased reactive oxygen levels, increased mitochondrial membrane potential, decreased phosphatidylserine eversion ratio, increased cell migration ability, reduced expression of annexin A1, transmembrane protein, and heat shock protein 90 on the cell surface, and reduced adhesion amount of cells to COM and COD. Under the same conditions, the adhesion ability of cells to COD crystals was weaker than that to COM crystals.

Conclusions

As the sulfate content in SLPs increases, the ability of SLPs to recover damaged HK-2 cells and inhibit crystal adhesion increases. SLP3 with high -OSO3- content may be a potential drug to prevent kidney stones.

Carboxymethylation of Corn Silk Polysaccharide and Its Inhibition on Adhesion of Nanocalcium Oxalate Crystals to Damaged Renal Epithelial Cells

The purpose of this study was to explore the repair effect of carboxymethyl-modified corn silk polysaccharide (CSP) on oxidatively damaged renal epithelial cells and the difference in adhesion between cells and calcium oxalate crystals. The CSP was degraded and modified through carboxymethylation. An oxidatively damaged cell model was constructed by oxalate damage to human kidney proximal tubular epithelial (HK-2) cells. Then, the damaged cells were repaired by modified polysaccharides, and the changes in biochemical indexes and adhesion ability between cells and crystals before and after repair were detected. Four modified polysaccharides with carboxyl group (-COOH) contents of 3.92% (CSP0), 7.75% (CCSP1), 12.90% (CCSP2), and 16.38% (CCSP3) were obtained. Compared with CSP0, CCSPs had stronger antioxidant activity, could repair damaged HK-2 cells, and could reduce phosphorylated serine eversion on the cell membrane, the expression of osteopontin (OPN) and Annexin A1, and crystal adhesion. However, its effect on the expression of hyaluronic acid synthase was not substantial. The carboxymethyl modification of the CSP can improve its ability to repair cells and inhibit crystal adhesion and aggregation. A high carboxymethylation degree results in strong polysaccharide activity. CCSPs are expected to reduce the risk of kidney stone formation and recurrence.

Effect of autophagy on oxalate-induced toxicity of human proximal renal tubular epithelial cell

OBJECTIVES

To investigate the role of autophagy in oxalate-induced toxicity of human proximal renal tubular epithelial cell (HK-2).

METHODS

HK-2 cells were exposed to oxalate (1 mmol/L) for 2 h and 3-methyladenine (3-MA) was used to inhibit autophagy. Then Western blotting was used to measure the expression of autophagy-related protein LC3II. Cell viability and cell apoptosis were measured by MTT assay and flow cytometry assay, respectively.

RESULTS

Cytoplasmic vacuolization was observed in HK-2 cells after treating with oxalate for 2 h. However, 3-MA showed no effects on the formation of cytoplasmic vacuolization regardless of the dose at 1 or 5 mmol/L. The expression of LC3II protein was significantly increased in the HK-2 cells in the presence of oxalate (0.62±0.03 vs 0.35±0.02, P<0.05). The expression of LC3II protein in HK-2 cells was downregulated by 3-MA at both 1 and 5 mmol/L compared with the blank control (0.17±0.03 vs 0.35±0.02, 0.16±0.03 vs 0.35±0.02, both P<0.05). Oxalate-induced upregulation of LC3II was reversed by 3-MA only at the concentration of 5 mmol/L (0.47±0.04 vs 0.62±0.03, P<0.05) rather than 1 mmol/L (0.61±0.04 vs 0.62±0.03, P>0.05). Oxalate attenuated viability [(77.32±2.69)% vs 100%, P<0.05] and increased the apoptosis [(8.32±1.05)% vs (2.36±0.29)%, P<0.05] in HK-2 cells, and these effects were reversed by 3-MA only at the concentration of 5 mmol/L [(91.91±3.36)% vs (77.32±2.69)%, (3.45±0.21)% vs (8.32±1.05)%, respectively, both P<0.05] rather than 1 mmol/L [(80.48±3.41)% vs (77.32±2.69)%, (7.81±0.47)% vs (8.32±1.05)%, both P>0.05, respectively].

CONCLUSIONS

Autophagy of HK-2 cells is enhanced by oxalate at the concentration of 1 mmol/L. Inhibition of 3-MA-induced autophagy protects HK-2 cells from the oxalate-induced cytotoxicity.

Inhibition of Calcium Oxalate Formation and Antioxidant Activity of Carboxymethylated Poria cocos Polysaccharides

Three carboxymethylated Poria cocos polysaccharides (PCP-C1, PCP-C2, and PCP-C3) with -COOH contents of 6.13%, 10.24%, and 16.22%, respectively, were obtained by carboxymethylation of the original polysaccharide (PCP-C0), which has a molecular weight of 4 kDa and a carboxyl (-COOH) content of 2.54%. The structure of the PCP-Cs was characterized by FT-IR, ¹H NMR, and ¹³C NMR spectra. The four PCP-Cs exhibited antioxidant activity, and their ability to scavenge radicals (hydroxyl and DPPH) and chelate ferrous ions was positively correlated with the degree of carboxymethylation. As the content of -COOH groups in the PCP-Cs increases, their ability to regulate the growth of calcium oxalate (CaOx) crystals was enhanced, thus inhibiting the growth of calcium oxalate monohydrate (COM) crystals and inducing the formation of more calcium oxalate dihydrate (COD) crystals. The formed CaOx crystal was more round and blunt, the absolute value of the Zeta potential on the crystal surface increased, and the aggregation between crystals was inhibited. Thermogravimetric analysis curves showed that the proportions of PCP-C0, PCP-C1, PCP-C2, and PCP-C3 incorporated into the crystal were 20.52%, 15.60%, 10.65%, and 9.78%, respectively, in the presence of 0.4 g/L PCP-Cs. PCP-C protection resisted oxidative damages of human kidney proximal tubular epithelial cells (HK-2) caused by oxalate, resulting in increased cell viability and superoxide dismutase activity and decreased reactive oxygen species levels, malondialdehyde content, and 8-hydroxy-deoxyguanosine expression. Hence, PCP-Cs, especially PCP-C3, can inhibit the formation of CaOx crystals and may have the potential to be an alternative antistone drug.