Effects of Porphyra yezoensis Polysaccharide with Different Molecular Weights on the Adhesion and Endocytosis of Nanocalcium Oxalate Monohydrate in Repairing Damaged HK-2 Cells

The adhesion and endocytosis of renal epithelial cells to urinary microcrystals are closely related to kidney stone formation; however, the mechanism of cell state changes that affect adhesion and endocytosis remains unclear. In this study, a damaged cell model was established using oxalate to impair human kidney proximal tubular epithelial cells (HK-2). Then, we used four degraded Porphyra yezoensis polysaccharides (PYPs), namely, PYP1, PYP2, PYP3, and PYP4, with molecular weight of 576.2, 49.5, 12.6, and 4.02 kDa, respectively, to repair the damaged cells. After repairing the damaged HK-2 cells by PYPs, the cell morphology gradually recovered to near normal; the cell migration speed increased; the phosphatidylserine eversion ratio and osteopontin expression decreased; and the intracellular adenosine triphosphate was promoted. The adhesion and endocytosis of calcium oxalate monohydrate (COM) crystals were closely related to cell state. Normal cells could endocytose crystals more than the damaged cells, whereas damaged cells could adhere to crystals more than the normal cells. The cells repaired by PYPs inhibited the adhesion of nano-COM crystals and promoted the endocytosis of the adherent crystals, thereby reducing the adhesion of crystals on the cell surface under both effects. As the molecular weight of PYP decreased, the ability of PYP to repair cells, inhibit crystal adhesion, and promote endocytosis of cells was enhanced; that is, PYP4, which had the lowest molecular weight, exhibited the best biological activity. Therefore, PYPs, especially PYP4, may become an optional green drug to inhibit the formation and recurrence of calcium oxalate stones.