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Protective effect of salvianolic acid B against oxidative injury associated with cystine stone formation

The aim of this study was to investigate the role of oxidative stress in cystine crystal formation and whether salvianolic acid B, a natural antioxidant, could prevent cystine-mediated oxidative injury in vivo and in vitro. The levels of oxidative stress and antioxidase activity in cystine stone patients were assessed. Then, the oxidative stress exerted by cystine on human kidney-2 (HK-2) cell viability and biochemical parameters including antioxidase activity and antioxidant protein expression were evaluated, and the protective action of salvianolic acid B was also examined. Finally, salvianolic acid B was tested to determine whether it could prevent or reduce renal crystal formation in Slc7a9 knockout mice. The activity levels of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were decreased, and the amount of malondialdehyde (MDA) was increased in patients with cystine stones compared with people without cystine stones (p < 0.05). Significant reductions in cell viability, antioxidase activity and antioxidant protein expression levels were found in the cystine group compared with controls. However, such oxidative injuries were prevented by salvianolic acid B. In the animal study, loose crystals with white spots were seen in the renal parenchyma, bilateral renal pelvis and bladders in the Slc7a9 knockout group. In contrast, no renal crystals were seen in the control group, and markedly fewer crystals with significantly higher antioxidase activity and diminished oxidative stress were detected in the salvianolic acid B group. Cystine cytotoxicity in vitro and cystine stone formation in vivo were associated with oxidative stress, and salvianolic acid B could protect against cystine stone-induced injury.

Size-dependent toxicity and interactions of calcium oxalate dihydrate crystals on Vero renal epithelial cells

Urinary crystals in normal and kidney stone patients often have varying sizes; the interaction between renal epithelial cells and COD crystals generated in the tubular fluid could play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. This study aims to compare the cytotoxicity of micro/nano-calcium oxalate dihydrate (COD) crystals (50 nm, 100 nm, 600 nm, 3 μm, and 10 μm) toward African green monkey renal epithelial (Vero) cells to reveal the mechanism of kidney stone formation at the molecular and cellular levels.

METHODS

Vero cells were exposed to COD crystals of varying sizes at a concentration of 200 μg mL^-1 for 6 h. The effects of COD crystals on Vero cell viability, apoptosis rate, and cellular biochemical parameters [lactate dehydrogenase (LDH), superoxide dismutase (SOD), reactive oxygen species (ROS), hyaluronic acid (HA), osteopontin (OPN), and mitochondrial membrane potential (Δψ_m)] were determined using biochemical and morphological analyses.

RESULTS

Vero cell viability and apoptotic rate were closely associated with the size of COD crystals; lower cell viability and higher apoptosis rate were observed in cells exposed to smaller COD crystal size. The expression of SOD, ROS, HA and OPN also changed in a size-dependent manner after exposure to the five different sizes of COD crystals. The area ratio of the (100) face with a high density of Ca²⁺ ions to the total surface area was also found to influence the severity of cell injury. Cell injury induced by COD crystals was mainly caused by excessive expression of intracellular ROS and reduction of free-radical scavenger SOD. Moreover, binding of large crystals on the cell membrane surface takes more time to cause cell injury than internalized small-sized crystals. The cell death rate was found to be positively correlated with the amount of internalized COD crystals.

CONCLUSIONS

although the COD toxicity is often disregarded, the size-dependent cytotoxicity of COD crystals toward Vero cells is demonstrated in this study.