1,2,3,4,6-Penta-O-galloyl-beta-D-glucose reduces renal crystallization and oxidative stress in a hyperoxaluric rat model

Abstract

Adhesion of calcium oxalate (CaOx) crystals to kidney cells may be a key event in the pathogenesis of kidney stones associated with marked hyperoxaluria. Previously, we found that 1,2,3,4,6-penta-O-galloyl-β-D-glucose (PGG), isolated from a traditional medicinal herb, reduced CaOx crystal adhesion to renal epithelial cells by acting on the cells as well as on the crystal surface. Here we used the ethylene glycol (EG)-mediated hyperoxaluric rat model and found evidence of oxidant stress as indicated by decreases in the activities of the renal antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase, with increased kidney cell apoptosis and serum malondialdehyde levels, all evident by 21 days of EG treatment. These effects of hyperoxaluria were reversed by concurrent PGG treatment along with decreased urinary oxalate levels and CaOx supersaturation. Renal epithelial cell expression of the crystal binding molecule hyaluronan increased diffusely within 7 days of EG initiation, suggesting it is not a result of but precedes crystal deposition. Renal cell osteopontin (OPN) was also upregulated in EG-treated animals, and PGG significantly attenuated overexpression of both OPN and hyaluronan. Thus, our findings demonstrate that PGG reduces renal crystallization and oxidative renal cell injury, and may be a candidate chemopreventive agent for nephrolithiasis.

Figure 1. Effect of 1,2,3,4,6-penta-O-galloyl-b-D-glucose (PGG) on calcium oxalate (CaOx) crystal deposition in ethylene glycol (EG)-treated rat urine and kidneys

(a) Twenty-four hour rat urine samples on days 7, 14, and 21 were collected on ice in a metabolic cage and CaOx crystals with tetragonal bipyramidal habit were counted in a hemocytometer at X400 magnification. Graph represents the average number of urinary CaOx crystals in the rat urine per high power field. (b) Histological specimens of rat kidney tissues (n=6/group) obtained on days 7, 14, and 21 following EG treatment were stained with hematoxylin and eosin (H&E), and the number of crystal depositions was counted. Graph represents the average number of crystal deposits in the kidney per high power field. Data represent means±s.d. *P<0.05, **P<0.01, and ***P<0.001 versus untreated control; ###P<0.001 versus EG; and !!!P<0.001 versus EG+P4 two-way analysis of variance followed by a post hoc analysis. C, untreated control (distilled water); EG, EG-treated group (0.8% EG/1% ammonium chloride (AC) (NH4Cl) in drinking water); and EG+P4 and EG=P20, two EG- and PGG-treated groups (0.8% EG/1% AC + 4 or 20 mg/kg of PGG in 2% methylcellulose).

Figure 2. Effect of 1,2,3,4,6-penta-O-galloyl-b-D-glucose (PGG) on ROS production in human renal cells (HRCs) exposed to calcium oxalate (1mM) and on the serum malondialdehyde (MDA) level in ethylene glycol (EG)-treated rats

(a) The levels of ROS in HRCs were measured using ROS-sensitive fluorometric probe, 2,7-dichlorofluorescein by flow cytometric analysis. Data are expressed as % cells positive. Data represent means±s.d. #P<0.05 versus untreated control and **P<0.01 versus oxalate. (b) The level of serum MDA was determined on days 7, 14, and 21 following EG treatment (n=6/group) by enzyme-linked immunosorbent assay colorimetric method. Data represent means±s.d. ***P<0.001 versus untreated control and ###P<0.001 versus EG, two-way analysis of variance followed by a post hoc analysis. C, untreated control (distilled water); EG, EG-treated group (0.8% EG/1% ammonium chloride (AC; NH4Cl) in drinking water); and EGþP4 and EGþP20, two PGG-treated groups (0.8% EG/1% ACþ4 or 20 mg/kg of PGG in 2% methylcellulose).

Figure 3. Effect of 1,2,3,4,6-penta-O-galloyl-b-D-glucose (PGG) on antioxidant enzyme activity in ethylene glycol (EG)-treated rat kidneys

(a) Immunohistochemical staining for superoxide dismutase (SOD) expression in rat kidney tissues (n¼6/group) obtained on days 7, 14, and 21 following EG treatment was performed and the average number of positive stained cells per high power field was counted from three independent experiments. Data represent means±s.d. ***P<0.001 versus untreated control; #P<0.05 and ###P<0.001 versus EG; and !!!P<0.001 versus EG+P4, two-way analysis of variance followed by a post hoc analysis. (b–c) Western blot analysis in EG-treated rat kidneys on day 21 following EG treatment for Cu/Zn SOD (b), catalase (c), glutathione peroxidase (c), and b-actin. Data of protein expression represent means±s.d. *P<0.05 versus untreated control and ##P<0.01 versus EG, one-way analysis of variance followed by a post hoc analysis. C, untreated control (distilled water); EG, EG-treated group (0.8% EG/1% ammonium chloride (AC; NH4Cl) in drinking water); and EG+P4 and EG+P20, two PGG-treated groups (0.8% EG/1% AC+4 or 20 mg/kg of PGG in 2% methylcellulose).

Figure 4. Effect of 1,2,3,4,6-penta-O-galloyl-b-D-glucose (PGG) on osteopontin (OPN) expression in ethylene glycol (EG)-treated rat kidneys

(a) Immunohistochemical staining for OPN in rat kidney tissues (n¼6/group) obtained on day 21 following EG treatment was performed and the average number of stained cells per high power field was counted from three independent experiments. Data represent means±s.d. (b) Western blot analysis in EG-treated rat kidneys for OPN and b-actin. ***P<0.001 versus untreated control; ###P<0.001 versus EG; and !!!P<0.001 versus EG+P4, one-way analysis of variance followed by a post hoc analysis. C, untreated control (distilled water); EG, EG-treated group (0.8% EG/1% ammonium chloride (AC; NH4Cl) in drinking water); and EG+P4 and EG+P20, two PGG-treated groups (0.8% EG/1% ACþ4 or 20 mg/kg of PGG in 2% methylcellulose).

Figure 5. Effect of PGG on cell death index TUNEL staining in EG treated rat kidneys

Cell death was assessed by TUNEL assay in rat kidney tissues (n¼6/group) obtained on day 21 following EG treatment. Graph represents the average number of TUNEL positive stained cells per high power field. Data represent means±s.d. ###P<0.001 versus untreated control, and *P<0.05 and ***P<0.001 versus untreated control, ###P<0.001 versus EG, two-way analysis of variance followed by a post hoc analysis. C, untreated control (distilled water); EG, EG treated group (0.8% EG/1% AC (NH4Cl) in drinking water) and, EG+P4 and EG+P20; two PGG-treated groups (0.8% EG/1% AC+4 or 20mg/kg of PGG in 2% methylcellulose).

Figure 6. Effect of 1,2,3,4,6-penta-O-galloyl-b-D-glucose (PGG) on hyaluronan expression in ethylene glycol (EG)-treated rat kidneys

(a) Immunohistochemical staining for renal hyaluronan expression in EG-treated rat kidneys (n¼6/group) obtained on days 7, 14, and 21 following EG treatment. (b) The average number of hyaluronan-positive stained cells per high power field. Data represent means±s.d. *P<0.05 and ***P<0.001 versus untreated control; ###P<0.001 versus EG; and !P<0.05 versus EGþP4, two-way analysis of variance followed by a post hoc analysis. C, untreated control (distilled water); EG, EG-treated group (0.8% EG/1% ammonium chloride (AC; NH4Cl) in drinking water); and EG+P4 and EG+P20, two PGG-treated groups (0.8% EG/1% ACþ4 or 20 mg/kg of PGG in 2% methylcellulose).