Study on the Efficacy and Mechanism of Lycium barbarum Polysaccharide against Lead-Induced Renal Injury in Mice

Abstract

Lead is one of the most common heavy metal pollutants in the environment. Prolonged exposure to lead will induce oxidative stress, inflammation, and apoptosis in the kidneys, which in turn causes kidney injury. Lycium barbarum polysaccharide (LBP) is well known for its numerous pharmacological properties. This study aims to explore the efficacy and mechanism of LBP against lead-induced kidney damage in mice. Symptoms of renal injury were induced in mice by using 25 mg/kg lead acetate (PbAc₂), and different doses of LBP (200, 400, and 600 mg/kg BW) were orally administrated to PbAc₂-treated mice for five weeks. The results of the pharmacodynamics experiment showed that the renal pathological damages, serum creatinine (Cre), blood urea nitrogen (BUN), and kidney index of PbAc₂-treated mice could be significantly alleviated by treatment with LBP. Further, LBP treatment significantly increased the weight and feed intake of PbAc₂-treated mice. The dose effect results indicated that a medium dose of LBP was superior to high and low doses. The results of mechanistic experiments showed that LBP could attenuate oxidative stress, inflammation, and apoptosis in the kidneys of mice with lead toxicity by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway.

Keywords: Lycium barbarum polysaccharide; Nrf2 signaling pathway; apoptosis; inflammatory; lead-induced renal injury; oxidative stress.

Figure 1

Pharmacodynamic evaluation index for LBP against lead-induced renal injury. The results are expressed as the mean ± SD. * Statistically significant compared to control group, * p < 0.05, ** p < 0.01. ^# Statistically significant compared to model group, ^# p < 0.05, ^## p < 0.01. (a) Weight change of mice; (b) feed intake of mice; (c) renal index; (d) expression level of BUN; (e) expression level of Cre.

Figure 2

Light micrographs of the kidney cortex. (a) Control; (b) model; (c) low dose; (d) middle dose; (e) high dose. Glomerulus (blue arrow), urinary space (red arrow), damaged renal tubules with vacuolated cytoplasm (green arrow), and inflammatory cells in the interstitial tissue (yellow arrow). Original magnification: 400.

Figure 3

Effects of LBP on oxidative stress markers. The results are expressed as the mean ± SD, n = 10. * Statistically significant compared to control group, * p < 0.05, ** p < 0.01. ^# Statistically significant compared to model group, ^## p < 0.01. (a) Expression of superoxide dismutase (SOD); (b) Expression of malondialdehyde (MDA); (c) Expression of glutathione S-transferase (GST); (d) Expression of glutathione (GSH).

Figure 4

Effects of LBP on renal inflammatory biomarkers. The results are expressed as the mean ± SD, n = 10. * Statistically significant compared to control group, * p < 0.05, ** p < 0.01. ^# Statistically significant compared to model group, ^# p < 0.05, ^## p < 0.01. (a) Expression of tumor necrosis factor-α (TNF-α); (b) Expression of interleukin-1β (IL-1β); (c) Expression of nitric oxide.

Figure 5

Effects of LBP on apoptotic biomarkers. The results are expressed as the mean ± SD, n = 10. * Statistically significant compared to control group, * p < 0.05, ** p < 0.01. ^# Statistically significant compared to model group, ^## p < 0.01. (a) Expression of caspase-3 (Casp-3); (b) Expression of Bax; (c) Expression of Bcl-2.

Figure 6

Effects of LBP on Nrf2-related protein expression. I, control; II, model; III, low dose; IV, middle dose; V, high dose. The results are expressed as the mean ± SD, n = 10. * Statistically significant compared to control group, ** p < 0.01. ^# Statistically significant compared to model group, ^## p < 0.01. (a) Western blot analysis of proteins related to nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. (b) Expression of Nrf2; (c) Expression of Kelch-like ECH-associated protein 1 (Keap1); (d) Expression of Oxygenase-1 (HO-1) (e) Expression of NAD(P)H dehydrogenase, quinone 1 (NQO1).

Figure 6

Effects of LBP on Nrf2-related protein expression. I, control; II, model; III, low dose; IV, middle dose; V, high dose. The results are expressed as the mean ± SD, n = 10. * Statistically significant compared to control group, ** p < 0.01. ^# Statistically significant compared to model group, ^## p < 0.01. (a) Western blot analysis of proteins related to nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. (b) Expression of Nrf2; (c) Expression of Kelch-like ECH-associated protein 1 (Keap1); (d) Expression of Oxygenase-1 (HO-1) (e) Expression of NAD(P)H dehydrogenase, quinone 1 (NQO1).

Figure 7

Results of multivariate statistical analysis. (a) Principal component analysis diagram; (b) Orthogonal partial least squares discriminant analysis diagram; (c) Verification diagram of orthogonal partial least squares discriminant analysis.

Figure 8

Clustering heatmap results. “n” indicates the number of mice, Kn the control group, Mn the model group, LD the low-dose group, MD the medium-dose group, and HD the high-dose group. Nitric oxide (NO); Tumor necrosis factor-α (TNF-α); Malondialdehyde (MDA); Interleukin-1β (IL-1β); Serum creatinine (Cre); Blood urea nitrogen (BUN); Caspase-3 (Casp-3); Superoxide dismutase (SOD); Glutathione S-transferase (GST); Glutathione (GSH).

Figure 9

The mechanism of lead-induced renal injury in mice and the mechanism of LBP against lead-induced renal injury. Intragastric administration (i.g); Lead acetate (PbAc₂); Nitric oxide (NO); Tumor necrosis factor-α (TNF-α); Malondialdehyde (MDA); Interleukin-1β (IL-1β); Serum creatinine (Cre); Blood urea nitrogen (BUN); Caspase-3 (Casp-3); Superoxide dismutase (SOD); Glutathione S-transferase (GST); Glutathione (GSH); Cullin 3 (Cul3); Nuclear factor erythroid 2-related factor 2 (Nrf2); Kelch-like ECH-associated protein 1 (Keap1); Oxygenase-1 (HO-1); NAD(P)H dehydrogenase, quinone 1 (NQO1); Lycium barbarum polysaccharide (LBP); Antioxidant response element(ARE); Indicates up-regulation or recovery (↑); Indicates downregulation or inhibition (↓).