Nephroprotective potential of syringic acid in experimental diabetic nephropathy: Focus on oxidative stress and autophagy

Abstract

Background: Diabetic nephropathy (DN) is a chronic hyperglycemic manifestation of microvascular damage in the kidneys. Widespread research in this area suggests the involvement of perturbed redox homeostasis and autophagy in renal cells phrase- promote the progression of DN.

Materials and methods: Reframed sentences-The present study investigates the pharmacological effect of Syringic acid (SYA), in streptozotocin (STZ, 55 mg/kg, i.p) induced diabetic nephropathy model and in high glucose (30 mM) challenged rat renal epithelial cells (NRK 52E) cells with a focus on oxidative stress and autophagy mechanisms.

Results: Both in vivo and in vitro experimental data revealed elevated oxidative stress markers along with compromised levels of nuclear factor erythroid 2-related factor 2 (Nrf2), a pivotal cellular redox-regulated transcription factor in renal cells upon glycemic stress. Elevated blood glucose also reduced the autophagy process as indicated by low expression of light chain (LC) 3-IIB in diabetic kidney and in NRK 52E cells subjected to excess glucose. SYA (25 and 50 mg/kg, p.o.) administration for 4 weeks to diabetic rats, Reframed sentence-preserved the renal function as evidenced by reduced serum creatinine levels as well as improved urine creatinine and urea levles as compared to non treated diabetic animals. At the molecular level, SYA improved renal expression of Nrf2 and autophagy-related proteins (Atg5, Atg3, and Atg7) in diabetic rats. Similarly, SYA (10 and 20 μM) co-treatment in high glucose-treated NRK 52E cells displayed increased levels of Nrf2 and autophagy induction.

Conclusion: Results from this study signify the renoprotective effect of SYA and highlight the modulation of oxidative stress and autophagy mechanisms to mitigate diabetic kidney disease.

Keywords: Antioxidant enzymes; autophagy; diabetic nephropathy; oxidative stress; syringic acid.

Figure 1

(a) Effect of SYA on the diabetes induced renal histological change. Representative microscopic images of renal sections stained with haematoxylin and eosin as well as periodic acid stain. (b) Effect of SYA on oxidative stress in diabetic kidney. The values are expressed in terms of mean ± SEM (n = 3). ND nondiabetic, ND + SYA-50 nondiabetic rats treated with SYA at 50 mg/kg STZ-D diabetic, STZ-D + SYA-25 diabetic rats treated with SYA at 25 mg/kg, STZ-D + SYA-50 diabetic rats treated with SYA m. SYA = Syringic acid, SEM = Standard error of mean, ND = Nondiabetic, STZ-D = Streptozotocin-diabetic

Figure 2

(a) Representative Western blot images of NQO1 and Nrf2 and with corresponding densitometry analysis of the immunoblot. (b) Representative IHC images of renal tissue stained for Nrf2 and the bar graph representing percentage immunopositivity. The values are expressed in terms of mean ± SEM (n = 3). ND nondiabetic, ND + SYA-50 nondiabetic rats treated with SYA at 50 mg/kg STZ-D diabetic, STZ-D + SYA-25 diabetic rats treated with SYA at 25 mg/kg, STZ-D + SYA-50 diabetic rats treated with SYA mg/kg. IHC: Immunohistochemistry, SYA = Syringic acid, SEM = Standard error of mean, ND: Nondiabetic, STZ-D = Streptozotocin-diabetic, Nrf2 = Nuclear factor erythroid 2-related factor 2

Figure 3

(a) Effect of SYA on the autophagy in renal tissue. Representative western blots of autophagy proteins Atg 5, Atg3, Atg7, Beclin 1, and p62; the bar graph represents the densitometry analysis of corresponding immunoblot. (b) Representative fluorescence images of LC-3B staining in renal sections counterstained with DAPI and the bar graph represents the percentage immunopositivity of LC-3B. The values are expressed in terms of mean ± SEM (n = 3). ND nondiabetic, ND + SYA-50 nondiabetic rats treated with SYA a. SYA = Syringic acid, LC: Light chain, ND: Nondiabetic, SEM = Standard error of the mean

Figure 4

(a) Representative Immunoblot images demonstrating the effect of SYA on NQO1, Nrf2, Atg7, and p62 in NRK 52E cells challenged with high glucose. (b) Immunofluorescence images of NRK 52E cells immunostained with LC-3 and Lysotracker red. (c) Immunofluorescence images depicting immunostaining of Nrf2 in NRK 52E cells. The values are expressed in terms of mean ± SEM (n = 3). NC = Normal NRK 52E cells, NC + SYA-20: Normal NRK 52E cells treated with SYA at 20 μM HG-NRK 52E cells challenged with 30 mM glucose. SYA = Syringic acid, LC: Light chain, SEM = Standard error of the mean, NRK: Normal rat kidney, Nrf2 = Nuclear factor erythroid 2-related factor 2