Crocin protects against endoplasmic reticulum stress-related tubular injury in diabetic nephropathy via the activation of the PI3K/AKT/Nrf2 pathway

Abstract

Objectives: Diabetic nephropathy (DN) is the main cause of end-stage renal disease, but the current treatment is not satisfactory. Crocin is a major bioactive compound of saffron with antioxidant and anti-endoplasmic reticulum stress (ERS) abilities used to treat diabetes. This study specifically investigated whether crocin has a regulatory role in renal injury in DN.

Materials and methods: The experiment was divided into control, (db/m mice), model (db/db mice), and experimental groups (db/db mice were intraperitoneally injected with 40 mg/kg crocin). Renal function-related indicators (Scr, BUN, FBG, UP, TG, TC, ALT, and AST) and oxidative stress-related indicators (ROS, MDA, GSH, SOD, and CAT) were assessed. The pathological changes of renal tissues were confirmed by HE, Masson, PAS, and TUNEL staining. The levels of ERS-related proteins (GRP78 and CHOP), apoptosis-related proteins, and PI3K/AKT and Nrf2 pathways-related proteins in renal tissue were detected.

Results: In db/db mice, renal function-related indicators, apoptotic cells of renal tissues, the contents of ROS and MDA as well as the expressions of CHOP, GRP78, and Bax were increased, the degree of renal tissue damage was aggravated, while the contents of GSH, SOD, and CAT, as well as the protein levels of Nrf2, PARP, anti-apoptotic proteins (Mcl-1, Bcl-2, Bcl-xl) were decreased compared to the db/m mice. However, crocin treatment reversed the above-mentioned situation. The expressions of the PI3K/AKT and Nrf2 pathways-related proteins were also activated by crocin.

Conclusion: Crocin inhibited oxidative stress and ERS-induced kidney injury in db/db mice by activating the PI3K/AKT and Nrf2 pathways.

Keywords: Crocin; Diabetic nephropathy; Endoplasmic reticulum – stress; Kidney injury; PI3K/AKT.

Figure 1

Content of serum creatinine (Scr) (A), blood urea nitrogen (BUN) (B), fasting blood glucose (FBG) (C), urinary protein (UP) (D), triglyceride (TG) (E), total cholesterol (TC) (F), alanine aminotransferase (ALT) (G), and aspartate aminotransferase (AST) (H) was measured in db/m mice and db/db mice treated with or without crocin

Figure 2

Histopathological changes in mouse kidney (A) H&E staining. (B) Masson staining. (C) PAS staining

Figure 3

Apoptosis cells of mouse kidney tissue

Figure 4

Immunohistochemical analysis of the expression of GRP78 (A) and CHOP (B) in mice kidney tissue

Figure 5

Immunofluorescence analysis of the expression of GRP78 (A) and CHOP (B) in mouse kidney tissue

Figure 6

Content of reactive oxygen species (ROS) (A), malondialdehyde (MDA) (B), glutathione (GSH) (C), superoxide dismutase (SOD) (D), and catalase (CAT) (E) in mouse kidney tissue homogenate was measured

Figure 7

Protein levels of mice kidney tissue were measured by western blot. (A) Protein levels of Nrf2 and PARP. (B) Protein levels of Bax, Mcl-1, Bcl-2, and Bcl-xl. (C) Protein levels of p-Akt/Akt and p-PI3K/PI3K