Baicalin Alleviates Oxidative Stress and Inflammation in Diabetic Nephropathy via Nrf2 and MAPK Signaling Pathway

Abstract

Background

Oxidative stress and inflammation play essential roles in the development and progression of diabetic nephropathy (DN). Baicalin (BAI), a natural flavonoid, has been showed to have a renoprotective effect in various renal diseases. However, its underlying mechanisms in DN remain unclear. In this study, we explored the potential effects and underlying mechanisms of BAI on DN using a spontaneous DN model.

Methods

The protective effects of BAI on DN have been evaluated by detecting DN-related biochemical indicators, kidney histopathology and cell apoptosis. After that, we examined the level of renal oxidative stress and inflammation to explain BAI’s renoprotective effects. Then, Nrf2 pathway was tested to clarify its antioxidant activity, and kidney transcriptomics was conducted to elucidate its anti-inflammatory activity. Finally, Western blot was applied for final mechanism verification.

Results

Our results found that BAI effectively ameliorated diabetic conditions, proteinuria, renal histopathological changes and cell apoptosis in DN. BAI significantly improved the kidney levels of glutathione peroxidase (GSH-PX), superoxide dismutase (SOD) and catalase (CAT), and reduced malondialdehyde (MDA) level. Meanwhile, the infiltration of inflammatory cells including T-lymphocytes, T-helper cells, neutrophils and macrophages, and the mRNA levels of pro-inflammatory cytokines (IL-1β, IL-6, MCP-1 and TNFα) were also obviously inhibited by BAI. Afterward, Western blot found that BAI significantly activated Nrf2 signaling and increased the expression of downstream antioxidant enzymes (HO-1, NQO-1). Kidney transcriptomics revealed that the inhibition of MAPK signaling pathway may contribute to BAI’s anti-inflammatory activity, which has also been verified in later experiment. BAI treatment did obviously inhibit the activation of canonical pro-inflammatory signaling pathway MAPK family, such as Erk1/2, JNK and P38.

Conclusion

In summary, our data demonstrated that BAI can treat DN by alleviating oxidative stress and inflammation, and its underlying mechanisms were associated with the activation of Nrf2-mediated antioxidant signaling pathway and the inhibition of MAPK-mediated inflammatory signaling pathway.

Keywords:

• baicalin
• diabetic nephropathy
• oxidative stress
• inflammation
• Nrf2
• MAPK

Abbreviations

DN, Diabetic nephropathy; BAI, Baicalin; CKD, chronic kidney disease; DM, diabetes mellitus; ESRD, End-stage renal disease; ACEIs, Angiotensin-converting enzyme inhibitors; ARBs, Angiotensin receptor blockades; ROS, Reactive oxygen species; FBG, Fasting blood glucose; GTT, Glucose tolerance test; ITT, Insulin tolerance test; HOMA-IR, Homeostasis model assessment insulin resistance; BUN, Urea nitrogen; Cr, Creatinine; AER, Urine albumin excretion rate; GSH-PX, Glutathione peroxidase; SOD, Superoxide dismutase; CAT, Catalase; MDA, Malonaldehyde; GO, Gene ontology; KEGG, Kyoto Encyclopedia of Genes and Genomes; DEG, Differentially expressed gene; SEM, Scanning electron microscopy; TEM, Transmission electron microscopy; GBM, Glomerular basement membrane; TUNEL, Terminal deoxynucleotidyl transferase dUTP nick end labeling; ARE, Antioxidant response element; Nrf2, Nuclear factor erythroid-derived 2-related factor 2; HO-1, heme oxygenase-1; NQO-1, NAD(P)H: quinone oxidoreductase-1; MAPK, Mitogen-activated protein kinase; O²⁻, Superoxide anion; HO•, Hydroxyl radical; H₂O₂, Hydrogen peroxide; ONOO⁻, Peroxynitrite; HClO, Hypochlorous acid; NO, Nitric oxide; DAG, Diacylglycerol; PKC, Protein kinase C; GST, Glutathione S-transferase; GPx-1, Glutathione peroxidase.

Data Sharing Statement

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Ethics Approval and Informed Consent

All of the procedures were reviewed and approved by the Animal Ethics Committee of Tongji Hospital of Tongji Medical College of Huazhong University of Science and Technology according to the Guideline for Ethical Review of Animal Welfare (GB/T 35892–2018).

Author Contributions

All authors contributed to data analysis, drafting or revising the article, gave final approval of the version to be published, agreed to the submitted journal, and agreed to be accountable for all aspects of the work.

Disclosure

The authors declare no conflict of interest.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (No. 81974567), and TCM Modernization Research of National Key Research and Development Program (No. 2018YFC1704202).