Modulation of Autophagy and Nitric Oxide Signaling via Glycyrrhizic Acid and 7-Nitroindazole in MPTP-induced Parkinson's Disease Model

Abstract

Background: Parkinson's disease (PD) is characterized by dopaminergic (DA) neuron loss, Lewy body build-up, and motor dysfunction. One of the primary pathogenic mechanisms of PD development is autophagy dysfunction and nitric oxide-mediated neurotoxicity.

Purpose: The current study focuses on autophagy and nitric oxide (NO) signaling roles in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated PD mice and their protection by their modulators.

Method: BALB/c mice were administered MPTP (30 mg/kg/i.p/day) for five consecutive days in order to create a PD model. Following MPTP poisoning, the doses of GA (16.8 mg/kg/day/i.p.), 7-nitroindazole (7-NI) (10 mg/kg/day/i.p.), and their combination were administered once daily for 14 days. Animals were observed for behavioral and locomotor changes, biochemical examination, inflammatory mediators, and analysis of molecular markers.

Results: GA, 7-NI alone significantly reduced MPTP-induced locomotor, behavioral, and oxidative damage. Additionally, in MPTP-intoxicated animals, 7-NI and GA had protective effects on dopamine levels, TH positive DA neurons, inflammatory cytokines interleukin 1β (IL-1β), tumor necrosis factor-alpha (TNF-α), nuclear factor-kappa B (NF-κB), and cyclooxygenase-2 (Cox-2) concentration. Furthermore, GA increases LC3BII expression, which in turn increases autophagy. It also decreases total NO content, and a significant response of 7-NI demonstrates their interaction, which is neuroprotective.

Conclusion: Present research suggests that dysregulation of autophagy and NO-mediated neuroinflammation are involved in the pathogenesis and progression of MPTP-induced PD. The use of two pharmacotherapeutics, GA and 7-NI, respectively, significantly reduces MPTP-induced PD distortions and their interaction enhances the overall protective effect, suggesting that these pharmacological agents may be used for the treatment of PD.

Keywords: MPTP; Parkinson’s disease; autophagy; neuroinflammation; nitric oxide.

Figure 1.. GA and 7-NI Attenuated the Neurobehavioral Changes in MPTP-induced Mice.

Figure 2.. GA and 7-NI Attenuated the Oxidative Stress Parameters in MPTP-induced Mice. (a) Lipid Peroxidation Level (MDA) was Measured in Brain Striatum of MPTP-induced Mice. (b and c) Brain Enzymic Antioxidant Activities; SOD and CAT were Determined.

Figure 3.. Proinflammatory Cytokines; IL-1β and TNF-α are Involved in Neuroinflammatory Consequences of MPTP-induced PD Model. (a and b) Both Cytokines were Assessed Through Sandwich ELISA in SnPc of Mice Brain. (c) Dopamine Level in Striatum of MPTP-induced Mice was Determined by HPLC Analysis.

Figure 4.. GA and 7-NI Attenuated the Major Inflammatory Mediators in MPTP-induced Mice. (a and b) Effect of GA and 7-NI on NF-κB and Cox-2 Levels Through ELISA Estimation. (c) Total NO Level in MPTP-induced Mice Brain.

Figure 5.. Immunofluorescence Staining of TH in SN of PD Mice Brain.

Figure 6.. Attenuation of MPTP-induced Changes in Immunofluorescence Staining of LC3BII Level.

Figure 7.. Diagram Showing the Interaction Between Autophagy and nNOS-mediated NO Regulation, as well as how GA and 7-NI Reduced the Neurotoxicity Caused by MPTP in an in vivo Model of PD.