Paeoniflorin attenuates neuroinflammation and dopaminergic neurodegeneration in the MPTP model of Parkinson's disease by activation of adenosine A1 receptor

Abstract

1. This study examined whether Paeoniflorin (PF), the major active components of Chinese herb Paeoniae alba Radix, has neuroprotective effect in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). 2. Subcutaneous administration of PF (2.5 and 5 mg kg(-1)) for 11 days could protect tyrosine hydroxylase (TH)-positive substantia nigra neurons and striatal nerve fibers from death and bradykinesia induced by four-dose injection of MPTP (20 mg kg(-1)) on day 8. 3. When given at 1 h after the last dose of MPTP, and then administered once a day for the following 3 days, PF (2.5 and 5 mg kg(-1)) also significantly attenuated the dopaminergic neurodegeneration in a dose-dependent manner. Post-treatment with PF (5 mg kg(-1)) significantly attenuated MPTP-induced proinflammatory gene upregulation and microglial and astrocytic activation. 4. Pretreatment with 0.3 mg kg(-1) 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A1 receptor (A1AR) antagonist, 15 min before each dose of PF, reversed the neuroprotective and antineuroinflammatory effects of PF. 5. In conclusion, this study demonstrated that PF could reduce the MPTP-induced toxicity by inhibition of neuroinflammation by activation of the A1AR, and suggested that PF might be a valuable neuroprotective agent for the treatment of PD.

Figure 1

Effects of PF on MPTP-induced dopaminergic neuron loss in the SNc with pretreatment. Quantitative analysis of the TH-positive cells (a) and Nissl-stained neurons (b) in the SNc of mice. Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^**P<0.01 compared with saline-treated mice, ^##P<0.01 compared with MPTP-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 2

Effects of PF on MPTP-induced dopaminergic fiber loss in the striatum with pretreatment. Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^**P<0.01 compared with saline-treated mice, ^##P<0.01 compared with MPTP-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 3

Effects of PF on MPTP-induced motor deficit in mice with pretreatment. Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^**P<0.01 compared with saline-treated mice, ^#P<0.05, ^##P<0.01 compared with MPTP-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 4

Effects of PF on MPTP-induced dopaminergic neuron loss in the SNc with post-treatment. Quantitative analysis of the TH-positive cells (a) and Nissl-stained neurons (b) in the SNc of mice. Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^**P<0.01 compared with saline-treated mice, ^##P<0.01 compared with MPTP-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 5

Effects of PF on MPTP-induced dopaminergic fiber loss in the striatum with post-treatment. Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^**P<0.01 compared with saline-treated mice, ^##P<0.05 compared with MPTP-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 6

Effects of PF on MPTP-induced motor deficit in mice with post-treatment. Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^**P<0.01 compared with saline-treated mice, ^#P<0.05, ^##P<0.01 compared with MPTP-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 7

Effects of PF on MPTP-induced microglial activation in the SNc and striatum. Cd11b immunohistochemistry in the SNc (a–c) and striatum (d–f) of mice. (a, d) saline-treated mice, (b, e) MPTP-treated mice, (c, f) MPTP plus PF-treated mice. Microglial activation after MPTP were attenuated by PF treatment in both the SNc and striatum, n=8, scale bar, 100 μm.

Figure 8

Effects of PF on MPTP-induced astrocytic activation in the SNc and striatum. GFAP immunohistochemistry in the SNc (a–c) and striatum (d–f) of mice, (a, d) saline-treated mice, (b, e) MPTP-treated mice, (c, f) MPTP plus PF-treated mice. Astrocytic activation after MPTP were attenuated by PF treatment in both the SNc and striatum, n=8, scale bar, 100 μm.

Figure 9

Effects of DPCPX on the dopaminergic neuron-protective effects of PF in the SNc. TH immunohistochemistry in the SNc (a, b), quantitative analysis of the TH-positive cells (c) and Nissl-stained neurons (d) in the SNc of mice. (a) MPTP plus PF-treated mice, (b) MPTP plus PF-treated mice that pretreated with DPCPX before PF administration. The protective effect of PF (5 mg kg⁻¹) on dopaminergic neurons in the SNc was abolished by pretreatment with the selective A₁AR antagonist DPCPX (0.3 mg kg⁻¹). Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^##P<0.01 compared with MPTP-treated mice, ^$$P<0.01 compared with MPTP plus PF-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison), scale bar, 200 μm.

Figure 10

Effects of DPCPX on the dopaminergic fiber-protective effects of PF in the striatum. TH immunohistochemistry in the striatum (a, b), quantitative analysis of the TH optical density in the striatum of mice (c). (a) MPTP plus PF-treated mice, (b) MPTP plus PF-treated mice that pretreated with DPCPX before PF administration. The protective effect of PF (5 mg kg⁻¹) on dopaminergic fibers in the striatum was abolished by pretreatment with the selective A₁AR antagonist DPCPX (0.3 mg kg⁻¹). Each column and vertical bar represents the mean±s.e.m. of results from eight mice. ^##P<0.01 compared with MPTP-treated mice, ^$$P<0.05 compared with MPTP plus PF-treated mice (one-way ANOVA followed by Dunnett's post hoc comparison), scale bar, 500 μm.

Figure 11

Effect of DPCPX on the microglia-modulating effects of PF. Cd11b immunohistochemistry in the SNc (a, b) and striatum (c, d), (a, c) MPTP plus PF-treated mice, (b, d) MPTP plus PF-treated mice that pretreated with DPCPX before PF administration. The microglia-modulating effects of PF (5 mg kg⁻¹) were reversed by pretreatment with DPCPX (0.3 mg kg⁻¹), n=8, scale bar, 100 μm.

Figure 12

Effect of DPCPX on the astrocyte-modulating effects of PF. GFAP immunohistochemistry in the SNc (a, b) and striatum (c, d) of mice. (a, c) MPTP plus PF-treated mice, (b, d) MPTP plus PF-treated mice that pretreated with DPCPX before PF administration. The astrocyte-modulating effects of PF (5 mg kg⁻¹) were reversed by pretreatment with DPCPX (0.3 mg kg⁻¹), n=8, scale bar, 100 μm.