6-Shogaol, an active compound of ginger, protects dopaminergic neurons in Parkinson's disease models via anti-neuroinflammation

Abstract

Aim: 6-Shogaol [1-(4-hydroxy-methoxyphenyl)-4-decen-one], a pungent compound isolated from ginger, has shown various neurobiological and anti-inflammatory effects. The aim of this study was to examine the effects of 6-shogaol on neuroinflammatory-induced damage of dopaminergic (DA) neurons in Parkinson's disease (PD) models.

Methods: Cultured rat mesencephalic cells were treated with 6-shogaol (0.001 and 0.01 μmol/L) for 1 h, then with MPP(+)(10 μmol/L) for another 23 h. The levels of TNF-α and NO in medium were analyzed spectrophotometrically. C57/BL mice were administered 6-shogaol (10 mg·kg(-1)·d(-1), po) for 3 d, and then MPTP (30 mg/kg, ip) for 5 d. Seven days after the last MPTP injection, behavioral testings were performed. The levels of tyrosine hydroxylase (TH) and macrophage antigen (MAC)-1 were determined with immunohistochemistry. The expression of iNOS and COX-2 was measured using RT PCR.

Results: In MPP(+)-treated rat mesencephalic cultures, 6-shogaol significantly increased the number of TH-IR neurons and suppressed TNF-α and NO levels. In C57/BL mice, treatment with 6-shogaol reversed MPTP-induced changes in motor coordination and bradykinesia. Furthermore, 6-shogaol reversed MPTP-induced reductions in TH-positive cell number in the substantia nigra pars compacta (SNpc) and TH-IR fiber intensity in stratum (ST). Moreover, 6-shogaol significantly inhibited the MPTP-induced microglial activation and increases in the levels of TNF-α, NO, iNOS, and COX-2 in both SNpc and ST.

Conclusion: 6-Shogaol exerts neuroprotective effects on DA neurons in in vitro and in vivo PD models.

Figure 1

Chemical structure of 6-shogaol.

Figure 2

The protective effects of 6-shogaol against MPP⁺-induced neurotoxicity in primary mesencephalic cells. Cells were treated with 6-shogaol for 1 h and then exposed to MPP⁺ for a further 23 h. After the cells were fixed and stained, the number of tyrosine hydroxylase (TH)-immunoreactive neurons was measured (A). Representative images of experiments are shown (B). Scale bar=50 μm. Values are indicated as mean±SEM. ^cP<0.01 compared with the control group. ^fP<0.01 compared with the MPP⁺-only treated group.

Figure 3

Inhibitory effects of 6-shogaol on MPP⁺-induced neuroinflammatory factors in primary mesencephalic cells. After the cells were treated with 6-shogaol and/or MPP⁺, the culture supernatant was used to measure NO (A) and TNF-α levels (B). Values are indicated as mean±SEM. ^cP<0.01 compared with the control group. ^fP<0.01 compared with the MPP⁺-only treated group.

Figure 4

Inhibitory effects of 6-shogaol on MPTP-induced movement impairment in a mouse PD model. Saline or 6-shogaol (10 mg/kg; po) was administered to mice once per day for 3 d, and then MPTP (30 mg/kg) was injected intraperitoneally for 5 d. Seven days after the last MPTP injection, the time required for the mouse to turn completely downward (A, T-turn) and the time required to arrive at the floor (B, T-LA) were recorded, using a cut-off limit of 60 s. Values are indicated as mean±SEM. ^cP<0.01 compared with the control group. ^fP<0.01 compared with the MPTP-only treated group.

Figure 5

Protective effect of 6-shogaol against MPTP-induced dopaminergic neuron damage in a mouse PD model. Seven days after 6-shogaol and/or MPTP treatment, tyrosine hydroxylase (TH) tyrosine hydroxylase was detected immunohistochemically. Dopaminergic cells were quantified by counting the number of TH-immunoreactive cells in the ST(A) and by measuring the optical intensity in the SNpc(B). Representative photomicrographs are shown (C). Scale bar=200 μm. Values are indicated as mean±SEM. ^cP<0.01 compared with the control group. ^fP<0.01 compared with the MPTP-only treated group.

Figure 6

Inhibitory effect of 6-shogaol on MPTP-induced microglial activation in a mouse PD model. One day after the last MPTP treatment, MAC-1 was detected immunohistochemically. MAC-1-immunoreactive cells were quantified by counting the number of MAC-1-IR cells and measuring the optical intensity in the ST(A) and SNpc(B). Representative photomicrographs are shown (C). Scale bar=200 μm. Values are indicated as mean±SEM. ^cP<0.01 compared with the control group. ^eP<0.05, ^fP<0.01 compared with the MPTP-only treated group.

Figure 7

Inhibitory effects of 6-shogaol on MPTP-induced iNOS and COX-2 overexpression in the SNpc and ST. One day after the last MPTP treatment, brain tissues were dissociated and real-time RT-PCR and Western blot were used to determine the expression of iNOS in the SNpc (A and E) and in the ST (B and F), and COX-2 in the SNpc (C and G) and in the ST (D and H). Values are indicated as mean±SEM. ^bP<0.05, ^cP<0.01 compared with the control group. ^eP<0.05, ^fP<0.01 compared with the MPTP-only treated group.