Magnolin Inhibits Paclitaxel-Induced Cold Allodynia and ERK1/2 Activation in Mice

Abstract

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of anti-cancer drugs. The main symptoms often include sensory disturbances and neuropathic pain, and currently there is no effective treatment for this condition. This study aimed to investigate the suppressive effects of magnolin, an extracellular signal-regulated kinase (ERK) inhibitor substance derived from a 95% EtOH extract of the seeds of Magnolia denudata, on the symptoms of CIPN. A taxol-based anti-cancer drug paclitaxel (PTX) was repeatedly injected (2 mg/kg/day, total 8 mg/kg) into mice to induce CIPN. A neuropathic pain symptom was assessed using a cold allodynia test that scores behaviors of licking and shaking paw after plantar administration of acetone drop. Magnolin was administered intraperitoneally (0.1, 1, or 10 mg/kg) and behavioral changes to acetone drop were measured. The effect of magnolin administration on ERK expression in the dorsal root ganglion (DRG) was investigated using western blot analysis. The results showed that the repeated injections of PTX induced cold allodynia in mice. Magnolin administration exerted an analgesic effect on the PTX-induced cold allodynia and inhibited the ERK phosphorylation in the DRG. These results suggest that magnolin could be developed as an alternative treatment to suppress paclitaxel-induced neuropathic pain symptoms.

Keywords: ERK; allodynia; magnolin; neuropathic pain; paclitaxel.

Figure 1

UHPLC-PDA chromatogram of the 70% EtOH extract from M. denudata (A) and magnolin ((B); R_t 16.0 min). Kobusin and aschantin were detected at R_t 15.5 and 16.4, respectively. Data collected by Thermo Vanquish UHPLC system equipped with Thermo Hypersil GOLD column (1.9 μm, 150 mm× 2.1 mm I.D.). The mobile phase was subjected to a series of linear gradients with a flow rate of 0.3 mL/min: 0–3 min, 10% B; 3–35 min, 100% B; 35–42 min, 100% B; 42–43 min 10% B.

Figure 2

Chemical structures of magnolin (1), kobusin (2), and aschantin (3) isolated from the seeds of M. denudata.

Figure 3

Induction of cold allodynia symptom following repetitive injection of PTX. (A) Experimental schedule. (B) Increased behavioral response to plantar application of acetone drop in mice treated with PTX. (Vehicle group, n = 5; PTX group, n = 6; **** p < 0.0001, day 7 and 14; ** p < 0.01, day 24; Two-way repeated measures ANOVA followed by Sidak’s multiple comparisons test, compared to the control group).

Figure 4

Attenuation of PTX-induced cold allodynia by magnolin treatment. (A) No significant behavioral change in PTX group mice treated with 0.1 mg/kg magnolin (Vehicle group, n = 8; Magnolin group, n = 9). (B) Significant attenuation of PTX-induced cold allodynia in mice treated with 1 mg/kg magnolin (Vehicle group, n = 9; Magnolin group, n = 10). (C) Significant attenuation of PTX-induced cold allodynia in mice treated with 10 mg/kg magnolin (Vehicle group, n = 13; Magnolin group, n = 14). Behavior levels at baseline (before PTX, e.g., day 0) were displayed with each test result. Statistical comparisons were performed at each time point (**** p < 0.0001; Two-way repeated measures ANOVA followed by Sidak’s multiple comparisons test, compared to the vehicle-treated control group).

Figure 5

Attenuation of PTX-induced ERK activity by magnolin treatment. (A) Significantly lower levels of pERK/ERK ratio (arbitrary unit, %) in the magnolin-treated mice compared to the untreated group (n = 4 per group; each data point pooling 3 subject samples; animal subject N = 12 per group) (* p < 0.05; Kruskal–Wallis test followed by Dunn’s multiple comparisons test, compared to the control group). (B) Protein expression demonstrated by western blot data.