The Beneficial Effects of Ultramicronized Palmitoylethanolamide in the Management of Neuropathic Pain and Associated Mood Disorders Induced by Paclitaxel in Mice

Abstract

Chemotherapy-induced peripheral neuropathy (CIPN) is a common complication of antineoplastic drugs, particularly paclitaxel (PTX). It can affect the quality of patients' lives and increase the risk of developing mood disorders. Although several drugs are recommended, they yielded inconclusive results in clinical trials. The aim of the present work is to investigate whether the palmitoylethanolamide (PEA) would reduce PTX-induced CIPN and associated mood disorders. Moreover, the role PPAR-α and the endocannabinoid system will also be investigated. CIPN was induced by intraperitoneally injection of PTX (8 mg/kg) every other day for a week. PEA, 30 mg/kg, was orally administrated in a bioavailable form (i.e., ultramicronized PEA, um-PEA) one hour after the last PTX injection, for 7 days. In the antagonism experiments, AM281 (1 mg/kg) and GW6471 (2 mg/kg) were administrated 30 min before um-PEA. Our results demonstrated that um-PEA reduced the development of hypersensitivity with the effect being associated with the reduction in spinal and hippocampal pro-inflammatory cytokines, as well as antidepressive and anxiolytic effects. Moreover, the PPAR-α and CB1 receptor antagonists blocked the behavioral and antinociceptive effects of um-PEA. Our findings suggest that um-PEA is a promising adjunct in CIPN and associated mood disorders through the activation of PPAR-α, which influences the endocannabinoid system.

Keywords: PPAR-α; behavior; cannabinoids; inflammation; neuropathic pain; paclitaxel; um-PEA.

Figure 1

Effect of um-PEA on depressive- and anxiety-like behavior. (A) Time (in seconds) spent immobile in the TST; (B) time (in seconds) spent immobile in the FST test; (C) number of entries in the open arms of EPM test; (D) distance travelled (in cm) in the OF test; ** p < 0.01 versus vehicle group; ° p < 0.05 versus PTX group. Data are presented as mean ± SEM (n = 8). Differences were evaluated by ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 2

Effect of um-PEA on depressive- and anxiety-like behavior in presence of CB1 or PPAR-α antagonists. (A) Time (in seconds) spent immobile in the tail suspension test; (B) time (in seconds) spent immobile in the forced swim test; (C) number of entries in the open arms of elevated plus-maze test; (D) distance travelled (in cm) in the open field test; ° p < 0.05 and °° p < 0.01 versus PTX group; ^# p < 0.05 and ^## p < 0.01 versus PTX+ um-PEA. Data are presented as mean ± SEM (n = 8). Differences were evaluated by ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 3

Pro-inflammatory cytokine levels in the hippocampi of vehicle- or um-PEA-treated mice injected with PTX. (A) Fold expression of mRNA for pro-inflammatory TNF-α; (B) fold expression of mRNA for pro-inflammatory IL-1β; (C) fold expression of mRNA for pro-inflammatory IL-6; (D) fold expression of mRNA for anti-inflammatory IL-10; * p < 0.05, ** p < 0.01, *** p < 0.001 versus vehicle group; ° p < 0.05 versus PTX group. Data are presented as mean ± SEM (n = 8). Differences were evaluated by ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 4

Pro-inflammatory cytokine levels in the spinal cords of vehicle- or um-PEA-treated mice injected with PTX. (A) Fold expression of mRNA for pro-inflammatory TNF-α; (B) fold expression of mRNA for pro-inflammatory IL-1β; (C) fold expression of mRNA for pro-inflammatory COX-2; (D) fold expression of mRNA for anti-inflammatory iNOS; * p < 0.05 and *** p < 0.001 versus vehicle group; ° p < 0.05 and °° p < 0.01 versus PTX group. Results are shown as mean ± SEM. Differences were analyzed using ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 5

Effect of um-PEA on peripheral neuropathy. Results of the (A) von Frey test to evaluate mechanical allodynia; (B) Randall–Selitto test to assess mechanical hyperalgesia; (C) acetone evaporation test to evaluate thermal allodynia; (D) Hargreaves test to evaluate thermal hyperalgesia; ** p < 0.01; *** p < 0.001 versus vehicle group; ° p < 0.05 versus PTX group. Data are presented as mean ± SEM (n = 8). Differences were evaluated by ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 6

Effect of um-PEA on peripheral neuropathy in presence of CB1 or PPAR-α antagonists. Results of the (A) von Frey test to evaluate mechanical allodynia; (B) Randall–Selitto test to assess mechanical hyperalgesia; (C) Hargreaves test to evaluate thermal hyperalgesia; ^# p < 0.05 and ^## p < 0.01 versus PTX+um-PEA; ° p < 0.05 versus PTX-vehicle group. Data are presented as mean ± SEM (n = 8). Differences were evaluated by ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 7

Western blotting analyses for CB1 (A) and PPAR-α (B) receptors in spinal cords. Immunoblots representative of all tissues analyzed are shown. Densitometric analysis of protein bands are reported: the levels are expressed as the density ratio of target to control protein bands (β-actin). * p < 0.05 versus vehicle group; ° p < 0.05 and °° p < 0.005 versus PTX group. Values are expressed as mean ± SEM (n = 3). Differences were evaluated by ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.