Muscle pain in models of chemotherapy-induced and alcohol-induced peripheral neuropathy

Abstract

Objective: While inflammatory pain is well described in skeletal muscle, neuropathic muscle pain remains to be clarified. We used 3 well-established rodent models of peripheral neuropathy to evaluate for muscle pain.

Methods: In rats exposed to either of 2 neurotoxic cancer chemotherapies, paclitaxel or oxaliplatin, or to alcohol consumption, we assessed the evolution of mechanical hyperalgesia in skeletal muscle and skin, in the same animal. To explore the involvement of protein kinase C epsilon (PKCε), a second messenger implicated in some forms of neuropathic pain, antisense oligodeoxynucleotides (AS-ODNs) or mismatch ODNs (MM-ODNs) for PKCε were administered intrathecally.

Results: Rats submitted to models of chemotherapy-induced and alcohol-induced neuropathy developed persistent muscle hyperalgesia, which evolved in parallel in muscle and skin. The administration of PKCε AS, which has been shown to mediate cutaneous hyperalgesia in paclitaxel and ethanol models of neuropathic pain, also inhibited muscle hyperalgesia induced by these agents. Stopping AS-ODN was associated with the reappearance of hyperalgesia at both sites. The AS-ODN to PKCε treatment was devoid of effect in both muscle and skin in the oxaliplatin neuropathy model.

Interpretation: Our results support the suggestion that neuropathic muscle pain may be a greater clinical problem than generally appreciated.

Figure 1. Cutaneous and muscle hyperalgesia in paclitaxel-induced peripheral neuropathy

(A) Time course of nociceptive mechanical threshold in rat hind paw skin (open bars) and gastrocnemius muscle (solid bars) after i.p. paclitaxel (ptxl) injections (arrows). Separate one way repeated measures ANOVAs followed by pairwise contrasts (10 levels) were used to reveal time points significantly different from baseline for cutaneous and muscle nociceptive thresholds. Cutaneous and muscle nociceptive thresholds decreased significantly by day 4 (p < 0.001), and remained significantly decreased until day 16 (p < 0.001) and day 23 (p < 0.001), respectively. (B) Effect of ODN AS to PKCε on paclitaxel-induced cutaneous hyperalgesia. The two way repeated measures ANOVA showed a significant group × time interaction (F_6,132= 19.135; p < 0.001) and a significant main effect of group (F_1,22= 13.221; p = 0.001), indicating that the two groups differed significantly in both time course and magnitude. Multivariate analysis showed that cutaneous hyperalgesia was significantly attenuated by the AS-treatment (solid bars) compared to the MM-treatment (open bars) on days 2 through 7 (p < 0.003 at days 2, 3 and 7), with recovery observed by day 11. (C) Effect of ODN AS to PKCε on paclitaxel-induced muscle hyperalgesia. The two way repeated measures ANOVA showed a significant group × time interaction (F_6,132= 53.465; p < 0.001) and a significant main effect of group (F_1,22= 04.964; p < 0.001), indicating that the two groups differed significantly in both time course and magnitude. Multivariate analysis showed that muscle hyperalgesia was significantly attenuated by the AS-treatment (solid bars) compared to the MM treatment (open bars) on days 1 through 7 (p < 0.001) and also on day 11 (p = 0.001), with recovery observed on day 13.

Figure 2. Cutaneous and muscle hyperalgesia in oxaliplatin-induced peripheral neuropathy

(A) Time course of cutaneous and muscle hyperalgesia induced by intravenous oxaliplatin administration. One-way repeated measures ANOVA followed by simple contrasts revealed significant cutaneous (open squares) and muscle (solid triangles) hyperalgesia beginning on day 1 and lasting through day 21, the last day of testing (p < 0.001 on all days for both groups). (B) Effect of ODN AS to PKCε (solid bars) compared to MM (open bars) on cutaneous (left panel) or muscle (right panel) hyperalgesia during early phase oxaliplatin-induced neuropathy (days 1 to 7 after oxaliplatin injection). The two-way repeated measures ANOVA for cutaneous testing was not significant for either the time × group interaction (F_5,100= 1.192; p = 0.321) or the main effect of group (F_1,20= 3.098; p = 0.094); a similar analysis for muscle hyperalgesia showed a significant time × group interaction (F_5,100= 4.382; p = 0.003) but not a significant main effect of group (F_1,20= 0.741; p = 0.399). Based on the significant interaction, a multivariate analysis failed to reveal any time points at which the AS and MM groups differed significantly. (C) Effect of ODN AS to PKCε (solid bars) compared to MM (open bars) on cutaneous (left panel) or muscle (right panel) hyperalgesia during late phase oxaliplatin-induced neuropathy (days 21 to 28 after oxaliplatin injection). The two-way repeated measures ANOVA for cutaneous testing was not significant for either the time × group interaction (F_4,88= 1.567; p = 0.190) or the main effect of group (F_1,22= 1.132; p = 0.299); a similar analysis for muscle hyperalgesia was also not significant for either the time × group interaction (F_4,88= 0.847; p = 0.467) or the main effect of group (F_1,22= 2.342; p = 0.140).

Figure 3. Effect of binge alcohol consumption on cutaneous and muscle hyperalgesia

(A) Time course of cutaneous and muscle hyperalgesia induced by chronic alcohol consumption. Three cycles of ethanol diet (ED; 4 days on 3 days off) were administered. Although both cutaneous and muscle hyperalgesia were induced in this model, muscle hyperalgesia was delayed about one week with respect to cutaneous hyperalgesia. (B) Effect of ODN AS to PKCε on alcohol-induced cutaneous hyperalgesia. The two way repeated measures ANOVA showed a significant group × time interaction (F_7,154= 23.864; p < 0.001) and a significant main effect of group (F_1,22= 16.886; p = 0.001), indicating that the two groups differed significantly in both time course and magnitude. Multivariate analysis showed that cutaneous hyperalgesia was significantly attenuated by the AS-treatment (open bars) compared to the MM treatment (solid bars) on days 2 through 8 (p = 0.007 at days 2, 3 and 8), with recovery observed by day 10. (C) Effect of ODN AS to PKCε on alcohol-induced muscle hyperalgesia. The two way repeated measures ANOVA showed a significant group × time interaction (F_7,154= 40.363; p < 0.001) and a significant main effect of group (F_1,22= 84.242; p < 0.001), indicating that the two groups differed significantly in both time course and magnitude. Multivariate analysis showed that cutaneous hyperalgesia was significantly attenuated by the AS-treatment (open bars) compared to the MM treatent (solid bars) on days 1 through 12 (p < 0.001 at days 1, 2, 3, 8, 10, and 12), with recovery observed by day 15.