Multimodal assessment of painful peripheral neuropathy induced by chronic oxaliplatin-based chemotherapy in mice

Abstract

Background: A major clinical issue affecting 10-40% of cancer patients treated with oxaliplatin is severe peripheral neuropathy with symptoms including cold sensitivity and neuropathic pain. Rat models have been used to describe the pathological features of oxaliplatin-induced peripheral neuropathy; however, they are inadequate for parallel studies of oxaliplatin's antineoplastic activity and neurotoxicity because most cancer models are developed in mice. Thus, we characterized the effects of chronic, bi-weekly administration of oxaliplatin in BALB/c mice. We first studied oxaliplatin's effects on the peripheral nervous system by measuring caudal and digital nerve conduction velocities (NCV) followed by ultrastructural and morphometric analyses of dorsal root ganglia (DRG) and sciatic nerves. To further characterize the model, we examined nocifensive behavior and central nervous system excitability by in vivo electrophysiological recording of spinal dorsal horn (SDH) wide dynamic range neurons in oxaliplatin-treated mice

Results: We found significantly decreased NCV and action potential amplitude after oxaliplatin treatment along with neuronal atrophy and multinucleolated DRG neurons that have eccentric nucleoli. Oxaliplatin also induced significant mechanical allodynia and cold hyperalgesia, starting from the first week of treatment, and a significant increase in the activity of wide dynamic range neurons in the SDH.

Conclusions: Our findings demonstrate that chronic treatment with oxaliplatin produces neurotoxic changes in BALB/c mice, confirming that this model is a suitable tool to conduct further mechanistic studies of oxaliplatin-related antineoplastic activity, peripheral neurotoxicity and pain. Further, this model can be used for the preclinical discovery of new neuroprotective and analgesic compounds.

Figure 1

Body weight decreases after oxaliplatin (OHP) treatment. Mice treated with oxaliplatin3.5 mg/kg/iv twice weekly (n = 8) lost a significant amount of body weight compared to naïve mice (n = 8) °p < 0.05, * p < 0.01, ** p < 0.0001 vs. naïve, ANOVA with repeated measures.

Figure 2

Oxaliplatin (OHP) induces mechanical and cold allodynia but not heat hyperalgesia. (a) Mice treated with oxaliplatin 3.5 mg/kg/iv twice weekly (n = 8) had a significant decrease in mechanical threshold from baseline and compared to naïve mice (n = 8) that started after the first week of treatment and persisted for at least four weeks. **p < 0.001 vs. baseline, Friedman Test; #p < 0.001 vs. naïve, Mann Whitney U Test. (b) Mice treated with oxaliplatin 3.5 mg/kg/iv twice weekly (n = 8) had a significant increase in cold threshold from baseline and compared to naïve mice (n = 8) that started after the first week of treatment and persisted for at least four weeks. *p < 0.01 vs. baseline, ANOVA with Repeated Measures; #p < 0.05 vs. naïve, Student's T Test. (c) Mice treated with oxaliplatin 3.5 mg/kg/iv twice weekly (n = 8) had no change heat threshold from baseline and were not different from naïve mice throughout the duration of the experiment. P > 0.05 vs. baseline, ANOVA with Repeated Measures; p > 0.05 vs. naïve, Student's T Test.

Figure 3

Oxaliplatin (OHP) decreases NCV in caudal and digital nerves. (a) Mice treated with oxaliplatin 3.5 mg/kg/iv twice weekly for four weeks (gray bars; n = 8) had a significant decrease in caudal NCV compared to naïve mice (black bars; n = 8). (b) The oxaliplatin-treated mice had a significant decrease in caudal nerve action potential amplitude compared to naïve mice. (c) The oxaliplatin-treated mice had a significant decrease in digital NCV compared to naïve mice. (d) The oxaliplatin-treated mice had no difference in the amplitude of the digital nerve action potential compared to naïve mice. **p < 0.0001 vs. naive, #p < 0.001 vs. naive, Student's T Test.

Figure 4

Oxaliplatin induces nucleolar segregation and axonopathy. (a, b) Light microscopy revealed that DRG neurons from mice treated with oxaliplatin 3.5 mg/kg/iv twice weekly for four weeks (b; n = 3) had segregated nucleoli (arrow heads) that were eccentric (black arrow) compared to DRGs from naïve mice (a; n = 3). (c, d) Electron microscopy also showed segregated nucleoli in DRG neurons from oxaliplatin-treated mice (d; n = 3) but not naïve mice (c; n = 3). Light microscope examination demonstrated that myelinated fibers in the sciatic nerve of mice treated with oxaliplatin 3.5 mg/kg/iv twice weekly for four weeks (f; n = 3) had evidence of changes indicative of axonopathy (white arrows) that were not found in sciatic nerve from naïve mice (e; n = 3).

Figure 5

Oxaliplatin (OHP) treatment causes decreased the area of DRG cell body and nucleolus. Morphometric analysis revealed that DRG neurons from mice treated with oxaliplatin 3.5 mg/kg/iv twice weekly for four weeks (n = 3) had a significant decrease in the area (mm²) of the cell bodies (a) and nucleoli (c) compared to DRG neurons from naïve mice (n = 3). (b) There was no difference in the areas of the nuclei from oxaliplatin-treated and naïve mice. °p < 0.05 vs naïve, #p < 0.001 vs naïve, Student's T Test.

Figure 6

Representative raw data trace of wide dynamic range neurons. Example raw data used to construct a histogram of the stimulus-response to brush (10 second stimulus), pressure (2 second stimulus) and pinch (2 second stimulus) of an individual wide dynamic range neuron in a naïve mouse (a) or 2 days after the final dose of oxaliplatin 3.5 mg/kg/iv in the fourth week (b). The waveforms to the right of each trace show a representative spike that was analyzed.

Figure 7

Oxaliplatin (OHP) increases activity of wide dynamic range neurons in the spinal dorsal horn. Two days after the final injection of oxaliplatin 3.5 mg/kg/iv, the peak number of spikes per second were higher in the oxaliplatin-injected (gray bars) mice compared with naïve mice (black bars). **p < 0.001 and #p < 0.01 vs. naive, Student's T Test.