Genetic inactivation and pharmacological blockade of sigma-1 receptors prevent paclitaxel-induced sensory-nerve mitochondrial abnormalities in mice

FR Nieto1,3, E Fernández-Segura2,3, FJ Cañizares2,3, CM Cendán1,3, MA Cubero2,3, JM Vela4, JM Baeyens1,3. 1University of Granada, Department of Pharmacology and Institute of Neuroscience, 18012, Spain, 2University of Granada, Department of Histology and Institute of Neuroscience, 18012, Spain, 3University of Granada, Biomedical Research Centre, 18100, Spain, 4Esteve, Drug Discovery and Preclinical Development, 08041, Spain

Antecedents

Paclitaxel is widely used for the treatment of solid tumors, but it has side effects like neuropathic pain. Unfortunately, there are no clinically validated treatments to prevent or ameliorate this painful neuropathy. Paclitaxel administration to rodents induces mitochondrial alterations that are relevant to neuropathic pain. The sigma-1 (σ1) receptor is a ligand-regulated molecular chaperone involved in mitochondrial calcium homeostasis and pain hypersensitivity. We have demonstrated that σ1 receptors have a key role in paclitaxel-induced neuropathic pain, but it is unknown whether they are related to these mitochondrial abnormalities. To test this possibility, we evaluated whether genetic inactivation and/or pharmacological blockade of σ1 receptors prevents the neuropathic pain behaviors and the mitochondrial changes induced by paclitaxel administration.

Methods

Paclitaxel 2 mg/kg was administered i.p. once per day during five consecutive days to WT and σ1 receptor knockout (σ1-KO) female CD-1 mice weighing 25-30 g. In separate experiments, WT mice were treated with the σ1 receptor antagonist BD-1063 (32 mg/kg, s.c.), 30 min before each paclitaxel injection. Cold- and mechanical-allodynia were tested previously to these treatment, and 10 and 28 days after them. Cold-allodynia (acetone test) was tested by touching the plantar skin of the hind paws with an acetone drop and subsequent measure of the duration of paw licking/biting with a stopwatch. Mechanical-allodynia was tested using an electronic Von Frey apparatus (Ugo Basile, Italy) that applied an increasing force (from 0 to 10 g) with a single filament, and permit to measure the paw withdrawal threshold force. Following behavioral tests, mice were transcardially perfused under anaesthesia and portions of saphenous nerves were removed and appropriately processed for electron microscopy study. Differences between values were analyzed with two-way repeated measures ANOVA followed by the Bonferroni test. The experimental protocol was approved by the University of Granada Research Ethics Commitee.

Results

WT mice treated with paclitaxel developed cold- (pre-treatment value: 1.14±0.23 s, post-treatment value: 9.52±2.01 s; p<0.01) and mechanical-allodynia (pre-treatment value: 5.73±0.11 g, post-treatment value: 3.62±0.16 g; p<0.01). Paclitaxel also induced a significant increase in the frequency of swollen and vacuolated mitochondria in myelinated Aβ fibers (pre-treatment value: 3.15±1.19%, post-treatment value: 20.26±3.57%; p<0.01), a non-significant increase in myelinated Aδ fibers (pre-treatment value: 3.90±2.98%, post-treatment value: 14.81±3.97%; p>0.05) and no changes in C-fibers (pre-treatment value: 21.05±5.64%, post-treatment value: 34.28±2.99%; p>0.05) of the saphenous nerve. However, there was no evidence of paclitaxel-induced axonal degeneration, myelin damage, or microtubule changes. Behavioral and morphological alterations were marked at 10 days after paclitaxel administration and had resolved by day 28. In contrast, WT mice pretreated with BD-1063 and σ1-KO mice did not develop statistically significant signs of neuropathic pain or mitochondrial abnormalities after paclitaxel treatment.

Conclusion

These results suggest that activation of σ1 receptors is required for the appearance of paclitaxel-induced neuropathic pain and sensory nerve mitochondrial damage. Therefore, σ1 receptor antagonists might have therapeutic value for prevention of paclitaxel-induced neuropathic pain.

Supported by Junta-Andalucía (CTS-109), MEC (SAF2006-06122) and MEC-FPU (FRN).