Peripheral neuropathy is a common adverse effect of paclitaxel treatment. To analyze the contribution of transient receptor potential vanilloid 1 (TRPV1) in the development of paclitaxel-induced thermal hyperalgesia, TRPV1 expression in the rat dorsal root ganglion (DRG) was analyzed after paclitaxel treatment. Behavioral assessment using the tail-flick test showed that intraperitoneal administration of 2 and 4 mg/kg paclitaxel induced thermal hyperalgesia after days 7, 14, and 21. Paclitaxel-induced thermal hyperalgesia after day 14 was significantly inhibited by the TRP antagonist ruthenium red (3 mg/kg, s.c.) and the TRPV1 antagonist capsazepine (30 mg/kg, s.c.). Paclitaxel (2 and 4 mg/kg) treatment increased the expression of TRPV1 mRNA and protein in DRG neurons. Immunohistochemistry showed that paclitaxel (4 mg/kg) treatment increased TRPV1 protein expression in small and medium DRG neurons 14 days after treatment. Antibody double labeling revealed that isolectin B4-positive small DRG neurons co-expressed TRPV1. TRPV1 immunostaining was up-regulated in paw skin day 14 after paclitaxel treatment. Moreover, in situ hybridization histochemistry revealed that most of the TRPV1 mRNA-labeled neurons in the DRG were small or medium in size. These results suggest that paclitaxel treatment increases TRPV1 expression in DRG neurons and may contribute to functional peripheral neuropathic pain.

Background: Peripheral cold neuropathic pain is a serious side effect of oxaliplatin treatment. However, the mechanism of oxaliplatin-induced cold hyperalgesia is unknown. In the present study, we investigated the effects of oxaliplatin on transient receptor potential ankyrin 1 (TRPA1) in dorsal root ganglion (DRG) neurons of rats. Results: Behavioral assessment using the acetone spray test showed that 3 and 6 mg/kg oxaliplatin (i.p.) induced acute cold hypersensitivity after 1, 2, 4, and 7 days. Real-time PCR showed that oxaliplatin (6 mg/kg) significantly increased TRPA1 mRNA expression in DRGs at days 1, 2, and 4. Western blotting revealed that oxaliplatin significantly increased TRPA1 protein expression in DRGs at days 2, 4, and 7. Moreover, in situ hybridization histochemistry revealed that most TRPA1 mRNA-labeled neurons in the DRGs were small in size. Oxaliplatin significantly increased co-localization of TRPA1 expression and isolectin B4 binding in DRG neurons. Oxaliplatin induced a significant increase in the percent of TRPA1 mRNA-positive small neurons in DRGs at days 1, 2, and 4. In addition, we found that intrathecal administration of TRPA1 antisense, but not TRPA1 mismatched oligodeoxynucleotides, knocked down TRPA1 expression and decreased oxaliplatin-induced cold hyperalgesia. Double labeling showed that p-p38 mitogen-activated protein kinase (MAPK) was co-expressed in TRPA1 mRNA-labeled neurons at day 2 after oxaliplatin administration. Intrathecal administration of the p38 MAPK inhibitor, SB203580, significantly decreased oxaliplatin-induced acute cold hypersensitivity. Conclusions: Together, these results demonstrate that TRPA1 expression via activation of p38 MAPK in DRG neurons, at least in part, contributes to the development of oxaliplatin-induced acute cold hyperalgesia.

Peripheral neuropathic pain is a serious side effect of paclitaxel treatment. However, the mechanism of this paclitaxel-induced neuropathic pain is unknown. In this study, we investigated the effects of paclitaxel on the voltage-dependent calcium channel (VDCC) current in rat dorsal root ganglion (DRG) neurons using the whole-cell patch clamp technique. Behavioral assessment using von Frey filament stimuli showed that 2 and 4 mg/kg paclitaxel treatment induced mechanical allodynia/hyperalgesia. Paclitaxel-induced mechanical hyperalgesia was significantly inhibited by gabapentin (100 mg/kg). Using the patch clamp method, we observed that paclitaxel (4 mg/kg) treatment significantly increased the VDCC current in small- and medium-diameter DRG neurons. Moreover, paclitaxel-induced increase in the VDCC current in medium-diameter DRG neurons was completely inhibited by 10 and 100 μM gabapentin. Similar effects in small-diameter DRG neurons were only seen with 100 μM gabapentin. Western blotting revealed that paclitaxel increased protein levels of the VDCC subunit α2δ-1 (Cavα2δ-1) in DRG neurons. Immunohistochemistry showed that paclitaxel treatment increased Cavα2δ-1 protein expression in DRG neurons. Thus, paclitaxel treatment increases the VDCC current in small- and medium-diameter DRG neurons and upregulates Cavα2δ-1. The antihyperalgesic action of gabapentin may be due to inhibition of paclitaxel-induced increases in the VDCC current in DRG neurons.

Painful peripheral neuropathy is a common adverse effect of paclitaxel (PTX) treatment. To analyze the contribution of transient receptor potential vanilloid 1 (TRPV1) in the development of PTX-induced mechanical allodynia/hyperalgesia and thermal hyperalgesia, TRPV1 expression in the rat spinal cord was analyzed after intraperitoneal administration of 2 and 4 mg/kg PTX. PTX treatment increased the expression of TRPV1 protein in the spinal cord. Immunohistochemistry showed that PTX (4 mg/kg) treatment increased TRPV1 protein expression in the superficial layers of the spinal dorsal horn 14 days after treatment. Behavioral assessment using the paw withdrawal response showed that PTX-induced mechanical allodynia/hyperalgesia and thermal hyperalgesia after 14 days was significantly inhibited by oral or intrathecal administration of the TRPV1 antagonist AMG9810. We found that intrathecal administration of small interfering RNA (siRNA) to knock down TRPV1 protein expression in the spinal cord significantly decreased PTX-induced mechanical allodynia/hyperalgesia and thermal hyperalgesia. Together, these results demonstrate that TRPV1 receptor expression in spinal cord contributes, at least in part, to the development of PTX-induced painful peripheral neuropathy. TRPV1 receptor antagonists may be useful in the prevention and treatment of PTX-induced peripheral neuropathic pain.

Background: Capecitabine plus oxaliplatin (XELOX) has been established as a first-line treatment for metastatic colorectal cancer. Adherence is particularly important with capecitabine to maintain appropriate curative effect. In this study, we monitored the adherence to capecitabine on XELOX treatment and investigated which factors might decrease compliance. Methods: The study included 242 consecutive patients who received XELOX treatment for metastatic colorectal cancer between October 2009 and March 2012. Adherence to capecitabine was checked by pharmacists with a patient-reported treatment diary at a pharmaceutical outpatient clinic. Adherence rate was defined as the number of times that a patient took capecitabine in a 14-day cycle/28 prescribed doses. We retrospectively surveyed median relative dose intensities of capecitabine and the factors deteriorating adherence across eight cycles from electronic patient records and examined differences in compliance rates according to age. Results: The study included 144 male and 98 female patients. The overadherence rate was 1.5% (n=23). The median adherence rate was 93.5% (n=242) in the first cycle of XELOX treatment, which gradually rose to 96.1% (n=148) in the eighth cycle. The median relative dose intensity of capecitabine was 79.2%. The main factors contributing to decreased adherence to capecitabine were diarrhea (22.5%, 352 instances) and nausea/vomiting (13.8%, 215 instances). The rate of missed dose was 12.1%. Analysis of adherence issues in relation to patient age showed a trend toward worse adherence to capecitabine therapy in the group of patients aged ≥80 years (hazard ratio =3.83; 95% confidence interval 2.48–5.91, P<0.001 versus 70–80 years group and versus <70 years group, chi-square test). Conclusion: Patient-reported adherence to capecitabine on XELOX treatment in clinical practice is high but adversely affected by side effects. Patients aged 80 years or more exhibit a significant decrease in compliance compared with younger patients.