Cisplatin-induced changes in calcitonin gene-related peptide or TNF-α release in rat dorsal root ganglia in vitro model of neurotoxicity are not reverted by rosiglitazone.

INTRODUCTION: Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of anticancer drugs which affect the peripheral nervous system, as occurs with cisplatin treatment. Nowadays, one strategy in development to prevent, minimize and/or revert CIPN is neuroprotection. Therefore, we have evaluated the signaling pathways involved in CIPN and the effect of rosiglitazone, a peroxisome proliferator-activated receptor γ (PPAR-γ) agonist. METHODS: Dorsal Root Ganglia (DRG) were harvested from Wistar rats (Rattus norvegicus), the cells were dissociated, plated, and maintained with nerve growth factor for 9 days. On day 8, the cells were treated with cisplatin, rosiglitazone and/or T0070907 (PPAR-γ antagonist) for 24 h. The cell viability was measured by trypan blue exclusion method, the mRNA was quantified by real-time RT-PCRq and the release of TNF-α and calcitonin gene-related peptide (CGRP) was evaluated by ELISA. RESULTS: Cisplatin, rosiglitazone or T0070907 treatments did not decreased the cell viability on the primary DRG cultures cells. Cisplatin treatment induced a decrease of PPAR-γ and -ß/δ mRNA, while the co-treatment with rosiglitazone inhibited this cisplatin-induced effect. Moreover, T0070907 did not change the observed results, indicating that the rosiglitazone's effect could be due to mechanisms beyond PPAR-γ activation. Also, the rosiglitazone effect is not exclusively to DRG cells since there was an increase of PPAR-γ mRNA expression in 3T3-L1 cells. Furthermore, rosiglitazone did not modulate the cisplatin decrease neuronal function of DRG cells (TNF-α and CGRP release). CONCLUSION: Cisplatin decreased the gene expression of PPAR-γ and -ß/δ, while the rosiglitazone treatment inhibited these effects via PPAR-γ independent pathway. Rosiglitazone did not show improvement in modulation of TNF-α or CGRP release impaired by cisplatin.

Peripheral inflammatory hyperalgesia depends on the COX increase in the dorsal root ganglion.

It is well established that dorsal root ganglion (DRG) cells synthesize prostaglandin. However, the role that prostaglandin plays in the inflammatory hyperalgesia of peripheral tissue has not been established. Recently, we have successfully established a technique to inject drugs (3 µL) directly into the L5-DRG of rats, allowing in vivo identification of the role that DRG cell-derived COX-1 and COX-2 play in the development of inflammatory hyperalgesia of peripheral tissue. IL-1ß (0.5 pg) or carrageenan (100 ng) was administered in the L5-peripheral field of rat hindpaw and mechanical hyperalgesia was evaluated after 3 h. Administration of a nonselective COX inhibitor (indomethacin), selective COX-1 (valeryl salicylate), or selective COX-2 (SC-236) inhibitors into the L5-DRG prevented the hyperalgesia induced by IL-1ß. Similarly, oligodeoxynucleotide-antisense against COX-1 or COX-2, but not oligodeoxynucleotide-mismatch, decreased their respective expressions in the L5-DRG and prevented the hyperalgesia induced by IL-1ß in the hindpaw. Immunofluorescence analysis demonstrated that the amount of COX-1 and COX-2, constitutively expressed in TRPV-1(+) cells of the DRG, significantly increased after carrageenan or IL-1ß administration. In addition, indomethacin administered into the L5-DRG prevented the increase of PKCε expression in DRG membrane cells induced by carrageenan. Finally, the administration of EP1/EP2 (7.5 ng) or EP4 (10 µg) receptor antagonists into L5-DRG prevented the hyperalgesia induced by IL-1ß in the hindpaw. In conclusion, the results of this study suggest that the inflammatory hyperalgesia in peripheral tissue depends on activation of COX-1 and COX-2 in C-fibers, which contribute to the induction and maintenance of sensitization of primary sensory neurons.

Reduced expression of SynGAP, a neuronal GTPase-activating protein, enhances capsaicin-induced peripheral sensitization.

Synaptic GTPase-activating protein (SynGAP) is a neuronal-specific Ras/Rap-GAP that increases the hydrolysis rate of GTP to GDP, converting Ras/Rap from the active into the inactive form. The Ras protein family modulates a wide range of cellular pathways including those involved in sensitization of sensory neurons. Since GAPs regulate Ras activity, SynGAP might be an important regulator of peripheral sensitization and pain. Therefore, we evaluated excitability, stimulus-evoked release of the neuropeptide calcitonin gene-related peptide (CGRP), and nociception from wild-type (WT) mice and those with a heterozygous mutation of the SynGAP gene (SynGAP(+/-)). Our results demonstrate that SynGAP is expressed in primary afferent sensory neurons and that the capsaicin-stimulated CGRP release from spinal cord slices was two-fold higher from SynGAP(+/-) mice than that observed from WT mouse tissue, consistent with an increase in expression of the capsaicin receptor, transient receptor potential cation channel subfamily V member 1 (TRPV1), in SynGAP(+/-) dorsal root ganglia. However, there was no difference between the two genotypes in potassium-stimulated release of CGRP, the number of action potentials generated by a ramp of depolarizing current, or mechanical hypernociception elicited by intraplantar injection of capsaicin. In contrast, capsaicin-induced thermal hypernociception occurred at lower doses of capsaicin and had a longer duration in SynGAP(+/-) mice than WT mice. These results provide the first evidence that SynGAP is an important regulator of neuropeptide release from primary sensory neurons and can modulate capsaicin-induced hypernociception, demonstrating the importance of GAP regulation in signaling pathways that play a role in peripheral sensitization.