Métrologie de la douleur animale sur modèles expérimentaux : développement et validation de biomarqueurs neuroprotéomiques

Pain is a complex and dynamic phenomenon including a primary and sensory process, nociception, to which are added psychophysiological defense and alarm reactions. This leads to the development of a true memory of pain, individual and modulated (neuronal plasticity) by previous experiences of pain, including nociceptive sensitivity. Animal models mimicking human pathologies are crucial to understand the mechanisms of central sensitization. We proposed a series of translational experimental approaches by developing experimental models of bovine, canine and murine pain in order to characterize spinal proteome modifications according to the level of pain perceived by the animal and consequently, to identify the biomarkers (s) potentially modulated by nociceptive sensitization.  By using a neuroproteomic method, in a bovine model of visceral pain, the transthyretin (TTR) protein was identified and down-regulated in the spinal proteome in the presence of pain, and this was verified in a canine model of chronic pain related to surgical osteoarthritis (OA) induction. These findings suggest the possibility of considering TTR as a potential biomarker of chronic pain. Our discovery of the relationship between spinal levels of TTR by neuroproteomic and pain hypersensitivity in bovine and canine models supports the involvement of inflammatory, nociceptive and immune components. Subsequently, procedures for metrological validation of acclimatization protocols and environmental conditions of manipulation have identified the most reliable and sensitive methods of pain assessment. The chemical model (intraarticular injection of monosodium iodoacetate) of chronic pain induction related to OA in rats also allowed us to demonstrate that an increase in the temporal expression of excitatory spinal neuropeptides such as substance P, calcitonin gene-related peptide, bradykinin and the anti-nociceptive somatostatin, is associated with central sensitization phenomenon in this model, as also supported by functional evaluations. The differences observed on functional results between the analgesic drugs were supported by different influences on spinal neuropeptide concentrations, thus increasing the validity and psychometric sensitivity of quantitative sensory testing and biomechanical pain assessment methods. In the aim to elaborate an experimental model of chronic pain related to OA reproducing more closely post-traumatic progression, the development of a surgical model in rodent has shown the possibility of inducing changes compatible with chronic pathological pain. The surgical model of OA pain induction generated quantifiable neurophysiological changes associated with central sensitization. These changes in functional alterations were concomitant with the release of spinal neuropeptides. The comparison with the chemical model showed more persistent and less aggressive modifications which would be potentially useful for the evaluation of therapeutic modalities in OA. The use of objective proteomic methods combined with subjective evaluation to quantify pain could lead to a completely new management of pain and animal welfare.

Keyphrases: neuropeptide, validation, biomarker, neuroproteomic, central sensitization, pain, animal model, neuropeptide, pain metrology, validation