Sickle cell disease (SCD) is an inherited hematologic disorder accompanied by severe pain, inflammation and vascular injury. We propose that nociceptor activation by ongoing hypoxia/reperfusion (H/R) injury leads to the release of neuropeptides by sensory nerves in the skin, stimulating vascular insult and mast cell activation in SCD. In turn, mast cell tryptase activates protease activated receptor 2 (PAR 2) on sensory nerve endings maintaining nociceptor sensitization and release of SP and CGRP resulting in exaggerated neuroinflammation, vascular injury and central sensitization in SCD. Sickle mice show hyperalgesia which is further elevated by H/R and attenuated by non-selective cannabinoid receptor agonist CP55940. Our preliminary data indicate that mast cell activity and Evans blue dye leakage are increased in the skin of sickle mice Vs control, which are inhibited by CP55940. Our general hypothesis is that neurogenic inflammation contributes to pain in SCD and that cannabinoids offer the unique advantage of providing analgesia by disrupting neurogenic inflammation and nociceptor sensitization, thereby preventing central sensitization. We also hypothesize that objective, non-invasive measures of pain - EEC and functional MRI - can be used to optimize analgesic treatments in SCD. These hypotheses will be tested in the following aims. SA#1. A multicellular repertoire involving mast-, endothelial-, glial and neuronal cells orchestrates neurogenic inflammation and hyperalgesia via distinct cellular receptors and signaling pathways, which will be intercepted by cannabinoids utilizing specific cannabinoid receptors (CBR). SA#2. Cannabinoids will attenuate central sensitization in sickle mice and pain in human subjects. SA#3. Simultaneous non-invasive fMRI/EEG multimodal neuroimaging will provide an effective means to quantify pain. We propose to use transgenic sickle mice, and individual cells involved in evoking pain, to perform this translational study. A proof of principl study in humans will be undertaken to examine the effect of Cannabis ion pain in sickle patients. We expect that the multidisciplinary approach combining biochemistry, neurophysiology, pharmacology, behavior and biomedical engineering will advance the treatment of pain in SCD.
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