Key Points Heme, released from hemoglobin, elicits vaso-occlusion in transgenic sickle mice via endothelial TLR4 signaling. Heme/TLR4 signaling activates NF-κB and triggers vaso-occlusion through Weibel-Palade body degranulation and adhesion molecule expression.

Sickle cell disease causes severe pain. We examined pain-related behaviors, correlative neurochemical changes, and analgesic effects of morphine and cannabinoids in transgenic mice expressing human sickle hemoglobin (HbS). Paw withdrawal threshold and withdrawal latency (to mechanical and thermal stimuli, respectively) and grip force were lower in homozygous and hemizygous Berkley mice (BERK and hBERK1 ,

Key Points• Inhibition of mast cells with cromolyn or imatinib results in reduced systemic inflammation and neurogenic inflammation in sickle mice.• Pharmacological inhibition or genetic depletion of mast cells in sickle mice ameliorates chronic and hypoxia/reoxygenationinduced pain.Sickle cell anemia (SCA) is an inherited disorder associated with severe lifelong pain and significant morbidity. The mechanisms of pain in SCA remain poorly understood.We show that mast cell activation/degranulation contributes to sickle pain pathophysiology by promoting neurogenic inflammation and nociceptor activation via the release of substance P in the skin and dorsal root ganglion. Mast cell inhibition with imatinib ameliorated cytokine release from skin biopsies and led to a correlative decrease in granulocyte-macrophage colony-stimulating factor and white blood cells in transgenic sickle mice. Targeting mast cells by genetic mutation or pharmacologic inhibition with imatinib ameliorates tonic hyperalgesia and prevents hypoxia/reoxygenation-induced hyperalgesia in sickle mice. Pretreatment with the mast cell stabilizer cromolyn sodium improved analgesia following low doses of morphine that were otherwise ineffective. Mast cell activation therefore underlies sickle pathophysiology leading to inflammation, vascular dysfunction, pain, and requirement for high doses of morphine. Pharmacological targeting of mast cells with imatinib may be a suitable approach to address pain and perhaps treat SCA. (Blood. 2013;122(11):1853-1862

Inflammation may play an essential role in vaso-occlusion in sickle cell disease. Sickle patients have high white counts and elevated levels of serum C-reactive protein (CRP), cytokines, and adhesion molecules. In addition, circulating endothelial cells, leukocytes, and platelets are activated. We examined 4 transgenic mouse models expressing human ␣-and sickle ␤-globin genes to determine if they mimic the inflammatory response seen in patients. These mouse models are designated NY-S, Berk-S Antilles , NY-S/S Antilles (NY-S ؋ Berk-S Antilles ), and Berk-S. The mean white counts were elevated 1.4-to 2.1-fold (P < .01) in the Berk-S Antilles , NY-S/S Antilles , and Berk-S mice, but not in the NY-S mice compared with controls. Serum amyloid P-component (SAP), an acute-phase response protein with 60% to 70% sequence homology to CRP, was elevated 8.5-to 12.1-fold (P < .001) in transgenic sickle mice. Similarly, serum interleukin-6 (IL-6) was elevated 1.6-to 1.9-fold (P < .05). Western blots, confirming immunohistochemical staining, showed vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), and platelet-endothelial cell adhesion molecule (PECAM) were up-regulated 3-to 5-fold (P < .05) in the lungs of sickle mice. Ribonuclease protection assays (RPAs) demonstrated VCAM mRNA also was elevated in sickle mice 1.2-to 1.4-fold (P < .01). Nuclear factor B (NF-B), a transcription factor critical for the inflammatory response, was elevated 1.9-fold (P < .006) in NY-S sickle mouse lungs. We conclude that transgenic sickle mice are good models to study vascular inflammation and the potential benefit of anti-inflammatory therapies to prevent vasoocclusion in sickle cell disease. (Blood. 2003; 101:3953-3959)

Morphine does not affect the onset of tumour development, but it promotes growth of existing tumours, and reduces overall survival in mice. MOR may be associated with morphine-induced cancer progression, resulting in shorter survival. Mast cell activation by morphine may contribute to increased cytokine and SP levels, leading to cancer progression and refractory pain.