Sickle Cell Disease (SCD) is the most common monogenic red blood cell disorder characterized by a remarkable phenotypic complexity. Common complications of SCD are unpredictable episodic and chronic pain. Transgenic homozygous HbSS-BERK mice expressing >99% human sickle hemoglobin and exhibiting both pain and neurochemical changes similar to humans, and HbAA control mice expressing normal human hemoglobin, were used to determine the contribution of the prostaglandin E2 glyceryl ester (PGE2-G), to mechanical and heat hyperalgesia and the mechanism of its pro-nociceptive effect. Mechanical hyperalgesia was defined by a decrease in paw withdrawal threshold, and heat hyperalgesia was defined by a decrease in paw withdrawal latency to radiant heat applied to the plantar hind paw. Considering that prostaglandin E2-G (PGE2-G) is the product of oxidation of 2-arachidonylglycerol (2-AG) by cycloxygenase-2 (COX-2), the expression of COX-2 protein and COX-2 activity was measured in dorsal root ganglia (DRG). The levels of 2-AG and PGE2-G in DRG were determined by HPLC-MS. Mechanical and heat hyperalgesia in HbSS mice were associated with a decreased level of 2-AG and increased level of PGE2-G in DRGs of HbSS mice due to elevated level of COX-2 protein and COX-2 activity. In HbAA control mice, intraplantar (i.pl.) injection of PGE2-G (1 µg/10 µl) produced mechanical hyperalgesia in the injected paw independently from PGE2 receptors. Also, PGE2-G (1 µg/10 µl, i.pl.) produced mechanical and heat hyperalgesia in the injected paw in C3H mice. The hyperalgesia was blocked by co-injection of PGE2-G with MRS 2578, the purinergic P2Y6 receptor antagonist (1.4 mg/10 ml, i.pl.). Importantly, MRS 2578 (4.7 mg/50 ml, i.p.) also attenuated hyperalgesia in HbSS mice. Thus, increased expression of COX-2 in DRG neurons of HbSS mice results in the oxidation of 2-AG and production of PGE2-G, a pronociceptive mediator. PGE2-G produced mechanical and heat hyperalgesia in HbAA and C3H mice, and these effects were mediated by P2Y6 receptors.

Acknowledgments: Supported by the National Heart, Lung and Blood Institute (HL135895-16).

Disclosures

Gupta:Novartis: Honoraria; Tau tona: Consultancy.

Author notes

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Asterisk with author names denotes non-ASH members.

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