Inhibition of DAGLβ as a therapeutic target for pain in sickle cell disease

Abstract

Sickle cell disease (SCD) is the most common inherited disease. Pain is a key morbidity of SCD and opioids are the main treatment but their side effects emphasize the need for new analgesic approaches. Humanized transgenic mouse models have been instructive in understanding the pathobiology of SCD and mechanisms of pain. Homozygous (HbSS) Berkley mice express >99% human sickle hemoglobin and several features of clinical SCD including hyperalgesia. Previously, we reported that the endocannabinoid 2-arachidonoylglycerol (2-AG) is a precursor of the pro-nociceptive mediator prostaglandin E2-glyceryl ester (PGE2-G) which contributes to hyperalgesia in SCD. We now demonstrate the causal role of 2-AG in hyperalgesia in sickle mice. Hyperalgesia in HbSS mice correlated with elevated levels of 2-AG in plasma, its synthesizing enzyme diacylglycerol lipase β (DAGLβ) in blood cells, and with elevated levels of PGE2 and PGE2-G, pro-nociceptive derivatives of 2-AG. A single intravenous injection of 2-AG produced hyperalgesia in non-hyperalgesic HbSS mice, but not in control (HbAA) mice expressing normal human HbA. JZL184, an inhibitor of 2-AG hydrolysis also produced hyperalgesia in non-hyperalgesic HbSS or hemizygous (HbAS) mice, but did not influence hyperalgesia in hyperalgesic HbSS mice. Systemic and intraplantar administration of KT109, an inhibitor of DAGLβ, decreased mechanical and heat hyperalgesia in HbSS mice. The decrease in hyperalgesia was accompanied by reductions in 2-AG, PGE2 and PGE2-G in the blood. These results indicate that maintaining the physiological level of 2-AG in the blood by targeting DAGLβ may be a novel and effective approach to treat pain in SCD.

Persistent inflammation promotes endocannabinoid release and presynaptic cannabinoid 1 receptor desensitization

“…One intriguing possibility is that inflammation-induced increases in 2-AG contribute to hyperalgesia and CB1R desensitization is a compensatory response that protects synapses. Indeed, there is precedent for cannabinoids to contribute to hyperalgesia (Dunford et al 2021, Khasabova et al 2022). Understanding the behavioral consequences of this altered cannabinoid signaling within the vlPAG after persistent inflammation, the generalizability to other brain areas, and the reversibility of this process have important implications for future drug development.…”

Pain mechanisms in sickle cell disease. Are we closer to a breakthrough?

“…Following on from their previous study 6 showing that sensitization of nociceptors by PGE 2 -G in mice with SCD contributes to hyperalgesia (defined as an increased sensitivity to pain), Khasabova et al 1 now go on to show that the majority, but not all, of SCD mice (HbSS Berkeley model) studied exhibit strong mechanical and heat hyperalgesia and that this hyperalgesia is associated with significantly higher plasma levels of 2-AG, as compared to mice without SCD (HbAA) and to SCD mice that are not hyperalgesic. Endocannabinoids, such as 2-AG, are endogenous bioactive lipids that have been proposed as novel therapeutic targets for modulating inflammatory nociceptive pain.…”

“…In this issue of Haematologica , Khasabova et al 1 demonstrate a role for accelerated biosynthesis of the endocannabinoid, 2-arachidonoylglycerol (2-AG), and thereby prostaglandin E 2 -glycerol (PGE 2 -G) generation, in the hyperalgesia observed in a murine model of sickle cell disease (SCD). Pain is a hallmark of SCD and is a major cause of morbidity in patients, with significant negative effects on quality of life.…”

“…The use of COX-2 inhibitors has previously been suggested for managing chronic pain in SCD, 2 , 8 especially given evidence of elevated COX-2 expression and/or activity in the leukocytes of mice and patients with SCD, 1 , 6 , 9 with Khasabova et al previously reporting on the analgesic efficacy of R -flurbiprofen in mice with SCD. 6 However, observations in the latest study by Khasabova and colleagues indicate that elevation of 2-AG, upstream of COX-2, may be specific to those SCD mice displaying hyperalgesia, 1 meaning that approaches that can decrease DAGLβ-mediated biosynthesis of 2-AG could provide targeted relief for hyperalgesia in SCD, with theoretically fewer side effects than those of COX inhibitors. 10 Furthermore, combined administration of a selective DAGLβ inhibitor together with opioids could potentially lower the dose of opioid required for analgesia of SCD pain.…”

“… 10 Furthermore, combined administration of a selective DAGLβ inhibitor together with opioids could potentially lower the dose of opioid required for analgesia of SCD pain. 1 , 2 …”