Purpose: Sickle Cell Disease (SCD) is a major cause of morbidity and mortality worldwide, and affects more than 100,000 people in the US. Recurrent episodes of acute, vaso-occlusive pain crisis, a hallmark of the disease, lead to chronic pain for many patients, though the mechanisms of this transition are poorly understood. Although opioids remain the standard of care to treat SCD chronic pain, their myriad adverse side effects (e.g., constipation, respiratory depression, abuse liability, dependence) as well as the fact that SCD chronic pain requires prolonged opioid treatment that results in tolerance, severely limit their therapeutic utility. Thus, a pressing need exists to identify effective non-opioid analgesic strategies to reduce SCD chronic pain. Humanized mouse models of SCD, such as the Berkeley (BERK) model, provide a useful tool to investigate disease pathophysiology and evaluate novel therapeutic strategies. Dorsal Root Ganglion (DRG) neurons are peripheral sensory neurons essential for the transmission of nociceptive afferents to the CNS. In rodent models of neuropathic pain, harvested DRG neurons show hyperexcitability. Inhibitors of the major degradative enzyme of 2-arachidonoylglycerol, monoacylglycerol lipase (MAGL), reduce nociceptive behavior in neuropathic and inflammatory preclinical models of pain through cannabinoid receptor-dependent and -independent mechanisms. As MAGL inhibitors have yet to be tested in BERK mice, here we test whether this approach will ameliorate the hyper-nociceptive phenotype of HbSS-BERK mice. Materials and methods: Male and female HbSS-BERK (sickle) and HbAA-BERK (control) mice were used as subjects for these experiments. Nociceptive behaviors were assessed using the von Frey and Hot Plate tests. Motor-functional behavior was assessed using the Grip Strength and Nesting assays. Neuronal hyperexcitability was assessed using whole cell patch clamp electrophysiology of L4-S1 DRG neurons. Data were analyzed as two- and three-way ANOVAs followed by Tukey post-hoc analysis when appropriate (p < 0.05 considered significant). Results: HbSS-BERK mice displayed profound mechanical, thermal and deep tissue/musculoskeletal hypersensitivity. HbSS-BERK mice also exhibited deficits in nest-building behavior. Patch clamp studies revealed that DRG neurons harvested from HbSS-BERK mice displayed extremely hyperexcitability. MJN-110 dose-dependently reduced mechanical allodynia and thermal hyperalgesia, and ameliorated deficits in grip strength in HbSS-BERK mice. Importantly, seven days of daily injections of MJN-110 (5 mg/kg) continued to ameliorate the hyper-nociceptive phenotype of HbSS-BERK mice, which did not undergo tolerance. Moreover, DRG harvested from the MJN-treated HbSS-BERK mice showed similar DRG neuronal activity as seen in control mice. Conclusion: These findings validate that HbSS-BERK mice show hypersensitive responses to mechanical and heat stimuli, and exhibit motor-functional deficits in grip strength and nest building behavior. Additionally, this work demonstrates hyperexcitability of sensory neurons from the lower lumbar region of the spine of HbSS-BERK mice. Finally, the observations that MJN110 reduces these hyper-nociceptive behaviors and ameliorates neuronal hyperexcitability in HbSS-BERK mice suggest that MAGL inhibition represents a viable strategy to reduce chronic pain related to sickle cell disease. The authors do not declare any conflict of interest
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Oct 1, 2024
Min-Hee Yi 
Open Access