Increased anandamide uptake by sensory neurons contributes to hyperalgesia in a model of cancer pain

Abstract

Opioids do not effectively manage pain in many patients with advanced cancer. Because anandamide (AEA) activation of cannabinoid type-1 receptors (CB1R) on nociceptors reduces nociception, manipulation of AEA metabolism in the periphery may be an effective alternative or adjuvant therapy in the management of cancer pain. AEA is hydrolyzed by the intracellular enzyme fatty acid amide hydrolase (FAAH), and this enzyme activity contributes to uptake of AEA into neurons and to reduction of AEA available to activate CB1R. We used an in vitro preparation of adult murine dorsal root ganglion (DRG) neurons co-cultured with fibrosarcoma cells to investigate how tumors alter the uptake of AEA into neurons. Evidence that the uptake of [3H]AEA into dissociated DRG cells in the co-culture model mimicked the increase in uptake that occurred in DRG cells from tumor-bearing mice supported the utility of the in vitro model to study AEA uptake. Results with the fluorescent AEA analog CAY10455 confirmed that an increase in uptake in the co-culture model occurred in neurons. One factor that contributed to the increase in [3H]AEA uptake was an increase in total cellular cholesterol in the cancer condition. Treatment with the FAAH inhibitor URB597 reduced CAY10455 uptake in the co-culture model to the level observed in DRG neurons maintained in the control condition (i.e., in the absence of fibrosarcoma cells), and this effect was paralleled by OMDM-1, an inhibitor of AEA uptake, at a concentration that had no effect on FAAH activity. Maximally effective concentrations of the two drugs together produced a greater reduction than was observed with each drug alone. Treatment with BMS309403, which competes for AEA binding to fatty acid binding protein-5, mimicked the effect of OMDM-1 in vitro. Local injection of OMDM-1 reduced hyperalgesia in vivo in mice with unilateral tumors in and around the calcaneous bone. Intraplantar injection of OMDM-1 (5 µg) into the tumor-bearing paw reduced mechanical hyperalgesia through a CB1R-dependent mechanism and also reduced a spontaneous nocifensive behavior. The same dose reduced withdrawal responses evoked by suprathreshold mechanical stimuli in naive mice. These data support the conclusion that OMDM-1 inhibits AEA uptake by a mechanism that is independent of inhibition of FAAH and provide a rationale for the development of peripherally restricted drugs that decrease AEA uptake for the management of cancer pain.

Peripheral gating of pain signals by endogenous lipid mediators

“…Moreover, growth of painful bone tumors is associated with enhanced FAAH expression in the paw bearing the tumor and the DRG innervating it 24 . This effect – along with a parallel, but independent increase in carrier-mediated anandamide uptake by neurons and/or other cells of the DRG 56 – may be responsible for the observed deficit in anandamide mobilization 52 .…”

“…Experiments with Raw264.7 macrophages suggest that the PLC/phosphatase pathway mediates the initial spike in anandamide production 29 (Figure 3), whereas the delayed decline in OEA and PEA results from a down-regulation in NAPE-PLD transcription due to reduced acetylation of histone proteins bound to the NAPE-PLD promoter 84 . The ability of tissue damage to suppress FAE mobilization has been documented using multiple animal models of inflammation and peripheral neuropathy 53,56,70,83 . Adding clinical relevance to these observations, one study found that the concentrations of OEA and PEA in synovial fluid are lower in subjects with rheumatoid arthritis and osteoarthritis than in healthy controls 85 .…”

“…This idea was tested using pharmacological agents that selectively block the cysteine hydrolase, N -acylethanolamine acid amidase (NAAA) 53,56,83 , which catalyzes the deactivating hydrolysis of OEA and PEA in macrophages 49 (Figure 4). Topical administration of the NAAA inhibitor, N-[(3S)-2-oxo-3-oxetanyl]-3-phenylpropanamide, in mice reinstates normal PEA levels in activated leukocytes and blunts inflammatory responses induced by LPS or carrageenan 83 .…”

JZL184 is anti-hyperalgesic in a murine model of cisplatin-induced peripheral neuropathy

“…During extraction of lipids, 5 pmol of deuterated ( d) 8 -AEA and 100 pmol of d 8 -2-AG and d 8 -palmitoylethanolamine (PEA, Cayman Chemical, Ann Arbor, Michigan) were added as internal standards. PEA is included in this report because it is another fatty acid ethanolamide that modulates transduction of noxious stimuli [32]. The total lipid weight was determined by weighing the vials containing the dried organic phases of each sample.…”

Revealing the role of the endocannabinoid system modulators, SR141716A, URB597 and VDM-11, in sleep homeostasis

“…An additional actor of the endocannabinoid system includes the anandamide membrane transporter (AMT) which displays a key role in modulating anandamide's biological functions (Chicca et al, 2012;Fowler, 2013;Khasabova et al, 2013;Leung et al, 2013;Nicolussi and Gertsch, 2015). The available evidence indicates that injections of blocker of AMT known as VDM-11 promote sleep in rats (Murillo-Rodrı´guez et al, 2008.…”