Selective targeting of peripheral cannabinoid receptors prevents behavioral symptoms and sensitization of trigeminal neurons in mouse models of migraine and medication overuse headache
ABSTRACT/UNASSIGNED:Migraine affects âˆ¼15% of the world's population greatly diminishing their quality of life. Current preventative treatments are effective in only a subset of migraine patients, and while cannabinoids appear beneficial in alleviating migraine symptoms, central nervous system (CNS) side effects limit their widespread use. We developed peripherally-restricted cannabinoids (PRCBs) that relieve chronic pain symptoms of cancer and neuropathies, without appreciable CNS side effects or tolerance development. Here we determined PRCB effectiveness in alleviating hypersensitivity symptoms in mouse models of migraine and medication overuse headache (MOH). Chronic glyceryl trinitrate (GTN, 10 mg/kg) administration led to increased sensitivity to mechanical stimuli, and increased expression of phosphorylated protein kinase A (p-PKA), neuronal nitric oxide synthase (nNOS), and transient receptor potential ankyrin 1 (TRPA1) proteins in trigeminal ganglia. PRCB pretreatment, but not posttreatment, prevented behavioral and biochemical correlates of GTN-induced sensitization. Low pH- and allyl isothiocyanate-activated currents in acutely isolated trigeminal neurons were reversibly attenuated by PRCB application. Chronic GTN treatment significantly enhanced these currents. Chronic sumatriptan treatment also led to development of allodynia to mechanical and cold stimuli which was slowly reversible after sumatriptan discontinuation. Subsequent challenge with a previously ineffective low-dose GTN (0.1-0.3 mg/kg) revealed latent behavioral sensitization and increased expression of p-PKA, nNOS, and TRPA1 proteins in trigeminal ganglia. PRCB pretreatment prevented all behavioral and biochemical correlates of allodynia and latent sensitization. Importantly, chronic PRCB treatment alone did not produce any behavioral or biochemical signs of sensitization. These data validate peripheral cannabinoid receptors as potential therapeutic targets in migraine and MOH.
Nanotechnology for pain management: Current and future therapeutic interventions
Pain is one of the most common medical conditions and affects more Americans than diabetes, heart disease, and cancer combined. Current pain treatments mainly rely on opioid analgesics and remain unsatisfactory. The life-threatening side effects and addictive properties of opioids demand new therapeutic approaches. Nanomedicine may be able to address these challenges as it allows for sensitive and targeted treatments without some of the burdens associated with current clinical pain therapies. This review discusses the physiology of pain, the current landscape of pain treatment, novel targets for pain treatment, and recent and ongoing efforts to effectively treat pain using nanotechnology-based approaches. We highlight advances in nanoparticle-based drug delivery to reduce side effects, gene therapy to tackle the source of pain, and nanomaterials-based scavenging to proactively mediate pain signaling.
Peripheral Nerve Resident Macrophages and Schwann Cells Mediate Cancer-induced Pain
Although macrophages (MÎ¦) are known to play a central role in neuropathic pain, their contribution to cancer pain has not been established. Here we report that depletion of sciatic nerve resident MÎ¦s (rMÎ¦) in mice attenuates mechanical/cold hypersensitivity and spontaneous pain evoked by intraplantar injection of melanoma or lung carcinoma cells. MÎ¦-colony stimulating factor (M-CSF) was upregulated in the sciatic nerve trunk and mediated cancer-evoked pain via rMÎ¦ expansion, transient receptor potential ankyrin 1 (TRPA1) activation, and oxidative stress. Targeted deletion of Trpa1 revealed a key role for Schwann cell TRPA1 in sciatic nerve rMÎ¦ expansion and pain-like behaviors. Depletion of rMÎ¦s in a medial portion of the sciatic nerve prevented pain-like behaviors. Collectively, we identified a feed-forward pathway involving M-CSF, rMÎ¦, oxidative stress and Schwann cell TRPA1 that operates throughout the nerve trunk to signal cancer-evoked pain.
Targeting G protein-coupled receptors for the treatment of chronic pain in the digestive system
Chronic pain is a hallmark of functional disorders, inflammatory diseases and cancer of the digestive system. The mechanisms that initiate and sustain chronic pain are incompletely understood, and available therapies are inadequate. This review highlights recent advances in the structure and function of pronociceptive and antinociceptive G protein-coupled receptors (GPCRs) that provide insights into the mechanisms and treatment of chronic pain. This knowledge, derived from studies of somatic pain, can guide research into visceral pain. Mediators from injured tissues transiently activate GPCRs at the plasma membrane of neurons, leading to sensitisation of ion channels and acute hyperexcitability and nociception. Sustained agonist release evokes GPCR redistribution to endosomes, where persistent signalling regulates activity of channels and genes that control chronic hyperexcitability and nociception. Endosomally targeted GPCR antagonists provide superior pain relief in preclinical models. Biased agonists stabilise GPCR conformations that favour signalling of beneficial actions at the expense of detrimental side effects. Biased agonists of Âµ-opioid receptors (MOPrs) can provide analgesia without addiction, respiratory depression and constipation. Opioids that preferentially bind to MOPrs in the acidic microenvironment of diseased tissues produce analgesia without side effects. Allosteric modulators of GPCRs fine-tune actions of endogenous ligands, offering the prospect of refined pain control. GPCR dimers might function as distinct therapeutic targets for nociception. The discovery that GPCRs that control itch also mediate irritant sensation in the colon has revealed new targets. A deeper understanding of GPCR structure and function in different microenvironments offers the potential of developing superior treatments for GI pain.
Agonist that activates the Âµ-opioid receptor in acidified microenvironments inhibits colitis pain without side effects
OBJECTIVE:The effectiveness of Âµ-opioid receptor (MOPr) agonists for treatment of visceral pain is compromised by constipation, respiratory depression, sedation and addiction. We investigated whether a fentanyl analogue, (Â±)-N-(3-fluoro-1-phenethylpiperidine-4-yl)-N-phenyl propionamide (NFEPP), which preferentially activates MOPr in acidified diseased tissues, would inhibit pain in a preclinical model of inflammatory bowel disease (IBD) without side effects in healthy tissues. DESIGN/METHODS:Antinociceptive actions of NFEPP and fentanyl were compared in control mice and mice with dextran sodium sulfate colitis by measuring visceromotor responses to colorectal distension. Patch clamp and extracellular recordings were used to assess nociceptor activation. Defecation, respiration and locomotion were assessed. Colonic migrating motor complexes were assessed by spatiotemporal mapping of isolated tissue. NFEPP-induced MOPr signalling and trafficking were studied in human embryonic kidney 293 cells. RESULTS:NFEPP inhibited visceromotor responses to colorectal distension in mice with colitis but not in control mice, consistent with acidification of the inflamed colon. Fentanyl inhibited responses in both groups. NFEPP inhibited the excitability of dorsal root ganglion neurons and suppressed mechanical sensitivity of colonic afferent fibres in acidified but not physiological conditions. Whereas fentanyl decreased defecation and caused respiratory depression and hyperactivity in mice with colitis, NFEPP was devoid of these effects. NFEPP did not affect colonic migrating motor complexes at physiological pH. NFEPP preferentially activated MOPr in acidified extracellular conditions to inhibit cAMP formation, recruit Î²-arrestins and evoke MOPr endocytosis. CONCLUSION/CONCLUSIONS:In a preclinical IBD model, NFEPP preferentially activates MOPr in acidified microenvironments of inflamed tissues to induce antinociception without causing respiratory depression, constipation and hyperactivity.
Legumain Induces Oral Cancer Pain by Biased Agonism of Protease-Activated Receptor-2
Oral squamous cell carcinoma (OSCC) is one of the most painful cancers, which interferes with orofacial function including talking and eating. We report that legumain (Lgmn) cleaves protease-activated receptor-2 (PAR2) in the acidic OSCC microenvironment to cause pain. Lgmn is a cysteine protease of late endosomes and lysosomes that can be secreted; it exhibits maximal activity in acidic environments. The role of Lgmn in PAR2-dependent cancer pain is unknown. We studied Lgmn activation in human oral cancers and oral cancer mouse models. Lgmn was activated in OSCC patient tumors, compared to matched normal oral tissue. After intraplantar, facial or lingual injection, Lgmn evoked nociception in wild-type (WT) female mice but not in female mice lacking PAR2 in NaV1.8-positive neurons (Par2Nav1.8), nor in female mice treated with a Lgmn inhibitor, LI-1. Inoculation of an OSCC cell line caused mechanical and thermal hyperalgesia that was reversed by LI-1. Par2Nav1.8 and Lgmn deletion attenuated mechanical allodynia in female mice with carcinogen-induced OSCC. Lgmn caused PAR2-dependent hyperexcitability of trigeminal neurons from WT female mice. Par2 deletion, LI-1 and inhibitors of adenylyl cyclase or protein kinase A prevented the effects of Lgmn. Under acidified conditions, Lgmn cleaved within the extracellular N-terminus of PAR2 at Asn30â†“Arg31, proximal to the canonical trypsin activation site. Lgmn activated PAR2 by biased mechanisms in HEK293 cells to induce Ca2+ mobilization, cAMP formation and protein kinase A/D activation, but not Î²-arrestin recruitment or PAR2 endocytosis. Thus, in the acidified OSCC microenvironment Lgmn activates PAR2 by biased mechanisms that evoke cancer pain.SIGNIFICANCE STATEMENTOral squamous cell carcinoma (OSCC) is one of the most painful cancers. We report that legumain (Lgmn), which exhibits maximal activity in acidic environments, cleaves protease-activated receptor-2 (PAR2) on neurons to produce OSCC pain. Active Lgmn was elevated in OSCC patient tumors, compared to matched normal oral tissue. Lgmn evokes pain-like behavior through PAR2 Exposure of pain-sensing neurons to Lgmn decreased the current required to generate an action potential through PAR2 Inhibitors of adenylyl cyclase and protein kinase A prevented the effects of Lgmn. Lgmn activated PAR2 to induce calcium mobilization, cAMP formation and activation of protein kinase D and A, but not Î²-arrestin recruitment or PAR2 endocytosis. Thus, Lgmn is a biased agonist of PAR2 that evokes cancer pain.
Epidemiologic factors in patients with advanced head and neck cancer treated with radiation therapy
BACKGROUND:Approximately 50% of patients with head and neck cancer (HNC) initially were seen with advanced disease. We aimed to evaluate the association of epidemiologic factors with advanced HNC at diagnosis. METHODS:The OraRad multicenter prospective cohort study enrolled HNC patients receiving curative-intent radiation therapy. Factors assessed for association with advanced HNC presentation at diagnosis included demographics, social and medical history, cancer characteristics, human papilloma virus (HPV) status, and dental disease measures. RESULTS:We enrolled 572 participants; 77% male and mean (SD) age of 61.7 (11.2) years. Oropharyngeal squamous cell carcinomas (88% HPV-related) were seen with smaller tumors, but more frequent nodal involvement. Private medical insurance and no Medicaid were associated with smaller tumors. A higher dental disease burden was associated with larger tumors. CONCLUSIONS:Insurance status, cancer type/location, and dental disease are associated with advanced HNC and may represent potentially modifiable factors or factors to be considered in the screening process of new lesions.
Assessment of metastatic lymph nodes in head and neck squamous cell carcinomas using simultaneous 18F-FDG-PET and MRI
In this study, we investigate the feasibility of using dynamic contrast enhanced magnetic resonance imaging (DCE-MRI), diffusion weighted imaging (DWI), and dynamic positron emission tomography (PET) for detection of metastatic lymph nodes in head and neck squamous cell carcinoma (HNSCC) cases. Twenty HNSCC patients scheduled for lymph node dissection underwent DCE-MRI, dynamic PET, and DWI using a PET-MR scanner within one week prior to their planned surgery. During surgery, resected nodes were labeled to identify their nodal levels and sent for routine clinical pathology evaluation. Quantitative parameters of metastatic and normal nodes were calculated from DCE-MRI (ve, vp, PS, Fp, Ktrans), DWI (ADC) and PET (Ki, K1, k2, k3) to assess if an individual or a combination of parameters can classify normal and metastatic lymph nodes accurately. There were 38 normal and 11 metastatic nodes covered by all three imaging methods and confirmed by pathology. 34% of all normal nodes had volumes greater than or equal to the smallest metastatic node while 4 normal nodes had SUVâ€‰>â€‰4.5. Among the MRI parameters, the median vp, Fp, PS, and Ktrans values of the metastatic lymph nodes were significantly lower (pâ€‰=â€‰<0.05) than those of normal nodes. ve and ADC did not show any statistical significance. For the dynamic PET parameters, the metastatic nodes had significantly higher k3 (p valueâ€‰=â€‰8.8â€‰Ã—â€‰10-8) and Ki (p valueâ€‰=â€‰5.3â€‰Ã—â€‰10-8) than normal nodes. K1 and k2 did not show any statistically significant difference. Ki had the best separation with accuracyâ€‰=â€‰0.96 (sensitivityâ€‰=â€‰1, specificityâ€‰=â€‰0.95) using a cutoff of Kiâ€‰=â€‰5.3â€‰Ã—â€‰10-3Â mL/cm3/min, while k3 and volume had accuracy of 0.94 (sensitivityâ€‰=â€‰0.82, specificityâ€‰=â€‰0.97) and 0.90 (sensitivityâ€‰=â€‰0.64, specificityâ€‰=â€‰0.97) respectively. 100% accuracy can be achieved using a multivariate logistic regression model of MRI parameters after thresholding the data with Kiâ€‰<â€‰5.3â€‰Ã—â€‰10-3Â mL/cm3/min. The results of this preliminary study suggest that quantitative MRI may provide additional value in distinguishing metastatic nodes, particularly among small nodes, when used together with FDG-PET.
Peripheral nerve injury and sensitization underlie pain associated with oral cancer perineural invasion
Cancer invading into nerves, termed perineural invasion (PNI), is associated with pain. Here we show that oral cancer patients with PNI report greater spontaneous pain and mechanical allodynia compared with patients without PNI, suggesting unique mechanisms drive PNI-induced pain. We studied the impact of PNI on peripheral nerve physiology and anatomy using a murine sciatic nerve PNI model. Mice with PNI exhibited spontaneous nociception and mechanical allodynia. PNI induced afterdischarge in A high threshold mechanoreceptors (AHTMRs), mechanical sensitization (i.e., decreased mechanical thresholds) in both A and C HTMRs, and mechanical desensitization in low threshold mechanoreceptors (LTMRs). PNI resulted in nerve damage, including axon loss, myelin damage, and axon degeneration. Electrophysiological evidence of nerve injury included decreased conduction velocity, and increased percentage of both mechanically-insensitive and electrically-unexcitable neurons. We conclude that PNI-induced pain is driven by nerve injury and peripheral sensitization in HTMRs.
The Histopathology of Oral Cancer Pain in a Mouse Model and a Human Cohort
Oral cancer patients often have severe, chronic, and mechanically induced pain at the site of the primary cancer. Oral cancer pain is initiated and maintained in the cancer microenvironment and attributed to release of mediators that sensitize primary sensory nerves. This study was designed to investigate the histopathology associated with painful oral cancers in a preclinical model. The relationship of pain scores with pathologic variables was also investigated in a cohort of 72 oral cancer patients. Wild-type mice were exposed to the carcinogen, 4-nitroquinoline 1-oxide (4NQO). Nociceptive (pain) behavior was measured with the dolognawmeter, an operant device and assay for measuring functional and mechanical allodynia. Lesions developed on the tongues and esophagi of the 4NQO-treated animals and included hyperkeratoses, papillomas, dysplasias, and cancers. Papillomas included lesions with benign and dysplastic pathological features. Two histologic subtypes of squamous cell carcinomas (SCCs) were identified-SCCs with exophytic and invasive components associated with papillary lesions (pSCCs) and invasive SCCs without exophytic histology (iSCCs). Only the pSCC subtype of tongue cancer was associated with nociceptive behavior. Increased tumor size was associated with greater nociceptive behavior in the mouse model and more pain experienced by oral cancer patients. In addition, depth of invasion was associated with patient-reported pain. The pSCC histology identifies 4NQO-induced tongue cancers that are expected to be enriched for expression and release of nociceptive mediators.