Epidermal growth factor receptor transactivation by the cannabinoid receptor (CB1) and transient receptor potential vanilloid 1 (TRPV1) induces differential responses in corneal epithelial cells

MUC1‑ND interacts with TRPV1 to promote corneal epithelial cell proliferation in diabetic dry eye mice by partly activating the AKT signaling pathway

Although both mucin1 (MUC1) and transient receptor potential cation channel subfamily V member 1 (TRPV1) have been reported to be associated with dry eye (DE) disease, whether they interact and their regulatory roles in diabetic DE disease are unknown. Diabetic DE model mice were generated by streptozotocin induction and assessed by corneal fluorescein staining, tear ferning (TF) tests, phenol red thread tests, hematoxylin and eosin staining of corneal sections and periodic acid Schiff staining of conjunctival sections. Cell proliferation was measured by CCK8 assay. Western blotting was performed to measure protein expression. Primary mouse corneal epithelial cells (MCECs) were cultured after enzymatic digestion. Immunofluorescence staining of MCECs and frozen corneal sections was conducted to assess protein expression and colocalization. Coimmunoprecipitation was performed to detect protein‑protein interactions. It was found that, compared with control mice, diabetic DE mice exhibited increased corneal epithelial defects, reduced tear production, poorer TF pattern grades and impaired corneal and conjunctival tissues. In vivo and in vitro experiments showed that hyperglycemia impaired cell proliferation, accompanied by decreased levels of the MUC1 extracellular domain (MUC1‑ND) and TRPV1. Additionally, it was found that capsazepine (a TRPV1 antagonist) inhibited the proliferation of MCECs. Notably, MUC1‑ND was shown to interact with the TRPV1 protein in the control group but not in the diabetic DE group. It was also found that the AKT signaling pathway was attenuated in the diabetic DE mice and downstream of TRPV1. MUC1‑ND interacted with TRPV1, partly activating the AKT signaling pathway to promote MCEC proliferation. The present study found that the interaction of MUC1‑ND with TRPV1 promotes MCEC proliferation by partly activating the AKT signaling pathway, providing new insight into the pathogenesis of corneal epithelial dysfunction in diabetic DE disease.

Protective effects of fatty acid amide hydrolase inhibition in UVB-activated microglia

Neuroinflammation is a hallmark of several neurodegenerative disorders that has been extensively studied in recent years. Microglia, the primary immune cells of the central nervous system (CNS), are key players in this physiological process, demonstrating a remarkable adaptability in responding to various stimuli in the eye and the brain. Within the complex network of neuroinflammatory signals, the fatty acid N-ethanolamines, in particular N-arachidonylethanolamine (anandamide, AEA), emerged as crucial regulators of microglial activity under both physiological and pathological states. In this study, we interrogated for the first time the impact of the signaling of these bioactive lipids on microglial cell responses to a sub-lethal acute UVB radiation, a physical stressor responsible of microglia reactivity in either the retina or the brain. To this end, we developed an in vitro model using mouse microglial BV-2 cells. Upon 24 h of UVB exposure, BV-2 cells showed elevated oxidative stress markers and, cyclooxygenase (COX-2) expression, enhanced phagocytic and chemotactic activities, along with an altered immune profiling. Notably, UVB exposure led to a selective increase in expression and activity of fatty acid amide hydrolase (FAAH), the main enzyme responsible for degradation of fatty acid ethanolamides. Pharmacological FAAH inhibition via URB597 counteracted the effects of UVB exposure, decreasing tumor necrosis factor α (TNF-α) and nitric oxide (NO) release and reverting reactive oxidative species (ROS), interleukin-1β (IL-1β), and interleukin-10 (IL-10) levels to the control levels. Our findings support the potential of enhanced fatty acid amide signaling in mitigating UVB-induced cellular damage, paving the way to further exploration of these lipids in light-induced immune responses.

Risk factors for pterygium: Latest research progress on major pathogenesis

A pterygium is a wedge-shaped fibrovascular growth of the conjunctiva membrane that extends onto the cornea, which is the outer layer of the eye. It is also known as surfer's eye. Growth of a pterygium can also occur on the either side of the eye, attaching firmly to the sclera. Pterygia are one of the world's most common ocular diseases. However, the pathogenesis remains unsolved to date. As the pathogenesis of pterygium is closely related to finding the ideal treatment, a clear understanding of the pathogenesis will lead to better treatment and lower the recurrence rate, which is notably high and more difficult to treat than a primary pterygium. Massive studies have recently been conducted to determine the exact causes and mechanism of pterygia. We evaluated the pathogenetic factors ultraviolet radiation, viral infection, tumor suppressor genes p53, growth factors, oxidative stress, apoptosis and neuropeptides in the progression of the disease. The heightened expression of TRPV1 suggests its potential contribution in the occurrence of pterygium, promoting its inflammation and modulating sensory responses in ocular tissues. Subsequently, the developmental mechanism of pterygium, along with its correlation with dry eye disease is proposed to facilitate the identification of pathogenetic factors for pterygia, contributing to the advancement of understanding in this area and may lead to improved surgical outcomes.

TRPV1-Dependent Antiproliferative Activity of Dioecious Maclura pomifera Extracts in Estrogen Receptor-Positive Breast Cancer Cell Lines Involves Multiple Apoptotic Pathways

Globally, breast cancer is a significant cause of mortality. Recent research focused on identifying compounds regulating the transient receptor potential vanilloid 1 (TRPV1) ion channel activity for the possibility of developing cancer therapeutics. In this study, the antiproliferative properties and mechanisms of action through TRPV1 of Maclura pomifera, a dioecious tree native to the south-central USA, have been investigated. Male and female extracts of spring branch tissues and leaves (500 µg/mL) significantly reduced the viability of MCF-7 and T47D cells by 75-80%. M. pomifera extracts induced apoptosis by triggering intracellular calcium overload via TRPV1. Blocking TRPV1 with the capsazepine antagonist and pretreating cells with the BAPTA-AM chelator boosted cell viability, revealing that M. pomifera phytochemicals activate TRPV1. Both male and female M. pomifera extracts initiated apoptosis through multiple pathways, the mitochondrial, ERK-induced, and endoplasmic reticulum-stress-mediated apoptotic pathways, demonstrated by the expression of activated caspase 3, caspase 9, caspase 8, FADD, FAS, ATF4, and CHOP, the overexpression of phosphorylated PERK and ERK proteins, and the reduction of BCL-2 levels. In addition, AKT and pAKT protein expressions were reduced in female M. pomifera-treated cells, revealing that female plant extract also inhibits PI3K/Akt signaling pathways. These results suggest that phytochemicals in M. pomifera extracts could be promising for developing breast cancer therapeutics.

Functional Selectivity of Cannabinoid Type 1 G Protein-Coupled Receptor Agonists in Transactivating Glycosylated Receptors on Cancer Cells to Induce Epithelial-Mesenchymal Transition Metastatic Phenotype

Understanding the role of biased G protein-coupled receptor (GPCR) agonism in receptor signaling may provide novel insights into the opposing effects mediated by cannabinoids, particularly in cancer and cancer metastasis. GPCRs can have more than one active state, a phenomenon called either 'biased agonism', 'functional selectivity', or 'ligand-directed signaling'. However, there are increasing arrays of cannabinoid allosteric ligands with different degrees of modulation, called 'biased modulation', that can vary dramatically in a probe- and pathway-specific manner, not from simple differences in orthosteric ligand efficacy or stimulus-response coupling. Here, emerging evidence proposes the involvement of CB1 GPCRs in a novel biased GPCR signaling paradigm involving the crosstalk between neuraminidase-1 (Neu-1) and matrix metalloproteinase-9 (MMP-9) in the activation of glycosylated receptors through the modification of the receptor glycosylation state. The study findings highlighted the role of CB1 agonists AM-404, Aravnil, and Olvanil in significantly inducing Neu-1 sialidase activity in a dose-dependent fashion in RAW-Blue, PANC-1, and SW-620 cells. This approach was further substantiated by findings that the neuromedin B receptor inhibitor, BIM-23127, MMP-9 inhibitor, MMP9i, and Neu-1 inhibitor, oseltamivir phosphate, could specifically block CB1 agonist-induced Neu-1 sialidase activity. Additionally, we found that CB1 receptors exist in a multimeric receptor complex with Neu-1 in naïve, unstimulated RAW-Blue, PANC-1, and SW-620 cells. This complex implies a molecular link that regulates the interaction and signaling mechanism among these molecules present on the cell surface. Moreover, the study results demonstrate that CB1 agonists induce NFκB-dependent secretory alkaline phosphatase (SEAP) activity in influencing the expression of epithelial-mesenchymal markers, E-cadherin, and vimentin in SW-620 cells, albeit the impact on E-cadherin expression is less pronounced compared to vimentin. In essence, this innovative research begins to elucidate an entirely new molecular mechanism involving a GPCR signaling paradigm in which cannabinoids, as epigenetic stimuli, may traverse to influence gene expression and contribute to cancer and cancer metastasis.

TRPV1 Channel in Human Eosinophils: Functional Expression and Inflammatory Modulation

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel expressed on sensory neurons and immune cells. We hypothesize that TRPV1 plays a role in human eosinophil function and is modulated by inflammatory conditions. TRPV1 expression on human eosinophils was examined by qPCR, flow cytometry, and immunohistochemistry, respectively. TRPV1 functionality was analyzed by investigating calcium flux, apoptosis, modulation by cytokines and acidic pH, and CD69 externalization using flow cytometry. Activation of TRPV1 induced calcium influx and prolonged survival. Although eosinophils were not directly activated by TRPV1 agonists, activation by IL-3 or GM-CSF was mainly restricted to TRPV1-positive eosinophils. TRPV1 surface content was increased by acidic pH, IL-3, IL-31, IL-33, TSLP, TNF-α, BDNF, and NGF-β. Interestingly, TRPV1 was also expressed by eosinophils located in proximity to peripheral nerves in atopic dermatitis (AD) skin. In conclusion, eosinophils express functional TRPV1 channels which are increased by extracellular acidification and AD-related cytokines. Since eosinophils also express TRPV1 in AD skin, our results indicate an important role of TRPV1 for neuroimmune interaction mechanisms in itchy, inflammatory skin diseases, like AD.

IUPHAR review: Navigating the role of preclinical models in pain research

Chronic pain is a complex and challenging medical condition that affects millions of people worldwide. Understanding the underlying mechanisms of chronic pain is a key goal of preclinical pain research so that more effective treatment strategies can be developed. In this review, we explore nociception, pain, and the multifaceted factors that lead to chronic pain by focusing on preclinical models. We provide a detailed look into inflammatory and neuropathic pain models and discuss the most used animal models for studying the mechanisms behind these conditions. Additionally, we emphasize the vital role of these preclinical models in developing new pain-relief drugs, focusing on biologics and the therapeutic potential of NMDA and cannabinoid receptor antagonists. We also discuss the challenges of TRPV1 modulation for pain treatment, the clinical failures of neurokinin (NK)- 1 receptor antagonists, and the partial success story of Ziconotide to provide valuable lessons for preclinical pain models. Finally, we highlight the overall success and limitations of current treatments for chronic pain while providing critical insights into the development of more effective therapies to alleviate the burden of chronic pain.

Combination chemotherapy in rodents: a model for chemotherapy-induced neuropathic pain and pharmacological screening

Chemotherapy-induced neuropathic pain (CINP) remains a therapeutic challenge, with no US-FDA approved drugs or effective treatments available. Despite significant progress in unravelling the pathophysiology of CINP, the clinical translation of this knowledge into tangible outcome remains elusive. Here, we employed behavioural and pharmacological approaches to establish and validate a novel combination-based chemotherapeutic model of peripheral neuropathy. Male Sprague Dawley rats were subjected to chemotherapy administration followed by assessment of pain behaviour at different time-points post-chemotherapy. Paclitaxel-treated animals displayed an enhanced thermal and mechanical hypersensitivity from day four onwards which continued till day thirty-five post last paclitaxel injection. Notably, rats subjected to combination chemotherapy, displayed prolonged hypersensitivity that emerged on day four and persisted until day fifty-six. RT-PCR analysis revealed significant upregulation in DRG and spinal mRNA expressions of TRP channels (TRPA1, TRPV1, & TRPM8), pro-inflammatory cytokines (TNF-α & IL-1β) and neuropeptides, Substance P and CGRP in both the pain models. Interestingly, the combination chemotherapy model demonstrated a significant increase in DRG and spinal NR2B expressions compared to rats solely treated with paclitaxel. Pharmacological investigations revealed that gabapentin treatment substantially mitigates pain hypersensitivity in both the combined chemotherapy and paclitaxel-administered groups, with the simultaneous reversal of cellular and molecular changes observed in the lumbar DRG and spinal cord of rats. The findings from this study suggests that combination chemotherapy model exhibits heightened and prolonged hypersensitivity in comparison to the conventional paclitaxel-induced neuropathic pain model. This model not only recapitulates clinical biomarkers of neuropathy but also presents a potential alternative platform for screening analgesic drugs targeted at CINP.

Neurophysiology of corneal neuropathic pain and emerging pharmacotherapeutics

The altered activity generated by corneal neuronal injury can result in morphological and physiological changes in the architecture of synaptic connections in the nervous system. These changes can alter the sensitivity of neurons (both second-order and higher-order projection) projecting pain signals. A complex process involving different cell types, molecules, nerves, dendritic cells, neurokines, neuropeptides, and axon guidance molecules causes a high level of sensory rearrangement, which is germane to all the phases in the pathomechanism of corneal neuropathic pain. Immune cells migrating to the region of nerve injury assist in pain generation by secreting neurokines that ensure nerve depolarization. Furthermore, excitability in the central pain pathway is perpetuated by local activation of microglia in the trigeminal ganglion and alterations of the descending inhibitory modulation for corneal pain arriving from central nervous system. Corneal neuropathic pain may be facilitated by dysfunctional structures in the central somatosensory nervous system due to a lesion, altered synaptogenesis, or genetic abnormality. Understanding these important pathways will provide novel therapeutic insight.

Modulating Growth Factor Receptor Signaling to Promote Corneal Epithelial Homeostasis

The corneal epithelium is the first anatomical barrier between the environment and the cornea; it is critical for proper light refraction onto the retina and prevents pathogens (e.g., bacteria, viruses) from entering the immune-privileged eye. Trauma to the highly innervated corneal epithelium is extremely painful and if not resolved quickly or properly, can lead to infection and ultimately blindness. The healthy eye produces its own growth factors and is continuously bathed in tear fluid that contains these proteins and other nutrients to maintain the rapid turnover and homeostasis of the ocular surface. In this article, we review the roles of growth factors in corneal epithelial homeostasis and regeneration and some of the limitations to their use therapeutically.

Unravelling a novel role for cannabidivarin in the modulation of subventricular zone postnatal neurogenesis

Postnatal neurogenesis has been shown to rely on the endocannabinoid system. Here we aimed at unravelling the role of Cannabidivarin (CBDV), a non-psychoactive cannabinoid, with high affinity for the non-classical cannabinoid receptor TRPV1, on subventricular zone (SVZ) postnatal neurogenesis. Using the neurosphere assay, SVZ-derived neural stem/progenitor cells (NSPCs) were incubated with CBDV and/or 5'-Iodoresinferotoxin (TRPV1 antagonist), and their role on cell viability, proliferation, and differentiation were dissected. CBDV was able to promote, through a TRPV1-dependent mechanism, cell survival, cell proliferation and neuronal differentiation. Furthermore, pulse-chase experiments revealed that CBDV-induced neuronal differentiation was a result of cell cycle exit of NSPCs. Regarding oligodendrocyte differentiation, CBDV inhibited oligodendrocyte differentiation and maturation. Since our data suggested that the CBDV-induced modulation of NSPCs acted via TRPV1, a sodium-calcium channel, and that intracellular calcium levels are known regulators of NSPCs fate and neuronal maturation, single cell calcium imaging was performed to evaluate the functional response of SVZ-derived cells. We observed that CBDV-responsive cells displayed a two-phase calcium influx profile, being the initial phase dependent on TRPV1 activation. Taken together, this work unveiled a novel and untapped neurogenic potential of CBDV via TRPV1 modulation. These findings pave the way to future neural stem cell biological studies and repair strategies by repurposing this non-psychoactive cannabinoid as a valuable therapeutic target.

Repurposing EGFR Inhibitors for Oral Cancer Pain and Opioid Tolerance

Oral cancer pain remains a significant public health concern. Despite the development of improved treatments, pain continues to be a debilitating clinical feature of the disease, leading to reduced oral mobility and diminished quality of life. Opioids are the gold standard treatment for moderate-to-severe oral cancer pain; however, chronic opioid administration leads to hyperalgesia, tolerance, and dependence. The aim of this review is to present accumulating evidence that epidermal growth factor receptor (EGFR) signaling, often dysregulated in cancer, is also an emerging signaling pathway critically involved in pain and opioid tolerance. We presented preclinical and clinical data to demonstrate how repurposing EGFR inhibitors typically used for cancer treatment could be an effective pharmacological strategy to treat oral cancer pain and to prevent or delay the development of opioid tolerance. We also propose that EGFR interaction with the µ-opioid receptor and glutamate N-methyl-D-aspartate receptor could be two novel downstream mechanisms contributing to pain and morphine tolerance. Most data presented here support that repurposing EGFR inhibitors as non-opioid analgesics in oral cancer pain is promising and warrants further research.

Targeting TRPV1 and TRPA1: A feasible strategy for natural herbal medicines to combat postoperative ileus

Under physiological or pathological conditions, transient receptor potential (TRP) channel vanilloid type 1 (TRPV1) and TRP ankyrin 1 (TRPA1) possess the ability to detect a vast array of stimuli and execute diverse functions. Interestingly, increasing works have reported that activation of TRPV1 and TRPA1 could also be beneficial for ameliorating postoperative ileus (POI). Increasing research has revealed that the gastrointestinal (GI) tract is rich in TRPV1/TRPA1, which can be stimulated by capsaicin, allicin and other compounds. This activation stimulates a variety of neurotransmitters, leading to increased intestinal motility and providing protective effects against GI injury. POI is the most common emergent complication following abdominal and pelvic surgery, and is characterized by postoperative bowel dysfunction, pain, and inflammatory responses. It is noteworthy that natural herbs are gradually gaining recognition as a potential therapeutic option for POI due to the lack of effective pharmacological interventions. Therefore, the focus of this paper is on the TRPV1/TRPA1 channel, and an analysis and summary of the processes and mechanism by which natural herbs activate TRPV1/TRPA1 to enhance GI motility and relieve pain are provided, which will lay the foundation for the development of natural herb treatments for this disease.

Multimodal roles of transient receptor potential channel activation in inducing pathological tissue scarification

Transient receptor potential (TRP) channels are a class of transmembrane proteins that can sense a variety of physical/chemical stimuli, participate in the pathological processes of various diseases and have attracted increasing attention from researchers. Recent studies have shown that some TRP channels are involved in the development of pathological scarification (PS) and directly participate in PS fibrosis and re-epithelialization or indirectly activate immune cells to release cytokines and neuropeptides, which is subdivided into immune inflammation, fibrosis, pruritus and mechanical forces increased. This review elaborates on the characteristics of TRP channels, the mechanism of PS and how TRP channels mediate the development of PS, summarizes the important role of TRP channels in the different pathogenesis of PS and proposes that therapeutic strategies targeting TRP will be important for the prevention and treatment of PS. TRP channels are expected to become new targets for PS, which will make further breakthroughs and provide potential pharmacological targets and directions for the in-depth study of PS.

Cannabidiol nanoemulsion for eye treatment - Anti-inflammatory, wound healing activity and its bioavailability using in vitro human corneal substitute

Cannabidiol (CBD) is the non-psychoactive component of the plant Cannabis sativa (L.) that has great anti-inflammatory benefits and wound healing effects. However, its high lipophilicity, chemical instability, and extensive metabolism impair its bioavailability and clinical use. Here, we report on the preparation of a human cornea substitute in vitro and validate this substitute for the evaluation of drug penetration. CBD nanoemulsion was developed and evaluated for stability and biological activity. The physicochemical properties of CBD nanoemulsion were maintained during storage for 90 days under room conditions. In the scratch assay, nanoformulation showed significantly ameliorated wound closure rates compared to the control and pure CBD. Due to the lower cytotoxicity of nanoformulated CBD, a higher anti-inflammatory activity was demonstrated. Neither nanoemulsion nor pure CBD can penetrate the cornea after the four-hour apical treatment. For nanoemulsion, 94 % of the initial amount of CBD remained in the apical compartment while only 54 % of the original amount of pure CBD was detected in the apical medium, and 7 % in the cornea, the rest was most likely metabolized. In summary, the nanoemulsion developed in this study enhanced the stability and biological activity of CBD.

TFOS Lifestyle: Impact of lifestyle challenges on the ocular surface

Many factors in the domains of mental, physical, and social health have been associated with various ocular surface diseases, with most of the focus centered on aspects of dry eye disease (DED). Regarding mental health factors, several cross-sectional studies have noted associations between depression and anxiety, and medications used to treat these disorders, and DED symptoms. Sleep disorders (both involving quality and quantity of sleep) have also been associated with DED symptoms. Under the domain of physical health, several factors have been linked to meibomian gland abnormalities, including obesity and face mask wear. Cross-sectional studies have also linked chronic pain conditions, specifically migraine, chronic pain syndrome and fibromyalgia, to DED, principally focusing on DED symptoms. A systematic review and meta-analysis reviewed available data and concluded that various chronic pain conditions increased the risk of DED (variably defined), with odds ratios ranging from 1.60 to 2.16. However, heterogeneity was noted, highlighting the need for additional studies examining the impact of chronic pain on DED signs and subtype (evaporative versus aqueous deficient). With respect to societal factors, tobacco use has been most closely linked to tear instability, cocaine to decreased corneal sensitivity, and alcohol to tear film disturbances and DED symptoms.

Cannabinoids Transmogrify Cancer Metabolic Phenotype via Epigenetic Reprogramming and a Novel CBD Biased G Protein-Coupled Receptor Signaling Platform

The concept of epigenetic reprogramming predicts long-term functional health effects. This reprogramming can be activated by exogenous or endogenous insults, leading to altered healthy and different disease states. The exogenous or endogenous changes that involve developing a roadmap of epigenetic networking, such as drug components on epigenetic imprinting and restoring epigenome patterns laid down during embryonic development, are paramount to establishing youthful cell type and health. This epigenetic landscape is considered one of the hallmarks of cancer. The initiation and progression of cancer are considered to involve epigenetic abnormalities and genetic alterations. Cancer epigenetics have shown extensive reprogramming of every component of the epigenetic machinery in cancer development, including DNA methylation, histone modifications, nucleosome positioning, non-coding RNAs, and microRNA expression. Endocannabinoids are natural lipid molecules whose levels are regulated by specific biosynthetic and degradative enzymes. They bind to and activate two primary cannabinoid receptors, type 1 (CB1) and type 2 (CB2), and together with their metabolizing enzymes, form the endocannabinoid system. This review focuses on the role of cannabinoid receptors CB1 and CB2 signaling in activating numerous receptor tyrosine kinases and Toll-like receptors in the induction of epigenetic landscape alterations in cancer cells, which might transmogrify cancer metabolism and epigenetic reprogramming to a metastatic phenotype. Strategies applied from conception could represent an innovative epigenetic target for preventing and treating human cancer. Here, we describe novel cannabinoid-biased G protein-coupled receptor signaling platforms (GPCR), highlighting putative future perspectives in this field.

Anoctamins and Calcium Signalling: An Obstacle to EGFR Targeted Therapy in Glioblastoma?

Glioblastoma is the most common form of high-grade glioma in adults and has a poor survival rate with very limited treatment options. There have been no significant advancements in glioblastoma treatment in over 30 years. Epidermal growth factor receptor is upregulated in most glioblastoma tumours and, therefore, has been a drug target in recent targeted therapy clinical trials. However, while many inhibitors and antibodies for epidermal growth factor receptor have demonstrated promising anti-tumour effects in preclinical models, they have failed to improve outcomes for glioblastoma patients in clinical trials. This is likely due to the highly plastic nature of glioblastoma tumours, which results in therapeutic resistance. Ion channels are instrumental in the development of many cancers and may regulate cellular plasticity in glioblastoma. This review will explore the potential involvement of a class of calcium-activated chloride channels called anoctamins in brain cancer. We will also discuss the integrated role of calcium channels and anoctamins in regulating calcium-mediated signalling pathways, such as epidermal growth factor signalling, to promote brain cancer cell growth and migration.

Structural analysis of cannabinoids against EGFR-TK leads a novel target against EGFR-driven cell lines

Epidermal growth factor receptor (EGFR) is a member of the ErbB family of proteins and are involved in downstream signal transduction, plays prominent roles in cell growth regulation, proliferation, and the differentiation of many cell types. They are correlated with the stage and severity of cancer. Therefore, EGFRs are targeted proteins for the design of new drugs to treat cancers that overexpress these proteins. Currently, several bioactive natural extracts are being studied for therapeutic purposes. Cannabis has been reported in many studies to have beneficial medicinal effects, such as anti-inflammatory, analgesic, antibacterial, and anti-inflammatory effects, and antitumor activity. However, it is unclear whether cannabinoids reduce intracellular signaling by inhibiting tyrosine kinase phosphorylation. In this study, cannabinoids (CBD, CBG, and CBN) were simulated for binding to the EGFR-intracellular domain to evaluate the binding energy and binding mode based on molecular docking simulation. The results showed that the binding site was almost always located at the kinase active site. In addition, the compounds were tested for binding affinity and demonstrated their ability to inhibit kinase enzymes. Furthermore, the compounds potently inhibited cellular survival and apoptosis induction in either of the EGFR-overexpressing cell lines.

Transient Receptor Potential Channels: Important Players in Ocular Pain and Dry Eye Disease

Dry eye disease (DED) is a multifactorial disorder in which the eyes respond to minor stimuli with abnormal sensations, such as dryness, blurring, foreign body sensation, discomfort, irritation, and pain. Corneal pain, as one of DED’s main symptoms, has gained recognition due to its increasing prevalence, morbidity, and the resulting social burden. The cornea is the most innervated tissue in the body, and the maintenance of corneal integrity relies on a rich density of nociceptors, such as polymodal nociceptor neurons, cold thermoreceptor neurons, and mechano-nociceptor neurons. Their sensory responses to different stimulating forces are linked to the specific expression of transient receptor potential (TRP) channels. TRP channels are a group of unique ion channels that play important roles as cellular sensors for various stimuli. These channels are nonselective cation channels with variable Ca²⁺ selectivity. TRP homologs are a superfamily of 28 different members that are subdivided into 7 different subfamilies based on differences in sequence homology. Many of these subtypes are expressed in the eye on both neuronal and non-neuronal cells, where they affect various stress-induced regulatory responses essential for normal vision maintenance. This article reviews the current knowledge about the expression, function, and regulation of TRPs in ocular surface tissues. We also describe their implication in DED and ocular pain. These findings contribute to evidence suggesting that drug-targeting TRP channels may be of therapeutic benefit in the clinical setting of ocular pain.

The role of the PI3K/AKT signalling pathway in the corneal epithelium: recent updates

Phosphatidylinositol 3 kinase (PI3K)/AKT (also called protein kinase B, PKB) signalling regulates various cellular processes, such as apoptosis, cell proliferation, the cell cycle, protein synthesis, glucose metabolism, and telomere activity. Corneal epithelial cells (CECs) are the outermost cells of the cornea; they maintain good optical performance and act as a physical and immune barrier. Various growth factors, including epidermal growth factor receptor (EGFR) ligands, insulin-like growth factor 1 (IGF1), neurokinin 1 (NK-1), and insulin activate the PI3K/AKT signalling pathway by binding their receptors and promote antiapoptotic, anti-inflammatory, proliferative, and migratory functions and wound healing in the corneal epithelium (CE). Reactive oxygen species (ROS) regulate apoptosis and inflammation in CECs in a concentration-dependent manner. Extreme environments induce excess ROS accumulation, inhibit PI3K/AKT, and cause apoptosis and inflammation in CECs. However, at low or moderate levels, ROS activate PI3K/AKT signalling, inhibiting apoptosis and stimulating proliferation of healthy CECs. Diabetes-associated hyperglycaemia directly inhibit PI3K/AKT signalling by increasing ROS and endoplasmic reticulum (ER) stress levels or suppressing the expression of growth factors receptors and cause diabetic keratopathy (DK) in CECs. Similarly, hyperosmolarity and ROS accumulation suppress PI3K/AKT signalling in dry eye disease (DED). However, significant overactivation of the PI3K/AKT signalling pathway, which mediates inflammation in CECs, is observed in both infectious and noninfectious keratitis. Overall, upon activation by growth factors and NK-1, PI3K/AKT signalling promotes the proliferation, migration, and anti-apoptosis of CECs, and these processes can be regulated by ROS in a concentration-dependent manner. Moreover, PI3K/AKT signalling pathway is inhibited in CECs from individuals with DK and DED, but is overactivated by keratitis.

Cannabinoid Receptor-1 suppresses M2 macrophage polarization in colorectal cancer by downregulating EGFR

Cannabinoid receptors, CB1 and CB2, have been implicated as emerging targets for cancer therapy. Herein, we investigated the potential regulation mechanism of CB1 and its implications in colorectal cancer. CB1 and EGFR expression were examined in colorectal cancer cell lines. The effects of CB1 agonist ACEA and its antagonist AM251 on the proliferation, migration and invasion of colorectal cancer cells and the expression of M1 and M2 macrophage markers were examined. EGFR overexpression was performed with plasmids containing EGFR gene. Tumor xenografts were constructed to explore the effects of CB1 activation on tumorigenesis. We showed that CB1 was downregulated while EGFR was upregulated in colorectal cancer cells. The activation of CB1 suppressed the proliferation, migration and invasion of colorectal cancer cells and the differentiation of M2 macrophages, while CB1 inhibition had opposite effects. Moreover, the alterations in tumorigenesis and M2 macrophage activation induced by CB1 activation were counteracted by EGFR overexpression. Besides, CB1 silencing promoted tumor cell proliferation and M2 polarization which was counteracted by EGFR knockdown. In vivo, CB1 activation also repressed tumorigenesis and M2 macrophage activation. The present study demonstrated that CB1 activation suppressed M2 macrophage through EGFR downregulation in colorectal cancers. These findings first unveiled the potential avenue of CB1 as a targeted therapy for colorectal cancer.

Identification and validation of MicroRNA-mRNA Networks in Dorsal Root Ganglia after Peripheral Nerve Injury

Changes in DRG after nerve injury involve neuronal damage, apoptosis, pain transmission, and activation of regenerative programs. It is unclear which genes and microRNAs may play a major role in this process. Therefore, this study performed a meta-analysis of previously published gene expression data to reveal the potential microRNA-mRNA network in dorsal root ganglia (DRG) after peripheral nerve injury. We searched 5 mRNA and 3 microRNA expression data sets, obtained 447 differentially expressed genes (DEGs) and 5 differentially expressed miRNAs, determined the biological pathways enriched by these DEGs, and further predicted new microRNA-mRNA interactions, such as miR-21/Hmg20a, miR-221/Ube2ql1, miR-30c-1/Rhoq, miR-500/Sema3c, and miR-551b/Cdc42se2. We verified these hub mRNA and miRNA in rats by qRT-PCR and found the results were consistent with the bioinformatics analysis. And we predicted transcription factors associated with these genes (gTFs) and TFs associated with these microRNAs (mTFs) and constructed the mTF-miRNA-gene-gTF regulatory network to further explore the molecular mechanism in DRG. Finally, we compared the DRG transcriptome after PNI to that of chronic constriction injury (CCI), and found that PNI caused greater damage to DRG compared to CCI. At the same time, the related mechanisms of pain caused by the two pathophysiological process may be different.

Interleukin-6 and lactate dehydrogenase expression in a novel ex vivo rocking model of equine corneal epithelial wound healing

PURPOSE

To establish a physiologically relevant ex vivo model of equine corneal epithelial wound healing.

METHODS

Fourteen equine corneas were randomly assigned to one of two groups: wounded (n = 8) or unwounded (n = 6) controls. In the wounded group, the axial corneal epithelium was removed by applying a 6 mm filter paper disk soaked in 1N-NaOH for 60 s. Corneas were subsequently cultured using an air-liquid interface model. Evaluation of corneal healing was performed daily, and culture medium was collected. Corneas were randomly assigned to undergo processing via histopathology and RNAscope in situ hybridization for interleukin-6 (IL-6) and alpha-smooth muscle actin (αSMA) expression at T24, T48, and T72 h after wounding. Media of the cultured corneas were evaluated for the presence of lactate dehydrogenase (LDH) by a colorimetric assay.

RESULTS

The ulcerated area of the wounded corneas decreased over time and all corneas healed within 72 h. Histologically, normal corneal architecture was observed including healthy epithelium (in areas other than the ulcerated ones), minimal stromal edema, intact endothelium, and Descemet's membrane. IL-6 expression was increased in wounded corneas compared with unwounded controls. LDH expression was elevated for both wounded and unwounded corneas at T24 but decreased substantially and was not detected at T48 in media from wounded and unwounded corneas, respectively. No αSMA expression was detected from either wounded or unwounded corneas.

CONCLUSIONS

The equine air-liquid interface, ex vivo, corneal epithelial wound healing model is effective and physiologically relevant. This model can be used in future studies evaluating various corneal therapies.

Pharmacological Properties, Therapeutic Potential and Molecular Mechanisms of JWH133, a CB2 Receptor-Selective Agonist

The endocannabinoid system has attracted attention as a pharmacological target for several pathological conditions. Cannabinoid (CB2)-selective agonists have been the focus of pharmacological studies because modulation of the CB2 receptor (CB2R) can be useful in the treatment of pain, inflammation, arthritis, addiction, and cancer among other possible therapeutic applications while circumventing CNS-related adverse effects. Increasing number of evidences from different independent preclinical studies have suggested new perspectives on the involvement of CB2R signaling in inflammation, infection and immunity, thus play important role in cancer, cardiovascular, renal, hepatic and metabolic diseases. JWH133 is a synthetic agonist with high CB2R selectivity and showed to exert CB2R mediated antioxidant, anti-inflammatory, anticancer, cardioprotective, hepatoprotective, gastroprotective, nephroprotective, and immunomodulatory activities. Cumulative evidences suggest that JWH133 protects against hepatic injury, renal injury, cardiotoxicity, fibrosis, rheumatoid arthritis, and cancer as well as against oxidative damage and inflammation, inhibits fibrosis and apoptosis, and acts as an immunosuppressant. This review provides a comprehensive overview of the polypharmacological properties and therapeutic potential of JWH133. This review also presents molecular mechanism and signaling pathways of JWH133 under various pathological conditions except neurological diseases. Based on the available data, this review proposes the possibilities of developing JWH133 as a promising therapeutic agent; however, further safety and toxicity studies in preclinical studies and clinical trials in humans are warranted.

Anandamide Concentration-Dependently Modulates Toll-Like Receptor 3 Agonism or UVB-Induced Inflammatory Response of Human Corneal Epithelial Cells

Photodamage-induced and viral keratitis could benefit from treatment with novel nonsteroid anti-inflammatory agents. Therefore, we determined whether human corneal epithelial cells (HCECs) express members of the endocannabinoid system (ECS), and examined how the endocannabinoid anandamide (AEA, N-arachidonoyl ethanolamine) influences the Toll-like receptor 3 (TLR3) agonism- or UVB irradiation-induced inflammatory response of these cells. Other than confirming the presence of cannabinoid receptors, we show that endocannabinoid synthesizing and catabolizing enzymes are also expressed in HCECs in vitro, as well as in the epithelial layer of the human cornea in situ, proving that they are one possible source of endocannabinoids. p(I:C) and UVB irradiation was effective in promoting the transcription and secretion of inflammatory cytokines. Surprisingly, when applied alone in 100 nM and 10 μM, AEA also resulted in increased pro-inflammatory cytokine production. Importantly, AEA further increased levels of these cytokines in the UVB model, whereas its lower concentration partially prevented the transcriptional effect of p(I:C), while not decreasing the p(I:C)-induced cytokine release. HCECs express the enzymatic machinery required to produce endocannabinoids both in vitro and in situ. Moreover, our data show that, despite earlier reports about the anti-inflammatory potential of AEA in murine cornea, its effects on the immune phenotype of human corneal epithelium may be more complex and context dependent.

CannabinEYEds: The Endocannabinoid System as a Regulator of the Ocular Surface Nociception, Inflammatory Response, Neovascularization and Wound Healing

The endocannabinoid system (ECS) is a complex regulatory system, highly conserved among vertebrates. It has been widely described in nearly all human tissues. In the conjunctiva and cornea, the ECS is believed to play a pivotal role in the modulation of the local inflammatory state as well as in the regulation of tissue repair and fibrosis, neo-angiogenesis and pain perception. This review aims to summarize all the available data on ECS expression and its function in ocular surface structures to provide a specific insight concerning its modulation in dry eye disease, and to propose directions for future research.

Cannabinoid Receptors: An Update on Cell Signaling, Pathophysiological Roles and Therapeutic Opportunities in Neurological, Cardiovascular, and Inflammatory Diseases

The identification of the human cannabinoid receptors and their roles in health and disease, has been one of the most significant biochemical and pharmacological advancements to have occurred in the past few decades. In spite of the major strides made in furthering endocannabinoid research, therapeutic exploitation of the endocannabinoid system has often been a challenging task. An impaired endocannabinoid tone often manifests as changes in expression and/or functions of type 1 and/or type 2 cannabinoid receptors. It becomes important to understand how alterations in cannabinoid receptor cellular signaling can lead to disruptions in major physiological and biological functions, as they are often associated with the pathogenesis of several neurological, cardiovascular, metabolic, and inflammatory diseases. This review focusses mostly on the pathophysiological roles of type 1 and type 2 cannabinoid receptors, and it attempts to integrate both cellular and physiological functions of the cannabinoid receptors. Apart from an updated review of pre-clinical and clinical studies, the adequacy/inadequacy of cannabinoid-based therapeutics in various pathological conditions is also highlighted. Finally, alternative strategies to modulate endocannabinoid tone, and future directions are also emphasized.

Calcium Entry through TRPV1: A Potential Target for the Regulation of Proliferation and Apoptosis in Cancerous and Healthy Cells

Intracellular calcium (Ca2+) concentration ([Ca2+]i) is a key determinant of cell fate and is implicated in carcinogenesis. Membrane ion channels are structures through which ions enter or exit the cell, depending on the driving forces. The opening of transient receptor potential vanilloid 1 (TRPV1) ligand-gated ion channels facilitates transmembrane Ca2+ and Na+ entry, which modifies the delicate balance between apoptotic and proliferative signaling pathways. Proliferation is upregulated through two mechanisms: (1) ATP binding to the G-protein-coupled receptor P2Y2, commencing a kinase signaling cascade that activates the serine-threonine kinase Akt, and (2) the transactivation of the epidermal growth factor receptor (EGFR), leading to a series of protein signals that activate the extracellular signal-regulated kinases (ERK) 1/2. The TRPV1-apoptosis pathway involves Ca2+ influx and efflux between the cytosol, mitochondria, and endoplasmic reticulum (ER), the release of apoptosis-inducing factor (AIF) and cytochrome c from the mitochondria, caspase activation, and DNA fragmentation and condensation. While proliferative mechanisms are typically upregulated in cancerous tissues, shifting the balance to favor apoptosis could support anti-cancer therapies. TRPV1, through [Ca2+]i signaling, influences cancer cell fate; therefore, the modulation of the TRPV1-enforced proliferation-apoptosis balance is a promising avenue in developing anti-cancer therapies and overcoming cancer drug resistance. As such, this review characterizes and evaluates the role of TRPV1 in cell death and survival, in the interest of identifying mechanistic targets for drug discovery.

Cannabis and the Cornea

Purpose: While cannabis has the potential to reduce corneal pain, cannabinoids might induce side effects. This review article examines the effects of cannabinoids on the cornea. As more states and countries consider the legalization of adult cannabis use, health-care providers will need to identify ocular effects of cannabis consumption.Methods: Studies included in this review examined the connection between cannabis and the cornea, more specifically anti-nociceptive and anti-inflammatory actions of cannabinoids. NCBI Databases from 1781 up to December 2019 were consulted.Results: Five studies examined corneal dysfunctions caused by cannabis consumption (opacification, decreased endothelial cell density). Twelve studies observed a reduction in corneal pain and inflammation (less lymphocytes, decreased corneal neovascularization, increased cell proliferation and migration).Conclusion: More than half of the studies examined the therapeutic effects of cannabinoids on the cornea. As the field is still young, more studies should be conducted to develop safe cannabinoid treatments for corneal diseases.

Capsaicin attenuates cell migration via SIRT1 targeting and inhibition to enhance cortactin and β-catenin acetylation in bladder cancer cells

We have studied the chemopreventive property of capsaicin, a major active component in chili pepper, and found that it exhibited apoptotic activity against various lines of cancer cells. Interestingly, accumulating data has revealed that, in addition to cytotoxicity, capsaicin also plays regulatory role on cell migration and invasion. However, its effect on cell migration is paradoxical and not completely understood. Here, we set out to elucidate the molecular events underlying capsaicin-inhibited cell migration in bladder cancer cells. Our results show that the capsaicin-reduced cell migration was associated with down-regulation of sirtuin 1 (SIRT1) deacetylase, possibly through proteasome-mediated protein degradation. More importantly, we employed a cellular thermal shift assay (CETSA) to demonstrate that there was a direct binding between capsaicin and SIRT1. The engagement with capsaicin and protein degradation diminished the deacetylase of SIRT1, which in turn, enhanced acetylation of cortactin and β-catenin to decrease MMP-2 and MMP-9 activation, resulting in cell migration impairment in bladder cancer cells.

Cannabidiol-loaded microspheres incorporated into osteoconductive scaffold enhance mesenchymal stem cell recruitment and regeneration of critical-sized bone defects

Recruitment of mesenchymal stem cells (MSCs) to an injury site and their differentiation into the desired cell lineage are implicated in deficient bone regeneration. To date, there is no ideal structure that provides these conditions for bone regeneration. In the current study, we aim to develop a novel scaffold that induces MSC migration towards the defect site, followed by their differentiation into an osteogenic lineage. We have fabricated a gelatin/nano-hydroxyapatite (G/nHAp) scaffold that delivered cannabidiol (CBD)-loaded poly (lactic-co-glycolic acid) (PLGA) microspheres to critical size radial bone defects in a rat model. The fabricated scaffolds were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and then analyzed for porosity and degradation rate. The release profile of CBD from the PLGA microsphere and CBD-PLGA-G/nHAp scaffold was analyzed by fluorescence spectroscopy. We performed an in vitro assessment of the effects of CBD on cellular behaviors of viability and osteogenic differentiation. Radiological evaluation, histomorphometry, and immunohistochemistry (IHC) analysis of all defects in the scaffold and control groups were conducted following transplantation into the radial bone defects. An in vitro migration assay showed that CBD considerably increased MSCs migration. qRT-PCR results showed upregulated expression of osteogenic markers in the presence of CBD. Histological and immunohistochemical findings confirmed new bone formation and reconstruction of the defect at 4 and 12 week post-surgery (WPS) in the CBD-PLGA-G/nHAp group. Immunofluorescent analysis revealed enhanced migration of MSCs into the defect areas in the CBD-PLGA-G/nHAp group in vivo. Based on the results of the current study, we concluded that CBD improved bone healing and showed a critical role for MSC migration in the bone regeneration process.

Epiregulin is released from intervertebral disks and induces spontaneous activity in pain pathways

Introduction:

Lumbar radicular pain after disk herniation is associated with local release of many inflammatory molecules from nucleus pulposus (NP) cells leaking out of the intervertebral disk. Here, we have used a rat model to investigate the role of epiregulin (EREG), a member of the epidermal growth factor (EGF) family, in this process.

Methods:

A protein immunoassay was chosen to confirm the release of EREG from the NP tissue. Single unit recordings were used to demonstrate the effect of recombinant EREG applied onto the dorsal nerve roots in vivo. Intracellular responses induced by recombinant EREG were studied in cultured dorsal root ganglion (DRG) cells by phosphoprotein assay. Changes in EGF receptor expression induced by NP in the DRG were examined by quantitative polymerase chain reaction.

Results:

The protein immunoassay showed that EREG was released from the NP tissue. Moreover, application of EREG onto the spinal dorsal nerve roots induced a decrease in the evoked responses, but an increase in spontaneous activity in the dorsal horn neurons. Interestingly, the EREG activated the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in the DRG, a pathway previously linked to cellular growth, proliferation, and tissue regeneration. An NP-induced upregulation of the EGF receptor HER3 in the DRG was also revealed.

Conclusion:

Taken together, the present observations indicate that EREG may induce changes in the DRG and spontaneous activity in the pain pathways. We suggest that EREG signaling may be involved in the pathophysiological process leading to sensory deficits and neuropathic pain in patients after disk herniation.

TRPM8 Activation via 3-Iodothyronamine Blunts VEGF-Induced Transactivation of TRPV1 in Human Uveal Melanoma Cells

In human uveal melanoma (UM), tumor enlargement is associated with increases in aqueous humor vascular endothelial growth factor-A (VEGF-A) content that induce neovascularization. 3-Iodothyronamine (3-T₁AM), an endogenous thyroid hormone metabolite, activates TRP melastatin 8 (TRPM8), which blunts TRP vanilloid 1 (TRPV1) activation by capsaicin (CAP) in human corneal, conjunctival epithelial cells, and stromal cells. We compare here the effects of TRPM8 activation on VEGF-induced transactivation of TRPV1 in an UM cell line (92.1) with those in normal primary porcine melanocytes (PM) since TRPM8 is upregulated in melanoma. Fluorescence Ca²⁺-imaging and planar patch-clamping characterized functional channel activities. CAP (20 μM) induced Ca²⁺ transients and increased whole-cell currents in both the UM cell line and PM whereas TRPM8 agonists, 100 μM menthol and 20 μM icilin, blunted such responses in the UM cells. VEGF (10 ng/ml) elicited Ca²⁺ transients and augmented whole-cell currents, which were blocked by capsazepine (CPZ; 20 μM) but not by a highly selective TRPM8 blocker, AMTB (20 μM). The VEGF-induced current increases were not augmented by CAP. Both 3-T₁AM (1 μM) and menthol (100 μM) increased the whole-cell currents, whereas 20 μM AMTB blocked them. 3-T₁AM exposure suppressed both VEGF-induced Ca²⁺ transients and increases in underlying whole-cell currents. Taken together, functional TRPM8 upregulation in UM 92.1 cells suggests that TRPM8 is a potential drug target for suppressing VEGF induced increases in neovascularization and UM tumor growth since TRPM8 activation blocked VEGF transactivation of TRPV1.

Warming Up to New Possibilities with the Capsaicin Receptor TRPV1: mTOR, AMPK, and Erythropoietin

BACKGROUND

Transient receptor potential (TRP) channels are a superfamily of ion channels termed after the trp gene in Drosophila that are diverse in structure and control a wide range of biological functions including cell development and growth, thermal regulation, and vascular physiology. Of significant interest is the transient receptor potential cation channel subfamily V member 1 (TRPV1) receptor, also known as the capsaicin receptor and the vanilloid receptor 1, that is a non-selective cation channel sensitive to a host of external stimuli including capsaicin and camphor, venoms, acid/basic pH changes, and temperature.

METHODS

Given the multiple modalities that TRPV1 receptors impact in the body, we examined and discussed the role of these receptors in vasomotor control, metabolic disorders, cellular injury, oxidative stress, apoptosis, autophagy, and neurodegenerative disorders and their overlap with other signal transduction pathways that impact trophic factors.

RESULTS

Surprisingly, TRPV1 receptors do not rely entirely upon calcium signaling to affect cellular biology, but also have a close relationship with the mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), and protein kinase B (Akt) that have roles in pain sensitivity, stem cell development, cellular survival, and cellular metabolism. These pathways with TRPV1 converge in the signaling of growth factors with recent work highlighting a relationship with erythropoietin (EPO). Angiogenesis and endothelial tube formation controlled by EPO requires, in part, the activation of TRPV1 receptors in conjunction with Akt and AMPK pathways.

CONCLUSION

TRPV1 receptors could prove to become vital to target disorders of vascular origin and neurodegeneration. Broader and currently unrealized implementations for both EPO and TRPV1 receptors can be envisioned for for the development of novel therapeutic strategies in multiple systems of the body.

Vascular Endothelial Growth Factor (VEGF) Induced Downstream Responses to Transient Receptor Potential Vanilloid 1 (TRPV1) and 3-Iodothyronamine (3-T1AM) in Human Corneal Keratocytes

This study was undertaken to determine if crosstalk among the transient receptor potential (TRP) melastatin 8 (TRPM8), TRP vanilloid 1 (TRPV1), and vascular endothelial growth factor (VEGF) receptor triad modulates VEGF-induced Ca²⁺ signaling in human corneal keratocytes. Using RT-PCR, qPCR and immunohistochemistry, we determined TRPV1 and TRPM8 gene and protein coexpression in a human corneal keratocyte cell line (HCK) and human corneal cross sections. Fluorescence Ca²⁺ imaging using both a photomultiplier and a single cell digital imaging system as well as planar patch-clamping measured relative intracellular Ca²⁺ levels and underlying whole-cell currents. The TRPV1 agonist capsaicin increased both intracellular Ca²⁺ levels and whole-cell currents, while the antagonist capsazepine (CPZ) inhibited them. VEGF-induced Ca²⁺ transients and rises in whole-cell currents were suppressed by CPZ, whereas a selective TRPM8 antagonist, AMTB, increased VEGF signaling. In contrast, an endogenous thyroid hormone-derived metabolite 3-Iodothyronamine (3-T₁AM) suppressed increases in the VEGF-induced current. The TRPM8 agonist menthol increased the currents, while AMTB suppressed this response. The VEGF-induced increases in Ca²⁺ influx and their underlying ionic currents stem from crosstalk between VEGFR and TRPV1, which can be impeded by 3-T₁AM-induced TRPM8 activation. Such suppression in turn blocks VEGF-induced TRPV1 activation. Therefore, crosstalk between TRPM8 and TRPV1 inhibits VEGFR-induced activation of TRPV1.

Decisive role of P42/44 mitogen-activated protein kinase in Δ9-tetrahydrocannabinol-induced migration of human mesenchymal stem cells

In past years, medical interest in Δ⁹-tetrahydrocannabinol (THC), the major psychoactive ingredient of the Cannabis plant, has been renewed due to the elucidation of the endocannabinoid system and diverse other receptor targets involved in biological cannabinoid effects. The present study therefore investigates the impact of THC on the migration of mesenchymal stem cells (MSCs) which are known to be involved in various regenerative processes such as bone healing. Using Boyden chamber assays, THC was found to increase the migration of adipose-derived MSCs. Migration by THC was almost completely suppressed by the CB₁ receptor antagonist AM-251 and to a lesser extent by the CB₂ receptor antagonist AM-630. By contrast, the TRPV1 antagonist capsazepine as well as the G protein-coupled receptor 55 (GRP55) agonist O-1602 did not significantly interfere with the promigratory effect of THC. Furthermore, increased migration by THC was fully suppressed by PD98059, an inhibitor of p42/44 mitogen-activated protein kinase (MAPK) activation, and was accompanied by a time-dependent activation of this pathway accordingly. In line with the migration data, additional inhibitor experiments pointed towards a decisive role of the CB₁ receptor in conferring THC-induced activation of p42/44 MAPK. Collectively, this study demonstrates THC to exert a promigratory effect on MSCs via a CB₁ receptor-dependent activation of p42/44 MAPK phosphorylation. This pathway may be involved in regenerative effects of THC and could be a target of pharmacological intervention.

Corneal Nerve Fiber Structure, Its Role in Corneal Function, and Its Changes in Corneal Diseases

Recently, in vivo confocal microscopy is used to examine the human corneal nerve fibers morphology. Corneal nerve fiber architecture and its role are studied in healthy and pathological conditions. Corneal nerves of rats were studied by nonspecific acetylcholinesterase (NsAchE) staining. NsAchE-positive subepithelial (stromal) nerve fiber has been found to be insensitive to capsaicin. Besides, NsAchE-negative but capsaicin-sensitive subbasal nerve (leash) fibers formed thick mesh-like structure showing close interconnections and exhibit both isolectin B4- and transient receptor potential vanilloid channel 1- (TRPV1-) positive. TRPV1, TRPV3, TRPA (ankyrin) 1, and TRPM (melastatin) 8 are expressed in corneal nerve fibers. Besides the corneal nerve fibers, the expressions of TRPV (1, 3, and 4), TRPC (canonical) 4, and TRPM8 are demonstrated in the corneal epithelial cell membrane. The realization of the importance of TRP channels acting as polymodal sensors of environmental stresses has identified potential drug targets for corneal disease. The pathophysiological conditions of corneal diseases are associated with disruption of normal tissue innervation, especially capsaicin-sensitive small sensory nerve fibers. The relationships between subbasal corneal nerve fiber morphology and neurotrophic keratopathy in corneal diseases are well studied. The recommended treatment for neurotrophic keratopathy is administration of preservative free eye drops.

Immunolocalization of cannabinoid receptor type 1 and CB2 cannabinoid receptors, and transient receptor potential vanilloid channels in pterygium

Cannabinoids, as multi-target mediators, activate cannabinoid receptors and transient receptor potential vanilloid (TRPV) channels. There is evidence to support a functional interaction of cannabinoid receptors and TRPV channels when they are coexpressed. Human conjunctiva demonstrates widespread cannabinoid receptor type 1 (CB1), CB2 and TRPV channel localization. The aim of the present study was to investigate the expression profile for cannabinoid receptors (CB1 and CB2) and TRPV channels in pterygium, an ocular surface lesion originating from the conjunctiva. Semi-serial paraffin-embedded sections from primary and recurrent pterygium samples were immunohistochemically examined with the use of specific antibodies. All of the epithelial layers in 94, 78, 96, 73 and 80% of pterygia cases, exhibited CB1, CB2, TRPV1, TRPV2 and TRPV3 cytoplasmic immunoreactivity, respectively. The epithelium of all pterygia cases (100%) showed strong, mainly nuclear, TRPV4 immunolocalization. In the pterygium stroma, scattered cells demonstrated intense CB2 immunoreactivity, whereas vascular endothelial cells were immunopositive for the cannabinoid receptors and all TRPV channels. Quantitative analyses of the immunohistochemical findings in epithelial cells demonstrated a significantly higher expression level in conjunctiva compared with primary pterygia (P=0.04) for CB1, but not for CB2 (P>0.05). Additionally, CB1 and CB2 were significantly highly expressed in primary pterygia (P=0.01), compared with recurrent pterygia. Furthermore, CB1 expression levels were significantly correlated with CB2 expression levels in primary pterygia (P=0.005), but not in recurrent pterygia (P>0.05). No significant difference was detected for all TRPV channel expression levels between pterygium (primary or recurrent) and conjunctival tissues (P>0.05). A significant correlation between the TRPV1 and TRPV3 expression levels (P<0.001) was detected independently of pterygium recurrence. Finally, TRPV channel expression was identified to be significantly higher than the expression level of cannabinoid receptors in the pterygium samples (P<0.001). The differentiated expression of cannabinoid receptors in combination with the presence of TRPV channels, in primary and recurrent pterygia, imply a potential role of these cannabinoid targets in the underlying mechanisms of pterygium.

Epiregulin and EGFR interactions are involved in pain processing

The EGFR belongs to the well-studied ErbB family of receptor tyrosine kinases. EGFR is activated by numerous endogenous ligands that promote cellular growth, proliferation, and tissue regeneration. In the present study, we have demonstrated a role for EGFR and its natural ligand, epiregulin (EREG), in pain processing. We show that inhibition of EGFR with clinically available compounds strongly reduced nocifensive behavior in mouse models of inflammatory and chronic pain. EREG-mediated activation of EGFR enhanced nociception through a mechanism involving the PI3K/AKT/mTOR pathway and matrix metalloproteinase-9. Moreover, EREG application potentiated capsaicin-induced calcium influx in a subset of sensory neurons. Both the EGFR and EREG genes displayed a genetic association with the development of chronic pain in several clinical cohorts of temporomandibular disorder. Thus, EGFR and EREG may be suitable therapeutic targets for persistent pain conditions.

TRPV4 Regulates Tight Junctions and Affects Differentiation in a Cell Culture Model of the Corneal Epithelium

TRPV4 (transient receptor potential vanilloid 4) is a cation channel activated by hypotonicity, moderate heat, or shear stress. We describe the expression of TRPV4 during the differentiation of a corneal epithelial cell model, RCE1(5T5) cells. TRPV4 is a late differentiation feature that is concentrated in the apical membrane of the outmost cell layer of the stratified epithelia. Ca²⁺ imaging experiments showed that TRPV4 activation with GSK1016790A produced an influx of calcium that was blunted by the specific TRPV4 blocker RN-1734. We analyzed the involvement of TRPV4 in RCE1(5T5) epithelial differentiation by measuring the development of transepithelial electrical resistance (TER) as an indicator of the tight junction (TJ) assembly. We showed that TRPV4 activity was necessary to establish the TJ. In differentiated epithelia, activation of TRPV4 increases the TER and the accumulation of claudin-4 in cell-cell contacts. Epidermal Growth Factor (EGF) up-regulates the TER of corneal epithelial cultures, and we show here that TRPV4 activation mimicked this EGF effect. Conversely, TRPV4 inhibition or knock down by specific shRNA prevented the increase in TER. Moreover, TRPP2, an EGF-activated channel that forms heteromeric complexes with TRPV4, is also concentrated in the outmost cell layer of differentiated RCE1(5T5) sheets. This suggests that the EGF regulation of the TJ may involve a heterotetrameric TRPV4-TRPP2 channel. These results demonstrated TRPV4 activity was necessary for the correct establishment of TJ in corneal epithelia and as well as the regulation of both the barrier function of TJ and its ability to respond to EGF. J. Cell. Physiol. 232: 1794-1807, 2017. © 2016 Wiley Periodicals, Inc.

Capsaicin mediates caspases activation and induces apoptosis through P38 and JNK MAPK pathways in human renal carcinoma

BACKGROUND

Renal cell carcinoma (RCC) is one of the tumors most refractory to chemotherapy to date. Therefore, novel therapeutic agents are urgently needed for this disease. Capsaicin (CPS), a natural active ingredient of green and red peppers, and a ligand of transient receptor potential vanilloid type 1 (TRPV1), has been showed potential in suppression of tumorigenesis of several cancers. Nonetheless, the anti-cancer activity of CPS has never been studied in human RCC.

METHODS

CCK8 analysis, LDH release activity and ROS generation analysis, flow cytometry analysis, and nuclear staining test were performed to test the influence of CPS in cultured cells in vitro, meanwhile western blot was done to uncover the precise molecular mechanisms. 786-O renal cancer xenografts were builded to investigate the antitumor activity of CPS in vivo.

RESULTS

We found treatment of CPS reduced proliferation of renal carcinoma cells, which could be attenuated by TRPV1 representative antagonist capsazepine (CPZ). CPS induced obvious apoptosis in renal carcinoma cells. These events were associated with substantial up-regulation of pro-apoptotic genes including c-myc, FADD, Bax and cleaved-caspase-3, -8, and -9, while down-regulation of anti-apoptotic gene Bcl2. Besides, CPS-treatment activated P38 and JNK MAPK pathways, yet P38 and JNK inhibitors afforded protection against CPS-induced apoptosis by abolishing activation of caspase-3, -8, and -9. Furthermore, CPS significantly slowed the growth of 786-O renal cancer xenografts in vivo.

CONCLUSIONS

Such results reveal that CPS is an efficient and potential drug for management of human RCC.

Turning Down the Thermostat: Modulating the Endocannabinoid System in Ocular Inflammation and Pain

The endocannabinoid system (ECS) has emerged as an important regulator of both physiological and pathological processes. Notably, this endogenous system plays a key role in the modulation of pain and inflammation in a number of tissues. The components of the ECS, including endocannabinoids, their cognate enzymes and cannabinoid receptors, are localized in the eye, and evidence indicates that ECS modulation plays a role in ocular disease states. Of these diseases, ocular inflammation presents a significant medical problem, given that current clinical treatments can be ineffective or are associated with intolerable side-effects. Furthermore, a prominent comorbidity of ocular inflammation is pain, including neuropathic pain, for which therapeutic options remain limited. Recent evidence supports the use of drugs targeting the ECS for the treatment of ocular inflammation and pain in animal models; however, the potential for therapeutic use of cannabinoid drugs in the eye has not been thoroughly investigated at this time. This review will highlight evidence from experimental studies identifying components of the ocular ECS and discuss the functional role of the ECS during different ocular inflammatory disease states, including uveitis and corneal keratitis. Candidate ECS targeted therapies will be discussed, drawing on experimental results obtained from both ocular and non-ocular tissue(s), together with their potential application for the treatment of ocular inflammation and pain.

TRPV1: A Target for Rational Drug Design

Transient Receptor Potential Vanilloid 1 (TRPV1) is a non-selective, Ca²⁺ permeable cation channel activated by noxious heat, and chemical ligands, such as capsaicin and resiniferatoxin (RTX). Many compounds have been developed that either activate or inhibit TRPV1, but none of them are in routine clinical practice. This review will discuss the rationale for antagonists and agonists of TRPV1 for pain relief and other conditions, and strategies to develop new, better drugs to target this ion channel, using the newly available high-resolution structures.