NGF Signaling Exacerbates KOA Peripheral Hyperalgesia via the Increased TRPV1-Labeled Synovial Sensory Innervation in KOA Rats.

Objectives: Knee osteoarthritis (KOA) pain is caused by nociceptors, which are actually sensory nerve fiber endings that can detect stimuli to produce and transmit pain signals, and high levels of NGF in synovial tissue led to peripheral hyperalgesia in KOA. The purpose of this study is to investigate how sensory nerve fibers respond to the NGF/TrKA signal pathway and mediate the peripheral hyperalgesia in KOA rats. Methods: Forty SD male rats were randomly divided into 4 groups: normal, KOA, KOA + NGF, and KOA + siRNA TrKA. KOA model rats were induced by anterior cruciate ligament transection (ACLT). Mechanical and cold withdrawal thresholds (MWT and CWT) were measured 4 times in each group. The synovial tissues were harvested on day 28, and the expressions of NGF, TrKA, TRPV1, IL-1ß, and PGP9.5 were determined using western blot, qPCR, and immunofluorescence staining. The primary rat fibroblast-like synoviocytes (FLSs) and DRG cells were divided into 4 groups as in vivo. The expressions of NGF, TrKA, TRPV1, and CGRP in vitro were determined using western blot and qPCR. Results: KOA and intra-articular injection with NGF protein increased both mRNA and protein levels, not only TRPV1, PGP 9.5, and IL-1ß in the synovial tissue, but also TRPV1, PGP 9.5, and S100 in the DRG tissue, while above changes were partly reversed after siRNA TrKA intervention. Besides, siRNA TrKA could improve peripheral hyperalgesia and decreased the TRPV1 positive nerve fiber innervation in synovial tissue. The results in vitro were consistent with those in vivo. Conclusion: This study showed the activation of the NGF/TrKA signaling pathway in KOA promoted the release of pain mediators, increased the innervation of sensory nerve fibers in the synovium, and worsened peripheral hyperalgesia. It also showed increased TRPV1 positive sensory innervation in KOA was mediated by NGF/TrKA signaling and exacerbated peripheral hyperalgesia.

Nerve growth factor (Ngf) gene-driven semaphorin 3a (Sema3a) expression exacerbates thoracic aortic aneurysm dissection in mice.

Thoracic aortic aneurysm and dissection (TAAD) is a life-threatening disease and currently there is no pharmacological therapy. Sympathetic nerve overactivity plays an important role in the development of TAAD. Sympathetic innervation is mainly controlled by nerve growth factor (NGF, a key neural chemoattractant) and semaphoring 3A (Sema3A, a key neural chemorepellent), while the roles of these two factors in aortic sympathetic innervation and especially TAAD are unknown. We hypothesized that genetically manipulating the NGF/Sema3A ratio by the Ngf -driven Sema3a expression approach may reduce aortic sympathetic nerve innervation and mitigate TAAD progression. A mouse strain of Ngf gene-driven Sema3a expression (namely NgfSema3a/Sema3a mouse) was established by inserting the 2A-Sema3A expression frame to the Ngf terminating codon using CRISPR/Cas9 technology. TAAD was induced by ß-aminopropionitrile monofumarate (BAPN) both in NgfSema3a/Sema3a mice and wild type (WT) littermates. Contrary to our expectation, the BAPN-induced TAAD was severer in NgfSema3a/Sema3a mice than in wild-type (WT) mice. In addition, NgfSema3a/Sema3a mice showed higher aortic sympathetic innervation, inflammation and extracellular matrix degradation than the WT mice after BAPN treatment. The aortic vascular smooth muscle cells isolated from NgfSema3a/Sema3a mice and pretreated with BAPN in vivo for two weeks showed stronger capabilities of proliferation and migration than that from the WT mice. We conclude that the strategy of Ngf -driven Sema3a expression cannot suppress but worsens the BAPN-induced TAAD. By investigating the aortic phenotype of NgfSema3a/Sema3a mouse strain, we unexpectedly find a path to exacerbate BAPN-induced TAAD which might be useful in future TAAD studies.

Ocular adverse events of cenegermin used in neurotrophic keratopathy: an analysis of the FDA adverse event reporting system database.

BACKGROUND: Cenegermin, a recombinant human nerve growth factor, is an orphan drug approved for neurotrophic keratitis. The safety information on the label is incomplete, and the adverse reactions noted are mostly mild and tolerable. However, the occurrence of painful epithelial plagues and irreversible corneal deposits after cenegermin usage have been reported. Real-world data on long-term ocular safety are lacking. We aimed to assess the cenegermin-associated eye safety profile in the FDA pharmacovigilance database. METHODS: The signals of cenegermin-related ocular adverse events (AEs) from 2018 to 2022 were quantified using the reporting odds ratio (ROR) and information component (IC). The grading system was used to prioritize the signals. RESULTS: We identified 3288 cases of cenegermin-related ocular AEs and 56 positive ocular-related signals. Fifty unexpected signals of ocular AE were identified. Eye ulcer was classified as a designated medical event. Twenty AEs, including corneal perforation, eye infection, corneal deposits, and eye inflammation, were recognized as important medical event. The median onset time for ocular AEs was 6 days (interquartile range [IQR]: 1-29 days). CONCLUSION: This study revealed new cenegermin-related ocular AE signals. Clinical practice requires close monitoring to early identify and manage adverse reactions that may cause occurrence of serious irreversible consequences.

Effect of cilostazol on preventing paclitaxel-induced neuropathy in patients with breast cancer: A randomized controlled trial.

STUDY OBJECTIVE: Paclitaxel-induced peripheral neuropathy is a significant clinical problem can markedly deteriorate patient's quality of life (QoL). Preclinical evidence exists about the preventive capacity of cilostazol against peripheral neuropathy. However, this hypothesis has not yet been clinically investigated. This proof-of-concept study evaluated the effect of cilostazol on the incidence of paclitaxel-induced peripheral neuropathy in patients with non-metastatic breast cancer. DESIGN: This is a parallel randomized placebo-controlled trial. SETTING: The Oncology Center at Mansoura University, Egypt. PATIENTS: Patients with breast cancer scheduled to receive paclitaxel 175 mg/m2 biweekly. INTERVENTIONS: Patients were randomized to either cilostazol group who received cilostazol tablets 100 mg BID, or to control group who received placebo instead. MEASUREMENTS: The primary endpoint was the incidence of paclitaxel-induced neuropathy evaluated through common terminology criteria for adverse event (NCI-CTCAE) version 4. Secondary endpoints included assessment of the patient's QoL by the Functional Assessment of Cancer Therapy/Gynecologic Oncology Group-Neurotoxicity (FACT-GOG-NTx) subscale. Exploratory outcome measures included changes in serum levels of biomarkers namely nerve growth factor (NGF), and neurofilament light chain (NfL). MAIN RESULTS: The incidence of grade 2 and 3 peripheral neuropathies were significantly lower in the cilostazol group (40%) compared to the control group (86.7%) (p < 0.001). The incidence of clinically significant worsening in neuropathy-related QoL was higher in control group compared to the cilostazol group (p = 0.001). A higher percent increase from baseline in serum NGF was observed in the cilostazol group (p = 0.043). The circulating levels of NfL deemed comparable between the two arms at the end of the study (p = 0.593). CONCLUSION: Adjunctive use of cilostazol is as a novel option that might reduce the incidence of paclitaxel-induced peripheral neuropathy and improve the patients' QoL. Future larger clinical trials are warranted to confirm these findings.

Electrophysiological, histopathological, and biochemical evaluation of the protective effect of probiotic supplementation against pentylenetetrazole-induced seizures in rats.

BACKGROUND AND PURPOSE: Research on the relationship between the gut microbiome and epilepsy is accumulating. The present study was conducted to evaluate the effect of probiotic supplementation on pentylenetetrazole (PTZ)-induced seizures in rats. METHODS: Twenty-one adult male Wistar albino rats were included. The animals were divided into three groups of seven rats. Group 1 was a control group, whereas Group 2 rats received PTZ treatment and Group 3 rats had PTZ+PB (probiotic) treatment. For 6 weeks, Groups 1 and 2 were given saline (1 ml), whereas Group 3 had probiotic supplement. In the 5th week, tripolar electrodes were attached to the rats. Electrophysiological, behavioral, biochemical, and immunohistochemical evaluations were performed in the 6 weeks after the treatment. RESULTS: PB treatment significantly reduced seizures. In the PTZ group, expression levels of brain-derived neurotrophic factor, nerve growth factor (NGF), and Sox2 (SRY sex-determining region Y-box 2) in rat brains decreased significantly compared to the control group, whereas the expression levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), total oxidant status (TOS), and nitric oxide (NO) levels increased. In the PTZ+PB group, NGF expression increased significantly compared to the PTZ group, whereas TNF-α, IL-6, TOS, and NO levels decreased. In histopathological examination, an abundance of necrotic neurons was notable in the PTZ group, which was less in the PTZ+PB group. In addition, body weight of the group supplemented with probiotics decreased after the treatment. CONCLUSIONS: Our results suggest that probiotic supplementation may alleviate seizure severity and exert neuroprotective effects by reducing neuroinflammation and oxidative stress and altering the expression of neurotrophins in epileptogenic brains.

Eight months follow-up of corneal nerves and sensitivity after treatment with cenegermin for neurotrophic keratopathy.

BACKGROUD: Cenegermin (Oxervate, Dompè Farmaceutici, Milan, IT), a recombinant human NGF, is a potentially healing new drug for neurotrophic keratopathy (NK), a rare but challenging disease affecting the cornea. To date, studies that evaluate its mid-term effect on corneal nerves and sensitivity are lacking. OBJECTIVE: To evaluate the recovery and morphology of subbasal corneal nerves in patients treated with Cenegermin for NK and assess their correlation with corneal sensitivity. METHODS: This prospective, observational case series study was carried out between May 2018 and August 2020 at the Ophthalmic Clinic of the University of Verona. Clinical evaluation, sensitivity, and in vivo confocal microscopy (IVCM) were performed in the central and all four corneal sectors at baseline, the end of therapy (8 weeks), and 2, 4, and 8 months after therapy. Consecutive patients with NK (stage 2-3), treated with Cenegermin (1 drop 6 times daily for 8 weeks), were enrolled. During each visit, Corneal nerve fiber length (CNFL), corneal nerve fiber total branch density (CTBD), corneal nerve fiber fractal dimension (CNFraD) and Cochet-Bonnet esthesiometry (CBE) were measured. RESULTS: We enrolled 18 patients. Complete NK healing was noted in 14/18(78%) patients after 8 weeks of treatment; then in 14(78%), 15(83%), and 13(72%) patients at 2-, 4-, and 8-months, respectively. Starting at 8 weeks through 4-month follow-up there was progressive improvement in CBE in all corneal sectors (p ≤ 0.01), which continued thereafter. There was significant corneal nerve regrowth especially in the peripheral cornea: centripetal progression starting at 8 weeks (CNFL and CNFrad) and significant branching starting at 2 months (CTBD), which continued through to the end of follow up. Sector-coupled IVCM and CBE findings correlated at all evaluations (all r ≥ 0.62 starting at 2 months, with highest values in the peripheral sectors). CONCLUSIONS: After Cenegermin we observed a subbasal corneal nerve regeneration, a recovery of sensitivity and a lasting epithelial healing, suggesting that the effect of its action persists several months after discontinuation in patients with NK.

Somatosensory behavioral alterations in a NGF-induced persistent low back pain model.

Low back pain (LBP) is a major global burden in part due to the underlying pathophysiological mechanisms being poorly understood. A LBP rat model involving two injections of nerve growth factor (NGF, an endogenous pain-related neurotrophin) into trunk musculature was recently developed. Additional behavioral work in this NGF-LBP rat model is required to better characterize local and remote somatosensory alterations related to NGF-induced peripheral and central sensitization. This work characterizes the time-dependent development of hypersensitivity to trunk and hindpaw cutaneous mechanical stimulation and deep muscle mechanical hyperalgesia in adult male Sprague-Dawley rats (n = 6/group). Behavioral assays were performed at baseline (Day 0, D0), D2, D5 (pre- and 4 h post-2nd NGF or control injection), D7, D10, and D14 in NGF and control groups. Trunk and hindpaw cutaneous mechanical hypersensitivity were tested using von Frey filaments. Deep trunk mechanical hyperalgesia was determined using a small animal algometer. NGF rats demonstrated increased cutaneous sensitivity to ipsilateral trunk mechanical stimuli at D7, D10, and D14. NGF rats also demonstrated ipsilateral deep mechanical hyperalgesia on D2, D5 + 4 h, D7, D10, and D14. Cutaneous hypersensitivity was delayed compared to deep hyperalgesia in NGF rats. No additional sensory changes were noted. Together, these results indicate that male mechanical somatosensory changes develop primarily locally in the ipsilateral trunk following unilateral NGF injections. These findings contrast with a previous report in female rats using this NGF-LBP model showing more widespread (bilateral) hyperalgesia and remote mechanical hypersensitivity. Future studies will examine potential sex-related pain behavioral differences in the NGF model.

Acute Calcific Band Keratopathy as an Adverse Effect of Recombinant Human Nerve Growth Factor (Cenegermin): A Multicenter Case Series.

PURPOSE: Cenegermin, (OXERVATE) a recently Food and Drug Administration-approved topical formulation of recombinant human nerve growth factor, has been used for the treatment of neurotrophic keratopathy (NK). Corneal deposits have been previously reported as a potential adverse effect; however, the clinical characteristics, visual significance, and treatment options have not been fully described. The purpose of this article is to better characterize corneal deposits occurring during treatment with cenegermin for neurotrophic keratopathy. METHODS: This was a retrospective, multicenter consecutive case series. RESULTS: We identified 5 patients from 3 institutions who developed a white opacity in varying layers of the cornea, consistent with calcium deposition, during treatment with cenegermin. In all cases, the opacity occurred rapidly over the course of a few weeks after initiation of treatment. Histopathologic examination of the cornea from one corneal patient demonstrated extensive calcification of the stroma extending to 90% depth. Before treatment, all patients had stage 2 or 3 NK (Mackie classification). The deposits were visually significant in all patients and did not resolve after cessation of cenegermin. There were no differences in age, sex, etiology of the NK, corneal transplant status, or concurrent medications between the patients who developed a deposit and 15 other patients with stage 2 or 3 NK who did not. One patient was successfully treated with superficial keratectomy with ethylenediaminetetraacetic acid chelation, one patient underwent penetrating keratoplasty, and one patient received a Boston keratoprosthesis. CONCLUSIONS: We report the rapid onset of a corneal opacity after initiation of treatment with cenegermin in patients with stage 2 or 3 NK, consistent with acute calcific band keratopathy. This visually significant adverse finding has not previously been described. We could not identify any risk factors for development. We recommend close monitoring of patients receiving cenegermin therapy because the opacity may be irreversible and may require keratoplasty for visual rehabilitation.

Microinjection of pruritogens in NGF-sensitized human skin.

Single intradermal injections of nerve growth factor (NGF) evoke prolonged but temporally distinct sensitization patterns to somatosensory stimuli. Focal administration of the non-histaminergic pruritogen cowhage but not histamine resulted in elevated itch at day 21 after NGF administration. Here, we injected bovine adrenal medulla peptide 8-22 (BAM8-22), ß-alanine (ß-ALA) and endothelin-1 (ET-1) into NGF-treated skin of 11 healthy volunteers and investigated the corresponding itch/pain and flare reactions. ß-ALA was the weakest pruritogen, while BAM8-22 and ET-1 were equally potent as histamine. NGF did not sensitize itch or flare reactions induced by any compound, but injection and evoked pain were increased at day 21 and 49. The involvement of histamine H1 receptors in itch was explored in eight subjects after oral cetirizine. ET-1-induced itch and flare were significantly reduced. BAM8-22 and ß-ALA itch were not affected, but flare responses after BAM8-22 reduced by 50%. The results indicate that a single NGF injection does not sensitize for experimentally induced itch but increases pain upon pruritogen injection. In healthy humans, pruritic and algetic processing appear differentially regulated by NGF. However, in patients suffering chronic itch, prolonged elevation of NGF-levels under inflammatory conditions may contribute to elevated itch.

Local anaesthesia decreases nerve growth factor induced masseter hyperalgesia.

The aim of this investigation was to evaluate the effects of local anaesthesia on nerve growth factor (NGF) induced masseter hyperalgesia. Healthy participants randomly received an injection into the right masseter muscle of either isotonic saline (IS) given as a single injection (n = 15) or an injection of NGF (n = 30) followed by a second injection of lidocaine (NGF + lidocaine; n = 15) or IS (NGF + IS; n = 15) in the same muscle 48 h later. Mechanical sensitivity scores of the right and left masseter, referred sensations and jaw pain intensity and jaw function were assessed at baseline, 48 h after the first injection, 5 min after the second injection and 72 h after the first injection. NGF caused significant jaw pain evoked by chewing at 48 and 72 h after the first injection when compared to the IS group, but without significant differences between the NGF + lidocaine and NGF + IS groups. However, the mechanical sensitivity of the right masseter 5 min after the second injection in the NGF + lidocaine group was significantly lower than the second injection in the NGF + IS and was similar to the IS group. There were no significant differences for the referred sensations. Local anaesthetics may provide relevant information regarding the contribution of peripheral mechanisms in the maintenance of persistent musculoskeletal pain.

Epithelial Plaque Formation Secondary to Recombinant Human Nerve Growth Factor.

PURPOSE: To report a case of corneal epithelial plaque formation associated with recombinant human nerve growth factor (cenegermin 0.002%; Oxervate, Dompe[Combining Acute Accent] US Inc., Boston, MA), an as-yet unreported adverse event. METHODS: A case report and review of literature. RESULTS: A 45-year-old woman presented with a nonhealing 3.25- × 4.25-mm corneal epithelial defect secondary to multifactorial neurotrophic keratitis in the right eye. The epithelial defect was resistant to maximal medical therapy, and so cenegermin 0.002% was initiated, resulting in resolution of the corneal epithelial defect. After 6.5 weeks of treatment, she developed an unusual corneal epithelial plaque, decreased visual acuity, and eye pain. Cenegermin was ceased, after which the lesion resolved, visual acuity improved, and eye pain resolved. CONCLUSIONS: Cenegermin 0.002% has emerged as a promising treatment for neurotrophic keratitis. Reported adverse events with this agent have been minor and typically not vision threatening. Here, we describe corneal epithelial plaque formation as a visually significant adverse event that resolved with cessation of cenegermin 0.002%. Although the underlying mechanism is unknown, clinicians should be alerted to the possibility of epithelial plaque formation in patients being treated with recombinant human nerve growth factor for neurotrophic keratitis.

Topical Recombinant Human Nerve Growth Factor (Cenegermin) for Neurotrophic Keratopathy: A Multicenter Randomized Vehicle-Controlled Pivotal Trial.

PURPOSE: To evaluate the efficacy and safety of topical cenegermin (recombinant human nerve growth factor) in patients with neurotrophic keratopathy. DESIGN: Multicenter, randomized, double-masked, vehicle-controlled trial. PARTICIPANTS: Patients with neurotrophic persistent epithelial defect with or without stromal thinning. METHODS: The NGF0214 trial, conducted among 11 sites in the United States, randomized 48 patients 1:1 to cenegermin 20 µg/ml or vehicle eye drops, 6 drops daily for 8 weeks of masked treatment. Follow-up was 24 weeks. Safety was assessed in all patients who received study drug. Efficacy was assessed by intention to treat. MAIN OUTCOME MEASURES: The primary end point was healing of the neurotrophic lesion (persistent epithelial defect or corneal ulcer) after 8 weeks of masked treatment. Masked central readers measured neurotrophic lesions in randomized clinical pictures, then assessed healing status conventionally (<0.5 mm of fluorescein staining in the greatest dimension of the lesion area) and conservatively (0-mm lesion staining and no other residual staining). Secondary variables included corneal healing at 4 weeks of masked treatment (key secondary end point), overall changes in lesion size, rates of disease progression, and changes in visual acuity and corneal sensitivity from baseline to week 8. RESULTS: Conventional assessment of corneal healing showed statistically significant differences at week 8: compared to 7 of 24 vehicle-treated patients (29.2%), 16 of 23 cenegermin-treated patients (69.6%) achieved less than 0.5 mm of lesion staining (+40.4%; 95% confidence interval [CI], 14.2%-66.6%; P = 0.006). Conservative assessment of corneal healing also reached statistical significance at week 8: compared to 4 of 24 vehicle-treated patients (16.7%), 15 of 23 cenegermin-treated patients (65.2%) achieved 0 mm of lesion staining and no other residual staining (+48.6%; 95% CI, 24.0%-73.1%; P < 0.001). Moreover, the conservative measure of corneal healing showed statistical significance at week 4 (key secondary end point). Compared to vehicle, cenegermin-treated patients showed statistically significant reductions in lesion size and disease progression rates during masked treatment. Cenegermin was well tolerated; adverse effects were mostly local, mild, and transient. CONCLUSIONS: Cenegermin treatment showed higher rates of corneal healing than vehicle in neurotrophic keratopathy associated with nonhealing corneal defects.

Painless Nerve Growth Factor: A TrkA biased agonist mediating a broad neuroprotection via its actions on microglia cells.

Nerve Growth Factor (NGF) is a therapeutic candidate for Alzheimer's disease, based on its well known actions on basal forebrain cholinergic neurons. However, because of its pro-nociceptive activity, in current clinical trials NGF has to be administered intraparenchymally into the brain by neurosurgery via cell or gene therapy approaches. To prevent the NGF pain-inducing collateral effects, thus avoiding the necessity for local brain injection, we developed painless NGF (hNGFp), based on the human genetic disease Hereditary Sensory and Autonomic Neuropathy type V (HSAN V). hNGFp has similar neurotrophic activity as wild type human NGF, but its pain sensitizing activity is tenfold lower. Pharmacologically, hNGFp is a biased receptor agonist of NGF TrkA receptor. The results of recent studies shed new light on the neuroprotective mechanism by hNGFp and are highly relevant for the planning of NGF-based clinical trials. The intraparenchymal delivery of hNGFp, as used in clinical trials, was simulated in the 5xFAD mouse model and found to be inefficacious in reducing Aß plaque load. On the contrary, the same dose of hNGFp administered intranasally, which was rather widely biodistributed in the brain and did not induce pain sensitization, blocked APP processing into amyloid and restored synaptic plasticity and memory in this aggressive neurodegeneration model. This potent and broad neuroprotection by hNGFp was found to be mediated by hNGFp actions on glial cells. hNGFp increases inflammatory proteins such as the soluble TNFα receptor II and the chemokine CXCL12. Independent work has shown that NGF has a potent anti-inflammatory action on microglia and steers them towards a neuroprotective phenotype. These studies demonstrate that microglia cells are a new target cell of NGF in the brain and have therapeutic significance: i) they establish that the neuroprotective actions of hNGFp relies on a widespread exposure of the brain, ii) they identify a new anti-neurodegenerative pathway, linking hNGFp to inflammatory chemokines and cytokines via microglia, a common target for new therapeutic opportunities for neurodegenerative diseases, iii) they extend the neuroprotective potential of hNGFp beyond its classical cholinergic target, thereby widening the range of neurological diseases for which this neurotrophic factor might be used therapeutically, iv) they help interpreting the results of current NGF clinical trials in AD and the design of future trials with this new potent therapeutic candidate.

Experimental muscle hyperalgesia modulates sensorimotor cortical excitability, which is partially altered by unaccustomed exercise.

Impaired corticomotor function is reported in patients with lateral epicondylalgia, but the causal link to pain or musculotendinous overloading is unclear. In this study, sensorimotor cortical changes were investigated using a model of persistent pain combined with an overloading condition. In 24 healthy subjects, the effect of nerve growth factor (NGF)-induced pain, combined with delayed-onset muscle soreness (DOMS), was examined on pain perception, pressure pain sensitivity, maximal force, and sensorimotor cortical excitability. Two groups (NGF alone and NGF + DOMS) received injections of NGF into the extensor carpi radialis brevis (ECRB) muscle at day 0, day 2, and day 4. At day 4, the NGF + DOMS group undertook wrist eccentric exercise to induce DOMS in the ECRB muscle. Muscle soreness scores, pressure pain thresholds over the ECRB muscle, maximal grip force, transcranial magnetic stimulation mapping of the cortical ECRB muscle representation, and somatosensory-evoked potentials from radial nerve stimulation were recorded at day 0, day 4, and day 6. Compared with day 0, day 4 showed in both groups: (1) increased muscle soreness (P < 0.01); (2) reduced pressure pain thresholds (P < 0.01); (3) increased motor map volume (P < 0.01); and (4) decreased frontal N30 somatosensory-evoked potential. At day 6, compared with day 4, only the DOMS + NGF group showed: (1) increased muscle soreness score (P < 0.01); (2) decreased grip force (P < 0.01); and (3) decreased motor map volume (P < 0.05). The NGF group did not show any difference on the remaining outcomes from day 4 to day 6. These data suggest that sustained muscle pain modulates sensorimotor cortical excitability and that exercise-induced DOMS alters pain-related corticomotor adaptation.

Effects of nerve growth factor experimentally-induced craniofacial muscle sensitization on referred pain frequency and number of headache days: A double-blind, randomized placebo-controlled study.

OBJECTIVE: To assess if repeated intramuscular injections of nerve growth factor into the temporalis and masseter muscles increase mechanical sensitivity and entropy scores. Furthermore, to investigate if increased mechanical sensitivity would lead to increased prevalence of referred pain in the studied individuals. Finally, if increased muscle sensitization would lead to an increase in number of headache days during the experimental period. METHODS: The present double-blind, randomized placebo-controlled study recruited 16 healthy participants who were injected with nerve growth-factor, on 2 days, into the masseter and temporalis muscles and isotonic saline on the contralateral side. Mechanical sensitivity was assessed at seven different time-points (total of 21 days) by application of three different forces to 15 different sites of both muscles. Participants were asked after each force application if they experienced referred pain and were asked to keep a headache diary during the experimental period. RESULTS: In summary, a) repeated intramuscular injections of nerve-growth-factor caused an increase in mechanical sensitivity for the masseter but not the temporalis muscle, and an increase in entropy scores when compared to the isotonic saline side. b) Both referred pain frequency and number of headache days were not increased following nerve-growth-factor injections. CONCLUSIONS: These findings support the idea that mechanical sensitization in the masseter and temporalis muscles differs following injections of nerve growth factor. Furthermore, referred pain and headache frequency do not seem to be related to nerve growth factor sensitization in this model. These findings support the idea that in healthy individuals referred pain may be an epiphenomenon of the muscle in response to noxious input.

UVB- and NGF-induced cutaneous sensitization in humans selectively augments cowhage- and histamine-induced pain and evokes mechanical hyperknesis.

Exaggerated itch responses to pruritic chemical provocations and mechanical stimuli are evident in patients with chronic itch, for example, in atopic dermatitis. Currently used human models of itch do not account for such itch sensitization features, and the mechanisms underlying clinical itch sensitization are unknown. This study utilized two established human models of cutaneous nociceptive sensitization to explore how pre-established inflammatory hyperalgesia (ultraviolet-B-irradiation; "UVB") and non-inflammatory neurotrophic pain sensitization (nerve growth factor; "NGF") alter sensitivity to chemical and mechanically evoked itch. Twenty healthy volunteers participated in the UVB experiment. Six volar forearm areas (2 cm diameter) were UVB irradiated with ≤2 × minimal erythemal dose, and two non-irradiated areas were used as controls. Sixteen healthy volunteers participated in the NGF experiment and had 2 µg intradermally injected (4 × 50 µL in 2 cm diameter areas) into both volar forearms. Isotonic saline was applied as control. Pain sensitivity measurements (mechanical and heat pain thresholds) were conducted to validate the models. Subsequently, itch was evoked using histamine and cowhage spicules in the sensitized skin areas, and itch/pain was rated using visual analogue scales. Mechanical hyperknesis (increased itch to punctuate stimuli) was probed with von Frey filaments before/after each itch provocation. Both UVB- and NGF models induced robust primary mechanical hyperalgesia (P < .01) and hyperknesis (P < .05). Neither of the models augmented itch in response to chemical itch provocations but significant increases specifically for pain ratings were observed for both histamine and cowhage (P < .05). This suggests that these models are of limited value as proxies for itch sensitization to pruritogens observed, e.g., in inflammatory dermatoses.

Nerve growth factor derivative NGF61/100 promotes outgrowth of primary sensory neurons with reduced signs of nociceptive sensitization.

Nerve Growth Factor (NGF) is being considered as a therapeutic candidate for Alzheimer's disease. However, the development of an NGF-based therapy is limited by its potent pain activity. We have developed a "painless" derivative form of human NGF (NGF61/100), characterized by identical neurotrophic properties but a reduced nociceptive sensitization activity in vivo. Here we characterized the response of rat dorsal root ganglia neurons (DRG) to the NGF derivative NGF61/100, in comparison to that of control NGF (NGF61), analyzing the expression of noxious pro-nociceptive mediators. NGF61/100 displays a neurotrophic activity on DRG neurons comparable to that of control NGF61, despite a reduced activation of PLCγ, Akt and Erk1/2. NGF61/100 does not differ from NGF61 in its ability to up-regulate Substance P (SP) and Calcitonin Gene Related Peptide (CGRP) expression. However, upon Bradykinin (BK) stimulation, NGF61/100-treated DRG neurons release a much lower amount of SP and CGRP, compared to control NGF61 pre-treated neurons. This effect of painless NGF is explained by the reduced up-regulation of BK receptor 2 (B2R), respect to control NGF61. As a consequence, BK treatment reduced phosphorylation of the transient receptor channel subfamily V member 1 (TRPV1) in NGF61/100-treated cultures and induced a significantly lower intracellular Ca2+ mobilization, responsible for the lower release of noxious mediators. Transcriptomic analysis of DRG neurons treated with NGF61/100 or control NGF allowed identifying a small number of nociceptive-related genes that constitute an "NGF pain fingerprint", whose differential regulation by NGF61/100 provides a strong mechanistic basis for its selective reduced pain sensitizing actions.

Cenegermin for the treatment of neurotrophic keratitis.

The trigeminal nerve provides corneal sensitivity and trophic supply to corneal tissues. The impairment of corneal innervation leads to development of neurotrophic keratitis (NK). NK is a rare, degenerative corneal disease characterized by corneal hypo/anesthesia and development of nonhealing corneal epithelial defects and ulcers. NK is a challenging condition with high medical need due to the lack of approved treatments that can restore corneal integrity. Current treatment of NK aims at stimulating corneal healing and preventing disease progression. Cenegermin is a recombinant human nerve growth factor that was safe and well tolerated in preclinical and clinical studies. Cenegermin eye drops were safe and effective in restoring corneal integrity in two phase II clinical trials in patients with NK. The European Commission granted a full marketing authorization to cenegermin eye drops for the treatment of moderate to severe NK in July 2017.

The chemokine CXCL12 mediates the anti-amyloidogenic action of painless human nerve growth factor.

Nerve growth factor is a therapeutic candidate for Alzheimer's disease. Due to its pain-inducing activity, in current clinical trials nerve growth factor is delivered locally into the brain by neurosurgery, but data on the efficacy of local nerve growth factor delivery in decreasing amyloid-ß deposition are not available. To reduce the nerve growth factor pain-inducing side effects, thus avoiding the need for local brain injection, we developed human painless nerve growth factor (hNGFp), inspired by the human genetic disease hereditary sensory and autonomic neuropathy type V. hNGFp has identical neurotrophic potency as wild-type human nerve growth factor, but a 10-fold lower pain sensitizing activity. In this study we first mimicked, in the 5xFAD mouse model, the intraparenchymal delivery of hNGFp used in clinical trials and found it to be ineffective in decreasing amyloid-ß plaque load. On the contrary, the same dose of hNGFp delivered intranasally, which was widely biodistributed in the brain and did not induce pain, showed a potent anti-amyloidogenic action and rescued synaptic plasticity and memory deficits. We found that hNGFp acts on glial cells, modulating inflammatory proteins such as the soluble TNFα receptor II and the chemokine CXCL12. We further established that the rescuing effect by hNGFp is mediated by CXCL12, as pharmacological inhibition of CXCL12 receptor CXCR4 occludes most of hNGFp effects. These findings have significant therapeutic implications: (i) we established that a widespread exposure of the brain is required for nerve growth factor to fully exert its neuroprotective actions; and (ii) we have identified a new anti-neurodegenerative pathway as a broad target for new therapeutic opportunities for neurodegenerative diseases.

Treatment of cerebral radiation necrosis with nerve growth factor: A prospective, randomized, controlled phase II study.

PURPOSE: A prospective, placebo controlled phase II trial was conducted to test the efficacy of Nerve Growth Factor (NGF) for the treatment of symptomatic temporal lobe necrosis (TLN). MATERIALS AND METHODS: Patients with progressive TLN were randomly assigned to either the control or the study group in a 1:1 ratio. The control group received corticosteroids with gradually reduced dosage. The study group received NGF with corticosteroids. NGF was dissolved in 2mL normal saline and injected intramuscularly at 18µg/time, once a day for 2months. The efficacy was evaluated by both the objective and subjective methods every 3-4months after treatment. The objective method compared volumes of the necrotic masses on MRI before and after treatment. The subjective method compared the neurocognitive score as evaluated by the mini-mental status examination (MMSE). RESULTS: Twenty-eight cases were enrolled into this study. The objective evaluation showed that the response rate (RR) in the study group was higher than the control group. The ratio was 10 versus 2 (p=0.006), and 12 versus 3 (p=0.002) at 3-4months and 6-8months after intervention, respectively. The subjective evaluation demonstrated both groups were effective in controlling the necrosis related symptoms in the first 6months after treatment. But NGF was more effective than corticosteroids at 9months (13 versus 4, p=0.001). The only observed side effect was mild pain at the injection site in 3 patients in the study group. CONCLUSIONS: Our results demonstrated that the process of TLN is not irreversible. NGF is more effective in recovering TLN than corticosteroids with little side effect. NGF has a longer duration in controlling the necrosis related symptoms than corticosteroids.