Joint capsule treatment with enkephalin-encoding HSV-1 recombinant vector reduces inflammatory damage and behavioural sequelae in rat CFA monoarthritis

Enkephalins and Pain Modulation: Mechanisms of Action and Therapeutic Perspectives

Enkephalins, a subclass of endogenous opioid peptides, play a pivotal role in pain modulation. Enkephalins primarily exert their effects through opioid receptors located widely throughout both the central and peripheral nervous systems. This review will explore the mechanisms by which enkephalins produce analgesia, emotional regulation, neuroprotection, and other physiological effects. Furthermore, this review will analyze the involvement of enkephalins in the modulation of different pathologies characterized by severe pain. Understanding the complex role of enkephalins in pain processing provides valuable insight into potential therapeutic strategies for managing pain disorders.

Disease-modifying rdHSV-CA8* non-opioid analgesic gene therapy treats chronic osteoarthritis pain by activating Kv7 voltage-gated potassium channels

Chronic pain is common in our population, and most of these patients are inadequately treated, making the development of safer analgesics a high priority. Knee osteoarthritis (OA) is a primary cause of chronic pain and disability worldwide, and lower extremity OA is a major contributor to loss of quality-adjusted life-years. In this study we tested the hypothesis that a novel JDNI8 replication-defective herpes simplex-1 viral vector (rdHSV) incorporating a modified carbonic anhydrase-8 transgene (CA8*) produces analgesia and treats monoiodoacetate-induced (MIA) chronic knee pain due to OA. We observed transduction of lumbar DRG sensory neurons with these viral constructs (vHCA8*) (~40% of advillin-positive cells and ~ 50% of TrkA-positive cells colocalized with V5-positive cells) using the intra-articular (IA) knee joint (KJ) route of administration. vHCA8* inhibited chronic mechanical OA knee pain induced by MIA was dose- and time-dependent. Mechanical thresholds returned to Baseline by D17 after IA KJ vHCA8* treatment, and exceeded Baseline (analgesia) through D65, whereas negative controls failed to reach Baseline responses. Weight-bearing and automated voluntary wheel running were improved by vHCA8*, but not negative controls. Kv7 voltage-gated potassium channel-specific inhibitor XE-991 reversed vHCA8*-induced analgesia. Using IHC, IA KJ of vHCA8* activated DRG Kv7 channels via dephosphorylation, but negative controls failed to impact Kv7 channels. XE-991 stimulated Kv7.2-7.5 and Kv7.3 phosphorylation using western blotting of differentiated SH-SY5Y cells, which was inhibited by vHCA8* but not by negative controls. The observed prolonged dose-dependent therapeutic effects of IA KJ administration of vHCA8* on MIA-induced chronic KJ pain due to OA is consistent with the specific activation of Kv7 channels in small DRG sensory neurons. Together, these data demonstrate for the first-time local IA KJ administration of vHCA8* produces opioid-independent analgesia in this MIA-induced OA chronic pain model, supporting further therapeutic development.

Enkephalin Rescues Temporomandibular Joint Pain-Related Behavior in Rats

Temporomandibular joint disorders include a variety of clinical syndromes that are difficult to manage if associated with debilitating severe jaw pain. Thus, seeking additional experimental therapies for temporomandibular joint pain reduction is warranted. Targeted enkephalin gene therapy approaches provide clear promise for pain control. The studies detailed here indicate significant analgesia and protection of joint tissue are provided after injection of an overexpression viral vector gene therapy near the joint. The viral vector gene therapy described provides overexpression of naturally occurring opioid peptides after its uptake by trigeminal nerve endings. The viral vectors act as independent "minipump" sources for the opioid peptide synthesis in the neuronal cytoplasm producing the intended biological function, reduction of pain, and tissue repair. The antinociceptive effects provided with this delivery method of opioid expression persist for over 4 weeks. This is coincident with the expected time frame for the duration of the transgene overproduction of the endogenous opioid peptide before its diminution due to dormancy of the virus. These experimental studies establish a basis for the use of replication-defective herpes simplex type 1-based gene therapy for severe chronic inflammatory temporomandibular joint destruction and pain. As innovative means of significantly reducing joint inflammation and preserving tissue architecture, gene therapies may extend their clinical usefulness for patients with temporomandibular joint disorders.

Dual enkephalinase inhibitor PL265: a novel topical treatment to alleviate corneal pain and inflammation

Ocular pain is a core symptom of inflammatory or traumatic disorders affecting the anterior segment. To date, the management of chronic ocular pain remains a therapeutic challenge in ophthalmology. The main endogenous opioids (enkephalins) play a key role in pain control but exhibit only transient analgesic effects due to their rapid degradation. The aim of this study was to explore the antinociceptive and anti-inflammatory effects of topical administration of PL265 (a dual enkephalinase inhibitor) on murine models of corneal pain. On healthy corneas, chronic PL265 topical administration did not alter corneal integrity nor modify corneal mechanical and chemical sensitivity. Then, on murine models of corneal pain, we showed that repeated instillations of PL265 (10 mM) significantly reduced corneal mechanical and chemical hypersensitivity. PL265-induced corneal analgesia was completely antagonized by naloxone methiodide, demonstrating that PL265 antinociceptive effects were mediated by peripheral corneal opioid receptors. Moreover, flow cytometry (quantification of CD11b+ cells) and in vivo confocal microscopy analysis revealed that instillations of PL265 significantly decreased corneal inflammation in a corneal inflammatory pain model. Chronic PL265 topical administration also decreased Iba1 and neuronal injury marker (ATF3) staining in the nucleus of primary sensory neurons of ipsilateral trigeminal ganglion. These results open a new avenue for ocular pain treatment based on the enhancement of endogenous opioid peptides' analgesic effects in tissues of the anterior segment of the eye. Dual enkephalinase inhibitor PL265 seems to be a promising topical treatment for safe and effective alleviation of ocular pain and inflammation.

Effects of Treadmill Exercise on Advanced Osteoarthritis Pain in Rats

OBJECTIVE

Exercise is commonly recommended for patients with osteoarthritis (OA) pain. However, whether exercise is beneficial in ameliorating ongoing pain that is persistent, resistant to nonsteroidal antiinflammatory drugs (NSAIDs), and associated with advanced OA is unknown.

METHODS

Rats treated with intraarticular (IA) monosodium iodoacetate (MIA) or saline underwent treadmill exercise or remained sedentary starting 10 days postinjection. Tactile sensory thresholds and weight bearing were assessed, followed by radiography at weekly intervals. After 4 weeks of exercise, ongoing pain was assessed using conditioned place preference (CPP) to IA or rostral ventromedial medulla (RVM)-administered lidocaine. The possible role of endogenous opioids in exercise-induced pain relief was examined by systemic administration of naloxone. Knee joints were collected for micro-computed tomography (micro-CT) analysis to examine pathologic changes to subchondral bone and metaphysis of the tibia.

RESULTS

Treadmill exercise for 4 weeks reversed MIA-induced tactile hypersensitivity and weight asymmetry. Both IA and RVM lidocaine D35, administered post-MIA, induced CPP in sedentary but not exercised MIA-treated rats, indicating that exercise blocks MIA-induced ongoing pain. Naloxone reestablished weight asymmetry in MIA-treated rats undergoing exercise and induced conditioned place aversion, indicating that exercise-induced pain relief is dependent on endogenous opioids. Exercise did not alter radiographic evidence of OA. However, micro-CT analysis indicated that exercise did not block lateral subchondral bone loss or trabecular bone loss in the metaphysis, but did block MIA-induced medial bone loss.

CONCLUSION

These findings support the conclusion that exercise induces pain relief in advanced, NSAID-resistant OA, likely through increased endogenous opioid signaling. In addition, treadmill exercise blocked MIA-induced bone loss in this model, indicating a potential bone-stabilizing effect of exercise on the OA joint.

Nonviral vector plasmid DNA encoding human proenkephalin gene attenuates inflammatory and neuropathic pain-related behaviors in mice

Inflammatory pain and neuropathic pain are major clinical health issues that represent considerable social and economic burden worldwide. In the present study, we investigated the anti-nociceptive efficacy of delivery of human proenkephalin gene by a plasmid DNA vector (pVAX1-PENK) on complete Freund's adjuvant (CFA) induced inflammatory pain and spared nerve injury (SNI) induced neuropathic pain in mice. Mice were intramuscularly or intrathecally administered pVAX1 or pVAX1-PENK, respectively. Pain thresholds in the pVAX1-PENK treated mice were significantly higher at day 3, then reached a peak at day 7 and lasted until day 28 after gene transfer, and the analgesic effect of pVAX1-PENK was blocked with naloxone hydrochloride. In contrast, pVAX1 treated mice did not significantly improve pain thresholds. These results indicate that peripheral or spinal delivery of a plasmid encoding human proenkephalin gene provides a potential therapeutic strategy for inflammatory pain and neuropathic pain.

Efficacy of Herpes Simplex Virus Vector Encoding the Human Preproenkephalin Gene for Treatment of Facial Pain in Mice

AIMS

To determine whether herpes simplex virus-based vectors can efficiently transduce mouse trigeminal ganglion (TG) neurons and attenuate preexisting nerve injury-induced whisker pad mechanical hypersensitivity in a trigeminal inflammatory compression (TIC) neuropathic pain model.

METHODS

Tissue transduction efficiencies of replication-conditional and replication-defective vectors to mouse whisker pads after topical administration and subcutaneous injection were assessed using quantitative real-time PCR (qPCR). Tissue tropism and transgene expression were assessed using qPCR and reverse-transcriptase qPCR following topical application of the vectors. Whisker pad mechanical sensitivities of TIC-injured mice were determined using graduated von Frey fibers before and after application of human preproenkephalin expressing replication-conditional vector (KHPE). Data were analyzed using one-way analysis of variance (ANOVA) and post hoc tests.

RESULTS

Transduction of target TGs was 8- to 50-fold greater after topical application than subcutaneous injection and ≥ 100-fold greater for replication-conditional than replication-defective vectors. Mean KHPE loads remained constant in TGs (4.5-9.8 × 10(4) copies/TG) over 3 weeks but were below quantifiable levels (10 copies/tissue) within 2 weeks of application in other nontarget cephalic tissues examined. Transgene expression in TGs was maximal during 2 weeks after topical application (100-200 cDNA copies/mL) and was below quantifiable levels (1 cDNA copy/mL) in all nontarget tissues. Topical KHPE administration reduced TIC-related mechanical hypersensitivity on whisker pads 4-fold (P < .05) for at least 1 week.

CONCLUSION

Topically administered KHPE produced a significant antinociceptive effect in the TIC mouse model of chronic facial neuropathic pain. This is the first report in which a gene therapeutic approach reduced trigeminal pain-related behaviors in an established pain state in mice.

Relief of pain induced by varicella-zoster virus in a rat model of post-herpetic neuralgia using a herpes simplex virus vector expressing enkephalin

Acute and chronic pain (post-herpetic neuralgia or PHN) are encountered in patients with herpes zoster that is caused by reactivation of varicella-zoster virus (VZV) from a state of neuronal latency. PHN is often refractory to current treatments, and additional strategies for pain relief are needed. Here we exploited a rat footpad model of PHN to show that herpes simplex virus (HSV) vector-mediated gene delivery of human preproenkephalin (vHPPE) effectively reduced chronic VZV-induced nocifensive indicators of pain. VZV inoculated at the footpad induced prolonged mechanical allodynia and thermal hyperalgesia that did not develop in controls or with ultraviolet light-inactivated VZV. Subsequent footpad administration of vHPPE relieved VZV-induced pain behaviors in a dose-dependent manner for extended periods, and prophylactic vector administration prevented VZV-induced pain from developing. Short-term pain relief following low-dose vHPPE administration could be effectively prolonged by vector re-administration. HPPE transcripts were increased three- to fivefold in ipsilateral ganglia, but not in the contralateral dorsal root ganglia. VZV hypersensitivity and its relief by vHPPE were not affected by peripheral delivery of opioid receptor agonist or antagonist, suggesting that the efficacy was mediated at the ganglion and/or spinal cord level. These results support further development of ganglionic expression of enkephalin as a novel treatment for the pain associated with Zoster.

Gene therapy for trigeminal pain in mice

The aim of this study was to test the efficacy of a single direct injection of viral vector encoding for encephalin to induce a widespread expression of the transgene and potential analgesic effect in trigeminal behavioral pain models in mice. After direct injection of HSV-1 based vectors encoding for human preproenkephalin (SHPE) or the lacZ reporter gene (SHZ.1, control virus) into the trigeminal ganglia in mice, we performed an orofacial formalin test and assessed the cumulative nociceptive behavior at different time points after injection of the viral vectors. We observed an analgesic effect on nociceptive behavior that lasted up to 8 weeks after a single injection of SHPE into the trigeminal ganglia. Control virus injected animals showed nociceptive behavior similar to naïve mice. The analgesic effect of SHPE injection was reversed/attenuated by subcutaneous naloxone injections, a μ-opioid receptor antagonist. SHPE injected mice also showed normalization in withdrawal latencies upon thermal noxious stimulation of inflamed ears after subdermal complete Freund’s adjuvans injection indicating widespread expression of the transgene. Quantitative immunohistochemistry of trigeminal ganglia showed expression of human preproenkephalin after SHPE injection.

Direct injection of viral vectors proved to be useful for exploring the distinct pathophysiology of the trigeminal system and could also be an interesting addition to the pain therapists’ armamentarium.

Gene-based approaches in pain research and exploration of new therapeutic targets and strategies

Large panel of gene-based techniques is used for many years specifically in the pain research field. From the first identification (cloning) of some "mythic" genes, such as those encoding opioid or capsaicin receptors allowing then the creation of first-generation knockout mice, to the today conditional (time, tissue, cell-type and even pathology-dependent) and regulatable modulation of a gene function, these approaches largely contributed to fundamental leaps forward in our understanding of the function of some proteins and of their interest as possible druggable targets. Perhaps one of the most remarkable evolution in the last years is the passage of these approaches from the bench to the patient; whether it concerns the identification of genes involved in inherited pain insensibility/susceptibility, the search for genetic markers of pain types, the individual pharmacogenomics or even the first gene therapy trials. From many possible variants of gene-grounded techniques used in pain research we focus here on gene knockouts and some recent developments, on viral vectors-based gene transfer and on transgenic models for the tracing of pain pathways. Through these selected examples we attempted to emphasize the immense potential of these approaches and their already well-recognized contribution in both the basic and clinical pain research.

Modulating pain in the periphery: gene-based therapies to enhance peripheral opioid analgesia: Bonica lecture, ASRA 2010

This article provides a brief overview of earlier work of our group on the peripheral signaling of pain, summarizes more recent studies on the role of opioids in chronic neuropathic pain, and speculates on the future of gene-based therapies as novel strategies to enhance the peripheral modulation of pain. Neurophysiologic and psychophysical studies have revealed features of primary afferent activity from somatic tissue that led to improved understanding of the physiology and pathophysiology of pain signaling by nociceptive and nonnociceptive fibers. The demonstration of peripheral opioid mechanisms in neuropathic pain suggests a potential role for these receptors in the modulation of pain at its initiation site. Our work has focused on characterizing this peripheral opioid analgesia in chronic neuropathic pain such that it can be exploited to develop novel and potent peripheral analgesics for its treatment. Ongoing research on virus-mediated gene transfer strategies to enhance peripheral opioid analgesia is presented.

Gene therapy for the treatment of chronic peripheral nervous system pain

Chronic pain is a major health concern affecting 80 million Americans at some time in their lives with significant associated morbidity and effects on individual quality of life. Chronic pain can result from a variety of inflammatory and nerve damaging events that include cancer, infectious diseases, autoimmune-related syndromes and surgery. Current pharmacotherapies have not provided an effective long-term solution as they are limited by drug tolerance and potential abuse. These concerns have led to the development and testing of gene therapy approaches to treat chronic pain. The potential efficacy of gene therapy for pain has been reported in numerous pre-clinical studies that demonstrate pain control at the level of the spinal cord. This promise has been recently supported by a Phase-I human trial in which a replication-defective herpes simplex virus (HSV) vector was used to deliver the human pre-proenkephalin (hPPE) gene, encoding the natural opioid peptides met- and leu-enkephalin (ENK), to cancer patients with intractable pain resulting from bone metastases (Fink et al., 2011). The study showed that the therapy was well tolerated and that patients receiving the higher doses of therapeutic vector experienced a substantial reduction in their overall pain scores for up to a month post vector injection. These exciting early clinical results await further patient testing to demonstrate treatment efficacy and will likely pave the way for other gene therapies to treat chronic pain.

The role of TNFα in the periaqueductal gray during naloxone-precipitated morphine withdrawal in rats

Tolerance and dependence are common complications of long-term treatment of pain with opioids, which substantially limit the long-term use of these drugs. The mechanisms underlying these phenomena are poorly understood. Studies have implicated the midbrain periaqueductal gray (PAG) in the pathogenesis of morphine withdrawal, and recent evidence suggests that proinflammatory cytokines in the PAG may play an important role in morphine withdrawal. Here we report that chronic morphine withdrawal-induced upregulation of glial fibrillary acidic protein (GFAP), tumor necrosis factor alpha (TNFα) and phosphorylation of ERK1/2 (pERK1/2) in the caudal ventrolateral PAG (vlPAG). Microinjection of recombinant TNFα into the vlPAG followed by intraperitoneal naloxone resulted in morphine withdrawal-like behavioral signs, and upregulation of pERK1/2, expression of Fos, and phosphorylation of cAMP response element binding (pCREB) protein. We used a herpes simplex virus (HSV)-based vector expressing p55 soluble TNF receptor (sTNFR) microinjected into the PAG to examine the role of the proinflammatory cytokine TNFα in the PAG in the naloxone-precipitated withdrawal response. Microinjection of HSV vector expressing sTNFR into the PAG before the start of morphine treatment significantly reduced the naloxone-precipitated withdrawal behavioral response and downregulated the expression of GFAP and TNFα in astrocytes of the PAG. TNFR type I colocalized with neuronal pERK1/2. Microinjection of HSV vector expressing sTNFR into the PAG also significantly reduced the phosphorylation of both ERK1/2 and CREB, and reduced Fos immunoreactivity in neurons of the PAG following naloxone-precipitated withdrawal. These results support the concept that proinflammatory cytokines expressed in astrocytes in the PAG may play an important role in the pathogenesis of morphine withdrawal response.

Gene-based approaches in the study of pathological pain

Chronic pathological pain is characterized by extensive plasticity of the systems involved in pain signal transmission and modulation and tissue remodeling in several CNS structures. These long-lasting alterations are mediated by, or associated with, changes in the production of key molecules of nociceptive processing. Gene-based approaches offer the unique possibility of using local or even cell-type specific interventions to correct the abnormal production of some of these proteins, modulate the activity of signal transduction pathways, or overproduce various therapeutic secreted proteins. We showed that certain viral-derived vectors are particularly suitable for mediating gene transfer highly preferential for instance into the primary sensory neurons or into the spinal cord glial cells that represent particularly pertinent targets in the search for new therapeutic strategies of pathological pain.

Sensory and vascular changes in a rat monoarthritis model: prophylactic and therapeutic effects of meloxicam

OBJECTIVE AND DESIGN

The objective of this study was to determine the ability of meloxicam prophylaxis and therapy to blunt the effect of complete Freund's adjuvant (CFA) induced monoarthritis.

MATERIALS AND METHODS

First the validity of this animal model was established by examining joint changes at multiple levels after injecting CFA into the tibio-tarsal joint. Next, meloxicam (5 mg/kg) or vehicle was administered on days 0-7 (prophylactic) and on days 7-16 (therapeutic) in separate groups of animals.

RESULTS

The CFA-injected joint demonstrated hallmark histological and structural changes such as pannus formation, bone remodeling, cartilage erosion and immune cell infiltration. Both prophylactic and therapeutic treatment with meloxicam effectively reduced swelling (ankle circumference), oedema and extravasation of Evans blue dye in the affected joint. Moreover, meloxicam reduced loss in range of motion and also reduced mechanical stimulus evoked pain scores. Notably, these effects persisted after discontinuing drug treatment.

CONCLUSION

The present study provides a unique comparison of prophylactic versus therapeutic effects of meloxicam in the CFA-induced model of monoarthritis.

Endogenous opiates and behavior: 2008

This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).