Shivani B. Ruparel

Persistent Nociception Triggered by Nerve Growth Factor (NGF) Is Mediated by TRPV1 and Oxidative Mechanisms

Nerve growth factor (NGF) is elevated in certain chronic pain conditions and is a sufficient stimulus to cause lasting pain in humans, but the actual mechanisms underlying the persistent effects of NGF remain incompletely understood. We developed a rat model of NGF-induced persistent thermal hyperalgesia and mechanical allodynia to determine the role of transient receptor potential vanilloid 1 (TRPV1) and oxidative mechanisms in the persistent effects of NGF. Persistent thermal hypersensitivity and mechanical allodynia require de novo protein translation and are mediated by TRPV1 and oxidative mechanisms. By comparing effects after systemic (subcutaneous), spinal (intrathecal) or hindpaw (intraplantar) injections of test compounds, we determined that TRPV1 and oxidation mediate persistent thermal hypersensitivity via peripheral and spinal sites of action and mechanical allodynia via only a spinal site of action. Therefore, NGF-evoked thermal and mechanical allodynia are mediated by spatially distinct mechanisms. NGF treatment evoked sustained increases in peripheral and central TRPV1 activity, as demonstrated by increased capsaicin-evoked nocifensive responses, increased calcitonin gene-related peptide release from hindpaw skin biopsies, and increased capsaicin-evoked inward current and membrane expression of TRPV1 protein in dorsal root ganglia neurons. Finally, we showed that NGF treatment increased concentrations of linoleic and arachidonic-acid-derived oxidized TRPV1 agonists in spinal cord and skin biopsies. Furthermore, increases in oxidized TRPV1-active lipids were reduced by peripheral and spinal injections of compounds that completely blocked persistent nociception. Collectively, these data indicate that NGF evokes a persistent nociceptive state mediated by increased TRPV1 activity and oxidative mechanisms, including increased production of oxidized lipid TRPV1 agonists.

Omega-3 Fatty Acid Inhibition of Prostate Cancer Progression to Hormone Independence Is Associated With Suppression of mTOR Signaling and Androgen Receptor Expression

Currently, progression of prostate cancer to androgen independence remains the primary obstacle to improved survival. In order to improve overall survival, novel treatment strategies that are based upon specific molecular mechanisms that prolong the androgen-dependent state and that are useful for androgen-independent disease need to be identified. Both epidemiological as well as preclinical data suggest that omega-3 fatty acids are effective primary tumor prevention agents; however, their efficacy at preventing and treating refractory prostate cancer has not been as thoroughly investigated. We used an in vitro model of androgen ablation to determine the effect of treatment with omega-3 fatty acids on the progression to an androgen-independent state. The omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were able to prevent progression of LNCaP cells while the omega-6 fatty acid arachidonic acid (AA) actually promoted cell growth under conditions of hormone depletion. These results correlated with a decrease in the expression of the androgen receptor as well as suppression of the Akt/mTOR signaling pathway. Connecting the mechanisms by which omega-3 fatty acids affect phenotypic outcome is important for effective exploitation of these nutrient agents as a therapeutic approach. Understanding these processes is critical for the development of effective dietary intervention strategies that improve overall survival.

Role of endogenous TRPV1 agonists in a postburn pain model of partial-thickness injury.

Summary Endogenous TRPV1 agonists, oxidized linoleic acid metabolites, are released via the cytochrome P450 enzyme system and contribute to thermal allodynia in an in vivo model of burn injury. Abstract Oxidized linoleic acid metabolites (OLAMs) are a class of endogenous transient receptor potential vanilloid 1 (TRPV1) channel agonists released on exposure of tissue to transient noxious temperatures. These lipid compounds also contribute to inflammatory and heat allodynia. Because persistent pain after a burn injury represents a significant clinical challenge for treatment, we developed an in vivo rat model of partial‐thickness cutaneous thermal injury and examined whether TRPV1 and specific OLAM metabolites play a role in mediating postburn pain injury. This peripheral model of burn injury had marked thermal allodynia peaking at 24 h after thermal injury, with allodynia being maintained for up to 7 d. Immunohistochemical characterization of tissue taken from injury sites revealed an increase in leukocyte/macrophage infiltration that was colocalized with TRPV1‐positive fibers. Using this peripheral thermal injury model, we found that pharmacological blockade of peripheral TRPV1 receptors reduced thermal allodynia by about 98%. Moreover, there was a significant increase in OLAM levels compared to naive controls in hind paw skin biopsies. Additional studies of the metabolism of [C14]‐linoleic acid in skin biopsies revealed the role of the cytochrome P450 (CYP) system in mediating the metabolism of linoleic acid after thermal injury. Finally, we demonstrated that direct inhibition of OLAMs using OLAM antibodies and indirect inhibition using the CYP inhibitor ketoconazole significantly reduced postburn thermal allodynia. Collectively, these findings point to a novel role of the OLAMs and CYP‐related enzymes in generating postburn allodynia via activation of peripheral TRPV1.

The cytochrome P450 inhibitor, ketoconazole, inhibits oxidized linoleic acid metabolite-mediated peripheral inflammatory pain

BackgroundOxidized linoleic acid metabolites (OLAMs) are a class of endogenous agonists to the transient receptor potential V1 (TRPV1) receptor. Although TRPV1 mediates inflammatory heat hyperalgesia, it is not known if the OLAMs contribute to the peripheral activation of this receptor during tissue inflammation. In the present study, we evaluated whether the OLAM system is activated during inflammation and whether cytochrome P450 enzymes mediate OLAM contributions to heat hyperalgesia using the complete Freund’s adjuvant (CFA) model of inflammation.ResultsOur results demonstrate that the intraplantar (ipl) injection of anti-OLAM antibodies significantly reversed CFA-induced heat hyperalgesia. Moreover, application of lipid extracts from inflamed rat skin to cultured sensory neurons triggered a significant release of iCGRP that is blocked by co-treatment with I-RTX, a TRPV1 antagonist. To determine the role of CYP enzymes in mediating OLAM effects, we used a broad spectrum CYP inhibitor, ketoconazole. Pretreatment with ketoconazole inhibited the release of TRPV1 agonists in lipid extracts from inflamed skin and significantly reversed CFA-induced heat hyperalgesia by a peripheral mechanism of action. Moreover, the ipl injection of linoleic acid to rats 24 hr after CFA evoked spontaneous nocifensive behaviors that were significantly reduced by capsazepine, by knockout of the TRPV1 gene, or by pretreatment with either anti-OLAM antibodies or ketoconazole.ConclusionsTaken together, our data suggests that OLAMs contribute to inflammatory nociception in the periphery and that cytochrome P450 enzymes play a crucial role in mediating OLAM contributions to inflammatory heat hyperalgesia.

Prolactin regulates TRPV1, TRPA1, and TRPM8 in sensory neurons in a sex-dependent manner: Contribution of prolactin receptor to inflammatory pain.

Prolactin (PRL) is a hormone produced in the anterior pituitary but also synthesized extrapituitary where it can influence diverse cellular processes, including inflammatory responses. Females experience greater pain in certain inflammatory conditions, but the contribution of the PRL system to sex-dependent inflammatory pain is unknown. We found that PRL regulates transient receptor potential (TRP) channels in a sex-dependent manner in sensory neurons. At >20 ng/ml, PRL sensitizes TRPV1 in female, but not male, neurons. This effect is mediated by PRL receptor (PRL-R). Likewise, TRPA1 and TRPM8 were sensitized by 100 ng/ml PRL only in female neurons. We showed that complete Freund adjuvant (CFA) upregulated PRL levels in the inflamed paw of both male and female rats, but levels were higher in females. In contrast, CFA did not change mRNA levels of long and short PRL-R in the dorsal root ganglion or spinal cord. Analysis of PRL and PRL-R knockout (KO) mice demonstrated that basal responses to cold stimuli were only altered in females, and with no significant effects on heat and mechanical responses in both sexes. CFA-induced heat and cold hyperalgesia were not changed in PRL and PRL-R KO compared with wild-type (WT) males, whereas significant reduction of heat and cold post-CFA hyperalgesia was detected in PRL and PRL-R KO females. Attenuation of CFA-induced mechanical allodynia was observed in both PRL and PRL-R KO females and males. Thermal hyperalgesia in PRL KO females was restored by administration of PRL into hindpaws. Overall, we demonstrate a sex-dependent regulation of peripheral inflammatory hyperalgesia by the PRL system.

Plasticity of cytochrome P450 isozyme expression in rat trigeminal ganglia neurons during inflammation

TOC summary CYP enzymes are coexpressed with TRPV1 in trigeminal neurons, are upregulated after inflammation, and catalyze the formation of endogenous TRPV1 agonists after application of linoleic acid to cultured neurons. ABSTRACT Recently, specific oxidized linoleic acid metabolites (OLAMs) have been identified as transient receptor potential vanilloid 1 (TRPV1) channel agonists that contribute to inflammatory and heat hyperalgesia mechanisms, yet the specific mechanism responsible for OLAM synthesis in sensory neurons is unknown. Here, we use molecular, anatomical, calcium imaging, and perforated patch electrophysiology methods to demonstrate the specific involvement of cytochrome P450 enzymes (CYPs) in the oxidation of linoleic acid leading to neuronal activation and show that this is enhanced under inflammatory conditions. Additional studies evaluated CYP expressions in the native rat trigeminal ganglia (TG) tissue and cultures as well as changes in their expression pattern following the induction of peripheral inflammation. Fourteen of 20 candidate transcripts were detected in native TG, and 7 of these displayed altered expression under cultured conditions. Moreover, complete Freund’s adjuvant‐induced inflammation of vibrissal pad selectively increased expression of CYP3A23/3A1 and CYP2J4 transcripts in TG. In situ hybridization studies demonstrated broad expression pattern of CYP3A23/3A1 and CYP2J4 within TG neurons. Anatomical studies characterized the expression of CYP3A1 and the CYP2J families within TG sensory neurons, including those with TRPV1, with about half of all TRPV1‐positive neurons showing more prominent CYP3A1 and CYP2J expression. Together, these findings show that CYP enzymes play a primary role in mediating linoleic acid‐evoked activation of sensory neurons and furthermore, implicate the involvement of specific CYPs as contributing to the formation of OLAMs that act as TRPV1 agonists within this subpopulation of nociceptors.

Oxidized linoleic acid metabolite-cytochrome P450 system (OLAM-CYP) is active in biopsy samples from patients with inflammatory dental pain.

Summary The oxidized metabolites of linoleic acid (OLAM)‐cytochrome P450 machinery may play a role in activating peripheral pain pathways even in human tissues such as the dental pulp under inflammatory conditions, thereby suggesting a novel strategy of targeting the OLAMs to inhibit inflammatory pain conditions. Abstract Endogenous TRPV1 agonists such as oxidized linoleic acid metabolites (OLAMs) and the enzymes releasing them [eg, cytochrome P450 (CYP)] are up‐regulated after inflammation in the rat. However, it is not known whether such agonists are elevated in human inflammatory pain conditions. Because TRPV1 is expressed in human dental pulp nociceptors, we hypothesized that OLAM‐CYP machinery is active in this tissue type and is increased under painful inflammatory conditions such as irreversible pulpitis (IP). The aim of this study was to compare CYP expression and linoleic acid (LA) metabolism in normal vs inflamed human dental pulp. Our data showed that exogenous LA metabolism was significantly increased in IP tissues compared to normal tissues and that pretreatment with a CYP inhibitor, ketoconazole, significantly inhibited LA metabolism. Additionally, extracts obtained from LA‐treated inflamed tissues evoked significant inward currents in trigeminal ganglia neurons and were blocked by pretreatment with the TRPV1 antagonist IRTX. Moreover, extracts obtained from ketoconazole‐pretreated inflamed tissues significantly reduced inward currents in trigeminal ganglia neurons. These data suggest that LA metabolites produced in human inflamed tissues act as TRPV1 agonists and that the metabolite production can be targeted by CYP inhibition. In addition, immunohistochemical analysis of 2 CYP isoforms, CYP2J and CYP3A1, were shown to be predominately expressed in immune cells infiltrating the inflamed dental pulp, emphasizing the paracrine role of CYP enzymes in OLAM regulation. Collectively, our data indicate that the machinery responsible for OLAM production is up‐regulated during inflammation and can be targeted to develop potential analgesics for inflammatory‐induced dental pain.

Direct Effect of Endodontic Sealers on Trigeminal Neuronal Activity

INTRODUCTION Endodontic sealers are selected on the basis of their antimicrobial properties and ability to provide a tight seal. Sealer extrusions, whether intentional or unintentional, are common during obturation procedures. Such events have been correlated with increased postoperative discomfort and persistent pain states. However, the mechanisms underlying this phenomenon are largely unknown. Thus, we sought to evaluate the effect of commonly used endodontic sealers on peripheral nociceptors. We hypothesized that endodontic sealers can directly activate trigeminal nociceptors in a concentration-dependent manner, resulting in release of calcitonin gene-related peptide (CGRP), a potent modulator of neurogenic inflammation. METHODS Rat trigeminal sensory neurons were exposed in vitro to vehicle, zinc oxide-eugenol (ZOE)-based sealer, AH Plus, EndoSequence BC sealer, or RealSeal SE. Neuronal activation was measured by quantification of neuropeptide (CGRP) release. In addition, cultured neurons were also subjected to the set form of all 4 sealers. The concentration of CGRP released was quantified by using a radioimmunoassay. Data were analyzed by using one-way analysis of variance with Newman-Keuls multiple comparison post hoc test. RESULTS Both ZOE-based sealer and AH Plus in their fresh form evoked greater CGRP release than the control groups. Conversely, EndoSequence BC and RealSeal sealers both reduced basal GCRP release at all concentrations tested. Evaluation of the set sealers revealed that only ZOE-based sealer evoked significant CGRP release compared with its control group. CONCLUSIONS Overall, our results suggest that sealers can directly activate trigeminal nociceptors, leading to a robust release of CGRP, and may therefore lead to pain and neurogenic inflammation. This direct activation along with the immunologic response may underlie the symptoms and flare-up occurrences often seen with sealer extrusions.

Central activation of TRPV1 and TRPA1 by novel endogenous agonists contributes to mechanical and thermal allodynia after burn injury

The primary complaint of burn victims is an intense, often devastating spontaneous pain, with persistence of mechanical and thermal allodynia. The transient receptor potential channels, TRPV1 and TRPA1, are expressed by a subset of nociceptive sensory neurons and contribute to inflammatory hypersensitivity. Although their function in the periphery is well known, a role for these TRP channels in central pain mechanisms is less well defined. Lipid agonists of TRPV1 are released from peripheral tissues via enzymatic oxidation after burn injury; however, it is not known if burn injury triggers the release of oxidized lipids in the spinal cord. Accordingly, we evaluated whether burn injury evoked the central release of oxidized lipids. Analysis of lipid extracts of spinal cord tissue with HPLC-MS revealed a significant increase in levels of the epoxide and diol metabolites of linoleic acid: 9,10-DiHOME, 12,13-DiHOME, 9(10)-EpOME, and 12(13)-EpOME, that was reduced after intrathecal (i.t.) injection of the oxidative enzyme inhibitor ketoconazole. Moreover, we found that these four lipid metabolites were capable of specifically activating both TRPV1 and TRPA1. Intrathecal injection of specific antagonists to TRPV1 (AMG-517) or TRPA1 (HC-030031) significantly reduced post-burn mechanical and thermal allodynia. Finally, i.t. injection of ketoconazole significantly reversed post-burn mechanical and thermal allodynia. Our data indicate that spinal cord TRPV1 and TRPA1 contributes to pain after burn and identifies a novel class of oxidized lipids elevated in the spinal cord after burn injury. Since the management of burn pain is problematic, these findings point to a novel approach for treating post-burn pain.

Effect of Bacterial Biofilm on the Osteogenic Differentiation of Stem Cells of Apical Papilla

Introduction Although clinical success in regenerative endodontics is substantially high, histological success is limited to finding bone/cementum‐like tissue instead of dentin within the canal space. The aims of this study were to investigate (1) the effect of bacterial biofilm on osteogenic gene expression in stem cells of the apical papilla (SCAP) and (2) the effect of bacterial antigens on the functional differentiation of SCAP into a mineralizing phenotype. Methods Using an ex vivo organotypic root canal model and an American Association of Endontists‐recommended regenerative endodontic procedures, we evaluated SCAP differentiation in the presence and absence of an Enterococcus faecalis biofilm. Gene expression analysis for dentinogenic and osteoblastic markers was performed with real‐time polymerase chain reaction. The effect of E. faecalis antigens on SCAP differentiation into mineralizing cells in vitro was evaluated with 2 functional assays: Alizarin Red and alkaline phosphatase activity assays. Results After regenerative endodontic procedures, residual bacteria continued to sustain within the root canal system. SCAP in the presence of E. faecalis biofilm significantly downregulated dentinogenic genes such as dentin sialophosphoprotein and upregulated osteoblastic genes such as bone sialoprotein, osteocalcin, distal‐less homeobox 5, and runt‐related transcription factor 2. E. faecalis antigens significantly inhibited SCAP differentiation into a mineralizing phenotype when alizarin red staining and alkaline phosphatase assays were used in vitro. Conclusions Current disinfection protocols were ineffective in eliminating bacteria from root tips and the levels of the residual bacterial biofilm, and its byproducts, were able to significantly alter osteogenic‐differentiation of SCAP.