Propargylglycine decreases neuro-immune interaction inducing pain response in temporomandibular joint inflammation model

Sulfide and polysulfide as pronociceptive mediators: Focus on Cav3.2 function enhancement and TRPA1 activation

Reactive sulfur species including sulfides, polysulfides and cysteine hydropersulfide play extensive roles in health and disease, which involve modification of protein functions through the interaction with metals bound to the proteins, cleavage of cysteine disulfide (S-S) bonds and S-persulfidation of cysteine residues. Sulfides over a wide micromolar concentration range enhance the activity of Cav3.2 T-type Ca2+ channels by eliminating Zn2+ bound to the channels, thereby promoting somatic and visceral pain. Cav3.2 is under inhibition by Zn2+ in physiological conditions, so that sulfides function to reboot Cav3.2 from Zn2+ inhibition and increase the excitability of nociceptors. On the other hand, polysulfides generated from sulfides activate TRPA1 channels via cysteine S-persulfidation, thereby facilitating somatic, but not visceral, pain. Thus, Cav3.2 function enhancement by sulfides and TRPA1 activation by polysulfides, synergistically accelerate somatic pain signals. The increased activity of the sulfide/Cav3.2 system, in particular, appears to have a great impact on pathological pain, and may thus serve as a therapeutic target for treatment of neuropathic and inflammatory pain including visceral pain.

Weakening of M1 macrophage and bone resorption in periodontitis cystathionine γ-lyase-deficient mice

OBJECTIVES

Cystathionine-γ-lyase (CTH) has been proved to involve in inflammation and bone remolding, implying its potential role in the progression of periodontitis. This study was aimed to investigate the function of CTH and its relation to the macrophage polarization in periodontitis.

MATERIALS AND METHODS

Bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Cth knockout (Cth-/- ) mice were stimulated with lipopolysaccharide (LPS) in vitro and pro-inflammatory cytokines were analyzed by qRT-PCR. Ligature-induced periodontitis was established on WT and Cth-/- mice. Histological analysis, tartrate-resistant acid phosphatase staining, immunostaining, and Western blot were performed to analyze the periodontium destruction and M1 macrophage polarization.

RESULTS

Cth expression in BMDMs was upregulated upon increasing LPS stimulation. Deletion of Cth suppressed BMDMs inflammatory response with decreased Il1b, Il6, and Tnf mRNA. Cth-/- mice with periodontitis showed attenuated bone loss and impaired osteoclast differentiation compared with WT. Moreover, Cth knockout hindered M1 macrophage polarization, reduced the expression of IL-1β, IL-6, and TNF-α in periodontally diseased tissue.

CONCLUSION

This study demonstrated that CTH played an important role in regulating the inflammatory responses and periodontitis tissue destruction. Importantly, Cth knockout suppressed M1 macrophages polarization in periodontitis.

Preclinical orofacial pain assays and measures and chronic primary orofacial pain research: where we are and where we need to go

Chronic primary orofacial pain (OFP) conditions such as painful temporomandibular disorders (pTMDs; i.e., myofascial pain and arthralgia), idiopathic trigeminal neuralgia (TN), and burning mouth syndrome (BMS) are seemingly idiopathic, but evidence support complex and multifactorial etiology and pathophysiology. Important fragments of this complex array of factors have been identified over the years largely with the help of preclinical studies. However, findings have yet to translate into better pain care for chronic OFP patients. The need to develop preclinical assays that better simulate the etiology, pathophysiology, and clinical symptoms of OFP patients and to assess OFP measures consistent with their clinical symptoms is a challenge that needs to be overcome to support this translation process. In this review, we describe rodent assays and OFP pain measures that can be used in support of chronic primary OFP research, in specific pTMDs, TN, and BMS. We discuss their suitability and limitations considering the current knowledge of the etiology and pathophysiology of these conditions and suggest possible future directions. Our goal is to foster the development of innovative animal models with greater translatability and potential to lead to better care for patients living with chronic primary OFP.

Triangular-shaped homologous heterostructure as photocatalytic H2S scavenger and macrophage modulator for rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is a chronic arthropathy causing cartilage destruction, bone erosion, and even disability. Although some advances in RA treatment have been made based on inflammatory cytokine inhibition, long-term treatment and drug effect have been restrained by severe side effects. Herein, we developed a resveratrol (RSV)-loaded Ag/Ag₂S triangular-shaped homologous heterostructure with polyethylene glycol/folic acid (PEG/FA) modification (Ag/Ag₂S-PEG-FA/RSV NTs) to simultaneously suppress inflammatory cytokine over-expression through photocatalytic H₂S scavenging and macrophage polarization stimulation. On one hand, the over-expressed H₂S, which acted as a pro-inflammatory mediator to activate the MAPK/ICAM-1 pathway and exacerbate inflammation, was eliminated through photocatalysis. The homologous Ag and Ag₂S of the heterostructure enhanced electron separation and transfer by acting as a charge acceptor and electron generator, respectively, which restrained electron/hole recombination and promoted photocatalysis efficiency. Additionally, the intrinsic superoxide dismutase (SOD) and catalase (CAT) activity of Ag decomposed the reactive oxygen species (ROS) over-expressed in the RA microenvironment, which supplied O₂ for the photocatalytic H₂S scavenging progress. On the other hand, RSV, a natural product with anti-inflammatory activity, could be delivered to the inflammatory joint by the targeting effect of PEG-FA, thus inhibiting the IκB/NF-κB pro-inflammatory pathway to induce macrophage interconversion balance from M1 to M2. As expected, the Ag/Ag₂S-PEG-FA/RSV NTs exhibited H₂S scavenging capacity and modulated macrophage polarization to reduce the inflammatory cytokine level and halt RA progression in vitro and in vivo. Overall, this study revealed a therapeutic strategy with high efficacy, which opens broad prospects for RA treatment.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Limonene, a citrus monoterpene, non-complexed and complexed with hydroxypropyl-β-cyclodextrin attenuates acute and chronic orofacial nociception in rodents: Evidence for involvement of the PKA and PKC pathway

BACKGROUND

Chronic orofacial pain is a serious public health problem with a prevalence of 7-11% in the population. This disorder has different etiologies and characteristics that make pharmacological treatment difficult. Natural products have been shown to be a promising source of treatments for the management of chronic pain, as an example the terpenes.

PURPOSE

The aim of this study was to evaluate the anti-nociceptive and anti-inflammatory effects of one of these terpenes, d-limonene (LIM - a common monoterpene found in citrus fruits) alone and complexed with hydroxypropyl-β-cyclodextrin (LIM/HPβCD) in preclinical animal models.

METHODS

Orofacial pain was induced by the administration of hypertonic saline on the corneal surface, the injection of formalin into the temporomandibular joint (TMJ), or chronic constriction injury of the infraorbital nerve (CCI-IoN). The study used male Wistar rats and Swiss mice treated with LIM (50 mg/kg), LIM/HPβCD (50 mg/kg), vehicle (control), gabapentin or morphine, and eyes wiping (induced by hypertonic saline), face rubbing (formalin-induced in TMJ) or mechanical hyperalgesia (provoked by CCI-IoN) were assessed. Additionally, ELISA was used to measure TNF-α, and western blot analysis to assess levels of PKAcα, NFκB, p38MAPK and phosphorylated PKC substrates. Serum levels of aspartate aminotransferase (AST) and alanine transferase (ALT) were also evaluated.

RESULTS

LIM and LIM/HPβCD significantly reduced (p < 0.001) corneal nociception and formalin-induced TMJ nociception. In addition, both substances attenuated (p < 0.001) mechanical hyperalgesia in the CCI-IoN model. The antinociceptive effect induced by LIM and HPβCD/LIM was associated with decreased TNF-α levels, downregulation of the NFκB and p38MAPK signalling pathways and reduced PKC substrate phosphorylation and PKA immunocontent. Moreover, the results demonstrated that complexation with HPβCD was able to decrease the therapeutic dose of LIM.

CONCLUSION

LIM was found to be a promising molecule for the treatment of orofacial pain due to its capacity to modulate some important mediators essential to the establishment of pain, and HPβCD can be a key tool to improve the profile of LIM.

TNFα regulates the expression of the CSE gene in HUVEC

The hydrogen sulfide (H₂S)/cystathionine γ-lyase (CSE) signaling pathway is involved in several inflammatory conditions, where tumor necrosis factor-α (TNFα) is one of the inflammatory cytokines activated during sepsis. Therefore, the present study investigated the role of the NF-κB transcription factor binding site in the transcriptional regulation of the CSE gene in 293T cells following treatment with TNFα using luciferase assays, as well as using western blotting and reverse transcription-quantitative PCR to examine the effect of TNFα on CSE expression in HUVECs. After transfected 293T cells were incubated with various concentrations of TNFα for 1, 3, and 6 h, the wild-type promoter of the CSE gene increased significantly at 1 h compared to 0 h. By contrast, after the transfected 293T cells were incubated with various concentrations of TNFα for 1 h, the mutant-type promoter activity of the CSE gene decreased significantly compared to the wild-type. These results revealed that the DNA sequence GGGACATTCC on the CSE gene promoter was directly associated with the transcriptional regulation of the CSE gene in Human cells (293T cells) that's were treated with TNFα. This suggests that TNFα affects CSE gene expression, such that vascular endothelial cells respond to TNFα in the blood by regulating CSE expression. The regulatory mechanisms associated with the effects of TNFα on the transcriptional regulation of the CSE gene in HUVECs and the NF-κB pathway warrant further investigation.

A Systematic Review of Rat Models With Temporomandibular Osteoarthritis Suitable for the Study of Emerging Prolonged Intra-Articular Drug Delivery Systems

PURPOSE

Development of minimally invasive therapies for temporomandibular joint osteoarthritis (TMJOA) has focused on drug intra-articular injections to avoid the systemic adverse effects experienced when these substances are administered orally. Therefore, we performed a systematic review to answer the question "Which method of induction of a TMJOA-related pain model in rats leads to prolonged painful symptoms, allowing the best assessment of a sustained drug delivery system?"

MATERIALS AND METHODS

Following the PRISMA guidelines, we searched MEDLINE for papers published from 1994 to July 2020 on a TMJ arthritis model using rats. We identified the means of pain induction and of nociception assessment. We assessed protocol bias using an adaptation of the QUADAS-2 tool. Animal selection, the reference standard method of pain assessment, applicability of a statistical assessment, and flow and timing were assessed.

RESULTS

Of the 59 full papers we reviewed, 41 performed no pain assessment after the first 7 days following induction of the TMJ-related pain model. We eventually identified 18 long-term TMJOA-related pain models. Pain was induced by injection of toxic substances, most commonly Freund's complete adjuvant (50 μg per 50 μl), formalin at various concentrations, or monosodium iodoacetate (0,5 mg per 50 μl), into the TMJ, or by physical methods. Few studies reported data on pain after 21 days of follow-up. Heterogeneity of induction methods, pain assessment methods, and flow and timing biases precluded a meta-analysis.

CONCLUSIONS

Given that pain is 1 of the main symptoms of TMJOA, experimental study protocols should include long-term pain assessment.

Role of H2S in pain: Growing evidences of mystification

There have been studies suggesting the pain attenuating as well as pain inducing actions of hydrogen sulfide (H₂S). Exogenous administrated H₂S may be antinociceptive or pronociceptive, while the endogenous H₂S is pronociceptive. Experimental studies have shown that pharmacological inhibitors of H₂S biosynthetic enzymes may attenuate nociceptive as well as neuropathic pain. It suggests that nerve injury or inflammatory agents may induce the expression of H₂S biosynthetic enzymes to increase the endogenous production of H₂S, which acts as a pain neurotransmitter to produce pain. The endogenous H₂S may act through different mechanisms including opening of T-type calcium channels, activation of voltage-gated sodium channels, suppression of potassium channels, activation of TRPA1, TRPV1 and TRPC6 channels, upregulation of spinal NMDA receptors and sensitization of purinergic receptors. Exogenous administration of H₂S/precursors/donors attenuates or facilitates pain. It may be hypothesized that local administration of H₂S may cause pain; while it's systemic administration may attenuate pain. The doses of H₂S may also influence the pain response and H₂S in low doses may contribute in reducing pain, while H₂S in high doses may contribute in relieving pain. Accordingly, enzymatic inhibitors of H₂S synthesis or systemic administration of slow H₂S releasing agents/low dose H₂S donors may be useful in attenuating nociceptive and neuropathic pain. The present review describes the dual role of H₂S in pain attenuation and pain induction along with possible mechanisms.

Progesterone Attenuates Allodynia of Inflamed Temporomandibular Joint through Modulating Voltage-Gated Sodium Channel 1.7 in Trigeminal Ganglion

Background

Women with temporomandibular disorders (TMDs) experience some amelioration of pain during pregnancy. Progesterone increases dramatically and steadily during pregnancy. Sodium channel 1.7 (Nav1.7) plays a prominent role in pain perceptions, as evidenced by deletion of Nav1.7 alone leading to a complete loss of pain. In a previous study, we showed that Nav1.7 in trigeminal ganglion (TG) is involved in allodynia of inflamed temporomandibular joint (TMJ). Whether progesterone modulates allodynia of inflamed TMJ through Nav1.7 in TG remains to be investigated.

Methods

The effects of progesterone on sodium currents of freshly isolated TG neurons were examined using whole-cell recording. Female rats were ovariectomized and treated with increasing doses of progesterone for 10 days. Complete Freund's adjuvant was administered intra-articularly to induce TMJ inflammation. TMJ nociceptive responses were evaluated by head withdrawal thresholds. Real-time PCR and Western blotting were used to examine Nav1.7 mRNA and protein expression in TG. Immunohistofluorescence was used to examine the colocalization of progesterone receptors (PRα/β) and Nav1.7 in TG.

Results

Whole-cell recording showed that progesterone could attenuate sodium currents. Moreover, progesterone dose-dependently downregulated Nav1.7 mRNA expression and reduced the sensitivity of TMJ nociception in ovariectomized rats. Furthermore, treatment with progesterone attenuated allodynia of inflamed TMJ in a dose-dependent manner and repressed inflammation-induced Nav1.7 mRNA and protein expression in ovariectomized rats. The progesterone receptor antagonist, RU-486, partially reversed the effect of progesterone on allodynia of inflamed TMJ and TMJ inflammation-induced Nav1.7 mRNA and protein expression.

Conclusion

Progesterone, by modulating trigeminal ganglionic Nav1.7, may represent a promising agent to prevent allodynia of inflamed TMJ.