Substance P enhances expression of lipopolysaccharide-induced inflammatory factors in dental pulp cells

Role of Lipopolysaccharide, Derived from Various Bacterial Species, in Pulpitis—A Systematic Review

Lipopolysaccharide (LPS) is widely used for induction of inflammation in various human tissues, including dental pulp. The purpose of this study was to summarize current medical literature focusing on (1) cell types used by researchers to simulate dental pulp inflammation, (2) LPS variants utilized in experimental settings and how these choices affect the findings. Our study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We searched for studies reporting outcomes of lipopolysaccharide application on dental pulp cells in vitro using electronic databases: MEDLINE, Web of Science and Scopus. Having gathered data from 115 papers, we aimed to present all known effects LPS has on different cell types present in dental pulp. We focused on specific receptors and particles that are involved in molecular pathways. Our review provides an essential foundation for further research using in vitro models of pulpitis.

The SP-TLR axis, which locally primes the nasal mucosa, is impeded in patients with allergic rhinitis

Background

Substance P (SP) and toll‐like receptors (TLRs) contribute to airway disease, particularly during viral infection. We recently demonstrated that SP can act as an initial response to viral stimuli in the upper airway by upregulating TLRs in the nasal epithelia (the SP‐TLR axis). Patients with allergic rhinitis (AR) suffer from prolonged airway infections. The aim of the present study was to examine if patients with AR exhibit a disturbance in the SP‐TLR axis.

Method

Human nasal biopsies and human nasal epithelial cells (HNEC) from healthy volunteers and patients with AR were cultured in the presence of SP. Epithelial expression of TLR4, neutral endopeptidase (NEP) and neurokinin 1 (NK1) were evaluated with flow cytometry and/or quantitative polymerase chain reaction after 30 min to 24 h. The effect of SP on nasal lipopolysaccharide‐induced interleukin‐8 (IL‐8) release was investigated.

Results

SP stimulation of tissue from healthy volunteers resulted in a transient increase of the TLR4 expression, whereas stimulation of AR patient‐derived material led to a delayed and prolonged upregulation of TLR4. NEP expression in HNEC was lower in AR than healthy controls whereas NK1 receptor expression was increased. SP pretreatment increased TLR4‐dependent IL‐8 expression in healthy controls, but not in AR.

Conclusions

SP‐induced regulation of TLR4 in the human nasal mucosa is disturbed in AR. An altered SP‐mediated innate immune response may contribute to the dysfunctional and often prolonged responses to infection in AR.

Overexpression of receptor for advanced glycation end products and high-mobility group box 1 in human dental pulp inflammation

High mobility group box 1 (HMGB1), a nonhistone DNA-binding protein, is released into the extracellular space and promotes inflammation. HMGB1 binds to related cell signaling transduction receptors, including receptor for advanced glycation end products (RAGE), which actively participate in vascular and inflammatory diseases. The aim of this study was to examine whether RAGE and HMGB1 are involved in the pathogenesis of pulpitis and investigate the effect of Prevotella intermedia (P. intermedia) lipopolysaccharide (LPS) on RAGE and HMGB1 expression in odontoblast-like cells (OLC-1). RAGE and HMGB1 expression levels in clinically inflamed dental pulp were higher than those in healthy dental pulp. Upregulated expression of RAGE was observed in odontoblasts, stromal pulp fibroblasts-like cells, and endothelial-like cell lining human pulpitis tissue. Strong cytoplasmic HMGB1 immunoreactivity was noted in odontoblasts, whereas nuclear HMGB1 immunoreactivity was seen in stromal pulp fibroblasts-like cells in human pulpitis tissue. LPS stimulated OLC-1 cells produced HMGB1 in a dose-dependent manner through RAGE. HMGB1 translocation towards the cytoplasm and secretion from OLC-1 in response to LPS was inhibited by TPCA-1, an inhibitor of NF-κB activation. These findings suggest that RAGE and HMGB1 play an important role in the pulpal immune response to oral bacterial infection.

Role of SIRT1 in heat stress- and lipopolysaccharide-induced immune and defense gene expression in human dental pulp cells

INTRODUCTION

Although bacterial infection and heat stress are common causes of injury in human dental pulp cells (HDPCs), little is known about the potential defense mechanisms mediating their effects. This study examined the role of SIRT1 in mediating heat stress and lipopolysaccharide (LPS)-induced immune and defense gene expression in HDPCs.

METHODS

HDPCs were exposed to heat stress (42°C) for 30 minutes after stimulation with LPS (1 μg/mL) for 48 hours. The expression of defense genes was evaluated by reverse-transcriptase polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay.

RESULTS

LPS and heat stress synergistically increased the expression of SIRT1 and immune and defense genes such as interleukin (IL)-8, hemeoxygenase-1 (HO-1), and human β-defensin 2 (hBD-2). Resveratrol enhanced LPS- and heat stress-induced expression of HO-1 and hBD-2 but reduced IL-8 messenger RNA levels. The stimulation of HO-1 and hBD-2 messenger RNA expression by LPS and heat stress was inhibited by sirtinol; SIRT1 small interfering RNA; and inhibitors of p38, ERK, JNK, and nuclear factor κB.

CONCLUSIONS

These results show for the first time that SIRT1 mediates the induction of immune and defense gene expression in HDPCs by LPS and heat stress. SIRT1 may play a pivotal role in host immune defense system in HDPCS.

Localization of substance P-induced upregulated interleukin-8 expression in human dental pulp explants

AIM

To localize ex vivo expression of interleukin-8 (IL-8) induced by substance P (SP) in human dental pulps.

METHODOLOGY

Intact caries-free, freshly extracted third molars (n = 20) were collected from patients (15-25 years old). The teeth were split and pulpal tissue was obtained and stored in Dulbecco's modified Eagle medium. Human dental pulp tissue explants were stimulated with SP. Expression of IL-8 in pulp explants was detected and localized by immunohistochemistry.

RESULTS

Moderated IL-8 immunoreactivities were detected mainly in the cell-rich zone in pulp tissues 12 h after tumour necrosis factor alpha (TNF-alpha) stimulation (positive controls), whereas only weak IL-8 expression was observed in tissues stimulated with SP at the same time interval. These data did not differ from those in negative controls. Increased IL-8 expression in pulp explants after 24 h of SP stimulation was noted compared with negative controls and located in fibroblast-like cells, blood vessel-associated cells and extracellular matrix in the central zone and cell-rich zone of pulp explants. Tissues stimulated with TNF-alpha for 24 h (positive controls) revealed weak IL-8 immunoreactivities with altered cell morphology.

CONCLUSIONS

Substance P induces IL-8 expression and was located in fibroblast-like pulp cells, blood vessel-associated cells and extracellular matrix of human dental explants. These data support the hypothesis that neuropeptide (SP) coordinates the modulation of pulpal inflammation via up-regulating chemokine IL-8.

Substance P-induced cyclooxygenase-2 expression in human umbilical vein endothelial cells

Substance P (SP) is a neuropeptide involved in neurogenic inflammation and an agonist for NK(1), NK(2), and NK(3) receptors. SP induces prostaglandin (PG) production in various cell types, and these eicosanoids are responsible for numerous inflammatory and vascular effects. Cyclooxygenase (COX) are needed to convert arachidonic acid to PGs. The study evaluated the effect of SP on COX expression in human umbilical vein endothelial cells (HUVEC). COX-2 protein expression was upregulated by SP with a peak at 100 nM and at 20 h; in the same experimental conditions COX-1 protein expression was unchanged. A correlation between COX-2 expression and PGI(2) and PGE(2) release was detected. Dexamethasone (DEX) inhibited SP-mediated COX-2 expression. Mitogen-activated protein kinases (MAPK) p38 and p42/44 were activated by SP, whereas SB202190 and PD98059, inhibitors of these kinases, blocked COX-2 expression. 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2(5H)-furanone (DFU), an experimental selective COX-2 inhibitor, blocked SP-induced PG release. By RT-PCR and Western blot analysis, we demonstrated that NK(1) and NK(2) but not NK(3) receptors are present on HUVEC. Selective NK(1) and NK(2) agonists, namely [Sar(9), Met(O(2))(11)]SP and [beta-Ala(8)] NKA(4-10), upregulated COX-2 protein expression and PG production, whereas senktide (Suc-Asp-Phe-MePhe-Gly-Leu-Met-NH(2)), a selective NK(3) agonist, was ineffective in this respect. The NK(1) selective antagonist L703,606 ((cis)-2-(diphenylmethyl)-N-((2-iodophenyl)-methyl)-1-azabicyclo(2.2.2)octan-3-amine) and the NK(2) selective antagonist SR 48,968 ((S)-N-methyl-N-(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4 dichlorophenyl)butyl) benzamide) competitively antagonised SP-induced effects. The study shows HUVEC to possess functional NK(1) and NK(2) receptors, which mediate the ability of SP to induce expression of COX-2 in HUVEC, thus showing a previously-undetected effect of SP on endothelial cells.

Interleukin-1 α Alters the Expression of Matrix Metalloproteinases and Collagen Degradation by Pulp Fibroblasts

Matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs) have been suggested to play a role in dental pulp destruction. This study examined the effects of interleukin (IL)-1 alpha on pulp fibroblasts. The ability of these cells to degrade collagen was determined with or without IL-1 alpha utilizing a cell-mediated collagen degradation assay. Reverse transcriptase-polymerase chain reaction was utilized to examine the mRNA expression of multiple MMPs and TIMPs with and without IL-1 alpha, while Western blot analyses and zymography were utilized to examine their protein expression. The collagen degradation mediated by these cells was stimulated by IL-1 alpha and inhibited by MMP inhibitors. IL-1 alpha increased the mRNA expression of MMP-1 and MMP-3, as well as induced MMP-7. Western blot analyses confirmed these results. IL-1 alpha increased the secreted protein level of TIMP-1, while only slightly affected the level of TIMP-2. These results suggest that IL-1 alpha can induce pulp destruction by differentially regulating MMPs and TIMPs.

The effect of cavity preparation on substance P expression in human dental pulp

Substance P (SP) plays an important role during neurogenic inflammation of dental pulp. The purpose of this study was to use a radioimmunoassay for determining the effect of cavity preparation on SP expression in healthy human dental pulp. Ten pulp samples were obtained from healthy premolars where extraction was indicated for orthodontic reasons. Deep cavity preparation (<1 mm remaining dentine thickness) was performed before extraction in five of these bicuspids. All samples were processed and I-SP labeled; SP was quantified by competition assay. The results revealed SP expression in all human pulp samples. Mann-Whitney's U test revealed statistically significant higher expression in pulp from teeth where cavity preparation had been performed compared to control values (p < 0.05). These findings suggest that SP is released during common dental procedures (such as cavity preparation) and its expression may have an important clinical significance in terms of experiencing inflammation and pain.

Expression and Characterization of Vanilloid Receptor Subtype 1 in Human Dental Pulp Cell Cultures

The expression of the vanilloid receptor subtype 1 (VR1, TRPV1) was detected in human dental pulp fibroblasts (PF-10) using RT-PCR, Western blotting, and immunocytochemical analysis. As revealed by ELISA, capsaicin induced IL-6 expression in PF-10 cells, and the VR1 antagonist capsazepine dose-dependently inhibited capsaicin-induced IL-6 production, indicating that capsaicin-induced IL-6 expression is related to VR1 activation. The interaction between capsaicin and mitogen-activated protein kinases (MAPKs) was investigated. The phosphorylation of p38 MAPK and c-Jun NH2-terminal kinase (JNK) were detected after capsaicin stimulation. p38 MAPK is involved in capsaicin-induced IL-6 production, as shown by the use of specific inhibitors of this kinase. The result of EMSA showed that capsaicin inhibited tumor necrosis factor-alpha (TNF-alpha)-induced nuclear factor-kappa B (NF-kappaB) activation in PF-10 cell cultures. These results suggest that the activation of VR1 plays an important role in dental pulp inflammation.

Substance P activates p38 mitogen-activated protein kinase to promote IL-6 induction in human dental pulp fibroblasts

Substance P (SP) induces the expression of proinflammatory cytokines, such as interleukin (IL)-6, which are implicated in pulp inflammation. To determine the signal pathway of SP-induced IL-6, we examined the activities of the mitogen-activated protein kinases (MAPKs) in human dental pulp cell (PF-10) cultures. SP induced the phosphorylation of p38 MAPK within 5 min; this activation persisted for up to 40 min and was independent of the activation of extracellular signal-related kinases (ERK-1 and ERK-2) that were induced after SP stimulation of PF-10 cells. As shown by electrophoretic mobility shift assay p38 MAPK was not involved in SP-induced activation of nuclear factor-kappa B (NF-kappaB). However, p38 MAPK mediated SP-induced IL-6 production, as shown by the use of specific inhibitors of this kinase. Our results suggest that the activation of p38 MAPK is important for NF-kappaB-independent regulator of neurogenic inflammation in dental pulp tissues.