Antimicrobial Peptides and Biomarkers Induced by Ultraviolet Irradiation Have the Potential to Reduce Endodontic Inflammation and Facilitate Tissue Healing

Abstract

Background: Ultraviolet (UV) irradiation can modulate host immune responses and this approach is a novel application for treating endodontic infections and inflammation in root canals.

Methods: A dataset of UV-induced molecules was compiled from a literature search. A subset of this dataset was used to calculate expression log2 ratios of endodontic tissue molecules from HEPM cells and gingival fibroblasts after 255, 405, and 255/405 nm UV irradiation. Both datasets were analyzed using ingenuity pathway analysis (IPA, Qiagen, Germantown, MD, USA). Statistical significance was calculated using Fisher's exact test and z-scores were calculated for IPA comparison analysis.

Results: The dataset of 32 UV-induced molecules contained 9 antimicrobial peptides, 10 cytokines, 6 growth factors, 3 enzymes, 2 transmembrane receptors, and 2 transcription regulators. These molecules were in the IPA canonical pathway annotations for the wound healing signaling pathway (9/32, p = 3.22 × 10^-11) and communication between immune cells (6/32, p = 8.74 × 10^-11). In the IPA disease and function annotations, the 32 molecules were associated with an antimicrobial response, cell-to-cell signaling and interaction, cellular movement, hematological system development and function, immune cell trafficking, and inflammatory response. In IPA comparison analysis of the 13 molecules, the predicted activation or inhibition of pathways depended upon the cell type exposed, the wavelength of the UV irradiation used, and the time after exposure.

Conclusions: UV irradiation activates and inhibits cellular pathways and immune functions. These results suggested that UV irradiation can activate innate and adaptive immune responses, which may supplement endodontic procedures to reduce infection, inflammation, and pain and assist tissues to heal.

Keywords: UV; UVA; UVB; UVC; antimicrobial peptides; chemokines; cytokines; endodontic; inflammation; pain; tissue healing; ultraviolet irradiation.

Figure 1

A schematic diagram of the proposed effects of UV irradiation on endodontic infection and inflammation, pain, and tissue healing. UV irradiation can kill microorganisms directly (blue line). UV irradiation can also induce host cells to express antimicrobial peptides (AMPs) and chemokines, cytokines, and biomarkers (CCBMs) (blue lines). AMPs can kill microorganisms (red line); induce the production of CCBMs (brown line); and induce chemotaxis, modulate immune responses, assist in wound healing, play a role in angiogenesis, and reduce pain (red lines). CCBMs can kill microorganisms (green line); induce the production of AMPs (brown line); and induce chemotaxis, modulate immune responses, assist in wound healing, play a role in angiogenesis, and reduce pain (green lines).

Figure 2

Expression Log2 ratios of 13 chemokine, cytokine, and biomarker (CCBMs) concentrations reported in tissue culture media of HEPM cells and gingival fibroblasts at 0, 24, and 48 h after treatment with 255 nm, 405 nm, or 255/405 nm UV irradiation. Expression was calculated as the log2 ratio of the mean of each treatment after UV irradiation over the mean of the untreated control for that same cell type, UV irradiation wavelength, and time period. Groups are shown as a heatmap, where blue represents inhibition (negative values), white represents midpoint, and orange represents activation (positive values).

Figure 3

IPA comparison analysis of 18 observations from fibroblasts (observations 1–9) and HEPM cells (observations 10–18) at 0 h (observations 1–3, 10–12), 24 h (observations 4–6, 13–15), and 48 h (observations 7–9, 16–18) after treatment with 255 nm (observations 1, 4, 7, 10, 13, and 16), 405 nm (observations 2, 5, 8, 11, 14, 17), or 255/405 nm (observations 3, 6, 9, 12, 15, and 18) irradiation. Groups are shown as a heatmap, where blue represents inhibition (negative values), white represents midpoint, and orange represents activation (positive values). Numerous IPA canonical pathways were inhibited shortly after irradiation (0 h) but activated at 24 and 48 h. Fibroblasts and HEPM cells both were strongly activated by 405 nm and 255/405 nm UV irradiation treatments.

Figure 4

Schematic diagrams of the wound healing signaling pathway, prepared using Ingenuity Pathway Analysis software (IPA, Qiagen, Germantown, MD), showing both inhibited and activated pathway signaling in HEPM cells 48 h after (A) 255 nm irradiation, (B) 405 nm irradiation, and (C) 255/405 nm irradiation. Signaling starts via TNF binding to the TNF receptor; EGF and TGFA binding to the EGFR; and TGFB binding to the TGFBR. These pathways signal through TRADD and TRAF2 to JNK and through RAS, RAF, and MEK to ERK1/2. Signaling continues to NF-κB, CEBPB, and AP-1 to activate additional CCBMs, leading to proinflammatory responses, disruption of desmosomes, chemoattraction of leukocytes, migration and proliferation of fibroblasts and cells, collagen matrix remodeling, and wound healing pathways. Pathway molecules in red indicate activation and molecules in green indicated inhibition. Signaling connections in orange indicate pathway activation and signaling connections in blue indicate pathway inhibition.

Figure 4

Schematic diagrams of the wound healing signaling pathway, prepared using Ingenuity Pathway Analysis software (IPA, Qiagen, Germantown, MD), showing both inhibited and activated pathway signaling in HEPM cells 48 h after (A) 255 nm irradiation, (B) 405 nm irradiation, and (C) 255/405 nm irradiation. Signaling starts via TNF binding to the TNF receptor; EGF and TGFA binding to the EGFR; and TGFB binding to the TGFBR. These pathways signal through TRADD and TRAF2 to JNK and through RAS, RAF, and MEK to ERK1/2. Signaling continues to NF-κB, CEBPB, and AP-1 to activate additional CCBMs, leading to proinflammatory responses, disruption of desmosomes, chemoattraction of leukocytes, migration and proliferation of fibroblasts and cells, collagen matrix remodeling, and wound healing pathways. Pathway molecules in red indicate activation and molecules in green indicated inhibition. Signaling connections in orange indicate pathway activation and signaling connections in blue indicate pathway inhibition.

Figure 4

Schematic diagrams of the wound healing signaling pathway, prepared using Ingenuity Pathway Analysis software (IPA, Qiagen, Germantown, MD), showing both inhibited and activated pathway signaling in HEPM cells 48 h after (A) 255 nm irradiation, (B) 405 nm irradiation, and (C) 255/405 nm irradiation. Signaling starts via TNF binding to the TNF receptor; EGF and TGFA binding to the EGFR; and TGFB binding to the TGFBR. These pathways signal through TRADD and TRAF2 to JNK and through RAS, RAF, and MEK to ERK1/2. Signaling continues to NF-κB, CEBPB, and AP-1 to activate additional CCBMs, leading to proinflammatory responses, disruption of desmosomes, chemoattraction of leukocytes, migration and proliferation of fibroblasts and cells, collagen matrix remodeling, and wound healing pathways. Pathway molecules in red indicate activation and molecules in green indicated inhibition. Signaling connections in orange indicate pathway activation and signaling connections in blue indicate pathway inhibition.