**1. Introduction**

Physical traumas, factures, erosions, and local infections, including caries and periodontal disease, on human teeth are among the conditions that lead to endodontic disease [1]. These conditions often create 'barrier defects' that allow entry of opportunistic oral microbiota into the underlying dental pulp tissue. Invading microorganisms can then develop into polymicrobial biofilms containing *Archaebacteria*, *Eubacteria*, yeast, and fungal species [2–4]. The resulting infections can induce inflammation and pain in the root canal systems. The associated craniofacial pain can be severe and significantly impact the patient's quality of life and day-to-day comfort.

Current standard-of-care treatment for endodontic emergencies and treatment include opening the tooth; exposing underlying inflammatory tissue or infection; and creating an open instrumented root canal to the tooth apex, removing the inflammatory tissue, canal

**Citation:** Morio, K.A.; Sternowski, R.H.; Zeng, E.; Brogden, K.A. Antimicrobial Peptides and Biomarkers Induced by Ultraviolet Irradiation Have the Potential to Reduce Endodontic Inflammation and Facilitate Tissue Healing. *Pharmaceutics* **2022**, *14*, 1979. https://doi.org/10.3390/ pharmaceutics14091979

Academic Editors: Scavello Francesco, Jean-Eric Ghia and Amiche Mohamed

Received: 18 August 2022 Accepted: 13 September 2022 Published: 19 September 2022

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exudate, necrotic tissue, and tissue debris [3]. The root canal is then irrigated with sodium hypochlorite (NaOCl) to cleanse and dissolve the canal of the remaining tissue and debris, followed by the irrigation of ethylenediaminetetraacetic acid (EDTA) to remove the smear layer and open the dentinal tubules. The root canal is completed by sealing the canal space with endodontic sealer and gutta percha. The access opening is filled with amalgam or a composite material, and in some cases, a crown is advocated to enhance tooth integrity and adequate seal.

Unfortunately, the standard-of-care treatment is unable to completely clean the canal space and residual pulp tissue debris, missed areas of infection, and remnant microorganisms in the dentin tubules along the sides of the root canal can be left; resulting in potential persist reinfections and apical chronic inflammation [3]. Irrigation with NaOCl is the gold standard, but extrusion of this irrigant apically can be extremely detrimental to the apical tissues. The damaged apical tissues by the NaOCl have little chance to regenerate and heal with no opportunities for activation of local innate or adaptive immune responses in the area.

An emerging and novel concept is to treat instrumented root canals with ultraviolet (UV) irradiation during the standard-of-care treatment procedure [5,6]. UVC irradiation kills microorganisms isolated from endodontic infections [6–8]. Brief treatment with UV irradiation would also modulate host immune responses [9,10]. UV irradiation induces an influx of cells and the production of antimicrobial peptides (AMPs); chemokines, cytokines, and biomarkers (CCBMs); and other molecules that alter lesion pathogenesis and facilitates local tissue healing [9,10]. UVC induces the secretion of CCBMs in HEPM cells and gingival fibroblasts related to endodontic tissue regeneration [6].

In this study, we were interested in identifying molecules expressed or secreted from cells and tissues after UV irradiation. We first searched the PubMed literature to identify AMPs or CCBMs reported to have up- or down-levels of mRNA expression or secretion in response to UV irradiation treatment. We used a bioinformatics approach with ingenuity pathway analysis (IPA, Qiagen, Germantown, MD, USA) to associate their expression with specific innate and adaptive immune responses. We then used the concentrations of 13 CCBMs in tissue culture media of HEPM cells and gingival fibroblasts after treatment with 255, 405, or 255/405 UV irradiation [6] as (i) wet lab experimental data to validate claims from the bioinformatics data, and (ii) to assess the ability of UV irradiation to activate or inhibit cellular pathways related to innate and adaptive immune responses. We hypothesized that UV irradiation would induce host cells and tissues to express AMPs and CCBMs (Figure 1) and these molecules would be important in future treatments designed to reduce endodontic infection and inflammation, modulate endodontic pain, and assist in endodontic tissue healing.

**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).
