## 1 Introduction  
In periodontal disease, bacteria that cause periodontitis trigger the body's inflammatory immune response, resulting in the release of inflammatory cytokines [1]. Inflammatory cytokine production in periodontal tissues induces the production of other cytokines that promote and regulate inflammatory responses [2]. Interleukin (IL)-1\(\beta\) is a potent proinflammatory cytokine with multiple physiological activities [3]. IL-1\(\beta\) has been detected in the periodontal tissues of patients with periodontitis and has been implicated in the progression of periodontitis [4]. The production of inflammatory cytokines involves the induction of reactive oxygen species (ROS) [5], which is a broad classification for chemical compounds containing oxygen that are not fully reduced and, when overexpressed, have cytotoxic properties that damage proteins and DNA [6]. In periodontal disease, the induction of ROS is stimulated, resulting in redox imbalance in the periodontal tissue and oxidative stress [7].  
There are a number of naturally occurring substances, many of which have been shown to be effective as therapeutic agents and have been used extensively against disease [8]. Shikonin (molecular formula: C\({}_{16}\)H\({}_{16}\)O\({}_{5}\), structural formula: Figure 1), a natural naphthalene, is one such bioactive compound extracted from Lithospermrum erythrohizon [9]. Interest in shikonin has increased owing to its beneficial effects, such as the promotion of wound healing and antitumor, antibacterial, and anti-inflammatory effects [10]. Shikonin has been reported to delay the onset of arthritis [11] and improve sepsis-induced lung injury [12]. Shikonin has been reported to cause cell necrosis at high concentrations by inducing the overproduction of intracellular ROS [13]; however, at low concentrations, an increasing number of studies have shown the antioxidant and anti-inflammatory effects of shikonin. Shikonin has been reported to reduce oxidative stress and inflammation and attenuate acute liver injury [14]. It has been suggested that shikonin may also be effective against periodontal disease by inhibiting the production of inflammatory cytokines in periodontal ligament cells [15].  
Non-protein-coding RNA molecules known as microRNAs (miRNAs) consist of short nucleotide sequences [16]. They are involved in the post-transcriptional regulation and modulation of target messenger RNA (mRNA) expression [17]. MiRNAs are involved in the expression of many mRNAs and influence processes such as cell proliferation, differentiation, and inflammation [18]. One of the miRNAs, miRNA (miR)-146a, has been reported to be involved in many diseases, including diabetes and osteoporosis [19; 20]. It has been suggested that miR-146a expression is higher in gingiva with periodontitis in healthy gingiva [21]. MiR-146a may contribute to the regulation of inflammatory and oxidative stress responses and play an important role in the pathogenesis and treatment of periodontal diseases [22].  
Previously, our findings indicated that shikonin, when adjusted for concentration, enhanced wound healing in human gingival fibroblasts (hGFs), which is crucial for the regeneration of periodontal tissues [23]. However, the effects of concentration-adjusted shikonin on other responses in periodontal tissues are unknown. We hypothesized that shikonin may have an inhibitory effect on inflammatory response and oxidative stress in periodontal tissue and that miR-146a may be involved in this effect. Therefore, this study sought to examine shikonin's anti-inflammatory and antioxidant properties in human gingival fibroblasts (hGFs) under IL-1\(\beta\)-stimulated inflammation. Additionally, this study aimed to explore how shikonin influences the expression of miR-146a.