Exploring Biological Activities of a Thai Traditional Remedy Called “Ruean-Mhoon-Nok” and its Plant Ingredient Extracts for the Treatment of Dermatitis

Background: Ruean-Mhoon-Nok (RMN) remedy has been used to treat skin inflammatory diseases (e.g., dermatitis and psoriasis). However, its bioactivities related to traditional use remain unclear. Objective: To investigate the biological activities related to dermatitis treatment of the RMN and its plant ingredient extracts, including the determination of bioactive compounds and stability study. Methods: In vitro anti-inflammatory activities were assessed through the inhibition of NO using Griess reagent in RAW 264.7 cells, as well as IL-6 and TNF-α production using an ELISA test kit. The anti-allergic activity was performed via degranulation assay in RBL-2H3 cells. The microtiter plate-based antibacterial assay was used to assess MIC and MBC. The bioactive compound in the RMN extract was measured by HPLC, while its stability was evaluated under accelerated storage conditions. Results: The RMN extract exhibited a potential inhibitory effect on NO and IL-6 production, while it had a limited effect on inhibition of β-hexosaminidase release. In addition, the RMN extract displayed antibacterial activity against Gram-positive bacteria, including S. epidermis, S. aureus, and MRSA. Among individual plants, Piper wallichii extract displayed outstanding results in all assays compared to the others. The HPLC results confirmed that hydroxychavicol is a major RMN extract constituent, demonstrating potent inhibitory activity on NO and IL-6 productions. However, the RMN extract was unstable when stored under accelerated conditions. Discussion: In this study, we have demonstrated for the first time that the RMN remedy extract could efficiently inhibit some pro-inflammatory cytokines and pathogenic bacteria related to skin inflammation. Key individual plant ingredients (Piper wallichii, Alpinia galanga, and Datura metel) and the major constituent, hydroxychavicol, largely contribute to these effects. Furthermore, the stability of the RMN extract, particularly its hydroxychavicol content, is critical for maintaining its bioactivity, as evidenced by a significant decrease over time under accelerated conditions, emphasizing the need for optimal storage. Conclusion: The RMN remedy and its bioactive compound, hydroxychavicol, have highly promising anti-inflammatory and anti-bacterial properties that might support its traditional use. However, further investigations related to the pathogenesis of dermatitis are required, including preclinical and clinical studies.