In vitro Anti-infammatory efects of Thai herb essential oils Nancharee Homnan 1 , Suchitra Thongpraditchote 2 , Mullika Chomnawang 1 , Krit Thirapanmethee 1* 1 Department of Microbiology, Faculty of Pharmacy, Mahidol University, Bangkok, Thailand 2 Department of Physiology, Faculty of Pharmacy, Mahidol University, Bangkok, Thailand ABSTRACT Infammation is a common mechanism of the immune system that protects the host body from injuries caused by physical wounds and non-self-invaders, while chronic infammation might cause tissue damages and is associated with many diseases such as rheumatoid arthritis, Alzheimer’s disease, and various physical dysfunctions. The non-steroidal anti-infammatory drugs (NSAIDs) are widely used because of cyclooxygenase-2 (COX-2) inhibitory function. However, the drugs can also act on COX-1 leading to an unfavorable condition such as irritation of the stomach and increase the risk of bleeding. The aim of this study was to evaluate anti-infammatory efects of 11 Thai herb essential oils on lipopolysaccharide (LPS)-induced infammation in phorbol 12-myristate 13-acetate (PMA) diferentiated human monocyte cell-line (THP-1) cells., The COX-2 activity and level of prostaglandin E2 (PGE2) were examined. The results showed that among 11 Thai herb essential oils, lesser galanga essential oils exhibited the signifcant COX-2 and PGE2 inhibitory activities. β-ocimene, the major compound of lesser galanga essential oil, was further evaluated for the anti-infammatory efects. It was clearly demonstrated that β-ocimene efectively inhibited COX-2 activity and lowered PGE2 level in a dose- dependent manner with IC 50 of 75.64 and less than 20 µg/mL, respectively. It was noteworthy that lesser galanga essential oil possessed higher inhibitory efect on COX-2 activity and PGE2 levels than its major compound, β-ocimene. In conclusion, essential oil of lesser galanga and its major compound could be potentially developed as the anti-infammatory agents. 1. INTRODUCTION Infammation is a common mechanism of the immune system that protects against injuries caused by physical wounds and non-self-invaders. The infammation response is lead to vascular changes and white blood cell recruitment at the site which has been invaded or can be stimulated throughout the body. During infammation, white blood cells secrete many infammatory cytokines such as interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) and infammatory mediators such as nitric oxide (NO) and prostaglandin E 2 (PGE 2 ), which are generated by inducible nitric Research article https://www.pharmacy.mahidol.ac.th/journal/ © Faculty of Pharmacy, Mahidol University (Thailand) 2020 *Corresponding author: krit.thi@mahidol.edu Pharmaceutical Sciences Asia Pharm Sci Asia 2020; 47 (2), 153-163 DOI:10.29090/psa.2020.02.018.0047 KEYWORDS: THP-1 cell line; Anti-infammatory; Cyclooxygenase-2; Prostaglandin E2; Essential oils