Inhibitory Effect of Lignans from Myristica fragrans on LPS-induced NO Production in RAW264.7 Cells

Abstract

Inflammation is a beneficial host response to foreign challenge or tissue injury that leads ultimately to the restoration of tissue structure and function. Inflammation involves a complex web of intercellular cytokine signals. Activated monocytes and/or macrophages release a variety of inflammatory mediators, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), reactive oxygen species, prostaglandin E2 (PGE2) and nitric oxide (NO). A normal inflammatory response is self-limiting and involves the down-regulation of pro-inflammatory protein expression, increased expression of anti-inflammatory proteins and a reversal in the vascular changes that facilitated the initial immune cell recruitment process. Nitric oxide (NO) is a short-living free radical that is produced from L-arginine by catalytic reaction of NO synthases (NOSs) within mammalian immune, cardiovascular and neural systems, where it functions as a signaling or cytotoxic molecule. Cyclooxygenase (COX), an enzyme also known as prostaglandin (PG) H synthase (EC 1.14.99.1), converts arachidonic acid to prostaglandins, which play a crucial role as mediators of inflammatory responses. Myristica fragrans Houtt (Myristicaceae) is an aromatic evergreen tree cultivated in South Africa India, and other tropical countries. The seed and aril of the fruit of M. fragrans are commonly known as nutmeg and mace, respectively. Since the Middle Ages, nutmeg has been used as a carminative, stimulant, narcotic, emmenagogue and abortifacient. Nutmeg is also prescribed for medicinal purposes in Asia to treat many diseases, such as rheumatism, muscle spasm, decreased appetite and diarrhea. It has shown antioxidant, anti-inflammatory, protein tyrosine phosphatase 1B inhibitory, hepatoprotective and acetylcholine esterase inhibitory activities. In continuing investigation for discovering inhibitors on LPS-induced NO production in macrophage RAW264.7 cells, studies of the EtOAc-soluble fraction from the seeds of M. fragrans resulted in the isolation of a new lignan (1), along with five known ones (2-6). This paper describes the isolation and structural elucidation of the isolates, as well as the evaluation of their inhibitory activity on LPS-induced NO production in macrophage RAW264.7 cells. The MeOH extract of the seeds of M. fragrans was partitioned into hexane-, EtOAcand n-BuOH-soluble fractions. Chromatographic purification of the ethyl acetate fraction led to the isolation of six compounds (1-6) (Fig. 1). The structures of known compounds were identified as (8R,8'S)-