Inhibition of LPS-induced NO production by the oleogum resin of Commiphora wightii and its constituents

Abstract

Three new (1–3) and five known compounds (4–8) were isolated from the oleogum resin of Commiphora wightii (Arnott.) Bhanol. Their structures were elucidated by spectroscopic and chemical methods. The MeOH extract and the EtOAc-sol. fraction were found to demonstrate significant inhibition of NO formation in lipopolysaccharide (LPS)-activated murine macrophages J774.1 in vitro (IC₅₀ values of 16.4 and 12.8 μg/ml, respectively). When compared with curcumin (IC₅₀ value of 12.3 μM), Z- and E-Guggulsterones (4 and 5, respectively) were the most potent inhibitors of NO production (IC₅₀ values of 1.1 and 3.3 μM, respectively), followed by myrrhanol A (7) and myrrhanone A (8) (IC₅₀ values of 21.1 and 42.3 μM, respectively). Guggulsterone-M (1) and its didehydro derivative (2) were weak inhibitors, while guggulsterols I (6) and Y (3) were inactive (IC₅₀ >500 μM).

Introduction

Nitric oxide (NO) is an important mediator released by murine macrophages and other cells after activation. In response to cytokines and other inflammatory stimuli such as bacterial lipopolysaccharides (LPS), NO is synthesized from l-argenine by the inducible enzyme, nitric oxide synthase (iNOS) (Moncada, 1999, Salvemini et al., 1996, Stuehr and Marletta, 1987). There is growing evidence that overproduction of NO is associated with oxidative stress and with the pathophysiology of various diseases such as rheumatoid arthritis, diabetes, cardiovascular diseases, and chronic inflammation (Moncada et al., 1991). In the search for biologically active compounds from crude drugs that are employed in traditional medicine, the MeOH extract of the oleogum resin of Commiphora wightii was found to demonstrate potent inhibitory activity of NO production in LPS-activated murine macrophages with IC₅₀ value of 16.4 μg/ml) (Table 1).

C. wightii (Arnott.) Bhanol. [syn.=C. mukul (Hook, ex Stocks) Engl.] (Fam. Burseraceae) (Sarin, 1996) is endemic to the Indian peninsula and grows wild in the arid and semi-arid regions of Rajasthan, as well as Sind in Pakistan. The oleogum resin of C. wightii (known as guggul) was reported to be efficacious in the treatment of rheumatoid arthritis, obesity and allied disorders (Nadkarni, 1954). This exudate possesses a variety of pharmacological activities; anti-inflammatory, antirheumatic (Dash, 1974), and hypolipidemic (Satyavati, 1991). Most of these activities are due to the presence, among the secondary metabolites, of a series of steroids, named guggulsterols (such as 4–6), (Bajaj and Dev, 1982, Patil et al., 1972, Kumar and Dev, 1987). Guggulipid, the EtOAc-soluble fraction of guggul, was found to offer considerable benefit for preventing and treating atherosclerotic vascular disease. Z- and E-Guggulsterones (4 and 5, respectively) showed significant inhibition of platelet aggregation (Mester et al., 1979), total serum lipid and total cholesterol (Satyavati, 1991). Other biologically active compounds were recently isolated from guggul (Kimura et al., 2001, Zhu et al., 2001). In order to validate the traditional use of guggul as antiinflammatory remedy and to clarify its pharmacological effects, the MeOH extract of guggul was investigated with the specific objective of identifying the constituents responsible for the inhibitory effect of guggul on LPS-induced NO production in murine macrophage J774.1 cells. Subsequent fractionation of the MeOH extract has led to the isolation and characterization of eight compounds (including three new) from the EtOAc-soluble fraction. This paper reports the isolation and structure elucidation of these compounds, as well as their inhibitory effects of LPS-induced NO formation.