Inhibition of nitric oxide by phenylethanoids in activated macrophages

Nitric oxide (NO) is one of the pro-inflammatory molecules. Some phenylethanoids have been previously shown to possess anti-inflammatory effects. Seven phenylethanoids from the stems of Cistanche deserticola, viz. isoacteoside, tubuloside B, acteoside, 2′-O-acetylacteoside, echinacoside, cistanoside A and tubuloside A, were tested for their effect on NO radical generation by activated murine macrophages. At the concentration of 100–200 μM, all the phenylethanoids reduced (6.3–62.3%) nitrite accumulation in lipopolysaccharide (0.1 μg/ml)-stimulated J774.1 cells. At 200 μM, they inhibited by 32.2–72.4% nitrite accumulation induced by lipopolysaccharide (0.1 μg/ml)/interferon-γ (100 U/ml) in mouse peritoneal exudate macrophages. However, these compounds did not affect the expression of inducible nitric oxide (iNOS) mRNA, the iNOS protein level, or the iNOS activity in lipopolysaccharide-stimulated J774.1 cells. Instead, they showed a clear scavenging effect (6.9–43.9%) at the low concentrations of 2–10 μM of about 12 μM nitrite generated from an NO donor, 1-propanamine-3-hydroxy-2-nitroso-1-propylhydrazino (PAPA NONOate). These results indicate that the phenylethanoids have NO radical-scavenging activity, which possibly contributes to their anti-inflammatory effects.