Effects of a natural prolyl oligopeptidase inhibitor, rosmarinic acid, on lipopolysaccharide-induced acute lung injury in mice

Abstract

Rosmarinic acid (RA), a polyphenolic phytochemical, is a natural prolyl oligopeptidase inhibitor. In the present study, we found that RA exerted potent anti-inflammatory effects in in vivo models of acute lung injury (ALI) induced by lipopolysaccharide (LPS). Mice were pretreated with RA one hour before challenge with a dose of 0.5 mg/kg LPS. Twenty-four hours after LPS was given, bronchoalveolar lavage fluid (BALF) was obtained to measure pro-inflammatory mediator and total cell counts. RA significantly decreased the production of LPS-induced TNF-a, IL-6, and IL-1β compare with the LPS group. When pretreated with RA (5, 10, or 20 mg/kg) the lung wet-to-dry weight (W/D) ratio of the lung tissue and the number of total cells, neutrophils and macrophages in the BALF were decreased significantly. Furthermore, RA may enhance oxidase dimutase (SOD) activity during the inflammatory response to LPS-induced ALI. And we further demonstrated that RA exerts anti-inflammation effect in vivo models of ALI through suppresses ERK/MAPK signaling in a dose dependent manner. These studies have important implications for RA administration as a potential treatment for ALI.

Figure 1

Effects of RA on TNF-α, IL-6, and IL-1β expression from mice with ALI. Mice were given RA (5 mg/kg, 10 mg/kg, and 20 mg/kg) by intraperitoneal injected 1 h before challenge with LPS. BALF was collected at 24 h following LPS challenge to analyze the inflammatory cytokines TNF-α (A), IL-6 (B), and IL-1β (C).

Figure 2

Effects of RA on the number of total cells, neutrophils, and macrophages in the BALF of LPS-induced ALI mice. Mice were given RA (5 mg/kg, 10 mg/kg, or 20 mg/kg) 1 h prior to an i.n. administration of LPS. BALF was collected at 24 h following LPS challenge to measure the number of total cells (A), neutrophils (B), and macrophages (C).

Figure 3

Effects of RA on the lung W/D ratio and total protein level in the BALF of LPS-induced ALI mice. Mice were given RA (5 mg/kg, 10 mg/kg, and 20 mg/kg) 1 h prior to an i.n. administration of LPS. The lung W/D ratio (A) and total protein concentration in the BALF (B) were determined 24 h after the LPS challenge.

Figure 4

Effects of RA on SOD activity in BALF of LPS-induced mice. BALF was prepared from mice 24 h after LPS challenge. SOD activity was determined by SOD-specific ELISA kits.

Figure 5

Effects of RA on histopathological changes in lung tissues in LPS-induced ALI mice. (A) PBS-challenged mice; (B) RA along treated mice (20 mg/kg); (C) LPS-challenged mice; (D) LPS-challenged mice treated with RA (5 mg/kg); (E) LPS-challenged mice treated with RA (10 mg/kg); (F) LPS-challenged mice treated with RA (20 mg/kg).

Figure 6

Effects of RA on MAPK activation in vivo. Total cellular proteins from lung were analyzed by Western blot with specific antibodies. Experiments were repeated three times and similar results were obtained.

Figure 7

Chemical structure of RA.