The effects of arginase inhibitor on lung oxidative stress and inflammation caused by pneumoperitoneum in rats

Abstract

Background: Pneumoperitoneum-induced oxidative stress and organ injury are known to be associated with nitric oxide (NO) inactivation. Because arginase competes with NO synthase (NOS) for a common substrate, L-arginine, arginase inhibition may increase NO bioavailability. Therefore, we evaluated the ability of the arginase inhibitor, 2 (S)-amino-6-boronohexanoic acid (ABH), to attenuate pneumoperitoneum-induced decrease of NO bioavailability and lung injury.

Methods: Thirty rats were randomly divided into the following groups: 1) the PP-ABH group received a subcutaneous injection of ABH (5 mg/kg) 1 h before induction of pneumoperitoneum (insufflation to intraperitoneal pressure of 15 mmHg for 60 min); 2) the PP group received saline by subcutaneous injection 1 h before induction of pneumoperitoneum; and 3) the control group received saline by subcutaneous injection before a sham procedure with no gas insufflation. After desufflation, blood was collected to determine levels of plasma nitrite, NOS, inflammatory cytokines, and malondialdehyde, a marker of oxidative stress. Lung tissue was obtained for histological evaluation.

Results: We found that plasma nitrite levels were lower in the PP group and higher in the PP-ABH group, compared with controls (P <0.01 and P <0.05, respectively). In the PP group, endothelial NOS activity was decreased and inducible NOS activity was increased compared with the PP-ABH and control groups. Malondialdehyde levels increased 3-fold in the PP group and 2-fold in the PP-ABH group compared with controls. Tumor necrosis factor-α, interleukin-6, and interleukin-1ß levels were elevated in the PP group compared to the control group, but the increase in cytokine production was attenuated or blocked in the PP-ABH group. Lung injury scores were 4.8-fold higher in the PP group and 2-fold higher in the PP-ABH group compared with controls (P <0.001 and P <0.01, respectively).

Discussion: Pneumoperitoneum decreases NO bioavailability and increases the inflammation cytokines, resulting in organ injuries. Inhibition of arginase activity could maintain NO bioavailability by attenuating pneumoperitoneum-induced changes in NOS activity. In addition, arginase inhibition attenuated the oxidative stress and inflammation and decreased the severity of lung injury caused by pneumoperitoneum.

Conclusions: By increasing NO bioavailability and suppressing oxidative stress and inflammation, pretreatment with an arginase inhibitor may protect against lung injury caused by pneumoperitoneum.

Fig. 1

Arginase II expression and activity. a Arginase II expression did not differ significantly among the treatment groups. b However, arginase II activity was increased significantly in the PP group compared with the PP-ABH and control groups. ^**P <0.01

Fig. 2

Plasma nitrite levels. Plasma nitrite, a stable metabolite of NO, was decreased in the PP group but increased in the PP-ABH group compared to controls. ^*P <0.05, ^**P <0.01, ^***P <0.001

Fig. 3

Expression and activity of endothelial and inducible nitric oxide synthase. a Expression of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) did not differ significantly among the three treatment groups. b However, eNOS activity was significantly lower and iNOS activity was higher in the PP group, compared with the PP-ABH and control groups. ^*P <0.05, ^**P <0.01, ^***P <0.001

Fig. 4

Oxidative stress. Levels of the oxidative stress marker malondialdehyde (MDA) were increased in the PP and PP-ABH groups compared to the control group, and were higher in the PP group than in the PP-ABH group. ^*P <0.05, ^***P <0.001

Fig. 5

Inflammatory cytokines. a Serum levels of TNF-α were increased in the PP and the PP-ABH groups compared with the control group, and were higher in the PP group than in the PP-ABH group. b IL-6 and c IL-1β were increased significantly in the PP group compared with the PP-ABH and control groups. ^*P <0.05, ^**P <0.01, ^***P <0.001

Fig. 6

Lung histology. a Normal lung histology in the control group. b Lung tissue in the PP group shows inflammatory cell infiltration and protein exudation. c Pneumoperitoneum-induced inflammatory changes and protein exudation were attenuated in the PP-ABH group. Hemorrhage levels were comparable among the three groups