The relationship between lung inflammation and carcinogenesis is controversial. Some studies observed that inflammation suppresses lung cancer formation. However, other studies showed an association between chronic lung inflammation and carcinogenesis. The cytochrome 1A1 (CYP1A1) is an enzyme whose increased level is an indicator for lung carcinogenesis. Therefore, this study aimed to investigate the effect of lipopolysaccharide (LPS)-mediated lung inflammation on CYP1A1 expression before or after its induction using sheep model. For that purpose, 15 male lambs (8-10 weeks old) were randomly allocated into three groups, each of five. Group one (control) was intratracheally (IT) instilled with five ml distilled water (DW) on days zero and three using fiberoptic endoscope and intraperitoneally injected with the CYP1A1 inducer, beta-naphthoflavone (50 mg/kg BW; BNF) on days one and two. Group two (early inflammation group) was intratracheally instilled with LPS (500 µg/kg in five ml DW, on day zero) to induce lung inflammation and intraperitoneally injected with BNF on days one and two to induce CYP1A1. Group three (late inflammation) was intraperitoneally injected with BNF on days one and two and intratracheally instilled with LPS (500 µg/kg in 5 ml DW) on day three. All lambs were sacrificed on day four and tissues from fresh right lung and liver were collected for microsomal preparation to determine the CYP1A1 and CYP2B4 activities (7-ethoxyresorufin-O-deethylase, EROD and 7-pentoxyresorufin-O-deethylase, PROD, respectively) and protein quantity by western blot. Moreover, frozen tissues were immediately collected in liquid nitrogen for quantification of mRNA of pulmonary and hepatic CYP1A1 and pulmonary inducible nitric oxide synthase (iNOS) by quantitative real time-PCR. The left lung lobes were inflated with 10% NBF for histopathology. Before sacrificed, blood samples were collected for differential leucocytic count. Results showed that LPS caused lung inflammation manifested as areas of red hepatization. The LPS-mediated lung inflammation significantly (P≤ 0.5) inhibited pulmonary CYP1A1 activity, protein, and mRNA regardless of the time of induction (i.e. before or after inflammation). Moreover, lung EROD and PROD activities were significantly inhibited (P≤ 0.5) by IT instillation of LPS. However, hepatic EROD and PROD were not significantly affected by pulmonary inflammation. The pulmonary and not the hepatic iNOS was significantly increased (P≤ 0.5) by LPS bronchoscopic instillation of LPS. Differential leucocytic count did not show significant changes among the three groups. Histopathological examinations showed numerous multinucleated cells surrounded by large numbers of mononuclear inflammatory cells in the lung parenchyma. Taken together, these results suggest that pulmonary inflammation suppresses CYP1A1 expression in sheep lung either before or after exposure to the inducer and this model is localized to lung and does not affect liver. The result resolves the conflict of relationship between lung inflammation and carcinogenesis where pneumonia suppresses the occurrence of lung cancer in this particular sheep. Increased level of iNOS and hence NO could be the possible mechanism. The study was successful to present a sheep model that can be used to extrapolate relationship between lung inflammation and carcinogenesis in human.
Keywords: induced CYP1A1 – EROD- iNOS – lipopolysaccharides Sheep– lung inflammation – PROD - RT-PCR