Effect Of High Cholesterol Diet On Urethane Induced Lung Carcinogenesis In C57BL/6J Mice

Background： Due to the discrepancy of epidemiological studyoutcomes and lack of related mechanism, the relationship between highcholesterol diet and the risk of lung carcinogenesis is still not clear.Objective: To explore the effects of high cholesterol diet on thesusceptibility of urethane induced lung carcinogenesis and underlinedmechanism in C57BL/6J mice.Methods: Male C57BL/6J mice (6-8weeks old) were fed either a highcholesterol diet (HCD) or a matching normal diet (ND), respectively.Following3weeks diet adapting, mice in each group were further randomlyassigned to receive weekly intraperitoneal injections of either urethane (1g/kg body weight) or normal saline control for10consecutive weeks,followed by15weeks latency period, and then all mice were sacrificed andthe lung tissue were removed. During the autopsy procedure, the tumorlesions on lung surfaces were carefully counted and the lesion diameter wasmeasured. Meanwhile, in order to explore the mechaism of the differenttumors in two diet fed mice, the blood serum, bronchoalveolar lavage fluid (BALF) and lung tissues of different groups mice were collected afterintraperitoneal injections of10consecutive weeks (the experiment weeks13W). Cholesterol level in blood and lung tissues were detected usingenzymatic method; The white blood cells in blood were counted; Thenumber of total cells were counted and inflammatory cytokines weremeasured applying the antibody microarray technology in BALF;Inflammation related proteins TLR2/4, NF-B and LXR ligand signalingpathways associated proteins LXR-and ABCA1in lung tissues weremeasured using western blotting. To further verify the effects of LXRactivation on urethane induced lung carcinogenesis in mice, LXR agonistexperimental model was established: The same multidose urethane injectioninduced lung cancer model was used. Simultaneously, the urethane treatednormal diet fed wild type C57BL/6J mice were intranasal administrated witheither vehicle (DMSO) or T0901317(50mg/kg body weight) twice a weekfor10consecutive weeks. Lung carcinogenesis assessments were taken after15weeks latency period.Results：Compared with the ND-fed mice, the serum total cholesterollevel of HCD-fed mice increased significantly, so hypercholesterolemiamouse model was successfully established. In multidose urethane inducedC57BL/6J mice lung cancer model, HCD-fed mice exhibited decreasedtumor multiplicity compared with the ND-fed mice and attenuatedpulmonary tumor related inflammation, which including reduced influx of leukocyte into the BALF, downregulated tumor-promoting relatedinflammatory cyto-/chemokine profile in BALF and decreased TLR2/4expression and NF-B activation in the lung. Further mechanism studyfound that LXR-and ABCA1was up-regulated in urethane treatedHCD-fed mice lungs compared with ND-fed mice lungs, accompanied withdecreased pulmonary free cholesterol content and suppressed tumor cellproliferation. Furthermore, intranasal administration of LXR agonistT0901317alleviated urethane induced lung carcinogenesis.Conclusions：Intrapulmonary cholesterol homeostasis is important inlung carcinogenesis, and LXR activation might partly contribute to theinhibitory role of high cholesterol diet on urethane induced lungcarcinogenesis.