Maternally Administered Lipopolysaccharide Upregulates The Expression Of Heme Oxygenase-1 In Mouse Placenta And Fetal Liver

Heme oxygenase (HO) is an enzyme that catalyzes the rate-limiting step in the degradation of heme to biliverdin, carbon monoxide and iron. Three isoforms of the HO protein designated as HO-1, HO-2 and HO-3 have been identified. There is increasing evidence that HO plays important protective roles in the cellular defense against oxidative stress and the deleterious effects of proinflammatory cytokines. In the present study, we aimed to investigate the effects of maternal lipopolysaccharide (LPS) exposure on the expression of HO-1 in mouse placenta and fetal liver, and to assess the potential role of reactive oxygen species (ROS), nitric oxide (NO) and tumor necrosis factor alpha (TNF-α) on LPS-induced upregulation of HO-1 in mouse placenta and fetal liver.1 The effects of LPS exposure on the expression of HO-1 in mouse fetal liverTo investigate the effects of LPS on the expression of HO-1 in fetal liver, the pregnant mice were administered with LPS in two different modes. In mode A, the pregnant mice were intraperitoneally (i.p.) injected with LPS (75μg/kg) on gestational day (gd) 16 or 17 and sacrificed at different time point (2 h, 12 h, 24 h or 48 h) after LPS. In mode B, the pregnant mice were injected with different doses of LPS (1, 10, 75μg/kg, i.p.) on gd 17 and sacrificed 24 h after LPS. The expressions of HO-1 and HO-2 in fetal liver were determined by Western blotting. The study showed that a basal expression of HO-1 and HO-2 was detected in fetal liver. When the pregnant mice were challenged with LPS, the expression of HO-1 in fetal liver was upregulated in time-dependent manner, whereas HO-2 did not change at the various time points observed. LPS significantly induced lipid peroxidation and glutathione (GSH) depletion in fetal liver, which was significantly attenuated after the pregnant mice were pretreated with alpha-phenyl-N-t-butylnitrone (PBN), a free radical spin trapping agent. Furthermore, PBN pretreatment blocked LPS-induced upregulation of HO-1 in fetal liver. However, aminoguanidine (AG), a selective inhibitor of inducible nitric oxide synthase (iNOS), and pentoxifylline (PTX), an inhibitor of tumor necrosis factor alpha (TNF-α) synthesis, had little effect on LPS-induced upregulation of HO-1 in fetal liver. Taken together, these results indicate that maternally-administered LPS upregulates the expression of HO-1 in fetal liver. ROS, rather than TNF-αor NO, are involved in LPS-induced upregulation of HO-1 in fetal liver. The expression of HO-1 can be used as a marker for oxidative stress in fetal liver during maternal inflammation and infection.2 The effects of LPS exposure on the expression of HO-1 in mouse placentaTo investigate the effects of LPS on the expression of HO-1 in mouse placenta, the pregnant mice were administered with LPS in two different modes. In mode A, the pregnant mice were injected with LPS (75μg/kg, i.p.) on gd 16 or 17 and sacrificed at different time point (2 h, 12 h, 24 h or 48 h) after LPS. In mode B, the pregnant mice were injected with different doses of LPS (1, 10, 75μg/kg, i.p.) on gd 17 and sacrificed 24 h after LPS. The expressions of HO-1 and HO-2 in placenta were determined by Western blotting. The study showed that a basal expression of HO-1 and HO-2 was detected in mouse placenta. When the pregnant mice were challenged with LPS, the expression of HO-1 in mouse placenta was upregulated in time- and dose-dependent manner, whereas HO-2 did not change at the various time points observed. LPS significantly induced lipid peroxidation and GSH depletion in mouse placenta. PBN, a free radical spin trapping agent, pretreatment significantly attenuated LPS-induced lipid peroxidation and GSH depletion. Correspondingly, PBN blocked LPS-induced upregulation of HO-1 in mouse placenta. Furthermore,PTX, an inhibitor of TNF-α synthesis, also significantly attenuated LPS-induced upregulation of placental HO-1. However, AG, a selective inhibitor of iNOS, had little effect on LPS-induced upregulation of HO-1 in mouse placenta. Taken together, these results indicate that LPS upregulates the expression of HO-1 in mouse placenta. LPS-induced upregulation of placental HO-1 is probably mediated by ROS and TNF-α, rather than nitric oxide.