Effects of Antenatal Dexamethasone on Antioxidant Enzymes and Nitric Oxide Synthase in the Rat Lung

Oxygen and steroids affect the regulatory role of natriuretic peptide receptor-C on surfactant secretion by type II cells

Atrial natriuretic peptide (ANP) and its receptors natriuretic peptide receptor (NPR)-A and NPR-C are all highly expressed in alveolar epithelial type II cells (AEC2s) in the late-gestation ovine fetal lung and are dramatically decreased postnatally. However, of all the components, NPR-C stimulation inhibits ANP-mediated surfactant secretion. Since alveolar oxygen increases dramatically after birth, and steroids are administered to mothers antenatally to enhance surfactant lung maturity, we investigated the effects of O₂ concentration and steroids on NPR-C-mediated surfactant secretion in AEC2s. NPR-C expression was highest at 5% O₂ while being suppressed by 21% O₂, in cultured mouse lung epithelial cells (MLE-15s) and/or human primary AEC2s. Surfactant protein-B (SP-B) was significantly elevated in media from both in vitro and ex vivo culture at 13% O₂ versus 21% O₂ in the presence of ANP or terbutaline (TER). Both ANP and C-ANP (an NPR-C agonist) attenuated TER-induced SP-B secretion; this effect was reversed by dexamethasone (DEX) pretreatment in AEC2s and by transfection with NPR-C siRNA in MLE-15 cells. DEX markedly reduced AEC2 NPR-C expression, and pregnant ewes treated with betamethasone showed reduced ANP in fetal sheep lung fluid. These data suggest that elevated O₂ downregulates AEC2 NPR-C and that steroid-mediated NPR-C downregulation in neonatal lungs may provide a novel mechanism for their effect on perinatal surfactant production.

Hormones and oxidative stress: an overview

In aerobes, oxygen is essential for maintenance of life. However, incomplete reduction of oxygen leads to generation of reactive oxygen species. These oxidants oxidise biological macromolecules present in their vicinity and thereby impair cellular functions causing oxidative stress (OS). Aerobes have evolved both enzymatic and nonenzymatic antioxidant defences to protect themselves from OS. Although hormones as means of biological coordination involve in regulation of physiological activities of tissues by regulating metabolism, any change in their normal titre leads to pathophysiological states. While, hormones such as melatonin, insulin, oestrogen, progesterone display antioxidant features, thyroid hormone, corticosteroids and catecholamines elicit free radical generation and OS, and the role of testosterone in inducing OS is debateable. This review is an attempt to understand the impact of free radical generation and cross talk between the hormones modulating antioxidant defence system under various pathophysiological conditions.

Screening and pharmacodynamic evaluation of the anti-respiratory syncytial virus activity of butene lactones in vitro and in vivo

A series of butene lactones were synthesized and these compounds were tested for anti-respiratory syncytial virus (RSV) activity in vitro. Three compounds exhibited an antiviral effect, the highest of which was compound 6b3 with an effective concentration 50% of 6.35 μM. The effects of 6b3 were then evaluated in vivo and a significant reduction in the lung index caused by RSV was detected. Reduced inflammatory infiltration and necrosis of the lungs were revealed by histopathology and gross pathology. Activation of an early immune response by 6b3 was also observed by cytokine analysis via a real-time polymerase chain reaction. These results indicated that 6b3 has an anti-RSV effect both in vitro and in vivo, and is a possible candidate compound for the development of an anti-RSV drug in the future.

Silymarin attenuates paraquat-induced lung injury via Nrf2-mediated pathway in vivo and in vitro

The present study aims to investigate the impacts and mechanisms of silymarin on paraquat (PQ)-induced lung injury in vivo and in vitro. In in vivo experiments, a total of 32 male Sprague-Dawley (SD) rats were randomly divided into four groups. The rats were killed on day 3. Histopathological changes in lung tissue were examined using HE and Masson's trichrome staining. Biomarkers of neutrophil activation, pulmonary oedema, pulmonary fibrosis, lung permeability and oxidative stress were detected. Several proinflammatory mediators and antioxidant related proteins were measured. In in vitro experiments, A549 cells were transfected with Nrf2 special siRNA to investigate the roles of Nrf2. The results show that silymarin administration abated PQ-induced lung histopathologic changes, decreased inflammatory cell infiltration and lung wet weight/dry weight (W/D) ratio, suppressed myeloperoxidase (MPO) activity and nitric oxide (NO)/inducible nitric oxide synthases (iNOS) expression, downregulated hydroxyproline (HYP) levels, reduced total protein concentration and proinflammatory mediator release, and improved oxidative stress (malondialdehyde, MDA; superoxide dismutase, SOD; catalase, CAT; and glutathione peroxidase, GSH-Px) in lung tissue and serum. Meanwhile, treatment with silymarin upregulated the levels of nuclear factor-erythroid-2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase-1(NQO1). However, the addition of Nrf2 siRNA reduced the expression of Nrf2-mediated antioxidant protein HO-1 and thus reversed the protective effects of silymarin against oxidative stress and inflammatory response. These results suggest that silymarin may exert protective effects against PQ-induced lung injury. Its mechanisms were associated with the Nrf2-mediated pathway. Therefore, silymarin may be a potential therapeutic drug for lung injury.

Exposure to dexamethasone reduces pituitary volume and gonadotropic cell number in rat fetuses

Overexposure to glucocorticoids during the fetal period induces changes in developmental processes in various fetal tissues. The aim of this study was to investigate the effects of the synthetic glucocorticoid, dexamethasone (Dx), on pituitary volume and gonadotropic cells during a critical period of pituitary development. The effects of Dx on stereological parameters of the pituitary gland and FSH and LH cells were investigated in 19 and 21-day old fetuses. On day 16 of pregnancy, the experimental dams received 1.0 mg Dx/kg b.w. subcutaneously, followed by 0. 5mg Dx/kg b.w./day on days 17 and 18 of gestation. The control gravid females received the same volume of saline. FSH and LH cells were stained immunohistochemically by the peroxidase-antiperoxidase method (PAP). In 19-day old fetuses, exposure to Dx caused a significant decrease of pituitary volume, estimated by Cavalieri's principle. Also, the total number of FSH and LH cells per pituitary, determined by physical fractionator counting technique, was significantly reduced. These changes persisted until fetal day 21. Volume densities and numerical densities of FSH and LH cells after exposure to Dx in 19 and 21-day old fetuses remained unaffected. Our results suggest that altered stereological parameters in pituitary gland after exposure to dexamethasone in fetal period could be long-lasting.

Oxidative stress indices in rats under immunosuppression

Immunosuppressants lead to generation of reactive oxygen species (ROS). Oxidative stress (OxS) can initiate chronic allograft nephropathy (CAN). The most active antioxidant enzymes, superoxide dysmutase (SOD) and catalase (CAT), are present in erythrocytes. Glutathione peroxidase (GPx) is produced in the proximal tubules of nephrons. Malonyldialdehyde (MDA) concentrations are a marker of OxS intensity in plasma. In vitro and animal model studies have shown increased or decreased OxS during treatment with tacrolimus (Tac) or cyclosporine (CyA). Results obtained in humans after solid organ transplantation have been contradictory, because of confounding factors such as ischemia-reperfusion injury, donor and recipient ages, endothelial injury, and comorbidity. The aim of this study was to assess the intensity of OxS among rats under chronic immunosuppression (IS) without a transplantation. We examined 49 male Wistar rats. IS started at 12 weeks of age was continued for 6 months: group I were controls (n=7); group II, Tac+sirolimus (Rapamycin [Rapa])+corticosteroids (CS; n=6); group III, CyA+Rapa+CS (n=4 of which 2 died); group IV, Rapa+mycophenolate mofetil (MMF)+CS (n=6); group V, CyA+MMF+CS (n=6); group VI, CsA+MMF+CS for 3 months followed by conversion to Rapa (n=6); group VII, Tac+MMF+CS (n=6 rats); and group VIII, Tac+MMF+CS for 3 months followed by conversion to Rapa (n=6). The drug doses were as follows: Tac 4 mg/kg/d; MMF 20 mg/kg/d; CyA 5mg/kg/d; Rapa 0.5 mg/kg/d; and CS 4 mg/kg/d. Multiple regression analysis revealed that all IS drugs decreased GPx activity (P<.001) except CS, which increased it (P<.0001). Multiple regression analysis showed that CsA and Tac decreased plasma MDA concentrations (P<.01), whereas CS increased them (P<.05). In conclusion, all IS drugs except CS damage proximal tubules of nephrons.

Unbiased stereological estimation of the rat fetal pituitary volume and of the total number and volume of TSH cells after maternal dexamethasone application

Glucocorticoids have an inhibitory influence on proliferation activity of the pituitary cells while stimulating apoptosis. Therefore, it was hypothesized that the synthetic glucocorticoid, dexamethasone (DX), has an inhibitory influence on the number of thyroid-stimulating hormone (TSH) cells during fetal development. The effects of maternal administration of DX on stereological parameters of TSH cells, and TSH serum concentration were investigated in 21-day-old rat fetuses. On day 16 of pregnancy, the experimental dams received 1.0 mg DX/kg b.w. subcutaneously, followed by 0.5 mg DX/kg b.w./day on days 17 and 18 of gestation. The control gravid females received the same volume of saline vehicle. TSH cells were stained immunocytochemically by the peroxidase-antiperoxidase (PAP) method. The fetal pituitary volumes were estimated using Cavalieri's principle. A physical disector counting technique in combination with the fractionator sampling method was used for estimation of pituitary TSH cell number. Cell and nuclear volumes were measured with a planar rotator. Maternal DX application was found to cause a significant decrease of pituitary volume and number of TSH cells per pituitary in 21-day-old fetuses in comparison with the control fetuses. TSH cell number expressed per body weight unit declined significantly after maternal DX administration. These results indicate an inhibitory DX influence on proliferative activity of precursors and likely differentiated TSH cells and increased apoptotic prevalence. The histological appearance, volume of TSH cells and TSH serum concentration suggest intensive synthetic activity in TSH cells of DX exposed fetuses.

Antenatal glucocorticoid therapy accelerates ATP production with creatine kinase increase in the growth-enhanced fetal rat heart

BACKGROUND

Previous study has demonstrated the increase of several cardiac function-related proteins, including creatine kinase (CK) as an important enzyme in the process of ATP synthesis in the fetal heart of rats administered glucocorticoid (GC) antenatally. In the present study the effect of antenatal GC administration on the CK expression in fetal and neonatal hearts was demonstrated.

METHODS AND RESULTS

Dexamethasone was administered to pregnant rats on days 19 and 20 of gestation. The mRNA levels of the CK isoforms, CK-M and Mi-CK, in 21-day-old fetal and 1-day-old neonatal hearts were significantly increased after antenatal GC administration. CK protein levels were also increased in both cultured cardiomyocytes and the mitochondria of the hearts. Uptake of 5, 5', 6, 6'-tetrachloro-1, 1', 3, 3'-tetraethyl-benzimidazolocarbocyanine iodide by mitochondria was significantly increased. An increased ATP level accompanied the CK increase in the neonatal hearts. Furthermore, in vitro these effects were mediated though the GC receptor of cardiomyocytes. Peroxisome proliferator-activated receptor gamma as the upstream transcription factor of CK was significantly increased in fetal hearts.

CONCLUSIONS

These results suggest that antenatal GC administration accelerates ATP synthesis through increased CK and may contribute to maturation of the premature heart so that it is ready for preterm delivery. (Circ J 2010; 74: 171 - 180).

Antenatal steroids and antioxidant enzyme activity in preterm infants: influence of gender and timing

Antenatal steroids have improved the survival of preterm infants; however, the mechanism of action is not fully understood. We aimed to establish an association between antenatal steroids and antioxidant activity and postnatal oxidative stress. In a prospective cohort study, extremely preterm neonates receiving antenatal steroids (CORT) or not (NOCORT) were enrolled. An association between antenatal steroids and activities of antioxidant enzymes and glutathione cycle enzymes in cord blood was found. In addition, reduced oxidative stress (GSH/GSSG ratio, CORT vs. NOCORT, 35.68 + or - 12.20 vs. 28.38 + or - 9.92; p < 0.01) and, decreased oxidation of proteins (ortho-tyrosine/phenylalanine ratio, CORT vs. NOCORT, 8.66 + or - 2.45 vs. 12.55 + or - 4.41; p < 0.01) and DNA (8oxodG/2dG ratio, CORT vs. NOCORT, 6.73 + or - 2.18 vs. 9.53 + or - 3.83; p < 0.01) also was found. Antenatal steroids were associated with reduced oxygen supplementation, mechanical ventilation, and conditions such as bronchopulmonary dysplasia, intra-periventricular hemorrhage, or retinopathy of prematurity. The maximal effectiveness was when steroids were administered 2-4 days before delivery. Female preterm infants had less oxidative stress and increased antioxidant activity and better clinical outcomes than did male infants, independent of receiving or not antenatal steroids. Antenatal steroids are accompanied by a reduction in postnatal oxidative-stress-derived conditions and increased antioxidant enzyme activity. Both these effects seem to be influenced by specific timing and female gender.