Cell-specific alterations in expression of hyperoxia-induced mRNAs of lung

Metal profiling in coronary ischemia-reperfusion injury: Implications for KEAP1/NRF2 regulated redox signaling

Coronary ischemia-reperfusion (IR) injury results from a blockage of blood supply to the heart followed by restoration of perfusion, leading to oxidative stress induced pathological processes. Nuclear factor erythroid 2-related factor 2 (NRF2), a master antioxidant transcription factor, plays a key role in regulating redox signaling. Over the past decades, the field of metallomics has provided novel insights into the mechanism of pro-oxidant and antioxidant pathological processes. Both redox-active (e.g. Fe and Cu) and redox-inert (e.g. Zn and Mg) metals play unique roles in establishing redox balance under IR injury. Notably, Zn protects against oxidative stress in coronary IR injury by serving as a cofactor of antioxidant enzymes such as superoxide dismutase [Cu-Zn] (SOD1) and proteins such as metallothionein (MT) and KEAP1/NRF2 mediated antioxidant defenses. An increase in labile Zn2+ inhibits proteasomal degradation and ubiquitination of NRF2 by modifying KEAP1 and glycogen synthase kinase 3β (GSK3β) conformations. Fe and Cu catalyse the formation of reactive oxygen species via the Fenton reaction and also serve as cofactors of antioxidant enzymes and can activate NRF2 antioxidant signaling. We review the evidence that Zn and redox-active metals Fe and Cu affect redox signaling in coronary cells during IR and the mechanisms by which oxidative stress influences cellular metal content. In view of the unique double-edged characteristics of metals, we aim to bridge the role of metals and NRF2 regulated redox signaling to antioxidant defenses in IR injury, with a long-term aim of informing the design and application of novel therapeutics.

Tissue Inhibitor of Matrix Metalloproteinases-1 (TIMP-1) and Pulmonary Involvement in COVID-19 Pneumonia

Background: The aim of the study was to longitudinally evaluate the association between MMP-2, MMP-9, TIMP-1 and chest radiological findings in COVID-19 patients. Methods: COVID-19 patients were evaluated based on their hospital admission (baseline) and three months after hospital discharge (T post) and were stratified into ARDS and non-ARDS groups. As a control group, healthy donors (HD) were enrolled. Results: At the baseline, compared to HD (n = 53), COVID-19 patients (n = 129) showed higher plasma levels of MMP-9 (p < 0.0001) and TIMP-1 (p < 0.0001) and the higher plasma activity of MMP-2 (p < 0.0001) and MMP-9 (p < 0.0001). In the ARDS group, higher plasma levels of MMP-9 (p = 0.0339) and TIMP-1 (p = 0.0044) and the plasma activity of MMP-2 (p = 0.0258) and MMP-9 (p = 0.0021) compared to non-ARDS was observed. A positive correlation between the plasma levels of TIMP-1 and chest computed tomography (CT) score (ρ = 0.2302, p = 0.0160) was observed. At the T post, a reduction in plasma levels of TIMP-1 (p < 0.0001), whereas an increase in the plasma levels of MMP-9 was observed (p = 0.0088). Conclusions: The positive correlation between TIMP-1 with chest CT scores highlights its potential use as a marker of fibrotic burden. At T post, the increase in plasma levels of MMP-9 and the reduction in plasma levels of TIMP-1 suggested that inflammation and fibrosis resolution were still ongoing.

Animal models of bronchopulmonary dysplasia. The preterm and term rabbit models

Bronchopulmonary dysplasia (BPD) is an important lung developmental pathophysiology that affects many premature infants each year. Newborn animal models employing both premature and term animals have been used over the years to study various components of BPD. This review describes some of the neonatal rabbit studies that have contributed to the understanding of BPD, including those using term newborn hyperoxia exposure models, premature hyperoxia models, and a term newborn hyperoxia model with recovery in moderate hyperoxia, all designed to emulate aspects of BPD in human infants. Some investigators perturbed these models to include exposure to neonatal infection/inflammation or postnatal malnutrition. The similarities to lung injury in human premature infants include an acute inflammatory response with the production of cytokines, chemokines, and growth factors that have been implicated in human disease, abnormal pulmonary function, disordered lung architecture, and alveolar simplification, development of fibrosis, and abnormal vascular growth factor expression. Neonatal rabbit models have the drawback of limited access to reagents as well as the lack of readily available transgenic models but, unlike smaller rodent models, are able to be manipulated easily and are significantly less expensive than larger animal models.

Serum MMP-8 and TIMP-1 in critically ill patients with acute respiratory failure: TIMP-1 is associated with increased 90-day mortality

BACKGROUND

Matrix metalloproteinases (MMPs) likely have an important role in the pathophysiology of acute lung injury. In a recent study, high matrix metalloproteinases (MMP-8) levels in tracheal aspirates of pediatric acute respiratory distress syndrome (ARDS) patients were associated with worse outcome. In patients with sepsis, an imbalance between MMPs and their tissue inhibitors (TIMPs) has been associated with impaired survival. We hypothesized that the elevated systemic MMP-8 and TIMP-1 are associated with worse outcome in acute respiratory failure.

METHODS

This was a substudy of the observational FINNALI study conducted in 25 Finnish intensive care units over an 8-week period. All patients older than 16 years requiring mechanical ventilation for >6 hours were included. MMP-8 and TIMP-1 levels were analyzed from blood samples taken on enrollment in the study and 48 hours later. Laboratory analyses were performed by using immunofluorometric assay for MMP-8 and ELISA for TIMP-1. MMP-8 and TIMP-1 levels were compared between 90-day survivors and nonsurvivors. Survival was compared in quartiles based on TIMP-1 levels, and ROC analysis was performed to calculate areas under the curves. The relationship between MMP-8 and TIMP-1 levels and degree of hypoxemia was examined.

RESULTS

The final analyses included 563 patients. Admission TIMP-1 levels were higher in nonsurvivors, median 367 ng/mL (interquartile range 199-562), than survivors, median 240 ng/mL (interquartile range 142-412), WMWodds 1.68 (95% confidence interval [CI], 1.43-2.08). MMP-8 levels may have differed between survivors and nonsurvivors, WMWodds 1.20 (95% CI, 1.01-1.43), but no difference was found in the MMP-8/TIMP-1 molar ratio, WMWodds 0.83 (95% CI, 0.67-1.04). Difference in survival between quartiles based on TIMP-1 was significant (log-rank, P < 0.001). ROC analysis produced an area under the curve 0.63 (95% CI, 0.58-0.69) for TIMP-1. TIMP-1 was associated with severity of hypoxemia. TIMP-1 levels were higher in an ARDS subgroup than in the whole cohort, WMWodds 1.65 (95% CI, 1.15-2.44).

CONCLUSIONS

MMP-8 levels were possibly higher in 90-day nonsurvivors but performed poorly in predicting outcome. Increased systemic levels of TIMP-1 were associated with more severe hypoxemia and worse outcome in a large cohort of mechanically ventilated critically ill patients and in a subgroup of ARDS patients.

Metallothionein-induced zinc partitioning exacerbates hyperoxic acute lung injury

Hypozincemia, with hepatic zinc accumulation at the expense of other organs, occurs in infection, inflammation, and aseptic lung injury. Mechanisms underlying zinc partitioning or its impact on extrahepatic organs are unclear. Here we show that the major zinc-binding protein, metallothionein (MT), is critical for zinc transmigration from lung to liver during hyperoxia and preservation of intrapulmonary zinc during hyperoxia is associated with an injury-resistant phenotype in MT-null mice. Particularly, lung-to-liver zinc ratios decreased in wild-type (WT) and increased significantly in MT-null mice breathing 95% oxygen for 72 h. Compared with female adult WT mice, MT-null mice were significantly protected against hyperoxic lung injury indicated by reduced inflammation and interstitial edema, fewer necrotic changes to distal airway epithelium, and sustained lung function at 72 h hyperoxia. Lungs of MT-null mice showed decreased levels of immunoreactive LC3, an autophagy marker, compared with WT mice. Analysis of superoxide dismutase (SOD) activity in the lungs revealed similar levels of manganese-SOD activity between strains under normoxia and hyperoxia. Lung extracellular SOD activity decreased significantly in both strains at 72 h of hyperoxia, although there was no difference between strains. Copper-zinc-SOD activity was ~4× higher under normoxic conditions in MT-null compared with WT mice but was not affected in either group by hyperoxia. Collectively the data suggest that genetic deletion of MT-I/II in mice is associated with compensatory increase in copper-zinc-SOD activity, prevention of hyperoxia-induced zinc transmigration from lung to liver, and hyperoxia-resistant phenotype strongly associated with differences in zinc homeostasis during hyperoxic acute lung injury.

Effects of recombinant human keratinocyte growth factor on surfactant, plasma, and liver phospholipid homeostasis in hyperoxic neonatal rats

Respiratory distress and bronchopulmonary dysplasia (BPD) are major problems in preterm infants that are often addressed by glucocorticoid treatment and increased oxygen supply, causing catabolic and injurious side effects. Recombinant human keratinocyte growth factor (rhKGF) is noncatabolic and antiapoptotic and increases surfactant pools in immature lungs. Despite its usefulness in injured neonatal lungs, the mechanisms of improved surfactant homeostasis in vivo and systemic effects on lipid homeostasis are unknown. We therefore exposed newborn rats to 85% vs. 21% oxygen and treated them systemically with rhKGF for 48 h before death at 7 days. We determined type II pneumocyte (PN-II) proliferation, surfactant protein (SP) mRNA expression, and the pulmonary metabolism of individual phosphatidylcholine (PC) species using [D(9)-methyl]choline and tandem mass spectrometry. In addition, we assessed liver and plasma lipid metabolism, addressing PC synthesis de novo, the liver-specific phosphatidylethanolamine methyl transferase (PEMT) pathway, and triglyceride concentrations. rhKGF was found to maintain PN-II proliferation and increased SP-B/C expression and surfactant PC in both normoxic and hyperoxic lungs. We found increased total PC together with decreased [D(9)-methyl]choline enrichment, suggesting decreased turnover rather than increased secretion and synthesis as the underlying mechanism. In the liver, rhKGF increased PC synthesis, both de novo and via PEMT, underlining the organotypic differences of rhKGF actions on lipid metabolism. rhKGF increased the hepatic secretion of newly synthesized polyunsaturated PC, indicating improved systemic supply with choline and essential fatty acids. We suggest that rhKGF has potential as a therapeutic agent in neonates by improving pulmonary and systemic PC homeostasis.

Spatial and temporal expression of surfactant proteins in hyperoxia-induced neonatal rat lung injury

Background

Bronchopulmonary dysplasia, a complex chronic lung disease in premature children in which oxidative stress and surfactant deficiency play a crucial role, is characterized by arrested alveolar and vascular development of the immature lung. The spatial and temporal patterns of expression of surfactant proteins are not yet fully established in newborn infants and animal models suffering from BPD.

Methods

We studied the mRNA expression of surfactant proteins (SP) A, -B, -C and -D and Clara cell secretory protein (CC10) with RT-PCR and in situ hybridization and protein expression of CC10, SP-A and -D with immunohistochemistry in the lungs of a preterm rat model, in which experimental BPD was induced by prolonged oxidative stress.

Results

Gene expression of all surfactant proteins (SP-A, -B, -C and -D) was high at birth and initially declined during neonatal development, but SP-A, -B, and -D mRNA levels increased during exposure to hyperoxia compared to room-air controls. Peak levels were observed in adult lungs for SP-A, SP-C and CC10. Except for SP-A, the cellular distribution of SP-B, -C, -D and CC10, studied with in situ hybridization and/or immunohistochemistry, did not change in room air nor in hyperoxia. Exposure to normoxia was associated with high levels of SP-A mRNA and protein in alveolar type 2 cells and low levels in bronchial Clara cells, whereas hyperoxia induced high levels of SP-A expression in bronchial Clara cells.

Conclusion

The increased expression of SP-A mRNA under hyperoxia can be attributed, at least in part, to an induction of mRNA and protein expression in bronchial Clara cells. The expanded role of Clara cells in the defence against hyperoxic injury suggests that they support alveolar type 2 cell function and may play an important role in the supply of surfactant proteins to the lower airways.

Nitric oxide and zinc homeostasis in acute lung injury

Among putative small molecules that affect sensitivity to acute lung injury, zinc and nitric oxide are potentially unique by virtue of their interdependence and dual capacities to be cytoprotective or injurious. Nitric oxide and zinc appear to be linked via an intracellular signaling pathway involving S-nitrosation of metallothoinein--itself a small protein known to be an important inducible gene product that may modify lung injury. In the present article, we summarize recent efforts using genetic and fluorescence optical imaging techniques to: (1) demonstrate that S-nitrosation of metallothionein affects intracellular zinc homeostasis in intact pulmonary endothelial cells; and (2) reveal a protective role for this pathway in hyperoxic and LPS-induced injury.

Hyperoxia-induced cell death in the lung--the correlation of apoptosis, necrosis, and inflammation

Prolonged exposure to hyperoxia causes tissue damage in many organs and tissues. Since the entire surface area of lung epithelium is directly exposed to O2 and other inhaled agents, hyperoxia leads to the development of both acute and chronic lung injuries. These pathologic changes in the lung can also be seen in acute lung injury (ALI) in response to other agents. Simple strategies to mitigate hyperoxia-induced ALI might not be effective by virtue of merely reducing or augmenting the extent of apoptosis of pulmonary cells. Identification of the specific cell types undergoing apoptosis and further understanding of the precise timing of the onset of apoptosis may be necessary in order to gain a greater understanding of the connection between apoptosis and tolerance to hyperoxia and ALI. Attention should also be focused on other forms of non-apoptotic programmed cell death.

Cytoprotection by metallothionein against gastroduodenal mucosal injury caused by ethanol in mice

Metallothionein (MT) is a small, cysteine-rich protein that can act as a free radical scavenger at least in vitro. To test the hypothesis that MT participates in gastroduodenal cytoprotection, we studied sensitivity to gastroduodenal mucosal injury caused by ethanol in MT-null mice that have null mutations in MT-I and MT-II genes. MT-null mice and wild-type mice were orally treated with ethanol (60% or 99.5%, 0.2 ml/mouse). The macroscopic gastric lesion indices were significantly higher in MT-null mice than in wild-type mice 90 minutes after ethanol treatment. Histopathological examination in ethanol-treated MT-null mice showed vacuolar degeneration, necrosis of the epithelial cells, and hemorrhage throughout the tunica mucosa. Moreover, the duodenum also showed morphologic changes, including marked degeneration and coagulative necrosis of the entire villi, desquamation of the degenerated epithelial cells, and hemorrhage. In contrast, histopathologic changes were less prominent in the wild-type mice treated with ethanol. MT was not detected either in the stomach or duodenum of MT-null mice, whereas gastric and duodenal zinc contents were not significantly different between MT-null mice and wild-type mice. These results provide direct evidence that intrinsic MT plays a cytoprotective role in gastroduodenal mucosal injury caused by ethanol.

Increased endothelial cell expression of platelet-endothelial cell adhesion molecule-1 during hyperoxic lung injury

Lung injury is a frequent consequence of oxygen (O2) therapy administered to newborns and adults with respiratory distress. Acute exposure to hyperoxia results in a well-described pathophysiologic response in the lungs. Because inflammation is an important component of pulmonary O2 toxicity, we have an interest in identifying the inflammatory mediators that increase during hyperoxia. Platelet-endothelial cell adhesion molecule-1 (PECAM-1), a member of the immunoglobulin superfamily that is expressed at the junctions between endothelial cells, is essential to the transendothelial migration of leukocytes. We hypothesized that increased expression of PECAM-1 occurs in pulmonary endothelial cells during hyperoxic lung injury. Adult mice were exposed to 100% O2 for up to 96 h. We analyzed PECAM-1 expression by RNA blot hybridization, in situ hybridization, and immunohistochemistry. A increase in PECAM-1 mRNA was seen as soon as 2 d of hyperoxia relative to unexposed control mice. PECAM-1 mRNA and protein were found in endothelial cells of both large and small arteries. The expression of PECAM-1 in capillary vessels was further confirmed using in situ hybridization at the electron microscope level. This increase in PECAM-1 expression coincided with the appearance of leukocytes in lung tissue. These observations suggest that PECAM-1 expression is a relatively early step in the inflammation cascade, and intervention at this phase may be critical to the prevention of further damage.

Oxygen tension regulates heme oxygenase-1 gene expression in mammalian cell lines

The gene expression of heme oxygenase-1 (HO-1) was studied in mammalian cell lines exposed to hyperoxia. Northern blot analysis demonstrated that hyperoxic exposure increased the HO-1 mRNA levels in various types of cells, including human hepatoma (HepG2) cells. This increase was time- and dose-dependent, and reversible. The HO-1 mRNA levels in HepG2 cells were increased to 2.3- and 4.2-fold of the control by hyperoxic exposure of 6 and 23 h, respectively. Cycloheximide and actinomycin D inhibited the increases in the HO-1 mRNA level produced by hyperoxia, indicating that response to hyperoxia is dependent on de novo protein synthesis and mRNA transcription. Antioxidants, desferrioxamine (DES) and o-phenanthroline (OP) partially inhibited the HO-1 mRNA elevation by hyperoxia. In addition to hyperoxia, sodium arsenite (NaAsO2), cadmium chloride (CdCl(2)) and hydrogen peroxide (H2O2), which are reactive oxygen intermediates (ROI) generators, increased the HO-1 mRNA level by 11-, 22- and 2.5-fold, respectively. OP, an antioxidant and a bivalent metal chelator, blocked the HO-1 mRNA elevation induced either by hyperoxia or by the three ROI generators. In contrast to OP, N-acetylcysteine (NAC), an antioxidant and membrane-permeable reducing reagent, enhanced the HO-1 mRNA elevation induced by hyperoxia, although NAC inhibited the mRNA elevation induced by NaAsO2, CdCl2 and H2O2. These results indicate that oxygen tension regulates HO-1 gene expression and suggest that hyperoxia-specific and redox-sensitive regulators may be involved in hyperoxia-mediated HO-1 gene expression.

Metallothionein expression in human lung and its varying levels after lung transplantation. Toulouse Lung Transplantation Group

The aim of this study was to determine the lung levels of metallothionein (MT), a free radical scavenger, because oxygen-derivated free radicals (ODFRs) have been involved both in reperfusion injury of transplanted lungs and in cardiac or renal allograft destruction. First, MT localization was evaluated in 14 normal human lung biopsy specimens. Then, in lung transplant recipients, MT content in BAL fluid (BALF) and its transcription rate in alveolar macrophages (AMs) were determined. The BALFs of 69 patients were separated into six groups: lung transplant recipients in clinically stable condition (CSR), those with acute rejection (AR), asymptomatic cytomegalovirus infection (ACMV), cytomegalovirus pneumonitis (CMVP), bronchiolitis obliterans syndrome (BOS), and patients without transplants who served as control subjects (NTCs). In normal lungs, 83% of AMs were positively stained. MT staining was also observed in pleural endothelial cells and basal cells from bronchial epithelium. In lung transplant recipients, MT levels in BALF were significantly higher in patients with CSR, AR, ACMV, and CMVP compared with NTCs, while during BOS, MT had a significantly lower level compared with other lung transplant groups. However, no difference among groups was found concerning MT-II messenger RNA expression in AMs, showing that, as in normal lung, AMs are not the only cells that produce MT. These data report for the first time to our knowledge MT cell distribution in human lung with specific emphasis on its enhanced levels after lung transplantation, even in the absence of complication. Possible correlation among MT levels, ODFRs, cytokine levels, and corticosteroid treatment during complications of lung transplantation are discussed.

Induction and characterization of metallothionein in chicken epiphyseal growth plate cartilage chondrocytes

Following exposure to cadmium or zinc, chickens were sacrificed and the liver, kidney, and bone epiphyseal growth plates harvested. When cytosolic extracts of the growth plate cartilage were fractionated by gel filtration chromatography, a protein with high metal-binding capacity and low ultraviolet (UV) absorbance eluted in the same position as liver metallothionein (MT) and a MT standard. Cd or Zn treatment resulted in a 25-fold or 5-fold induction in growth plate MT, respectively. In liver the greatest level of MT induction was seen with short-term Cd exposures. In contrast, MT levels in the growth plate increased as the duration of Cd exposure increased. Induction of MT in growth plate chondrocyte cell cultures was observed for media Cd concentrations of > or = 0.1 microM and Zn concentrations of > or = 100 microM. Basal and inducible levels of MT declined through the culture period and were lowest in the terminally differentiated mineralized late stages of the culture. Alkaline phosphatase activity was also lowest in the late-stage cultures, while total cellular protein increased throughout the culture period. Treatment of chondrocytes with Zn prior to Cd exposure resulted in a protective induction of MT. Pre-treatment of chondrocytes with dexamethasone resulted in suppressed synthesis of MT upon Cd exposure and greater Cd toxicity. Both Cd and Zn resulted in significantly increased levels of MT mRNA in chondrocyte cell cultures. Dexamethasone treatment resulted in an approximate 2- to 3-fold increase in MT mRNA. This is contrary to the finding that MT protein levels were decreased by dexamethasone. The findings suggest that an increased rate of MT degradation in dexamethasone-treated and late-stage chondrocyte cultures may be associated with the terminally differentiated phenotype.

Exposure to hyperoxia induces p53 expression in mouse lung epithelium

Cells that are exposed to free radicals have increased levels of DNA strand breaks with accumulation of the tumor suppressor protein p53, which induces cell cycle arrest and/or apoptosis. Because oxidants injure pulmonary epithelial cells, it was hypothesized that exposure to hyperoxia promotes DNA strand breaks in lung epithelium, resulting in increased expression of p53 and loss of epithelial cell function. Adult male C57Bl/6J mice were exposed to > 95% oxygen for 72 h and DNA integrity was determined in their lungs by terminal transferase immunoreactivity. Both nonimmunoreactive and lightly stained nuclei were observed in cells comprising the airway and parenchyma. Exposure to hyperoxia resulted in a marked increase in the intensity of nuclear staining in distal bronchiolar epithelium and alveolar epithelial and endothelial cells. Airway epithelial cells from control lungs contained detectable levels of p53 protein, which markedly increased in both nuclei and cytoplasm of distal bronchiolar epithelial cells and to a lesser extent in alveolar epithelial cells that were morphologically consistent with type II cells. Western and Northern blot analyses revealed that hyperoxia increased total lung p53 protein expression but not levels of mRNA. Changes in terminal transferase immunoreactivity and p53 expression were not observed in large airway cells, fibroblasts underlying distal airway, or smooth muscle cells. Expression of SP-B mRNA modestly increased and Clara cell secretory protein and cytochrome P-450 2F2 mRNAs decreased, providing additional evidence that hyperoxia injured pulmonary epithelial cells. These findings support the concept that hyperoxia damages DNA of pulmonary epithelial cells, which respond by accumulating p53 and changes in epithelial cell-specific gene expression.

Effects of retinol deficiency and hyperoxia on collagen gene expression in rat lung

Exposure to hyperoxia results in lung injury and a decrease in lung collagen. Retinol is known to influence collagen gene expression, and retinol deficiency has been shown to potentiate hyperoxic lung injury. To investigate the combined effects of retinol deficiency and hyperoxia on lung collagen expression, retinol-deficient rats were exposed to acute hyperoxia, and expression of the alpha-1 chains of type I procollagen [pro alpha 1 (I)] and type III procollagen [pro alpha 1 (III)] were determined using Northern hybridization analyses and immunohistochemical staining. Hyperoxia alone reduced pro alpha 1 (I) mRNA by 60 +/- 4% (p < .05) and pro alpha 1 (III) mRNA by 30 +/- 5% (p < .05), and retinol deficiency alone reduced pro alpha 1 (I) mRNA abundance by 49 +/- 8.8% (p < .05) and pro alpha 1 (III) mRNA abundance by 14 +/- 7.5% (p = not significant), respectively. Retinol deficiency plus hyperoxia did not cause any further reduction in procollagen mRNA than that seen with oxygen exposure alone. Immunohistochemical staining demonstrated decreased staining for type I collagen in retinol-deficient animals. Hyperoxic exposure resulted in decreased connective tissue staining and increased alveolar wall staining for type I collagen. Retinol deficiency and hyperoxia together resulted in a marked increase in alveolar exudates staining for type I collagen. No changes in type III collagen staining were seen. These findings demonstrate that while retinol deficiency does not potentiate hyperoxia-induced reductions in procollagen mRNA, it is associated with alterations in collagen staining in distal lung and immunohistologic evidence of collagen fragments in alveolar exudates.

Comparison of adult and newborn pulmonary cytokine mRNA expression after hyperoxia

Neonatal animals of several species are more tolerant of hyperoxic exposure than are adults. However, the mechanisms of increased neonatal tolerance are unknown, as are the cell types that contribute to oxygen resistance. This study examined hyperoxic lung injury in neonatal and adult C57BL/6 mice. Adults and neonatal mice were exposed to > 95% oxygen for 78 h and 10 days, respectively. Lung mRNAs were assayed by RNase protection assay. After 72 h of exposure, the messages encoding tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta and 6 (IL-1 beta, IL-6) were increased 2-fold in adult lungs. However, at this time point these mice are near or at lethality. No alterations in neonatal lung mRNAs were detected until 7 days of oxygen exposure. At that time neonatal mice demonstrated increases in lung mRNAs encoding TNF-alpha, IL-1 beta, and IL-6 of 3-, 5-, and 8-fold, respectively. Acute alveolitis and slight edema were detected, but lethality wasn't observed until 10 days of exposure. In situ hybridization in neonatal mice suggests accumulation of TNF-alpha and IL-1 beta transcripts in pulmonary interstitial macrophages and in a subset of neutrophils after 7 days of exposure. Messages encoding IL-1 alpha, IL-2, IL-3, IL-4, IL-5,IL-10 interferon-gamma (IFN-gamma), and TNF-beta were not altered from controls in either adult or neonatal mice at any time point examined. In conclusion, adult mice demonstrate little change in cytokine mRNA until lethality is imminent, whereas newborn mice demonstrate an acute induction of TNF-alpha, IL-1 beta, and IL-6 early in the development of hyperoxic injury, which suggests that a rapid cytokine response early in the development of hyperoxic injury may play an important role in the adaptation of neonatal lungs to toxicity from prolonged oxygen exposure.

Overexpression of metallothionein decreases sensitivity of pulmonary endothelial cells to oxidant injury

Metallothionein (MT) is a low-molecular-weight cysteine-rich protein with extensive metal binding capacity and potential nonenzymatic antioxidant activity. Despite the sensitivity of vascular endothelium to either heavy metal toxicity or oxidative stress, little is known regarding the role of MT in endothelial cells. Accordingly, we determined the sensitivity of cultured sheep pulmonary artery endothelial cells (SPAEC) that overexpressed MT to tert-butyl hydroperoxide (t-BOOH), hyperoxia, or 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN; peroxyl radical generator). Nontoxic doses of 10 microM Cd increased MT levels from 0.21 +/- 0.03 to 2.07 +/- 0.24 microg/mg and resulted in resistance to t-BOOH and hyperoxia as determined by reduction of Alamar blue or [3H]serotonin transport, respectively. SPAEC stably transfected with plasmids containing either mouse or human cDNA for MT were resistant to both t-BOOH and hyperoxia. In addition, we examined transition metal-independent, noncytotoxic AMVN-induced lipid peroxidation after metabolic incorporation of the oxidant-sensitive fluorescent fatty acid cis-parinaric acid into phospholipids and high-performance liquid chromatography separation. SPAEC that overexpressed MT after gene transfer completely inhibited peroxyl oxidation of phosphatidylserine, phosphatidylcholine, and sphingomyelin (but not phosphatidylethanolamine) noted in wild-type SPAEC. These data show for the first time that MT can 1) protect pulmonary artery endothelium against a diverse array of prooxidant stimuli and 2) directly intercept peroxyl radicals in a metal-independent fashion, thereby preventing lipid peroxidation in intact cells.

Opposite effects of metallothionein I and spermine on mitochondrial function

Previously, we reported that the stress-induced protein metallothionein I (MT) modulated the oxygen consumption (VO2) of isolated rat liver mitochondria [Life Sci. 55 221-226, 1994]. We now present confirmation of this finding, and the additional observations that in rat liver mitochondria, MT caused swelling and depolarization. These actions of MT were inhibited by the aliphatic polyamine, spermine. Our findings suggest that mitochondrial function could be influenced by the balance between MT and spermine.

P-selectin is upregulated early in the course of hyperoxic lung injury in mice

While treatment with supplemental oxygen is often essential in patients with lung disease, prolonged therapy may cause lung injury by itself. Although the mechanisms responsible for initiating hyperoxic lung damage almost certainly involve primary oxidative transformations, the possible contributions of inflammation to the tissue injury have been attracting increasing research activity. Increases in intercellular adhesion molecule-1 (ICAM-1) coincide with the inflammation, but in other models of inflammation transient adhesion mediated by members of the Selectin gene family was found to be essential before ICAM-1/beta 2 interactions could occur. We, therefore, wondered whether a similar sequence of initial transient adhesion followed by subsequent responses would be observed in hyperoxic lung inflammation. We, therefore, determined the effects of hyperoxia exposure on lung mRNA for P- and E-Selectin in mouse lungs. We found that there was no detectable mRNA for E-Selectin through 72 h of hyperoxia exposure by Northern blotting, but that mRNA for P-Selectin was detectable as early as 48 h after initiation of hyperoxia. To determine the location of P-Selectin upregulation we examined hyperoxia-exposed mouse lungs by in situ hybridization and found that the upregulation of P-Selectin at 48 h was localized to large muscularized vessels, at 72 h expression was detected in some medium size muscularized vessels, and at 96 h abundant expression was observed also on nonmuscularized small vessels. In conclusion, increases in mRNA for P-Selectin early in the course of hyperoxia exposure suggest that P-Selectin expression in hyperoxic lungs increases in parallel with upregulation of ICAM-1, leading to the accumulation of neutrophils in hyperoxic lungs, and that interventions targeting these two adhesion molecules may lead to a diminution in hyperoxic lung inflammation and lung injury.

Sheep lung cytochrome P4501A1 (CYP1A1): cDNA cloning and transcriptional regulation by oxygen tension

Lung cytochrome P450 activity has been linked to neoplasia and may produce reactive oxidant species and potent arachidonic acid metabolites. In lamb lung, oxygen breathing increases lung P450 activity, and inhibition of lung cytochrome P450 activity reduces oxygen-induced lung injury. The P4501A1 (CYP1A1) isozyme is present in many lung cells, including endothelial cells, and may therefore be involved in the pathogenesis of hyperoxic injury to microvascular endothelium. Therefore, to test the hypothesis that oxygen regulates P4501A1 gene expression in the lung, we cloned the sheep P4501A1 cDNA, and examined its regulation by oxygen breathing significantly increased lung P4501A1 RNA levels and that this increase preceded the increase in isozyme activity. Oxygen exposure also promptly increased P4501A1 RNA levels in cultured lamb lung microvascular endothelial cells but not in endothelial cells isolated from the main pulmonary artery or in lung smooth muscle cells. The oxygen-stimulated increase in P4501A1 RNA levels was not serum dependent, was unaffected by cycloheximide treatment, and could not be mimicked by treatment of the cells with oxygenated medium, conditioned medium, or by chemical oxidants. By nuclear run-on assay in cultured lung endothelial cells, oxygen increased the transcription rate of P4501A1 by almost fourfold after 90 min of oxygen exposure but had no significant effect on P4501A1 RNA stability. We conclude that oxygen tension, but not chemical oxidants, increases P4501A1 gene expression pretranslationally in lung microvascular endothelial cells. We speculate that oxygen induction of P450 activity in these cells may contribute to microvascular injury during oxygen breathing.

Enhanced sensitivity to oxidative stress in cultured embryonic cells from transgenic mice deficient in metallothionein I and II genes

Embryonic cells from transgenic mice with targeted disruption of metallothionein I and II genes expressed no detectable metallothionein either constitutively or after treatment with cadmium, in contrast to cultured cells that were wild type or heterozygous for the loss of the metallothionein genes. Metallothionein null cells were most sensitive to the cytotoxic effects of cadmium, the membrane permeant oxidant tert-butylhydroperoxide, and the redox cycling toxin paraquat. No marked differences were seen among the wild type, heterozygous, or metallothionein null cells in glutathione levels or in the activity of CuZn-superoxide dismutase, glutathione peroxidase, or catalase. Nevertheless, metallothionein null cells were more sensitive to tert-butylhydroperoxide-induced oxidation as ascertained by confocal microscopic imaging of dichlorofluoroscein fluorescence. These results indicate basal metallothionein levels can function to regulate intracellular redox status in mammalian cells.

Increased expression of basic fibroblast growth factor in hyperoxic-injured mouse lung

Basic fibroblast growth factor (bFGF) is a mitogenic polypeptide for a wide variety of cell types and has been immunolocalized in the rodent and human lung. We investigated the mRNA and protein expression of bFGF in hyperoxic-injured adult mouse lungs using northern blot analysis and immunohistochemistry. Mice (6-8 weeks) were continuously exposed to 80% oxygen up to 4 days. Levels of bFGF mRNA were increased from room air control on days 3 and 4 of hyperoxia. mRNA levels of acidic fibroblast growth factor (aFGF), fibronectin, and transin/stromelysin were also examined in this injury model. Similar to bFGF, the fibronectin and transin/stromelysin mRNA levels were increased after 3 days of hyperoxia. In contrast, the aFGF mRNA levels were gradually reduced on each day of hyperoxia. A rabbit polyclonal anti-bFGF antibody was used to determine the distribution and levels of expression in the hyperoxic-injured lungs. The room air control and day 1 hyperoxic-exposed lungs exhibited staining for bFGF in the basement membranes of the blood vessels, airways, and alveoli. Patchy but intense alveolar staining was prominent on day 4 of hyperoxia. The bFGF immunoreactivity of blood vessels and airways was unaffected by the hyperoxia exposure. These results suggest that bFGF may play a role in the alveolar response to hyperoxic-induced injury by virtue of the altered mRNA levels and protein distribution in this injury model.

Targeted disruption of metallothionein I and II genes increases sensitivity to cadmium

We inactivated the mouse metallothionein (MT)-I and MT-II genes in embryonic stem cells and generated mice homozygous for these mutant alleles. These mice were viable and reproduced normally when reared under normal laboratory conditions. They were, however, more susceptible to hepatic poisoning by cadmium. This proves that these widely expressed MTs are not essential for development but that they do protect against cadmium toxicity. These mice provide a means for testing other proposed functions of MT in vivo.

Clara cell differentiation in the mouse: ultrastructural morphology and cytochemistry for surfactant protein A and Clara cell 10 kD protein

The morphologic and functional differentiation of the nonciliated columnar (Clara) cell, one of two secretory cell types in distalmost bronchioles in mammals, was studied in the mouse. Lungs from embryos (16-19 days of developmental age, dDA; birth on day 19), postnatal animals (5-20 days postnatally dPN), and adult animals were investigated by transmission electron microscopy, using standard staining procedures and immunogold (GAR-Au10) labeling for SP-A and Clara cell 10 kD antigen (CCA). At 16 dDa, all the columnar epithelial cells lining prospective distalmost bronchioles lacked distinctive features. By 17 dDa, some cells displayed a few cilia or apical dense granules. At 18 dDa, many nonciliated columnar cells had apical protrusions, as are seen in adult Clara cells. Apical concentrations of glycogen observed in nonciliated columnar cells perinatally were absent by 5 dPN, whereas apical dense granules became more abundant. Profiles of smooth and rough endoplasmic reticulum (ER), which had been randomly distributed, exhibited a selective, adult distribution at 20 dPN (apical vs. basal cytoplasmic domains). Labeling for SP-A and CCA, which was almost absent between 17 and 19 dDa, reached adult levels at the same time. The two proteins differed in distribution. SP-A predominated in adluminal cytoplasmic areas, where it was found over dense granules, vesicles, and multivesicular bodies; it was also present in bronchiolar lumens and intercellular spaces but not in rough ER or Golgi apparatus. In contrast, CCA showed a more uniform distribution; it was present over the same structures as SP-A and in the synthetic organelles. Ciliated columnar cells were virtually devoid of SP-A and CCA. We conclude that mouse Clara cells acquire a mature phenotype by 20 dPN. They are likely to be involved in recycling and/or degradation of SP-A that is internalized from airway lumens through their apical or lateral cell borders; furthermore, they synthesize the Clara cell 10 kD protein. These two Clara cell functions (first detectable late prenatally) reach mature levels by 20 dPN.

Tissue inhibitor of metalloproteinases (TIMP, aka EPA): structure, control of expression and biological functions

The TIMPs play an important role in regulating the activity of the secreted metalloproteinases (collagenases, stromelysins, gelatinases). Two different TIMPS have been well characterized, each capable of inhibiting all tested eukaryotic metalloproteinases but showing specific binding to a particular gelatinase at a site distinct from the active site. They influence the activation of the prometalloproteinase and act to modulate proteolysis of extracellular matrix, notably during tissue remodeling and inflammatory processes. On certain cell types, they can exhibit growth factor-like activity, and they can inhibit the tumorigenic and metastatic phenotype of cancer cells.

Rat lung metallothionein and heme oxygenase gene expression following ozone and zinc oxide exposure

We have conducted exposures in rats to determine pulmonary responses following inhalation of two common components of welding fumes, zinc oxide and ozone. To examine their effects on target-inducible gene expression, we measured mRNA levels of two metal-responsive genes, metallothionein (MT) and heme oxygenase (HO), in lung tissue by RNA slot-blot analysis. A 3-hr exposure to ZnO fume via a combustion furnace caused a substantial elevation in lung MT mRNA at all concentrations tested. Exposures to 5 and 2.5 mg/m3 ZnO resulted in peak 8-fold increases in MT mRNA levels (compared to air-exposed control animal values) immediately after exposure, while 1 mg/m3 ZnO exposure caused a 3.5-fold elevation in MT mRNA. These levels returned to approximate control gene expression values 24 hr after exposure. In addition, ZnO exposure caused an immediate elevation in lung HO gene expression levels, with 8-, 11-, and 5-fold increases observed after the same ZnO exposure levels (p < 0.05). Like MT gene induction, HO mRNA values returned to approximate control levels 24 hr after exposure. In striking contrast to the induction of MT and HO gene expression after ZnO exposures, there was no elevation in gene expression following a 6-hr exposure to 0.5 and 1 ppm ozone, even when lungs were examined as late as 72 hr after exposure. Our results demonstrate the induction of target gene expression following the inhalation of ZnO at concentrations equal to, and below, the current recommended threshold limit value of 5 mg/m3 ZnO. Furthermore, the lack of effect of ozone exposure on MT and HO gene expression suggests no involvement of these genes in the acute respiratory response to this oxidant compound.

Differential accumulation of surfactant protein A, B, and C mRNAs in two epithelial cell types of hyperoxic lung

The physiologic response of the lung to oxygen toxicity is complex, and similar among all mammals studied. Acute exposure to 100% O2 results in severe decreases in respiratory function and is accompanied by alterations in pulmonary surfactant metabolism, including the regulation of surfactant proteins A, B, and C (SP-A, SP-B, SP-C). Because surfactant proteins and their mRNAs can be expressed in alveolar epithelial type II cells, and nonciliated bronchial epithelial (Clara) cells, we were interested in determining if alterations in the abundance of SP-A, SP-B, and SP-C mRNAs occurred differentially in these two cell types during hyperoxic lung injury. Using quantitative in situ hybridization, we found that hyperoxic lung injury resulted in nearly 20-fold increases in SP-A and SP-B mRNAs in Clara cells, with relatively small (2-fold or less) increases in type II cells. Immunohistochemical analysis suggested a commensurate increase in SP-A protein in Clara cells. SP-C mRNA was only detected in type II cells, and changed little in hyperoxic lung. Because Clara cells are not known to produce surfactant, and appear to lack SP-C mRNA, these observations suggest that increased SP-A and SP-B may serve nonsurfactant functions in hyperoxic lung.