Endotoxin treatment protects rats against ozone-induced lung edema: with evidence for the role of manganese superoxide dismutase

Macrophages and tissue injury: agents of defense or destruction?

The past several years have seen the accumulation of evidence demonstrating that tissue injury induced by diverse toxicants is due not only to their direct effects on target tissues but also indirectly to the actions of resident and infiltrating macrophages. These cells release an array of mediators with cytotoxic, pro- and anti-inflammatory, angiogenic, fibrogenic, and mitogenic activity, which function to fight infections, limit tissue injury, and promote wound healing. However, following exposure to toxicants, macrophages can become hyperresponsive, resulting in uncontrolled or dysregulated release of mediators that exacerbate acute tissue injury and/or promote the development of chronic diseases such as fibrosis and cancer. Evidence suggests that the diverse activity of macrophages is mediated by distinct subpopulations that develop in response to signals within their microenvironment. Understanding the precise roles of these different macrophage populations in the pathogenic response to toxicants is key to designing effective treatments for minimizing tissue damage and chronic disease and for facilitating wound repair.

Mitochondrial antioxidant function is a potential mechanism for organ differences in interleukin-1-mediated tolerance to oxidative injury

BACKGROUND

Pretreatment with interleukin-1 (IL-1) induces resistance to lung injury from hyperoxia exposure and to cardiac dysfunction after ischemia-reperfusion in animal models. In contrast, IL-1 pretreatment did not produce tolerance to ischemia-reperfusion injury and did not seem to alter antioxidant enzyme activities in the kidney. Recently, we determined that mitochondria scavenge superoxide anion via a nonenzymatic mechanism and that this newly identified intracellular antioxidant function was inducible in the lung. Based on these observations, we hypothesized that organ differences after IL-1 pretreatment between the lung and the heart, which become tolerant, and the kidney, which does not become tolerant, were a consequence of differential responses in mitochondrial superoxide scavenging.

METHODS

Rats were given IL-1alpha (50 ng intratracheally, 36 hrs before assay) and lung and kidney mitochondria were isolated. Mitochondrial scavenging of superoxide anion was then determined by using an assay that we developed and published previously. We then tested the effects of IL-1 pretreatment on lung mitochondrial scavenging of superoxide after hyperoxia exposure.

RESULTS

We found that intratracheal administration of IL-1 did not affect lung mitochondrial superoxide scavenging but decreased kidney mitochondrial superoxide scavenging by 75%. In addition, IL-1 pretreatment preserved lung mitochondrial superoxide scavenging in rats exposed to hyperoxia (95% O2 for 24 hours) compared with untreated rats exposed to hyperoxia in which lung mitochondrial superoxide scavenging was decreased by more than 50%.

CONCLUSIONS

We conclude that IL-1 pretreatment has divergent effects on mitochondrial antioxidant function in the lung and the kidney and speculate that this may reflect previously unidentified tissue-specific differences in mitochondrial function during systemic inflammation. This study offers new insights into why the lung, but not the kidney, acquires tolerance to subsequent oxidative injury after IL-1 pretreatment.

Effects of intratracheal pretreatment with yttrium chloride (YCl3) on inflammatory responses of the rat lung following intratracheal instillation of YCl3

We investigated pulmonary clearance of yttrium (Y) and acute lung injury following intratracheal instillation (i.t.) of yttrium chloride (YCl3) in saline- or YCl3-pretreated rats (30 days before the second challenge). About 67% of the initial dose of Y remained in the lung even 31 days after the i.t. treatment. The pretreatment with YCl3 significantly reduced i.t.-YCl3-induced increases in biochemical inflammatory indicators in bronchoalveolar lavage fluid (BALF), such as lactate dehydrogenase, beta-glucuronidase, and alkaline phosphatase activities and protein concentration, while the pretreatment increased the number of polymorphonuclear leukocyte (PMN) in BALF. These results suggest that the augmentation of PMN infiltration does not play an important role, if any, in i.t. YCl3-induced increases in biochemical indicators in BALF. The reduction of the increases in those biochemical inflammatory indicators may be due, at least in part, to the increase of manganese-superoxide dismutase (Mn-SOD) activity in the lung tissue, because the lung Mn-SOD activity in the YCl3-pretreated group was two times higher than that of the saline-pretreated group.

Role of oxidants in influenza virus-induced gene expression

Influenza virus-induced epithelial damage may be mediated, in part, by reactive oxygen intermediates (ROIs). In this study, we investigated the role of ROIs in the influenza virus-induced gene expression of antioxidant enzymes and in the activation of nuclear factor-kappa B (NF-kappa B), an oxidant-sensitive transcriptional factor. Influenza virus infection increased production of intracellular ROIs in A549 pulmonary epithelial cells. Induction of manganese superoxide dismutase (MnSOD) mRNA correlated with increased MnSOD protein and enzyme activity. Influenza virus infection also activated NF-kappa B binding as determined by an electrophoretic mobility shift assay. Pretreatment of A549 cells with N-acetyl-L-cysteine attenuated virus-induced NF-kappa B activation and interleukin (IL)-8 mRNA induction but did not block induction of MnSOD mRNA. In contrast, pyrrolidine dithiocarbamate blocked activation of NF-kappa B and induction of MnSOD and IL-8 mRNAs. Treatment with pyrrolidine dithiocarbamate also markedly decreased virus-induced cell death. Thus oxidants are involved in influenza virus-induced activation of NF-kappa B, in the expression of IL-8 and MnSOD, and in virus-induced cell death.

Development of an experimental model of epilepsy in rats exposed to ozone

Paroxysmal activity has been reported in the olfactory bulb of rabbits chronically exposed to ozone (O3), postulating that this gas provokes alterations in the electrical activity of the central nervous system. The effects of 1 ppm of O3 inhaled daily for 1 or 3 h prior to each stimulation were studied using the kindling model of epilepsy. Results showed that O3 decreased the duration of the amygdaloid after-discharges during the development of kindling and shortened the latency to the onset of the first generalized seizure in rats exposed for 1 h to O3, while the group exposed for 3 h also decreased the after-discharge duration but delayed the appearance of seizures. Spread of seizure activity, defined as the latency to reach behavioral and electrographic signs of tonic clonic seizures was faster in the 1 h O3 exposed rats and slower in those exposed for 3 h. These findings demonstrate that O3 or its reaction products, such as free radicals, could affect the mechanisms involved in kindling course, such changes being dependent of the time of O3 exposure.

Cloning and characterization of the murine manganous superoxide dismutase-encoding gene

The murine manganous superoxide dismutase-encoding gene (MnSOD) is highly homologous in both sequence and organization to its rat homolog. MnSOD is encoded by five exons spanning approx. 7 kb of DNA. RNA blot analysis indicated multiple RNA species, with the major RNA corresponding to a 960-bp message. This major transcript is highly inducible by tumor necrosis factor (TNF) in murine fibroblasts. Analysis of other murine tissues demonstrated ubiquitous expression. RNase protection and primer extension assays used to map the 5' end of the gene revealed a series of closely spaced multiple transcription start points. Sequence analysis of the 1.7 kb of 5' flanking DNA showed high homology to the 5' proximal 950 bp of the rat homolog. Within this region, multiple potential regulatory elements are present, including several SP1 sites, two NF kappa B sites and an antioxidant-response element. However, no TATA box was identified, placing MnSOD in the family of inducible genes that lack consensus TATA-box elements and contain G+C-rich promoter regions.