The role of inflammatory mediators in the synergistic toxicity of ozone and 1-nitronaphthalene in rat airways

Pharmaceutical Effects of Inhibiting the Soluble Epoxide Hydrolase in Canine Osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease that causes pain and bone deterioration driven by an increase in prostaglandins (PGs) and inflammatory cytokines. Current treatments focus on inhibiting prostaglandin production, a pro-inflammatory lipid metabolite, with NSAID drugs; however, other lipid signaling targets could provide safer and more effective treatment strategies. Epoxides of polyunsaturated fatty acids (PUFAs) are anti-inflammatory lipid mediators that are rapidly metabolized by the soluble epoxide hydrolase (sEH) into corresponding vicinal diols. Interestingly, diol levels are increased in the synovial fluid of humans with OA, warranting further research on the biological role of this lipid pathway in the progression of OA. sEH inhibitors (sEHI) stabilize these biologically active, anti-inflammatory lipid epoxides, resulting in analgesia in both neuropathic, and inflammatory pain conditions. Most experimental studies testing the analgesic effects of sEH inhibitors have used experimental rodent models, which do not completely represent the complex etiology of painful diseases. Here, we tested the efficacy of sEHI in aged dogs with natural arthritis to provide a better representation of the clinical manifestations of pain. Two sEHI were administered orally, once daily for 5 days to dogs with naturally occurring arthritis to assess efficacy and pharmacokinetics. Blinded technicians recorded the behavior of the arthritic dogs based on pre-determined criteria to assess pain and function. After 5 days, EC1728 significantly reduced pain at a dose of 5 mg/kg compared to vehicle controls. Pharmacokinetic evaluation showed concentrations exceeding the enzyme potency in both plasma and synovial fluid. In vitro data showed that epoxyeicosatrienoic acid (EETs), epoxide metabolites of arachidonic acid, decreased inflammatory cytokines, IL-6 and TNF-α, and reduced cytotoxicity in canine chondrocytes challenged with IL1β to simulate an arthritic environment. These results provide the first example of altering lipid epoxides as a therapeutic target for OA potentially acting by protecting chondrocytes from inflammatory induced cytotoxicity. Considering the challenges and high variability of naturally occurring disease in aged dogs, these data provide initial proof of concept justification that inhibiting the sEH is a non-NSAID, non-opioid, disease altering strategy for treating OA, and warrants further investigation.

Increased lung resistance after diesel particulate and ozone co-exposure not associated with enhanced lung inflammation in allergic mice

Exposure to diesel exhaust particulate matter (DEP) exacerbates asthma. Likewise, similar effects have been reported with exposure to the oxidizing air pollutant ozone (O(3)). Since levels of both pollutants in ambient air tend to be simultaneously elevated, we investigated the possible synergistic effect of these agents on the exacerbation of allergic airways disease in mice. Male BALB/c mice were sensitized ip with ovalbumin (Ova) or vehicle only, then exposed once per week for 4 wk via nose-only inhalation (4 h) to the PM(2.5) fraction of DEP (2 mg/m(3)), O(3) (0.5 ppm), DEP and O(3), or filtered air, and then challenged with aerosolized ovalbumin. Ova sensitization in air-exposed mice enhanced pulmonary inflammatory cell infiltration, several indicators of injury in the lung (lactate dehydrogenase, albumin and total protein), and lung resistance (R(L)) and elastance (E(L)) in response to methacholine (MCh) aerosol challenge. DEP exposure did not enhance the Ova-induced increase in pulmonary cell infiltration, indicators of injury, or R(L) and E(L). O(3) exposure enhanced the Ova-induced increase in inflammatory cell infiltration and N-acetylglucosaminidase (NAG) in the lung, but had no effect on R(L) or E(L). DEP co-exposure significantly attenuated the O(3)-induced increase in cell infiltration and indicators of injury; co-exposure had no effect on E(L) relative to air-exposed Ova-sensitized mice. However, only DEP-O(3) co-exposure significantly increased the Ova-induced increase in R(L). Thus, O(3) and DEP co-exposure exacerbated airways hyperresponsiveness, a response that was not associated with parallel increases in pulmonary inflammation and one that may be mediated by a unique mechanism.

HPLC/MS/MS-based approaches for detection and quantification of eicosanoids

Eicosanoids are oxygenated, endogenous, unsaturated fatty acids derived from arachidonic acid. Detection and quantification of these compounds are of great interest because they play important roles in a number of significant diseases, including asthma, chronic obstructive pulmonary disease (COPD), cardiovascular disease, and cancer. Because the endogenous levels of eicosanoids are quite low, sensitive and specific analytical methods are required to reliably quantify these compounds. High-performance liquid chromatography mass spectrometry (HPLC/MS) has emerged as one of the main techniques used in eicosanoid profiling. Herein, we describe the main LC/MS techniques and principles as well as their application in eicosanoid analysis. In addition, a protocol is given for extracting eicosanoids from biological samples, using bronchoalveolar lavage fluid (BALF) as an example. The method and instrument optimization procedures are presented, followed by the analysis of eicosanoid standards using reverse phase HPLC interfaced with an ion trap mass spectrometer (LC/MS/MS). This protocol is intended to provide a broad description of the field for readers looking for an introduction to the methodologies involved in eicosanoid quantification.

Toxicity and metabolism of methylnaphthalenes: comparison with naphthalene and 1-nitronaphthalene

Naphthalene and close structural analogues have been shown to cause necrosis of bronchiolar epithelial cells in mice by both inhalation exposure and by systemic administration. Cancer bioassays of naphthalene in mice have demonstrated a slight increase in bronchiolar/alveolar adenomas in female mice, and in inflammation and metaplasia of the olfactory epithelium in the nasal cavity. Similar work in rats demonstrated a significant, and concentration-dependent increase in the incidence of respiratory epithelial adenomas and neuroblastomas in the nasal epithelium of both male and female rats. Although the studies on the acute toxicity of the methylnaphthalene derivatives are more limited, it appears that the species selective toxicity associated with naphthalene administration also is observed with methylnaphthalenes. Chronic administration of the methylnaphthalenes, however, failed to demonstrate the same oncogenic potential as that observed with naphthalene. The information available on the isopropylnaphthalene derivatives suggests that they are not cytotoxic. Like the methylnaphthalenes, 1-nitronaphthalene causes lesions in both Clara and ciliated cells. However, the species selective lung toxicity observed in the mouse with both naphthalene and the methylnaphthalenes is not seen with 1-nitronaphthalene. With 1-nitronaphthalene, the rat is far more susceptible to parenteral administration of the compound than mice. The wide-spread distribution of these compounds in the environment and the high potential for low level exposure to humans supports a need for further work on the mechanisms of toxicity in animal models with attention to whether these processes are applicable to humans. Although it is tempting to suppose that the toxicity and mechanisms of toxicity of the alkylnaphthalenes and nitronaphthalenes are similar to naphthalene, there is sufficient published literature to suggest that this may not be the case. Certainly the enzymes involved in the metabolic activation of each of these substrates are likely to differ. The available data showing extensive oxidation of the aromatic nucleus of naphthalene, nitronaphthalene and the methylnaphthalenes (with some oxidation of the methyl group) contrast with the isopropylnaphthalene derivatives, where the major metabolites involve side chain oxidation. Overall, these data support the view that ring epoxidation is a key step in the process involved in cytotoxicity. Whether the epoxide itself or a downstream metabolite mediates the toxic effects is still not clear even with naphthalene, the best studied of this group of compounds. Additional work is needed in several areas to further assess the potential human health consequences of exposure to these agents. These studies should involve the definition of the extent and severity of methylnaphthalene toxicity after single dose exposures with attention to both the nasal and respiratory epithelia. The cytochromes P450 responsible for the initial activation of these agents in rodents with subsequent complimentary studies in primate models should help determine whether key metabolic processes responsible for toxicity occur also in primates. Finally, the precise involvement of reactive metabolite formation and adduction of cellular proteins in toxicity will be important in not only assessing the potential for human toxicity, but also in developing an understanding of the genetic and environmental factors which could alter the toxicity of these agents.

Long-term ozone exposure attenuates 1-nitronaphthalene-induced cytotoxicity in nasal mucosa

1-Nitronaphthalene (1-NN) and ozone are cytotoxic air pollutants commonly found as components of photochemical smog. The mechanism of toxicity for 1-NN involves bioactivation by cytochrome P450s and subsequent adduction to proteins. Previous studies have shown that 1-NN toxicity in the lung is considerably higher in rats after long-term exposure to ozone compared with the corresponding filtered air-exposed control rats. The aim of the present study was to establish whether long-term exposure to ozone alters the susceptibility of nasal mucosa to the bioactivated toxicant, 1-NN. Adult male Sprague-Dawley rats were exposed to filtered air or 0.8 ppm ozone for 8 hours per day for 90 days, followed by a single treatment with 0, 12.5, or 50.0 mg/kg 1-NN by intraperitoneal injection. The results of the histopathologic analyses show that the nasal mucosa of rats is a target of systemic 1-NN, and that long-term ozone exposure markedly lessens the severity of injury, as well as the protein adduct formation by reactive 1-NN metabolites. The antagonistic effects were primarily seen in the nasal transitional epithelium, which corresponds to the main site of histologic changes attributed to ozone exposure (goblet cell metaplasia and hyperplasia). Long-term ozone exposure did not appear to alter susceptibility to 1-NN injury in other nasal regions. This study shows that long-term ozone exposure has a protective effect on the susceptibility of nasal transitional epithelium to subsequent 1-NN, a result that clearly contrasts with the synergistic toxicological effect observed in pulmonary airway epithelium in response to the same exposure regimen.