O,S,S,-trimethyl phosphorodithioate-induced lung damage in rats and mice

Dichlorvos exposure to the Kölliker-fuse nuclei is sufficient but not necessary for OP induced apnea

Patients exposed to organophosphate (OP) compounds demonstrate a central apnea. The Kölliker-fuse nuclei (KF) are cholinergic nuclei in the brainstem involved in central respiratory control. We hypothesize that exposure of the KF is both necessary and sufficient for OP induced central apnea. We performed an animal study of acute OP exposure. Anesthetized and spontaneously breathing Wistar rats (n=24) were exposed to a lethal dose of dichlorvos using three experimental models. Experiment 1 (n=8) involved systemic OP poisoning using subcutaneous (SQ) 2,2-dichlorovinyl dimethyl phosphate (dichlorvos) at 100mg/kg or 3× LD50. Experiment 2 (n=8) involved isolated poisoning of the KF using stereotactic microinjections of dichlorvos (625μg in 50μl) into the KF. Experiment 3 (n=8) involved systemic OP poisoning with isolated protection of the KF using SQ dichlorvos (100mg/kg) and stereotactic microinjections of organophosphatase A (OpdA), an enzyme that degrades dichlorvos. Respiratory and cardiovascular parameters were recorded continuously. Animals were followed post exposure for 1h or until death. There was no difference in respiratory depression between animals with SQ dichlorvos and those with dichlorvos microinjected into the KF. Despite differences in amount of dichlorvos (100mg/kg vs. 1.8mg/kg) and method of exposure (SQ vs. CNS microinjection), 10min following dichlorvos both groups (SQ vs. microinjection respectively) demonstrated a similar percent decrease in respiratory rate (51.5 vs. 72.2), minute ventilation (49.2 vs. 68.8) and volume of expired gas (17.5 vs. 0.0). Animals with OpdA exposure to the KF during systemic OP exposure demonstrated less respiratory depression, compared to SQ dichlorvos alone (p<0.04). No animals with SQ dichlorvos survived past 25min post exposure, compared to 50% of animals with OpdA exposure to the KF. In conclusion, exposure of the KF is sufficient but not necessary for OP induced apnea. Protection of the KF during systemic OP exposure mitigates OP induced apnea.

Role of the lung in accumulation and metabolism of xenobiotic compounds--implications for chemically induced toxicity

The mammalian lung is exposed to and affected by many airborne and bloodborne foreign compounds. This review summarizes the role of lung in accumulation and metabolism of xenobiotics, some of which are spontaneously reactive or are metabolically activated to toxic intermediates. The specific architectural arrangement of mammalian lung favors that so-called pneumophilic drugs are filtered out of the blood and are retained within the tissue as shown in particular for amphetamine, chlorphentermine, amiodarone, imipramine, chlorpromazine, propranolol, local anaesthetics, and some miscellaneous therapeutics. There is strong evidence that intrapulmonary distribution activity and regulation of drug-metabolizing enzymes in lung is distinct from liver. This review focuses on the metabolic rate of selected compounds in lung such as 5-fluoro-2'-deoxyuridine, local anesthetics, nicotine, benzo(alpha)pyrene, ipomeanol, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone. It is widely accepted that the formation of radical species is a key event in the pneumotoxic mechanisms induced by bleomycin, paraquat, 3-methylindole, butylhydroxytoluene, or nitrofurantoin. Finally, methodological approaches to assess the capacity of lung to eliminate foreign compounds as well as biochemical features of the pulmonary tissue are evaluated briefly.

Effects of injury on [3H]putrescine uptake by types I and II cells in rat lung slices

The capacity of different lung parenchymal cells to accumulate putrescine was investigated by incubating slices of rat lung in a medium containing the tritiated compound. Quantitative examination of autoradiographs, by electron microscopy, indicated that accumulation of putrescine occurred in both the Type I and Type II cells of the alveolar epithelium. Putrescine uptake was abolished by the addition of spermidine to the medium or by incubating at 0 degrees C. Lung samples from rats dosed with the pneumotoxin O,S,S-trimethyl phosphorodithioate (OSSMeO), which selectively damages Type I pneumocytes, showed a large reduction in the uptake of label by both Type I and Type II cells. This treatment also resulted in an increase in the labeling of alveolar macrophages. Control samples, from undosed rats, were incubated in medium containing tritiated 5-hydroxytryptamine; this compound did not accumulate in epithelial cells but it was concentrated in the endothelium of the alveolar capillaries and in the blood cells within these vessels. The demonstration of putrescine uptake by both Type I and Type II pneumocytes, together with its reduction by dosing with OSSMeO, has vindicated the use of this activity, in lung slices, as an index of damage to the alveolar epithelium.

Morphogenesis of O,O,S-trimethyl phosphorothioate-induced pulmonary injury in mice

The purpose of this study was to establish and characterize an experimental model in mice that examined the pulmonary effects of O,O,S-trimethyl phosphorothioate (OOS-TMP), a contaminant present in commercially important organophosphorus insecticides. Characterization of the model will allow the delineation of comparative effects between species and its possible extrapolation to man, and provide an additional experimental animal species satisfactory for mechanistic-oriented studies on OOS-TMP and related compounds. The morphogenesis of pulmonary injury induced by OOS-TMP was studied in mice by light and transmission electron microscopy. Weanling female C57BL/Ka mice received OOS-TMP dissolved in corn oil by intraperitoneal injection and were studied at intervals from 6 to 168 hr after treatment. Morphologic changes were observed in Clara cells only at the initial time period examined. Injury of pulmonary parenchymal cell populations, including the endothelium and type I alveolar epithelium, occurred after morphologic changes indicative of severe cell injury and necrosis in Clara cells. Endothelial cell injury was accompanied by significant increases in wet lung weight and percentage lung water content. Type I alveolar epithelial cell injury and loss resulted in a bare basal lamina, followed by attenuation, hypertrophy, and hyperplasia of type II alveolar epithelial cells. The results of this study document the successful establishment of a mouse experimental model of OOS-TMP-induced pulmonary toxicity. It is concluded that the Clara cell was the initial and most severely affected pulmonary cell population in mice receiving OOS-TMP. The administration of OOS-TMP in mice also results in marked morphologic alterations in the pulmonary parenchyma that were accompanied by significant changes in lung weight and composition.

Pulmonary endothelial and alveolar epithelial lesions induced by O,O,S-trimethyl phosphorothioate in rats

The morphogenesis of pulmonary injury induced by an impurity present in a commercially important organophosphorus insecticide, O,O,S-trimethyl phosphorothioate (OOS-TMP), was studied by combined light and transmission electron microscopy. Weanling female WAG/Rij rats received OOS-TMP dissolved in corn oil by gavage and were studied at intervals from 6 to 168 h after treatment. Sequestration of neutrophils was initially observed at 12 h after treatment and was accompanied by interstitial oedema. Plasmalemma alterations in endothelium lining capillaries and small arteries and veins were observed from 12 to 120 h after treatment and were accompanied by endothelial cell detachment and separation from the basal lamina. Abundant aggregates of fibrin were sequentially observed in intravascular, interstitial, and alveolar spaces. Platelet aggregation and degranulation were occasionally observed in capillaries as early as 12 h after treatment, and frequently observed in capillaries and small vessels from 24 to 96 h after treatment. Significant increases in wet lung weight and lung water content occurred at the same time that morphologic changes were observed in pulmonary endothelium. Alterations in type I alveolar epithelial cells were initially observed at 24 h after treatment. Cell swelling, fragmentation, and necrosis were observed in both type I and type II cells and resulted in a bare basal lamina. Marked attenuation, hypertrophy, and proliferation of type II epithelial cells followed alveolar epithelial cell injury and loss. Minimal changes were observed in non-ciliated bronchiolar epithelial (Clara) cells; predominant changes included the loss of surface microvilli and apical cytoplasmic bulge. The results of this study indicate that the endothelium and alveolar epithelium are the predominant cell types in the rat lung injured following OOS-TMP administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary hydroxyproline content and production following treatment of mice with O,S,S-trimethyl phosphorodithioate

The systemic administration of O,S,S-trimethyl phosphorodithioate (OSS), a contaminant of various organophosphorus insecticides, induces delayed damage to rat and mouse lung tissue. The lesion, particularly in the rat, closely resembles that produced by butylated hydroxytoluene (BHT) in mice. Although the time course of cell damage and repair has been studied in both species, it is not clear whether excess collagen, indicative of fibrosis, is deposited. Changes in pulmonary hydroxyproline content and synthesis, indices of collagen metabolism, were analysed in mice treated with 45 mg/kg OSS. A significant increase in total lung hydroxyproline was evident 21 days after treatment compared to both pair-fed and ad libitum controls. This increase was not augmented by subsequent treatment with 35 mg/kg 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or exposure to 70% oxygen for 7 days. The rate at which lung tissue synthesized hydroxyproline was increased 7-14 days after treatment with OSS. These data demonstrate that treatment of mice with OSS results in changes indicative of pulmonary fibrosis. However, in contrast to some other lung-toxic chemicals, this lesion was not enhanced by subsequent treatment with BCNU or hyperoxia.