Progressive Pulmonary Pathology of Two Organofluorine Compounds in Rats

Reactive oxygen species produced in metal-catalyzed oxidation of bis(trifluoromethyl)disulfide and protection by ZE

Bis(trifluoromethyl)disulfide (TFD), used as an industrial fumigant, was found to generate a thiyl free radical as seen by EPR/spin trapping. Oxygen appears to be an absolute requirement for radical production. The results obtained in this investigation implicate the production of thiyl and reactive oxygen species (ROS), superoxide radical anion and hydroxyl radicals, during TFD autoxidation. The rate of production of these free radical intermediates was found to increase in the presence of iron(III) and copper(II). In addition, the metal ion chelator DETAPAC and ROS scavengers ethanol, mannitol, and PEG-SOD/catalase were found to inhibit free radical production. Reactive oxygen species were not formed when a high-potency zinc plus antioxidant, ZE caps, was present. These results provide support for the pro-oxidation of TFD and a protective role for zinc.

Retention of inhaled perfluoroisobutene in the rat

Perfluoroisobutene (PFIB) is produced by the pyrolysis, and as a by-product during the manufacture, of polytetrafluoroethylene. When inhaled it produces a fulminating and sometimes fatal pulmonary oedema similar to that of phosgene after a latent period of 6-8 h. As part of a study to determine the retained dose and the factors that control the amount retained, this study has investigated the retention in rats of inhaled PFIB at concentrations of 10, 50 and 250 micrograms l-1 in a flow-through system combining head-only exposure and plethysmography. Uptake of PFIB was measured by gas chromatography during elevated and reduced inspired volume and respiratory rate induced by exposure to increased CO2 and injection of pentobarbitone, respectively. The percentage of PFIB retained in the upper airways and lungs was found to be 27.5, 28.1 and 23.7% of the amount inspired at the three concentrations tested. The rate of uptake (nmol min-1 kg-1) of PFIB was a power law of the amount inhaled, an n-fold increase in minute volume producing an nb-fold increase in uptake, where b varied between 0.4 and 0.85. Thus, doubling the inhaled dose produces a 1.3-1.8-fold increase in uptake with a corresponding decrease in percentage retained. The relative contribution of respiratory rate and tidal volume upon PFIB retention could not be defined.

Protection by cysteine esters against chemically induced pulmonary oedema

Perfluoroisobutene (PFIB) is a hydrophobic reactive gas produced by the pyrolysis of polytetrafluoroethane which induces pulmonary oedema similar to that induced by phosgene when inhaled. When a lethal dose is inhaled by Porton strain rats total non-protein thiol (NPSH) and glutathione (GSH) in the lung are reduced by between 30 and 49%, respectively. If the endogenous levels of thiols in the lung are reduced by pretreatment with buthionine sulfoximine (BSO) 16 hr before exposure to PFIB, the rats become more susceptible to the effects of the gas. The effect of BSO pretreatment on toxicity was prevented by pretreatment 30 min before exposure, with 5 mmol/kg N-acetylcysteine (NAc). NAc increased the levels of cysteine (CySH) in the lung by 150% and GSH was unaffected. Similarly pretreatment with 3 mmol/kg CySH also protected against toxicity and raised CySH levels by 100%. A series of cysteine esters and cystine dimethyl ester (CDME) have been synthesised which selectively raise lung levels of CySH in the rat lungs after intraperitoneal (i.p.) injection. The methyl ester and CDME raised lung levels of CySH by 4000 and 2000%, respectively, 10 min after i.p. injection whilst GSH levels remained unchanged. Cysteine isopropyl ester raised lung levels of CySH by 10,600% but liver levels by only 1400%. All esters except the t-butyl ester (CTBE) also raised maximal plasma levels of NPSH by up to 500%; however, when NAc was injected plasma levels increased by over 1500%. Rats treated with these esters at 3 mmol/kg and with NAc at 5 mmol/kg were protected against lethal doses of PFIB in all cases except when CTBE was used. It appears that these cysteine esters may distribute preferentially into the lung, unlike NAc. The selective enhancement of pulmonary CySH levels may provide a method for the protection of lungs against inhaled reactive toxicants by increasing intracellular CySH. Levels of CySH may also be raised in epithelial lining fluid thus reducing access of gaseous toxicants to pulmonary tissue.

The effects of exercise following exposure to bis(trifluoromethyl) disulfide

Bis(trifluoromethyl) disulfide (TFD) was originally designed for use as an agricultural fumigant. Inhalation of toxic doses of TFD results in varying degrees of pulmonary edema. The purpose of this study was to determine if exhaustive exercise would potentiate the toxic effects of TFD. One group of treadmill-acclimated rats was exercised to exhaustion following a 10-minute whole-body exposure to TFD. A second group was similarly exposed but not exercised. Two other groups of rats were sham exposed; one was exercised while one remained sedentary following the sham exposure. Twenty-four hours after exposure, the animals were sacrificed; the lungs were removed and weighed, and a portion was collected for histopathologic examination. The remaining lung tissue was allowed to dry to constant weight. There was no difference in endurance times between exposed and sham-exposed rats. There was a significant increase in the amount of pulmonary edema and associated pulmonary pathology in rats exercised following exposure to TFD. Eleven of twelve animals exercised following exposure to TFD and three of twelve animals which remained sedentary following exposure died by 24 hours. The degree of pulmonary pathology in all rats exposed to TFD was profound.