Inhibition of cholinephosphotransferase activity in lung injury induced by 2-chloroethyl ethyl sulfide, a mustard analog

Abstract

Exposure to mustard gas causes inflammatory lung diseases including acute respiratory distress syndrome (ARDS). A defect in the lung surfactant system has been implicated as a cause of ARDS. A major component of lung surfactant is dipalmitoyl phosphatidylcholine (DPPC) and the major pathway for its synthesis is the cytidine diphosphocholine (CDP-choline) pathway. It is not known whether the ARDS induced by mustard gas is mediated by its direct effects on some of the enzymes in the CDP-choline pathway. In the present study we investigated whether mustard gas exposure modulates the activity of cholinephosphotransferase (CPT) the terminal enzyme by CDP-choline pathway. Adult guinea pigs were intratracheally infused with single doses of 2-chloroethyl ethyl sulfide (CEES) (0.5 mg/kg b.wt. in ethanol). Control animals were injected with vehicles only. The animals were sacrificed at different time and the lungs were removed after perfusion with physiological saline. CPT activity increased steadily up to 4 h and then decreased at 6 h and stabilized at 7 days in both mitochondria and microsomes. To determine the dose-dependent effect of CEES on CPT activity we varied the doses of CEES (0.5-6.0 mg/kg b.wt.) and sacrificed the animals at 1 h and 4 h. CPT activity showed a dose-dependent increase of up to 2.0 mg/kg b.wt. of CEES in both mitochondria and microsomes then decreased at 4.0 mg/kg b.wt. For further studies we used a fixed single dose of CEES (2.0 mg/kg b.wt.) and fixed exposure time (7 days). Lung injury was determined by measuring the leakage of iodinated-bovine serum albumin into lung tissue and expressed as the permeability index. CEES exposure (2.0 mg/kg b.wt. for 7 days) caused a significant decrease of both CPT gene expression (approximately 1.7-fold) and activity (approximately 1.5-fold) in the lung. This decrease in CPT activity was not associated with any mutation of the CPT gene. Previously we reported that CEES infusion increased the production of ceramides which are known to modulate PC synthesis. To determine whether ceramides affect microsomal CPT activity the lung microsomal fraction was incubated with different concentrations of C(2)-ceramide prior to CPT assay. CPT activity decreased significantly with increasing dose and time. The present study indicates that CEES causes lung injury and significantly decreases CPT gene expression and activity. This decrease in CPT activity was not associated with any mutation of the CPT gene is probably mediated by accumulation of ceramides. CEES induced ceramide accumulation may thus play an important role in the development of ARDS by modulating CPT enzyme.

Inflammatory effects of inhaled sulfur mustard in rat lung

“…We found that SM exposure resulted in a time-dependent decrease in native SP-D expression in bronchiolar epithelial cells which was directly correlated with inflammation and tissue injury. These results are consistent with reports that mustards damage type II cells and alter the surface tension of BAL, and suggest a potential mechanism leading to the development of acute respiratory distress syndrome in SM-exposed individuals (van Helden et al, 2004; Sinha Roy et al, 2005; Mukhopadhyay et al, 2008). Interestingly, SP-D staining increased in alveolar macrophages following SM exposure which was likely due to uptake of the protein by these phagocytic cells.…”

Surfactant phospholipid metabolism

“…The two forms of CPT are localized in ER/microsomes and mitochondria in the fetal lung and type II epithelial cells that differ by their substrate specificity based on preference for unsaturated or saturated DAGs, K m values, and sensitivity to inhibitors [89, 90]. CPT levels appear also to be regulated at the level of protein stability [91] and by inhibitory lipids such as ceramides [90, 92]. CPT activity is upregulated just prior to birth, decreasing in the adult lung [93].…”