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.