Received for publication February 4, 2005.
Revised April 11, 2005.
Accepted for publication April 18, 2005.

Consequences of abrupt glutathione depletion in murine Clara cells: ultrastructural and biochemical investigations into the role of glutathione loss in naphthalene cytotoxicity

Abstract

Glutathione plays many critical roles within the cell, including offering protection from reactive chemicals. The bioactivated toxicant naphthalene forms chemically reactive intermediates that can deplete glutathione and covalently bind to cellular proteins. Naphthalene selectively injures the non-ciliated epithelial cells of the intrapulmonary airways (i.e. Clara cells). This study attempted to define what role glutathione loss plays in naphthalene cytotoxicity by comparing Swiss-Webster mice treated with naphthalene to those treated with the glutathione depletor diethylmaleate. High-resolution imaging techniques were employed to evaluate acute changes in Clara cell ultrastructure, membrane permeability, and cytoskeleton structure. A single dose of either diethylmaleate (1000 mg/kg) or naphthalene (200 mg/kg) caused similar glutathione losses in intrapulmonary airways (<20% of control). Diethylmaleate did not increase membrane permeability, disrupt mitochondria, or lead to cell death; hallmark features of naphthalene cytotoxicity. However, diethylmaleate treatment did cause Clara cell swelling, plasma membrane blebs, and actin cytoskeleton disruptions similar to naphthalene treatment. Structural changes in mitochondria and Golgi bodies were also noted. Changes in ATP levels were measured as an indication of overall cell function, in isolated airway explants incubated with diethylmaleate, naphthalene, or naphthalene metabolites in vitro. Only the reactive metabolites of naphthalene caused significant ATP losses. Unlike the lethal injury caused by naphthalene, the disruptive cellular changes associated with glutathione loss from diethylmaleate appeared to be reversible, following recovery of glutathione levels. This suggests that glutathione depletion may be responsible for some aspects of naphthalene cytotoxicity, but is not sufficient to cause cell death without further stresses.

Key words: Clara cells, diethylmaleate, glutathione, naphthalene, respiratory toxicology, ultrastructure

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