The Clara cell: an electron microscopy examination of the terminal bronchioles of rats and monkeys following inhalation of hexachlorocyclopentadiene

Early onset of neurological symptoms in fragile X premutation carriers exposed to neurotoxins

We present four cases of fragile X premutation carriers with early neurological symptoms, including symptoms consistent with multiple sclerosis (MS) and fragile X-associated tremor/ataxia syndrome (FXTAS). Each patient had significant exposure to one or more environmental neurotoxicants that have documented neurotoxicity (i.e. hexachlorocyclopentadiene or C56, Agent Orange, and 2,4- or 2,6-toluene diisocyanate and dichlormate). We hypothesize that premutation carriers are a vulnerable group to neurotoxins because elevated mRNA in the premutation can lead to early cell death and brain disease, leading to neuropsychiatric and neurological symptoms consistent with FXTAS.

Ultrastructural changes in rat Clara cells induced by bis(4-amino-3-methylcyclohexyl)methane

Repeated oral administration of bis(4-amino-3-methylcyclohexyl)methane to rats induced unusual ultrastructural changes in Clara cells of the bronchiolar epithelium, involving marked accumulation of electron-dense inclusion bodies with a lamellar structure in the cytoplasm. The appearance of the inclusion bodies was speculated to result from accumulation of complexes formed between the agent and phospholipids within lysosomes, a condition known as drug-induced lipidosis. This finding appeared noteworthy, since it might reflect high potential for metabolism of xenobiotic compounds in Clara cells.

Ultrastructural effects of phosphorothionates and other inhibitors of lung monooxygenases: protection against trialkylphosphorothiolate-induced lung injury

An oral dose (25 mg/kg) of O,O,S-triethylphosphorothiolate (OOSEtO) to rats results in selective injury of type I pneumocytes, degranulation of Clara cells, and pronounced increase in lung weight. A dose (12.5 mg/kg) of the related compound O,O,S-trimethylphosphorothionate (OOSMeS) causes neither injury nor degranulation but, when administered 2 h before OOSEtO (25 mg/kg), protects against all the signs of lung injury that would otherwise result from this dose of the compound. The administration of OOSMeS also results in the formation of large, electron-lucent granules within the apical cytoplasm of the Clara cells. The granules are not birefringent, and histochemical procedures indicate that they do not contain carbohydrate but may consist of lipid accumulated around a proteinaceous core. Similar granules are also observed after administration of p-xylene, pseudocumene, and the pesticide bromophos. These compounds, like OOSMeS, inhibit 7-ethoxycoumarin O-deethylase activity in the lung and are capable of protecting against trialkylphosphorothiolate toxicity. This inhibition of 7-ethoxycoumarin O-deethylase activity suggests loss of pulmonary cytochrome P-450. This loss may account for both the protective action of these compounds and the formation of abnormal granules within Clara cells.

Comparative cytotoxicity of naphthalene and its monomethyl- and mononitro-derivatives in the mouse lung

Male Swiss-Webster mice were exposed to naphthalene, 1-methyl-, 2-methyl-, 1-nitro- and 2-nitronaphthalene by intraperitoneal injection of peanut oil solutions over a dose range of 0.5-3.0 mmol kg-1 body weight. Treated mice were killed at times from 6 hours to 14 days post-treatment. Tissues were analyzed for cytotoxic effects by optical and electron microscopy, and for cell proliferation by autoradiography following in vitro labeling of lung slices with 3H-thymidine. The naphthalene derivatives varied widely in their cytotoxic effects. The most toxic was 1-nitronaphthalene with no mice surviving doses greater than 1 mmol kg-1. Naphthalene and 2-methylnaphthalene were about equally toxic, followed by 2-nitro- and 1-methylnaphthalene, in decreasing order of toxicity. In all cases the first evidence of cytotoxic effects was seen in the Clara cells of the bronchiolar epithelium, and, at the highest doses, toxic effects were found in the adjacent ciliated cells. Changes could be detected at the ultrastructural level at all doses, and within 6 hours after treatment. Only slight effects were seen in other cell types. Increased cell proliferation following chemical treatment was seen only in the bronchiolar epithelium, among cells tentatively identified as Clara cells or their precursors. Cytotoxic effects of naphthalene and its 1- and 2-methyl derivatives were confined to the lung, with minimal evidence of toxicity in the liver and kidney. The mononitronaphthalenes both produce small areas of centrizonal necrosis in the liver, but no discernible effects in the kidney. The experiments demonstrate the effect of small structural differences on the cytotoxicity of this group of environmental pollutants and also illustrate the sensitivity of the Clara cell as a target for xenobiotics.

The Clara cell and pulmonary surfactant: a study using selective chemical ablation

Administration of 3-hydroxymethylfuran-N-ethylcarbamate (HFC) to female hamsters via the jugular vein under pentobarbitone anaesthetic at 20 mg per kg body weight produced pronounced necrosis of the Clara cells without apparent morphological effect on other cell types as judged by transmission electron microscope examination. The surfactant material recoverable by minimal lavage followed by purification by sucrose gradient ultracentrifugation increased, reaching a maximum around 48 h after treatment. At this time static pressure/volume measurements on isolated lungs indicated an increase in airway surface compliance. Lavageable surfactant phospholipid composition was examined by 31P nuclear magnetic resonance (n.m.r.). The distribution of phospholipids between the various classes was unchanged by HFC treatment. No change in the total lung surfactant pool size was seen. These results are discussed in relation to the possible roles of the Clara cell in influencing airway surfactant levels.