DNA damage detected by the alkaline comet assay in the liver of mice after oral administration of tetrachloroethylene.

Induction of DNA damage in the liver and kidney of male CD1 mice was studied by means of the alkaline Comet assay after oral administration of tetrachloroethylene at the doses of 1000 and 2000 mg/kg/day. A statistically significant dose-related increase in tail intensity was established in hepatocytes, indicating that tetrachloroethylene induced DNA damage in the liver. No effect on DNA damage was observed in the kidney. The results are in agreement with carcinogenicity data in mice, in which tetrachloroethylene induced tumours in the liver but not in the kidney, and support that a genotoxic mode of action might be involved in liver carcinogenicity in mice. An alternative interpretation of the results conveyed by the Study director at the test facility, involving that tetrachloroethylene did not induce DNA damage in the liver and kidney of mice, is also presented and discussed.

Uptake of cobalt from the nasal mucosa into the brain via olfactory pathways in rats.

In the olfactory epithelium the primary olfactory neurons are in contact with the environment in the nasal cavity and they are also connected to the olfactory bulbs of the brain. These neurons may therefore provide a pathway by which foreign materials may reach the brain. Inhalation of cobalt-containing dust or fumes occurs in several workplaces, which may result in high exposure of the nasal tissues. In the present study, we used autoradiography and gamma-spectrometry to examine the transport of cobalt in the olfactory system after intranasal administration of 57Co2+ in rats. The results showed an uptake of the metal in the olfactory mucosa and a transport to the olfactory bulbs of the brain. The metal accumulated in the olfactory nerve layer and the terminals of the primary olfactory neurons in the glomerular layer of the bulb. In addition, low levels of cobalt were seen to migrate into the interior of the bulbs and the anterior parts of the olfactory cortex, indicating that the metal is able to leave the terminals of the primary olfactory neurons. Occupational exposure to cobalt, which is a neurotoxic metal, occurs in several workplaces, e.g. the hard metal industry. Memory deficits have been observed among workers exposed to hard metal via inhalation, and it was considered that cobalt may be the neurotoxic component of the hard metal. We propose that inhaled hard metal (as a dust powder or in a mist form) is deposited in the nasal passages and that released cobalt, after uptake into the brain via the olfactory pathway, may cause neurotoxicity. We consider that the olfactory route of entry of cobalt into the brain may be important and should be taken into account when risk assessments are performed concerning occupational inhalation of this metal.

Transport and subcellular distribution of intranasally administered zinc in the olfactory system of rats and pikes.

Zinc is an essential element, which can act as a neuromodulator and also is bound in zinc proteins in the brain. The olfactory bulb contains high concentrations of zinc. In the present study, 65Zn(2+) was applied on the olfactory epithelium of rats and pikes and the transport of the metal in the olfactory system was then examined. Administration of 65Zn(2+) in the nasal cavity of rats or the olfactory chambers in pikes resulted in an uptake of the metal in the olfactory epithelium and a transport of the metal along the primary olfactory neurons to their terminations in the olfactory bulbs. Low levels of 65Zn(2+) passed these terminals and continued into the interior of the bulbs. In the rats 65Zn(2+) was also detected in the anterior parts of the olfactory cortex. Subcellular fractionations of the olfactory mucosa and olfactory bulb of rats given 65Zn(2+) intranasally showed that the metal is bound both to particulate cellular constituents and to cytosolic components in these tissues. Gel chromatography indicated that some of the zinc in the cytosol is bound to metallothionein in the olfactory mucosa and bulb. Inhalation of zinc-containing dusts or fumes occurs in some work-places and may imply high exposure of the nasal tissues. It is not known whether neurotoxicity may be related to uptake of zinc in the olfactory system. However, this is an issue which deserves attention, since zinc dysregulation has been implied to play a role in Alzheimer's disease. In addition, impairment of the sense of smell and degenerative changes of the olfactory tissues have been seen in early stages of some neurodegenerative disorders.

Cadmium-metallothionein interactions in the olfactory pathways of rats and pikes.

Deposition of cadmium onto the olfactory epithelium results in transport of the metal along the primary olfactory neurons to the olfactory bulbs of the brain. The present investigation was undertaken to determine the intracellular ligand binding of cadmium during this process. (109)Cd(2+) was applied on the olfactory epithelium of rats and pikes, and the subcellular distribution of the metal in the olfactory pathways was then examined. Two groups of rats were used: one pretreated with intranasal instillations of nonlabeled cadmium and the other given physiological saline (controls). Cellular fractionations showed that the (109)Cd(2+) was predominantly present in the cytosol of all samples, both in the rats and the pikes. Gel filtrations of the olfactory epithelium of control rats killed 2 h after the (109)Cd(2+) instillation showed that the metal was recovered in two peaks with elution volumes corresponding to metallothionein (MT) and glutathione (GSH)-the latter peak being the predominant one. However, in the epithelium of the cadmium-pretreated rats killed at 2 h, (109)Cd(2+) was recovered in one peak corresponding to MT. In the olfactory epithelium and bulbs of both groups of rats killed at 48 h, as well as in the olfactory epithelium, nerves, and bulbs of pikes killed at this interval, (109)Cd(2+) was recovered in one peak corresponding to MT. Immunohistochemistry of the olfactory system of rats given cadmium in the right nasal cavity showed induction of MT in the neuronal, sustentacular, and basal cells of the right olfactory epithelium, in the nerve fascicles in the lamina propria of the right olfactory mucosa, and in the olfactory nerve layer of the right olfactory bulb. On the left side, the immunoreactivity was low in these structures. MT immunoreactivity was observed in the glomeruli of both the right and the left olfactory bulbs. However, the staining was homogeneously distributed within the entire glomeruli of the right bulb, whereas it showed a mesh-like pattern corresponding to the localization of astrocytes in the glomeruli of the left bulb. We conclude that exposure of the olfactory epithelium to cadmium results in induction of MT in the primary olfactory neurons and a transport of the metal in these neurons as a cadmium-metallothionein (CdMT) complex. Our results further indicate that GSH is a ligand that can interact with cadmium before the metal binds to MT.