Chronic exposure to formaldehyde: relationship to hepatic metallothionein synthesis, indices of oxidant stress, and immunotoxicity

ABSTRACT

This study included forty male albino rats divided into four groups. Each group consisted of ten rats. The first group was exposed to formaldehyde for two weeks, the second for four weeks and the third for six weeks. The last group of animals served as controls and received phosphate buffered saline, the vehicle used to dissolve formaldehyde. Immediately after sacrifice, the liver of each animal was homogenized and used for determination of glutathione-S- transferase [GST], metallothionein, total thiols, catalase, lipid peroxides [LPER], nitric oxide[NO] and adenosine deaminase [ADA]. The study revealed significant increase in GST which remained significant irrespective to the time of exposure. Metallothionein was significantly increased in these animals in a time dependant manner. The levels of GST activity and metallothionein were significantly correlated reflecting the carcinogenic potential of formaldehyde. Meanwhile, rats exposed to formaldehyde exhibited significantly decreased levels of total thiols which remained significant in the three groups due to involvement of glutathione in the metabolism of formaldehyde. Oral administration of formaldehyde was associated with increased oxidant stress manifested by significantly decreased catalase activity and enhanced lipid peroxides and ceruloplasmin after two weeks of oral exposure. Thereafter, such oxidant stress was gradually corrected as manifested by gradual increase in catalase activity and decrease of lipid peroxides and ceruloplasmin. These changes could be due to enhancement of metallothionein which has an important antioxidant action; a viewpoint supported by the significant positive correlations between metallothionein and catalase. NO levels showed significantly decreased levels in the three groups of animals