Decreased Extractability of DNA from Proteins in the Rat Nasal Mucosa after Acetaldehyde Exposure

Decreased Extractability of DNA from Proteins in the Rat NasalMucosa after Acetaldehyde Exposure. LAM, C.-W., CASANOVA, M.,AND HECK, H. D'A. (1986). Fundam. Appl. Toxicol. 6, 541–550.Acetaldehyde and formaldehyde have been found to induce nasalcancer in two species of rodents. To understand the mechanismof carcinogenesis by acetaldehyde, studies were carried Outto determine whether acetaldehyde can react with DNA in targettissues of the rat nasal cavity. When fresh homogenates of thenasal respiratory mucosa were incubated with acetaldehyde (distilledunder N at concentrations of 10, 100, or 500 mM, followed bysolubilization and extraction with a strongly denaturing aqueous-immiscibleorganic solvent mixture, a decrease was observed in the amountof DNA partitioned into the aqueous phase at the two higheracetaldehyde con centrations. The absent DNA was recovered fromthe interfacial layer by proteolytic digestion. Similarly, incubationof calf thymus nucleohistones with acetaldehyde (100, 300, or1000 mM) or with formaldehyde (10, 30, or 100 mM) followed byprecipitation of the DNA with H₂SO₄ and analysis of the supematantsby sodium dodecyl sulfate-polyacrylamide gel electrophoresisresulted in concentration-dependent decreases in the quantitiesof histone proteins released from the DNA. These results indicatethat acetaldehyde as well as formaldehyde can form DNA-proteincrosslinks in vitro. A single 6-hr exposure of male Fischer-344rats to acetaldehyde (100, 300, 1000, or 3000 ppm) resultedin a significant increase relative to air-exposed controls inthe percent interfacial DNA from the nasal respiratory mucosaat concentrations equal to or greater than 1000 ppm. No increasein the interfacial DNA from the olfactory mucosa was detectedafter a single 6-hr exposure (1000 or 3000 ppm), but a significantincrease was found in rats exposed repeatedly (6 hr/day for5 days) to acetaldehyde (1000 ppm). Thus, evidence has beenobtained for the formation of DNA-protein crosslinks by acetaldehydein target tissues of the rat nasal cavity at concentrationssimilar to those that induced nasal cancer.