Dose Dependence of Covalent Binding of Acrylonitrile to Tissue Protein and Globin in Rats

The dose dependence of acrylonitrile (AN) covalent binding totissue protein, following a single acute exposure over a 100-foldrange in dose, was measured. Covalent binding was a linear functionof AN dose in the lower dose range (0.0–0.95 mmol AN/kg).The slopes of the dose-response curves indicated that tissuesvaried by nearly 10-fold in their reactivity with AN. The relativeorder of covalent binding was as follows: blood > kidney= liver > forestomach = brain > glandular stomach >muscle. Similar dose-response behavior was observed for globintotal covalent binding and for globin N-(2-cyanoethyl)vallne(CEValine) adduct formation. The latter adduct was found torepresent only 0.2% of the total AN adduction to globin. Regressionof tissue protein binding versus globin total covalent bindingor globin CEValine adduct indicated that both globin biomarkerscould be used as surrogates to estimate the amount of AN boundto tissue protein. At higher AN doses, above approximately 1mmol/kg, a sharp break in the covalent binding dose-responsecurve was observed. This knot value is explained by the nearlycomplete depletion of liver glutathione and the resultant terminationof AN detoxification. The toxicity of AN is known to increasesharply above this dose. The data suggest that a comparisonof specific tissue proteins labeled by AN above and below thisthreshold dose may provide some insight into the mechanism ofAN-induced toxicity.