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.     

Biological Markers of Acute Acrylonitrile Intoxication in Rats as a Function of Dose and Time

Three markers of acute acrylonitrile (AN) intoxication, namely,tissue glutathione (GSH), tissue cyanide (CN), and covalentbinding to tissue protein, were studied as a function of doseand time. Doses administered and responses expected were 20mg/kg (LD0), 50 mg/kg (LD10), 80 mg/kg (LD50), and 115 mg/kg(LD90). Liver GSH was the most sensitive marker of AN exposure.At 80 mg/kg AN, virtually complete depletion of liver GSH wasobserved within 30 min with no recovery through 120 mm. KidneyGSH showed a similar, but less intense depletion; while bloodand brain GSH were more refractory to AN. Whole blood and brainCN rose progressively during the first 60 mm in a dose-dependentfashion. At the lowest dose, CN levels decreased thereafter,whereas, at the three higher doses, CN levels were maintainedor continued to increase through 120 min. At the highest dose,blood and brain CN remained at acutely toxic levels through240 mm. Covalent binding increased rapidly in all tissues duringthe first 30 mm at all doses. At the lowest dose, little additionalcovalent binding was observed beyond 30 mm, while at the threehigher doses, covalent binding increased, although at a slowerrate. The data indicate that these three biologic markers ofacute AN intoxication respond dramatically in a time-dependentmanner in the toxic dosage range. Furthermore, the data provideevidence that AN toxicity is gated by GSH depletion in liverwith the resultant termination of AN detoxification.