Studies on the mechanism of acetonitrile toxicity. I: Whole body autoradiographic distribution and macromolecular interaction of 2-14C-acetonitrile in mice.

Acetonitrile, a commonly used solvent is known to cause central nervous system dysfunctions. In order to gain an insight onto the mechanism of acetonitrile toxicity, we studied the kinetics of acetonitrile distribution in mice. Male ICR mice were given a tracer dose of 2-14C-acetonitrile intravenously (60 mu mol/kg or 684 mu Ci/kg, spec. act. 11.4 mCi/mmol). At various time intervals (5 min., 0.5, 1, 4, 8, 24 and 48 hr) after treatment, mice were anaesthetized and frozen by immersion in a dry ice/hexane mixture, or they were dissected for collection of organs and tissues. Frozen mice were processed for whole body autoradiography, which allows the detection of non-volatile metabolites of acetonitrile at their sites of accumulation. Covalent binding of acetonitrile metabolites in tissues was determined using trichloroacetic acid followed by ethanol/ether extraction techniques. Whole body autoradiography revealed heavy localization of acetonitrile metabolites in the gastrointestinal tissues and bile. At 5 min., the highest levels of radioactivity occurred in the liver and kidney; levels declined over time. At 24 and 48 hr, acetonitrile derived radioactivity were detected in the gastrointestine, thymus, liver and male reproductive organs. Covalent binding studies at 24 and 48 hr after treatment indicated that 40-50% of the total radioactivity present in the liver was bound to the macromolecular fractions of the tissues. The radioactivity contents of other organs were, in large part (40-50% of total), present in the lipid fraction of the tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the mechanism of haloacetonitrile-induced gastrointestinal toxicity: interaction of dibromoacetonitrile with glutathione and glutathione-S-transferase in rats.

The haloacetonitrile, dibromoacetonitrile (DBAN), is a direct-acting genotoxic agent that has been detected in drinking water. In a time course study, male Sprague-Dawley rats were treated with DBAN (75 mg/kg PO), and killed at 0.5, 1, 2, and 4 hr after treatment. In a dose response study, animals were treated orally with various doses of DBAN (25, 50, 75, and 100 mg/kg) and killed at one-half hour after treatment. Control animals received 1 ml/kg PO of the vehicle dimethyl sulfoxide (DMSO). In both experiments blood and organs were collected and stored at -80 degrees C until the time of analysis. At 0.5 hr after treatment, a single oral dose of DBAN caused a significant decrease of glutathione (GSH) concentrations in liver (54% of control) and stomach (6% of control). Hepatic GSH depletion was maximal at 0.5 hr and rebound to the control levels by 4 hr. In contrast, gastric GSH concentrations remained low at all time points. DBAN caused an insignificant change in both kidney and blood GSH levels. DBAN significantly inhibited glutathione-S-transferase (GST) activity in liver and stomach. Hepatic GST inhibition was maximal (34% of control) at 2 hr and minimal (80% of control) at 4 hr. Meanwhile, in the stomach GST activity was inhibited at 1 hr (60% of control) and remained low at all times after treatment. Both GSH depletion and GST inhibition were dose-dependent. This study indicates that GSH and GST play an important role in the metabolism and detoxification of DBAN in rats. The prolonged depletion of GSH and inhibition of GST in the gastrointestinal (GI) tissues suggest that the GI tract is a major target for DBAN toxicity.

Studies on the mechanism of haloacetonitriles toxicity: inhibition of rat hepatic glutathione S-transferases in vitro.

Acetonitrile (AN) and seven of its halogenated derivatives known to be water disinfectant by-products were evaluated for their action on hepatic cytosolic glutathione S-transferase (GST) activity using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. Increasing concentrations of acetonitrile, monofluoroacetonitrile (MFAN), monochloroacetonitrile (MCAN), and monobromoacetonitrile (MBAN) up to 10 mM failed to produced 50% inhibition of the activity of GST enzyme. However, dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), dibromoacetonitrile (DBAN), and monoiodoacetonitrile (MIAN) were potent inhibitors with 150 values of 2.49, 0.34, 0.82, and 4.44 mM, respectively. At concentrations equivalent to their 150, MIAN, DCAN, and DBAN decrease both apparent Km and Vmax of the enzyme activity toward glutathione (GSH) to 20-50% of control. TCAN significantly increases both apparent Km and Vmax for GSH to 650 and 120% of control values, respectively. The inhibitory effect of haloacetonitriles (HAN) on hepatic GST activity toward CDNB was found to be a mixed type. The inhibitory effect of DCAN, DBAN, and TCAN on the hepatic GST activity was found to be reversible and the activity was completely recovered after dialysis of the inhibited enzyme. MIAN, however, inhibited GST activity in an irreversible manner. Haloacetonitriles' induced inhibition of hepatic GST activity in vitro is consistent with that observed in vivo. The data presented in this study show that haloacetonitriles induced reversible inhibition of hepatic GST activities, and this effect may lead to decreased detoxification of other electrophilic chemicals.