Efficacy of tacrine as a nerve agent pretreatment.

Tacrine (THA) was evaluated in vitro and in vivo as a pretreatment for nerve agent intoxication. In vitro experiments showed that the primary effect of THA was direct inhibition of purified fetal bovine serum acetylcholinesterase (AChE) with a slight effect on slowing the aging rate of nerve agent-inhibited AChE. THA produced significant behavioral effects at doses above 1.7 mg/kg, i.m., in the mouse and 3.4 mg/kg, i.m., in the guinea pig. At the no observable effect level (NOEL) for mice (1.7 mg/kg), THA was effective (P < or = 0.05) in reducing tabun- and soman-, but not sarin-induced lethality in mice. Experiments in the guinea pig showed that at the NOEL (3.4 mg/kg, i.m.) THA was not effective in decreasing lethality due to soman exposure. Since there was significant overlap between pharmacologically effective doses of THA and those which produce behavioral toxicity, THA was not considered a suitable pretreatment for nerve agent intoxication.

Comparison of methemoglobin formers in protection against the toxic effects of cyanide.

1. Certain compounds that oxidize hemoglobin to methemoglobin (MHb) also protect against cyanide. 2. Evidence presented here suggests that other mechanisms may be involved. 3. Male Swiss ICR mice were pretreated intraperitoneally (i.p.) with various doses of primaquine phosphate (primaquine), WR6026 (6-methoxy-8-(6-diethylamino-hexylamino) lepidine dihydrochloride), WR238605 (8-[(4-amino-1-methylbutyl) amino]-2,6-dimethoxy-4-methyl-5-(3-trifluoromethylphenoxy) quinoline succinate), p-aminooctoyl-phenone (PAOP), or p-aminopropiophenone (PAPP). 4. The compounds were administered 15 or 60 min before an intramuscular (i.m.) challenge with a 2 x LD50 dose (5.0-5.6 mg/kg) of sodium cyanide (NaCN). 5. Twenty-four hr mortality was assessed and survivors were tested for motor incapacitation. 6. Primaquine, PAPP and PAOP increased survival compared to untreated controls, while the other MHb formers were not effective (P less than 0.05). 7. PAOP is believed to form sufficient MHb only after 3 to 4 hr after administration; however it was found to be effective when administered 15 min before NaCN challenge in this study. 8. This suggests that MHb formation may not be the only factor responsible for PAOP's anti-cyanide efficacy.

Methylthiazolidine-4-carboxylate for treatment of acute T-2 toxin exposure.

The effect of T-2 toxin on hepatic glutathione content and the protective effect of 2-methyl-thiazolidine-4-carboxylate (MTCA), an L-cysteine prodrug, were studied in mice. Acute exposure to T-2 toxin (4 mg kg-1, s.c.) resulted in a progressive decrease in glutathione content, reaching a minimum 6-8 h after toxin administration. Because T-2 toxin caused decreased food consumption, a condition known to deplete hepatic glutathione, glutathione was measured in both fed and fasted control and toxin-treated mice. Glutathione content (mumol g-1 tissue) was 9.01 +/- 0.66 (control) and 4.26 +/- 0.41 (toxin) for fed mice, 4.45 +/- 0.39 (control) and 2.45 +/- 0.26 (toxin) for 16-h fasted mice, and 7.18 +/- 0.26 (control) and 3.76 +/- 0.65 (toxin) for mice fed before, but fasted after exposure to toxin. In all cases, toxin treatment resulted in significant decreases in glutathione content compared to controls. Treatment of T-2-intoxicated mice with MTCA (750 mg kg-1, i.p.) not only maintained glutathione content at control levels or higher but significantly improved survival as well. Therefore, the toxicity and lethality of T-2 toxin may be associated with decreased hepatic glutathione content, since MTCA maintained glutathione content and improved survival.

Beneficial effect of dexamethasone in decreasing the lethality of acute T-2 toxicosis.

1. Steroidal and non-steroidal anti-inflammatory agents were evaluated for effectiveness for treatment of acute T-2 toxicosis in mice. 2. Non-steroidal agents, indomethacin, phenylbutazone, and acetylsalicylic acid, either were ineffective, or potentiated the lethality of T-2 toxin. 3. Of the anti-inflammatory steroids tested, dexamethasone was the most effective. 4. Dexamethasone was administered before, at the same time as, or after injection of T-2 toxin. 5. As the time between toxin exposure and treatment was increased, there was a corresponding increase in lethality. 6. In conclusion, steroidal, but not non-steroidal, anti-inflammatory agents were effective in decreasing T-2 toxin-induced lethality.

Assessment of efficacy of activated charcoal for treatment of acute T-2 toxin poisoning.

"Superactive" charcoal was assessed for efficacy in decreasing the lethality of both oral and parenteral exposure to T-2 toxin, a fungal metabolite which can cause death or illness upon ingestion. In vitro binding studies, analyzed using the Langmuir adsorption isotherm, showed that activated charcoal had a maximal binding capacity of 0.48 mg toxin/mg charcoal and a dissociation constant of 0.078 mg charcoal/l. In vivo, orally administered, activated charcoal was assessed for treatment of acute oral or parenteral exposure to T-2 toxin in mice. Following oral toxin administration (5 mg/kg), untreated mice showed only 6% survival after 72 hr. Charcoal treatment (7 g/kg,po) either immediately or 1 hr after toxin exposure resulted in significant improvement in survival with values of 100% and 75%, respectively. Following parenteral toxin exposure (2.8 mg/kg, sc), untreated and charcoal-treated (7 g/kg, po) mice showed 50% and 90% survival, respectively, after 72 hr. LD50 value for T-2 toxin, determined at 96 hr after intoxication, increased significantly from 2 mg/kg for untreated controls to 4.5 mg/kg for activated charcoal treatment.

Prodrugs of L-cysteine as protective agents against acetaminophen-induced hepatotoxicity. 2-(Polyhydroxyalkyl)- and 2-(polyacetoxyalkyl)thiazolidine-4(R)-carboxylic acids.

Eight prodrugs of L-cysteine (1a-h) were synthesized by the condensation of the sulfhydryl amino acid with naturally occurring aldose monosaccharides containing three, five, and six carbon atoms. The resulting 2-(polyhydroxyalkyl)thiazolidine-4(R)-carboxylic acids (TCAs) are capable of releasing L-cysteine and the sugars by nonenzymatic ring opening and hydrolysis. Thus, when added to rat hepatocyte preparations in vitro, these TCAs (1.0 mM) raised cellular glutathione (GSH) levels 1.2-2.1-fold relative to controls. On the basis of this finding, the cysteine prodrugs were tested as protective agents against acetaminophen-induced hepatotoxicity in a mouse model. The TCA derived from D-ribose and L-cysteine (RibCys, 1d) showed the greatest therapeutic promise of the series, with a 100% (12/12) survival profile compared to 17% without treatment. However, the degree of stimulation of GSH production in rat hepatocytes by these prodrugs did not correlate with the extent of protection afforded in mice, suggesting that pharmacokinetic parameters must supervene in vivo. To evaluate the effect of increased lipid solubility, we prepared prodrugs 2a-c by using peracetylated aldehydic sugars in the condensation reaction. These compounds, however, displayed acute toxicity to mice, possibly due to liberation of the acetylated sugars themselves. Nevertheless, the efficacy of the unacetylated TCAs, and RibCys (1d) in particular, suggests that the prodrug approach for the delivery of L-cysteine to the liver represents a viable means of augmenting existing detoxication mechanisms in protecting cells against xenobiotic substances that are bioactivated to toxic, reactive metabolites.