Effect of chlorpromazine on cyanide intoxication

Previous reports from our laboratory indicated that prophylactic protection against cyanide intoxication in mice can be enhanced by administration of chlorpromazine when it is given with sodium thiosulfate. The mechanism of potentiation of sodium thiosulfate by chlorpromazine was studied alone and in combination with sodium nitrite. Although chlorpromazine was found to induce a hypothermic response, the mechanism of enhancement of the antagonism of cyanide by chlorpromazine does not correlate with the hypothermia produced. Various other possible mechanisms were investigated, such as rate of methemoglobin formation, enzymatic activity of rhodanese and cytochrome oxidase, and alpha-adrenergic blockade. The alpha-adrenergic blocking properties of chlorpromazine may provide a basis for its antidotal effect, since this protective effect can be reversed with an alpha-agonist, methoxamine.     

Multiple forms of phenolsulphotransferase in human tissues: Selective inhibition by dichloronitrophenol

Evidence is presented for two functional forms of phenolsulphotransferase in human tissues: (1) activity ratios, using dopamine and phenol as substrates, varied 30-fold between different tissues, whereas the dopamine to tyramine activity ratio was relatively constant; (2) incubation at 37° caused a selective decrease in activity towards dopamine compared with phenol; and (3) phenol sulphoconjugation was selectively inhibited by dichloronitrophenol and pentachlorophenol compared with that of dopamine and tyramine. The two forms, which have been designated M (monoamines) and P (phenol), were both present in platelets, jejunum, adrenal and brain.     

Protection against mercuric chloride by nephrotoxic agents which do not induce thionein

Kidney damage caused by the ip administration of 1.1 mg/kg mercury given as HgCl₂ was less marked in 7-week-old male rats when mercury was given 7 days after the administration of one of the following nephrotoxic agents: 20 mg/kg sodium chromate, 100 mg/kg p-aminophenol, or 500 mg/kg sodium maleate, or 14 days after the injection of 4.0 mg/kg uranyl acetate. All four nephrotoxic agents were given in sufficient doses to cause renal damage. In the first 3–4 days after the administration of the nephrotoxic agents they increased the urinary excretion of alkaline phosphatase, glutamic oxaloacetic transaminase, and lactic dehydrogenase and caused widespread necrosis in the proximal tubular cells. In the first 24 hr after the injection of mercury, the urinary excretion of the three enzymes tested was lower in pretreated than in nonpretreated rats. Tubular cell necrosis was also less extensive in pretreated than in nonpretreated rats, and calcification could be seen 10 days after mercury only in the kidneys of the nonpretreated rats. The decreased susceptibility of regenerating kidneys to the tubulotoxic effect of mercuric chloride seems to be a general phenomenon which is unrelated to the renal concentration of metallothionein or change in renal mercury uptake.     

Comparison of protein, RNA, and DNA binding and cell-cycle-specific growth inhibitory effects of nickel compounds in cultured cells

Crystalline NiS particles are potent inducers of morphological transformation and are actively phagocytosed by cells. Water-soluble nickel compounds are less potent, possibly because the total amount of nickel that enters cells is less, and its subcellular distribution differs in a number of ways from that following the entry of NiS in the form of an internalized particle. To further study this problem, we have examined the binding of ⁶³Ni to DNA, RNA, and protein isolated from cultured Chinese hamster ovary cells treated with either crystalline ⁶³NiS or ⁶³NiCl₂. Treatment of cultured cells with ⁶³NiS at 10 μg/ml for 3 days resulted in binding of nickel to DNA, RNA, or protein in the range of 1 μg of nickel bound per milligram macromolecule. However, similar treatment of cells with ⁶³NiCl₂ at 10 μg/ml for 1 to 5 days resulted in approximately one to several orders of magnitude less nickel bound to DNA, RNA, and protein. In the case of ⁶³NiCl₂ treatment, cellular proteins contained about 100 times more ⁶³Ni bound than the respective RNA or DNA fractions. However, the protein fraction obtained from cells treated with crystalline NiS contained about 15 times more nickel bound than the same fraction isolated from cells that were similarly treated with ⁶³NiCl₂. RNA or DNA had 300 to 2000 times more bound nickel following crystalline NiS treatment compared to cells treated similarly with NiCl₂. In contrast to the selective binding of ⁶³NiCl₂ to protein, cultured cells treated with crystalline ⁶³NiS had equivalent levels of nickel associated with RNA, DNA, and protein. Since the interaction of ⁶³Ni with these macromolecules following crystalline ⁶³NiS treatment was not due to the binding of the actual particles, the dissolution of intracellular ⁶³NiS particles probably plays an important role in governing the distribution of ⁶³Ni ions available for binding. The greater intracellular macromolecular binding of ⁶³Ni resulting from treatment of cells with ⁶³NiS compared to cultures similarly exposed to ⁶³NiCl₂ paralleled the more potent effects of crystalline NiS in slowing and arresting cell proliferation. Crystalline NiS caused pronounced cell cycle specific blockage at a considerably lower concentration than was required for NiCl₂ to similarly arrest cell growth. Flow cytometry analysis showed that both compounds selectively blocked cell cycle progression in S phase (DNA synthetic stage). These results are suggestive of a common mechanism and site of toxicity inherent to both compounds and related to the cell growth phase during which DNA is replicated.     

Deuterium isotope effect on the metabolism and toxicity of 1,2-dibromoethane

The metabolism, hepatotoxicity, and hepatic DNA damage of 1,2-dibromoethane (EDB) and tetradeutero-1,2-dibromoethane (d₄EDB) were compared in male Swiss-Webster mice. In vitro studies that measured bromide ion released from the substrate to monitor the rate of metabolism showed that the hepatic microsomal metabolism of EDB was significantly reduced by deuterium substitution, while metabolism by the hepatic glutathione S-transferases was unaffected. Three hours after ip administration of EDB or d₄EDB (50 mg/kg), there was 42% less bromide in the plasma of d₄EDB-treated mice than in the plasm of EDB-treated mice. This difference demonstrates a significant deuterium isotope effect on the metabolism of EDB in vivo. Although the metabolism of d₄EDB was less than that of EDB 3 hr after exposure, the DNA damage caused by both analogs was not significantly different at this time point. At later time points (8, 24, and 72 hr), d₄EDB caused significantly greater DNA damage than EDB. Since the decreased metabolism of d₄EDB was apparently due to a reduced rate of microsomal oxidation, these data support the hypothesis that conjugation with GSH is responsible for the genotoxic effects of EDB.     

Interference of thiosulfate with potentiometric analysis of cyanide in blood and its elimination

Studies with cyanide in combination with various antidotal regimens indicated that sodium thiosulfate interfered with the potentiometric determination of cyanide. The basis for this interference is ascribed to an enhanced biotransformation of thiosulfate in the presence of blood. A microdiffusion technique, coupled with a silver/sulfide ion-specific electrode, caused falsely elevated cyanide levels when samples contained thiosulfate. The contaminant causing the falsely elevated cyanide level is believed to be sulfide anion. This sulfide contaminant can be removed by oxidation with hydrogen peroxide, and the excess hydrogen peroxide subsequently can be eliminated with sodium sulfite. The toxicologic implication of the potentiometric determination of cyanide in the presence of sodium thiosulfate is important because sodium thiosulfate is employed widely as an antidote in cyanide poisoning.     

Evaluation of the role of ionized calcium in sodium fluoroacetate (“1080”) poisoning

Fluoroacetate, which is an inhibitor of the tricarboxilic acid cycle, is widely used as a rodenticide. Fluoroacetate is converted in the body to fluorocitrate, which is an inhibitor of the enzyme aconitate hydrase. As a result, energy production goes down, and citrate accumulates. As citrate is a potent chelator of calcium ion, we postulated that ionized calcium concentration in the blood would drop. Fluoroacetate, 0.03 mmol/kg, was injected iv into anesthetized cats. Ionized calcium concentration in anaerobically drawn arterial blood samples was measured with an ion-exchange electrode. Samples were taken immediately before and 40 min after the poisoning, after which the animals were either used as controls (six cats) or treated with an infusion of iv CaCl₂ (another six cats), so as to restore ionized calcium levels to normal values. Forty minutes after fluoroacetate injection, the ionized calcium levels fell by an average of 27.2%, from 1.09 ± 0.07 to 0.79 ± 0.14 mM. There was a corresponding prolongation of the QTc interval of the ECG (r = 0.82). Treatment with CaCl₂ significantly prolonged the life of the treated animals as compared to the control animals (p < 0.0016 by the Mann-Whitney rank sum test). Our findings suggest that reduced levels of ionized calcium play an important role in the pathogenesis of fluoroacetate poisoning. The reduced levels of Ca²⁺ are an adequate explanation for the toxic effects of fluoroacetate, and may be the missing link between the biochemistry of the poisoning and the clinical manifestations.     

Repeated inhalation toxicity of diphenyl oxide in experimental animals.

Repeated inhalation studies using rats, rabbits, and dogs were conducted at mean exposure concentrations of 0, 4.9, and 10.0 ppm diphenyl oxide (DPO) vapor. Exposures were 7 hr per day, 5 days per week for a total of 20 exposures. Additional groups of rats were exposed 7 hr per day to 0 or 20 ppm DPO vapor for a total of 20 exposures. No signs of toxicity or irritation were observed in animals exposed to 4.9 ppm. Eye and nasal irritation were observed in rats and rabbits but not dogs exposed to 10.0 ppm and in rats exposed to 20 ppm. Aside from this irritation no other signs of toxicity were discerned.     

Pharmacological study on the venom of the marine snail Conus textile

The pharmacological effects of Conus textile venom on the rabbit aorta, the guinea-pig left atria, vas deferens and ileum, and the mouse diaphragm were examined. The venom caused a marked, transient contraction of the ileum which was abolished by atropine and tetrodotoxin. The venom exhibited a positive inotropic effect on the left atria which was almost completely inhibited by verapamil. Activity on the ileum was retained after heating at 70°C for 1 hr, exposure to 1 N HCl or 1 N NaOH and incubation with proteases. Active material(s) in the venom passed through a UM2 filter, suggesting a molecular weight lower than 1000.     

The effects of sodium chromate and carbon tetrachloride on the urinary excretion and tissue distribution of cadmium in cadmium-pretreated rats

Rats were administered nontoxic doses of Cd²⁺ by the oral or intraperitoneal routes. They were subsequently treated with either Na₂CrO₄ (10 or 20 mg/kg, sc) or CCl₄ (0.5 or 1 ml/kg, intragastric). Evidence of renal damage was obtained from the determination in urine of total protein and amino acids and from the analysis of the urinary proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Liver damage was evaluated by determining the serum activities of sorbitol dehydrogenase and glutamate pyruvate transaminase. The effects of CCl₄ on the urinary excretion and the tissue distribution of Cd²⁺ vary depending on whether liver damage is associated or not with extensive renal lesions. When renal function was not or only moderately altered, induction of liver damage by CCl₄ resulted in a transfer of Cd²⁺ from the liver to the kidney. This transfer was evidenced by a decrease of total Cd²⁺ as well as metallothionein-bound Cd²⁺ in the liver and an increase of the same parameters in the kidney. The urinary excretion of Cd²⁺ was only slightly increased. When liver damage induced by CCl₄ was associated with extensive kidney lesions, the accumulation of Cd²⁺ released from the liver in the kidney was considerably reduced and large amounts of Cd²⁺ were excreted in urine. Administration of Na₂CrO₄ to Cd²⁺-pretreated rats gave rise to a sharp and reversible increase in the urinary excretion of Cd²⁺. This increase was proportional to the amount of Cd²⁺ stored in kidney and to the dose of Na₂CrO₄ administered. The Cd²⁺ excreted in urine originated mainly from the kidney in which total Cd²⁺ and metallothionein-bound Cd²⁺ were reduced in proportion to the dose of Na₂CrO₄ administered. These results suggest that two mechanisms may lead to an increased urinary excretion of Cd²⁺; a direct release of Cd²⁺ into urine from damaged kidney (i.e., Na₂CrO₄) or a decreased tubular reabsorption of plasma circulating Cd²⁺ evidenced when large amounts of Cd²⁺ are released into blood from damaged liver (i.e., CCl₄). These results tend to support the hypothesis that kidney damage due to chronic Cd²⁺ poisoning may lead to an increased loss of the Cd²⁺ stored in the kidney.     

The effect of anti-cancer drugs on pharmacokinetics of antipyrine in vitamin A deficiency

The pharmacokinetics of orally and intravenously administered antipyrine-¹⁴C in individual rats were investigated to examine the effects of vitamin A deficiency and/or cytotoxic anti-cancer drugs, like cyclophosphamide, methotrexate, 5-fluorouracil and actinomycin-D. Both vitamin A deficiency and pretreatment of rats with anti-cancer drugs led to impairment in the absorption from the gastro-intestinal tract and the plasma elimination of antipyrine. Pretreatment of vitamin A deficient rats with anti-cancer drugs further retarded the absorption and plasma clearance of antipyrine. Apparent volume of distribution of antipyrine was reduced (P < 0.001) by inducing vitamin A deficiency in rats. whereas pretreatment of rats with anti-cancer drugs did not show any effect.Cytotoxic drugs, and vitamin A deficiency increased the area under the plasma concentration vs. time curve of orally administered antipyrine (AUC_oral). In vitro findings suggest that the most probable cause of delayed clearance/prolonged half-life and increased AUC_oral values was the reduction in hepatic cytochrome P-450 dependent mixed function oxidase system.     

Potassium prevention of lithium-induced loss of water and sodium in rats

Lithium was administered to rats with the food in amounts leading to serum lithium concentrations of 0.6–0.8 mmol/liter. The animals had free access to water and 0.46 m NaCl solution. Some of the rats were given a diet to which 500 mmol/kg of either potassium chloride or potassium phosphate had been added, while other rats received food without extra potassium. In the course of 3 weeks the water and sodium intakes increased in all groups, but they increased significantly less in the rats given potassium than in those given no extra potassium. During 6 hr of fluid deprivation the rats given extra potassium showed significantly less urine production, weight loss, and increase in serum sodium concentration. When access to NaCl solution was withdrawn the animals given extra potassium were almost unaffected whereas within 14 days the animals not given extra potassium developed lithium intoxication characterized by weight loss, decreased intake of water and food, lowered serum sodium concentration, and increased serum lithium concentration; two of the seven rats in this group died. In none of the experiments was there any difference between rats given potassium chloride and rats given potassium phosphate. The data indicate that a high potassium content in the food prevents lithium-induced renal inability to retain water and sodium.     

Inhibition of cholinesterase activity by isocyanates

Exposure of workers to isocyanates may result in irritation and/or sensitization of the respiratory tract. An immunologic mechanism for sensitization has been presented previously. This investigation explored whether, as a possible mechanism for the irritation reaction, the toxic respiratory effect of isocyanates might be due to their ability to inhibit cholinesterases. Hexamethylene diisocyanate (HDI), hexyl isocyanate (HI), and 2,6-toluene diisocyanate (2,6-TDI) were found to completely inhibit purified human serum cholinesterase when added at molar ratios of 4:1 to 8:1 (isocyanate:enzyme). By contrast, molar ratios of 50:1 or greater were required for 50% enzyme inhibition by 2,4-toluene diisocyanate (2,4-TDI), phenyl isocyanate, or o-tolyl isocyanate. Enzyme inhibition was also achieved by exposure of purified cholinesterase to atmospheres containing 1 ppm isocyanates. Under these conditions, HDI and HI were again the most potent enzyme inhibitors with much less reactivity shown by 2,4-TDI and 2,6-TDI. Under more physiologic conditions, when whole human plasma was the source of cholinesterase, HDI and HI were still potent enzyme inhibitors. However, with the latter two isocyanates, the molar concentrations needed to effect 50% enzyme inhibition suggested affinity labeling by these reagents. The potent cholinesterase inhibition shown by HDI and HI may offer explanation for observed respiratory symptomatology noted upon exposure to these isocyanates.     

Induction of cytosolic and microsomal epoxide hydrolases by the hypolipidaemic compound nafenopin in the mouse liver

The repeated oral administration of nafenopin, a hypolipidaemic compound, at a dose of 100 mg/kg to male C57BL/6, DBA/2, Balb c and C3H mice caused an increase in the specific activity of liver cytosolic epoxide hydrolase, the activity of microsomal epoxide hydrolase was also increased in all except the C3H mice. The dose dependence and the specificity of this induction was investigated in male DBA/2 mice. In the range of 10-200 mg/kg nafenopin the induction of the two hydrolase activities was found to increase with increasing doses of the test compound. Two other cytosolic enzyme activities, lactate dehydrogenase and glutathione S-transferase, remained essentially unchanged within the dose range investigated.     

In vitro and in vivo inhibition by benserazide of clorgyline-resistant amine oxidases in rat cardiovascular tissues

Benserazide (d, l-serine 2-[2,3,4-trihydroxybenzyl]-hydrazide) has been shown to inhibit the clorgyline-resistant amine oxidase (CRAO) activities which metabolize benzylamine in homogenates of rat aorta, heart and brown adipose tissue. In vitro studies showed a concentration- and timedependent inhibition of CRAO in heart and aorta which was reversed by dialysis for 18hr. At high concentrations (10^?4?10^?3M) benserazide appeared to increase enzyme activity towards and occasionally above control value. These increases became more prominent after long periods of preincubation (especially in the presence of saturating benzylamine concentrations) and remained after dialysis of those homogenates preincubated with benserazide. The administration of benserazide for one or seven days in daily doses of 5–150 mg/kg also inhibited CRAO activity in vivo in a dose-dependent manner, with greater inhibition after seven days treatment. Reversal of inhibition, by dialysis of tissue homogenates from benserazide-treated rats, was much slower than was found with homogenates incubated in vitro with the drug. After benserazide administration to rats, MAO-A activity towards 5-hydroxytryptamine was generally not inhibited, and in fact was significantly increased in some cases. The administration of l-DOPA (250 mg/kg) together with benserazide (40 mg/kg) resulted in a similar degree of CRAO inhibition m aorta and heart to that seen after benserazide alone. These findings are discussed with regard to the use of these drugs in the therapy of Parkinson's Disease, although the paucity of information about the physiological function of CRAO makes the significance of its inhibition by benserazide unclear.     

Inhibition of dog brain synaptosomal Na+ -K+ ATPase and K+-stimulated phosphatase activities by long chain n-alkyl-amine and -piperidine, and N'-alkylnicotinamide derivatives

The effects of piperidine, primary amine, and nicotinamide aliphatic derivatives on dog brain snyaptosomal Na⁺-K⁺ ATPase were investigated. These derivatives inhibited the enzyme activity in a manner dependent on alkyl chain length. Kinetic studies revealed that inhibition of Na⁺-K⁺ ATPase activity by long chain alkyl derivatives (C₁₂-C₁₈) was biphasic and non-competitive with respect to the inhibitor and substrate (ATP) concentrations respectively. These long alkyl derivatives caused changes in the Hill coefficient that suggest the occurrence of a possible conformational change in the enzyme molecule. Dual-inhibitor experiments showed that both saturated and unsaturated pentadecylpiperidine (C₁₅-pip) derivatives inhibited Na⁺-K⁺ ATPase by the same mechanism. Oleylamine (C_18:1-NH₂), and N-dodecylnicotinamide (C₁₂-NA⁺Cl^?) derivatives apparently inhibited the enzyme activity by a mechanism different from that of piperidine derivatives. Low concentrations of C_15:1-pip, C_18:1-NH₂, and C₁₂-NA⁺Cl^? inhibited dog brain Na⁺-K⁺ ATPase activity only, but at higher inhibitor concentrations K⁺-stimulated phosphatase activity was inhibited as much as Na⁺-K⁺ ATPase. It is concluded that long chain n-alkyl derivatives of piperidines, amines, and nicotinamide have a cationic detergent-like action on Na⁺-K⁺ ATPase, possibly by the disruption of protein-phospholipid interactions. The mechanism by which these compounds inhibit the overall Na⁺-K⁺ ATPase may involve two different inhibitory sites: one, a high affinity inhibitory site, binding to which inhibits the Na⁺-stimulated phosphorylation reaction, and the other, a low affinity inhibitory site, binding to which inhibits the K⁺-stimulated dephosphorylation reaction. These possible mechanisms may provide an explanation for the observed biphasic inhibition kinetics.