Histopathological and hemodynamic studies supporting hypoxia and vascular disruption as explanation to phenytoin teratogenicity.

The limb plates and craniofacial regions in rabbit fetuses were examined shortly after the last dose of phenytoin on day 16 after daily administration by gavage with either 150 mg/kg on days 14-16 or 300 mg/kg on days 15-16. Both treatment regimens resulted in similar changes. Histologically, the digital areas of the limb plates showed extensive edema and dilated blood vessels within 2 h. After 8 h, vascular disruption occurred with hemorrhages. At 24-48 h after dosing, mesenchymal necrosis and, on some occasions, amputation of digits was observed. In the craniofacial region, well-defined superficial hemorrhage was seen in the frontal and nasal region at 8 h. Histologically, subectodermal hemorrhage caused by vascular disruption and microfocal mesenchymal necrosis was observed. At 48 h, some fetuses showed severe diffuse intracranial and superficial hemorrhage, resulting in massive tissue damage, also in the central nervous system (CNS). Maternal heart rate, blood pressure, PO2, and PCO2 were also measured in awake pregnant rabbits 6 h after the last dose on day 16 after daily administration with 150 mg/kg during gestational days 14-16. An attempt was also made to measure fetal heart rate in anesthetized rabbits. The maternal heart rate and blood pressure decreased with about 15% in phenytoin-treated animals, resulting in a decrease in PO2 (approximately 15%) and an increase in PCO2 (approximately 15%). A decrease in fetal heart rate was also registered. The results thus indicate that phenytoin exerts its teratogenic effects by inducing fetal hypoxia, leading to vascular disrupture and necrosis of existing and developing structures.

Mutagenicity testing of condensates of smoke from titanium dioxide/hexachloroethane and zinc/hexachloroethane pyrotechnic mixtures.

Condensates of smoke from titanium dioxide/hexachloroethane and zinc/hexachloroethane pyrotechnic mixtures were investigated for their potential to produce genetic damage in the tester strains TA98, TA100, TA1535 and TA1537 of Salmonella typhimurium and in the mouse bone marrow micronucleus assay. Both smoke condensates contained several chlorinated hydrocarbons among which tetrachloroethylene, hexachloroethane, hexachlorobutadiene and hexachlorobenzene were identified by GC/MS. Condensate of smoke from titanium dioxide/hexachloroethane showed a dose-related positive response in the Salmonella assay with strains TA98 and TA100 in the absence of metabolic activation from rat liver S9 fraction. Both smoke condensates were negative in the micronucleus assay but produced a small but significant depression of erythropoietic activity. The results indicate that smoke condensate from titanium dioxide/hexachloroethane mixtures contains unidentified compound(s) that may be considered mutagenic in the Salmonella assay.

Organophosphorus anticholinesterases do not mediate analgesia through inhibition of enkephalin degradation.

The effect on enkephalin degradation of the four highly potent organophosphorus anticholinesterases, soman, sarin, tabun and DFP was studied in synaptosomal fractions of rat brain striata. None of the agents effected any of the enkephalin degrading enzymes, the puromycin sensitive aminopeptidase, the p-hydroxymercurybenzoate (p-HMB) sensitive dipeptidyl aminopeptidase or the phosphoramidon sensitive enkephalinase. Furthermore, no peptidase function of acetylcholinesterase was found, when Leu-enkephalin was used as substrate at low concentrations (27 nM). Supporting the in vitro data, no difference was obtained in the striatal levels of Met- and Leu-enkephalin between rats receiving a high single dose of soman and controls. The results show that the analgesic effect of anticholinesterases are more likely due to mechanisms other than inhibition of enkephalin degradation.

Effects of mercuric chloride on the membrane integrity of cultured cell lines.

The effects of mercuric chloride on the membrane integrity of neuronal (N1E115), glial (138MG), muscle (L6) and liver (BRL123) cells in culture were studied. Alterations in passive membrane permeability were investigated in a perfusion system by following the efflux of radioactivity from cells preloaded with tritiated 2-deoxy-D-glucose. The efflux increased rapidly in the presence of a low concentration of HgCl2 (10(-5) M). The cell lines exhibited differential sensitivity to HgCl2 in the following order: BRL greater than L6 greater than N1E115 greater than 138MG. This differential sensitivity was confirmed by the alterations in the structure of the cell surfaces as observed in the scanning electron microscope. It is suggested that 2-deoxy-D-[3H]glucose may be a suitable probe in studies of membrane lesions caused by toxic substances.

Studies in vitro on the inactivation of mitochondrial rat-liver aldehyde dehydrogenase by the alcohol-sensitizing compounds cyanamide, 1-aminocyclopropanol and disulfiram.

The inhibition of the low-Km, rat-liver mitochondrial aldehyde dehydrogenase (ALDH) by the alcohol-sensitizing agents cyanamide, 1-aminocyclopropanol (ACP) and disulfiram was studied in vitro. All three compounds caused a progressive decline in the enzyme activity. Restoration of activity could not be achieved by gel-filtration, dilution or by the addition of excess thiol. High concentrations of acetaldehyde partly restored the activity of the cyanamide-inactivated enzyme but had no effects on the disulfiram- or ACP-inactivated enzyme. In the presence of saturating concentrations of the coenzyme (NAD+), the inactivation process followed first-order kinetics at fixed concentrations of the inhibitors. Plots of the apparent first-order rate constants against inhibitor concentration were curved, suggesting the formation of saturable, reversible holoenzyme-inhibitor complexes prior to the covalent reactions. In the absence of NAD+, the rate of inactivation by disulfiram was biphasic and considerably higher than that in the presence of NAD+. In contrast, no inactivation was obtained with cyanamide in the absence of NAD+. Likewise, the presence of NAD+ greatly promoted the inactivation by ACP. The esterase activity of the enzyme was also affected by the inhibitors, although to a lesser extent than was the dehydrogenase activity. The results obtained suggest that all three inhibitors inactivate the enzyme through covalent reactions with the thiol groups at the active site. It is proposed that binding of NAD+ limits access of disulfiram to the thiols at the active site but provides a situation that favours an electrophilic attack of cyanamide and ACP on the thiol groups.

Determination of acetaldehyde in rat blood by the use of rat liver aldehyde dehydrogenase.

A method has been developed for the determination of low concentrations of acetaldehyde in rat blood. The method involves extraction of blood in perchloric acid followed by a fluorimetric determination of acetaldehyde in neutralized extracts by the use of a low K(m) aldehyde dehydrogenase isolated from rat liver mitochondria. Acetaldehyde concentrations down to 2 to 3 microM could be detected in blood samples of 0.1 ml containing high concentrations of ethanol (10-40 mM). Due to its simplicity, sensitivity, and the use of a low-cost fluorimeter, this enzymatic method should be a valuable complement to gas chromatographic methods for acetaldehyde determination.

A comparative study on the effects of disulfiram, cyanamide and 1-aminocyclopropanol on the acetaldehyde metabolism in rats.

1-aminocyclopropanol (ACP) is a potent inhibitor of aldehyde dehydrogenase (ALDH) in vivo and in vitro. Like cyanamide it has a rapid onset of action in vivo with the highest inhibition occurring after 2--24 hrs. and a long duration of action like disulfiram with measurable inhibition after 144 hrs. All the three inhibitors decreased the activity of the mitochondrial low-Km ALDH strongly in vivo, however, in markedly different doses. Cyanamide inhibited the high-Km ALDH only in vivo, whereas in vitro, the hihgh-Km ALDH was unaffected by cyanamide but significantly inhibited by disulfiram and ACP. The inhibition produced by the inhibitors appeared to be irreversible. Acetaldehyde protected the low-Km enzyme at different extents depending on the inhibitor used. The inhibition of ALDH in intoxicated and control rats and its relation to acetaldehyde oxidation and the disulfiram-ethanol reaction are discussed.

The presence of an aldehyde dehydrogenase inhibitor in animal diets and its effects on the experimental results in alcohol studies.

1. The effects of chronic ethanol administration on the metabolism of ethanol and acetaldehyde were studied in rats fed on a commercial diet containing an aldehyde dehydrogenase inhibitor, calcium cyanamide (calcium carbimide), as a contaminant in the calcinated bone-meal fraction of the diet. 2. Rats given an ethanol solution (150 ml/l) for 3 months and fed on a diet containing calcinated bone meal showed two times higher activity of the low-Km acetaldehyde dehydrogenase in the liver, 26% higher rate of ethanol elimination, and two to three times lower acetaldehyde levels in blood during ethanol elimination compared with control rats pair-fed on the same diet. 3. The results obtained from the ethanol-treated rats were similar to those obtained in experiments on control rats fed on diets not containing calcinated bone meal. 4. Experiments performed in vitro and in vivo on the inhibition of the acetaldehyde metabolism by cyanamide suggested that the apparent effects of chronic ethanol intake were really caused by calcium cyanamide in the diet.