Analysis of mutagenic DNA repair in a thermoconditional repair mutant of Saccharomyces cerevisiae. I. Influence of cycloheximide on UV-irradiated stationary phase rev2ts cells

Using the thermoconditional yeast mutant rev2ts that controls an apparently site-specific step of mutagenic DNA repair it was possible to measure the time course of REV2 dependent UV-induced reversion of the ochre allele his5-2 and recovery of survival for UV-treated stationary phase cells: due to the rev2ts coded protein being active at 23 degrees C, survival and mutation frequencies increased with duration of incubation under permissive conditions in growth medium before the temperature was shifted to 36 degrees C (restrictive temperature). This increase was abolished in the presence of the protein synthesis inhibitor, cycloheximide. Furthermore, the REV2 dependent recovery of survival could be blocked or nearly blocked by cycloheximide added at any time during repair. Therefore, REV2 dependent repair can be characterized as a process requiring concomitant protein synthesis. These findings give further support to the concept that in yeast, mutagenesis involves UV inducible components of DNA repair.

Serum cholinesterase inhibitors in the commercial hexane impurities

Commercial hexane was concentrated by distillation. The distillation residue (0.43 ml/l original solvent) contains material which inhibits human serum cholinesterase (ChE) "in vitro" with a slight effect on acetylcholinesterase. Phosphorus was detected equivalent to 0.33 mumol monophosphorus compound/litre original solvent. The inhibition was progressive with the enzyme-inhibitor preincubation time. A partial reactivation of the inhibited enzyme was obtained by treatment with hydroxylamine and 2-PAM. The results are coherent with a covalent inactivation by more than one inhibitor which acylate (probably phosphorylate) ChE, although it seems likely that a reversible but unstable inhibitor could also be present in the hexane residue. The results are discussed in the context of the known neurotoxic effects of n-hexane and some organophosphorus esters.

An experimental study of the combined effects of n-hexane and methyl ethyl ketone

This study was intended to determine whether or not methyl ethyl ketone (MEK) enhances the neurotoxicity of n-hexane at low concentration and after long term exposure. Separate groups of eight rats were exposed to 100 ppm n-hexane, 200 ppm MEK, 100 ppm n-hexane plus 200 ppm MEK, or fresh air in an exposure chamber for 12 hours a day for 24 weeks. The body weight, motor nerve conduction velocity (MCV), distal motor latency (DL), and mixed nerve conduction velocities (MNCVs) were measured before exposure and after four, eight, 12, 16, 20, and 24 weeks' exposure. One rat of each group was histopathologically examined after 24 weeks' exposure. Exposure of 100 ppm n-hexane did not significantly decrease the functions of the peripheral nerve throughout the experiment. Exposure to 200 ppm MEK significantly increased MCV and MNCVs and decreased DL after four weeks' exposure, but at this later stage no significant changes were found throughout the experiment by comparison with the controls. Mixed exposure to 100 ppm n-hexane plus 200 ppm MEK significantly decreased by comparison with the controls. On histopathological examination of the tail nerve, however, no changes were found in any of the exposed groups or the controls. These results suggest that MEK might enhance the neurotoxicity of n-hexane at a low concentration, and mixed exposures to n-hexane and MEK should be avoided.

Pulmonary mechanics in conscious Fischer 344 rats: multiple evaluations using nonsurgical techniques

An adaptation of the method reported by Amdur and Mead (1958, Amer. J. Physiol. 192, 364-368) was used to evaluate pulmonary mechanics in conscious rats, utilizing a flow plethysmograph and intraesophageal catheter to determine compliance, resistance, respiratory flow, thoracic pressure, tidal volume, frequency, and minute volume. The procedure did not require surgery, and repeat evaluations were made in conscious rats. Real time calculations of pulmonary parameters were accomplished with an analog computer interfaced with a digital computer for display and data storage. Multiple evaluations (1, 3, 6, 13, 18, 24, 30, and 36 weeks) in 40 rats are reported. The utility of the system in establishing a base line against which pulmonary impairment, related to the effects of known pulmonary toxicants, e.g., ANTU and NO2, could be measured, was evaluated.

Effects of nitrous oxide-induced inactivation of cobalamin on methionine and S-adenosylmethionine metabolism in the rat

Inhalation of nitrous oxidises cobalamin and, in turn, inactivates methionine synthetase which forms methionine from homocysteine and which requires cob[I]alamin as a co-factor. This study was planned to determine the effect of virtual cessation of methionine synthesis via a cobalamin-dependent pathway, on tissue levels of methionine, S-adenosylmethionine and on related enzymes. The level of methionine in liver fell initially after exposure to N2O but was restored to pre-N2O levels after 6 days despite continuing N2O exposure. Brain methionine fell within 12 h of N2O exposure but the fall was not significant. The restoration of methionine levels is accompanied by an increase in activity of betaine homocysteine methyltransferase in liver but this enzyme was not detected in brain. The activity of methionine synthetase remained very low in both liver and brain as long as N2O inhalation was continued. There was an initial rise in liver S-adenosylmethionine levels followed by a steady fall to 40% of its initial level after 11 days of N2O exposure. However, there was no change in the level of S-adenosylmethionine in brain during this period. The data indicate that either brain meets its requirement by increased methionine uptake from plasma or that there are alternate pathways in brain for methionine synthesis other than those requiring a cobalamin coenzyme.

Neurotoxicity and protein binding of 2,5-hexanedione in the hen

Previous studies in this laboratory have demonstrated 2,5-dimethylpyrrole adduct formation during in vitro exposure of protein amino groups to the neurotoxic n-hexane metabolite 2,5-hexanedione (2,5-HD). The present investigation reports in vivo pyrrole adduct formation in neural and nonneural protein from 2,5-HD-treated animals. Adult, White-Leghorn hens were given daily doses of either 200 or 70 mg 2,5-HD/kg, po, for up to 55 or 135 days, respectively. Additional animals were given 70 mg/kg for 63 days and then allowed to recover for 72 more days. Protein separation by gel electrophoresis followed by staining with a pyrrole-specific reagent yielded evidence of widespread adduct formation in protein from serum, liver, kidney, brain, and purified myelin. Binding was particularly strong in serum albumin nd myelin basic protein. Quantitation of the adduct in these tissues revealed that its formation reached peak levels at 20 days in high dose and 30 days in low-dose animals. Levels subsequently declined, suggesting the presence of a clearance mechanism capable of removing altered protein during continuing 2,5-HD exposure. Protein from animals on the recovery regimen contained no detectable pyrrole adduct. Pyrrole adduct formation was also detected in neurofilament protein preparations, although protein yields were too low to allow assessment of clearance. Hens at both dosages displayed clinical signs indicative of CNS and PNS neuropathy. Histologic findings included axonal swelling and degeneration in peripheral nerve and some spinal cord nerve tracts. A hypothesis is proposed involving differential clearance of pyrrole adduct from neural vs nonneural tissue to explain the mechanism of action and target organ specificity of 2,5-hexanedione.

The morphogenesis of testicular degeneration induced in rats by orally administered 2,5-hexanedione

The neurotoxic hexacarbon 2,5-hexanedione (2,5-HD) produces testicular atrophy in experimental animals. To examine the morphogenesis of the testicular lesion, 1.0% 2,5-HD was provided in the drinking water of adult F-344 rats for up to 6 weeks. After 3 weeks of administration, there were occasional large vacuoles in the basal region of the germinal epithelium. At 4 weeks, these vacuoles were much larger and more numerous; electron microscopy demonstrated that they were derived from the smooth endoplasmic reticulum. The vacuoles were preferentially associated with stages 12, 13, 14, and 1 of the spermatogenic cycle. Additionally, at 4 weeks there was a significant decrease in the number of tubules in stages 7 and 13, and a concomitant increase in the percentage of tubules in stages 3, 5, and 6. By Week 5, most Golgi-phase and cap-phase spermatids were visibly affected, showing margination of nuclear chromatin, and were becoming dissociated from Sertoli cells. Frequent multinucleated giant cells were seen and electron microscopy of these cells suggested that they were derived from fused spermatocytes or spermatids. After 6 weeks, fewer giant cells were present, most tubules contained cellular debris, and many showed empty lumina encircled by a thin ring of cytoplasm near the basement membrane. Interstitial tissue appeared unaffected. These studies indicate that the Sertoli cell is probably an initial target for 2,5-HD action in the testis.

Chronic cryptogenic polyneuropathy. The search for a cause

91 patients with chronic symptoms of polyneuropathy without any previously known underlying disorder underwent extensive clinical and laboratory investigations in an attempt to reveal the cause of the polyneuropathy. A definite or probable origin of polyneuropathy was detected in only 8 patients (9%) and a possible but questionable cause was found in 16 (17%), while the cause in 74% remained undetermined. In only 1 patient could effective treatment be instituted. No evidence was found for an association between polyneuropathy and reduced glucose tolerance without manifest diabetes mellitus. The findings suggest that only a limited investigation is justified in most cases of chronic polyneuropathy without obvious cause.

Plasmid R46 fails to protect Escherichia coli against double-strand DNA-binding agents but increases their mutagenic activities

Plasmid R46 was tested for its ability to increase survival and mutagenesis of Escherichia coli strain AB1157 following exposure to agents that produce a variety of structural defects in DNA. The plasmid enhanced the mutagenic activities of adriamycin (ADM), N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU), bleomycin (BLM), methyl methanesulphonate (MMS), mitomycin C (MTC), nitrofurazone (NFZ), 4-nitroquinoline-N-oxide (NQO), cis-platinum (II) diaminodichloride (PDD) and proflavine (PF). Furthermore, R46, which is known to protect against BLM and MMS, increased the survival of strain AB1157 following exposure to NFZ, NQO or PDD but not ADM, BCNU, MTC or PF. In fact the plasmid appeared to slightly sensitise its host to the latter drugs. The results are discussed in terms of the nature of the DNA damage produced by these inhibitors and the possible role of plasmid-encoded products in the repair of DNA.

Metabolic activation as a basis for organ-selective toxicity

Historically, the concept of metabolic activation was first forwarded to explain the in vivo activity of certain carcinogenic chemicals that without prior metabolism were chemically inert and biologically inactive. Subsequently, the concept has been extended to explain the effects of many different classes of chemicals causing diverse toxicities. Because of its major role in drug metabolism, the liver is a prominent site for toxic injury by agents requiring metabolic activation. The liver can also be the source of reactive metabolites that damage extrahepatic organs. But, organ selective toxicity can also result from the in situ metabolic activation of foreign chemicals in extrahepatic target tissues such as the lungs and the kidneys. Moreover, extrahepatic tissues generally are much more heterogeneous in cellular composition compared to the liver, and the localization of drug metabolizing enzymes in certain cell populations may result in highly cell selective toxic injury. The significance of metabolic activation and toxicity--and the importance of the particular chemical structure of individual compounds, as well as host factors such as species, age, sex, and pretreatment effects--on target-organ-selective toxicity by reactive metabolites are illustrated by studies with various furan derivatives, an important class of environmental chemicals.

Interaction of catecholamine-derived alkaloids with central neurotransmitter receptors

Catecholamine-derived alkaloids of the simple tetrahydroisoquinoline, 1-benzyl-tetrahydroisoquinoline and tetrahydroprotoberberine classes have been tested for their ability to inhibit the binding of seven different radioligands to neurotransmitter receptors of brain synaptic membranes. Alkaloids of all three classes were active in inhibiting 3H-clonidine binding to alpha 2-adrenergic receptors. Stereoselectivity of tetrahydropapaveroline in binding to alpha 2-adrenergic receptors was evidenced by the marked activity of the S-(--) isomer (IC50 = 0.65 microM) in comparison to the R-(+) enantiomer (IC50 = 50 microM). The simple tetrahydroisoquinolines (3,4-dihydroxytetrahydroisoquinoline and salsolinol), the four isomeric mono-O-methyl derivatives of 2,3,10,11-tetrahydroxyberbine and tetrahydropapaveroline were the most potent inhibitors of 3H-apomorphine binding to dopaminergic receptor agonist sites. The tetrahydroprotoberberines, as a class, were the most potent inhibitors of 3H-spiroperidol binding to dopaminergic receptor antagonist sites and of 3H-WB-4101 binding to alpha 1-adrenergic receptors. The 1-benzyl-tetrahydroisoquinolines exhibited varying degrees of interaction with beta 1-adrenergic receptors. Tetrahydropapaveroline (IC50 = 0.3 microM) was the most active of the 24 alkaloids tested in inhibiting binding of 3H-dihydroalprenolol to beta 1-adrenergic receptors. None of the alkaloids significantly affected 3H-QNB binding to muscarinic-cholinergic receptors, and selected alkaloids from each class interacted only moderately with serotonergic receptors.

Ethanol and tetrahydroisoquinoline alkaloids do not produce narcotic discriminative stimulus effects

Male Sprague-Dawley rats were trained in a two lever food-reinforced procedure to discriminate between the effects of saline and the synthetic narcotic analgesic fentanyl (0.04 mg/kg). After acquisition of this discrimination, generalization tests with morphine, ethanol and some tetrahydroisoquinoline alkaloids were conducted. The rats dose-dependently generalized the effect of morphine but did not generalize the effects of either ethanol, tetrahydropapaveroline, salsolinol or 3-carboxysalsolinol to the fentanyl discriminative stimulus. Thus, these date do not support a biochemical link between ethanol and opiates.

Guide to the analysis of phencyclidine and its metabolites in biological material

Phencyclidine was introduced as an anaesthetic in 1960; and has now become a major drug of abuse in some countries. The rapid advance in the various fields of analytical chemistry during the past decades has made it possible to measure the levels of the compounds in tissues and body fluids. These methods may also be used to study the metabolism and pharmacokinetics of PCP. The resulting publication is an updated guide to these analyses particularly with the application of these techniques in human intoxication.

Regulation of the capacity for O6-methylguanine removal from DNA in human lymphoblastoid cells studied by cell hybridization

Hybrids were made between a ouabain-resistant, thioguanine-resistant human lymphoma line able to remove O6-methylguanine from its DNA (Mex+) and human lymphoblastoid lines deficient in this capability (Mex-). The formation of hybrids was confirmed by chromosomal analysis. Hybrid cells had an O6-methylguanine removal capacity per mole of guanine about one third to one half that of the Mex+ parents, i.e., about the same per cell. Cell hybrids removed the same amount of the alkylation adduct 3-methyladenine as did their parents per mole of guanine, i.e., about twice as much per cell. Although the cell hybrids had intermediate resistance to the cytotoxic action of N-methyl-N'-nitro-N-nitrosoguanidine used to induce O6-methylguanine and 3-methyladenine, there is evidence that the ability to remove O6-methylguanine and resistance to the cytotoxic effect of N-methyl-N'-nitro-N-nitrosoguanidine are dissociable characteristics.

Effects of phenobarbital and 3-methylcholanthrene on the in vivo distribution, metabolism and covalent binding of 4-ipomeanol in the rat; implications for target organ toxicity

The effects of phenobarbital (PB) and 3-methylcholanthrene (MC) on the distribution, metabolism and covalent binding of 4-ipomeanol were examined in the rat. An analysis of tissue extracts by high-pressure liquid chromatography (HPLC) showed that both treatments markedly decreased the concentrations of unmetabolized 4-ipomeanol at all times examined. PB treatment increased the urinary excretion of nonbound 4-ipomeanol metabolites, while MC treatment did not alter their excretion. Analysis of urine by HPLC indicated that the increased concentration of urinary metabolites found in the phenobarbital-treated rats was attributable primarily to an increased excretion of ipomeanol-4-glucuronide. These data indicate that the decreased pulmonary covalent binding and lethality of 4-ipomeanol in the rat after MC and PB were caused by alterations in the tissue distribution of the parent compound. Pulmonary concentrations of unmetabolized 4-ipomeanol were decreased by MC through an increased metabolism of 4-ipomeanol in the liver, primarily to toxic products that bind covalently in that tissue and lead to hepatoxicity. PB produced a similar decrease in unmetabolized 4-ipomeanol concentrations in lung but by an enhanced in vivo metabolism and clearance of 4-ipomeanol, primarily through a "nontoxic" pathway, glucuronidation, and did not lead to hepatotoxicity.

Ability of tryptophan derivatives to mimic melatonin's action upon the Syrian hamster reproductive system

The ability of 18 different tryptophan derivatives to induce gonadal regression in Syrian hamsters when injected daily at either midday or late evening has been examined. The compounds chosen have either been identified within mammalian pineal glands or are thought to be possible metabolic derivatives of melatonin. Of the compounds tested, only melatonin and 5-methoxytryptamine were found to possess antigonadotropic activity. 5-Methoxy-tryptamine's potency, however, was 1/10th that of melatonin and, like melatonin, 5-methoxytryptamine was effective when injected in the evening but not when injected during midday. In addition to the general survey of tryptophan derivatives for antigonadal capability when injected, 5-methoxytryptamine, melatonin, and 5-methoxytryptophol were compared relative to their abilities to prevent photo-induced gonadal regression when administered within beeswax implants. Again 5-methoxytryptamine and melatonin, but not 5-methoxytryptophol, were effective with 5-methoxytryptamine's potency being less than that of melatonin. These results indirectly support the contention that melatonin is the pineal product which mediates photoperiodic effects upon the Syrian hamster reproductive system.

Mechanisms of oxygen activation by nitrofurantoin and relevance to its toxicity

Purified ferredoxin-(cytochrome c)-NADP+ oxidoreductase and xanthine oxidase were found to catalyse the reduction of nitrofurantoin to the free radical. Under aerobic conditions, the nitrofurantoin radical underwent autoxidation to regenerate the parent compound with the concomitant production of superoxide and eventually hydrogen peroxide. The nitrofurantoin radical was also shown to react with hydrogen peroxide to generate a highly reactive species which was capable of oxidising methionine to ethylene. This active oxygen radical appeared to be identical with the crypto-OH . radical, previously proposed as being formed from the analogous reaction of the methyl viologen radical with hydrogen peroxide [R.J. Youngman and E.F. Elstner, FEBS Lett. 129, 265 (1981)]. Catalase inhibited nitrofurantoin-dependent ethylene formation in both enzyme systems, whereas superoxide dismutase was only inhibitory in the xanthine oxidase mediated reaction. Although the primary function of the respective enzyme systems is to generate the nitrofurantoin radical, the xanthine oxidase reaction is markedly more complex than that of ferredoxin-(cytochrome c)-NADP+ oxidoreductase. The differences between the two enzyme reactions appear to be due to the endogenous autoxidation of xanthine oxidase. The aerobic activation of nitrofurantoin by xanthine oxidase involved the superoxide anion as an intermediate, whereas the nitrofuran was directly reduced by ferredoxin-(cytochrome c)-NADP+ oxidoreductase without a requirement for active oxygen species.

Urinary excretion of n-hexane metabolites. A comparative study in rat, rabbit and monkey

Exposure to n-hexane, a component of many industrial solvent mixtures, is known to cause polyneuropathy in man. The concentration of metabolites in urine following exposure may be useful in biological monitoring. In a comparative study experimental animals (rat, rabbit and monkey) were subjected to single inhalatory treatments of 6, 12 and 24 h with 5,000 ppm of pure n-hexane. At the end of the treatments and at intervals thereafter, urine, and in rats also blood, were collected and analyzed for n-hexane and its metabolites. While the urine of rats contained 2-hexanol, 3-hexanol, methyl n-butyl ketone, 2,5-dimethylfuran, y-valerolactone and 2,5-hexanedione, rabbit and monkey urine were found to contain only 2-hexanedione, rabbit and monkey urine were to contain only 2-hexanol, 3-hexanol, methyl n-butyl ketone and 2,5-hexanedione. Within 72 h of the end of exposure, the principal metabolite was 2,5-dimethylfuran in rats and 2-hexanol in rabbits and monkeys. In all three species the excretion rates of methyl n-butyl ketone, 3-hexanol and 2-hexanol peaked several hours earlier than 2,5-hexanedione (and gamma-valerolactone and 2,5-dimethylfuran in rats). In all species 2,5-hexanedione was still detectable in urine 60 h following exposure. n-Hexane metabolites in rat blood were 2-hexanol, methyl-n-butyl ketone, 2,5-dimethylfuran and 2,4-hexanedione. The first two, as well as n-hexane itself, were found in maximum concentration immediately after termination of exposure, while 2,5-dimethylfuran and 2,5-hexanedione, with the longer exposure times, peaked some hours later. The data from urine collected at the end of exposure were compared with those obtained in a parallel study in humans occupationally exposed to a mixture of hexane isomers. Humans chronically exposed to 10-140 ppm n-hexane had 2,5-hexanedione concentrations in urine ranging from 0.4 to 21.7 mg/l, i.e., in the same proportion as rats exposed once for 6 or 12 h to 5,000 ppm.

Mechanisms of superoxide radical-mediated toxicity

Free radicals generated from metabolism of foreign compounds can have extremely detrimental consequences on cell function and survival. Due to their high reactivity, free radicals may potentially perturb a wide spectrum of important cellular macromolecules such as nucleic acids, proteins, lipids and polysaccharides. Recently, the toxicity of several xenobiotics has been suggested to be mediated by formation of free radicals derived from reduction of molecular oxygen, forming superoxide anion (O(2)) and hydroxyl radical (OH .). For example, the pulmonary toxicity of the bipyridylium herbicide paraquat has been attributed to an enzymatically catalyzed one-electron redox cycling of the parent molecule, resulting in generation of O(2). Examples of other compounds that are subject to redox cycling with associated O(2) formation are those agents containing quinone or aromatic nitro structural elements. An important aspect of free-radical-mediated toxicity is that it is moderated by several cellular defense mechanisms including superoxide dismutase, catalase, glutathione peroxidase, vitamin E and reduced glutathione. Thus, toxicity mediated by free radical generation may not occur unless defense mechanisms are overwhelmed by radical production.

Regulation of the capacity for O6-methylguanine removal from DNA in human lymphoblastoid cells studied by cell hybridization

Hybrids were made between a ouabain-resistant, thioguanine-resistant human lymphoma line able to remove O6-methylguanine from its DNA (Mex+) and human lymphoblastoid lines deficient in this capability (Mex-). The formation of hybrids was confirmed by chromosomal analysis. Hybrid cells had an O6-methylguanine removal capacity per mole of guanine about one third to one half that of the Mex+ parents, i.e., about the same per cell. Cell hybrids removed the same amount of the alkylation adduct 3-methyladenine as did their parents per mole of guanine, i.e., about twice as much per cell. Although the cell hybrids had intermediate resistance to the cytotoxic action of N-methyl-N'-nitro-N-nitrosoguanidine used to induce O6-methylguanine and 3-methyladenine, there is evidence that the ability to remove O6-methylguanine and resistance to the cytotoxic effect of N-methyl-N'-nitro-N-nitrosoguanidine are dissociable characteristics.

Neurotoxic action of 2,5-hexanedione on the autonomic nervous system: ultrastructural and functional alterations in the rat sympathetic superior cervical ganglion

In rats treated for 14 days with 2,5-hexanedione, the efficiency of ganglionic transmission was markedly reduced whereas only faint ultrastructural changes occurred in a few preganglionic fibers; evident signs of axonal pathology were observed on the 30th day of treatment. Choline acetyltransferase activity and acetylcholine formation showed no alteration at any time. The autonomic system is affected early during 2,5-hexanedione neuropathy, functional changes being more marked than morphological lesions.

Evidence for cytochrome P-450 mediated metabolism in the bronchiolar damage by naphthalene

Intraperitoneal administration of the volatile hydrocarbon, naphthalene, resulted in severe bronchiolar epithelial cell necrosis in mice, while hepatic or renal necrosis was not observed. Pulmonary damage and mortality by naphthalene were increased by prior treatment with diethyl maleate and decreased by prior treatment with piperonyl butoxide (1600 mg/kg). SKF 525A pretreatment had no effect on naphthalene-induced pulmonary damage. Administration of [14C]naphthalene resulted in the covalent binding of radiolabel to tissue macromolecules. Highest levels of binding occurred in lung, liver and kidney. Levels of covalent binding reached a maximum 2--4 h after treatment and corresponded to rapid glutathione depletion in lung and liver. Covalent binding was dose-dependent and showed a threshold between 200 and 400 mg/kg which coincided with almost total depletion of tissue glutathione levels. Covalent binding of reactive metabolites was increased 3--4-fold by prior treatment with diethyl maleate, and was decreased 3--4-fold by pretreatment with piperonyl butoxide. These studies support the view that naphthalene-induced pulmonary damage is mediated by the cytochrome P-450-dependent metabolism of naphthalene and that glutathione plays an important role in the detoxification of the lung damaging metabolite(s).

Distribution and metabolism of the pulmonary alkylating agent and cytotoxin, 4-ipomeanol, in control and diethylmaleate-treated rats

Diethylmaleate (DEM), an agent which depletes tissue glutathione (GSH), increased the covalent binding and toxicity of 4-ipomeanol [1-(3-furyl)-4-hydroxypentanone] in rats. The distribution of unmetabolized 4-ipomeanol-[5-14C] and its metabolites were studied in tissue extracts by high-pressure liquid chromatography (HPLC) in control and DEM-treated rats. At all time periods examined, DEM treatment produced no significant effect on the tissue distribution of unchanged 4-ipomeanol. In both groups, the relative tissue concentrations of unmetabolized 4-ipomeanol were in the order blood greater than lung greater than liver. In control rats, the relative tissue concentrations of nonbound, solvent-extractable 4-ipomeanol metabolites (hereafter referred to simply as "4-ipomeanol metabolites"), as well as the covalently bound 4-ipomeanol metabolites (hereafter referred to as "covalently bound 4-ipomeanol equivalents" to distinguish from all other metabolites) were in the order lung greater than liver greater than blood. The pulmonary levels of both the covalently bound 4-ipomeanol equivalents and the 4-ipomeanol metabolites were increased markedly by DEM treatment at all time periods examined. The total pool of urinary 4-ipomeanol metabolites was significantly decreased by DEM treatment, but the total amounts of excreted ipomeanol-4-glucuronide, the major metabolite of 4-ipomeanol in rats, were not significantly different in the control and DEM-treated rats. These data are consistent with the view that the increased pulmonary covalent binding and toxicity of 4-ipomeanol produced by diethylmaleate treatment in rats are due to the depletion of pulmonary GSH by the DEM and not a major DEM-induced alteration in the tissue distribution of the parent 4-ipomeanol.

Protective role of endogenous pulmonary glutathione and other sulfhydryl compounds against lung damage by alkylating agents. Investigations with 4-ipomeanol in the rat

Because endogenous glutathione is known to participate in the detoxification of highly reactive, hepatotoxic drug metabolites, we studied the role of this substance in the pulmonary toxicity of 4-ipomeanol [1-(3-furyl)-4-hydroxypentanone] in rats. 4-Ipomeanol was an appropriate model for these studies since previous investigations have indicated that an alkylating metabolite, formed in situ, is responsible for selective lung damage by 4-ipomeanol. Toxic doses of 4-ipomeanol preferentially depleted rat lung glutathione. Pretreatment of animals with piperonyl butoxide, an inhibitor of the metabolic activation of 4-ipomeanol, prevented both the depletion of lung glutathione and the pulmonary toxicity of 4-ipomeanol. Prior depletion of lung glutathione by diethylmaleate increased both the pulmonary covalent binding and the toxicity of 4-ipomeanol, whereas administration of cysteine and cysteamine decreased both the covalent binding and the toxicity. These in vivo studies, in conjunction with previous in vitro studies which showed inhibitory effects of sulfhydryl compounds on the covalent binding of 4-ipomeanol, are consistent with the view that pulmonary glutathione plays a protective role against pulmonary alkylation and lung toxicity by 4-ipomeanol, probably by reacting with the toxic metabolite(s) to form nontoxic conjugate(s). Pulmonary glutathione may similarly provide protection against other electrophilic drugs or metabolites that can damage the lungs.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase in normal and dystrophic hamsters

The activity and diurnal variation of 3-hydroxy-3-methyglutaryl-CoA reductase (EC 1.1.1.34; HMG-CoA reductase), the rate-limiting enzyme in the cholesterol-biosynthetic pathway, of normal and dystrophic hamsters was determined. Liver enzyme activity showed a diurnal pattern in the normal male, but not in the dystrophic male. Enzyme values in normal males at the midpoint of the 12 h dark period were 10 times those in dystrophic males. No evidence for diurnal variation in the HMG-CoA reductase of the brain was observed, and similar activities were found for normal and dystrophic animals. The apparent Km for HMG-CoA reductase from the liver of normal or dystrophic hamsters was approx. 9 microM, and the Vmax. was 5.9 and 21.7 pmol/min per mg of protein for dystrophic and normal hamsters respectively.

Neurotoxicity of continuous (90 days) inhalation of technical grade methyl butyl ketone in hens

Neurotoxicity was produced in 1-yr-old hens (five hens per treatment) by continual 90-d exposure in inhalation chambers to atmospheres containing 50, 100, 200, or 400 ppm technical grade methyl butyl ketone (MBK) containing 70% methyl n-butyl ketone (MnBK) and 30% methyl isobutyl ketone (MiBK). A 30-d observation period followed. Severity of clinical condition and progression or improvement of neurological deficit signs were dependent on the concentration of MBK and duration of exposure. Hens exposed to the two highest levels developed ataxia and paralysis; they died or were sacrificed before the designated exposure period ended. The intermediate level of MBK (100 ppm) caused severe ataxia; most treated hens showed no change in clinical condition during the observation period. Hens exposed to 50 ppm exhibited gross ataxia, with most demonstrating partial regression of neurological deficit after the exposure ceased. Hens exposed to the lowest tested level (10 ppm) remained normal. Only hens exposed to 400 or 200 ppm showed significant weight loss. Some hens from the 50-400 ppm treatment groups showed unequivocal histopathologic changes in the spinal cord and peripheral nerves. Severity of histopathologic changes depended on the level and duration of MBK exposure. These changes were characterized by excessive swelling, phagocytosis, degeneration, and demyelination of the axons.

Concentration of 3-methylindole (3MI) and distribution of radioactivity from 14C-3MI in goat tissues associated with acute pulmonary edema

3-Methylindole (3MI) can cause acute pulmonary edema in goats. Because of known lipophilic properties and direct effects on biological membranes, the concentration of 3MI and distribution of radioactivity from 14C-3MI in tissues was investigated during development of 3MI-induced APE. Goats were given a 2 hr jugular infusion of 3MI containing 14C-3MI using propylene glycol as the vehicle. Groups of 3 goats were killed at 0, 5, 2 and 4 hr and 2 goats were killed at 8 and 24 hr. Plasma, lung, liver, kidney and other selected tissues were collected. 3MI was rapidly cleared from blood plasma and tissues after infusion, and 81% of the radioactivity was excreted in the urine by 24 hr. Maximum concentrations of unmetabolized 3MI in the tissues ranged from 2.6 to 15 micrograms 3MI/g, including 7.5 micrograms 3MI/g in the lung. The ratios of equivalent radioactivity to unmetabolized eMI indicated rapid metabolism and the presence of metabolites in all tissues studied. The lung contained the highest proportion of metabolites with ratios of radioactivity to unmetabolized 3MI of about 50, 10, 250, 150 and 80 at 0.5, 2, 4, 8 and 24 hr. The data demonstrate that 3MI does not selectively concentrate in the lung and that the concentrations are lower than those usually associated with direct membrane damage. They also indicate that 3MI is rapidly metabolized and that metabolites are present in tissues, especially the lung. These results suggest that direct effects of 3MI on biological membranes are not primarily responsible for lung injury in goats.

Carcinogenicity examination of betel quid. II. Effect of vitamin A deficiency on rats fed semipurified diet containing betel nut and calcium hydroxide

The effect of vitamin A deficiency on the carcinogenicity of betel quid was studied, using long-term feeding of vitamin-A-deficient and -sufficient diets with and without betel nut and calcium hydroxide in ACI rats. A high incidence of focal epithelial hyperplasia was observed in the upper digestive tract (tongue, buccal oral mucosa, esophagus, and forestomach) of rats in the group given the vitamin-A-deficient diet mixed with betel nut and calcium hydroxide. The vitamin-A-deficient group also showed a high incidence of squamous papilloma in the tongue, buccal mucosa, and forestomach. The incidence of hyperplastic lesions of the tongue and buccal oral mucosa was significantly higher in this group than in the group receiving the vitamin-A-sufficient diet with betel nut and calcium hydroxide. These results suggest that the vitamin-A-deficient condition enhanced the growth of epithelial hyperplasia that was due to the administration of the betel quid ingredients. However, vitamin A did not protect against the development of altered liver cell foci, which were frequently seen with a small number of hepatocellular neoplasms in all groups given the diets containing betel nut and calcium hydroxide (both vitamin-A-deficient and -sufficient groups).

[Investigations on neurotoxicity of chemical substances at the workplace. II. Determination of the motor and sensory nerve conduction velocity in persons occupationally exposed to pentachlorophenol (author's transl)]

We examined eighteen workers (three women, 15 men) in a pentachlorophenol (PCP) processing factory, with a mean activity of 12 years. PCP in blood and urine samples was analyzed by gas chromatography. To evaluate the peripheral nervous system the maximal motor as well as sensory nerve conduction velocities of the ulnar and/or median nerve were measured. The PCP-levels in plasma ranged between 0.02 and 1.5 ng/l, median 0.25 ng/l, and in urine between 13 and 1,224 micrograms/l, median 112 micrograms/l, or between 11 and 2,111 micrograms/g creatinine, median 111 micrograms/g creatinine. The median values of the neurophysiological parameters showed a mild degree of slowing in the PCP-collective. In the case of the sensory nerve conduction velocities, this decrease was significant. A dose-effect relationship between internal PCP-load and the different nerve conduction velocities could not be demonstrated. The individual evaluation of the toxicological and neurophysiological results gave hints that in some cases decreased nerve conduction velocity is caused by chronic exposure to PCP.