Short-term toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in laboratory animals: effects, mechanisms, and animal models.
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Animals↗
Biomedical subjects
J Tuomisto
Publications and source records attributed to J Tuomisto.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induced ethoxyresorufin-O-deethylase (EROD) and aldehyde dehydrogenase (ALDH3) activities in the brain and liver. A comparison between the most TCDD-susceptible and the most TCDD-resistant rat strain.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent inducer of ethoxyresorufin O-deethylase (EROD) and aldehyde dehydrogenase (EC 1.2.1.3., ALDH3) enzyme activities in the liver. Little is known about their inducibility by TCDD in the brain, although it may be a target organ for TCDD toxicity. Two strains of rat, Long-Evans (L-E) and Han/Wistar (H/W) exhibit an over 1000-fold difference in their LD50-values for TCDD. The induction of EROD and ALDH3 in discrete brain regions and in the liver of L-E and H/W rats were now compared at 10 days after TCDD exposure to assess the role of these responses in the strain difference. Liver EROD and ALDH3 were maximally induced at 5 micrograms/kg and 50 micrograms/kg, respectively, in both strains. In the brain 50 micrograms/kg TCDD was mostly needed to enhance EROD activity in both strains. The induction occurred especially in olfactory bulbs, but was also seen in the midbrain plus thalamus of both rat strains. The induced EROD activity in the olfactory bulb was almost totally abolished by a monoclonal antibody (Mab) 1-7-1 raised against CYP1A1. ALDH3 activities were increased more dose dependently in olfactory bulbs of H/W than L-E rats. In other brain areas measured, ALDH3 activities were induced more in L-E rats. Kinetic factors did not explain the differential induction of EROD and ALDH3 among discrete brain regions. We conclude that both EROD and ALDH3 are induced in the brain by TCDD although the activities are much lower than in the liver. The induction in the brain is region specific with olfactory bulbs being the most responsive area. As in the liver, the TCDD-induced activity of EROD in the brain is primarily associated with CYP1A1. According to the present findings, enzyme induction in the brain does not seem to have a crucial role in determining the strain susceptibility to the acute lethality of TCDD.
Aldehyde Dehydrogenase↗
Exposure to 2,3,7,8-tetrachlorodibenzo-para-dioxin leads to defective dentin formation and pulpal perforation in rat incisor tooth.
A single dose of 1000 micrograms 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg body weight was given to TCDD-resistant (Han/Wistar) young adult male rats. Changes in the skulls and the continuously erupting incisor teeth were evaluated 16 weeks after the administration of TCDD. The skulls of the experimental rats (N = 11) were significantly smaller than those of the control rats (N = 11), and the upper and lower incisor teeth of all experimental rats were significantly thinner than the control rat teeth. The pulps of the lower incisors of all experimental rats were lingually exposed to the oral cavity at their incisal ends. Also in 3 cases the pulps of the upper incisors were exposed, but never in the control rats. Whereas the labial surfaces of the incisors of the control rats were brown, those of the experimental rat teeth appeared greyish and mottled. Histological examination revealed that the pulp chambers in the incisal halves of the affected teeth were larger than normal, at the expense of the thickness of dentin. Towards the incisal tooth ends, odontoblasts gradually lost their polarity and the pulp tissue became necrotic. A dentin zone next to the pulp chambers was irregular. Lingual tapering of the teeth was pronounced, which gave them a mesiodistally flattened appearance. The superficial zone of the otherwise regular enamel was poorly pigmented. In conclusion, a single injection of TCDD was shown to impair normal growth of the skull and incisor tooth formation in rats. The small size of the incisors, their aberrant shape and the defective dentin (and enamel) formation could be mediated by vitamin A metabolism, known to be interfered with by TCDD.
Animals↗
Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on plasma and tissue beta-endorphin-like immunoreactivity in the most TCDD-susceptible and the most TCDD-resistant rat strain.
The salient sign of acutely lethal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) intoxication in rats is hypophagia along with a prominent body weight loss. Endogenous opioid peptides have been implicated as modulators of food intake. In the present study, female rats of both the most TCDD-susceptible (Long-Evans [L-E]; LD50 9.8 micrograms/kg) and the most TCDD-resistant strain (Han/Wistar [H/W]; LD50 > 7200 micrograms/kg) were exposed to a single dose of 50 micrograms/kg TCDD ip. This treatment is usually lethal within 1-6 weeks to all L-E rats and nonlethal to all H/W rats. The animals were killed at 1, 4 or 10 days after the treatment. beta-Endorphin-like immunoreactivity (beta-END-LI) was determined by a validated RIA method in the hypothalamus, pituitary, pancreas, duodenum and plasma. TCDD decreased plasma beta-END-LI concentration by 24-37% at every time point of measurement in L-E rats alone. By contrast, feed-restricted controls exhibited an increase of similar magnitude on day 4. Pancreatic beta-END-LI was also elevated in feed-restricted controls at that time point as compared with either the ad libitum control or TCDD group. TCDD appeared to shrink the pituitary gland in both strains by day 4. Pituitary weight was similarly lowered in TCDD-treated rats and feed-restricted controls at the last time point and this reduction was reflected in pituitary beta-END-LI content. Thus, TCDD affects selectively plasma beta-END-LI levels and this impact correlates with its lethality in these strains.
Animals↗
Cytogenetic effects of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) in rat peripheral lymphocytes in vitro and in vivo.
3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is a potent direct-acting Salmonella mutagen found in wood pulp chlorination effluents and chlorinated drinking water. In cultured rat peripheral lymphocytes, MX induced significant dose-related increases in sister-chromatid exchanges (SCEs) and chromosome aberrations at doses of 20-60 micrograms/ml and of 60-80 micrograms/ml, respectively. MX produced primarily chromatid-type as opposed to chromosome-type aberrations. The peripheral lymphocytes of male and female rats exposed to MX by gavage 5 days a week for 14-18 weeks showed significant dose-related increases in SCEs at both levels of exposure (30 and 45-75 mg/kg) in both sexes. The present results demonstrate for the first time that MX is genotoxic in vivo.
Animals↗
Comparative acute lethality of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2,3,7,8-pentachlorodibenzo-p-dioxin and 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin in the most TCDD-susceptible and the most TCDD-resistant rat strain.
We have previously demonstrated a more than 300-fold difference in acute LD50 values for 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) between male Long-Evans (Turku AB; L-E) and Han/Wistar (Kuopio; H/W) rats after intraperitoneal exposure. In the present study, we compared the acute lethality of TCDD, 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PCDD) and 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (HCDD) in these strains by intragastric administration. In agreement with previous data, H/W rats proved to be strikingly resistant to TCDD, since even the highest dose tested, 7200 micrograms/kg, was below the LD50 level for both genders. The corresponding LD50 values for female and male L-E rats were 9.8 and 17.7 micrograms/kg, respectively. A similar strain difference was discovered for PCDD: the LD50 value was > 1620 micrograms/kg for female H/W rats and between 20 and 60 micrograms/kg for female L-E rats. Surprisingly, the acute lethality of HCDD did not follow the same pattern. Female H/W rats turned out to be only about 10 times less susceptible to that congener than female L-E rats (LD50 values 1871 and between 120 and 360 micrograms/kg, respectively). These findings do not support the widely accepted concept that sufficiently high doses of all dioxin congeners will produce the same effects. Either the higher chlorinated dioxins have toxic effects distinct from those of TCDD or the relative contribution of toxic impacts varies among these compounds.
Animals↗
[Toxic factors and brain].
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Blood-Brain Barrier↗
Puffing behavior during the smoking of a single cigarette in a naturalistic environment.
The 36 participants in this study were habitual low-yield cigarette smokers, medium-yield cigarette smokers, and switchers from medium- to low-yield cigarettes. All participants smoked both low- (0.4 mg) and medium-nicotine (0.9 mg) cigarettes during the study. Puffing indices were recorded during the first two cigarettes, after an overnight abstinence of smoking, by a portable flowmeter processor unit in a naturalistic environment. The puff volumes per cigarette and per day were significantly lower while switching to higher-yield cigarettes, mainly due to a decrease in the number of puffs and longer interpuff intervals, but also due to a decline in puff duration and flow rate. However, the downregulation by puff volume was incomplete, at most two thirds, as calculated by machine smoking yields. Within the course of smoking a single cigarette, the flow rate was quite stable, puff duration and puff volume decreased toward the end of the cigarette, and interpuff interval was longest during the middle of the cigarette. Total puff volumes per cigarette were similar in the first two cigarettes of the day after an overnight abstinence of smoking, with no significant differences in other puff parameters. Diurnal cotinine excretion revealed that nicotine titration in switching situations was very accurate among switchers and medium-yield cigarette smokers, but not among the low-yield cigarette smokers, and so called oversmoking was found with the higher-nicotine brand. Preferred cigarette type had little effect on the puffing patterns of smokers in single cigarettes.
Adult↗
Effects of smoking abstinence and chain-smoking on puffing topography and diurnal nicotine exposure.
Effects of chain-smoking, a 15-h smoking abstinence, and the nicotine yield of cigarettes on puff indices were studied in eight healthy smokers by using a controlled crossover study design. Puff parameters were measured puff by puff with a portable measuring device when 10 or 20 cigarettes, with nicotine yields of 0.3 and 1.0 mg, were smoked per day. The interval between sessions was 1 h, and the 20 cigarettes per day were chain-smoked 2 at a time. Serum cotinine indicated that smokers compensate completely for the lower nicotine delivery from the 0.3-mg cigarette. Smokers almost doubled total puff volume per cigarette and per day mainly by taking more puffs from the low-nicotine cigarettes and slightly prolonging puff duration. However, nicotine deprivation and chain-smoking had a relatively minor effect on puffing indices with both brands, a fact that agrees poorly with the nicotine titration hypothesis. However, in the course of every single cigarette of the day smokers significantly reduced puff duration and puff volume toward the end of the cigarette, which probably involves satiation of the nicotine crave but may also be due to changes in taste of the smoke.
Adult↗
A new method for the measurement of spontaneous motor activity of laboratory animals.
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Amphetamine↗
Pharmacokinetics in rat of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a drinking water mutagen, after a single dose.
The pharmacokinetics of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) was evaluated after a single oral or intravenous administration in the rats using 14C-labelled compound. Twenty to 35% of the dose was absorbed into circulation from the gastrointestinal tract as assessed from the excretion in urine. The mean elimination half-life of the radioactivity in blood (T1/2 k10) was 3.8 hr. Traces of radioactivity remained in the blood for several days. The tissues lining the gastrointestinal and urinary tract, kidneys, stomach, small intestines and urinary bladder contained the highest radioactivity. The activity declined slowest in the kidneys. Urine was the main excretion route. Seventy-seven % of the total amount excreted appeared in urine in 12 hr and 90% in 24 hr. No radioactivity was exhaled in air suggesting that elimination through respiration did not occur. After an intravenous administration of 14C-MX, the T1/2 k10, was much longer, 22.9 hr, and the total elimination half-life (T1/2 beta), 42.1 hr. The results indicate that MX is absorbed from the gastrointestinal tract to a considerable degree and it is excreted in urine very rapidly. A fraction of MX or its metabolites is retained in blood for a longer period of time. The pharmacokinetics of MX does not suggest extensive cumulation of MX in tissues after continuous exposure.
Absorption↗
Acute neurobehavioural effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Han/Wistar rats.
The neurobehavioural effects of a single non-lethal dose (1000 micrograms/kg intraperitoneally) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were assessed in young male Han/Wistar rats, highly resistant to acute lethality of TCDD. TCDD decreased body weight significantly compared with ad libitum fed controls. TCDD did not change the behaviour or the motility of rats in the open field test 8 days after the treatment nor did it affect the spontaneous motor activity up to 27 days after the exposure. In the elevated plus-maze test for anxiety, TCDD-treated rats did not differ from either ad libitum fed controls or pair-fed controls. In the 24-hr passive avoidance test, the learning of TCDD-treated rats did not differ significantly from that of ad libitum fed controls or pair-fed controls from 8 hr to 16 days after the treatment. TCDD did not affect the motor coordination or the maintenance of balance on the rotating rod but it impaired them slightly in the elevated horizontal bridge test 16 hr after exposure. It did not affect nociception in the hot plate test 16 hr or 8 days after the injection. The results suggest that a single sublethal dose of TCDD does not alter markedly the general behaviour of Han/Wistar rats, in contrast to its striking effect on feeding behaviour which results in a marked decrease in body weight gain.
Animals↗
Identification of aromatic moieties and mycosamine in antifungal heptaenes with high-performance liquid chromatography, high-performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry.
A high-performance liquid chromatographic (HPLC) method for the determination of the aromaticity of heptaene polyene antibiotics has been developed. The released aromatic moiety of the heptaene polyenes aureofungin, candicidin, candimycin, hamycin and trichomycin was assayed after alkaline hydrolysis. The presence of p-aminoacetophenone (PAAP) and N-methyl-p-aminoacetophenone (N-methyl-PAAP) in the hydrolysates was determined by HPLC, HPLC-mass spectrometry (HPLC-MS) and gas chromatography-MS (GC-MS). Candicidin and hamycin contained only the PAAP residue; aureofungin contained both PAAP and N-methyl-PAAP. Trichomycin contained PAAP and also some unknown component of molecular weight 179. The aromatic nature of the individual components of the heptaene complex was demonstrated using radioactivity flow detection for the determination of the incorporation of [14C]-p-aminobenzoic acid to individual candicidin components. Ammonia chemical ionization MS was successfully used for the GC-MS identification of the acetylated mycosamine moiety of heptaenes.
4-Aminobenzoic Acid↗
Do new hypotheses on the mechanism of action of dioxins help in risk evaluation?
The mechanism of action of chlorinated dibenzodioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is not known, but the prevailing hypothesis is the binding to a specific protein, the Ah-receptor, and subsequent alteration of the expression of specific genes. This Ah-receptor hypothesis does not explain all aspects of toxicity, notably the extreme variation of toxicity between different animal species. We have found two rat strains that differ widely in their sensitivity to TCDD. The resistant Han/Wistar (H/W) rat tolerates doses up to 3000 micrograms kg-1, while 20 micrograms kg-1 is lethal to Long-Evans (L-E) rats. Several morphological, biochemical and endocrinological parameters as well as pharmacokinetics have been screened, but the strains behave by and large similarly. However, there is a clear behavioural difference: TCDD causes anorexia in both strains, but H/W rats start eating again in 1-2 weeks, whereas the reduction of feed intake is permanent in L-E rats until they die in about 3 weeks. Han/Wistar rats, which recover after a single large dose of TCDD, behave aberrantly for months; they seem to have a supersensitive satiety response while they do not respond normally to energy deficiency. Therefore the regulation of feed intake or of body weight seem to be altered permanently by TCDD. It is also of interest that TCDD is more toxic after a central than after a peripheral administration. These findings may be of importance for the risk evaluation of dioxins, because they might help to explain the wide species/strain variation which complicates the assessment of dioxin risk to humans.
Animals↗
Polyene antibiotics increase the ionic permeability of synaptosomal plasma membranes.
The effects of antifungal heptaene antibiotics candicidin and amphotericin B were investigated in isolated cerebral cortical nerve terminals (synaptosomes). The synaptosomes were incubated with candicidin or amphotericin B in the presence or absence of external Ca2+. Candicidin (0.4-0.8 I.U./mL) increased intrasynaptosomal free Ca2+ significantly. This increase was not significantly suppressed by 30 microM verapamil or 2 microM nifedipine. In the absence of extrasynaptosomal Ca2+ intrasynaptosomal free Ca2+ was not changed by candicidin. Amphotericin B increased intrasynaptosomal free Ca2+ as well. Candicidin (0.05-0.6 I.U./mL) increased the respiration rate up to 3.5-fold above the basal rate. This response was not affected by the absence of extracellular Ca2+. Ouabain completely blocked the increase of respiration caused by candicidin, whereas tetrodotoxin was ineffective. The plasma membrane depolarized in a dose-dependent manner after candicidin (0.2-0.8 I.U./mL). The mitochondrial membrane potential was little affected and only at the highest concentrations. The results indicate that heptaene polyenes increase synaptosomal ionic permeability, which is reflected in increased Ca2(+)-influx and accelerated respiration. The increment in synaptosomal free calcium takes place probably as a nonspecific leak via typical polyene-cholesterol channels. The respiration is accelerated by increased Na(+)-permeability through the plasma membrane which stimulates the function of Na+, K(+)-ATPase and thus increases the energy demand.
Amphotericin B↗
Smoking behavior in low-yield cigarette smokers and switchers in the natural environment.
Urinary cotinine and puffing parameters were studied in 36 smoking students. Three smoking groups, formed according to the tar content of their preferred cigarette, were compared. Eighteen students had always smoked low-yield, 10 medium-yield and 8 were switchers from medium- to low-yield cigarettes. The subjects smoked their preferred brand (the first week), low-yield cigarettes (the second week) and medium-yield cigarettes (the third week). Day urine samples were collected for cotinine analysis during the two last days of the test weeks. Puffing indices were reported on the last day of every test week with a portable microcomputer assisted analyzer with flowhead cigarette holder. Urinary cotinine concentrations were rather constant within the groups, but lower among the low-yield cigarette smokers as compared to the switchers (p less than 0.05). Also the female smokers had lower cotinine concentrations than the male smokers (p less than 0.05). The compensatory behavior seen in every smoking group while they were smoking low-yield cigarettes was based on up-regulation in single puff volume, puff duration and total smoking time when compared to values with medium-yield cigarettes. The correlation between cotinine concentration and diurnal puff volume (1/day) was poor. It is concluded that the benefit possibly gained with low-yield cigarettes is not long lasting.
Adult↗
Binding of the strong bacterial mutagen, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) to bovine serum albumin.
Binding of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) to bovine serum albumin (BSA) was studied. MX bound mainly reversibly to BSA but, for a minor part, also irreversibly. It was possible to extract the main part of the reversibly bound MX with ethyl acetate and the extractable compound was chromatographically identical to MX. The affinity-binding characteristics of the interaction with albumin were K = 1.6 x 10(7) M-1, n = 3.4. Furthermore, mutagenicity studies indicated that reversibly bound MX remained mutagenic but that irreversibly bound MX was no longer mutagenic in the Ames test. These results suggest that the binding of MX to albumin is an important factor for both the toxicological effects and the toxicokinetics of MX.
Animals↗
TCDD decreases rapidly and persistently serum melatonin concentration without morphologically affecting the pineal gland in TCDD-resistant Han/Wistar rats.
The highly toxic environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was recently reported to decrease serum melatonin levels throughout the circadian cycle in the most TCDD-susceptible strain of rat, Long-Evans. To find out whether this effect is related to the mechanism of acute lethality of TCDD, serum melatonin levels were measured at the nocturnal peak phase in the most TCDD-resistant rat strain variant, Han/Wistar rats, 6 hr to 28 days after TCDD exposure. The same dose as used in the previous study, 50 micrograms/kg, decreased serum melatonin levels to approximately half the control values by the first day after the treatment. Melatonin concentrations remained at this reduced level over the whole observation period. In an auxiliary experiment, Han/Wistar rats were dosed with 1000 micrograms/kg TCDD and killed on day 3. Neither light nor electron microscopic examination of their pineal glands revealed any alteration attributable to TCDD treatment. These findings might indicate that the reduction of serum melatonin levels in the rat by TCDD is not related to its lethal effect and is not due to a direct damage of the pineal gland.
Animals↗