Reproductive toxicity and toxicokinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin. 2. Problem of paternally-mediated abnormalities in the progeny of rat

Possible effects on the next generation after long-term exposure (subcutaneous administration) of male rats to very high doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were studied. Two dose regimes were applied: TCDD-25 (initial dose: 25 micrograms/kg body wt; maintenance dose: 5 micrograms/kg body wt, once weekly) and TCDD-75 (initial dose: 75 micrograms/kg body wt; maintenance dose: 15 micrograms/kg body wt). Male rats were treated for 10 weeks before mating and then throughout the entire 12 week mating period. They were mated to unexposed virgin females. One group of pregnant females was used for teratological evaluations, and another group was allowed to deliver. No significant differences were observed in the number of implantations or fetuses per litter, and resorption rate, and fetal weight between the controls and TCDD-treated groups. No gross-structural anomalies occurred in any of the fetuses sired by TCDD-treated males. In the TCDD-25 group an increased frequency of two types of variations was observed which also occur in controls: incompletely ossified fingers (TCDD-25 = 5.1%, controls = 2.6%), and incompletely ossified ossa zygomatica (TCDD-25 = 1.8%, controls = 0.5%). In the TCDD-25 group a slight but statistically significant increase was observed in the rate of stillbirths (TCDD-25 = 1.3%, controls = 0.1%), apparently due to an unusually low frequency occurring in the controls (overall historical controls = 0.6%). There was no difference in postnatal mortality (TCDD-25 = 1.3%, controls = 1.3%). Taken together, despite the very high doses of TCDD used, the data do not provide evidence for biologically significant paternally-mediated developmental toxicity in the fetuses and newborn.

Teratogenicity of the 13-cis and all-trans-isomers of the aromatic retinoid etretin: correlation to transplacental pharmacokinetics in mice during organogenesis after a single oral dose

NMRI mice were treated on day 11 (day 0 = plug day) of gestation with a single oral dose of 100 mg/kg of either all-trans-etretin (acitretin) or 13-cis-etretin. For teratology studies mice were sacrificed on day 18 of gestation, and the fetuses were examined for malformations. For pharmacokinetic studies, groups of 5 mice were sacrificed after 5, 10, and 30 min and 1, 2, 4, and 8 h. The concentrations of retinoids in maternal plasma and in embryos were determined by a newly developed HPLC gradient method. All-trans-etretin induced malformations in 94% of the fetuses, mainly in fore and hind limbs and cleft palate. 13-cis-etretin did not show any teratogenic or embryo-lethal effects at the dose level used. These findings could be explained by a transplacental pharmacokinetic study. The maximum peak level and also the AUC (area under the concentration-time curve) value of all-trans-etretin in the embryos was 7-8 times higher than corresponding values for 13-cis-etretin, probably due to extensive transport of the trans-isomer and limited transport of the cis-isomer from maternal plasma to the embryos. The concentration quotient between embryo and the maternal plasma was between 0.43 and 1.10 for all-trans-etretin, and only 0.16-0.31 for 13-cis-etretin over the time period studied. An in vivo isomerization of the compounds was also observed which was more extensive for 13-cis-etretin than for all-trans-etretin. Our results indicate that the low teratogenic potency of 13-cis-etretin is due to a limited placental transfer of this compound; on the other hand, the potent teratogen all-trans-etretin is rapidly and extensively transferred to the embryo.

Ofloxacin in juvenile non-human primates and rats. Arthropathia and drug plasma concentrations

Arthropathia in juvenile animals is the most important toxic effect induced by quinolones. We conducted pharmacokinetic and morphological studies with ofloxacin on non-human primates (Callithrix jacchus, Marmosets) and rats. In the marmoset, electron microscopy and the application of immuno-morphological methods proved to be suitable for the detection of specific alterations in cartilage (e.g. loss of proteoglycans and altered chondrocytes). Subsequently performed electron microscopic examinations in rats showed similar specific alterations of the femur cartilage surface after multiple oral applications of 600 mg ofloxacin/kg body wt. These results were correlated with pharmacokinetic data obtained for the same species. After single oral application of 100, 300 or 600 mg ofloxacin/kg body wt to 5 week-old rats peak plasma levels were achieved 15-45 min after administration indicating a rapid absorption of the drug. The following peak concentrations were measured for the three doses applied (mean +/- SD): 8.9 +/- 2.1, 22.6 +/- 7.5 mg/l and 33.5 +/- 9.8 mg/l, respectively. After 360 min the concentrations were 1.1 +/- 0.4, 5.9 +/- 2.5 and 15.9 +/- 5.1 mg/l, respectively. After subcutaneous injection of 100 mg ofloxacin/kg body wt the mean peak concentration was 27.7 +/- 2.6 mg/l after 45 min (0.5 +/- 0.2 mg/l after 360 min). In the marmoset higher plasma concentrations were measured with comparable doses. One, 3, and 6 h after the last of nine administrations of 200 mg ofloxacin/kg body wt, the mean (+/- SD) plasma concentrations were: 42.7 +/- 16.7, 40.6 +/- 9.5, and 26.5 +/- 3.6 mg ofloxacin/l plasma. Typical alterations of the joint cartilage of juvenile rats (e.g. opened chondrocyte cavities, swelling of rough endoplasmic reticulum and mitochondrial swelling in the chondrocytes) were induced by oral administration of ofloxacin at doses that were approximately 100 times higher than therapeutic ones, but led to peak plasma concentrations which were only approximately 10 times above the therapeutic level.

Reproductive toxicity and pharmacokinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin. 1. Effects of high doses on the fertility of male rats

A study on the reproductive toxicity of 14C-TCDD in male rats was performed. Two dose regimes were applied subcutaneously: TCDD-25 (initial dose: 25 micrograms/kg body wt; maintenance dose: 5 micrograms/kg body wt) and TCDD-75 (initial dose: 75 micrograms/kg body wt; maintenance dose: 15 micrograms/kg body wt); the maintenance dose was administered once weekly. The rats were treated for 10 weeks before they were mated and throughout the entire mating period. The dose regime TCDD-75 led to a mortality rate of 93% within a period of 16 weeks. The first animals died during 4 weeks, and an LD50 was reached after 8 weeks. The dose regime TCDD-25 did not cause any mortality over a period of 12 weeks; but an LD10 was reached within 13-20 weeks. The body weight was significantly decreased in both groups treated with TCDD after 1 week of treatment. It stabilized in the TCDD-25-group 4 weeks after treatment and stayed at this level until the end of the treatment period. The most significant finding is the delayed fertilization by the treated males; 15% of the males were found to be sterile. The mating index (84%) and fertility index (14 +/- 11 days) of the TCDD-25-group were lower when compared with controls (95%, 8 +/- 5), but the pregnancy index was not reduced. Application of the chosen TCDD doses led to clear-cut morphological changes of the testes. The Sertoli cells were changed (increased occurrence of vacuoles, swelling of endoplasmatic cavities), and the contact between the Sertoli cells and spermatogonia was disturbed, which might indicate an inhibited maturation of spermatozoa precursors.

Pharmacokinetics and biological activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin. 2. Pharmacokinetics in rats using a loading-dose/maintenance-dose regime with high doses

Wistar rats were treated initially with very high single doses of 14C-2,3,7,8-TCDD (either 75 or 25 micrograms/kg body wt) followed by weekly maintenance doses of 15 and 5 micrograms/kg body wt, respectively. 14C-radioactivity was measured in various organs over a period of 22 weeks. 1) 75 micrograms TCDD/kg body wt (followed by the maintenance doses) was lethal for all the rats within a period of 9 weeks. While the concentration of 14C-TCDD equivalents in liver and thymus stayed reasonably constant during this period in the surviving rats, the concentration in adipose tissue and kidneys clearly increased in the same animals. 2) The dose of 25 micrograms TCDD/kg body wt (followed by weekly doses of 5 micrograms/kg body wt) proved to be a just tolerable dose over a period of 22 weeks for our strain of rats. 3) Within the individual variabilities the TCDD concentrations in the investigated organs showed no clear-cut decline, indicating that the animals were exposed to fairly constant levels of TCDD throughout the study. Thus, this dosing regime is suitable for maintaining constant TCDD exposure during long-term studies.

Teratogenicity and placental transfer of all-trans-, 13-cis-, 4-oxo-all-trans-, and 4-oxo-13-cis-retinoic acid after administration of a low oral dose during organogenesis in mice

13-cis-Retinoic acid (isotretinoin) is teratogenic in humans at therapeutic doses (0.5-1.5 mg/kg) but only marginally teratogenic in the mouse at a high dose of 100 mg/kg. Previous results explained why the cis isomer of retinoic acid was much less teratogenic than the trans isomer in mice. It was found that the placental transfer of all-trans retinoic acid to the mouse embryo was far greater than that of the 13-cis isomer. Since our previous study had been performed with exceedingly high doses (100 mg/kg) of 13-cis-retinoic acid and all-trans-retinoic acid, we have now performed additional experiments with 10-fold lower doses. Studies were also done with the main metabolites of the two retinoids (the 4-oxo-derivatives) to elucidate the metabolism, pharmacokinetics, and teratogenicity of each single compound. It was shown that all-trans-retinoic acid and 4-oxo-all-trans-retinoic acid were extremely teratogenic, whereas their corresponding cis isomers caused only 2% cleft palate. Embryonic exposure to the trans isomers was likewise higher than that to the cis isomers, as shown by the far higher embryonic peak concentrations and by the 30-fold higher areas under the concentration-time curve values reached for the trans isomers compared with the cis isomers. At 8 hr, embryo/maternal plasma ratios were higher than 1 after administration of the all-trans compounds. Concentrations found in the placenta and yolk sac were higher for the trans forms than for the cis forms. We propose a model for a facilitated transport of the all-trans forms to the developing embryo and suggest that the conversion to the trans isomer and trans metabolite could play a major role in the teratogenicity of 13-cis-retinoic acid in humans.

Transplacental pharmacokinetics and teratogenicity of a single dose of retinol (vitamin A) during organogenesis in the mouse

Pregnant mice received 10 or 100 mg retinol/kg body wt. by gavage on day 11 of gestation (plug day = day 0). One group of animals was used for a pharmacokinetic study. At various times after dosing, plasma and tissue samples were collected and analyzed by HPLC for retinyl esters, retinol, 13-cis- and all-trans-retinoic acid and 13-cis-4-oxo and all-trans-4-oxoretinoic acid. In the other group the fetuses were removed on day 18 and examined for malformations. After 10 mg/kg retinol, no teratogenic effect was observed. The pharmacokinetic investigation revealed a moderate increase of retinyl esters, retinol and all-trans-retinoic acid in plasma, embryonic tissue, placenta, yolk sac membranes and extraembryonic fluid. A high incidence of severe fetal malformations occurred after 100 mg/kg retinol. These malformations included limb defects (81% of fetuses) and cleft palate (55% of fetuses) which are characteristically found after administration of a single teratogenic dose of an active retinoid on day 11 of gestation. The concentration-time profile of retinoids after 100 mg/kg on day 11 showed a pronounced increase of retinyl esters and retinol in all compartments including the embryo and a massive generation of the polar metabolites all-trans-retinoic acid and all-trans-4-oxoretinoic acid. These polar metabolites were found in the embryo with peak concentrations of 327 +/- 115 and 143 +/- 20.7 ng/g (mean +/- SE) wet tissue, respectively. It is likely that all-trans-retinoic acid and all-trans-4-oxoretinoic acid, both well-known teratogens, largely contributed to the teratogenic outcome. The in-vivo oxidation of retinol may be an important factor in the teratogenic activity of high doses of vitamin A.

Hypertension and nephrotoxic lesions in rats 1 year after prenatal exposure to gentamicin

Using the aminoglycoside antibiotic gentamicin persistent functional and morphological changes were induced prenatally in the rat kidney. After 6 days of s.c. treatment (110 mg gentamicin/kg body wt) from day 10 to 15 of pregnancy complete resorption was noticed in 8 of the 14 treated animals. Fifty-three newborn were obtained from six dams. One year later only 26 rats (16 male, 10 female) were still alive. The systolic arterial pressure of the female offspring was significantly increased (139 +/- 15 mm Hg versus 112 +/- 9 mmHg) compared with controls. No statistically significant effect could be noticed in the male offspring (128 +/- 15 mm Hg versus 118 +/- 21 mm Hg). Corresponding results were obtained from analysis of urea plasma concentrations. Another cohort of pregnant rats received daily injections of gentamicin from day 15 to 20 of pregnancy (110 mg/kg body wt s.c.). In this group 59 newborn from a total of 109 died within the first 5 days after birth. Six litters were observed postnatally. One year after birth the following blood pressure values were determined: 122 +/- 14 mm Hg (male) and 132 +/- 17 mm Hg (female). Urea plasma concentrations were significantly higher in female, but not in male, offspring. Light and electron microscopic inspection revealed pathological changes in the kidneys of the female offspring only. The degree of maternal kidney damage - which shows considerable variations - was monitored during the treatment period. For this purpose the plasma gentamicin and urea concentrations were measured on 3 days of treatment in all of the pregnant animals. The postnatal data (mortality, blood pressure, and urea plasma concentrations) show a correlation to the degree of maternal kidney impairment.

Gross-structural defects in rats after acyclovir application on day 10 of gestation

Following three s.c. injections of acyclovir (100 mg acyclovir/kg) into rats on day 10 of pregnancy 19 litters were evaluated on day 21 of gestation and the effects were compared to the results obtained from controls (nine litters) which received the vehicle (0.1 N NaOH) only. The following results were obtained (treated group versus control group): 1) Implantations/litter: 11.2 +/- 1.3 versus 10.2 +/- 1.1; 2) resorptions/implantations: 27.7% versus 2.2%; 3) number of viable fetuses evaluated: 154 versus 90; 4) fetuses with anomalies of the skull: 78% versus 12%; 5) fetuses with anomalies of the vertebral column: 38% versus 13%; 6) gross-structural anomalies predominantly affected the skull and tail. The most frequently registered defects were: os tympanicum (smaller): 23%, os tympanicum (missing): 23%; missing tail: 7%; protruding tongue (15%); none of these defects were seen in the control fetuses. Postnatally we observed a high mortality rate among the offspring. From a total of 85 newborn (nine litters) we obtained 73 viable offspring (9.1 +/- 3.4); 81% of them had tail alterations. In the control group of eight litters (9.4 +/- 2.3) no tail alterations occurred. On day 21 postnatally 40 viable offspring were alive (mortality rate: 38.8%). Nearly all of these animals had visible alterations at multiple sites of their bodies; most frequently observed were: tail impairment, closed eyes, dragging hind-limbs, and urogenital alterations (e.g. testicular atrophy). These studies how for the first time that prenatal treatment with acyclovir induces gross-structural defects which persist postnatally.(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal toxicity of acyclovir in rats

Pregnant rats were treated during organogenesis with s.c. injections of acyclovir and the embryos were evaluated on day 11.5 of gestation (crown-rump length, somites, protein content, score, abnormalities, histological examination). After eight injections of 50 mg/kg body wt on days 9, 10, and 11 of pregnancy a reduction of the crown-rump length was noticed. After 100 mg/kg this effect was more pronounced. With two or three applications of this dose on day 10 specific embryonic abnormalities were visible: the shape of the head was abnormal, the width of the skull had decreased resembling a beak-like visceral cranium. With a single administration of 200 mg/kg on day 10 we found a similar but slightly more pronounced outcome. A drastic change of all variables was obtained after eight injections of 100 mg/kg on days 9, 10, and 11. Comparatively we measured maternal plasma concentrations of acyclovir 1 h after the administration of 50, 100 or 200 mg/kg body wt. After an injection of 50 mg/kg on days 9, 10, and 11 of gestation (three injections/day) the plasma levels ranged from 19.1 to 40.0 mg/l (1 mg/l = 4.44 microM). No cumulation was observed. In contrast, a cumulative effect was detected following a dose of 100 mg/kg. After the first injection of this dose a mean value (+/- SD) of 60.3 +/- 14.7 mg/l (n = 16) was obtained. In this case a third injection increased the mean plasma level to 124.6 +/- 16.6 mg/l (n = 5). Further injections, however, led to decreasing levels. One hour after administration of 200 mg/kg body wt acyclovir levels ranged from 120.0 to 163.9 mg/l. We conclude that acyclovir, at doses leading to plasma concentrations well above the therapeutic level in the dam, interferes with the embryonic development in the rat. Acyclovir induces typical gross structural abnormalities which have been first observed using a whole embryo culture system.

Gentamicin plasma concentrations in pregnant and non-pregnant rats and fetuses after single and multiple injections

As part of our studies on the prenatal induction of renal dysfunctions in rats by gentamicin we measured maternal plasma levels of the drug. Additionally, the gentamicin concentrations in the plasma of rat fetuses after single s.c. injections of gentamicin were measured. The following results were obtained: 1) Non-pregnant rats excrete the drug faster than pregnant rats; 2) after a single s.c. injection of 110 mg gentamicin/kg body wt to six pregnant rats on day 21 of gestation the following pharmacokinetic variables were calculated: t1/2(inv): 27.0 +/- 6.1 min, t1/2(elim): 54.7 +/- 3.8 min, Cmax: 166.2 +/- 22.7 mg/l, tmax: 53 +/- 6.7 min, AUC: 431.7 +/- 53.4 mg/l x h; 3) plasma concentrations increase with the duration of pregnancy; 4) fetal plasma concentrations were determined between 45 and 660 min after single injections of 150 mg/kg to the dams. The concentrations showed minimum variation over this time period. Thus, the ratio of maternal to fetal plasma levels decreases drastically during this period; 5) 8 h after s.c. injection of 110 mg/kg to six dams (day 21 of gestation) individual plasma concentrations in the plasma of mother animals and in the plasma of 65 fetuses were determined. All fetal plasma samples showed higher concentrations than the corresponding maternal ones; 6) after multiple injections a significant increase in plasma concentrations can be seen. A considerable individual variance is obvious at all times and with both doses investigated; 7) since maternal plasma concentrations vary considerably in individual animals, especially after multiple injections, fetal exposure must also be variable in different litters. This would also affect the extent of postnatal dysfunction in various litters.

Principles and problems in assessing prenatal toxicity

The terminology to be used in reproductive (or in prenatal) toxicology has to be in accord with other fields and principles of toxicology; the reasons are briefly discussed. In addition it is essential to assess prenatal toxicity in comparison to adult (maternal) toxicity. Since pharmacokinetics in laboratory animals (e.g. rodents) usually differ considerably from that in man, this fact has to be considered when planning and evaluating studies on prenatal toxicity. Up till now this aspect has seldom been taken into account. A special problem in prenatal toxicity is the inter- and intralitter variability of the toxic manifestation (especially in polytocal animals). This problem has to be recognized by the investigators and means of dealing with it have to be developed. Like all other toxic effects, embryo-/fetotoxic manifestations occur dose dependently. Little information is available in the literature on clean dose-response-curves for teratogenic effects. Some data from our laboratory are presented. Risk assessment of teratogenic effects up till now represents a major problem. While qualitative risk assessment for man on the basis of animal data is possible, quantitative extrapolation from such data to the situation possibly existing in man is still difficult, because basic principles and strategies are largely lacking (e.g. may a "threshold" be assumed or not?). The results of some activities towards this goal are presented from our laboratory.

Embryotoxic effects of magnesium deficiency and stress on rats and mice

Pregnant rats an mice received a magnesium (Mg)-deficient diet with different Mg contents from 40 t 360 ppm. The control received 2,000 ppm. At the end of gestation, the Mg concentration in the maternal serum was found to have decreased by up to 0.3 mmole/liter, depending on the Mg content of the food. Mg-dose-dependent embryotoxic effects (resorptions, retardation, disturbed bone development, and skeletal malformations) were observed only below a threshold value of 0.7 mmole/liter of the maternal serum Mg concentration. Noise stress in rats, in addition to a mild Mg deficiency (360 ppm Mg), which by itself had no effects, increased the rate of resorptions only.