Teratogenic effects of 5-fluoro-2'-deoxyuridine in pregnant mice

Fetal anemia following maternal exposure to 5-fluorouracil in the rat

Previous studies from our laboratory have shown that maternal 5-fluorouracil (5-FU) exposure on day 14 of gestation (GD14) in the rat results in dose-dependent retardation of both cell cycle progression and growth of embryonic liver. At this developmental stage, hepatic erythropoiesis is the primary source of new circulating fetal erythrocytes. This study examined dose-dependent hematological changes in the fetus after maternal 5-FU exposure (0, 20, 30, 40 mg/kg on GD14) to assess 1) hematopoiesis as a potential target for 5-FU developmental toxicity and 2) the role of the observed 5-FU-induced fetal anemia in adverse developmental outcome. Standard clinical hematological parameters, including hematocrit, hemoglobin content, and erythrocyte counts, were measured in fetal blood drawn by cardiac puncture. Dose-related deficits were observed in all of these parameters within 48 hr of 5-FU administration. Calculation of various red cell indices revealed a concomitant increase in mean cell volume and mean cell hemoglobin. These changes were preceded by depletion of hepatic precursor populations which was evident by 24 hr after maternal exposure to 30 or 40 mg/kg. At doses of 20 and 30 mg/kg there was full and moderate recovery, respectively, in these endpoints by 72 hr after dosing, but persistent deficits were observed at 40 mg/kg. Fluorescence microscopy of Höechst-stained fetal blood smears revealed that at both 48 and 72 hr after dosing, the proportion of nucleated yolk sac-derived erythrocytes was increased relative to control.(ABSTRACT TRUNCATED AT 250 WORDS)

Limb development in mouse embryos. III. Cellular events underlying the determination of altered skeletal patterns following treatment with 5'fluoro-2-deoxyuridine

A potent inhibitor of thymidylate synthetase, 5-Fluorodeoxyuridine (FUdR), produced dose- and stage-dependent skeletal defects in embryos of mice injected during early development (10th--13th day). The dose of 25 mg/kg was teratogenic producing few resorptions and little reduction in fetal weight. Hindlimbs were much more sensitive to the drug than were the forelimbs and showed dose-dependent long bone reductions. Specific long bone reductions occurred after treatment on the 11th or 11.5 day and were accompanied by preaxial polydactyly; treatment on the 12th or 12.5 day produced high incidence of ectrodactyly but no long bone reductions. Limbs were insensitive on the 13th day of development and beyond. Limb buds in organ culture demonstrated a direct action of FUdR on undifferentiated mesenchymal cells, incurring what has been previously termed "thymineless" cell death. Dose-dependent reduction of viable cell number led to a reduction in chondrogenic expression in vitro--more so in the hindlimb than the forelimb. Similar occurrence of cell death was also noted after in utero exposure, and here, it was followed by a process of recovery. The recovery phase was characterized by the formation of a distal synchronized cell population derived from undamaged subridge cells leaving damaged cells at the proximal extent of the subridge zone. Limb segments maintained their temporal sequence of differentiation, and their regulatory capability was related to the time allotted for repopulation of the subridge zone. We propose that a faster growth during early development of the elements of the hindlimb versus analogous ones of the forelimb allows the former less time for regulation--and hence, higher sensitivity to antiproliferative agents such as FUdR.

The effects of 5-fluorouracil and 5-fluorodeoxyuridine used alone and in combination with normal nucleic acid precursors on development of mice in lines selected for low and high expression of Strong's luxoid gene

Pregnant female mice selected for plus- and minus-modifying genes of the limb-skeleton effects of Strong's luxoid gene (1st) were injected ip on day 10 of gestation with 10 or 20 mg/kg 5-fluorouracil (5-FU) or 5-fluorodeoxyuridine (5-FUdR). The incidence and degree of expression of the effects (polydactyly, ectrodactyly, radial hemimelia, tibial hemimelia, pelvic girdle shifts, deformed caudal vertebrae) varied according to the teratogen and dose level. The addition of an equimolecular amount of thymidine, thymine, or uracil greatly potentiated the effects of 20 mg/kg 5-FU, usually resulting in death of the embryos. The addition of an equimolecular amount of thymidine but not of the embryos. The addition of an equimolecular amount of thymidine but not of thymine or uracil partly protected against the effects of 5-FUdR. Both teratogens increased the expression of ist on the limb skeleton. The interactions of the teratogens with the major gene were inhibited by minus- and promoted by plus-modifying genes of 1st. The effects of the teratogenic treatments may be mediated by cell death.

Taratogenic effects of the pyrimidine analogues 5-iododeoxyuridine and cytosine arabinoside in late fetal mice and rats

Pregnant mice and rats were treated daily with 5-iododeoxyuridine (IUDR) or cytosine arabinoside (CA) on 3 consecutive days, beginning on day 16 and 18 of pregnancy, respectively. Offspring were killed at 10 and 20 days of age and the cerebellum, eye, and kidney examined histologically. All offspring of mice treated with 400 mg/kg IUDR were stillborn or died within the first 48 h of life, and deaths occurred at other dosages in both species. In IUDR-exposed mice and rats there was persistence of granule cells in the external granular layer, and scattered foci of microcystic tubular change in the renal cortices. In both species CA produced segmental cerebellar hypoplasia and focal microcystic renal cortical dysplasia. Retinal dysplasia occurred in rats exposed to 50 mg/kg. Lesions were concentrated in the central retina, corresponding with the stage of development at the time of administration of CA. The teratogenic effects of IUDR were minimal and were induced by dosages much higher than normally used in human medicine. On the other hand, lesions were more extensive in mice and rats exposed to CA. Thus, in addition to other known causes of congenital retinal dysplasia, defective development may be drug induced, in this case by the prenatal administration of CA.

The effect of D-penicillamine of the skeletal development of rat foetuses

Rats received 20, 50 or 100 mg/animal D-penicillamine i.p. twice daily on days 15, 16, 17, 18, and 19 of gestation, i.e. a total dose of 200, 500 resp. 1000 mg/animal. At all dosages the number of fetal resorptions did not increase significantly. Weight of the 20 day old embryos as well as length of the long bones in the extremities in the 100 mg-group showed a significant decrease. Numerous skeletal alterations could be observed in the 1000 mg-group such as absence, deformations or incomplete mineralisation of bones. Light microscopic examinations revealed an inhibition of the ossification as well as a decrease of number and size of the trabecula and of the thickness of the perichondrial bone sheath. A swelling of the collagenous fibrils can be demonstrated with the electron microscope. The first apatite crystals aggregate in collagen-free areas. The fusion of these aggregates to homogenously mineralized trabecula is inhibitied. In contrast to bones from untreated embryos, mineralized areas show varying content of collagen and apatide crystals. A regular spatial relationship between apatite crystals and collagenous fibrils does not develop. These findings show that even after the so-called "critical period" malformations can be pproduced by substances which disturb synthesis and maturation of the mesenchymal intercellular substance.