Incorporation of 5-fluorouracil-2-C-14 by mouse embryos

Reproductive and developmental toxicities of 5-fluorouracil in model organisms and humans

Chemotherapy, as an important clinical treatment, has greatly enhanced survival in cancer patients, but the side effects and long-term sequelae bother both patients and clinicians. 5-Fluorouracil (5-FU) has been widely used as a chemotherapeutic agent in the clinical treatment of various cancers, but several studies showed its adverse effects on reproduction. Reproductive toxicity of 5-FU often associates with developmental block, malformation and ovarian damage in the females. In males, 5-FU administration alters the morphology of sexual organs, the levels of reproductive endocrine hormones and the progression of spermatogenesis, ultimately reducing sperm numbers. Mechanistically, 5-FU exerts its effect through incorporating the active metabolites into nucleic acids directly, or inhibiting thymidylate synthase to disrupt the function of DNA and RNA, leading to profound effects on cellular metabolism and viability. However, some studies suggested that the toxicity of 5-FU on reproduction is reversible and certain drugs used in combination with 5-FU during chemotherapy could protect reproductive systems from 5-FU damage both in females and males. Herein, we summarise the recent findings and discuss underlying mechanisms of the 5-FU-induced reproductive toxicity, providing a reference for future research and clinical treatments.

Early events following maternal exposure to 5-fluorouracil lead to dysmorphology in cultured embryonic tissues

The chemotherapeutic agent 5-fluorouracil (5-FU) is teratogenic in a number of species, yet the mechanism(s) of its developmental toxicity are not fully understood. Administration of 5-FU to the pregnant CD rat on day 14 of gestation results in dose-dependent growth retardation and numerous malformations in near-term fetuses, including hindlimb defects and cleft palate. Following treatment, a number of rapid biochemical and cellular alterations are detectable in embryonic hindlimbs, craniofacial and other tissues, which include thymidylate synthetase (TS) inhibition and altered cell cycle progression. In order to assess the importance of these early events in 5-FU-induced dysmorphogenesis, embryonic mid-facial tissues and hindlimbs were dissected 3 or 6 hr after administration of 5-FU to the dam and placed in explant culture. After 5 days in culture, craniofacial explants were evaluated morphologically for palatal closure and growth was assessed by measuring total protein and DNA content. Hindlimb explants were stained for cartilage using alcian blue to evaluate development of the digits. Craniofacial explants cultured at either 3 or 6 hr after exposure exhibited dose-dependent growth retardation and defects of palatal fusion at the end of the culture period. Deficits in protein and DNA content were similar to those in craniofacial tissues that continued to develop in utero after treatment, although morphological defects in cultured explants did not correlate well with the incidence of cleft palate in vivo. Dose-dependent deficits in metatarsal and phalanx development were observed in hindlimb explants dissected either 3 or 6 hr after maternal treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

The in vitro embryotoxicity of 5-fluorouracil in rat embryos

The fluorinated pyrimidine 5-fluorouracil (5-FU) is an effective chemotherapeutic agent that is teratogenic in a number of species. The mechanism for the embryopathic effect of the drug is unknown. We examined the effects of this compound on gestation day 10.5 rat embryos cultured for 48 hours in a rodent whole embryo culture system. Embryos were exposed for 1-4 hours to various doses of 5-FU. Embryolethality was minimal in all treatment groups. The malformation frequency increased with higher doses; within a dose, the malformation frequency increased with longer exposure to the drug. The tail and hindlimb bud were the most commonly affected structures in vitro; tail and leg defects are produced in several species by exposure to the drug in vivo. The embryopathic drug concentration in the culture media (2-8 micrograms/ml) is similar to the plasma level of 2-17 micrograms/ml, which is associated with embryopathy in vivo. Results from this study suggest that the whole embryo culture system is an appropriate model for developmental toxicity studies of 5-FU.

Ultrastructural and cytochemical observations on 5-fluorouracil-induced cleft-palate development in hamster

Sequential alterations in 5-fluorouracil-treated hamster fetal palate were studied by light and electron microscopy and by acid phosphatase cytochemistry. At an early stage in 5-fluorouracil-treated fetuses, when the palatal shelves were vertical, lysosomes first appeared in cells of the prospective fusion epithelium and then in the cells of subjacent mesenchyme. In contrast to controls, increasing numbers of both the epithelial and mesenchymal cells of the vertical palate showed lysosomal injury in 5-fluorouracil-treated fetuses as development progressed. Subsequently, the basal lamina in the vertical palate showed alterations, characterized initially by disturbances in lamina lucida, by fingerlike extensions of lamina densa, and ultimately by its complete breakdown. At a later stage, when shelves became horizontal, the lysosomes were absent in both the epithelial and mesenchymal cells, and the basal lamina continuity was restored. Unlike controls, however, 5-fluorouracil-treated horizontal shelves never contacted one another. Instead, the epithelia of the horizontal shelves underwent stratification. It appears that premature formation of lysosomes in palatal epithelial and mesenchymal cells following 5-fluorouracil treatment disrupts normal cytodifferentiation and affects the integrity of the basal lamina; both effects are associated with cleft-palate development.

Reduced interlitter variability in rats resulting from a restricted mating period, and reassessment of the ""litter effect''

Rats were mated for two or 15 hours and variability of day-12-embryos in weight, protein content, and [3H]thymidine incorporation was compared in the long mating period (LMP) and short mating period (SMP) groups by a 2-level nested analysis of variance. Variability in day-20 fetal weight was similarly compared. In both groups day-12 embryonic weight was relatively more variable than day-20 fetal weight, and variability was less in SMP than LMP animals for each comparison made, although statistical significance was attained only for thymidine incorporation. ""Litter effects'' were noted but not of the magnitude reported by other investigators. It was concluded that inappropriate statistical methods have encouraged the belief that among-litter variability usually exceeds within-litter fetal weight variability. The teratological implications of reduced development variability and the ""litter effect'' are discussed.

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.

Effects of 5-fluorouracil on secondary palatal development of 129-J mice

Palatal morphology and the sequence of palate development from the 13th to the l7th day of development were compared in experimental and control groups of pregnant 129/J mice injected with 5-fluorouracil.