Early postimplantation embryolethality in mice following in utero inhibition of adenosine deaminase with 2'-deoxycoformycin

Effect of ADA1 mother-fetus and wife-husband phenotypic differences on the ratio birth weight/placental weight in fertile women and on reproductive success in couples with RSA

OBJECTIVES

To study the effect Adenosine Deaminase locus 1 (ADA(1)) mother-fetus and wife-husband phenotypic differences on the ratio Birth Weight/Placental Weight (BW/PW) in fertile women and on reproductive success in couples with repeated spontaneous abortion (RSA).

METHODS

209 couples with primary RSA and a consecutive series of 379 healthy puerperae with their newborn infants from the White Caucasian population of central Italy were studied. In primary RSA women reproductive success was indicated by the presence of at least one live-born infant within 5 years of follow up. Two way contingency tables were analyzed by chi-square.

RESULTS

The proportion of primary RSA couples with at least a live-born infant shows the highest value in couples mother ADA(1)1/father carrier of ADA(1)*2 allele (55.2%) and the lowest value in reciprocal couples mother carrier of ADA(1)*2 allele /father ADA(1)1 (18.7%) (O.R. = 5.33; P = 0.023). The highest ratio BW/PW is observed in the class mother ADA(1)1/newborn carrier of ADA(1)*2 allele while the lowest ratio is observed in the reciprocal class mother carrier of ADA(1)*2 allele/ newborn ADA(1)1.

CONCLUSIONS

Differences between mother and fetus in ADA(1) phenotype may influence the ratio BW/PW in healthy women and reproductive success in RSA women.

Repeated spontaneous abortion. Cooperative effects of ADA and ACP1 genetic polymorphisms

PROBLEM

In consideration of the effect of adenosine deaminase (ADA) and ACP1 (a low-molecular-weight protein tyrosine phosphatase) on T-cell receptor activity, we have analysed the joint distribution of these polymorphisms in a sample of women with primary repeated spontaneous abortion (RSA) to search for possible interactive effects on susceptibility to RSA.

METHOD OF STUDY

ACP1 and ADA phenotypes were determined in 170 women with primary RSA in 79 healthy consecutive puerperae and in 160 female newborns from the Caucasian population of Rome and in 357 healthy consecutive puerperae from the Caucasian population of Penne. Chi-square test of independence and three way contingency table analysis by a log-linear model were performed.

RESULTS

Women with low-ADA activity and high-ACP1 activity show the lowest susceptibility to RSA. Women with high-ADA activity and low-ACP1 activity, on the contrary, show the highest susceptibility to RSA and also the highest incidence of auto antibodies and of A blood group incompatibility.

CONCLUSION

The data are in agreement with those expected on the basis of the effects of ACP1 and ADA genetic variability on T-cell receptor activity and suggest a cooperative effect of the two polymorphic systems in the susceptibility/resistance to repeated spontaneous abortion.

Transcription factor gene AP-2 gamma essential for early murine development

Transcription factor gene AP-2 gamma belongs to a family of four closely related genes. AP-2 gamma had been implicated in multiple functions during proliferation and differentiation based on its expression pattern in trophoblast, neural crest, and ectoderm cells in murine embryos. In order to address the question of the role of AP-2 gamma during mammalian development, we generated mice harboring a disrupted AP-2 gamma allele. AP-2 gamma heterozygous mice are viable and display reduced body sizes at birth but are fertile. Mice deficient for AP-2 gamma, however, are growth retarded and die at days 7 to 9 of embryonic development. Immunohistochemical analysis revealed that the trophectodermal cells that are found to express AP-2 gamma fail to proliferate, leading to failure of labyrinth layer formation. As a consequence, the developing embryo suffers from malnutrition and dies. Analysis of embryo cultures suggests that AP-2 gamma is also implicated in the regulation of the adenosine deaminase (ADA) gene, a gene involved in purine metabolism found expressed at the maternal-fetal interface. Therefore, AP-2 gamma seems to be required in early embryonic development because it regulates the genetic programs controlling proliferation and differentiation of extraembryonic trophectodermal cells.

Exposure-disease continuum for 2-chloro-2'-deoxyadenosine, a prototype ocular teratogen. 1. Dose-response analysis

BACKGROUND

Treatment of pregnant mice with 2-chloro-2'-deoxyadenosine (2CdA) on day 8 of gestation induces microphthalmia through a mechanism coupled to the p53 tumor suppressor gene. The present study defines 2CdA dosimetry with respect to exposure (pharmacokinetics), p53 protein induction, and disease (microphthalmia).

METHODS

Pregnant CD-1 mice dosed with 0.5-10.0 mg/kg 2CdA on day 8 provided fetuses for teratological evaluation; 2CdA was measured by HPLC in the antimesometrium through 180 min postexposure, and p53 was assessed with immunostaining of the embryo through 270 min. 5'-/3'-RACE was used to sequence the candidate gene for 2CdA bioactivation from target cells.

RESULTS

Microphthalmia appeared first in the dose-response curve. The highest 2CdA dose having no observable adverse effect (NOAEL) was 1.5 mg/kg; the benchmark dose that produced an extra 5% risk of microphthalmia (BMD(5)) was 2.5 mg/kg, and the lower confidence limit (BMDL) was 2.0 mg/kg. Pharmacokinetic parameters for doses encompassing the threshold (1.5-2.5 mg/kg) were modeled at 1.0-1.8 microM (C(max)) and 30-80 microM-min (AUC). The p53 response was not detected below the BMDL; however, a low-grade response appeared 4.5 hr after a teratogenic dose (5.0 mg/kg), and high-grade induction followed an embryolethal dose (10.0 mg/kg). RACE identified a novel splice variant of mitochondrial deoxyguanosine kinase, dGK-3, as the likely candidate for 2CdA bioactivation in the embryo.

CONCLUSIONS

Microphthalmia represented the critical effect malformation of 2CdA. The findings suggest a mitochondrial mechanism for 2CdA bioactivation, leading to an embryonic p53 response only after 2CdA elimination and implying pharmacodynamic coupling to the exposure-disease continuum. Published 2001 Wiley-Liss, Inc.

Intracellular, nonreceptor-mediated signaling by adenosine: induction and prevention of neuronal apoptosis

Inhibitory effect of adenosine on the isolated heart muscle and vascular system were first described in 1929. Since then, numerous reviews have been published on the diverse actions of this nucleoside on a wide variety of cell types. Essentially all effects of adenosine in neurons and non-neuronal cells are mediated by activation of nucleoside membrane receptors coupled to specific intracellular second messenger pathways. This brief review describes two novel actions of adenosine in peripheral sympathetic neurons, which are not mediated by adenosine receptors. First is described how adenosine and related nucleosides are able to induce apoptosis during the initial stages of neuronal growth and development in vitro and in vivo. Second is discussed how adenosine is able to prevent or delay apoptosis in more mature sympathetic neurons subjected to nerve growth factor deprivation in culture. Both the induction and prevention of apoptosis are independent of receptor activation, and totally dependent on the intracellular accumulation and subsequent phosphorylation of adenosine. The physiological significance and mechanisms by which adenosine can induce apoptosis in one situation, and rescue from apoptosis in another, are described in this article.

Ontogeny of adenosine deaminase in developing trophoblast and decidual cells of rat and hamster

The enzyme adenosine deaminase (ADA) is expressed at high level in the tissue of foeto-maternal interface during early pregnancy. As the main constituents of this interface are trophoblast (TR) and decidual cells (DC), the enzyme was estimated in isolated TR and DC to determine the extent of contribution by the respective cells. The enzyme level was estimated in cytosolic fraction, cell lysate and in conditioned media of these cells in rat and hamster. In both species the concentration of ADA was found to be markedly high in cytosolic fraction over to the cell lysate and the conditioned media in both TR and DC. Species-wise, it was higher in hamster. Cell-wise, the enzyme activity was significantly higher in TR than DC in rat but equal in hamster. In the conditioned medium, also, the enzyme activity was higher in TR in both species. The inference drawn from the results are: 1) the maximum enzyme activity in cytosolic fraction of TR and DC of both species clearly indicates equal involvement of the cells that constitute foeto-maternal unit, 2) the enhanced level of enzyme in TR and DC of hamster over to those of rat is possibly due to the higher proliferative activity in the cells of this species because of shorter gestation (16-17 days in hamster and 22-23 days in rats).

Regulation of duodenal specific expression of the human adenosine deaminase gene

Formation of the mammalian gastrointestinal tract is an ordered process of development and differentiation. Yet, the adult small intestine also retains the plasticity to respond to cues both internal and environmental to modulate intestinal function. The components that regulate this development, differentiation, and modulation at the molecular level are only now being elucidated. We have used the human adenosine deaminase (ADA) gene as a model to identify potential cis-regulatory components involved in these processes within the small intestine. In mammals, high levels of ADA in the small intestine are limited specifically to the differentiated enterocytes within the duodenal region. These studies describe the identification of a region of the human ADA gene, completely distinct from the previously identified T-cell enhancer, which is capable of directing the human intestinal expression pattern in the intestine of transgenic mice. The reporter gene expression pattern observed in these transgenic mice is identical to the endogenous gene along both the cephalocaudal and crypt/villus axis of development. Timing of this transgene activation, however, varies from that of the endogenous mouse gene in that the transgene is activated approximately 2 weeks earlier in development. Even so, this precocious activation is also limited to the epithelium of the developing villi strictly within the duodenal region of the small intestine.

Genetically engineered mice demonstrate that adenosine deaminase is essential for early postimplantation development

Adenosine deaminase (ADA) is an essential enzyme of purine metabolism that is enriched at the maternal-fetal interface of mice throughout postimplantation development. During early postimplantation stages Ada is highly expressed in both maternally derived decidual cells and zygotically derived trophoblast cells. For the current study we utilized genetically modified mice to delineate the relative contribution and importance of decidual and trophoblast ADA at the maternal-fetal interface. In females genetically engineered to lack decidual ADA a striking pattern of expression was revealed in giant trophoblast cells that surround the early postimplantation embryo. Embryos within gestation sites lacking both decidual and trophoblast ADA died during the early postimplantation period, whereas expression in trophoblast cells alone was sufficient for survival through this period. Severe disturbances in purine metabolism were observed in gestation sites lacking decidual ADA, including the accumulation of the potentially toxic ADA substrates adenosine and 2′-deoxyadenosine. These experiments provide genetic evidence that Ada expression at the maternal-fetal interface is essential for early postimplantation development in mice.

Developing allantois is a primary site of 2'-deoxycoformycin toxicity

In this study, an assessment of normal mouse allantoic development and its sensitivity to 2'-(R)-deoxycoformycin (dCF; Pentostatin) exposure were examined. Both dissecting microscopy and scanning electron microscopy were used to describe the normal growth and morphogenesis of the mouse allantois over gestational days 7-10 as a preliminary step in evaluating potential abnormal allantoic ontogeny and its effect on umbilical cord and placental development. Two abnormal allantoic/umbilical cord phenotypes were observed subsequent to injecting pregnant mice with 5 mg dCF/kg, i.p., on gestational day 7 (GD 7) and evaluating litters on GD 10, 11, and 12. Abnormal phenotypes included: (1) an allantois which extended approximately halfway across the exocoelom but failed to establish a functional contact with the chorion; and (2) a phenotype characterized by reduced expansion of the allantois across the chorionic surface, a very thin umbilical cord, and aberrant vascularization throughout the structure. Both abnormal phenotypes exhibited either an agenesis or hypogenesis of the umbilical cord and chorioallantoic plate, respectively. Neither abnormal phenotype, however, exhibited errors in the directionality of allantoic growth toward the chorion nor in the formation of aberrant contacts between allantois and adjacent yolk sac or amnionic mesenchyme. Statistical interpretation of the experimental data strongly suggested that abnormalities in allantoic/umbilical cord development were directly associated with embryolethality as evidenced by a decline in the frequency of abnormal allantoic/umbilical cord phenotypes over GD 10-12 (73, 36, and 4%; respectively) and a concomitant increase in the frequency of implantation site resorptions over the same time period (7, 47, and 78%). These results strongly suggest that the developing allantois is very sensitive to the effects of dCF exposure, and that interference with its development leads to embryolethality by GD 12.

Modelling of purine nucleoside metabolism during mouse embryonic development: relative routes of adenosine, deoxyadenosine, and deoxyguanosine metabolism

The individual activities for adenosine kinase, deoxyadenosine kinase, adenosine deaminase, deoxyguanosine kinase, and purine nucleoside phosphorylase were determined during days 7 to 13 of mouse embryonic development. Adenosine deaminase increased 74-fold between days 7 and 9; deoxyadenosine kinase increased 5.4-fold during the same interval. Adenosine kinase, deoxyguanosine kinase, and purine nucleoside phosphorylase exhibited less than 2-fold changes in activity between days 7 and 13. Using Michaelis constants for each enzyme and the maximal velocities determined from enzyme assay, the relative routes of adenosine and deoxyadenosine metabolism via phosphorylation or deamination were modeled as a function of nucleoside concentration for days 7 through 13. For days 7 and 8, phosphorylation of adenosine is the principle route of metabolism at physiological concentrations. A switch occurred at day 9 and following where deamination is at least 5-fold greater than phosphorylation at all substrate concentrations. Deoxyadenosine phosphorylation was at most 10% of deamination at day 7 and then declined to less than 1% for days 9 to 13. Phosphorolysis was the principle route of deoxyguanosine metabolism through the 7 to 13 day period. Thus catabolism rather than phosphorylation was the principle pathway for purine deoxynucleoside metabolism during this period.

Activation of apoptosis in early mouse embryos by 2'-deoxyadenosine exposure

Adenosine deaminase (ADA) catalyzes the irreversible hydrolytic deamination of adenosine and deoxyadenosine to nontoxic derivatives. The importance of this reaction in the female reproductive tract of mice is suggested by pronounced utero-placental expression of ADA, and by embryolethality of the potent ADA-inhibitor deoxycoformycin (dCF) on day 7-8 of gestation. The present study investigated the effects of dCF, adenosine, and deoxyadenosine on the mouse neurula. Morphological cell death was monitored by the acridine orange reaction (AOR), and biochemical cell death by internucleosomal DNA cleavage (IDC). A strong AOR appeared in day 7-8 embryos between 3 and 4.5 hr post-exposure to dCF in utero; there was no apparent effect on day 6 or day 9 embryos. Most embryonic tissues were responsive, although the heart and extraembryonic membranes were resistant. Up to 75% of the embryonic chromatin was degraded in a regular pattern in concert with the AOR. Immediate activation of "whole-body" apoptosis was reproduced in short-term whole embryo culture with 0.1 mM deoxyadenosine in the presence of 0.01 mM dCF. This was not activated by exposure to dCF alone nor to adenosine; however, high concentrations of adenosine completely blocked the response to deoxyadenosine, whereas niacinamide inhibited the AOR without changing IDC. The cytotoxic effect of deoxyadenosine was correlated with an expansion of embryonic dATP pools determined by high-performance liquid chromatography analysis. The results suggest that deoxyadenosine is the embryotoxic metabolite which accumulates in the antimesometrium of pregnant mice treated with dCF. Exposure to this metabolic toxin activates apoptosis in day 7-8 embryos through an adenosine-sensitive, NAD-dependent mechanism.

Uterine cell death during implantation and early placentation

During blastocyst implantation and placentation in common laboratory rodents, trophoblast cells come into increasingly more intimate associations with the endometrium and, eventually, are in contact with maternal blood. Uterine cell death is one mechanism for removing uterine tissues, primarily epithelial cells, and decidual cells that intervene between trophoblast cells and maternal blood. Mechanisms of cell death and the signals that initiate and regulate it are not well understood. According to current theories, cell death is either gene-directed or the result of traumatic injury, and classification of cell death is based on ultrastructural and biochemical criteria that hypothetically reflect underlying molecular mechanisms. Although the term apoptosis is extensively used to describe all aspects of gene-directed cell death and the term necrosis to describe traumatic death, ultrastructural studies indicate that there are morphological variations of the established criteria, and these could reflect variations of underlying mechanisms. Recent light and electron microscopic work has shown that timing and ultrastructure of uterine cell death at the gestation site varies with region suggesting that initiation and control of cell death is complicated and that more than one mechanism of cell death may be operative. Current information indicates that uterine cell death is most likely part of an intrinsic response of the endometrium to the conceptus, and other than acting as a stimulus to elicit the uterine response, the conceptus probably plays only a minor role in regulating the death of endometrial cells in these species.

Occurrence of embryotoxicity in mouse embryos following in utero exposure to 2'-deoxycoformycin (pentostatin)

Previous investigations had shown that i.p. injection of 2'-deoxycoformycin (dCF; pentostatin; 5 mg/kg) on either E7 or E8 into pregnant mice results in a 61-81% resorption rate at E17. The incidence of visible gross malformations among the surviving conceptuses was exceptionally low (3%) at the time of necropsy on E17 and was unrelated to dCF dose (Knudsen et al., Teratology, 40:5-626, '89; Teratology, 45:91-103, '92). These findings demonstrated the embryotoxicity of dCF but provided no clues as to the site(s) of dCF action. To define the lesion site(s), we have now examined embryos at 72 h (E10), 96 h (E11), and 120 h (E12) following administration of a highly embryotoxic dose of 5 mg dCF/kg to dams on E7. Deoxycoformycin caused multiple abnormalities and growth retardation, and the temporal sequence between maximal abnormal embryo incidence and resorption frequency was established. The quantitative data show that the maximal occurrence of abnormal embryos on E10 (71%) was followed by a maximal resorption rate on E12 (78%). There was a strong correlation (r = -0.82; P < 0.05) between the rapid decline of percent abnormal embryos over E10-E12 and the simultaneous increase in resorption rate, with linear regression analysis showing nearly equal but opposite slopes (-31.2% vs. +35.8% per gestational day, respectively). This suggests that one or more of the abnormalities seen at E10 is associated with the death and resorption of the embryo at E12. The dCF treatment perturbed a wide spectrum of developmental events, including neural tube closure, craniofacial and limb development, turning of the embryo, and growth retardation. None of the individual abnormalities, however, can quantitatively account for the high percentage of dead and resorbed embryos. Therefore, the specific cause of dCF-induced embryolethality is not clear. There is evidence both for direct dCF toxicity at specific embryonic sites as well as for a generalized retardation in the rate of development.

Adenosine levels in the postimplantation mouse uterus: quantitation by HPLC-fluorometric detection and spatiotemporal regulation by 5'-nucleotidase and adenosine deaminase

Extracellular adenosine has the potential to influence many aspects of target cell metabolism. The present study has determined the endogenous levels of adenosine in the pregnant mouse uterus and developing embryo-decidual unit with respect to the expression of two key enzymes of adenosine metabolism, 5'-nucleotidase (5'-NT; EC 3.1.3.5) and adenosine deaminase (ADA; EC 3.5.4.4). To measure adenosine levels, nucleoside extracts were etheno-derivatized and quantitated by high-performance liquid chromatography-fluorescence detection (0.03 pmol/mg protein sensitivity). Adenosine levels were determined to be 0.18 nmol/mg protein in the nonpregnant uterus; however, two statistically significant changes were identified in the pregnant uterus: (1) a periimplantation surge between day 3 (0.24 nmol/mg protein) and day 5 (0.59 nmol/mg protein) of gestation (plug day 0; implantation day 4); and (2) an early postimplantation decline between day 6 (0.54 nmol/mg protein) and day 7 (0.10 nmol/mg protein). The periimplantation adenosine surge coincided with uterine expression of 5'-NT, an enzyme which catalyzes the irreversible dephosphorylation of 5'-AMP to adenosine. 5'-NT expression was shown by Northern blot analysis to peak in the embryo-decidual unit on day 5 of gestation and then to decline through day 9; transcripts remained elevated in the placenta between day 9 and day 13 (the latest day examined in this study). By use of specific enzyme histochemistry, most 5'-NT activity was localized to the primary decidual zone on day 5. This expression subsequently declined during regression of the primary decidua; however, 5'-NT appeared on giant trophoblast (days 7-13) and the metrial gland (days 11-13). Other purine catabolic enzymes degrading AMP (adenylate deaminase) or generating adenosine (S-adenosylhomocysteine hydrolase) were not detected in the embryo-decidual unit suggesting that the net flux of utero-placental AMP catabolism proceeds with adenosine as an intermediate, this being the major pathway of adenosine formation. The sharp drop in adenosine levels between day 6 and day 7 coincided with a rise in the activity and mRNA expression of ADA, an enzyme which catalyzes the irreversible deamination of adenosine to inosine. ADA was previously localized to the secondary decidual zone (days 6-11), secondary giant cells (days 7-13), and spongiotrophoblasts (days 8-13) in the mouse (Knudsen et al., 1991). Results of developmental Northern blot analysis demonstrated a direct correlation of relative 5'-NT/ADA mRNA band intensity to adenosine content between day 4 and day 9 of gestation, suggesting that the local availability of adenosine in the antimesometrium is dependent upon the distribution of these enzymatic activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of (R)-deoxycoformycin (pentostatin) on intrauterine nucleoside catabolism and embryo viability in the pregnant mouse

The viability of early mouse embryos is acutely sensitive to (R)-deoxycoformycin (pentostatin), a tight-binding inhibitor of adenosine deaminase (ADA). Previous studies have shown that a single 5-mg/kg dose on day 7 (plug = day 0) of gestation fully inhibits uteroplacental ADA activity within 0.5 h; causes massive cell death in the neural plate and primary mesenchyme by 6 h, major craniofacial anomalies by day 10, and resorption by day 12 (Knudsen et al., '89; Airhart et al., '91). The present study has examined further the developmental toxicity and early effects of this inhibitor on ADA metabolism. (R)-Deoxycoformycin was administered to pregnant CD-1 (ICR) mice as a single intraperitoneal dose of 0.5-10 mg/kg total body weight on days 6-11 of gestation. The major adverse effect, early resorption, was dose dependent and specific to day 7-8 exposure. Treatment with 5 mg/kg on day 7 resulted in 85% resorptions, 15% malformations, and a 24% reduction in mean fetal weight, whereas the same dose of (S)-deoxycoformycin had no effect. Levels of adenosine and 2'-deoxyadenosine, which are the endogenous substrates of ADA, were monitored in the embryo/decidual unit (E/D) by reversed-phase high-performance liquid chromatography (RP-HPLC). In response to the inhibitor, both nucleosides increased transiently in the antimesometrial compartment (antimesometrial decidua + embryo). Peak levels (Cmax) of adenosine and 2'-deoxyadenosine were dose dependent over the range tested (0.05-10 mg/kg). Exposure to 5 mg/kg on day 7 raised adenosine levels within 0.5 h to 42-fold over the basal level of 0.06 nmol/mg protein. There was an even stronger effect on 2'-deoxyadenosine levels, which were elevated 674-fold over the detection limit of 0.0005 nmol/mg protein. Direct exposure to the inhibitor in serum-free E/D culture produced similar results: 50 microM (R)-deoxycoformycin within 1 h raised adenosine levels 26-fold and 2'-deoxyadenosine levels 410-fold. In vivo studies also showed a general correlation between embryolethality and the length of adenine nucleoside pool expansion, apparent for exposure on day 7, 8, or 9 but not on day 6, suggesting that the embryo becomes sensitive to adenosine or 2'-deoxyadenosine once the neural plate has formed.

Coordinate developmental regulation of purine catabolic enzyme expression in gastrointestinal and postimplantation reproductive tracts

Using histochemical detection, we have visualized in situ the complete metabolic pathway for the degradation of purine nucleotides. From the tongue to the ileum, diverse epithelial cell types lining the lumen of the mouse gastrointestinal (GI) tract strongly coexpress each of the five key purine catabolic enzymes. Dramatic increases in the expression of each enzyme occurred during postnatal maturation of the GI tract. Using in situ hybridization, an intense accumulation of adenosine deaminase (ADA) mRNA was detected only within GI epithelial cells undergoing postmitotic differentiation. In a similar manner, at the developing maternal-fetal interface, high level expression of the purine catabolic pathway also occurred in a unique subset of maternal decidual cells previously known to express high levels of alkaline phosphatase and ADA. This induction occurred almost immediately after implantation in the periembryonic maternal decidual cells, shortly thereafter in antimesometrial decidual cells, and later in cells of the placental decidua basalis: all of which contain cell types thought to be undergoing programmed cell death. The expression of the pathway at the site of embryo implantation appears to be critical because its pharmacologic inhibition during pregnancy has been found to be embryolethal or teratogenic. Purine destruction at these nutritional interfaces (placenta and gastrointestinal tract) seem to override any potential economy of purine salvage, and may represent biochemical adaptation to nucleic acid breakdown occurring in the context of dietary digestion or extensive programmed cell death.

Developmental toxicity of pentostatin (2'-deoxycoformycin) in rats and rabbits

The developmental toxicity of the potent adenosine deaminase (ADA) inhibitor, pentostatin (2'-deoxycoformycin), was investigated in pregnant rats and rabbits administered daily iv doses during organogenesis. Rats received 0, 0.01, 0.10, or 0.75 mg/kg on gestation days 6-15 and rabbits received 0, 0.005, 0.01, or 0.02 mg/kg on gestation days 6-18 and maternal and fetal parameters were evaluated on gestation day 21 (rats) or 30 (rabbits). Live fetuses were examined for external, visceral, and skeletal malformations and variations. In rats, maternal body weight gain and food consumption were significantly suppressed at doses of 0.10 and 0.75 mg/kg during the treatment period but returned to control levels during posttreatment. Increased postimplantation loss and decreased numbers of live fetuses, litter size, and fetal body weight were observed at 0.75 mg/kg. A statistically significant increase in the incidence of vertebral malformations occurred at 0.75 mg/kg. The incidence of certain skeletal variations (extra presacral vertebrae, extra ribs, hypoplastic vertebrae) was also increased at 0.75 mg/kg. Ossification of cervical centra was reduced at 0.75 mg/kg compared with controls. In rabbits, marked maternal toxicity (death, body weight loss, and decreased food consumption) and reproductive toxicity (abortion and premature delivery) occurred in all pentostatin-treated groups. However, there were no significant effects on number of live fetuses, pre- or postimplantation loss, litter size, or fetal body weights in the animals with live litters. There was also no apparent increase in the incidence of malformations or variations in the live fetuses of pentostatin-treated rabbits. Thus, these studies demonstrate developmental toxicity of pentostatin in rats and rabbits, and teratogenicity in rats, at maternally toxic doses.

Structural and functional analysis of the murine adenosine deaminase gene

We describe the structural and functional analysis of cosmid clones that span the entire murine adenosine deaminase gene. Functional analysis indicated that these clones are capable of encoding murine adenosine deaminase activity when introduced into human cell lines. Structural analysis revealed that the gene consists of 12 exons distributed over approximately 25 kb. The exact size of each exon and the sequence of each exon/intron junction were determined. The results show that the 1056-nucleotide open reading frame for adenosine deaminase extends from exon 1 to exon 11, and that exon 12 contains untranslated sequences only. During the course of these investigations, we discovered that a gene encoding an abundant 1.3-kb polyadenylated transcript overlaps the 3' end of the murine adenosine deaminase gene and is transcribed from the opposite strand.

Developmental expression of adenosine deaminase in the upper alimentary tract of mice

The distribution and localization of adenosine deaminase (ADA) was studied during postnatal development of the alimentary tract in mice. There was detectable enzyme activity in all organs examined, but a range of more than 10,000 fold in the relative levels of specific activity was observed among adult tissues. A comprehensive survey of multiple adult tissues revealed that the highest levels of ADA occur in the upper alimentary tract (tongue, esophagus, forestomach, proximal small intestine). Immunohistochemical analysis revealed that ADA was predominantly localized to the epithelial lining of the alimentary mucosa: the keratinized squamous epithelium that lines the forestomach, esophagus, and surface of the tongue; and the simple columnar epithelium of the proximal small intestine (duodenum, proximal jejunum). Biochemical analysis revealed that ADA was one of the most abundant proteins of these mucosal tissue layers, accounting for 5%-20% of the total soluble protein. Tissue-specific differences in ADA activity correlated both with levels of immunoreactive protein and RNA abundance. The level of ADA activity in the upper alimentary tissues was subject to pronounced developmental control, being low at birth and achieving very high levels within the first few weeks of postnatal life. The appearance in development of ADA-immunoreactivity coincided with maturation of the mucosal epithelium. These results suggest that ADA is subject to strong cell-specific developmental regulation during functional differentiation of certain foregut derivatives in mice.