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A complete mode of action human relevance analysis--as distinct from mode of action (MOA) analysis alone--depends on robust information on the animal MOA, as well as systematic comparison of the animal data with corresponding information from humans. In November 2003, the International Life Sciences Institute's Risk Science Institute (ILSI RSI) published a 2-year study using animal and human MOA information to generate a four-part Human Relevance Framework (HRF) for systematic and transparent analysis of MOA data and information. Based mainly on non-DNA-reactive carcinogens, the HRF features a "concordance" analysis of MOA information from both animal and human sources, with a focus on determining the appropriate role for each MOA data set in human risk assessment. With MOA information increasingly available for risk assessment purposes, this article illustrates the further applicability of the HRF for reproductive, developmental, neurologic, and renal endpoints, as well as cancer. Based on qualitative and quantitative MOA considerations, the MOA/human relevance analysis also contributes to identifying data needs and issues essential for the dose-response and exposure assessment steps in the overall risk assessment.

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Relative to species tested in laboratory studies, the human fetus displays higher vulnerability to enalapril and other angiotensin-converting enzyme inhibitors (ACEI) exhibiting a malformative syndrome that does not appear to have a similar counterpart in experimental animals. An important reason for this higher vulnerability is the earlier intrauterine development of the kidney and the renin-angiotensin-aldosterone (RAS) system in humans, organ systems that are specific targets of ACEI's pharmacological effect. In humans, these systems begin developing prior to the onset of skeletal ossification at the end of the first trimester, with continuing vulnerability throughout the pregnancy. In most animal species tested, these target systems develop close to term, when the fetus is relatively more mature and less vulnerable to the effects of developmental toxicants. For this reason, animal studies that follow standard protocols and evaluate developmental toxicity only for exposures during embryogenesis will miss developmental effects arising secondary to disruption of target systems that develop after the period of major organogenesis. Thus, although the animal mode of action (MOA) for enalapril and other ACEI is plausible in humans, differences in the timing of development of critical target organ systems, particularly the renal system and RAS, explain the absence of definitive structural abnormalities in test animals.

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The scientific community is developing a compelling body of evidence that shows the importance of the in utero environment (including chemical and hormonal levels) to the ultimate health of the child and even of the aging adult. This article summarizes the evidence that shows this impact begins with conception. Only a full life-cycle evaluation will help us understand these impacts, and only such an understanding will produce logically prioritized mitigation strategies to address the greatest threats first. Clearly, the time for analysis begins when the next generation is but a twinkle in the eye.

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BACKGROUND: Atenolol, 4-2'-hydroxy-3'-isopropyl-aminopropoxy) phenylacetamide, is a beta-adrenoreceptor blocker used for treatment of hypertension in pregnancy. Beta-blockers are reported to cause fetal harm (such as decreased birth weight) when administered to a pregnant woman. We evaluate published human and animal evidence of atenolol developmental toxicity and compare the manifestations in humans and in routinely-used animal models. METHODS: The comparison is based on the following criteria: comparability of pharmacokinetic/pharmacodynamic characteristics, type of adverse outcome, lowest adverse effect levels, and specificity and selectivity of effect. RESULTS: Manifestations of atenolol prenatal toxicity (placental changes, intrauterine growth retardation and changes in fetal weight in the absence of structural malformations) are similar in the tested animal species (rats and rabbits) and humans. The human seems to be more sensitive, however, because adverse embryo-fetal effects are reported at doses much lower than those in the tested species. In humans and rats, adverse embryo-fetal effects are induced by doses that are not maternally toxic. In the rabbit, however, such effects are seen only at maternally toxic doses, suggesting that in this species, developmental toxicity may be maternally mediated. CONCLUSIONS: The available data suggest animal-human concordance with regard to the nature and manifestations of atenolol prenatal toxicity. The animal models "predicted" developmental toxicity manifests as placental changes, intrauterine growth retardation and fetal weight decrease in the absence of structural malformations. Thus far, this is concordant with the data from humans, in whom intrauterine growth retardation has been observed but not structural abnormalities.

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BACKGROUND: Adverse pregnancy outcomes following the use of angiotensin-converting enzyme (ACE) inhibitors, including enalapril, have been reported in descriptive studies. However, no analytical studies on the relationship between the adverse outcomes and enalapril gestational exposures are available. OBJECTIVES: To explore the association between enalapril exposure and adverse outcomes in pregnancy, taking into account other possible risk factors. METHODS: We analyzed a series of all usable cases reported to the FDA between 1986 and 2000 in which enalapril was a suspect drug for the observed adverse outcomes (N = 110). Parameters of exposure and reported outcomes as well as information on potentially confounding variables were systematically abstracted from this series by a single physician. Because exposure to ACE inhibitors after the first trimester of pregnancy had been associated with adverse outcomes in the existing literature, we divided the cases into those exposed in the first trimester only (considered as the baseline group) and cases exposed beyond or after this time. Frequency of reported adverse outcomes in the second group was compared with those in the baseline group; odds ratios were computed, taking account of potentially confounding variables by logistic regression where appropriate. RESULTS: Exposure to enalapril after the first trimester of pregnancy was strongly associated with oligohydramnios and specific adverse outcomes thought to be secondary to reduced amniotic fluid volume (limb deformities, cranial ossification deficits, lung hypoplasia), as well as with neonatal renal failure. The relationship did not change after taking numerous potential confounders into account, including duration of exposure, concomitant drug use, maternal age, concurrent disease, neonatal gender, and gestational age at birth. Such a pattern of abnormalities is considered to be a consequence of the effect of ACE inhibition on fetal renal function that develops after the first trimester. CONCLUSION: The specificity and temporality of the observed adverse manifestations suggest a causal relationship to enalapril exposure.

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