Appropriate Exposure Routes and Doses in Studies Designed to Assess Developmental Toxicity: A Case Study of Inorganic Arsenic

Zika Virus affects neurobehavioral development, and causes oxidative stress associated to blood-brain barrier disruption in a rat model of congenital infection

Zika virus (ZIKV) is a mosquito-borne flavivirus associated with several neurodevelopmental outcomes after in utero infection. Here, we studied a congenital ZIKV infection model with immunocompetent Wistar rats, able to predict disabilities and that could pave the way for proposing new effective therapies. We identified neurodevelopmental milestones disabilities in congenital ZIKV animals. Also, on 22nd postnatal day (PND), blood-brain barrier (BBB) proteins disturbances were detected in the hippocampus with immunocontent reduction of β_Catenin, Occludin and Conexin-43. Besides, oxidative stress imbalance on hippocampus and cortex were identified, without neuronal reduction in these structures. In conclusion, even without pups' microcephaly-like phenotype, congenital ZIKV infection resulted in neurobehavioral dysfunction associated with BBB and oxidative stress disturbances in young rats. Therefore, our findings highlighted the multiple impact of the congenital ZIKV infection on the neurodevelopment, which reinforces the continuity of studies to understand the spectrum of this impairment and to provide support to future treatment development for patients affected by congenital ZIKV.

Monomethylarsonic acid and dimethylarsinic acid: developmental toxicity studies with risk assessment

BACKGROUND

The toxicity of arsenic compounds is highly dependent on the valence and methylation state of the compound. Although there is extensive published literature on the potential developmental toxicity of inorganic arsenic compounds, little exists on organic arsenic compounds and, in particular, studies conducted in accordance with conventional regulatory guidelines appropriate for risk assessment are rare. The organic arsenic compounds, monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV, also called cacodylic acid), are the active ingredients in pesticide products that are used mainly for weed control. MMAV and DMAV are also metabolites of inorganic arsenic formed intracellularly by most living organisms (animals, plants and bacteria). In mammals, this occurs predominantly in liver cells.

METHODS

Conventional developmental toxicity studies of orally administered MMAV and DMAV in the Sprague-Dawley rat and New Zealand White rabbit were conducted in commercial contract laboratories in the late 1980 s for regulatory compliance. The results of these studies are summarized and presented to broaden the data available in the public domain.

RESULTS

In both species, data shows an absence of dose-related effects at organic arsenic exposures that were not maternally toxic. MMAV doses of 0, 10, 100, and 500 mg/kg/day (rat) and 0, 1, 3, 7, and 12 mg/kg/day (rabbit) and DMAV doses of 0, 4, 12, and 36 mg/kg/day (rat) and 0, 3, 12, and 48 mg/kg/day (rabbit) were administered by oral gavage daily during organogenesis (Gestation Day [GD] 6-15, rat; GD 7-19, rabbit) and the litters examined at maternal sacrifice (GD 20, rat; GD 29, rabbit). After treatment with MMAV, maternal and fetal toxicity were observed at the highest doses of 500 mg/kg/day (rat) and 12 mg/kg/day (rabbit), but no treatment-related developmental toxicity at the lower doses, even in the presence of minimal maternal toxicity in the rat at 100 mg/kg/d. There was no evidence of teratogenicity associated with MMAV treatment. With DMAV, maternal and developmental toxicity were observed in the rat at 36 mg/kg/day, with a higher than spontaneous incidence of fetuses with diaphragmatic hernia. In the rabbit at 48 mg/kg/day, there was marked maternal toxicity, culminating for most females in abortion and with no surviving fetuses for evaluation. There was no treatment-related maternal or developmental toxicity in the rat or rabbit at 12 mg/kg/day. Based on pregnancy outcome, the developmental toxicity no observed adverse effect level (NOAEL) for orally administered MMAV were 100 and 7 mg/kg/day in the rat and rabbit, respectively, and for DMAV were 12 mg/kg/day in both species.

CONCLUSIONS

Margins of exposure estimated based on conservative estimates of daily intakes of arsenic in all of its forms indicate that exposure to MMAV or DMAV at environmentally relevant exposure levels, by the oral route (the environmentally relevant route of exposure) is unlikely to pose a risk to pregnant women and their offspring.

Teratogen update: inorganic arsenic

BACKGROUND

Inorganic arsenic has been used by many laboratories to study the pathogenesis of exencephaly in rodents. These studies, which used predominantly injection exposures, coupled with the paucity of epidemiology data, resulted in the erroneous inference that inorganic arsenic should be considered a human teratogen.

METHODS

This study assembles and assesses literature analyses of older human and animal investigations together with the results of new experimental studies. These recent studies were performed according to modern regulatory guidelines, and relevant exposure routes (inhalation and ingestion) were used to evaluate the potential risk of developmental effects in humans.

RESULTS

The existing epidemiological data are inadequate to support risk assessment because of the failure to confirm or measure arsenic exposure during early gestation and the deficiencies in accounting for potential confounding factors. The animal data revealed that inorganic arsenic caused malformations in offspring only when it was injected into the veins or peritoneal cavity of pregnant animals during early gestation. Exposure via inhalation or oral ingestion, even at concentrations that were nearly fatal to pregnant females, caused no arsenic-related malformations.

CONCLUSIONS

Inorganic arsenic poses virtually no danger to developing offspring when maternal exposure occurs by relevant routes (oral and inhalation) at concentrations that are likely to be experienced in the environment or in the workplace.