Mechanism-Based Approaches for the Reversal of Drug Neurobehavioral Teratogenicity

Reversal of chlorpyrifos neurobehavioral teratogenicity in mice by allographic transplantation of adult subventricular zone-derived neural stem cells

Neurobehavioral teratogenicity can be reversed with transplantation of neural stem cells. However, the usefulness of this therapy would be greatly enhanced by employing adult stem cells. In pursuit of this this goal, we developed a model that uses subventricular zone (SVZ) cells. HS/Ibg mice were exposed prenatally to chlorpyrifos on gestational days 9-18 (3 mg/kg/day, SC) in order to induce deficits in their performance in the Morris water maze test. Both the control and the exposed offspring were transplanted with SVZ cells (or vehicle) on postnatal day 35; this actually represents an allogenic transplantation, because the HS/Ibg strain is a heterogeneous stock. The transplanted cells were later observed in the host brain by DiI tracing, and their initial differentiation to cholinergic neurons and astrocytes was ascertained. On postnatal day 80, animals that had been exposed prenatally to chlorpyrifos displayed impaired Morris water maze performance, requiring more time to reach the platform. Transplantation of adult SVZ-derived neural stem cells (NSC) reversed the deficits. Applying autologous transplantation provides an important demonstration that the methodological obstacles of immunological rejection and the ethical concerns related to using embryonic stem cells may be successfully bypassed in developing stem cell therapies for neurodevelopmental disorders.

Isolated congenital tracheal stenosis in a preterm newborn

Severe tracheal stenosis, resulting in functional atresia of the trachea is a rare congenital malformation with an estimated occurrence of two in 100,000 newborns. If no esophagotracheal fistula is present to allow for spontaneous breathing, this condition is usually fatal. We report on a male infant born at 32 weeks of gestation. The patient presented with respiratory distress immediately after delivery due to severe congenital tracheal stenosis resulting in functional atresia of the trachea. Endotracheal intubation failed and even emergency tracheotomy did not allow ventilation of the patient lungs. The patient finally succumbed to prolonged hypoxia due to functional tracheal atresia. The etiology of tracheal atresia and tracheal stenosis is still unclear, but both conditions are frequently combined with other anomalies of the VACTERL (vertebral anomalies, anal atresia, cardiovascular anomalies, tracheoesophageal fistula, esophageal atresia, renal/radial anomalies and limb defects) and TACRD (tracheal agenesis, cardiac, renal and duodenal malformations) association. Conclusion Successful treatment of severe congenital tracheal stenosis and tracheal atresia depends on either prenatal diagnosis or recognition of this condition immediately after birth to perform tracheotomy without delay. Nevertheless, despite any efforts, the therapeutical results of severe tracheal stenosis and tracheal atresia are still unsatisfactory.

Survival, differentiation, and reversal of heroin neurobehavioral teratogenicity in mice by transplanted neural stem cells derived from embryonic stem cells

Cell therapies in animal models of neurobehavioral defects are normally derived from neural stem cells (NSC) of the developing cortex. However, the clinical feasibility of NSC therapies would be greatly improved by deriving transplanted cells and from a tissue culture source that is self-renewing, containing cells that potentially differentiate into the desired neuronal phenotypes. These cultures can be engineered to contain the appropriate factors to support their therapeutic action and likely evoke lesser immune reactions. In the current study, we employed our model of mice neurobehaviorally impaired via prenatal exposure to heroin, to test the therapeutic efficacy of NSC derived from murine embryonic stem cells culture (ESC). The culture contained elongated bipolar cells, 90% of which are positive for nestin, the intermediate filament protein found in neural precursors. After removal of growth factors, the NSC differentiated into neurons (34.0% +/- 3.8% NF-160 positive), including cholinergic cells (ChAT positive), oligodendrocytes (29.9% +/- 4.2% O(4)), and astrocytes (36.1% +/- 4.7% GFAP positive). Reverse transcriptase polymerase chain reaction (RT-PCR) analysis confirmed the immunocytochemical findings. Mice made deficient in Morris maze behavior by prenatal heroin exposure (10 mg/kg heroin s.c. on gestational days 9-18) were transplanted into the hippocampus region on postnatal day 35 with the ES culture-derived NSC (ES-NSC) labeled with dialkylcarbocyanine (Dil) cell tracker. Dil+ and NF160+ cells were detected in the hippocampal region (50% +/- 8% survival). The transplantation completely restored maze performance to normal; e.g., on day 3, transplantation improved the behavior from the deficient level of 11.9-sec latency to the control of 5.6-sec latency (44.5% improvement).

Protein kinase C is a target for diverse developmental neurotoxicants: transcriptional responses to chlorpyrifos, diazinon, dieldrin and divalent nickel in PC12 cells

Unrelated developmental neurotoxicants can elicit similar functional outcomes, whereas agents in the same class may differ. We compared two organophosphate insecticides (chlorpyrifos, diazinon) with an organochlorine (dieldrin) and a metal (Ni(2+)) for similarities and differences in their effects on gene expression encoding subtypes of protein kinase C and their modulators, a cell signaling cascade that integrates the actions of neurotrophic factors involved in brain development. We conducted evaluations in PC12 cells, a model for neuronal development, with each agent introduced at 30 microM for 24 or 72 h, treatments devoid of cytotoxicity. Chlorpyrifos evoked by far the largest effect, with widespread upregulation of multiple genes; the effects were greater during neurodifferentiation than when cells were exposed prior to differentiation. Diazinon had smaller and less widespread effects, consistent with its lesser long-term impact on synaptic function and behavior noted for in vivo exposures in developing rats. Surprisingly, the effects of diazinon, dieldrin and Ni(2+) showed basic similarities despite the fact that all three come from different classes of toxicants. Our findings provide some of the first evidence for a specific mechanistic cascade contributing to the cholinesterase-independent developmental neurotoxicant actions of chlorpyrifos and its differences from diazinon, while at the same time identifying mechanistic convergence between otherwise unrelated toxicants that provides predictions about common neurodevelopmental outcomes. These results further show how combined use of cell cultures and microarray technology can guide future in vivo work on diverse developmental neurotoxicants.