Category: Preclinical Development
Purpose: Prenatal exposure to tobacco smoke and nicotine is believed to interfere with fetal brain development predisposing offspring to different neurobehavioral and neuropsychological disorders. Included in this is increased neonatal vulnerability to hypoxic-ischemic encephalopathy (HIE) which is a major cause of neonatal death and child disability in the US. These effects could be, in part, mediated by fetal nicotine exposure. Use of electronic cigarettes (e-Cigs), commonly known as vaping, has been rapidly increasing in recent times in the general population, including women of reproductive age. E-Cig use during pregnancy is also increasing because of the addictive properties of nicotine along with the perception of the relative safety of e-Cigs. In this study, we aimed to investigate both short-term and long-term effects of maternal e-Cig use on neonatal brain development and HIE with a focus on brain energy metabolism utilizing a combination of in vitro and in vivo models. The results of this study could pave way to development of new targeted therapeutics to counteract fetal neurotoxic effects of nicotine/e-Cigs.
Methods: Pregnant CD1 mice were exposed to e-Cig vapor (2.4% nicotine) from gestational day 5 to 7 days after delivery of pups. Primary cortical neurons were isolated from e-Cig exposed fetus and cultured for seven days with subsequent exposure to oxygen-glucose deprivation followed by reoxygenation (OGD/R) to mimic ischemia-reperfusion injury. Hypoxic-ischemic brain injury was induced in 8-9 days old mouse pups by a combination of left common carotid artery ligation and 15 minutes exposure to 8% oxygen. Short-term brain injury was evaluated after 24 hours by triphenyltetrazolium chloride staining. Long-term neurological outcomes were investigated at postnatal day 45 by open field test, novel object recognition test, Morris water maze test, and foot fault test to evaluate locomotor function, recognition memory, spatial learning & memory, and motor coordination respectively.
Results: We found that e-Cig exposed cortical neurons demonstrated decreased cell viability and increased cleaved PARP1 expression in OGD/R condition. These effects were accompanied by decreased glucose uptake & glucose transporter expression, and decreased ATP content. We have also observed increased sensitivity to HI brain injury in prenatally e-Cig exposed mouse pups with a decrease in brain glucose transporters expression. Additionally, in utero e-Cig exposed mice offspring displayed a significantly increased level of hyperactivity, impaired learning & memory, and motor incoordination at adolescence.
Conclusion: These results indicate that maternal e-Cig exposure could lead to offspring behavioral abnormalities and enhance HI brain injury. Further studies are needed to elucidate the mechanisms of enhanced HI brain injury in e-Cig exposed offspring pups. This study is instrumental in elucidating the possible deleterious effects of maternal e-Cig use in the general population and identifies a growing population that may benefit from safe smoking cessation therapy for mothers or CNS targeted therapy for offspring.