Effects of binge alcohol exposure in the second trimester on intracerebral arteriolar function in third trimester fetal sheep

Modeling the enigma of complex disease etiology

BACKGROUND

Complex diseases often present as a diagnosis riddle, further complicated by the combination of multiple phenotypes and diseases as features of other diseases. With the aim of enhancing the determination of key etiological factors, we developed and tested a complex disease model that encompasses diverse factors that in combination result in complex diseases. This model was developed to address the challenges of classifying complex diseases given the evolving nature of understanding of disease and interaction and contributions of genetic, environmental, and social factors.

METHODS

Here we present a new approach for modeling complex diseases that integrates the multiple contributing genetic, epigenetic, environmental, host and social pathogenic effects causing disease. The model was developed to provide a guide for capturing diverse mechanisms of complex diseases. Assessment of disease drivers for asthma, diabetes and fetal alcohol syndrome tested the model.

RESULTS

We provide a detailed rationale for a model representing the classification of complex disease using three test conditions of asthma, diabetes and fetal alcohol syndrome. Model assessment resulted in the reassessment of the three complex disease classifications and identified driving factors, thus improving the model. The model is robust and flexible to capture new information as the understanding of complex disease improves.

CONCLUSIONS

The Human Disease Ontology's Complex Disease model offers a mechanism for defining more accurate disease classification as a tool for more precise clinical diagnosis. This broader representation of complex disease, therefore, has implications for clinicians and researchers who are tasked with creating evidence-based and consensus-based recommendations and for public health tracking of complex disease. The new model facilitates the comparison of etiological factors between complex, common and rare diseases and is available at the Human Disease Ontology website.

Vascular Contributions to the Neurobiological Effects of Prenatal Alcohol Exposure

Fetal alcohol spectrum disorders (FASD) are often characterized as a cluster of brain-based disabilities. Though cardiovascular effects of prenatal alcohol exposure (PAE) have been documented, the vascular deficits due to PAE are less understood, but may contribute substantially to the severity of neurobehavioral presentation and health outcomes in persons with FASD.

Methods

We conducted a systematic review of research articles curated in PubMed to assess the strength of the research on vascular effects of PAE. 40 pertinent papers were selected, covering studies in both human populations and animal models.

Results

Studies in human populations identified cardiac defects, and defects in vasculature, including increased tortuosity, defects in basement membranes, capillary basal hyperplasia, endarteritis, and disorganized and diminished cerebral vasculature due to PAE. Preclinical studies showed that PAE rapidly and persistently results in vasodilation of large afferent cerebral arteries, but to vasoconstriction of smaller cerebral arteries and microvasculature. Moreover, PAE continues to affect cerebral blood flow into middle-age. Human and animal studies also indicate that ocular vascular parameters may have diagnostic and predictive value. A number of intervening mechanisms were identified, including increased autophagy, inflammation and deficits in mitochondria. Studies in animals identified persistent changes in blood flow and vascular density associated with endocannabinoid, prostacyclin and nitric oxide signaling, as well as calcium mobilization.

Conclusion

Although the brain has been a particular focus of studies on PAE, the cardiovascular system is equally affected. Studies in human populations, though constrained by small sample sizes, did link pathology in major blood vessels and tissue vasculature, including brain vasculature, to PAE. Animal studies highlighted molecular mechanisms that may be useful therapeutic targets. Collectively, these studies suggest that vascular pathology is a possible contributing factor to neurobehavioral and health problems across a lifespan in persons with a diagnosis of FASD. Furthermore, ocular vasculature may serve as a biomarker for neurovascular health in FASD.

Prenatal exposure to alcohol: mechanisms of cerebral vascular damage and lifelong consequences

Alcohol is a well-known teratogen, and prenatal alcohol exposure (PAE) leads to a greater incidence of many cardiovascular-related pathologies. Alcohol negatively impacts vasculogenesis and angiogenesis in the developing fetal brain, resulting in fetal alcohol spectrum disorders (FASD). Ample preclinical evidence indicates that the normal reactivity of cerebral resistance arterioles, which regulate blood flow distribution in response to metabolic demand (neurovascular coupling), is impaired by PAE. This impairment of dilation of cerebral arteries may carry implications for the susceptibility of the brain to cerebral ischemic damage well into adulthood. The focus of this review is to consolidate findings from studies examining the influence of PAE on vascular development, give insights into relevant pathological mechanisms at the vascular level, evaluate the risks of ethanol-driven alterations of cerebrovascular reactivity, and revisit different preventive interventions that may have promise in reversing vascular changes in preclinical FASD models.

In utero exposure to alcohol alters reactivity of cerebral arterioles

Our goal was to examine whether in utero exposure to alcohol impaired reactivity of cerebral arterioles during development. We fed Sprague-Dawley dams a liquid diet with or without alcohol (3% ethanol) for the duration of pregnancy (21-23 days). Around 4-6 weeks after birth, we examined reactivity of cerebral arterioles to eNOS- (ADP) and nNOS-dependent (NMDA) agonists in the offspring. We found that in utero exposure to alcohol attenuated responses of cerebral arterioles to ADP and NMDA, but not to nitroglycerin in rats exposed to alcohol in utero. L-NMMA reduced responses to agonists in control rats, but not in rats exposed to alcohol in utero. Treatment of dams with apocynin for the duration of pregnancy rescued the impairment in reactivity to ADP and NMDA in the offspring. Protein expression of NOX-2 and NOX-4 was increased in alcohol rats compared to control rats. We also found an increase in superoxide levels in the cortex of rats exposed to alcohol in utero. Our findings suggest that in utero exposure to alcohol impairs eNOS and nNOS reactivity of cerebral arterioles via a chronic increase in oxidative stress.

Fetal Cerebral Circulation as Target of Maternal Alcohol Consumption

Alcohol (ethanol [EtOH]) is one of the most widely used psychoactive substances worldwide. Alcohol consumption during pregnancy may result in a wide range of morphological and neurodevelopmental abnormalities termed fetal alcohol spectrum disorders (FASD), with the most severe cases diagnosed as fetal alcohol syndrome (FAS). FAS and FASD are not readily curable and currently represent the leading preventable causes of birth defect and neurodevelopmental delay in the United States. The etiology of FAS/FASD remains poorly understood. This review focuses on the effects of prenatal alcohol exposure (PAE) on fetal cerebrovascular function. A brief introduction to the epidemiology of alcohol consumption and the developmental characteristics of fetal cerebral circulation is followed by several sections that discuss current evidence documenting alcohol-driven alterations of fetal cerebral blood flow, artery function, and microvessel networks. The material offers mechanistic insights at the vascular level itself into the pathophysiology of PAE.

Alcohol exposure during late gestation: multiple developmental outcomes in sheep

Alcohol consumption during pregnancy remains common in many countries. Exposure to even low amounts of alcohol (i.e. ethanol) in pregnancy can lead to the heterogeneous fetal alcohol spectrum disorders (FASD), while heavy alcohol consumption can result in the fetal alcohol syndrome (FAS). FAS is characterized by cerebral dysfunction, growth restriction and craniofacial malformations. However, the effects of lower doses of alcohol during pregnancy, such as those that lead to FASD, are less well understood. In this article, we discuss the findings of recent studies performed in our laboratories on the effects of fetal alcohol exposure using sheep, in which we investigated the effects of late gestational alcohol exposure on the developing brain, arteries, kidneys, heart and lungs. Our studies indicate that alcohol exposure in late gestation can (1) affect cerebral white matter development and increase the risk of hemorrhage in the fetal brain, (2) cause left ventricular hypertrophy with evidence of altered cardiomyocyte maturation, (3) lead to a decrease in nephron number in the kidney, (4) cause altered arterial wall stiffness and endothelial and smooth muscle function and (5) result in altered surfactant protein mRNA expression, surfactant phospholipid composition and pro-inflammatory cytokine mRNA expression in the lung. These findings suggest that fetal alcohol exposure in late gestation can affect multiple organs, potentially increasing the risk of disease and organ dysfunction in later life.

Ethanol exposure during pregnancy persistently attenuates cranially directed blood flow in the developing fetus: evidence from ultrasound imaging in a murine second trimester equivalent model

BACKGROUND

Ethanol (EtOH) consumption during pregnancy can lead to fetal growth retardation, mental retardation, and neurodevelopmental delay. The fetal brain initiates neurogenesis and vasculogenesis during the second trimester, and depends on maternal-fetal circulation for nutrition and growth signals. We used high-resolution in vivo ultrasound imaging to test the hypothesis that EtOH interferes with fetal brain-directed blood flow during this critical developmental period.

METHODS

Pregnant mice were lightly anesthetized on gestational day 12 with an isoflurane/oxygen mixture. We assessed the effect of single and repeated binge-like maternal EtOH exposures at 3 g/kg, administered by intragastric gavage or intraperitoneal injection, on maternal circulation and fetal umbilical, aortic, internal carotid, and middle cerebral arterial circulation.

RESULTS

Binge maternal EtOH exposure, regardless of exposure route, significantly reduced fetal arterial blood acceleration and velocity time integral (VTI), from umbilical to cerebral arteries, without a change in fetal heart rate and resistivity indices. Importantly a single maternal binge EtOH exposure induced persistent suppression of fetal arterial VTI for at least 24 hours. Repeated binge episodes resulted in a continuing and persistent suppression of fetal VTI. Qualitative assessments showed that maternal EtOH exposure induced oscillatory, nondirectional blood flow in fetal cerebral arteries. Maternal cardiac and other physiological parameters remained unaltered.

CONCLUSIONS

These data show that binge-type maternal EtOH exposure results in rapid and persistent loss of blood flow from the umbilical artery to the fetal brain, potentially compromising nutrition and the maternal/fetal endocrine environment during a critical period for neuron formation and angiogenesis in the maturing brain.