Prenatal Alcohol Exposure Affects Progenitor Cell Numbers in Olfactory Bulbs and Dentate Gyrus of Vervet Monkeys

Effects of prenatal alcohol exposure on the olfactory system development

Fetal Alcohol Spectrum Disorders (FASD), resulting from maternal alcohol consumption during pregnancy, are a prominent non-genetic cause of physical disabilities and brain damage in children. Alongside common symptoms like distinct facial features and neurocognitive deficits, sensory anomalies, including olfactory dysfunction, are frequently noted in FASD-afflicted children. However, the precise mechanisms underpinning the olfactory abnormalities induced by prenatal alcohol exposure (PAE) remain elusive. Utilizing rodents as a model organism with varying timing, duration, dosage, and administration routes of alcohol exposure, prior studies have documented impairments in olfactory system development caused by PAE. Many reported a reduction in the olfactory bulb (OB) volume accompanied by reduced OB neuron counts, suggesting the OB is a brain region vulnerable to PAE. In contrast, no significant olfactory system defects were observed in some studies, though subtle alterations might exist. These findings suggest that the timing, duration, and extent of fetal alcohol exposure can yield diverse effects on olfactory system development. To enhance comprehension of PAE-induced olfactory dysfunctions, this review summarizes key findings from previous research on the olfactory systems of offspring prenatally exposed to alcohol.

Chronic alcohol intake regulates expression of SARS-CoV2 infection-relevant genes in an organ-specific manner

BACKGROUND

Chronic alcohol consumption and alcohol use disorder have a tremendous impact on the patient's psychological and physiological health. There is evidence that chronic alcohol consumption influences SARS-CoV2 infection risk, but so far, the molecular mechanism underlying such an effect is unknown.

METHODS

We generated the expression data of SARS-CoV2 infection-relevant genes (Ace2, Tmprss2, and Mas) in different organs in rat models of chronic alcohol exposure and alcohol dependence. Ace2 and Tmprss2 represent the virus entry point, whereas Mas activates the anti-inflammatory response once the cells are infected.

RESULTS

Across three different chronic alcohol test conditions, we found a consistent upregulation of Ace2 gene expression in the lung, which has been shown to be the most affected organ in COVID-19 patients. Other organs such as liver, ileum, kidney, heart, and brain also showed upregulation of Ace2 and Mas gene expression but less consistently across the different animal models, while Tmprss2 expression was unaffected in all conditions.

CONCLUSIONS

We conclude that alcohol-induced upregulation of Ace2 gene expression can lead to an elevated stochastic probability of virus entry into cells and may thus confer a molecular risk for SARS-CoV2 infection.

Dose-Related Reduction in Hippocampal Neuronal Populations in Fetal Alcohol Exposed Vervet Monkeys

Fetal alcohol spectrum disorder (FASD) is a chronic debilitating condition resulting in behavioral and intellectual impairments and is considered the most prevalent form of preventable mental retardation in the industrialized world. We previously reported that 2-year-old offspring of vervet monkey (Chlorocebus sabeus) dams drinking, on average, 2.3 ± 0.49 g ethanol per Kg maternal body weight 4 days per week during the last third of pregnancy had significantly lower numbers of CA1 (−51.6%), CA2 (−51.2%) and CA3 (−42.8%) hippocampal neurons, as compared to age-matched sucrose controls. Fetal alcohol-exposed (FAE) offspring also showed significantly lower volumes for these structures at 2 years of age. In the present study, we examined these same parameters in 12 FAE offspring with a similar average but a larger range of ethanol exposures (1.01–2.98 g/Kg/day; total ethanol exposure 24–158 g/Kg). Design-based stereology was performed on cresyl violet-stained and doublecortin (DCX)-immunostained sections of the hippocampus. We report here significant neuronal deficits in the hippocampus with a significant negative correlation between daily dose and neuronal population in CA1 (r² = 0.486), CA2 (r² = 0.492), and CA3 (r² = 0.469). There were also significant correlations between DCX population in the dentate gyrus and daily dose (r² = 0.560). Both correlations were consistent with linear dose-response models. This study illustrates that neuroanatomical sequelae of fetal ethanol exposure are dose-responsive and suggests that there may be a threshold for this effect.

Retinal structure and function in monkeys with fetal alcohol exposure

Exposure to ethanol in utero leads to several brain development disorders including retinal abnormalities whose underlying cellular pathogenesis remains elusive. We recently reported that fetal alcohol exposure (FAE) in vervet monkeys induces anomalies of full-field electroretinogram (ERG) waveforms that suggest premature aging of the retina. The goal of this study is to characterize the anatomo-functional mechanisms underlying the retinal changes observed in fetal alcohol exposed (FAE) monkeys, and age- and sex-matched normals. First, we examined in vivo the fundus of the eyes, measured intraocular pressure (IOP) and assessed cone activity using flicker ERG. Second, we investigated ex vivo, protein expression and anatomical organization of the retina using Western blotting, classical histology and immunohistochemistry. Our results indicated that the fundus of the eyes showed both, increased vascularization (tessellated fundus) and IOP in FAE monkeys. Furthermore, light-adapted flicker responses above 15 Hz were also significantly higher in FAE monkeys. Although there were no obvious changes in the overall anatomy in the FAE retina, Glial Fibrillary Acidic Protein (GFAP, a potent marker of astrocytes) immunoreactivity was increased in the FAE retinal ganglion cell layer indicating a strong astrogliosis. These alterations were present in juvenile (2 years old) monkeys and persist in adults (8 years old). Moreover, using specific cell type markers, no significant modifications in the morphology of the photoreceptors, horizontal cells, bipolar cells, and amacrine cells were observed. Our data indicate that FAE does indeed induce anatomical changes within the retinal ganglion cell layer that are reflected in the increased photosensitivity of the cone photoreceptors.

Neurological and neuropsychological effects of low and moderate prenatal alcohol exposure

Several explanations for the diverse results in research on foetal alcohol spectrum disorders or alcohol-related neurodevelopmental disorder might be at hand: timing, amount and patterns of alcohol exposure, as well as complex epigenetic responses. The genetic background of the offspring and its interaction with other prenatal and post-natal environmental cues are likely also of importance. In the present report, key findings about the possible effects of low and moderate doses of maternal alcohol intake on the neuropsychological development of the offspring are reviewed and plausible mechanisms discussed. Special focus is put on the serotonergic system within developmental and gene-environment frameworks. The review also suggests guidelines for future studies and also summarizes some of to-be-answered questions of relevance to clinical practice. Contradictory findings and paucity of studies on the effects of exposure to low alcohol levels during foetal life for the offspring's neuropsychological development call for large prospective studies, as well as for studies including neuroimaging and multi-omics analyses to dissect the neurobiological underpinnings of alcohol exposure-related phenotypes and to identify biomarkers. Finally, it remains to be investigated whether any safe threshold of alcohol drinking during pregnancy can be identified.

Fetal Alcohol Exposure: The Common Toll

Alcohol has always been present in human life, and currently it is estimated that 50% of women of childbearing age consume alcohol. It has become increasingly clear over the last years that alcohol exposure during fetal development can have detrimental effects on various organ systems, and these effects are exerted by alcohol through multiple means, including effects on free radical formation, cellular apoptosis, as well as gene expression. Fetal alcohol exposure can lead to a spectrum of short term as well as long-term problems, with Fetal Alcohol Syndrome being on the more severe end of that spectrum. This syndrome is morbid, yet preventable, and is characterized by midfacial hypoplasia, thin upper lip, widely spaced small eyes, long smooth philtrum and inner epicanthal folds. Other findings include growth restriction as well as various neurodevelopmental abnormalities. This article is the first comprehensive review combining the molecular as well as the gross physiological and anatomical effects of alcohol exposure during pregnancy on various organ systems in the body. Our knowledge of these various mechanisms is crucial for our understanding of how alcohol exposure during fetal development can lead to its detrimental effects.