Prenatal Zinc Deficient Mice as a Model for Autism Spectrum Disorders

Glyphosate as a direct or indirect activator of pro-inflammatory signaling and cognitive impairment

Glyphosate-based herbicides are widely used around the world, making it likely that most humans have significant exposure. Because of habitual exposure, there are concerns about toxicity including neurotoxicity that could result in neurological, psychiatric, or cognitive impairment. We recently found that a single injection of glyphosate inhibits long-term potentiation, a cellular model of learning and memory, in rat hippocampal slices dissected 1 day after injection, indicating that glyphosate-based herbicides can alter cognitive function. Glyphosate-based herbicides could adversely affect cognitive function either indirectly and/or directly. Indirectly, glyphosate could affect gut microbiota, and if dysbiosis results in endotoxemia (leaky gut), infiltrated bacterial by-products such as lipopolysaccharides could activate pro-inflammatory cascades. Glyphosate can also directly trigger pro-inflammatory cascades. Indeed, we observed that acute glyphosate exposure inhibits long-term potentiation in rat hippocampal slices. Interestingly, direct inhibition of long-term potentiation by glyphosate appears to be similar to that of lipopolysaccharides. There are several possible measures to control dysbiosis and neuroinflammation caused by glyphosate. Dietary intake of polyphenols, such as quercetin, which overcome the inhibitory effect of glyphosate on long-term potentiation, could be one effective strategy. The aim of this narrative review is to discuss possible mechanisms underlying neurotoxicity following glyphosate exposure as a means to identify potential treatments.

Postnatal zinc deficiency due to giardiasis disrupts hippocampal and cerebellar development

BACKGROUND

Giardiasis and zinc deficiency have been identified as serious health problems worldwide. Although Zn depletion is known to occur in giardiasis, no work has investigated whether changes occur in brain structures.

METHODS

Three groups of gerbils were used: control (1), orogastrically inoculated on day 3 after birth with trophozoites of two isolates of Giardia intestinalis (HGINV/WB) group (2 and 3). Estimates were made at five ages covering: establishment of infection, Giardia population growth, natural parasite clearance and a post-infection age. QuantiChrome zinc assay kit, cresyl violet staining and TUNEL technique were used.

RESULTS

A significant decrease (p<0.01) in tissue zinc was observed and persisted after infection. Cytoarchitectural changes were observed in 75% of gerbils in the HGINV or WB groups. Ectopic pyramidal neurons were found in the cornus ammonis (CA1-CA3). At 60 and 90 days of age loss of lamination was clearly visible in CA1. In the dentate gyrus (DG), thinning of the dorsal lamina and abnormal thickening of the ventral lamina were observed from 30 days of age. In the cerebellum, we found an increase (p<0.01) in the thickness of the external granular layer (EGL) at 14 days of age that persisted until day 21 (C 3 ± 0.3 μm; HGINV 37 ± 5 μm; WB 28 ± 3 μm); Purkinje cell population estimation showed a significant decrease; a large number of apoptotic somas were observed scattered in the molecular layer; in 60 and 90 days old gerbils we found granular cell heterotopia and Purkinje cell ectopia. The pattern of apoptosis was different in the cerebellum and hippocampus of parasitized gerbils.

CONCLUSION

The morphological changes found suggest that neuronal migration is affected by zinc depletion caused by giardiasis in early postnatal life; for the first time, the link between giardiasis-zinc depletion and damaged brain structures is shown. This damage may explain the psychomotor/cognitive delay associated with giardiasis. These findings are alarming. Alterations in zinc metabolism and signalling are known to be involved in many brain disorders, including autism.

Gestational hypothyroxinemia induces ASD-like phenotypes in behavior, proinflammatory markers, and glutamatergic protein expression in mouse offspring of both sexes

Background

The prevalence of autism spectrum disorder (ASD) has significantly risen in the past three decades, prompting researchers to explore the potential contributions of environmental factors during pregnancy to ASD development. One such factor of interest is gestational hypothyroxinemia (HTX), a frequent condition in pregnancy associated with cognitive impairments in the offspring. While retrospective human studies have linked gestational HTX to autistic traits, the cellular and molecular mechanisms underlying the development of ASD-like phenotypes remain poorly understood. This study used a mouse model of gestational HTX to evaluate ASD-like phenotypes in the offspring.

Methods

To induce gestational HTX, pregnant mice were treated with 2-mercapto-1-methylimidazole (MMI), a thyroid hormones synthesis inhibitor, in the tap-drinking water from embryonic days (E) 10 to E14. A separate group received MMI along with a daily subcutaneous injection of T4, while the control group received regular tap water during the entire pregnancy. Female and male offspring underwent assessments for repetitive, anxious, and social behaviors from postnatal day (P) 55 to P64. On P65, mice were euthanized for the evaluation of ASD-related inflammatory markers in blood, spleen, and specific brain regions. Additionally, the expression of glutamatergic proteins (NLGN3 and HOMER1) was analyzed in the prefrontal cortex and hippocampus.

Results

The HTX-offspring exhibited anxious-like behavior, a subordinate state, and impaired social interactions. Subsequently, both female and male HTX-offspring displayed elevated proinflammatory cytokines in blood, including IL-1β, IL-6, IL-17A, and TNF-α, while only males showed reduced levels of IL-10. The spleen of HTX-offspring of both sexes showed increased Th17/Treg ratio and M1-like macrophages. In the prefrontal cortex and hippocampus of male HTX-offspring, elevated levels of IL-17A and reduced IL-10 were observed, accompanied by increased expression of hippocampal NLGN3 and HOMER1. All these observations were compared to those observed in the Control-offspring. Notably, the supplementation with T4 during the MMI treatment prevents the development of the observed phenotypes. Correlation analysis revealed an association between maternal T4 levels and specific ASD-like outcomes.

Discussion

This study validates human observations, demonstrating for the first time that gestational HTX induces ASD-like phenotypes in the offspring, highlighting the need of monitoring thyroid function during pregnancy.

Zinc Water Prevents Autism-Like Behaviors in the BTBR Mice

This study aims to explore the effects of zinc water on autism-like behavior, convulsion threshold, and neurogenesis in ASD model animals. This study used the young BTBR ASD mouse model to explore the effect of a 6-week zinc water supplementation on ASD-like behaviors such as repetitive behavior and social communication disorder, seizure threshold, and the correlation with excitability regulation. The mice were divided into four groups of normal controls (B6) and models (BTBR) who did and did not receive zinc supplementation in water (B6, B6 + zinc, BTBR, and BTBR + zinc). For morphological changes in the hippocampus, we selected two indicators: hippocampal mossy fiber sprouting and neurogenesis. ASD-like behavior testing, seizure threshold determination, Timm staining, and neurogenesis-related assays-represented by Ki67 and DCX-were performed after 6 weeks of zinc supplementation. Our results show that zinc water can prevent autism-like behavior, reduce susceptibility to convulsions, and increase the proliferation of hippocampal progenitor cells in BTBR mice but has less effect on mossy fiber sprouting and neural progenitor cell differentiation. Zinc water reduces autism-like behavior in a partially inherited autism model mice-BTBR-which may be associated with hippocampal neural precursor cell proliferation and reversed hyperexcitability.

Examining Prenatal Dietary Factors in Association with Child Autism-Related Traits Using a Bayesian Mixture Approach: Results from 2 United States Cohorts

Background

Prior work has suggested relationships between prenatal intake of certain nutrients and autism.

Objectives

We examined a broad set of prenatal nutrients and foods using a Bayesian modeling approach.

Methods

Participants were drawn from the Early Autism Risks Longitudinal Investigation (n = 127), a cohort following women with a child with autism through a subsequent pregnancy. Participants were also drawn from the Nurses' Health Study II (NHSII, n = 713), a cohort of United States female nurses, for comparison analyses. In both studies, information on prospectively reported prenatal diet was drawn from food frequency questionnaires, and child autism-related traits were measured by the Social Responsiveness Scale (SRS). Bayesian kernel machine regression was used to examine the combined effects of several nutrients with neurodevelopmental relevance, including polyunsaturated fatty acids (PUFAs), iron, zinc, vitamin D, folate, and other methyl donors, and separately, key food sources of these, in association with child SRS scores in crude and adjusted models.

Results

In adjusted analyses, the overall mixture effects of nutrients in Early Autism Risks Longitudinal Investigation and foods in both cohorts on SRS scores were not observed, though there was some suggestion of decreasing SRS scores with increasing overall nutrient mixture in NHSII. No associations were observed with folate within the context of this mixture, but holding other nutrients fixed, n-6 PUFAs were associated with lower SRS scores in NHSII. In both cohorts, lower SRS scores were observed with higher intake of some groupings of vegetables, though for differing types of vegetables across cohorts, and some vegetable groups were associated with higher SRS scores in NHSII.

Conclusions

Our work extends prior research and suggests the need to further consider prenatal dietary factors from a combined effects perspective. In addition, findings here point to potential differences in nutrient associations based on a family history of autism, which suggests the need to consider gene interactions in future work.

Plasma zinc, copper and serum ceruloplasmin levels of autism spectrum disorder children in Bangladesh

Neural and cognitive processes require zinc and copper homeostasis and a normal zinc/copper ratio. Ceruloplasmin, an intrinsic antioxidant protein, maintains copper homeostasis, which might also influence autism spectrum disorder (ASD). ASD children are frequently reported with altered levels of these elements with wide geographical variations. This study evaluated any alteration in plasma zinc, copper, zinc/copper ratio and serum ceruloplasmin levels in Bangladeshi ASD children with respect to healthy controls. A cross-sectional study was conducted on 67 children aged 2 to 9 years of both sexes. Among them, 35 had ASD, while 32 were age, sex and body mass index (BMI) matched apparently healthy children. Plasma zinc and copper levels were estimated by the flame atomic absorption spectrophotometry method. Serum ceruloplasmin levels were estimated by the immunoturbidimetric method. Zinc and zinc/copper ratio in the 2-9 years old ASD children group were significantly lower (p=0.032 and p=0.002 respectively). On the other hand, copper (p=0.020) and ceruloplasmin (p = 0.045) levels were significantly higher than those of apparently healthy children. ASD was significantly associated with zinc deficiency (p=0.000) and copper toxicity (p=0.05). All children were again divided into 2-5 and 6-9 years age groups according to laboratory reference values for zinc and copper. Copper toxicity was significantly associated with ASD in the 2-5 years old age group (p=0.011), with a significant difference in plasma copper levels (p=0.009) and zinc/copper ratio (p=0.001) but not serum ceruloplasmin levels (p=0.110) compared to healthy controls. Serum ceruloplasmin was positively associated with plasma copper in ASD children of all age groups. This study shows that ASD in Bangladesh can be associated with low plasma zinc and high plasma copper and serum ceruloplasmin levels.

A Timm-Nissl multiplane microscopic atlas of rat brain zincergic terminal fields and metal-containing glia

The ability of Timm's sulphide silver method to stain zincergic terminal fields has made it a useful neuromorphological marker. Beyond its roles in zinc-signalling and neuromodulation, zinc is involved in the pathophysiology of ischemic stroke, epilepsy, degenerative diseases and neuropsychiatric conditions. In addition to visualising zincergic terminal fields, the method also labels transition metals in neuronal perikarya and glial cells. To provide a benchmark reference for planning and interpretation of experimental investigations of zinc-related phenomena in rat brains, we have established a comprehensive repository of serial microscopic images from a historical collection of coronally, horizontally and sagittally oriented rat brain sections stained with Timm's method. Adjacent Nissl-stained sections showing cytoarchitecture, and customised atlas overlays from a three-dimensional rat brain reference atlas registered to each section image are included for spatial reference and guiding identification of anatomical boundaries. The Timm-Nissl atlas, available from EBRAINS, enables experimental researchers to navigate normal rat brain material in three planes and investigate the spatial distribution and density of zincergic terminal fields across the entire brain.

Metal Profiles in Autism Spectrum Disorders: A Crosstalk between Toxic and Essential Metals

Since hundreds of years ago, metals have been recognized as impacting our body's physiology. As a result, they have been studied as a potential cure for many ailments as well as a cause of acute or chronic poisoning. However, the link between aberrant metal levels and neuropsychiatric illnesses such as schizophrenia and neurodevelopmental disorders, such as autism spectrum disorders (ASDs), is a relatively new finding, despite some evident ASD-related consequences of shortage or excess of specific metals. In this review, we will summarize past and current results explaining the pathomechanisms of toxic metals at the cellular and molecular levels that are still not fully understood. While toxic metals may interfere with dozens of physiological processes concurrently, we will focus on ASD-relevant activity such as inflammation/immune activation, mitochondrial malfunction, increased oxidative stress, impairment of axonal myelination, and synapse formation and function. In particular, we will highlight the competition with essential metals that may explain why both the presence of certain toxic metals and the absence of certain essential metals have emerged as risk factors for ASD. Although often investigated separately, through the agonistic and antagonistic effects of metals, a common metal imbalance may result in relation to ASD.

The Role of Zinc and NMDA Receptors in Autism Spectrum Disorders

NMDA-type glutamate receptors are critical for synaptic plasticity in the central nervous system. Their unique properties and age-dependent arrangement of subunit types underpin their role as a coincidence detector of pre- and postsynaptic activity during brain development and maturation. NMDAR function is highly modulated by zinc, which is co-released with glutamate and concentrates in postsynaptic spines. Both NMDARs and zinc have been strongly linked to autism spectrum disorders (ASDs), suggesting that NMDARs are an important player in the beneficial effects observed with zinc in both animal models and children with ASDs. Significant evidence is emerging that these beneficial effects occur via zinc-dependent regulation of SHANK proteins, which form the backbone of the postsynaptic density. For example, dietary zinc supplementation enhances SHANK2 or SHANK3 synaptic recruitment and rescues NMDAR deficits and hypofunction in Shank3^ex13-16-/- and Tbr1^+/- ASD mice. Across multiple studies, synaptic changes occur in parallel with a reversal of ASD-associated behaviours, highlighting the zinc-dependent regulation of NMDARs and glutamatergic synapses as therapeutic targets for severe forms of ASDs, either pre- or postnatally. The data from rodent models set a strong foundation for future translational studies in human cells and people affected by ASDs.

Prevalence of low dietary zinc intake in women and pregnant women in Ireland

Background

In humans, zinc is involved in many biological functions acting as signaling ion, neurotransmitter, structural component of proteins, and cofactor for many enzymes and, through this, is an important regulator of the immune and nervous system. Food supplies zinc to the human body, but a high prevalence of inadequate dietary zinc intake has been reported worldwide.

Aims

The objective of this study was to investigate the zinc intake and bioavailability of over 250 women (pregnant and non-pregnant) based in Ireland, in order to evaluate the dietary inadequacy of zinc.

Methodology

We used a food frequency questionnaire designed to assess the zinc intake and bioavailability of the participants.

Results

Our results show that 58% of participants are at risk of inadequate zinc intake and that 29% may be zinc deficient. The prevalence of inadequate zinc intake was lower for pregnant women (zinc deficient 9%, at risk 38%) than for non-pregnant women due to more frequent consumption of supplements. Low zinc intake was not correlated with the age of participants and resulted from a combination of inadequate intake of zinc-rich food and relatively higher intake of food items rich in phytate, a major zinc uptake inhibitor.

Conclusions

We conclude that at present, low zinc intake may be prevalent in as much as 87% of women, including 47% of pregnant women. Therefore, zinc status needs to be considered as a factor impacting the health of women, and in particular pregnant women, also in industrialized and developed countries such as Ireland.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11845-022-03181-w.