Mercury and Autism Spectrum Disorder: Exploring the Link through Comprehensive Review and Meta-Analysis

Mercury exposure and childhood outcomes: An overview of systematic reviews

OBJECTIVE

The objective of this review was to summarize recent and relevant systematic reviews (SRs) that assessed relationships between mercury (Hg) exposure during pregnancy, lactation, and childhood and child outcomes.

EVIDENCE REVIEW

Three electronic databases were searched for SRs published between January 2018 to December 2024 about Hg exposure (of any form or source, including seafood), during pregnancy, lactation or childhood and child outcomes including: anthropometrics, neurodevelopment, attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), exposure biomarkers, cardiometabolic health, immunity, and birth outcomes. All articles were screened at title/abstract and full-text levels by two independent reviewers. A MeaSurement Tool to Assess systematic Reviews (AMSTAR) 2 critical appraisal tool was used to assess the methodological quality of the included SRs.

FINDINGS

Twenty-nine SRs of observational studies were identified that assessed Hg during pregnancy (n = 19) and/or childhood (n = 17). During pregnancy, results from the SRs suggested that higher Hg may be associated with higher risk of birth defects, pre-term birth, ADHD, ASD, and low birth weight, length, and head circumference. Results varied for neurodevelopment outcomes in the child, likely due to co-exposure with seafood during pregnancy, variation in response by sex of the child, and etiological differences among developmental domains. During childhood, SRs suggested that higher Hg may be associated with higher risk of ADHD and adverse neurodevelopment, growth, and body composition outcomes. Also, Hg concentrations were higher in children with ASD than those without in case-control studies but longitudinal data were lacking. Evidence on methylmercury exposure from seafood during pregnancy and childhood was limited and inconclusive.

CONCLUSION AND RELEVANCE

Mercury exposure during pregnancy and childhood is recognized as a major public health concern. However, more research is needed that specifically examines methylmercury from seafood to better inform future dietary recommendations.

Critical period of exposure to mercury and the diagnostic of autism spectrum disorder: A systematic review

Autism spectrum disorder (ASD) is characterized by repetitive behaviors and deficits in social interaction. Its etiology is not completely clear, but both genetic and environmental factors contribute to and influence its development and course. The increased number of autism cases in recent years has been strongly associated with increased exposure to heavy metals. Mercury (Hg) has gained prominence in the scientific literature as a result of its presence as an urban pollutant and well-described neurotoxicity. This review assessed the relationship between Hg exposure in the pre- and post-natal period and ASD. The systematic review identified observational clinical studies and pre-clinical trials in journals indexed in the PubMed, Embase, ProQuest, and LILACS databases. The aim of this study was to investigate the association between exposure to Hg and ASD and to define the critical period of exposure. A total of 57 articles were selected for this review, with 35 articles (61.40%) identifying a positive association between ASD and Hg, while 22 articles (38.60%) did not find the same outcome. The biological samples most used to analyze Hg body burdens were hair (36.84%) and blood (36.84%). Most case-control studies found an increase in Hg levels in individuals with ASD who were exposed to a polluted environment in the post-natal period. Taken together, the studies suggest that these patients have a deficient detoxification system, and this could worsen the symptoms of the disorder. However, new studies addressing the influence of Hg on the post-natal nervous system and its relationship with ASD should be carried out.

Changes of Target Essential Trace Elements in Multiple Sclerosis: A Systematic Review and Meta-Analysis

(1) Background: Multiple sclerosis (MS) is a chronic, complex, and demyelinating disease closely associated with altered levels of trace elements. Although the first studies into the role of trace elements in MS were published in the 1970s, for five decades it has remained unknown whether trace elements can be part of this heterogeneous neurological disease. (2) Materials and methods: To drive toward at a potential solution, we conducted a systematic review and meta-analysis to elucidate whether there were differences in circulating levels of neurologically important essential trace elements (Zn, Fe, Co, Cu, Mn, and Se) between MS cases and controls. (3) Results: This study revealed significantly lower serum/plasma Zn and Fe levels and higher Cu levels in MS-affected individuals compared to controls. At the same time, no significant differences were found between the MS cases and controls regarding their serum/plasma levels of Co, Mn, or Se. Thus, the loss of Fe and Zn should be considered in supplementation/nutrition strategies for MS patients. On the other hand, since high serum Cu levels indicate a burden on the bloodstreams of MS patients, Cu should be excluded from mineral supplement strategies. Furthermore, all three trace elements (Fe, Zn, and Cu) should be considered from an etiological point of view, and, most importantly, their levels in the bloodstreams of MS patients should be monitored. (4) Conclusions: This study highlights the way for personalized and targeted strategies in the management of MS.

Essential trace element levels in multiple sclerosis: Bridging demographic and clinical gaps, assessing the need for supplementation

BACKGROUND

Multiple sclerosis (MS) is a chronic demyelinating disorder intricately linked to perturbations in trace element levels. While previous studies have explored circulating trace elements in a limited sample, understanding the impact of demographic and clinical variables on the elemental profile within a larger cohort remains elusive.

METHODS

This study aimed to evaluate essential trace elements (Cr, Mn, Co, Cu, Zn, and Se) in the sera of 215 MS patients compared to a meticulously matched control group of 100 individuals with similar gender and age. Our main objective was to identify potential variations in elemental profiles based on demographic and clinical parameters among MS patients, elucidating the prospective relevance of supplementing specific essential trace elements.

RESULTS

Data indicated a significant decrease in serum levels of Mn, Co, Zn, and Se, and an increase in Cr in MS patients compared to controls. These trace elements not only discriminated between MS patients and controls but also exhibited distinctive capabilities among demographic subgroups. Gender, smoking habits, and age strata (20-40 years and 41-60 years) revealed discernible variations in elemental profiles between MS patients and their control counterparts. Se demonstrated the singular ability to stratify cases of extreme MS severity, mild relapsing-remitting MS (RRMS) and highly severe secondary progressive MS (SPMS). In contrast, Co significantly differentiated RRMS from primary progressive MS (PPMS), while Cu significantly differentiated SPMS from PPMS. Additionally, Cu showed a negative correlation with MSSS, while Mn and Zn showed a positive correlation with EDSS.

CONCLUSION

These findings underscore a substantive deficiency in Mn, Co, Zn, and Se in the MS cohort, supporting targeted supplementation with these trace elements. This study provides a comprehensive understanding of the intricate relationship between essential trace elements and MS, paving the way for further research into personalized nutritional interventions for this complex neurological disorder.

The Impact of C-3 Side Chain Modifications on Kynurenic Acid: A Behavioral Analysis of Its Analogs in the Motor Domain

The central nervous system (CNS) is the final frontier in drug delivery because of the blood-brain barrier (BBB), which poses significant barriers to the access of most drugs to their targets. Kynurenic acid (KYNA), a tryptophan (Trp) metabolite, plays an important role in behavioral functions, and abnormal KYNA levels have been observed in neuropsychiatric conditions. The current challenge lies in delivering KYNA to the CNS owing to its polar side chain. Recently, C-3 side chain-modified KYNA analogs have been shown to cross the BBB; however, it is unclear whether they retain the biological functions of the parent molecule. This study examined the impact of KYNA analogs, specifically, SZR-72, SZR-104, and the newly developed SZRG-21, on behavior. The analogs were administered intracerebroventricularly (i.c.v.), and their effects on the motor domain were compared with those of KYNA. Specifically, open-field (OF) and rotarod (RR) tests were employed to assess motor activity and skills. SZR-104 increased horizontal exploratory activity in the OF test at a dose of 0.04 μmol/4 μL, while SZR-72 decreased vertical activity at doses of 0.04 and 0.1 μmol/4 μL. In the RR test, however, neither KYNA nor its analogs showed any significant differences in motor skills at either dose. Side chain modification affects affective motor performance and exploratory behavior, as the results show for the first time. In this study, we showed that KYNA analogs alter emotional components such as motor-associated curiosity and emotions. Consequently, drug design necessitates the development of precise strategies to traverse the BBB while paying close attention to modifications in their effects on behavior.