30
Apr
Meta-Analysis Catalogues Pesticides’ Adverse Impact on How Genes Function
(Beyond Pesticides, April 30, 2024) Researchers found epigenetic changes, including changes relating to “DNA methylation, histone modification, and differential microRNA expression [which ‘can alter the expression of many disease-related genes’],” in a systematic review and meta-analysis of existing literature published in Environmental Epigenetics. “Our review did provide evidence that pesticide exposure could lead to epigenetic modifications, possibly altering global and gene-specific methylation levels, epigenome-wide methylation, and micro-RNA differential expression,” researchers share in the conclusion of the study.
This study is an amalgamation of various studies on epigenetic changes based on a literature review process: “Article review involved [3,529 articles found through] extensive searches across major human health databases, including PubMed, Embase, and Cochrane, and BVS (Biblioteca Virtual em Saúde – the Latin American Health Database). Searches covered articles published through December 2020. Considering the diverse terminologies used to describe the same epigenetic mechanism in this field, the search strategy aimed to encompass all relevant articles by combining a variety of search terms in titles and abstracts. This approach was implemented across PubMed, Embase and Cochrane databases to ensure comprehensive coverage.” Studies were not included if the participants were not considered “healthy individuals” or if the participants had “known inherent/congenital or acquired genetic disorder[s].” Out of 3,529 articles initially found, 28 articles were finalized after going through eligibility criteria.
“When a modification occurs in a gene’s promoter region, it impedes the binding of activating transcription factors and triggers the formation of a closed chromatin structure through specific histone modifications,” the researchers explain in describing the relationship between pesticide exposure and biomolecular alterations that impact an individual’s epigenetics. “Assessing sperm samples from military veterans of Operation Ranch Hand exposed to Agent Orange, Kelsey et al. (2019) associated loss of DNA methylation in four different CpG sites of the TEAD3 gene with dioxin exposure,” says researchers in the study. DNA methylation is essential to the development and transfer of genes. “In addition, by assessing regional DNA methylation changes, 36 gene regions, including the region of the imprinted gene H19 were found to have altered DNA methylation associated with high dioxin exposure compared to the low dioxin exposure group.”
One of the selected studies involves the tracking of micro-RNA (miRNA) profiles from urine of farmworkers exposed to organophosphate pesticides. “A cohort of mother-child farmworker pairs exposed to organophosphate pesticides and non-farmworker pairs was studied by measuring urinary microRNA profiles []. Significant differences in miRNA profiles were found between adult farmworkers and non-farmworkers and also between seasons. During the post-harvest season, six miRNAs were identified as being positively associated with farmworkers.”
Epigenetic changes through pesticide exposure have been documented by various scientific studies focusing on different adverse health effects. For example, a 2023 study published in Endocrine notes that endocrine-disrupting chemicals (including primary ingredients in herbicides such as glyphosate and organophosphate and carbamate insecticides) can bind to hormone receptors, dysregulating hormone receptor expression, disrupting the production and metabolism of the steroid hormone (steroidogenesis), and altering the epigenetic (heritable traits) mechanisms. The resulting reproductive outcomes from endocrine-disrupting chemical (EDC) exposure include poor semen quality, increased sperm DNA fragmentation, increased gonadotropin levels, a slightly increased risk of hereditary malformations (e.g., cryptorchidism and hypospadias), and testicular tumor development. Regarding prenatal exposure, maternal exposure to EDCs increases the predisposition for testicular tumor development, as well.
Additionally, a 2023 study published in Environmental Health Perspectives observed life-long exposure to glyphosate increases the risk of mosaic loss of chromosome Y (loss of chromosome Y occurs to many men in some cells due to aging [mLOY]) that impacts a noticeable contingent of cells. Although the loss of this sex chromosome does not cause cell death, like the loss of autosomal chromosomes, the risk of mLOY is a biomarker for genotoxicity (the damage of genetic information within a cell causing mutations from chemical exposure, which may lead to cancer) and expansion of cellular response to glyphosate, resulting in the precursor for hematological (blood) cancers. For a broader history of independent and peer-reviewed scientific literature in this field of study, see the Daily News Blog section on epigenetics.
Beyond Pesticides has discussed extensively the impact of pesticide exposure on human health, particularly in its relationship with epigenetics and environmental obesogens. Environmental obesogens are chemicals that are proven to have a health impact on metabolic systems relating to obesity. As a keynote speaker at Beyond Pesticides’ 36th National Pesticide Forum, “Organic Neighborhoods: For healthy children, families, and ecology,” Bruce Blumberg, PhD broke down the impacts of prenatal obesogens in the session Cutting Edge Science. “In the obesogen-exposed animals, this structure is disturbed, and that leads to heritable changes in which genes are expressed. This altered structure is inherited, and that leads us to get this leptin-resistant thrifty phenotype four generations later, as published in [a 2017 Nature Communications study which determined] ancestral perinatal obesogen exposure results in a transgenerational thrifty phenotype in mice.”
There are several aspects of obesogens that scientists are still determining, including the number of obesogens and the degree to which prenatal exposure alters adult phenotype from babies as they grow up from ancestors who have intergenerational interactions with obesogens. There is also a 2024 Chemosphere study that describes associations between type 2 diabetes, obesity, and pesticide exposure, specifically β-Hexachlorocyclohexane (β-BHC) and oxadiazon.
Long-term pesticide exposure, and exposure to a mixture of various chemicals, has impacts on a far range of health consequences not just to human health, but to ecosystem integrity in its entirety. Beyond Pesticides acknowledges the decades of advocacy toward organic principles not only for agricultural purposes, but for broader land management strategies to prevent the unnecessary spread of toxic petrochemical pesticides. See Eating With A Conscience to learn about the toxic pesticides commonly used in conventionally grown fruits and produce to make a more informed decision ahead of your next grocery store run. See Keeping Organic Strong to learn how to strengthen National Organic Program standards in service of public health, climate action, and consumer interests.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Environmental Epigenetics
