Current opinion in toxicology最新文献

The regulation of thyroid hormones (THs) production and physiological action is complex and can be adversely disrupted by a broad spectrum of chemicals at environmentally relevant concentrations through different and intricate mechanisms. This study reviews the current knowledge on how chemicals, in particular pesticides, can disrupt TH homeostasis. These include a) inhibition of TH biosynthesis in the thyroid follicular cells resulting in perturbation of the hypothalamic–pituitary–thyroid (HPT) axis; b) interference with TH transport proteins in the bloodstream; c) liver enzyme induction leading to increased inactivation and further excretion of TH from the body; d) interference with conversion of TH into the active form in peripheral tissues; e) interference with the transport of TH through cell membranes; and f) binding to intracellular TH receptors and further dysregulation of downstream gene expression sensitive to TH. Most pesticides included in the cumulative assessment group “hypothyroidism” by EFSA affect the HPT axis through upregulation of TH elimination pathways. A better understanding of the molecular mechanism behind the adverse effects, or at least the mode of action of each pesticide, reduces the uncertainty when the combined risk of dietary exposure to pesticides is assessed according to the dose-addition model.

Persistent organic pollutants (POPs) are a group of organic chemicals, as defined by the Stockholm Convention that are persistent in the environment and accumulate in organisms including humans. Most POPs are restricted in use or no longer manufactured because of this persistence, bioaccumulation, and toxicity. In addition, an association between POP exposure and human disease has been suggested. Regarding toxicological effects and particularly cancer, most POPs have been shown to induce hepatic tumors when chronically administered to rodents. Understanding the mechanisms by which POPs induce liver cancer is important in developing meaningful human cancer risk evaluation to these compounds. In this article, we have reviewed the probable mechanisms of hepatic cancer induced by POPs mode of action and molecular initiating events and the relationship of these mechanisms to potential human cancer risk.

Consumer demand for organic food is mostly based on the belief that organic products are healthier because they are less contaminated with pesticides. We explain why health benefits from a decreased exposure to pesticides through organic food consumption remain unsubstantiated. There is sufficient evidence to conclude that nonorganic food products contain higher levels of synthetic pesticides. However, a link between the consumption of an organic diet with health benefits is confounded by a number of lifestyle and demographic covariates. We recommend dietary intervention studies be conducted such as randomized double-blind placebo-controlled investigations to determine if a group of individuals consuming an organic wholefood diet or an equivalent nonorganic diet present any differences in health status.

The human gut microbiome is considered critical for establishing and maintaining intestinal function and homeostasis throughout life. Evidence for bidirectional communication with the immune and nervous systems has spawned interest in the microbiome as a key factor for human and animal health. Consequently, appreciation of the microbiome as a target of xenobiotics, including environmental pollutants such as heavy metals, has risen steadily because disruption of a healthy microbiome (dysbiosis) has been linked to unfavorable health outcomes. Thus, toxicology must consider toxicant effects on the host's microbiome as an integral part of the holobiont. We discuss current findings on the impact of toxic metals on the composition, diversity, and function of the gut microbiome as well as the modulation of metal toxicity by the microbiome. Present limitations and future needs in elucidating microbiome-metal interactions and the potential of harnessing beneficial traits of the microbiota to counteract metal toxicity are also considered.

Immune cells are able to release a variety of inflammation mediators, activating proinflammatory and antiinflammatory processes and regulating intracellular pathways. Consequences of chronic or early-life exposure to pesticides may be extended beyond innate immune dysfunction to the increased risk of late-life chronic inflammatory-based diseases. This study aims to summarize some of the most recent advancements in occupational toxicology, focusing on biological mechanisms linking environmental exposure to pesticides, inflammation, and cytokine modulation, as well as genetic polymorphisms or epigenetic modifications which can represent factors of vulnerability for exposed workers. Choosing appropriate toxicity biomarkers is also one of the main concerns in the field of immunotoxicology; for this purpose, new technologies have been introduced for the monitoring of pesticides blood levels along with molecular alterations. These approaches will allow the assessment of the actual body burden of environmental pollutants associating it with a screening for the early diagnosis of pathologies.

Investigations of the obesity epidemic implicate environmental toxins that affect hormone systems, including the estrogen disruptor bisphenol acetate (BPA). This review concentrates on effects of BPA exposure on central nervous system areas involved in the control of feeding and body weight, drawing parallels between central nervous system effects of estrogens and of BPA. Conflicting findings abound because of methodological differences in species and sex, as well as BPA dose, timing of exposure, and specific model systems used. Nonetheless, common factors include the hypothalamic feeding-inhibitory peptide, pro-opiomelanocortin, and neuroimmune signaling in the hypothalamus, which may involve neuronal and non-neuronal cells. Receptor and intracellular mechanisms remain elusive but likely involve nuclear factor-kappa B signaling via interactions between nuclear estrogen receptors and peroxisome proliferator–activated receptor gamma.

Methylmercury (MeHg) is a globally relevant environmental neurotoxic pollutant. Recent evidence from the Faroe Islands and Seychelles cohort studies suggest that maternal exposure to MeHg via consumption of contaminated fish and seafood results in transplacental exposure of the fetus to MeHg, seriously affecting fetal neurodevelopment. In birth cohorts, with mercury exposure below the existing tolerable weekly intake (1.3 μg/kg b.w., European Food Safety Authority) MeHg exposure associations to adverse neurodevelopmental effects have been observed. However, there are inconsistencies between studies, attributing confounding factors as the primary source of data variability. We summarize current knowledge of MeHg-mediated effects during nervous system development. Major molecular targets are thiols and selenols and, in particular, selenoenzymes, resulting in exacerbated oxidative stress–related damage. Generation of reactive oxygen species (ROS) is an underlying trigger for apoptosis. Low levels of MeHg can induce apoptotic death in cerebellar neurons, and MeHg can induce endoplasmic reticulum stress, disrupt calcium homeostasis, and cause mitochondrial disruption. At a cellular level, the effects of MeHg exposure involve the dysfunction of a myriad of neurodevelopment and neurobehavioral functions.

Daily oral exposure to vast numbers (>10¹³/adult/day) of micron or nanosized persistent particles has become the norm for many populations. Significant airborne particle exposure is deleterious, so what about ingestion? Titanium dioxide in food grade form (fgTiO₂), which is an additive to some foods, capsules, tablets, and toothpaste, may provide clues. Certainly, exposed human populations accumulate these particles in specialized intestinal cells at the base of large lymphoid follicles (Peyer's patches) and it is likely that a degree of absorption goes beyond this, that is, lymphatics to blood circulation to tissues. The authors of this study critically review the evidence and pathways. Regarding potential adverse effects, the authors primary message, for today's state-of-the-art, is that in vivo models have not been good enough and at times woeful. The authors provide a ‘caveats list’ to improve approaches and experimentation and illustrate why studies on biomarkers of particle uptake, and lower gut/mesenteric lymph nodes as targets, should be prioritized.