[
Toxics,
2020]
Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals that were widely used in manufacturing and are now present in the environment throughout the world. It is known that various PFAS are quantifiable in human in blood, but potential adverse health outcomes remain unclear. Sentinel and non-traditional model species are useful to study potential toxicity of PFAS in order to understand the relationship between environmental and human health. Here, we present a critical review of studies on the neurotoxicity of PFAS in sentinel and non-traditional laboratory model systems, including <i>Caenorhabditis elegans</i> (nematode), <i>Dugesia japonica</i> (planarian), <i>Rana pipiens</i> (frogs), <i>Danio rerio</i> and <i>Oryzias melastigma</i> (fish), and <i>Ursus maritimus</i> (polar bears). PFAS have been implicated in developmental neurotoxicity in non-traditional and traditional model systems as well as sentinel species, including effects on neurotransmitter levels, especially acetylcholine and its metabolism. However, further research on the mechanisms of toxicity needs to be conducted to determine if these chemicals are affecting organisms in a similar manner. Overall, findings tend to be similar among the various species, but bioaccumulation may vary, which needs to be taken into account in future studies by quantifying target organ concentrations of PFAS to better compare different species. Furthermore, data on the majority of PFAS is lacking in neurotoxicity testing, and additional studies are needed to corroborate findings thus far.
[
Comp Biochem Physiol C Toxicol Pharmacol,
2002]
Oxygen is essential for most life forms, but it is also inherently toxic due to its biotransformation into reactive oxygen species (ROS). In fact, the development of many animal and plant pathological conditions, as well as natural aging, is associated with excessive ROS production and/or decreased antioxidant capacity. However, a number of animal species are able to tolerate, under natural conditions, situations posing a large potential for oxidative stress. Situations range from anoxia in fish, frogs and turtles, to severe hypoxia in organs of freeze-tolerant snakes, frogs and insect larvae, or diving seals and turtles, and mild hypoxia in organs of dehydrated frogs and toads or estivating snails. All situations are reminiscent of ischemia/reperfusion events that are highly damaging to most mammals and birds. This article reviews the responses of anoxia/hypoxia-tolerant animals when subjected to environmental and metabolic stresses leading to oxygen limitation. Abrupt changes in metabolic rate in ground squirrels arousing from hibernation, as well as snails arousing from estivation, may also set up a condition of increased ROS formation. Comparing the responses from these diverse animals, certain patterns emerge. The most commonly observed response is an enhancement of the antioxidant defense. The increase in the baseline activity of key antioxidant enzymes, as well as ''secondary'' enzymatic defenses, and/or glutathione levels in preparation for a putative oxidative stressful situation arising from tissue reoxygenation seem to be the preferred evolutionary adaptation. Increasing the overall antioxidant capacity during anoxia/hypoxia is of relevance for species such as garter snakes (Thamnophis sirtalis parietalis) and wood fogs (Rana sylvatica), while diving freshwater turtles (Trachemys scripta elegans) appear to rely mainly upon high constitutive activities of antioxidant enzymes to deal with oxidative stress arising during tissue reoxygenation. The possibility that some animal species might control post-anoxic ROS generation cannot be excluded.