Mitochondria Mediated Outcomes of Developmental Exposure to Low-level Chemical Mixtures in Zebrafish Danio rerio

Exposure to drinking water contaminants has been linked to developmental outcomes in both epidemiological and model organism studies. However, low level mixture effects, on early development has yet to be explored. It is hypothesized that early chemical exposures may increase disease susceptibility later in life. This work aimed to investigate impacts of a variety of chemicals and concentrated on metals arsenic (As), cadmium (Cd), vanadium (V), and lead (Pb) due to their presence in drinking water and known developmental toxicity. To determine the effects of a metal and organic contaminant co-exposure, the ubiquitously used herbicide glyphosate was also explored. The zebrafish (Danio rerio) model was used to elucidate developmental impacts of lowlevel chemical mixture exposure with a focus on mitochondrial function. An in-depth analysis exploring embryonic oxygen consumption rate (eOCR) in response to all iterations of a 5-part chemical mixture of glyphosate, As, Cd, V, and Pb showed that mitochondria are highly sensitive to mixture toxicity, and that pre-exposure to a metal mixture leave the mitochondria more susceptible to acute chemical stress through depleted reserve capacity. Altered mitochondrial function, along with changes in gene expression and histology suggested that early mixture exposure may contribute to the endemic of chronic kidney disease of unknown etiology (CKDu). To investigate underlying molecular mechanisms that may contribute to CKDu susceptibility, RNA seq data from zebrafish embryos exposed to mixtures of As, Cd, V, and Pb, (+/- glyphosate) and glyphosate alone, suggest that exposure to metal and organic mixtures may be altering the extracellular matrix of kidney tissue. This combined with impaired mitochondrial function, could leave individuals more susceptible to kidney injury CKDu progression. To determine phenotypes associated with mixture exposure, changes in behavior after exposure to a large collection of water samples were explored. A cluster analysis of metals found in drinking water samples were coupled to changes in behavior and revealed that concentrations of Pb, Cd, As, Uranium (U) and Nickel (Ni), should be taken into special consideration when determining drinking water standards. These data suggest that impaired mitochondria, as a result of low-level mixture exposure, may function in the early onset of disease, such as CKDu, and further impair organism development