Date of Award
August 2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Environmental Health Sciences
First Advisor
Kurt Svoboda
Abstract
Chloroxylenol (CHX) and benzethonium chloride (BEC) are replacement compounds being used after the ban (U.S. FDA) of triclosan and triclocarban in 2016 from personal care products. Moreover, these two compounds are recommended by the World Health Organization (WHO) as disinfectants to use against COVID-19. Toxicity data for both CHX and BEC are available, however, neurotoxicity studies for both compounds are still limited. Here, we determined the consequences of CHX and BEC exposure on neurodevelopment and neural crest cell (NCC) development using the zebrafish model (Danio rerio). Zebrafish embryos were exposed to CHX (1, 2.5, and 5 mg/L) and BEC (1, 2.5, and 5 mg/L) in five unique windows of embryogenesis to probe unique endpoints with were related to nervous system development. Zebrafish embryos/larvae at 23 hours post fertilization (hpf), 30 hpf, 48 hpf, and 72 hpf were analyzed for: spontaneous coiling of the musculature, primary motoneuron (PMN) development, spinal excitatory and inhibitory interneuron development, secondary motoneuron (SMN) axonal pathfinding, and muscle fiber development, respectively.Exposure to CHX resulted in a decrease in spontaneous coiling of the musculature as well as increased PMN and SMN axonal pathfinding errors. SMN axonal pathfinding errors occurred when zebrafish were exposed from 5 to 72 hpf, but not when the exposure occurred from 24 to 72 hpf. SMN axonal pathfinding errors mirrored the MiP axonal pathfinding errors that were caused by the exposure. In contrast, alterations in slow muscle development were observed in embryos exposed within both windows of exposure, suggesting that changes in SMN axonal pathfinding may be occurring independently of changes in muscle biology. The impact of CHX and BEC exposures on neural crest cell (NCC) development were also evaluated in this study. Zebrafish embryos/larvae were exposed to CHX and BEC within various windows of development associated with NCC migration and NCC differentiation. Three cell types derived from NCCs were analyzed including pigment, dorsal root ganglion (DRG) neurons, and craniofacial (jaw) development. The windows of exposure chosen for pigment and jaw development were used to determine if abnormal phenotypes were the result of disruptions in NCC migration or differentiation. Our study demonstrated that exposure to CHX resulted in the alterations in pigment, DRG, and chondrocyte (jaw) development in zebrafish embryos/larvae. In contrast, BEC exposure only impacted jaw development. Moreover, CHX was able to induce coiling/swimming in embryonic and larval zebrafish. Exposure to BEC did not result in changes in motor outputs. Further experiments identified a potential cellular/receptor-based mechanism underlying CHX ability to turn on coiling/swimming. Spinal mechanosensory neurons known as Rohon-Beard (RB) cells are the likely cells being activated by CHX to produce coiling. Chronic CHX exposure also altered RB cell development as revealed by changes in tubulin distribution in RB peripheral processes and an increase in RB somata size. These findings support that CHX is more neurotoxic than BEC. For public health, humans can be exposed to CHX and BEC via using consumer products that contain them or from their residuals that are found in the environment. The occurrence of residual CHX and BEC has been reported in wastewater, bio-solids, and sediments. Also, CHX has also been detected in urine samples of pregnant women and children. If the exposure to CHX and BEC occurs in pregnant women, the developing fetus can be affected.
Recommended Citation
Rerkamnuaychoke, Wuttiporn, "ASSESSING THE TOXICITY OF ANTIMICROBIAL COMPOUNDS CHLOROXYLENOL AND BENZETHONIUM CHLORIDE IN DEVELOPING ZEBRAFISH" (2024). Theses and Dissertations. 3617.
https://dc.uwm.edu/etd/3617