Medium- and high-throughput screening of neurotoxicants using C. elegans

Abstract

The U.S. National Toxicology Program, the U.S. Environmental Protection Agency, and other national and international agencies are committing significant resources towards the development of alternative species to be used as replacements for mammalian models in toxicological studies. Caenorhabditis elegans is a well-characterized soil nematode that is becoming a useful model in the assessment of neurotoxicants. To determine the effects of potential neurotoxicants on C. elegans, four medium-throughput (feeding, growth, reproduction and locomotion) and two high-throughput (growth and reproduction) assays have been developed. Three of these assays use the COPAS Biosort, a flow cytometer capable of rapidly measuring thousands of nematodes in minutes. Medium-throughput feeding, growth, and reproduction assays were used to assess the toxicity of eight suspected neurotoxicants. For several of the neurotoxicants examined, significant effects were observed at similar concentrations between assays. High-throughput reproduction and growth assays were used to estimate the toxicity of thousands of chemicals in two libraries. These assays will prove useful in evaluating the role of alternative toxicological models in tiered toxicity testing of thousands of chemicals.

Figure 1. Effects of chlorpyrifos oxon on C. elegans feeding

For each of two replicate experiments (shown as blue and red), groups of 25 adult C. elegans were exposed to one of five concentrations of chlorpyrifos oxon (plus controls) for 24 h. Medians of log(RFP)/log(TOF) values are plotted and the data fit to the Hill equation. inset, adult C. elegans pharynx.

Figure 2. Effects of hexachlorophene on C. elegans reproduction

For each of three replicate experiments (shown as blue, red, and green), groups of five L4 nematodes were exposed to one of five concentrations of hexachlorophene for 48 h. The numbers of observations (larvae and embryos) were fit to the Hill equation. inset, region around an L4 C. elegans vulva: I, intestine; UL, uterine lumen; Hyp, hypodermis; Vul, vulva.

Figure 3. Effects of chlorpyrifos on C. elegans growth

For each of three replicate experiments (shown as blue, red, and green), groups of 50 L1 nematodes were exposed to one of five concentrations of chlorpyrifos for 48 h. Left panel, observations measured and estimated means fit to Hill equation. Right panel, modeled frequency histograms showing the effects of different concentrations of chlorpyrifos (0, 0.1, 0.3, 1.0, 3.0, and 10 μM) on nematode size distribution (log(EXT)) for one of the replicates.

Figure 4. Effects of methyl mercury on C. elegans movement

Groups of 40 L4 nematodes were tracked after exposure to one of five concentrations of methyl mercury for 4 h. Left panel, average velocity of C. elegans motion, mean ± s.e. Right panel, computer generated tracks for control nematodes (top) and those exposed to 10 μM methyl mercury (bottom).