Toxic effects induced by nonylphenol (NP) and ethoxylated nonylphenol (NP-9) in Caenorhabditis elegans
De la Parra Guerra, Ana Cristina | 2020
Needs in the field of cleanliness and asepsis have evolved over
time. Among the most widely used chemicals in the world
today are emerging pollutants. One of these contaminants is
nonylphenol ethoxylate (NP-9), also known as Tergitol, and
its degradation product, nonylphenol (NP), active
ingredients present in nonionic surfactants used as
herbicides, cosmetics, paints, plastics, disinfectants and
detergents. These chemicals and their metabolites are
commonly found in environmental matrices.
The objectives of this research work were: 1. To assess the
toxicity of NP and NP-9 in C. elegans. 2. To determine the
gene expression profile for different toxicity mechanisms in
C. elegans. 3. To determine the intergenerational effects
caused by exposure to NP-9 in C. elegans. 4. To identify
possible intergenerational neurotoxic effects from exposure
to NP-9 in C. elegans. Wild-type L4 larvae were exposed to
different concentrations of the surfactants to measure
functional endpoints like; lethality, length, width, locomotion
and lifespan. Transgenic green fluorescent protein (GFP)
strains were employed to estimate changes in relative gene
expression and promote the activation of toxicity signaling
pathways related to mtl-2, gst-1, gpx-4, gpx-6, sod-4, hsp-70
and hsp-4. Additionally, stress response was also assessed
using a daf-16::GFP transgenic strain. RT-qPCR was utilized
to measure mRNA expression for neurotoxicity-related
genes (unc-30, unc-25, dop-3, dat-1, mgl-1, and eat-4).
In the results of the first aim, lethality was concentration
dependent, with 24-h LC50 of 122 μM and 3215 μM for NP
and NP-9, respectively. Both compounds inhibited nematode
growth, although NP was more potent; and at non-lethal
concentrations, nematode locomotion was reduced. The
increase in the expression of tested genes was significant at
10 μM for NP-9 and 0.001 μM for NP, implying a likely role
for the activation of oxidative and cellular stress, as well as
metabolism pathways. Except for glutathione peroxidase,
which has a bimodal concentration-response curve for NP,
typical of endocrine disruption, the other curves for this
xenobiotic in the strains evaluated were almost flat for most
concentrations, until reaching 50–100 μM, where the effect
peaked. NP and NP-9 induced the and nuclear translocation
of DAF-16, suggesting that transcription of stress-response
genes may be mediated by the insulin/IGF-1 signaling
pathway. In contrast, NP-9 induced a concentrationdependent response for the sod-4 hsp-4 mutants, with
higher fluorescence induction than NP at similar levels.
For the second aim, data were obtained from parent worms
(P0) and the first generation (F1). Lethality of the nematode
was concentration-dependent, with 48 h-LC50 values of
3215 and 1983 μM in P0 and F1, respectively. Non-lethal
concentrations of NP-9 reduced locomotion. Lifespan was
also decreased by the xenobiotic, but the negative effect was
greater in P0 than in F1. Non-monotonic concentrationresponse curves were observed for body length and width in
both generations. The gene expression profile in P0 was
different from that registered in F1, although the expression
of sod-4, hsp-70, gpx-6 and mtl-2 increased with the
surfactant concentration in both generations. None of the
tested genes followed a classical concentration-neurotoxicity
relationship. In P0, dopamine presented an Inverted-U
curve, while GABA and glutamate displayed a bimodal type.
However, in F1, inverted U-shaped curves were revealed for
these genes.
In short, NP and NP-9 affect the physiology of C. elegans and
modulate gene expression related to reactive oxygen species
(ROS) production, cellular stress and metabolism of
xenobiotics. Additionally, the NP-9 isomer induced
intergenerational responses in nematode through
mechanisms involving ROS, and alterations of the GABA,
glutamate, and dopamine pathways.
LEER