Inhalation toxicity of indoor air pollutants in Drosophila melanogaster using integrated transcriptomics and computational behavior analyses

Stress Pathways Induced by Volatile Anesthetics and Failure of Preconditioning in a Mitochondrial Complex I Mutant

BACKGROUND

Carriers of mutations in the mitochondrial electron transport chain are at increased risk of anesthetic-induced neurotoxicity. To investigate the neurotoxicity mechanism and to test preconditioning as a protective strategy, this study used a Drosophila melanogaster model of Leigh syndrome. Model flies carried a mutation in ND23 (ND2360114) that encodes a mitochondrial electron transport chain complex I subunit. This study investigated why ND2360114 mutants become susceptible to lethal, oxygen-modulated neurotoxicity within 24 h of exposure to isoflurane but not sevoflurane.

METHODS

This study used transcriptomics and quantitative real-time reverse transcription polymerase chain reaction to identify genes that are differentially expressed in ND2360114 but not wild-type fly heads at 30 min after exposure to high- versus low-toxicity conditions. This study also subjected ND2360114 flies to diverse stressors before isoflurane exposure to test whether isoflurane toxicity could be diminished by preconditioning.

RESULTS

The ND2360114 mutation had a greater effect on isoflurane- than sevoflurane-mediated changes in gene expression. Isoflurane and sevoflurane did not affect expression of heat shock protein (Hsp) genes (Hsp22, Hsp27, and Hsp68) in wild-type flies, but isoflurane substantially increased expression of these genes in ND2360114 mutant flies. Furthermore, isoflurane and sevoflurane induced expression of oxidative (GstD1 and GstD2) and xenobiotic (Cyp6a8 and Cyp6a14) stress genes to a similar extent in wild-type flies, but the effect of isoflurane was largely reduced in ND2360114 flies. In addition, activating stress response pathways by pre-exposure to anesthetics, heat shock, hyperoxia, hypoxia, or oxidative stress did not suppress isoflurane-induced toxicity in ND2360114 mutant flies.

CONCLUSIONS

Mutation of a mitochondrial electron transport chain complex I subunit generates differential effects of isoflurane and sevoflurane on gene expression that may underlie their differential effects on neurotoxicity. Additionally, the mutation produces resistance to preconditioning by stresses that protect the brain in other contexts. Therefore, complex I activity modifies molecular and physiologic effects of anesthetics in an anesthetic-specific manner.

EDITOR’S PERSPECTIVE

The effect of cigarette smoke extract exposure on the size and sexual behaviour of Drosophila melanogaster

Drosophila melanogaster is a widely used animal model in human diseases and to date it has not been applied to the study of the impact of tobacco use on human sexual function. Hence, this report examines the effects of different concentrations of cigarette smoke extract (CSE) exposure on the size and sexual behavior of D. melanogaster. Wild-type flies were held in vials containing CSE-infused culture media at concentrations of 10%, 25%, and 50% for three days, and their offspring were reared under the same conditions before measuring their body size and mating behavior. CSE exposure during development reduced the tibia length and body mass of emerging adult flies and prolonged the time required for successful courtship copulation success, while courtship behaviors (wing extension, tapping, abdomen bending, attempted copulation) remained largely unchanged. Our findings indicate that CSE exposure negatively affects the development of flies and their subsequent reproductive success. Future experiments should investigate the CSE effect on male female fertility.

Mixture and individual effects of benzene, toluene, and formaldehyde in zebrafish (Danio rerio) development: Metabolomics, epigenetics, and behavioral approaches

In this study, we aimed to investigate the potential hazards of volatile organic compounds (VOCs) on the development of zebrafish. To this end, zebrafish embryos were exposed in two different windows, either alone or in a mixture with VOCs (benzene, toluene, and formaldehyde) [EW1: 4 ± 2 h post-fertilization (hpf) to 24 hpf and EW2: 24 ± 2 hpf to 48 hpf]. Alterations in global DNA methylation and related gene expression, behavioral responses, and stress-related gene expression were observed. In addition to these endpoints, non-targeted NMR-based global metabolomics followed by pathway analysis showed significant changes in the metabolism of various amino acids during VOC exposure. Regardless of the analyzed endpoints, toluene was the most toxic chemical when exposed individually and possibly played the most pivotal role in the mixture treatment conditions. In conclusion, our data show that exposure to VOCs at embryonic developmental stages causes physiological perturbations and adverse outcomes at later life stages.

Effects of plant growth retardant daminozide (Alar) on neuromuscular co-ordination behavior in Drosophila melanogaster

Daminozide (alar), a plant growth retardant, is used in different fruit orchard to make fruits attractive and reduce pre-harvest losses. Previously data demonstrated that acute daminozide exposure affected reproductive fitness and produced neurodegeneration in Drosophila melanogaster. The goal of this study was to determine whether continuous exposure to daminozide affects neuromuscular co-ordination in D. melanogaster as manifested in various behavioral responses. Fruit flies were exposed to 200 or 400 mg/L concentration of daminozide for two successive generations. Treated D. melanogaster were examined for the behaviors indicative of neuromuscular coordination and cognitive abilities, that include climbing, social interaction, adult grooming, migration, flight, male aggression, and adult courtship. Aberrant behavioral responses were noted among treated D. melanogaster of both sexes as evidenced by the following parameters: reduction in flight duration, abnormal social interaction, altered copulatory acts, and over-aggressiveness. Data suggest that daminozide produces impairment in neuromuscular coordination and cognitive ability in Drosophila, which was reflected as altered behavioral patterns. As Drosophila is considered as a reliable in vivo model utilized in toxicity testing, our findings may help us to anticipate and monitor potential daminozide-induced toxicity in animals and humans.

Inhibition of Staphylococcus aureus Efflux Pump by O-Eugenol and Its Toxicity in Drosophila melanogaster Animal Model

Background

Efflux pumps are transmembrane proteins that expel drugs out of a bacterial cell contributing to microorganism drug resistance. Several studies addressing the use of natural products with medicinal properties have intensified given the above. Thus, the aim of the present study was to investigate the antibacterial activity and the O-eugenol potential in Staphylococcus aureus resistance reversal by efflux pump inhibition, as well as to evaluate its toxicity in the Drosophila melanogaster arthropod model. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) and the O-eugenol efflux pump inhibition. For the D. melanogaster toxicity assays, mortality and locomotor system damage were performed using the fumigation method.

Results

O-eugenol presented a MIC of 1024 μg/mL against S. aureus. The association of this compound with the antibiotic tetracycline demonstrated a synergistic effect (p < 0.0001), this also being observed when the antibiotic was associated with ethidium bromide (p < 0.0001); thus, these results may be attributable to an efflux pump inhibition. The D. melanogaster mortality and geotaxis assays revealed the compound is toxic, with an EC₅₀ of 18 μg/mL within 48 hours of exposure.

Conclusions

While we can conclude that the tested product has an efflux pump inhibitory effect, further studies are needed to elucidate its mechanisms of action, in addition to assays using other strains to verify whether the substance has the same inhibitory effect.

Effect of fungal indoor air pollutant 1-octen-3-ol on levels of reactive oxygen species and nitric oxide as well as dehydrogenases activities in drosophila melanogaster males

Fungal pollution of indoor environments contributes to several allergic symptoms and represents a public health problem. It is well-established that 1-octen-3-ol, also known as mushroom alcohol, is a fungal volatile organic compound (VOC) commonly found in damp indoor spaces and responsible for the typical musty odor. Previously it was reported that exposure to 1-octen-3-ol induced inflammations and disrupted mitochondrial morphology and bioenergetic rate in Drosophila melanogaster. The aim of this study was to examine the influence of 1-octen-3-ol on dehydrogenase activity, apoptotic biomarkers, levels of nitric oxide (NO) and reactive oxygen species (ROS), as well as antioxidant enzymes activities. D. melanogaster flies were exposed to an atmosphere containing 1-octen-3-ol (2.5 or ∞l/L) for 24 hr. Data demonstrated that 1-octen-3-ol decreased dehydrogenases activity and NO levels but increased ROS levels accompanied by stimulation of glutathione-S-transferase (GST) and superoxide dismutase (SOD) activities without altering caspase 3/7 activation. These findings indicate that adverse mitochondrial activity effects following exposure of D. melanogaster to 1-octen-3-ol, a fungal VOC, may be attributed to oxidant stress. The underlying mechanisms involved in adverse consequences of indoor fungal exposure appear to be related to necrotic but not apoptotic mechanisms. The adverse consequences were sex-dependent with males displaying higher sensitivity to 1-octen-3-ol. Based upon on the fact that the fly genome shares nearly 75% of disease-related genes to human exposure to this fungus may explain the adverse human responses to mold especially for males.

Acute and Chronic Effects of Fin Amputation on Behavior Performance of Adult Zebrafish in 3D Locomotion Test Assessed with Fractal Dimension and Entropy Analyses and Their Relationship to Fin Regeneration

Simple Summary

Fin amputation is a routinely conducted procedure for various experiments, especially in zebrafish. However, no study compares the acute and chronic effects of the amputation of each fin on their behaviors. In addition, although some analgesics have been applied after the fin amputation procedure, the long-term effects of these drugs in have not been evaluated yet. In this study, we found that amputation in the caudal fin resulted in the most pronounced behavior alterations and their behavior was fully recovered before the caudal fin was fully regenerated, indicating that these behavioral changes came from pain elicited from the fin amputation. Finally, while lidocaine treatment could ameliorate the behavioral effects after the amputation procedure, it did not accelerate the behavior recovery process; instead, it caused the fish to display some slight side effects.

Abstract

The fin is known to play an important role in swimming for many adult fish, including zebrafish. Zebrafish fins consist of paired pectoral and pelvic with unpaired dorsal, anal, and caudal tail fins with specific functions in fish locomotion. However, there was no study comparing the behavior effects caused by the absence of each fin. We amputated each fin of zebrafish and evaluated their behavior performance in the 3D locomotion test using fractal dimension and entropy analyses. Afterward, the behavior recovery after the tail fin amputation was also evaluated, together with the fin regeneration process to study their relationship. Finally, we conducted a further study to confirm whether the observed behavior alterations were from pain elicited by fin amputation procedure or not by using lidocaine, a pain-relieving drug. Amputation in the caudal fin resulted in the most pronounced behavior alterations, especially in their movement complexity. Furthermore, we also found that their behavior was fully recovered before the caudal fin was fully regenerated, indicating that these behavioral changes were not majorly due to a mechanical change in tail length; instead, they may come from pain elicited from the fin amputation, since treatment with lidocaine could ameliorate the behavioral effects after the amputation procedure. However, lidocaine did not accelerate the behavior recovery process; instead, it caused the fishes to display some slight side effects. This study highlights the potential moderate severity of fin amputation in zebrafish and the importance of analgesia usage. However, side effects may occur and need to be considered since fin amputation is routinely conducted for various research, especially genomic screening.

Effects of long-term and low-concentration exposures of benzene and formaldehyde on mortality of Drosophila melanogaster

Single-chemical thresholds cannot comprehensively evaluate the risk of chemical mixture exposure in indoor air. Moreover, a large number of researches have focused on short-term and high-concentration co-exposure scenarios related to different species, based on diverse endpoints, which hampers the application and improvement of existing risk evaluation models of chemical mixture exposures. More importantly, current risk evaluation models are not user-friendly for construction practitioners who do not have sufficient toxicological knowledge. Therefore, in this study, an inhalation experiment system and a hazard index (HI) were developed to investigate the risks associated with low-concentration and long-term inhalation exposure scenarios of formaldehyde and benzene, individually and combined, based on Drosophila melanogaster mortality. The results showed that the system exhibited good reproducibility in providing stable exposure concentrations during D. melanogaster life cycle. Furthermore, in a range of experimental concentrations, the interaction between formaldehyde and benzene was additive or synergistic, which was concentration- and ratio-dependent. This study is of great significance in harmonising and providing toxicity data under long-term and low-concentration exposure scenarios, which is beneficial for establishing a new user-friendly risk evaluation model for indoor chemical mixture exposures. It should be noted that the proposed HI value could indicate the hazard degrees of long-term inhalation exposures of formaldehyde and benzene, individually and combined, to D. melanogaster. However, the applicability of this index requires further experiments to evaluate the exposure risks of other volatile organic compounds (VOCs) to D. melanogaster.

Permutation Entropy as a Universal Disorder Criterion: How Disorders at Different Scale Levels Are Manifestations of the Same Underlying Principle

What do bacteria, cells, organs, people, and social communities have in common? At first sight, perhaps not much. They involve totally different agents and scale levels of observation. On second thought, however, perhaps they share everything. A growing body of literature suggests that living systems at different scale levels of observation follow the same architectural principles and process information in similar ways. Moreover, such systems appear to respond in similar ways to rising levels of stress, especially when stress levels approach near-lethal levels. To explain such communalities, we argue that all organisms (including humans) can be modeled as hierarchical Bayesian controls systems that are governed by the same biophysical principles. Such systems show generic changes when taxed beyond their ability to correct for environmental disturbances. Without exception, stressed organisms show rising levels of 'disorder' (randomness, unpredictability) in internal message passing and overt behavior. We argue that such changes can be explained by a collapse of allostatic (high-level integrative) control, which normally synchronizes activity of the various components of a living system to produce order. The selective overload and cascading failure of highly connected (hub) nodes flattens hierarchical control, producing maladaptive behavior. Thus, we present a theory according to which organic concepts such as stress, a loss of control, disorder, disease, and death can be operationalized in biophysical terms that apply to all scale levels of organization. Given the presumed universality of this mechanism, 'losing control' appears to involve the same process anywhere, whether involving bacteria succumbing to an antibiotic agent, people suffering from physical or mental disorders, or social systems slipping into warfare. On a practical note, measures of disorder may serve as early warning signs of system failure even when catastrophic failure is still some distance away.

Spatial Movement Patterns and Local Co-Occurrence of Nutria Individuals in Association with Habitats Using Geo-Self-Organizing Map (Geo-SOM)

Nutrias (Myocastor coypus) were imported to South Korea for farming in 1985; individuals escaped captivity and established wild populations in natural ecosystems in the late 1990s. Numerous studies have focused on their monitoring and management; however, information on the continuous movement of individuals is not available. In this study, telemetry data from field conditions were used to identify the nearest-neighbor distances of individuals in association with environmental factors, including plant type, land cover, and biological parameters. The minimum nearest-neighbor distances for the different sexes were, overall, according to the minimum distances for the same sex. Local co-occurrences of individuals, either of the same or different sex, were seasonal. Tall grasslands, followed by herbaceous vegetation, were associated with the co-occurrence of different sexes. Conversely, floating-leaved hydrophytes, followed by xeric herbaceous vegetation, were correlated with the co-occurrence of the same sex. Local female-male co-occurrences were negatively associated with male-male co-occurrences but not with female-female co-occurrences, suggesting male dominance in group formations. Movement and co-occurrence information extracted using Geo-self-organizing maps furthers our understanding of population dispersal and helps formulate management strategies for nutria populations.

Effects of air pollution exposure on social behavior: a synthesis and call for research

BACKGROUND

There is a growing literature from both epidemiologic and experimental animal studies suggesting that exposure to air pollution can lead to neurodevelopmental and neuropsychiatric disorders. Here, we suggest that effects of air pollutant exposure on the brain may be even broader, with the potential to affect social decision-making in general.

METHODS

We discuss how the neurobiological substrates of social behavior are vulnerable to air pollution, then briefly present studies that examine the effects of air pollutant exposure on social behavior-related outcomes.

RESULTS

Few experimental studies have investigated the effects of air pollution on social behavior and those that have focus on standard laboratory tests in rodent model systems. Nonetheless, there is sufficient evidence to support a critical need for more research.

CONCLUSION

For future research, we suggest a comparative approach that utilizes diverse model systems to probe the effects of air pollution on a wider range of social behaviors, brain regions, and neurochemical pathways.

Using a safe and effective fixative to improve the immunofluorescence staining of bacteria

The emerging and development of green chemistry has once again drawn the researchers' attention to eliminating the use and generation of hazardous materials. Here we report the use of a safe and effective fixative, chlorine dioxide (ClO₂), instead of traditional hazardous fixatives for the cross-linking of cellular proteins to improve immunofluorescence staining of bacteria. The concentration of ClO₂needed for 100% fixation is 50μg ml^-1, which is much lower than that of traditional fixatives (1000-10000μg ml^-1). The ClO₂mediated cross-linking can preserve the integrity of bacterial cells and prevent cell loss through lysis. Meanwhile, lysozyme can permeabilize the bacterial cells, allowing the labelled antibodies to diffuse to their intracellular target molecules. By usingE. coliO157:H7/RP4 as a gram-negative bacteria model, immunofluorescence staining assays for both intracellular protein and surface polysaccharide were carried out to investigate the effect of ClO₂fixation on the staining. The results demonstrated that ClO₂fixation could prevent the target antigens from cracking off the bacteria without damage on the interaction between the antibodies and antigens (either for polysaccharide or protein). As a safe and effective fixative, ClO₂has potential practical applications in immunofluorescence staining and fluorescencein situhybridization for single bacteria/cell analysis.

Fungal compound 1-octen-3-ol induces mitochondrial morphological alterations and respiration dysfunctions in Drosophila melanogaster

Fungal volatile organic compounds (VOCs) comprise a group of compounds commonly found in damp or water-damaged indoor places affecting air quality. Indoor fungal pollution is a severe threat to human health, contributing to the onset of allergic diseases. The compound 1-octen-3-ol, known as "mushroom alcohol", is the most abundant VOC and confers the characteristic mold odor. Exposure to 1-octen-3-ol induces inflammatory markers and episodes of allergic rhinitis and conjunctivitis; however, the effects of this compound towards mitochondria are fairly known. The present study aimed to evaluate the effects of 1-octen-3-ol on inflammatory targets and on mitochondrial morphology and bioenergetic rate in D. melanogaster. Drosophilas were exposed by inhalation to 2.5 μL/L and 5 μL/L of 1-octen-3-ol for 24 h. Observation showed a decreasing in the survival and locomotor ability of flies. Superoxide dismutase (SOD) activity was induced whereas Catalase (CAT) activity was inhibited. Analysis of the mitochondria respiration, detected inhibition of complex I and II in the electron transport chain and a decreased bioenergetic rate. Electronic microscopy provided morphological insights of the mitochondrial status in which a disarrangement in mitochondrial cristae profile was observed. 1-Octen-3-ol induced increased activity of caspase 3/7 and ERK phosphorylation. The mRNA relative steady-state levels of p38^MAPK and JNK were down-regulated, whereas NF-κB and p53 were up-regulated. In parallel, nitrite levels were induced in relation to the non-exposed group. These findings point to the mitochondria as a crucial target for the toxicity of 1-octen-3-ol in parallel with activation of pro-inflammatory factors and apoptotic signaling pathway cascade.

Drosophila melanogaster as model organism for monitoring and analyzing genotoxicity associated with city air pollution

This study evaluated the genotoxic potential of atmospheric pollution associated with urbanization using the model organism Drosophila melanogaster and the Comet assay with hemolymph cells. Larvae were exposed to atmospheric compounds in an urban and a rural area in the municipality of Vitória de Santo Antão, Pernambuco, Brazil, for 6 days (from the embryo stage to the third larval stage) in April 2015 and April 2017. The results were compared to a negative environmental control group exposed to a preserved area (Catimbau National Park) and to a negative control exposed to the laboratory room conditions. The Comet assay demonstrated significant genetic damage in the organisms exposed to the urban area compared with those exposed to the rural area and negative control groups. The evidences were supported by particulate matter analysis showing higher photopeaks of chemical elements such as aluminum, silicon, sulfur, potassium, calcium, titanium, and iron, associated to road dust fraction in urban environment. Once again, the results confirm D. melanogaster an ideal bioindicator organism to monitor genotoxic hazard associated with atmospheric pollution.

Changes in gene expression in chronic allergy mouse model exposed to natural environmental PM2.5-rich ambient air pollution

Particulate matter (PM) air pollution has been associated with an increase in the incidence of chronic allergic diseases; however, the mechanisms underlying the effect of exposure to natural ambient air pollution in chronic allergic diseases have not been fully elucidated. In the present study, we aimed to investigate the cellular responses induced by exposure to natural ambient air pollution, employing a mouse model of chronic allergy. The results indicated that exposure to ambient air pollution significantly increased the number of eosinophils in the nasal mucosa. The modulation of gene expression profile identified a set of regulated genes, and the Triggering Receptor Expressed on Myeloid cells1(TREM1) signaling canonical pathway was increased after exposure to ambient air pollution. In vitro, PM2.5 increased Nucleotide-binding oligomerization domain-containing protein 1 (Nod1) and nuclear factor (NF)-κB signaling pathway activation in A549 and HEK293 cell cultures. These results suggest a novel mechanism by which, PM2.5 in ambient air pollution may stimulate the innate immune system through the PM2.5-Nod1-NF-κB axis in chronic allergic disease.

Implementation of Fractal Dimension and Self-Organizing Map to Detect Toxic Effects of Toluene on Movement Tracks of Daphnia magna

Movement behaviors of an indicator species, Daphnia magna, in response to contaminants have been implemented to monitor environmental disturbances. Complexity in movement tracks of Daphnia magna was characterized by use of fractal dimension and self-organizing map. The individual movement tracks of D. magna were continuously recorded for 24 hours before and after treatments with toluene at the concentration of 10 mg/L, respectively. The general complexity in movement tracks (10 minutes) was characterized by fractal dimension. Results showed that average fractal dimension of movement tracks was decreased from 1.62 to 1.22 after treatments. The instantaneous movement parameters of movement segments in 5 s were input into the self-organizing map to investigate the swimming pattern changes under stresses of toluene. Abnormal behaviors of D. magna are more frequently observed after treatments than before treatments. Computational methods in ecological informatics could be utilized to obtain the useful information in behavioral data of D. magna and would be further applied as an in situ monitoring tool in water environment.