Genomics analysis of hexanoic acid exposure in Drosophila species.

Drosophila sechellia is a dietary specialist endemic to the Seychelles islands that has evolved to consume the fruit of Morinda citrifolia. When ripe, the fruit of M. citrifolia contains octanoic acid and hexanoic acid, two medium-chain fatty acid volatiles that deter and are toxic to generalist insects. Drosophila sechellia has evolved resistance to these volatiles allowing it to feed almost exclusively on this host plant. The genetic basis of octanoic acid resistance has been the focus of multiple recent studies, but the mechanisms that govern hexanoic acid resistance in D. sechellia remain unknown. To understand how D. sechellia has evolved to specialize on M. citrifolia fruit and avoid the toxic effects of hexanoic acid, we exposed adult D. sechellia, D. melanogaster and D. simulans to hexanoic acid and performed RNA sequencing comparing their transcriptional responses to identify D. sechellia specific responses. Our analysis identified many more genes responding transcriptionally to hexanoic acid in the susceptible generalist species than in the specialist D. sechellia. Interrogation of the sets of differentially expressed genes showed that generalists regulated the expression of many genes involved in metabolism and detoxification whereas the specialist primarily downregulated genes involved in the innate immunity. Using these data, we have identified interesting candidate genes that may be critically important in aspects of adaptation to their food source that contains high concentrations of HA. Understanding how gene expression evolves during dietary specialization is crucial for our understanding of how ecological communities are built and how evolution shapes trophic interactions.

Integrating in vitro chemical transplacental passage into a generic PBK model: A QIVIVE approach.

With the increasing application of cell culture models as primary tools for predicting chemical safety, the quantitative extrapolation of the effective dose from in vitro to in vivo (QIVIVE) is of increasing importance. For developmental toxicity this requires scaling the in vitro observed dose-response characteristics to in vivo fetal exposure, while integrating maternal in vivo kinetics during pregnancy, in particular transplacental transfer. Here the transfer of substances across the placental barrier, has been studied using the in vitro BeWo cell assay and six embryotoxic compounds of different kinetic complexity. The BeWo assay results were incorporated in an existing generic Physiologically Based Kinetic (PBK) model which for this purpose was extended with rat pregnancy. Finally, as a "proof of principle", the BeWo PBK model was used to perform a QIVIVE based on developmental toxicity as observed in various different in vitro toxicity assays. The BeWo results illustrated different transport profiles of the chemicals across the BeWo monolayer, allocating the substances into two distinct groups: the 'quickly-transported' and the 'slowly-transported'. BeWo PBK exposure simulations during gestation were compared to experimentally measured maternal blood and fetal concentrations and a reverse dosimetry approach was applied to translate in vitro observed embryotoxicity into equivalent in vivo dose-response curves. This approach allowed for a direct comparison of the in vitro dose-response characteristics as observed in the Whole Embryo Culture (WEC), and the Embryonic Stem Cell test (cardiac:ESTc and neural:ESTn) with in vivo rat developmental toxicity data. Overall, the in vitro to in vivo comparisons suggest a promising future for the application of such QIVIVE methodologies for screening and prioritization purposes of developmental toxicants. Nevertheless, the clear need for further improvements is acknowledged for a wider application of the approach in chemical safety assessment.

Comprehensive multi-omics approaches reveal the hepatotoxic mechanism of perfluorohexanoic acid (PFHxA) in mice.

Perfluorohexanoic acid (PFHxA), one of the short-chain perfluoroalkyl acids (PFAAs), is considered as a substitute of perfluorooctane sulfonate (PFOS). This emerging organic pollutant is persistent and highly bioavailable to humans, raising concerns about its potential health risks. There are currently few researches on the toxicity of PFHxA. Liver has been suggested to be the main target of PFHxA toxicity, and the mechanism remains unclear. Herein, we investigated the transcriptomic, proteomic, and metabolomic landscape in PFHxA-exposed mice. Using these approaches, we identified several valuable biological processes involved in the process of liver injury, comprising fatty acid biosynthesis and degradation pathways, which might be induced by peroxisome proliferator-activated receptor (PPAR) signaling pathway. These processes further promoted oxidative stress and induced liver injury. Meanwhile, abnormalities in purine metabolism and glutathione metabolism were observed during the liver injury induced by PFHxA, indicating the production of oxidative stress. Finally, our present multi-omics studies provided new insights into the mechanisms involved in PFHxA-induced liver injury.

Comparison of zebrafish in vitro and in vivo developmental toxicity assessments of perfluoroalkyl acids (PFAAs).

Perfluoroalkyl acids (PFAAs) are persistent environmental contaminants that are associated with various adverse health outcomes. Perfluorooctanoic acid (PFOA) is one of the most prominently detected PFAAs in the environment, which is now replaced with shorter chain carbon compounds including perfluorohexanoic acid (PFHxA) and perfluorobutyric acid (PFBA). The aim of this study was to compare the toxicity of four PFAAs as a function of chain length and head group (carboxylate versus sulfonate) with in vitro and in vivo zebrafish assessments, which were subsequently compared to other cell and aquatic models. Mortality rate increased with chain length (PFOA > PFHxA ≫ PFBA) in both whole embryo/larvae and embryonic cell models. The sulfonate group enhanced toxicity with perfluorobutane sulfonate (PFBS) showing higher toxicity than PFBA and PFHxA in both larvae and cells. Toxicity trends were similar among different aquatic models, but sensitivities varied. Discrepancies with other zebrafish studies were confirmed to be associated with a lack of neutralization of acidic pH of dosing solutions in these other investigations, demonstrating the need for rigor in reporting pH of exposure solutions in all experiments. The zebrafish embryonic cell line was also found to be similar to most other cell lines regardless of exposure length. Overall, results agree with findings in other cell lines and organisms where longer chain length and sulfonate group increase toxicity, except in investigations not neutralizing the exposure solutions for these acidic compounds.

Antimicrobial activity of organic acids against Campylobacter spp. and development of combinations-A synergistic effect?

Contaminated poultry meat is considered to be the main source of human infection with Campylobacter spp., a pathogen that asymptomatically colonizes broiler chickens during fattening and contaminates carcasses during slaughter. To prevent or reduce the colonization of broiler flocks with Campylobacter spp., applying different organic acids, especially in combinations, via feed or drinking water seems to be a promising approach. However, only very few combinations of organic acids have been tested for their antibacterial efficacy against Campylobacter spp. Therefore, the in vitro susceptibility of 30 Campylobacter spp. isolates (20 C. jejuni and ten C. coli) to ten organic acids and ten combinations was determined. The testing of minimum inhibitory concentration (MIC) values was performed at pH 6.0 and 7.3 by using the broth microdilution method and included the following organic acids: Caprylic acid, sorbic acid, caproic acid, benzoic acid, ascorbic acid, propionic acid, acetic acid, formic acid, fumaric acid and tartaric acid and combinations thereof. The lowest MIC values were seen for caprylic acid (MIC range at pH 7.3: 0.5-2 mmol/L) and sorbic acid (MIC range at pH 7.3: 1-4 mmol/L). One to two dilution steps lower MIC values were determined at the lower pH value of 6.0. Furthermore, ten combinations consisting of three to five organic acids were developed. In addition to the tested antibacterial activity, other criteria were included such as approval as feed additives, reported synergistic effects and chemical properties. For nine of ten combinations, the MIC90 values of the organic acids decreased 1.25- to 241.5-fold compared to the MIC90 values for the individual substances. Furthermore, nine of ten combinations exhibited synergistic activities against two or more of the tested C. jejuni and C. coli isolates. A combination of caprylic acid, sorbic acid and caproic acid exhibited synergistic activities against the largest number of Campylobacter spp. isolates (six C. jejuni and four C. coli) with fractional inhibitory concentration (FIC) indices (∑FIC) ranging from 0.33 to 1.42. This study shows in vitro synergistic activities of different organic acids in combinations against the major Campylobacter species and could therefore be a promising basis for reducing Campylobacter spp. in vivo.

RIFM fragrance ingredient safety assessment, hexyl hexanoate, CAS Registry Number 6378-65-0.

The existing information supports the use of this material as described in this safety assessment. Hexyl hexanoate was evaluated for genotoxicity, repeated dose toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, and environmental safety. Data from read-across analog hexyl isobutyrate (CAS # 2349-07-7) show that hexyl hexanoate is not expected to be genotoxic. The repeated dose, reproductive, and local respiratory toxicity endpoints were evaluated using the threshold of toxicological concern (TTC) for a Cramer Class I material, and the exposure to hexyl hexanoate is below the TTC (0.03 mg/kg/day, 0.03 mg/kg/day, and 1.4 mg/day, respectively). The skin sensitization endpoint was completed using the dermal sensitization threshold (DST) for non-reactive materials (900 µg/cm2); exposure is below the DST. The phototoxicity/photoallergenicity endpoints were evaluated based on ultraviolet (UV) spectra; hexyl hexanoate is not expected to be phototoxic/photoallergenic. The environmental endpoints were evaluated; hexyl hexanoate was found not to be persistent, bioaccumulative, and toxic (PBT) as per the International Fragrance Association (IFRA) Environmental Standards, and its risk quotients, based on its current volume of use in Europe and North America (i.e., Predicted Environmental Concentration/Predicted No Effect Concentration [PEC/PNEC]), are <1.

RIFM fragrance ingredient safety assessment, ethyl (E)hex-3-enoate, CAS registry number 26553-46-8.

The existing information supports the use of this material as described in this safety assessment. Ethyl (E)hex-3-enoate was evaluated for genotoxicity, repeated dose toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, and environmental safety. Data from read-across analog methyl 3-hexenoate (CAS # 2396-78-3) show that ethyl (E)hex-3-enoate is not expected to be genotoxic. The repeated dose, reproductive, and local respiratory toxicity endpoints were evaluated using the Threshold of Toxicological Concern (TTC) for a Cramer Class I material, and the exposure to ethyl (E)hex-3-enoate is below the TTC (0.03 mg/kg/day, 0.03 mg/kg/day, and 1.4 mg/day, respectively). The skin sensitization endpoint was completed using Dermal Sensitization Threshold (DST) for non-reactive materials (900 µg/cm2); exposure is below the DST. The phototoxicity/photoallergenicity endpoints were evaluated based on ultraviolet (UV) spectra; ethyl (E)hex-3-enoate is not expected to be phototoxic/photoallergenic. The environmental endpoints were evaluated; ethyl (E)hex-3-enoate was found not to be persistent, bioaccumulative, and toxic (PBT) as per the International Fragrance Association (IFRA) Environmental Standards, and its risk quotients, based on its current Volume of Use in Europe and North America (i.e., Predicted Environmental Concentration/Predicted No Effect Concentration [PEC/PNEC]), are <1.

RIFM fragrance ingredient safety assessment, 4-methylpentanoic acid, CAS Registry Number 646-07-1.

The existing information supports the use of this material as described in this safety assessment. 4-Methylpentanoic acid was evaluated for genotoxicity, repeated dose toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, and environmental safety. Data from read-across analog 2-ethylbutyric acid (CAS # 88-09-5) show that 4-methylpentanoic acid is not expected to be genotoxic and provide a calculated margin of exposure (MOE) > 100 for the repeated dose toxicity and reproductive toxicity endpoints. The skin sensitization endpoint was completed using the dermal sensitization threshold (DST) for non-reactive materials (900 µg/cm2); exposure is below the DST. The phototoxicity/photoallergenicity endpoints were evaluated based on ultraviolet (UV) spectra; 4-methylpentanoic acid is not expected to be phototoxic/photoallergenic. The local respiratory toxicity endpoint was evaluated using the threshold of toxicological concern (TTC) for a Cramer Class I material, and the exposure to 4-methylpentanoic acid is below the TTC (1.4 mg/day). The environmental endpoints were evaluated; 4-methylpentanoic acid was found not to be persistent, bioaccumulative, and toxic (PBT) as per the International Fragrance Association (IFRA) Environmental Standards, and its risk quotients, based on its current volume of use in Europe and North America (i.e., Predicted Environmental Concentration/Predicted No Effect Concentration [PEC/PNEC]), are <1.

Toxicokinetics of perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) in male and female Hsd:Sprague dawley SD rats following intravenous or gavage administration.

Poly- and perfluorinated alkyl substances (PFAS) are environmentally persistent chemicals associated with many adverse health outcomes. The National Toxicology Program evaluated the toxicokinetics (TK) of several PFAS to provide context for toxicologic findings.Plasma TK parameters and tissue (liver, kidney, brain) concentrations are reported for perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA) or perfluorodecanoic acid (PFDA) after single-dose administration in male and female Hsd:Sprague-Dawley® (SD) rats.Generally, longer Tmax and elimination half-lives, and slower clearance f, were correlated with longer chain length. Male rats administered PFOA had a prolonged half-life compared to females (215 h vs. 2.75), while females had faster clearance and smaller plasma area under the curve (AUC). Females administered PFHxA had a shorter half-life (2 h vs. 9) than males and faster clearance with a smaller plasma AUC, although this was less pronounced than PFOA. There was no sex difference in PFDA half-life. Female rats administered PFDA had a higher plasma AUC/dose than males, and a slower clearance. PFDA had the highest levels in the liver of the PFAS evaluated.Profiling the toxicokinetics of these PFAS allows for comparison among subclasses, and more direct translation of rodent toxicity to human populations.

Comparisons of tissue distributions and health risks of perfluoroalkyl acids (PFAAs) in two fish species with different trophic levels from Lake Chaohu, China.

Perfluoroalkyl acids (PFAAs) are a type of persistent organic pollutants that are widely distributed in multiple environmental media and organisms and have a teratogenic effect on and toxicity to animals and humans. The residual levels of seventeen PFAAs in the tissues of two regular consumption fish species, Culter erythropterus and Aristichthys nobilis in Lake Chaohu were measured by a high-performance liquid chromatograph - mass spectrometer (HPLC-MS). The distributions of PFAAs and the effect of the lipid contents were analyzed, and the health risks of typical PFAAs were evaluated. The results showed that perfluorohexanoic acid (PFHxA) was the predominant contaminant (80.50 ±â€¯58.31 ng/g and 19.17 ±â€¯12.57 ng/g wet weight, ww), followed by perfluorooctanesulfonic acid (PFOS) (55.02 ±â€¯34.82 and 14.79 ±â€¯6.24 ng/g, ww) in both fish. The level of total PFAAs was the highest in the liver tissues of Culter erythropterus (359.87 ng/g, ww) and the lowest in the kidney tissues in A. nobilis (10.06 ng/g, ww). Due to the higher trophic level of C. erythropteru, the total PFAA concentrations were significantly higher in all tissues than those in A. nobilis. Liver muscle ratio of C. erythropteru was the highest, indicating the most accumulation in the liver. The concentrations of PFAAs in fish tissues were influenced by the lipid content, resulting in a difference between the lipid-normalized concentrations and the wet weight concentrations of the PFAAs. The non-carcinogenic risks of PFOS were higher than those of PFOA through the ingestion of C. erythropterus and A. nobilis. Both the carcinogenic and non-carcinogenic risks of C. erythropterus were greater than those of A. nobilis, and fish tissue intake could cause an increasing of risks up to 60%, indicating that long-term and large amount ingestion of carnivorous fish and related tissues with higher trophic level, such as C. erythropterus should be avoided.

In vitro and in silico modeling of perfluoroalkyl substances mixture toxicity in an amphibian fibroblast cell line.

Poly and perfluoroalkyl substances (PFAS) are a large group of emerging organic pollutants that can persist in the environment and bioaccumulate in biota. They are found in complex mixtures, and although the exact number of PFAS is unknown, it has been estimated to be in the thousands. The objective of this study was two-fold. First, we examined the cytotoxicity of PFAS singly and in binary mixtures using an amphibian fibroblast cell line. Second, we used this experimental data to develop quantitative structure-activity relationship (QSAR) models for single and binary mixtures. We tested the cytotoxicity of four common PFAS: perfluorooctane sulfonate (PFOS); perfluorooctanoic acid (PFOA); perfluorohexane sulfonate (PFHxS); and perfluorohexanoic acid (PFHxA). PFOS was the most toxic and PFHxA the least cytotoxic. Binary mixtures allowed for the construction of isobolograms to test for additivity, synergism, or antagonism. Using this data, QSAR modeling was used for predicting the toxicity of 24 single and 1380 binary mixtures (theoretically generated). Overall, our experimental and modeling results showed that mixtures were approximately additive, with the exception of PFOS and PFOA, which were found to be weakly synergistic. This data shows that certain mixtures of PFAS may have increased toxicity potential above what the simple sum of PFAS concentrations would suggest. More studies are needed that test the toxicity of PFAS mixtures.