Investigation of mechanisms of toxicity and exclusion by transporters of the preservatives triclosan and propylparaben using batteries of Schizosaccharomyces pombe strains

A strategy for the investigation of toxic mechanisms and protection by efflux pumps using Schizosaccharomyces pombe strains: Application to rotenone

Effects not related with the inhibition of complex I of the mitochondrial electron transport chain are studied in S. pombe, which lacks it. This study aims: First, the use of a strategy with S. pombe strains to investigate the toxicity, mechanisms of action, interactions and detoxication by efflux pumps. Second, to investigate the mechanisms of toxic action of rotenone. In the dose-response assessment, the yeast presented a good correlation with the toxicity in Daphnia magna for 15 chemicals. In the mechanistic study, the mph1Δ strain presented marked specificity to the interaction with microtubules by carbendazim. DNA damage caused by hydroxyurea, an inhibitor of deoxynucleotide synthesis, was identified with marked specificity with the rad3Δ strain. The sty1Δ strain was very sensitive to the oxidative and osmotic stress induced by hydrogen peroxide and potassium chloride, respectively, being more sensitive to oxidative stress than the pap1Δ strain. The protection by exclusion pumps was also evaluated. Rotenone presented low toxicity in S. pombe due to the lack of its main target, and the marked protection by the exclusion transporters Bfr1, Pmd1, Caf5 and Mfs1. Marked cellular stress was detected. Finally, the toxicity of rotenone could be potentiated by the fungicide carbendazim and the antimetabolite hydroxyurea. In conclusion, the use of S. pombe strains is a valid strategy to: a) assess global toxicity; b) investigate the main mechanisms of toxic action, particularly spindle and DNA interferences, and osmotic and oxidative stress not related to complex I inhibition; c) explore the detoxication by efflux pumps; and d) evaluate possible chemical interactions. Therefore, it should be useful for the investigation of adverse outcome pathways.

Characterizing temporal variability and repeatability of dose-dependent functional genomics approach for evaluating triclosan toxification

Dose-dependent functional genomics approach has shown great advantage in identifying the molecular initiating event (MIE) of chemical toxification and yielding point of departure (POD) at genome-wide scale. However, POD variability and repeatability derived from experimental design (settings of dose, replicate number, and exposure time) has not been fully determined. In this work, we evaluated POD profiles perturbed by triclosan (TCS) using dose-dependent functional genomics approach in Saccharomyces cerevisiae at multiple time points (9 h, 24 h and 48 h). The full dataset (total 9 concentrations with 6 replicates per treatment) at 9 h was subsampled 484 times to generate subsets of 4 dose groups (Dose A - Dose D with varied concentration range and spacing) and 5 replicate numbers (2 reps - 6 reps). Firstly, given the accuracy of POD and the experimental cost, the POD profiles from 484 subsampled datasets demonstrated that the Dose C group (space narrow at high concentrations and wide dose range) with three replicates was best choice at both gene and pathway levels. Secondly, the variability of POD was found to be relatively robustness and stability across different experimental designs, but POD was more dependent on the dose range and interval than the number of replicates. Thirdly, MIE of TCS toxification was identified to be the glycerophospholipid metabolism pathway at all-time points, supporting the ability of our approach to accurately recognize MIE of chemical toxification at both short- and long-term exposure. Finally, we identified and validated 13 key mutant strains involved in MIE of TCS toxification, which could serve as biomarkers for TCS exposure. Taken together, our work evaluated the repeatability of dose-dependent functional genomics approach and the variability of POD and MIE of TCS toxification, which will benefit the experimental design for future dose-dependent functional genomics study.

Antifungal activity of boric acid, triclosan and zinc oxide against different clinically relevant Candida species

BACKGROUND

The genus Candida includes about 200 different species, but only a few are able to produce disease in humans. The species responsible for the highest proportion of human infections is Candida albicans. However, in the last two decades there has been an increase in the proportion of infections caused by other Candida species, including C. glabrata (Nakaseomyces glabrata), C. parapsilosis, C. tropicalis, C. krusei (Pichia kudriavzevi) and more recently C. auris. Decolonisation of patients has been used as an infection control strategy for bacterial infections, but information about decolonisation products used in clinical practice for Candida and other fungal pathogens is limited. Compounds with antimicrobial activity, such as triclosan (TR), boric acid (BA) and zinc oxide (ZO), are mainly used in personal care products. These products can be used for long periods of time without an abrasive skin effect and are a possible alternative for patient decolonisation in healthcare settings.

OBJECTIVE

The aim of this study was to evaluate the antifungal activity of boric acid (BA), triclosan (TR) and zinc oxide (ZO), individually and combined, against clinically relevant Candida species.

MATERIALS AND METHODS

Compounds to be screened for antifungal activity were evaluated at different concentrations, alone, and combined, using a well diffusion assay. The statistical evaluation was performed using analysis of variance (ANOVA) and a post hoc analysis using the multiple comparisons method.

RESULTS

Individually, BA and TR showed antifungal activity against all Candida species evaluated but ZO did not show any antifungal activity. Mixtures of BA [5%]-TR [0.2%]; BA [5%]-TR [0.3%]; BA [5%]-TR [0.2%]-ZO [8.6%]; and BA [5%]-TR [0.2%]-ZO [25%] yielded the highest antifungal activity. An increased antifungal effect was observed in some mixtures when compared with individual compounds.

CONCLUSIONS

We demonstrated antifungal activity of BA and TR against multiple Candida species, including against a clade of the emerging healthcare-associated pathogen C. auris. Additionally, this study shows enhancement of the antifungal effect and no antagonism among the mixtures of these compounds. Further research is needed to determine whether these compounds can reduce the burden of Candida on skin.

Ascorbic acid mitigates cadmium-induced stress, and contributes to ionome stabilization in fission yeast

Cadmium is a highly toxic environmental pollutant which through enhancement of reactive oxygen species (ROS) production triggers oxidative stress to the cell. Cell growth, a fundamental feature of all living organisms is closely connected to the cell shape and homeostasis. As these processes largely depend on cell fitness status and environmental conditions we have analyzed, the impact of different cadmium concentrations and the effect of ascorbic acid (ascorbate, AsA) supplementation on cell growth parameters, cell morphology, and ionome balance maintenance in Schizosaccharomyces pombe. We show that cadmium causes membrane lipid peroxidation resulting in cell shape alterations leading to growth impairment and through mineral elements disequilibrium affects ionome homeostasis in a dose- and time-dependent manner. AsA recognized as one of the most prominent antioxidants, when overdosed, displays considerable pro-oxidant activity, though precise dosing of its supplementation is desired. We present here that AsA under efficacious concentration largely improves cell condition affected by cadmium. Although, we clearly demonstrate the beneficial feature of AsA, further studies are required to fully understand its protective nature on cell homeostasis maintenance under conditions of the broken environment.