Biological and chemical studies on aryl hydrocarbon receptor induction by the p53 inhibitor pifithrin-α and its condensation product pifithrin-β

Alphaherpesvirus manipulates retinoic acid metabolism for optimal replication

Retinoic acid (RA), derived from retinol (ROL), is integral to cell growth, differentiation, and organogenesis. It is known that RA can inhibit herpes simplex virus (HSV) replication, but the interactions between alphaherpesviruses and RA metabolism are unclear. Our present study revealed that alphaherpesvirus (HSV-1 and Pseudorabies virus, PRV) infections suppressed RA synthesis from ROL by activating P53, which increased retinol reductase 3 (DHRS3) expression-an enzyme that converts retinaldehyde back to ROL. This process depended on the virus-triggered DNA damage response, the degradation of class I histone deacetylases, and the subsequent hyperacetylation of histones H3 and H4. Counteracting DHRS3 or P53 enabled higher RA synthesis and reduced viral growth. RA enhanced antiviral defenses by promoting ABCA1- and ABCG1-mediated lipid efflux. Treatment with the retinoic acid receptor (RAR) agonist palovarotene protected mice from HSV-1 infection, thus providing a potential therapeutic strategy against viral infections.

SQLE Knockdown inhibits bladder cancer progression by regulating the PTEN/AKT/GSK3β signaling pathway through P53

Bladder cancer (BCa) is one of the most common malignancies worldwide. However, the lack of accurate and effective targeted drugs has become a major problem in current clinical treatment of BCa. Studies have demonstrated that squalene epoxidase (SQLE), as a key rate-limiting enzyme in cholesterol biosynthesis, is involved in cancer development. In this study, our analysis of The Cancer Genome Atlas, The Genotype-Tissue Expression, and Gene Expression Omnibus databases showed that SQLE expression was significantly higher in cancer tissues than it was in adjacent normal tissues, and BCa tissues with a high SQLE expression displayed a poor prognosis. We then confirmed this result in qRT-PCR and immunohistochemical staining experiments, and our vitro studies demonstrated that SQLE knockdown inhibited tumor cell proliferation and metastasis through the PTEN/AKT/GSK3β signaling pathway. By means of rescue experiments, we proved that that P53 is a key molecule in SQLE-mediated regulation of the PTEN/AKT/GSK3β signaling pathway. Simultaneously, we verified the above findings through a tumorigenesis experiment in nude mice. In conclusion, our study shows that SQLE promotes BCa growth through the P53/PTEN/AKT/GSK3β axis, which may serve as a therapeutic biological target for BCa.

mTORC1 promotes mineralization via p53 pathway

The objectives of our study were to investigate the roles of mTORC1 in odontoblast proliferation and mineralization and to determine the mechanism by which mTORC1 regulates odontoblast mineralization. In vitro, MDPC23 cells were treated with rapamycin (10 nmol/L) and transfected with a lentivirus for short hairpin (shRNA)-mediated silencing of the tuberous sclerosis complex (shTSC1) to inhibit and activate mTORC1, respectively. CCK8 assays, flow cytometry, Alizarin red S staining, ALP staining, qRT-PCR, and western blot analysis were performed. TSC1-conditional knockout (DMP1-Cre⁺ ; TSC1^f/f , hereafter CKO) mice and littermate control (DMP1-Cre^- ; TSC1^f/f , hereafter WT) mice were generated. H&E staining, immunofluorescence, and micro-CT analysis were performed. Transcriptome sequencing analysis was used to screen the mechanism of this process. mTORC1 inactivation decreased the cell proliferation. The qRT-PCR and western blot results showed that mineralization-related genes and proteins were downregulated in mTORC1-inactivated cells. Moreover, mTORC1 overactivation promoted cell proliferation and mineralization-related gene and protein expression. In vivo, the micro-CT results showed that DV/TV and dentin thickness were higher in CKO mice than in controls and H&E staining showed the same results. Mineralization-related proteins expression was upregulated. Transcriptome sequencing analysis revealed that p53 pathway-associated genes were differentially expressed in TSC1-deficient cells. By inhibiting p53 alone or both mTORC1 and p53 with rapamycin and a p53 inhibitor, we elucidated that p53 acts downstream of mTORC1 and that mTORC1 thereby promotes odontoblast mineralization. Taken together, our findings demonstrate that the role of mTORC1 in odontoblast proliferation and mineralization, and confirm that mTORC1 upregulates odontoblast mineralization via the p53 pathway.

Pifithrin-α alters p53 post-translational modifications pattern and differentially inhibits p53 target genes

Pifithrin-α (PFT-α) is a small molecule which has been widely used as a specific inhibitor of p53 transcription activity. However, its molecular mechanism of action remains unclear. PFT-α has also been described to display potent p53-independent activity in cells. In this study, we addressed the mechanism of action of PFT-α. We found that PFT-α failed to prevent the effects of Mdm2 inhibitor Nutlin-3 on cell cycle and apoptosis in several cancer cell lines. However, PFT-α rescued normal primary fibroblasts from growth inhibition by Nutlin-3. PFT-α displayed a very limited effect on p53-dependent transcription upon its activation by Nutlin-3. Moreover, PFT-α inhibitory effect on transcription was highly dependent on the nature of the p53 target gene. PFT-α attenuated post-translational modifications of p53 without affecting total p53 protein level. Finally, we found that PFT-α can decrease the level of intracellular reactive oxygen species through activation of an aryl hydrocarbon receptor (AHR)-Nrf2 axis in a p53-independent manner. In conclusion, PFT-α inhibits only some aspects of p53 function, therefore it should be used with extreme caution to study p53-dependent processes.

Induction of EROD and BFCOD activities in tissues of barbel (Barbus callensis) from a water reservoir in Algeria

EROD and BFCOD activities were measured in liver and gills of barbel (Barbus callensis, a native North African species) captured at Beni Haroun lake, the most important water reservoir in Algeria. This lake receives wastewater from different origins. Thus, we assessed the level of pollution through the induction of detoxification activities in tissues of barbel, evaluating simultaneously the suitability of this species to be used as a sentinel. Fish were collected between March 2015 and January 2016 at three locations taking into account the pollution sources and accessibility. In liver, EROD and BFCOD showed the highest induction in October specially in the location of the dam that received pollutants. In gills, only EROD, but not BFCOD, activity was detected. Maximal EROD induction was noted in samples from January. Fish cell lines (RTG-2 and PLHC-1) were exposed to sediments extracts collected at Beni Haroun lake and enzyme activities (EROD and BFCOD, respectively) were measured. Sediment extracts did not induce BFCOD activity. The EROD induction observed in RTG-2 cells was in line with the results observed in fish tissues. Our results suggest that the lake is at risk from pollution and that Barbus callensis is a good sentinel species.

Self-assembly of pifithrin-α-loaded layered double hydroxide/chitosan nanohybrid composites as a drug delivery system for bone repair materials

The self-assembly of pifithrin-α-loaded layered double hydroxide/chitosan nanohybrid composites as a drug delivery system was demonstrated for the first time to improve the cytocompatibility and enhance the osteoinductivity for the treatment of bone defects.

Detection of effects caused by very low levels of contaminants in riverine sediments through a combination of chemical analysis, in vitro bioassays, and farmed fish as sentinel

Aquatic organisms are often exposed to mixtures of low levels of pollutants whose presence and effects can pass easily unnoticed if only traditional monitoring strategies are employed. The main aim of this work was to assess the presence and effects of trace levels of pollutants in a scarcely affected area through the combination of chemical and biological approaches. Sediments were collected along a river with little anthropogenic pressure and assayed for cytochrome P450 (Cyp1a)-dependent ethoxyresorufin-O-deethylase (EROD) activity with the rainbow trout gonadal cell line RTG-2. Chemical analyses were performed in these sediments using two-dimensional gas chromatography-time-of-flight mass spectrometry. Sediment samples induced EROD activity, and chemical analyses evidenced the presence of a wide variety of contaminants in the range of nanograms per gram of dry weight. Correlation analysis between EROD induction and chemical analyses data showed an r value of 0.840 (p < 0.05). In addition, fish from a fish farm located downstream of the sampling points exhibited high hepatic EROD levels as well as an induced expression of cyp1a and cyp3a. In conclusion, only an appropriate combination of biological and chemical techniques allowed the detection of the presence of trace levels of contaminants in a theoretically nonaffected river.

Effect of different river flow rates on biomarker responses in common carp (Cyprinus carpio)

The present study investigated effects of different river flow rates on basal activities of selected biomarkers and the occurrence of oxidative stress in the common carp (Cyprinus carpio). Juvenile carp were exposed to different river flow rates (5-120 cm/s) by caging for 3 weeks. After this period, one half of the fish were sacrificed and used for analysis. The other half received a single intraperitoneal injection of 3-methylcholanthrene (3-MC) and after 6 days were sacrificed and used for analysis. In order to investigate whether the physical activity of carp in the environment will influence the condition status of carp, following biomarkers were measured - activities of glutathione S-transferase (GST), catalase (CAT) and ethoxyresorufin-O-deethylase (EROD) and concentration of protein carbonyls (PC). The results showed that different flow rates significantly influenced biochemical biomarkers. The basal activity of GST did not change significantly after exposure to different river flow rates, whereas the activity of CAT increased with increasing river flow rates. The application of 3-MC caused significant increases in GST and CAT activities, but there were no difference between 3-MC control and 3-MC different flow rates. The occurrence of oxidative stress as a result of exposure to increased physical activity, i.e. increased river flow rates, was confirmed by measurement of PC levels - the level of PC increased with increasing river flow rates. Measurement of EROD basal activity showed that at lower river flow rates the EROD activity increased and at higher river flow rates decreased towards control levels demonstrating a close relationship between oxidative stress, PC levels and EROD activity. Obviously, biomarker responses in carp of different condition status can differ substantially. It can be concluded that flow rate may be an important factor in biomonitoring of rivers using biomarkers and since at different locations river water flow rate can vary significantly, the site selection is extremely important for proper design of river biomonitoring studies involving caging.

Chlorotriazines do not activate the aryl hydrocarbon receptor, the oestrogen receptor or the thyroid receptor in in vitro assays

Atrazine, prometryn, propazine and simazine are chlorotriazines that are commonly employed as herbicides. However, their use is a major cause of concern, due to their reported endocrine disrupting effects in different taxa. Data from studies on the molecular and cellular processes underlying the hormonal action of these substances are contradictory. The ability of these chlorotriazines and the atrazine metabolites, desethyl-s-chlorotriazine and desisopropyl-s-chlorotriazine, to trigger responses mediated by the oestrogen receptor (ER), aryl hydrocarbon receptor (AhR) and thyroid receptor (TR), was studied by using in vitro approaches. Transcriptional activation assays were applied to observe the activation of ER and TR. The induction of ethoxyresorufin-O-deethylase (EROD) activity in the RTG-2 cell line served as an indicator of AhR activation. No responses were found in any of the assays, with any of the six chlorotriazines tested. Our observations indicate that the chlorotriazines tested are unlikely to cause their endocrine effects via these receptors.

Use of fish farms to assess river contamination: combining biomarker responses, active biomonitoring, and chemical analysis

Here we addressed the possible effects of trace levels of contaminants on fish by means of a combination of biomarker responses, active biomonitoring (ABM), and chemical analysis. In environmental studies, cytochromes P4501A (Cyp1A) and Cyp3A and related enzyme activities (7-ethoxyresorufin-O-deethylase, EROD, and benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase, BFCOD, respectively) are commonly used as biomarkers for evidencing exposure to a variety of contaminants. In a rainbow trout (Oncorhynchus mykiss) fish farm that is routinely sampled to obtain references regarding normal levels of such enzyme activities in freshwater fish, we observed a strong and punctual increase in these activities at the end of 2011. In order to shed light on the causes of this induction, we transferred some fish to a fish farm with controlled conditions and examined them using an active biomonitoring (ABM) approach. EROD activity showed a decrease of 80% from the original values after 7 days in the control farm, while BFCOD activity was also reduced after 15 days. Although not significant, a decrease in cyp1A and cyp3A mRNA levels was also observed. To determine the presence of pollutants, water and sediment samples from the river feeding the fish farm were analyzed by two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOF-MS). The screening study reflected a weak inflow of pollutants in the monitored area, which is located far from any industrial activity or densely populated cities. Trace levels of polyaromatic hydrocarbons (PAHs) and personal care products (the polycyclic musk fragrance HHCB, and triclosan) were detected in sediments, at concentrations ranging from 0.01 to 38 ng/g dry weight, and in water from 4 to 441 ng/L. The approach followed in this study proved useful as a biomonitoring technique for the early detection of trace contaminants.

Endocrine disruption caused by oral administration of atrazine in European quail (Coturnix coturnix coturnix)

The widely used herbicide atrazine (ATZ) has been reported to exhibit reproductive toxicity in rats, fish and amphibians, with an avian LD(50) of 5000 mg/kg. In the present work, ATZ was administered as a single oral dose of 25 or 100 mg/kg to female European quail (Coturnix coturnix coturnix) at days 0, 5 and 10 of the experiment, being the animals sampled at days 15, 30 and 45. ATZ significantly increased the expression of hepatic estrogen receptor α (ERα) at both doses at day 30. An important increase was also observed in plasma 17β-estradiol (E2) concentrations. ATZ at 100 mg/kg increased the circulating concentration of vitellogenin (Vtg), but this effect was not related with an increase in hepatic Vtg mRNA levels. ATZ had no effect on the hepatic expression of both cytochrome P450 1A4 (CYP1A4) or the related biotransformation activity ethoxyresorufin-O-deethylase (EROD). These results led to the conclusion that ATZ provokes an estrogenic effect in sexually mature females of European quail. Further studies are necessary to establish the effect on sexual development or reproduction of female and male birds in the wild.

Differences in the induction of cyp1A and related genes in cultured rainbow trout Oncorhynchus mykiss. Additional considerations for the use of EROD activity as a biomarker

Two rainbow trout Oncorhynchus mykiss fish farms were repeatedly sampled in order to observe the variability of ethoxyresorufin-O-deethylase (EROD) activity and of related genes in the liver. Fish coming from fish farm A exhibited EROD levels that could be considered as basal according to the scientific literature, however, EROD activity in fish coming from fish farm B was significantly increased. This was accompanied by augmented aryl hydrocarbon receptor (ahr) and cytochrome P4501A (cyp1A) messenger RNA expression and reduced oestrogen receptor (er) and vitellogenin (vtg) transcription. Only sediment extracts from the entry channel of fish farm B induced EROD activity in O. mykiss cultured cells, however, this induction could not be explained by the levels of polyaromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) measured in the sediments. The results of this study point out that O. mykiss cultured in fish farms could be used as sentinels for indication of pollution. In this particular work, however, no conclusive evidence has been found for a relationship between the presence of PAHs and PCBs and the observed EROD induction.