The toxicological effects of nano titanium dioxide on target organs and mechanisms of toxicity

Nano-titanium dioxide (TiO2 NPs) is widely used for its extremely high stability, corrosion resistance, and photocatalytic properties and has penetrated into various fields of production and life. Assessing its toxicity to different organs should be a key part of preclinical toxicity assessment of TiO2 NPs, which is relatively incomprehensive yet. Therefore, this review focuses on the toxic effects of TiO2 NPs on various organs in mammals and biological mechanisms from different organs. The commonality of toxic effects on various target organs reflected in tissue structure damage and dysfunction, such as liver damage and dysfunction; pulmonary fibrosis; and renal impairment (including hematuria and nephritis); damage of brain tissue and neurons; alteration of intestinal villi; and weight loss. And effects on the reproductive system are affected by different sexes, including ovarian dysfunction, testicular development damage, and sperm viability reduction. We believe that the toxic mechanisms of TiO2 NPs in target organs have commonalities, such as oxidative stress, inflammatory responses, and organelle damage. However, different target organ toxicities also have their specificities. TiO2 NPs disturb the intestinal flora and cause undesirable changes in feces products. And in spleen are infiltration of neutrophils and lymphadenopathy and eventually immune deficiency. Although the toxic pathways are different, but there may be a close link between the different toxic pathways. In this article, the main manifestations of the toxic effects of titanium dioxide nanoparticles on major mammalian organs are reviewed, in order to provide basic data for their better application from a medical perspective.

Mixture Effects of Per- and Polyfluoroalkyl Substances on Embryonic and Larval Sheepshead Minnows (Cyprinodon variegatus)

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous and persistent environmental contaminants originating from many everyday products. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are two PFAS that are commonly found at high concentrations in aquatic environments. Both chemicals have previously been shown to be toxic to fish, as well as having complex and largely uncharacterized mixture effects. However, limited information is available on marine and estuarine species. In this study, embryonic and larval sheepshead minnows (Cyprinodon variegatus) were exposed to several PFAS mixtures to assess lethal and sublethal effects. PFOS alone was acutely toxic to larvae, with a 96 h LC50 of 1.97 mg/L (1.64-2.16). PFOS + PFOA resulted in a larval LC50 of 3.10 (2.62-3.79) mg/L, suggesting an antagonistic effect. These observations were supported by significant reductions in malondialdehyde (105% ± 3.25) and increases in reduced glutathione concentrations (43.8% ± 1.78) in PFOS + PFOA exposures compared to PFOS-only treatments, indicating reduced oxidative stress. While PFOA reduced PFOS-induced mortality (97.0% ± 3.03), perfluorohexanoic acid (PFHxA) and perfluorobutanoic acid (PFBA) did not. PFOS alone did not affect expression of peroxisome proliferator-activated receptor alpha (pparα) but significantly upregulated apolipoprotein A4 (apoa4) (112.4% ± 17.8), a downstream product of pparα, while none of the other individually tested PFAS affected apoa4 expression. These findings suggest that there are antagonistic interactions between PFOA and PFOS that may reduce mixture toxicity in larval sheepshead minnows through reduced oxidative stress. Elucidating mechanisms of toxicity and interactions between PFAS will aid environmental regulation and management of these ubiquitous pollutants.

A review of pulmonary neutrophilia and insights into the key role of neutrophils in particle-induced pathogenesis in the lung from animal studies of lunar dusts and other poorly soluble dust particles

The mechanisms of particle-induced pathogenesis in the lung remain poorly understood. Neutrophilic inflammation and oxidative stress in the lung are hallmarks of toxicity. Some investigators have postulated that oxidative stress from particle surface reactive oxygen species (psROS) on the dust produces the toxicopathology in the lungs of dust-exposed animals. This postulate was tested concurrently with the studies to elucidate the toxicity of lunar dust (LD), which is believed to contain psROS due to high-speed micrometeoroid bombardment that fractured and pulverized lunar surface regolith. Results from studies of rats intratracheally instilled (ITI) with three LDs (prepared from an Apollo-14 lunar regolith), which differed 14-fold in levels of psROS, and two toxicity reference dusts (TiO2 and quartz) indicated that psROS had no significant contribution to the dusts' toxicity in the lung. Reported here are results of further investigations by the LD toxicity study team on the toxicological role of oxidants in alveolar neutrophils that were harvested from rats in the 5-dust ITI study and from rats that were exposed to airborne LD for 4 weeks. The oxidants per neutrophils and all neutrophils increased with dose, exposure time and dust's cytotoxicity. The results suggest that alveolar neutrophils play a critical role in particle-induced injury and toxicity in the lung of dust-exposed animals. Based on these results, we propose an adverse outcome pathway (AOP) for particle-associated lung disease that centers on the crucial role of alveolar neutrophil-derived oxidant species. A critical review of the toxicology literature on particle exposure and lung disease further supports a neutrophil-centric mechanism in the pathogenesis of lung disease and may explain previously reported animal species differences in responses to poorly soluble particles. Key findings from the toxicology literature indicate that (1) after exposures to the same dust at the same amount, rats have more alveolar neutrophils than hamsters; hamsters clear more particles from their lungs, consequently contributing to fewer neutrophils and less severe lung lesions; (2) rats exposed to nano-sized TiO2 have more neutrophils and more severe lesions in their lungs than rats exposed to the same mass-concentration of micron-sized TiO2; nano-sized dust has a greater number of particles and a larger total particle-cell contact surface area than the same mass of micron-sized dust, which triggers more alveolar epithelial cells (AECs) to synthesize and release more cytokines that recruit a greater number of neutrophils leading to more severe lesions. Thus, we postulate that, during chronic dust exposure, particle-inflicted AECs persistently release cytokines, which recruit neutrophils and activate them to produce oxidants resulting in a prolonged continuous source of endogenous oxidative stress that leads to lung toxicity. This neutrophil-driven lung pathogenesis explains why dust exposure induces more severe lesions in rats than hamsters; why, on a mass-dose basis, nano-sized dusts are more toxic than the micron-sized dusts; why lung lesions progress with time; and why dose-response curves of particle toxicity exhibit a hockey stick like shape with a threshold. The neutrophil centric AOP for particle-induced lung disease has implications for risk assessment of human exposures to dust particles and environmental particulate matter.

Nanoparticles-induced potential toxicity on human health: Applications, toxicity mechanisms, and evaluation models

Nanoparticles (NPs) have become one of the most popular objects of scientific study during the past decades. However, despite wealth of study reports, still there is a gap, particularly in health toxicology studies, underlying mechanisms, and related evaluation models to deeply understanding the NPs risk effects. In this review, we first present a comprehensive landscape of the applications of NPs on health, especially addressing the role of NPs in medical diagnosis, therapy. Then, the toxicity of NPs on health systems is introduced. We describe in detail the effects of NPs on various systems, including respiratory, nervous, endocrine, immune, and reproductive systems, and the carcinogenicity of NPs. Furthermore, we unravels the underlying mechanisms of NPs including ROS accumulation, mitochondrial damage, inflammatory reaction, apoptosis, DNA damage, cell cycle, and epigenetic regulation. In addition, the classical study models such as cell lines and mice and the emerging models such as 3D organoids used for evaluating the toxicity or scientific study are both introduced. Overall, this review presents a critical summary and evaluation of the state of understanding of NPs, giving readers more better understanding of the NPs toxicology to remedy key gaps in knowledge and techniques.

Massive tramadol ingestion resulting in fatal brain injury - a pharmacokinetic study with discussion on the involved mechanisms of toxicity

BACKGROUND

Tramadol-attributed toxicity may involve opioid-like, serotoninergic, and noradrenergic mechanisms. We investigated the mechanisms of toxicity in a massive tramadol ingestion case by examining serial clinical, imaging, electroencephalography, pharmacokinetics, and genotyping data.

CASE REPORT

A 32-year-old female who presumably ingested 9000 mg sustained-release tramadol was found comatose without hypoglycemia, bradypnea, hypotension, marked hypoxemia or seizures. She developed eyelid myoclonus and non-reactive mydriasis. Electroencephalogram showed non-reactive encephalopathy. MRI showed extensive brain injury. Despite supportive care and ventricular derivation, brain death occurred on day 12.

METHODS

Plasma concentrations of tramadol and metabolites were measured using a liquid chromatography-tandem mass spectrometry assay. Genotyping for the presence of metabolizing cytochrome P450 (CYP) gene polymorphisms was performed.

RESULTS

Plasma concentrations of tramadol and metabolites were extremely high (∼70-fold the therapeutic concentrations) and slowly decreased during the first ∼146 h post-admission, possibly due to prolonged gastrointestinal absorption. Elimination half-lives were 2-3-fold longer than usual values. The patient was an intermediate CYP2D6 metabolizer with decreased CYP3A4 and CYP2B6 activities. Clinical and electroencephalographic data did not support the hypotheses of opioid or serotoninergic toxicity nor prolonged/repeated seizures. Based on serial imaging showing progressive extension of ischemic edema in the context of prolonged high plasma concentrations, we hypothesized a cerebral vasospasm as mechanism of injury.

CONCLUSION

Massive tramadol ingestion with prolonged high plasma concentrations can result in severe brain injury, possibly involving vasospasm.

Toxic Metal Species and 'Endogenous' Metalloproteins at the Blood-Organ Interface: Analytical and Bioinorganic Aspects

Globally, human exposure to environmental pollutants causes an estimated 9 million deaths per year and it could also be implicated in the etiology of diseases that do not appear to have a genetic origin. Accordingly, there is a need to gain information about the biomolecular mechanisms that causally link exposure to inorganic environmental pollutants with distinct adverse health effects. Although the analysis of blood plasma and red blood cell (RBC) cytosol can provide important biochemical information about these mechanisms, the inherent complexity of these biological matrices can make this a difficult task. In this perspective, we will examine the use of metalloentities that are present in plasma and RBC cytosol as potential exposure biomarkers to assess human exposure to inorganic pollutants. Our primary objective is to explore the principal bioinorganic processes that contribute to increased or decreased metalloprotein concentrations in plasma and/or RBC cytosol. Furthermore, we will also identify metabolites which can form in the bloodstream and contain essential as well as toxic metals for use as exposure biomarkers. While the latter metal species represent useful biomarkers for short-term exposure, endogenous plasma metalloproteins represent indicators to assess the long-term exposure of an individual to inorganic pollutants. Based on these considerations, the quantification of metalloentities in blood plasma and/or RBC cytosol is identified as a feasible research avenue to better understand the adverse health effects that are associated with chronic exposure of various human populations to inorganic pollutants. Exposure to these pollutants will likely increase as a consequence of technological advances, including the fast-growing applications of metal-based engineering nanomaterials.

[Effect of Tripterygium Glycosides Tablets on reproductive toxicity in male rats with Ⅱ type collagen induced arthritis]

The aim of this paper was to observe the toxic effect of Tripterygium Glycosides Tablets on the reproductive system of Ⅱ type collagen induced arthritis(CIA) male rats, and to explore the toxic mechanism preliminarily. Fifty SD rats were randomly divided into normal control group(Con), model group(CIA), Tripterygium Glycosides Tablets clinical equivalent dose groups of 1, 2, 4 times(9, 18, 36 mg·kg~(-1)), 10 rats in each group, and were given by gavage once a day for 42 days after the first immunization. The organ index of testis and epididymis were calculated on days 21 and 42. Histopathological and morphological changes of testis and epididymis were observed under optical microscope. Sperm count, sperm malformation rate and sperm kinetic parameters in epididymal tissues were observed by computer assisted sperm analysis(CASA). The concentration of testosterone(T), nitric oxide synthase(NOS) and aromatase(CYP19 A1) in serum were detected by ELISA. Immunohistochemistry was used to observe the expression of Bax and Bcl-2 related proteins in the apoptosis pathway of testis and epididymis. The results showed that, compared with Con group, CIA group significantly increased the rate of testicular spermatogenic tubule lesion and sperm malformation, decreased the average path speed, and no significant changes were observed in other groups. Tripterygium Glycosides Tablets at 4 times clinical equivalent dose can significantly reduce the testis index(P<0.01), each dose group can reduce the epididymis index(P<0.05). Each dose group of Tripterygium Glycosides Tablets could cause different degrees of damage to the testis and epididymis, the proportion of testicular histopathology lesions increased, the number of spermatogenic cells in the seminiferous tubules decreased, and so on. It could reduce the number of sperm, increase the rate of sperm deformity, make the parameters of sperm dynamics abnormal, and so on. Tripterygium Glycosides Tablets at 4 times dose could significantly reduce the content of serum sex hormone T and key enzyme of androgen synthesis(P<0.05 or P<0.01), but had no effect on CYP19 A1. The expression of Bax and Bcl-2 in testis and epididymis were increased by 2 and 4 times doses of Tripterygium Glycosides Tablets(P<0.05, P<0.01 or P<0.01). The results showed that 21 d administration of Tripterygium Glycosides Tablets at equal or higher doses could induce obvious toxic effect to the reproductive organs of CIA male rats, and lower the level of serum sex hormone T and the key enzyme of androgen synthesis, NOS. The mechanism of abnormal changes of Bax and Bcl-2 in Testis and epididymis is still to be elucidated.

[Effect of Tripterygium Glycosides Tablets on reproductive toxicity in female rats with Ⅱ type collagen induced arthritis]

The aim of this paper was to observe the toxic effect of Tripterygium Glycosides Tablets( TG) on the reproductive system of Ⅱ type collagen induced arthritis( CIA) male rats,and to explore the toxic mechanism preliminarily. Fifty SD rats were randomly divided into normal control group( Con),model group( CIA),Tripterygium Glycosides Tablets clinical equivalent dose groups of 1,2,4 times( 9,18,36 mg·kg-1),10 rats in each group,and were given by gavage once a day for 42 days after the first immunization.The organ indexes of uterine and ovarian were calculated on days 21 and 42. Histopathological and morphological changes of uterine and ovarian were observed under optical microscope. The concentration of estradiol( E2),follicle-stimulating hormone( FSH),luteinizing hormone( LH),17α-hydroxylase( CYP17 A1) and cytochrome P450 19 A1( CYP19 A1) in serum were detected by ELISA. Immunohistochemistry was used to observe the expression of Bax and Bcl-2 related proteins in the apoptosis pathway of uterus and ovary. The results showed that compared with the Con group,CIA group could reduce the number of uterine glands( P<0.05),but no significant changes were observed in other groups. Compared with the CIA group,there were no significant changes in the coefficients of uterus and ovary in the Tripterygium Glycosides Tablets groups. The number of uterine glands,total follicles in the ovary,mature follicles and corpus luteum,the distribution of blood vessels and mitochondria had a certain inhibitory trend,and also slightly increased the number of atresia follicles,but the histopathological quantitative indicators were not statistically different. Except that 2 times clinical dose of Tripterygium Glycosides Tablets could significantly reduce the content of CYP19 A1( P<0. 05) after 42 d administration,there were no significant changes in serum estrogen E2,FSH,LH and estrogen synthesis key enzymes CYP17 A1 in each administration group. Medium and high doses of Tripterygium Glycosides Tablets could increase the expression of apoptotic protein Bax in uterine and ovarian tissues( P<0. 05,P<0. 01),and all the administration groups could inhibit the expression of apoptotic inhibiting protein Bcl-2( P <0. 05,P<0. 01,P<0.001),42 d was more obvious than 21 d. In conclusion,4 times and less than 4 times Tripterygium Glycosides Tablets did not cause obvious toxicity and histopathological changes in the reproductive organs of CIA rats,but it could reduce the level of serum estrogen synthesis key enzyme CYP19 A1 and affect the content of apoptosis-related proteins Bax and Bcl-2 in uterus and ovary tissues. The relevant mechanism needs further study.

Azaspiracids Increase Mitochondrial Dehydrogenases Activity in Hepatocytes: Involvement of Potassium and Chloride Ions

BACKGROUND

Azaspiracids (AZAs) are marine toxins that are produced by Azadinium and Amphidoma dinoflagellates that can contaminate edible shellfish inducing a foodborne poisoning in humans, which is characterized by gastrointestinal symptoms. Among these, AZA1, -2, and -3 are regulated in the European Union, being the most important in terms of occurrence and toxicity. In vivo studies in mice showed that, in addition to gastrointestinal effects, AZA1 induces liver alterations that are visible as a swollen organ, with the presence of hepatocellular fat droplets and vacuoles. Hence, an in vitro study was carried out to investigate the effects of AZA1, -2, and -3 on liver cells, using human non-tumor IHH hepatocytes.

RESULTS

The exposure of IHH cells to AZA1, -2, or -3 (5 × 10^-12-1 × 10^-7 M) for 24 h did not affect the cell viability and proliferation (Sulforhodamine B assay and ³H-Thymidine incorporation assay), but they induced a significant concentration-dependent increase of mitochondrial dehydrogenases activity (MTT reduction assay). This effect depends on the activity of mitochondrial electron transport chain complex I and II, being counteracted by rotenone and tenoyl trifluoroacetone, respectively. Furthermore, AZAs-increased mitochondrial dehydrogenase activity was almost totally suppressed in the K⁺-, Cl^--, and Na⁺-free media and sensitive to the specific inhibitors of K_ATP and hERG potassium channels, Na⁺/K⁺, ATPase, and cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels.

CONCLUSIONS

These results suggest that AZA mitochondrial effects in hepatocytes derive from an imbalance of intracellular levels of K⁺ and, in particular, Cl^- ions, as demonstrated by the selective reduction of toxin effects by CFTR chloride channel inhibition.

Plasma membrane is the target of rapid antibacterial action of silver nanoparticles in Escherichia coli and Pseudomonas aeruginosa

Introduction

Silver nanoparticles (AgNP) are widely used in consumer products and in medicine, mostly due to their excellent antimicrobial properties. One of the generally accepted antibacterial mechanisms of AgNP is their efficient contact with cells and dissolution in the close vicinity of bacterial cell envelope. Yet, the primary mechanism of cell wall damage and the events essential for bactericidal action of AgNP are not elucidated.

Materials and methods

In this study we used a combination of various assays to differentiate the adverse effects of AgNP on bacterial cell envelope: outer membrane (OM) and plasma membrane (PM).

Results

We showed that PM was the main target of AgNP in gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa: AgNP depolarized PM, induced the leakage of the intracellular K⁺, and inhibited cellular respiration. The results of bacterial bioluminescence inhibition assay in combination with AgNP dissolution and oxidation assays demonstrated that the adverse effects of AgNP occurred at concentrations 7–160 µM. These toxic effects occurred already within the first few seconds of contact of bacteria and AgNP and were driven by dissolved Ag⁺ ions targeting bacterial PM. However, the irreversible inhibition of bacterial growth detected after 1-hour exposure occurred at 40 µM AgNP for P. aeruginosa and at 320 µM AgNP for E. coli. In contrast to effects on PM, AgNP and Ag⁺ ions had no significant effect on the permeability and integrity of bacterial OM, implying that AgNP indeed targeted mainly PM via dissolved Ag⁺ ions.

Conclusion

AgNP exhibited antibacterial properties via rapid release of Ag⁺ ions targeting the PM and not the OM of gram-negative bacteria.

Investigating cell type specific mechanisms contributing to acute oral toxicity

The replacement of animals in acute systemic toxicity testing remains a considerable challenge. Only animal data are currently accepted by regulators, including data generated by reduction and refinement methods. The development of Integrated Approaches to Testing and Assessment (IATA) is hampered by an insufficient understanding of the numerous toxicity pathways that lead to acute systemic toxicity. Therefore, central to our work has been the collection and evaluation of the mechanistic information on eight organs identified as relevant for acute systemic toxicity (nervous system, cardiovascular system, liver, kidney, lung, blood, gastrointestinal system and immune system). While the nervous and cardiovascular systems are the most frequent targets, no clear relationship emerged between specific mechanisms of target organ toxicity and the level (category) of toxicity. From a list of 114 chemicals with acute oral in vivo and in vitro data, 98 were identified with target organ specific effects, of which 93% were predicted as acutely toxic by the 3T3 neutral red uptake cytotoxicity assay and 6% as non-toxic. This analysis will help to prioritise the development of adverse outcome pathways for acute oral toxicity, which will support the assessment of chemicals using mechanistically informed IATA.

MicroRNA-155 targets cyb561d2 in zebrafish in response to fipronil exposure

MicroRNAs (miRNAs), which are a class of small noncoding RNAs, can modulate the expression of many protein-coding genes when an organism is exposed to an environmental chemical. We previously demonstrated that miR-155 was significantly downregulated in adult zebrafish (Danio rerio) in response to fipronil (5-amino-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl) sulphinyl]-1H-pyrazole-3-carbonitrile) exposure. However, the regulation of this miRNA's predicted target gene cyb561d2, which is a member of the cytochrome b561 (cyt b561) family involved in electron transfer, cell defence, and chemical stress, has not been experimentally validated to date. In this study, we evaluated the effects of fipronil on miR-155 and cyb561d2 in zebrafish. The expression of miR-155 was downregulated, whereas cyb561d2 was upregulated in both mRNA and protein level in a dose-dependent manner upon stimulation of fipronil. The dual luciferase report assay demonstrated that miR-155 interacted with cyb561d2 3'-untranslated regions (3'-UTR). The expression of cyb561d2 was reduced in both mRNA and protein levels when ZF4 cells were transfected with an miR-155 mimic, whereas its expression levels of both mRNA and protein were increased when endogenous miR-155 was inhibited by transfection with an miR-155 inhibitor. The results improved our understanding of molecular mechanism of toxicity upon fipronil exposure, and presents miR-155 as a potential novel toxicological biomarker for chemical exposure. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 877-886, 2016.