Effect of titanium dioxide nanoparticles on glucose homeostasis after oral administration

Nanomedicines based on trace elements for intervention of diabetes mellitus

Epidemiology shows that the incidence of diabetes mellitus (DM) is increasing year by year globally. Proper interventions are highly aspired for diabetics to improve the quality of life and prevent development of chronic complications. Trace elements, also known as microelements, are chemical substances that are present in our body in minute amounts. They are necessitated by the body for growth, development and functional metabolism. For the past few years, trace element nanoparticles have aroused considerable interest as a burgeoning form of nanomedicines in antidiabetic applications. These microelement-based nanomedicines can regulate glucose metabolism in several ways, showing great potential for diabetes management. Starting from the pathophysiology of diabetes, the state-of-the-art of diabetes treatment, the physiological roles of trace elements, various emerging trace element nanoparticles specific for diabetes were comprehensively reviewed in this work. Our findings disclose that trace element nanoparticles can fight against diabetes by lowering blood glucose, promoting insulin secretion, alleviating glucose intolerance, improving insulin sensitivity, ameliorating lipid profile, anti-inflammation and anti-oxidant stress, and other mechanisms. In conclusion, trace element nanoparticles can be applied as nanomedicines or dietary modifiers for effective intervention for diabetes.

Exposure to MoS2 nanosheets or bulk activated Kruppel-like factor 4 in 3D Caco-2 spheroids in vitro and mouse intestines in vivo

MoS₂ nanosheets (NSs) are novel 2D nanomaterials (NMs) being used in many important fields. Recently, we proposed the need to evaluate the influences of NMs on Kruppel-like factors (KLFs) even if these materials are relatively biocompatible. In this study, we investigated the influences of MoS₂ NSs or bulk on KLF4 signaling pathway in 3D Caco-2 spheroids in vitro and mouse intestines in vivo. Through the analysis of our previous RNA-sequencing data, we found that exposure to MoS₂ NSs or bulk activated KLF4 expression in 3D Caco-2 spheroids. Consistently, these materials also activated KLF4-related gene ontology (GO) terms and down-regulated a panel of KLF4-downstream genes. To verify these findings, we repeatedly exposed mice to MoS₂ NSs or bulk materials via intragastrical administration (1 mg/kg bodyweight, once a day, for 4 days). It was shown that oral exposure to these materials decreased bodyweight, leading to relatively higher organ coefficients. As expected, exposure to both types of materials increased Mo elements as well as other trace elements, such as Zn, Fe, and Mn in mouse intestines. The exposure also induced morphological changes of intestines, such as shortening of intestinal villi and decreased crypt depth, which may result in decreased intestinal lipid staining. Consistent with RNA-sequencing data, we found that material exposure increased KLF4 protein staining in mouse intestines and decreased two KLF4 downstream proteins, namely extracellular signal-regulated kinase (ERK) and serine/threonine kinase (AKT). We concluded that MoS₂ materials were capable to activate KLF4-signaling pathway in intestines both in vivo and in vitro.

The effect and underlying mechanisms of titanium dioxide nanoparticles on glucose homeostasis: A literature review

Titanium dioxide (TiO₂ ) is used extensively as a white pigment in the food industry, personal care, and a variety of products of everyday use. Although TiO₂ has been categorized as a bioinert material, recent evidence has demonstrated different toxicity profiles of TiO₂ nanoparticles (NPs) and a potential health risk to humans. Studies indicated that titanium dioxide enters the systemic circulation and accumulates in the lungs, liver, kidneys, spleen, heart, and central nervous system and may cause oxidative stress and tissue damage in these vital organs. Recently, some studies have raised concerns about the possible detrimental effects of TiO₂ NPs on glucose homeostasis. However, the findings should be interpreted with caution due to the methodological issues. This article aims to evaluate current evidence regarding the effects of TiO₂ NPs on glucose homeostasis, including possible underlying mechanisms. Furthermore, the limitations of current studies are discussed, which may provide a comprehensive understanding and new perspectives for future studies in this field.

Adverse Outcome Pathways Associated with the Ingestion of Titanium Dioxide Nanoparticles-A Systematic Review

Titanium dioxide nanoparticles (TiO₂-NPs) are widely used, and humans are exposed through food (E171), cosmetics (e.g., toothpaste), and pharmaceuticals. The oral and gastrointestinal (GIT) tract are the first contact sites, but it may be systemically distributed. However, a robust adverse outcome pathway (AOP) has not been developed upon GIT exposure to TiO₂-NPs. The aim of this review was to provide an integrative analysis of the published data on cellular and molecular mechanisms triggered after the ingestion of TiO₂-NPs, proposing plausible AOPs that may drive policy decisions. A systematic review according to Prisma Methodology was performed in three databases of peer-reviewed literature: Pubmed, Scopus, and Web of Science. A total of 787 records were identified, screened in title/abstract, being 185 used for data extraction. The main endpoints identified were oxidative stress, cytotoxicity/apoptosis/cell death, inflammation, cellular and systemic uptake, genotoxicity, and carcinogenicity. From the results, AOPs were proposed where colorectal cancer, liver injury, reproductive toxicity, cardiac and kidney damage, as well as hematological effects stand out as possible adverse outcomes. The recent transgenerational studies also point to concerns with regard to population effects. Overall, the findings further support a limitation of the use of TiO₂-NPs in food, announced by the European Food Safety Authority (EFSA).

Landscape of lipidomic metabolites in gut-liver axis of Sprague-Dawley rats after oral exposure to titanium dioxide nanoparticles

Background

The application of titanium dioxide nanoparticles (TiO₂ NPs) as food additives poses a risk of oral exposure that may lead to adverse health effects. Even though the substantial evidence supported liver as the target organ of TiO₂ NPs via oral exposure, the mechanism of liver toxicity remains largely unknown. Since the liver is a key organ for lipid metabolism, this study focused on the landscape of lipidomic metabolites in gut-liver axis of Sprague Dawley (SD) rats exposed to TiO₂ NPs at 0, 2, 10, 50 mg/kg body weight per day for 90 days.

Results

TiO₂ NPs (50 mg/kg) caused slight hepatotoxicity and changed lipidomic signatures of main organs or systems in the gut-liver axis including liver, serum and gut. The cluster profile from the above biological samples all pointed to the same key metabolic pathway and metabolites, which was glycerophospholipid metabolism and Phosphatidylcholines (PCs), respectively. In addition, absolute quantitative lipidomics verified the changes of three PCs concentrations, including PC (16:0/20:1), PC (18:0/18:0) and PC (18:2/20:2) in the serum samples after treatment of TiO₂ NPs (50 mg/kg). The contents of malondialdehyde (MDA) in serum and liver increased significantly, which were positively correlated with most differential lipophilic metabolites.

Conclusions

The gut was presumed to be the original site of oxidative stress and disorder of lipid metabolism, which resulted in hepatotoxicity through the gut-liver axis. Lipid peroxidation may be the initial step of lipid metabolism disorder induced by TiO₂ NPs. Most nanomaterials (NMs) have oxidation induction and antibacterial properties, so the toxic pathway revealed in the present study may be primary and universal.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00484-9.

Nutrient molecule corona: An update for nanomaterial-food component interactions

The adsorption of biological molecules to nanomaterials (NMs) will significantly impact NMs' behavior in complex microenvironments. Previously we proposed the need to consider the interactions between food components and NMs for the evaluation of oral toxicity of NMs. This review updated this concept as nutrient molecule corona, that the adsorption of nutrient molecules alters the uptake of nutrient molecules and/or NMs, as well as the signaling pathways to induce a combined toxicity due to the biologically active nature of nutrient molecules. Even with the presence of protein corona, nutrient molecules may still bind to NMs to change the identities of NMs in vivo. Furthermore, this review proposed the binding of excessive nutrient molecules to NMs to induce a combined toxicity under pathological conditions such as metabolic diseases. The structures of nutrient molecules and physicochemical properties of NMs determine nutrient molecule corona formation, and these aspects should be considered to limit the unwanted effects brought by nutrient molecule corona. In conclusion, similar to other biological molecule corona, the formation of nutrient molecule corona due to the presence of food components or excessive nutrient molecules in pathophysiological microenvironments will alter the behaviors of NMs.

The Intestinal Barrier—Shielding the Body from Nano- and Microparticles in Our Diet

Nano- and microparticles are an implicit part of the human diet. They are unknowingly ingested with our food that contains them as additives or pollutants. However, their impact on human health is not yet understood and controversially discussed. The intestinal epithelial barrier shields our body against exogenous influences, such as commensal bacteria, pathogens, and body-foreign particles and, therefore, protects our body integrity. Breakdown of the intestinal epithelial barrier and aberrant immune responses are key events in the pathogenesis of inflammatory bowel disease (IBD). Epithelial lesions might enable systemic translocation of nano- and microparticles into the system, eventually triggering an excessive immune response. Thus, IBD patients could be particularly vulnerable to adverse health effects caused by the ingestion of synthetic particles with food. The food-additive titanium dioxide (TiO2) serves as a coloring agent in food products and is omnipresent in the Western diet. TiO2 nanoparticles exacerbate intestinal inflammation by activation of innate and adaptive immune response. Because of serious safety concerns, the use of TiO2 as a food additive was recently banned from food production within the European Union. Due to environmental pollution, plastic has entered the human food chain, and plastic microparticles have been evidenced in the drinking water and comestible goods. The impact of plastic ingestion and its resulting consequences on human health is currently the subject of intense research. Focusing on TiO2 and plastic particles in the human diet and their impact on epithelial integrity, gut homeostasis, and intestinal inflammation, this review is addressing contemporary hot topics which are currently attracting a lot of public attention.

Exploring urine biomarkers of early health effects for occupational exposure to titanium dioxide nanoparticles using metabolomics

Many experimental studies have demonstrated that titanium dioxide nanoparticles (TiO2 NPs) could induce adverse health effects in vivo and in vitro. But epidemiological evidence and biomarkers related to early health effects are still lacking. This study aimed to explore biomarkers in the urine samples of workers occupationally exposed to a relatively low concentration of TiO2 NPs. A cross-sectional study was conducted in Jinan, China, involving 132 employees of a TiO2 NP manufacturing plant, among which the exposed group and control group were 1 : 1 matched by confounding factors such as gender, age, BMI, smoking and drinking. Untargeted metabolomics was performed in urine samples using high performance liquid chromatography-mass spectrometry (HPLC-MS) technology. The differential metabolites between the TiO2 NP exposed group and the control group were analyzed and then screened for potential biomarkers using bioinformatics methods. Metabolomics found a total of 1760 differentially expressed metabolites in the TiO2 NP exposed group, of which 60 differential metabolites were simultaneously confirmed by one-dimensional and multi-dimensional statistical analysis. Among these 60 differential metabolites, the relative expression of 27 metabolites increased, and the remaining 33 decreased. Pathway enrichment analysis further found that the metabolic pathway of long chain acyl-coa dehydrogenase deficiency (Lcad) was significantly enriched. Ten differential metabolites were selected as potential biomarkers of occupational exposure to TiO2 NPs using machine learning methods, including dibenzyl ether, quassimarin, tryptophan, etc. The receiver operating characteristic curves (ROCs) of these potential biomarkers showed good sensitivity and specificity. These potential biomarkers also had biological basis for occupational exposure to TiO2 NPs. Therefore, urine metabolites represented by dibenzyl ether are considered as good biomarkers of early health effects for occupational exposure to TiO2 NPs.

Toxic effects of TiO2 NPs in the blood-milk barrier of the maternal dams and growth of offspring

Titanium dioxide nanoparticles (TiO₂ NPs) are amongst the most frequently used nanomaterial in everyday consumer products, and their widespread applications have raised concerns of the consequent deleterious effects on human health, particularly to vulnerable populations, such as lactating females remains elusive. Therefore, this study was initiated to investigate the detrimental effects and toxic mechanisms induced by TiO₂ NPs in maternal dams and offspring during the lactation period. Dams were randomly divided into three groups. The water (Control; Group I) and TiO₂ NPs (100 mg/kg; Group II) were orally administered from postnatal day 1-20, respectively. The results indicated that TiO₂ NPs could cause toxicity in the dams, such as pathological damages to mammary gland tissues. The excessive accumulation of TiO₂ NPs could induce oxidative stress in the mammary gland, leading to the dysfunctional blood-milk barrier; besides, TiO₂ NPs could also be transferred to offspring via breastfeeding, causing abnormal development of infant. We further accessed the possible underlying molecular mechanism; for this, we orally administered TiO₂ NPs with vitamin E (100 mg/kg; Group III). The results revealed that toxicity induced by TiO₂ NPs was rescued. Collectively, this study presented the deleterious pathological effects of oral exposure to TiO₂ NPs in the mammary gland tissues and blood-milk barrier via the production of reactive oxygen species (ROS) in dams and developmental concerns in offspring. However, the administration of VE could mitigate the toxic effects induced by the TiO₂ NPs.

Effects of titanium dioxide nanoparticles on nutrient absorption and metabolism in rats: distinguishing the susceptibility of amino acids, metal elements, and glucose

Food grade titanium dioxide (TiO₂) containing nanofractions, is commonly applied to whiten and brighten food products, which put consumers under health risks of ingesting TiO₂ nanoparticles (NPs). Although the oral toxicity of TiO₂-NPs has been evaluated in several studies, gaps in knowledge exist regarding interactions between NPs and food components. Therefore, this study aimed to estimate the influence of TiO₂-NPs on nutrient absorption and metabolism through an in situ intestinal loop experiment which conducted on adult Sprague Dawley (SD) rats after 30-d gastrointestinal exposure to TiO₂-NPs of two different sizes (N-TiO₂ and M-TiO₂). Results showed that exposure to TiO₂-NPs caused flat apical membranes with sparse and short microvilli and inflammatory infiltration in small intestine. Both particles were absorbed into small intestinal cells, but N-TiO₂ with smaller size could more easily be transported through gut and raise the blood titanium (Ti) levels. Changes in serum levels of amino acid were also different after exposure to these two particles. After injecting mixed solution of nutrients into in situ intestinal loop, the N-TiO₂ exposure groups displayed significant absorption inhibition of the added histidine (His) and metabolism disorder of some non-added amino acid. However, no influence was observed on metal elements or glucose levels. This study identified TiO₂-NPs with small sizes could affect nutrient absorption and metabolism by inducing intestinal epithelium injury, and amino acids were more susceptible than metal elements and glucose. These findings suggested that foods supplemented with TiO₂-NPs should be carefully consumed by people with high protein requirements, such as children, the elderly, and patients with high metabolic disease or intestinal inflammation.

Oral exposure of titanium oxide nanoparticles induce ileum physical barrier dysfunction via Th1/Th2 imbalance

In this work, we aimed to evaluate the adverse effects and the mechanism of intestinal barrier caused by titanium dioxide nanoparticles (TiO₂ NPs). Here, the effects of two different dosages (300 and 1200 mg/kg) of TiO₂ NPs on female mice (n = 5) were investigated. After 28-day oral exposure, the results of Ti content were significantly increased in the ileum in comparison with the control. The histopathological structure index of the ileum was significantly changed after TiO₂ NPs exposure; villi height and crypt depth were decreased and increased, respectively. Meanwhile, TiO₂ NPs treatment also significantly altered the transcription levels of genes. First, the GATA-3 and STAT-4 were upregulation and downregulation, respectively. Second, gene expressions of the Zonula Occludens-1, claudin (CLDN)-12, occludin, and myosin light chain kinase were significantly upregulated, while the CLDN-3 was decreased. Finally, the caspase-3, caspase-9, and caspase-12 were upregulated. The results of TUNEL staining indicated apoptosis in the ileum. In general, TiO₂ NPs treatment significantly changed the intestine physical barrier in a dose-dependent manner. The toxicity of TiO₂ NPs could be through the imbalance in the Th1/Th2.

[Effects of titanium dioxide nanoparticles on fecal metabolome in rats after oral administration for 90 days]

OBJECTIVE

To explore the effects and related mechanisms of oral exposure titanium dioxide nanoparticles (TiO₂ NPs) for 90 days on the intestinal and the gut microbiota of rats, through fecal metabolomics.

METHODS

Twelve 4-week-old clean-grade Sprague Dawley (SD) rats were randomly de-vided into 2 groups by body weight, treated with TiO₂ NPs at dose of 0 or 50 mg/kg body weight everyday respectively for 90 days. The solution of each infection was freshly prepared and shocked fully by ultrasonic. Characterization of the particle size, crystal form, purity, and specific surface area of TiO₂ NPs was conducted. And the fresh feces of the rats were collected on the 90th day. After lyophilized and hydrophilic phase extraction, ultra performance liquid chromatography-Q-exactive orbitrap-high-resolution mass spectrometry system (UPLC-QEMS) was utilized for non-targeted determination of fecal meta-bolites. The metabolites were identified and labeled through Compound Discoverer 3.0 software, and used for subsequent metabolomics analysis. Bioinformatics analysis was carried out including unsupervised principal component analysis and supervised orthogonal projection to latent structure discriminant analysis for the differential metabolites between the two groups. The differential metabolites were followed-up for Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis.

RESULTS

Compared with the control group, the body weight of the rats was significantly reduced (P<0.05) in the treatment group. A total of 22 metabolites in fecal metabolomics showed significant changes. Among them, xanthine, 1-methyladenine, 3-hydroxypyridine, methionine sulfoxide, pyridoxine, 1,5-isoquinolinediol, N-acetylornithine, N-acetyl-D-galactosamine, L-citrulline, L-methionine, leucine, DL-tryptophan, L-ornithine, 4-methyl-5-thiazoleethanol, and L-glutamic acid totaled 15 metabolites increased significantly. N-acetylhistamine, D-pipecolinic acid, imidazolelactic acid, L-valine, 2,3,4,6-tetramethylpyrazine, caprolactam, and histamine totaled 7 metabolites decreased significantly. N-acetylhistamine, L-valine and methionine sulfoxide were changed more than 16 times. Analysis of KEGG pathway revealed that the two metabolic pathways arginine biosynthesis and aminoacyl-tRNA biosynthesis were significantly changed (false discover rate < 0.05, pathway impact > 0.1).

CONCLUSION

Oral exposure to TiO₂ NPs for 90 days could disrupt the metabolism of the intestine and gut microbiota, causing significant changes in metabolites and metabolic pathways which were related to inflammatory response, oxidative stress, glucose homeostasis, blood system and amino acid homeostasis in rat feces. It is suggested that the toxic effect of TiO₂ NPs on rats may be closely related to intestinal and gut microbiota metabolism.

[Effect of subchronic combined oral exposure of titanium dioxide nanoparticles and glucose on levels of serum folate and vitamin B12 in young SD rats]

OBJECTIVE

To explore the effect of subchronic combined oral exposure of titanium dioxide nanoparticles and glucose on levels of serum folate and vitamin B₁₂ in young SD rats.

METHODS

At first, the physical and chemical properties of titanium dioxide nanoparticles, such as particle size, shape, crystal form and agglomeration degree in solution system, were characterized in detail. Eighty 4-week-old young SD rats were randomly divided into 8 groups (10 rats in each group, half male and half female). The rats were exposed to titanium dioxide nanoparticles through intragastric administration at 0, 2, 10 and 50 mg/kg body weight with or without 1.8 g/kg glucose daily for 90 days. At last, the concentrations of serum folate and vitamin B₁₂ were detected.

RESULTS

Titanium dioxide nanoparticles were anatase crystals, closely spherical shape, with an average particle size of (24±5) nm. In male young rats, compared with the control group, the serum folate concentration was significantly increased when exposed to titanium dioxide nanoparticles (10 mg/kg) and glucose. The difference was statistically significant (P<0.05). However, in female and male young rats, compared with glucose (1.8 g/kg) exposure group, titanium dioxide nanoparticles (50 mg/kg) and glucose significantly reduced the serum folate concentration. The difference was statistically significant (P<0.05). Through statistical analysis of factorial design and calculation of interaction, obvious antagonistic effect was observed between titanium dioxide nanoparticles and glucose on the serum folate concentration in the young female SD rats. The combined oral exposure of titanium dioxide nanoparticles and glucose had little effect on the concentration of serum vitamin B₁₂ in the young SD rats, with no significant interaction between the two substances. It was only found that titanium dioxide nanoparticles (2 mg/kg) and glucose significantly increased the serum vitamin B₁₂ concentration, compared with glucose (1.8 g/kg) exposure group. The difference was statistically significant (P<0.05).

CONCLUSION

Subchronic combined oral exposure of titanium dioxide nanoparticles and glucose had an obvious antagonistic effect on serum folate concentrations in young SD rats.

Association of twenty-three plasma elements with fasting serum glucose among Chinese population from four areas with different pollution level

BACKGROUND

Association between fasting serum glucose (FSG) and certain mineral elements has been extensively reported. Investigation regarding multi-element exposure among subjects with different exposure level is warranted to confirm the association and further explore dose-dependent relationship.

METHODS

A total of 3488 participants were recruited from four counties of Hunan province, South China. Basic characteristics were collected by face to face interview and 23 elements in plasma were determined by inductively coupled plasma mass spectrometry. We applied fully adjusted generalized linear regression model and multivariable restricted cubic spline function to test the association and dose-response relationship of FSG with 23 elements.

RESULTS

The results indicated that FSG was positively associated with plasma78selenium level [regression coefficient (β), 0.001; 95 % confidence interval (CI), 0.001, 0.001] in a dose-dependent manner, robust to the adjustment for suspected covariates and stratification by age, gender, BMI and smoking status. A negative association was found between FSG and plasma 208lead (β, -0.004; 95 % CI, -0.016, -0.002), 52chromium (β, -0.002; 95 % CI, -0.004, -0.001) and 47titanium (β, -0.001; 95 % CI, -0.002, -0.001).

CONCLUSION

78selenium was positively while 208lead, 52chromium and 47titanium were negatively associated with FSG in the present study. However, prospective studies are needed to confirm the results.

Effect of oral exposure to titanium dioxide nanoparticles on lipid metabolism in Sprague-Dawley rats

Ingestion of titanium dioxide nanoparticles (TiO2 NPs) via dietary and environmental exposure may pose health risks. The research about the potential effect of orally ingested nanoparticles on nutritional metabolism has been limited. We conducted an animal experiment to investigate the effect of oral exposure to TiO2 NPs on lipid metabolism in Sprague-Dawley rats. The rats were treated with TiO2 NPs (29 ± 9 nm) orally at doses of 0, 2, 10, 50 mg per kg bw daily for 90 days. Lipid metabolism is evaluated by biomarkers of serum lipids and lipidomics. TiO2 NPs caused a significant decrease of body weight in rats after exposure at doses of 10 and 50 mg kg-1 from the 8th to 13th week. The level of triglycerides (TG) decreased (0.398 ± 0.114 vs. 0.248 ± 0.058 nmol L-1) and the lipidomic signature changed significantly in the serum of rats treated with TiO2 NPs (50 mg kg-1). Sixty-nine well-matched lipophilic metabolites were differentially expressed and the glycerophospholipid metabolism pathway significantly changed. The concentrations of 32 metabolites including 19 kinds of phosphatidylcholines (PCs) increased and 37 metabolites including lysophosphatidylcholines (LysoPCs) and glycerophosphocholine decreased significantly in the TiO2 NP exposed group (50 mg kg-1). The accumulation of the lipid peroxidation product (malondialdehyde, MDA) and the decreased activity of the antioxidant enzyme SOD were observed and closely related to differential metabolites. In conclusion, orally ingested TiO2 NPs (50 mg kg-1) could have an impact on lipid metabolism, for which the strong induction of oxidative stress may be the main reason. The present study led to a better understanding of the oral toxicity of food-related TiO2 NPs.

Titanium dioxide nanoparticles via oral exposure leads to adverse disturbance of gut microecology and locomotor activity in adult mice

Titanium dioxide nanoparticles (TiO₂NPs) have been widely used as food additives in daily life. However, the impact of oral intake of TiO₂NPs on the nervous system is largely unknown. In this study, 7-week-old mice were treated with either vehicle or TiO₂NPs suspension solution at 150 mg/kg by intragastric administration for 30 days. Our results demonstrated that oral exposure to TiO₂NPs resulted in aberrant excitement of enteric neurons, although unapparent pathological changes were observed in gut. We also found the richness and evenness of gut microbiota were remarkably decreased and the gut microbial community compositions were significantly changed in the TiO₂NP-treated group as compared with vehicle controls. Interestingly, oral exposure to TiO₂NPs was capable to induce the inhibitory effects on locomotor activity, but it did not lead to significant change on the spatial learning and memory ability. We further revealed the mechanism that TiO₂NPs could specifically cause locomotor dysfunction by elevating the excitement of enteric neuron, which might spread to brain via gut-brain communication by vagal pathway. However, inflammation response, enteric neurotransmitter 5-HT and major gut peptides might not be involved in this pathological process. Together, these findings provide valuable insights into the novel mechanism of TiO₂NP-induced neurotoxicity. Understanding the microbiota-gut-brain axis will provide the foundation for potential therapeutic or prevention approaches against TiO₂NP-induced gut and brain-related disorders.

Hepatotoxicity and the role of the gut-liver axis in rats after oral administration of titanium dioxide nanoparticles

Background

Due to its excellent physicochemical properties and wide applications in consumer goods, titanium dioxide nanoparticles (TiO₂ NPs) have been increasingly exposed to the environment and the public. However, the health effects of oral exposure of TiO₂ NPs are still controversial. This study aimed to illustrate the hepatotoxicity induced by TiO₂ NPs and the underlying mechanisms. Rats were administered with TiO₂ NPs (29 nm) orally at exposure doses of 0, 2, 10, 50 mg/kg daily for 90 days. Changes in the gut microbiota and hepatic metabolomics were analyzed to explore the role of the gut-liver axis in the hepatotoxicity induced by TiO₂ NPs.

Results

TiO₂ NPs caused slight hepatotoxicity, including clear mitochondrial swelling, after subchronic oral exposure at 50 mg/kg. Liver metabolomics analysis showed that 29 metabolites and two metabolic pathways changed significantly in exposed rats. Glutamate, glutamine, and glutathione were the key metabolites leading the generation of energy-related metabolic disorders and imbalance of oxidation/antioxidation. 16S rDNA sequencing analysis showed that the diversity of gut microbiota in rats increased in a dose-dependent manner. The abundance of Lactobacillus_reuteri increased and the abundance of Romboutsia decreased significantly in feces of TiO₂ NPs-exposed rats, leading to changes of metabolic function of gut microbiota. Lipopolysaccharides (LPS) produced by gut microbiota increased significantly, which may be a key factor in the subsequent liver effects.

Conclusions

TiO₂ NPs could induce slight hepatotoxicity at dose of 50 mg/kg after long-term oral exposure. The indirect pathway of the gut-liver axis, linking liver metabolism and gut microbiota, played an important role in the underlying mechanisms.

Transcriptome changes in undifferentiated Caco-2 cells exposed to food-grade titanium dioxide (E171): contribution of the nano- and micro- sized particles

The food additive titanium dioxide (TiO2), or E171, is a white food colorant. Recent studies showed after E171 ingestion a significantly increased number of colorectal tumours in a colorectal cancer mouse model as well as inflammatory responses and dysregulation of the immune system in the intestine of rats. In the mouse colon, E171 induced gene expression changes related to oxidative stress, impairment of the immune system, activation of signalling and cancer-related processes. E171 comprises nanoparticles (NPs) and microparticles (MPs). Previous in vitro studies showed that E171, NPs and MPs induced oxidative stress responses, DNA damage and micronuclei formation. This study aimed to investigate the relative contribution of the NPs and MPs to effects of E171 at the transcriptome level in undifferentiated Caco-2 cells by genome wide microarray analysis. The results showed that E171, NPs, and MPs induce gene expression changes related to signalling, inflammation, immune system, transport and cancer. At the pathway level, metabolism of proteins with the insulin processing pathway and haemostasis were specific to E171 exposure. The gene expression changes associated with the immune system and inflammation induced by E171, MPs, and NPs suggest the creation of a favourable environment for colon cancer development.

Effects of oral exposure to titanium dioxide nanoparticles on gut microbiota and gut-associated metabolism in vivo

The antibacterial activity of titanium dioxide nanoparticles (TiO2 NPs) has been extensively documented and applied to food packaging or environmental protection. Ingestion of TiO2 NPs via dietary and environmental exposure may pose potential health risks by interacting with gut microbiota. We conducted an animal experiment to investigate the effects of oral exposure to TiO2 NPs on gut microbiota and gut-associated metabolism in Sprague-Dawley rats. Rats were administered with TiO2 NPs (29 ± 9 nm) orally at population-related exposure doses (0, 2, 10, 50 mg kg-1) daily for 30 days. Changes in the gut microbiota and feces metabolomics were analyzed through bioinformatics. TiO2 NPs caused significant changes of colon morphology in rats, manifested as pathological inflammatory infiltration and mitochondrial abnormalities. 16S rDNA sequencing analysis showed that the structure and composition of gut microbiota in rats were modulated after exposure to TiO2 NPs. Monitoring data demonstrated that differentially expressed bacterial strains were obtained until exposure for 14 days and 28 days, including increased L. gasseri, Turicibacter, and L. NK4A136_group and decreased Veillonella. Fecal metabolomics analysis showed that 25 metabolites and the aminoacyl-tRNA biosynthesis metabolic pathway have changed significantly in exposed rats. The increased metabolites were represented by N-acetylhistamine, caprolactam, and glycerophosphocholine, and the decreased metabolites were represented by 4-methyl-5-thiazoleethanol, l-histidine, and l-ornithine. Metabolic disorders of gut microbiota and subsequently produced lipopolysaccharides (LPS) led to oxidative stress and an inflammatory response in the intestine, which was considered to be a key and primary indirect pathway for toxicity induced by oral exposure to the TiO2 NPs. In conclusion, orally ingested TiO2 NPs could induce disorders of gut microbiota and gut-associated metabolism in vivo. The indirect pathway of oxidative stress and inflammatory response, probably due to dysbiosis of gut microbiota primarily, played an important role in the mechanisms of toxicity induced by oral exposure to TiO2 NPs. This may be a common mechanism of toxicity caused by oral administration of most nanomaterials, as they usually have potential antimicrobial activity.

Role of Endocrine-Disrupting Engineered Nanomaterials in the Pathogenesis of Type 2 Diabetes Mellitus

Nanotechnology has enabled the development of innovative technologies and products for several industrial sectors. Their unique physicochemical and size-dependent properties make the engineered nanomaterials (ENMs) superior for devising solutions for various research and development sectors, which are otherwise unachievable by their bulk forms. However, the remarkable advantages mediated by ENMs and their applications have also raised concerns regarding their possible toxicological impacts on human health. The actual issue stems from the absence of systematic data on ENM exposure-mediated health hazards. In this direction, a comprehensive exploration on the health-related consequences, especially with respect to endocrine disruption-related metabolic disorders, is largely lacking. The reasons for the rapid increase in diabetes and obesity in the modern world remain largely unclear, and epidemiological studies indicate that the increased presence of endocrine disrupting chemicals (EDCs) in the environment may influence the incidence of metabolic diseases. Functional similarities, such as mimicking natural hormonal actions, have been observed between the endocrine-disrupting chemicals (EDCs) and ENMs, which supports the view that different types of NMs may be capable of altering the physiological activity of the endocrine system. Disruption of the endocrine system leads to hormonal imbalance, which may influence the development and pathogenesis of metabolic disorders, particularly type 2 diabetes mellitus (T2DM). Evidence from many in vitro, in vivo and epidemiological studies, suggests that ENMs generally exert deleterious effects on the molecular/hormonal pathways and the organ systems involved in the pathogenesis of T2DM. However, the available data from several such studies are not congruent, especially because of discrepancies in study design, and therefore need to be carefully examined before drawing meaningful inferences. In this review, we discuss the outcomes of ENM exposure in correlation with the development of T2DM. In particular, the review focuses on the following sub-topics: (1) an overview of the sources of human exposure to NMs, (2) systems involved in the uptake of ENMs into human body, (3) endocrine disrupting engineered nanomaterials (EDENMs) and mechanisms underlying the pathogenesis of T2DM, (4) evidence of the role of EDENMs in the pathogenesis of T2DM from in vitro, in vivo and epidemiological studies, and (5) conclusions and perspectives.

Combined effect of titanium dioxide nanoparticles and glucose on the cardiovascular system in young rats after oral administration

Titanium dioxide nanoparticles (TiO₂ NPs) have already been used as food additive in various products and are usually consumed with a considerable amount of sugar. Oral consumption of TiO₂ NPs poses concerning health risks; however, research on the combined effect of ingested TiO₂ NPs and glucose is limited. We examined young Sprague-Dawley rats administrated TiO₂ NPs orally at doses of 0, 2, 10 and 50 mg/kg body weight per day with and without 1.8 g/kg body weight glucose for 30 and 90 days. Heart rate, systolic and diastolic blood pressure, blood biochemical parameters and histopathology of cardiac tissues was assessed to quantify cardiovascular damage. The results showed that oral exposure to TiO₂ NPs and high doses of glucose both could induce cardiovascular injuries. The toxic effects were dose-, time- and gender-dependent. The interaction effects between oral-exposed TiO₂ NPs and glucose existed and revealed to be antagonism in most of the biological parameters. However, toxic effects of the high-dose glucose seemed to be more severe than TiO₂ NPs and the interaction of TiO₂ NPs with glucose. These results suggest that it may be more important to control the sugar intake than TiO₂ NPs for protecting the health of TiO₂ NP consumers.